An Analysis on Students’ Difficulties in Speaking

The purpose of this research is to analyze the students‟ difficulties in speaking English especially in introducing themselves self at MTS NW Al Hidayah Baremayung. Besides, this study tries to identify what the students‟ difficulties in speaking English and what the factors of students‟ difficulties in speaking English especially in introducing themselves. The method of collecting data was observation, recording, and interview. The data were taken from the subject of the research in the form of teaching learning process, interview and recording. The result of this research shows that the students‟ difficulties in speaking English especially in introducing themselves are: (a) the student‟s low vocabulary mastery; (b) the students had difficulties in pronouncing certain words; (c) the students were still confused in arranging words; (d) the students were often afraid in speaking English.

INTRODUCTION
English is learned seriously by many people to have a good prospect in the community of international world. Recently, English becomes important. Since it is important, English is taught widely at formal schools starting from elementary school up to universities, even at informal school i.e. courses (Naghdipour 2016). The use of English as the second language in oral communication is complex activities to be considered when teaching the English language (Al Nakhalah 2016).
In Learning English, we need to understand the four skills namely: listening, speaking, reading, and writing because these four skills can help us to master English easily. As one of the skills in learning language, speaking enables people to send and receive information or messages to others.
According to (Pérez, Carreiras, and Duñabeitia 2017) "speaking is an interactive process of constructing meaning that involves producing and receiving and processing information". In addition (Ting-Toomey and Dorjee 2018) states that "speaking is a process of building and sharing meaning through the uses of verbal and non-verbal symbol in various contexts". Speaking is one of the four Introduction is a way to connect with other human beings. Before we establish relationships with other humans we must introduce ourselves first so that we can know information about each other's personal data. Introduction is very important to do before we want to make friends with others (Zemach and Rumisek 2016). It has become a tradition that have to be done well when we start going to school, going to college, but in reality there are a lot of EFL students still find difficult to introduce themselves properly and correctly (Kwon 2017). According to (Machado et al. 2017) "expressing yourself is defined as an activity that expresses how you are reacting to a situation that occurred at that moment and provides information about past experiences".
The problem that many students face when introducing themselves is they are shy, lack of ideas, afraid, and lack of vocabulary (Megawati and Mandarani 2016). This research want to find out the difficulties of the students" at speaking skills, factors that cause students" difficulties and their strategies which is used to overcome difficulties in Speaking English.

RESEARCH METHOD
In this research, the researchers used descriptive qualitative method. According to (Creswell and Poth 2016) "Descriptive qualitative research is a research method that is based on the philosophy of post positivism which is usually used to examine conditions objective nature in which the researchers acts as a key instrument". Descriptive research tends to use analysis. The process and meaning (subject perspective) is more highlighted in qualitative research. The theoretical foundation is used as a guide so that the focus of research is in accordance with the facts in the field.
The population of this study was all the eighth grade students in MTS NW Baremayung. that consist of 18 students as the sample. In this study the present researchers collected the data by using some instruments namely interview, questioner and observation. In process collecting the data the researchers directly asked the participants some questions about self introduction.
According to (Zina 2021),"Research instruments are simply devices for obtaining information relevant to your research project". The instrument used in this research was interview, questionnaire and observation.
In the process of collecting data, the present researchers used interview, questionnaire and observation. Interview is often referred to oral questionnaires, it is a dialogue conducted by the interviewer to obtain information from the person being interviewed, (Powney and Watts 2018).
Interview is used by researcherss to assess a person's situation, for example to look for data about student"s background variables, parents, education, attention, and behavior. See also (Muhid, Machmoed, and Hakim Yassi 2020) According to (Rini 2020) that questionnaires are doubtless one of the primary sources of obtaining data in any research endeavor. Questionnaires are a number of written questions that are used to obtain information from respondents about something to be studied. Observation is one of the techniques that are used to collect the data. The researchers are able to find the answers by focusing and taking participant in an event or activity. According to (Chambliss and Schutt 2018)observation is taking regular conscious notice classroom action and occurrences, which are particularly relevant to the issues or topics investigating.
The researchers used an observation involving collecting the data, reducing the data, presenting the data and drawing conclusion. After collecting the data, the researchers reduce and present the data. In reducing the data, the researchers reject meaningless data, so the researchers got the important points of finding. It is followed by presenting the data, it means that the researchers presents about the data systematically and logically, so the meaning of every clear event. By the end of collecting the data, the researchers tried to verify the data based on reduction and data presentation.

FINDING AND DISCUSSION
The research results were gained from two resources namely a questionnaire and interview.
The questionnaire results can be shown in Table 1. Notes :SA (strongly Agree, A (Agree), N (Neutral), D (Disagree), SD (strongly Disagree)

Based on the interview conducted by the present researchers in MTS, NW Al Hidayah
Baremauyung, it showed most students" did not know how to introduce them; they still found some obstacles in introducing themselves. The researchers found that students" very difficult to pronounce words fluently and they have very little vocabulary. The level of students" in introducing themselves can be said very weak based on the results of the interviews and questions. Based on table above, it can be interpreted that there are some factors that influence the students" difficulties in speaking especially in introducing themselves, those are lack of vocabulary, unable to produce words correctly, the student are not confident in introducing themselves, and lack of practice of students" in speaking English. Furthermore, from all questions, there was one question that all students" answer the students" really need more attention from the teacher especially English teacher because seen from the ability of students" and their interest in English very less. Even one of students" said "English is a hypocritical language, different written other way of saying it, so why should learn English" from that statement it was very clear his disinterest in learning English. The reason had become a culture among students" they considered learning English very difficult.
From the result of the interview and questionnaire, it was found that there are some main problems in speaking especially in introducing themselves. The first is lack of vocabulary. When the students were speaking to introduce themselves they are often speechless because they had a lot of vocabulary in condition was caused by lack of emphasis on memorizing vocabulary by the teacher.
The second factor is difficulty in producing words correctly. In this case, the present researchers found that most of students" wrongly in mention words. Most of the students" does not want to speak because they do not know how to produce the words. This condition was caused by the students seldom learn how to spell the words. The third is the students" confidence. When the researchers asked the students to introduce themselves in front of their friends, most of them feel shy and afraid.
This condition occurred because students are not accustomed to speak English and rarely practice.
Based on the explanation above, the present researchers claim that there are three main problem that face by students" in speaking especially in introducing themselves. According to (Baker and Burri 2016)"the problem which is often faced by the students is about pronunciation. They felt difficult to pronounce certain words because in English, between pronunciation and writing are different. Therefore, they did not recognize yet". From all the difficulties, students had the most difficulty in pronouncing words correctly and did not have a large of vocabulary. In addition, based on relevant study that was conducted by Sari (2017) entitled students" difficulties in speaking skill at the eleventh grade of SMA Muhammadiyah 1 Karanganyar. It was found that every student had different difficulties in speaking. They are inhibition, nothing to say, event participant, and mother tongue. Based on the result of previous research above, the present researchers concluded that the students" difficulty in speaking especially in introducing themselves was caused by inhibition, nothing to say, un-event participant, and mother tongue.

CONCLUSION
Based on this research finding the present researchers concluded that the students" difficulty of MTS NW Al Hidayah Baremayung in speaking especially in introducing themselves are, students" of MTS NW Baremayung has lack of vocabulary, they cannot produce words correctly, and they are not confident when introduce themselves. The level of students" in introducing themselves is very weak, because the students" seldom learn how to spell the words. This condition occurred because students are not accustomed to speak English and rarely practice and lack of emphasis on memorizing vocabulary by the teacher.


EDUCATIONAL OR SCIENTIFIC CAREER ?

One problem that arises when teaching in higher educational institutions is conducted by university professors is that the educator spends most of the time on their own scientific activities, to the detriment of the pedagogical orientation of the learning process and methodology. In addition, their requirements for research and publication activity are constantly increasing, and so we often encounter the concentration of teachers' attention on a scientific orientation. As a result, these teachers sometimes neglect the process of teaching students, which leads to a loss in the importance of the pedagogical component of the educational process. The overall nature of the problem lies in the importance of teaching in universities, which must be places where teaching is considered a priority activity, comparable to science and research. Therefore, in our environment, we can observe a gradually increasing offering of programs to strengthen the pedagogical competencies of teachers. In this article, we decided to focus on the pedagogical component of the educational process of teachers of higher educational institutions of the Chuvash Republic and their participation in the educational program. Purpose of the study: to analyze how university teachers perceive and evaluate their pedagogical competencies, that is, how university teachers perceive themselves as a teacher, and at the same time how they evaluate professional development programs that are focused on systematic improvement of the level of their pedagogical competencies. The research problem lies in the dilemma between the pedagogical development of university teachers (participation in professional development programs) and their concentration on the research component of teaching. The central point of this entire study is the perception of university teachers of their own pedagogical development and the assessment of the quality of professional development programs. We chose to conduct detailed interviews with 25 teachers from the Chuvash State University of the Chuvash Republic as the central method for data collection. The respondents perceive other university professors not only as scientific experts in their discipline, but also as teachers capable of providing high-quality teaching. At the same time, none of the respondents called themselves a scientific expert in their field. All respondents would like to reduce the scientific component in IJASOSInternational E-Journal of Advances in Social Sciences, Vol. VII, Issue 19, April 2021 http://ijasos.ocerintjournals.org 133 their pedagogical work, leaving it for some specialized scientific centers. Also, all respondents would like to pay more attention to the pedagogical process of teaching students transferring knowledge, communicating with students or teaching students logical thinking, and forming high-quality professional competencies in their pupils. They also pointed out that attempting to save time in the learning process of students forms a "time bomb,” which will further negatively affect the socio-cultural development of our society. Most of the respondents believe that the best way to develop their pedagogical competencies is to regularly communicate with their mentors, who are people who they deem as more professionally competent. They do not believe that the use of advanced training programs is of paramount importantance.

Purpose of the study: to analyze how university teachers perceive and evaluate their pedagogical competencies, that is, how university teachers perceive themselves as a teacher, and at the same time how they evaluate professional development programs that are focused on systematic improvement of the level of their pedagogical competencies. The research problem lies in the dilemma between the pedagogical development of university teachers (participation in professional development programs) and their concentration on the research component of teaching.
The central point of this entire study is the perception of university teachers of their own pedagogical development and the assessment of the quality of professional development programs. We chose to conduct detailed interviews with 25 teachers from the Chuvash State University of the Chuvash Republic as the central method for data collection.
The respondents perceive other university professors not only as scientific experts in their discipline, but also as teachers capable of providing high-quality teaching. At the same time, none of the respondents called themselves a scientific expert in their field. All respondents would like to reduce the scientific component in

INTRODUCTION
In recent years, there has been a significant increase in the number of teachers who have decided to take up research work, which in turn advances their career growth. Of course, this criterion is still relatively small in the system of advanced training, but still there is a noticeable increase in the number of teachers who want to form their own competencies through research (Legostaeva, 2009, pp. 33-37;Maralova, 2013, pp. 73-80).
Each person has a career choice. Someone decides not to "conquer" the career ladder and work for their own pleasure, and some try to advance in their position by any means necessary. To do this, one must plan their academic activities. Only then will their own scientific and pedagogical career will become manageable.
One of the problems associated with teaching by university professors in higher educational institutions is that the teachers spend most of their time on their own scientific activities, to the detriment of the pedagogical orientation of the educational process and methodology. In addition, the requirements for research and publication activity are constantly growing, and we often encounter the concentration of teachers' attention on the scientific direction. As a result, these teachers sometimes neglect the process of teaching students, which leads to the loss of the importance of the pedagogical component of the educational process (Pan'kova, 2013, pp. 4-13).
Today's teaching career requires special attention. The developing community does not care who will work as a teacher, whether it is an impassive performer or a professional striving to reveal his own creative potential to a greater extent (Reznik, Makarova, 2010;Nikolaev, 2012). This dictates the need for research and implementation, in the educational sphere, of concepts, programs, and models for building the careers of the teaching staff, which are aimed at helping, supporting, encouraging and applying all the real skills of career growth (Reznik, 2011, pp. 49-54).
If we consider the career growth of a teacher as a dynamic process, then it should be noted that it is directly related to professional growth, as well as to the readiness of the individual for self-development and selfimprovement, within the framework of their own professional activities (Reznik, 2010, pp. 70-76).
The most important thing in professional growth is the teacher themself, as well as their expectations, ideas about his working futurethe future as a teacher or researcher.
The general nature of the problem lies in the importance of teaching in universities, where teaching is considered a priority activity, comparable to science and research. Therefore, in our pedagogical environment, we can observe a gradually increasing offering of programs to strengthen the pedagogical competencies of teachers, as well as increasing requirements for the scientific component of the pedagogical process (Reznik, Vdovina, 2013).
In this article, we decided to focus on the pedagogical and scientific component of the educational process of teachers of the Chuvash State University and evaluate their participation in educational programs (advanced training programs).

OBJECTIVE OF THE STUDY
Analyze how Chuvash University teachers perceive and evaluate their pedagogical competencies; that is, how teachers perceive themselves as a teacher and a researcher, and at the same time, how they evaluate professional development programs aimed at systematically increasing the level of pedagogical competencies in the career and growth structure.

METHODOLOGY
The central point of this entire study is the perception of university teachers of their own pedagogical development and the assessment of the quality of advanced training programs. As the main method of data collection, we chose a detailed interview with 25 teachers of the Chuvash State University of the Chuvash Republic. The respondents were 25 University professors, of whom 15 were women and 10 were men. The average age of the respondents was 65 ± 3.2 years.
In the structure of the questionnaires, the following questions were posed: 1) Does the HR department of the University deal with planning the career of teachers (that is, the personal profile that the teaching staff has or does not have contain a continuing education trajectory for teachers, e.g., a calendar of professional development for the teacher)? 2) Does the training program contribute to the development of teacher's pedagogical competencies? 3) Did they expect, during their postgraduate studies, that they would be engaged in scientific and pedagogical activities at the volume in which they are currently engaged? 4) What prevents teachers from engaging in scientific activities. 5) Are they satisfied with your teaching work? 6) What do they consider important to advance your career. 7) What motivated them to choose scientific and pedagogical activity.

RESULTS AND THEIR DISCUSSION
During the analysis, it was noted that 35% do not know the answer to the question "does the University HR department do career planning for teachers?", 53% believe that the HR department is not involved in teacher career planning, and only 12% answered the question positively.
We believe that the results obtained indicate a problem in structuring the activities of teachers within the walls of the University. It is more difficult for teachers to keep track of constantly changing training programs to expand their competencies, since the number of these programs is constantly increasing. Teachers are not able to keep track of, and keep abreast of, these programs, in view of their pedagogical and scientific workload.
On this issue, the following conclusion can be drawnthe University Human Resources Department should independently organize the planning of continuing education programs for the University's teachers. Moreover, the University can expand the necessary level of competencies among teachers, required at a given time and in a specific discipline, to create the conditions for improving the educational process of the University.
On the second question of the interview, the majority of respondents (78%) believe that the best way to develop their pedagogical competencies is to regularly communicate with their mentorsmore professionally competent people. They do not believe that using training programs is so important.
If we consider the career growth of a teacher as a dynamic process, then it should be noted that it is directly related to professional growth, as well as the readiness of the individual for self-development and selfimprovement within the framework of his own professional activity. The teacher themself is of fundamental importance in professional growth, as well as his expectations and ideas about their working future.
A comprehensive approach to solving this problem is necessary. We believe that for professional growth and to improve pedagogical competencies, it is necessary both to create discussion round tables with university mentors and to use various programs to improve qualifications.
On the third question of the interview, the majority of the respondents (83%) did not plan to engage in scientific and pedagogical activities in the volume in which they are engaged at a given time, 15% of the respondents coincided with reality, 2% found it difficult to answer this question.
We can draw the following conclusion that, while studying for a postgraduate program, future teachers are faced with a small amount of work that concerns both teaching and research activities. As a rule, the "life" of doctoral students does not coincide with the actual workplace requirements for teaching and research activities.
Thus, during the training of doctoral students, it is necessary to bring them closer to the real requirements of a scientific and pedagogical career. It is possible to realize these real conditions by increasing the load on pedagogical activity and scientific and publication activity.
On the fourth and fifth question, all respondents indicated only one reasonlack of time. They would all like to devote more time to the pedagogical component of their work.
If we want to achieve better results in the scientific component in a pedagogical career, then the results obtained must be taken into account when compiling the teaching load along an hourly trajectory for each teacher; that is, the hourly load of the pedagogical component must be reduced. This is possible by increasing in the number of staff members in the structure of the department or the university as a whole. This problem opens up a number of tasks for the leadership of the University and the departments under the jurisdiction of which this University is located. However, all respondents (100%) would like to reduce the scientific component in their pedagogical work, leaving it to separate specialized scientific centers.
Also, almost all respondents (93%) would like to pay more attention to the very pedagogical process of teaching studentstransferring knowledge, communicating with students or teaching students logical thinking, as well as the formation of high-quality professional competencies in their students. They also noted that attempting to save time in the process of teaching students creates a "time bomb", which will negatively affect the socio-cultural development of society in the future (94% of respondents expressed this sentiment).
On the sixth question, the opinion of respondents about the methods of promotion was revealed, which were distributed as follows: On the 1 st place is "The ability to be in sight of the authorities", on the 2 nd -"Getting to know the right people", and of 3 rd -place importance to the interviewed teachers is the belief that promotion can be obtained if there is professional competence and knowledge and good work results; On the 4th place is "The ability to show initiative and responsibility." On the 5 th place -"High working capacity". This arrangement of methods, especially 1 st place, is more likely due to the fact that the current situation in the country enforces upon teachers such an idea of moving up the career ladder.
From the analysis of the motives that made the teachers choose scientific and pedagogical activity, it should be noted that 5% of the respondents noted the possibility of self-realization, for 60%the social usefulness of work, 10%the possibility of a creative approach to work, 20%the relative stability of the workplace, 5% useful contacts, acquaintances.
It was interesting for us to analyze the choice of motives based on gender. Women have 10% more opportunities for self-realization than men, and for women, a creative approach to work is also more important. The paradox of the motive was that for men, labor activity is not an opportunity for "part-time work." In general, we can conclude that the woman is more inclined to analyze.

CONCLUSIONS
How to answer this questionin a scientific or pedagogical career, everyone decides for themself. As a result of the questionnaire survey, it was revealed that teachers would like to engage in scientific activities, but they do not have enough time. At the same time, in the completion of their activities, they become a part of the pedagogical processthey participate in the transfer of knowledge and communication with students or teaching students logical thinking, as well as in the formation of high-quality professional competencies of their students. They also noted that an attempt to save time in the process of teaching students forms a "time bomb", which in the future will negatively affect the socio-cultural development of society. And in order to improve the pedagogical component, it is necessary to use not only advanced training programs, but also closer communication with university mentors when organizing the educational process. It is impossible, however, to point out the priority path, whether it be continuing education programs or closer communication with mentors, since the development of scientific and pedagogical competencies is possible with an integrated approach. At the same time, advanced training, vocational training, and retraining of scientific and pedagogical personnel are today one of the priority areas in public policy, and also become the "strategic goal of creating an innovative university"


APPLICATION OF MIND MAP IN TEACHING GEOMETRY IN GRADE 4

When it comes to mathematics education and learning, mind maps are a graphical representation of ideas and concepts widely used. A mind map can significantly improve student learning and teacher teaching activities by its unique structure and characteristics. This study demonstrates the feasibility and effectiveness of incorporating a mind map into the geometry curriculum for fourth-grade students. The findings of an experiment conducted on 44 primary students demonstrate that, with the teacher's guidance, most students can create an appropriate mind map to review a lesson and that the mind map contributes to increasing students' learning motivation and subject interests. Several students responded positively to a survey about their attitudes toward using mind maps in mathematics learning, which revealed that they have favorable attitudes toward using mind maps.

, are multi-sensory tools that utilize visuospatial orientation to integrate information, and consequently, assist students to organize and retain information (D'Antoni et al., 2010;Mamontova et al., 2016).
In a mind map, text content is represented visually, and the connections between different levels of hierarchy and stages of development are shown (Anas et al., 2018;Katagall et al., 2015;Pribadi & Susilana, 2021;Santiago, 2011;Serrat, 2017). In line with this, Buzan and Buzan (2006) defined a mind map as a radial branch-like visual organizer in which concepts are structured hierarchically or associatively (as cited in Stokhof, 2019;Merchie et al., 2021). According to Liu et al. (2015), a mind map consists of words or concepts (with verbal and symbolic elements (Dhindsa, 2011), colors and pictures (D'Antoni, 2010;Merchie et al., 2021)) connected by lines with associated prepositional phrase where a line indicates the relationship between the words (Liu et al., 2015). A mind map, in particular, is a network or nonlinear diagram that begins with a key or main idea in the center and expands outward from there to include subtopics radially around the main idea. The subtopics group and similar cluster ideas branch out to lower-level topics (Arthur, 2012;D'Antoni et al., 2010;Dhindsa et al., 2011;Serrat, 2017).
According to Buzan (2005), there are four important features of a mind map, including: (1) attention to the subject is provided by a picture at the center of the diagram; (2) main topics of the subject are formed thanks to the branches regarding the picture at the center; (3) branches state a key picture or keyword on the connected lines; and (4) branches have a structure related to each other (as cited in Erdem, 2017). In addition, lines closer to the center should be thicker than those far from the center; the employment of images tagged to the branches is encouraged; and the use of color, especially for grouping and encoding, is also recommended (Santiago, 2011). These characteristics align with the points of view in the research of Bhattacharya and Mohalik (2020). Figure 1 illustrates a mind map. According to Norman (2012), a mind map can serve various functions. They can be used to depict the information presented in an informational text (representation), provide a classifying framework for text information (organization), explain abstract ideas by depicting them more concretely (interpretation), or provide mnemonics to help readers remember the text by making it more concrete and meaningful (transformation) (Norman, 2012). Many researchers concluded that the structure of the mind map aligns with the brain's neural network (Merchie et al., 2021), and the mind map itself taps into the natural nonlinear thinking process of the brain and potentiate learning by using both left-right brain capacities (Erdem, 2017;Santiago, 2011).
Research by Stokhof et al. (2019) and Stokhof et al. (2020) has shown that mind maps, especially digital mind maps, are suitable for primary education. Five specific characteristics shown in Stokhof et al. (2019) include: (1) mind maps support recording, exchanging and comparing information (Näykki & Järvelä, 2008); (2) mind maps have a flexible structure in which relations between concepts are easily visualized (Eppler, 2006); (3) fast elaboration and continuous alterations in the conceptual structure are made possible by digital mind maps in particular (Eppler, 2006); (4) Digital mind maps can serve as data repositories for storing and exchanging new information (Tergan, 2005); and (5) Building a mind map necessitates adherence to a few simple rules: To create branches, start with a single word, then split them at the end and add text on top. Color should be used consistently throughout (Buzan & Buzan, 2006), and according to Merchie and Van Keer (2012), even elementary school students should have no problem learning and applying these guidelines (as cited in Stokhof et al., 2019).
A few advantages of using mind maps have been outlined by Serrat (2017), including (1) the process of creating a mind map is more interesting and entertaining than writing a report or drawing up a standard chart or table, and (2) mind maps can be used to visualize information; (2) Because of mind maps' visual quality, users can more easily identify, clarify, classify, summarize, consolidate, highlight, and present a subject's structural elements than with a standard set of notes; (3) While linearly taking notes, keywords and images are more easily forgotten when using mind maps to organize your thoughts. The advantages of mind maps include their compactness, lack of extraneous words, ease of drawing, flexibility, and ability to condense pages of information into a single visual representation; and (5) In order to fill in information gaps and make complex issues more understandable, using mind maps can be beneficial (Serrat, 2017).
Previous studies have proved many benefits when applying mind maps in the teaching and learning process. Due to the mind map's characteristics, it contributes to more intensive collective knowledge construction as well as more effective information organization (Cendros Araujo & Gadanidis, 2020;D'Antoni et al., 2010;Dhindsa et al., 2011;Erdem, 2017;Mamontova et al., 2016;Pribadi & Susilana, 2021;Stokhof et al., 2019;Stokhof et al., 2020). Thus, according to Dhindsa et al. (2011) Pribadi and Susilana (2021), mind maps help students to promote the occurrence of longterm memory. For the brain, a mind map, which is multi-colored, multi-dimensional and provides visually stimulating stimulation, is more attractive than one colored traditional note and more effective in remembrance (Erdem, 2017). Furthermore, Santiago (2011) and Brandner (2020, as cited in Pribadi & Susilana, 2021) showed that mind maps can facilitate students in structuring information, helping to analyze, comprehend, synthesize, recall and generate new ideas better. Therefore, mind maps can positively affect students' conceptual understanding (Anas et al., 2018;Dhindsa et al., 2011), critical thinking (Anas et al., 2018;D'Antoni et al., 2010;Dhindsa et al., 2011;Pribadi & Susilana, 2021;Santiago, 2011) and creativity thinking (D'Onofrio et al., 2017;Erdem, 2017). On the other hand, using mind maps in the classroom also improves students' interaction (Cendros Araujo & Gadanidis, 2020;Dhindsa et al., 2011;Liu et al., 2015) and motivation (Anas et al., 2018;Erdem, 2017;Stokhof et al., 2019). In a study on pre-service mathematics teachers, Cendros Araujo and Gadanidis (2020) described their interaction while engaging in collaborative mind mapping. Firstly, participants develop discourse by adding comments, asking questions, sharing life experiences, and referring to class activities and resources. Moreover, secondly, they also develop leadership by engaging in behaviors such as building a base, making aesthetic decisions, resolving technical issues, giving directions, grouping topics, highlighting, filling or leaving blanks, and overcoming leadership obstacles (Cendros Araujo & Gadanidis, 2020).
Because of its benefits, mind maps are widely applied in teaching and learning in our day. It enables students to develop problem-solving capabilities, highlighting opinions, note-taking, recalling information, and tasks preparation and organization (Buran & Filyukov, 2015). Mind maps can be utilized as note-taking in learning-teaching, and they are an effective technique. -taking that differs significantly from the traditional note-taking method taking shape, aiding in remembrance with its colorful structure and links based on the active use of both lobes of the brain, making it convenient for constructivist learning (Erdem, 2017). Mind mapping is commonly used for the following purposes: (1) taking notes during meetings, whether individual or group; (2) summarizing the discussion: (3) to generate new ideas and viewpoints that lead to better solutions; (4) to simplify complex concepts; (5) to provide an overview of the gathered data; (6) to provide simple and creative information by the provided format (Elmansy, 2020; as cited in Pribadi & Susilana, 2021).
Along with conventional mind maps, an interactive mind map is an effective tool for new teaching and learning application of modern technology (Anas et al., 2018;Cendros Araujo & Gadanidis, 2020;Liu et al., 2015;Maksimenkova et al., 2018;Mamontova et al., 2016). There are lots of available software that allow the creation of mind maps, such as Blummind, FreeMind, XMind, GoConqr, MindMup2, WiseMappinf, MindMeister, MINDMAP 9, Mindjet MindManager, Coggle (Cendros Araujo & Gadanidis, 2020;Liu et al., 2015, Maksimenkova et al., 2018Mamontova et al., 2016;Santiago, 2011). In addition, researchers have studied the method of presenting a mind map online. Accordingly, Liu et al. (2015) developed a web application that provides an interface allowing users to create a knowledge mind map. With the online mind map tool, the electronic learning resource will be discovered and shared in the form of a subjectoriented package (Liu et al., 2015).
Nevertheless, using a mind map for teaching and learning creates some challenges for mind map adaptation (Maksimenkova et al., 2018). In general, grading students' mind maps is one of the challenges teachers have to overcome. Assuredly, teaching with a mind map requires the teacher to gather students' mind maps and evaluate them. Evaluation, in this case, is the process with rising laboriousness. The great difficulty of evaluation makes educational mind mapping a poor scalable technique. With a digital mind map, the first challenge is a selection of software suitable to educational needs. However, the automatization of this process can increase scalability. So, the questions of automatic mind maps evaluation are on the front of the burner (Maksimenkova et al., 2018).
The question of educational mind map evaluation is quite complicated and requires exact and consistent grading rules (Maksimenkova et al., 2018). According to Stokhof et al. (2020), to determine if students attained curricular objectives, three quality indicators in the student mind maps were operationalized: similarity to the core curriculum, elaboration of the core curriculum, and structure quality (Stokhof et al., 2020). D'Antoni et al. (2010) developed the mind map assessment rubric (MMAR) using weighted scores including concept links, cross-links, hierarchies, examples, invalid components, pictures and colors (D'Antoni et al., 2010;Santiago, 2011). Besides, Maksimenkova et al. (2018) introduced the automatic grader for educational mind maps (AGEMM) which acts like a teacher's assistant and calculates several quantitative metrics. Results demonstrate that the AGEMM may be transformed to scales or criteria levels used to evaluate (Maksimenkova et al., 2018).

Research Objectives
Geometry is an important branch in the mathematics curriculum of primary education, which provides students with practical knowledge associated with real life. Due to the intellectual characteristics of primary students, the teaching of geometric elements cannot yet be based on deduction but mainly on visualization to help them approach basic geometric features and properties of some geometric figures. Due to the need to innovate methods of teaching mathematics and other subjects in primary school, as well as the benefits of using mind mapping in teaching, the study aims to: 1) Analyze primary students' ability to use mind maps to support learning geometry.
2) Analyze students' attitudes towards using mind maps in learning geometry.

Participants
The experiment was conducted with 44 students in grade 4 of Mac Dinh Chi Primary School in Can Tho City, Vietnam.

Procedure and Instrument 3.2.1 Procedure
The experiment was divided into two phases. -Instructing students to color in the designed mind map of the lesson "Parallelogram" (Figure 2). . -Requirements: Coloring the topic image prominently; coloring the main branches (level 1) and keywords in different colors to distinguish them; colors of the branches closer to the central topic have to stand out from the branch farther away from the central topic; painting or adding appropriate, realistic images if possible.
-Evaluating students' products and analyzing the students' mistakes, and guiding students to overcome them. -Teacher hands out A4 paper and asks students to draw and color a mind map of "Rhombus" in 20 minutes.
-Requirements: Students can draw a complete mind map by themselves, with three or more branches, exact keywords and knowledge. The central topic stands out; the main branches are thicker (larger) or more prominently colored than the sub-branches; the main branches are colored differently to distinguish from each other.
-Evaluating students' products and analyzing the students' mistakes, and guiding students to overcome them.

Instrument
A mind map-making procedure is shown in Figure 3. Step 1: Drawing the central topic. Students need to draw the central topic from which other ideas are developed. Students can draw large-sized images with surrounding colors so that the subject stands out and attracts attention. The topic draw should not be framed or obscured. Words can be added to the topic drawing if the topic is not clear.
Step 2: Drawing main branches (level 1). The branch titles are the main points or ideas of the topic, arranged around the central topic and connected to the central topic by bold lines. Level 1 branches should be drawn diagonally so that more sub-branches can be deployed more easily. The keywords in the title need to be brief, concise and be differentiated in color and size.
Step 3: Drawing sub-branches. Sub-branches are branches that are developed from sub-branches of level 1. These are the detailed contents of the main ideas. Level 2, 3 branches (maybe more, depending on topic content) will be connected by thin lines and merged into level 1 branches. It is recommended to draw more branches connected by curves than straight lines; this will make the mind map not rigid and more flexible, thus easier to remember. Keywords and symbols should be used in each branch, and only one keyword should be used. This makes it easy for new keywords and other ideas to be appended to existing keywords. All branches should have the same color to distinguish the content of the branches easily. Step 4: Adding illustrating images. In this step, to enhance the imagination and make the brain remember knowledge more easily, students can add more illustrations or annotate some ideas to increase the richness of the content and the effectiveness of the mind map.
During the experiment, the research team designed lessons with the support of mind maps, based on the requirements of teaching geometry for students of grade 4 as specified in the current curriculum: Students are required to be able to (1) identify and correctly name acute, obtuse, and flat angles, know its relationship with right angles and recognize angles in learned shapes; (2) identify relationships between two lines such as: intersecting, perpendicular to each other, parallel to each other; (3) identify the features of the sides of parallelograms and rhombus, know how to calculate the area of a parallelogram, a rhombus; (4) know how to draw squares, rectangles according to the measure of sides (with a ruler); know how to cut, match, and fold shapes (with samples); (5) initially develop thinking manipulations, geometric imagination; (6) know how to apply formulas to solve problems with geometric content.

The results of familiarizing and coloring the designed mind map
The results obtained from students' designed mind map coloring of "Parallelogram" are shown in Table 1: In Table 1, the number of a well-colored mind map is 29, accounting for 65.91%, the number of an unsatisfactory mind map is 15, accounting for 34.09% of total mind maps obtained. The results were very positive, showing that most students understood how to represent the central topic and the levels of branches in the mind map. Furthermore, the colors in each diagram represent the individual identity of each student. Here are some illustrations of good mind maps (Figure 4, 5, 6).

Results of students' drawing and coloring their mind maps to review knowledge in the lesson Rhombus
The results obtained from allowing students to draw and color the "Rhombus" mind map by themselves are shown in Table 2: According to the quality assessment of the mind maps students create to review their knowledge of the Rhombus lesson, there are 34 good mind maps, accounting for 72.27%, and ten inappropriate mind maps, accounting for 27.73%, in the table above. The results show that even though they have only just been acquainted with and approached the use of digital maps in reviewing geometry lessons through Phase 1, most students can already draw a complete mind map by themselves to review the knowledge of the lesson "Rhombus" in particular as well as review the knowledge of geometry in general. Through classroom observation, it can be noticed that the children drew mind maps with enthusiasm and excitement. The mind map of the geometry knowledge with colors, images, and connections drawn by themselves makes students feel more interested in the subject, motivating them to learn and deepen their knowledge. Here are some illustrations of good mind maps (Figures 9, 10, 11, 12, 13):

Results of students' survey
The results of interviewing 44 students through questionnaires obtained the following results: Question 1: How do you like using mind maps to review geometry knowledge?
Students' attitudes towards using mind maps to review geometry knowledge are shown in Table 3: In Table 3, the percentage of students choosing the Extremely like and Like level accounted for 84.09%. Most students like to use the mind map to review the knowledge of geometry in particular and mathematics in general. The remaining 15.91% of students chose the level of Neutral, accounting for a relatively low rate. Especially, no student chose the level of Dislike and Extremely disliked. This result shows that using a mind map to review mathematical knowledge for students is feasible and suitable to their actual needs and interests.
Question 2: Can you draw a mind map yourself to review mathematics knowledge?
The results are shown in Table 4:  Table 4 shows that 86.36% of the students surveyed claim to draw mind maps on their own. This high rate proves that most students have mastered the basic steps to draw a mind map and are confident that they can draw one by themselves to review mathematics knowledge. The number of students who feel unable to draw by themselves accounts for a very low percentage, specifically 13.64% of the surveyed students.
Question 3: What are common difficulties you encountered when drawing mind maps to review geometry knowledge?
The results of the survey on students' difficulties when drawing a map are shown in Table 5:

Number of choices
It is hard to find ideas, illustrate images 32 It is difficult to organize ideas 28 It is difficult to identify and distinguish different levels of branches 9 Drawing ability is not good 8 It is difficult to represent the central topic 4 Through Table 5, it can be concluded that students find the most popular difficulties when drawing mind maps are finding ideas and images and organizing them, with a high number of choices are 32 and 28, respectively. Teachers need to pay attention to help students overcome these difficulties. To get accurate ideas and organize them logically, teachers can suggest that students find and organize collected ideas individually and through discussion groups. Besides, there are some other difficulties with a relatively low number of choices, such as difficulty identifying and distinguishing the levels of branches with nine students, drawing ability with eight students, and difficulty in representing the central topic with four students. Teachers also need to support students overcome these obstacles to become more confident to draw a mind map to review mathematics knowledge. With the difficulties related to the structure of a mind map, teachers can re-instruct the process of creating a mind map more detailed, introducing and analyzing some good mind maps to enhance students' understanding of drawing a mind map.

Question 4:
What do you think about the benefits of applying mind maps to review geometry?
The results of students' opinions about the benefits of using mind maps to review geometry are shown in Table 4: The students' survey results about the benefits of using mind maps to review geometry knowledge in Table 6 show that most students think mind maps help to remember knowledge longer (39/44 students). The students themselves create funny drawings and harmonious colors on the mind map to review the lesson, so that knowledge will naturally and deeply be engraved. Stimulating creativity is a benefit that also accounted for the second-highest number of votes, with up to 32/44 students choosing. Use a mind map to help students break free of old ways of thinking and unleash their creative potential in notebooks and on paper. Thereby, it stimulates the activity of the left brain to increase the efficiency of memory and creativity. Other benefits such as faster memorization, brief knowledge organization, and raising subject interests accounted for a high number of votes, around 50%. In addition, students also add some benefits such as: making them smarter, helping them know how to match colors. The above results show that a map is undoubtedly a useful tool that supports the review of geometry and mathematics knowledge of students. It also makes them more relaxed in class, which fosters the development of important skills for students, such as creativity, logical reasoning, and self-study.
Question 5: How do you think about applying a mind map in other activities? Students' opinions on applying mind maps to other activities are shown in Table  7: In addition to reviewing the knowledge of geometry, most students also think that mind maps can also be used to review and study other subjects such as Geography, Science, History, English, Vietnamese, Writing. Besides, students think that a mind map can also be used to plan for an exam or meals, to show students' interests, summarize the interests of family members, and decorate. The mind map has various applications in many areas of life and especially in learning and reviewing knowledge.
With the results obtained from two experimental parts, students can familiarize themselves with a mind map and draw a mind map themselves to review their knowledge of geometry. Through students' opinion surveys and classroom observations, the research team found that using a mind map in teaching geometry for grade 4 primary students is effective, especially in reviewing students' knowledge.
Primary students especially like vivid, colorful pictures and especially love to draw. Drawing and coloring their mind maps to review mathematics knowledge can raise their interests and help deepen their knowledge. Although they have just approached the mind map through two experimental phases, most students have grasped the process and principles and can draw complete mind maps themselves. This successful result is beyond expectations and shows that using a mind map in geometry is appropriate and suitable for primary students, especially for grades 4 and 5. In addition, the student's identity shows the pure and naughty thinking of the primary school age, and it also shows the very creative thinking of each student. In addition, a mind map also supports students in thinking and relating geometry knowledge with real-life phenomena, making it easier to understand and deepen students' understanding.

Conclusion
Through the experimental process, the research team found that a mind map is an effective and suitable tool supporting teaching geometry in grade 4. Applications of mind maps in teaching mathematics can raise the interests of students. The introduction of a mind map into the subject has created a positive atmosphere for the class, aroused interest and motivation in students' learning (Anas et al., 2018;Cendros Araujo & Gadanidis, 2020;Dhindsa et al., 2011;Erdem, 2017;Liu et al., 2015;Stokhof et al., 2019). Moreover, most students can draw a mind map following a complete mind map; each mind map shows students' style. The mind map has various colors and playful images suitable for primary age but still ensures the correct content of mathematics knowledge and the characteristics of mind maps. The geometry knowledge combined with colors and funny images from the mind maps makes the subject more interesting and helps students remember the knowledge they have learned deeply. This result is consistent with the study of the authors Dhindsa et al (2011) Pribadi and Susilana (2021). The experimental process shows that this mathematics tool supports very well the review of geometry knowledge for students. Therefore, using mind maps in teaching geometry in grade 4 is suitable with the subject's characteristics, primary students' age characteristics, and the "studentcentered" educational perspective (Stokhof et al., 2019;Stokhof et al., 2020).
In addition to the positive results achieved, there are also some limitations of the study, such as some students are still unfamiliar with withdrawing a mind map; it is difficult to manage the classroom, and the students' drawing time is relatively long under short-term experiments.
From the results and limitations of the study, new studies can be carried out on applying mind mapping software or online drawing tools, using mind map evaluation software to grade students' products. In addition, studies can be conducted with a longterm plan, with a larger number of students, in various content and levels of study.

Conflict of Interest Statement
The authors declare no conflicts of interests.
About the Authors Lu Kim Ngan graduated with honors from Can Tho University with a Master's degree in Mathematics Education. The field of education holds a special interest for her, and she has a strong interest in scientific research in this area. Duong Huu Tong is an associate professor and senior lecturer at Can Tho University's School of Education in Can Tho City, Vietnam. He also works as a consultant in addition to his academic positions. Over the past 17 years, he has developed expertise in various fields, including mathematics education, educational evaluation, and curriculum development, among others. Bui Phuong Uyen works as a principal lecturer at Can Tho University's School of Education. In 2016, she received her doctorate in mathematics education. In particular, she is interested in developing students' capacity for learning, testing and assessing student learning outcomes, and using information technology in teaching and learning settings. Nguyen Duc Minh is a final-year student at Can Tho University's School of Education, majoring in Primary Education. The pursuit of scientific knowledge excites him, especially when it comes to developing active teaching methods.


Twenty Years’ Development of Teacher Identity Research: A Bibliometric Analysis

This study aims to demonstrate a detailed knowledge map of teacher identity research via a 20-year data set from the Web of Science (WoS) database. A bibliometric analysis was employed for analyzing the articles published between 2001 and 2021 to show the status of teacher identity research in the past 20 years, research topics on teacher identity, and future research directions. Using the keyword “teacher identity” and filtering data by selecting articles and early access in teaching and education, 848 articles were retrieved. Through production, content, and citation analysis with the help of a bibliometric tool, this study found that teacher identity remained a popular research theme in the academic field over the past 20 years, and its booming production involved many authors, institutions, and sources, and countries. Furthermore, teachers’ “beliefs,” “emotions,” “professional development,” and “context” impacting the construction and reconstruction of teacher identity were the popular topics in teacher identity research, and fundamental issues, including “identity,” “teacher identity,” “professional identity,” “development,” “teacher development,” “beliefs,” and “intersectionality” of teacher identity keep good topics in future research.

INTRODUCTION Teacher Identity Research
The teacher identity has played an essential role in education research and teacher education (Lopes and Pereira, 2012;Jupp and Lensmire, 2016) because the construction of teacher identity is related to the teacher's professional development, thus impacting their teaching practices and attitudes (Pennington, 2014;Schutz et al., 2018). Moreover, the factors and the context influencing the construction of teacher identity enlighten the teacher education program and school managers to enhance program quality and management. Just as Beijaard et al. (2004) argued that teacher education programs could be improved by gaining a complete understanding of identity generally and teacher identity in particular. Furthermore, we could better design our teacher education programs through learning about teacher identity from the literature.
There is no doubt that academic publications on the development of teacher identity have been booming over the past 20 years, and they contribute to the development of various aspects of teacher identity research. However, it also becomes increasingly unfeasible to keep pace with everything being published simultaneously. In terms of teacher identity research, there are increasingly more studies on the topics related to it, and several reviews related to some specific aspects of teacher identity have been done. However, there has been a dearth of research on a general and an overall picture of teacher identity research in the past 20 years. A bibliometric analysis adopted in this study will give insights into current research status, research topics, and future research directions in teacher identity. We believe that this study is a valuable tool for practitioners and scholars in the research field of teacher identity. Early researchers interested in teacher identity can provide them with the knowledge needed to begin their research. For experienced teacher identity researchers, this study also serves to better understand the field's development and promote networking and collaboration between institutions and authors.

Bibliometrics Analysis Tool
Under the background of big data, there is a vast amount of literature in various research fields. However, many studies are scattered and hard to be arranged in an organized and transparent way. Consequently, quickly and accurately finding out the critical literature closely related to the research topic has always been perplexing (Aria and Cuccurullo, 2017). The study of teacher identity is taken as an example. There is too much relevant literature on teacher identity, covering multiple directions. It makes it more difficult for researchers to screen the literature they need the most.
A bibliometric analysis characterized by a quantitative analysis of the articles published in a specific field (Baker et al., 2020) is one of the literature reviewing approaches to accumulate knowledge and organize previous findings. It is a particularly prevalent method when investigating various aspects of science and how institutions and universities are ranked worldwide (Ellegaard and Wallin, 2015). A bibliometric analysis is based on the Bibliometrix package in R, an open-source ecosystem encompassing statistical algorithms, mathematical functionality, and visualization capabilities (Derviş, 2019). At present, the bibliometric analysis is applied to a vast range of research fields, including tsunami research (Chiu and Ho, 2007), in the management and organization (Zupic and Èater, 2015), in tourism (Koseoglu et al., 2016), TB research (Nafade et al., 2018), Economics in Latin America (Bonilla et al., 2015), and the COVID-19 pandemic (Gautam et al., 2020). The bibliometric method in this study has significantly powerful functions and plays an increasingly important role in research thanks to its scalable and reliable statistics. Compared with other approaches, it may introduce a systematic, transparent, and reproducible review process based on the statistical measurement of science, scientists, or scientific activity (Pritchard, 1969;Diodato, 1994). As a particularly suitable method for science mapping, it adapts to when the emphasis on empirical contributions produces voluminous, fragmented, and controversial research streams (Aria and Cuccurullo, 2017). The increasing number of publications applying bibliometric analysis in all fields indicates that it fulfills the need of policymakers, researchers who demand valuable and exact research based on massive literature. In addition to the benefits of researchers, the overall result produced by the bibliometric tool also benefits policymakers by helping them access the performance of scholars and institutions.
It is evident that some review studies on the topic of teacher identity have been done, such as teacher identity in the university context (van Lankveld et al., 2016), non-native English teacher identity research (Yuan and Mak, 2018), teacher educators' identity (Izadinia, 2014), issues in the teacher identity literature, and implications for teacher education (Beauchamp and Thomas, 2009). This study, however, contributes to teacher identity research by providing a knowledge map of this field. By employing a bibliometric analysis, we hope that this knowledge map will serve as a valuable tool for early researchers to find out knowledge and research findings to begin their research as soon as possible. We also hope that this study serves as an effective way for experienced researchers to understand the development of teacher identity research in the past 20 years, find research gaps that they can fill in the future, and help them find out potential cooperators. Furthermore, we expect that this study will serve as a reliable measure for some rating agencies to evaluate the performance of authors, institutions' sources, and countries in teacher identity research effectively and quickly.

Research Questions
The present study aims to identify and provide evidence for the state and impact of teacher identity research in the past 20 years. This study analyzed the research topic, publication pattern, research area, authors, highly cited articles, journals, and institutions that contributed most to teacher identity research in the past 20 years. The following questions were designed to plan the review of teacher identity articles in the Web of Science (WoS) database: (1) What was the research status of teacher identity research in the past 20 years? (2) What were the research topics on teacher identity research in the past 20 years? (3) What are the future research directions in teacher identity research? This study offered productivity, citation, and content analysis to answer these questions, such as the number of documents published and citations, co-occurrence of keywords, most relevant sources, authors and institutions, collaboration network, word cloud, and trend topics.

Data Sources
In this study, all data were retrieved from the WoS core collection database [including the citation Index Social Sciences Citations Index (SSCI) and Arts and Humanities Citation Index]. WoS is widely used for academic and bibliometric studies as it gives consistent journal coverage of scholarly published articles (Li et al., 2018;Birkle et al., 2020). The data were retrieved on July 16, 2021, and the research term was "teacher identity, " with a published timespan from 2001 to 2021. The literature types were mainly restricted to studies and early access. The literature data obtained included the complete records (the author's title, source year, abstract, keyword, DOI number, citation frequency, etc.) and the references cited in the article.

Data Collection and Data Analysis
This research selected the WoS that contained the data from 2001 to 2021, filtered the core document set according to the title of the study, and exported the 848 data from the selected database. Data collection was divided into three substages. The first was data retrieval. This research chose the WoS as a source of bibliographic information. We selected the articles and early access stored in the SSCI and arts & humanities citation index (AHCI) to analyze research questions. The second substage was data cleaning. We checked articles to avoid data repetition. In the third substage, files were downloaded and compressed. We downloaded 500 references the first time and 348 references the second time. Then, the two article files were compressed for employing bibliometric tools. Nowadays, different tools are available to perform bibliometric studies, including CiteSpace, HistCite, VOSviewer, and CitNetExplorer (Moral-Muñoz et al., 2020). This study adopted a biblioshiny program to acquire a general picture of teacher identity research in the past 20 years. Biblioshiny was developed by Massimo Aria and Corrado Cuccurullo from the University of Naples and the University of Campania's Luigi Vanvitelli (Hao, 2018). It is powered by Bibliometrix and its web-based graphical interface based on WoS, Scopus, and Dimensions data (Aria and Cuccurullo, 2017). In an up-to-date review on software tools for conducting a bibliometric analysis in science, Moral-Muñoz et al. (2020) have already given an introduction on biblioshiny. According to them, the interface of biblioshiny is intuitive and well organized, and the main menu is divided according to the Science Mapping Analysis (SMA) workflow (Moral-Muñoz et al., 2020). The menu in biblioshiny will conduct performance analysis from source, author, and document dimensions, and conceptual, intellectual, and social structures of knowledge also will be done through this menu. The analysis options are mainly subdivided into eight categories: (1) data set, (2) sources, (3) authors, (4) documents, (5) clustering, (6) conceptual structures, (7) intellectual structure, and (8) social structure. Several kinds of file formats can be exported, maps can be shipped to Pajek and Html, and tables can be copied to the clipboard or saved as excel, pdf, or printed.
The retrieved data in this study were analyzed for bibliometric indicators using the Rstudio software with bibliometric R-package v.4.0.4. First, the bibliometric analysis was activated in the R environment using the R language "install. packages ("bibliometrics, " dependencies = TRUE)." The command code opened a biblioshiny web interface on the google chrome browser. Raw data in WoS were imported into the biblioshiny and analyzed. Then, the author described and interpreted the findings indicated by statistics and pictures, which is a crucial part of this research. This study applied relevant authors, institutions, countries, articles, top highly cited publications, keyword co-occurrence, word cloud, thematic map, trend topics, and conceptual structure to answer three different research questions.

The Status of Teacher Identity Research in the Past 20 Years
For the first question: what was the research status of teacher identity in the past 20 years? In this study, a productivity analysis was performed. Preliminary information about data, most relevant authors, institutions and documents, countries dominating the teacher identity study, and the co-citation of authors and sources were presented to show the status of teacher identity research in the past 20 years. Table 1 presents general and comprehensive teacher identity research from 2001 to 2021. The sources of the teacher identity study involved 238, including journals and books. There were 848 documents in total. The average years from publication, average citation per document, and average citations per year per document were 6.2, 19.48, and 2.197, respectively. Moreover, the reference contained in the articles reached 27,422, which shows the popularity of the study of teacher identity in the past 20 years. The 751 articles accounted for the most significant published document types. In terms of document contents, the keyword plus and the author's keywords were 805 and 1,773, respectively. It indicates a wide range of research content in teacher identity research. We also know that 1,447 scholars from 2001 to 2021  published articles and contributed to teacher identity. There were 317 authors of single-author documents and 1,130 authors of multi-author articles. The documents per author, authors per document, coauthors per document, and collaboration index were 0.586, 1.71, 2.04, and 2.34, respectively. It suggests that more scholars paid attention to teacher identity research, and cooperation between authors was the most effective means for teacher identity research in the past 20 years.

Main Information About Data
The annual production about teacher identity is shown in Figure 1. This study concludes that scholars generally paid increasing attention and output during this period achieved a dramatic growth from less than 10 in 2001 to more than 80 in 2018. The booming research about teacher identity during 2018 indicates a research climax in teacher identity research. Additionally, in recent years, the productivity of teacher identity remained high and stable. We can conclude that teacher identity remained a hot research topic and gained momentum in recent years. From Figure 2, we get that the article citation reached a peak in 2006. It indicates that the study of teacher identity was actually in the preliminary stage, and there were relatively fewer publications. It coincides with Figure 1, which shows fewer annual scientific production in 2006. The stable average citation per year after 2014 in Figure 2 shows that teacher identity studies remained stable recently. Therefore, we can conclude that teacher identity research was in a phase of steady growth. Table 2 presents the top 20 relevant sources, which considered teacher identity and topics related to it as important research content and theme. It suggests that the journal Teaching and Teacher Education was the essential research front of teacher identity as it published 106 relevant articles and has 38 h-index, 78 g-index, 2.1 m-index, and 6,175 total citations in the past 20 years. Followed by 34 in Teachers and Teaching and 30 in European Journal of Teacher Education, it is proved that the journal Teaching and Teacher Education was far away ahead in all aspects of teacher identity research and the journal Teachers and Teaching and the journal European Journal of Teacher Education were also the two essential research fronts after Teaching and Teacher Education in teacher identity research in the past 20 years. Teacher identity was undoubtedly a hot topic in this study indicated by the fact that increasing more journals devoted themselves to teacher identity research. From Table 3 of Source Growth, we can see that many journals paid much more attention to teacher identity research. Among them, the publication of Teaching and Teacher Education increased more quickly than the publication in other journals. It coincides with that this journal served as a leading role in teacher identity research in the past 20 years. Table 4 presents the top 20 critical persons in the research field of teacher identity by presenting their document numbers, index, local citation, and total citation. John Trent was the most significant researcher with 17 articles and 11 h-index, 16 gindex, and 0.8 m-index. John Trent was critical in exploring many topics related to teachers' professional identity in the past 20 years. For instance, he studied teacher education as identity construction from action research (Trent, 2010), and the practice, language, and identity in a teaching practicum from learner to teacher (Trent, 2013), the native-speaking English teachers, and educational discourse in Hong Kong (Trent, 2012) and other relevant topics about teachers' professional development. Rui Yuan followed John Trent with 11 articles and 5 h-index, 10 gindex, and 0.7 m-index. Rui Yuan played an essential role in understanding pre-service teachers' professional development, motivation, and emotion (Yuan and Lee, 2014;Yuan and Mak, 2018) and student-teachers (Yuan and Burns, 2016;Yuan and Lee, 2016). Following Rui Yuan, Sonja Lutovac published 8 articles with 4 h-index, 6 g-index, and 0.3 m-index. Reviewing his study, we can conclude that he paid much more attention to teacher identities in mathematical education, such as pre-service teachers' future-oriented mathematical identity work, pre-service elementary school, and mathematics teachers' narrated possible selves about how failure shapes teacher identities. We can conclude that these three authors were the most prolific and fundamental in teacher identity research. Beijaard and Meijer (2017) were also the key authors in terms of local citation and total citation. It was proved that they were essential scholars and researchers in studying teacher identity, and their theories and views might provide a theoretical and practical framework for further research. It was around these authors that research circles of teacher identity had been shaped.

Most Relevant Authors
Most of the other authors had relatively average four to five articles and a similar index, which shows that they were also indispensable persons promoting the further development of teacher identity research.      resulted from the joint efforts of many institutions that focused on issues in teacher identity.  Table 7 presents the top 20 total cited documents and their global citation, normalized total, and normalized global citation. According to Table 7, the Reconsidering research on teachers' professional identity was most wildly cited by having 251 local citations and 1,062 global citations, and it also had 14.6 normalized local citations and 11.79 normalized global citations, which ranked first among all other articles. In this study, Beijaard et al. (2004) reviewed and classified the research of the last decades into three types: (1) studies focusing on the formation of teachers' professional identity, (2) studies focusing on the characteristic of teachers' professional identity, and (3) studies focusing on the teachers' stories for teachers' professional identity. The four essential features of teachers' professional identity were listed. They are: (1) professional identity is an ongoing process of interpretation, and reinterpretation of experience (Kerby, 1991), (2) person and context are implied in the professional identity, (3) subidentities are embraced in the teachers' professional identity, and (4) agency is an essential element in the teachers' professional identity. However, in this overview, the concept of professional identity was hard to agree with or not defined at all. However, Beijaard et al. (2004) concluded that the studies mainly focused on the teacher's practical knowledge, but its relationship and professional identity remained unclear. They also directed future research to the study that focuses on the concept of "identity, " "self, " and the "role of context" from more perspectives. The top two most globally cited documents were context, which shapes and reshapes new teachers' identities: a multi-perspective study written by Flores and Day (2006). In this study, they explored how the professional identities of 14 new teachers were shaped and reshaped in their first 2 years of teaching through the interplay between personal, professional, and contextual factors.

Most Relevant Documents
Through semi-structured interviews, questionnaires, and teachers' annual reports, this study found that the three main factors influence the construction, deconstruction, and reconstruction of teachers' professional identities: (1) prior influences, which means teachers' previous experiences as pupils; (2) initial teacher training and teaching practice, such as teachers' motivation and general assessment of their professional learning experiences and its influence on the formation of teachers' identity; and (3) contexts of teaching, which include the classroom practice, school culture, and leadership. This study concluded that teachers' personal histories and contextual factors of the workplace have a powerful influence on the construction of teachers' professional identities and suggested that the influence of pre-service programs might be strengthened by providing more opportunities for teachers' biographical reflection. Lasky (2005) produced one of the top three most globally cited documents. In A sociocultural approach to understanding teacher identity, agency, and professional vulnerability in a context of secondary school reform (2005), Lasky adopted a sociocultural approach to understanding the dynamic interplay among teacher identity, agency, and context. According to this study, the early influences on teacher identity and the current reform context are the primary mediational systems that shape teacher agency and professional vulnerability. Data from interviews and surveys revealed that the political and social context and early teacher development play an essential role in forming a teacher's professional identity, and there was a gap between teachers' expectations and the reality of reform. Moreover, the research suggested that a longitudinal study of how teachers' identity and agency are mediated over time is essential to explore. Generally, these top local and global cited documents revealed which document had the most significant influence on the perception of a teacher's professional identity and the production of other works in teacher identity research. Moreover, this table again proves that the journal Teaching and Teacher Education was the most relevant institution contributing to teacher identity research because most of these top most influential documents were published on Teaching and Teacher Education.

Co-citation Analysis of Authors and Institutions
Co-citation networks can illustrate and analyze the performance of authors and institutions in teacher identity research in the past 20 years. Figure 3 sheds light on the connection network of authors. A node represents an author, and the node's size signifies the total number of citations of the authors. A link between the two nodes represents a co-citation relationship, and the thicker the link was, the more frequently the author has been cited. According to the size of nodes and connection between them, this study can conclude that Douwe Beijaard had the most intensive network, followed by Catherine Beauchamp, Christopher Day, Maria Flores, and Sue Lasky, which is in line with the fact that these authors were also the most globally cited author and their documents had a significant influence on teacher identity research. The other two clusters show that the authors in the periphery of the network have also started to publish articles about teacher identity and its related topics, and they have already developed a solid co-citation network. The intensive co-citation networks suggest that the development of teacher identity research involves joint efforts and cooperation among many scholars and researchers. Figure 4 shows a structure of the co-citation of sources. Similarly, the nodes represent the cited sources, and the node's size and color signify the source's citation and connection. To be specific, the larger the node is, the more frequently the source is cited. According to Figure 4, it is well presented that three co-citation clusters were shaped, and each collection had numerous nodes, which shows that these journals were highcited and had an extensive co-citation network. Among these journals, the journal Teaching and Teacher Education had the  most intensive network, which shows this journal was most cited and contributed most to the development and progress of teacher identity research. Around the journal Teaching and Teacher Education, intensive co-citation networks among many journals, including Teachers and Teaching European Journal of Teacher Education, and Cambridge Journal of Education are formed. It shows that they were research fronts of teacher identity research and contributed significantly to the progress of teacher identity research. Other sources in the other two clusters indicate that increasingly more authorities paid attention to issues in teacher identity and co-citation network has been formed among them, such as the co-citation network among Language Teaching, System and TESOL Quarterly in the green cluster, the co-citation network among Teacher Education Quarterly, Teaching Education, and Curriculum Inquiry in the blue collection. It is proved that the development of teacher identity research was owned by joint efforts of authors and institutions who contributed to the productivity of teacher identity research.

Research Topics in Teacher Identity Research in the Past 20 Years
For the second question: What were the research topics on teacher identity in the past 20 years? This study intended to answer it through content analysis. Word Cloud, word growth,  thematic map, conceptual structure map, and co-occurrence of author's keywords were used to present research topics in teacher identity research in the past 20 years. Figures 5, 6 show Word Cloud measured by keywords plus and author's keywords plus on teacher identity research from 2001 to 2021. With a visual representation of the biblioshiny, words with higher volume and keyword density were displayed in a larger and more prominent font. Word Cloud was applied to analyze the frequently used term to show research topics in teacher identity research. Different words had distinct colors, and the size and position of words represented the frequency of the words. To be specific, the more central the word was, the more frequently it was used. We chose the top 20 words according to keyword plus and author's keyword plus. First, from Figure 5 of keyword plus mapping, we know that "education" was most frequently used to study teacher identity. It was followed by "knowledge, " "beliefs, " "professional identity, " and "experiences." This figure shows that teacher identity was an essential research topic in the education field in the past 20 years.

Word Cloud
According to Figure 6, shaped by the author's keyword, "teacher identity" was the most frequently employed keyword in their articles. The items, such as "professional identity, " "identity, " "teacher education, " and the "teacher", were also intensively used as keywords by authors who studied teacher identity. It shows that they were fundamental topics. Moreover, according to Figure 7, the item "education" employed in the teacher identity increased more quickly, which signifies that teacher identity was an indispensable topic in education research and significantly impacted education development. Figure 8 presents the status quo of topic groups in teacher identity research. Different colors represent different clusters, and the keywords in the same collection signify high relatedness. A thematic map is divided into four quadrants according to centrality degree and density. The high centrality and high density in the upper right quadrant indicate well-developed motor themes in the research field. As it can be seen, "professional, " "teacher professional identity, " and "development" were the focus and core of the research and had excellent prospects of development.

Thematic Map
The high density and low centrality in the second quadrant indicate niche themes whose development situation is good but has little influence on the research field. It can be seen that "high education, " "gender, " and "curriculum, " and "professional development, " "teacher professional identity, " and "science education" have formed independent research groups. However, their development prospects in the future were uncertain. In the lower-left quadrant, subject clusters had a low centrality and low density. It indicates that various kinds of "teaching training" "teaching" were marginalized. It means that they were emerging or declining topics. The high centrality and low density in the fourth quadrant signified that "teachers, " "identity, " "discourse analysis, " and "teacher education" were the fundamental themes in education. It can be inferred that their theoretical systems were more complete and mature, and these basic themes may provide the theoretical foundation, rationale, and method to teacher identity study. However, their development prospect is not promising.

Conceptual Structure Map
The biblioshiny for Bibliometrix allows, using the Conceptual Structure Map, to perform multiple correspondence analysis (MCA) to draw a conceptual structure of the field and identify clusters of documents that express common concepts (Aria and Cuccurullo, 2017). MCA makes it possible to conduct a mathematical and graphical investigation of ostensible multivariate information (Greenacre and Blasius, 2006). As seen in Figure 9, the keywords were divided into two clusters using MCA. The colors represent different clusters, the distance between keywords implies the relatedness, the vertex illustrates the word, and the node's size is proportional to its occurrence. In the red collection, "identity, " "teacher identity, " and "teacher  development" frequently appeared. The items "behavior" and "education" were integrated into the blue cluster. Figure 9 shows that a central research theme of teacher identity was formed, and some research topics around teacher identity were relatively well developed. The teachers at various stages, including "initial teacher education, " "novice teacher, " "students teacher, " "preservice teacher, " and "beginning teacher, " have been studied. The teacher identity of diverse subjects has been intensively explored, including "language teacher identity, " "science teacher, " and "physics teacher." Furthermore, the teacher identity study was connected to education, including "pedagogy, " "curriculum, " and "theory." The intersectional and sociocultural features of teacher identity, including agency, social justice, gender in the formation of teacher identity, was an increasingly popular topic.

Co-occurrence of Author's Keywords
To understand the research topics of teacher identity in the past 20 years, we have identified that the co-occurrence of keywords analysis is an effective tool to provide an overall knowledge structure. Figure 10 shows the keyword co-occurrence network of publications. The co-occurrence of the author's keywords suggests the frequency with which keywords, in other words, co-occur in publications. A node represents a keyword, and the bigger the node is, the more citations the keyword has. A link between two nodes represents the co-occurrence of two keywords, and the thicker the line is, the more frequent they co-occur. Similarly, there were five clusters indicated by five colors in Figure 10. Specifically, "teacher identity" and "teacher education" were prominent in the red cluster and frequently co-occurred. It means that these two topics were emphasized in teacher identity research, and teacher identity research was almost inseparable from teacher education research, the same with "identity" and "teacher" highlighted in the blue cluster. The "personal identity" was prominent in the purple circle, but it did not connect with other words. However, it had a mild relationship with "preservice teachers, " "students teachers, " and "teaching." Besides, from the occurrence of the keywords and link between orange and green nodes, this study finds that "language teacher identity" and "community of practice" were usually explored together, and "development" and "professional" research were connected. However, the size of nodes and the thin line between them indicated that they were not researched deeply by now.
In sum, many keywords were employed in the study of teacher identity. "Teacher identity, " "professional identity, " "teacher education, " and "identity" were central and had the highest co-occurrence with other words. It proves that they were fundamental and core research topics in teacher identity research. In the periphery of the network, there was also co-occurrence of other keywords, like "pedagogy, " "teacher agency, " and "teacher training." It shows that a broader range of research topics in teacher identity research was explored. For all the differences, we can conclude that "teacher identity, " "identity, " and "professional identity" were primary and core research themes, the "beliefs, " "knowledge, " and "experiences" which influence the construction of teacher identity were also popular research contents in the field of teacher identity research.

Future Research Direction in Teacher Identity Research
For the third question: What are the future research directions in teacher identity? With the help of the bibliometric tool, this article used Thematic Evolution and Thematic Trends to predict future research directions.

Thematic Evolution
Thematic Evolution and Trend Topics can show hot research topics and future research directions. In Thematic Evolution, different themes are represented by different colors, and the rectangle area indicates the degree of research. Figure 11 shows that many research themes are involved in teacher identity research, and the research focus was not static but changed dynamically over time. As time went by, "identity, " "teacher identity, " and "professional identity" remained to be popular research topics. However, the study focus changed from "identity" to "teacher identity, " and the emerging issues, including "teacher, " "professional learning, " "language teacher identity, " and "change" of teacher identity, "teacher professional identity" became more prevalent in 2017-2021. It can be inferred that these topics have a great potential to continue to develop in the future.

Trend Topic
In the Trend Topic, the size of nodes indicates the publication number of topics and the time when the topics were popular. According to the size of blue node in Figure 12, we can get that the research of "teacher identity, " "identity, " and "professional identity" thrived in 2017, indicated by their high productivity. It is again proved that they were fundamental and core topics in teacher identity research in recent years, and they are possible to be paid great attention to in the future. It coincided with the Thematic Evolution in 2017-2021. Besides, recently, emerging topics such as "development, " "teacher development, " and "beliefs" remained popular. The "intersectionality" of teacher identity was an emerging research topic that occurred in 2019, and it would keep as a promising research topic in the future, indicated by its high productivity in 2020. It can be concluded that these topics, including "teacher identity, " "identity, " "professional identity, " "development, " "teacher development, " "beliefs, " and "intersectionality, " have a great potential to thrive in teacher identity research in the future.

CONCLUSION AND IMPLICATION
This study employed a bibliometric tool to analyze the 20-year development of teacher identity research in a detailed manner. Using the visualization method's productivity analysis, content analysis, and citation analysis, we acquired information about research status and research topics of teacher identity research in the past 20 years. Moreover, future research directions were predicted to enlighten scholars and researchers interested in the issues related to teacher identity research.
First, through the bibliometric analysis in 20 years of development of teacher identity research, this study concluded that teacher identity is an encompassing concept and remains a popular topic in the academic field. Among the numerous research topics, "teacher identity, " "professional identity, " and "identity" were the fundamental and core themes. "Education, " "knowledge, " "beliefs, " "agency, " and "experiences", which shape that teacher identity was also active and popular topic in the teacher identity research. Teacher identity was an everlasting research theme that involved diverse research topics in the past 20 years.
Second, teacher identity studies involved many authors, institutions, sources, and countries, and the cooperation mainly conducted its survey among different authors and institutions in other countries. Douwe Beijaard, Maria Flores, and Sun Lasky played a crucial role in teacher identity research as their documents contributed a lot to the production of other research articles. An increasing number of researchers devoted themselves to teacher identity research indicates that teacher identity research in education has practical significance for many aspects of human society. In terms of the documents, the documents Reconsidering research on teacher's professional identity (Beijaard et al., 2004), Context, which shapes and reshapes new teachers' identities: a multi-perspective study (Flores and Day, 2006), and A sociocultural approach to understanding teacher identity, agency, and professional vulnerability in a context of secondary school reform (Lasky, 2005) were the three most essential documents in teacher identity research. The journal Teachers and Teacher Education, Teachers and Teaching, and European Journal of Teachers Education were the institutions that had the most significant impact on the study of teacher identity. The United States, United Kingdom, and China were the top three countries that contributed to the development of teacher identity research, and strong collaborations and networks among them were formed. These aspects in the teacher identity research are closely connected as the most cited person contributes to the formation of the countries, institutions, and articles that have considerable influences on teacher identity research. All types of this information benefit greatly to stakeholders in the education field. It may help novice and experienced researchers find the most relevant knowledge about teacher identity research and look for potential cooperators in this field. Moreover, it can provide policymakers with a standard to evaluate the performance of institutions, universities, and authors in teacher identity research.
Third, through an analysis of Thematic Evolution and Trend Topic, we can conclude that fundamental and core topics in teacher identity research, including "identity, " "teacher identity, " and "professional identity, " are possible to be paid more attention to in the future, which coincides with the Thematic Evolution in 2017-2021. Besides, recently, the emerging topics, including "development, " "teacher development, " and "beliefs" remained popular topics. Remarkably, the "intersectionality" of teacher identity, which shows the influence of gender, social justice, race, and other sociocultural factors on the construction and reconstruction of teacher identity, is an emerging and promising topic in the future indicated by its high productivity. It can be concluded that these topics have the potential to thrive in teacher identity research in the future. This trend agrees with the postmodern stance on teacher identity because it holds that the construction and reconstruction of teacher identity result from the interaction between the individual and context. Moreover, teacher identity development is a relational phenomenon, and sociocultural factors offer a more practicable perspective on teacher identity development.
Although bibliometric methods effectively reveal a research field's knowledge structure and research topics and can predict future research directions, it is not a substitute for extensive reading. The broad task remains a premise for an in-depth understanding of the research field. Furthermore, in the future, the quantitative method in the teacher identity should be applied more to challenge the psychological feature of methodology in the research. Moreover, an integrated method uses qualitative and quantitative methods in future teacher identity research.

LIMITATION
As a quantitative study with a bibliometric tool based on the data collected from a database, the focus is on the presentation of pictures and statistics, but the qualitative method for data collection and data analysis is absent. Furthermore, it is a review study providing an overall view of teacher identity research in the past 20 years based on the bibliometric analysis, but it has not delved into a specific aspect of teacher identity to give a thorough investigation. To provide a more extensive understanding of teacher identity, we insist that future research could expand the study to employ a variety of data collection to explore more specific issues in teacher identity research.

DATA AVAILABILITY STATEMENT
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.