1. Field of the Invention
The present invention relates to a method for forming a probe of an information reading and/or input apparatus, an apparatus therefor, and an information reading and/or input apparatus equipped with a mechanism for reforming the probe. Such information reading and/or input apparatus is utilized, for example, in a surface observing apparatus such as a scanning tunnel microscope (STM), a high-density record/reproducing apparatus capable of recording and reading information in the size of atomic order (several Angstroms), an encoder for fine positioning, measurement of dimension or distance, positional measurement for speed measurement, particularly measurement and control requring a resolving power of atomic order, or the like.
Recent development of the scanning tunnel microscope capable of directly observing the electronic structure of the surface of a substance or in the vicinity of the surface [G. Binning et al., Helvetica Physica Acta, 55, 726 (1982)] has enabled to measure the real space image with a high resolving power, both in the monocrystalline and amorphous substances. Applications of a wide range are expected for such scanning tunnel microscope, as it is usable for various materials, allowing observation with a low electric power without damage to the specimen by the electric current and being capable of functioning not only in high vacuum but also in air or in solution.
The scanning tunnel microscope is based on a current generated between a metal probe and a conductive material when they are brought to a small distance of about 1 nm, with a voltage therebetween. Said current is very sensitive to the change in the distance of both members, and the surface information of real space can only be obtained by moving the probe in scanning motion so as to maintain said current or the average distance of both members constant. In such case a resolving power of 1 .ANG. or less can be obtained in the direction along the surface.
In the conventional ordinary scanning tunnel microscopes, there is employed a method of detecting the tunnel current flowing between the surface of conductive specimen and the pointed end of the detecting conductive probe (probe electrode), effecting electric feedback control on the distance between the specimen surface and the detecting probe so as to maintain a constant tunnel current, and displaying the structure of atoms and molecules as an image. The resolving power of such scanning tunnel microscope is determined by the radius of curvature of the pointed end of the probe. For improving the resolving power, therefore, the pointed end of the probe has to be made sharper.
On the other hand, the recording capacity in data recording apparatus has been increasing year after year, and such tendency calls for reduction in size of the recording unit and increase in the density thereof. For example, in the digital audio disk utilizing optical recording, the recording unit has been reduced as small as about 1 .mu.m.sup.2.
The above-explained principle of the scanning tunnel microscope can be utilized in realizing information recording with a recording unit of 0.001 .mu.m.sup.2 or smaller, by employing a material with memory effect for the voltage-current switching such as a thin film of an organic compound with .pi.-electron system or a charcogenide, as the recording medium. An apparatus for high-density information recording and reproduction with such recording medium is generally equipped with a vernier control mechanism or an X-Y stage for maintaining a probe electrode at a small distance of about several nanometers to the recording layer and mutually moving said probe electrode and recording layer, in order to effect the recording and reproduction in an arbitrary position in the recording layer.
For achieving high-density recording and reproduction, there are required not only a recording medium with small recording unit, but also a probe electrode of which pointed end, governing the resolving power in the direction of recording layer, sharpened to the atomic or molecular level.
Thus, in an observing system such as the scanning tunnel microscope for observing a specimen with a resolving power of atomic order or in a high-density information record/reproducing apparatus in the atomic order utilizing the principle of such scanning tunnel microscope, the pointed end of the probe electrode has to be made very sharp.
For this reason, the probe electrode is generally composed of a platinum or tungsten rod of which an end is pointed in a conical shape by mechanical polishing or electrolytic polishing.
However, in the actual operation of such surface observing apparatus or information record/reproducing apparatus, the pointed probe electrode may be brought into contact with the information bearing member such as the observed specimen or recording medium, as they are maintained at a very short distance of several nanometers. Also in the operation in the air, the pointed end of the probe electrode may be contaminated by the dusts in the air. In such case the probe electrode loses the resolving power of atomic or molecular level, and there will result a loss in the resolving power or recording density of the entire apparatus, in the reliability and overall performance thereof. It therefore becomes necessary to replace or regenerate the probe electrode. The replacement is made with a probe electrode formed in advance by electrolytic polishing or electrolytic discharge forming. Also for regeneration, there are known a method of applying a strong electric field while heating the pointed end portion of the probe in a vacuum chamber as disclosed in the Japanese Laid-open Patent Application No. 63-265101 and a method of effecting electrolytic evaporation in an ultra high vacuum chamber.
However, such conventional methods have been associated with a drawback that the formed or regenerated shape of probe inevitably fluctuates, so that the resolving power in the surface observation with the scanning tunnel microscope or in the recording and reproduction of the information record/reproducing apparatus varies depending on the mounted electrode or on each regeneration.
A third example utilizing a probe electrode pointed to atomic order is the encoder mentioned above.
Conventional encoders have a reference scale having positional or angular information and detecting means for detecting said positional or angular information by relative movement to said reference scale, and are classified into several types, such as optical, magnetic and electrostatic capacitative encoders, by the systems employed in said reference scale and detecting means.
Also as an encoder with resolving power of atomic order, there is already known an apparatus for detecting the amount of parallel displacement disclosed in the Japanese Laid-Open Patent Application No. 62-209302 and utilizing the basic principle of the scanning tunnel microscope disclosed in the U.S. Pat. No. 4,343,993.
Such encoder is equipped with a reference scale for length and a probe positioned close to said reference scale, and has a function of obtaining the current generated between the reference scale and the probe which are provided with a driving mechanism, and encoding thus obtained information on said current.
The probe for detecting the tunnel current in said encoder is generally composed of a sharp needle formed by known electrolytic polishing method. Also mechanical polishing may be used for this purpose.
The performance of the probe with sharpness of atomic order for detecting the tunnel current is the heart of the encoder and is directly related to the performance of the encoder. However, in order to detect the tunnel current of pA - nA order generated between the reference scale and the probe, the distance therebetween has to be maintained as small as several nanometers, so that there may result mutual contact by eventual vibration of floor or by noises. The pointed end of the probe will be damaged by such contact and will lose the ability of length measurement of the atomic order. Also the replacement or regeneration of such probe results in the aforementioned drawback that the resolving power fluctuates depending on said replacement or regeneration.