the carbon nanotubes 13 the laser evaporation method utilizes the same principles of the electron beam evaporation method except for a laser beam is used instead of the electron beam in the cvd method a reactive gas having the same composition as a material for the protective membrane 15 is sprayed over the carbon nanotubes 13 at a constant rate to be deposited on the carbon nanotubes 13 in the sol gel method a material for the protective membrane 15 is dissolved in a solution and coated on the carbon nanotubes 13 next the solvent is removed by vaporization to result in the protective membrane 15 the protective membrane 15 is formed of a material with electrophilicity chemical stability thermal stability and strong hardness for example nitrides carbides oxides etc suitable nitrides for the protective membrane 15 include boron nitride bn aluminium nitride aln boron carbon nitride bcn gallium nitride gn etc suitable carbides for the protective membrane 15 include diamond diamond like carbon dlc etc suitable oxides for the protective membrane 15 include magnesium oxide mgo silicon dioxide sio 2 aluminium oxide al 2 o 3 etc 0038 fig4 is a transmission electron microscopic tem photograph of a field emitter device according to an embodiment of the present invention including carbon nanotubes having a protective membrane compared with the conventional carbon nanotubes of fig1 having no protective membrane the tips of the carbon nanotubes appear to be unclear due to the protective membrane of boron nitride appearing to be slightly dark as indicated by reference numeral 10 0039 fig5 a is a graph of current emission versus time showing field emission characteristics of an embodiment of.