Thin films of α-TeO2 (paratellurite) were prepared by the vacuum evaporation from a quartz crucible. The dispersion properties of the refractive index and the absorption coefficient of these films are obtained by the measurement of transmittance in the range of the near ultraviolet through visible light. These results are discussed using a formula involving a complex dielectric constant. The dispersion of the refractive index is explained by introducing an additional oscillator at 3.99eV to the two oscillators on the single crystal. The existence of an impurity band is suggested from the fact that the measured effective forbidden gap of the film (about 3.7eV) is narrower than the gap of the single crystal (4.02 eV). Localized impurity levels are evaluated at 3.40, 3.00, and 2.45eV. Although another 3.80eV absorption level is evaluated, this may be an effective level of the impurity band. The wavelength dependence of the photoconductivity is similar to the curve of the absorption coefficient, namely, the photosensitivity in the ultraviolet region is higher than that of the visible light region.
Investigations were made on the effect of polarization on the surface migration of metal atoms which is induced by a thermal-field during remolding. Experimental results show that the end-form of the thermal-field build-up of a crystal plane on tungsten and rhenium emitters is determined by the anisotropic feature of the free energy of the surface, which in turn is influenced by the adsorption of gases and the polariza-tion of surface metal atoms caused by the remolding field. Discussions are given on possible causes of the thermal-field build-up of the (001) crystal plane on a tungsten emitter exposed to CO2 or O2 gases of about 10-7 Torr. The remolding conditions that provide highly narrow angular confinement of field electrons from <013> and <001> oriented tungsten emitters are also described.
Thin hafnium films have been prepared by evaporation by electron beam heating on the following three substrates, CaF2 (111), KBr(100) and carbon coated CaF2 (111). The film thickness was made 500Å or 1000Å and the environment of deposition was held at an ultrahigh vacuum. The threshold of substrate temperature required to form single crystal films were found to be about the same on the three substrates and very low compared with the hafnium melting temperature (2222°C). In the case of CaF2 (111) substrate, the threshold temperature was as low as 380°C, being the epitaxial temperature at which bcc (111) Hf is parallel to (111)CaF2. The films took three different crystal structures, hcp (α-phase), fcc and bcc (β-phase), depending on their substrate temperatures (Ts). In the case of carbon coated CaF2 (111) substrate, the film structures were the following; hcp structure for Ts_??_350°C, fcc structure for 300_??_Ts_??_450°C and bcc structure for Ts_??_400°C. The lattice constant of fcc structure film was found to be a0=4.98Å.
Recently, much interest has been shown in the application of acoustic surface waves to micro-wave devices and many fundamental or applied research about acoustic surface waves are being reported. Acoustic surface waves are also applicable to the research of surface state physics as well as to engineering, and, as an example of such, this paper reports the theore-tical and experimental results of the observation of surface roughness, using nonlinear effects in acoustic surface waves. It is found that the amplitude of second harmonic waves of acoustic surface waves on dispersive media changes periodically. The volocity dispersion can be evaluated from the peak to peak length of the amplitude. In addition, it is known that the velocity of acoustic surface waves propagating along rough surfaces is dispersive. Therefore, the roughness of surfaces can be evaluated from observations on the two phenomena above. Our experiments on LiNbO3 gave values of surface roughness which are about 20_??_40Å in height. These values agree well with those observed by the electron microscope.
Methods and modulation characteristics of current-modulated He-Ne lasers are presented. The discharge current of the laser tube is alternately varied between the pumping level of optimum lasing and that of excess excita-tion. The current control is made by a simple transistor circuit and an on-off modulation up to 500 kHz is obtained with the peak laser output of 0.2 mW. Applications to picture recording are also briefly noted.