Fumio Akao

Anomalies of Acoustic Attenuation and Velocity at the β-γ Phase Transition in Ag3SI

The acoustic attenuation and velocity of Ag 3 SI single crystal were measured between 140 K and 300 K with 10 MHz longitudinal wave propagating along the (100) axis. It was found that there are two transition points on cooling. The transition temperatures at 161 K and 157 K correspond to the order-disorder transition and the β-γ structural phase transition, respectively. Hysterisis phenomenon was observed at the structural phase transition and the two transition points overlapped on heating from the γ-phase.

Hypersonic Attenuation in Sb Doped Germanium

Hypersonic attenuation in Sb doped Ge is measured. In the attenuation vs. temperature curve, a large peak is found at 1.8°K. A hypersonic sournd used is longitudinal waves of 1 GHz propagating along the axis of Ge crystal which contained about 1×1014, 1×1015 and 1×1016/cm3 donors. The above attenuation peak seems to be due to the electronic relaxation between the singlet and the triplet states of the donors in Ge, as discussed by M. Pomerantz in the case of As- or P-doped Ge.

Contribution of the Si s Electronic State to the Density of State of CoSi2 at Fermi Energy by Soft X-Ray Emission Spectroscopy

A clear modification is observed between an electron-excited Si L2.3 valence band (VB) soft X-ray emission spectrum (SXES) for CoSi2 and the one for Si. From this fact, it is concluded that a fair amount of the Si s electronic state is included in the upper half, especially at the Fermi edge, of the VB density of state (VB-DOS) of CoSi2. This fact is a clear contrast to many proposals given so far, where it is claimed that the upper part of the VB-DOS of CoSi2 is constructed only by the electronic states due to Co(3d)-Si(3p) hybridization.

Hypersonic Attenuation in Antimony-Doped Germanium and Its Magnetic Field Dependence

The temperature and magnetic-field dependence of hypersonic attenuation in Sb-doped Ge is measured at liquid He temperatures. It is found that (1) the temperature dependence of attenuation in a sample with 1×10 16 Sb atoms/cm 3 is quantitatively explained by the simple relaxation formula; (2) the attenuation is anomalously large in a sample with 1×10 15 /cm 3 Sb atoms; (3) the attenuation shows maxima as a function of magnetic field and this behavior cannot be explained by existing theories even when the Zeeman effect and internal stresses are taken into account.

Magnetic Field Effect on the Hypersonic Attenuation by Shallow Donors in Ge

The magnetic field effect on the hypersonic attenuation in Sb-doped Ge has been measured over the range from 0 to 200 kG at liquid He temperatures. The attenuation was observed to decrease as the magnetic field was increased at high field. The magnetic field dependence of the attenuation in the case of 1×10 15 /cm 3 doped specimen differs from that of 1×10 16 /cm 3 doped specimen. The experimental results are not quantitatively explained by the theoretical treatment which takes into consideration only the Zeeman effect on the single and the triplet states. If it is assumed that the effective Bohr radius of the donor electron is larger than the known values by other experimental methods, the semiquantitative agreement is obtained by calculating the shrinkage effect of the donor wave function.

Magnetic Field Dependence of Ballistic Heat-Pulse Scattering in As-Doped Ge

Heat-pulse propagation along the [100] axis of As (1.5 ×10 14 /cm 3 and 0.9 ×10 15 /cm 3 )-doped Ge has been studied as a function of the magnetic field H //[100] and of the heat-pulse temperatures ranging from 6.6 K to 9.3 K. It is shown that the transmitting heat-pulse intensity detected by CdS bolometer increases with increasing magnetic field up to 60 kG at sample temperatures ranging from 1.8 K to 4.2 K. The magnetic field dependence of the detected heat-pulse amplitude is compared with a calculation based on the Suzuki-Mikoshiba theory.

X-ray photoelectron spectroscopy study of band offsets in a-Si0·2C0·8:H/p-(a-Si:H) and a-Si0·2C0·8:H/n-(a-Si:H) heterojunctions

Abstract Valence-band offsets ΔEv have been evaluated from an X-ray photoelectron spectroscopy (XPS) study of heterojunctions of a-Si0·2C0·8:H/p-(a-Si:H) and a-Si0·2C0·8:H/n-(a-Si:H). The values of ΔEv for a-Si0·2C0·8:H/p-(a-Si:H) heterojunctions are estimated to range from 1·2 ± 0·05 to 1·5 ± 005 eV depending on the amounts of dopant in the a-Si:H. For a-Si0·2C0·8:H/n-(a-Si:H), ΔEv is 0·7 ±005eV. The origin of the difference in the values for different types and levels of doping in a-Si: H is discussed. Reported electron transport properties are discussed using the band structure at the hetero-interfaces obtained from the present XPS study.

Variable mixing frequency method for accurate and convenient measurement of ultrasonic velocity

A simple and convenient method for the accurate measurement of ultrasonic velocity is presented using a commercially available pulsed ultrasonic oscillator and receiver. The principle of operation of the present method belongs to the variable frequency method. The cw signal by the rf signal generator is provided not only for the purpose of the superposition of the same frequency rf pulse transmitted through the specimen in the form of the ultrasonic pulse, but also for the purpose of the triggering of the pulsed ultrasonic oscillator via a frequency divider. The phase matching of the cw signal of the signal generator with the rf pulse, which was generated by the ultrasonic oscillator, is detected sensitively by the video signal on the oscilloscope. The through‐transmission technique makes it easy to measure the ultrasonic velocity of a highly attenuated signal, as in case of the critical phenomena.

Uniaxial Stress Effect on Acoustic Attenuation in Sb-Doped Ge

The acoustic attenuation in lightly Sb-doped (1∼2×10 15 Sb/cm 3 ) Ge was measured in the temperature range from 1.4 to 4.2 K at frequency about 700 MHz under uniaxial stress up to 3×10 8 dyn/cm 2 . It was found that the uniaxial stress changed the acoustic attenuation remarkably and the behavior depended strongly on the direction of the applied stress. The experimental results are compared with the theory in which the relaxation of the system into an instantaneous local thermal equilibrium under acoustic waves and the contribution of each valley to the donor wave function under uniaxial stress are considered.

Ultrasonic Attenuation Measurements on Single Crystal of V3Si near Tc

The normal and the superconducting states of a single crystal V 3 Si were studied by the usual pulse-echo method of ultrasonics at about 100 MHz. The magnetic field dependence of the ultrasonic attenuation slightly below T c showed a complicated behavior characterized by four critical fields, which indicated the mixture of cubic and tetragonal phases. It was found that the critical temperature in the tetragonal phase T c (Tet.) should be a little bit (∼0.1 K) lower than that in the cubic phase T c (Cub.). It was also found that both the second critical fields H c2 (Cub.) and H c2 (Tet.) showed a linear Δ T (≡ T c - T )-dependence in the same way as those of usual type-II superconductors. The ratio of the H c2 (Tet.) to the H c2 (Cub.) was about 0.84, which may correspond to the ratio of the Fermi velocity in the cubic phase to that in the tetragonal phase. From the temperature dependence of the critical attenuations Δ α, the values of the ultrasonic attenuation at each critical field, we obtained a formul...