Goroh Tominaga

Growth of Bismuth Layers on Si(100) Surfaces

The adsorption of bismuth on Si(100) surfaces is studied by quadrupole mass spectrometry, LEED and AES. Two adsorption states are observed: one is a two-dimensional (first) phase with saturation coverage and the other a bulk-like (second) phase without saturation coverage. When the two-dimensional phase of Bi was formed at a high substrate temperature, the LEED patterns from the Si surfaces showed an Si(100)2×1 structure with weak fractional order spots. In the Auger amplitude vs. deposition time curves, break points were observed at the completion of the first-phase adsorption. These points shift towards the higher coverage side with decreasing substrate temperature during deposition in accordance with the increase in the amount of adsorbed bismuth atoms.

Kinetics of deposition of bismuth film by a molecular beam method

Abstract The growth processes of bismuth films on Si(111) surfaces were studied using quadrupole mass spectrometry, AES, and LEED. At higher substrate temperatures, the adsorption occurs only in a tightly bound state. The LEED pattern from these surfaces shows a Si(111) √3 × √3−30° -Bi structure. At lower temperatures, the orientation relationship of Bi(0001) ∥ Si(111) was observed for thick films.

Structure and electrical properties of thin bismuth films

Abstract The resistivity of thin Bi films on silicon was measured for films of various thicknesses. The experimentally obtained thickness dependence of the resistivity was compared with the result of a numerical calculation based on the equation which was proposed by Mayadas and Shatzkes. At 290 K the experimental curve fitted the numerical one with surface and grain boundary reflection coefficients of 0.6 and 0.12 respectively.

Photon Stimulated Desorption of Positive Ions from LiF

Photon stimulated desorption (PSD) of positive ions from LiF is observed in the photon energy region between 30 and 70 eV. The creation of the Li+(1s→2s) core exciton leads to the rapid rise of both Li+ and F+ desorption yields. It is found that PSD of positive ions from LiF is due to the interatomic Auger transition. The yield spectrum of F+ ions is different from that of Li+ ions above 60 eV. The F+ yield spectrum has a deep valley at around 63 eV, while the Li+ spectrum shows a plateau in the same region. However the difference in the yield spectra of Li+ and F+ ions can not be explained at present.

Adsorption of bismuth on Si(110) surfaces

Abstract The adsorption of bismuth on Si(110) surfaces has been studied by means of quadrupole mass spectrometry (QMS), LEED and AES. The existence of three main adsorption states (the first, second and third phases) were observed. Two of them (the first and second phases) are two-dimensional phases and the other (the third phase) is a three-dimensional phase. After the completion of the first phase at a high substrate temperature, the LEED pattern showed a clear Si(110) 2 × 3 structure. A shift of the saturation coverage of the two-dimensional phase with the change of the deposition condition was also observed.

An influence of the first adlayer structure on the sticking coefficient of the successive adsorption in a system of bismuth on silicon (111) surface

Mass spectrometric measurements on the initial stage of the growth process of bismuth film on Si(111) surfaces have been made using an impinging molecular beam containing Bi and Bi2. Two adsorption phases are found, one is a tightly-bound phase with saturation coverage and the other is the second phase. The structure orderness of the first adsorption phase, which is a two-dimensional adlayer with a saturation coverage of about 3 × 1014atomscm2 changes with the substrate temperature during deposition. At 760 K, a LEED pattern of this layer shows a Si(111)√3 × √3 − 30° Bi structure, which becomes diffusive with decreasing substrate temperature during deposition. The influence of the structural disorder of the tightly-bound phase on the growth of the second adsorption phase has been studied in terms of a sticking coefficient. When the substrate temperature is kept at 600 K, the sticking coefficient of bismuth to a tightly-bound phase formed at 600 K showing 1 × 1 structure (LEED pattern) is about twice as large as that on the first adlayer formed at 760 K showing a clear √3 × √3 structure. The degree of supersaturation when the nucleation growth of the three-dimensional second phase takes place on the first adlayer is found to be greater than 10 on the 1 × 1 structure, and 100 on the √3 × √3 structure, respectively.

An Analysis of the Transient Responses of Acoustic Delay Lines

Transient responses of acoustic delay lines (ADLs) were simulated on the assumptions that gas molecules in each segment of an ADL were in thermal equilibrium and that the straight-through component in the intruding gas was negligibly small. The flow rate of gas through an orifice was evaluated by using expressions of orifice conductance applicable in a wide pressure range. In order to examine the adequateness of the present method, the results of simulations were compared with several experimental data. The influence of the location of vacuum pumps and of arranging a high speed shutter at the entrance of an ADL were also simulated.

Mean Adsorption Time of Oil Molecules Measured by Non-Stationary Flow Method

The mean adsorption time, τ, of DOP (usually used as high vacuum pumping fluid) on borosilicate glass, is obtained from the measurement of the time lag in setting up the stationary flow of the vapor through a glass tube evacuated to ultrahigh vacuum. In the experiment, the time variation of flow rate of oil vapor is measured by an ionization gauge cooled by liquid nitrogen. The glass tube was maintained at a temperature between 65°C and 90°C. Although τ for adsorption of an approximately monomolecular layer cannot be expressed by a simple expression, τ for further adsorption follows the relation τ=τ0exp (E/RT), where E=22.4 kcal/mole and τ0=1.1×10-16 sec. Some discussions are made on the first molecular layer adsorption.

An UHV Evaporator for Thin Film Growth Study

The design concept and the performance of an UHV evaporator are described. The evaporator is capable of maintaining the low 10-10 Torr range throughout the evaporation period. A stainless steel bell jar, 0.5 m in diameter and 0.6 m high, and a chamber for evaporation sources are connected with each other by two 7 mm diameter openings. These two chambers are pumped separately by the respective sets of sorption, sputter-ion and Ti sublimation pumps. The bell jar contains a large liquid N2–cooled shroud of 4.3 m2 total area, within which 1.3 m2 faces the vapour sources. Seven samples for electron microscopy which correspond to successive stages of film growth can be obtained in a single evaporation run. Gold has successfully been deposited at 1×10-10 Torr at a rate of 0.01 A/s. Pressure bursts during the rapid deposition of a second layer, carbon anchoring film, were up to the 10-9 Torr range.

Adsorption Studies of Oil Molecules on Borosilicate Glass Surface Using Molecular Beam Techniques

A Pyrex glass surface is subjected into collision with molecular beams of di-2-ethyl-hexyl phthalate (DOP). Temperatures of the glass and of the molecules are controlled in a range 100°C~160°C. The molecules that initially impinge on a thoroughly outgassed surface form a tight adsorption layer 1.1~1.4×1014 molec./cm2 in density (first layer). The adsorption time τ of the molecules constituting the first layer is too long to measure. For the surface on which the first layer has formed, however, τ decreases with time and approaches a final value: τ=5×10-12exp (20×103/RT) s, when both the molecular beam and the glass surface are kept at temperature T (R: gas constant). By using the adsorption time obtained at various temperatures of the target and impinging molecules, the thermal accommodation coefficient is estimated to be 0.2~0.3 for the first layer. These results jointly indicate that relaxation effects are important in the adsorption of DOP on Pyrex glass.