No description available.

No description available.

No description available.

Silicon is the heart of modern semiconductor devices. The dominance of Si in semiconductor technology depends on the superior quality and properties of thermally grown SiO(,2) compared with the oxide that can be placed on any other semiconductor. For this reason, Si-SiO(,2) interface has been an interesting and important research subject for many years.;The well established quasistatic and conductance methods used in the study of the Si-SiO(,2) interface are improved by using (i) an effectively thin composite insulator, (ii) low carrier concentration substrates, and most importantly (iii) low-level illumination at a wavelength that creates electron-hole pairs. Accurate measurements of both the total density of interface states and its major components as a function of energy in the forbidden gap have been made over four decades (10('10) - 10('14) states/eV-cm('2)) due to items (i) and (ii). Item (iii) decreases the response time of the slow states (those in the lower half of the band gap for n-type samples), so the quasistatic condition is well satisfied and the conductance method can be used to study the interface states throughout the band gap on a single sample. Without illumination, the quasistatic condition is not satisfied even for ramp rates on the lower side of those used previously and complementary n- and p-type samples are needed for the conductance method.;The samples investigated have a thermally grown oxide prepared in dry oxygen. They were never exposed to H(,2) or H(,2)O at an elevated temperature. We speculate that this processing provides an abrupt Si-SiO(,2) interface. The composite gate insulator was completed by having an e-gun deposited 250(ANGSTROM) layer on LaF(,3). The resulting interface, subjected to the improved experimental method, yields a wealth of distinctive structure rather than the often-reported featureless U-shaped interface-state density.

We present a thermoelastic derivation of ultrasonic waves propagating in a solid in which an applied homogeneous stress is superimposed on a nonzero initial stress. We also derive the temperature dependence of the elastic coefficients and the linear relationship between the applied stress and a newly defined parameter--the thermal acoustic constant. The stress acoustic constant is defined and its relationship to the acoustic natural velocity is discussed. Experimental considerations pertinent to the ultrasonic measurement techniques used in the investigation are described. The results of the stress-strain and thermal strain experiments verify the predictions of the theory. Finally, we derive an improved formula for correcting the effects of the transducer and the transducer bonding material in ultrasonic standing wave phase velocity measurements. The results are verified by computer models and laboratory experiments.

Amorphous alloys of VAl and VSi have been prepared by a process of r.f. sputtering onto cryogenic substrates. The Nuclear Magnetic Resonance has been examined in an effort to understand how the electronic structure of these amorphous alloys compares to that of the corresponding crystalline alloys, and to extend the study of the electronic properties of these alloy systems into composition ranges where the crystalline alloys do not exist, because of solubility limits.;The Al('27) and V('51) Knight shifts were measured at 77(DEGREES)K and 300(DEGREES)K, for Al concentrations extending from 15 to 85 atomic percent, in amorphous VAl. The results are found not only to agree with those of the crystalline alloys below 40 atomic percent Al (the solubility limit), but to extend the crystalline behavior right into the region of immiscibility. In amorphous VSi only the V('51) Knight shift was measured. The V('51) Knight shift, before annealing, was found to be nearly constant with both temperature and alloy composition. After annealing the amorphous VSi alloys, however, a strong temperature dependence was observed in the V('51) shift, probably due to the formation of the compound V(,3)Si upon crystallization.;These results are explained in terms of a model which treats the amorphous alloys as though they were crystalline but with an extended solubility range. The case of V(,3)Si is considered as an exception due to its peculiar crystal structure and resulting electronic behavior.;The V('51) NMR linewidths were also measured in both amorphous VAl and amorphous VSi. These are discussed in terms of the short range order found in the amorphous alloys.

Amorphous alloys of the form Ni(,1-x)P(,x) and (Ni(,1-y)Co(,y))(,1-x)P(,x) were prepared by two methods, electroplating (EP) and electroless deposition (EL). Two metastable phases of differing physical densities and NMR properties were noted, and analysed by measurement of the Knight Shifts, relaxation times, physical densities, etc. A comparison is made between the data and a hybridized band model which yields an expression for the enhanced susceptibility of the phosphorous valence band.

Zero, longitudinal and transverse magnetic field uSR has been used to investigate (mu)('+) diffusion and trapping in Nb. The ambiguity in the interpretation of the 'double humped' temperature dependence of the depolarisation rate for the transverse field case has been resolved. A discussion of how the zero and longitudinal measurements can distinguish between the trapping and detrapping phenomena is presented with (mu)SR data analysis in mind. Muon mobility is shown to increase monotonically with temperature. The width of the local magnetic field distribution due to Nb nuclear moments and the rate for trapping and detrapping of muons have been measured at several temperatures.;Data from an earlier study of aluminum doped with .1 at. % Si, Ag and Mg showing complex structure in the linewidth parameter have been analyzed further using a multi-trap nonequilibrium model to obtain trap concentration, binding energies and diffusion rates for the host and the traps.

The molecular motions are studies in two disordered materials that undergo glass transitions. Glycerol is a conventional glass former and cyclohexanol is an orientational glass former.;The technique used in the glycerol experiments was spectral hole burning. Chemical shift anisotropy produces inhomogeneous broadening of NMR lines in orientationally disordered and polycrystalline solids. By saturating or inverting a portion of the anisotropic line, 'burning a hole', molecules of certain orientations are tagged. Subsequent molecular reorientations result in spectral diffusion which is not related to spin-spin interactions. By measuring the broadening and recovery of the hole as a function of time, detailed knowledge of the reorientation is obtained. For example, the mean jump rate and the lower limit of angular reorientations are determined. The reorientation rate in supercooled glycerol is followed from 10('-2)s('-1) to 10('2) s('-1). Our measurements agreed with previous results and extended them to lower frequencies. The mean jump size was determined to be greater than 45 degrees. The hole recovery curves were not exponential, but were fitted with the Williams-Watts function, exp = ((tau)/(tau)(,0))('(beta)) with (beta) = 0.5.;The motions in the rotor phase of solid cyclohexanol are studied with proton NMR from the melt down to 5 K. Particular attention is paid to the variation of the linewidth with temperature and to the temperature and frequency dependences of T(,1). We find there are two distinct motions that cause minima in T(,1) as a function of temperature. These two motions were observed in dielectric experiments. From the proton line narrowing and C('13) high-resolution solid state spectra, the high temperature '(alpha)' motion is identified as overall molecular rotation. The low temperature '(beta)' motion is identified as a uniaxial internal rotation of the cyclohexyl ring about the CO bond, with the COH group remaining stationary. This explains both the strong spin relaxation and the weak dielectric relaxation peak associated with the (beta) motion. Both motions have distributions of correlation times, as seen from the shallow T(,1) minima and the weak temperature and frequency dependences of T(,1). From 100 K to 5 K, the temperature dependence continues to be weak. The frequency dependence remains less than (omega)(,0)('2). These results indicate that some components of the motion remain faster than the NMR frequency (omega)(,0) even at 5K. The behavior of cyclohexanol is compared to that of other disordered solids.

Quantitative verification of the existence of static acoustic displacements generated by acoustic waves propagating in single crystal samples of intrinsic silicon is presented. Measurements are made of the static displacements generated by 30 MHz acoustic compressional waves propagating along the 111 , 110 , and 100 crystalline directions. From these measurements the nonlinearity parameters are calculated and found to have the value 3.87 along the 111 direction, 4.23 along the 110 direction, and 2.13 along the 100 direction. These results are in agreement with values obtained independently from harmonic generation and pressure derivative measurements. Implications of the present work to the thermodynamics of single crystals are discussed.