High Resolution Electron Microscopy (HREM) was used to study microstructural changes related to the CoSi/Si-CoSi/CoSi2/Si-CoSi2/Si transformations. CoSi is found to grow epitaxially on Si with [111]Si // [111]CoSi and < 110 >Si // < 112 >CoSi. Two CoSi non-equivalent orientations (rotated by 180° around the substrate normal) can occur in this plane. They can be clearly distinguished by HRTEM on cross-sections ( electron beam along [110]Si). At about 500°C CoSi transforms to CoSi2. Experimental results show that the type B orientation relationship satisfying [110]Si // [112]CoSi is preserved after the initial stage of CoSi2 formation. At this stage an epitaxial CoSi/CoSi2/Si(111) system is obtained. The atomic scale investigation of the CoSi2/Si interface shows that a 7-fold coordination of the cobalt atoms is observed in both type A and type B epitaxies.

The early stages of the nucleation and growth of nickel silicides in Ni-Si multilayers evaporated onto oxide-stripped <100> Si substrates and annealed at 150 °C have been studied by cross-section transmission electron microscopy (TEM). Observed differences in the interaction of evaporated Ni with amorphous silicon and single crystal <100> Si have been explained by thermodynamic modeling of the Ni-Si system. The as-deposited films show a 3 nm amorphous Ni-Si intermixed layer at all Ni-Si interfaces, including that with the single-crystal Si substrate. Crystalline Ni2Si formed in all annealed films, consuming the elemental Ni layers. The amorphous alloy layer grows concurrently with Ni2Si during the reaction with a-Si; however, there is no amorphous phase present at the Ni2Si - <100> Si interface. Thermodynamic calculations show that at 150 °C metastable equilibrium might be expected between a-Si, the amorphous phase, and Ni2Si; but not between Ni2Si, the amorphous phase, and crystalline Si. The composition of the amorphous phase is very close to a-Ni50Si50. After a 6 hour anneal at 150 °C, crystalline NiSi forms between the a-Si and the Ni2Si layers by crystallization of the amorphous phase. Further annealing is necessary to form NiSi at the <100> Si - Ni2Si interfaces.

We introduce quantitative Auger lineshape analysis methods to study the room temperature reaction of nickel on Si(111). We show that coexisting phases may be separated by numerically fitting the composite lineshapes using a linear combination of single phase “fingerprint” spectra, obtained by scraping bulk compounds in situ. The reaction proceeds in three stages. For nickel coverage below 1 Å, the growth is layerwise, forming NiSi2. For nickel coverage from 3 to 12 Å, islands of Ni2Si are formed. For nickel coverage above 12 Å, islands of pure nickel are formed. The overlayer reactions appear to be a kinetically limited form of Stranski-Krastanov growth, with multiple compound formation.

Near edge X-ray absorption spectra (XANES) have been obtained from the Ti K-edge for several series of titanium silicide samples produced by different techniques. Samples were fabricated by depositing Ti on silicon wafers and subsequently annealing them up to temperatures from 100°C to 900°C in UHV, vacuum furnace, or in a Rapid Thermal Annealing system. Measurements were done in the fluorescence and total electron yield modes. The XANES measurements were correlated with Raman scattering measurements. The XANES data of several reference compounds were obtained, and the data showed a high sensitivity to changes in the film structure. Ti metallic bonding and Ti-Si bonds can be distinguished and their evolution as a function of annealing is related to previous results. For the samples with increased impurities, Ti regions were stable at higher temperatures. The XANES spectra of samples annealed under N2 indicate the formation of a surface nitride.

An electron excited Si L2,3 valence band soft x-ray emission spectrum (SXES) for Ni(or Co)Si2 showed a clear modification from that for Si. From the SXES study, a fair amount of the Si(3s) valence band density of state (VB-DOS) is concluded to be included in the upper part of the VB-DOS for the transition metal(TM) disilicides due to the TM-Si bond formation, which is a clear contrast to proposals given so far. Non-destructive structural analysis of a NiSi2 (tens of nm)/Si(111) contact is also carried out successfully using the SXES.

The kinematical approximation is valid for High-Energy Transmission Electron Diffraction from monolayers in planview. We use this fact to study quantitatively the attack of Si (111) 7×7 by 02. Oxygen is found to bind in the bridging position of the adatom backbonds and render the structure very stable during subsequent 02 exposure. Electron-beam exposure during dosing additionally creates rapid disordering which is presumed to represent SiOx formation.

We describe the analysis of Fresnel contrast seen at a free silicon surface in order to characterise the initial clean surface and the formation in situ of the first atomic layers of oxide.

The technique of spin dependent recombination (SDR) allows the electron spin resonance (ESR) observation of electrically-active point defects in a single metal-oxide-semiconductor field-effect transistor (MOSFET) with surface areas of only 10-4 cm2 and Si/Si02 interface point defect densities of ∼1011/cm2. With SDR's enhanced sensitivity, devices with different processing details are explored. Differences in the E' spectra for variations in the oxidation processing are discussed.

We have used solid state nuclear magnetic resonance (NMR) spectroscopy to study both “wet” and “dry” thermally grown films of SiO2 on silicon substrates. For the 5000 § wet film, grown at 1050 °C we observed a single Lorentzian line of 6 kHz HWHM (half width at half maximum). For the 500 § dry film, we observed a convolution of two lines: a) a Lorentzian of 4 kHz HWHM and b) a Gaussian of 20 kHz HWHM. The hydrogen distributions in both oxides are interpreted as a function of these lines.

The local densities of states (LDOS) of epitaxial SiO, layers on Si(100) surfaces have been calculated using the recursion method combined with the Harrison's universal tight-binding model. The interface states associated with strained epitaxial layers of β-cristobalite (√2×√2)R45° and tridymite (1010)<0001> || Si(100)<011> were examined. In the β-cristobalite layer, gap states due to the surface Si dangling bonds appeared while they were eliminated by H termination. In the tridymite layer, the interface states primarily composed of the surface Si back bonds appeared near the Si conduction band minimum. Comparing the calculated DOS with photoelectron spectra for initial oxidation processes of clean Si(100), it was found that the valence band spectrum from the initial oxide formed at ∼300°C resembled that of the β-cristobalite layer.

Weak-beam imaging is used to characterize the interface structure of hematite (α-Fe2O3)/ sapphire (α-Al2O3) heterojunctions parallel to (0001). The heterojunctions were prepared by lowpressure chemical vapor deposition of hematite directly onto electron-transparent sapphire substrates. Bright-field imaging and selected-area diffraction show that the growth is epitactic. The 5.5% lattice misfit at the interface is found to be accommodated by one of two different hexagonal dislocation networks: (1) b = 1/3<1210> or (2) b = 1/3<1010>. The latter are associated with a “basal twin”-type orientation relationship of the hematite and the alumina.

An analysis of the Fowler-Nordheim tunneling (FNT) theory and its application to temperature dependent current-voltage characteristics, of very thin films of SiO2 on silicon, is presented. The final results are believed to provide the most complete examination of FN emission theory and predict the breakdown electric field in thin SiO2 films. The role of the roughness, at the Si-SiO2 interface, in determining the FNT current in these structures is also discussed.

Low energy electron microscopy (LEEM) is briefly introduced and its application to the study of surface defects, surface phase transitions on Si(111), crystal growth and sublimation on Si(100) is illustrated.

The tight-binding total energy formalism developed for tetrahedrally coordinated compound semiconductors has been extended to rutile-structure oxides and applied to calculate the surface atomic geometry and electronic structure of SnO2 (001). Two stable structures, separated by an energy barrier, are found. The first consists of slightly relaxed surface geometry with the top layer oxygen atoms relaxed outward by approximately 0.12A, and cations inward by 0.25A. The second geometry is a more massively reconstructed surface in which the four-coordinate surface Sn atoms attain highly distorted tetrahedral coordination.

An interstitial dimer, which is symmetric and recessed from the surface, is proposed as a new defect structure on reconstructed Si(100) surfaces. The structure of the interstitial dimer is studied using ab initio molecular-dynamics simulations, and shown to be stable. Possible arrangements of the new defects are discussed.

Through application of a lattice model of the Si(001) surface, implemented in a Monte Carlo growth simulation we investigate the structural evolution of the Si(001) surface during molecular beam epitaxy. Particular emphasis is placed upon identifying the role of both enhanced diffusion and directional bonding.

For the first time the (1102) surface of sapphire has been investigated by X-ray photoelectron spectroscopy to ascertain chemical changes resulting from annealing in vacuum at 1300° C and 1450° C. As received substrates had a substantial surface C contaminant. For substrates that were chemically cleaned before inserting them into the MBE system no trace of carbon is detected. A residual flourine contaminant results from the cleaning procedure and is desorbed by the vacuum annealing. Spectra of annealed substrates are compared to the unannealed chemically cleaned substrates. The annealed substrates exhibit 0.4 to 0.5 eV shift to higher binding energy of the Al peak and a 0.3 eV shift to higher binding energy of the O peak. In addition, a 2% depletion of oxygen from the surface occurs.

A model for chemisorption based on the Lewis theory is proposed and developed. The model reproduces the observed relationship between aqueous solubility and band gap for covalent oxides. A relationship is shown between the calculated free-energy of the surface reactions and the observed effect of water on the wear of these materials. This relationship is explained in terms of surface reaction rate and equilibrium. Similar calculations for the adsorption of -CH3 functional groups are presented. The results are compared to water adsorption calculations and related to experimental wear test results for model fluids on covalent oxides. The effect of water on lubricant adsorption is discussed.

Scanning Tunneling Microscopy combined with optical excitation techniques is used to study non-equilibrium electronic properties of clean silicon surfaces with high spatial resolution. Tunneling potentiometry is performed to measure the excess carrier distributions via the surface photovoltage effect. Well-ordered regions of Si(111)-(7×7) show a uniform surface photovoltage effect, while strong decreases are observed near defects. The decreases in the photovoltage are attributed to an increase in the rate of recombination of electron-hole pairs in the vicinity of the defects.

A scanning tunnelling microscope is described which operates inside a transmission electron microscope in the reflection mode. The device is used to study the mechanism of STM contrast in graphite and semiconductors. It allows for the observation of any strain during tunnelling, using the reflection electron diffraction contrast mechanism. The first results of our new transputer-based digital imaging system for STM are reported.