Applications of Surface Science最新文献

DC conductivity and Hall coefficient studies were made on MIS structures of n-type Pb_0.8Sn_0.2Te thin films grown by a flash evaporation technique in the temperature range 77–400 K. The decrease in R_H with positive gate field and increase in R_H with negative gate field have been attributed to the accumulation and depletion of charge carriers due to bending of bands. Mobility-temperature data have been analyzed in terms of various scattering mechanisms.

The structure of thin silicon oxide films 5 nm in thickness, which were prepared by electron beam evaporation of SiO₂ glass onto a NaCl substrate, has been examined by high resolution electron microscopy and diffraction. Although the films which were prepared with substrate temperatures ranging from room up to 400°C gave rise to amorphous haloes, lattice fringes in areas 1–2 nm in extent were, however, seen in the micrographs. It is shown that the film is composed of α-quartz micro-crystallites. Crystals of α-cristobalite with sizes of several tens of nanometers appeared at a substrate temperature of 500°C. At a substrate temperature of 600°C, β-cristobalite crystals with sizes of several tens of nanometers appeared. The structural changes due to the substrate temperature were attributed to incorporation of sodium atoms from the substrate into the SiO₂ film.

UV photoemission, low energy electron diffraction and high-resolution electron energy loss spectroscopy (EELS) have been used in situ to study the nature of 1–25 Å of Au and Pd deposited on Si(111) at temperatures of 20 and 300 K. New information is obtained regarding the formation, nature and microstructure of these metallic layers. We describe and apply a theoretical analysis of EELS which allows the determination of DC transport properties in these ultrathin layers. All metallic layers exhibit significantly higher resistivities than expected in comparison to bulk metal silicides or metallic glass phases, and can be attributed to diffuse scattering of conduction electrons at the interface. The interaction and behavior of atomic hydrogen with these films as detected by EELS is also described and found to convey additional information about their microstructure.

When the spectra corresponding to successively greater adsorbate coverages are superimposed, there is often a singular point through which they all pass. This is recognized as an isosbestic point, which is shown should be present whenever there is only a single adsorbate overlying the substrate. The lack of such a point consequently indicates the existence of multiple adsorbate species. These criteria are applied to the adsorption of O₂, H₂S and benzenethiol on Cu(410). For H₂S, two species are detected and assigned to surface and incorporated sulfur.

Crystalline films composed of mixtures (1) Fe, Fe₃O₄ and FeO, (2) FeO and Fe₃O₄, and (3) Fe₃O₄ were obtained by evaporating FeO powder (1) in a vacuum of 10⁻⁵ Torr; (2) in an oxygen atmosphere of 10⁻⁴−10⁻³ Torr; and (3) in an oxygen atmosphere of 10⁻¹ Torr, respectively. Films of γ-Fe₂O₃ were obtained by evaporating Fe₃O₄ powder in an oxygen atmosphere of 10⁻⁴ Torr, or by evaporating α-Fe₂O₃ powder in a vacuum of 10⁻⁵ Torr. The γ-Fe₂O₃ films gave only amorphous haloes in electron diffraction patterns. High resolution electron microscope images of the films showed crossed lattice fringes (whose spacings were assigned to the γ-Fe₂O₃ crystal) in areas 2 nm in extent. The formation of various iron oxide films is discussed in connection with experimental results from the oxidation of iron.

Three different methods of oxidation - thermal, TCE, and anodic — were applied to n-type (111) silicon 10 ohm cm resistivity samples. MOS test samples were fabricated and their interface state properties were characterized by C-V and AC field effect techniques. From C-V measurements the interface state density at mid gap was found to be less in TCE (2 × 10¹⁰ cm⁻² eV⁻¹) and anodic (1 × 10¹⁰ cm⁻² eV⁻¹) samples than in dry (5 × 10¹⁰ cm⁻² eV⁻¹) oxidized samples. The mobile charges were also less in TCE (2 × 10¹⁰ cm⁻²) and anodic (5 × 10¹⁰ cm⁻²) samples. Using the AC field effect technique, the frequency (2–100 kHz) and temperature dependence of field effect mobility, μ_FE, were studied. By applying Garrett's theory of frequency dependence of μ_FE, the relaxation times of interface states were found to vary from 30 to 3 μs in dry, 8 to 4 μs in TCE, and 4.5 to 1.5 μs in anodic samples in the temperature range 230 to 370 K. Using Rupprecht's theory of temperature dependence of relaxation times, thedominant energy levels, E_c - E_T, were found to be shallower in TCE (0.04 eV) and anodic (0.06 eV) than in dry (0.1 eV) oxidized samples. The capture cross-section of these samples was found to be small, in the range 10⁻²⁰ to 10⁻²¹ cm². In TCE and anodic samples the shallow interface state levels indicate stronger interactions between silicon and oxygen atoms at the interface. The observed low densities of interface states and mobile charges in these samples also show improved passivation of silicon.

C40-type, hexagonal VSi₂, MoSi₂ and WSi₂ have been grown epitaxially on (111)Si. V, Mo or W thin films, 250–300 rA in thickness, were electron gun deposited on (111)Si. Epitaxial growth of metal disilicides were induced by thermal annealing in vacuum. For VSi₂ on (111)Si, epitaxial regions, 1–2 μm in size, were found to grow in samples 400–1000°C two-step annealed. MoSi₂ grains, 0.2–2 μm in size, were observed to grow epitaxially on (111)Si following 1100°C annealing. WSi₂ epitaxy, 0.4–1.2 μm in size, on (111)Si was obtained in samples annealed at 1050–1100°C. The orientation relationships between these metal silicides MSi₂ and substrate Si were determined to be $\text{(0001)}\text{MSi}{}_2\text{(111)}\text{Si}\text{, (22}\text{4}\text{0)}\text{MSi}{}_2\text{(22}\text{4}\text{)}\text{Si}$ and $\text{(20}\text{2}\text{0)}\text{MSi}{}_2\text{(20}\text{2}\text{)}\text{Si}$. Regular interfacial dislocation networks were observed at silicides/Si interfaces. The dislocations were identified to be of edge type with ₆¹〈112〉 Burgers vectors. The average spacings of dislocations are 250, 100 and 40 Å for VSi₂/Si, MoSi₂/Si and WSi₂/Si systems, respectively. The disparities in dislocation spacings are attributed to the differences in lattice mismatches and thermal expansion coefficients among these silicide/Si systems. The discovery of a number of new epitaxial silicides presents the exciting possibilities that novel devices with desirable characteristics may be realized.

Amorphous silicon has been deposited at high rates using an RF-excited hollow cathode. Films of 0.6 μm have been formed in 6 min, thus overcoming an important barrier to economic fabrication of amorphous silicon devices. In addition, the films are resistant to abrasion, which may be a consequence of the extremely high ion bombardment which the growing films are subject to. Infrared spectra have confirmed that the bonding of hydrogen is predominantly in the preferred monohydride form, without any external substrate heating.

The backscattering factor is the most important parameter for matrix effect corrections in quantitative Auger analysis. Some of the methods previously published are reviewed. A new method is described for determining the backscattering factor using information provided by the background which is usually ignored in an Auger spectrum. Complicated calculations such as The Monte Carlo method were avoided, and the accuracy might be further improved since both the intensity of Auger electrons and the energy distribution of backscattered electrons were obtained under the same experimental conditions. The results are illustrated by a quantitative analysis of two copper alloys, Au-Cu and Ag-Cu.

Optical techniques are widely used as non-destructive methods for determining the thickness and effective optical constants of vacuum deposited thin films. Implicit inmany such analyses is the use of an ideal morphological model of a thin film. The morphology of vacuum deposited thin films, however, may be far from ideal. The influence of morphological features on normal incidence reflectance and transmittance spectra of thin films is discussed. In particular, the interpretation of the non-ideal surface of a thin film as either a region giving rise to scattering of incident light or, by applying effective medium theory, as a region of graded refractive index will be considered. The results of a comparative study of the normal incidence reflectance and transmittance spectra of a number of sputtered thin films using both surface scattering and surface region of graded refractive index models is presented. It is shown that the latter model is preferred for films with surface features with dimensions of up to a considerable fraction of wavelength. The implications of these normal incidence results for ellipsometric measurements are also discussed.