L. Cota-Araiza

Nuclear reactions as a probe of fluorine content in SnO2:F thin films

Abstract The resonant nuclear reaction technique has been applied to the determination of fluorine content in SnO 2 thin films prepared by spray pyrolysis. γ rays from the nuclear reaction 19 F(p, αγ) 16 O, which presents a narrow resonance at a 340 keV proton bombarding energy, were observed. The excitation curves obtained indicate the fluorine concentration and distribution in the sample. The interface between the film and the substrate is also clearly marked. Auger electron spectroscopy was used as an alternative technique to observe the fluorine, but it was very difficult to detect. The reason for this difficulty is assumed to be electron-induced desorption of fluorine atoms.

Plasma enhanced chemical vapor deposition of SiO 2 films at low temperatures using SiCl 4 and O 2

Silicon dioxide films have been deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD) technique using SiCl4 and O2 as reactive materials. Infra-red transmittance, Auger electron spectroscopy analysis, ellipsometry, electrical, and chemical etch measurements have been used to characterize these films. It is possible to obtain good quality oxides at a substrate temperature of 200° C using a low flow of reactant gases. High flow of reactant gases results in highly non-homogeneous porous films. The best oxide films obtained show destructive breakdown at electrical fields above 4 MV/cm and a fixed charge density of the order of 2.6 × 1011 charges/cm2.

SiO2 prepared by remote plasma-enhanced chemical vapor deposition using SiCl4 and O2 at substrate temperatures of less than 200 °C

Silicon dioxide films have been prepared by the remote plasma-enhanced chemical vapor deposition technique using SiCl4 and O2 as source materials. The structural quality of the films was analyzed by infrared transmittance, ellipsometry, Auger electron spectroscopy and chemical etch rate measurements. The electrical integrity was analyzed by I-V and C-V measurements performed in metal-oxide-semiconductor structures prepared using the deposited oxides. Good-quality oxides have been obtained at substrate temperatures in the range of 100 to 150 °C. At lower temperatures (25 and 50 °C) oxide films with good insulating qualities are obtained but the level of interface states is large. The deposition rate is only slightly dependent on the substrate temperature. The chemical etch rate is similar to that obtained for oxides prepared at higher temperatures. Destructive breakdown is in the range from 6.7 to 8.9 MV cm−1. Fixed charge densities are in the range from 5 X 1010 to 5.2 X 1011 charges cm−2.

Diamond films grown on p-type microcrystalline-SiC:H/crystalline-Si substrates

Abstract In this work we have used a two-step process to prepare diamond thin films. A boron-doped microcrystalline SiC (p-type μc-SiC:H) buffer layer was first deposited onto smooth crystalline silicon (x-Si) substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD). Secondly, diamond polycrystalline films were grown by hot-filament CVD on the μ c-SiC:H x-Si substrates. The resulting films were characterized by Auger electron spectroscopy, electron energy loss spectroscopy, secondary electron microscopy and Raman spectroscopy. The effect of the substrate preparation on the nucleation and growth of diamond films on μ c-SiC:H x-Si substrates is discussed in terms of the presence of Si and SiC microcrystalline clusters embedded in the amorphous network structure of the μc-SiC:H films.

Preparation of cubic boron nitride films by plasma-enhanced chemical vapour deposition of BF3, N2 and H2 gas mixtures

Abstract Boron nitride thin films were prepared by plasma-enhanced chemical vapour deposition (PECVD) of BF 3 , H 2 and N 2 gas mixtures. Fourier transform IR (FTIR) spectroscopy and X-ray analysis reveal that the films deposited on crystalline substrates show signs of cubic and hexagonal phases present within the atomic network. The index of refraction and the film thickness were determined by ellipsometry. The deposition rate increases with temperature and saturates at high plasma powers. Values of n are in the range 1.63–1.77, and the optical gap varies from 5.0 to 5.6 eV depending on the preparation conditions (the presence of contaminants also alters this property). The ratio of N 2 to H 2 in the flow affects the properties of the films.

Surface analysis of the environmental corrosion of zinalco (Zn–22Al–2Cu) alloy

Abstract The surface of a set of zinalco (Zn–22Al–2Cu) samples was prepared by mechanical polishing (MP) and by electropolishing (EP). Samples were subjected to environmental corrosion during 56 days and studied by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Differences in relative atomic concentration ratio of Al/Zn in oxides of the surface layer were obtained and they are related to the bulk microstructure. A different corrosion behavior is observed between MP and EP samples and it is explained in terms of the surface composition and morphology. The initial growth of corrosion products was observed in EP samples and a corrosion model is proposed. The surface of both types of samples can be modified by low energy argon ion bombardment.

Optical properties of boron nitride thin films

Abstract Boron nitride thin films were deposited onto crystalline silicon and alkali halide substrates by plasma-enhanced chemical vapour deposition of BF3, N2, H2 and Ar gas mixtures. Films were prepared on both powered and grounded electrodes of the capacitatively coupled system. The deposits were analysed by ellipsometry. Fourier transform IR spectroscopy and UV spectroscopy to determine their optical properties. The relative composition was determined using nuclear reactions induced by 1 MeV deuteron bombardment and Auger spectroscopy. Ion bombardment during growth was found to affect the optical properties of the material, since films prepared with low flows of argon and those placed on the live electrode have smaller refractive indices, larger IR absorption peaks for the cubic phase, and wider optical gaps.

CdTe and CdMTe (M = Fe, In, Sb) thin film studies by Mössbauer spectroscopy and other techniques

Abstract Non-destructive characterization of the atomic and electronic structures hasbeen carried out for CdTe and CdMTe (M = Fe, In or Sb) thin films. These films were grown either by sputtering or by close-spaced vapour transport techniques. Characterization was performed using the time-of-flight technique and four spectroscopies: Mossbauer, X-ray diffraction, Auger electron and photoluminescence. Different kinds of compound materials can be obtained when CdTe and indium (or antimony) are co-sputtered. A monotonic increase in indium concentration leads to the successive formation of Cd0.83In0.34Te1.34, CdIn2Te4 and InTe; we demonstrate the role of indium substituting for cadmium. A monotonic increase in antimony in CdSbTe films leads to amorphization of its atomic structure; it is probable that antimony has an amphoteric behaviour, with nearly equal chances of substituting for either cadmium or tellurium in the CdTe lattice. The ionicity of iron was used in order to determine the amorphous: crystalline ratio in CdFeTe films. Finally, low temperature photoluminescence, measured in CdTe polycrystalline films, is compared with electron and hole lateral mobilities measured on the same films. This comparison shows that the intracrystalline and/or intercrystalline density of defects is larger in large grain films than in small grain films. In any case, charge carrier (both electrons and holes) transport in the films is a trap-controlled process.

Selected area, stationary beam cratering for high sensitivity depth profiling with a computerized Auger microprobe

Abstract The use of improved methods of “crater edge profiling” as a viable alternative to conventional depth profiling by sputter etching and Auger analysis is discussed. The emphasis is placed upon utilizing a stationary ion beam (full width at half- maximum, about 200 μm) from a differentially pumped gun, the beam of which can be selectively positioned on the sample surface for localized cratering. A variety of samples of Au/Cu, Au/Zr, Ag/Si and silicon either uncoated or coated in situ with metal were used for demonstrating different aspects of this experimental approach and for mapping with Auger, secondary and elastically backscattered electrons. A thin oxide layer on silicon ( d OX ≈ 1.2 nm) was very easily detected and measured by line scans across shallow craters (tan α ≈ 10 -5 ).

PEELS and EXELFS characterization of diamond films grown by the HF-CVD technique on non-scratched Si substrates

Abstract We present a detailed energy loss characterization of natural diamond and diamond films grown on non-scratched Si substrates by the hot-filament chemical vapor deposition technique (with the help of a SiC buffer layer). The energy loss experiments were performed in a transmission electron microscope (TEM) with a GATAN-666 parallel electron energy loss spectrometer (PEELS) attachment. Diamond particles are in the 0.5–1 μm size range as observed by TEM. PEELS spectra show that the plasmon and carbon K-edge main features are very similar (in position and shapes) in both natural and our diamond film. The radial distribution function around the carbon atoms was obtained through the Fourier transform of the extended fine structure located in a 300 eV range beyond the carbon K-edge in the energy loss spectra. The values obtained for the C-C distances are very close (within 0.003 nm) to those of natural cubic diamond structure. These results confirm the good quality of the diamond films produced by our experimental technique.