L.L. Levenson

Thermal decomposition of nickel carbide: an Auger lineshape study

A carbon Auger spectrum indicative of nickel carbide is detected in thin films of nickel evaporated onto graphite in ultrahigh vacuum. Isothermal heating of the films leads to an irreversible change in the carbon Auger lineshape. This change is interpreted as evidence for the decomposition of the nickel carbide. Initial and final spectra are representative of carbide and graphite, respectively. It is seen that intermediate phases in the Auger lineshape transition are closely approximated by linear combinations of carbide and graphite spectra. This approximation allows the retrieval of the relative amount of nickel carbide present in the film as a function of time during a heating period. Rate constants are calculated for a number of temperatures. An energy of activation for the decomposition process is then obtained. The results of this experiment are in good agreement with previous measurements employing bulk techniques.

Formation and properties of metallic organotin films

Abstract Semiconductive and conductive films of metallic appearance are formed by glow discharge of appropriate organometallic compounds. Tetramethyltin is used as a starting compound for the film-forming experiments. The resulting films contain carbon, tin and hydrogen with a carbon-to-tin atomic ratio of 2.5 or less. These films are semiconductors with conductivities between 2 × 10-1 and 1 × 10 -2 Ω -1 cm -1 . Transmission electron microscopy shows the films to be amorphous. Films of a certain composition are transformed to β-Sn on exposure to an electron beam. Thermal treatment increases the conductivity gradually to values of about 1 × 10 2 Ω -1 cm -1 .

Interface composition and adhesion of glow‐discharge‐formed organo–tin polymers

The interface composition and bonding of thin organo–tin polymers, plasma‐deposited on Al, are determined by AES, ESCA, and pull testing. A tin oxide species is formed between the bulk organo–tin polymer and the Al surface within an interfacial region of about 10 nm. This is evidenced by the change in the profile of the Sn‐MNN Auger signal and by the energy shift of the Sn 3d3/2 and 3d5/2 peaks in the ESCA spectrum. No tin oxide formation is observed at the interface of organo–tin films deposited under similar conditions on stainless steel. The composition at the interface is also shown to depend on the position of the sample in the glow discharge during film deposition.

The composition of organo-tin polymer films on metallic substrate materials☆

Abstract Glow discharge films with various ratios of carbon to tin were deposited on various metals and on glass. The ratio of carbon to tin was determined quantitatively by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The AES data correlated well with the XPS data. The X-ray beam and electron impact effects on organo-tin films influence the composition and are discussed in detail. The ratio of carbon to tin was not constant throughout the glow discharge reactor and this inhomogeneity is accounted for by the prevalence of “atomic” polymerization rather than “molecular” polymerization. We demonstrated that the substrate material had a definite influence on the composition of the films.

Nickel carbide: Its formation and characterization by transmission electron diffraction, Auger electron spectroscopy and electron spectroscopy for chemical analysis☆

Abstract Nickel carbide (NiC 3 ) films are formed by the carburization of nickel films in CO at 350°C. The presence of Ni 3 C is demonstrated by transmission electron diffraction. The carbon Auger electron signal of Ni 3 C is identical with the carbon Auger spectra attributed to Ni 3 C by previous authors. The position of the C 1s electron spectroscopy for chemical analysis peak is within 1 eV of the C 1s peak produced by graphite. The grain size of polycrystalline Ni 3 C is significantly larger than the grain size of the nickel film from which it is grown.

Diffusion of nickel in silicon below 475 °C

Abstract Nickel films were deposited on (100) and (111) surfaces of single-crystal silicon and were then annealed. The conditions under which the nickel is deposited determine whether or not an NiSi compound forms on annealing. It is postulated that defects are necessary for the formation of an NiSi compound at annealing temperatures below at least 475 °C, although the presence of defects may not necessarily cause the formation of a silicide. For substrate temperatures below 70 °C, defects are created during the vapor deposition of nickel on silicon. These defects always result in the formation of nickel silicide when the sample is annealed at higher temperatures. When nickel is deposited on defect-free silicon at temperatures of about 250 °C no defects are generated and, although interdiffusion of nickel and silicon occurs, silicide formation does not take place upon subsequent annealing below 475 °C. The activation energies for the diffusion of nickel into (100) silicon and (111) silicon were determined.

Binding of nickel on pyrolytic graphite

Binding of nickel atoms deposited on a clean pyrolytic graphite surface is studied in ultrahigh vacuum using Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS). The amount of deposition is measured with a quartz crystal microbalance. AES reveals that nickel islands are probably formed during the deposition process. It is also observed that the Auger signal changes gradually from ’’graphitic’’ to ’’carbide’’ type with increasing coverage. TDS shows that there is only one binding state of nickel with a binding energy of 4.0±0.2 eV/atom. These results are compared with previous works using other method reported by various authors.

The observation of pseudodiffusion of nickel in single-crystal silicon by in-depth Auger electron spectroscopy☆

Nickel films r.f. sputtered onto the (100) surface of single-crystal silicon diffuse into the substrate when annealed at temperatures between 250 and 350°C. The change in the concentration gradient is measured by recording the Ni and Si Auger electron signals during ion sputtering. The diffusion coefficient is given by the equation D = 10-13 exp(-0.27 eV/kT>) cm2 s-1

Selective deposition of SiO2 thin films in acid baths

We report observation of deposition of SiO2 thin films on a variety of surfaces in nitric acid and hydrochloric acid solutions. Scanning electron microscopy shows that the films are composed of closely packed spheres 1000 A in diameter. Chemical identification is made with Auger electron spectroscopy. The films are generally between 1000 and 2000 A thick and are possibly hydrated. Deposition occurs in either acid for molarities in the 1–8 M range and at temperatures between 80 and 100 °C. The effects for molarities greater than 8 M and temperatures greater than 100 °C have not been investigated. Materials on which the films form in nitric acid are tantalum, gold, silicon, niobium and Al2O3; in hydrochloric acid, films will form on tantalum, gold, silicon and Al2O3. Materials which are insoluble in the acids but upon which films have not been observed to form are graphite, platinum, chromium (nitric acid) and niobium (hydrochloric acid). Deposition occurs inside a sealed vessel made entirely of Pyrex-type glass. Vessels are partially filled with acid and are heated so that the upper glass surfaces (not in contact with the acid reservoir) are about 10–30 °C cooler than the reservoir. Acid vapors condense on the cooler glass surfaces forming droplets that run down the vessel walls to the reservoir. This process of acid flow on the walls leaches SiO2 from the glass and increases the SiO2 concentration in the reservoir until the SiO2 films form. It is believed that a supersaturated condition is present during SiO2 deposition. Experiments show that cessation of acid condensation halts film formation. Attack of the vessel provides the sole source of SiO2. Preliminary kinetic measurements indicate that vessels must be heated for periods longer than 150 h before deposition occurs. Iron can be incorporated into the SiO2 films by the dissolution of iron metal in the acid before sealing of the vessel.