D. A. Pawlik

Characterization of as‐prepared and annealed hydrogenated carbon films

Hydrogenated amorphous carbon films were obtained from the decomposition of methane using a rf‐couple glow‐discharged system at power densities ranging from 0.4 to 4.8 W/cm2 . The structure of as‐prepared and annealed films were characterized by Raman spectroscopy, infrared absorption, photoluminescence, energy‐loss spectroscopy, and x‐ray diffraction. The results indicate that the incorporated hydrogen concentration is an important parameter in determining the structure and properties of the films. Carbon films deposited at a lowest rf power density contain a large amount of hydrogen with most of the C–H bonds in CH3 configurations, whereas films produced at higher rf powers reveal dominant CH2 bonding structures. According to Raman scattering measurements the sp2 domains in as‐prepared samples are disordered due perhaps to bond‐angle distortions. Upon annealing, hydrogen leaves the film at a temperature that depends on the initial hydrogen concentration. Once most of the hydrogen has been driven out, cr...

Thermal Stability of W/C Multilayer Films

W(10A)/C(40A), W(15A)/C(15A) and W(40A)/C(10A) periodic multilayer films were prepared by magnetron sputtering and subsequently annealed at 730°C. The resulting change of the layered and crystal structures was studied by X-ray diffraction. The resulting structures largely depended on the thickness ratio of W to C. For example, in the W(15Å)/C(15Å) sample a-W as formed without any peaks of carbon crystals; in W(40Å) C(10Å)only W2C (orthorhombic) peaks appeared.

Characterization of as-prepared and annealed W/C multilayer thin films

Tungsten/carbon (W/C) multilayer thin films were prepared by dc magnetron sputtering. All samples consisted of 30 layer pairs with a nominal d spacing varying from 2.5 to 14 nm, the W layer thickness was kept at 2 nm in all samples. The W/C multilayers were subjected to isochronal anneals in a quartz tube furnace at the temperature range from 500 to 950 °C under a flow of high purity Ar gas. X‐ray diffraction, Raman scattering, and Auger depth profile were used to characterize the structure of the as‐prepared and annealed multilayer films. Both the W and C layers appear to be amorphous as‐prepared. An overcoat of 30 nm of plasma enhanced chemical vapor deposited silicon nitride was found to inhibit oxidation during annealing. For those multilayers containing thinner carbon layers (<1 nm), the formation of crystalline W2C occurs at annealing temperature as low as 500 °C and a very small expansion (<2%) in the layer d spacing is observed. On the other hand, for all multilayers with carbon layer thickness eq...

Structure and Optical Characterization of ZnxCd1-xTe Thin Films Prepared by the Close Spaced Vapor Transport Method

Zinc cadmium telluride (ZnxCd1−xTe ) solid solution films with 0≤x≤0.12 were deposited by the close spaced vapor transport method and characterized using photoluminescence, x‐ray diffraction, and scanning electron microscopy. The two former techniques indicate that films with high crystalline quality can be prepared with moderate substrate temperatures and low argon pressures. Under these conditions deposition rates of up to 1000 A/s are achieved and Zn concentration in the film is the same as that of the source. The electron micrographs show grain sizes comparable to the film thickness.

The effect of oxygen on the structure of annealed w/c multilayer thin films

Abstract W/C multilayers were prepared on unheated Si substrates by RF sputtering method. Raman scattering, x-ray diffraction and Auger depth profile were used to characterize the structure of the as-prepared and annealed multilayers in the range of 300 to 800 C. The results were compared in samples subjected to three different annealing conditions: 1) in air, 2) in high purity Ar atmosphere and 3) in evacuated and sealed (∼10 −4 torr) ampules. The result of Auger profiles indicates that the penetration depth of oxygen in the films depends on the annealing conditions, annealing temperature and layering structure. It also shows the loss of compositional modulation and the oxidation of W in the region reached by the oxygen. Raman scattering from the oxidized top layer(s) displays a spectrum with lines associated with crystalline tungsten oxide and segregated microcrystalline graphite particles.

Superconductivity in Fluorinated Copper Oxide Ceramics

It is difficult to do justice to the scientific and technological impact of the recent discoveries in high Tc superconducting ceramic oxides. It is now clear that the oxides that were the basis of the lanthanum copper oxide ceramics which moved the superconducting temperature from 23 to 30 to 40K (1) have been around for some time.(2,3)

Characterization of as-prepared and oxidized Hf/Fe multilayer films

Abstract As-prepared and oxidized Hf(50 A)/Fe(50 A) multilayer films were studied by various analytical techniques. As-prepared films consisted of layered microcrystalline α-Fe and X-ray amorphous hafnium. Transition to an amorphous alloy phase was achieved through thermal annealing at 500 °C under ultrahigh vacuum conditions. Oxidized films could be categorized into two types depending on the oxidation conditions. Both hafnium and iron were oxidized in type I films which consisted of three distinct regions. The top region, near the front surface, contained Fe2O3 only. Equal amounts of Fe2O3 and HfO2 were found in the bottom region. The middle section acted as a transition area between the above two regions. Microvoids were observed at the interfaces. In type II films, hafnium was preferentially oxidized to form HfO2; most iron remained in its metallic phase throughout the films. The middle of the films had a thin iron-enriched layer (about 1000 A) resulting from the ripening growth mechanism. The rest of the film was a mixture of fine grains of HfO2 and α-Fe. Increased film thickness after oxidation observed by cross-section scanning electron microscopy was associated with the decreased film density after oxidation.

RAMAN SCATTERING AND X-RAY DIFFRACTION CHARACTERIZATION OF AMORPHOUS SEMICONDUCTOR MULTILAYER INTERFACES

In the present study, Raman spectroscopy (RS) and x-ray diffraction have been used to characterize semiconductor multilayer interfaces. A model for Raman spectra of multilayers is developed and applied to the specific case of the interfaces of a-Si/a-Ge multilayers. Quantification of the ‘blurring’ of interfaces is possible because RS is capable of directly ‘counting’ the total number of chemical bonds of a given type in the film. Multilayers, prepared by various deposition techniques, are compared. Several a-Si/a-Ge multilayers deposited by UHV evaporation (MBD) exhibit exceptionally sharp interfaces (intermixing width

Structural changes induced by thermal annealing in W/C multilayers

Tungsten/carbon (W/C) multilayer thin films with a nominal d spacing varying from 2.5 to 14 nm were prepared by magnetron sputtering technique. The thicknesses of the W and C layers were varied from 0.5 to 12 nm. The multilayers were subjected to isochronal anneals in a quartz tube furnace in the range of 300 to 1000 C under high purity Ar flow conditions. X-ray diffraction, Raman scattering and Auger depth profiling were used to characterize the structure of the as-prepared and annealed films. It is found that an overcoat layer of silicon nitride (30-50 nm) prevents the multilayers from oxidation during the 1 hr heat treatment at temperatures as high as 1000 C in Ar flow. In all studied W/C multilayers, the carbon layers are amorphous (up to 12 nm). The tungsten layers are also amorphous when their thicknesses are less than 5 nm. Tungsten layers thicker than 5 nm show crystalline W peaks in addition to the amorphous W feature. Annealing of samples with a silicon nitride protective layer results in several structural changes which depend on annealing temperature, d spacing, the as-deposited W layer structure and the layer thickness ratio of W to C. For W layer thicker than C layer and W layer thickness > 4 nm and/or C layer thickness < 1 nm, the multilayers show the initial crystal formation of microcrystalline W2C occurring at C-W interfaces (that interface in which C was deposited on W) after 600 C anneal, followed by a second crystallization of a-W or a-W and WC at W-C interfaces (W was deposited on C) at the annealing temperature of 900 C. They reveal a relatively small (< 5 %) or essentially no layer expansion. For those multilayers having thin W layers (2 nm) and the same or thicker C layer thicknesses, the initial crystallization takes place at both W-C and C-W interfaces at 900 C or higher. The crystal formed is a-W or a-W and WC. The layer pair period of the multilayers in this group increases monotonically with increasing annealing temperature. Expansion is up to 16 % of the original d spacing and occurs in both W and C layers at approximately equal rates. The expansion in all multilayers is interpreted to be associated mainly with the structural ordering processes in the amorphous W and C layers.