Search

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 (

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.

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...

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.

This study reports a Si RITD whose characteristics improve with increasing anneal time, resulting in a peak current density (JP) and PVCR up to 2.97 kA/cm2 and 3.08, respectively.

The structures of Ovonic multi-element, multi-phase Zr-based transition metal alloys for hydrogen storage are studied. The alloys are designed to be multi-phase materials. The hexagonal and diamond cubic structures, known as C14 and C15 Laves structures respectively, are the two major hydrogen storage phases in the alloys. In both C14 and C 15 structures, Zr and Ti are the elements typically occupying the hydride former (A) sites and V, Cr, Mn, Fe, Co and Ni the catalytic (B) sites. Based on the application of Ovshinsky's design principles for disordered materials, both A and B sites are compositionally disordered by the corresponding elements in cubic (C15) structure. However, the hexagonal (C14) structure has two distinct B sites, B(I) and B(Il) with a 1:3 ratio. Preliminary neutron diffraction studies indicate that the B(I) sites are predominantly occupied by Ni and the B(ll) sites are randomly mixed with V, Cr, Mn, Fe, and Ni. It is then proposed that the formula of the hexagonal structure should become A2B(I)IB(II) 3 in the current multi-element Zr-based alloys. Minor phases close to the structures of Zr7Ni10, Zr9Ni11, and ZrO2 are also present in some alloys. The average electron concentration factor (e/a) derived from the alloy composition dictates the alloy structures. The alloys with higher electron concentration factor (> 7.1) favor the diamond cubic structure. On the other hand, the hexagonal structure is associated with the alloys with lower electron concentration factor (< 6.5). The alloys having electron concentration factors in between are mixtures of the diamond cubic and hexagonal structures.

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.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The crystallization properties of Te-Ge and Te-Ge-Sb alloys prepared by thermal evaporation were analyzed using various characterization techniques. Similar to previous results, our data for Te-Ge shows that alloys that deviate slightly from Te50Ge50 stoichiometry show drastically slower crystallization kinetics. Raman spectroscopy and x-ray diffraction show that alloys having non-stoichiometric atomic ratios phase separate during crystallization into a Te50Ge50 phase plus pure crystalline tellurium or germanium. It is this relatively slow process of phase segregation which limits the crystallization rate. Phase segregation during crystallization of non-stoichiometric Te-Ge can be eliminated by adding antimony to samples having a tellurium concentration of from 45 to 55 atomic percent over a wide range of Ge:Sb ratios. These alloys can have laser induced crystallization times of less than 50 nsec. The thermal crystallization temperature is reduced only slightly when antimony is substituted for germanium.

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)

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...

Raman spectroscopy (RS) and low-angle x-ray diffraction (LAXRD) have been used to characterize semiconductor multilayer interfaces. In the present study 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 peak heights in the Raman spectra of thin films are proportional to the number of scatterers, thus 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. The relative roles of LAXRD and RS in investigating interfaces are contrasted. Several a-Si/a-Ge multilayers deposited by ultra-high vacuum (UHV) evaporation (MBD) are found to exhibit very regular periodicities and exceptionally sharp interfaces (

Arstract:W(15 Å)/C(15 Å), W(50 Å)/C(50 Å) and W(100 Å)/C(100 Å) periodic multilaver films were prepared by magnetron sputtering and suhsequently annealed at 980, 730 and 500°C. The changes of layered and crystal structures were studied by x-ray diffraction. The results depended largely on the thickness of W layers and their initial crystal struictures of W. The kinds of transformations are classified into two types: one is the non-reacting type in the case of multilayers having the thinner W layers like W(15 Å)/C(15 Å), in which the crystallization of W layers prevails over the reactions between W and C layers; the other, the reacting type in the multilayers having thicker W layers like W(50 Å)/C(50 Å) and W(100 Å)/C(100 Å), in which reactions Prevail over crystallization. A tentative model in which the effective reaction rate between amorphous–W and amornhous–C is much smaller than that of crystalline-W(beta phase) and amorphous-C is proposed to explain the origin of the phenomena.

Fluorine substitution for oxygen in the high Tc superconducting ceramic oxides is not only fundamentally but also technologically interesting. We have previously reported the observation of superconducting zero resistance transition at 155–168K, subsequently confirmed by several other groups. We have also observed diamagnetic signals and flux trapping at temperatures as high as 305K. The samples were made from solid-state reaction in a pressed pellet form. Because of the BaF2 formation and the small volume fraction, we have not yet been able to identify the specific high Tc phases.In the course of elucidating and optimizing the fluorination effect, we have carried out other means of low-temperature fluorination experiments. The zero resistance at 154K was repeated.In addition to the observation of these high 1c results, we found that a dopant amount of fluorine promotes the oriented crystal growth. We also found that the replacement of weakly bonded oxygen by fluorine can greatly enhance the material's stability by eliminating the serious problem of oxygen diffusion.