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With their impressive energy performance and their outstanding power capability, Ni-MH batteries are equally suitable for use in pure and hybrid electric vehicles. This is due to the basic nickel-metal hydride technology. For one thing, hydrogen can be stored in metal-hydride alloys at very high volumetric densities, comparable to the density in liquid hydrogen, leading to the superior energy density of metal-hydride batteries. The operating principles of the Ni-MH battery are described as is their construction and manufacture. The on-road performance of Ni-MH batteries and hybrid electric vehicle batteries are discussed.

Although GeTe-${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ (GST) alloys are widely used in data storage, many fundamental issues are still under debate. Here, we demonstrate that the presence of vacancies in the crystalline phase has far-reaching consequences, namely, a triad of twofold coordinated Te atoms with lone-pair electrons generated around the vacancy enables the formation of soft three-center four-electron bonds, whose properties provide an explanation for the unusual characteristics of GST, in particular, the increase in local disorder upon crystallization, the co-existence of a very fast switching rate with a large property contrast, the possibility of a solid-solid amorphization process that excludes conventional melting, and the drastic difference in crystallization behavior between GST and the ideal binary GeTe. Anisotropy of the three-center bonds may serve as an additional degree of freedom for information recording and provide a unified explanation for a variety of unique effects observed in lone-pair semiconductors.

The crystallization of amorphous carbon films, under inert atmospheres, occurs at annealing temperatures above 800 °C. In this work we have found that when the annealing of carbon films is performed under atmospheric conditions, crystallization occurs at temperatures as low as 200 °C. The catalytic effect of oxygen in the crystallization process is understood in terms of the generation of a porous structure in the carbon film due to the vaporization of carbon oxides.

We report the effect that thermal annealing in inert and oxidizing atmospheres, and with and without encapsulating layers, has on the structure of tungsten/carbon [W/C] multilayer thin films. This study focuses on the tungsten component and deals mainly with multilayers where the ratio of thickness of tungsten layers is equal to or greater than for the carbon layers (that is, γ ≤ 0.5). This is in contrast to prior studies where the tungsten layer thickness was generally held constant and the carbon layer was varied. Thermal annealing in inert atmospheres produces reactions and other structural changes in the tungsten and carbide layers which depend on the as-deposited multilayer structure which depends, in turn, on the thickness of the tungsten layer. In samples where both the tungsten and carbide fractions of the multilayer are completely amorphous as deposited, which is the case for thin tungsten layers (thickness of tungsten (tw)4 nm/period), the reactions in the tungsten layer forming crystalline tungsten and tungsten carbide occur at annealing temperatures above 900°C. The layer pair spacing, or period, (d), in this group shows an expansion of up to 10-15% of the original value as has been reported in the past. Changes in both the tungsten and carbide layers, and their interfaces, contribute to changes in d spacing and relative thickness of the high and low Z components. When the tungsten layer thickness exceeds 4 nm per period the tungsten is partially crystallized in as-prepared samples. In such multilayers interfacial reactions, producing an oriented partially crystalline W2C/C superlattice, occur at temperatures of 600°C and below. The fact that W2C crystallites in one period can form a structure which is correlated to W2C crystallites in neighboring layers is somewhat surprising, since layers are presumably still separated by amorphous carbon which is still visible via Raman. The expansion of the layer pair spacing is relatively small (5%) in this group and, more importantly, mostly involves increases in the thickness of the high Z components. Samples annealed in air at temperatures below 300°C are progressively destroyed by the oxidation of both tungsten and carbide layers. Encapsulation of similar multilayers with a thin (30 nm) dielectric layer of any of several types can retard oxidation to 600°C. The silicon-containing encapsulants generally perform better. Failure at this temperature is seen to occur from pinhole formation.

Widespread use of electric vehicles can have significant impact on urban air quality, national energy independence, and international balance of trade. An efficient battery is the key technological element to the development of practical electric vehicles. The science and technology of a nickel metal hydride battery, which stores hydrogen in the solid hydride phase and has high energy density, high power, long life, tolerance to abuse, a wide range of operating temperature, quick-charge capability, and totally sealed maintenance-free operation, is described. A broad range of multi-element metal hydride materials that use structural and compositional disorder on several scales of length has been engineered for use as the negative electrode in this battery. The battery operates at ambient temperature, is made of nontoxic materials, and is recyclable. Demonstration of the manufacturing technology has been achieved.

High-quality epitaxial YBa 2 Cu 3 O 7−δ (F) films were grown directly on r-plane (1 1 02) sapphire by a pulsed laser deposition technique using a multiphase fluorinated target. X-ray diffraction data showed that the film is highly c -axis oriented and in-plane aligned. The c -axis and in-plane mosaic spread are 1.1° and 2.4°, respectively. The microwave surface resistance measured by a con-focal resonator configuration is 56 mΩ at 94.1 GHz at 77 K which is the best reported value for a YBCO film on sapphire. The improved film quality is attributed to the fluorine which is transported from the target to the growing surface of the film where it acts as an etching and/or catalytic agent to preferentially remove defects and second phase impurities and to promote better in-plane epitaxy.

High quality epitaxial YBa 2 Cu 3 O 7-δ (F) films were grown directly on r -plane (1102) sapphire by a pulsed laser deposition technique using a multiphase fluorinated target. X-ray diffraction data showed that the film is highly c -axis oriented and in-plane aligned. The c -axis and in-plane mosaic spread are 1.1° and 2.4°, respectively. The film has a Tc(R=) of 89K with a transition width less than 0.25K. The microwave surface resistance R s measured by a con-focal resonator configuration is 56mΩ at 94.1 GHz at 77K which is the best reported value for a YBCO film on sapphire. The magnetization critical current density is as high as 3x10 7 A/cm 2 at 5K and 2x10 6 A/cm 2 at 77K. A bandpass filter which is centered at 8.1 GHz is fabricated. A very low insertion loss (

The environmental advantages of ovonic NiH/sub 2/ batteries, due to the nontoxicity of ovonic alloys, are briefly discussed, and their general performance is described. Commercial progress in their development is summarized. Their use in electric vehicles is examined. >

This paper describes a basic new scientific and technological approach for information and computing use. It is based on Ovonic cognitive devices that utilize an atomically engineered Ovonic chalcogenide material as the active medium. We demonstrate how such a device possesses many unique functions including an intrinsic neurosynaptic functionality that permits the processing of information in a manner analogous to that of biological neurons and synapses. Our Ovonic cognitive devices can not only accomplish conventional binary computing, but are capable of non-binary generation of information, storage, encryption, higher mathematics, modular arithmetic and factoring. Uniquely, almost all of these functions can be accomplished in a single nanosized device. These devices and systems are robust at room temperature (and above). They are non-volatile and also can include other volatile devices such as the Ovonic Threshold Switch and Ovonic multi-terminal threshold and memory devices that can replace transistors.

Hydrogen is called the “ultimate fuel.” It is also the ultimate element. It was born in the Big Bang and almost all of known matter is composed of it. Its condensation into a star, our sun, through fusion, provides us the energy and the photons which power our earth and which we can utilize in the form of photovoltaics to break apart water and generate hydrogen as an energy source on earth.The hydrogen economy is here. It has been initiated by the electric and hybrid vehicles which depend upon it for their operation through nickel metal hydride batteries and hydrogen as a fuel for the internal combustion engine and by outwitting the Carnot cycle for use as a fuel cell.I will discuss the complete system needed for the hydrogen economy from generation to storage to infrastructure and use. Any one part of this loop is necessary but not sufficient.Our global economy is based upon energy and the societal needs for a nonpolluting, non-climate change fuel which does not require strategic military defense as does oil. The transition from fossil fuels to hydrogen is of revolutionary import not only for its societal impact but also for the new materials science that it absolutely requires in all of its aspects. New science and new technologies build much needed new industries, which provide not only jobs but also feedback on our educational system.Recall that the ages of civilization are known by their materials. Truly, the presentage will be known by the materials that make up the twin pillars of our global economy – energy and information. Therefore, I will address the new science, technology and atomic engineering of the materials so necessary to make positive, realistic and productive this revolutionary transition of energy from its fossil fuel beginnings to the present.

The authors have investigated variations in the a-Si deposition process to achieve a high V/sub oc/ a-Si solar cell to be used as the top cell of a triple-junction stacked solar cell. In this investigation, a-Si n-i-p solar cells were deposited on stainless steel substrates in a multichamber RF PECVD deposition system. Different deposition conditions were explored for the intrinsic a-Si layer with the goal of obtaining high V/sub oc/. After process optimization, the authors have achieved a V/sub oc/ of 1.04 V for a-Si n-i-p solar cells with the intrinsic layer deposited at 150/spl deg/C at high hydrogen dilution. This V/sub oc/ is higher than any V/sub oc/ achieved for a single-junction solar cell using a-SiC as the intrinsic layer. This high V/sub oc/ a-Si material is a better choice for the top cell i layer of a triple-junction a-Si alloy solar cell than high bandgap a-SiC alloys.

In order to improve further the economies of scale which are inherent in continuous roll-to-roll amorphous silicon alloy solar cell manufacturing processes, the authors have developed a concept for a serpentine web plasma CVD deposition process to maximize throughput while keeping the size of the deposition chambers small. When this technique is incorporated into a continuous roll-to-roll PV manufacturing process, it will maximize the throughput for a high volume production plant, reduce the machine cost, improve gas utilization, reduce power consumption, and improve the solar cell stability. To demonstrate the serpentine web deposition concept, the authors have constructed a single loop serpentine deposition chamber to deposit an a-Si for n-i-p structure solar cells. During the initial process of optimization, the authors have produced single-junction a-Si solar cells with an 8.6% efficiency, and triple-junction a-Si solar cells with a 9.5% initial efficiency, where the top cell intrinsic layer was deposited in the serpentine deposition chamber.

The engineering principles used to make >20-A-s/sup -1/ intrinsic layers of good-photovoltaic-quality amorphous silicon over large areas are addressed. Deposition equipment was designed and installed in a plasma-assisted CVD (chemical vapor deposition) roll-to-roll processor. Films were made in this machine with gas mixtures containing silane. Same-bandgap tandem solar cells using this material had 8.2% (average) to 8.6% (best cell) conversion efficiencies. >

The V-Ti-Zr-Ni-Cr alloy system has been developed for Ni-MH batteries. The authors discuss alloy characteristics, implications for cell construction, and advances in cycle life performance for a variety of practical conditions. These alloys have high hydrogen storage capacity, low cost, excellent mechanical and chemical properties, and are easy to manufacture. General performance characteristics of these Ni-MH batteries allow drop-in replacement for Ni-Cd batteries. Cycle life has been established at over 400 cycles under aggressive 100% depth of discharge conditions and under several test conditions emphasizing overcharge and deep discharge. Advanced cell designs have achieved over 700 cycles under 100% DOD conditions, with projections that 1000 cycles may be possible. >

Microcrystalline Si p-layers have been widely used in a-Si solar cell technology to achieve high efficiency. To improve the solar cell performance further, the authors have studied the deposition of high quality /spl mu/c-Si p-layer material using a modified VHF plasma enhanced CVD process and consequently have improved the solar cell current. This improvement was primarily in the blue response which leads to a 6-10% improvement in the overall solar cell efficiency. In addition, they have explored the deposition of a-Si at high rates using VHF plasma and compared these VHF i-layers with RF plasma deposited i-layers. With improved deposition conditions, VHF intrinsic layers deposited at a rate up to 15 /spl Aring//s show similar device performance and light stability to VHF and RF i-layers deposited at low rates and show higher stability than RF i-layers deposited at high rates in the same deposition system. A 10.9% efficient single-junction solar cell was fabricated using a VHF deposited i-layer.

Nickel-metal hydride batteries are in high volume commercial production for mass market portable applications due to an excellent cost to performance ratio, application to a versatile product mix and environmental acceptability. Ovonic Battery Company Inc. (OBC) a subsidiary of Energy Conversion Devices Inc. (ECD) has established the dominant position in Ni-MH batteries by establishing a fundamental patent portfolio, a network of licensees and business affiliates, and continued product improvement based upon its atomic engineering approach. The largest opportunities for Ni-MH market growth are portable power tools, EV, HEV and fuel cell electric vehicles. These applications benefit from improvements in specific energy, cycle life, high temperature performance, activation/formation, and in particular specific power. Advances in materials technology have enabled performance improvements in specific energy (100 Wh/kg), specific power (1000 W/kg), high temperature operation, charge retention, cycle life and voltage stability. While electrode configuration and packaging are important factors in cell design, at the core of next generation Ni-MH technology are the continuing fundamental improvements to the metal hydride and nickel hydroxide active materials. In this paper, advances in performance, applications and cost reduction are discussed with particular emphasis on the improved proprietary metal hydride and nickel hydroxide materials that make such advances possible.

Performance data for batteries based on multicomponent hydrogen storage alloys using the principles of atomic engineering are presented. In particular, the successful scale-up of this technology for electric vehicle applications is shown. >

Hydrogen $({\mathrm{H}}_{2})$ dilution of the source gas is known to be a key factor in producing hydrogenated amorphous silicon films that demonstrate a high degree of optoelectronic stability. In this work, we investigate, using Raman spectroscopy and high-resolution transmission electron microscopy (TEM), whether microstructural differences exist between such films and those made with no ${\mathrm{H}}_{2}$ dilution (i.e., that have greater instabilities). The key variable is the ${\mathrm{H}}_{2}$ dilution, which ranges from none to very high levels, producing amorphous and microcrystalline silicon films. The TEM results show that embedded within the amorphous matrix are chainlike objects (CLO's) having \ensuremath{\sim}3 nm widths, \ensuremath{\sim}30 nm lengths, and showing a high degree of order along their length. Such order implies vanishing levels of bond-angle distortion (BAD). These CLO's are present in all samples investigated, but their density increases with the level of ${\mathrm{H}}_{2}$ dilution. The Raman spectra show a TO band centered at $490 {\mathrm{cm}}^{\ensuremath{-}1}$ $(37\ifmmode\pm\else\textpm\fi{}3{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ full width). Quantitative analysis shows this band to exist in all samples investigated, but increases in magnitude with increasing ${\mathrm{H}}_{2}$ dilution. In the highest dilutions when microcrystallites are observed, the band is distinctly evident. Its position and width are also consistent with very low (crystallinelike) levels of BAD \ensuremath{\sim}0\ifmmode^\circ\else\textdegree\fi{}. It is thus likely the $490 {\mathrm{cm}}^{\ensuremath{-}1}$ Raman band is a signature of the intermediate ordered CLO's.

Phase change technology has progressed from the original invention of Ovshinsky to become the leading choice for rewritable optical disks. ECD's early work in phase change materials and methods for operating in a direct overwrite fashion were crucial to the successes that have been achieved. Since the introduction of the first rewritable phase change products in 1991, the market has expanded from CD-RW into rewritable DVD with creative work going on worldwide. Phase change technology is ideally suited to address the continuous demand for increased storage capacity. First, laser beams can be focused to ever-smaller spot sizes using shorter wavelength lasers and higher performance optics. Blue lasers are now commercially viable and high numerical aperture and near field lenses have been demonstrated. Second, multilevel approaches can be used to increase capacity by a factor of three or more with concomitant increases in data transfer rate. In addition, ECD has decreased manufacturing costs through the use of innovative production technology. These factors combine to accelerate the widespread use of phase change technology. As in all our technologies, such as thin film photovoltaics, nickel metal hydride batteries, hydrogen storage systems, fuel cells, electrical memory, etc., we have invented the materials, the products, the production machines and the production processes for high rate, low-cost manufacture.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

Microcrystalline silicon (μc-Si) p-layers have been widely used in amorphous silicon (a-Si) solar cell research and manufacturing to achieve record high solar cell efficiency. In order to further improve the solar cell performance and achieve wider parameter windows for the process conditions, we studied the deposition of high quality μc-Si p-layer material using a very high frequency (VHF) plasma enhanced CVD process. A design of experiment (DOE) approach was used for the exploration and optimization of deposition parameters. The usage of DOE leads to a quick optimization of the deposition process within a short time frame. In addition, by using a modified VHF deposition process, we have improved the solar cell blue response which leads to a 6–10% improvement in the solar cell efficiency. Such an improvement is likely due to an improved microcrystalline formation in the p-layer.

We report the results of production start-up efforts at the 2 MW Sovlux photovoltaic production line. Triple-junction solar cells with higher than 10% initial efficiency were produced in this production line with subcell yield up to 96%. The production process demonstrated high reproducibility and consistency from run to run. 2 ft/sup 2/ and 4 ft/sup 2/ modules assembled in the Sovlux plant using these solar cell material have demonstrated an initial efficiency of 9.4%. The solar cell material produced in Sovlux was also shipped to ECD to assemble large area 1.3 ft. by 20 ft. rooftop modules. Lightweight, flexible rooftop modules with initial efficiency up to 9.3% were produced at a high yield.

Proprietary, multicomponent hydrogen storage materials have been developed making use of the principles of disorder by atomic engineering of the short-range and intermediate -range order. These materials form the basis for Ovonic Nickel-Metal Hydride batteries which have emerged as the leading battery technology for electric vehicle applications. Ovonic Batteries have the highest volumetric energy density available extending the practical range of electric vehicles from under 100 miles to over 200 miles.

Energy Conversion Devices, Inc. (ECD) has designed and constructed a 2 Megawatt (mW) manufacturing line that produces triple‐junction spectrum‐splitting a‐Si alloy solar cells in a continuous roll‐to‐roll process. This manufacturing line has reliably and consistently produced high efficiency solar cells. We have demonstrated the production of 4ft 2 triple‐junction two band‐gap a‐Si alloy PV production modules with 8% stable aperture area efficiency. The production line has successfully incorporated: 1) a band‐gap profiled a‐Si‐Ge narrow band‐gap solar cell deposited in a continuous roll‐to‐roll process using a proprietary gas distribution manifold and cathode configuration; and 2) a textured Ag/ZnO back‐reflector deposited in a continuous roll‐to‐roll sputtering machine with production subcell yields greater than 99%.

Tungsten/carbon (W/C) multilayer thin films prepared by sputtering on unheated Si(100) substrates were encapsulated with various types of layer having low x-ray absorption. Isochronal annealings for 1 hr in the temperature range from 300 to 600 degree(s)C and isothermal annealings at 300 and 400 degree(s)C were carried out under ambient conditions (in air) on coated and uncoated multilayers. The encapsulated layers are: SiN x and SiO 2 prepared by plasma enhanced chemical vapor deposition (PECVD) and SiC, Al 2 O 3 , C and B 4 C prepared by sputtering techniques. Previous studies have shown that unprotected W/C multilayers annealed in air exhibit oxidation at relatively low temperatures (approximately 300 degree(s)C). In the present study, we have used Raman scattering (RS), Auger depth profiling and scanning electron microscopy (SEM) to investigate the effects of thermal treatments on the encapsulated W/C multilayers. The results indicate that oxidation of both W and C layers takes place during annealing at temperatures which depend on the type of protective layer. For example, in the isochronal annealing experiments, multilayers coated with C, Al 2 O 3 and B 4 C suffer oxidation during annealing at 400 degree(s)C, whereas multilayers coated with the other three types of protective films prevent multilayers from oxidation at annealing temperatures as high as 600 degree(s)C. SEM micrographs show that the formation of pinholes through the protective layer occurred during annealing at the temperatures for which oxidation was first detected. Auger profiling shows the loss of compositional modulation in the region reached by oxygen. A WO 3 phase is identified by RS in the oxidized region, and the loss of the C layers is most likely due to the formation of carbon oxide vapors.

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.

We report on evidence that fluorine, properly incorporated into a-Si, replaces weakly bonded hydrogen and improves the material stability under light soaking. Our fluorinated amorphous silicon (a-Si:H:F) is made by if glow discharge at high deposition temperatures up to 430 C from a gas mixture of SiH4 or Si2H6 and F2. These a-Si:H:F films show much lower density of states in the light soaking saturated state than device quality a-Si:H prepared in the same deposition system. It is evident from our results that fluorine incorporated into the network at such high deposition temperature makes for a new configuration which minimizes dangling bonds and other defects.

The thermal activation energy, AE, of the conductivity in amorphous chalcogenide semiconductors is usually about half of the optical gap energy E. This is commonly interpreted as (intrinsic) conduction at the mobility edge by carriers whose concentration is governed by the Fermi energy EF which is pinned near the gap center. Small changes in glass composition and the presence of impurities usually have little effect on the properties except for small changes in EO and AE with composition. The insensitivity to impurities is ascribed to the fact that in a material lacking long-range order each foreign atom can satisfy its valency requirement,(1) and, thus, will not act as an electrically active center. The origin of the various states in the gap (DECs) (2,3) and the pinning of EF is attributed to those DECs which are inherent valence alternation defect centers.

The US Department of Energy is probably the best known body to have claimed that photovoltaic conversion devices cannot compete with fossil tuels or uranium until at the earliest 1986, or more likely 2000. Such statements are based on the known current technological problems of three types of silicon—single crystal, polycrystalline, and amorphous. With amorphous silicon the chief difficulty has been the high density of states (as explained by Taylor on p 672) which restricts the necessary current flow.

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 very difficult in 10 minutes to give you more than an overview of what is involved in the field of amorphous semiconductors. Also, I think you probably are more interested in applications at this conference rather than the physics involved.

Photovoltaic devices based on amorphous alloys of silicon with H and/or F have recently generated substantial interest in the photovoltaic community and the larger solid state physics and electronics communities as well. These developments have been reviewed recently by D. Carlson of RCA Labs(1). It was Carlson’s early collaboration with C. Wronski(2) which served to rekindle scientific and technological interest in a-Si:H produced by the glow discharge induced decomposition of SiH4 gas and the deposition of Si-rich fragments of this gas onto substrates held at 200–300°C(3–5).

On Sir Nevill’s 80th birthday, I wish to continue the discussion which 1 outlined in my contributions to his 65th and 75th birthday festschrifts [1,2], and I look forward to further exploring these concepts in the festschrift for his 85th.

The problems of our modern society are directly related to materials. Depletable fossil fuels, shrinking silver supplies, the high cost of gold, platinum and other precious metals all are interfering with industrial growth and creating societal problems. The fossil fuels and uranium supply us with energy without which no society or civilization can endure. However, there is a tendency to focus only on the fuel aspects of materials and ignore the larger materials picture, that is, that materials such as platinum, palladium and iridium, which are the core of the catalytic and electrochemical industries, affect not only the generation but the use of energy in a dramatic fashion.

During the past year a large number of models have been proposed to explain high Tc superconductivity in Cu-0 ceramic compounds. A nearly equal number of novel charge carrier pairing mechanisms have been invoked in these models as alternatives to the conventional phonon mediated process described in the BCS theory. Some of these models have recently been reviewed by Rice.(1)

We view amorphous materials as being ideal matrices for the encoding of information by optical or other means.1–10 The result can be the storage and reproduction of information serially or in parallel. The laser is ideal for the digital storage of information. One can achieve an exceedingly high density (one micron spots closely spaced) with a high signal to noise ratio, and utilize the same laser for reading, writing, and erasing. For higher densities, scanning electron beams are used.8

There are three key issues that challenge amorphous photovoltaics, namely, efficiency, stability, and production. In this paper we will review the current status of our amorphous photovoltaics at ECD in terms of these three issues and demonstrate how we have broken the efficiency-stability-production barrier.

The electronic nature of Ovonic threshold switching (1) has been definitively established.(2–8) Electronic action is also the initiating factor in our memories and the electronic concept has proven useful in establishing information encoding in an imaging manner as well.(9–22) It is now appropriate to elucidate the physical and chemical basis for such action.

It is fitting to discuss in this festschrift for Hellmut Fritzsche the phenomena which first interested him in the amorphous field.

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)

It is well known in crystalline tetrahedral semiconductors that conventional incorporation of atoms by substitutional doping increases the electrical conductivity by many orders of magnitude. Such doping is the basis of the crystalline semiconducting industry and has recently been extended to amorphous silicon and germanium, with hydrogen appearing to play an important compensating role.(1–3)

The holographic response (Keneman, 1971; Ohmachi and Igo, 1972) of evaporated AS2S3 at 4880A has been ascribed to photo-polymerization of a hard-sphere As4S6 glass (deNeufville et al., 1973). The effect of illumination is to shift the location of the optical absorption edge (ΔE=-0.06eV), and to increase the refractive index (An=0.08). A comparable increase in refractive index occurs during annealing of evaporated As2S3 at 189 C, near its glass transition temperature, accompanied by a smaller edge shift (Δn=-0.03eV). While the optical absorption edge can be reversibly cycled by exposure at 25°C and annealing at 180°C (ΔE=-0.03eV), the accompanying index changes are relatively small (ΔE=**0.01). Furthermore, the X-ray diffraction pattern is unaffected by cycling, suggesting that the optical effects arise from the creation (exposure) and elimination (annealing) of a nonequilibrium concentration of trapped charge carriers rather than from an innate structural change.

An important difference between crystalline and amorphous structures is that while in crystals the local environment is the same everywhere, in amorphous materials one finds a large spectrum of 3-dimensionally varying spatial and bonding relationships. This gives rise to unique energy interactions, orbital overlaps and bonding configurations of the lone pair electrons associated with the group VI chalcogen atoms which do not occur in crystals. We present the ‘ball and spoke’ models we have built to test out the concepts of lone pair relationships discussed earlier (Ovshinsky 1972, Ovshinsky 1973, Ovshinsky and Fritzsche 1973).

There is a need for alternative energy sources. Photovoltaics are an attractive possibility, but their application has been limited by economic considerations in single-crystal materials, and for physical reasons such as grain boundaries in poly-crystalline materials. Amorphous semiconductors are especially attractive in this regard because they are basically much less expensive than their crystalline counterparts and because they possess a direct band gap with a high value for the optical absorption coefficient. We report here the development of a new alloy that eliminates the physical problems associated with the silicon-hydrogen alloys.

Professor Grigorovici has made important contributions to the understanding and development of amorphous materials. In his long and productive career, he has been particularly involved with the structural basis underlying amorphicity.

A working model is offered to explain the mechanism of high temperature superconductivity in ceramic materials. In this model there are several interdependent, subtly balanced processes which combine to create new and unique phenomena due to the stereochemical nature of these materials.