Abstract: We report a study of the oxidation of TiN. In previous work, the oxidation kinetics for 350–450 °C were reported and an initiation time prior to fast oxidation was identified. In this study, x‐ray photoelectron spectroscopy was used to investigate the oxidation mechanisms at 350 °C during this initiation time period. The oxide thickness increases slowly with oxidation time and the film appears to change from an amorphous TiO2 layer to a crystalline TiO2 layer. Spectral features which are intermediate between TiO2 and TiN are reported and a model involving grain boundary oxidation is proposed. One of the thicker oxides studied was annealed in vacuum to 700 °C. Following oxidation, some of the capping oxide and much of the intermediate material is no longer in the analysis volume and we suggest that the oxygen and nitrogen is being dissolved into the bulk in much the same way that nonevaporable getters are activated before use.

Abstract: A general formalism for multicomponent diffusion in simple phases is presented in some detail. The formalism is mainly based on previous work by various authors. The purpose of the present work is to develop the formalism to such an extent that it is suitable for implementation on a computer. Expressions for the multicomponent diffusion‐coefficient matrix is given. The concentration dependence of the kinetic coefficients is discussed in terms of simple models.

Abstract: Thermography and thermal wave techniques can be combined to provide in a short‐time low‐frequency phase angle images where nonthermal features can be suppressed. The principle is optical thermal wave generation simultaneously on the whole sample surface and sequential monitoring of all pixels using both thermographic techniques and lock‐in data analysis. Due to parallel stationary excitation one can use low modulation frequencies allowing for a depth range that is of relevance for applications.

Abstract: Aluminum‐doped zinc oxide films have been deposited on soda lime glass substrates from diethyl zinc, triethyl aluminum, and ethanol by atmospheric pressure chemical‐vapor deposition in the temperature range 367–444 °C. Film roughness was controlled by the deposition temperature and the dopant concentration. The films have resistivities as low as 3.0 × 10−4 Ω cm, infrared reflectances close to 90%, visible transmissions of 85%, and visible absorptions of 5.0% for a sheet resistance of 4.0 Ω/⧠. The aluminum concentration within doped films measured by electron microprobe is between 0.3 and 1.2 at. %. The electron concentration determined from Hall coefficient measurements is between 2.0 × 1020 and 8.0 × 1020 cm−3, which is in agreement with the estimates from the plasma wavelength. The Hall mobility, obtained from the measured Hall coefficient and dc resistivity, is between 10.0 and 35.0 cm2/V s. Over 90% of the aluminum atoms in the film are electrically active as electron donors. Scanning electron microscopy and x‐ray diffraction show that the films are crystalline with disklike structures of diameter 100–1000 nm and height 30–60 nm. The films have the desired electrical and optical properties for applications in solar cell technology and energy efficient windows.

Abstract: The experimentally observed dependence of effective surface recombination velocity Seff at the Si‐SiO2 interface on light‐induced minority carrier excess concentration is compared with theoretical predictions of an ‘‘extended Shockley–Read–Hall (SRH) formalism.’’ The calculations of SRH‐recombination rates at the Si‐SiO2 interface are based on the theory of a surface space charge layer under nonequilibrium conditions and take into account the impact of illumination level, gate metal work function, fixed oxide charge density, and the energy dependence of capture cross sections σn, σp and interface state density Dit. Applying this theory to p‐type silicon surfaces covered by high quality thermal oxides, the experimentally observed strong increase of Seff with decreasing minority carrier excess concentration could quantitatively be attributed to the combined effect of the σn/σp ratio of about 1000 at midgap and the presence of a positive fixed oxide charge density Qf of about 1×1011 charges/cm2. Due to the f...

Abstract: Flash laser heating using short‐pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1 μm. This is very useful because micron‐ and submicron‐sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser‐cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laserirradiation. This permits the effective removal of particles smaller than ∼20 μm, down to as small as 0.1 μm, from a solid surface using a modest ultraviolet laser fluence of ∼0.1 J/cm2.

Abstract: A finite charging energy, e2/2C’, is required in order to place a single electron onto a small isolated electrode lying between two tunnel junctions and having a total capacitance C’ to its external environment. Under suitable conditions, this elemental charging energy can effectively block all tunnel events near zero bias voltage in series arrays of ultrasmall junctions, an effect that has come to be known as the ‘‘Coulomb blockade.’’ This article outlines a new approach to the design of digital logic circuits utilizing the Coulomb blockade in capacitively biased double‐junction series arrays. A simple ‘‘on’’/‘‘off ’’ switch is described and complementary versions of this switch are then employed to design individual logic gates in precise correspondence with standard complementary metal–oxide semiconductor architecture. A planar nanofabrication technique is also described that may eventually allow the integration of Coulomb blockade logic onto conventional semiconductor chips, thereby realizing hybrid i...

Abstract: GaN films have been epitaxially grown onto (001) Si by electron cyclotron resonance microwave‐plasma‐assisted molecular‐beam epitaxy, using a two‐step growth process, in which a GaN buffer is grown at relatively low temperatures and the rest of the film is grown at higher temperatures. This method of film growth was shown to lead to good single‐crystalline β‐GaN and to promote lateral growth resulting in smooth surface morphology. The full width at half‐maximum of the x‐ray rocking curve in the best case was found to be 60 min. Optical‐absorption measurements indicate that the band gap of β‐GaN is 3.2 eV and the index of the refraction below the absorption edge is 2.5. Conductivity measurements indicate that the films may have a carrier concentration below 1017 cm−3.

Abstract: A steady‐state model for the resistivity of composites is presented, based on the idea that the resistance through a composite is the result of a series of a large number of resistors combined in series and parallel. There are three separate contributions to the resistance: constriction resistance at the contacts, tunneling resistance at the contacts, and the intrinsic filler resistance through each particle, with tunneling resistance generally dominating the magnitude of the overall resistance. The model predicts resistivity increases with increasing filler hardness and/or elastic modulus and insulating film thickness, while resistivity decreases with increasing particle size and intrinsic stress. The room‐temperature dc resistivity behavior of conductor‐filled silicone rubber composites was investigated to verify the model. Comparison of the model to this experimental data showed that good agreement could be obtained for filler materials in which the tarnish layer was a known quantity for a given powder...

Abstract: Tin‐doped indium oxide (ITO) films with the resistivity less than 1.35×10−4 Ω cm were formed by low voltage dc magnetron sputtering (LVMS) and highly dense plasma‐assisted electron beam (EB) evaporation using the arc plasma generator (HDPE). The structural properties of these films were investigated using x‐ray diffraction, scanning electron microscope, and electron spectroscopy for chemical analysis, in comparison with the films formed by conventional magnetron sputtering and EB evaporation, in order to clarify the key factors for low resistivity. With decreasing plasma impedance and sputtering voltages from 540 to 380 V, the resistivity of the films deposited at Ts=400 °C decreased from 1.92 to 1.34×10−4 Ω cm, due mostly to increase in the carrier density. This LVMS film showed higher crystallinity because of lower damages of high‐energy particles during the deposition, which might increase the number of electrically active species. For HDPE, the film with resistance of 1.23×10−4 Ω cm was deposited at T...

Abstract: The effect of source/drain (S/D) parasitic resistance has been experimentally investigated for amorphous silicon (a‐Si:H) thin film transistors (TFTs). In general, the apparent field effect mobility decreases with decreasing channel length. However, the apparent threshold voltage is relatively constant. This may be attributed to an ohmic parasitic resistance due to the use of ion‐implanted n+ S/D regions. Self‐consistent results were obtained from both TFTs and from independent test structures for the TFT parasitic resistance, contact resistance, and sheet resistance. The results showed that the current spreading under the S/D regions is most critical in determining the magnitude of the total parasitic resistance. In this regard, both the S/D ion implantation and the S/D to gate overlap reduce the total parasitic resistance. Finally, the parasitic resistance is modeled as a gate voltage‐modulated channel resistance, under the gate overlap, in series with a constant minimum contact resistance.

Abstract: Ion beam assisted evaporation was used to deposit cubic and hexagonal boron nitride thin films. Boron was evaporated and bombardment was by argon and nitrogen ions. The effect of preparation conditions on the resulting phase was studied, and the relationship between the phase and the energy and momentum transferred into the film through ion bombardment was examined. It is shown that for a given temperature, the controlling factor in the resulting thin film phase is the momentum transferred into the film per depositing boron atom. At 300–400 °C a sharp threshold value of momentum‐per‐atom exists below which films are hexagonal and above which they are cubic. For 400 °C this threshold occurred at 200 (eV×amu)1/2 which is equal to 3.3×10−21 m kg s−1. Depositions performed using krypton and xenon instead of argon as the second bombarding gas confirmed this momentum‐per‐atom value. A second threshold was also observed, which was bombarding species dependent, above which either complete resputtering of the deposited material or reversion to the hexagonal phase occurred. Cubic boron nitride deposition was seen to occur in a window of momentum‐per‐atom values between these two thresholds. Using this information it was possible to grow cubic boron nitride using only nitrogen bombardment, although the window of momentum‐per‐atom values for nitrogen is very narrow. The effect of substrate temperature was studied, and it was found to be difficult to grow predominantly cubic phase films below 300–400 °C. The relationship between intrinsic stress and phase of the films is also discussed. A diagram is presented showing film phase as a function of bombardment, substrate temperature, and system chemistry. The parameter of momentum‐per‐atom is shown to combine into a single value the variables of ion beam assisted deposition: deposition rate, ion energy, ion flux, and ion species. It is suggested that, in general, for properties affected by ion bombardment the momentum‐per‐atom transferred into the film is the controlling factor. The results are shown to support momentum transfer as the dominant process in cubic boron nitride thin film formation.

Abstract: A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

Abstract: Forces between particles aligned into chains by an applied electric field in an electrorheological (ER) fluid are calculated using finite‐element techniques and, approximately, using a dipole approximation with local‐field effects. Evaluation of the effective dielectric constant is emphasized and the shear modulus is derived from the shear dependence. For high‐frequency (f≳0.1–1 kHz) applied electric fields, the forces and the modulus depend upon the dielectric constants of the suspending fluid and the dispersed particles. For low‐frequency or dc electric fields, the conductivities of the components are dominant. These effects are treated within a Maxwell–Wagner approach. If the ratio of particle‐to‐fluid conductivities substantially exceeds the ratio of dielectric constants, a large enhancement of the modulus is found. Implications for the design of ER fluids are discussed briefly.

Abstract: The elastic constants of single‐crystal NbN, VN, and TiN films were determined from surface acoustic wave (SAW) dispersion curves obtained by the use of an acoustic microscope with a line‐focus beam. Measurements were carried out for single‐crystal nitride films grown on the (001) plane of single‐crystal cubic‐symmetric MgO substrates. The phase velocities measured as functions of the angle of propagation display the expected anisotropy. Dispersion curves of SAWs propagating along the symmetry axes were obtained by measuring the wave velocities for various film thicknesses and frequencies. Using a modified simplex method, an inversion of the SAW dispersion data yielded the elastic constants of cubic symmetry, namely c11, c12, and c44. The Rayleigh surface wave velocities calculated from the determined elastic constants and known mass densities agree well with a result measured by Brillouin scattering spectroscopy reported elsewhere.

Abstract: Carbon thin films have been prepared by 248 nm excimer laser vaporization of graphite targets. The effect of a variety of process parameters on the film properties is investigated. Deposition at or below room temperature yields diamond‐like films with low hydrogen content, high optical transmission, and high resistivity. Electron energy loss spectra indicate sp3 bond fractions of 70–85%. Detailed analyses of the pseudodielectric functions, measured using spectroscopic ellipsometry, show the films to have normal dispersion and an index of refraction of 2.5 in the visible wavelength region. The effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.

Abstract: Epitaxial thin films of Ba2YCu3O7−x (BYC) were prepared on (001) LaAlO3 single‐crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high‐temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low‐oxygen partial pressures. Superconducting films of 70 nm thickness with zero‐field critical current densities greater than 5×106 A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830 °C in 2.5 × 10−4–1 × 10−3 atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c‐axis normal BYC near the film/substrate interface with the overlying mater...

Abstract: This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10−3 to 10.4× 10−3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10−3 to 11.6 × 10−3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. ...

Abstract: A Michelson interferometer and an optical beam deflection configuration (both shot noise and diffraction limited) are compared for application in an atomic force microscope. The comparison shows that the optical beam deflection method and the interferometer have essentially the same sensitivity. This remarkable result is explained by indicating the physical equivalence of both methods. Furthermore, various configurations using optical beam deflection are discussed. All the setups are capable of detecting the cantilever displacements with atomic resolution in a 10 kHz bandwidth.

Abstract: Gallium doped zinc oxide films have been deposited in the temperature range 150 to 470 °C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations. The films are polycrystalline with crystallite sizes varying between 275 and 500 A for undoped films and between 125 and 400 A for doped films. Only those films deposited above 430 °C are highly oriented and have their c axes perpendicular to the substrate plane. The electron density, conductivity, and mobility always increase with temperature. Thicker films have higher conductivity and mobility than thinner films. The refractive index is reduced from 1.96 to 1.73 when the electron density is increased from zero to 3.7×1020 cm−3. For films deposited at 370 °C with a gallium concentration of about 2.5 at. %, the ratio of conductivity to visible absorption coefficient increases from 0.03 to 1.25 Ω−1 when the film thickness increases from 0.11 to 1.2 μm. A film deposited at 470 °C with a gallium concentration of 2.4 at. % and a thickness o...

Abstract: Experiments are reported on two techniques for melt‐texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper‐rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser‐heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: ‘‘faceted plane front,’’ ‘‘cellular dendritic’’ or ‘‘equiaxed blocky.’’ The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the ‘‘root’’ of the solidification front dropped, but temperature of the solidification front ‘‘tip’’ did not. A solidification model is ...

Abstract: Vapor transport equilibration was used to prepare lithium niobate crystals of a variety of controlled off‐congruent compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature Tc and measurement of the temperature for noncritical phase matching TPM of second‐harmonic generation from both 1.064‐ and 1.32‐μm laser sources. Across the majority of the single‐phase region, both Tc and TPM were observed to vary nearly linearly with Li/Nb ratio. The variation in TPM with Li/Nb ratio was observed to change direction within the single‐phase region at some small but finite compositional interval away from the Li‐rich phase boundary. Crystals equilibrated to the Li‐rich phase boundary had excellent optical homogeneity. Preparation of Li‐poor crystals was hampered by extremely slow lithium diffusivity and problems with second‐phase precipitation.

Abstract: The formation mechanisms and properties of TiSi2 on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi2 films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either by in situ annealing or deposition onto heated substrates. The island formation of TiSi2 and surface and interface morphologies of TiSi2 were examined by scanning electron microscopy and transmission electron microscopy. The TiSi2 formation process was monitored with in situ Auger electron spectroscopy and low‐energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi2. Titanium film thicknesses from 50 to 400 A were examined. For all thicknesses studied, the C49 TiSi2 phase is observed to nucleate. Immediately after low‐temperature deposition, the interface morphology was smo...

Abstract: Apparatus and methods for Compton scattering tomography employ a source of monoenergetic gamma rays and a detector capable of detecting the energy of scattered photons and determining the detector location both disposed on one side of an object to be imaged. Based on analysis of the measurement of the energy of the detected photons and the detector locations, a circle of possible scattering locations is determined as to each scattering event. By performance of a number of experiments as a function of detector location and energy, the density of the object can be reconstructed by filtering and back-projecting the data to yield an image responsive to variation in the density of the material of the object to be imaged.

Abstract: High‐quality gallium nitride (GaN) film was obtained using a GaN buffer layer on a sapphire substrate. Using low‐temperature Hall measurements, we obtained a maximum mobility about 3000 cm2/V s, at around 70 K. This mobility value is the highest reported, to our knowledge, for GaN films. The infrared radiation transmission intensity oscillations, which were caused by interference effects, were observed by means of an infrared radiation thermometer during GaN growth. The growth process of GaN film with GaN buffer layers was almost the same as that of GaN film with AlN buffer layers except when the thickness of GaN buffer layers was small. When the thickness of GaN buffer layers was small, an additional new growth process, in which the surface of GaN film became rough during the growth, was observed. The GaN growth with GaN buffer layers had a tendency to improve the surface morphology even if it became poor due to excess Si doping or low buffer layer thickness.

Abstract: The systematic study of band‐edge luminescence in pseudomorphic Si/Si1−xGex/Si double‐heterostructure layers is reported for a wide composition range, 0.12