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Diagnosis and monitoring of corrosion at high temperatures are common challenges in many industries, such as conventional power plants and next generation molten-salt reactor (MSR) nuclear power plants. A simple, noninvasive, in situ acoustic technique was developed to monitor wall loss due to corrosion in a model molten-salt vessel, operating at 500°C to 600°C. This work demonstrated the feasibility of high-temperature corrosion monitoring experimentally, and validated the concept with physical and microstructural analysis, modeling, and numerical simulations. The results of this work could form the basis for the development of a general-purpose, extended-range acoustic monitoring and inspection technique for corrosion at high temperatures (with expected upper range of approximately 900°C), which does not currently exist. Such a technique could be critical for the safe operation of MSRs in the future, as well as for rapid, nondestructive testing of new reactor component materials.

Supercritical water desalination (SCWD) is zero liquid discharge technology that can potentially control the solubility of different electrolytes. However, SCWD is an energy-intensive process and requires high-quality thermal heat (> 450 °C). This study proposes the integration of a high-temperature heat pump to reduce the SCWD energy requirement. The integrated system energy consumption improves by 36% for 3.5% feed concentration and 14% for 20% feed, and the distillate cost reduces by 15% and 10%. Another benefit of the proposed integration is the system can be operated using only electricity as a heat source, as is the case with commonly used high-recovery thermal desalination technology. The integrated SCWD-heat pump system shows superior performance compared to the commercially used brine concentrator and crystallizer system. It is approximately 20% more energy-efficient for 25% feed concentration and 8% cheaper. Hence, the integrated SCWD-heat pump has the potential to outperform the pre-existing high-recovery desalination technology.

We report the studies on the effect of grain alignment on lateral carrier transport in nominally 〈001〉-oriented aligned-crystalline silicon (ACSi) films on polycrystalline substrates. With improving grain alignment, energy barrier height at the grain boundaries was reduced from 150 to less than 1 meV, and both conductivity and Hall mobility became less sensitive to hydrogen passivation. This suggests that the dangling bonds in ACSi films are a major source of trapping sites, and that they become less dominant with improving grain alignment. These results demonstrate that improving grain alignment enhances the lateral carrier transport in small-grained (≤1 μm) polycrystalline silicon films, by reducing dangling bond density at the grain boundaries.

We have grown MgB/sub 2/ films using the deposition technique of reactive evaporation. This method allows high-quality, large-area, double-sided films to be grown on a large variety of substrate materials. These films are therefore well suited for applications, several of which may exploit the low-loss high-frequency properties of MgB/sub 2/, including passive microwave resonators and filters, nuclear magnetic resonance coils, and RF cavities for particle accelerators. Determining the surface resistance and nonlinear properties of our films can thus give us an idea of their suitability for these applications, as well as tell us something about their fundamental superconducting nature. We have begun measuring the microwave properties of our films using both a parallel plate technique and by patterning the films into stripline resonators and lumped-element resonators and filters. The films display very low surface resistance values.

The effect of process conditions on the biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) was studied. The texture showed a strong dependence on the Ar+/MgO flux ratio, but a weak dependence on the divergence of Ar+ beam. One hundred-nanometer-thick epi-MgO on less than 10-nm-thick textured IBAD-MgO films that were grown on 7-nm-thick Y2O3 layers on fused silica, metal alloy tape, and polished Si substrates showed biaxial texture with in- and out-of-plane orientation distributions of less than 4° and 2°, respectively. These results strengthen the notion that the IBAD technique could serve as a universal technological process to integrate amorphous and polycrystalline substrates with various oxide and semiconductor films that need to be grown with good biaxial texture.

New discoveries on collective processes in materials fabrication and performance are emerging in the mesoscopic size regime between the nanoscale, where atomistic effects dominate, and the macroscale, where bulk-like behavior rules. For semiconductor electronics and photonics, dimensional control of the architecture in this regime is the limiting factor for device performance. Epitaxial crystal growth is the major tool enabling simultaneous control of the dimensions and properties of such architectures. Although size-dependent effects have been studied for many small-scale systems, they have not been reported for the epitaxial growth of Si crystalline surfaces. Here, we show a strong dependence of epitaxial growth rates on size for nano to microscale radial wires and planar stripes. A model for this unexpected size-dependent vapor phase epitaxy behavior at small dimensions suggests that these effects are universal and result from an enhanced surface desorption of the silane (SiH4) growth precursor near facet edges. Introducing phosphorus or boron dopants during the silicon epitaxy further decreases the growth rates and, for phosphorus, gives rise to a critical layer thickness for single crystalline epitaxial growth. This previously unknown mesoscopic size-dependent growth effect at mesoscopic dimensions points to a new mechanism in vapor phase growth and promises greater control of advanced device geometries.

Our work on tunable rf and microwave devices based on 90° off-axis magnetron sputtered Ba0.6Sr0.4TiO3 epitaxial thin films is reviewed. In particular, we have studied the effects of energetic bombardment during deposition on the structural and electrical properties of these films. The fundamental result of changing the energetic bombardment conditions during deposition is to affect the stress/strain state of the films. We show that high bombardment conditions result in films with significantly extended out-of-plane lattice constants and depressed dielectric constants and tunabilities.

We present a comprehensive study of broadband (0–2 GHz) electrodynamic properties of coplanar waveguides made from high-temperature superconducting thin-film YBa2Cu3O7−δ electrodes on nonlinear dielectric single-crystal SrTiO3 substrates. The waveguides exhibit strong dielectric nonlinearities, in addition to temperature-, dc-bias-, and frequency-dependent dissipation and refractive index. By using parameters determined from small-signal (linear) transmission characteristics of the waveguides as a function of dc bias, we develop a model equation that successfully predicts and describes large-signal (nonlinear) behavior.

Microwave devices using coplanar waveguide (CPW) structures which incorporate bilayers of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ and nonlinear dielectric SrTiO/sub 3/ on 1 cm/spl times/1 cm/spl times/0.5 mm LaAlO/sub 3/ substrates. The microwave devices include voltage-tunable phase shifters and delay lines, voltage-tunable mixers, and voltage-tunable and adaptive bandpass filters. Under dc voltage bias, these compact CPW devices exhibit more than 360/spl deg/ relative phase shift at 2 GHz, more than 30 dB tunability in mixed microwave power between 0.7 GHz and 5.9 GHz, and fine-tunable symmetric filter profile at around 2.5 GHz with less than 2% bandwidth and more than 15% adaptive range.

We have studied voltage-tunable (0–200 V) broadband (0.1–5.1 GHz) microwave properties at room temperature and the liquid nitrogen temperature of two coplanar waveguide devices made from a Au / Sr0.5Ba0.5TiO3 bilayer and a YBa2Cu3O7-x / SrTiO3 bilayer, respectively. The experimental results agree well with the predictions of simple quasistatic and quasi-TEM models. © 1995 John Wiley & Sons, Inc.

We present a summary of our work on the dc electric field effect on the microwave properties of YBa2Cu3O7/SrTiO3 (YBCO/STO) layered structures. We briefly describe the fabrication of these layered structures, their structural and electrical properties related to the microwave response, and experimental methods to investigate dc electric field effects at microwave frequencies. Analysis of microwave measurements shows that dc electric field modulated changes in both the complex conductivity of YBCO layers and the dielectric properties of the STO layers contribute to the overall device response. At low temperatures (

A noncontact cryogenic microwave measurement system has been developed for the characterization of passive and active superconducting devices by means of an unloaded quality factor measurement technique. The measurement system was designed specifically for the characterization of planar thin film resonant structures as a function of temperature (4–300 K), frequency (100 MHz–26.5 GHz), and dc voltage bias (≤100 V). It has been used for basic device studies of novel active superconducting lumped components made of metal‐oxide superconductor/insulator heterostructures.

The growth of epitaxial semiconductor nanostructures and films at low temperatures is important for semiconductor technology because it allows the possibility of monolithically integrating different high-performance single-crystalline semiconductor structures directly onto low cost technologically important substrates. At sufficiently low temperatures this can enable, for example, Si or Ge device fabrication on flexible substrates such as plastics. We have studied the reduced-temperature liquid-mediated growth of Ge nanostructures and films on crystalline template layers on non-single-crystalline substrates in a low-pressure chemical vapor deposition (LPCVD) system. The heteroepitaxial process is implemented by the Au seeded vapor-liquidsolid (VLS) catalytic growth technique with germane below 400 ºC. Crystalline template layers were prepared with ion-beam-assisted-deposition (IBAD) texturing and electron-beam evaporation on glass substrates. A thin layer of e-beam evaporated Au forms the catalyst layer, upon which we grew Ge films at 386 ºC. Scanning electron microscopy and x-ray diffraction results indicated that both Ge islands and nanowires grew heteroepitaxially on the crystalline template layers on glass substrates with good alignment over large areas.

Using pulsed laser deposition, the authors have prepared epitaxial heterostructures of a new insulating perovskite Sr/sub 2/AlTaO/sub 6/ (SAT) and the high-temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) on LaAlO/sub 3/ substrates. X-ray rocking curve and Rutherford backscattering channeling measurements on

Dynamic time expansion or compression of a small-amplitude input signal generated with an initial scale is performed using a nonlinear waveguide. A nonlinear waveguide having a variable refractive index is connected to a bias voltage source having a bias signal amplitude that is large relative to the input signal to vary the reflective index and concomitant speed of propagation of the nonlinear waveguide and an electrical circuit for applying the small-amplitude signal and the large amplitude bias signal simultaneously to the nonlinear waveguide. The large amplitude bias signal with the input signal alters the speed of propagation of the small-amplitude signal with time in the nonlinear waveguide to expand or contract the initial time scale of the small-amplitude input signal.

We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate. We have incorporated both time- and frequency-domain measurements to determine small-signal effective refractive index and loss tangent as functions of frequency (up to 4 GHz), dc bias (up to 106 V/m), and cryogenic temperature (17 and 60 K). The large-signal impulse response of the devices and the associated phenomenological nonlinear wave equation illustrate how dissipation and nonlinearity combine to produce the overall response in the large-signal regime.

We have studied electromagnetic pulse shaping in coplanar waveguide delay lines made from superconducting YBa2Cu3O7−δ electrodes on nonlinear dielectric SrTiO3 single-crystal substrates. The delay lines exhibited bias- and temperature-dependent nonlinearity and dispersion, with associated pulse-shaping effects. At low temperatures and under certain bias conditions, the interplay of dispersion and nonlinearity has led to stable and compact wave forms, reminiscent of microwave solitons.

We summarize recent progress in growth and characterization of aligned-crystalline silicon (ACSi) films on polycrystalline metal and amorphous glass substrates. The ACSi deposition process uses, as a key technique, ion-beam-assisted deposition (IBAD) texturing on a non-single-crystalline substrate to achieve a biaxially-oriented (i.e., with preferred out-of-plane and in-plane crystallographic orientations) IBAD seed layer, upon which homo- and hetero-epitaxial buffer layers and hetero-epitaxial silicon (i.e., ACSi) films with good electronic properties can be grown. We have demonstrated the versatility of our approach by preparing ACSi films on customized architectures, including fully insulating and transparent IBAD layer and buffer layers based on oxides on glass and flexible metal tape, and conducting and reflective IBAD layer and buffer layers based on nitrides on flexible metal tape. Optimized 0.4-μm-thick ACSi films demonstrate out-of-plane and in-plane mosaic spreads of 0.8° and 1.3°, respectively, and a room-temperature Hall mobility of ∼90 cm2/V.s (∼50% of what is achievable with epitaxial single-crystalline Si films, and ∼1000 times that of amorphous Si films) for a p-type doping concentration of ∼4×1016 cm−3. By using various experimental techniques, we have confirmed the underlying crystalline order and the superior electrical characteristics of low-angle (+–type diode fabricated using a 4.2-μm-thick ACSi film shows minority carrier lifetime of ∼3 μs, an estimated diffusion length of ∼30 μm in the p-Si layer with a doping concentration of 5×1016 cm−3, and external quantum efficiency of ∼80% at 450 nm with the addition of an MgO film anti-reflector.

We present an ion-beam based fabrication method for growth of single-crystal-like films that does not utilize epitaxy on single crystal substrates. We use ion-beam assisted texturing to obtain biaxial crystalline alignment in a film. This ion-beam assisted deposition (IBAD) texturing can be done on arbitrary, but smooth substrates, including flexible polycrystalline metal tapes. With IBAD texturing of MgO and subsequent homoepitaxial growth we have demonstrated an in-plane mosaic spread FWHM as low as 2° and out-of-plane alignment of 1°. The deposition system we use includes reel-to-reel tape transport for a linear transport of substrate materials through the deposition zones. This allows for high-throughput experimentation via a linear combinatorial experimental design.

We have studied the microwave properties of 0.4 μm thick YBa2Cu3O7−x (YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistance Rs values of about 0.5 mΩ at 76 K and 0.15 mΩ at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films.

We present an experimental, analytical, and numerical investigation of the passage of electromagnetic signals through a device with voltage-dependent differential capacitance. This dependence gives rise to the device's nonlinear response, which can then be tuned by an externally applied static electric field. The system is modeled with a wave equation for the current and the charge density with continuity conditions at the boundaries between two linear regions and the nonlinear medium they sandwich. We derive asymptotic formulae for transmission and reflection coefficients of a monochromatic signal and its nonlinearity-induced second harmonics. Predictions based on this analysis are then compared with numerical and experimental results, across a range of parameter values, including those tuning the nonlinearity by means of an imposed voltage. The experiments are carried out at microwave frequencies using 1cm2 devices consisting of a superconducting thin film meandering waveguide on a nonlinear dielectric ...

We have prepared an electrically tunable and adaptive 3‐pole half‐wave bandpass coplanar waveguide filter incorporating a 1.2‐μm‐thick paraelectric SrTiO3 bottom layer and a 0.4‐μm‐thick superconducting YBa2Cu3O7−x top electrode layer on a LaAlO3 substrate. By applying a separate bias voltage on each pole and also on each coupling capacitance of the device at 4 and 76 K, the filter response is not only fine tuned to achieve symmetric and optimized filter characteristics with less than 2% bandwidth centered around 2.5 GHz, but also broadband tuned to shift the passband by more than 15%.

Conductive RuO2 thin films have been heteroepitaxially grown by pulsed laser deposition on Si substrates with yttria‐stabilized zirconia (YSZ) buffer layers. The RuO2 thin films deposited under optimized processing conditions are a‐axis oriented normal to the Si substrate surface with a high degree of in‐plane alignment with the major axes of the (100) Si substrate. Cross‐sectional transmission electron microscopy analysis on the RuO2/YSZ/Si multilayer shows an atomically sharp interface between the RuO2 and the YSZ. Electrical measurements show that the crystalline RuO2 thin films are metallic over a temperature range from 4.2 to 300 K and are highly conductive with a room‐temperature resistivity of 37±2 μΩ cm. The residual resistance ratio (R300 K/R4.2 K) above 5 for our RuO2 thin films is the highest ever reported for such films on Si substrates.

We have prepared electrically tunable microwave resonators incorporating superconducting YBa2Cu3O7−x (YBCO) and paraelectric SrTiO3 (STO) layers on LaAlO3 substrates. The top YBCO layer for each sample was patterned into a 8 mm long coplanar transmission line with a 40 μm gap and a 20 μm center line width. The microwave transmission through the coplanar transmission line exhibits resonances corresponding to standing microwaves along the coplanar transmission line. These resonances are modulated by applying a bias voltage between the center line and the ground planes. Samples with a 0.5 μm thick (2 μm thick) bottom STO layer show, for a resonance at around 8 GHz (5 GHz), a frequency modulation of about 4% (24%) and a quality factor Q of about 200 (50) under 100 V bias at 80 K.

A pulsed laser deposition (PLD) oscillating target scanning technique, in which the laser ablates the target from opposing directions as the deposition proceeds, is described and compared to the conventional technique of target rotation over a cumulative ablation exposure of ∼1500 shots/site. Using conventional rotation the plume direction is eventually displaced by 6° while both the number density and size of PLD associated particles increase. In contrast, the oscillating technique results in a spatially stable plume (displacement

In this work, we have used the Warren-Averbach method to analyze the x-ray diffraction patterns of several Ba/sub 0.6/Sr/sub 0.4/TiO/sub 3/ (BST) epitaxial thin films deposited via 90/spl deg/ off-axis rf-magnetron sputtering. This method allows for the determination of the coherent strains, incoherent strains, crystallite sizes, and defect densities in these films. Results indicate that for BST (60/40) films, the incoherent strain normal to the substrate is smaller on LAO compared to MgO for films 200 /spl Aring/ - 3000 /spl Aring/ thick. However, the opposite relationship holds for the coherent strains. The thickest films showed dielectric constants of 1350 and 925 on MgO and LAO, respectively (at 1 MHz). All showed dielectric loss on the order of 0.007 with the room temperature tunability being 3 times greater for the films on MgO. In-plane measurements of the coherent strain were also completed, showing good agreement with theoretical predictions of the effects of strain on the dielectric properties.

We report on ex situ fabrication of gold contacts onto patterned YBa2Cu3O7−x films. Gold seed layers were blanket sputtered onto photoresist defined over the patterned films. In a second photo process, openings were aligned to the original pads and 8‐μm‐thick contacts were electroplated. The two layers of photoresist and sputtered gold were removed leaving defined contacts. We obtained specific contact resistance of 2.6×10−7 Ω cm2 on post‐annealed samples at 79 K. Microwave filters with contacts showed 4.2 dB loss at 9 GHz and 77 K, while comparable filters in copper showed 18 dB loss.

Using in situ deposited thin‐film Y1Ba2Cu3O7−δ on LaAlO3 substrates, we have developed a pseudo‐interdigital three‐pole stripline filter with a minimum passband loss under 3.5 dB at 9.5 GHz and 77 K. The passband is very narrow, having a bandwidth of only 50 MHz (0.5%). The filter occupies a volume of less than 0.1 cm3. An equivalent copper filter produced a loss of 18.5 and 28 dB at 77 and 300 K, respectively. The input and output coupling is achieved by ex situ sputtered Au thin‐film contacts defined on the Y1Ba2Cu3O7−δ by a lift‐off technology and ultrasonically bonded to hermetic K connectors. Some of the major concerns in the realization of narrow band filters such as air gaps between high dielectric constant substrates and uniformity of the substrate’s dielectric constant are addressed.

We have used a coplanar waveguide structure to study broadband electrodynamic properties of single-crystal and thin-film strontium titanate (STO), and thin-film barium strontium titanate (BSTO). We have implemented low-frequency capacitance (100 Hz - 1 MHz), swept-frequency transmittance (45 MHz - 4 GHz), and time-domain transmittance (dc - several GHz) measurements to determine effective refractive index (or, dielectric constant), and dissipation factor (or, loss tangent) as a function of dc bias (up to 4×106 V/m) and temperature (20 - 300 K). The STO samples used superconducting electrodes and were designed to operate at cryogenic temperatures, whereas BSTO samples used normal conducting electrodes and exhibited optimal performance around room temperature. By using nearly identical electrode geometries for all devices, we were able to conduct a direct comparative study among them, and investigate not only single-crystal vs thin-film, but also cryogenic vs room-temperature applications.

We have prepared electrically tunable and active microwave devices incorporating (superconducting YBa2Cu3O7-x)/(nonlinear dielectric SrTiO3) or (normal metal Au)/(nonlinear dielectric Sr0.5Ba0.5TiO3) bilayers. The dielectric layer thickness for these samples varied between 0.5 μm and 2 μm. The top electrode layer for each sample was patterned into a coplanar waveguide device structure. We have configured these devices as voltage-tunable resonators, voltage-tunable phase shifters, voltage-tunable mixers, and voltage-tunable filters. Under dc voltage bias, these prototype devices have exhibited up to 30% resonant frequency modulation, about 1°/mm-GHz phase shift, more than 40 dB change in mixed microwave power, and finetunable symmetric filter profile with less than 2% bandwidth and more than 15% adaptive range.

We have studied the feasibility of a d. c. voltage bias controlled superconducting microwave lumped-circuit capacitor as an active device. A series-LC circuit was designed and fabricated using YBa2Cu3O7/SrTiO3 films. When a d. c. bias of 35 V was applied across the STO film at ~20 K, the total series capacitance of the circuit, measured at 1 MHz by an LCR meter, decreased by ~3% and the microwave resonant frequency of ~14 GHz increased by ~1.4%, in consistence with the predictions of a simple series-LC resonator model.

A high-Ta field-effect transistor-like structure (SuFET) was made which consisted of an ultrathinYBa2Cu3O (YBCO) film, a dielectric SrTiO3 layer and a gold gate electrode. The use of ultrathin filmsof a few unit cells thickness and an epitaxially grown dielectric layer allowed a relative change in the arealcarrier density of YBCO in excess of 20%. A comparable amount of modulation was obtained in normal

The authors report studies of the effect of grain alignment on interface trap density of thermally oxidized aligned-crystalline silicon (ACSi) films by means of capacitance-voltage (C-V) measurements. C-V curves were measured on metal-oxide-semiconductor (MOS) capacitors fabricated on ⟨001⟩-oriented ACSi films on polycrystalline substrates. From high-frequency C-V curves, the authors calculated a decrease of interface trap density from 2×1012to1×1011cm−2eV−1 as the grain mosaic spread in ACSi films improved from 13.7° to 6.5°. These results demonstrate the effectiveness of grain alignment as a process technique to achieve significantly enhanced performance in small-grained (⩽1μm) polycrystalline Si MOS-type devices.