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Electron beam irradiation was utilized to fabricate planar Josephson junctions in Y 1 Ba 2 Cu 3 O 7 thin films. After the micron-size bridges had been fabricated by way of standard optical lithography, they were modified using a well focused nanometer STEM probe with beam energy within the range of 80 – 120 keV. Modified junctions exhibit a two-step normal/superconductor transition. We attribute the lower transition temperature, which is of the order of 77 K, to the transition of the damaged region. Shapiro steps under applied microwave radiation of the frequency 10–15 GHz, as well as oscillation of the critical current in a magnetic field were observed up to 70 K. A comparison with the RSJ model is made and a possible damage mechanism is discussed.

Hysteresis observed in the resistive semiconductor-to-metal phase transition in VO2 causes problems in bolometric readout, and thus is an obstacle in utilizing this strong phase transition in bolometric sensor applications. It is possible to avoid the unwanted hysteresis when operating in limited temperature ranges within the hysteresis loop of VO2. Nonhysteretic branches (NHB-s) traced in such limited temperature intervals turned out to have much higher temperature coefficient of resistance (TCR) than VO2 at room temperature: while TCR at 25° C in VO2 is close to 3%, peak TCR values in NHB-s reach 6% in VO2 films on Si/SiO2 substrates and 21% in films on crystalline sapphire substrates. At the same time, the nanoscopic-scale mixture of semiconducting and metallic phases in VO2 within its hysteresis loop provides for partially shunted low resistivity, thus creating an unprecedented combination of record high semiconducting TCR and metal-like low resistance. This combination may benefit the uncooled focal plane array microbolometer IR visualization technology.

Electron beam irradiation has been used to induce controllable variations in the properties of YBa 2 Cu 3 O 7-x biepitaxial grain boundary Josephson junctions. Electron irradiation decreased the critical current of the junctions IC and increased the normal state specific resistivities. The junction parameters can be adjusted controllably by applying an appropriate dose. The original properties of the junctions could be partly restored by isothermal annealing A correlation between the transport properties and the microstructure was obtained by determining the ratio of a barrier thickness to the dielectric constant of the junctions with different barriers. The experiment also demonstrates frequency tunability in a resonant soliton oscillator. Preliminar results of irradiation on (103) YBCO films have been given demonstrating differences from data on c -axis films, as partly expected from the anisotropy of these materials.

of the samples. Furthermore, Tc decreases slower in irradiated YBa2Cu3Oy than in YBa2(Cu12xZnx) 3Oy . This may be well explained by the model that the scattering due to in-plane oxygen defects is more anisotropic than that due to Zn impurities. The different behavior of the reduced slopes ( dHc2 /dT)T c /(dHc2 /dT)T c0 in these two types of samples can also be understood in this context. @S0163-1829~99!08309-5# The symmetry of the order parameter in high-temperature superconductors ~HTSC’s ! has been actively debated. While there are now substantial evidences supporting the anisotropic pairing symmetry with line nodes and sign changes, which is consistent with d-wave symmetry, 1,2 this scenario still faces challenges for quantitative reconciliation between certain experiments and the theoretical models. One of these problems is Tc suppression rate due to nonmagnetic impurities in HTSC’s. In d-wave superconductors, nonmagnetic impurity scattering may lead to pair breaking and extreme Tc suppression. 3‐6 Furthermore, assuming that the change of the carrier concentration caused by impurities is negligible, most d-wave pair breaking models 3‐6 lead to an approximately universal dependence of Tc suppression on the residual resistivity r 0 independent of the types of impurities and the details of the pairing mechanism. However, the observed T c suppression rates dTc /dr0 due to different types of impurities or defects are not universal, 7‐10 though they all qualitatively follow the predicted Abrikosov-Gorkov function. 11 Especially, the comprehensive studies of Tc suppression due to in-plane oxygen defects in YBa2Cu3Oy ~YBCO! lead to a Tc suppression rate which is at least twice slower than the simple d-wave pair breaking model predicts. 7,8,12,13 Several

The properties of YBa 2 Cu 3 O 7− x grain boundary Josephson junctions have been reproducibly modified by a focused electron beam irradiation. The original junctions were fabricated by using the biepitaxial technique on (110) SrTiO 3 substrates. The technique utilizes the property of YBa 2 Cu 3 O 7− x film to grow (103)-oriented on the bare substrate and (001)-oriented on the part of the substrate with the MgO seed layer, providing Josephson junctions of good quality and excellent reproducibility. The junction parameters can be adjusted controllably by applying an appropriate irradiation dose. Electron irradiation reduced the critical current of the junctions I C and increased the normal state specific resistivity. The disappearance of the excess current and the shift of the voltage position of the Fiske steps were also observed. Isothermal annealing partly restores the original junction properties. We also speculate that some aspects of the nature of the grain boundary barriers can be better understood from the study of the transport properties of irradiated junctions. PACS: 74.50+r, 74.72Bk, 74.76Bz, 85.25Cp

The effect of large hydrogen concentrations (\ensuremath{\approx}30% atomic), on the superconducting transition temperature ${T}_{c}$ of Nb films is discussed. The hydrogen is incorporated in solutionlike phases which occur at these concentrations because the (\ensuremath{\alpha} to \ensuremath{\beta}) hydride transition in these films is suppressed. X-ray-diffraction data show an asymmetric expansion of the [110] Nb interplanar spacing. This can be as high as a 6--8 % expansion perpendicular to the plane of the film for the addition of \ensuremath{\sim}70% hydrogen, with only a 1--2 % change in the plane of the film. ${T}_{c}$ is depressed to a value near 50% of that of the undoped film with about 30% atomic hydrogen, and returns to its initial value when the hydrogen is removed. A discussion is given of how both disorder and changes in the electronic structure can affect ${T}_{c}.$

The properties of the Y 1 Ba 2 Cu 3 O 7-x biepitaxial Josephson junctions were reproducibly modified by a focused electron beam irradiation of the interface region. The original structures are based on 45° a-axis tilt grain boundaries. The junction parameters can be controllably adjusted by applying an appropriate irradiation dose. Electron irradiation reduced the critical current of the junctions and increased the normal state specific resistivity The disappearance of the excess current and the shift of the voltage position of the Fiske steps were also observed. Isothermal annealing partly restores the original junction properties. Some aspects of the nature of the grain boundary barriers can be better understood from the study of the properties of irradiated junctions.

Electron-beam irradiation has been used to induce controllable variations in the properties of YBa2Cu3O72x biepitaxial grain-boundary Josephson junctions. A correlation between the transport properties and the microstructure was obtained by determining the ratio of a barrier thickness to the dielectric constant of the junctions with different barriers. These results give evidence of the role of the oxygen content and the dielectric constant of the interface region in transport phenomena. The experiment also demonstrates frequency tunability in a resonant soliton oscillator. @S0163-1829~98!51322-2#

We have studied the temperature dependence of the critical current in planar high-T/sub c/ Josephson junctions fabricated in YBa/sub 2/Cu/sub 3/O/sub 7/ thin films by focused electron irradiation. We show that in the range of critical current densities spanning more than five orders of magnitude and temperature range 0.1

Effects of 7-min cardiac arrest and individual behavior on free radical-mediated processes and nitric oxide synthase (NOS) activity was evaluated in brains of male Wistar rats one hour and one week after resuscitation. "Emotional resonance” test was used for the behavioral selection of rats. The test includes factors of significance for rats: the choice between large and lighted or small and dark space as well as signals of pain of another rat. Free radical generation (using chemiluminescence method), superoxide scavenging/generating activity, substances reacting with 2-thiobarbituric acid and NOS activity (by measuring mononitrosyl iron complex of NO with diethyl dithiocarbamate and endogenous brain Fe2+ by electron spin resonance spectroscopy) were determined in cerebral cortex, cerebellum and hippocampus. Cardiac arrest induced oxidative stress accompanied by the loss of NOS activity, as well as compensatory changes of free radical-mediated processes in cerebral cortex. Oxidative stress was also evident in cerebellum and, to a lesser extent, in hippocampus. Most of neurochemical differences between behavioral groups were induced by cardiac arrest. These differences were global, related to a specific brain region or became apparent in cerebral lateralization of biochemical indices.

Rats were subjected to 15 min cardiac arrest and sacrificed 1 h or 15-20 days after resuscitation. Homogenates of brain regions were assayed for nitric oxide synthase (NOS) activity (by measuring the mononitrosyl iron complex of NO with diethyl dithiocarbamate and endogenous brain Fe2+ using electron spin resonance spectroscopy) and generation of free radicals (FRG; by measuring H2O2-induced, luminol-dependent chemiluminescence). Cardiac arrest induced marked decrease of NOS activity and the increase of FRG, most prominent in cerebellum and less marked in cerebral cortex. Two groups of rats were revealed 15-20 days after cardiac arrest: with NOS activity significantly lower than control and not different from control. Positive linear inter-regional cross-correlations of both NOS activity and FRG (except of the group 1 h after resuscitation) as well as negative correlations between NOS and FRG were demonstrated.

Ordered arrays of columnar defects have been fabricated by direct electron-beam writing on ${c}_{\ensuremath{\perp}}$-oriented $\mathrm{Ya}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}(\mathrm{YBCO})$ thin films. Serving as strong pinning sites, columnar defects cause a 70% enhancement of critical current density ${J}_{c}$ at $T=77$ K in magnetic fields parallel to the $c$ axis. The matching effect of the pinning force density has been observed, due to commensurability between flux lines and arrays of columnar defects. The pinning strength of columnar defects has been compared with that of point defects, and found to be greater than the latter in YBCO films. These results suggest that this way of pinning center fabrication could be a promising tool in studies of the pinning mechanism in high-temperature superconductors.

The effect of electron irradiation with incident energy ( E ≤ 40 keV) lower than the threshold for displacement of in-plane atoms on T c , resistivity and Hall coefficient has been studied on fully oxygenated YBa 2 Cu 3 O 7−δ thin. films. In contrast to the known T c suppression at high-energy particle irradiation, an increase in T c has been found as well as a factor of two increase in both the T -linear resistivity slope and the Hall coefficient as a function of radiation fluence. It has been shown that the changes observed in transport properties can be explained as being caused by disruption of the conductivity of CuO chains by radiation-induced chain oxygen defects.

The influence of in-plane oxygen defects on the critical temperature, resistivity, and Hall coefficient was studied in YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} (YBCO) films with different oxygen contents ({ital T}{sub {ital c}0} ranging from 30 to 93 K) with emphasis on the underdoped {open_quote}{open_quote}spin-gap phase.{close_quote}{close_quote} A strong {ital T}{sub {ital c}} suppression was observed, but no influence of the defects on {open_quote}{open_quote}spin-gap{close_quote}{close_quote} features in the transport properties was found. A comparison is made with {ital T}{sub {ital c}} suppression by other in-plane defects such as Zn substitutions for Cu, Pr substitutions for Y in YBCO, and radiation defects in Bi-2201 and Bi-2212 high-{ital T}{sub {ital c}} superconductors. {ital T}{sub {ital c}} suppression by defects is shown to occur in a universal way which is independent of the {ital T}{sub {ital c}0}, carrier concentration, and number of CuO{sub 2} planes per unit cell. It is shown that, independent of whether the in-plane defects induce localized magnetic moments or not, {ital T}{sub {ital c}} is a universal function of the impurity scattering rate, which can be described by the pair-breaking theory for potential scatterers in {ital d}-wave superconductors, but requires that the pair-breaking rate be a factor of 3 smaller than thatmore » suggested by the transport data. An alternative description of the {ital T}{sub {ital c}} suppression in terms of the phase fluctuation theory proposed recently by Emery and Kivelson is also discussed. {copyright} {ital 1996 The American Physical Society.}« less

The effect of electron irradiation with energy from 20 to 120 keV on the resistivity, Hall coefficient, and superconducting critical temperature ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ thin films has been studied. The threshold energy of incident electrons for ${\mathit{T}}_{\mathit{c}}$ suppression has been found, and the displacement energy for oxygen in ${\mathrm{CuO}}_{2}$ planes has been evaluated as 8.4 eV for irradiation along the c axis. The kinetics of production of the in-plane oxygen vacancies has been studied and found to be governed by athermal recombination of vacancy-interstitial pairs. The evaluated recombination volume constitutes about 21 unit cells. The increase in the T-linear resistivity slope and Hall coefficient at unchanged ${\mathit{T}}_{\mathit{c}}$ was observed in irradiations with subthreshold incident energies and was ascribed to the effect of chain oxygen displacements. The upper limit on the displacement energy for chain oxygen has been estimated as 2.8 eV. In x=0.9 samples the ${\mathit{T}}_{\mathit{c}}$ suppression by in-plane oxygen defects and increase in residual resistivity have been found to be, respectively, -280 K and 1.5 m\ensuremath{\Omega} cm per defect in the unit cell. It is shown that ${\mathit{T}}_{\mathit{c}}$ suppression by in-plane oxygen defects is a universal function of the transport impurity scattering rate and can be described qualitatively by pair-breaking theory for d-wave superconductors with nonmagnetic potential scatterers. Evaluation of scattering and pair-breaking rates as well as the scattering cross section and potential is given. A comparison of the influence of in-plane oxygen defects on transport properties with that of other in-plane defects, such as Zn and Ni substitutions for Cu, is also made. \textcopyright{} 1996 The American Physical Society.

Experimental and clinical investigations of patients resuscitated after cardiac arrest or terminal states, testify to the fact that in the post-resuscitation period alongside processes of recovery and compensation, a number of new pathological phenomena develop. The latter differ substantially from those caused by ischemia and hypoxia. These post-resuscitation processes involve not only the CNS, but also the entire body and may lead to severe disability and even death of the seemingly successfully revived body. The data available suggests that this post-resuscitation pathology is a new nosological entity — a post-resuscitation disease. This disease has it own specific etiology, pathogenesis, variants of the clinical course (a number of syndromes) and the system of treatment and rehabilitation. In view of the ever wider use of resuscitation in clinical practice, it is expedient to organize an all-round study of this nosological entity, the optimum systems of its treatment, and to include this entity into International Classification of Diseases of WHO.

A description is given of the fabrication method and Josephson properties of high temperature superconducting junctions produced by focused electron beam writing. The nature of a weak link, I-V characteristics, transition to flux flow, and magnetic field modulation are discussed in some detail. The materials aspects such as the mechanism of e-beam damage to HTS, threshold energy, junction stability, and some technological issues such as reproducibility and uniformity are also addressed. >

This chapter contains sections titled: Introduction Hysteretic semiconductor-metal phase transition in VO 2 - major and minor loops How hysteresis causes problems in bolometric readout - forward and backward excursions Nonhysteretic branches in resistivity Theoretical model NHBs in optical reflectivity - testing the theoretical model Resistive microbolometers in NHB regime Summary

Electron beam irradiation has been used to induce controllable variations in the properties of YBa2Cu3O7, biepitaxial grain boundary Josephson junctions. Electron irradiation decreased the critical current of the junctions Ic and increased the normal state specific resistivities. The junction parameters can be adjusted controllably by applying an appropriate dose. The original properties of the junctions could be partly restored by isothermal annealing A correlation between the transport properties and the microstructure was obtained by determining the ratio of a barrier thickness to the dielectric constant of the junctions with different barriers. The experiment also demonstrates frequency tunability in a resonant soliton oscillator. Preliminar results of irradiation on (103) YBCO films have been given demonstrating differences from data on c-axis films, as partly expected from the anisotropy of these materials.

The properties of YBa2Cu3O7-x grain boundary Josephson junctions have been reproducibly modified by a focused electron beam irradiation. The original junctions were fabricated by using the property of YBa2Cu3O7-x film to grow (103)-oriented on the bare (110) SrTiO3 substrate and (001)-oriented on the part of the substrate with the MgO seed layer. The junction parameters can be adjusted controllably by applying an appropriate irradiation dose. Electron irradiation reduced the critical current of the junctions Ic and increased the normal state specific resistivity. The shift of the voltage position of the Fiske steps was also observed. Isothermal annealing partly restores the original junction properties. A correlation between the transport properties and the microstructure was obtained by determining the ratio of a barrier thickness to the dielectric constant of the junctions with different barriers. These results give evidence of the role of the oxygen content and the dielectric constant of the interface region in transport phenomena. The experiment also demonstrates frequency tunability in a resonant soliton oscillator.

The properties of the Y1Ba2Cu3O7-x biepitaxial Josephson junctions a ere reproducibly modified by a focused electron beam irradiation of the interface region. The original structures are based on 45 degrees a-axis tilt rain boundaries The junction parameters can be controllably adjusted by applying an appropriate irradiation dose Electron irradiation reduced the critical current of the junctions and increased the normal stare specific resistivity. The disappearance of the excess current and the shift of the voltage position of the Fiske steps were also observed Isothermal annealing partly restores the original junction properties Some aspects of the nature of the grain boundary barriers can be better understood from the study of the properties of irradiated junctions.

The properties of the Y1Ba2Cu3O7−x biepitaxial Josephson junctions were reproducibly modified by a focused electron beam irradiation of the interface region. The junctions were fabricated by depositing Y1Ba2Cu3O7−x thin film by cylindrical magnetron sputtering technique on the (110) SrTiO3 substrate, partially covered by a pregrown MgO seed layer. The junction parameters can be adjusted controllably by applying an appropriate dose. Electron irradiation decreased the critical current of the junctions IC and increased the normal state resistance times area to values of the order of 1(μ Ω cm2). Some other effects, such as the disappearance of the excess current, were also observed. The original properties of the junctions could be partly restored by isothermal annealing. We also speculate that some aspects of the nature of the grain boundary barriers can be better understood from the study of the properties of irradiated junctions.

The temperature dependence of the critical current in planar high‐Tc Josephson junctions fabricated in YBa2Cu3O7 thin films by focused electron irradiation has been studied. It is shown that in the range of critical current densities spanning more than five orders of magnitude and temperature range 0.1≤T/Tc≤1, the critical current density jc varies as (1−T/Tc)2. The T dependence of the critical current, however, is affected by the transition from the narrow junction to the wide junction limit as jc increases. An expression for the Josephson penetration depth in thin‐film coplanar structures is derived, and magnetic field penetration depth in junction banks is extracted from the Ic(T) dependences.

We have investigated dc superconducting quantum interference devices (SQUIDs) with loop areas 8 and 64 μm2 made by direct electron beam writing in YBa2Cu3O7−x films with thickness 25 and 50 nm. The SQUIDs have maximum peak‐to‐peak voltage modulation of about 20 μV, which corresponds to the transfer factor dV/dΦ0∼50–60 μV/Φ0 at 30–40 K. By measuring the mutual inductance of the SQUID signal line as a function of temperature and comparing the data with the numerical calculations and the two‐fluid model, we extracted the values of the London penetration depth for YBa2Cu3O7−x thin films.

We have implemented a simple circuit of the rapid single‐flux‐quantum (RSFQ) logic family using a single‐layer YBa2Cu3O7−x thin‐film structure with 14 in‐plane Josephson junctions formed by direct electron beam writing. The circuit includes two dc/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip‐flop, and an SFQ/dc converter (readout SQUID). Low‐frequency testing has shown that the dc‐current‐biased circuit operates correctly and reliably at T∼30 K, a few degrees below the effective critical temperature of the junctions. Prospects for a further increase of the operation temperature and implementation of more complex RSFQ circuits are discussed in brief.

High‐Tc Josephson junctions have been fabricated by direct electron beam writing over YBa2Cu3O7 thin‐film microbridges, using scanning transmission electron microscope (STEM) with an accelerating voltage of 80–120 kV. Annealing at 330–380 K increases Tc and Ic of the junctions and makes them more stable. In the operating range of a few degrees below Tc, the junctions show 100% magnetic field modulation of the critical current, microwave‐induced Shapiro steps oscillating according to the resistively shunted junction (RSJ) model, and RSJ current‐voltage characteristics with IcRn product up to 0.5–0.6 mV at 75 K and 0.3 mV at 77 K.

Micro-scale bridges are fabricated in superconducting thin films of YBCO. The bridges are modified using a highly focussed, nanometer diameter, ≤30keV energy electron probe. Data are presented on the modified bridges which indicate that this approach may be useful for fabricating weak links and Josephson junctions. Consideration is given to mechanisms which may be responsible for modification of the YBCO thin film.

The effect of oral administration of succinic acid was studied in 66 rats exposed to 10 min cardiac arrest with further resuscitation. A total of 30 mg/kg of the drug were administered daily for 5 days starting with day 3 up to day 7 after resuscitation. The experiments have revealed that treatment with succinic acid caused normalization of the orienting behavior in an 'open field' test, decrease of the intensity of response to electric shock, normalization of free radical formation in the brain and serum and reduced cerebral morphological changes. The succinic acid prevented the increase of cholesterol, triglyceride and low density lipoproteins in the blood. The data suggested that after additional trials the succinic acid could be used to prevent development of postresuscitation encephalopathies (3 months after reanimation).

Effects of 7-min cardiac arrest and individual behavior on free radical-mediated processes and nitric oxide synthase (NOS) activity was evaluated in brains of male Wistar rats one hour and one week after resuscitation. "Emotional resonance" test was used for the behavioral selection of rats. The test includes factors of significance for rats: the choice between large and lighted or small and dark space as well as signals of pain of another rat. Free radical generation (using chemiluminescence method), superoxide scavenging/generating activity, substances reacting with 2-thiobarbituric acid and NOS activity (by measuring mononitrosyl iron complex of NO with diethyl dithiocarbamate and endogenous brain Fe2+ by electron spin resonance spectroscopy) were determined in cerebral cortex, cerebellum and hippocampus. Cardiac arrest induced oxidative stress accompanied by the loss of NOS activity, as well as compensatory changes of free radical-mediated processes in cerebral cortex. Oxidative stress was also evident in cerebellum and, to a lesser extent, in hippocampus. Most of neurochemical differences between behavioral groups were induced by cardiac arrest. These differences were global, related to a specific brain region or became apparent in cerebral lateralization of biochemical indices.

The goal of this program was to develop ultra-fast superconducting digital technology based on HTS Josephson junctions on silicon substrates. Working Josephson junctions and SQUID's were successfully fabricated on silicon, and an Yttrium-Barium-Copper-Oxide RSFQ rs flip-flop with 14 junctions and I/O test structures was successfully designed, fabricated, and tested. The kinetic inductance and London penetration depth of the films on silicon were determined from measurements of SQUIDs on silicon. Minimizing kinetic inductance through the use of thicker films will be required in future devices. An approach to alleviating film stress in these thicker films due to thermal expansion coefficient mismatch is outlined. This proposed solution involves fabricating a functionally graded buffer layer that can flow plastically to relieve stress while at the same time, allows nucleation and growth of heteroepitaxial films. A wafer bonding facility was constructed and utilized to demonstrate the successful bonding of silicon and BPSG coated wafers, a key step in the compliant substrate fabrication procedure.

We have successfully fabricated and tested the first All-High-Tc circuit of the Rapid Single Flux Quantum (RSFQ) logic family using a single-layer YBa2Cu3O(7-x) thin-film structure with 14 in-plane Josephson junctions formed by direct electron beam writing. The circuit includes two DC/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip-flop, and an SFQ/DC converter (readout SQUID). Low-frequency testing has shown that the dc-current biased circuit operates correctly and reliably at T-30 K, a few degrees below the effective critical temperature of the junctions. We have also made and studied the first SQUIDs on silicon substrates using the same method to demonstrate the feasibility of integrating HTS with silicon based technology.

In the resistive phase transition in VO 2 , temperature excursions taken from points on the major hysteresis loop produce minor loops. For sufficiently small excursions these minor loops degenerate into single-valued, nonhysteretic branches NHBs linear in log versus T and having essentially the same or even higher temperature coefficient of resistance TCR as the semiconducting phase at room temperature. We explain this behavior based on the microscopic picture of percolating phases. Similar short NHBs are found in otherwise hysteretic optical reflectivity. We discuss the opportunities NHBs present for infrared imaging technology based on resistive microbolometers. It is possible to choose a NHB with 10 2 ‐10 3 times smaller resistivity than in a pure semiconducting phase, thus providing a microbolometer operating without hysteresis, with low tunable resistivity, and high TCR. Unique features of the proposed method and projected figures of merit are discussed in the context of uncooled focal plane array IR visualization technology. © 2009 American Institute of Physics. doi:10.1063/1.3243286

The subject of tunneling in high temperature superconductors (HTSC) is too wide for a comprehensive review a few pages long. This brief account is by necessity imcomplete and subjective — a frame taken out of a movie.

We describe a relatively simple, reliable, and reproducible preparation technique, the precursor oxidation process, for making VO2 films with strong semiconductor-to-metal phase transition. Sputter-deposited metal precursor V films were oxidized in situ in the deposition chamber for 2.5–7h at 370–415°C in 0.2Torr O2 to form 22–220nm VO2. The strength [resistivity ratio, RR=ρS∕ρM] and sharpness (hysteresis width ΔTC) of T-dependent semiconductor-to-metal hysteretic phase transition in VO2 were our most immediate and relevant quality indicators. In 200-nm-range films, the process was optimized to yield RR=(1–2)×103, ΔTC∼11°C and absolute resistivity in a semiconducting phase ρS=0.4±0.2Ωm, close to resistivity in bulk single crystals of VO2. Films were characterized by scanning electron microscopy, atomic force microscopy, grazing-incidence x-ray diffraction, and Raman spectroscopy, and found to be polycrystalline single-phase VO2. We also measured optical reflectivity RT(λ) from 200to1100nm, and Rλ(T) from ...

We have studied the effects of oxygen defects in CuO2 planes by 80 keV electron irradiation on YBCO thin films. Similar to the results of Zn-doped YBCO, a significant increase in eesidual resistivity accompaniesTc suppression, and the relation could be described in the framework of pair-breaking. However, theTc suppression rate is three times as slow, as predicted byd-wave pairing symmetry. For irradiated samples, (dHc2/dT) nearTc is consistent with the scenario of double pair-breaking, in contrast to the case of Pr-doped YBCO.

The low-temperature electrical resistivity has been measured for the high-${T}_{c}$ $A15$ compounds ${\mathrm{Nb}}_{3}$Sn, ${\mathrm{Nb}}_{3}$Al, and ${\mathrm{Nb}}_{3}$Ge and also a low-${T}_{c}$ compound ${\mathrm{Mo}}_{3}$Ge. It is found that most of the high-${T}_{c}$ $A15'\mathrm{s}$ exhibit a ${T}^{2}$ dependence in the temperature range ${T}_{c}lT\ensuremath{\lesssim}40$ K, while ${\mathrm{Mo}}_{3}$Ge shows a ${T}^{5}$ dependence on temperature. Data are also presented for irradiated ${\mathrm{Nb}}_{3}$Sn which show that the ${T}^{2}$ power law is preserved for increasing residual resistivity $\ensuremath{\rho}(0)$. Previous analyses of $A15$ resistivity are examined in some detail to show that the ${T}^{2}$ dependence in the low-temperature resistivity of high-${T}_{c}$ $A15$ materials is an intrinsic effect and is not crucially dependent on the real phonon structure in these materials. It is argued that the observed ${T}^{2}$ dependence remains an unsolved theoretical problem.

Al films deposited on Nb can be oxidized and used to make Josephson junction devices. We studied the structure of Al films deposited under ‘‘warm’’ (estimated to be near 200 °C) and ‘‘cold’’ (near room temperature) conditions because the cold films produced better Josephson junction devices. For the warm case, the Al film was composed of islands with open channels between them, which we attribute to a high mobility of the Al atoms that lowers the island nucleation density. The Nb surface was extremely flat, which we ascribe to the high surface atom mobility at the higher deposition temperature. The cold Al film was of uniform thickness which can be explained by a high island nucleation density. The cold Nb films had an undulating surface, caused by the lack of surface atom mobility during deposition. There was no evidence of Al‐Nb interdiffusion, even after postdeposition heating to 300 °C. Auger spectroscopy, transmission electron microscopy, and scanning electron microscopy were needed to obtain these d...

The change in electrical resistance with time for bulk, thick-film, and thin-film Ba2YCu3Ox at atmospheric pressure is described as a function of the oxygen partial pressure (100 to 0.001%) and temperature (320°–750°C). The potential usefulness of these materials as oxygen sensors is demonstrated. The rate of equilibration is faster during oxygen uptake than during its loss. Time constants τ to reach equilibration (1/e remaining), qualitatively scale with sample dimensions. For a 1μm film at 600° C,τ

NbnAlm multilayer films grown on oxidized Si(100) at room temperature by magnetron sputtering have Nb[110] and A[111] texture. The films have ∼1% coherency strains which decrease with increasing modulation wavelength. The composition modulation is approximately a trapezoidal wave with interfacial regions ∼11 A thick as a result of grain boundary diffusion.

We have prepared high quality tunnel junctions on thin films of Nb 3 Sn, Nb 3 Ge, Nb 3 Al and TiN with artificial tunnel barriers of Al-oxide and AlZr-oxide. The Nb 3 Sn/AlZr-oxide/Pb tunnel junctions prepared on Sn-deficient material showed no measurable proximity effect. Whereas the tunnel spectra of Sn deficient A15 NbSn could be satisfactorily analyzed by the standard Rowell-McMillan inversion procedure, the reduced density of states of the stoichiometric samples exhibited characteristic deformations in form of an overswing at energies far above the highest phonon energy. These deformations can be fitted by proximity analysis but it is shown that they can also be referred to the influence of an electronic density of states which is strongly structured in the range of phonon energies near the Fermi level. A very similar behavior is found for Nb 3 Ge and to a smaller extent for Nb 3 Al. Furthermore first tunneling results are presented for the B1 superconductors NbN and TiN. For NbN the Eliashberg function in the energy region of the acoustic phonons was determined and an upper limit for the coupling strength of the optical phonons is estimated. For TiN we show second derivative data. The energetic location of the minima in these curves agrees well with the position of maxima of the photon density of states.

Resistivity saturation is a general phenomenon observed in metals whose electrons have short mean free paths. The approach to saturation can be described rather well by the parallel-resistor formula $\frac{1}{\ensuremath{\rho}}=\frac{1}{{\ensuremath{\rho}}_{\mathrm{ideal}}}+\frac{1}{{\ensuremath{\rho}}_{\mathrm{sat}}}$, where ${\ensuremath{\rho}}_{\mathrm{ideal}}$ is calculated by the usual theory and ${\ensuremath{\rho}}_{\mathrm{sat}}$ represents a constant "shunt" resistor. In this work it is shown that the requirement of the minimum time between collisions (Ioffe-Regel criterion), incorporated in the distribution of free times, leads to the parallel-resistor formula.

Data are presented which show that the density of states changes dramatically, as does ${T}_{c}$, in both ${\mathrm{Nb}}_{3}$Sn and ${\mathrm{Nb}}_{3}$Ge samples which were disordered by $\ensuremath{\alpha}$-particle irradiation. The density of states is derived from the strong-coupling modifications to the theory of type-II superconduction along with measurements of ${(\frac{d{H}_{c2}}{\mathrm{dT}})}_{\mathrm{Tc}}$ and the residual normal-state resistance ${\ensuremath{\rho}}_{0}$.

A straightforward method for producing metal nitrides, which we call Thin Film Diffusion (TFD), has been developed. With this technique we produced films of cubic nitrides (NbN, ZrN, VN, TiN) with superconducting transition temperatures up to 17.25K in NbN (equal to the highest known in this material), and up to 9.4K in VN (0.6K higher than the highest previously reported value). Resistive transitions are less than 0.1K in width, indicating, together with x-rays, that the samples are homogeneous and essentially single BI phase. In NbN the relatively low resistivity ρ(20K) = 65 μΩcm and metallic resistance ratio ρ(300K)/ρ(20K) - 1.2 were found. TFD films open up new possibilities in tunneling and other experiments on cubic nitrides. Our present results include determination of the strong coupling parameter 2Δ(0)kT c = 4.31 and of the electron-phonon coupling function \alpha^{2} F(\omega) in NbN. \alpha^{2} F(\omega) is found to have a peak at ∼13 meV, which explains the strong-coupling nature of NbN. In resistive studies we found an interesting similarity between the low temperature resistivity behavior of cubic nitrides and A-15 superconductors.

Resistivity was measured from ${T}_{c}$ to 1100 K for ${\mathrm{La}}_{1.825}$${\mathrm{Sr}}_{0.175}$${\mathrm{CuO}}_{4}$, where it is linear to 1100 K, and for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, where it is linear to 600 K, increases faster than linear at Tg600 K because of loss of oxygen, and changes slope at the 950-K structural transition. The observed absence of saturation in the linear parts of the data implies weak electron-phonon coupling in both superconductors, thus excluding the possibility of phonon-mediated superconductivity. Values of the plasma energy are derived in combination with other experimental data.