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In this study, we demonstrate the use of bacterial templates of differing morphology for the facile synthesis of magnetic micron-sized spheres, tetrads of spheres, filaments, and coils. These microstructures were synthesized by a platinum catalyzed electroless deposition of nickel under mild aqueous conditions using D. radiodurans, genetically elongated E. coli, and R. rubrum as templates, respectively. Analysis by SEM/EDS, TEM, and SQUID magnetometry indicates the formation of superparamagnetic metallic microfilaments, which possess a blocking temperature of ¨70 K with no observable exchange anisotropy. XPS analysis of the metallic microfilaments supports the presence of NiB, which is diamagnetic, thus supporting the hypothesis that the morphologically unique microbial templates are encapsulated within a biosurface-bound NiB shell that contains embedded nickel nanoparticles (12–20 nm). The use of microorganisms as templates, which may be recombinantly modified, may therefore serve as alternative means for magnetic microstructure and core–shell synthesis.

The microstructural properties of secondary phase particles formed in epitaxial CoxTi1−xO2 anatase thin films grown on (0 0 1)LaAlO3 by a reactive RF magnetron co-sputter deposition are examined. These films exhibit ferromagnetic behavior in magnetization measurements, showing a M–H loop at room temperature with a saturation magnetization on the order of 0.7 μB /Co. X-ray photoemission spectrometry indicates that the Co cations are in the Co2+ valence state. Cross-section electron microscopy reveals that a significant fraction of the cobalt segregates into Co–Ti–O secondary phase particles. Selected area electron diffraction shows that the secondary phase particles are cobalt-rich anatase. While the cobalt is concentrated in the segregated particles, local energy dispersive spectrometry indicates some Co throughout the film.

Implantation of Co or Mn into single-crystal BaTiO3(K), SrTiO3 or KTaO3(Ca), followed by annealing at 700 � C, produced ferromagnetic behavior over a broad range of transition metal concentrations. For BaTiO3, both Co and Mn implantation produced magnetic ordering temperatures near 300 K with coercivities 670 Oe. The M–T plots showed either a near-linear decrease of magnetization with increasing temperature for Co and a non-Brillouin shaped curve for Mn. No secondary phases were detected by high-resolution X-ray diffraction. The same basic trends were observed for both SrTiO3 and KTaO3, with the exception that at high Mn concentrations (� 5 at.%) the SrTiO3 was no longer ferromagnetic. Our results are consistent with recent reports of room temperature ferromagnetism in other perovskite systems (e.g. LaBaMnO3) and theoretical predictions for transition metal doping of BaTiO3 [Nakayama et al., Jap. J. Appl. Phys. 40 (2001) L1355].

Bulk single crystals of Sn-doped ZnO were implanted with Co or Mn at doses designed to produce transition metal concentrations of 3–5 at.% in the near-surface (� 2000 A region. The implantation was performed at � 350 Ct o promote dynamic annealing of ion-induced damage. Following annealing at 700 C, temperature-dependent magnetization measurements showed ordering temperatures of � 300 K for Co- and � 250 K for Mn-implanted ZnO. Clear hysteresis loops were obtained at these temperatures. The coercive fields were 6 100 Oe for all measurement temperatures. X-ray diffraction showed no detectable second phases in the Mn-implanted material. One plausible origin for the ferromagnetism in this case is a carrier-induced mechanism. By sharp contrast, the Co-implanted material showed evidence for the presence of Co precipitates with hexagonal symmetry, which is the cause of the room temperature ferromagnetism. Our results are consistent with the stabilization of ferromagnetic states by electron doping in transition metal-doped ZnO predicted by Sato and Katayama–Yoshida [Jpn. J. Appl. Phys. 40 (2001) L334]. This work shows the excellent promise of Mn-doped ZnO for potential room temperature spintronic applications. 2003 Elsevier Ltd. All rights reserved.

C 60 films up to 1000 A in thickness have been grown by room-temperature sublimation onto Si(100) and Si(111) substrates that have been prepared with surfaces passivated against dangling bonds. X-ray diffraction measurements reveal that films deposited on such substrates have a high degree of (111)-textured crystallinity which is absent in films deposited on untreated Si. Examination of surface topographies with tapping mode atomic force microscopy shows a thickness-dependent increase in roughness which is greater for the treated samples. Our results are placed in context with respect to what is presently known about the growth of C 60 films on a variety of substrates. Implications for possible device applications will also be discussed.

Single-phase (Ga,Mn)N layers grown by molecular beam epitaxy with ∼3 at. % Mn were exposed to 2H or 1H plasmas under conditions designed to permeate layers with hydrogen. No evidence of the formation of Mn–H complexes could be detected from either infrared spectroscopy or the changes in magnetic properties. However, the residual magnetization increased ∼20% after hydrogenation, consistent with passivation of crystal defects in (Ga,Mn)N. Hydrogenation may be an attractive method for improving the magnetic properties of these heteroepitaxial materials.

We report here an interpretation of the electrical resistivity (ρ) below 15 K of two Fe–Cr multilayers (30 layers of 20 A Fe/10 and 12 A Cr) produced by Xe ion-beam sputter deposition. These multilayers have a negative giant magnetoresistance (GMR) of ∼21% at 4.2 K and Hsat=13 kOe. Very high-resolution resistance measurements (better than 3 ppm) were made down to 2.3 K at every (100±10) mK. Excellent results were obtained when the ρ(T) data in the ferromagnetic state (H=Hsat) were fitted to an equation containing the residual resistivity [ρ(0)], electron–phonon interband s–d scattering (Bloch–Wilson integral) and a magnetic BT2 term, where B is proportional to s–d interaction strength responsible for the electron–magnon s–s scattering. The value of B is found to be typically (9±2)×10−5 μΩ cm K−2 compared to the much smaller value of 1.5×10−5 μΩ cm K−2 for bulk crystalline Fe. The fits without the magnetic term are distinctly inferior as seen from their residuals plotted against T. However, the data in the...

Bismuth thin films deposited onto glass substrates by thermal sublimation are polycrystalline with short mean free paths, multiple grain orientations, and disappointingly small magnetoresistance when compared to single crystals. Direct deposition onto thin gold buffer layers followed by a post-deposition anneal leads to significantly improved properties, namely, large grains oriented in the trigonal direction and a 5-T magnetoresistance higher than 250% at room temperature. For a Bi0.93Au0.07 stoichiometry, we show that optimal results are obtained when the annealing temperature is above the BiAu eutectic point (241 °C) and below the melting temperature (271 °C) of bismuth, thus indicating a mechanism in which the presence of gold in the bismuth facilitates grain-boundary motion and grain growth.

Thin-film multilayer structures with up to 20 repeat layers have been grown in a high-vacuum chamber by sequential deposition of aluminum (Al) and fullerene (${\mathrm{C}}_{60}$) onto room-temperature substrates. The periodicity of the layers is confirmed by x-ray-diffraction and in situ resistance measurements. The presence of underlying layers of ${\mathrm{C}}_{60}$ reduces the critical thickness at which Al becomes conducting from \ensuremath{\sim}35 to \ensuremath{\sim}20 \AA{}. In addition, there is a sudden increase in resistance that occurs when each Al layer is covered by a monolayer of ${\mathrm{C}}_{60}$. These observations, together with the measurement of a downward shift in frequency of a considerably broadened Raman-active ${\mathit{A}}_{\mathit{g}}$(2) pentagonal-pinch mode, imply that up to six electrons per ${\mathrm{C}}_{60}$ are transferred from the Al to the ${\mathrm{C}}_{60}$ layer. This demonstration of charge transfer across planar metal-${\mathrm{C}}_{60}$ interfaces suggests that multilayers may be a useful vehicle for forming fullerene interface compounds in two-dimensional structures.

The unpretentious origins in pure carbon soot of the highly symmetric C 60 molecule and the ease in which pure C 60 solids can be intercalated with alkali metals provide the essential motivation behind much of the current research activity on superconductivity in the doped fullerenes. In this paper the salient experimental phenomenology of these new superconductors is briefly reviewed and placed into context with respect to what is known about other classes of superconductors. Although the ‘soot to superconductivity’ story has had an auspicious beginning, a conclusion to the story is not yet in sight and additional experimental results and theoretical analyses are needed.

We report the observation and assignment of the doping-induced features in the UV-visible and near-IR optical spectra of ${\mathrm{C}}_{60}$ thin films and their direct correlations with electrical resistivity. A pronounced bleaching and several induced absorptions are observed upon doping with the alkali metals, potassium and rubidium. The absence of a strong dependence of the induced spectra upon intercalant suggests that the induced features observed are intrinsic to the host fullerene film. The evolution of these transitions, as doping proceeds from pristine ${\mathrm{C}}_{60}$ to ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$, is consistent with a two-domain picture for the formation of the metallic state. As the intercalation proceeds beyond the resistance minimum, an overall change in spectral shape begins to occur and energy shifts of many of the features become apparent. These observations indicate changes in the electronic bands accompanying the structural phase transformations from ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ to ${\mathrm{K}}_{6}$${\mathrm{C}}_{60}$. There is no spectral evidence for the presence of ${\mathrm{K}}_{4}$${\mathrm{C}}_{60}$ during doping.

Van der Waals forces that bind C[sub 60] molecular solids are found to be sufficiently strong to allow the reproducible fabrication of free-standing C[sub 60] membranes on (100) silicon wafers. Membranes, 2,000 to 6,000 angstroms thick, were fabricated by a modified silicon micromachining process and were found to be smooth, flat, and mechanically robust. An important aspect of the silicon-compatible fabrication procedure is the demonstration that C[sub 60] films can be uniformly and nondestructively thinned in a CF[sub 4] plasma. Young's modulus and fracture strength measurements were made on membranes with areas larger than 6 millimeters by 6 millimeters. It may be possible to use C[sub 60] membranes for physical property measurements and applications. 20 refs., 5 figs.

Photoemission spectra of vacuum deposited layers of C 60 , before and after exposure to K vapor, show that the K donates its conduction electron into the band derived from the lowest unoccupied molecular orbital. A compound with composition of K 3 C 60 , corresponding to the maximum conductivity, has been prepared. In it the potassium atoms presumably occupy both the octahedral and the two tetrahedral interstitial sites of the face-centered-cubic (fcc) C 60 structure.

The authors report measurements of the real 4He superfluid density, sigma s, as a function of temperature and coverage on hydrogen and C60 substrates using a high-Q Al oscillator. Sub-kelvin measurements of the helium mass loading of a 780 nm thick C60 film deposited on the active surface of the oscillator show that helium does not significantly permeate the interstitial sites of the C60 matrix, in either its superfluid or normal phase. In fact, the Kosterlitz-Thouless superfluid transition is observed on the C60 at very modest mass loadings. The superfluid behaviour on C60 is found to be very similar to that observed for helium on solid hydrogen, namely a suppression of sigma s(Tc) in transitions near 1 K and excess vapour dissipation in the normal phase.

Temperature and magnetic-field-dependent measurements of the longitudinal ${\mathit{R}}_{\mathit{x}\mathit{x}}$ and transverse ${\mathit{R}}_{\mathit{x}\mathit{y}}$ resistance of amorphous indium oxide thin-film superconductors reveal the presence of distinct insulating phases for sufficiently high disorder and/or magnetic field. For field-swept transitions at fixed disorder and low temperatures there is a critical field where ${\mathit{R}}_{\mathit{x}\mathit{x}}$ diverges and the superconductor is transformed into a Bose-glass insulator with localized Cooper pairs. At higher fields there is a second critical field where ${\mathit{R}}_{\mathit{x}\mathit{y}}$ appears to diverge, the pairs unbind, and localized single electrons characterizing a Fermi-glass insulator dominate.

A brief review is presented discussing the role of charge transfer and the appearance of superconductivity in the three-dimensional (3D) alkali-metal-doped fullerene compounds (A3C60). An argument is made that similar phenomenology may occur in two dimensions (2D) when a C60 monolayer is doped by charge transfer from an adjacent planar metal layer. Illustrative data are presented showing that charge transfer gives rise to a decrease in resistance when C60 is deposited onto a thin smooth nickel film. Accordingly, the physics of charge transfer and electron delocalization, which plays such an important role in the superconductivity of the 3D A3C60 compounds, could well play a similar role in these 2D analogues where a C60 monolayer is doped to a conducting state by charge transfer from an underlying metal.

We present a study of quantum corrections to the conductivity of thin ferromagnetic gadolinium films. In situ magnetotransport measurements were performed on a series of thin films with thickness $dl150\text{ }\text{\AA{}}$. For sheet resistances ${R}_{0}\ensuremath{\le}2840\text{ }\ensuremath{\Omega}$ and temperatures $T\ensuremath{\le}30\text{ }\text{K}$, we observe a localizing, linear in temperature contribution to the conductivity in addition to the logarithmic temperature dependence expected from well-known quantum corrections in two dimensions. We show that such a linear $T$ dependence can arise from a spin-wave-mediated Altshuler-Aronov-type correction.

The influence of oxygen exposure on the Raman spectrum of C60 microscrystalline films under laser irradiation is described. In the frequency region of the symmetric Ag pentagonal pinch mode, exposure of vacuum grown C60 films to 16O2, 18O2, or air results in the appearance of a peak at 1467 cm-1, a mode previously attributed to pure C60. The time dependence of this mode in the laser beam, as well as the Raman spectrum of pristine C60 are discussed.

The resolution of electrostatic force microscopy (EFM) is enhanced when multiwalled carbon nanotubes are used as extensions on conventional silicon cantilevers. Multiwalled nanotubes provide robust, high aspect ratio, conducting tips that minimize topographic dependence of gradients in the capacitance between the tip/cantilever and the substrate. Comparison of simultaneously acquired topographical and EFM images taken at the intersection of overlapping electrodes of electrically biased Al–Al2O3–Al tunnel junctions confirm the improved performance. This enhancement enables us to determine the surface contact potential differences between individual nanotubes within a bundle with resolutions of 5 mV and 10 nm.

Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

When high quality bismuth or graphite crystals are placed in a magnetic field directed along the c-axis (trigonal axis for bismuth) and the temperature is lowered, the resistance increases as it does in an insulator but then saturates. We show that the combination of unusual features specific to semimetals, i.e., low carrier density, small effective mass, high purity, and an equal number of electrons and holes (compensation), gives rise to a unique ordering and spacing of three characteristic energy scales, which not only is specific to semimetals but which concomitantly provides a wide window for the observation of apparent field induced metal-insulator behavior. Using magnetotransport and Hall measurements, the details of this unusual behavior are captured with a conventional multi-band model, thus confirming the occupation by semimetals of a unique niche between conventional metals and semiconductors., 4 pages, 4 figs, data and discussion on bismuth added, final published version

We summarize recent progress in creating dilute magnetic semiconductors such as (Ga,Mn)N, (Ga,Mn)P, (Zn,Mn)O, (Si,Mn)C, and (Zn,Mn)SiGeN/sub 2/ exhibiting room temperature ferromagnetism through the use of ion implantation, the origins of the magnetism and its potential applications in novel device such as spin-polarized light emitters and spin field effect transistors.

N‐channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element. Measurements on C60 thin films in ultrahigh vacuum show on‐off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V s.

Magnetotransport has been investigated in high purity bismuth crystals in static magnetic fields as high as 20 T and temperatures as low as 25 mK. This high B/T ratio permits observation of pronounced Shubnikov-de Haas oscillations over a wide field range and up to fields where most of the carriers are in the lowest Landau level. For transport currents in the bisectrix or binary directions and field in the perpendicular trigonal direction, we have observed doublet splittings centered on each Shubnikov-de Haas oscillation. These splittings exhibit a quadratic dependence on field and disappear before the last oscillation. Our observations allow us to conclude unambiguously that already when the Landau level index is as high as 2 the carriers are fully polarized and that the g-factor for holes with the field in the trigonal direction is 35.3(4)., 4 pages, 3 figures

The structure and magnetic properties of Co-doped ZnO films are discussed in relation to cobalt doping levels and growth conditions. Films were deposited by pulsed-laser deposition (PLD) from ZnO targets containing cobalt concentrations from 0 to 30 at.%. The structure of the films is examined by x-ray diffraction (XRD) and transmission electron microscopy (TEM), and optical absorption is used to infer the substitution of cobalt inside the ZnO lattice. Magnetic properties are characterized by superconducting quantum interference device (SQUID) magnetometry. Films doped with cobalt concentrations of a few per cent appear to be composed of two magnetic components: a paramagnetic component and a low-field ferromagnetic component. Films doped with 30% cobalt show a larger FM signature at room temperature with clear hysteretic shape, but films grown at low pressure are plagued by the precipitation of metallic cobalt nanoparticles within the lattice which can be easily detected by XRD. These particles are well oriented with the ZnO crystal structure. By increasing the base pressure of the vacuum chamber to pressures above 1×10−5 Torr, metallic cobalt precipitates are undetectable in XRD scans, whereas the films still show an FM signature of ∼0.08 μB/Co. Depositions in the presence of oxygen background gas at 0.02 mTorr decreases the magnetization. The decreased magnetization with oxygen suggests that the activation of ferromagnetism depends on defects, such as oxygen vacancies, created during growth. Optical absorption measurements show a sequential increase in the Co+2 absorption peaks in these films, along with an almost linearly increasing bandgap with cobalt concentration suggesting a large solubility of cobalt in ZnO. Bright-field TEM imaging and electron diffraction do not show signs of precipitation; however, dark-field imaging shows circular areas of varying contrast which could be associated with cobalt precipitation. Therefore, the possibility that ferromagnetism results from secondary phases cannot be ruled out.

We present a systematic in situ study of the effect of postdeposition low-energy (200eV) ion bombardment on resistance and surface topography of ultrathin iron (

Ion implantation of Mn at concentrations of 1–5 at. % was performed in AlxGa1−xP:C (x=0, 0.24, 0.38, and 0.54) epilayers grown by gas source molecular beam epitaxy. Ferromagnetic-like ordering at 300 K was observed for Mn doses up to 3 at. % for all Al subfractions in superconducting quantum interference device measurements. The calculated magnetic moment was found to peak at 3 at. % Mn in plots of magnetization versus Mn for all four Al subfractions. For a given Mn concentration, the magnetic moment was found to initially increase then decrease in plots of magnetization versus Al subfraction. Structural characterization revealed the presence of the Mn2P and Mn3Ga phases in Al0.54Ga0.46P:C layers implanted with 5 at. % Mn, while no second phases were observed in any other combinations of Al and Mn. A substantial increase in magnetic ordering temperature predicted by theory for AlxGa1−xP:C films compared to GaP:C films with Mn incorporation was not observed.

Carbon-doped (p ∼ 10 1 9 cm - 3 ) GaMnP with ∼5 atom % Mn grown by gas-source molecular beam epitaxy showed ferromagnetism to

ZnO nanorods with typical lengths and diameters of /spl sim/2 /spl mu/m and 15-30 nm, respectively, were grown on Ag-coated Si substrate by catalyst-driven Molecular Beam Epitaxy and subsequently implanted with Mn/sup +/ or Co/sup +/ ions of dose ranging from 1-5/spl times/10/sup 16/ cm/sup -2/. The samples were then annealed at 700/spl deg/C for 5 minutes. The structural properties were unaffected, but they exhibited ferromagnetism that persisted up to temperatures of 225-300 K. Coersive fields were /spl les/100 Oe even at 10 K. The results are similar to those obtained for implantation of Mn/sup +/ and Co/sup +/ ions in bulk, single-crystal ZnO, indicating the promise of nanorods for nanoscale spintronics.

We have measured the 2D 4 He superfluid density, σ s , on hydrogen and C 60 using a high-Q Al oscillator, operated in an open geometry. We find that only 1/2 layer of helium remains normal well below the transition on hydrogen as opposed to 4 layers on the surface of bare C 60 .

Measurements of resistive transitions, critical fields, and magnetoconductance as a function of increasing normal-state sheet resistance ${R}_{N}$ reveal the systematics of a pronounced change from superconducting to insulating behavior in thin $\frac{\mathrm{In}}{\mathrm{In}{\mathrm{O}}_{x}}$ composite films. With increasing ${R}_{N}$, a rapid suppression of the transition temperature together with a decreasing critical-field slope parameter are observed. These results are modeled using a pair-breaking formalism in which the pair-breaking rate is found to be proportional to ${R}_{N}$ and independent of temperature.

Transmission electron microscopy has been used to study the microstructural trends of thin film composites prepared by sputtering of a metal (aluminum, copper, indium, lead or tin) target with argon ions in the presence of a reactive gas (oxygen). Results of these studies reveal that there is a general progression in the metal component microstructure which correlates with an increasing metal oxide component in the films and can be classified as belonging to an agglomerated-columnar-granular-amorphous sequence. These structural trends and the concomitant effect on film properties, such as resistivity, adhesion and mechanical stability, are a direct consequence of the metal-metal oxide interaction and the inhibiting effect which the native metal oxides have on metal atom diffusion during film formation.

Low-frequency techniques are used to examine the predictions of the equilibrium Kosterlitz-Thouless theory of the vortex-pair unbinding transition in indium/indium-oxide composite superconducting thin films. The renormalized superfluid density obtained from independent measurements of the kinetic inductance and the exponent of the current-dependent resistance are in agreement. At the transition temperature ${T}_{c}$, the critical value of the superfluid density agrees with theory for a finite measurement length. Experimental sensitivity is such that the resistance near ${T}_{c}$, measured to be about 9 orders of magnitude below the normal resistance, is explained by the motion of a single thermally excited free vortex in a superfluid background renormalized by bound-vortex pairs. The corresponding critical magnetic field for flux entry is also measured. The resistance of the thermally excited free-vortex plasma and the correlation length above the transition temperature obey the qualitative prediction of the theory. Nonuniversal constants in the renormalization-group theory are obtained from the experiment and are found to be sample dependent.

A systematic correlation between krypton ion beam cleaning time and critical current density has been observed in Josephson tunnel junctions fabricated from thermally evaporated PbIn alloys which were ion milled prior to room temperature oxidation under water saturated O 2 . The observed effect is strongly nonlinear and is in a direction such that the critical current density increases with increased ion milling. Auger and x-ray photoemission studies have revealed that the ratio of lead oxide to indium oxide also increases with increased milling time. The lead oxide is observed to be spatially concentrated at the oxide/ambient interface rather than being uniformly distributed. Vacuum annealing of the alloy subsequent to ion milling but preceding the oxidation step systematically reduces both the critical current density and the quantity of lead oxide observed in the films. These results have a direct bearing on the technological problem of obtaining uniformity and day-to-day reproducibility of Josephson critical currents.

Organic disulfides, chemisorbed as monolayers on aluminum and silicon oxides, have been found to induce significant changes in the morphologies of thermally evaporated Au and Ag films for film thicknesses (mass average) up to 100–200 A. Measurements of the electrical conductivities as a function of film thickness show a marked shift of the onset of conduction to lower thickness for films deposited on treated substrates compared to films on untreated substrates. Transmission electron microscopy shows that the conductivities correlate qualitatively with sample morphology. In particular, films on treated substrates show metal clusters of higher densities which connect at lower coverages than do films on untreated substrates.

Periodicities associated with columnar microstructure have been observed in the electron diffraction patterns obtained from a thin-film overlay structure. This structure consists of a copper/copper-oxide film containing a small regularly-spaced array of columns and covered by a polycrystalline gold film. Both the transmitted and diffracted beams within the gold film act as independent incident beams for the underlying copper film, the latter giving rise to the formation of sub-diffraction rings around strongly-diffracted spots of gold lines. These sub-rings, appearing only because of this double diffraction effect, were found to represent the spatially-periodic distribution of columns in the copper film.

We present results of a superconducting magnetic levitation experiment which provide evidence for the existence of fractional charge on matter. Three niobium balls heat-treated on a tungsten substrate were found to have residual charges of $(+0.337\ifmmode\pm\else\textpm\fi{}0.009)e$, $(\ensuremath{-}0.001\ifmmode\pm\else\textpm\fi{}0.025)e$, and $(\ensuremath{-}0.331\ifmmode\pm\else\textpm\fi{}0.070)e$. All five niobium balls heat-treated on a niobium substrate had residual charges near zero.

Composite In/InOx films 5 nm thick were deposited by reactive ion beam sputtering of In in a controlled partial pressure of O2, incorporation of which reduces the free-electron density to 1020 cm−3. Previous microscopy on similar-prepared thick films showed a composite of amorphous In and crystalline indium oxide, with 295 K resistivity ∼10−3 ohms cm and superconducting Tc⪅3.4 K. The present field-effect device uses a mylar-insulated gate to modulate electrical conductance with charge, interpreted as a field-effect mobility μ = 40 cm2V−1s−1.The charge-induced variation in Tc, measured to be at most 8%, correlates with the dependence of Tc on the 295 K sheet resistance, a dependence determined by the controlled reversible desorption/adsorption of O2 in the films near 300 K. For an areal electron density in the as-deposited films near 3 × 1013 cm−2, a 20% change should induce a factor of 2 change in Tc.

Granular lead films were deposited using the technique of reactive ion beam sputtering of a lead target with argon ions in the presence of an oxygen background. The superconducting properties of these films reveal that the primary means of electron transport is by tunneling across insulating lead oxide barriers separating clusters of lead grains. Results of x‐ray and TEM studies confirm this interpretation and show that the films consist of randomly‐oriented lead grains, less than 500 A in diameter, embedded in an insulating matrix which contains at least two identifiable oxides of lead. These unique structural properties are most likely responsible for the excellent mechanical and electrical stability observed for these films.

Using a high-{ital Q} silicon mechanical oscillator we have studied flux lattice melting in two-dimensional amorphous composite In/InO{sub {ital x}} superconducting films. In addition to the previously observed solid and liquid phases, the flux lattice exhibits a third stable phase, intermediate between the solid and liquid, which exists at high sheet resistances, large magnetic fields, and low temperatures. For a range of sheet resistances, this phase coexists at a tricritical point with the liquid and solid phases. In the limit of high sheet resistance, only this new phase is stable, preempting the solid phase. We argue that this intermediate phase is unlikely to be an hexatic phase, and is more likely to be an amorphous solid phase.

Sputtering of a magnesium target with a beam of argon ions in the presence of a partial pressure of reactive oxygen gas has been found to yield smooth MgOx thin‐film dielectrics with low electrical loss, good mechanical stability, and excellent reproducibility. The films consist of polycrystalline MgO with a grain size ≲50 A and an OH‐containing component. The thickness dependence of the areal capacitance is discussed in the context of a two‐layer model in which this oxygen‐rich phase (x≂1.4) overlays a thin (≲40 A) stoichiometric phase (x≂1.0). Observation of superconducting tunneling characteristics in trilayer Au‐MgOx‐Pb structures confirms pinhole‐free coverage which may have possible application as artificial tunnel barriers.

The mechanical response, comprising longitudinal sound velocity and damping, of amorphous In/InOx films is studied as a function of normal state sheet resistance. The films are sputtered directly onto a high Q oscillator fabricated from single crystal silicon. With a resonant frequency near 3 KHz, the oscillators have Q’s of 105 and a frequency stability of 10-8. This allows for a unique measurement of the dynamics of magnetic vortices, induced by a field perpendicular to the plane of the sample. The melting of the vortex lattice is signaled by a peak in the attenuation and a frequency shift of the silicon oscillator. The zero field melting temperature and the magnitude of the frequency shift are described by a model of Kosterlitz-Thouless melting due to D.S. Fisher. The temperature dependence of the melting does not agree with this calculation.