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A simple method to fabricate dome-shaped particles of various materials, with different sizes and compositions, is presented. This versatility enables us to engineer multifunctional particles with the desired properties for specific biological applications.

Due to strong electron-phonon interactions, strain engineering is a powerful tool to control quantum critical phenomena in strongly correlated oxides. Exploring this possibility requires understanding the nanoscale structure of quantum materials and the role it plays in forming the strain landscape. Here, we used a combination of x-ray nanoimaging and reciprocal space mapping to study the nanostructure of the archetypal Mott insulator ${\mathrm{VO}}_{2}$, featuring an insulator-to-metal and structural phase transitions. We found that ${\mathrm{VO}}_{2}$ thin films grown on r-cut sapphire consist of two intertwined crystal lattices, permanently inclined with respect to each other. This persistent pattern of twin domains stands out from the symmetry breaking induced by the structural phase transition and conceivably originates from the post-growth strain relaxation process. We propose a model explaining the formation of twin domains and the emergence of anisotropy in the film nanostructure. Our work suggests using miscut substrates to suppress either one or the other twin that can serve as a new tool to control strain in ${\mathrm{VO}}_{2}$ films.

A brief review of experiments directed to study a gradual localization of charge carriers and metal-insulator transition in samples of disordered monolayer graphene is presented. Disorder was induced by irradiation with different doses of heavy and light ions. Degree of disorder was controlled by measurements of the Raman scattering spectra. The temperature dependences of conductivity and magnetoresistance (MR) showed that at low disorder, conductivity is governed by the weak localization and antilocalization regime. Further increase of disorder leads to strong localization of charge carriers, when the conductivity is described by the variable-range-hopping (VRH) mechanism. It was observed that MR in the VRH regime is negative in perpendicular fields and is positive in parallel magnetic fields which allowed to reveal different mechanisms of hopping MR. Theoretical analysis is in a good agreement with experimental data., 25 pages, pdf. arXiv admin note: text overlap with arXiv:1507.01429

We measured the photon count rate (PCR) and dark count rate (DCR) of a superconducting nanowire single photon detector (SNSPD) exposed to either a DC magnetic field (up to 60 mT) or to a low-amplitude oscillating field ( 0.12 – 0.48 mT, up to 50 kHz). In both cases, the results show an increase in the PCR and the DCR as the DC field or the frequency of the AC field increase. However, the ratio DCR/(PCR + DCR) increases significantly with an increasing DC field, whereas this ratio is approximately constant as the frequency of the AC field increases up to frequencies in the kHz regime. The results suggest a more favorable effect of AC fields on the operation of the SNSPD.

Utilizing self-assembled DNA structures in the development of nanoelectronic circuits requires transforming the DNA strands into highly conducting wires. Toward this end, we investigate the use of DNA self-assembled nanowires as templates for the deposition of a superconducting material. Nanowires formed by the deposition of superconducting NbN exhibit thermally activated and quantum phase slips as well as exceptionally large negative magnetoresistance. The latter effect can be utilized to suppress a significant part of the low temperature resistance caused by the quantum phase slips.

Magnetoresistance measurements in a granular Nb nanoring reveal current-induced crossover between two distinct quantum coherence effects. At low bias currents, Cooper-pair coherence is manifested by Little-Parks oscillations with flux periodicity of h/2 e. At high bias currents, magnetoresistance oscillations with flux periods of h/ e are observed and interpreted as Aharonov-Bohm oscillations, reflecting the phase coherence of individual quasi-particles. The model explaining these data views the ring as a chain of superconducting grains weakly coupled by tunnel junctions. Low bias currents allow coherent tunneling of Cooper pairs between the grains. Increasing the current above the critical current of all the junctions creates a quasi-particles conduction channel along the ring, allowing for quantum interference of quasi-particles.

Directing neuronal migration and growth has an important impact on potential post traumatic therapies. Magnetic manipulation is an advantageous method for remotely guiding cells. In the present study, we have generated highly localized magnetic fields with controllable magnetic flux densities to manipulate neuron-like cell migration and organization at the microscale level. We designed and fabricated a unique miniaturized magnetic device composed of an array of rectangular ferromagnetic bars made of permalloy (Ni80Fe20), sputter-deposited onto glass substrates. The asymmetric shape of the magnets enables one to design a magnetic landscape with high flux densities at the poles. Iron oxide nanoparticles were introduced into PC12 cells, making the cells magnetically sensitive. First, we manipulated the cells by applying an external magnetic field. The magnetic force was strong enough to direct PC12 cell migration in culture. Based on time lapse observations, we analysed the movement of the cells and estimated the amount of MNPs per cell. We plated the uploaded cells on the micro-patterned magnetic device. The cells migrated towards the high magnetic flux zones and aggregated at the edges of the patterned magnets, corroborating that the cells with magnetic nanoparticles are indeed affected by the micro-magnets and attracted to the bars' magnetic poles. Our study presents an emerging method for the generation of pre-programmed magnetic micro-'hot spots' to locate and direct cellular growth, setting the stage for implanted magnetic devices.

The conductivity and Hall effect were measured in CVD-grown monolayer graphene as a function of the gate voltage, $V_{g}$, at temperatures down to $T$ = 2 K and in magnetic fields up to $B$ = 8 T. The minimal conductivity was observed at positive $V_{g}$ which shows the position of the charge neutrality point, $V_{NP}$. With decreasing $T$, $V_{NP}$ first decreases, but stop to decrease at low $T$. Hysteresis of conductivity shows similar behavior: it decreases with decreasing $T$ and disappears at low $T$. A significant asymmetry was observed at low density of charge carriers $|n|=(n,p)$: mobility of holes was less than mobility of electrons. The asymmetry decreases with increasing $|n|$. It was observed that the value of $|n|$ determined from the Hall effect is less than the full value induced by $V_{g}$. In strong perpendicular $B$, Shubnikov-de Haas (SdH) oscillations were observed in the longitudinal conductivity, $\sigma_{xx}$, together with half-integer quantum Hall plateaus. It was found that $|n|$ determined from SdH oscillations is equal to the full value induced by $V_{g}$ as opposed to the Hall effect. Explanatory models for all observed phenomena are discussed., Comment: 8 pages, 6 figures

Transition metal oxides (TMOs) are complex electronic systems which exhibit a multitude of collective phenomena. Two archetypal examples are VO2 and NdNiO3, which undergo a metal-insulator phase-transition (MIT), the origin of which is still under debate. Here we report the discovery of a memory effect in both systems, manifest through an increase of resistance at a specific temperature, which is set by reversing the temperature-ramp from heating to cooling during the MIT. The characteristics of this ramp-reversal memory effect do not coincide with any previously reported history or memory effects in manganites, electron-glass or magnetic systems. From a broad range of experimental features, supported by theoretical modelling, we find that the main ingredients for the effect to arise are the spatial phase-separation of metallic and insulating regions during the MIT and the coupling of lattice strain to the local critical temperature of the phase transition. We conclude that the emergent memory effect originates from phase boundaries at the reversal-temperature leaving `scars` in the underlying lattice structure, giving rise to a local increase in the transition temperature. The universality and robustness of the effect shed new light on the MIT in complex oxides., 18 pages, 4 figures, supporting information in publisher web-site

The metal-insulator transition (MIT) properties of correlated oxides thin films, such as VO2, are dramatically affected by strain induced at the interface with the substrate, which usually changes with deposition thickness. For VO2 grown on r-cut sapphire, there is a minimum deposition thickness required for a significant MIT to appear, around 60 nm. We show that in these thicker films an interface layer develops, which accompanies the relaxation of film strain and enhanced electronic transition. If these interface dislocations are stable at room temperature, we conjectured, a new route opens to control thickness of VO2 films by postdeposition thinning of relaxed films, overcoming the need for thickness-dependent strain-engineered substrates. This is possible only if thinning does not alter the films' electronic properties. We find that wet etching in a dilute NaOH solution can effectively thin the VO2 films, which continue to show a significant MIT, even when etched to 10 nm, for which directly deposited films show nearly no transition. The structural and chemical composition were not modified by the etching, but the grain size and film roughness were, which modified the hysteresis width and magnitude of the MIT resistance change.

Many strongly correlated transition metal oxides exhibit a metal-insulator transition (MIT), the manipulation of which is essential for their application as active device elements. However, such manipulation is hindered by lack of microscopic understanding of mechanisms involved in these transitions. A prototypical example is VO2, where previous studies indicated that the MIT resistance change correlate with changes in carrier density and mobility. We studied the MIT using Hall measurements with unprecedented resolution and accuracy, simultaneously with resistance measurements. Contrast to prior reports, we find that the MIT is not correlated with a change in mobility, but rather, is a macroscopic manifestation of the spatial phase separation which accompanies the MIT. Our results demonstrate that, surprisingly, properties of the nano-scale spatially-separated metallic and semiconducting domains actually retain their bulk properties. This study highlights the importance of taking into account local fluctuations and correlations when interpreting transport measurements in highly correlated systems., 15 p, 4 figures

We study the effect of topographic nano-cues on neuronal growth-morphology using invertebrate neurons in culture. We use photolithography to fabricate substrates with repeatable line-pattern ridges of nano-scale heights of 10-150 nm. We plate leech neurons atop the patterned-substrates and compare their growth pattern to neurons plated atop non-patterned substrates. The model system allows us the analysis of single neurite-single ridge interactions. The use of high resolution electron microscopy reveals small filopodia processes that attach to the line-pattern ridges. These fine processes, that cannot be detected in light microscopy, add anchoring sites onto the side of the ridges, thus additional physical support. These interactions of the neuronal process dominantly affect the neuronal growth direction. We analyze the response of the entire neuronal branching tree to the patterned substrates and find significant effect on the growth patterns compared to non-patterned substrates. Moreover, interactions with the nano-cues trigger a growth strategy similarly to interactions with other neuronal cells, as reflected in their morphometric parameters. The number of branches and the number of neurites originating from the soma decrease following the interaction demonstrating a tendency to a more simplified neuronal branching tree. The effect of the nano-cues on the neuronal function deserves further investigation and will strengthen our understanding of the interplay between function and form.

We study the role of nano-scale cues in con- trolling neuronal growth. We use photolithography to fabricate substrates with repeatable line-pattern ridges of nano-scale heights. We find that neuronal processes, which are of micron size, have strong interactions with ridges even as low as 10 nm. The interaction between the neuronal process and the ridge leads to a deflection of growth direc- tion and a preferred alignment with the ridges. The interac- tion strength clearly depends on the ridges' height. For 25 nm ridges approximately half of the neuronal processes are modified, while at 100 nm the majority of neurites change their original growth direction post interaction. In addition, the effect on growth correlates with the incoming angle between the neuronal process and the ridge. We underline the adhesion as a key mechanism in directing neuronal growth. Our study highlights the sensitivity of growing neurites to nano-scale cues thus opens a new avenue of research for pre-designed neuronal growth and circuitry. Biotechnol. Bioeng. 2012;xxx: xxx-xxx.

Growth factors play an important role in nerve regeneration and repair. An attractive drug delivery strategy, termed &ldquo, magnetic targeting&rdquo, aims to enhance therapeutic efficiency by directing magnetic drug carriers specifically to selected cell populations that are suitable for the nervous tissues. Here, we covalently conjugated nerve growth factor to iron oxide nanoparticles (NGF-MNPs) and used controlled magnetic fields to deliver the NGF&ndash, MNP complexes to target sites. In order to actuate the magnetic fields a modular magnetic device was designed and fabricated. PC12 cells that were plated homogenously in culture were differentiated selectively only in targeted sites out of the entire dish, restricted to areas above the magnetic &ldquo, hot spots&rdquo, To examine the ability to guide the NGF-MNPs towards specific targets in vivo, we examined two model systems. First, we injected and directed magnetic carriers within the sciatic nerve. Second, we injected the MNPs intravenously and showed a significant accumulation of MNPs in mouse retina while using an external magnet that was placed next to one of the eyes. We propose a novel approach to deliver drugs selectively to injured sites, thus, to promote an effective repair with minimal systemic side effects, overcoming current challenges in regenerative therapeutics.

Nb nano-rings connected serially by Nb wires exhibit, at low bias currents, the typical parabolic Little-Parks magnetoresistance oscillations. As the bias current increases, these oscillations become sinusoidal. This result is ascribed to the generation of Josephson junctions caused by the combined effect of current-induced phase slips and the non-uniformity of the order parameter along each ring due to the Nb wires attached to it. This interpretation is validated by further increasing the bias current, which results in magnetoresistance oscillations typical of a SQUID.

Gradual localization of charge carriers was studied in a series of micro-size samples of monolayer graphene fabricated on the common large scale film and irradiated by different doses of C$^+$ ions with energy 35 keV. Measurements of the temperature dependence of conductivity and magnetoresistance in fields up to 4 T showed that at low disorder, the samples are in the regime of weak localization and antilocalization. Further increase of disorder leads to strong localization regime, when conductivity is described by the variable-range-hopping (VRH) mechanism. A crossover from the Mott regime to the Efros-Shklovskii regime of VRH is observed with decreasing temperature. Theoretical analysis of conductivity in both regimes showed a remarkably good agreement with experimental data., Latex, 5 pages, 5 eps Figures. As accepted for publication in Graphene

Magnetoresistance (MR) of ion irradiated monolayer graphene samples with variable-range hopping (VRH) mechanism of conductivity was measured at temperatures down to $T = 1.8$ K in magnetic fields up to $B = 8$ T. It was observed that in perpendicular magnetic fields, hopping resistivity $R$ decreases, which corresponds to negative MR (NMR), while parallel magnetic field results in positive MR (PMR) at low temperatures. NMR is explained on the basis of the "orbital" model in which perpendicular magnetic field suppresses the destructive interference of many paths through the intermediate sites in the total probability of the long-distance tunneling in the VRH regime. At low fields, a quadratic dependence ($|\Delta R/R|\sim B^2$) of NMR is observed, while at $B > B^*$, the quadratic dependence is replaced by the linear one. It was found that all NMR curves for different samples and different temperatures could be merged into common dependence when plotted as a function of $B/B^*$. It is shown that $B^*\sim T^{1/2}$ in agreement with predictions of the "orbital" model. The obtained values of $B^*$ allowed also to estimate the localization radius $\xi$ of charge carriers for samples with different degree of disorder. PMR in parallel magnetic fields is explained by suppression of hopping transitions via double occupied states due to alignment of electron spins., Comment: 14 pages, 9 figures. As accepted for publication on Physica E

Scanning tunneling spectroscopy of Au–YBa2Cu3O7−δ bilayers reveals proximity effect features that reflect the anisotropic d x 2 − y 2 -wave order parameter in YBa2Cu3O7−δ (YBCO). No proximity effect takes place at the (001)YBCO–Au interface, manifesting the quasi two-dimensional nature of the order parameter. Proximity gaps are induced in the gold primarily via (100)YBCO facets, and their size decays exponentially on a scale of ∼30 nm, in good agreement with estimations for the dirty limit. In the nodal (110)YBCO–Au interface, the proximity effect manifests itself by the penetration of Andreev bound states into the gold. The corresponding zero bias conductance peaks are nearly constant in magnitude for Au layers thinner than 7 nm, and then decay abruptly with Au thickness, vanishing above 10 nm, on the scale of the (ballistic) mean free path.

The Raman scattering spectra (RS) of two series of monolayer graphene samples irradiated with various doses of C$^{+}$ and Xe$^{+}$ ions were measured after annealing in high vacuum, and in forming gas (95\%Ar+5\%H$_{2}$). It was found that these methods of annealing have dramatically different influence on the RS lines. Annealing in vacuum below 500$^{\circ}$C leads to significant decrease of both D-line, associated with defects, and 2D-line, associated with the intact lattice structure, which can be explained by annealing-induced enhanced doping. Further annealing in vacuum up to 1000$^{\circ}$C leads to significant increase of 2D-line together with continuous decrease of D-line, which gives evidence of partial removal of defects and recovery of the damaged lattice. Annealing in forming gas is less effective in this sense. The blue shift of all lines is observed after annealing. It is shown that below 500$^{\circ}$C, the unintentional doping is the main mechanism of shift, while at higher annealing temperatures, the lattice strain dominates due to mismatch of the thermal expansion coefficient of graphene and the SiO$_{2}$ substrate. Inhomogeneous distribution of stress and doping across the samples leads to the correlated variation of the amplitude and the peak position of RS lines., LaTeX, 7 pages, 11 eps files. Submitted to J. Appl. Phys

Raman scattering (RS) spectra and current-voltage characteristics at room temperature were measured in six series of small samples fabricated by means of electron-beam lithography on the surface of a large size (5x5 mm) industrial monolayer graphene film. Samples were irradiated by different doses of C${}^+$ ion beam up to $10^{15}$ cm${}^{-2}$. It was observed that at the utmost degree of disorder, the Raman spectra lines disappear which is accompanied by the exponential increase of resistance and change in the current-voltage characteristics.These effects are explained by suggestion that highly disordered graphene film ceases to be a continuous and splits into separate fragments. The relationship between structure (intensity of RS lines) and sample resistance is defined. It is shown that the maximal resistance of the continuous film is of order of reciprocal value of the minimal graphene conductivity $\pi h/4e^2\approx 20$ kOhm., Comment: 5 pages, 5 eps figures. As accepted for publication in PRB

The configuration and evolution of coexisting mesoscopic domains with contrasting material properties are critical in creating novel functionality through emergent physical properties. However, current approaches that map the domain structure involve either spatially resolved but protracted scanning probe experiments without real time information on the domain evolution, or time resolved spectroscopic experiments lacking domain-scale spatial resolution. We demonstrate an elegant experimental technique that bridges these local and global methods, giving access to mesoscale information on domain formation and evolution at time scales orders of magnitude faster than current spatially resolved approaches. Our straightforward analysis of laser speckle patterns across the first order phase transition of VO$_2$ can be generalized to other systems with large scale phase separation and has potential as a powerful method with both spatial and temporal resolution to study phase separation in complex materials., Comment: Published open access in Scientific Reports

Tunneling spectra measured on thin epitaxial YBa2Cu3O7-delta films are found to exhibit strong spatial variations, showing U and V-shaped gaps as well as zero bias conductance peaks typical of a d-wave superconductor. A full correspondence is found between the tunneling spectra and the surface morphology down to a level of a unit-cell step. Splitting of the zero bias conductance peak is seen in optimally-doped and overdoped films, but not in the underdoped ones, suggesting that there is no transition to a state of broken time reversal symmetry in the underdoped regime

Composites consisting of MgB2 and Al, 11% by volume, undergo a transition to superconductivity onset at TC = 38 K, close to the value reported for pure MgB2. The transition appears to have broadened, as determined by both magnetic and transport measurements, possible due to the proximity effect and disorder. Spatially resolved tunneling spectroscopy at 4.2 K exhibit a distribution of gap structures, from BCS-like spectra with 2D/kBTc = 3.2 to spectra that are typical for proximity superconductors., accepted to Journal of Physics Condensed Matter, revised version

Scanning tunneling spectroscopy along with magnetization measurements were employed in the study of Na-doped WO3. The magnetization data suggest that a superconducting phase is formed below TC = 91 K. Tunneling experiments reveal islands, 20–150 nm in size, having a superconductor-like density of states. These islands cover about 10% of the surface, the rest of which is insulating, and exhibit spectroscopic gaps having values up to 2Δ/kTC ~ 4. Therefore this material seems to be a non-cuprate superconductor with a high critical temperature.

WO3 crystals were doped with Na on the surface to ∼7% nominal atomic concentration. Scanning tunneling microscopy and spectroscopy were employed, together with magnetization measurements, in the study of these crystals. Tunneling experiments reveal superconducting islands, 20–150 nm in size, covering about 10% of the surface, the rest of which is insulating. Magnetization measurements show that the superconducting phase formed at the surface has a critical temperature of 91 K, while tunneling spectroscopy yields superconducting gaps having values up to 2Δ/kT c ∼ 4. Presumably most of the sodium is concentrated in these islands and therefore they are metallic in nature, above 30% in atomic concentration. This material is therefore a noncuprate superconductor with a high critical temperature.

We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

Temperature dependent dielectric spectroscopy measurements on vanadium dioxide thin films allow us to distinguish between the resistive, capacitive, and inductive contributions to the impedance across the metal-insulator transition (MIT). We developed a single, universal, equivalent circuit model to describe the dielectric behavior above and below the MIT. Our model takes account of phase-coexistence of metallic and insulating regions. We find evidence for the existence at low temperature of ultra-thin threads as described by a resistor-inductor element. A conventional resistor-capacitor element connected in parallel accounts for the insulating phase and the dielectric relaxation.

The influence of long-term ageing (about one year) on the Raman scattering (RS) spectra and the temperature dependence of conductivity has been studied in two series of monolayer graphene samples irradiated by different doses of C$^{+}$ and Xe$^{+}$ ions. It is shown that the main result of ageing consists of changes in the intensity and position of D- and G- and 2D-lines in RS spectra and in an increase of the conductivity. The observed effects are explained in terms of an increase of the radius of the \textquotedblleft activated\textquotedblright{} area around structural defects., Comment: LaTex, 5 pages, 6 eps Figures

We studied the effect of disorder on superconducting vortex pinning produced by arrays of artificial pinning sites. The magnetoresistance of samples with pinning configurations varying from a triangular array to an almost random distribution of pinning sites provides a controlled system for such studies. Interestingly even small degrees of order are sufficient to produce enhanced pinning at well-defined magnetic fields. These effects increase with increasing order and evolve toward the expected matching minima for a triangular array. Surprisingly, the position of the first matching minimum decreases with increasing disorder. Furthermore, additional matching minima appear at higher field values which do not coincide with commonly observed triangular pinning lattice matching minima.

The metal insulator transition of nano-scaled $VO_2$ devices is drastically different from the smooth transport curves generally reported. The temperature driven transition occurs through a series of resistance jumps ranging over 2 decades in amplitude, indicating that the transition is caused by avalanches. We find a power law distribution of the jump amplitudes, demonstrating an inherent property of the $VO_2$ films. We report a surprising relation between jump amplitude and device size. A percolation model captures the general transport behavior, but cannot account for the statistical behavior., 4 papers and 4 figures submitted to PRL

The spin injection and accumulation in metallic lateral spin valves with transparent interfaces is studied using d.c. injection current. Unlike a.c.-based techniques, this allows investigating the effects of the direction and magnitude of the injected current. We find that the spin accumulation is reversed by changing the direction of the injected current, whereas its magnitude does not change. The injection mechanism for both current directions is thus perfectly symmetric, leading to the same spin injection efficiency for both spin types. This result is accounted for by a spin-dependent diffusion model. Joule heating increases considerably the local temperature in the spin valves when high current densities are injected ($\sim$80--105 K for 1--2$\times10^{7}$A cm$^{-2}$), strongly affecting the spin accumulation., Comment: 6 pages, 5 figures

Thermal imaging based on room temperature bolometer sensors is a growing market, constantly searching for improved sensitivity. One important factor is the temperature coefficient of resistance (TCR), i.e., the sensitivity of the active material. Herein, the authors report the improved TCR properties attainable by the “ion beam assisted deposition” method for room temperature deposition. VyM1−yOx (M = Nb, Hf) thin-film alloys were fabricated on 1 μm thermal SiO2 atop Si (100) substrates by reactive magnetron cosputtering at room temperature using a low energy ion source, aimed at the film, to insert dissociated oxygen species and increase film density. The authors studied the influence of deposition parameters such as oxygen partial pressure, V to M ratio, and power of the plasma source, on resistance and TCR. The authors show high TCR (up to −3.7% K−1) at 300 K, and excellent uniformity, but also an increase in resistance. The authors emphasize that samples were prepared at room temperature with no heat ...

The SUPREX thin film refinement of x-ray diffraction XRD was used to quantitatively analyze the structure of thermally evaporated iron phthalocyanine FePc organic thin films as a function of growth temperature and postdeposition in situ annealing time. A bilayer model was necessary to refine the FePc XRD data. Results using this model provide clear evidence that the first molecular layer of FePc contacting the sapphire substrate differs from the subsequent uniformly spaced molecular layers, indicating a StranskiKrastanov growth mode. The -to- structural phase transformation of FePc was observed as a function of substrate temperature. No significant effect of postdeposition in situ annealing time was observed. Atomic force microscopy AFM measurements reveal a temperature-dependent morphology as the FePc changes from grains, to extended films, and finally shows crystallite formation for increasing deposition temperature. Structural characteristics obtained by SUPREX refinement and AFM quantitatively agree for surface roughness and average molecular layer spacing.

Scanning tunneling spectroscopy of $(110){\mathrm{Y}\mathrm{B}\mathrm{a}}_{2}{\mathrm{C}\mathrm{u}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}/\mathrm{A}\mathrm{u}$ bilayers reveal a proximity effect markedly different from the conventional one. While proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound states clearly penetrate into the metal. Zero bias conductance peaks are measured on Au layers thinner than 7 nm with a magnitude similar to those detected on the bare superconductor films. The peaks then decay abruptly with Au thickness and disappear above 10 nm. This length is shorter than the normal coherence length and corresponds to the (ballistic) mean free path.

Bulk and surface properties of high-quality single crystals of zirconium dodecaboride have been studied in the temperature range from $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ up to the superconducting transition temperature, which is found to be nearly $6.06\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Scanning tunneling spectroscopy data, together with $\mathrm{dc}$ and $\mathrm{ac}$ magnetization measurements, are consistent with the conventional $s$-wave pairing scenario, whereas they disagree in estimates of the electron-phonon coupling strength. We explain the divergence, supposing a great difference between the surface and bulk superconducting characteristics of the compound. This assertion is supported by our findings of a nonlinear magnetic response to an amplitude-modulated alternating magnetic field, testifying to the presence of surface superconductivity in the ${\mathrm{ZrB}}_{12}$ samples at $\mathrm{dc}$ fields exceeding the thermodynamic critical field.

Scanning tunneling spectroscopy of (110)YBa(2)Cu(3)O(7-delta)/Au bilayers reveal a proximity effect markedly different from the conventional one. While proximity-induced mini-gaps rarely appear in the Au layer, the Andreev bound states clearly penetrate into the metal. Zero bias conductance peaks are measured on Au layers thinner than 7 nm with a magnitude similar to those detected on the bare superconductor films. The peaks then decay abruptly with Au thickness and disappear above 10 nm. This length is shorter than the normal coherence length and corresponds to the (ballistic) mean free path.

Scanning tunneling spectroscopy on gold layers overcoating c-axis YBa(2)Cu(3)O(7-delta) (YBCO) films reveals proximity-induced gap structures. The gap size reduces exponentially with the distance from a-axis facets, indicating that the proximity effect is primarily due to the (100) YBCO facets. The penetration depth of superconductivity into the gold is approximately 30 nm, in good agreement with estimations for the dirty limit. The extrapolated gap at the interface is approximately 15 meV, similar to the value of an s-wave component of the order parameter measured at the YBCO surface in recent point-contact experiments.

Scanning tunneling spectroscopy on gold layers overcoating c-axis YBa(2)Cu(3)O(7-delta) (YBCO) films reveals proximity-induced gap structures. The gap size reduces exponentially with the distance from a-axis facets, indicating that the proximity effect is primarily due to the (100) YBCO facets. The penetration depth of superconductivity into the gold is approximately 30 nm, in good agreement with estimations for the dirty limit. The extrapolated gap at the interface is approximately 15 meV, similar to the value of an s-wave component of the order parameter measured at the YBCO surface in recent point-contact experiments.

Tunneling spectroscopy of epitaxial ~110! Y 12xCaxBa2Cu3O72d films reveals a doping-dependent transition from a pure dx22y 2 to dx22y 21is or dx22y 21idxy order parameter. The subdominant (is or idxy) component manifests itself in a splitting of the zero-bias conductance peak and the appearance of subgap structures. The splitting is seen in the overdoped samples, increases systematically with doping, and is found to be an inherent property of the overdoped films. It was observed in both local tunnel junctions, using scanning tunneling microscopy ~STM!, and in macroscopic planar junctions, for films prepared by either sputtering or laser ablation. The STM measurements exhibit a fairly uniform splitting size in @110# oriented areas on the order of 10 nm 2 but vary from area to area, indicating some doping inhomogeneity. U- and V-shaped gaps were also observed, with good correspondence to the local faceting, a manifestation of the dominant d-wave order parameter.

The electronic properties of arrays and isolated magnetite nanocrystals were studied using tunneling spectroscopy. Macroscopic tunnel junctions were used to study stacked arrays of the nanocrystals. The temperature dependent resistance measurements showed an abrupt increase of the resistance around 100 K, attributed to the Verwey metal-insulator transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak in the density of states near the Fermi energy. This conductance peak was sensitive to in-plane magnetic field showing large magnetoresistance. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope exhibit a gap-like structure below the transition temperature that gradually disappeared with increasing temperature, ending with a small peak structure around zero bias.

The growing field of oxide-electronics demands adequate fabrication methods that do not impair the material?s beneficial properties. To this end, we present a modified lift-off lithography method replacing the conventional polymer mask with an AlOx based mask. It can sustain the high-temperature and reactive gasses conditions commonly needed for oxide deposition, and is effectively wet-etched in dilute NaOH solutions. Here we demonstrate patterning of VO2 films. With its metal?insulator transition (MIT) near room temperature, it is attractive for various applications including sensors and transistors. But patterning is challenging since its properties are very sensitive to fabrication processes. We demonstrate patterning of 3 ?m wide VO2 electrodes and show they preserve the MIT magnitude and epitaxial growth of the non-patterned films. Some thinning of the VO2 is also observed. This process can be useful for patterning other materials that require harsh deposition conditions, and are resilient to low NaOH concentrations.