Abstract
The realization of hybrid superconductor–semiconductor quantum devices, in particular a topological qubit, calls for advanced techniques to readily and reproducibly engineer induced ...superconductivity in semiconductor nanowires. Here, we introduce an on-chip fabrication paradigm based on shadow walls that offers substantial advances in device quality and reproducibility. It allows for the implementation of hybrid quantum devices and ultimately topological qubits while eliminating fabrication steps such as lithography and etching. This is critical to preserve the integrity and homogeneity of the fragile hybrid interfaces. The approach simplifies the reproducible fabrication of devices with a hard induced superconducting gap and ballistic normal-/superconductor junctions. Large gate-tunable supercurrents and high-order multiple Andreev reflections manifest the exceptional coherence of the resulting nanowire Josephson junctions. Our approach enables the realization of 3-terminal devices, where zero-bias conductance peaks emerge in a magnetic field concurrently at both boundaries of the one-dimensional hybrids.
•Designed multilayer was deposited by microwave assisted magnetron sputtering method.•AR coating in designed wavelength range had transmittance higher than 97%.•The AR multilayer was hydrophobic and ...photocatalytically active.•AR coating was scratch resistant.•Deposited multilayer had higher hardness than the glass substrate.
Antireflection (AR) multilayer coating, based on combination of five TiO2 and SiO2 thin films, was deposited by microwave assisted reactive magnetron sputtering process on microscope glass substrates. In this work X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and wettability measurements were used to characterize the structural and surface properties of the deposited coating. These studies revealed that prepared coating was amorphous with low surface roughness. Photocatalytic properties were determined based on phenol decomposition reaction. Measurements of optical properties showed that transmittance in the visible wavelength range was increased after the deposition of AR coating as-compared to bare glass substrate. The mechanical properties were determined on the basis of nano-indentation and scratch resistance tests. Performed research has shown that deposition of an additional thin 10nm thick TiO2 thin film top layer, the prepared AR coating was photocatalytically active, hydrophobic, scratch resistant and had increased hardness as-compared to bare glass substrate. These results indicate that prepared AR multilayer could be used also as a self-cleaning and protective coating.
In our contribution we study the long-term durability of two different graphite felt materials serving as negative electrode in vanadium redox flow battery. Both electrodes differ in the precursor ...material and the way of activation which causes significant differences in relevant properties such as electric conductivity, specific surface area and electrochemical double layer capacitance. The performance stability of the felts within 2000 charge-discharge cycles conducted in lab-scale single-cell is evaluated from 4-point characterization before the cycling and after each 1000 cycles. Significant deterioration of electrocatalytic activity is observed for commercially activated polyacrylonitrile-based negative electrode, whereas the in-house activated rayon-based negative electrode provides stable performance over the whole tested period. A comprehensive post-mortem characterization is performed to identify the causes of different durability of both negative electrodes. X-ray photoelectron spectroscopy analysis reveals very similar changes in surface functionalization by oxygen-containing groups for both felts; however, the decrease of sp2-hybridized carbon and simultaneous increase of sp3-hybridized one is significantly higher for the unstable polyacrylonitrile-based felt. Although the performance deterioration of the polyacrylonitrile-based felt cannot be related to the decrease of the surface area or double-layer capacitance, the high surface area of activated rayon-based felt most probably contributes to its excellent performance stability.
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•Long-term durability of vanadium redox flow battery during 2000 cycles tested.•Two different felts tested as negative electrode under identical conditions.•Strong deactivation of PAN-based felt relates to increase of sp3-hybridized carbon.•Stable performance of high surface area rayon-based felt with thermal activation.
In this work multi-magnetron sputtering stand was used for the deposition of the mixed oxides thin films based on HfO2 and TiO2. In order to obtain various material composition the power released to ...each magnetron (containing metallic hafnium and titanium targets) was precisely selected. Structural, surface, optical, electrical and mechanical properties of as-deposited coatings were analyzed. Depending on the hafnium content in the deposited thin films various types of the microstructure was obtained, i.e. HfO2-monoclinic, amorphous and TiO2-rutile. Increase of Ti content above 28at. % in the as-prepared mixed oxides coatings caused their amorphization. It was found that with an increase of Ti content in prepared coatings their surface roughness and simultaneously water contact angle decreased. Performed measurements of electrical properties revealed that the lowest leakage current density in the range of 10−7–10−8A/cm2 was obtained for amorphous coatings. Moreover, the tailoring of the dielectric constant was possible by a proper selection of material composition and microstructure of the deposited thin films. Average transparency in the visible wavelength region was in the range of ca. 79–86%. The influence of material composition and structure on shifting of the fundamental absorption edge and optical band gap energy was also observed. The refractive index increased with an increase of Ti content, while extinction coefficient was the lowest for amorphous coatings. Additionally, hardness values were dependent on the material composition and optical packing density and were in the range from 7.6GPa to 10.1GPa.
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•Mixed HfO2-TiO2 coatings with Hf:Ti atomic ratios of ca. 70:30, 50:50 and 30:70 were deposited by magnetron sputtering•HfO2, TiO2 and film with Hf:Ti atomic ratio of 70:30 were nanocrystalline with crystallites below 10 nm.•Thin films with Hf:Ti atomic ratios of 50:50 and 30:70 were amorphous.•Amorphous thin films had the lowest leakage current density in the range of 10–7÷10–8 A/cm2 among all deposited coatings.•Amorphous thin films had the smoothest surface, the lowest extinction coefficient and the highest transparency.
•N+-ion bombardment changes physicochemical properties of the p-GaN(0 0 0 1) surface.•The bombardment modified semiconducting character from the p- into n-type.•Electron affinity of the ...p-GaN(0 0 0 1) surface is increased after the bombardment.•The bombardment increases the band bending at the vacuum/surface interface.
The p-GaN(0 0 0 1) crystal with a relatively low acceptor concentration of 5 × 1016 cm−3 is used in these studies, which are carried out in situ under ultrahigh vacuum (UHV) by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). The p-GaN(0 0 0 1)-(1 × 1) surface is achieved by thermal cleaning. N+-ion bombardment by a 200 eV ion beam changes the surface stoichiometry, enriches it with nitrogen, and disorders it. Such modified surface layer inverts its semiconducting character from p- into n-type. The electron affinity for the already cleaned p-GaN surface and that just after bombardment shows a shift from 2.2 eV to 3.2 eV, as well as an increase of band bending at the vacuum/surface interface from 1.4 eV to 2.5 eV. Proper post-bombardment heating of the sample restores the initial atomic order of the modified layer, leaving its n-type semiconducting character unchanged. The results of the measurements are discussed based on two types of surface states concepts.
Jin, Kleinhans, and Mazur have reported in this meeting that up to 100% of oocytes and 2-cell embryos survive vitrification in a 3-fold dilution of EAFS medium if warmed at 10,000,000°C/min by an IR ...laser pulse. The usual cooling rate was 69,000°C/min, but 95% also survived when cooled at 10,000°C/min. Thus, survival is far more dependent on the rate of warming than on the rate of cooling, the reason being that very high warming rates prevent or impede the recrystallization of intracellular ice. In all our experiments, the oocytes or embryos were held for 2.0min in 1/3×EAFS before vitrification That time was chosen because Pedro (1997) found it to produce the best survival after vitrification. EAFS media are strongly hyperosmotic so that oocytes/embryos placed in them, undergo an osmotic shrink-swell pattern with time. There is an initial rapid shrinkage to a minimum volume due to water loss, followed by a much slower re-swelling due to the slow influx of the permeating solutes. Based on Pedro’s data, that minimum occurs near 2min, and osmotic theory argues that at that point, the cells have lost 85% of their original water and very little permeating solute has entered them. The strong inference, then, is that the high subsequent survivals are a consequence of the 85% osmotic dehydration and are not due to the intracellular presence of permeating solutes. Supporting that conclusion is Jin and Mazur’s report that 77% of oocytes and 95% of 2-cell and 8-cell embryos survive vitrification when suspended in media containing only the non-permeating solutes sucrose provided they are warmed at 1×107°C/min by a pulse from our IR laser. None survived when warmed 100× more slowly in the absence of the laser. These findings are at odds with orthodox beliefs about the causes of injury from vitrification. They could possibly open the way to the successful vitrification of important cell types that to date have been partially or fully refractory to this approach.
•A number of AFM image artifacts are illustrated and some hints to reduce them are given.•Switching lines are defined and their use for disclosure of the image artifacts is shown.•Some procedures to ...obtain useful information despite the presence of tip-related artifacts are proposed.
Atomic force microscopy (AFM) has become an important tool in surface science and nanotechnology. It is obvious that the intrinsic limitations of AFM must be understood in order to get useful information about surface structure of the material under study. The ability to recognize artifacts should assist in reliable evaluation of instrument operation and in reporting of data. In this paper, we discuss the most frequently encountered image artifacts in atomic force microscopy. A variety of artifacts are illustrated by the results obtained with the aid of contact AFM (C-AFM), which can help avoid misinterpretations. It is shown that, despite inaccuracies in AFM image generation, in many cases valuable information can be obtained.
The proximity effect in semiconductor-superconductor nanowires is expected to generate an induced gap in the semiconductor. The magnitude of this induced gap, together with the semiconductor ...properties like spin-orbit coupling and g-factor, depends on the coupling between the materials. It is predicted that this coupling can be adjusted through the use of electric fields. We study this phenomenon in InSb/Al/Pt hybrids using nonlocal spectroscopy. We show that these hybrids can be tuned such that the semiconductor and superconductor are strongly coupled. In this case, the induced gap is similar to the superconducting gap in the Al/Pt shell and closes only at high magnetic fields. In contrast, the coupling can be suppressed which leads to a strong reduction of the induced gap and critical magnetic field. At the crossover between the strong-coupling and weak-coupling regimes, we observe the closing and reopening of the induced gap in the bulk of a nanowire. Contrary to expectations, it is not accompanied by the formation of zero-bias peaks in the local conductance spectra. As a result, this cannot be attributed conclusively to the anticipated topological phase transition and we discuss possible alternative explanations.
Abstract
Semiconductor nanowires coupled to superconductors can host Andreev bound states with distinct spin and parity, including a spin-zero state with an even number of electrons and a spin-1/2 ...state with odd-parity. Considering the difference in spin of the even and odd states, spin-filtered measurements can reveal the underlying ground state. To directly measure the spin of single-electron excitations, we probe an Andreev bound state using a spin-polarized quantum dot that acts as a bipolar spin filter, in combination with a non-polarized tunnel junction in a three-terminal circuit. We observe a spin-polarized excitation spectrum of the Andreev bound state, which can be fully spin-polarized, despite strong spin-orbit interaction in the InSb nanowires. Decoupling the hybrid from the normal lead causes a current blockade, by trapping the Andreev bound state in an excited state. Spin-polarized spectroscopy of hybrid nanowire devices, as demonstrated here, is proposed as an experimental tool to support the observation of topological superconductivity.
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