Nanoscale Fabrication by Intrinsic Suppression of Proximity-Electron Exposures and General Considerations for Easy & Effective Top-Down Fabrication

We present results of a planar process development based on the combination of electron-beam lithography and dry etching for fabricating high-quality superconducting photosensitive structures in the sub-100nm regime. The devices were fabricated by the application of an intrinsic proximity effect suppression procedure which makes the need for an elaborated correction algorithm redundant for planar design layouts which are orders of magnitude smaller than the backscattering length. In addition, we discuss the necessary considerations for extending the fabrication spatial scale of optical contactlithography with a mercury arc-discharge photon source down to the order of the exposure photon's wavelength ( sub-{\mu}m ), thereby minimizing the writing time on the electron-beam lithograph. Finally we developed a unique and novel technique for controlling the undercut during a planar lift-off fabrication procedure without cleaving the wafer.Comment: 10 figures, 51 reference

Dopant imaging of power semiconductor device cross sections

Several Scanning Probe Microscopy (SPM) methods allow to image dopant profiles in a range from 10(14) cm(-3) to 10(19) cm(-3) on semiconducting samples. In our work we present Scanning Capacitance Force Microscopy (SCFM) and Kelvin Probe Force Microscopy (KPFM) experiments performed on cross sections of silicon (Si) and silicon carbide (SiC) power devices and epitaxially grown calibration layers. The contact potential difference (CPD) shows under illumination a reduced influence on surface defect states. In addition results from numerical simulation of these microscope methods are discussed. (C) 2016 Elsevier B.V. All rights reserved

Current Assisted, Thermally Activated Flux Liberation in Ultrathin Nanopatterned NbN Superconducting Meander Structures

We present results from an extensive study of fluctuation phenomena in superconducting nanowires made from sputtered NbN. Nanoscale wires were fabricated in form of a meander and operated at a constant temperature T~0.4Tc(0). The superconducting state is driven close to the electronic phase transition by a high bias current near the critical one. Fluctuations of sufficient strength temporarily drive a section of the meander structure into the normal conducting state, which can be registered as a voltage pulse of nanosecond duration. We considered three different models (vortex-antivortex pairs, vortex edge barriers and phase slip centers) to explain the experimental data. Only thermally excited vortices, either via unbinding of vortex-antivortex pairs or vortices overcoming the edge barrier, lead to a satisfactory and consistent description for all measurements.Comment: 41 Pages, 5 Chapters, 7 Figures, 2 Tables, 30 Equations, 68 References; Selected for the January 15, 2010 Issue of the Virtual Journal of Applications of Superconductivit

Spin Fluctuation Theory for Quantum Tricritical Point Arising in Proximity to First-Order Phase Transitions: Applications to Heavy-Fermion Systems, YbRh2Si2, CeRu2Si2, and beta-YbAlB4

We propose a phenomenological spin fluctuation theory for antiferromagnetic quantum tricritical point (QTCP), where the first-order phase transition changes into the continuous one at zero temperature. Under magnetic fields, ferromagnetic quantum critical fluctuations develop around the antiferromagnetic QTCP in addition to antiferromagnetic ones, which is in sharp contrast with the conventional antiferromagnetic quantum critical point. For itinerant electron systems,} we show that the temperature dependence of critical magnetic fluctuations around the QTCP are given as chiQ \propto T^{-3/2} (chi0\propto T^{-3/4}) at the antiferromagnetic ordering (ferromagnetic) wave number q=Q (q=0). The convex temperature dependence of chi0^{-1} is the characteristic feature of the QTCP, which is never seen in the conventional spin fluctuation theory. We propose that the general theory of quantum tricriticality that has nothing to do with the specific Kondo physics itself, solves puzzles of quantum criticalities widely observed in heavy-fermion systems such as YbRh2Si2, CeRu2Si2, and beta-YbAlB4. For YbRh2Si2, our theory successfully reproduces quantitative behaviors of the experimental ferromagnetic susceptibility and the magnetization curve by choosing the phenomenological parameters properly. The quantum tricriticality is also consistent with singularities of other physical properties such as specific heat, nuclear magnetic relaxation time 1/T_1T, and Hall coefficient. For CeRu2Si2 and beta-YbAlB4, we point out that the quantum tricriticality is a possible origin of the anomalous diverging enhancement of the uniform susceptibility observed in these materials.Comment: 17 pages, 10 fugures, to appear in Journal of the Physical Society of Japan Vol.78 No.

The influence of cadmium stress on the content of mineral nutrients and metal-binding proteins in arabidopsis halleri

We investigated the influence of cadmium stress on zinc hyperaccumulation, mineral nutrient uptake, and the content of metal-binding proteins in Arabidopsis halleri. The experiments were carried out using plants subjected to long-term cadmium exposure (40 days) in the concentrations of 45 and 225 μM Cd2+. Inductively coupled plasma-mass spectrometry, size exclusion chromatography coupled with plasma-mass spectrometry, and laser ablation inductively coupled plasma-mass spectrometry used for ablation of polyacylamide gels were employed to assess the content of investigated elements in plants as well as to identify metal-binding proteins. We found that A. halleri is able to translocate cadmium to the aerial parts in high amounts (translocation index >1). We showed that Zn content in plants decreased significantly with the increase of cadmium content in the growth medium. Different positive and negative correlations between Cd content and mineral nutrients were evidenced by our study. We identified more than ten low-molecular-weight (<100 kDa) Cd-binding proteins in Cd-treated plants. These proteins are unlikely to be phytochelatins or metallothioneins. We hypothesize that low-molecular-weight Cd-binding proteins can be involved in cadmium resistance in A. halleri

Fabrication of metallic structures with lateral dimensions less than 15 nm and jc(T)-measurements in NbN micro- and nanobridges

We report about a process that enables us to manufacture nm-sized structures that are characterized in a four-point resistivity measurement. To define the nanostructures, we employ either a lift-off deposition process or a dry etching process. With the lift-off deposition, we were able to define line widths below 15 nm spatial dimension. The same technique allowed the fabrication of a current-carrying bridge with ≈30 nm × 10 nm cross section. The etch-process step allowed us to generate a superconducting meander structure covering an area of ≈13.5 μm × 10.5 μm. We also present critical-current measurements vs. temperature on sub-μm and μm sized bridges prepared by a different technique. These data support the idea of a geometrical edge barrier for vortex entry into sub-μm wide bridges

Hall effect across the quantum phase transition of CeCu_6-xAu_x

While CeCu66 is a Pauli-paramagnetic heavy-fermion (HF) system, Au doping introduces long-range incommensurate antiferromagnetism for x>xc≈0.1x>xc≈0.1. At the critical concentration xcxc, the system experiences a quantum phase transition (QPT). Here, both unusual magnetic fluctuations, studied by inelastic neutron scattering, and non-Fermi-liquid behavior, i.e. to anomalous low-temperature thermodynamic and transport properties have been observed. We report on Hall effect measurements that probe the electronic structure of heavy fermions across the critical concentration xcxc of the QPT

Current-induced critical state in NbN thin-film structures

The temperature dependence of the critical current of NbN thin-film bridges was experimentally studied. At low temperatures we observed significant enhancement (up to two times at 4 K) of the critical current density over de-pinning value in the sub-micrometer wide bridges. This enhancement can be described by an increase of the edge barrier for penetration of magnetic vortices into narrow superconducting strips