Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique

We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr tunnel junctions and SET transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x 60 nm^2 using a scanning transmission electron microscope for the e-beam exposure on Si_3N_4 membrane substrate. We discuss the electrical performance of the transistor samples as well as their noise behavior.Comment: 19 pages, 9 figure

Induction of Cytoplasmic Rods and Rings Structures by Inhibition of the CTP and GTP Synthetic Pathway in Mammalian Cells

Background: Cytoplasmic filamentous rods and rings (RR) structures were identified using human autoantibodies as probes. In the present study, the formation of these conserved structures in mammalian cells and functions linked to these structures were examined. Methodology/Principal Findings: Distinct cytoplasmic rods (,3–10 mm in length) and rings (,2–5 mm in diameter) in HEp-2 cells were initially observed in immunofluorescence using human autoantibodies. Co-localization studies revealed that, although RR had filament-like features, they were not enriched in actin, tubulin, or vimentin, and not associated with centrosomes or other known cytoplasmic structures. Further independent studies revealed that two key enzymes in the nucleotide synthetic pathway cytidine triphosphate synthase 1 (CTPS1) and inosine monophosphate dehydrogenase 2 (IMPDH2) were highly enriched in RR. CTPS1 enzyme inhibitors 6-diazo-5-oxo-L-norleucine and Acivicin as well as the IMPDH2 inhibitor Ribavirin exhibited dose-dependent induction of RR in.95 % of cells in all cancer cell lines tested as well as mouse primary cells. RR formation by lower concentration of Ribavirin was enhanced in IMPDH2-knockdown HeLa cells whereas it was inhibited in GFP-IMPDH2 overexpressed HeLa cells. Interestingly, RR were detected readily in untreated mouse embryonic stem cells (.95%); upon retinoic acid differentiation, RR disassembled in these cells but reformed when treated with Acivicin

Josephson voltage standard microwave circuit driven at 10 GHz

We have investigated a new type of microwave circuit for the generation of frequency-scaled Josephson voltages useful for the representation of highly accurate reference voltages. The circuit consists of a superconducting microstrip resonator and series arrays of Josephson junctions integrated within its rf current antinodes. The circuit is designed to operate at low frequencies of about 10 GHz to simplify the microwave techniques. At a resonator circuit with four Josephson junctions driven at 10.9 GHz we have obtained stable overlapping Shapiro steps up to 4.6 mV at a step width of about 70 µA. A more advanced double-resonator circuit with altogether 216 junctions allows to generate scaled reference voltages up to 0.16 V at steps of about 25 µA in width and at a microwave frequency of 11.1 GHz

Fabrication and Characterization of Single-Electron Transistors Based on Al/AlOx/Al and Nb/AlOx/Nb Tunnel Junctions

The SAIL (self-aligned in-line) technique has been applied to the preparation of ultrasmall metallic tunnel junctions. By using e-beam lithography and sputter methods the area of both Al/AlOx/Al and Nb/AlOx/Nb contacts has so far been reduced to less than 0.005µm2. At low temperatures high-ohmic double junctions with a small metallic island in between show the Coulomb blockade effect. The current through such a device can be modulated by a voltage applied to a gate electrode capacitively coupled to the island (single-electron transistor). Both these single-charge phenomena have been observed at temperatures of a few hundred mK