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

Single electron transistors with high quality superconducting niobium islands

Deep submicron Al-AlOx-Nb tunnel junctions and single electron transistors with niobium islands were fabricated by electron beam gun shadow evaporation. Using stencil masks consisting of the thermostable polymer polyethersulfone (PES) and germanium, high quality niobium patterns with good superconducting properties and a gap energy of up to 2Delta = 2.5 meV for the niobium were achieved. The I(U) characteristics of the transistors show special features due to tunneling of single Cooper pairs and significant gate modulation in both the superconducting and the normal state.Comment: 4 pages, 4 figure

Reduced chemistry for butanol isomers at engine-relevant conditions

Butanol has received significant research attention as a second-generation biofuel in the past few years. In the present study, skeletal mechanisms for four butanol isomers were generated from two widely accepted, well-validated detailed chemical kinetic models for the butanol isomers. The detailed models were reduced using a two-stage approach consisting of the directed relation graph with error propagation and sensitivity analysis. During the reduction process, issues were encountered with pressure-dependent reactions formulated using the logarithmic pressure interpolation approach; these issues are discussed and recommendations made to avoid ambiguity in its future implementation in mechanism development. The performance of the skeletal mechanisms generated here was compared with that of detailed mechanisms in simulations of autoignition delay times, laminar flame speeds, and perfectly stirred reactor temperature response curves and extinction residence times, over a wide range of pressures, temperatures, and equivalence ratios. The detailed and skeletal mechanisms agreed well, demonstrating the adequacy of the resulting reduced chemistry for all the butanol isomers in predicting global combustion phenomena. In addition, the skeletal mechanisms closely predicted the time-histories of fuel mass fractions in homogeneous compression-ignition engine simulations. The performance of each butanol isomer was additionally compared with that of a gasoline surrogate with an antiknock index of 87 in a homogeneous compression-ignition engine simulation. The gasoline surrogate was consumed faster than any of the butanol isomers, with tert-butanol exhibiting the slowest fuel consumption rate. While n-butanol and isobutanol displayed the most similar consumption profiles relative to the gasoline surrogate, the two literature chemical kinetic models predicted different orderings.Comment: 39 pages, 16 figures. Supporting information available via https://doi.org/10.1021/acs.energyfuels.6b0185

Aluminum Single Electron Transistors with Islands Isolated from a Substrate

The low-frequency noise figures of single-electron transistors (electrometers) of traditional planar and new stacked geometry were compared. We observed a correlation between the charge noise and the contact area of the transistor island with a dielectric substrate in the set of Al transistors located on the same chip and having almost similar electric parameters. We have found that the smaller the contact area the lower the noise level of the transistor. The lowest noise value 8*10E-6 e/sqrt(Hz) at f = 10 Hz. has been measured in a stacked transistor with an island which was completely isolated from a substrate. Our measurements have unambiguously indicated that the dominant source of the background charge fluctuations is associated with a dielectric substrateComment: Review paper, latex, 10 pages, 7 figures, to be publ. in JLTP, 2000; Proceeding of "Electron Transport in Mesoscopic Systems", August 12-15, 1999 Geteborg, Sweden, http://fy.chalmers.se/meso_satellite/index.html See also LT22 manuscript: http://lt22.hut.fi/cgi/view?id=S1113

Single-charge devices with ultrasmall Nb/AlOx/Nb trilayer Josephson junctions

Josephson junction transistors and 50-junction arrays with linear junction dimensions from 200 nm down to 70 nm were fabricated from standard Nb/AlOx/Nb trilayers. The fabrication process includes electron beam lithography, dry etching, anodization, and planarization by chemical-mechanical polishing. The samples were characterized at temperatures down to 25 mK. In general, all junctions are of high quality and their I-U characteristics show low leakage currents and high superconducting energy gap values of 1.35 meV. The characteristics of the transistors and arrays exhibit some features in the subgap area, associated with tunneling of Cooper pairs, quasiparticles and their combinations due to the redistribution of the bias voltage between the junctions. Total island capacitances of the transistor samples ranged from 1.5 fF to 4 fF, depending on the junction sizes. Devices made of junctions with linear dimensions below 100 nm by 100 nm demonstrate a remarkable single-electron behavior in both superconducting and normal state. We also investigated the area dependence of the junction capacitances for transistor and array samples.Comment: 19 pages incl. 2 tables and 11 figure

Storage capabilities of a 4-junction single electron trap with an on-chip resistor

We report on the operation of a single electron trap comprising a chain of four Al/AlOx/Al tunnel junctions attached, at one side, to a memory island and, at the other side, to a miniature on-chip Cr resistor R=50 kOhm which served to suppress cotunneling. At appropriate voltage bias the bi-stable states of the trap, with the charges differing by the elementary charge e, were realized. At low temperature, spontaneous switching between these states was found to be infrequent. For instance, at T=70 mK the system was capable of holding an electron for more than 2 hours, this time being limited by the time of the measurement.Comment: 3 pages of text and 2 figure