Tunable graphene system with two decoupled monolayers

The use of two truly two-dimensional gapless semiconductors, monolayer and bilayer graphene, as current-carrying components in field-effect transistors (FET) gives access to new types of nanoelectronic devices. Here, we report on the development of graphene-based FETs containing two decoupled graphene monolayers manufactured from a single one folded during the exfoliation process. The transport characteristics of these newly-developed devices differ markedly from those manufactured from a single-crystal bilayer. By analyzing Shubnikov-de Haas oscillations, we demonstrate the possibility to independently control the carrier densities in both layers using top and bottom gates, despite there being only a nanometer scale separation between them

Enhanced Shot Noise in Tunneling through a Stack of Coupled Quantum Dots

We have investigated the noise properties of the tunneling current through vertically coupled self-assembled InAs quantum dots. We observe super-Poissonian shot noise at low temperatures. For increased temperature this effect is suppressed. The super-Poissonian noise is explained by capacitive coupling between different stacks of quantum dots

Mobilities and Scattering Times in Decoupled Graphene Monolayers

Folded single layer graphene forms a system of two decoupled monolayers being only a few Angstroms apart. Using magnetotransport measurements we investigate the electronic properties of the two layers conducting in parallel. We show a method to obtain the mobilities for the individual layers despite them being jointly contacted. The mobilities in the upper layer are significantly larger than in the bottom one indicating weaker substrate influence. This is confirmed by larger transport and quantum scattering times in the top layer. Analyzing the temperature dependence of the Shubnikov-de Haas oscillations effective masses and corresponding Fermi velocities are obtained yielding reduced values down to 66 percent in comparison to monolayers.Comment: 4 pages, 5 figure

Low-temperature hysteresis in the field effect of bilayer graphene

Hysteresis in the field effect of bilayer graphene is observed at a low temperature. We attribute this effect to charge traps in the substrate. When the sweep rate of the back-gate voltage is increased to higher values, the hysteresis becomes more pronounced. By measuring the hysteresis in the field effect, the lifetime of the charge traps is estimated as 16.9 min. It is shown that the influence of charge traps on graphene is strongly affected by a magnetic field. Above 5 T the hysteresis remains constant. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.DFG/EXC/QUES

Phenotype-specific association of the TGFBR3 locus with nonsyndromic cryptorchidism

PURPOSE: Based on a genome-wide association study of testicular dysgenesis syndrome showing a possible association with TGFBR3, we analyzed data from a larger, phenotypically restricted cryptorchidism population for potential replication of this signal. MATERIALS AND METHODS: We excluded samples based on strict quality control criteria, leaving 844 cases and 2,718 controls of European ancestry that were analyzed in 2 separate groups based on genotyping platform (ie Illumina® HumanHap550, version 1 or 3, or Human610-Quad, version 1 BeadChip in group 1 and Human OmniExpress 12, version 1 BeadChip platform in group 2). Analyses included genotype imputation at the TGFBR3 locus, association analysis of imputed data with correction for population substructure, subsequent meta-analysis of data for groups 1 and 2, and selective genotyping of independent cases (330) and controls (324) for replication. We also measured Tgfbr3 mRNA levels and performed TGFBR3/betaglycan immunostaining in rat fetal gubernaculum. RESULTS: We identified suggestive (p ≤ 1× 10(-4)) association of markers in/near TGFBR3, including rs9661103 (OR 1.40; 95% CI 1.20, 1.64; p = 2.71 × 10(-5)) and rs10782968 (OR 1.58; 95% CI 1.26, 1.98; p = 9.36 × 10(-5)) in groups 1 and 2, respectively. In subgroup analyses we observed strongest association of rs17576372 (OR 1.42; 95% CI 1.24, 1.60; p = 1.67 × 10(-4)) with proximal and rs11165059 (OR 1.32; 95% CI 1.15, 1.38; p = 9.42 × 10(-4)) with distal testis position, signals in strong linkage disequilibrium with rs9661103 and rs10782968, respectively. Association of the prior genome-wide association study signal (rs12082710) was marginal (OR 1.13; 95% CI 0.99, 1.28; p = 0.09 for group 1), and we were unable to replicate signals in our independent cohort. Tgfbr3/betaglycan was differentially expressed in wild-type and cryptorchid rat fetal gubernaculum. CONCLUSIONS: These data suggest complex or phenotype specific association of cryptorchidism with TGFBR3 and the gubernaculum as a potential target of TGFβ signaling

Measurement of finite-frequency current statistics in a single-electron transistor

Electron transport in nano-scale structures is strongly influenced by the Coulomb interaction which gives rise to correlations in the stream of charges and leaves clear fingerprints in the fluctuations of the electrical current. A complete understanding of the underlying physical processes requires measurements of the electrical fluctuations on all time and frequency scales, but experiments have so far been restricted to fixed frequency ranges as broadband detection of current fluctuations is an inherently difficult experimental procedure. Here we demonstrate that the electrical fluctuations in a single electron transistor (SET) can be accurately measured on all relevant frequencies using a nearby quantum point contact for on-chip real-time detection of the current pulses in the SET. We have directly measured the frequency-dependent current statistics and hereby fully characterized the fundamental tunneling processes in the SET. Our experiment paves the way for future investigations of interaction and coherence induced correlation effects in quantum transport.Comment: 7 pages, 3 figures, published in Nature Communications (open access

Leaving A Bequest: Living on Through Charitable Gifts

Decisions taken in respect of the disposition of possessions often parallel a life transition or change in identity. In this article, we examine decisions taken in a will where disposition can be viewed not as a representation of the identities an individual wishes to shed, but rather as the continuation of those for which the deceased wishes to be remembered. We examine the meaning that such donors ascribe to their giving and the rich pattern of utility it offers both the individual and those he or she will ultimately leave behind. Using grounded theory, we report the results of 20 in-depth interviews conducted with individuals who had pledged a bequest to at least one U.K. charity. We demonstrate how the bequest gift is laden with symbolism, a function of the reminiscences of the individual and reflective of the need for the self to live on and achieve a degree of symbolic immortality