Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors

We report low-temperature electrical transport studies of molecule-scale silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade oscillations characteristic of charge addition to a single nanostructure with length scales up to at least 400 nm. Further studies demonstrate coherent charge transport through discrete single particle quantum levels extending the whole device, and show that the ground state spin configuration follows the Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that phase coherent single-dot characteristics are accessible in a regime where correlations are strong.Comment: 4 pages and 4 figure

Weak localization scattering lengths in epitaxial, and CVD graphene

Weak localization in graphene is studied as a function of carrier density in the range from 1 x 10(11) cm(-2) to 1.43 x 10(13) cm(-2) using devices produced by epitaxial growth onto SiC and CVD growth on thin metal film. The magnetic field dependent weak localization is found to be well fitted by theory, which is then used to analyze the dependence of the scattering lengths L-phi, L-i, and L-* on carrier density. We find no significant carrier dependence for L-phi, a weak decrease for L-i with increasing carrier density just beyond a large standard error, and a n(-1/4) dependence for L-*. We demonstrate that currents as low as 0.01 nA are required in smaller devices to avoid hot-electron artifacts in measurements of the quantum corrections to conductivity

Energy relaxation for hot Dirac fermions in graphene and breakdown of the quantum Hall effect

Energy loss rates for hot carriers in graphene are experimentally investigated by observing the amplitude of Shubnikov-de Haas oscillations as a function of electric field. The carrier energy loss in graphene follows the predictions of deformation potential coupling going as ∼T4 at carrier temperatures up to ∼100 K, and that deformation potential theory, when modified with a limiting phonon relaxation time, is valid up to several hundred Kelvin. Additionally we investigate the breakdown of the quantum Hall effect and show that energy loss rates in graphene are around ten times larger than GaAs at low temperatures. This leads to significantly higher breakdown currents per micrometer, and we report a measured breakdown current of 8 μA/μm. © 2012 American Physical Society

Photoresists as a high spatial resolution autoradiography substrate for quantitative mapping of intra- and sub-cellular distribution of Auger electron emitting radionuclides.

PURPOSE: To explore poly(methyl methacrylate) (PMMA950) as an autoradiography substrate. MATERIALS AND METHODS: PMMA950 was spin coated onto a silicon substrate. Resists were exposed to either a 25 or 50 keV electron beam (e-beam) with fluences of 0.1-33.6 μC/cm(2). The resulting patterns were analyzed by atomic force microscopy (AFM). The dependence of pattern sensitivity and resolution on resist thickness, development time and electron energy was evaluated and correlated with Monte Carlo (MC) modeling. Conventional micro-autoradiography (MAR) images were compared to AFM images of photoresist patterns obtained following exposure from (111)In-diethylenetriaminepentaacetic acid (DTPA)-human epidermal growth factor (hEGF) (4-6 MBq/μg, 40 nM DTPA-hEGF)-treated human breast cancer cells MDA-MB-468. RESULTS: MC simulation results confirmed the similarity of particle transport in PMMA950 exposed to either an (111)In point source or a 25 keV e-beam. Sensitivity was inversely related to resist thickness. Development conditions of the resists greatly affected image quality. Sensitivity of PMMA950 was similar to the UVIII™ resist (consisting of a copolymer of 4-hydroxystyrene and t- butylacrylate) at low electron fluence for both 25 and 50 keV e-beam exposure. AFM evaluation of the exposure patterns from (111)In-DTPA-hEGF treated cells and nuclei provides more detailed information in comparison with that from MAR. CONCLUSIONS: Photoresist autoradiography can provide information on both the distribution of radiation sources and their strengths within a biological sample; however, the choice of photoresist material and processing conditions greatly affects the outcome

Chemically amplified photoresist for high resolution autoradiography in targeted radiotherapy.

Evaluation of the intracellular distribution of radionuclides used for targeted radiotherapy (tRT) is essential for accurate dosimetry. Therefore, a direct and quantitative method for subcellular micro-autoradiography using radiation sensitive polymers (PMMA, UV1116 and AZ40XT) was developed. The electron exposure dose in radio-labelled cells due to Auger and internal conversion (IC) electron emissions of indium (¹¹¹In), a radionuclide currently used for tRT, was calculated using Monte Carlo (MC) simulation. Electron beam lithography using pre-defined exposure doses was used to calibrate the resist response. The topography of the exposed and developed resists was analysed with atomic force microscopy (AFM) and the resulting pattern depth was related to a specific exposure dose. UV1116 exhibited the best contrast as compared to AZ40XT and PMMA, while AZ40XT exhibited the highest sensitivity at low doses (<10 μC/cm²). AFM analysis of the exposure pattern from radio-labelled cells and nuclei in UV1116 revealed a non-uniform distribution of ¹¹¹In-EGF in the cell and nucleus, consistent with less well-resolved data from confocal microscopy and micro-autoradiography

Weak localization scattering lengths in epitaxial, and CVD graphene

Weak localization in graphene is studied as a function of carrier density in the range from 1×1011 cm-2 to 1.43×1013 cm -2 using devices produced by epitaxial growth onto SiC and CVD growth on thin metal film. The magnetic field dependent weak localization is found to be well fitted by theory, which is then used to analyze the dependence of the scattering lengths Lφ, Li, and L* on carrier density. We find no significant carrier dependence for L φ, a weak decrease for Li with increasing carrier density just beyond a large standard error, and a n-1/4 dependence for L*. We demonstrate that currents as low as 0.01 nA are required in smaller devices to avoid hot-electron artifacts in measurements of the quantum corrections to conductivity. © 2012 American Physical Society