316 research outputs found
Superconductivity in CVD Diamond Thin Film Well-Above Liquid Helium Temperature
Diamond has always been adored as a jewel. Even more fascinating is its
outstanding physical properties; it is the hardest material known in the world
with the highest thermal conductivity. Meanwhile, when we turn to its
electrical properties, diamond is a rather featureless electrical insulator.
However, with boron doping, it becomes a p-type semiconductor, with boron
acting as a charge acceptor. Therefore the recent news of superconductivity in
heavily boron-doped diamond synthesized by high pressure sintering was received
with considerable surprise. Opening up new possibilities for diamond-based
electrical devices, a systematic investigation of these phenomena clearly needs
to be achieved. Here we show unambiguous evidence of superconductivity in a
diamond thin film deposited by a chemical vapor deposition (CVD) method.
Furthermore the onset of the superconducting transition is found to be 7.4K,
which is higher than the reported value in ref(7) and well above helium liquid
temperature. This finding establishes the superconductivity to be a universal
property of boron-doped diamond, demonstrating that device application is
indeed a feasible challenge.Comment: 6 pages, 3 figure
Microscopic Evidence for Evolution of Superconductivity by Effective Carrier Doping in Boron-doped Diamond:11B-NMR study
We have investigated the superconductivity discovered in boron (B)-doped
diamonds by means of 11B-NMR on heteroepitaxially grown (111) and (100) films.
11B-NMR spectra for all of the films are identified to arise from the
substitutional B(1) site as single occupation and lower symmetric B(2) site
substituted as boron+hydrogen(B+H) complex, respectively. A clear evidence is
presented that the effective carriers introduced by B(1) substitution are
responsible for the superconductivity, whereas the charge neutral B(2) sites
does not offer the carriers effectively. The result is also corroborated by the
density of states deduced by 1/T1T measurement, indicating that the evolution
of superconductivity is driven by the effective carrier introduced by
substitution at B(1) site.Comment: 4 pages, 6 figures, to be published in Phys. Rev. B (Brief report
Low-energy electrodynamics of superconducting diamond
Heavily-boron-doped diamond films become superconducting with critical
temperatures well above 4 K. Here we first measure the reflectivity of
such a film down to 5 cm, by also using Coherent Synchrotron Radiation.
We thus determine the optical gap, the field penetration depth, the range of
action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral
function. We conclude that diamond behaves as a dirty BCS superconductor.Comment: 4 pages including 3 figure
Carbon materials-based sensors: State-of-the-art and future prospects
In this work, the focuses were made on carbon related materials such as diamond and graphene as solution-gate fieldeffect transistor (SGFET) towards pH sensing of carboxyl and amine functional groups and its compatibility with estrogen (17β-estradiol) aptamer. The functionalization of diamond graphene with carboxyl were achieved through anodization by applying a sequential potential scan in Carmody buffer solution (pH 7). The carboxyl-terminated surfaces were exposed to nitrogen radicals to generate an amine-terminated surface [1]. Raman spectroscopy was used to determine the defect density of the carbon related materials caused by the anodization. The sequential anodization in Carmody buffer solution at pH 7 had low defective effect on carbon structure and shows that the original structure
of carbon was conserved [2]. The pH sensitivity will be presented in detail and will be finalized with the compatibility with estrogen (17β-estradiol) aptamer, which the supporting DNA strands were immobilized and an aptamer was hybridized to prepare a detection pair to bind with any 17β-estradiol molecule, as the aptamer captures the 17βestradiol molecule naturally [3]. These detections will be demonstrated through optical (fluorescence microscopy) and electrical measurements (current-voltage) and summarized with carbon materials-based sensors towards the actual application of designing diamond/graphene-based biosensor
Reconstruction and thermal stability of the cubic SiC(001) surfaces
The (001) surfaces of cubic SiC were investigated with ab-initio molecular
dynamics simulations. We show that C-terminated surfaces can have different
c(2x2) and p(2x1) reconstructions, depending on preparation conditions and
thermal treatment, and we suggest experimental probes to identify the various
reconstructed geometries. Furthermore we show that Si-terminated surfaces
exhibit a p(2x1) reconstruction at T=0, whereas above room temperature they
oscillate between a dimer row and an ideal geometry below 500 K, and sample
several patterns including a c(4x2) above 500 K.Comment: 12 pages, RevTeX, figures 1 and 2 available in gif form at
http://irrmawww.epfl.ch/fg/sic/fig1.gif and
http://irrmawww.epfl.ch/fg/sic/fig2.gi
Photoemission study of electronic structure evolution across the metal-insulator transition of heavily B-doped diamond
We studied the electronic structure evolution of heavily B-doped diamond films across the metal-insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (E(F)) up to similar to 5k(B)T can be observed (k(B) is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near E(F). Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of E(F), can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT
Boron δ-doped (111) diamond solution gate field effect transistors.
A solution gate field effect transistor (SGFET) using an oxidised boron δ-doped channel on (111) diamond is presented for the first time. Employing an optimised plasma chemical vapour deposition (PECVD) recipe to deposit δ-layers, SGFETs show improved current-voltage (I-V) characteristics in comparison to previous similar devices fabricated on (100) and polycrystalline diamond, where the device is shown to operate in the enhancement mode of operation, achieving channel pinch-off and drain-source current saturation within the electrochemical window of diamond. A maximum gain and transconductance of 3 and 200μS/mm are extracted, showing comparable figures of merit to hydrogen-based SGFET. The oxidised device shows a site-binding model pH sensitivity of 36 mV/pH, displaying fast temporal responses. Considering the biocompatibility of diamond towards cells, the device's highly mutable transistor characteristics, pH sensitivity and stability against anodic oxidation common to hydrogen terminated diamond SGFET, oxidised boron δ-doped diamond SGFETs show promise for the recording of action potentials from electrogenic cells
Hyperbolic quenching problem with damping in the micro-electro mechanical system device
[[abstract]]We study the initial boundary value problem for the damped hyperbolic
equation arising in the micro-electro mechanical system device with
local or nonlocal singular nonlinearity. For both cases, we provide some criteria
for quenching and global existence of the solution. We also derive the
existence of the quenching curve for the corresponding Cauchy problem with
local source[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[countrycodes]]US
Some results on blow up for semilinear parabolic problems
The authors describe the asymptotic behavior of blow-up for the semilinear heat equation ut=uxx+f(u) in R×(0,T), with initial data u0(x)>0 in R, where f(u)=up, p>1, or f(u)=eu. A complete description of the types of blow-up patterns and of the corresponding blow-up final-time profiles is given. In the rescaled variables, both are governed by the structure of the Hermite polynomials H2m(y). The H2-behavior is shown to be stable and generic. The existence of H4-behavior is proved. A nontrivial blow-up pattern with a blow-up set of nonzero measure is constructed. Similar results for the absorption equation ut=uxx−up, 0<p<1, are discussed
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