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61.
Intermetallics that coexist with III-V’s in the bulk are expected to form thermodynamically stable overlayers when deposited
as a thin film. To the extent that adsorption kinetics do not play a role, these films should be abrupt and able to withstand
high temperature processing. Some of these films have been found to be epitaxial after heating in vacuum. FeAl has been found
to form pseudomorphic films on InP(l00) substrates and to grow in a layer-by-layer mode even when code-posited. To explore
the role of stoichiometry and crystal strain, we have used reflection high energy electron diffraction (RHEED) to compare
the growth of Fe
x
-Al1−x
on GaAs(l00) to its growth on InP substrates. In both cases RHEED intensity oscillations are observed at 200° C, indicating
two-dimensional island formation and layer-by-layer growth. For both, the growth is pseudomorphic on an AlAs buffer layer,
with any lattice constant change less than 0.3%. When the intermetallics were codeposited, the growth proceeded via double
layer formation forx < 0.7 and via single layers for largex. The films were stable to 550° C. Subsequent growth of AlAs was three dimensional. 相似文献
62.
Oliver Seitz Ayelet Vilan Hagai Cohen Jaehyung Hwang Marc Haeming Achim Schoell Eberhard Umbach Antoine Kahn David Cahen 《Advanced functional materials》2008,18(14):2102-2113
n‐Si/CnH2n + 1/Hg junctions (n = 12, 14, 16 and 18) can be prepared with sufficient quality to assure that the transport characteristics are not anymore dominated by defects in the molecular monolayers. With such organic monolayers we can, using electron, UV and X‐ray irradiation, alter the charge transport through the molecular junctions on n‐ as well as on p‐type Si. Remarkably, the quality of the self‐assembled molecular monolayers following irradiation remains sufficiently high to provide the same very good protection of Si from oxidation in ambient atmosphere as provided by the pristine films. Combining spectroscopic (UV photoemission spectroscopy (UPS), X‐ray photoelectron spectroscopy (XPS), Auger, near edge‐X‐ray absorption fine structure (NEXAFS)) and electrical transport measurements, we show that irradiation induces defects in the alkyl films, most likely C?C bonds and C? C crosslinks, and that the density of defects can be controlled by irradiation dose. These altered intra‐ and intermolecular bonds introduce new electronic states in the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the alkyl chains and, in the process, dope the organic film. We demonstrate an enhancement of 1–2 orders of magnitude in current. This change is clearly distinguishable from the previous observed difference between transport through high quality and defective monolayers. A detailed analysis of the electrical transport at different temperatures shows that the dopants modify the transport mechanism from tunnelling to hopping. This study suggests a way to extend significantly the use of monolayers in molecular electronics. 相似文献
63.
A major challenge in the study of cryptography is characterizing the necessary and sufficient assumptions required to carry out a given cryptographic task. The focus of this work is the necessity of a broadcast channel for securely computing symmetric functionalities (where all the parties receive the same output) when one third of the parties, or more, might be corrupted. Assuming all parties are connected via a point-to-point network, but no broadcast channel (nor a secure setup phase) is available, we prove the following characterization: It follows that, in case a third of the parties might be corrupted, broadcast is necessary for securely computing non-dominated functionalities (in which “small” subsets of the inputs cannot determine the output), including, as interesting special cases, the Boolean XOR and coin-flipping functionalities.
相似文献
- A symmetric n-party functionality can be securely computed facing \(n/3\le t<n/2\) corruptions (i.e., honest majority), if and only if it is \((n-2t)\) -dominated; a functionality is k-dominated, if any k-size subset of its input variables can be set to determine its output to some predetermined value.
- Assuming the existence of one-way functions, a symmetric n-party functionality can be securely computed facing \(t\ge n/2\) corruptions (i.e., no honest majority), if and only if it is 1-dominated and can be securely computed with broadcast.
64.
On the Trade-Off between Energy and Multicast Efficiency in 802.16e-Like Mobile Networks 总被引:1,自引:0,他引:1
In this paper, we define a new problem that has not been addressed in the past: the trade-off between energy efficiency and throughput for multicast services in 802.16e or similar mobile networks. In such networks, the mobile host can reduce its energy consumption by entering the sleep mode when it is not supposed to receive or transmit information. For unicast applications, the tradeoff between delay and energy efficiency has been extensively researched. However, for mobile hosts running multicast (usually push- based) applications, it is much more difficult to determine when data should be transmitted by the base station and when each host should enter the sleep mode. In order to maximize the channel throughput while limiting the energy consumption, a group of hosts needing similar data items should be active during the same time intervals. We define this as an optimization problem and present several algorithms for it. We show that the most efficient solution is the one that employs cross-layer optimization by dividing the hosts into groups according to the quality of their downlink physical (PHY) channels. 相似文献
65.
Hyundai Park Alexander W. Fang Oded Cohen Richard Jones Mario J. Paniccia John E. Bowers 《Photonics Technology Letters, IEEE》2007,19(4):230-232
We report a hybrid AlGaInAs-silicon evanescent amplifier incorporating a silicon waveguide with a III-V gain medium. The optical mode of the hybrid amplifier is mostly confined to the silicon waveguide and evanescently coupled to the AlGaInAs quantum-well (QW) region where optical gain is provided by electrical current injection. These two different material systems are bonded by low-temperature oxygen plasma assisted wafer bonding at 300 degC. The fabricated device shows 13 dB of maximum chip gain with 11 dBm of output saturation power. Evanescent coupling allows a lower active region confinement factor to provide a higher saturation output power than amplifiers with centered QWs, which is important for applications that require linear amplification 相似文献
66.
K. L. Fry C. P. Kuo C. A. Larsen R. M. Cohen G. B. Stringfellow A. Melas 《Journal of Electronic Materials》1986,15(2):91-96
We report the organometallic vapor phase epitaxial (OMVPE) growth of InP and Ga0.47In0.53As using a new organometallic indium source, ethyldimethylindium (EDMIn), rather than the traditional sources triethylindium
(TEIn) or trimethylindium (TMIn). EDMIn is a liquid at room temperature and its vapor pressure at 17° C was found to be 0.85
Torr using thermal decomposition experiments. The growth results using EDMIn were compared to those using TMIn in the same
atmospheric pressure reactor. For InP, use of EDMIn resulted in a high growth efficiency of 1.3 × 104 μm/ mole, which was independent of the growth temperature and comparable to the growth efficiency obtained with TMIn. The
high growth efficiency is consistent with the observation of no visible parasitic gas phase reactions upstream of the substrate.
The 4K photoluminescence (PL) spectra consist of a peak due to bound excitons and an impurity related peak 38 meV lower in
energy. This impurity peak is ascribed to conduction band to acceptor transitions from carbon, due to the decreasing relative
intensity of this peak with increasing V/III ratio. The relative intensity of the C impurity peak decreases by five times
when the growth temperature is increased from 575 to 675° C, with a corresponding increase in the room temperature electron
mobility from 725 to 3875 cm2/ Vs. For GalnAs lattice-matched to InP, use of EDMIn also resulted in a temperatureindependent high growth efficiency of
1.0 x 104 μm/mole, indicating negligible parasitic reactions with AsH3. The In distribution coefficient was nearly constant at a value of 0.9, however the run to run composition variation was
slightly higher for EDMIn than for TMIn. The 4K PL showed donor-acceptor pair transitions due to C and Zn. The C impurity
peak intensity decreased dramatically with increasing growth temperature, accompanied by an increase in the room temperature
electron mobility to 5200 cm2/Vs. Overall, the growth of both InP and GalnAs using EDMIn was qualitatively similar to that using TMIn, although the room
temperature electron mobilities were lower for the new source than for our highest purity bottle of TMIn. 相似文献
67.
An Efficient Algorithm for Spectral Analysis of Heart Rate Variability 总被引:21,自引:0,他引:21
Berger Ronald D. Akselrod Solange Gordon David Cohen Richard J. 《IEEE transactions on bio-medical engineering》1986,(9):900-904
We present a simple efficient algorithm for the derivation of a heart rate signal from the electrocardiogram. We demonstrate that the amplitude spectrum of this heart rate signal more closely matches that of the input signal to an integral pulse frequency modulation (IPFM) model of the heart's pacemaker than do the spectra of other ECG-derived heart rate signals. The applicability of this algorithm in cross-spectral analysis between heart rate and other physiologic signals is also discussed. 相似文献
68.
69.
70.
Cohen Andrew R. Bjornsson Christopher S. Temple Sally Banker Gary Roysam Badrinath 《IEEE transactions on pattern analysis and machine intelligence》2009,31(8):1386-1403
An algorithmic information-theoretic method is presented for object-level summarization of meaningful changes in image sequences. Object extraction and tracking data are represented as an attributed tracking graph (ATG). Time courses of object states are compared using an adaptive information distance measure, aided by a closed-form multidimensional quantization. The notion of meaningful summarization is captured by using the gap statistic to estimate the randomness deficiency from algorithmic statistics. The summary is the clustering result and feature subset that maximize the gap statistic. This approach was validated on four bioimaging applications: 1) It was applied to a synthetic data set containing two populations of cells differing in the rate of growth, for which it correctly identified the two populations and the single feature out of 23 that separated them; 2) it was applied to 59 movies of three types of neuroprosthetic devices being inserted in the brain tissue at three speeds each, for which it correctly identified insertion speed as the primary factor affecting tissue strain; 3) when applied to movies of cultured neural progenitor cells, it correctly distinguished neurons from progenitors without requiring the use of a fixative stain; and 4) when analyzing intracellular molecular transport in cultured neurons undergoing axon specification, it automatically confirmed the role of kinesins in axon specification. 相似文献