共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Plechinger F.‐X. Schrettenbrunner J. Eroms D. Weiss C. Schüller T. Korn 《固体物理学:研究快报》2012,6(3):126-128
We present a photoluminescence study of single‐layer MoS2 flakes on SiO2 surfaces. We demonstrate that the luminescence peak position of flakes prepared from natural MoS2, which varies by up to 25 meV between individual flakes, can be homogenized by annealing in vacuum. We use HfO2 and Al2O3 layers prepared by atomic layer deposition to cover some of our flakes. In these flakes, we observe a suppression of the low‐energy luminescence peak which appears in asprepared flakes at low temperatures. We infer that this peak originates from excitons bound to surface adsorbates. We also observe different temperature‐induced shifts of the luminescence peaks for the oxide‐covered flakes. This effect stems from the different thermal expansion coefficients of the oxide layers and the MoS2 flakes. It indicates that the single‐layer MoS2 flakes strongly adhere to the oxide layers and are therefore strained. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Andrew M. C. Dawes 《固体物理学:研究快报》2009,3(1):A17-A19
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Kwanpyo Kim William Regan Baisong Geng Benjamín Alemán B. M. Kessler Feng Wang M. F. Crommie A. Zettl 《固体物理学:研究快报》2010,4(11):302-304
We report in situ Joule heating on suspended single‐layer graphene in a transmission electron microscope (TEM). Thermally‐driven degradation of pre‐deposited nanoparticles on the membrane is monitored and used for local temperature estimation. By extrapolating the Joule heating power and temperature relation, we find that the suspended single‐layer graphene has exceptional thermal stability up to at least 2600 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Gerd Plechinger Philipp Nagler Julia Kraus Nicola Paradiso Christoph Strunk Christian Schüller Tobias Korn 《固体物理学:研究快报》2015,9(8):457-461
Single‐layer WS2 is a direct‐gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature‐dependent photoluminescence measurements on mechanically exfoliated single‐layer WS2, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n‐type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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Biswanath Chakraborty H. S. S. Ramakrishna Matte A. K. Sood C. N. R. Rao 《Journal of Raman spectroscopy : JRS》2013,44(1):92-96
We report resonant Raman scattering of MoS2 layers comprising of single, bi, four and seven layers, showing a strong dependence on the layer thickness. Indirect band gap MoS2 in bulk becomes a direct band gap semiconductor in the monolayer form. New Raman modes are seen in the spectra of single‐ and few‐layer MoS2 samples which are absent in the bulk. The Raman mode at ~230 cm−1 appears for two, four and seven layers. This mode has been attributed to the longitudinal acoustic phonon branch at the M point (LA(M)) of the Brillouin zone. The mode at ~179 cm−1 shows asymmetric character for a few‐layer sample. The asymmetry is explained by the dispersion of the LA(M) branch along the Γ‐M direction. The most intense spectral region near 455 cm−1 shows a layer‐dependent variation of peak positions and relative intensities. The high energy region between 510 and 645 cm−1 is marked by the appearance of prominent new Raman bands, varying in intensity with layer numbers. Resonant Raman spectroscopy thus serves as a promising non invasive technique to accurately estimate the thickness of MoS2 layers down to a few atoms thick. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Maria A. Augustyniak‐Jabłokow Krzysztof Tadyszak Mariusz Maćkowiak Yurii V. Yablokov 《固体物理学:研究快报》2011,5(8):271-273
We report electron paramagnetic resonance (EPR) evidence of the antiferromagnetic ordering in pristine single‐layer graphene. Temperature dependences of the parameters of EPR spectra obtained for vacuum‐processed samples were studied within the temperature range of 4.2–300 K. Our experiment has confirmed recent theoretical predictions that in single‐layer graphene the carrier‐mediated exchange interaction leads to antiferromagnetic coupling. We note some quantitative discrepancies between the theory and experimental findings and discuss their origins. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Reduction of low‐frequency noise in multilayer MoS2 FETs using a Fermi‐level depinning layer 下载免费PDF全文
Two‐dimensional transition metal dichalcogenides (TMDCs) are potential candidate materials for future thin‐film field effect transistors (FETs). However, many aspects of this device must be optimized for practical applications. In addition, low‐frequency noise that limits the design window of electronic devices, in general, must be minimized for TMD‐based FETs. In this study, the low‐frequency noise characteristics of multilayer molybdenum disulphide (MoS2) FETs were investigated in detail, with two different contact structures: titanium (Ti) metal–MoS2 channel and Ti metal–TiO2 interlayer–MoS2 channel. The results showed that the noise level of the device with a TiO2 interlayer reduced by one order of magnitude compared with the device without the TiO2 interlayer. This substantial improvement in the noise characteristics could be explained using the carrier number of fluctuation model. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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Jingzhi Shang Chunxiao Cong Jun Zhang Qihua Xiong Gagik G. Gurzadyan Ting Yu 《Journal of Raman spectroscopy : JRS》2013,44(1):70-74
Few‐layer graphene grown by chemical vapor deposition has been studied by Raman and ultrafast laser spectroscopy. A low‐wavenumber Raman peak of ~120 cm−1 and a phonon‐induced oscillation in the kinetic curve of electron–phonon relaxation process have been observed, respectively. The Raman peak is assigned to the low‐wavenumber out‐of‐plane optical mode in the few‐layer graphene. The phonon band shows an asymmetric shape, a consequence of so‐called Breit‐Wigner‐Fano resonance, resulting from the coupling between the low‐wavenumber phonon and electron transitions. The obtained oscillation wavenumber from the kinetic curve is consistent with the detected low‐wavenumber phonon by Raman scattering. The origin of this oscillation is attributed to the generation of coherent phonons and their interactions with photoinduced electrons. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Amirhasan Nourbakhsh Mirco Cantoro Bing Li Robert Müller Steven De Feyter Marc M. Heyns Bert F. Sels Stefan De Gendt 《固体物理学:研究快报》2012,6(2):53-55
We report a technique to tune the excess charge concentration in single‐layer graphene from p‐ to n‐type up to densities of |n | ~ 1.2 × 1013 cm–2, corresponding to a displacement electric field of ~2.5 V/nm. The tuning is achieved by engineering the interaction between graphene and the underlying Si/SiO2 substrate with an amino group‐terminated self‐assembled monolayer, and subsequent rinsing in aqueous solutions at controlled pH. Raman spectroscopy and electrical measurements on treated graphene devices confirm the occurrence of doping. Interestingly, we found the field‐effect mobility not to be significantly affected by the procedure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Current–voltage, radio‐frequency (RF) and noise characteristics of single‐wall multi‐tube carbon nanotube (CNT) transistors were measured at cryogenic temperatures. Compared to an ambient temperature (Ta) of 300 K, only a slight drain current increase at Ta = 77 K was observed. In addition, a weak dependence of the maximum value of the current gain cut‐off frequency (fT) on Ta was obtained, indicating that fT is rather limited by the device intrinsic quantum and extrinsic capacitances than by an improved mobility due to reduced optical phonon scattering at low Ta. A noise analysis of the devices at Ta = 10 K reveals that the noise factor (NF) improvement at very low temperatures is related to the reduced Nyquist noise of all resistive transistor noise contributors. Since the main noise source in CNTFETs is the shot noise, NF remains comparatively high even at Ta = 10 K.
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Yuanxin Li Ningning Dong Saifeng Zhang Xiaoyan Zhang Yanyan Feng Kangpeng Wang Long Zhang Jun Wang 《Laser \u0026amp; Photonics Reviews》2015,9(4):427-434
Strong two‐photon absorption (TPA) in monolayer MoS2 is demonstrated in contrast to saturable absorption (SA) in multilayer MoS2 under the excitation of femtosecond laser pulses in the near‐infrared region. MoS2 in the forms of monolayer single crystal and multilayer triangular islands are grown on either quartz or SiO2/Si by employing the seeding method through chemical vapor deposition. The nonlinear transmission measurements reveal that monolayer MoS2 possesses a nonsaturation TPA coefficient as high as ∼(7.62 ±0.15) ×103 cm/GW, larger than that of conventional semiconductors by a factor of 103. As a result of TPA, two‐photon pumped frequency upconverted luminescence is observed directly in the monolayer MoS2. For the multilayer MoS2, the SA response is demonstrated with the ratio of the excited‐state absorption cross section to ground‐state cross section of ∼0.18. In addition, the laser damage threshold of the monolayer MoS2 is ∼97 GW/cm2, larger than that of the multilayer MoS2 of ∼78 GW/cm2.
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Pseudogap in the Eliashberg approach based on electron‐phonon and electron‐electron‐phonon interaction 下载免费PDF全文
The properties of the superconducting and the anomalous normal state were described by using the Eliashberg method. The pairing mechanism was reproduced with the help of the Hamiltonian, which models the electron‐phonon and the electron‐electron‐phonon interaction (EEPh). The set of the Eliashberg equations, which determines the order parameter function (φ), the wave function renormalization factor (Z), and the energy shift function (χ), was derived. It was proven that for the sufficiently large values of the EEPh potential, the doping dependence of the order parameter () has the analogous course to that observed experimentally in cuprates. The energy gap in the electron density of states is induced by Z and χ ‐ the contribution from φ is negligible. The electron density of states possesses the characteristic asymmetric form and the pseudogap is observed above the critical temperature.
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Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. 相似文献
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S. Varr 《Fortschritte der Physik》2008,56(1):91-102
Correlations of detection events in two photodetectors placed at the opposite sides of a beam splitter are studied in the frame of classical probability theory. It is assumed that there is always only one photon present in the measuring apparatus during one elementary experiment (one measurement act). Due to the conservation of energy, there is always a strict anticorrelation in one elementary experiment, because the photon cannot excite both of the detectors at the same time. It is explicitely shown in several examples that the “bunching” and “anti‐bunching” of the counts in serieses of elementary single‐photon experiments is governed by the statistical properties of grouping the sequences of the elementary measurements. 相似文献
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I. Kup
i 《Journal of Raman spectroscopy : JRS》2012,43(1):1-5
The triple‐resonant (TR) second‐order Raman scattering mechanism in graphene is re‐examined. It is shown that the magnitude of the TR contribution to the photon‐G′ mode coupling function in graphene is one order of magnitude larger than the widely accepted two‐resonant coupling. Enhancement of the order of 100 in the Raman intensity, with respect to the usual double‐resonant model, is found for the G′ band in graphene, and is expected in the related sp2‐based carbon materials, as well. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Wenxu Yin Xue Bai Xiaoyu Zhang Jia Zhang Xupeng Gao William W. Yu 《Particle & Particle Systems Characterization》2019,36(2)
Molybdenum disulfide (MoS2) quantum dots (QDs) are known for their excitation‐wavelength‐dependent photoluminescent (PL) properties. However, the mechanism of this phenomenon is still unclear. Here, small size MoS2 QDs with a narrow size distribution are synthesized. Based on the decay study and PL dynamics, a reasonable radiation model is presented to understand the special PL properties, i.e., the carrier recombination in the localized surface defect states generated the PL. Accordingly, this optical property is used to fabricate multicolor light‐emitting devices with the same MoS2 QDs. The emission color covers the full visible spectrum from blue to red, only by adjusting the thickness of the down‐conversion QD layers. 相似文献