Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S51: Focus Session: Beyond Graphene Devices: Function, Fabrication, and Characterization VI |
Hide Abstracts |
Sponsoring Units: DMP Chair: Bernhard Urbaszek, CNRS Toulouse Room: Mile High Ballroom 1E |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S51.00001: The impact of crystalline inhomogeneity on electrical transport and 1/$f$ noise in MoS$_{2}$ field effect transistor Subhamoy Ghatak, Sumanta Mukherjee, D.D. Sarma, Arindam Ghosh We show that both conductivity and low frequency 1/$f$ noise are strongly influenced by the presence of localized trap states in ultra-thinMoS$_{2}$ field effect transistor. The trap states not only create Coulomb scattering of charge carriers but also slowly exchange carrier with channel. The trap density is quantitatively calculated which turns out two orders of magnitude higher than the typical SiO$_{2}$ surface trap density. This suggests a structural origin of the trap states in MoS$_{2}$ films. The result was also supported by similar noise measurement on MoS$_{2}$ devices on trap free hexagonal boron nitride substrate. The origin of these states is also investigated by spectroscopic studies, which indicate a possible presence of metallic 1T-patches inside the major semiconducting 2H phase. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S51.00002: Nanoscale friction for strain engineering: a case study of MoS$_2$ Jason Christopher, Alexander Kitt, Xuanye Wang, Anna Swan, Bennett Goldberg 2D materials are superior to 3D materials in their ability to withstand large deformations without failure and so large strains can be applied to engineer electrical and optical properties. To control precisely the location, magnitude and direction of a strain field it is critical to understand the friction between the 2D layer and supporting substrate since sliding alters the strain distribution. Here we use MoS$_2$ covered microchambers strain tuned by applying a variable external pressure that deflects the suspended membrane creating strain in both the suspended and supported regions. This allows us to determine the friction between mono, bi and tri layer MoS$_2$ and SiO$_2$ as well as discern the strain dependence of the band-gap and Gr\"{u}neissen parameters of MoS$_2$. The friction between MoS$_2$ and SiO$_2$ is compared with the friction between graphene and SiO$_2$. These results are essential for strain engineering applications of MoS$_2$ and to all 2D materials by establishing this method for measuring friction. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S51.00003: Temperature dependent optical properties and thermal conductivities of single- and few-layer MoS$_{2}$ Xian Zhang, Dezheng Sun, Gwan-Hyoung Lee, Yumeng You, Xu Cui, Tony Heinz, James Hone, Yilei Li The transition metal dichalcogenide, MoS$_{2}$ have shown unique optical and electrical properties, such as band structure transition, high mobility, and strong photoluminescence, in a monolayer form. Here we investigate the thermal transport properties in exfoliated monolayer and bilayer MoS$_{2}$. By measuring the Raman peak shift in response to laser heating, and the Raman peak shift with temperature variation, we obtain the room-temperature thermal conductivity and the interface conductance of about (75+34/-26)W/mK and (0.24+0.06/-0.06)MW/m$^2$K for supported monolayer MoS$_{2}$. And the thermal conductivity of the suspended monolayer MoS2 is around (81+12/-11)W/mK at room temperature, and (60+11/-9)W/mK at 500K. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S51.00004: Exciton dynamics in a single layer MoS2 Jonghwan Kim, Xiaoping Hong, Sufei Shi, Chenhao Jin, Yinghui Sun, Feng Wang In a low dimensional semiconductor, exciton plays a crucial role in the optical property. Recently, a single layer of MoS2 has attracted significant attention due to its unique excitonic features. For example, exciton in MoS2 is predicted to have order of magnitude larger binding energy than conventional direct band gap material. For deeper understanding on such properties, however, it is important to understand how exciton is formed and decays in time domain. Our work on exciton dynamics in MoS2 by pump probe spectroscopy will be presented with control of both power and wavelength. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S51.00005: Temperature Dependent Raman Studies on Liquid Phase Exfoliated MoS2 Mitchell Connolly, Andrew Winchester, Peter Hale, Keshav M. Dani, Saikat Talapatra We investigate on the temperature dependence of in-plane E12g and out-of-plane A1g Raman modes of few-layer MoS2 prepared using the liquid-phase exfoliation method. Structural characterization performed after exfoliation using transmission electron microscopy (TEM) indicate the resultant material contains small, submicron size, few-layer flakes. Raman measurements indicating material thickness of 6 layers or fewer were observed at room temperature using a 532 nm laser line (E12g$=$381.4 cm-1 and A1g$=$405.8 cm-1). The Raman peak shifts indicate a linear dependence on temperature within the range 293 K to 77 K. The measured temperature coefficients of E12g and A1g modes will be presented and compared with other similar experimental/theoretical data available. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S51.00006: Temperature and Power Dependent Photoluminescent Spectroscopy of MoS$_2$ M. Watson, J.R. Simpson, R. Yan, H.G. Xing, X. Wu, T. Luo, S. Bertolazzi, J. Brivio, A. Kis, A.R. Hight Walker We report temperature and power dependent photoluminescence (PL) of molybdenum disulphide (mos). Mechanical exfoliation of mos, from bulk provides single-layer flakes which are then transferred either to sapphire substrates or suspended over holes in Si/Si$_3 $N$_4$. We measure temperature dependence from $\approx$100\,K to 400\,K and power dependence from $\approx$6\,$\mu$W to $\approx$7\,mW using an Argon laser at 514.5\,nm and a HeNe laser at 632.8$\,$nm. The PL spectrum exhibits a main exitonic peak(A) at $\approx$1.87\,eV which consist of both neutral excitons and charged trions (A- or A+) [1]. The A exciton peak and the A- exciton peak redshift and broaden with increasing temperature and power. Along with the A peak, we observe a lower energy bound exciton (BE) that is likely related to defects. The BE,a broad peak centred at $\approx$1.7\,eV, linearly redshifts and narrows with increasing power. The power dependence of both the main and bound peak saturates above 0.5\,mW. Raman temperature and power dependence will also be discussed [2]. \\[4pt] [1] KF. Mak et al. Nat. Mat 12,207(2013).\\[0pt] [2] R.Yan and J.R.Simpson, S. Bertolazzi and J. Brivio, M. Watson, X.Wu and A. Kis, T.Luo, H.G.Xing, A.R. Hight Walker, (submitted ACS Nano 2013) [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:48AM |
S51.00007: Photoemission Spectroscopy of 2D Electron Systems Invited Speaker: ZX Shen |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S51.00008: Ultrafast Optical Spectroscopy of Excitons in Monolayer WSe$_{2}$ Grant Aivazian, Hongyi Yu, Sanfeng Wu, Aaron Jones, Nirmal Ghimire, Jiaqiang Yan, David Mandrus, David Cobden, Wang Yao, Xiaodong Xu Recently there has been tremendous interest in monolayer transition metal dichalcogenides due to their true two-dimensional nature and strong excitonic properties. Photoluminescence measurements have shown strong emission from both neutral and charged exciton species, as well as valley-selective optical excitation and even signatures of valley coherence. Here we report on the dynamic nature of these excitons by resonant optical excitation in monolayer tungsten diselenide. Using ultrafast degenerate pump/probe spectroscopy we probe the differential reflection signal as a function of excitation energy and time delay. We have developed a theory from which we are able to extract the excited exciton population and lifetimes. These measurements provided critical information for future excitonic devices involving tungsten diselenide and opens up future work investigating the rich two-dimensional physics inherent in this material. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S51.00009: Photoluminescence spectroscopy of monolayer MoSe$_2$ in magnetic fields David MacNeill, Colin Heikes, Zachary Anderson, Kin Fai Mak, Kathryn McGill, Jiwoong Park, Paul McEuen, Daniel Ralph Single layer transition metal dichalcogenides are direct gap semiconductors with unique luminescence properties, including large excitonic effects and coupling between photon handedness and the exciton valley degree of freedom. Furthermore, the luminescence spectra may change under magnetic field due to valley degeneracy breaking, the Zeeman effect and Landau level formation. Here we report measurements of photoluminescence spectra for monolayer MoSe$_2$ at temperatures ranging from 4.2K to 300K and in out-of-plane magnetic fields up to 7T. The measurements are performed using a scanning confocal microscope integrated with a superconducting magnet dewar, with light coupled in and out of the system via an optical fiber. We observe luminescence peaks from the neutral and charged exciton, and explore the evolution of the peak energies, linewidths and intensities as a function of applied field and gating. We will also discuss the magnetic field dependence of the photoluminescence handedness in the Faraday geometry and its implications. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S51.00010: Atomic Resolution Transmission Electron Microscopy of Defects in Hexagonal Boron Nitride and Graphene Ashley Gibb, Nasim Alem, Chengyu Song, Jim Ciston, Alex Zettl Monolayer sheets of sp2-bonded materials such as graphene and hexagonal boron nitride (h-BN) have been studied extensively due to their properties including high mechanical strength, thermal conductivity, stability, interesting electronic properties, and potential for integration into novel devices. Understanding the atomic scale structure of defects in these materials is important because defects can significantly affect the physical properties in these materials. In particular, understanding the dynamics of these defects explains much about the material's stability. We have synthesized h-BN and graphene using low pressure chemical vapor deposition and imaged defects using atomic resolution aberration corrected transmission electron microscopy. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S51.00011: Photocurrent spectroscopy of excitons in ultraclean two-dimensional semiconductors - Part I A.K.M. Newaz, A.R. Klots, Bin Wang, Sokrates Pantelides, Kirill Bolotin The intrinsic properties of a monolayer materials can be perturbed by substrate-related disorder. To decrease the amount of disorder in a representative 2D material, monolayer molybdenum disulfide (MoS$_2$), we have fabricated suspended field effect devices. Upon suspension, we have observed a tenfold increase in carrier field effect mobility. Further cleaning of suspended devices through thermal annealing renders them nearly insulating at small bias voltages, which is expected for a pristine semiconductor with its Fermi energy in the middle of the bandgap and precludes detailed electrical characterization. To probe the intrinsic properties further, we have conducted photocurrent (PC) spectroscopy measurements. In every measured device, we have observed the following universal features: (i) sharp peaks in PC at $\sim 1.9$eV and $\sim 2.1$eV attributable to the optical transitions due to band edge excitons; (ii) a rapid onset of PC above $\sim 2.5$eV peaked at $\sim 2.9$eV, which we attribute to an excitonic absorption due to the van Hove singularity of MoS$_2$. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S51.00012: Photocurrent spectroscopy of excitons in ultraclean two-dimensional semiconductors -- Part II Andrey Klots, A.K.M. Newaz, Bin Wang, Sokrates Pantelides, Kirill Bolotin We investigate excitonic physics in pristine suspended monolayer molybdenum disulfide (MoS$_{2})$ by means of low-temperature photocurrent spectroscopy. Measured photocurrent spectra exhibit a robust set of features, including peaks at $\sim$ 1.9, 2.1 and 2.9 eV. We interpret the peaks around 1.9 and 2.1 eV as due to optical absorption by direct band edge excitons of MoS$_{2}$ and ascribe the peak at 2.9 eV to an excitonic transition associated with the van Hove singularity of MoS$_{2}$. We interpret the nature and binding energy of these states using a combination of first-principles calculations and simple mathematical models. Furthermore, we use source-drain bias dependence of the photocurrent to investigate dissociation mechanisms of the excitons. Finally, we study the photocurrent response of bilayer and multilayer MoS$_{2}$ samples, as well as that of other transition metal dichalcogenides, such as MoSe$_{2}$ and WSe$_{2}$. Comparison of photocurrent spectra of these materials to that of monolayer MoS$_{2}$ allows us to investigate the effects of confinement and spin-orbit interaction. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S51.00013: Temperature Dependent Optical Spectroscopy of Defect States in Monolayer Molybdenum Disulphide Field Effect Transistors Changjian Zhang, Haining Wang, Wei Min Chan, Sandip Tiwari, Farhan Rana Understanding the properties of defects is critical for improving 2D metal dichalcogenide materials and devices, yet little work in this field has been reported. We present optical spectroscopy (photoluminescence and absorption) studies of defects states in monolayer MoS2 field effect devices at different temperature. At low temperatures, a very large defect peak around $\sim$ 1.7 eV is seen in the PL spectra but not in the absorption spectra. The PL intensity decreases exponentially with temperature and vanishes when the temperature exceeds $\sim$ 150K. The PL quantum efficiency becomes extremely large when a negative gate bias is applied. Our data suggests the presence of both bright and dark defect states that contribute to recombination, and that the occupation of these defect states is accompanied by lattice distortions. The competition in the recombination process between these two kinds of defect states explains the temperature dependence as well as the gate bias dependence of our data. We find that, occupation of the dark defect states is thermally activated and their occupation quenches the PL from the bright defects. We attribute the defect states to originate from sulfur or molybdenum vacancies or to the presence of oxygen atoms. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700