Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y17: Focus Session: Graphene Devices: Optical and Opto-electronics |
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Sponsoring Units: DMP Chair: Xiao Li, University of Maryland Room: 102AB |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y17.00001: Graphene- and quantum well-based dipolariton nanodevices for integrated optical circuits German V. Kolmakov, Tim Byrnes, Roman Ya. Kezerashvili Application of dipolaritons, which are a quantum superposition of photons, direct excitons and indirect excitons, in an optical microcavity for the design of nanoscale devices for optical computing is considered. In the proposed setup, a dipolariton condensate is formed in a patterned microcavity with an embedded two-layer gapped graphene. The condensate propagates in quasi-one dimensional channels formed by the pattern, and its propagation is controlled by the gate voltage applied to a positively-charged hole-carrying graphene layer. The advantage of the dipolartions, compared to the conventional polaritons formed by the direct excitons and photons, is in the possibility to drive the condensate by the electric force since the latter is directly applied the dipolaritons. A dipolariton switch based on a Y-shaped channel is considered and its performance is determined via numerical simulations of the dipolartion condensate dynamics. The tunability of the device functions by the application of an external electric field is discussed. The simulations for a Y-shaped switch is also performed for a patterned microcavity with embedded coupled quantum wells and the results are compared with those for a microcavity with graphene. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y17.00002: Terahertz hot electron bolometric detectors based on graphene quantum dots A El Fatimy, R.L. Myers-Ward, A. K. Boyd, K. M. Daniels, D.K. Gaskill, P. Barbara We study graphene quantum dots patterned from epitaxial graphene on SiC with a resistance strongly dependent on temperature. The combination of weak electron-phonon coupling and small electronic heat capacity in graphene makes these quantum dots ideal hot-electron bolometers. We measure and characterize the THz optical response of devices with different dot sizes, at operating temperatures from 2.5K to 80K. The high responsivity, the potential for operation above 80 K and the process scalability show great promise towards practical applications of graphene quantum dot THz detectors. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y17.00003: Position dependent photodetection of graphene field effect transistors Biddut Sarker, Edward Cazalas, Isaac Childres, Igor Jovanovic, Yong Chen The extraordinary optical and electronic properties of graphene make it a promising component of high-performance photodetectors. Most graphene photodetectors studied so far require light illumination either on the graphene or at the graphene/metal interface. In this talk, we report a study of the spatial dependence of photoresponse in back-gated graphene field effect transistors (GFET) on undoped semiconductor substrates by scanning a focused laser spot across and away from the GFETs. We find that the photocurrent and photoresponsivity can be varied by a few orders of magnitude depending on the laser illumination position. Our observation can be explained using a numerical model based on the charge transport of photoexcited carriers in the substrate. This work may enable position sensitive photodetectors and further developments of graphene-based optoelectronic devices. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y17.00004: Optical rectification at visible frequency in biased bilayer graphene F. Hipolito, Vitor M. Pereira The second order response of the electrical current to an electromagnetic field is analyzed within the framework of non-equilibrium many-body perturbation theory for the case of a two-dimensional electronic system such as graphene and its bilayer. The absence of inversion symmetry in a biased graphene bilayer allows a finite DC response in second order to an AC electromagnetic wave. The induced DC current is evaluated for biased bilayer at finite temperature, and its tunability is analyzed as a function of electron density, which can be experimentally varied by means of a global gate voltage applied to the sample. Both intrinsic and photon drag microscopic processes are considered, as they contribute on similar footing to the photocurrent in general. However, the dependencies of these two contributions on the polarization state of the incident light are different, which allows the manipulation of the relative contribution of intrinsic versus photon drag contributions by tuning the experimental parameters. For example, the photocurrent emerging from circularly polarized light stems entirely from photon drag, as the circular photogalvanic effect is forbidden by the $C_3$ rotation symmetry of the honeycomb lattice. [Preview Abstract] |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y17.00005: Graphene-Boron Nitride Heterostructure Based Electro-Optical Modulator Yuanda Gao, Ren-Jye Shiue, Xuetao Gan, James Hone, Dirk Englund Graphene, a two-dimensional atomic-scale carbon based material, exhibits uniform absorption of the incident light over a broad spectrum range from visible to mid-infrared. This absorption can be tuned by electrostatic doping, resulting in electro-absorptive modulation of the incident light. We propose and demonstrate a high-speed electro-optical modulator structure by using a high-mobility dual-layer graphene capacitor integrated with a planar silicon photonic crystal nanocavity. Strongly enhanced light-matter interaction of graphene in a sub-micron meter cavity enables efficient electrical tuning of the cavity reflection. We achieved a modulation depth of 3.2 dB within a voltage swing of only 2.5 V; we measured a 3dB cut-off frequency up to 1.2 GHz. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y17.00006: Asymmetric transmission of terahertz waves in graphene-loaded photonic systems Yu Zhou, Ren-Hao Fan, Qing Hu, Ru-Wen Peng, Mu Wang In this work, we have proposed two types of graphene-loaded photonic systems, through which terahertz(THz) waves present asymmetric transmission tuned by external magnetic field. One is a graphene-loaded metal grating. It is found that resonant modes in the system can be converted between transverse-electric and transverse-magnetic polarizations due to Hall conductivity of graphene. As a consequence, asymmetric transmission of THz waves through this graphene-loaded metal grating is achieved. The other is a photonic crystal cavity integrated with graphene. Non-reciprocal propagation of THz waves has been verified in this system. By adjusting the external magnetic field or the Fermi level of graphene, asymmetric wave propagation can be significantly tuned. Our investigations offer unique approaches to achieve potentially applications in the design of the graphene-loaded tunable devices such as THz isolators and diodes.\\[4pt] References: Y. Zhou, Y.Q. Dong, R.H. Fan, Q. Hu, R.W. Peng and M. Wang, Appl. Phys. Letts 105, 041114 (2014). Y. Zhou, Y.Q. Dong, K. Zhang, R.W. Peng, Q. Hu and M. Wang, EPL 107, 54001(2014). Y. Zhou, C. Wang, D.H. Xu, R.H. Fan, K. Zhang, R.W. Peng, Q. Hu and M. Wang, EPL 107, 34007 (2014). [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y17.00007: Photoresponse and light trapping in nanowire array-graphene interfaces Tito Huber, Scott Johnson, Quinton Barclift, Tina Brower, Jeffrey H. Hunt, John H. Belk Graphene is emerging as an optical material that features tunability by electrostatic doping and a photothermoelectric response, however it features low optical absorption. We studied interfaces between nanowire arrays and graphene and also other transparent electrodes such as indium tin oxide films. The nanowire arrays were fabricated using a template method. Graphene was transferred from copper substrates. The interfaces were characterized with a number of tools including Scanning Electron microscopy, Raman spectroscopy and optical reflectance. We also studied the photocurrent through the interface in particular the temporal and wavelength dependence that are revealing of the characteristic thermoelectric origin of the signal. In the photocurrent tests we employed devices composed of nanowire arrays which are capped with the transparent electrode. Interestingly, we observed that the interface has low optical reflectivity and high optical absorption, which we will discuss in terms of enhanced optical trapping. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y17.00008: Terahertz modulators based on multiple non-Bernal graphene layers Ioannis Chatzakis, Zhen Li, Alexander Benderskii, Stephen Cronin We investigate a THz modulator based on a stack of disoriented the non-Bernal stacks graphene layers (GLs) grown by chemical vapor deposition method (CVD) on SiO$_{2}$ substrate [1]. The non-Bernal stacking GLs results in the electron decoupling of the GLs, [1,2] higher interband absorption and exhibit the same energy spectrum of the charge carriers to that in individual GLs. The detection efficiency in room temperature is high due low probability of the high energy of the optical phonons ($\sim$ 0.2 eV) absorption. Using terahertz time- domain spectroscopy, we show that the multi graphene layers exhibit fairly high responsivity due to high quantum efficiency. \\[4pt] [1] V. Ryzhii, \textit{et al}., Opto-Electron. Rev., \textbf{20}, 1, (2012)\\[0pt] [2] M. Orlita, \textit{et al}., Semicond. Sci. Tech. \textbf{25}, 063001, (2010)\\[0pt] [3] M. Sprinkle, \textit{et al}., Phys. Rev. Lett. \textbf{103}, 226803 (2009) [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y17.00009: Optical Plasmonic Switch based on Graphene Kyungsun Moon, Suk-Young Park We have studied an electro-optical plasmonic waveguide, which controls the transmission of incident light by switching the coupling of the surface plasmon polariton (SPP) localized on graphene. It has been previously shown that the propagation length of the SPP localized on the copper surface can be effectively reduced by a factor of two or three by applying external bias potential. In our study, we have demonstrated that the propagation length of the SPP localized on graphene can be dramatically reduced by a factor of ten or so and the wavelength of SPP can be reduced by several hundredths of that of the incident light as well. We have also investigated the effect of scattering times of graphene and active Si layer on switching line shape. Switching occurs upon varying the carrier density of Si layer by ?n/n$_c$$\sim$1\% in the vicinity of switching region. For a fixed bias voltage applied just below the critical value, signal laser beam shone into the metal nano-particles may increase the carrier density as such, which will induce switching. This may help develop an all-optical nano-scale plasmonic switch. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y17.00010: Time-of-flight photoconductivity in polymer/graphene blends Gvido Bratina, Egon Pavlica, Srinivasa Rao Pathipati, Robert Nawrocki, Raveendra Penumala We have used time-of-flight (TOF) photoconductivity measurements to assess the electric charge transport parameters in thin layers of poly(3-hexyl thiophene-2,5-diyl) (P3HT) mixed with single and multiple-layer graphene nanoflakes. Thin layers were cast from a solution and two co-planar metal electrodes were deposited by vacuum evaporation on top. An electric field was set up between the electrodes A laser pulse was used to photogenerate charge carriers near the biased electrode, and time dependence of the photocurrent (I(t)) was measured at the opposite electrode. I(t) curves were confronted to I(t)s obtained by a Gaussian-disorder Monte Carlo simulations, adapted to thin-film geometry. The simulations included a position-dependent electric field between two coplanar electrodes, which importantly affects the charge carrier transport through the blend between the electrodes. Comparison between the simulated and measured I(t)s resulted in values for charge carrier mobility, average charge velocity and variation of charge velocity. Our results show that the hole mobility in blends is increased by more than an order of magnitude in comparison to the hole mobility of a neat layers of P3HT [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y17.00011: Optical and electronic properties study of bottom-up graphene nanoribbons for photovoltaic applications Cesar E.P. Villegas, Alexandre Rocha Graphene nanoribbons (GNRs), turn out to be serious contender for several optolectronic applications due to their physical properties. Recently, bottom-up methods, using the assembly of appropriate precursor molecules were shown to be an exciting pathway towards making precise nanoribbons. In particular, it has been demonstrated that so-called cove-shaped GNRs absorb light in the visible part of the spectrum, suggesting they could be used for photovoltaic applications. In solar cells, the key ingredient is the presence excitons and their subsequent diffusion along a donor material. This is influenced by the character of the different excitations taking place, as well as, the exciton binding energy. Thus, In this work we use many-body corrected density functional theory to simulate the optical properties of these nanoribbons. We elucidate the most important transitions occurring in these systems, and identify types of excitatiions that have not been previously observed in conventional nanoribbons. We also find that the exciton binding energies for all the structures we considered are in the eV range, which enhances the diffusion lengths for the particle-hole pairs. Finally, we estimate the potencial of these systems as solar cells by calculating the short-circuit current. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y17.00012: Graphene Oxide Liquid Crystals for Reflective Display without Polarizing Optics Zhuan Zhu, Liqun He, Jian Ye, Min Shuai, Xufeng Zhou, Yanan Wang, Yang Li, Zhihua Su, Haiyan Zhang, Ying Chen, Zhaoping Liu, Zhengdong Cheng, Jiming Bao The recent emergence of liquid crystals of atomically thin two-dimensional (2D) materials not only has allowed us to explore novel phenomena of macroscopically aligned 2D nanomaterials but also has provided a route toward their controlled assembly into three-dimensional functional macrostructures. Using flow-induced mechanical alignment, we prepared flakes of graphene oxide (GO) in different orientational orders and demonstrated that GO liquid crystal (LC) can be used as a rewritable medium for reflective display without polarizing optics. With a wire or stick as a pen, we can make the surface of GO LC reflective and bright, and we can then manually draw lines, curves, and any other patterns with dark appearance. The contrast between bright and dark features is due to anisotropic optical responses of ordered GO flakes. Since optical anisotropy is an intrinsic property of 2D structures, our observations and demonstration represent one of many potential applications of macroscopically aligned 2D nanomaterials. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y17.00013: Development of graphene oxide materials with controllably modified optical properties Anton Naumov, Charudatta Galande, Aditya Mohite, Pulickel Ajayan, R. Bruce Weisman One of the major current goals in graphene research is modifying its optical and electronic properties through controllable generation of band gaps. To achieve this, we have studied the changes in optical properties of reduced graphene oxide (RGO) in water suspension upon the exposure to ozone. Ozonation for the periods of 5 to 35 minutes has caused a dramatic bleaching of its absorption and the concurrent appearance of strong visible fluorescence in previously nonemissive samples. These observed spectral changes suggest a functionalization-induced band gap opening. The sample fluorescence induced by ozonation was found to be highly pH-dependent: sharp and structured emission features resembling the spectra of molecular fluorophores were present at basic pH values, but this emission reversibly broadened and red-shifted in acidic conditions. These findings are consistent with excited state protonation of the emitting species in acidic media. Oxygen-containing addends resulting from the ozonation were detected by XPS and FTIR spectroscopy and related to optical transitions in localized graphene oxide fluorophores by computational modeling. Further research will be directed toward producing graphene-based optoelectronic devices with tailored and controllable optical properties. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y17.00014: Determination of graphene layer thickness using optical image processing Monica Cook, R.G. Mani Graphene, a single atomic layer of carbon arranged in a hexagonal lattice structure, is a valuable material in a wide range of research. A significant impediment to graphene research is the need to manually characterize the thickness of high-quality graphene produced via mechanical exfoliation. Traditional methods of characterizing the layer thickness of graphene, including Raman spectroscopy and atomic force microscopy, require expensive equipment and can be damaging to the graphene sample. We examine here a known alternative method for quantitatively determining the layer thickness of graphene on SiO$_{2}$/Si based on optical image processing, which is quick, inexpensive, and non-invasive [1]. Using RGB images of a candidate graphene sample and a background image, taken with a simple optical microscope and charge-coupled device (CCD) camera, we process the images with an algorithm based on Fresnel's law to obtain the contrast spectrum. Each layer of graphene exhibits a unique contrast spectrum for its particular substrate, which is measured and used for accurate layer identification. We also discuss how this algorithm can be generalized to characterize the thickness of other promising two-dimensional materials as well as more complex structures on a variety of substrates. \\[4pt] [1] Ni, Z. H., H. M. Wang, J. Kasim, H. M. Fan, T. Yu, Y. H. Wu, Y. P. Feng, and Z. X. Shen. ``Graphene thickness determination using reflection and contrast spectroscopy.''~\textit{Nano letters}~7, no. 9 (2007): 2758-2763. [Preview Abstract] |
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