Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session V12: Optical and Electronic Properties of Graphene Nanoribbons and NanowiresFocus
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Sponsoring Units: DCMP Chair: Su Kong Chong, University of Utah Room: BCEC 153A |
Thursday, March 7, 2019 2:30PM - 2:42PM |
V12.00001: A Stretchable and Bendable CNT-based Resistive Pressure Sensor Anthony Palumbo, Runzhi Zhang, Kang Yan, Greg Hader, Jason Chang, Eui-Hyeok Yang Flexible electronics has directed development and research of unique instrumentation and measurement to achieve conformable sensors for a wide range of applications. Conventional high-performance electronic materials such as silicon are not flexible, whereas flexible materials such as conducting polymers, are often characterized by poor electric properties. Thus, high mobility materials in a flexible configuration are desirable, and carbon nanotubes (CNTs) are promising due to their excellent electric properties and flexibility. Here, we present an all-solid state flexible and stretchable pressure sensor composed of vertically aligned CNTs (VACNTs) partially embedded in polydimethylsiloxane (PDMS). VACNTs are grown via chemical vapor deposition (CVD) and transferred onto PDMS as a stretchable electrode. Two electrodes are placed face-to-face and increased pressure is directly proportional to a detectable change in resistance, enabled by increased contact between opposing electrodes. The resistance is maintained at stretching up to 180%, with a rapid response time during loading and unloading. As a proof-of-concept, the sensor is successfully tested for medical and e-skin applications by measuring biological signals of a person. |
Thursday, March 7, 2019 2:42PM - 2:54PM |
V12.00002: Optical absorption of atomic-precise graphene nanoribbons on insulating substrate Sihan Zhao, Gabriela Borin Barin, Ting Cao, TAIRU LYU, Steven G. Louie, Roman Fasel, Feng Wang We report the reflection contrast spectra of atomic-precise armchair graphene nanoribbons (GNRs) on insulating substrates. As-grown GNRs are transferred from gold to an insulating substrate by the “bubbling” method. Polarization control of light is employed to directly probe the one-dimensional (1D) optical resonances of armchair GNRs with different ribbon widths by the reflection contrast spectroscopy. We observed well-defined 1D optical resonances which are identified as optically-bright inter-band transitions in GNR samples. Our experimental interpretations are further supported by theoretical calculations within the GW framework, which reveals a strong excitonic effect with exceptionally large exciton binding energies. |
Thursday, March 7, 2019 2:54PM - 3:06PM |
V12.00003: Characterization of Atomically Precise Graphene Nanoribbons by Raman Spectroscopy Jan Overbeck, Gabriela Borin Barin, Colin R Daniels, Mickael Perrin, Oliver Braun, Pascal Ruffieux, Vincent Meunier, Roman Fasel, Michel Calame Graphene nanoribbons (GNRs) exhibit an electronic bandgap due to the lateral confinement of charge carriers and edge effects. They can be fabricated by bottom-up on-surface synthesis from molecular precursors resulting in atomically precise structures [1]. This approach promises tunable optical and electronic properties [2]. We use Raman spectroscopy to characterize different types of GNRs and investigate their interaction with growth and devices substrates. In particular, we investigate new geometry-dependent signatures beyond the radial breathing like mode (RBLM) and how they are correlated with charge transport properties. |
Thursday, March 7, 2019 3:06PM - 3:18PM |
V12.00004: Metallic graphene nanoribbons with tunable bandwidth and magnetic properties Jingwei Jiang, Ting Cao, Daniel Rizzo, Gregory Veber, Christopher Bronner, Ting Chen, Felix R Fischer, Michael F Crommie, Steven G. Louie It is known that 7-armchair graphene nanoribbon(AGNR) holds topological end states at its zigzag ends. A superlattice with such end states is predicted to give rise to in-gap bands whose energies differ from the bulk states’ significantly, which will form a well-isolated subspace. Utilizing these characters of the topological states, we develop a novel AGNR superlattice that possesses two zigzag edges per unit cell. We further show using first principle calculations that, by modifying the geometry of such GNRs, it is possible to get metallic GNRs with tunable bandwidth. Explicitly, the occurrence of five-membered rings would change the bandwidth drastically. After including substrate effects, we reach good agreement with experimental results. In addition, we predict that one of the structures would have ferrimagnetic orders based on Lieb’s theorem and confirmed by density functional theory (DFT) calculation. |
Thursday, March 7, 2019 3:18PM - 3:30PM |
V12.00005: Quantum Resonant Tunneling in In-Plate Graphene Nanoribbon/h-BN Heterojunctions Mitsuyoshi Tomiya, Shoichi Sakamoto The first principle calculations of the electrical properties of in-plate hetero-junctions of armchair graphene nanoribbon/hexagonal boron notride(AGNR/h-BN)s are presented. They are carried out using SIESTA package, which consists of numerical codes of the density functional theory(DFT) and the non-equilibrium Green's function(NEGF). The center part is made of two in-plate hetero-junctions of two transverse h-BN arrays embedded into the conductive (3n-1)-family of AGNR((3n-1)-AGNR) and remains two-dimensional. Adopting (3n-1)-AGNR to the both side lead parts, which must be metallic. Two transverse arrays of h-BN, which is wide-gap semi-conductor, act as a double barrier system. The quantum resonant tunneling through the double barrier system is found in the transmission function(TF)s clearly and I-V characteristics of 8, 11, 14-AGNR/h-BN. The TF has sharp peaks in a neighborhood of the Fermi energy due to the tunneling and the I-V characteristics becomes step-wise. The one-dimensional(1D) Dirac equation model is proposed to study double barrier system. Though the 1D Dirac model is very simple, it reproduces most of the peaks of the TF nearby the Fermi energy. The in-plate hetero-junctions of zigzag graphene nanoribbon/h-BN are also discussed. |
Thursday, March 7, 2019 3:30PM - 3:42PM |
V12.00006: Resonance Raman Spectroscopy of 7-Atom Wide Armchair Graphene Nanoribbons Viviane Valquíria Do Nascimento, Eliel Gomes da Silva Neto, Juan P Llinas, Cristiano Fantini, Gabriela Borin Barin, Akimitsu Narita, Müllen Klaus, Roman Fasel, Jeffrey Bokor Graphene Nanoribbons (GNRs) exhibit interesting electronic and optical properties strongly dependent on their width and edge.The bottom-up approach to fabricate graphene nanoribbons leads to a precise width and extremely high edge quality, and, as a consequence of this uniformity, the quantum confinement plays a significant role in its electronic and optical properties. This work reports the optical response of armchair graphene nanoribbons of width N=7 atom (7AGNR) on Si/SiO2 substrate using Raman spectroscopy. The 7AGNR presents a rich Raman spectrum, with more than 20 peaks, in good agreement with the theoretical predictions. At room temperature, the nanoribbons degrade in a few seconds under laser exposition as shown by time series Raman experiments. Under nitrogen atmosphere and low temperature, the degradation process is shown to be much slower, allowing us to perform resonance Raman spectroscopy of the 7AGNR in a wide range of excitation energies. The results show a strong dependence of the Raman spectrum with the excitation energy, with a resonance peak around 2.3 eV in agreement with reflectance experiments. |
Thursday, March 7, 2019 3:42PM - 3:54PM |
V12.00007: Light Emission in Graphene Nanoribbons: Insights from Ab-Initio Simulations Deborah Prezzi, Claudia Cardoso, Andrea Ferretti Graphene nanoribbons (GNRs) have attracted increasing attention in the last decade as a viable route for graphene-based opto-electronic applications, especially in view of the successful production of ultranarrow and atomically precise structures by means of bottom-up techniques. While GNR absorption properties have been addressed in depth [1, 2], emission properties are still largely unexplored. We here report on the optical response of finite-length GNRs as resulting from state-of-the-art ab initio calculations beyond mean field [3, 4]. Our results indicates that bulk-like excitations coexist with below-bandgap states localized at the GNR extremities, which are almost independent on the length. By investigating both the presence of defects and the coupling with a gold tip, our simulations allow us to identify unpredicted optical transitions in GNRs and to elucidate the origin of below-bandgap STM-induced light emission recently observed in suspended GNRs [3], providing a promising route for the realization of bright, robust, and controllable graphene-based light-emitting devices. |
Thursday, March 7, 2019 3:54PM - 4:06PM |
V12.00008: Evolution of bandgap with size in armchair and zigzag graphene quantum dots Ludmila Szulakowska, Yasser Saleem, Louis Najera baldo, Alain Delgado gran, Pawel Hawrylak We present here the evolution of the bandgap energy with size in armchair and zigzag graphene quantum dots (GQDs). The results of the tight binding model are analyzed by dividing zigzag graphene quantum dots into concentric rings. For each ring, the solutions are obtained analytically and then the effect of inter-ring tunneling on the energy gap is determined. The growth of zigzag terminated GQD into armchair GQD is shown to be associated with the addition of a one-dimensional Lieb lattice of carbon atoms with a shell of energy levels in the middle of the energy gap of the inner zigzag GQD. This causes a difference in the nature of the wave functions between zigzag and armchair GQD which manifests itself in the oscillation of the energy gap with increasing size. The evolution of the bandgap with the number of carbon atoms is compared with the notion of confined Dirac Fermions and tested against ab-initio calculations of Kohn-Sham and TD-DFT energy gaps. |
Thursday, March 7, 2019 4:06PM - 4:18PM |
V12.00009: Photoluminescence Quantum Efficiency of III−V Nanowires on Silicon Substrates Yui Clifford, Jiarong Cui, Ho Vinh, Yifei Wang, Vinh Q Nguyen The III−V nanowires monolithically grown on silicon substrates provide promising technologies for |
Thursday, March 7, 2019 4:18PM - 4:30PM |
V12.00010: Gate-tunable Aharonov-Bohm interference in Bi2O2Se nanowires Jianghua Ying, Huaixin Yang, Fanming Qu, Li Lu Semiconducting Bi2O2Se shows excellent air stability and high carrier mobility. High-quality single-crystalline Bi2O2Se nanowires were synthesized by means of gold-catalyzed vapor-liquid-solid growth. We fabricated nanowire-based devices and performed electron transport measurements down to low temperatures. Oscillations in magnetoresistance under the magnetic field oriented parallel to its axis with a period of the magnetic flux quantum were observed. The quantum oscillations which demonstrate the existence of coherent transport through closed-loop quantum states encircling the wire axis also show a tunable phase shift by the gate voltage. The results indicate clear gate-tuned Aharonov-Bohm interference of surface states in a semiconductor nanowire. |
Thursday, March 7, 2019 4:30PM - 4:42PM |
V12.00011: Structural and optical properties of Si2Te3nanowires Jiyang Chen, Jingbiao Cui, Xiao Shen, Thang Hoang, Keyue Wu Si2Te3 has recently attracted attention as a new class of layered 2D materials, which promise useful applications in thermal electrics and chemical sensing. Here, we report a study of the structural and optical properties of Si2Te3nanowires (NW) at various conditions. Single-crystalline Si2Te3NWs were synthesized by using gold nanoparticles as catalysts through the vapor-liquid-solid (VLS) mechanism. It was observed that these NWs prefer to grow along the [0001] direction, which is perpendicular to the 2D layers. Spectral and temporal characteristics of photoexcited carriers in these Si2Te3 NWs were investigated at various temperatures and excitation powers. Photoluminescence spectrum of Si2Te3 NWs was dominated by defect and surface states related emissions at both low and room temperatures. Consequently, the decay time of photoexcited carries strongly depends on the measurements at different temperatures and excitation powers. Our results quantitatively elucidate decay mechanisms that are important towards understanding and controlling of the electronic states in Si2Te3nanostructures for optoelectronic applications. |
Thursday, March 7, 2019 4:42PM - 4:54PM |
V12.00012: Electrically Driven Structural Phase Transition in Single Ag2Te Nanowire Devices Kasun Premasiri, Wei Zheng, Yue Wu, Xuan Gao Exploring new phase–change materials are instrumental in the progression of electronic memory devices. Ag2Te with its reversible structural phase transition, and in the form of nanowires becomes an apt candidate to potentially use in nanoscale memory devices. Here we report a study on the temperature– or electrically–driven phase change properties of crystalline Ag2Te nanowires. We first demonstrate that this structural phase change can be achieved via heating up the nanowires, which results in a sharp drop in conductance. Then we show that a DC voltage (< 1V) induced Joule heating can be used to reach the phase transition, even without any external heating. This work shows the potential of using Ag2Te nanowires as a phase–change material in low voltage and low power nanoscale devices. |
Thursday, March 7, 2019 4:54PM - 5:06PM |
V12.00013: Theoretical Study on VO2 Nanowire Structures for Energy Applications Prabal Bhuyan, Sanjeev K. Gupta, Yogesh Sonvane, P. N. Gajjar Recent studies on electronic, magnetic and optical properties of VO2 (vanadium dioxide) material motivates to explore one-dimensional VO2 nanowire. We have studied the structural and electronic, optical properties of monoclinic and rutile phase of VO2 nanowire by performing first-principles calculations. The monoclinic phase showed semiconducting behaviour with a band gap of 1.17eV, while its bulk form showed a band gap of 0.7eV. The rutile phase behaves like as spin gapless semiconducting material. The rutile phase of VO2 NW could find its applications in spintronic devices. We have also investigated the effect of SO2, CO2 and N2 gas dopant on the monoclinic structure of VO2 nanowire. The optical properties, density of states (DOS) have been investigated to understand the effect of dopant. It is clear from our results that the VO2 monoclinic NW could likely to open up its application as an optical gas sensor. |
Thursday, March 7, 2019 5:06PM - 5:18PM |
V12.00014: Nano-wire to Film Transitions During Pulsed-Laser Deposition: the Role of Plasma Plume Expansion Davide Del Gaudio, Carl T Boone, Kaitlyn Sallans, Erica Mason, Andrew Williamson, Sneha Yarlagadda, John Heron, Ilan Shalish, Rachel Goldman Due to their high conductivity, optical transparency, and high surface/volume ratio, indium-tin oxide (ITO) nanowires (NWs) are promising for flexible transparent electronics and gas sensors. During pulsed laser deposition (PLD) of ITO, NWs vs. films are typically selected via inert vs reactive atmospheres. In other studies, both NWs and films are observed during PLD in inert atmospheres.1 Here, we the consider the influence of the plasma plume expansion on NW vs film formation. For low pressure N2, we hypothesize that oxygen is strongly scattered, leaving a metal-rich plume, resulting in metal droplet formation, followed by vapor-liquid-solid growth of NW. As the N2 pressure is increased, the plasma plume and its metal rich core are compressed, resulting in a transition to films growth. This approach is likely applicable to a wide variety of metal-oxide NW core-shell structure for nanoscale devices. |
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