Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Q37: Focus Session: Beyond Graphene Devices: Function, Fabrication, and Characterization V |
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Sponsoring Units: DMP Chair: Wenjuan Zhu, IBM Watson Research Center Room: 705/707 |
Wednesday, March 5, 2014 2:30PM - 2:42PM |
Q37.00001: Graphene-MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics Lili Yu, Han Wang, Yi-Hsien Lee, Xi Ling, Yong-Cheol Shin, Elton J.G. Santos, Efthimios Kaxiras, Jing Kong, Tomas Palacios Two-dimensional (2D) materials have generated great interest in the last few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS$_{2})$ and insulating Boron Nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency and favorable transport properties for realizing electronic, sensing and optical systems on arbitrary surfaces. In this work, we develop several etch stop layer technologies that allow the fabrication of complex 2D devices and present for the first time the large scale integration of graphene with molybdenum disulfide (MoS$_{2})$, both grown using the fully scalable CVD technique. Transistor devices and logic circuits with MoS$_{2}$ channel and graphene as contacts and interconnects are constructed and show high performances. In addition, the graphene/MoS$_{2}$ heterojunction contact has been systematically compared with MoS$_{2}$-metal junctions experimentally and studied using density functional theory. The tunability of the graphene work function significantly improves the ohmic contact to MoS$_{2}$. These high-performance large-scale devices and circuits based on 2D heterostructure pave the way for practical flexible transparent electronics in the future. [Preview Abstract] |
Wednesday, March 5, 2014 2:42PM - 2:54PM |
Q37.00002: Sources of disorder in double-gated graphene-insulator-graphene tunneling devices Sergio de la Barrera, Tania Roy, Randall Feenstra, Eric Vogel We demonstrate vertical tunneling through layered graphene / hexagonal boron nitride / graphene heterostructures and investigate the resulting non-linear current-voltage characteristics and gated operation of this device. Some devices show negative differential resistance and steep switching due to a novel resonant tunneling mechanism caused by the graphene density of states, while other devices lack this intriguing feature. We explain the differences in experimental findings by modeling the dominant forms of disorder that can occur in these devices. While certain aspects of current experimental results can be explained in terms of finite-size effects and charge impurities in the surrounding materials and substrate, it is evident that additional forms of disorder remain to be understood. [Preview Abstract] |
Wednesday, March 5, 2014 2:54PM - 3:06PM |
Q37.00003: The Coherent Interlayer Resistance of a Single, Misoriented Interface between Two Graphite Stacks Roger K. Lake, K. M. Masum Habib, Somaia Sylvia, Supeng Ge, Mahesh Neupane The coherent, interlayer resistance of a misoriented, rotated interface between two stacks of AB graphite is determined for a variety of misorientation angles ranging from $0^{\circ}$ to $27.29^{\circ}$. The quantum-resistance of the ideal AB stack is on the order of 1 to 10 m$\Omega \mu{\rm m}^2$ depending on the Fermi energy. For small rotation angles $\leq 7.34^{\circ}$, the coherent interlayer resistance exponentially approaches the ideal quantum resistance at energies away from the charge neutrality point. Over a range of intermediate angles, the resistance increases exponentially with primitive cell size for minimum size cells. A change of misorientation angle by one degree can increase the primitive cell size by three orders of magnitude. These large cell sizes may not follow the exponential trend of the minimal cells especially at energies a few hundred meV away from the charge neutrality point. At such energies, their coherent interlayer resistance is likely to coincide with that of a nearby rotation angle with a much smaller primitive cell. The energy dependence of the interlayer transmission is described and analyzed. [Preview Abstract] |
Wednesday, March 5, 2014 3:06PM - 3:42PM |
Q37.00004: Van der Waals heterostructures Invited Speaker: Roman Gorbachev Research on graphene and other two-dimensional atomic crystals is intense and is likely to remain one of the leading topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. In this talk I will review our recent progress on fabrication and investigation of such heterostructures starting from ultrahigh quality graphene encapsulated in h-BN up to complex 6-layer structures comprised of several materials. Significant attention will be paid to Moir\'{e} patterns with associated Hofstadter-like states in graphene. [Preview Abstract] |
Wednesday, March 5, 2014 3:42PM - 3:54PM |
Q37.00005: Electrical transport properties of metal and graphene contacts to MoS$_2$ Yunqiu (Kelly) Luo, Hua Wen, Tiancong Zhu Two-dimensional crystals are an exciting class of materials for novel physics and nanoelectronics. MoS$_2$ and related transition metal dichalcogenides have received tremendous interest due to its native band gap and strong spin orbit coupling. Unlike graphene, the presence of the band gap leads to transistors with high on-off ratios. One important issue is the electrical properties of the contacts to the MoS$_2$. Recent studies have shown the presence of a Schottky barrier and its dependence on the metal workfunction, back gate voltage, and interfacial oxide barriers. In this work, we investigate the interfacial properties of metal to MoS$_2$ contact and graphene to MoS2 contact by studying the junction's Schottky barrier formation and bias dependence. We utilize a polymer based transfer method to precisely position exfoliated graphene flakes onto exfoliated MoS$_2$ flakes. We intensively study various junction combination between monolayer/few-layer graphene and monolayer/few-layer MoS$_2$. Dependence on temperature and back gate will be discussed. [Preview Abstract] |
Wednesday, March 5, 2014 3:54PM - 4:06PM |
Q37.00006: Carbon nanotube- MoS2 p-n junction: Fabrication and transport properties Udai Bhanu, Muahmmad Islam, Saiful Khondaker Integrating two different nanoscale semicondcutors of opposite carrier types are of great interest for many electronic and optical applications. Few layers molybdenum disulfide (MoS$_{2})$ is an n-type semiconductor while semiconductoing single walled carbon nanotubes (SWNT) show p-type behavior. In this work, we demonstrate a simple technique for integrating these two semiconductors for fabricating a p-n junction. Few layers MoS$_{2}$ device were mechanically exfoliated from a single crystal of MoS$_{2}$ and making electrical contact via electron beam lithography. Another pair of electrodes, which are orthogonal to MoS$_{2}$ device, is deposited and semiconducting reach SWNT(s-SWNT) solution was dielectrophoretically assembled between the second pair of electrodes. The s-SWNT goes over the MoS$_{2}$ and fabricates two p-n junctions. We will discuss the electronic transport properties of the fabricated devices. [Preview Abstract] |
Wednesday, March 5, 2014 4:06PM - 4:18PM |
Q37.00007: Charge transport and optoelectronic process in an atomically thin p-n junction Chul-Ho Lee, Gwan Hyung Lee, Arend van der Zande, Wenchao Chen, Yilei Li, Minyong Han, Xu Cui, Ghidewon Araffe, Colin Nuckolls, Tony F. Heinz, Jing Guo, James Hone, Philip Kim Heterostructures based on atomically thin van der Waals materials provide an unprecedented opportunity in new materials design. In particular, the ability to assemble two-dimensional (2D) materials into artificial heterostructures with atomically sharp interfaces, combined with recent rediscoveries of transition metal dichalcogenides as an atomically thin semiconductor, enables to build the unique 2D semiconductor heterojunction for fundamental studies as well as device applications. In this talk, we present the electronic and optoelectronic processes in an atomically thin p-n junction consisting of vertically stacked WSe$_{2}$ and MoS$_{2}$ monolayers. Unlike conventional p-n junctions, tunneling-mediated recombination governs the overall charge transport, and gate-tunable photovoltaic response is driven by charge transfer at the atomically sharp interface with large band offsets. Furthermore, the fully vdW heterostructured vertical p-n junctions with graphene electrodes will be discussed. [Preview Abstract] |
Wednesday, March 5, 2014 4:18PM - 4:30PM |
Q37.00008: Graphene/MoS$_{2}$ Schottky diodes and their integration for metal base transistors Amelia Barreiro, Jason Seol, Chul-ho Lee, Inanc Meric, Elton Santos, Lei Wang, Efthimios Kaxiras, James Hone, Ken Shepard, Jing Guo, Philip Kim In this contribution we present an experimental and theoretical investigation of graphene/MoS2 Schottky diodes and MoS2/graphene/MoS2 metal base transistors. We observe that the Schottky barrier height can be modulated by the chemical potential of the graphene and MoS2 layers with the back gate and tuned in the range of 0-450 meV. To extract further information regarding the quality of the graphene/MoS2 interfaces and the conduction mechanism across them, we analyze the ideality factor as a function of temperature and find it can vary from n$=$3 at 270 K to n$=$12.9 at 100 K. We attribute this strong temperature dependence to a spatial variation of the Schottky barrier, caused by 2D electrostatic effects. Moreover, we have fabricated MoS2/graphene/MoS2 metal base transistors that work as a permeable base transistors. [Preview Abstract] |
Wednesday, March 5, 2014 4:30PM - 4:42PM |
Q37.00009: Photo Sensor Devices Based on Atomically Thin TMDCs Nestor Perea, Ana L. Elias, Nihar Phradan, Zhong Lin, Bartolomeu Cruz-Viana, Luis Balicas, Humberto Terrones, Mauricio Terrones Few-layered films of different transition metal dichalcogenides (TMDCs) like MoS2, WS2, and WSe2 were successfully used as light sensors. The samples were structurally characterized by Raman spectroscopy, AFM, SEM, and HRTEM. The produced samples consisted of few layered sheets possessing up to 10 layers obtained by different synthetic or isolation methods including low-pressure CVD, atmospheric-pressure CVD and mechanical exfoliation. Current-voltage (I-V) and photo response measurements carried out by connecting the TMDC layered sample with Au/Ti contacts. The photocurrent measurements were carried out at different wavelengths from 400 to 800 nm. The results indicate that the electrical response strongly depends on the photon energy from the excitation lasers. In addition, it was found that the photocurrent varied non-linearly with the incident power, and the generated photocurrent in the WS$_{2}$ samples varied as a squared root of the incident power. The response time of the devices was measured and resulted in the order of few milliseconds. Because of its fast response, good responsivity and stability few-layered TMDCs are strong candidates for constructing novel optoelectronic devices. [Preview Abstract] |
Wednesday, March 5, 2014 4:42PM - 4:54PM |
Q37.00010: Exploiting Semiconductor to Metallic Phase Transformation in Layered Transition Metal Dichalcogenides for Ohmic contact Contacts Rajesh Kappera, Damien Voiry, Wesley Jen, Sibel Ebru Yalcin, Gautam Gupta, Aditya Mohite, Manish Chhowalla Achieving ohmic contacts to transition metal dichalcogenides (MoS$_{2}$, WS$_{2}$, WSe$_{2}$ and MoSe$_{2})$ has been a challenge for researchers owing to the formation of a large Schottky barrier between metal and semiconductor. This results in low on-currents, mobilities and sub-threshold swings in the devices made with these materials. Here we report a universal strategy using chemical approach to reversibly transform the semiconducting phase (2H) to metallic phase (1T). Taking advantage of the metallic phase, we have fabricated hybrid transistors, which have 1T phase contacts and semiconducting 2H phase of the material as the channel. The metallic phase dramatically reduces the Schottky barrier between the metal and the semiconductor thereby mitigating the high contact resistance issues. This strategy should be applicable to several other applications such as catalysis, supercapacitors and batteries. Detailed synthesis, structural, electrical and optical characterization will be described. [Preview Abstract] |
Wednesday, March 5, 2014 4:54PM - 5:06PM |
Q37.00011: Charge-Density Wave Driven Phase Transitions in Single-Layer MoS$_2$ Houlong L. Zhuang, Michelle D. Johannes, Richard G. Hennig Phase transitions in single-layer MoS$_2$ are frequently observed in experiments. We reveal that charge doping can induce the phase transition of single-layer MoS$_2$ from the 2$H$ to the 1$T$ structure. Further, the 1$T$ structure undergoes a second phase transition due to the occurrence of a charge-density wave (CDW). By comparing the energies of several possible resulting CDW structures, we find that the $\sqrt3a \times a$ orthorhombic structure is the most stable one, consistent with experimental observations. Moreover, we discover that the band structure of the $\sqrt3a \times a$ structure possesses a Dirac cone, which is split by spin-orbit interactions into a bandgap of 50 meV. We show that the underlying CDW transition mechanism is not electronic, but can be controlled by charge doping nonetheless. Finally, we calculate the interface energy and band offsets of a lateral heterostructure formed by the 2$H$ and $\sqrt3a \times a$ structures. [Preview Abstract] |
Wednesday, March 5, 2014 5:06PM - 5:18PM |
Q37.00012: Discovery of new monolayer material Nb$_{3}$SiTe$_{6}$ Jin Hu, Xue Liu, Chunlei Yue, Zhiqiang Mao, Jiang Wei The discovery of atomically-thin materials, such as graphene and monolayer transition metal dichalcogenides, has ushered in a new era of low-dimensional physics. Due to the quantum confinement effect in reduced dimensionality, the electronic structures of monolayer materials are reconstructed, leading to exotic physical properties such as Dirac fermions in graphene, large direct band gap and valley-spin coupling in MoS$_{2}$. Recently we prepared a new monolayer form of a complex material Nb$_{3}$SiTe$_{6}$. Nb$_{3}$SiTe$_{6}$ possesses a tetragonal structure with each Nb-Si lattice sheet sandwiched by two Te layers. The Te-Nb/Si-Te layers are coupled by Van der Waals gap. Similar to MoS$_{2}$, within Te-Nb/Si-Te layers each Nb forms six bonds with Te atoms, forming trigonal prismatic coordination. We successfully obtained mono-layer Nb$_{3}$SiTe$_{6}$ using micro-mechanical exfoliate technique. While bulk Nb$_{3}$SiTe$_{6}$ is metallic, the electronic properties of Nb$_{3}$SiTe$_{6}$ monolayer are expected to be distinct from those of bulk due to the quantum confinement effect. In this talk, we will report the preparation and electronic properties of Nb$_{3}$SiTe$_{6}$ monolayer. This success of preparing Nb$_{3}$SiTe$_{6}$ monolayer provides a new playground for studying low dimensional physics and nanotechnology. [Preview Abstract] |
Wednesday, March 5, 2014 5:18PM - 5:30PM |
Q37.00013: Peierl Transition Temperature and ac Conduction Study in Few Layer Blue Bronze (K$_{0.3}$MoO$_{3})$ Crystals Mehdi Jamei, Oscar Vazquez, Jairo Velasco, Alex Zettl, Michael Crommie K$_{\mathrm{x}}$MoO$_{3}$ (0.24\textless x\textless 0.3) or Potassium Molybdenum Blue Bronze is a monoclinic crystal with a layered structure. The presence of sliding charge-density waves (CDW) in Blue Bronze, and its potential to be cleaved and exfoliated, make this material an interesting candidate to investigate in 2D form. In this study, Blue Bronze crystals were grown by the electrochemical method. This method involves passing a DC current through a mixture of MoO$_{3}$ and K$_{2}$MoO$_{4}$, while the temperature is set right above the melting point. then exfoliated thin flakes (below 100nm) of Blue Bronze from these crystals and fabricated 2, 3 and 4-terminal devices using e-beam lithography. An Indium-Chrome-Gold tri-layer was used as the metal contact. Nitrogen plasma treatment before depositing the metal proved to make a dramatic improvement in the contact resistance. We studied the effect of thickness on the Peierl transition temperature. The ac-conductivity of these crystals was measured in cryogenic temperature. Also we investigated the induction of CDW into Graphene in a Blue Bronze-Graphene stack structure. [Preview Abstract] |
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