Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L1: Focus Session: Beyond Graphene - Phosphorene III |
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Sponsoring Units: DMP Chair: Yuanbo Zhang, Fudan University Room: 001A |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L1.00001: Toward Air-Stable Multilayer Phosphorene Thin-Films and Transistors Joon-Seok Kim, Yingnan Liu, Weinan Zhu, Seohee Kim, Di Wu, Li Tao, Ananth Dodabalapur, Keji Lai, Deji Akinwande Few-layer black phosphorus, also known as phosphorene, has recently rose into scientific limelight due to its promising characteristics for flexible device and optoelectronic applications, such as high mobilities beyond what is achievable in other 2D dichalcogenides. In addition, its direct thickness-dependent bandgap enables optoelectronics from the infrared to visible regions. However, a fundamental challenge lies on its lack of air stability, which is of paramount importance for practical device application. Physical degradation of unprotected phosphorene in a matter of hours in air was obvious from optical and atomic force microscopy (AFM). Moreover, microwave impedance microscopy (MIM) revealed that samples with thin capping layers, though more air-stable, began to degrade from the edges inward within a few days, where the degradation was primarily electronic with minor physical changes. Statistics from phosphorene field-effect transistors (FETs) have shown that double capping with dielectric and hydrophobic fluoropolymer films afford further improved and robust weeks-long air-stability. The simple capping methods represent a facile route for achieving air-stable phosphorene devices that can enable basic studies and potential applications. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L1.00002: Weak Localization in Bulk Black Phosphorus and Few-Layer Phosphorene Yuchen Du, Adam Neal, Hong Zhou, Peide Ye Most of the recent experimental research on black phosphorus (BP) or phosphorene has been focused on device applications with few systematic studies on electrical transport properties of single-layer or few-layer phosphorene. Here, we report on the magnetotransport experiments on thick BP films and few-layer phosphorene at low temperatures. The observed weak localization is well fitted by the Hikami-Larkin-Nagaoka model where the temperature dependence of the phase coherence length has demonstrated to be a power-law behavior of T$^{-0.5}$. In addition, the temperature dependence of Hall mobility as a function of the film thickness is also examined to uncover the limitation of mobility in few-layer phosphorene with different mechanisms. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L1.00003: Passivation of Exfoliated Black Phosphorus Transistors Against Ambient Degradation Spencer Wells, Joshua Wood, Deep Jariwala, Kan-Sheng Chen, EunKyung Cho, Vinod Sangwan, Xiaolong Liu, Lincoln Lauhon, Tobin Marks, Mark Hersam Unencapsulated exfoliated black phosphorus field-effect transistors are found to rapidly degrade upon exposure to ambient conditions, causing large increases in threshold voltage after only 6 h in ambient, followed by a $\sim$ 10$^{3}$ decrease in FET on/off ratio and mobility after 48 h. Careful investigation into the cause of this degradation suggests that H$_{2}$O irreversibly reacts with unprotected, exfoliated BP to form oxidized phosphorus species, as observed by AFM, TEM, XPS, Fourier transform infrared spectroscopy, and electrostatic force microscopy. This interpretation is further supported by the observation that BP degradation occurs more rapidly on hydrophobic octadecyltrichlorosilane self-assembled monolayers as opposed to hydrophilic SiO$_{2}$, implicating an edge-based intercalation of O$_{2}$ saturated H$_{2}$O in BP as the cause of degradation. Atomic layer deposited AlO$_{\mathrm{x}}$ overlayers were found to suppress ambient degradation, allowing encapsulated BP FETs to maintain high on/off ratios of $\sim$ 10$^{3}$ and mobilities of $\sim$ 100 cm$^{2}$/(Vs) for over one month in ambient, demonstrating the effective passivation of BP flakes against ambient degradation [1]. \\[4pt] [1] J.D. Wood, S.A. Wells \textit{et al., Nano Lett}. \textbf{ASAP}, DOI: 10.1021/nl5032293 [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L1.00004: Imperfect 2D phosphorus, yet an almost perfect semiconductor Evgeni Penev, Yuanyue Liu, Fangbo Xu, Ziang Zhang, Boris Yakobson The deep gap states created by defects in semiconductors typically deteriorate the performance of (opto)electronic devices. This has limited the applications of two-dimensional (2D) metal dichalcogenides (MX$_2$) and underscored the need for a new 2D semiconductor without defect-induced deep gap states. The talk will discuss why a 2D mono-elemental semiconductor can be a promising candidate. This is exemplified by a first-principles study of 2D phosphorus (``phosphorene'')~[1], a recently fabricated high-mobility semiconductor. Most of the defects, including intrinsic point defects and grain boundaries, are electronically inactive, thanks to the homoelemental bonding, which is not preferred in heteroelemental system such as MX$_2$. Unlike MX$_2$, where the edges create deep gap states and cannot be eliminated by passivation, the edge states of 2D P can be removed from the band gap by hydrogen termination. It is further found that both the type and the concentration of charge carriers in 2D P can be tuned by doping with foreign atoms. The work sheds light on the role of defects on the electronic structure of low-dimensional materials in general.\\[4pt] [1] Y. Liu, F. Xu, Z. Zhang, E. S. Penev, and B. I. Yakobson, Nano Lett. (2014), DOI: 10 [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L1.00005: Single/Bi-layer Silicene Field-Effect Transistors and their Air-Stability Li Tao, Eugenio Cinquanta, Carlo Grazianetti, Alessandro Molle, Deji Akinwande Silicene, the Si analogue of graphene, has the potential to be a widely tunable 2D material for novel nanoelectronics. Air-stability is a major issue for experimental investigation on silicene devices, which per this study has been greatly addressed by our encapsulated delamination with native electrodes (SEDNE) approach. SEDNE process preserves silicene/Ag interface during transfer and fabrication, and real-time Raman spectroscopy observes a short time window for Ag-removed silicene device stays intact and gradually degrades. In our predefined experiments, silicene devices exhibit an ambipolar charge transport behavior, corroborating theories on Dirac band in Ag-free silicene. Monolayer silicene device has extracted field-effect mobility within the theoretically predicted range and ON/OFF ratio greater than graphene, whereas bilayer silicene device shows lower mobilities and gate modulation similar to graphene. This work suggests a realistic prospect for improving air-stability of silicene devices and its tunable performance, which can be leveraged for other air-sensitive 2D materials. *Support from U.S. Army Research Office (W911NF-131-0364) and Future Emerging Technologies (270749) under European Commission are appreciated. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L1.00006: Black Phosphorus RF Transistor Han Wang, Xiaomu Wang, Fengnian Xia, Luhao Wang, Hao Jiang, Qiangfei Xia, Mattew L. Chin, Madan Dubey, Shu-jen Han Few-layer and thin film form of layered black phosphorus (BP) has recently emerged as a promising material for applications in high performance thin film electronics and infrared optoelectronics. Layered BP offers a $\sim$ 0.3eV bandgap and high mobility, leading to transistor devices with decent on/off ratio and high on-state current density. Here, we demonstrate the GHz frequency operation of black phosphorus field-effect transistor for the first time. BP transistors demonstrated here show excellent current saturation with an on-off ratio exceeding 2 $\times$ 10$^{3}$. The S-parameter characterization is performed for the first time on black phosphorus transistors, giving a 12 GHz short-circuit current-gain cut-off frequency and 20 GHz maximum oscillation frequency in 300 nm channel length devices. A current density in excess of 270 mA/mm and DC transconductance above 180 mS/mm are achieved for hole conductions. The results reveal the promising potential of black phosphorus transistors for enabling the next generation thin film transistor technology that can operate in the multi-GHz frequency range and beyond. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:48AM |
L1.00007: Phosphorene as a new 2D material for nanoelectronic and optoelectronic applications Invited Speaker: Peide Ye Phosphorus is one of the most abundant elements preserved in earth, constructing with a fraction of 0.1{\%} of the earth crust. In general, phosphorus has several allotropes including white, red, and black phosphorus. Black phosphorus, though rarely mentioned, is a layered semiconductor and have great potentials in optical and electronic applications. Remarkably, this layered material can be reduced to one single atomic layer in the vertical direction owing to the van der Waals structure, dubbed phosphorene, where the physical properties can be tremendously different from its bulk counterpart and needed to be further explored. In this talk, we trace back to the 100 years research history on black phosphorus from the synthesis to material properties, and extend the topic from black phosphorus to phosphorene. The physical and transport properties are highlighted, aiming at further applications in electronic and optoelectronics devices. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L1.00008: The Effect of Gas Absorption on Multilayer Black Phosphorus Field Effect Transistor Xue Liu, Jin Hu, Chunlei Yue, Nicholas Della Fera, Zhiqiang Mao, Jiang Wei Multilayer black phosphorus (BP) is drawing much attention recently due to its reported high mobility (up to 1000 cm$^{2}$V$^{-1}$s$^{-1})$ and on/off ratio (up to 10$^{5})$ as the channel material for field effect transistor (FET). We investigated the interplay between the electrical response of high performing BPFET and gas adsorbate introduced to its surrounding environment. Different type of gas including CO2, H2O, Ethanol, CO, NO, NH3, etc. has been tested. We observed that the absorption of gas molecules generally reduces the overall on-state conductance of the device with an order of 10 $\sim$ 100. And such reduction can be fully recovered by purging with inert gas or baking at mild temperature (about 100$^{\circ}$C). The absorption dynamics and detailed mechanism are also been investigated. We conclude that multilayer black phosphorus is an excellent material for chemical sensing. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L1.00009: Stability and Passivation of Phosphorene Field Effect Transistors Yexin Deng, Zhe Luo, Xianfan Xu, Peide Ye Phosphorene is a new 2D semiconducting material which has been intensively studied for its physical properties and potential device applications. Its high carrier mobility and thickness-dependent direct bandgap make its promising for high-performance field effect transistors and optoelectronic devices. However, even few layer phosphorene films are gradually degraded in air due to its irreversible chemical reactions with oxygen and water in ambient. In order to make stable phosphorene films for real device applications, we systematically studied the different passivation methods including PMMA, 2D hBN, and atomic layer deposited (ALD) dielectrics at different growth conditions. A combination of hBN and ALD could be one of the final solutions for realizing the environmentally stable phosphorene devices. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L1.00010: Electrical characterization of fully encapsulated ultra thin black phosphorous-based heterostructures with graphene contacts Ahmet Avsar, Ivan Jesus Vera-Marun, Jun You Tan, Kenji Watanabe, Takashi Taniguchi, Antonio Helio Castro Neto, Barbaros \"Ozyilmaz The presence of finite bandgap and high mobility in semiconductor few-layer black phosphorous offers an attractive prospect for using this material in future two-dimensional electronic devices. Here we present for the first time fully encapsulated ultrathin (down to bilayer) black phosphorous field effect transistors in Van der Waals heterostructures to preclude their stability and degradation problems which have limited their potential for applications. Introducing monolayer graphene in our device architecture for one-atom-thick conformal source-drain electrodes enables a chemically inert boron nitride dielectric to tightly seal the black phosphorous surface. This architecture, generally applicable for other sensitive two-dimensional crystals, results in stable transport characteristics which are hysteresis free and identical both under high vacuum and ambient conditions. Remarkably, our graphene electrodes lead to contacts not dominated by thermionic emission, solving the issue of Schottky barrier limited transport in the technologically relevant two-terminal field effect transistor geometry. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L1.00011: High Mobility Two-Dimensional Electron Gas in Black Phosphorus Likai Li, Guojun Ye, Vy Tran, Guorui Chen, Huichao Wang, Jian Wang, Kenji Watanabe, Takashi Taniguchi, Li Yang, Xianhui Chen, Yuanbo Zhang Black phosphorus has recently emerged as a new member in the family of two-dimensional (2D) atomic crystals. It is a semiconductor with a tunable bandgap and high carrier mobility - material properties that are important for potential opto-electronic and high-speed device applications. In this work, we achieve a record-high carrier mobility in black phosphorus by placing it on hexagonal boron nitride (h-BN) substrate. The exceptional mobility of the 2D electron gas created at the interface allows us to observe quantum oscillations for the first time in this material. The temperature and magnetic field dependence of the oscillations yields crucial information about the black phosphorus 2DEG, such as cyclotron mass of the charge carriers and their lifetime. Our results pave the way to future research on quantum transport in black phosphorus. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L1.00012: Oxidation pathways in Phosphorene: an {\it ab-initio} investigation Matheus Paes Paes Lima, Adalberto Fazzio, Antonio Jose Roque da Silva Phosphorene is a recently isolated single layer of Black Phosphorus. In this 2D material, the combination of a direct band gap with a high charge carrier mobility opens up the possibility of its use in nano devices. However, the exposure of Black Phosphorus to air leads to its fast degradation, which indicates the relevance to understand its oxidation processes. In the present work we investigate the initial steps of the oxidation process, focusing on the interaction of a single $O_2$ molecule with the phosphorene layer. We show the existence of oxidation pathways having only a single barrier of 0.13eV occurring between the free O2 (triplet) and the triplet-singlet potential energy surface (PES) crossing point. We estimate a room temperature triplet-singlet transition probability of $P_{t\rightarrow s}=0.015$, using the Landau-Zener model. Once the $O_2$ switches to the singlet PES, there is an oxygen incorporation with an energy gain of 4.2eV with respect to the PES crossing point, with the O2 molecule spontaneously dissociating without any barrier. In this process, the final geometry has one O bonded to a P lone pair, and the other located between two P atoms. Our investigations were performed with DFT calculations at the GGA level as implemented in the VASP code. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L1.00013: Tunability of Band Gap in Multilayer Phosphorene by External Electric Fields and Electron Dopings Seung Su Baik, Hyoung Joon Choi Black phosphorus (BP) and its two-dimensional derivative phosphorene are rapidly emerging nanoelectronic materials with potential applicability to field effect transistors and optoelectronic devices. Unlike the gapless semiconductor graphene, multilayer BP has a substantial band gap of $\sim$ 0.2 eV and the band-gap size is reportedly varied by external electric fields. To explore the extensibility of such band-gap modulation, we have investigated electronic band structures of multilayer BP by using the first-principles density-functional method as implemented in the SIESTA code. By controlling the electron doping concentrations and the resultant electric fields therefrom, we examine the manageability of the band-gap size and the anisotropic carrier mobility. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2013-C3-062). [Preview Abstract] |
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