Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B30: Emerging 2D Materials: Phosphorene, Silicene, and BeyondFocus
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Sponsoring Units: DMP Chair: Andrew Mannix, Northwestern University Room: 293 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B30.00001: Black Phosphorus/Phosphorene and Beyond Invited Speaker: Peide Ye Black phosphorus (BP) and its monolayer form phosphorene have been intensively studied due to its layered structure, high mobility, direct bandgap, and have great potentials in optical and electronic applications. In this talk, we review the rapid progress in the field, in particular, the recent demonstration of high performance BP transistors with drain current approaching 1A/mm with BN/Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ top gate and the observation of the negative Poisson's ratio under strain due to its unique puckered atomic structures. Air stability of BP/phosphorene is still a big concern for application driven research, although great efforts and significant progress have been made by BN and/or Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ passivation in controlled environment. Here, we also introduce a new van der Waals material which has high mobility, direct bandgap as BP/phosphorene plus its excellent air stability. Fundamental studies of its transport, optical, and mechanical properties will be presented. We acknowledge the close and fruitful collaborations with AFRL, TSMC and Prof. Xu, Prof. Lundstrom, Prof. Wu's groups at Purdue University. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:03PM |
B30.00002: Defects and doping in phosphorene Alexandra Carvalho, Antonio Castro Neto Defects and doping in phosphorene Most two-dimensional materials are unintentionally doped, due to the growth process or as a result of the interaction with the atmosphere or with other device components. Phosphorene is known to be normally p-type, nevertheless it can be used as a channel material for ambipolar field effect transistors able to operate both in the n- and p-type regimes. In this talk, we analyze how single vacancies and tin can contribute to the p-type conductivity in phosphorene. We will also consider the different stages of interaction with oxygen and how oxygen defects can be stabilized and deactivated. We will suggest how copper and alkali metals can be used to compensate the p-type conductivity or convert it to n-type. Finally, we will suggest how point defects can be used to engineer a sizable spin-orbit splitting in phosphorene, where it is otherwise practically undetectable. [Preview Abstract] |
Monday, March 13, 2017 12:03PM - 12:15PM |
B30.00003: Patterning and Thinning of Black Phosphorus with Scanning Probe Nanolithography Xiaolong Liu, Kan-Sheng Chen, Spencer Wells, Itamar Balla, Jian Zhu, Joshua Wood, Mark Hersam Two-dimensional (2D) black phosphorus (BP) has attracted significant interest due to its desirable electronic and optical properties. The preparation of thin BP layers primarily relies on exfoliation without precise control over flake size and thickness. We take advantage of the high chemical reactivity of BP in ambient conditions to realize patterning and layer-by-layer thinning of BP with conductive atomic force microscopy. It allows BP flakes to be locally patterned with lateral spatial resolution down to the \textasciitilde 10 nm scale. The locally oxidized phosphorus getters environmental water, resulting in a liquid-phase patterning byproduct that is easily removed by water rinsing. We further demonstrate an alternating current bias method that enables direct patterning of BP on dielectric substrates for device fabrication. Using this method, BP field-effect transistors with patterned channels show significant improvement in current modulation by up to a factor of 50. The generality of this patterning method suggests that it can be extended to other 2D materials, thereby facilitating fundamental research and device prototyping (X. Liu, M. C. Hersam, \textit{et al}. \textit{Advanced Materials}, 2016, DOI: 10.1002/adma.201604121). [Preview Abstract] |
Monday, March 13, 2017 12:15PM - 12:27PM |
B30.00004: The evolution of electronic structures in few-layer black phosphorus by infrared spectroscopy. Guowei Zhang, Andrey Chaves, Shenyang Huang, Chaoyu Song, Tony Low, Hugen Yan Black phosphorus (BP) is a newly discovered two-dimensional material with puckered lattice structures, exhibiting many intriguing properties, such as tunable direct bandgap, in-plane anisotropy and relatively high carrier mobility. In this work, we report the first systematic infrared study of mechanically exfoliated few-layer BP using FTIR (Fourier transform infrared spectrometer), with thickness ranging from 2 to 15 layers and photon energy spanning from 0.25 to 1.36 eV. Each few-layer BP exhibits a thickness-dependent unique infrared spectrum with a series of absorption resonances, which reveals the underlying electronic structure evolution and serves as an IR fingerprint. The evolution of electronic structures in few-layer BP is well understood within the framework of a tight binding model. Our study paves the way for BP applications in infrared optoelectronics. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B30.00005: Synthesis and Growth Mechanism Investigation for Black Phosphorus Xiaoyuan Liu, Sheng Li, Qingkai Yu, Bing Lv The recent successful synthesis of black phosphorus (BP) at lower pressure rather than historically high pressure Bridgman method through mineralizer-assisted reactions, and the prevailing properties that BP displayed, have warranted some more detail investigation for the growth mechanism of BP, as well as optimization of the synthetic routes for better quality and higher yield. We therefore carried out systematical studies to unravel the role of those mineralization additives during the BP growth, tentatively suggested a likely growth mechanism, and more importantly, pointed out some directions for further growth of BP with controllable thickness. [Preview Abstract] |
Monday, March 13, 2017 12:39PM - 12:51PM |
B30.00006: Unusually stable helical coil allotrope of phosphorus David Tomanek, Dan Liu, Jie Guan, Jingwei Jiang We have identified an unusually stable helical coil allotrope of phosphorus. Our {\em ab initio} density functional theory calculations indicate that the uncoiled, isolated straight 1D chain is equally stable as a monolayer of black phosphorus dubbed phosphorene. The coiling tendency and the attraction between adjacent coil segments add an extra stabilization energy of ${\approx}12$~meV/atom to the coil allotrope, similar in value to the ${\approx}16$~meV/atom inter-layer attraction in bulk black phosphorus. Thus, the helical coil structure is essentially as stable as black phosphorus, the most stable phosphorus allotrope known to date, and has a direct fundamental band gap similar to that of phosphorene monolayer structures. With an optimum radius of 2.4~nm, the helical coil of phosphorus may fit well and even form inside wide carbon nanotubes. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:03PM |
B30.00007: Half-layer-by-half-layer growth of a blue phosphorene monolayer on the GaN(001) substrate Jiang Zeng, Ping Cui, Zhenyu Zhang Black phosphorene (BlackP), consisting of a vertically corrugated yet single layer of phosphorus atoms, is a latest member of the expanding two-dimensional (2D) materials family with high carrier mobility and immense application potentials. Blue phosphorene (BlueP), an allotrope of BlackP with appealing properties of its own, consists of a more flatly arranged layer of phosphorus atoms. To date, direct growth of either BlackP or BlueP remains a daunting challenge. Using first-principles approaches, here we establish a novel kinetic pathway for fabricating BlueP via epitaxial growth. Our systematic energetic studies reveal that both BlackP and BlueP monolayers can be readily stabilized on Cu(111), Au(111), and GaN(001) substrates, but with contrasting thermodynamic stabilities. The semiconducting GaN(001) is further shown to be superior for fabricating BlueP, through an intriguing half-layer-by-half-layer (HLBHL) growth mechanism. Within this scheme, the GaN(001) surface is first preferentially covered by a half layer of phosphorus adatoms, followed by the addition of the other half. Once formed, such a BlueP monolayer is thermodynamically stable, as tested using \textit{ab initio} molecular dynamics simulations. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:15PM |
B30.00008: Templating sharp molecular-like states using domain boundaries of the 2D material silicene on ZrB$_2$ Cyrus F. Hirjibehedin, Ben Warner, Tobias G. Gill, Vasile Caciuc, Nicolae Atodiresei, Antoine Fleurence, Yasuo Yoshida, Yukio Hasegawa, Stefan Bluegel, Yukiko Yamada-Takamura To achieve the goal of scalable molecular electronics, it will be necessary to retain the functionality of molecular components even when the molecules are strongly bound to a surface. The structural and electronic properties of two-dimensional (2D) materials have already proven useful in templating molecules at the nanoscale. However, hybridization between substrate and molecule can often destroy the single molecule functionality essential for use in electronic devices. Here we use scanning tunneling microscopy (STM) and spectroscopy coupled with density functional theory (DFT) studies to show how the domain boundary structure of the 2D material silicene on ZrB$_2$ can be used to linearly template iron phthalocyanine (FePc) molecules, even at room temperature, while retaining sharp, molecular-like electronic states that are indicative of the isolated molecule. These results highlight the important role of the interface between molecules and 2D materials as well as their edges in controlling the properties of the combined system, and in determining its usefulness in future device applications. [Preview Abstract] |
Monday, March 13, 2017 1:15PM - 1:27PM |
B30.00009: From striped domain to single domain: Evolution of partial dislocations in epitaxial silicene Antoine Fleurence, Yukiko Yamada-Takamura Silicene is a graphene-analogue 2D material made of Si atoms. The mixed sp$^2$/sp$^3$ hybridization of the Si atom orbitals makes its atomistic structure particularly flexible. The epitaxial form of silicene that crystallizes spontaneously on the (0001) surface of zirconium diboride (ZrB$_2$) thin films grown on Si(111) features a periodic one-dimensional domain structure [1] resulting from the release of the stress. The domain boundaries are partial dislocations of the silicene lattice. The domain structure can be turned into a single domain by depositing an amount of silicon compensating the difference of Si atom density between the boundaries and the domains [2]. This transformation requires the coherent motion of a large number of Si atoms to suppress the dislocations and to allow for the incorporation of Si atoms, which needs to overcome the repulsion between the boundaries. The flexibility of the silicene structure permits the monitoring of the partial dislocations disappearing upon Si deposition by room-temperature scanning tunneling microscopy. These observations give insights into how the dislocations are introduced and removed in 2D materials. [1] A. Fleurence et al., Phys. Rev. Lett. 108 245501 (2012). [2] A. Fleurence et al., Appl. Phys. Lett. 108 151902 (2016). [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B30.00010: Electronic and structural properties of epitaxial silicene on h-BN-terminated ZrB$_{\mathrm{2}}$ Frank Wiggers, Antoine Fleurence, Kohei Aoyagi, Takahiro Yonezawa, Yukiko Yamada-Takamura, Haifeng Feng, Jincheng Zhuang, Yi Du, Alexey Kovalgin, Michel de Jong Silicene is a two-dimensional (2D) material consisting of an atomically buckled honeycomb lattice of Si atoms. Its attractive predicted properties include an electrically tunable bandgap and the quantum spin Hall effect. Free-standing silicene has not been synthesized to date, but epitaxial silicene layers have been reported on a number of metallic substrates, amongst which ZrB$_{\mathrm{2}}$(0001) thin films on Si(111) [1]. These substrates have a non-negligible effect on the electronic properties of the silicene due to hybridization effects. We have investigated epitaxial silicene on ZrB$_{\mathrm{2}}$(0001) surfaces terminated with an insulating, epitaxial h-BN monolayer [2]. I will discuss the electronic and structural properties of such silicene layers, based on synchrotron-based (angle-resolved) photoelectron spectroscopy and scanning tunneling microscopy studies. [1] A. Fleurence, et al., Phys. Rev. Lett. 108, 245501 (2012) [2] K. Aoyagi, et al., to be submitted. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B30.00011: $\pi -$conjugtion in Si(111)-($\surd $3x$\surd $3) surface: Bamboo hat ``silicene'' Wei Jiang, Zheng Liu, Miao Zhou, Xiaojuan Ni, Feng Liu The newly observed Si(111)-($\surd $3x$\surd $3) surface reconstruction that exhibits a 2D-Dirac state has been widely reported, yet its stability was poorly understood. Based on valence bond and conjugation theory, we propose a $\pi $-conjugation plus charge-transfer model underlying its structural stability and unique electronic properties. The ``bamboo hat'' surface geometry facilitates the formation of unusual planar Si-rings with $\pi $-conjugation and charge transfer from the rings to upper buckled Si atoms, to lower the surface dangling bond energy. This intriguing mechanism is confirmed by calculating surface energies and surface stress tensors, explaining the observation of the ($\surd $3x$\surd $3) surface grown on the Ag substrate rather than the bulk-terminated Si(111)-(2x1) surface. The same mechanism also applies to the metastable ($\surd $21x$\surd $21) surface reconstruction observed in recent experiments. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B30.00012: Optical properties of single and bilayer arsenene phases Deniz Kecik, Salim Ciraci, Engin Durgun An extensive investigation of the optical properties of single-layer buckled and washboard arsenene and their bilayers was performed, starting from layered three-dimensional (3D) crystalline phase of arsenic using density functional and many-body perturbation theories combined with Random Phase Approximation. Electron-hole interactions were taken into account by solving the Bethe-Salpeter equation, suggesting first bound exciton energies on the order of 0.7 eV. Thus, many-body effects were found to be crucial for altering the optical properties of arsenene. The light absorption of single layer and bilayer arsenene structures in general falls within the visible-ultraviolet (UV) spectral regime. Moreover, directional anisotropy, varying the number of layers and applying homogeneous or uniaxial in-plane tensile strain were found to modify the optical properties of two-dimensional (2D) arsenene phases, which could be useful for diverse photovoltaic and optoelectronic applications. [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B30.00013: High Temperature Ferromagnetism in $\pi $-Conjugated 2D Metal-Organic Frameworks Wenbin Li, Lei Sun, Jingshan Qi, Pablo Jarrilo-Herrero, Mircea Dinca, Ju Li We use first-principles calculations to design a new class of phthalocyanine (Pc) based 2D metal organic frameworks (MOFs) with square lattices that exhibit rich magnetic behavior. A MOF made from MnPc connected through Ni-bisphenylene-diimine moieties, NiMnPc, was found to exhibit a ferromagnetic ground state with a large exchange energy, resulting from the unique strong hybridization between the $d$/$\pi $ orbitals of Mn, the Pc ring, and the Ni nodes. Notably, we show that for NiMnPc there is a considerable difference between the ferromagnetic ordering temperature ($T_{\mathrm{c}})$ predicted by a 2D Ising model, which exceeds 600 K, and a $T_{\mathrm{c}}$ of 170 K predicted by our more realistic Monte Carlo simulation that includes magnetic anisotropy. In the bulk, 2D layers of NiMnPc adopt a slipped-parallel stacking configuration, and exhibit interlayer magnetic coupling that is sensitive to the relative in-plane displacement between adjacent layers. The results highlight the critical role of magnetic anisotropy in modeling the properties of 2D magnetic systems. More generally, it demonstrates that strong hybridization between open-shell ions and delocalized aromatic $\pi $ systems, combined with large magnetic anisotropy, will be an effective design strategy to realize ferromagnetic 2D MOFs with high $T_{\mathrm{c}}$. [Preview Abstract] |
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