Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session H17: Surface and Interface Studies of Transition Metal Chalcogenides |
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Dan Dougherty, North Carolina State University Room: LACC 306A |
Tuesday, March 6, 2018 2:30PM - 2:42PM |
H17.00001: Correlating Morphology and Electronic Structure of MoS2 on Au(111) Caio Silva, Daniela Dombrowski, Nicolae Atodiresei, Wouter Jolie, Ferdinand Farwick zum Hagen, Pardeep Thakur, Vasile Caciuc, Thomas Michely, Stefan Bluegel, Tien-Lin Lee, Carsten Busse Two-dimensional materials (2DMs) subjected to superperiodic potentials show exciting effects such as replica bands and minigaps in the electronic structure. In addition, the locally varying potential landscape can induce ordered superstructures of atoms, molecules and metallic clusters. Such superperiodic potentials can arise spontaneously in 2DMs epitaxially grown on metallic substrates, where the lattice mismatch leads to a moiré pattern. In consequence, depending on the strength of interaction, the 2DM can display a structural modulation (corrugation) which can show charge inhomogeneity and localized states. |
Tuesday, March 6, 2018 2:42PM - 2:54PM |
H17.00002: Photoemission Study of 1H-1T’ Phase-transition in Monolayer MoS2 on Gold Xinmao Yin, Liang Cao, Chi Sin Tang, Wenjing Zhang, Andrivo Rusydi, Andrew Thye Shen Wee We study the transition of monolayer-MoS2 on gold (MoS2/Au) from trigonal semiconducting 1H-phase to the distorted octahedral quasi-metallic 1T’-phase based on a high-temperature annealing-based process. Besides, we observe a tunable inverted gap(~0.50eV) in quasi-metallic (1T’-phase) monolayer-MoS2 upon the phase transition. With the focus on verifying the phase transition of MoS2/Au, we study the evolution of Mo-3d and S-2p core level, work function, and valence band spectra at different annealing temperatures using synchrotron-based photoemission spectroscopy. New spectra components at lower binding energies relative to the 1H-MoS2 doublet grow in intensity upon annealing and are maximized at 250oC. Combining our results with other experimental studies, we conclude that the temperature region of 250oC. Our study provides a good verification of the 1H-1T’ phase-transition process of MoS2/Au and that this annealing-based technique is a convenient and straightforward way of inducing a semiconductor-to-metal phase transition in 2D TMDs. |
Tuesday, March 6, 2018 2:54PM - 3:06PM |
H17.00003: Electronic structure of epitaxially-grown monolayer 1T’-MoTe2 Sung-Kwan Mo, Shujie Tang, Chaofan Zhang, Chunjing Jia, Thomas Devereaux, Zhi-Xun Shen, Hyejin Ryu, Choongyu Hwang, Makoto Hashimoto, Donghui Lu, Zhi Liu We have investigated the electronic structure of monolayer 1T’-MoTe2 grown by molecular beam epitaxy on bilayer graphene substrate. Angle-resolved photoemission measurements found the spin-orbit-coupling induced breaking of the band degeneracy points between the valence and conduction bands. The strength of spin-orbit-coupling is found to be insufficient to open a band gap, which makes monolayer 1T’-MoTe2 on bilayer graphene a semimetal. |
Tuesday, March 6, 2018 3:06PM - 3:18PM |
H17.00004: An Efficient Method of Calculating Exfoliation Energies Jong Hyun Jung, Cheol Hwan Park, Jisoon Ihm The exfoliation energy, the energy required to separate an atomic layer from the surface of a bulk material, is important in the science and engineering of two-dimensional materials. This is because the energy measures the feasibility of mechanical exfoliation of a surface layer. The traditional methods of calculating the exfoliation energy of a material require heavy computations. Our method is (i) considerably more efficient than the traditional approach, (ii) still valid even if there is a surface relaxation or reconstruction of any kind, (iii) capable of taking into account the relaxation of the single exfoliated layer, and (iv) easily combined with all kinds of many-body computational methods. As a proof of principles, we calculated exfoliation energies of representative two-dimensional materials using density-functional theory. |
Tuesday, March 6, 2018 3:18PM - 3:30PM |
H17.00005: Nanocrystal Stability in the π-phase IV-VI
Monochalcogenides Elad Segev, Ran Abutbul, Uri Argaman, Yuval Golan, Guy Makov A new cubic binary phase was recently discovered in the nanocrystalline IV-VI monochalcogenides tin monosulfide and tin monoselenide. Here, we explored the materials nanocrystal stability and present experimental results which help to elucidate the growth mechanism. The structure and properties of surfaces of the π phase were studied using density functional theory across the monochalcogenide systems including prediction for the Ge-monochalcogenides. The thin film band gaps and the (100) and (111) surface energies of the new phase were calculated and demonstrate properties which may be attractive for a variety of photovoltaic and photosensing applications. |
Tuesday, March 6, 2018 3:30PM - 3:42PM |
H17.00006: Substrate Effects of TiSe2 Thin Film on TiO2 Tao Jia, Slavko Rebec, Kejun Xu, Hafiz Sohail, Shujie Tang, Makoto Hashimoto, Donghui Lu, Robert Moore, Zhi-Xun Shen TiSe2 is a layered material in the family of Transition Metal Dichalcogenide, and bulk TiSe2 single crystal undegoes a Charge Density Wave transition at temperature below ~200 K. In this talk, I will talk about growth and analysis of TiSe2 thin films on TiO2 rutile substrates, and discuss the substrate effect on the electronic band structure and transport properties of TiSe2. A comparison between TiSe2 films on TiO2 and TiSe2 films on bilayer graphene will also be given. |
Tuesday, March 6, 2018 3:42PM - 3:54PM |
H17.00007: First Order Phase Transition in IrTe2 Studied by Optical Second Harmonic Generation Joel Taylor, Zhenyu Zhang, Guixin Cao, Rongying Jin, Louis Haber, E Plummer Optical second harmonic generation (SHG) is a powerful and versatile technique used to study the electronic symmetry of surfaces and interfaces. Transition metal compounds, such as IrTe2, are ideal candidates for broken symmetry studies. X-ray diffraction measurements of IrTe2 reveal that when cooling below Tc,bulk ~ 280 K a first order structural bulk phase transition from 1x1x1 (at high temperatures) to 5x1x5 (at low temperatures) occurs. On the surface electron diffraction shows 1x1 to 5x1 phase change at Tc,surface ~ 270 K. To understand the nature of this transition, SHG coupled with azimuthal sample rotation is used to probe the phase change across Tc,surface. We observe the hysteresis loop of SHG intensity with a ΔT of ~ 3K, in agreement with the previous electron diffraction measurement. Four polarization combinations are utilized allowing sensitivity to both the in-plane (Te-Te bonds) and out-of-plane (Ir-Te bonds) surface responses. In addition, rotational anisotropy SHG measurements above and below Tc,surface yield distinct surface symmetry patterns. Comparing the results of SHG to bulk properties, key insight into the nature of the phase transition is obtained. |
Tuesday, March 6, 2018 3:54PM - 4:06PM |
H17.00008: Magic Size Effects in the Au/MoS2 Systen Tim Kidd, Andrew Stollenwerk Magic size effects have been seen in a variety of metal/semiconductor thin film systems grown at low temperatures for stability. These electronic growth modes reflect the bulk Fermi wavelength of the metal and result in quantum size effects measuring two or three atomic layers. We have discovered the Au/MoS2 system exhibits quantum size effects that are much more pronounced, measuring several nanometers. Further, these systems can be created at or above room temperature. These results appear to be due to the unique properties arising from the growth of Au on a van der Waals semiconductor. The Au/MoS2 interface provides a weak bonding which is sufficient for epitaxial growth but still allows for sufficient freedom of movement for discrete cluster formation exhibiting a full range of quantum size effects. Interestingly, the integer heights correspond to the necks of the smaller necks of the Au Fermi surface rather than the bulk as is typically seen in these systems. In addition to providing a new set of systems for study of electronic growth modes, these results could impact the development of electronic contacts on MoS2 or other van der Waal surfaces. |
Tuesday, March 6, 2018 4:06PM - 4:18PM |
H17.00009: ARPES and STM studies of monolayer 1T-NbSe2 Yuki Nakata, Katsuaki Sugawara, Ryota Shimizu, Yoshinori Okada, Patrick Han, Taro Hitosugi, Keiji Ueno, Takashi Takahashi, Takafumi Sato Recently, monolayer transition-metal dichalcoenides (TMDs) are attracting particular attention due to realization of exotic physical properties distinct from the bulk counterpart. One of the most intriguing features of TMDs is variety of physical properties depending on the crystal structure such as trigonal prismatic 2H or octahedral 1T phases. Among the TMDs, 2H-NbSe2 has been intensively studied since it simultaneously exhibits charge density wave and superconductivity. In contrast, 1T-NbSe2 has not been well studied due to its structural instability. Here we report ARPES and STM studies of monolayer NbSe2 epitaxially grown on bilayer graphene. We have succeeded for the first time in selectively fabricating monolayer 2H- and 1T-NbSe2, and revealed electronic structure by using ARPES. We found that monolayer 2H-NbSe2 exhibits metallic behavior as in bulk, while monolayer 1T-NbSe2 shows insulating behavior in contrast to the band theory which predicts the metallic nature with half-filled bands. In the presentation, we will show how to selectively fabricate 2H- and 1T-NbSe2, and discuss the origin of unexpected insulating state in monolayer 1T-NbSe2. |
Tuesday, March 6, 2018 4:18PM - 4:30PM |
H17.00010: Schottky Barrier Heights of Metallic-Semiconducting Transition-Metal Dichalcogenide Vertical and Lateral Heterostructures ADIBA ZAHIN, Shanshan Su, Darshana Wickramaratne, Roger Lake Low resistance contacts to two-dimensional materials continue to be a limiting factor to obtaining the intrinsic performance limits of these materials. One approach to reduce the contact resistance to semiconducting transition metal dichalcogenides (TMDs) is to improve the interface between the metal and the TMD semiconductor. To address this, we investigate the use of 2D metallic TMDs (MX2; M=Ta, Nb; X= S, Se, Te) as metal contacts to 2D semiconducting TMDs (MX2; M=Mo, W; X= S, Se, Te). We determine the Schottky barrier heights of the monolayer semiconducting TMDs such as MoSe2, WSe2 and MoTe2 with the monolayer metallic TMDs such as TaS2, NbS2, NbSe2, TaSe2 in both vertical and horizontal heterostructures using ab initio density-functional theory (DFT). For the horizontal heterostructures, two types of interface geometries are considered, armchair and zigzag. A vertical MoTe2-NbSe2 heterostructure gives a minimum p-type Schottky barrier of 0.11 eV. The horizontal armchair MoSe2-TaS2 heterostructure results in a negative Schottky barrier of 61 meV. |
Tuesday, March 6, 2018 4:30PM - 4:42PM |
H17.00011: Energy and Charge Transfer in Heterobilayers formed by Transition Metal Dichalcogenides and Graphene Yongsheng Wang, Dawei He, Lixin Yi, Jiaqi He, Xinwu Zhang, Hui Zhao We report time-resolved measurements of Dexter-type energy transfer from transition metal dichalcogenide (TMD) monolayers to graphene monolayers by transient absorption measurements. Samples were fabricated by manually stacking together graphene monolayers and tungsten disulfide or molybdenum disulfide monolayers. Transient absorption measurements showed that the electron-hole pairs excited in the TMD layer transfer to graphene on a time scale shorter than the 100-fs laser pulses. Spatially resolved measurements revealed that the transfer is enhanced by an electric field, which indicates that the transfer is achieved by individual charge transfer of the electrons and holes. We further found that the transferred carriers can effectively alter the absorption coefficient of the TMD layer by screening effect. The observed ultrafast energy transfer from TMD monolayer to graphene and the control of TMD optical absorption by carriers in graphene suggest potential applications of TMD-graphene heterobilayers in optoelectronic devices. |
Tuesday, March 6, 2018 4:42PM - 4:54PM |
H17.00012: Studies of Dimensional Crossover of the Charge Density Waves in TiSe2 Meng-Kai Lin, Xinyue Fang, Hawoong Hong, Peng Chen, Tai-Chang Chiang TiSe2, a prototypical charge density wave (CDW) system with a 1T structure in the bulk, undergoes a simple (2 × 2 × 2) CDW transition at TB = 205 K in connection with the softening of a phonon mode at the zone boundary. We have successfully grown high quality single- and multi-layer films of TiSe2 on a bilayer-graphene-terminated SiC surface via molecular beam epitaxy (MBE). Our angle-resolved photoemission spectroscopy (ARPES) and x-ray diffraction (XRD) measurements using synchrotron light sources of the single-layer film show a (2 × 2) CDW transition at T1 = 232 K, which is substantially higher than the bulk transition temperature TB. For the 2-layer case, ARPES shows a mixture of two transitions, one at T1 and the other at TB. The nature of this mixed transition is an interesting question that requires further investigation. We have now performed XRD studies of the 2-layer case. The results show an apparent single transition at T2 = 228 K, which is very close to T1, and no apparent second transition at TB. The results are intriguing, and we are performing theoretical simulations to unravel the underlying physics in terms of the static and dynamic lattice distortions. |
Tuesday, March 6, 2018 4:54PM - 5:06PM |
H17.00013: Monolayer Honeycomb CuSe: A Candidate for Two–dimensional Dirac Nodal Line Fermions Shixuan Du Symmetry-protected Dirac nodal line semimetals (DNLSs) receive much attention because of their exotic physical properties and potential applications in dissipationless spin devices. DNLFs in 2D atomic crystal have rarely been explored because of their high vulnerability to symmetry breaking. Here we propose that free-standing monolayer CuSe with honeycomb structure is endowed with the exotic 2D DNLF protected by mirror reflection symmetry, based on first-principles calculation. The DNLF state is evidenced by nontrivial edge states that arise as the crossing bands open the gaps with spin-orbit coupling. The angle resolved photoemission spectroscopy on the as-prepared monolayer CuSe on a Cu(111) show excellent agreement with the calculated band structures of CuSe/Cu(111), which demonstrates that it is a monolayer CuSe with a distorted honeycomb lattice. |
Tuesday, March 6, 2018 5:06PM - 5:18PM |
H17.00014: Strain Induced High Curie Temperature in Molecular Beam Epitaxy Grown Cr2Te3 Thin Films with Perpendicular Magnetic Anisotropy Hongxi LI, Linjing Wang, Gan Wang, Fei Ye, Tao Yu, Liang Zhou, Hongtao He, Iam Keong Sou In this work, Cr2Te3 thin films with high Curie temperature from 191 to 280K on Al2O3 (0001) substrates were grown by Molecular Beam Epitaxy technique. In-situ long streaky reflection high energy electron diffraction patterns indicate that the Cr2Te3 thin films were grown with an atomic flat surface and single crystalline quality. X-ray diffraction study shows a significant increase of lattice constant of Cr2Te3 thin films along [001] direction. A ZnSe capping layer was used for tuning the compressive strain in Cr2Te3 thin films, resulting in a change of lattice constant along [001] orientation. A spin glass-like magnetic behavior is systematically investigated by zero-field-cooling and field-cooling magnetization characterizations. A strong perpendicular magnetic anisotropy is identified by measuring the field dependent magnetization curves along different crystalline directions. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700