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Title: Lateral epitaxy of atomically sharp WSe 2/WS 2 heterojunctions on silicon dioxide substrates

Abstract

Here, in recent years, 2-D transition-metal dichalcogenides (TMDCs) have received great interests because of the broader possibilities offered by their tunable band gaps, as opposed to gapless graphene which precludes application in digital electronics. TMDCs exhibit an indirect-to-direct band gap transition at the single atomic sheet state as well as optically accessible spin degree of freedom in valleytronics.

Authors:
 [1];  [2];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. National Univ. of Singapore (Singapore)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Chinese Academy of Sciences, Beijing (China)
Publication Date:
Research Org.:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Org.:
USDOE
OSTI Identifier:
1344284
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 28; Journal Issue: 20; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Chen, Jianyi, Zhou, Wu, Tang, Wei, Tian, Bingbing, Zhao, Xiaoxu, Xu, Hai, Liu, Yanpeng, Geng, Dechao, Tan, Sherman Jun Rong, Fu, Wei, and Loh, Kian Ping. Lateral epitaxy of atomically sharp WSe2/WS2 heterojunctions on silicon dioxide substrates. United States: N. p., 2016. Web. doi:10.1021/acs.chemmater.6b03639.
Chen, Jianyi, Zhou, Wu, Tang, Wei, Tian, Bingbing, Zhao, Xiaoxu, Xu, Hai, Liu, Yanpeng, Geng, Dechao, Tan, Sherman Jun Rong, Fu, Wei, & Loh, Kian Ping. Lateral epitaxy of atomically sharp WSe2/WS2 heterojunctions on silicon dioxide substrates. United States. doi:10.1021/acs.chemmater.6b03639.
Chen, Jianyi, Zhou, Wu, Tang, Wei, Tian, Bingbing, Zhao, Xiaoxu, Xu, Hai, Liu, Yanpeng, Geng, Dechao, Tan, Sherman Jun Rong, Fu, Wei, and Loh, Kian Ping. Fri . "Lateral epitaxy of atomically sharp WSe2/WS2 heterojunctions on silicon dioxide substrates". United States. doi:10.1021/acs.chemmater.6b03639. https://www.osti.gov/servlets/purl/1344284.
@article{osti_1344284,
title = {Lateral epitaxy of atomically sharp WSe2/WS2 heterojunctions on silicon dioxide substrates},
author = {Chen, Jianyi and Zhou, Wu and Tang, Wei and Tian, Bingbing and Zhao, Xiaoxu and Xu, Hai and Liu, Yanpeng and Geng, Dechao and Tan, Sherman Jun Rong and Fu, Wei and Loh, Kian Ping},
abstractNote = {Here, in recent years, 2-D transition-metal dichalcogenides (TMDCs) have received great interests because of the broader possibilities offered by their tunable band gaps, as opposed to gapless graphene which precludes application in digital electronics. TMDCs exhibit an indirect-to-direct band gap transition at the single atomic sheet state as well as optically accessible spin degree of freedom in valleytronics.},
doi = {10.1021/acs.chemmater.6b03639},
journal = {Chemistry of Materials},
number = 20,
volume = 28,
place = {United States},
year = {Fri Sep 30 00:00:00 EDT 2016},
month = {Fri Sep 30 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Citation Metrics:
Cited by: 15works
Citation information provided by
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  • In Van der Waals (vdW) p–n heterojunctions consisting of various 2D layer compounds are fascinating new artificial materials that can possess novel physics and functionalities enabling the next-generation of electronics and optoelectronics devices. Here, it is reported that the WSe 2/WS 2 p–n heterojunctions perform novel electrical transport properties such as distinct rectifying, ambipolar, and hysteresis characteristics. Intriguingly, the novel tunable polarity transition along a route of n-“anti-bipolar”–p-ambipolar is observed in the WSe 2/WS 2 heterojunctions owing to the successive work of conducting channels of junctions, p-WSe 2 and n-WS 2 on the electrical transport of the whole systems. Moreover,more » the type-II band alignment we obtained from first principle calculations and built-in potential in this vdW heterojunction can also facilitate the efficient electron–hole separation, thus enabling the significant photovoltaic effect and a much enhanced self-driven photoswitching response in this system.« less
  • Twisting adjacent layers in van der Waals solids can significantly alter their interlayer interactions for tunable optical and electronic properties. Here, we report theoretical calculations, fabrication, and detailed characterizations of WSe 2/WS 2 bilayer heterojunctions with various twist angles that were synthesized by artificially stacking monolayers of CVD-grown WS 2 and WSe 2. Density functional calculations predicted the formation of type-II heterojunctions for the stamped bilayers, with band structures that strongly depend on the interlayer twist angle. Raman spectroscopy reveals strong interlayer coupling with the appearance of a layer-number sensitive mode of WS 2 at 311 cm -1 in WSemore » 2/WS 2 bilayers. This strong interlayer coupling resulted in a 1~2 order of magnitude quenching of the photoluminescence. The broadening and shifts were observed in micro-absorption spectroscopy of WSe 2/WS 2 bilayers, which resulted in a net ~10% enhancement in integrated absorption strength across the visible spectrum with respect to the sum of the individual monolayer spectra. The observed 24 4 meV broadening of the WSe 2 A-exciton absorption band in the bilayers provided an estimate on the rate of charge transfer between the layers that ranged from 23 to 33 fs, and was supported by direct femtosecond pump-probe measurements. These results indicate that interlayer exciton formation and non-radiative decay channels dominate optical properties in these bilayers, which may be important for tunable future photovoltaics and detector applications.« less
  • “Strain engineering” has been widely used to tailor the physical properties of layered materials, like graphene, black phosphorus, and transition-metal dichalcogenides. Here, we exploit thermal strain engineering to construct two dimensional (2D) WS{sub 2} in-plane heterojunctions. Kelvin probe force microscopy is used to investigate the surface potentials and work functions of few-layer WS{sub 2} flakes, which are grown on SiO{sub 2}/Si substrates by chemical vapor deposition, followed by a fast cooling process. In the interior regions of strained WS{sub 2} flakes, work functions are found to be much larger than that of the unstrained regions. The difference in work functions,more » together with the variation of band gaps, endows the formation of heterojunctions in the boundaries between inner and outer domains of WS{sub 2} flakes. This result reveals that the existence of strain offers a unique opportunity to modulate the electronic properties of 2D materials and construct 2D lateral heterojunctions.« less
  • Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2}. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at Kmore » point, and therefore, direct optical transitions at H point should be expected in modulated reflectance spectra besides the direct optical transitions at the K point of Brillouin zone. This prediction is confirmed by experimental studies of the electronic band structure of MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2} crystals by CER, PR, and PzR spectroscopy, i.e., techniques which are very sensitive to critical points of Brillouin zone. For the four crystals besides the A transition at K point, an A{sub H} transition at H point has been observed in CER, PR, and PzR spectra a few tens of meV above the A transition. The spectral difference between A and A{sub H} transition has been found to be in a very good agreement with theoretical predictions. The second transition at the H point of Brillouin zone (B{sub H} transition) overlaps spectrally with the B transition at K point because of small energy differences in the valence (conduction) band positions at H and K points. Therefore, an extra resonance which could be related to the B{sub H} transition is not resolved in modulated reflectance spectra at room temperature for the four crystals.« less
  • Mixed polycrystals of p-WSe{sub 2}/WS{sub 2} with varied composition have been grown by the physical vapor transport technique by using the original compounds as starting materials. Three atomic ratios of WSe{sub 2}/WS{sub 2}, I(1:2), II(1:1), and III(2:1), were used. The mixed polycrystals were studied by scanning electron microscopy, X-ray fluorescence, and Auger electron spectroscopy. For the three syntheses, two types of polycrystals, rough (r) and smooth (s), were observed. The rough side had axial planes at the surface, while the smooth side had basal planes. The average size of the hexagonal single-crystal flakes, which form the polycrystal array, increased withmore » a decrease in the sulfur content; Ir(118 {micro}m) < IIr (256 {micro}m) < IIIr (295 {micro}m). Direct energy bandgaps of 1.78, 1.71, and 1.66 eV were calculated for compounds I, II, and III, respectively. These p-type semiconductors have been characterized as electrode materials in nonaqueous systems by using cyclic voltammetry and photovoltammetry. Without illumination compound Ir showed a diffusion control cyclic voltammogram with the highest dark current. This is due to the high density of axial to basal plane ratio. The flatband potential in acetonitrile in the dark decreased with a decrease in the sulfur content, from 1.12 for compound Ir to 0.78 V vs. SSCE for compound IIIr. The compound with the highest sulfur concentration (Ir) presented the highest underpotential in all the redox systems, while the compound with the lowest sulfur concentration showed the highest photocurrent. Compound IIr combines a large crystal size with an adequate sulfur concentration to present the highest conversion efficiency (0.36%) in a chloranil{sup 0/+1} (0.010M/0.001M) and TBAP 0.25M solution.« less