46 results on '"Yingqiu Zhou"'
Search Results
2. Far‐Field Excitation of Acoustic Graphene Plasmons with a Metamaterial Absorber
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Chunchao Wen, Xingqiao Chen, Jianfa Zhang, Wei Xu, Jie Luo, Yingqiu Zhou, Zhihong Zhu, Shiqiao Qin, and Xiaodong Yuan
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acoustics ,graphene plasmons ,metamaterials ,midinfrared range ,Applied optics. Photonics ,TA1501-1820 ,Optics. Light ,QC350-467 - Abstract
When a graphene sheet is placed near a metal surface, it supports a special type of highly confined and low‐loss electromagnetic mode called acoustic graphene plasmons (AGPs). AGPs squeeze infrared photons into extremely confined areas down to a subnanometric scale and provides a unique platform for strong light–matter interactions. However, the efficient excitation of AGPs is a challenge due to the large momentum mismatch between free‐space light and AGPs. With theoretical analysis and numerical simulations, it is shown that the far‐field excitation of AGPs is realized by integrating graphene in a metal–insulator–metal (MIM) metamaterial with magnetic resonance (MR). More than ten graphene plasmonic modes are excited in the midinfrared range, resulting in a multiresonant spectra with Fano‐like characteristics at each resonant wavelength. The proposal opens a new door to explore the strong plasmonic coupling between graphene and metallic metamaterials down to atomic scale for extreme nanophotonics. The potential applications range from ultracompact tunable metamaterials and ultrasensitive infrared spectroscopy to single‐molecule optics, quantum plasmonics, and others.
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- 2021
- Full Text
- View/download PDF
3. Chemical Vapor Deposition Growth of Two-Dimensional Monolayer Gallium Sulfide Crystals Using Hydrogen Reduction of Ga2S3
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Xiaochen Wang, Yuewen Sheng, Ren-Jie Chang, Ja Kyung Lee, Yingqiu Zhou, Sha Li, Tongxin Chen, Hefu Huang, Benjamin F. Porter, Harish Bhaskaran, and Jamie H. Warner
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Chemistry ,QD1-999 - Published
- 2018
- Full Text
- View/download PDF
4. Atomically thin optomemristive feedback neurons
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Ghazi Sarwat Syed, Yingqiu Zhou, Jamie Warner, and Harish Bhaskaran
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Biomedical Engineering ,General Materials Science ,Bioengineering ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics - Abstract
Cognitive functions such as learning in mammalian brains have been attributed to the presence of neuronal circuits with feed-forward and feedback topologies. Such networks have interactions within and between neurons that provide excitory and inhibitory modulation effects. In neuromorphic computing, neurons that combine and broadcast both excitory and inhibitory signals using one nanoscale device are still an elusive goal. Here we introduce a type-II, two-dimensional heterojunction-based optomemristive neuron, using a stack of MoS2, WS2 and graphene that demonstrates both of these effects via optoelectronic charge-trapping mechanisms. We show that such neurons provide a nonlinear and rectified integration of information, that can be optically broadcast. Such a neuron has applications in machine learning, particularly in winner-take-all networks. We then apply such networks to simulations to establish unsupervised competitive learning for data partitioning, as well as cooperative learning in solving combinatorial optimization problems.
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- 2023
5. Evidence for wetter climate recorded in the Jingxian red clay section since approximately 840 ka ago and its relationship with the East Asian summer monsoon intensity
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Le Cao, Guanglai Xu, Chunsheng Hu, Wenhui Li, and Yingqiu Zhou
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010506 paleontology ,geography ,Paleomagnetism ,Early Pleistocene ,Plateau ,geography.geographical_feature_category ,Outcrop ,010502 geochemistry & geophysics ,Monsoon ,01 natural sciences ,Loess ,Physical geography ,Precipitation ,Quaternary ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The Quaternary red clay (QRC) is one of the typical terrestrial sediments in southern China which contains abundant palaeoclimatic information. A natural QRC outcrop, named the Jingxian red clay section (JRCS), was developed in Jingxian City on the northern piedmont of Mt. Huangshan, offering a valuable archive for long-term palaeoclimatic study from a southern China perspective. The objective of this study is to reveal palaeoclimatic information of regional precipitation from the JRCS and its correlation with the East Asian summer monsoon (EASM) intensity, using grain-size measurements combined with dating via Electron Spin Resonance (ESR) and palaeomagnetism. The results indicate that: (1) Ten palaeoclimatic wetter periods (PWPs) designated as PWPI to PWPX from top to bottom were detected from the grain-size analysis results of the upper 9.4 m JRCS. These PWPs span a period from approximately 840 ka ago to present; (2) three PWPs (PWPVIII to PWPX) were basically determined to approximately 612–690, 720–762 and 792–822 ka ago, basically corresponding to China loess layers of L6, L7 and L8 and deep-sea isotope stages of MIS16, MIS18 and MIS20, respectively. Data suggests that the PWPs in the study area were observed mainly during glaciations; (3) regional precipitation in the study area should be negatively related to the EASM intensity since approximately 840 ka ago as a result of variations in North Hemisphere solar insolation and uplifts of the Tibetan Plateau; (4) the modern anti-phase of monsoonal rainfall at glacial-interglacial timescales seemed to have existed between northern China and southern China since the late Early Pleistocene (approximately 840 ka ago).
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- 2019
6. Photocurrent Direction Control and Increased Photovoltaic Effects in All-2D Ultrathin Vertical Heterostructures Using Asymmetric h-BN Tunneling Barriers
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Qianyang Zhang, Tongxin Chen, Hefu Huang, Yingqiu Zhou, Martin Tweedie, Linlin Hou, Yuewen Sheng, Viktoryia Shautsova, and Jamie H. Warner
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Photocurrent ,Quantitative Biology::Biomolecules ,Materials science ,Graphene ,business.industry ,Photovoltaic system ,Dangling bond ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,law.invention ,law ,Lattice (order) ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Quantum tunnelling - Abstract
Two-dimensional (2D) materials are atomically thick and without out-of-plane dangling bonds. As a result, they could break the confinement of lattice matching, and thus can be freely mixed and matched together to construct vertical van der Waals heterostructures. Here, we demonstrated an asymmetrical vertical structure of graphene/hexagonal boron nitride (h-BN)/tungsten disulfide (WS
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- 2019
7. 2D-Layer-Dependent Behavior in Lateral Au/WS2/Graphene Photodiode Devices with Optical Modulation of Schottky Barriers
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Linlin Hou, Hefu Huang, Qianyang Zhang, Jamie H. Warner, Tongxin Chen, Yingqiu Zhou, Yuewen Sheng, and Ren-Jie Chang
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Materials science ,Graphene ,business.industry ,Photodetector ,Schottky diode ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Photodiode ,law.invention ,law ,Monolayer ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Layer (electronics) ,Diode - Abstract
We investigate the 2D-layer-dependent electronic and optoelectronic properties of lateral Au/graphene/WS2 photodetecting diodes. All 2D materials used [graphene and WS2 domains [monolayer (1L) and ...
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- 2018
8. An Introduction to Text Classification with Applications to Medical Records
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Yingqiu Zhou
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Text corpus ,Artificial neural network ,Latent semantic analysis ,Computer science ,business.industry ,Computer Science::Information Retrieval ,Feature vector ,Feature extraction ,Computer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing) ,Pattern recognition ,ComputingMethodologies_PATTERNRECOGNITION ,Multilayer perceptron ,Feature (machine learning) ,Artificial intelligence ,business ,Curse of dimensionality - Abstract
We proposed and completed a real-life data mining problem, aka, text corpus classification. We extracted 15,500 medical documents relevant to ten different diseases and used the bag-of-words model to create a word occurrence vector for each document. The latent semantic analysis (LSA) method is then used to reduce the occurrence vector’s dimensionality to a feature vector of dimension 200. We selected a multilayer perceptron (MLP) neural network to do the final classification and report the performance comparison with the other six classifiers. We also completed the grid search for the best feature subspace dimensionality.
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- 2020
9. Revealing Strain-Induced Effects in Ultrathin Heterostructures at the Nanoscale
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Yingqiu Zhou, Jamie H. Warner, Harish Bhaskaran, Syed Ghazi Sarwat, Yuewen Sheng, Martin Tweedie, Benjamin F. Porter, and Jan A. Mol
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Kelvin probe force microscope ,Materials science ,Strain (chemistry) ,Graphene ,Mechanical Engineering ,Bioengineering ,Nanotechnology ,Heterojunction ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,law.invention ,law ,General Materials Science ,Work function ,0210 nano-technology ,Nanoscopic scale - Abstract
Two-dimensional materials are being increasingly studied, particularly for flexible and wearable technologies because of their inherent thickness and flexibility. Crucially, one aspect where our understanding is still limited is on the effect of mechanical strain, not on individual sheets of materials, but when stacked together as heterostructures in devices. In this paper, we demonstrate the use of Kelvin probe microscopy in capturing the influence of uniaxial tensile strain on the band-structures of graphene and WS2 (mono- and multilayered) based heterostructures at high resolution. We report a major advance in strain characterization tools through enabling a single-shot capture of strain defined changes in a heterogeneous system at the nanoscale, overcoming the limitations (materials, resolution, and substrate effects) of existing techniques such as optical spectroscopy. Using this technique, we observe that the work-functions of graphene and WS2 increase as a function of strain, which we attribute to the Fermi level lowering from increased p-doping. We also extract the nature of the interfacial heterojunctions and find that they get strongly modulated from strain. We observe that the strain-enhanced charge transfer with the substrate plays a dominant role, causing the heterostructures to behave differently from two-dimensional materials in their isolated forms.
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- 2018
10. Hydrogen-Assisted Growth of Large-Area Continuous Films of MoS2 on Monolayer Graphene
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Jamie H. Warner, Si Zhou, Yingqiu Zhou, Xiaochen Wang, Tongxin Chen, and Yuewen Sheng
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Photoluminescence ,Materials science ,Hydrogen ,Graphene ,business.industry ,Nucleation ,chemistry.chemical_element ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semimetal ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Monolayer ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Molybdenum disulfide - Abstract
We show how control over the chemical vapor deposition (CVD) reaction chemistry of molybdenum disulfide (MoS2) by hydrogen addition can enable the direct growth of centimeter-scale continuous films of vertically stacked MoS2 monolayer on graphene under atmospheric pressure conditions. Hydrogen addition enables longer CVD growth times at high temperature by reducing oxidation effects that would otherwise degrade the monolayer graphene. By careful control of nucleation density and growth time, high-quality monolayer MoS2 films could be formed on graphene, realizing all CVD-grown vertically stacked monolayer semimetal/semiconducting interfaces. Photoluminescence spectroscopy shows quenching of MoS2 by the underlying graphene, indicating a good interfacial charge transfer. We utilize the MoS2/graphene vertical stacks as photodetectors, with photoresponsivities reaching 2.4 A/W under 135 μW 532 nm illumination. This approach provides insights into the scalable manufacturing of high-quality two-dimensional elec...
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- 2018
11. Fluvial incision by the Qingyijiang River on the northern fringe of Mt. Huangshan, eastern China: Responses to weakening of the East Asian summer monsoon
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Shao-chen Liu, Yingqiu Zhou, Guang-lai Xu, Chunsheng Hu, and Chenqi Hu
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geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Fluvial ,Structural basin ,010502 geochemistry & geophysics ,Monsoon ,01 natural sciences ,Tectonic uplift ,Fluvial terrace ,Tributary ,Alluvium ,Physical geography ,Quaternary ,Geomorphology ,Geology ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
This paper focuses on climatic and tectonic controls to determine their relative importance to the Quaternary fluvial incision by the Qingyijiang River, eastern China. The Qingyijiang, which is one of longest tributaries of the lower Yangtze River, drains the northern piedmont of Mt. Huangshan. A field survey focused on three natural sections of the Qingyijiang in the Jingxian basin, where a well-preserved sequence of one alluvial platform (P) and three fluvial terraces (T3, T2, and T1) is presented. The heights of the platform and the terraces above river level are ~ 65, ~ 40, ~ 20, and ~ 7 m respectively. In this study, electron spin resonance (ESR), optical stimulated luminescence (OSL), and palaeomagnetic dating were applied to reconstruct the fluvial incision history of the Qingyijiang and evaluate the possible influence of tectonic uplift and/or climate change on the fluvial incision. The main results show that (1) the ages of P, T3, T2, and T1 were determined to be ∼ 1300, ∼ 900, ∼ 600, and ∼ 1.5 ka respectively, corresponding to four incision events in the Qingyijiang; (2) the East Asian summer monsoon (EASM) experienced four significant weakening events at ~ 1300, ~ 900, ~ 600, and ∼ 1.5 ka, according to previous research. Correspondingly, we propose that four significant increased periods of regional precipitation occurred at ~ 1300, ~ 900, ~ 600, and ∼ 1.5 ka in the study area because of the negative correlation between the intensity of the EASM and regional precipitation from 1960 to 2012; and (3) fluvial incision by the Qingyijiang arose as a result of the weakening of the EASM in combination with tectonic uplift, determined by matching fluvial incision history of the Qingyijiang with tectonic movement and EASM change. In addition, the weakening of the EASM climatically triggered fluvial incision by the Qingyijiang. This study supports the conclusion that major fluvial incision has been climatically triggered; however, it also suggests that the mechanism of river incision may be regionally distinctive in different climatic zones.
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- 2017
12. Electrical Breakdown of Suspended Mono- and Few-Layer Tungsten Disulfide via Sulfur Depletion Identified by in Situ Atomic Imaging
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Mark H. Rümmeli, Qu Chen, Yingqiu Zhou, Xiaowei Zhang, Haimei Zheng, Ye Fan, Jamie H. Warner, Nigel D. Browning, and Alex W. Robertson
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Materials science ,Graphene ,Tungsten disulfide ,General Engineering ,Electrical breakdown ,Analytical chemistry ,General Physics and Astronomy ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Amorphous carbon ,chemistry ,law ,Transmission electron microscopy ,Vaporization ,General Materials Science ,0210 nano-technology ,Joule heating - Abstract
The high-bias and breakdown behavior of suspended mono- and few-layer WS2 was explored by in situ aberration-corrected transmission electron microscopy. The suspended WS2 devices were found to undergo irreversible breakdown at sufficiently high biases due to vaporization of the WS2. Simultaneous to the removal of WS2 was the accompanying formation of few-layer graphene decorated with W and WS2 nanoparticles, with the carbon source attributed to organic residues present on the WS2 surface. The breakdown of few-layer WS2 resulted in the formation of faceted S-depleted WS2 tendrils along the vaporization boundary, which were found to exhibit lattice contraction indicative of S depletion, alongside pure W phases incorporated into the structure, with the interfaces imaged at atomic resolution. The combination of observing the graphitization of the amorphous carbon surface residue, W nanoparticles, and S-depleted WS2 phases following the high-bias WS2 disintegration all indicate a thermal Joule heating breakdown mechanism over an avalanche process, with WS2 destruction promoted by preferential S emission. The observation of graphene formation and the role the thin amorphous carbon layer has in the prebreakdown behavior of the device demonstrate the importance of employing encapsulated heterostructure device architectures that exclude residues.
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- 2017
13. 1 + 1 = 4? Balanced anaesthesia: A sum that is greater than its parts
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Hemal H. Patel, David M. Roth, and Yingqiu Zhou
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Pharmacology ,Binding Sites ,Balanced Anesthesia ,business.industry ,Extramural ,Anesthetics, General ,Anesthesia ,Medicine ,Receptors, GABA-A ,business ,Research Papers ,Anesthetics, Intravenous - Abstract
BACKGROUND AND PURPOSE: General anaesthetics can act on synaptic GABA(A) receptors by binding to one of three classes of general anaesthetic sites. Canonical drugs that bind selectively to only one class of site are etomidate, alphaxalone, and the mephobarbital derivative, R‐mTFD‐MPAB. We tested the hypothesis that the general anaesthetic potencies of mixtures of such site‐selective agents binding to the same or to different sites would combine additively or synergistically respectively. EXPERIMENTAL APPROACH: The potency of general anaesthetics individually or in combinations to cause loss of righting reflexes in tadpoles was determined, and the results were analysed using isobolographic methods. KEY RESULTS: The potencies of combinations of two or three site‐selective anaesthetics that all acted on a single class of site were strictly additive, regardless of which single site was involved. Combinations of two or three site‐selective anaesthetics that all bound selectively to different sites always interacted synergistically. The strength of the synergy increased with the number of separate sites involved such that the percentage of each agent's EC(50) required to cause anaesthesia was just 35% and 14% for two or three sites respectively. Propofol, which binds non‐selectively to the etomidate and R‐mTFD‐MPAB sites, interacted synergistically with each of these agents. CONCLUSIONS AND IMPLICATIONS: The established pharmacology of the three anaesthetic binding sites on synaptic GABA(A) receptors was sufficient to predict whether a mixture of anaesthetics interacted additively or synergistically to cause loss of righting reflexes in vivo. The principles established here have implications for clinical practice.
- Published
- 2019
14. High photoresponsivity in ultrathin 2D lateral graphene:WS2:graphene photodetectors using direct CVD growth
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Yuewen Sheng, Linlin Hou, Qianyang Zhang, Xiaochen Wang, Ren-Jie Chang, Hefu Huang, Tongxin Chen, Jamie H. Warner, and Yingqiu Zhou
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Materials science ,business.industry ,Graphene ,Schottky barrier ,Transistor ,Photodetector ,02 engineering and technology ,Chemical vapor deposition ,Orders of magnitude (numbers) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,0104 chemical sciences ,law.invention ,Responsivity ,law ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
We show that reducing the degree of van der Waals overlapping in all 2D ultrathin lateral devices composed of graphene:WS2:graphene leads to significant increase in photodetector responsivity. This is achieved by directly growing WS2 using chemical vapor deposition (CVD) in prepatterned graphene gaps to create epitaxial interfaces. Direct-CVD-grown graphene:WS2:graphene lateral photodetecting transistors exhibit high photoresponsivities reaching 121 A/W under 2.7 × 105 mW/cm2 532 nm illumination, which is around 2 orders of magnitude higher than similar devices made by the layer-by-layer transfer method. The photoresponsivity of our direct-CVD-grown device shows negative correlation with illumination power under different gate voltages, which is different from similar devices made by the transfer method. We show that the high photoresponsivity is due to the lowering of effective Schottky barrier height by improving the contact between graphene and WS2. Furthermore, the direct CVD growth reduces overlapping sections of WS2:Gr and leads to more uniform lateral systems. This approach provides insights into scalable manufacturing of high-quality 2D lateral electronic and optoelectronic devices.
- Published
- 2019
15. Grain boundaries as electrical conduction channels in polycrystalline monolayer WS2
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Harish Bhaskaran, Yingqiu Zhou, Syed Ghazi Sarwat, Markus J. Buehler, Gang Seob Jung, and Jamie H. Warner
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Kelvin probe force microscope ,Materials science ,Condensed matter physics ,Schottky barrier ,02 engineering and technology ,Substrate (electronics) ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Monolayer ,General Materials Science ,Electrical measurements ,Grain boundary ,Crystallite ,0210 nano-technology - Abstract
We show that grain boundaries (GBs) in polycrystalline monolayer WS2 can act as conduction channels with a lower gate onset potential for field-effect transistors made parallel, compared to devices made in pristine areas and perpendicular to GBs. Localized doping at the GB causes photoluminescence quenching and a reduced Schottky barrier with the metal electrodes, resulting in higher conductivity at lower applied bias values. Samples are grown by chemical vapor deposition with large domains of ∼100 μm, enabling numerous devices to be made within single domains, across GBs and at many similar sites across the substrate to reveal similar behaviors. We corroborate our electrical measurements with Kelvin probe microscopy, highlighting the nature of the doping-type in the material to change at the grain boundaries. Molecular dynamics simulations of the GB are used to predict the atomic structure of the dislocations and meandering tilt GB behavior on the nanoscale. These results show that GBs can be used to provide conduction pathways that are different to transport across GBs and in pristine area for potential electronic applications.
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- 2019
16. Grain Boundaries as Electrical Conduction Channels in Polycrystalline Monolayer WS
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Yingqiu, Zhou, Syed Ghazi, Sarwat, Gang Seob, Jung, Markus J, Buehler, Harish, Bhaskaran, and Jamie H, Warner
- Abstract
We show that grain boundaries (GBs) in polycrystalline monolayer WS
- Published
- 2019
17. High Photoresponsivity in Ultrathin 2D Lateral Graphene:WS
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Tongxin, Chen, Yuewen, Sheng, Yingqiu, Zhou, Ren-Jie, Chang, Xiaochen, Wang, Hefu, Huang, Qianyang, Zhang, Linlin, Hou, and Jamie H, Warner
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We show that reducing the degree of van der Waals overlapping in all 2D ultrathin lateral devices composed of graphene:WS
- Published
- 2019
18. Symmetry-Controlled Reversible Photovoltaic Current Flow in Ultrathin All 2D Vertically Stacked Graphene/MoS
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Yingqiu, Zhou, Wenshuo, Xu, Yuewen, Sheng, Hefu, Huang, Qianyang, Zhang, Linlin, Hou, Viktoryia, Shautsova, and Jamie H, Warner
- Abstract
Atomically thin vertical heterostructures are promising candidates for optoelectronic applications, especially for flexible and transparent technologies. Here, we show how ultrathin all two-dimensional vertical-stacked type-II heterostructure devices can be assembled using only materials grown by chemical vapor deposition, with graphene (Gr) as top and bottom electrodes and MoS
- Published
- 2019
19. Symmetry-controlled reversible photovoltaic current flow in ultrathin all 2D vertically stacked graphene/MoS2/WS2/graphene devices
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Yuewen Sheng, Linlin Hou, Wenshuo Xu, Hefu Huang, Yingqiu Zhou, Qianyang Zhang, Viktoryia Shautsova, and Jamie H. Warner
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Photocurrent ,Materials science ,business.industry ,Graphene ,Doping ,Heterojunction ,02 engineering and technology ,Chemical vapor deposition ,Dielectric ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,law.invention ,Semiconductor ,Stack (abstract data type) ,law ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
Atomically thin vertical heterostructures are promising candidates for optoelectronic applications, especially for flexible and transparent technologies. Here, we show how ultrathin all two-dimensional vertical-stacked type-II heterostructure devices can be assembled using only materials grown by chemical vapor deposition, with graphene (Gr) as top and bottom electrodes and MoS2/WS2 as the active semiconductor layers in the middle. Furthermore, we show that the stack symmetry, which dictates the type-II directionality, is the dominant factor in controlling the photocurrent direction upon light irradiation, whereas in homobilayers, photocurrent direction cannot be easily controlled because the tunnel barrier is determined by the doping levels of the graphene, which appears fixed for top and bottom graphene layers due to their dielectric environments. Therefore, the ability to direct photovoltaic current flow is demonstrated to be only possible using heterobilayers (HBs) and not homobilayers. We study the photovoltaic effects in more than 40 devices, which allows for statistical verification of performance and comparative behavior. The photovoltage in the graphene/transition-metal dichalcogenide-heterobilayer/graphene (Gr/TMD-HB (MoS2/WS2)/Gr) increases up to 10 times that generated in the monolayer TMD devices under the same optical illumination power, due to efficient charge transfer between WS2 and MoS2 and extraction to graphene electrodes. By applying external gate voltages ( Vg), the band alignment can be tuned, which in turn controls the photovoltaic effect in the vertical heterostructures. The tunneling-assisted interlayer charge recombination also plays a significant role in modulating the photovoltaic effect in the Gr/TMD-HB/Gr. These results provide important insights into how layer symmetry in vertical-stacked graphene/TMD/graphene ultrathin optoelectronics can be used to control electron flow directions during photoexcitation and open up opportunities for tandem cell assembly.
- Published
- 2019
20. Photoinduced Schottky Barrier Lowering in 2D Monolayer WS 2 Photodetectors
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Haijie Tan, Xiaochen Wang, Youmin Rong, Yingqiu Zhou, Ye Fan, and Jamie H. Warner
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Photocurrent ,Materials science ,Equivalent series resistance ,business.industry ,Schottky barrier ,Schottky diode ,Photodetector ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Semiconductor ,Monolayer ,Optoelectronics ,0210 nano-technology ,business - Abstract
Arrays of metal–semiconductor–metal (MSM) photodetectors are fabricated using chemical vapor deposition (CVD) grown 2D monolayer WS2 as the absorbing semiconductor (WS2) with gold electrodes. A study of the channel length dependence (0.2–6.4 μm) on the photoresponsivity and gain show substantial increase in performance is achieved when the length is reduced to 200 nm. A large gain factor of up to 480 is measured for 200 nm length devices and attributed to lowering of the Schottky barriers due to the filling of trapped states between the metal contact and WS2 by photogenerated carriers. Only photoexcited carriers close to the interface contribute to filling trap states and lowering the Schottky barrier and therefore increasing channel length only adds series resistance to the device that reduces performance. These results reveal detailed insights regarding the mechanisms for photocurrent generation in lateral MSM photodetectors that employ CVD grown monolayer WS2 material, which has important consequences for the commercial applications and large scale development of 2D imaging arrays.
- Published
- 2016
21. Controlling Photoluminescence Enhancement and Energy Transfer in WS 2 :hBN:WS 2 Vertical Stacks by Precise Interlayer Distances
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Yingqiu Zhou, Yuewen Sheng, Tian Jiang, Wenshuo Xu, Yizhi Wang, Michael S. Strano, Jamie H. Warner, and Daichi Kozawa
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Electron density ,Materials science ,Photoluminescence ,business.industry ,Doping ,Heterojunction ,02 engineering and technology ,General Chemistry ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,Biomaterials ,Monolayer ,Optoelectronics ,General Materials Science ,Quantum efficiency ,Photonics ,0210 nano-technology ,business ,Biotechnology - Abstract
2D semiconducting transition metal dichalcogenides (TMDs) are endowed with fascinating optical properties especially in their monolayer limit. Insulating hBN films possessing customizable thickness can act as a separation barrier to dictate the interactions between TMDs. In this work, vertical layered heterostructures (VLHs) of WS2 :hBN:WS2 are fabricated utilizing chemical vapor deposition (CVD)-grown materials, and the optical performance is evaluated through photoluminescence (PL) spectroscopy. Apart from the prohibited indirect optical transition due to the insertion of hBN spacers, the variation in the doping level of WS2 drives energy transfer to arise from the layer with lower quantum efficiency to the other layer with higher quantum efficiency, whereby the total PL yield of the heterosystem is increased and the stack exhibits a higher PL intensity compared to the sum of those in the two WS2 constituents. Such doping effects originate from the interfaces that WS2 monolayers reside on and interact with. The electron density in the WS2 is also controlled and subsequent modulation of PL in the heterostructure is demonstrated by applying back-gated voltages. Other influential factors include the strain in WS2 and temperature. Being able to tune the energy transfer in the VLHs may expand the development of photonic applications in 2D systems.
- Published
- 2019
22. Utilizing interlayer excitons in bilayer WS2 for increased photovoltaic response in ultrathin graphene vertical cross-bar photodetecting tunneling transistors
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Yuewen Sheng, Haijie Tan, Jamie H. Warner, Wenshuo Xu, Ye Fan, and Yingqiu Zhou
- Subjects
Materials science ,business.industry ,Graphene ,Photoconductivity ,Exciton ,Bilayer ,General Engineering ,General Physics and Astronomy ,Heterojunction ,02 engineering and technology ,Dielectric ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,0104 chemical sciences ,law.invention ,law ,Monolayer ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Quantum tunnelling - Abstract
Here we study the layer-dependent photoconductivity in Gr/WS2/Gr vertical stacked tunneling (VST) cross-bar devices made using two-dimensional (2D) materials all grown by chemical vapor deposition. The larger number of devices (>100) enables a statistically robust analysis on the comparative differences in the photovoltaic response of monolayer and bilayer WS2, which cannot be achieved in small batch devices made using mechanically exfoliated materials. We show a dramatic increase in photovoltaic response for Gr/WS2(2L)/Gr compared to monolayers because of the long inter- and intralayer exciton lifetimes and the small exciton binding energy (both interlayer and intralayer excitons) of bilayer WS2 compared with that of monolayer WS2. Different doping levels and dielectric environments of top and bottom graphene electrodes result in a potential difference across a ∼1 nm vertical device, which gives rise to large electric fields perpendicular to the WS2 layers that cause band structure modification. Our results show how precise control over layer number in all 2D VST devices dictates the photophysics and performance for photosensing applications.
- Published
- 2018
23. Utilizing Interlayer Excitons in Bilayer WS
- Author
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Yingqiu, Zhou, Haijie, Tan, Yuewen, Sheng, Ye, Fan, Wenshuo, Xu, and Jamie H, Warner
- Abstract
Here we study the layer-dependent photoconductivity in Gr/WS
- Published
- 2018
24. High-Performance All 2D-Layered Tin Disulfide: Graphene Photodetecting Transistors with Thickness-Controlled Interface Dynamics
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Haijie Tan, Hefu Huang, Xiaochen Wang, Jamie H. Warner, Benjamin F. Porter, Tongxin Chen, Yingqiu Zhou, Yuewen Sheng, Harish Bhaskaran, and Ren-Jie Chang
- Subjects
Materials science ,business.industry ,Graphene ,Schottky barrier ,Transistor ,chemistry.chemical_element ,Photodetector ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,chemistry ,Transition metal ,law ,Electrode ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Tin - Abstract
Tin disulfide crystals with layered two-dimensional (2D) sheets are grown by chemical vapor deposition using a novel precursor approach and integrated into all 2D transistors with graphene (Gr) electrodes. The Gr:SnS2:Gr transistors exhibit excellent photodetector response with high detectivity and photoresponsivity. We show that the response of the all 2D photodetectors depends upon charge trapping at the interface and the Schottky barrier modulation. The thickness-dependent SnS2 measurements in devices reveal a transition from the interface-dominated response for thin crystals to bulklike response for the thicker SnS2 crystals, showing the sensitivity of devices fabricated using layered materials on the number of layers. These results show that SnS2 has photosensing performance when combined with Gr electrodes that is comparable to other 2D transition metal dichalcogenides of MoS2 and WS2.
- Published
- 2018
25. Hydrogen-Assisted Growth of Large-Area Continuous Films of MoS
- Author
-
Tongxin, Chen, Yingqiu, Zhou, Yuewen, Sheng, Xiaochen, Wang, Si, Zhou, and Jamie H, Warner
- Abstract
We show how control over the chemical vapor deposition (CVD) reaction chemistry of molybdenum disulfide (MoS
- Published
- 2018
26. Lateral graphene‐contacted vertically stacked WS2/MoS2 hybrid photodetectors with large gain
- Author
-
Wenshuo Xu, Qu Chen, Xiaochen Wang, Chit Siong Lau, Yuewen Sheng, Martin Tweedie, Jamie H. Warner, Yingqiu Zhou, Haijie Tan, and Ye Fan
- Subjects
Materials science ,business.industry ,Graphene ,Mechanical Engineering ,Photoconductivity ,Photodetector ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Mechanics of Materials ,law ,Monolayer ,Density of states ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Order of magnitude ,Power density - Abstract
A demonstration is presented of how significant improvements in all-2D photodetectors can be achieved by exploiting the type-II band alignment of vertically stacked WS2 /MoS2 semiconducting heterobilayers and finite density of states of graphene electrodes. The photoresponsivity of WS2 /MoS2 heterobilayer devices is increased by more than an order of magnitude compared to homobilayer devices and two orders of magnitude compared to monolayer devices of WS2 and MoS2 , reaching 103 A W-1 under an illumination power density of 1.7 × 102 mW cm-2 . The massive improvement in performance is due to the strong Coulomb interaction between WS2 and MoS2 layers. The efficient charge transfer at the WS2 /MoS2 heterointerface and long trapping time of photogenerated charges contribute to the observed large photoconductive gain of ≈3 × 104 . Laterally spaced graphene electrodes with vertically stacked 2D van der Waals heterostructures are employed for making high-performing ultrathin photodetectors.
- Published
- 2017
27. Lateral Graphene-Contacted Vertically Stacked WS
- Author
-
Haijie, Tan, Wenshuo, Xu, Yuewen, Sheng, Chit Siong, Lau, Ye, Fan, Qu, Chen, Martin, Tweedie, Xiaochen, Wang, Yingqiu, Zhou, and Jamie H, Warner
- Abstract
A demonstration is presented of how significant improvements in all-2D photodetectors can be achieved by exploiting the type-II band alignment of vertically stacked WS
- Published
- 2017
28. Photoluminescence segmentation within individual hexagonal monolayer tungsten disulfide domains grown by chemical vapor deposition
- Author
-
Wenshuo Xu, Yingqiu Zhou, Xiaochen Wang, Yuewen Sheng, Mauricio Terrones, Siqi Ying, Ana Laura Elías, Alexander M. Korsunsky, Harish Bhaskaran, Zhong Lin, Kazunori Fujisawa, and Jamie H. Warner
- Subjects
Materials science ,Photoluminescence ,genetic structures ,Exciton ,Tungsten disulfide ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Crystallography ,chemistry ,Monolayer ,General Materials Science ,Reactivity (chemistry) ,Irradiation ,Trion ,0210 nano-technology - Abstract
We show that hexagonal domains of monolayer tungsten disulfide (WS2) grown by chemical vapor deposition (CVD) with powder precursors can have discrete segmentation in their photoluminescence (PL) emission intensity, forming symmetric patterns with alternating bright and dark regions. Two-dimensional maps of the PL reveal significant reduction within the segments associated with the longest sides of the hexagonal domains. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. Monolayers of WS2 hexagonal islands transferred to new substrates still exhibit this PL segmentation, ruling out local strain in the regions as the dominant cause. High-power laser irradiation causes preferential degradation of the bright segments by sulfur removal, indicating the presence of a more defective region that is higher in oxidative reactivity. Atomic force microscopy (AFM) images of topography and amplitude modes show uniform thickness of the WS2 domains and no signs of segmentation. However, AFM phase maps do show the same segmentation of the domain as the PL maps and indicate that it is caused by some kind of structural difference that we could not clearly identify. These results provide important insights into the spatially varying properties of these CVD-grown transition metal dichalcogenide materials, which may be important for their effective implementation in fast photo sensors and optical switches.
- Published
- 2017
29. Ultrathin 2D photodetectors utilizing chemical vapor deposition grown WS2 with graphene electrodes
- Author
-
Yingqiu Zhou, Haijie Tan, Qu Chen, Jamie H. Warner, Ye Fan, and Wenshuo Xu
- Subjects
Materials science ,Graphene ,business.industry ,Bilayer ,General Engineering ,General Physics and Astronomy ,Photodetector ,Heterojunction ,02 engineering and technology ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,law ,Electrode ,Monolayer ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Bilayer graphene - Abstract
In this report, graphene (Gr) is used as a 2D electrode and monolayer WS2 as the active semiconductor in ultrathin photodetector devices. All of the 2D materials are grown by chemical vapor deposition (CVD) and thus pose as a viable route to scalability. The monolayer thickness of both electrode and semiconductor gives these photodetectors ∼2 nm thickness. We show that graphene is different to conventional metal (Au) electrodes due to the finite density of states from the Dirac cones of the valence and conduction bands, which enables the photoresponsivity to be modulated by electrostatic gating and light input control. We demonstrate lateral Gr-WS2-Gr photodetectors with photoresponsivities reaching 3.5 A/W under illumination power densities of 2.5 × 10(7) mW/cm(2). The performance of monolayer WS2 is compared to bilayer WS2 in photodetectors and we show that increased photoresponsivity is achieved in the thicker bilayer WS2 crystals due to increased optical absorption. This approach of incorporating graphene electrodes in lateral TMD based devices provides insights on the contact engineering in 2D optoelectronics, which is crucial for the development of high performing ultrathin photodetector arrays for versatile applications.
- Published
- 2016
30. Negative Electro-conductance in Suspended 2D WS
- Author
-
Ye, Fan, Alex W, Robertson, Xiaowei, Zhang, Martin, Tweedie, Yingqiu, Zhou, Mark H, Rummeli, Haimei, Zheng, and Jamie H, Warner
- Abstract
We study the in situ electro-conductance in nanoscale electronic devices composed of suspended monolayer WS
- Published
- 2016
31. Negative electro-conductance in Suspended 2D WS2 nanoscale devices
- Author
-
Martin Tweedie, Yingqiu Zhou, Xiaowei Zhang, Haimei Zheng, Mark H. Rümmeli, Alex W. Robertson, Jamie H. Warner, and Ye Fan
- Subjects
Materials science ,business.industry ,Analytical chemistry ,Conductance ,02 engineering and technology ,Electron ,Inelastic scattering ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Semiconductor ,Transmission electron microscopy ,Monolayer ,Cathode ray ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business ,Beam (structure) - Abstract
We study the in-situ electro-conductance in nanoscale electronic devices composed of suspended monolayer 2D WS2 with metal electrodes inside an aberration-corrected transmission electron microscope. Monitoring the conductance changes when the device is exposed to the electron beam with 80keV energy reveals a decrease in conductivity with increasing beam current density. The response time of the electro-conductance when exposed to the electron beam is substantially faster than the recovery time when the beam is turned off. We proposed a charge trap model that accounts for excitation of electrons into the conduction band and localized trap states from energy supplied by inelastic scattering of incident 80keV electrons. These results show how monolayer transition metal dichalcogenide 2D semiconductors can be used as transparent direct electron detectors in ultrathin nanoscale devices.
- Published
- 2016
32. Revealing defect-state photoluminescence in monolayer WS2 by cryogenic laser processing
- Author
-
Wenshuo Xu, Jason M. Smith, Yingqiu Zhou, Xiaochen Wang, Youmin Rong, Yuewen Sheng, Jamie H. Warner, and Zhengyu He
- Subjects
Materials science ,Photoluminescence ,Tungsten disulfide ,General Engineering ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,Temperature cycling ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,chemistry.chemical_compound ,Transition metal ,chemistry ,Monolayer ,symbols ,Degradation (geology) ,General Materials Science ,0210 nano-technology ,Raman spectroscopy ,Spectroscopy - Abstract
Understanding the stability of monolayer transition metal dichalcogenides in atmospheric conditions has important consequences for their handling, life-span, and utilization in applications. We show that cryogenic photoluminescence spectroscopy (PL) is a highly sensitive technique to the detection of oxidation induced degradation of monolayer tungsten disulfide (WS2) caused by exposure to ambient conditions. Although long-term exposure to atmospheric conditions causes massive degradation from oxidation that is optically visible, short-term exposure produces no obvious changes to the PL or Raman spectra measured at either room temperature or even cryogenic environment. Laser processing was employed to remove the surface adsorbents, which enables the defect states to be detected via cryogenic PL spectroscopy. Thermal cycling to room temperature and back down to 77 K shows the process is reversible. We also monitor the degradation process of WS2 using this method, which shows that the defect related peak can be observed after one month aging in ambient conditions.
- Published
- 2016
33. Local and transient gene expression primes the liver to resist cancer metastasis
- Author
-
Tyler J. Goodwin, Sara Musetti, Rihe Liu, Leaf Huang, and Yingqiu Zhou
- Subjects
0301 basic medicine ,Male ,Pathology ,medicine.medical_specialty ,Inflammation ,CXCR4 ,Article ,Metastasis ,03 medical and health sciences ,Mice ,Cell Movement ,Cell Line, Tumor ,Medicine ,Animals ,Humans ,Neoplasm Invasiveness ,Molecular Targeted Therapy ,Neoplasm Metastasis ,Cell Proliferation ,Mice, Inbred BALB C ,CXCR4 antagonist ,business.industry ,Gene Expression Profiling ,Liver Neoplasms ,General Medicine ,DNA ,medicine.disease ,Primary tumor ,Chemokine CXCL12 ,Recombinant Proteins ,Gene Expression Regulation, Neoplastic ,Disease Models, Animal ,030104 developmental biology ,HEK293 Cells ,Interferometry ,Cancer cell ,Systemic administration ,Cancer research ,Nanoparticles ,Female ,medicine.symptom ,business ,Cell activation ,Immunosuppressive Agents ,Signal Transduction - Abstract
The liver is the primary site of metastasis for gastrointestinal cancers and is a location highly susceptible to the establishment of metastasis in numerous other primary cancers, including breast, lung, and pancreatic cancers. The current standard of care typically consists of primary tumor resection and systemic administration of potent but toxic chemotherapeutics, yielding a minimal improvement in the median survival rate. CXCL12, a chemokine, is a key factor for activating the migration/survival pathways of CXCR4+ cancer cells and for recruiting immunosuppressive cells to areas of inflammation. Therefore, reducing CXCL12 concentrations within the liver has the potential to decrease tumor and immunosuppressive cell activation/migration within the liver. However, because of off-target toxicities associated with systemic administration of anti-CXCL12 therapies, transient and liver-specific expression of a CXCL12 trap is necessary. To address this challenge, we developed a lipid calcium phosphate nanoparticle optimized for delivering plasmid DNA, encoding an engineered CXCL12 protein trap, to the nucleus of liver hepatocytes. This pCXCL12-trap formulation yielded transient (4 days) liver-specific expression, which greatly decreased the occurrence of liver metastasis in two aggressive liver metastasis models, including colorectal [CT-26(FL3)] and breast (4T1) cancers. Subsequent studies in an aggressive human colorectal liver metastasis model (HT-29) decreased the establishment of liver metastasis more effectively than did systemic administration of the CXCL12 protein trap and to a level comparable to a high-dose regimen of a potent CXCR4 antagonist (AMD3100).
- Published
- 2016
34. Biexciton Formation in Bilayer Tungsten Disulfide
- Author
-
Wenshuo Xu, Zhengyu He, Youmin Rong, Yuewen Sheng, Shaoqiang Guo, Yingqiu Zhou, Jamie H. Warner, Jason M. Smith, Junying Zhang, and Xiaochen Wang
- Subjects
Materials science ,Condensed matter physics ,Bilayer ,Exciton ,Binding energy ,General Engineering ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,symbols.namesake ,Monolayer ,symbols ,General Materials Science ,Direct and indirect band gaps ,0210 nano-technology ,Electronic band structure ,Raman spectroscopy ,Biexciton - Abstract
Monolayer transition metal dichalcogenides (TMDs) are direct band gap semiconductors, and their 2D structure results in large binding energies for excitons, trions, and biexcitons. The ability to explore many-body effects in these monolayered structures has made them appealing for future optoelectronic and photonic applications. The band structure changes for bilayer TMDs with increased contributions from indirect transitions, and this has limited similar in-depth studies of biexcitons. Here, we study biexciton emission in bilayer WS2 grown by chemical vapor deposition as a function of temperature. A biexciton binding energy of 36 �4 meV is measured in the as-grown bilayer WS2 containing 0.4% biaxial strain as determined by Raman spectroscopy. The biexciton emission was difficult to detect when the WS2 was transferred to another substrate to release the stain. Density functional theory calculations show that 0.4% of tensile strain lowers the direct band gap by about 55 meV without significant change to the indirect band gap, which can cause an increase in the quantum yield of direct exciton transitions and the emission from biexcitons formed by two direct gap excitons. We find that the biexciton emission decreases dramatically with increased temperature due to the thermal dissociation, with an activation energy of 26 � 5 meV. These results show how strain can be used to tune the many-body effects in bilayered TMD materials and extend the photonic applications beyond pure monolayer systems.
- Published
- 2016
35. Doping graphene transistors using vertical stacked monolayer WS2 heterostructures grown by chemical vapor deposition
- Author
-
Ben Porter, Jamie H. Warner, Harish Bhaskaran, Haijie Tan, Yingqiu Zhou, Chit Siong Lau, Zhengyu He, Ye Fan, Youmin Rong, and Shanshan Wang
- Subjects
Materials science ,Condensed matter physics ,Graphene ,Field effect ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,law ,Monolayer ,General Materials Science ,Work function ,Trion ,0210 nano-technology ,Bilayer graphene ,Graphene nanoribbons - Abstract
We study the interactions in graphene/WS2 two-dimensional (2D) layered vertical heterostructures with variations in the areal coverage of graphene by the WS2. All 2D materials were grown by chemical vapor deposition and transferred layer by layer. Photoluminescence (PL) spectroscopy of WS2 on graphene showed PL quenching along with an increase in the ratio of exciton/trion emission, relative to WS2 on SiO2 surface, indicating a reduction in the n-type doping levels of WS2 as well as reduced radiative recombination quantum yield. Electrical measurements of a total of 220 graphene field effect transistors with different WS2 coverage showed double-Dirac points in the field effect measurements, where one is shifted closer toward the 0 V gate neutrality position due to the WS2 coverage. Photoirradiation of the WS2 on graphene region caused further Dirac point shifts, indicative of a reduction in the p-type doping levels of graphene, revealing that the photogenerated excitons in WS2 are split across the heterostructure by electron transfer from WS2 to graphene. Kelvin probe microscopy showed that regions of graphene covered with WS2 had a smaller work function and supports the model of electron transfer from WS2 to graphene. Our results demonstrate the formation of junctions within a graphene transistor through the spatial tuning of the work function of graphene using these 2D vertical heterostructures.
- Published
- 2016
36. Fabrication and properties of ultraviolet photo-detectors based on SiC nanowires
- Author
-
Xiaoyan Yu, Yingqiu Zhou, He Yanlan, Gang Peng, and Gong-Yi Li
- Subjects
Diffraction ,chemistry.chemical_classification ,Materials science ,Fabrication ,business.industry ,Nanowire ,General Physics and Astronomy ,chemistry.chemical_element ,Polymer ,Zinc ,medicine.disease_cause ,chemistry.chemical_compound ,chemistry ,Ferrocene ,medicine ,Optoelectronics ,business ,Electrical conductor ,Ultraviolet - Abstract
A new type of ultraviolet photo-detectors (UVPDs) based on a bundle of highly aligned SiC nanowires was fabricated and the photo-electric properties of the UVPDs including I–V characteristics and time response were studied in this work. SiC nanowires were prepared by pyrolysis of a polymer precursor with ferrocene as the catalyst by a CVD route. The diameters of SiC nanowires varied from 100 to 200 nm while they were some centimeters long and the SiC nanowires were with zinc blended cubic form (β-SiC) tested by X-ray diffraction. A bundle of nanowires was fixed onto two legs’ base by conductive silver paste to form the UVPDs. The electrical measurement of the device showed a significant increase of current when the device was exposed to 254 nm UV light, and the rising time of the device is very short, but the falling time is relatively long. Our results show that the UVPDs based on SiC nanowires have excellent electrical and optical properties which can be potentially applied.
- Published
- 2012
37. Pseudo-cyclization through intramolecular hydrogen bond enables discovery of pyridine substituted pyrimidines as new Mer kinase inhibitors
- Author
-
H. Shelton Earp, Minjung Lee, Jacqueline Norris-Drouin, Yingqiu Zhou, Deborah DeRyckere, Wendy M. Stewart, Douglas K. Graham, Dehui Zhang, Michael J. Miley, Christopher Cummings, Mischa Machius, Stephen V. Frye, William P. Janzen, Xiaodong Wang, Debra Hunter, Susan Sather, Michael A. Stashko, Weihe Zhang, Dmitri Kireev, and Gregory Kirkpatrick
- Subjects
Stereochemistry ,Pyridines ,Receptor Protein-Tyrosine Kinases ,Antineoplastic Agents ,C-Mer Tyrosine Kinase ,Receptor tyrosine kinase ,Article ,chemistry.chemical_compound ,Structure-Activity Relationship ,Cell Line, Tumor ,Proto-Oncogene Proteins ,Drug Discovery ,Structure–activity relationship ,Humans ,Protein Kinase Inhibitors ,biology ,c-Mer Tyrosine Kinase ,Kinase ,Hydrogen Bonding ,Cyclohexanols ,Pyrimidines ,chemistry ,Biochemistry ,Cell culture ,Cyclization ,Drug Design ,biology.protein ,Molecular Medicine ,Phosphorylation ,Lead compound - Abstract
Abnormal activation or overexpression of Mer receptor tyrosine kinase has been implicated in survival signaling and chemoresistance in many human cancers. Consequently, Mer is a promising novel cancer therapeutic target. A structure-based drug design approach using a pseudo-ring replacement strategy was developed and validated to discover a new family of pyridinepyrimidine analogues as potent Mer inhibitors. Through SAR studies, 10 (UNC2250) was identified as the lead compound for further investigation based on high selectivity against other kinases and good pharmacokinetic properties. When applied to live cells, 10 inhibited steady-state phosphorylation of endogenous Mer with an IC50 of 9.8 nM and blocked ligand-stimulated activation of a chimeric EGFR-Mer protein. Treatment with 10 also resulted in decreased colony-forming potential in rhabdoid and NSCLC tumor cells, thereby demonstrating functional antitumor activity. The results provide a rationale for further investigation of this compound for therapeutic application in patients with cancer.
- Published
- 2013
38. Revealing Strain-Induced Effects in Ultrathin Heterostructures at the Nanoscale.
- Author
-
Sarwat, Syed Ghazi, Tweedie, Martin, Porter, Benjamin F., Yingqiu Zhou, Yuewen Sheng, Mol, Jan, Warner, Jamie, and Bhaskaran, Harish
- Published
- 2018
- Full Text
- View/download PDF
39. Experimental study of plasmon in a grating coupled graphene device with a resonant cavity
- Author
-
Yongtao Liu, Shiqiao Qin, Xueao Zhang, Jingyue Fang, Yingqiu Zhou, Bo Yan, and Renbing Li
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Graphene ,Terahertz radiation ,Chemical vapor deposition ,Grating ,Optical conductivity ,law.invention ,Optics ,law ,Optoelectronics ,business ,Bilayer graphene ,Graphene nanoribbons ,Plasmon - Abstract
Plasmon was probed from graphene which was grown by chemical vapor deposition using terahertz time-domain spectroscopy at room temperature. Graphene was laid on a resonant cavity, and metal grating was then deposited on top of them. For the THz light polarized along the grid fingers, the optical conductivity of graphene changed from Drude response into strongly Lorentz behavior with a peak formed in the THz-region. These experimental results are highly consistent with the theoretical prediction of a single layer graphene. It confirms that the graphene plasmon frequency can be tuned by the length of grating. Moreover, the extinction in the transmission of single-layer graphene can also be increased beyond 60%.
- Published
- 2015
40. UV-induced SiC nanowire sensors
- Author
-
Yingqiu Zhou, Xiaoyan Yu, Hossam Haick, Gong Y Li, He Yanlan, Gang Peng, and Xue A Zhang
- Subjects
Photocurrent ,Materials science ,Acoustics and Ultrasonics ,business.industry ,Schottky barrier ,Nanowire ,Photovoltaic effect ,Photoelectric effect ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,Charge carrier ,business ,Ohmic contact ,Dark current - Abstract
Ultraviolet (UV)-induced sensors based on a single SiC nanowire (NW) were fabricated and the photoelectric properties including I–V characteristics and time response of the UV sensors were studied. SiC NWs (NWs) were prepared through pyrolyzing a polymer precursor with ferrocene as the catalyst by a CVD route. To elucidate the physical mechanism giving rise to the photoelectrical response in SiC NW sensors, three kinds of contacts between electrodes and SiC NW were prepared, i.e. Schottky contact, p–n junction contact, and Ohmic contact. The photoelectric measurements of the device with Schottky contact indicates the lowest dark current and the largest photocurrent. The results suggest that photocurrent generated at SiC NW-electrode contacts is a result of the photovoltaic effect, in which a built-in electric field accelerates photo generated charge carriers to the electronic contacts. The UV sensors based on SiC NWs could be applied in a harsh environment due to the excellent physical stability and photoelectric properties.
- Published
- 2015
41. Local and transient gene expression primes the liver to resist cancer metastasis.
- Author
-
Goodwin, Tyler J., Yingqiu Zhou, Musetti, Sara N., Rihe Liu, and Huang, Leaf
- Subjects
METASTASIS ,CHEMOKINES ,CALCIUM phosphate ,GENE expression ,COLON cancer ,BREAST cancer - Abstract
The article discusses a study on the effect of reduced concentrations of the chemokine CXCL12 within the liver on cancer metastasis. The study used a lipid calcium phosphate nanoparticle optimized for delivering plasmid DNA in order to address transient and liver-specific expression of a CXCL12 trap. It showed a reduced occurrence of liver metastasis in colorectal and breast cancers.
- Published
- 2016
- Full Text
- View/download PDF
42. Correction to Pseudo-Cyclization through Intramolecular Hydrogen Bond Enables Discovery of Pyridine Substituted Pyrimidines as New Mer Kinase Inhibitors
- Author
-
Minjung Lee, Mischa Machius, Wendy M. Stewart, Henry Shelton Earp, Susan Sather, William P. Janzen, Yingqiu Zhou, Jacqueline Norris-Drouin, Stephen V. Frye, Michael A. Stashko, Xiaodong Wang, Christopher G. Cummings, Weihe Zhang, Dmitri Kireev, Deborah DeRyckere, Douglas K. Graham, Dehui Zhang, Michael J. Miley, Debra Hunter, and Gregory Kirkpatrick
- Subjects
chemistry.chemical_compound ,chemistry ,Stereochemistry ,Hydrogen bond ,Kinase ,Intramolecular force ,Drug Discovery ,Pyridine ,Molecular Medicine - Published
- 2014
43. Experimental study of plasmon in a grating coupled graphene device with a resonant cavity.
- Author
-
Bo Yan, Jingyue Fang, Shiqiao Qin, Yongtao Liu, Yingqiu Zhou, Renbing Li, and Xue-Ao Zhang
- Subjects
CHEMISTRY experiments ,GRAPHENE ,PLASMONS (Physics) ,RESONANT states ,CHEMICAL vapor deposition ,TERAHERTZ spectroscopy - Abstract
Plasmon was probed from graphene which was grown by chemical vapor deposition using terahertz time-domain spectroscopy at room temperature. Graphene was laid on a resonant cavity, and metal grating was then deposited on top of them. For the THz light polarized along the grid fingers, the optical conductivity of graphene changed from Drude response into strongly Lorentz behavior with a peak formed in the THz-region. These experimental results are highly consistent with the theoretical prediction of a single layer graphene. It confirms that the graphene plasmon frequency can be tuned by the length of grating. Moreover, the extinction in the transmission of single-layer graphene can also be increased beyond 60%. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
44. Chemical Vapor Deposition Growth of Two-Dimensional Monolayer Gallium Sulfide Crystals Using Hydrogen Reduction of Ga 2 S 3
- Author
-
Hefu Huang, Sha Li, Yuewen Sheng, Benjamin F. Porter, Xiaochen Wang, Harish Bhaskaran, Ren-Jie Chang, Ja Kyung Lee, Tongxin Chen, Yingqiu Zhou, and Jamie H. Warner
- Subjects
Materials science ,Hydrogen ,General Chemical Engineering ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,Chemical vapor deposition ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Gallium sulfide ,Article ,0104 chemical sciences ,law.invention ,lcsh:Chemistry ,Hydrogen carrier ,lcsh:QD1-999 ,chemistry ,Chemical engineering ,law ,Monolayer ,Electron microscope ,0210 nano-technology ,Ambient pressure - Abstract
Two-dimensional gallium sulfide (GaS) crystals are synthesized by a simple and efficient ambient pressure chemical vapor deposition (CVD) method using a single-source precursor of Ga2S3. The synthesized GaS structures involve triangular monolayer domains and multilayer flakes with thickness of 1 and 15 nm, respectively. Regions of continuous films of GaS are also achieved with about 0.7 cm2 uniform coverage. This is achieved by using hydrogen carrier gas and the horizontally placed SiO2/Si substrates. Electron microscopy and spectroscopic measurements are used to characteristic the CVD-grown materials. This provides important insights into novel approaches for enlarging the domain size of GaS crystals and understanding of the growth mechanism using this precursor system.
- Full Text
- View/download PDF
45. Super-Resolution Nanolithography of Two-Dimensional Materials by Anisotropic Etching
- Author
-
Bjarke Sørensen Jessen, Lauge Gammelgaard, Timothy J. Booth, Dorte R. Danielsen, Manh-Ha Doan, Yingqiu Zhou, Peter Bøggild, Anton Lyksborg-Andersen, and Kirstine E.S. Nielsen
- Subjects
Reactive ion etching ,Materials science ,Downsizing ,TMDs ,FOS: Physical sciences ,Applied Physics (physics.app-ph) ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Crystal ,chemistry.chemical_compound ,Etching (microfabrication) ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Tungsten diselenide ,General Materials Science ,Reactive-ion etching ,Nanostructuring ,Molybdenum disulfide ,Lithography ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Materials Science (cond-mat.mtrl-sci) ,Anisotropic etching ,Physics - Applied Physics ,2D materials ,021001 nanoscience & nanotechnology ,hBN ,0104 chemical sciences ,Nanolithography ,chemistry ,Electron beam lithography ,Optoelectronics ,Wulff constructions ,0210 nano-technology ,business ,Electron-beam lithography - Abstract
Nanostructuring allows altering of the electronic and photonic properties of two-dimensional (2D) materials. The efficiency, flexibility, and convenience of top-down lithography processes are, however, compromised by nanometer-scale edge roughness and resolution variability issues, which especially affect the performance of 2D materials. Here, we study how dry anisotropic etching of multilayer 2D materials with sulfur hexafluoride (SF6) may overcome some of these issues, showing results for hexagonal boron nitride (hBN), tungsten disulfide (WS2), tungsten diselenide (WSe2), molybdenum disulfide (MoS2), and molybdenum ditelluride (MoTe2). Scanning electron microscopy and transmission electron microscopy reveal that etching leads to anisotropic hexagonal features in the studied transition metal dichalcogenides, with the relative degree of anisotropy ranked as: WS2 > WSe2 > MoTe2 ∼MoS2. Etched holes are terminated by zigzag edges while etched dots (protrusions) are terminated by armchair edges. This can be explained by Wulff constructions, taking the relative stabilities of the edges and the AA′ stacking order into account. Patterns in WS2 are transferred to an underlying graphite layer, demonstrating a possible use for creating sub-10 nm features. In contrast, multilayer hBN exhibits no lateral anisotropy but shows consistent vertical etch angles, independent of crystal orientation. Using an hBN crystal as the base, ultrasharp corners can be created in lithographic patterns, which are then transferred to a graphite crystal underneath. We find that the anisotropic SF6 reactive ion etching process makes it possible to downsize nanostructures and obtain smooth edges, sharp corners, and feature sizes significantly below the resolution limit of electron beam lithography. The nanostructured 2D materials can be used themselves or as etch masks to pattern other nanomaterials.
- Full Text
- View/download PDF
46. UV-induced SiC nanowire sensors.
- Author
-
Gang Peng, Yingqiu Zhou, Yanlan He, Xiaoyan Yu, Xue A Zhang, Gong Y Li, and Hossam Haick
- Subjects
- *
ELECTRIC properties of nanowires , *ELECTRIC properties , *SILICON carbide , *COMPLEMENTARY metal oxide semiconductors , *ULTRAVIOLET detectors , *PHOTOVOLTAIC effect - Abstract
Ultraviolet (UV)-induced sensors based on a single SiC nanowire (NW) were fabricated and the photoelectric properties including I–V characteristics and time response of the UV sensors were studied. SiC NWs (NWs) were prepared through pyrolyzing a polymer precursor with ferrocene as the catalyst by a CVD route. To elucidate the physical mechanism giving rise to the photoelectrical response in SiC NW sensors, three kinds of contacts between electrodes and SiC NW were prepared, i.e. Schottky contact, p–n junction contact, and Ohmic contact. The photoelectric measurements of the device with Schottky contact indicates the lowest dark current and the largest photocurrent. The results suggest that photocurrent generated at SiC NW-electrode contacts is a result of the photovoltaic effect, in which a built-in electric field accelerates photo generated charge carriers to the electronic contacts. The UV sensors based on SiC NWs could be applied in a harsh environment due to the excellent physical stability and photoelectric properties. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
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