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315 results on '"Wu, Han-Chun"'

5. Photoluminescence of Monolayer WSe2 Enhanced by the Exciton Funnel Effect and the Interfacial Carrier Tunneling Effect When Integrated with 3D Si Wrinkled Structures.

Author

Lv, Yanhui, Wu, Gang, Chang, Guo-En, Coileáin, Cormac Ó, Hung, Kuan-Ming, Arora, Sunil K., Chang, Ching-Ray, Cheng, H. H., and Wu, Han-Chun

Subjects
QUANTUM tunneling, LIGHT emitting diodes, QUANTUM optics, PHOTONS, LIGHT sources
Abstract

Quantum optics and photonic quantum-information technologies require emitters that have good stability and brightness, coupled with fabrication scalability and on-chip integrability. Most quantized emitters are presently based on 1D and 3D sources. Recently, monolayer transition metal dichalcogenides (TMDCs) hosting spatially localized excitons with narrow linewidths have garnered great interest. Advantages such as large binding energies and long room-temperature lifetimes of intralayer excitons suggest that TMDCs are promising candidates for use in optical devices. Here, we propose an emitter based on a 2D WSe2 semiconductor monolayer integrated with a periodic 3D Si-based wrinkled pattern. Carriers confined within the wrinkled pattern can be electrically and optically pumped, and funneled, to boost emission from the 2D WSe2 layer. This in turn acts as a monochromated quantum light source for the Si or any Si-based quantum optic and photonic information technologies. The brightness of the emission is enhanced by a factor greater than 40 compared with monolayer WSe2 on conventional flat SiGe. Moreover, these monolayer 2D/3D semiconductor composite heterostructures are fully scalable and promisingly efficient chip-integrated emitters. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions

Author

Zhang, Liang, Yan, Yuan, Wu, Han-Chun, Yu, Dapeng, and Liao, Zhi-Min

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

Graphene-based vertical heterostructures, particularly stacks incorporated with other layered materials, are promising for nanoelectronics. The stacking of two model Dirac materials, graphene and topological insulator, can considerably enlarge the family of van der Waals heterostructures. Despite well understanding of the two individual materials, the electron transport properties of a combined vertical heterojunction are still unknown. Here we show the experimental realization of a vertical heterojunction between Bi2Se3 nanoplate and monolayer graphene. At low temperatures, the electron transport through the vertical heterojunction is dominated by the tunneling process, which can be effectively tuned by gate voltage to alter the density of states near the Fermi surface. In the presence of a magnetic field, quantum oscillations are observed due to the quantized Landau levels in both graphene and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an exotic gate-tunable tunneling resistance under high magnetic field, which displays resistance maxima when the underlying graphene becomes a quantum Hall insulator.

Published
2015
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12. Ballistic collective group delay and its Goos-H\'{a}nchen component in graphene

Author

Song, Yu and Wu, Han-Chun

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We theoretically investigate the experimental observable of the ballistic collective group delay (CGD) of all the particles on the Fermi surface in graphene. First, we reveal that, lateral Goos-H\"{a}nchen (GH) shifts along barrier interfaces contribute an inherent component in the individual group delay (IGD). Then, by linking the complete IGD to spin precession through a dwell time, we suggest that, the CGD and its GH component can be electrostatically measured by a conductance difference in a spin-precession experiment under weak magnetic fields. Such an approach is feasible for almost arbitrary Fermi energy. We also indicate that, it is a generally nonzero self-interference delay that relates the IGD and dwell time in graphene., Comment: 6 printed pages including 5 figures. arXiv admin note: text overlap with arXiv:1205.6984

Published
2013
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13. Negative differential resistances with back gate-controlled lowest operation windows in graphene double barrier resonant tunneling diodes

Author

Song, Yu, Wu, Han-Chun, and Guo, Yong

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We theoretically investigate negative differential resistance (NDR) of massless and massive Dirac Fermions in double barrier resonant tunneling diodes based on sufficiently short and wide graphene strips. The current-voltage characteristics calculated in a rotated pseudospin space show that, the NDR feature only presents with appropriate structural parameters for the massless case and the peak-to-valley current ratio can be enhanced exponentially by a tunable band gap. Remarkably, the lowest NDR operation window is nearly structure-free and can be almost solely controlled by a back gate, which may have potential applications in NDR devices with the operation window as a crucial parameter., Comment: 5 pages, 5 figures

Published
2012
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14. Giant Goos-H\'{a}nchen Shift in Graphene Double-barrier Structures

Author

Song, Yu, Wu, Han-Chun, and Guo, Yong

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Optics
Abstract

We report giant Goos-H\"{a}nchen shifts [Goos and H\"{a}nchen, Ann. Phys. 436, 333 (1947)] for electron beams tunneling through graphene double barrier structures. We find that inside the transmission gap for the single barrier, the shift displays sharp peaks with magnitudes up to the order of electron beam width and rather small full-widths-at-half-maximum, which may be utilized to design valley and spin beam splitters with wide tunability and high energy resolution. We attribute the giant shifts to quasibound states in the structures. Moreover, an induced energy gap in the dispersion can increase the tunability and resolution of the splitters., Comment: 5 pages including 5 figures

Published
2012
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15. Two-dimensional group delay in graphene probed by spin precession measurements

Author

Song, Yu, Wu, Han-Chun, and Guo, Yong

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We take graphene as an example to demonstrate that the present widely adopted expression is only the scattering component of a true 2D group delay in the condensed matter context, in which the spatial Goos-H\"{a}nchen (GH) shift along an interface contributes an intrinsic component. We relate the dwell time to spin precession and derive a relation between the 2D group delay and dwell time, whereby we for the first time reveal that, the group delay for 2D ballistic electronic systems can be directly observed by measuring a conductance difference in a weak-field spin precession experiment. This physical observable not only implies the group delay being a relevant quantity even in the condensed matter context, but also provides an experimental evidence for the intrinsic effect of the GH shift. Finally, we revisit the 2D Hartman effect, a central issue of the group delay, by analytically solving it via the vested relation and calculating the proposed observable at the Dirac point., Comment: 12 preprint pages and 6 figures

Published
2012

25. Enhanced interlayer coupling and efficient photodetection response of in-situ grown MoS2–WS2 van der Waals heterostructures.

Author

Sinha, Sneha, Kumar, Sujit, Arora, Sunil K., Sharma, Anjali, Tomar, Monika, Wu, Han-Chun, and Gupta, Vinay

Subjects
HETEROSTRUCTURES, PULSED laser deposition, VAN der Waals forces, HETEROJUNCTIONS
Abstract

Currently, 2D layered material (2DLM) based heterostructures, also known as van der Waals (vdW) heterostructures, are actively pursued owing to their great potential for optoelectronic applications. They are produced either by vertical stacking of individual layers or via in-plane stitching of 2DLMs. Producing vdW heterostructures with clean interfaces and growing them using direct growth methods are challenging. Herein, we report successful growth of large-area MoS2–WS2 vdW heterostructures (single- to few-monolayer, ML, the thickness of MoS2 and WS2) on oxidized Si (100) substrates using the catalyst-free Pulsed Laser Deposition technique. The in-plane (E12g) and out-of-plane (A1g) Raman-active phonon modes are used to probe the interlayer interactions between the constituent 2D layers. We observe a blueshift of 4.73 (1.63) cm−1 of the A1g peak corresponding to MoS2 (WS2) in the MoS2(1ML)–WS2(1ML) heterostructure compared to 1.27 (0.88) cm−1 for the homo-bilayers. The E12g mode also exhibited blueshift for the heterostructure and redshift for the bilayer of the constituent material. We show that the broadband photodetectors fabricated utilizing in situ grown MoS2–WS2 heterostructures exhibit responsivity, specific detectivity, and current on/off ratio as high as 2.51 × 105 A/W, 4.20 × 1014 Jones, and 1.05 × 105, respectively, under 24 μW/cm2 at 405 nm excitation. The successful fabrication of vdW heterostructures using a simple and scalable direct growth method and excellent photodetector performance pave the way for exploitation of their application potential and offer a playground to test some of the theoretical predictions. [ABSTRACT FROM AUTHOR]

Published
2021
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37. POSS-containing polynorbornene with pendant perylene diimide: from a unique supramolecular structure to tunable luminescence properties.

Author

Liu, Jie, Gao, Si-Yu, Zhang, Xin-Yi, Feng, Yakai, Wu, Han-Chun, Chen, Zhijian, Bermeshev, Maxim V., and Ren, Xiang-Kui

Abstract

POSS-containing polynorbornene with pendant perylene diimide (PPDI-POSS) has been synthesized, with alkyl-containing polynorbornene (PPDI-C10C8) as the reference. The supermolecular structure and photoluminescence properties were elucidated using UV-Vis absorption spectra, and one- and two-dimensional X-ray diffraction. The experimental results reveal that PPDI-C10C8 possesses a lamellar structure with close PDI stacking to meet the requirement for minimum free energy. However, the introduction of POSS cages endows PPDI-POSS with a unique hexagonal columnar structure and enhanced photoluminescence properties due to the steric hindrance of POSS cages. These results may contribute to the understanding of the structure–property relationship of the optical polymers and provide some useful information for the design of polymer materials with a controllable supramolecular structure and tunable luminescence properties. [ABSTRACT FROM AUTHOR]

Published
2022
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38. Photoluminescence of Monolayer WSe2Enhanced by the Exciton Funnel Effect and the Interfacial Carrier Tunneling Effect When Integrated with 3D Si Wrinkled Structures

Author

Lv, Yanhui, Wu, Gang, Chang, Guo-En, Coileáin, Cormac Ó, Hung, Kuan-Ming, Arora, Sunil K., Chang, Ching-Ray, Cheng, H. H., and Wu, Han-Chun

Abstract

Quantum optics and photonic quantum-information technologies require emitters that have good stability and brightness, coupled with fabrication scalability and on-chip integrability. Most quantized emitters are presently based on 1D and 3D sources. Recently, monolayer transition metal dichalcogenides (TMDCs) hosting spatially localized excitons with narrow linewidths have garnered great interest. Advantages such as large binding energies and long room-temperature lifetimes of intralayer excitons suggest that TMDCs are promising candidates for use in optical devices. Here, we propose an emitter based on a 2D WSe2semiconductor monolayer integrated with a periodic 3D Si-based wrinkled pattern. Carriers confined within the wrinkled pattern can be electrically and optically pumped, and funneled, to boost emission from the 2D WSe2layer. This in turn acts as a monochromated quantum light source for the Si or any Si-based quantum optic and photonic information technologies. The brightness of the emission is enhanced by a factor greater than 40 compared with monolayer WSe2on conventional flat SiGe. Moreover, these monolayer 2D/3D semiconductor composite heterostructures are fully scalable and promisingly efficient chip-integrated emitters.

Published
2024
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39. Magnetic properties of ultrathin magnetite films grown by molecular beam epitaxy

Author

Arora, S.K., Wu, Han-Chun, Yao, Hongzhi, Ching, W.Y., Choudhary, R.J., Shvets, I.V., and Mryasov, O.N.

Subjects
Epitaxy -- Analysis, Dielectric films -- Magnetic properties, Dielectric films -- Analysis, Thin films -- Magnetic properties, Thin films -- Analysis, Business, Electronics, Electronics and electrical industries
Abstract

Magnetic properties as a function of film thickness (2-55 nm) for magnetite ([Fe.sub.3] [O.sub.4]) thin films grown on MgO (100) substrates show that the small thickness films ([less than or equal to] 5 nm) are ferromagnetic and possess magnetization values which are much greater than that of bulk [Fe.sub.3] [O.sub.4]. The inverse thickness dependence of the magnetization points to an interface related mechanism. Whereas, our detailed spin polarized density functional theoretical calculations suggests that there is only a marginal enhancement in the local spin moments of Fe-atom in the vicinity of the [Fe.sub.3] [O.sub.4]-MgO interface and it turns out that the noncompensation of spin moments between the two magnetic sublattices of spinel [Fe.sub.3] [O.sub.4 ]is a major factor contributing to the enhancement of magnetization. Index Terms--Epitaxial layers, interface phenomena, magnetite, surfaces.

Published
2008

40. Light-Tunable Polarity and Erasable Physisorption-Induced Memory Effect in Vertically Stacked InSe/SnS2Self-Powered Photodetector

Author

Zhao, Yue, Cho, Jiung, Choi, Miri, Ó Coileáin, Cormac, Arora, Sunil, Hung, Kuan-Ming, Chang, Ching-Ray, Abid, Mohamed, and Wu, Han-Chun

Abstract

van der Waals heterojunctions with tunable polarity are being actively explored for more Moore and more-than-Moore device applications, as they can greatly simplify circuit design. However, inadequate control over the multifunctional operational states is still a challenge in their development. Here, we show that a vertically stacked InSe/SnS2van der Waals heterojunction exhibits type-II band alignment, and its polarity can be tuned by an external electric field and by the wavelength and intensity of an illuminated light source. Moreover, such SnS2/InSe diodes are self-powered broadband photodetectors with good performance. The self-powered performance can be further enhanced significantly with gas adsorption, and the device can be quickly restored to the state before gas injection using a gate voltage pulse. Our results suggest a way to achieve and design multiple functions in a single device with multifield coupling of light, electrical field, gas, or other external stimulants.

Published
2022
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45. Prospects and Opportunities of 2D van der Waals Magnetic Systems

Author

Wang, Meng‐Chien, primary, Huang, Che‐Chun, additional, Cheung, Chi‐Ho, additional, Chen, Chih‐Yu, additional, Tan, Seng Ghee, additional, Huang, Tsung‐Wei, additional, Zhao, Yue, additional, Zhao, Yanfeng, additional, Wu, Gang, additional, Feng, Yuan‐Ping, additional, Wu, Han‐Chun, additional, and Chang, Ching‐Ray, additional

Published
2020
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46. High Spin Hall Conductivity in Large‐Area Type‐II Dirac Semimetal PtTe 2

Author

Xu, Hongjun, primary, Wei, Jinwu, additional, Zhou, Hengan, additional, Feng, Jiafeng, additional, Xu, Teng, additional, Du, Haifeng, additional, He, Congli, additional, Huang, Yuan, additional, Zhang, Junwei, additional, Liu, Yizhou, additional, Wu, Han‐Chun, additional, Guo, Chenyang, additional, Wang, Xiao, additional, Guang, Yao, additional, Wei, Hongxiang, additional, Peng, Yong, additional, Jiang, Wanjun, additional, Yu, Guoqiang, additional, and Han, Xiufeng, additional

Published
2020
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47. Electrical Contact Barriers between a Three-Dimensional Metal and Layered SnS2

Author

Lv, Chengzhai, primary, Yan, Wenjie, additional, Shieh, Tung-Ho, additional, Zhao, Yue, additional, Wu, Gang, additional, Zhao, Yanfeng, additional, Lv, Yanhui, additional, Zhang, Duan, additional, Chen, Yanhui, additional, Arora, Sunil K., additional, Ó Coileáin, Cormac, additional, Chang, Ching-Ray, additional, Cheng, Hung Hsiang, additional, Hung, Kuan-Ming, additional, and Wu, Han-Chun, additional

Published
2020
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49. Highly Sensitive, Selective, Stable, and Flexible NO 2 Sensor Based on GaSe

Author

Zhao, Yan‐Feng, primary, Fuh, Huei‐Ru, additional, Coileáin, Cormac Ó, additional, Cullen, Conor P., additional, Stimpel‐Lindner, Tanja, additional, Duesberg, Georg S., additional, Leonardo Camargo Moreira, Óscar, additional, Zhang, Duan, additional, Cho, Jiung, additional, Choi, Miri, additional, Chun, Byong Sun, additional, Chang, Ching‐Ray, additional, and Wu, Han‐Chun, additional

Published
2020
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