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87 results on '"Pan, Guanzhong"'

2. Graphene-assisted preparation of large-scale single crystal Ag(111) nanoparticle arrays

Author

Dong, Yibo, Xie, Yiyang, Hu, Liangchen, Xu, Chen, Guo, Weiling, Pan, Guanzhong, Wang, Qiuhua, Qian, Fengsong, and Sun, Jie

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Surface plasmon resonance of metal nanostructures has broad application prospects in the fields of photocatalysis, optical sensing, biomarkers and surface-enhanced Raman scattering. This paper reports a graphene-assisted method for preparing large-scale single crystal Ag(111) nanoparticle arrays based on ion implantation technique. By surface periodic treatment and annealing of the implanted sample, regularly arranged Ag nanoparticles can be prepared on the sample surface. A new application for graphene is proposed, that is, as a perfect barrier layer to prevent metal atoms from evaporating or diffusing. All the Ag NPs show (111) crystal orientation. Besides, the Ag atoms are covered by graphene immediately when they precipitate from the substrate, which can prevent them from being oxidized. On the basis of this structure, as one of the applications of metal SPR, we measured the Raman enhancement effect, and found that the G peak of the Raman spectrum of graphene achieved about 20 times enhancement.

Published
2019

3. Longitudinal Multi-Cavity Coupled VCSELs With Narrow Linewidth and High Single Mode Power for Quantum Sensing

Author

Xun, Meng, Pan, Guanzhong, Sun, Yun, Zhou, Xiaoli, Wang, Yinuo, Liu, Yang, Yang, Chengyue, and Wu, Dexin

Abstract

We report a novel 795 nm VCSEL with longitudinal three coupled cavity. Because of large increasing the photon lifetime, the spectrum linewidth has been reduced to be 7.3 MHz (limited by the resolution) which is near the natural atomic linewidth. The additional epitaxial cavity spacers yield high diffraction losses for higher order transverse modes. High single mode output power of 4.6 mW was obtained under 25 °C. Rigorous coupled-wave analysis (RCWA) was developed and applied to analyze surface grating. The VCSEL integrated with surface grating remains high orthogonal polarization suppression ratio (OPSR) above 27 dB even at 85 °C, showing excellent polarization stability. The 795 nm high performance VCSELs could play an important role in future generation of high-performance quantum sensing systems.

Published
2024
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4. Thermal Properties of Multi-Junction Cascade Vertical Cavity Surface Emitting Lasers

Author

Zhou, Xiaoli, Wang, Yinuo, Xun, Meng, Pan, Guanzhong, Sun, Yun, Zhang, Runze, Wu, Weichao, Wu, Song, Fei, Yongming, Jiang, Xiaowei, and Wu, Dexin

Abstract

Multi-junction cascade vertical cavity surface emitting lasers (VCSELs) exhibit a noteworthy thermal issue because of their multiple active regions. We have designed and fabricated two six-junction cascade VCSELs with different oxide layers. The light-current–voltage (L–I–V) and divergence angle characteristics, as well as their thermal properties at various ambient temperatures, were analyzed to investigate the thermal problems. Based on the relationship between the emission spectra and power dissipation, we were able to obtain the corresponding thermal resistance values and active region temperatures of different structures afterward. It turned out that the multi-junction cascade VCSELs with multioxide layers have evident advantages of slope efficiency (SE) and optical output power over those with a single-oxide layer due to excellent current and optical confinement. However, owing to the low thermal conductivity of the oxide layers, it is difficult for the heat generated in the active regions to transfer to the surrounding area, resulting in an increase in the thermal resistance of multioxide VCSELs. Meanwhile, the divergence angle of multioxide VCSELs becomes larger because of the strong optical confinement. For better insight, a heat diffusion model of these two devices was established, and the temperature distribution was analyzed. Both the simulation and experimental results agreed fairly well.

Published
2024
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14. High Single Fundamental-Mode Output Power From 795 nm VCSELs With a Long Monolithic Cavity

Author

Xun, Meng, Pan, Guanzhong, Zhao, Zhuang Zhuang, Sun, Yun, Wu, Weichao, Jiang, Wenjing, Zhang, Runze, and Wu, Dexin

Abstract

A high fundamental-mode output power was achieved from a 795-nm vertical-cavity surface-emitting laser (VCSEL) with a long monolithic cavity. The epitaxial cavity spacer between active region and N-DBRs yields high diffraction losses for higher order transverse modes. The single mode optical power of 5.6mW under continuous wave was demonstrated in the long-cavity VCSELs with $4.5~\mu \text{m}$ oxide aperture. Above 10° reduction in divergence was found for long-cavity VCSELs. Decreased thermal resistance was also demonstrated in long cavity VCSELs due to additional homo-structure which can be as heat spreading layer. The change of VCSEL structure is only in epitaxy layer. So the fabrication process is completely same with the conventional fabrication, therefore, improves reproducibility and yield.

Published
2023
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17. Speculation or hedging?—Options trading prior to FOMC announcements.

Author

Jiang, George J. and Pan, Guanzhong

Subjects
OPTIONS (Finance), HEDGING (Finance), SPECULATION, ANNOUNCEMENTS, TRADE shows, STANDARD & Poor's 500 Index
Abstract

This paper investigates options trading activity before Federal Open Market Committee (FOMC) announcements. We find evidence that informed traders use options to speculate on their private information for the upcoming FOMC announcements. Specifically, abnormal trading volume of call options on S&P 500 index during the preannouncement window positively predicts postannouncement index returns, and this predictability mainly comes from near‐the‐money call options. Moreover, we further break down trading volume based on the direction of trades and show that buyer‐initiated call option trading volume positively predicts postannouncement index returns. We find no evidence that investors use options to hedge postannouncement market uncertainty. [ABSTRACT FROM AUTHOR]

Published
2022
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25. The Growth of Graphene on Ni-Cu Alloy Thin Films at a Low Temperature and Its Carbon Diffusion Mechanism

Author

Dong, Yibo, Guo, Sheng, Mao, Huahai, Xu, Chen, Xie, Yiyang, Cheng, Chuantong, Mao, Xurui, Deng, Jun, Pan, Guanzhong, Sun, Jie, Dong, Yibo, Guo, Sheng, Mao, Huahai, Xu, Chen, Xie, Yiyang, Cheng, Chuantong, Mao, Xurui, Deng, Jun, Pan, Guanzhong, and Sun, Jie

Abstract

Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni-Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni-Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni-Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2/Si substrate at a low temperature (similar to 600 degrees C)., QC 20200103

Published
2019
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29. Metal-Catalyst-Free Growth of Patterned Graphene on SiO2 Substrates by Annealing Plasma-Induced Cross-Linked Parylene for Optoelectronic Device Applications

Author

Dong, Yibo, primary, Cheng, Chuantong, additional, Xu, Chen, additional, Mao, Xurui, additional, Xie, Yiyang, additional, Chen, Hongda, additional, Huang, Beiju, additional, Zhao, Yongdong, additional, Deng, Jun, additional, Guo, Weiling, additional, Pan, Guanzhong, additional, and Sun, Jie, additional

Published
2019
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33. Graphene-assisted preparation of large-scale single-crystal Ag(111) nanoparticle arrays for surface-enhanced Raman scattering.

Author

Dong, Yibo, Xie, Yiyang, Hu, Liangchen, Xu, Chen, Guo, Weiling, Pan, Guanzhong, Wang, Qiuhua, Qian, Fengsong, and Sun, Jie

Subjects
SURFACE enhanced Raman effect, RAMAN scattering, SURFACE plasmon resonance, RAMAN effect, ION implantation, CRYSTAL orientation
Abstract

Surface plasmon resonance (SPR) of metal nanostructures has broad application prospects in the fields of sensing, energy, catalysis and optics. This paper reports a graphene-assisted method for preparing large-scale single-crystal Ag(111) nanoparticle (NP) arrays based on the ion implantation technique. By surface periodic patterning treatment and annealing of the implanted sample, regularly arranged Ag NPs can be prepared on the sample surface. A new application for graphene is proposed, that is, as a perfect barrier layer to prevent metal atoms from evaporating or diffusing. All the Ag NPs show (111) crystal orientation. Besides, the Ag atoms are covered by graphene immediately when they precipitate from the substrate, which can prevent them from being oxidized. On the basis of this structure, as one of the applications of the metal SPR, we have measured the surface-enhanced Raman scattering effect and found that the G peak of the Raman spectrum of the graphene achieved about 20 times enhancement. [ABSTRACT FROM AUTHOR]

Published
2021
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35. Transfer-free, lithography-free and fast growth of patterned CVD graphene directly on insulators by using sacrificial metal catalyst

Author

Dong, Yibo, primary, Xie, Yiyang, additional, Xu, Chen, additional, Fu, Yafei, additional, Fan, Xing, additional, Li, Xuejian, additional, Wang, Le, additional, Xiong, Fangzhu, additional, Guo, Weiling, additional, Pan, Guanzhong, additional, Wang, Qiuhua, additional, Qian, Fengsong, additional, and Sun, Jie, additional

Published
2018
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40. Biases in CAPM Beta Estimation

Author

Pan Guanzhong, Linda H. Chen, George J. Jiang, and Xingnong Zhu

Subjects
First-difference estimator, Linear regression, Statistics, Econometrics, Economics, Estimator, Capital asset pricing model, Endogeneity, Empirical evidence, Stock (geology)
Abstract

In this paper, we show that conditions derived under the CAPM ensure only weak exogeneity in a linear regression setting. Since strong exogeneity is not guaranteed, the OLS estimator of CAPM beta is only consistent but not necessarily unbiased. We provide empirical evidence that individual daily stock returns exibit regime-switching patterns and may violate strong exogeneity conditions. As such, the OLS estimator of CAPM beta is likely biased. Based on the empirical patterns of daily stock returns, we use three regime-switching models to illustrate thatthe OLS estimator of CAPM beta can be consistent but at the same time biased. Simulation results based on these three regime-switching models show that biases of the OLS beta estimator can be substantial.

Published
2016

47. Metal-Catalyst-Free Growth of Patterned Graphene on SiO2Substrates by Annealing Plasma-Induced Cross-Linked Parylene for Optoelectronic Device Applications

Author

Dong, Yibo, Cheng, Chuantong, Xu, Chen, Mao, Xurui, Xie, Yiyang, Chen, Hongda, Huang, Beiju, Zhao, Yongdong, Deng, Jun, Guo, Weiling, Pan, Guanzhong, and Sun, Jie

Abstract

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of parylene N is cross-linked by argon plasma bombardment. Under high-temperature annealing, the cross-linking layer of parylene N is graphitized into nanocrystalline graphene, which is a process that transforms organic to inorganic and insulation to conduction, while the parylene N molecules below the cross-linking layer decompose and vaporize at high temperature. Using this technique, the direct growth of a graphene film in a large area and with good uniformity is achieved. The thickness of the graphene is determined by the thickness of the cross-linking layer. Patterned graphene films can be obtained directly by controlling the patterns of the cross-linking region (lithography-free patterning). Graphene–silicon Schottky junction photodetectors are fabricated using the as-grown graphene. The Schottky junction shows good performance. The application of direct-grown graphene in optoelectronics is achieved with a great improvement of the device fabrication efficiency compared with transferred graphene. When illuminated with a 792 nm laser, the responsivity and specific detectivity of the detector measured at room temperature are 275.9 mA/W and 4.93 × 109cm Hz1/2/W, respectively.

Published
2019
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50. Transfer-free, lithography-free, and micrometer-precision patterning of CVD graphene on SiO2 toward all-carbon electronics.

Author

Dong, Yibo, Xie, Yiyang, Xu, Chen, Li, Xuejian, Deng, Jun, Fan, Xing, Pan, Guanzhong, Wang, Qiuhua, Xiong, Fangzhu, Fu, Yafei, and Sun, Jie

Subjects
GRAPHENE synthesis, CHEMICAL vapor deposition, SILICON oxide
Abstract

A method of producing large area continuous graphene directly on SiO2 by chemical vapor deposition is systematically developed. Cu thin film catalysts are sputtered onto the SiO2 and pre-patterned. During graphene deposition, high temperature induces evaporation and balling of the Cu, and the graphene “lands onto” SiO2. Due to the high heating and growth rate, continuous graphene is largely completed before the Cu evaporation and balling. 60 nm is identified as the optimal thickness of the Cu for a successful graphene growth and μm-large feature size in the graphene. An all-carbon device is demonstrated based on this technique. [ABSTRACT FROM AUTHOR]

Published
2018
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