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Morphological features and nanostructures generated during SiC graphitization process

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Chinese physics B 2023年第6期32卷 638-643页

作者：孔雯霞端勇章晋哲王剑心蔡群 state key laboratory of Surface physics&department of physics Fudan UniversityShanghai 200438China

Surface morphological features and nanostructures generated during SiC graphitization process can significantly affect fabrication of high-quality epitaxial graphene on semiconductor substrates.In this work,we investigate the surface morphologies and atomic structures during graphitization process of 4H-SiC(0001) using scanning tunneling microscopy.Our high-magnified scanning-tunneling-microscope images exhibit the appearance and gradual developments of SiC(1 × 1)nanostructures after 1100℃ cleaning treatments,irregularly distributed among carbon nanocaps and(√3×√3) reconstruction domains.A model for the formation and growth progression of SiC(1 × 1) nanostructures has been proposed.When post-annealing temperature reaches 1300 ℃,the nanoholes and nanoislands can be observed on the surface,and multilayer graphene is often detected lying on the top surface of those nanoislands.These results provide profound insights into the complex evolution process of surface morphology during SiC thermal decomposition and will shed light on fabrication of SiC nanostructures and graphene nanoflakes.

关键词： scanning tunneling microscopy(STM) SiC graphitization epitaxial graphene nanostructures

低对称性的亚波长阵列增强型的GeSe偏振探测器（英文）

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Science Bulletin 2023年第2期68卷 173-179页

作者：周子琦沈涛王盼郭泉林王卿赫马辰俊辛凯耀赵凯于雅俐秦彪刘岳阳杨珏晗洪浩刘开辉刘灿邓惠雄魏钟鸣 state key laboratory of Superlattices and Microstructures Institute of Semiconductors Chinese Academy of Sciences state key laboratory for mesoscopic physics Frontiers Science Centre for Nano-optoelectronics School of Physics Peking University Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences department of physics Renmin University of China

偏振敏感光电探测器可通过探测光偏振态的变化从而分辨纹理、应力和粗糙度等多种信息,在安全、医疗诊断和航空航天领域具有独特的优势.基于面内各向异性的二维材料的偏振光探测器可简化传统探测器的复杂透镜系统,促进了光电器件的集成... 详细信息

偏振敏感光电探测器可通过探测光偏振态的变化从而分辨纹理、应力和粗糙度等多种信息,在安全、医疗诊断和航空航天领域具有独特的优势.基于面内各向异性的二维材料的偏振光探测器可简化传统探测器的复杂透镜系统,促进了光电器件的集成化与小型化.然而,基于面内各向异性的二维材料的偏振光探测器的光电流各向异性比不足(通常小于10),限制了偏振信号的检测分辨率.本文设计了基于二维硒化亚锗(GeSe)的亚波长阵列(SWA)结构,进一步提高其各向异性灵敏度,并将光电流各向异性从1.6提高到18.本研究发现,SWA结构可以进一步增强电荷分布的不对称性,提高GeSe材料在扶手椅方向上的光吸收和光电跃迁概率,从而提高了偏振灵敏度.此外,基于GeSe SWA的光电探测器在808 nm的近红外波长下表现出宽的功率范围(40 dB)和弱光探测能力(0.1 LUX).该工作为提高二维材料的偏振灵敏度提供了可行性指导,将有利于促进高分辨率偏振成像传感器的发展.

关键词： Germanium selenium (GeSe) Polarization-sensitive photodetectors Sub-wavelength array Anisotropy ratio

Effects of aligning pulse duration on the degree and the slope of nitrogen field-free alignment

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Chinese physics B 2012年第5期21卷 288-293页

作者：王翡蒋红兵龚旗煌 department of physics&state key laboratory for mesoscopic physics Peking University

Through theoretical analysis,we show how aligning pulse durations affect the degree and the time-rate slope of nitrogen field-free alignment at a fixed pulse intensity.It is found that both the degree and the slope first increase,then saturate,and finally decrease with the increasing pump duration.The optimal durations for the maximum degree and the maximum slope of the alignment are found to be different.Additionally,they are found to mainly depend on the molecular rotational period,and are affected by the temperature and the aligning pump intensities.The mechanism of molecular alignment is also discussed.

关键词： field-free molecular alignment femtosecond phenomenon strong filed physics

Filamentation-assisted fourth-order nonlinear process in KTP crystal

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Chinese physics B 2010年第3期19卷 347-352页

作者：张喜鹏蒋红兵陈利蒋莹莹杨宏龚旗煌 state key laboratory for mesoscopic physics and department of physics Peking University

We present an experimental investigation of a filamentation-assisted fourth-order nonlinear optical process in KTP crystals pumped by intense 1.53 eV （807 nm） femtosecond laser pulses. Femtosecond light pulses at 2.58 eV （480 nm） are generated by the fourth-order nonlinear polarization （p（4）（ω2） = X（4）（ω2, ω, ω, ω, -ω1）E3 （ω）E＊（ω1）, where E（w） corresponds to the pump frequency and E（wl） to the supercontinuum generated through filamentation）. If the system is seeded by a laser beam at ω1 or ω2 and there are spatial and temporal overlaps with the pump beam, E（ω1） and E（ω2） are simultaneously amplified. When the intensity of the seed laser beam exceeds a certain intensity threshold, the contribution of p（4）（ω） = X（4）（ω, ω1, ω2, -ω, -ω）E（ω1）E（ω2）（E＊（ω））2 becomes non-negligible, and the amplification weakens. The conversion efficiency from the pump to the signal at 2.58 eV （480 nm） attains to 0.1%.

关键词： parametric amplification filamentation fourth-order nonlinear polarization KTP crys-tal

Study of narrow-band second harmonic generation from a broad-band fundamental pulse

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Chinese physics B 2010年第12期19卷 318-322页

作者：温静蒋红兵邓勇开龚旗煌 department of physics & state key laboratory for mesoscopic physics Peking University

This paper studies the type-I phase-matched second harmonic generation using 25-fs input laser pulses in a thick BBO crystal. The harmonic signal exhibits a narrow spectrum bandwidth, even though the input pulse has a... 详细信息

关键词： second harmonic generation cascaded process energy transfer chirp

Long-range surface plasmon polaritons with subwavelength mode expansion in an asymmetrical system

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Chinese physics B 2009年第8期18卷 3535-3541页

作者：陈建军李智龚旗煌 state key laboratory for mesoscopic physics and department of physics Peking University

Long-range surface plasmon polariton （LRSPP） modes in an asymmetrical system, in which the thin metal film is sandwiched between a semi-infinite substrate and a high permittivity polymer film with a finite thickness, are theoret~ ically calculated and analyzed. Due to the high permittivity of the polymer film, at proper polymer film thicknesses, the index-matching condition of the dielectrics at both sides of the metal can be satisfied for supporting LRSPP modes, and the electromagnetic field above the metal can be localized well. It is found that these LRSPP modes have both long propagation lengths and subwavelength mode expansion above the metal at the optimal polymer film thickncsses. Furthermore, the requirements on the refractive index and the thickness of the polymer film to support LRSPP modes at the optimal thicknesses are found to be not critical.

关键词： surface plasmon polaritons field intensity confinement long propagation length integrated optics

Ionization of atoms by chirped attosecond pulses

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Chinese physics B 2009年第11期18卷 4807-4814页

作者：谭放彭良友龚旗煌 state key laboratory for mesoscopic physics and department of physics Peking University

We investigate the ionization dynamics of atoms by chirped attosecond pulses using the strong field approximation method. The pulse parameters are carefully chosen in the regime where the strong field approximation method is valid. We analyse the effects of the chirp of attosecond pulses on the energy distributions and the corresponding left-right asymmetry of the ionized electrons. For a single chirped attosecond pulse, the ionized electrons can be redistributed and the left-right asymmetry shows oscillations because of the introduction of the chirp. For time-delayed double attosecond pulses at different intensities with the weaker one chirped, exchanging the order of the two pulses shows a relative shift of the energy spectra, which can be explained by the different effective time delays of different frequency components because of the chirp.

关键词： photoionization rate attosecond pulse asymmetry chirp

Graph-based discovery and analysis of atomic-scale one-dimensional materials

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National Science Review 2022年第6期9卷 114-123页

作者： Shunning Li Zhefeng Chen Zhi Wang Mouyi Weng Jianyuan Li Mingzheng Zhang Jing Lu Kang Xu Feng Pan School of Advanced Materials Peking University Shenzhen Graduate School state key laboratory of mesoscopic physics and department of physics Peking University Electrochemistry Branch Sensor and Electron Devices Directorate Power and Energy DivisionUS Army Research Laboratory

Recent decades have witnessed an exponential growth in the discovery of low-dimensional materials(LDMs), benefiting from our unprecedented capabilities in characterizing their structure and chemistry with the aid of advanced computational techniques. Recently, the success of two-dimensional compounds has encouraged extensive research into one-dimensional(1 D) atomic chains. Here, we present a methodology for topological classification of structural blocks in bulk crystals based on graph theory,leading to the identification of exfoliable 1 D atomic chains and their categorization into a variety of chemical families. A subtle interplay is revealed between the prototypical 1 D structural motifs and their chemical space. Leveraging the structure graphs, we elucidate the self-passivation mechanism of 1 D compounds imparted by lone electron pairs, and reveal the dependence of the electronic band gap on the cationic percolation network formed by connections between structure units. This graph-theory-based formalism could serve as a source of stimuli for the future design of LDMs.

关键词： low-dimensional materials 1D atomic chains graph theory topological classification density functional theory

A visible-near infrared tunable waveguide based on plasmonic gold nanoshell

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Chinese physics B 2008年第7期17卷 2567-2573页

作者：张海汐古英龚旗煌 state key laboratory for mesoscopic physics Department of PhysicsPeking University

A tunable plasmonic waveguide via gold nanoshells immerged in a silica base is proposed and simulated by using the finite difference time-domain （FDTD） method. For waveguides based on near-field coupling, transmission frequencies can be tuned in a wide region from 660 to 900 nm in wavelength by varying shell thicknesses. After exploring the steady distributions of electric fields in these waveguides, we find that their decay lengths are about 5.948-12.83 dB/1000 nm, which is superior to the decay length （8.947 dB/1000 nm） of a gold nanosphere plasmonic waveguide. These excellent tunability and transmittability are mainly due to the unique hollow structure. These gold nanoshell waveguides should be fabricated in laboratory.

关键词： waveguide surface plasmons energy transfer