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X-ray reflectivity and atomic force microscopy studies of MOCVD grown AI_xGa_(1-x)N/GaN superlattice structures

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Journal of Semiconductors 2011年第4期32卷 48-51页

作者：王元樟李金钗李书平陈航洋刘达艺康俊勇 Department of Mathematics and Physics Xiamen University of Technology Fujian Key Laboratory of Semiconductor Materials and Applications Xiamen University

The grazing incidence X-ray reflectivity(GIXR) technique and atomic force microscopy(AFM) were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown AlGaN/GaN superlattice structures.The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer.The presence of a smooth interface is responsible for the observation of intensity oscillation in GIXR,which is well correlated to step flow observation in AFM images of the surface.The structure with a low Al mole fraction(x = 0.25) and thin well width has a rather smooth surface for the R,of AFM data value is 0.45 nm.

关键词： metalorganic chemical vapor deposition interfaces surfaces nitrides superlattices high resolution X-ray diffraction

Distribution of Nb atom in the TiAl+Nb system

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Rare Metals 2001年第1期20卷 5-12页

作者： Xiaodong Ni, Xidong Hui, Guoliang Chen (Applied Science School, University of Science and Technology Beijing, Beijing 100083, China State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, China) Appl. Sci. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

Based on MEAM (the modified embedded atom method) potential and an average atom model similar to B-W (Bragg-Williams) method, the distribution of Nb atoms in TiAl+Nb compounds with various composition was calculated. The calculation results showed that Nb atoms prefer to occupy the Ti sublattice of L10 structure for all compounds in question. With increasing atomic fraction of Nb and Al, Nb atoms exhibited a trend of ordered distribution on the Ti sublattice and result in a new L10 derivative superlattice structure.

关键词： Computer simulation Intermetallics superlattices Ternary systems

Observation of trapped light induced by Dwarf Dirac-cone in out-of-plane condition for photonic crystals

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Chinese Physics B 2016年第10期25卷 314-322页

作者： Subir Majumder Tushar Biswas Shaymal K Bhadra Fiber Optics and Photonics Division CSIR-Central Glass and Ceramic Research Institute

Existence of out-of-plane conical dispersion for a triangular photonic crystal lattice is reported. It is observed that conical dispersion is maintained for a number of out-of-plane wave vectors（k;）. We study a case where Dirac like linear dispersion exists but the photonic density of states is not vanishing, called Dwarf Dirac cone（DDC） which does not support localized modes. We demonstrate the trapping of such modes by introducing defects in the crystal. Interestingly, we find by k-point sampling as well as by tuning trapped frequency that such a conical dispersion has an inherent light confining property and it is governed by neither of the known wave confining mechanisms like total internal reflection, band gap guidance. Our study reveals that such a conical dispersion in a non-vanishing photonic density of states induces unexpected intense trapping of light compared with those at other points in the continuum. Such studies provoke fabrication of new devices with exciting properties and new functionalities.

关键词： band structure photonic band gap materials multilayers superlattices photonic structures meta-materials

Experimental Studies on Thermal and Electrical Properties of Platinum Nanofilms

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Chinese Physics Letters 2006年第4期23卷 936-938页

作者：张兴张清光曹炳阳 FUJII Motoo TAKAHASHI Koji IKUTA Tatsuya Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Tsinghua University Beijing 100084 Institute for Materials Chemistry and Engineering Kyushu University Kasuga 816-8580 Japan Graduate School of Engineering Kyushu University Fukuoka 812-8581 Japan

We experimentally studied the in-plane thermal and electrical properties of a suspended platinum nanofilm in thickness of 15 nm. The measured results show that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient of the studied nanofilm are much less than those of the bulk material, while the Lorenz number is greater than the bulk value. Comparing with the results reported previously for the platinum nanofilm in thickness of 28 nm, we further find that the in-plane thermal conductivity, the electrical conductivity and the resistance-temperature coefficient decrease with the decreasing thickness of the nanotilm, while the Lorenz number increases with the decreasing thickness of the nanofilm. These results indicate that strong size effects exist on the in-plane thermal and electrical properties of platinum nanofilms.

关键词： TRANSPORT CONDUCTIVITY superlattices PHONON

In situ TEM observation of neck formation during oriented attachment of PbSe nanocrystals

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Nano Research 2019年第10期12卷 2549-2553页

作者： Yu Wang Xinxing Peng Alex Abelson Bing-Kai Zhang Caroline Qian Peter Ercius Lin-Wang Wang Matt Law Haimei Zheng Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCalifornia 94720USA Department of Materials Science and Engineering University of CaliforniaBerkeleyCalifornia 94720USA State Key Lab of Physical Chemistry of Solid Surfaces Collaborative Innovation Center of Chemistry for Energy MaterialsCollege of Chemistry and Chemical EngineeringXiamen UniversityXiamen 361005China Department of Chemistry University of CaliforniaIrvineCalifornia 92697USA National Center for Electron Microscopy Molecular FoundryLawrence Berkeley National LaboratoryBerkeleyCalifornia 94720USA

Oriented attachment of nanocrystals is an important route to constructing epitaxially-connected nanocrystal superlattices for various applications.During oriented attach me nt of semic on ductor nano crystals,neck can be formed betwee n nan ocrystals and it strongly influe nces the properties of the resulting superlattice.However,the neck formation mechanism is poorly understood.Here,we use in situ liquid cell transmission electro n microscopy(TEM)to directly observe the initiatio n and growth of homoepitaxial n ecks betwee n PbSe nano crystals with atomic details.We find that neck initiatio n occurs slowly(~10 s)whe n two nano crystals approach to each other within an edge-to-edge dista nee of 0.6 nm.During neck initiation,Pb and Se atoms defuse from other facets into the gap,forming"dynamic reversible"filaments.Once the filament(n eck)width is larger than a critical size of 0.9 nm,it gradually(15 s)widens into a 3-nm-wide n eck.The atomic structure of the neck is further obtained using ex situ aberration-corrected seanning TEM imaging.Neck initiation and growth mechanisms are elucidated with density functional theory calculati ons.Our direct unveiling of the atomic pathways of neck formatio n duri ng oriented attach me nt shed light into the fabrication of nanocrystal superlattices with improved structural order and electronic properties.

关键词： PbSe nanocrystals quantum dots superlattices necking oriented attachment liquid cell transmission electron microscopy(TEM)

Heteroepitaxial growth of InP/GaAs(100) by metalorganic chemical vapor deposition

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Chinese Optics Letters 2007年第7期5卷 422-425页

作者：熊德平任晓敏王琦周静舒伟吕吉贺蔡世伟黄辉黄永清 Key Laboratory of Optical Communication and Lightwave Technologies Ministry of Education Beijing University of Posts and TelecommunicationsBeijing 100876 Institute of Continuing Education Beijing University of Posts and Telecommunications Beijing 100876

Using two-step method InP epilayers were grown on GaAs（100） substrates by low-pressure metalorganic chemical vapor deposition （LP-MOCVD）. X-ray diffraction （XRD） and room-temperature （RT） photolu- minescence （PL） were employed to characterize the quality of InP epilayer. The best scheme of growing InP/GaAs（100） heterostructures was obtained by optimizing the initial low-temperature （LT） InP growth conditions, investigating the effects of thermal cycle annealing （TCA） and strained layer superlattice （SLS） on InP epilayers. Compared with annealing, 10-periods Ga0.1In0.9P/InP SLS inserted into InP epilayers can improve the quality of epilayers dramatically, by this means, for 2.6-#m-thick heteroepitaxial InP, the full-widths at half-maximum （FWHMs） of XRD ω and ω-28 scans are 219 and 203 arcsec, respectively, the RT PL spectrum shows the band edge transition of InP, the FWHM is 42 meV. In addition, the successful growth of InP/In0.53Ga0.47As MQWs on GaAs（100） substrates indicates the quality of device demand of InP/GaAs heterostructures.

关键词： Annealing Epitaxial growth Full width at half maximum Heterojunctions Metallorganic chemical vapor deposition Photoluminescence Semiconducting gallium arsenide superlattices X ray diffraction analysis

Elastic Modulus and Hardness of Cr-Nb Nano-Multilayers

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Chinese Physics Letters 2007年第9期24卷 2635-2638页

作者：杨孟锦赖文生潘峰 Laboratory of Advanced Materials Department of Materials Science and Engineering Tsinghua University Beijing 100084

Cr-Nb nano-multilayered films with various modulation wavelengths A are prepared by e-gun evaporation and their mechanical properties are investigated. Cr and Nb both have bcc structures with large differences in lattice constants and Young＇s modulus, which are supposed to favour modulus enhancement. Nevertheless, nano-indention measurements show no enhancement for the modulus and a slight decrease for the hardness with decreasing A down to 5 nm. This is mainly due to counter-contribution to modulus from adjacent layers subjected to reverse strains, in agreement with recent theoretical study, while the decrease of hardness arises from grain boundary sliding. Interestingly, at A = 3 nm, the hardness of the film has an increase of 44% relative to the value of a rule of mixture, owing to the emergence of a new phase for reconciling the structure difference at the interfaces.

关键词： NI THIN-FILMS MECHANICAL-PROPERTIES superlattices NICKEL FOILS CU NANOINDENTATION INDENTATION PALLADIUM STRESS

Land/groove optical recording with GeTe/Sb2Te3 superlattice-like structure

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Chinese Optics Letters 2004年第6期2卷 356-358页

作者：墙威 Luping Shi Towchong Chong 曹阳 School of Electronics Information Wuhan University Wuhan 430072 Data Storage Institute DSI Building 5 Engineering Drive 1 Singapore 117608 Sehool of Electronics Information Wuhan University Wuhan 430072 superlattice-like (SLL) structure was applied to phase-change optical recording. The recording layer consisting of alternating thin layers of two different phase-change materials GeTe and Sb2Te3 were grown by magnetron sputtering on polycarbonate substrates. Land/groove optical recording was adopted to suppress crosstalk and obtain a large track density. Dynamic properties of the SLL disc were investigated with the shortest 1T pulse duration of 8 ns. Clear eye pattern was observed after 10000 direct overwrite cycles. Erasability above 20 dB was achieved at a constant linear velocity of 19 m/s. Carrier-noise ratio (CNR) kept above 46 dB when the recording frequency reaches 21 VIHz. The SLL phase change optical disc demonstrates a better recording performance than the Ge1Sb2Te4 and Ge1Sb4Te7 discs in terms of CNR erasability and overwrite jitter.

A superlattice-like (SLL) structure was applied to phase-change optical recording. The recording layer consisting of alternating thin layers of two different phase-change materials, GeTe and Sb2Te3, were grown by magnetron sputtering on polycarbonate substrates. Land/groove optical recording was adopted to suppress crosstalk and obtain a large track density. Dynamic properties of the SLL disc were investigated with the shortest 1T pulse duration of 8 ns. Clear eye pattern was observed after 10000 direct overwrite cycles. Erasability above 20 dB was achieved at a constant linear velocity of 19 m/s. Carrier-noise ratio (CNR) kept above 46 dB when the recording frequency reaches 21 VIHz. The SLL phase change optical disc demonstrates a better recording performance than the Ge1Sb2Te4 and Ge1Sb4Te7 discs in terms of CNR, erasability, and overwrite jitter.

关键词： Crosstalk Magnetron sputtering Phase changing circuits Semiconducting tellurium compounds superlattices

Structural and optical characteristics of Al_xGa_(1-x)N/AlN superlattice

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Science China(Technological Sciences) 2009年第2期52卷 332-335页

作者： XIE ZiLi1, ZHANG Rong1, JIANG RuoLian1, LIU Bin1, GONG HaiMei2, XIU XiangQian1, CHEN Peng1, LU Hai1, HAN Ping1, SHI Yi1 & ZHENG YouDou1 1 Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, Physical Department of Nanjing University, Nanjing 210093, China 2 Shanghai Institute of Technical Physics, Chinese Academy of Science, Shanghai 200083, China Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials Physical Department of Nanjing University Nanjing China Shanghai Institute of Technical Physics Chinese Academy of Science Shanghai China

AlN/Al0.3Ga0.7N superlattices were grown on (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The superlattice period varies from 6 to 30. The layer thickness of different period stack was designed. GaN or AlGaN template was employed for growing AlN/AlGaN superlattices. Reflectivity, SEM, AFM and XRD data of the AlxGa1-xN/AlN superlattices are presented. It is found that the templates used have an intensive impact on surface roughness and interfacial properties of following AlN/AlGaN superlattices. The result of atomic force microscopy indicates that AlN/AlGaN superlattices grown on GaN template exhibit quasi-two-dimensional growth mode. The resulting superlattice has a smooth surface morphology and distinct interface. No crack is observed in the area of a 2-inch wafer.

关键词： MOCVD superlattices AlxGa1-xN/AlN