SrTiO_3(001)衬底上多层FeSe薄膜的分子束外延生长

近几年,由于用分子束外延法在SrTiO_3衬底表面制备的单层FeSe具有很高的超导转变温度而引发了极大的研究热潮,随之而来的是对多层FeSe薄膜日益增长的研究兴趣.但目前还没有对成功生长高质量多层FeSe薄膜的详细报道.本文利用高能电子衍射仪(RHEED)实时监控在不同生长条件下制备的多层FeSe薄膜,发现在FeSe薄膜的生长初期,RHEED图像的强度演化基本符合台阶密度模型的描述特征,即台阶密度ρ正相关于衍射条纹强度.FeSe(02)衍射条纹的强度在第一生长周期内呈现稳定而明显的峰型振荡,而且不受高能电子掠射角的影响,最适合用来标定FeSe薄膜的厚度.结合扫描隧道显微镜对FeSe薄膜质量的原位观察,确定了制备多层FeSe薄膜的最佳生长条件,为FeSe薄膜的物性研究提供了重要的材料基础.     

GaAs(001)衬底上分子束外延生长立方和六方GaN薄膜

采用分子束外延方法在GaAs(001)衬底上生长出了03微米厚的GaN薄膜,X射线双晶衍射和室温光荧光测试结果表明,采用GaAs氮化表面作为成核层可获得高纯度立方GaN薄膜而采用AlAs氮化表面作为成核层可获得高纯度六方GaN薄膜.这一研究结果表明在GaAs衬底上生长GaN薄膜的相结构可以通过选择不同的成核层来控制. 关键词：     

GaAs(001)衬底上分子束外延生长InNSb单晶薄膜

利用射频氮等离子辅助分子束外延(RF-MBE)技术在GaAs(001)衬底上生长稀氮 InNSb半导体薄膜,并通过原子力显微镜(AFM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和拉曼散射光谱等测量手段对样品的微结构和N组分等进行了表征.结果显示样品有较好的晶体质量,N组分可高达0.84%(XRD的结果).本文还对样品的输运性质进行了表征,结果显示样品在室温下具有较低的载流子浓度和较高的迁移率.另外,初步研究表明在InSb中掺入N可导致其室温磁阻明显下降. 关键词： 分子束外延 稀氮半导体 X射线衍射 拉曼光谱     

用激光分子束外延在Si衬底上外延生长高质量的TiN薄膜

采用激光分子束外延技术，利用两步法，在Si单晶衬底上成功地外延生长出TiN薄膜材料.原子力显微镜分析结果显示， TiN薄膜材料表面光滑，在10 μm×10 μm范围内，均方根粗糙度为0842nm.霍耳效应测量结果显示，TiN薄膜在室温条件下的电阻率为36×10^-5Ω·cm，迁移率达到5830 cm²/V·S，表明TiN薄膜材料是一种优良的电极材料.X射线θ—2θ扫描结果和很高的迁移率均表明，高质量的TiN薄膜材料被外延在Si衬底     

用激光分子束外延在Si衬底上外延生长高质量的TiN薄膜

采用激光分子束外延技术,利用两步法,在Si单晶衬底上成功地外延生长出TiN薄膜材料.原子力显微镜分析结果显示, TiN薄膜材料表面光滑,在10 μm×10 μm范围内,均方根粗糙度为0842nm.霍耳效应测量结果显示,TiN薄膜在室温条件下的电阻率为36×10^-5Ω·cm,迁移率达到5830 cm²/V·S,表明TiN薄膜材料是一种优良的电极材料.X射线θ—2θ扫描结果和很高的迁移率均表明,高质量的TiN薄膜材料被外延在Si衬底 关键词： 激光分子束外延 TiN单晶薄膜 外延生长     

分子束外延生长GaN薄膜的新方法

GaN是一种宽禁带半导体材料,非常适合于制作从蓝光到近紫外波段的光电器件,它也是Ⅱ-V族含氮化合物中研究得最充分的材料,近年来在国际上受到很大重视.在材料制备方面初步解决了p型掺杂的困难,从而制成了高功率的发光二极管. 目前生长GaN比较成功的方法是使用有机气体氮源的金属有机物化学汽相淀积.但它所生成的是纤锌矿(六角)结构,而且是生长在蓝宝石衬底上.生长温度也高达1000℃.要使得GaN材料有可能实用,需要采用低温生长的分子束外延(MBE)技术,并在GaAs,Si等半导体衬底上生长出闪锌矿(立方)结构的GaN薄膜.这样才有可能最终解决p型…     

界面超导新进展:外延于SrTiO_3衬底上的单层FeSe薄膜的超导转变温度超过40K

<正>界面超导概念的起源可追溯至50多年前物理学家对二维超导的研究。1968年,首次在实验上观测到界面增强超导现象,即当Al与Cu或者Sn混杂形成超晶格时,其超导转变温度提高接近1 K[1]。在1986年和2008年发现的铜基[2]和铁基[3]两大类高温超导体系都具有层状三明治结构,形成库珀对的载流子来源于氧化物电荷库层的掺杂。不仅铜基和铁基两大类高温超导体系,     

LaTiO3(110)薄膜分子束外延生长的精确控制和表面截止层的研究

LaTiO₃ 是一种典型的强关联电子材料, 其(110) 薄膜为通过晶格对称性、应变等的设计调控外延结构的物理性质提供了新的机会. 本文研究了SrTiO₃(110) 衬底表面金属La 和Ti 沉积所引起的微观结构变化, 进而利用电子衍射信号对分子束外延薄膜生长表面阳离子浓度的灵敏响应, 发展了原位、实时、精确控制金属蒸发源沉积速率的方法, 实现了高质量LaTiO₃(110) 薄膜的生长和对阳离子化学配比的精确控制. 由于LaTiO₃中Ti³⁺ 3d 电子的库仑排斥作用, 氧原子层截止的(110) 表面更容易实现极性补偿, 因此生长得到的薄膜表面暴露出单一类型的氧截止面.     

Si(001)衬底上分子束外延生长Ge0.975Sn0.025合金薄膜

使用低、高温两步法生长的高质量Ge薄膜作为缓冲层,在Si(001)衬底上采用分子束外延法生长出Ge_0.975Sn_0.025合金薄膜.X射线双晶衍射和卢瑟福背散射谱等测试结果表明,Ge_0.975Sn_0.025合金薄膜具有很好的晶体质量,并且没有发生Sn表面分凝.另外,Ge_0.975Sn_0.025合金薄膜在500 ℃下具有很好的热稳定性,有望在Si基光电器件中得到应用. 关键词： GeSn Ge 分子束外延 外延生长     

Co在GaAs(001)表面的分子束外延及其结构研究

报道了用高能电子衍射研究Co在GaAs(001)表面上分子束外延生长的实验结果.发现当生长温度为150℃时，Co膜的外延可以分为三个阶段：最初的3nm Co膜的晶体结构是体心立方亚稳相；接下来的4nm是复杂的多相结构；从7nm往后，Co膜则是单晶的六角密堆积结构热力学稳定相.这一新的实验结果，澄清了前人有关这一体系外延层晶体结构的矛盾之处，并清晰地建立了Co在GaAs(001)表面外延生长的物理图象. 关键词：     

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO_3（110） substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO 3（STO）（110） substrates.Inclined ZnO and cobalt-doped ZnO（ZnCoO） thin films are grown on unetched STO（110） substrates using oxygen plasma assisted molecular beam epitaxy,with the c-axis 42 inclined from the normal STO（110） surface.The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001].The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D 0 X emissions associated with A 0 X emissions,and the characteristic emissions for the 2 E（2G）→ 4A2（4F） transition of Co 2＋ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film,indicating the incorporation of Co 2＋ ions at the lattice positions of the Zn 2＋ ions.The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.     

Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

High-quality SrRuO₃ (SRO) thin films and SrTiO₃/SRO bilayer were grown epitaxially on SrTiO₃ (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction ϑ-2ϑ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΘ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials. Supported by the National Natural Science Foundation of China (Grant No. 10334070)     

Effect of polar distortion on electronic structures of (001) LaGaO3/SrTiO3 interface

First-principles calculations of electronic structures of (001) epitaxial LaGaO₃/SrTiO₃ heterostructures were performed in the framework of density functional theory. The effects of atomic relaxation on electronic characteristics of both n-type (LaO)⁺/(TiO₂)⁰ and p-type (GaO₂)⁻/(SrO)⁰ interfaces are investigated. It is found that the n-type interface remains metallic, whereas the p-type interface becomes insulating after atomic relaxation. Polar distortion in the LaGaO₃ layers associated with the atomic relaxation strongly screens the intrinsic electric field induced by periodically stacking (LaO)⁺ and (GaO₂)⁻ charged atomic layers on SrTiO₃ with charge neutral (001) atomic layers. This relieves the trend to a polar catastrophe and reduces the carrier charge density on the interface.     

Structural, magnetic and electric properties of HoMnO3 films on SrTiO3(001)

HoMnO₃ films were grown on pure and Nb-doped SrTiO₃ (001) substrates by pulsed laser deposition. The films grew epitaxially with the c-axis along the substrate normal. Varying the deposition temperature between 650 and 850 °C did not significantly affect the structural and magnetic properties of the films, whereas growth in oxygen partial pressures below 0.01 mbar lead to a degradation of the structural properties. Some of the films had a ferromagnetic-like magnetic phase transition at about 45 K, probably related to Mn₃O₄ precipitates; this magnetic response was isotropic. The Ho sublattice was found to be paramagnetic down to 5 K, but showing a pronounced anisotropy with the c-axis being the hard axis. The films showed a distinct dielectric anomaly at 16 K that depended on voltage and slightly on frequency in the range between 1 kHz and 1 MHz. The magnetoelectric effect was large with an in-plane field of 8 T suppressing the dielectric anomaly completely.     

金属有机分解法制备的SrTiO3薄膜的光学特性

采用金属有机分解法（MOD）在石英衬底上沉积了SrTiO3薄膜。所制备的薄膜是晶格常数为a=b=c=3.90?的多晶结构。通过测量190—1100nm波段内的透射光谱，采用包络方法计算了薄膜的光学常数（折射率n和消光系数k）。结果表明，采用MOD方法制备的薄膜的折射率大于采用射频磁控溅射、溶胶—凝胶和化学气相沉积方法制备的薄膜的折射率；薄膜的折射率色散关系满足单振子模型，其中振子强度S0为0.88′1014m-2，振子能量E0为6.40eV；薄膜的禁带宽度为3.68eV。     

Observation of room temperature photoluminescence in proton irradiated SrTiO3 single crystal

We have irradiated SrTiO₃ single crystal with 3 MeV-proton (H⁺) beam and found that blue -, green - and infrared - frequency photoluminescence (PL) are induced simultaneously at room temperature. TEM and EELS analyses show that an oxygen-deficient amorphous layer is formed at the crystal surface by the proton irradiation. Possible origin of the PL-effect is discussed.     

Molecular beam epitaxy and superconductivity of stoichiometric FeSe and KxFe2_ySe2 crystalline films

Our recent progress in the fabrication of FeSe and KxFe2_ySe2 ultra thin films and the understanding of their superconductivity properties is reviewed. The growth of high-quality FeSe and KxFe2_ySe2 films is achieved in a well controlled manner by molecular beam epitaxy. The high-quality stoichiometric and superconducting crystalline thin films allow us to investigate the intrinsic superconductivity properties and the interplay between the superconductivity and the film thickness, the local structure, the substrate, and magnetism. In situ low-temperature scanning tunneling spectra reveal the nodes and the twofold symmetry in FeSe, high-temperature superconductivity at the FeSe/SrTiO3 interface, phase separation and magnetic order in KxFe2_ySe2, and the suppression of superconductivity by twin boundaries and Fe vacancies. Our findings not only provide fundamental information for understanding the mechanism of unconventional superconductivity, but also demonstrate a powerful way of engineering superconductors and raising the transition temperature.     

Effect of thickness on the microstructure of GaN films on Al2O3 (0001) by laser molecular beam epitaxy

Heteroepitaxial GaN films are grown on sapphire (0001) substrates using laser molecular beam epitaxy. The growth processes are in-situ monitored by reflection high energy electron diffraction. It is revealed that the growth mode of GaN transformed from three-dimensional (3D) island mode to two-dimensional (2D) layer-by-layer mode with the increase of thickness. This paper investigates the interfacial strain relaxation of GaN films by analysing their diffraction patterns. Calculation shows that the strain is completely relaxed when the thickness reaches 15 nm. The surface morphology evolution indicates that island merging and reduction of the island-edge barrier provide an effective way to make GaN films follow a 2D layer-by-layer growth mode. The 110-nm GaN films with a 2D growth mode have smooth regular hexagonal shapes. The X-ray diffraction indicates that thickness has a significant effect on the crystallized quality of GaN thin films.     

表面吸附K原子的多层FeSe/SrTiO3(001)薄膜的抗磁响应的原位测量

SrTiO₃（001）单晶表面上生长的单层FeSe薄膜显示出了超乎寻常的高温超导电性,其超导增强机制的一个重要因素是电子由衬底转移到了单层FeSe薄膜当中.基于此认识,研究者们在吸附了钾（K）原子的多层FeSe薄膜表面上观察到了类似超导能隙的隧穿能谱和光电子能谱.但这种自上而下的电子掺入方式在多层FeSe薄膜表面上可能引起的高温超导电性,还缺乏零电阻或迈斯纳效应等物性测量实验的直接证实.本研究利用自行研制的一台特殊的多功能扫描隧道显微镜,在生长于SrTiO₃（001）衬底上的多层FeSe薄膜表面上,不但观察到了超导能隙随K吸附量的变化,而且利用原位双线圈互感测量技术,成功地的观察到了该薄膜的抗磁响应,并由此确定了该薄膜样品呈现迈斯纳效应的超导转变温度为23.9 K.其穿透深度随温度的变化呈二次幂指数关系,表明该体系的超导序参量很可能具有S^±配对对称性.