6H-SiC/3C-SiC/6H-SiC量子阱结构制备及其发光特性

利用固源分子束外延(SSMBE)生长技术, 在1350K的衬底温度下, 通过改变Si束流强度, 在6H-SiC(0001)面上外延生长6H-SiC/3C-SiC/6H-SiC量子阱结构薄膜, 并用反射高能电子衍射(RHEED)与光致发光(PL)谱对生长的薄膜的晶型和发光特性进行表征. RHEED 结果显示生长的薄膜为6H-SiC/3C-SiC/6H-SiC量子阱结构薄膜. 室温下He-Gd激光激发的光致发光(PL)谱显示, 薄膜在480-600 nm范围内存在衬底未观察到的较强发光. 拟合得到的发光峰与依据量子阱结构模型计算出的发光位置较为一致. 由此表明, 该强发光带可能是6H-SiC/3C-SiC/6H-SiC量子阱结构的发光.     

具有SiC缓冲层的Si衬底上直接沉积碳原子生长石墨烯

石墨烯是近年发现的一种新型多功能材料.在合适的衬底上制备石墨烯成为目前材料制备的一大挑战.本文利用分子束外延(MBE)设备,在Si 衬底上生长高质量的SiC 缓冲层,然后利用直接沉积C原子的方法生长石墨烯,并通过反射式高能电子衍射(RHEED)、拉曼(Raman)光谱和近边X 射线吸收精细结构谱(NEXAFS)等实验技术对不同衬底温度(800、900、1000、1100 °C)生长的薄膜进行结构表征.实验结果表明,在以上衬底温度下都能生长出具有乱层堆垛结构的石墨烯薄膜.当衬底温度升高时,碳原子的活性增强,其成键的能力也增大,从而使形成的石墨烯结晶质量提高.衬底温度为1000 °C时结晶质量最好.其原因可能是当衬底温度较低时,碳原子活性太低不足以形成有序的六方C-sp2环.但过高的衬底温度会使SiC 缓冲层的孔洞缺陷增加,衬底的Si 原子有可能获得足够的能量穿过SiC薄膜的孔洞扩散到衬底表面,与沉积的碳原子反应生成无序的SiC,这一方面会减弱石墨烯的生长,另一方面也会使石墨烯的结晶质量变差.     

溶胶-凝胶法制备LiCoO2薄膜的研究

以LiNO3和Co(NO3)2为主要原料、采用溶胶-凝胶旋涂法在(111)单晶硅片上制备了LiCoO2薄膜.X射线衍射结果表明,涂液中Li+离子和Co2+离子的总浓度与配比可影响薄膜的成分.薄膜的最佳烧结温度与最佳烧结时间分别为600～700℃和30～60min.涂液中柠檬酸、聚乙烯乙二醇、去离子水的含量与热处理时的升温速率对薄膜的形貌有很大影响.     

纳米晶双相稀土永磁合金透射电镜薄膜样品的制备

探讨了纳米晶双相稀土永磁合金在ＰＴＦＥ夹具园片抛光法和在离子薄化技术中的电镜薄膜样品的制备,比较了利用离子薄化和电解双喷加离子薄化技术获得的纳米晶双相稀土永磁合金的透射电分析结果,优化了两种方法制备电镜薄膜样品的实验条件及参数范围。探索出较佳的有竽透电镜观察的纳米双相稀土永磁合金薄膜样品的制备方法。     

激光分子束外延技术及其在氧化锌薄膜制备中的应用

与金属有机物化学气相沉积和磁控溅射相比, 激光分子束外延技术(L-MBE)是近年来发展的一种先进的薄膜生长技术, 在氧化锌薄膜生长的研究中因其独特的优越性显示出越来越强的竞争力.在讨论ZnO薄膜基本特性的基础上, 较为详细地论述了激光分子束外延技术及其在氧化锌薄膜制备中的应用和取得的新进展.     

YBCO涂层导体CeO2,Y2O3缓冲层的生长研究

采用反应溅射的方法在具有立方织构的Ni基底上制备了CeO2,Y2O3缓冲层.Ar/H2气氛下预沉积的引入,有效地抑制了基底的氧化.同时,为保证薄膜的外延取向,预沉积时间必须和总沉积时间满足线性关系.对比CeO2,Y2O3的生长条件,发现CeO2的外延生长区间比Y2O3宽,Y2O3的生长对温度、气压等条件更为敏感.最终制备的CeO2缓冲层是纯的(100)取向,其平面内φ扫描半高宽(FWHM)为8.5°;而Y2O3存在两种平面取向,一种是Y2O3(110)‖Ni(100),另一种是Y2O3(100)‖ Ni(100).俄歇能谱观察表明,CeO2/Ni界面优于Y2O3/Ni界面.扫描电镜照片显示,CeO2,Y2O3缓冲层的表面均匀致密,无裂纹生成,但两种薄膜中,都有呈三角形的胞状突起.     

电子功能外延薄膜的电沉积

电沉积作为一种在温和条件下从溶液中合成材料的技术已被广泛应用于在导体和半导体基底表面合成各种功能材料。电沉积一般由人为施加于基底的电刺激（如：施加电位/电流）来触发。这种电刺激通过氧化或还原靠近基底表面的溶液层内部的离子、 分子或配合物从而使该溶液层偏离其热力学平衡状态,随后引起目标产物在基底表面的沉积。在电沉积过程中, 许多实验参数都可能从不同的方面对沉积物的物化性质造成影响。迄今为止,已通过电沉积制备出多种单质（包括金属和非金属单质）、 化合物（例如：金属氧化物、金属氢氧化物、 金属硫化物等）以及复合材料。电沉积制备的这些材料大多为多晶、 织构或外延薄膜的形式。其中, 外延薄膜是一种具有特定的面外和面内晶体生长取向且其晶体取向受基底控制的类单晶薄膜。由于外延薄膜中高度有序的原子排列,它们常呈现出独特的电磁性质。本文总结了常见的电沉积合成路线及影响沉积物外延生长的关键实验因素。此外, 本文简要介绍了用于表征外延薄膜的技术。最后, 本文还讨论了一些采用电沉积制备的具有特殊电子、 电磁及光电特性的功能外延薄膜。     

柔性不锈钢基底上一维TiO_2纳米线薄膜的制备及表征

采用直流磁控溅射的方法在柔性不锈钢基底(50μm)上沉积纯钛薄膜,后在NaOH碱溶液中经水热法制备了非钛基大长径比的一维TiO2纳米线薄膜,并通过场发射扫描电子显微镜(FESEM)、X射线衍射(XRD)、透射电子显微镜(TEM)以及光电化学的方法对不锈钢基一维TiO2纳米线薄膜进行了表征.结果表明,纯钛薄膜的致密度、结晶性能以及与基底的结合强度均随衬底温度的升高而加强;在10mol·L-1NaOH浓度下,生长一维TiO2纳米线结构的适宜温度为130-150℃;TiO2纳米线长度达到几个微米,直径在10-30nm之间,并且相互交叉生长,构成一个三维网络结构.此外,在Na2SO4溶液中对TiO2纳米线薄膜进行了线性扫描和瞬态光电流测试,结果表明,一维TiO2纳米线薄膜电极较TiO2纳米颗粒电极表现出更优异的光电化学性能.这种磁控溅射与水热反应相结合的方法,为非钛异质基底上制备一维TiO2纳米线薄膜提供了新的思路.     

Tb2O3对磁光玻璃形成区及物理化学性质的影响

以分析纯的氧化铽、氢氧化铝、氧化硅和硼酸等为主要原料, 采用传统熔融冷却工艺制备了硼硅酸盐系稀土Tb2O3磁光玻璃, 讨论了Tb2O3对玻璃形成区及物理化学性质的影响. 采用示差扫描量热仪(DSC)、 自制的Verdet常数测试设备和紫外/可见/近红外分光光度计(UV/VIS/NIR)对玻璃的特征温度、 Verdet常数和吸收光谱进行表征. 结果表明: Tb3+离子的掺入量受玻璃形成区域的限制, 在Tb2O3含量为30%(摩尔分数)时, 玻璃形成能力较强, 热稳性好;玻璃密度和Verdet常数均与Tb3+离子浓度近似成线性关系;稀土玻璃吸收峰位置只与稀土离子种类有关, 吸收峰强度随Tb2O3含量的增加而增强.     

氮离子注入表面改性PBO薄膜及其性能

利用70keV能量的氮离子对聚苯并二噁唑(PBO)薄膜进行常温下离子注入表面改性,注入剂量(每平方厘米注入的氮离子数)从1×10~(15)N~+/cm~2到5×10~(16)N~+/cm~2。采用红外(FTIR)、拉曼(Raman)、光电子能谱(XPS)及原子力显微镜(AFM)对其表面结构、组成及形貌进行了表征。研究了氮离子注入剂量对PBO薄膜表面结构与性能的影响。结果表明:注入氮离子后,薄膜表面发生化学键的断裂和交联,近表面区域发生碳化。随氮离子注入剂量的增加,表面粗糙度增加,表面接触角从93°降低到60°,表面润湿性提高了35%,电导率提高到5.7×10~(-9)S/cm,比纯PBO薄膜增加了3个数量级。     

Fabrication of nanoparticulate porous LaOF films through film growth and thermal decomposition of ion-modified lanthanum diacetate hydroxide

This paper first reports fabrication of macro/nanotextured rare-earth oxyfluoride films. Usage of ion-modified lanthanum diacetate hydroxide (LDAH) as self-templates was successful in producing nanoparticulate lanthanum oxyfluoride (LaOF) films. LDAH template films were deposited on glass substrates through a chemical bath deposition in solutions composed of lanthanum acetate sesquihydrate, methanol, trifluoroacetic acid, and aqueous ammonia. The LDAH films had a unique, nestlike morphology owing to a two-dimensional hexagonal crystal growth. Modification of LDAH with trifluoroacetate ions led to formation of LaOF after pyrolyzing the template films at temperatures of 400-600 degrees C in air. The resultant LaOF films had a nanoparticulate porous microstructure, maintaining the morphology of the original LDAH template films. It was also successful to incorporate Eu3+ ions into LaOF through deposition of the LDAH film in a solution containing europium acetate tetrahydrate. The characteristic photoluminescence from Eu(3+) was observed with an ultraviolet-light excitation at 273 nm, indicating that Eu3+ was homogeneously distributed in LaOF host crystals. Thus the ion-modification of LDAH was also demonstrated to be a useful method for preparing nanostructured rare-earth oxyfluoride materials havingvarious cationic compositions.     

Supersonic molecular beam growth of thin films of organic materials: A novel approach to controlling the structure,morphology, and functional properties

Thin films of semiconducting molecular materials can be grown with a seeded supersonic molecular beam epitaxy (SuMBE), which provides unprecedented control over structural, morphological, and, therefore, functional properties. This novel technique of deposition takes full advantage of its ability to regulate the initial state of the molecular precursors in the beams and, in particular, the kinetic energy, to control the morphology, structure, and functional properties of growing films. This article reviews the state of the art of SuMBE, discussing the basic aspects of the technique and the major achievements so far. The major results obtained with respect to growth on dielectrics and metal substrates of films of oligothiophenes and pentacene and with respect to the codeposition of phthalocyanines and fullerenes are discussed and compared with the state of the art of more conventional organic molecular beam deposition. The potential impact of SuMBE in the field of π‐conjugated materials and devices is also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2501–2521, 2003     

PbTe(111)薄膜的分子束外延生长及其表面结构特性

采用分子束外延(MBE)方法在Ba F_2(111)衬底上直接外延生长了Pb Te薄膜。反射高能电子衍射(RHEED)实时监控的衍射图样揭示了Pb Te在Ba F_2(111)表面由三维生长向二维生长的变化过程。转动对称性的研究结合第一性原理密度泛函理论(DFT)的计算揭示了在富Pb及衬底温度(Tsub)为350°C的生长条件下,得到的Pb Te(111)薄膜具有稳定的(2×1)重构表面。Pb Te(111)-(2×1)表面覆盖Te膜后,通过300°C的退火处理,重构表面可完全复原,这为大气环境下Pb Te薄膜表面结构的保护提供了有效的方法。     

Atomistic study of GaSe/Ge(111) interface formed through van der Waals epitaxy

Layered materials can be grown on various substrates through van der Waals epitaxy (vdWE) regardless of lattice mismatch. The atomistic study of the film-substrate interface in vdWE is becoming increasingly important due to their expected applications as two-dimensional (2D) materials. In this contribution, we have grown GaSe thin films on Ge(111) substrates by molecular beam epitaxy and studied the GaSe/Ge(111) interface using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Cross-sectional HAADF-STEM observations revealed that the grown layers adopt predominantly the expected wurtzite-like structure and stacking, but layers with zinc-blende-like structure, similar to Ga₂Se₃ but apparently different, and other layer stacking sequences, exist locally near the film-substrate interface. These results demonstrate that even in vdWE, structural changes can occur in the grown layers adjacent to the substrate, highlighting the importance of such interface for synthesizing and applying ultimately thin 2D materials.     

Elimination of porosity in heavily rare-earth doped sol–gel derived silicate glass films

The combination of spin-coating and rapid thermal annealing is a very important sol–gel technique to prepare high quality silicate glass films, widely used in the fabrication of waveguides, photonic bandgap structures and other film-based optical devices. This work found that high rare-earth concentrations will seriously affect the optical quality of the films prepared by the spin-coating/rapid thermal annealing process, with pores with hundreds of nanometres in size being found in heavily rare-earth doped aluminosilicate glass films, causing significant light scattering. However, it was also found that a new recipe using acetylacetone was able to dramatically eliminate these pores and to improve the film optical quality, even for rare-earth concentrations as high as 15 mol%. This result will be useful for the fabrication of sol–gel derived devices based on rare-earth doped silicate glass films like active waveguides, functional films and photonic bandgap structures.     

First-principles studies of vanadia-titania catalysts: beyond the monolayer

Periodic density functional calculations have been used to investigate the structure and stability of epitaxial vanadium oxide films grown on the TiO(2)(001) anatase surface. The formation energy of films of V(2)O(5) stoichiometry, initially low, is found to rapidly increase with the film thickness, at variance to what is obtained for reduced pseudomorphic VO(2) films. This is in tune with results of oxygen-assisted molecular beam epitaxy. The oxidation of thick, viz. >2 monolayers (ML), VO(2) films yields a c(2 x 2) reconstructed surface, in agreement with low energy electron diffraction. These films are composed by partially reduced inner V atoms in a distorted-octahedral environment, and by isolated surface dioxovanadium centers exhibiting a distorted trigonal-bipyramidal coordination. Single scattering simulations of X-ray photoelectron diffraction patterns have also been performed, taking both 2- and 3-ML surface surface-oxidized films as models. Results are in fair agreement with experiments referring to films grown in oxidizing conditions, which suggests that coherent vanadia ultrathin films could be formed in vanadia-titania catalysts. The electronic structure of the films has been finally studied, finding that the terminal oxygens carried by the surface dioxovanadium species have a strong nucleophilic character, which makes them potential active centers for selective oxidation catalysis.     

Use of the liquid-liquid interface for generating ultrathin nanocrystalline films of metals, chalcogenides, and oxides

The air-water interface has traditionally been employed to prepare particle assemblies and films of metals and semiconductors. The interface between water and an organic liquid, however, has not been investigated sufficiently for possible use in preparing nanocrystals and thin films of materials. In this article, we demonstrate the use of the liquid-liquid interface as a medium for preparing ultrathin films of metals, chalcogenides and oxides. The method involves the reaction at the interface between a metal-organic compound in the organic layer and an appropriate reagent for reduction, sulfidation, etc. in the aqueous layer. Some of the materials discussed are nanocrystalline films of gold, CuS, CuSe, CuO, and Cu(OH)2 formed at the liquid-liquid interface. The results reported in this article should demonstrate the versatility and potential of the liquid-liquid interface for preparing nanomaterials and ultrathin films and encourage further research in this area.     

Fabrication of Highly Textured 2D SnSe Layers with Tunable Electronic Properties for Hydrogen Evolution

Hydrogen is regarded to be one of the most promising renewable and clean energy sources. Finding a highly efficient and cost-effective catalyst to generate hydrogen via water splitting has become a research hotspot. Two-dimensional materials with exotic structural and electronic properties have been considered as economical alternatives. In this work, 2D SnSe films with high quality of crystallinity were grown on a mica substrate via molecular beam epitaxy. The electronic property of the prepared SnSe thin films can be easily and accurately tuned in situ by three orders of magnitude through the controllable compensation of Sn atoms. The prepared film normally exhibited p-type conduction due to the deficiency of Sn in the film during its growth. First-principle calculations explained that Sn vacancies can introduce additional reactive sites for the hydrogen evolution reaction (HER) and enhance the HER performance by accelerating electron migration and promoting continuous hydrogen generation, which was mirrored by the reduced Gibbs free energy by a factor of 2.3 as compared with the pure SnSe film. The results pave the way for synthesized 2D SnSe thin films in the applications of hydrogen production.     

MOF-on-MOF heteroepitaxy: perfectly oriented [Zn2(ndc)2(dabco)]n grown on [Cu2(ndc)2(dabco)]n thin films

We report the successful heteroepitaxial growth of perfectly oriented hybrid MOF thin films. By employing step-by-step liquid-phase epitaxy (LPE), [Zn(2)(ndc)(2)(dabco)](n) was grown on [Cu(2)(ndc)(2)(dabco)](n), thus demonstrating that the MOF-on-MOF deposition scheme developed for powdered microcrystalline MOF materials can also be applied in connection with LPE for MOF thin films or multilayers. The deposition was monitored by surface plasmon resonance (SPR) spectroscopy, the resulting MOF heterostructures were characterized using IR spectroscopy and different types of X-ray diffraction (XRD)-based techniques. The results suggest that the LPE method is a promising way to fabricate and grow MOF heterostructures, and also demonstrates the potential of [Cu(2)(ndc)(2)(dabco)](n) MOF thin films as substrates for the LPE-based growth of different MOFs on top.     

Formation of langmuir-blodgett films containing two-dimensional monoatomic arrays of rare-earth cations

The work is focused on the preparation and characterisation of rare-earth containing stearic acid Langmuir-Blodgett (LB) films. Stearic acid monolayer behavior on the rare-earth containing aqueous subphase have been analyzed by thermodynamic measurements. The compression isotherm shape changed substantially under varying the anion type at the constant rare-earth cation content in aqueous subphase. The structure of formed multilayer rare-earth containing LB films was studied using small angle X-rays diffraction. The considerable structural defects in multilayer films were found when rare-earth chloride solution was exploited as aqueous subphase, caused presumably by electrostatic interactions at the monolayer surface under high binding of rare-earth cations. The use of monodentate complexones like acetic acid was proposed to form bulk phase quasi-neutral rare-earth complexes. The electroneutral ligand exchange reactions of such complexes with stearic acid monolayer allowed to neutralise monolayer surface under rare-earth cations binding and to form condenced monolayer below the triple-point temperature. The compression of such monolayer to the state of minimal compressibility and subsequent monolayer deposition resulted in the formation of high ordered LB films with high content of adsorbed multivalent rare-earth cations arranged in two-dimensional monoatomic arrays.