酞菁铜与MoS_2(0001)范德瓦耳斯异质结研究

利用光电子能谱、原子力显微镜以及低能电子衍射等表面研究手段系统研究了真空沉积生长的酞菁铜薄膜与衬底MoS2(0001)之间的范德瓦耳斯异质结界面电子结构和几何结构.角分辨光电子能谱清楚地再现了MoS2(0001)衬底在Γ点附近的能带结构.低能电子衍射结果表明,CuPc薄膜在MoS2(0001)表面沿着衬底表面[11ˉ20],[1ˉ210]和[ˉ2110]三个晶向有序生长,反映了衬底对CuPc的影响.原子力显微镜结果表明,CuPc在MoS2衬底上遵循层状-岛状生长模式:在低生长厚度下(单层薄膜厚度约为0.3 nm),CuPc分子平面平行于MoS2表面上形成均匀连续的薄膜;在较高的沉积厚度下,CuPc沿衬底晶向形成棒状晶粒,表现出明显的各向异性.光电子能谱显示界面偶极层为0.07 eV,而且能谱在膜厚1.2 nm饱和,揭示了酞菁铜与MoS2(0001)范德瓦耳斯异质结的能级结构.     

Single crystal RuO2/Ti and RuO2/TiO2 interface: LEED, Auger and XPS study

The interactions at the evolving RuO₂/titanium interface have been studied by LEED, AES and XPS. Titanium films of up to 5 monolayers were evaporated onto well ordered and ion sputtered ruthenium dioxide crystal surfaces of (110) and (100) orientation. Stabilization of the surface oxygen content under thermal treatment in UHV (up to 600°C) with increasing titanium coverage was established. After extended (up to 4 h) annealing in O₂ at 600°C an epitaxial ordering of TiO₂ on RuO₂(110) was observed. The (1 × 1) LEED patterns from the epitaxial layer exhibit a reduced background level when compared to the RuO₂ substrate itself. These findings are correlated with the XPS data and are interpreted in connection with the disappearance of the defect RuO₂ phase in the surface layer of the RuO₂. The appearance of the (1 × 2) surface reconstruction at the RuO₂(100)/Ti interface is discussed in the context of maximum cation coordination by oxygen atoms.     

高温氢退火还原V2O5制备二氧化钒薄膜及其性能的研究

过渡金属氧化物二氧化钒(VO₂)在温度340 K附近会发生金属绝缘体的转变(metal-insulator transition, MIT). 基于金属绝缘体的转变性质, VO₂薄膜材料具有很好的应用前景. 本文首先采用脉冲激光沉积制备了高质量的V₂O₅薄膜, 再通过高温氢退火还原V₂O₅薄膜制备出VO₂多晶薄膜. 研究了不同的退火温度、退火时间、退火气氛对VO₂薄膜制备的影响, 采用X射线衍射、X射线光电子能谱、变温电阻特性测量等手段对样品进行分析, 发现在H₂(5%)/Ar退火气氛下, 在一定的退火温度范围内(500–525 ℃), 退火 3 h, 得到了B相和M相共存的VO₂薄膜, 具有M相的VO₂的MIT特性, 而相同退火温度下退火时间达到4.5 h, 薄膜完全变成B相的VO₂. 通过纯Ar气氛下对B相VO₂再退火, 得到了转变温度为350 K, 电阻突变接近4个数量级的M相的VO₂薄膜. 实现了VO₂的B相和M相的相互转变. 关键词： 2薄膜')" href="#">VO₂薄膜 金属绝缘体转变 氢退火     

晶格失配应力对单晶(BiTm)_3(GaFe)_5O_(12)膜磁畴结构的影响

利用液相外延工艺在钆镓石榴石衬底上制得了单晶(BiTm)_3(GaFe)_5O_(12)膜,研究了晶格失配应力对其磁畴结构的影响.研究发现,生长速率越快,膜的晶格常数越大;晶格失配应力可以在一定范围内调整膜的垂直各向异性;随着晶格失配应力由较大张应力逐渐转变为较大压应力,磁畴形状先由磁泡畴转变成迷宫畴,然后转变为过渡态部分弯曲的条状畴,最终转变为整齐排列的条状畴;失配应力同时对畴宽也有影响,膜受到的失配应力越大,畴宽越大.这一实验研究对基于控制晶格失配应力来调控单晶膜的各向异性和磁畴结构有指导意义.     

Iron oxide thin film growth on Al2O3/NiAl(1 1 0)

The electronic structure and the growth morphology of iron oxide thin films were studied by means of Synchrotron Radiation Photoelectron Spectroscopy (SRPES) and Low Energy Electron Diffraction (LEED). A thin well-ordered alumina film on a NiAl(1 1 0) single crystal surface as a template for iron oxide growth was employed. Two different methods of iron oxide film preparation were applied. In the first attempt, iron deposited at room temperature was subsequently annealed in oxygen. Even though a whole layer of iron was oxidized, an expected long-range order was not achieved. The second attempt was to perform reactive deposition. For this reason iron was evaporated in oxygen ambient at elevated substrate temperature. This method turned out to be more efficient. Diffused but clear LEED patterns of six-fold symmetry indicating hexagonal surface atoms arrangement were observed. From the PES measurements, binding energies for Fe2p for grown iron oxide film were established as well as energy distribution curves for the valence band. Growth curves based on Fe3p core-level peak intensities for iron and iron oxide were plotted identifying type of film growth for both deposition methods. Based upon these results we have found evidence for interdiffusion in the interface between alumina and iron oxide at the early stages of growth. Further deposition led to formation of Fe₃O₄(1 1 1) (magnetite) overlayer. Moreover, the quality of the film could also be improved by long-time annealing at temperatures not exceeding 575 K. Higher annealing temperature caused disappearance of LEED pattern indicating loss of long-range ordering.     

GaSb基PECVD法制备SiO2薄膜的应力研究

为了实现在GaSb衬底上获得低应力的SiO₂薄膜,研究了等离子体增强化学气相沉积法（PECVD）在晶格失配较大的GaSb衬底上沉积SiO₂薄膜的应力情况。通过改变薄膜沉积时的工艺条件,如反应温度、射频功率、反应压强、气体流量比,并基于曲率法模型,对镀膜前后的曲率半径进行了实验测量,利用Stoney公式计算相关应力值并绘制应力变化曲线。详细讨论了PECVD工艺条件的改变对SiO₂薄膜应力所产生的影响。同时通过在Si衬底上沉积SiO₂薄膜,对比分析了导致薄膜应力产生的因素及变化过程。实验结果表明,在沉积温度为300℃、射频功率为20 W、腔体压强为90 Pa、气体流量比SiH₄/N₂O为125/70 cm³·min^-1的工艺参数下,PECVD法在GaSb衬底上沉积的SiO₂薄膜应力相对较小。     

A quantum chemical study of ZrO2 atomic layer deposition growth reactions on the SiO2 surface

Zirconium oxide (ZrO₂) is one of the leading candidates to replace silicon oxide (SiO₂) as the gate dielectric for future generation metal-oxide-semiconductor (MOS) based nanoelectronic devices. Experimental studies have shown that a 1–3 monolayer SiO₂ film between the high permittivity metal oxide and the substrate silicon is needed to minimize electrical degradation. This study uses density functional theory (DFT) to investigate the initial growth reactions of ZrO₂ on hydroxylated SiO₂ by atomic layer deposition (ALD). The reactants investigated in this study are zirconium tetrachloride (ZrCl₄) and water (H₂O). Exchange reaction mechanisms for the two reaction half-cycles were investigated. For the first half-reaction, reaction of gaseous ZrCl₄ with the hydroxylated SiO₂ surface was studied. Upon adsorption, ZrCl₄ forms a stable intermediate complex with the surface SiO₂–OH^* site, followed by formation of SiO₂–O–Zr–Cl^* surface sites and HCl. For the second half-reaction, reaction of H₂O on SiO₂–O–Zr–Cl^* surface sites was investigated. The reaction pathway is analogous to that of the first half-reaction; water first forms a stable intermediate complex followed by evolution of HCl through combination of a Cl atom from the surface site and an H atom from H₂O. The results reveal that the stable intermediate complexes formed in both half-reactions can lead to a slow film growth rate unless process parameters are adjusted to lower the stability of the complex. The energetics of the two half-reactions are similar to those of ZrO₂ ALD on ZrO₂ and as well as the energetics of ZrO₂ ALD on hydroxylated silicon. The energetics of the growth reactions with two surface hydroxyl sites are also described.     

基于熔融玻璃的预沉积法生长毫米级单晶MoS2及WS2-MoS2异质结

MoS₂是一种具有优异光电性能和奇特物理性质的二维材料,在电子器件领域具有巨大的应用潜力.高效可控生长出大尺寸单晶MoS₂是该材料进入产业应用所必须克服的重大难关,而化学气相沉积技术被认为是工业化生产二维材料的最有效手段.本文介绍了一种利用磁控溅射预沉积钼源至熔融玻璃上,通过快速升温的化学气相沉积技术生长出尺寸达1 mm的单晶MoS₂的方法,并通过引入WO₃粉末生长出了二硫化钼与二硫化钨的横向异质结(WS₂-MoS₂).拉曼和荧光光谱仪测试表明所生长的样品具有较好的晶体质量.利用转移电极技术制备出了背栅器件样品并对其进行了电学测试,在室温常压下开关比可达10~5,迁移率可达4.53 cm~2/(V·s).这种低成本高质量的大尺寸材料生长方法为二维材料电子器件的大规模应用找到了出路.     

石墨烯在Al_2O_3(0001)表面生长的模拟研究

基于密度泛函理论的广义梯度近似法,对用化学气相沉积法在蓝宝石(α-Al_2O_3)(0001)表面上生长石墨烯进行理论研究.研究结果表明:CH_4在α-Al_2O_3(0001)表面上的分解是吸热过程,由CH_4完全分解出C需要较高能量及反应能垒,这些因素不利于C在衬底表面的存在.在α-Al_2O_3(0001)表面,石墨烯形核的活跃因子并不是通常认为的C原子,而是CH基团.通过CH基团在α-Al_2O_3(0001)表面上的迁移聚集首先形成能量较低的(CH)_x结构.模拟研究(CH)_x对揭示后续石墨烯的形核生长机理具有重要意义.     

TEM investigation of YBa2Cu3O7 thin films on SrTiO3 bicrystals

YBa₂Cu₃O₇ films in c-axis orientation on bicrystalline SrTiO₃ substrates are investigated by TEM. The films and the substrates are examined in cross-section and in plane view. The grain boundary of the bicrystal substrate contains (110) faceted voids, but is otherwise straight on a nanometer scale. Contrary to this, the film grain boundary is not straight grain boundary can be up to 100 nm for a 100 nm thick film. The deviation from the intended position of the YBCO grain boundary can already occur at the film/substrate interface where it can be as much as ±50 nm.     

The adsorption of carbon monoxide on TiO2(110) supported palladium

Palladium overlayers deposited on TiO₂(110) by metal vapour deposition have been investigated using LEED, XPS and FT-RAIRS of adsorbed CO. Low coverages of palladium (<3 ML) deposited at 300 K adsorb CO exclusively in a bridged configuration with a band (B₁ at 1990 cm⁻¹) characteristic of CO adsorption on Pd(110) and Pd(100) surfaces. When annealed to 500 K, XPS and LEED indicate the nucleation of Pd particles on which CO adsorbs predominantly as a strongly bound linear species which we associate with edge sites on the Pd particles (L* band at 2085 cm⁻¹). Both bridged and linear CO bands are exhibited as increases in reflectivity at the resonant frequency, indicating the retention of small particle size during the annealing process. Palladium overlayers of intermediate coverages (10–20 ML) deposited at 300 K undergo some nucleation during growth, and adsorbed CO exhibits both absorption and transmission bands in the B₁ (1990 cm⁻¹) and B₂ (1940 cm⁻¹) regions. The latter is associated with the formation of Pd(111) facets. Highly dispersed Pd particles are produced on annealing at 500 K. This is evidenced by the dominance of transmission bands for adsorbed CO and a significant concentration of edge sites, which accommodate the strongly bound linear species at 300 K. Adsorption of CO at low temperature also allows the identification of the constituent faces of Pd and the conversion of Pd(110)/(100) facets to Pd(111) facets during the annealing process. High coverages of palladium (100 ML) produce only absorption bands in FT-RAIRS of adsorbed CO associated with the Pd facets, but annealing these surfaces also shows a conversion to Pd(111) facets. LEED indicates that at coverages above 10 ML, the palladium particles exhibit (111) facets parallel to the substrate and aligned with the TiO₂(110) unit cell, and that this ordering in the particles is enhanced by annealing.     

Substrate dependent growth studies of MgB2 films by electrocrystallization

The comparative study of MgB₂ film growth on Al₂O₃ and glass substrate by electrocrystallization technique is discussed. The precursor magnesium films were deposited by vacuum evaporation method. These magnesium films were then used as electrode for the growth of MgB₂ films by electrocrystallization. The structural, morphological and superconducting properties of the electrocrystallized MgB₂ films on Al₂O₃ substrate were examined by using XRD, SEM and electrical resistivity measurement techniques and compared with that of MgB₂ films grown on glass substrate. The films deposited on Al₂O₃ substrates showed enhanced crystallinity and relatively higher T_c value compared to films deposited on glass substrates.     

合成温度和N2/O2流量比对碳纤维衬底上生长的SnO2纳米线形貌及场发射性能影响

采用化学气相沉积法系统研究了合成温度和N₂/O₂流量对生长在碳纤维衬底上的SnO₂纳米线形貌及场发射性能的影响规律. 利用扫描电镜(SEM)、透射电镜(TEM), X射线衍射(XRD)及能谱仪(EDS)对产物细致表征, 结果表明, SnO₂纳米线长径比随反应温度的升高而增大; 随N₂/O₂流量比值的增大先增大后变小, 场发射测试表明, 合成温度780 ℃, N₂/O₂流量比为300 : 3 时SnO₂纳米线阵列具有最佳的场发射性能, 开启电场为1.03 V/μm, 场强增加到1.68 V/μm时, 发射电流密度达0.66 mA/cm², 亮度约2300 cd/m².     

衬底温度对共蒸发法制备Cu2ZnSnSe4太阳电池的影响

采用共蒸发法在不同衬底温度下沉积Cu_2ZnSnSe_4(简称CZTSe)薄膜,分析了衬底温度对CZTSe材料性质及电池性能的影响。研究表明:当衬底温度较低时(380℃),CZTSe薄膜中含有SnSe_x使电池失效;随着衬底温度的升高,CZTSe薄膜的结晶质量明显提升,电池开路电压增加。但当衬底温度达到460℃时,电池的转换效率反而下降;结合CZTSe的生长机理及器件模型分析了电池效率下降可能的原因。最终在衬底温度420℃的条件下制备出效率为3.12%(有效面积0.34 cm~2)的CZTSe太阳电池。     

Structure and optical properties of sol–gel derived Gd2O3 waveguide films

Pure and rare earth doped gadolinium oxide (Gd₂O₃) waveguide films were prepared by a simple sol–gel process and dip-coating method. Gd₂O₃ was successfully synthesized by hydrolysis of gadolinium acetate. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structure of Gd₂O₃ films annealed at different temperature ranging from 400 to 750 °C were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Gd₂O₃ starts crystallizing at about 400 °C and the crystallite size increases with annealing temperature. Oriented growth of (4 0 0) face of Gd₂O₃ has been observed when the films were deposited on (1 0 0) Si substrate and annealed at 750 °C. The laser beam (λ=632.8 nm) was coupled into the film by a prism coupler and propagation loss of the film measured by scattering-detection method is about 2 dB/cm. Luminescence properties of europium ions doped films were measured and are discussed.     

Na2O overlayers epitaxially prepared on Pd(100) and structure-sensitive CO2 adsorption

Sodium oxide overlayers prepared on Pd(100) were examined with AES, LEED and XPS. The oxides were grown by cycles of Na deposition followed by oxidation, maintaining the composition of Na₂O. The surface structure of the deposited oxide was sensitive to the annealing temperature after oxidation. The Na₂O/Pd(100) surfaces gave rise to a (3 × 3) LEED pattern when annealed at 600 K under vacuum. A model based on Na₂O(100) was proposed for the (3 × 3) overlayers, where the oxide was epitaxially aligned in a square periodicity on the substrate. Multilayered Na₂O was prepared maintaining the (3 × 3) pattern, by repeated cycles of preparation. Annealing at 700 K caused a c(4 × 6) pattern, for which a model based on Na₂O(110) was proposed. CO₂ was adsorbed on the (3 × 3) oxide of various thickness to form carbonate at 350 K, whereas the c(4 × 6) oxide was inert. The relationship of structure and reactivity is discussed in relation to the microscopic design of metal-oxide surfaces for base-catalysis.     

La1.3Sr1.7Mn2O7/SrTiO3-Nb异质结的整流和光伏特性

采用脉冲激光沉积法在SrTiO₃:0.7%Nb(100)单晶衬底上生长了La_1.3Sr_1.7Mn₂O₇(LSMO)薄膜, 并 研究了LSMO/SrTiO₃-Nb异质结的输运性质和光伏效应. 研究发现, 异质结具有良好的整流特征和明显的光生伏特效应. 在532 nm激光辐照下, 光生电压随温度升高先增大后减小, 并且在150 K达到最大值400 mV, 此温度点与LSMO薄膜发生金属-绝缘体转变的温度一致, 这表明异质结的光生伏特效应受LSMO薄膜内部的输运特征调控. 进一步, 从光生电压随时间的变化曲线中分析发现, 上升沿符合一阶指数函数, 这与载流子的迁移过程相关; 而下降沿符合二阶指数函数, 这与结两侧载流子的外部回路中和以及材料内部的电子-空穴湮灭有关. 值得注意的是, 上升沿和下降沿的时间常数均随着温度先增大后减小, 且最大值均出现在LSMO薄膜的金属-绝缘转变温度.     

Structural, optical and electrical studies on pulse electrodeposited CdIn2S4 thin films

CdIn₂S₄ thin films were prepared by pulse electrodeposition technique over F:SnO₂ glass and stainless steel substrates in galvanostatic mode from an aqueous acidic bath containing CdSO₄, InCl₃ and Na₂S₂O₃. The growth kinetics of the film has been studied and the deposition parameters such as electrolyte bath concentration, bath temperature, time of deposition, deposition current and pH of the bath are optimized. X-ray diffraction (XRD) analysis of the as deposited and annealed films shows polycrystalline nature. Energy dispersive analysis by X-ray (EDAX) confirms nearly stoichiometric CdIn₂S₄ nature of the film. Scanning electron microscope (SEM) studies show that, the deposited films are well adherent and grains are uniformly distributed over the surface of the substrate. The optical transmission spectra show a direct band gap of 2.16 eV. Conductivity measurements have been carried out at different temperatures and electrical parameters such as activation energy, trapped energy state and barrier heights etc. have been determined.     

Magnetic anisotropic properties in Fe3O4 and CoFe2O4 ferrite epitaxy thin films

Epitaxial thin films of Fe₃O₄ and CoFe₂O₄ on MgO (0 0 1) substrates were grown by molecular beam epitaxy at low temperature growth process. Magnetization and hysteresis loop of both films were measured to investigate magnetic anisotropic properties at various temperatures. Anomalous magnetic properties are found to be correlated with crystalline, shape, and stress anisotropies. The Fe₃O₄ film below Verwey structural transition has a change in crystal structure, thus causing many anomalous magnetic properties. Crystalline anisotropy and anomalous magnetic properties are affected substantially by Co ions. The saturation magnetization of Co–ferrite film becomes much lower than that of Fe₃O₄ film, being very different from the bulks. It indicates that the low temperature growth process could not provide enough energy to have the lowest energy state.