High temperature thermoelectric properties of highly c-axis oriented Bi₂Sr₂Co₂O_y thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3(001).Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m·Ω· cm and 202 μV/K at 980 K,resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples.A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature.The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices.     

Influence of the substrate material on the properties of pulsed laser deposited thin Li1+xMn2O4−δ films

Thin Li_1+xMn₂O_4−δ films were deposited on several substrate materials (stainless steel, p-doped silicon and glassy carbon) by pulsed laser deposition. To obtain the correct thin film stoichiometries, targets with a different amount of excess lithium were required (Li_1.03Mn₂O₄ + xLi₂O; x = 2.5 and 7.5 mol%). The resulting polycrystalline thin films were characterized with respect to their morphology and electrochemical activity. It was found that only thin Li_1+xMn₂O_4−δ films deposited on stainless steel and glassy carbon showed the typical insertion and deinsertion peaks of Li⁺ during cycling.     

In situ functionalized self-assembled monolayer surfaces for selective chemical vapor deposition of copper

Recent studies show that the self-assembled monolayer (SAM) is well suited to control the selectivity of chemical vapor deposition (CVD). Here, we reported the selective CVD for copper on the functionalized SAM surfaces (with -SH, -SS-, and -SO₃H terminal groups). The -SS- and -SO₃H terminal group surfaces were obtained through in situ chemical transformation of -SH terminal group surface of a 3-mercaptopropyltrimethoxysilane-SAM (MPTMS-SAM). As a result, the -SS- terminal group surface reduces copper deposition and the -SO₃H terminal group surface enhances copper deposition comparing to the -SH terminal group surface. In addition, the MPTMS-SAM was irradiated by UV-light through a photo mask to prepare SH-group and OH-group regions. Then, copper films were deposited only on the SH-group region of the substrate in chemical vapor deposition. Finally, patterns of copper films were formed in the way of UV-light irradiation. These results are expected for use of selective deposition of copper metallization patterns in IC manufacturing processes.     

Nanohole 3D-size tailoring through polystyrene bead combustion during thin film deposition

A novel approach is presented for nanohole 3D-size tailoring. The process starts with a monolayer of polystyrene (PS) beads spun coat on silicon wafer as a template. The holes can be directly prepared through combustion of PS beads by oxygen plasma during metal or oxide thin film deposition. The incoming particles are prevented from adhering on PS beads by H₂O and CO₂ generated from the combustion of the PS beads. The hole depth generally depends on the film thickness. The hole diameter can be tailored by the PS bead size, film deposition rate, and also the combustion speed of the PS beads. In this work, a series of holes with depth of 4-24 nm and diameter of 10-36 nm has been successfully prepared. The hole wall materials can be selected from metals such as Au or Pt and oxides such as SiO₂ or Al₂O₃. These templates could be suitable for the preparation and characterization of novel nanodevices based on single quantum dots or single molecules, and could be extended to the studies of a wide range of coating materials and substrates with controlled hole depth and diameters.     

The structure and optical characters of the ZnO film grown on GaAs/Al2O3 substrate

In this paper ZnO films are grown on GaAs/Al₂O₃ substrates at different temperature by metal-organic chemical vapor deposition (MOCVD). The GaAs/Al₂O₃ substrates are formed by depositing GaAs layer (∼35 nm) on the Al₂O₃ substrate. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that most of the Ga and As atoms form Ga-As bond and the GaAs layer does not present any orientation. The characters of the ZnO films grown on GaAs/Al₂O₃ substrates are investigated by XRD, photoluminescence (PL), atomic force microscopy (AFM) and Raman scattering. Compared with ZnO film grown on Al₂O₃ substrate, ZnO film prepared by our fabrication scheme has good crystal and optical quality. Meanwhile its grain size becomes bigger according to the AFM image. Raman analysis indicates that the intrinsic defects and the in-plane tensile stress are obviously reduced in ZnO/GaAs/Al₂O₃ samples.     

Ferromagnetism in noncompensated (Mn,Ga)-codoped ZnO films

Mn/Ga noncompensated codoped ZnO films were prepared on c-cut sapphire substrates via pulsed laser deposition. The structural, magnetic, transport, and optical properties of the films were then investigated. Addition of the Ga donor increases the electron concentration and enhances the magnetization in these films because of the net negative charge of the special noncompensated codoping, which can adjust the carrier concentration as well as the magnetic moment. Moreover, the Fermi level moves into the conduction band because of the increase in electron concentration, which results in an increase in the optical band gap value, from 3.28 eV for the undoped ZnO film to 3.61 eV for the (Mn,Ga)-codoped ZnO film.     

On the differentiability of depth distribution function of deposited energy, momentum and ion range

Based on the translational invariance of a medium,a new theorem has been proposed and proved rigorously:the depth distributions of the deposited energy,momentum and ion range must be infinitely differentiable functions in amorphous or polycrystalline infinite targets by ion bombardment,if these functions exist.The origin of the “discontinuity”,derived by Dr Glazov in 1995 in J.Phys.:Condens.Matter 7 6365,has been analysed in detail.For the power cross section,neglecting electronic stopping,the linear transport equations determining the depth distribution functions of the deposited energy and monentum (by taking the threshold enerkgy into account )have been solved asymptotically.An important formula derived by Dr Glazov has been confirmed and generalized.The results agree with the new theorem.     

Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO2 and mica substrates

<正>Deposition patterns of tetracyanoquinodimethane(TCNQ) molecules on different surfaces are investigated by atomic force microscopy.A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system,we investigate TCNQ thin film growth on both SiO_2 and mica surfaces.It is found that dense island patterns form at a high deposition rate,and a unique seahorse-like pattern forms at a low deposition rate.Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction.Finally,a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.     

A study of the interaction between perylene and the TiO2(1 1 0)-(1 × 1) surface-based on XPS, UPS and NEXAFS measurements

The interaction between a semi-large aromatic hydrocarbon compound (perylene) and the TiO₂(1 1 0)-(1 × 1) surface under ultra high vacuum conditions has been probed by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and near-edge X-ray absorption fine structure (NEXAFS) methods. UPS measurements of the adsorbate system have been compared with an experimental UPS spectrum of perylene in the gas phase and a calculated spectrum obtained by means of density functional theory (DFT) methods. NEXAFS results of perylene molecules adsorbed on TiO₂(1 1 0)-(1 × 1) were compared with data from an α-phase perylene single crystal. A novel analysis of the valence data has been employed to show that no strong chemical interaction takes place between perylene and the TiO₂(1 1 0)-(1 × 1) surface. Furthermore, angle-dependent NEXAFS measurements and the growth curve results suggest that the perylene molecules are oriented flat down onto the TiO₂ substrate due to weak van der Waals interactions.     

化学沉淀法制备硒化铅薄膜

采用化学沉淀的方法沉淀PbSe薄膜,分别加入缓冲剂联氨(方法A)和碘化钾(方法B)。对反应原理进行了分析,对制备过程进行了优化,分别制备出了高质量的PbSe薄膜。采用XRD、SEM、EDS以及红外光谱测试对所制备样品进行了分析。结果表明,两种方法制备均为PbSe多晶薄膜,方法A制备薄膜结晶质量更好,择优生长方向明显;薄膜颗粒度、表面粗糙度都小于方法B;两种薄膜的Pb元素与Se元素比例接近化学计量比,方法B含有少量I元素;两种方法制备样品的吸收边相对带边跃迁都发生蓝移。