Growth and characterizations of ZnO nanorod/film structures on copper coated Si substrates

ZnO deposits were obtained on electroless copper coated Si substrates using a conventional RF magnetron sputter deposition technique at room temperature. The deposition pressure was varied from 6.67 Pa to 0.667 Pa. The RF powers were from 100 to 200 W and the electrode distance was fixed at 5 cm. The ZnO deposition time was varied from 1 to 30 min. The deposits consist of ZnO nanorods and a ZnO film, with the roots of the nanorods embedded in the film. The growth of the nanorods far exceeds the growth of the film in the beginning of the deposition process. The nanorod lengthening rate then slows down and becomes lower than the film growth rate. Effects of sputter deposition parameters on the growth of ZnO nanorods/film structures were also investigated.     

Growth behavior of iridium on Si substrates prepared by plasma enhanced atomic layer deposition

Growth behavior of iridium (Ir) thin film on Si substrates prepared by plasma enhanced atomic layer deposition (PEALD) was systematically studied. Ir(EtCp)(COD) and oxygen was employed as a precursor and reactant, respectively. To obtain optimal conditions for depositing nanometer scale Ir thin film, deposition temperature, cycle dependence and precursor feeding time dependence were studied. Uniform 12 nm thick Ir layer with sharp interface was grown at the temperature range of 330-360 degrees C at the fixed deposition cycles of 300. The grown Ir film showed linear properties as a function of deposition cycles which is a typical self-limiting characteristic of ALD. The XRD patterns revealed that IrOx was not formed due to relatively low partial pressure of oxygen. The optimal conditions obtained for 12 nm thick Ir thin film were 330 degrees C of deposition temperature, 300 deposition cycles, and 10 sec of precursor feeding time.     

Growth of Ge islands on Si substrates

We present a study of Ge islands formation on Si(100) substrates using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). Samples were prepared by magnetron sputtering of a 5 nm thick Ge layer in a very high vacuum on Si(100) substrate held at different temperatures. The vertical cut (perpendicular to the surface) of the experimental 2D GISAXS pattern has been fitted using a Guinier approximation. The optimum temperature for the islands formation was 650 °C. At this temperature, islands grow in conical shape with very similar dimensions; however, inter-island distances varied significantly.     

Plasma oxidation of Al thin films on Si substrates

In this study, Al thin films deposited on silicon wafers by direct current magnetron sputtering were oxidized under radio frequency 13.56 MHz O₂ plasma at temperatures up to 550 °C. During oxidation, plasma powers as well as oxidation temperature and time were varied to investigate the oxidation behavior of the Al films. X-ray photoelectron spectroscopy and Auger electron spectroscopy results show that the apparent alumina could be observed after O₂ plasma treatment with powers above 200 W as well as at temperatures above 250 °C. However, no alumina increment could be discerned after individual either heat treatment at 550 °C or plasma treatment at room temperature. The thickness of alumina layers increased remarkably with plasma power and could reach about 60 nm when undergone 400 W O₂ plasma treatment at 550 °C for 2 h. Moreover, the thickness of alumina increased parabolically with time during plasma oxidation aided by thermal treatment. The deduced activation energy of such plasma oxidation was 19.1 ± 0.5 kJ/mol.     

AlN/Si衬底上ZnO薄膜的择优取向生长

当ZnO薄膜直接沉积在Si衬底上时,由于ZnO与Si的晶格失配度大,不易于获得高质量的ZnO薄膜.因此,选择合适的衬底材料沉积ZnO薄膜,对提高其质量非常重要.本文采用射频磁控溅射法,通过在Si(100)衬底上预沉积AlN作为ZnO薄膜生长的缓冲层,获得了择优取向的ZnO薄膜.我们还讨论了ZnO薄膜在AlN/Si衬底上的取向生长机理.     

Comparative study of the molecular aggregation state of alkyl organic monolayers prepared on Si and hydrogen-terminated Si substrates

A comparative study of the molecular aggregation states of n-octadecyltrichlorosilane (OTS) and octadecene monolayers was carried out based on water contact angle, x-ray reflectivity (XR), grazing incidence x-ray diffraction (GIXD), and Fourier transform infrared spectroscopy (FT-IR) measurements. Water contact angle, XR, and FT-IR measurements revealed that the packing density and orientational order of the OTS were higher than those of octadecene. The OTS monolayer was in a hexagonal crystalline state with (10) spacing of 0.417?nm, whereas the octadecene monolayer was in an amorphous state. The growth mechanisms of the OTS and octadecene monolayers are also proposed. The alkyl molecular aggregation states strongly depended on the chemical bonding state at the interface between the alkyl organic molecule and the substrate surface.     

The influence of Ni catalyst on the growth of carbon nanotubes on Si substrates

This article treats the influence of the treatment of a Ni catalyst upon the growth of carbon nanotubes in alcohol catalytic chemical vapour deposition (AC CVD) equipment. Prior to the growth of diamond, a thin film of Ni was deposited on a silicon substrate by magnetron sputtering. We observed that a combination of annealing of the Ni catalyst in vacuum and NH₃ had a positive effect upon the growth of carbon nanotubes (CNTs). The prepared CNTs were analysed by scanning electron microscopy and Raman spectroscopy.     

Growth of magnetic tunnel junctions on Si(001) substrates

We present in this work the growth of magnetic tunnel junctions on Si(001) substrates using a template layer technique and the implementation of the layer-by-layer method to form the oxide barrier layer. By using a Co₂Si template layer formed by deposition of Co on Si at a temperature of ∼ 300 °C, we show that it is possible to considerably reduce the reaction between transition metals with Si substrate. We have also investigated the growth of alumina (Al₂O₃) barrier layer by an alternative layer-by-layer deposition method, which consists of successive cycles of molecular-beam deposition of an Al monolayer and oxidation under an O₂ flux at room temperature. Numerous Co(Fe)/AlO_x/NiFe tunnel junctions have been fabricated on Si(001) substrates. The oxidation kinetics, the surface morphology as well as the interface roughness and abruptness are studied by means of Auger profilometry, transmission electron microscopy and atomic force microscopy. We show that it is possible to realize a uniform and homogeneous nanometer-thick AlO_x layer with smooth and sharp interfaces. Current-voltage and Kerr effect measurements are also used to investigate the electric and magnetic properties of these junctions.     

Characterization of sputter deposited Au/Ni/Al multilayers on Si substrates

Multilayered Au/Ni/Al thin film metallization deposited by DC sputtering on n⁺Si substrates has been investigated. AES depth profiling was performed to reveal the concentration depth profiles of the Au/Ni/Al multilayers before and after annealing at different temperatures in the range 623-723 K. It was found that Ni aluminide layers begin to form during heat treatments at temperatures above 623 K. In addition to this process, Ni was found to diffuse significantly through the Au layer and segregates at the surface, proportionally to the increased annealing temperature. Consequently, the Ni oxidation process was found to take place thus causing the degradation of electrical contact. On the other hand Ni diffuses faster as well toward the Si/Al interface. No contamination traces at interfaces were observed. Electrical measurements of the metallized diode forward characteristics showed minor influence of the metallization heat treatment on the series resistance. Degradations were observed only in the reverse characteristics if the annealing was performed above 723 K.     

利用电化学技术制备白钨矿薄膜的生长动力学研究

采用恒电流电化学技术直接在金属钼(Mo)或钨(W)片上制备了白钨矿钼酸盐、钨酸盐AMO4(A=Ba、Sr、BaxSr1-x、BaxSryCa1-x-y;M=W、Mo)晶态薄膜,制备时间分别为从薄膜开始生长到薄膜生长结束的不同时间间隔.利用场发射扫描电镜(FESEM)和电子能谱仪(EDX)等测试手段,分别对这些薄膜的生长特性进行了测试,并对测试结果进行了对比分析.结果表明,利用电化学技术制备白钨矿薄膜时,金属基片在不断的溶解;由于负离子配位多面体的沉积、构架和阳离子的不断填充,完成晶核的形成和晶粒的长大;随着时间的增加,光滑饱满的晶粒布满整个基片表面从而完成了薄膜的成膜过程;由于阳离子Ba2+、Sr2+、Ca2+填充速率依次降低,使得在沉积二元和三元薄膜时出现富钡现象.     

锶铁氧体包覆碳纳米管吸波材料的制备及表征

采用溶胶-凝胶法制备锶铁氧体包覆碳纳米管(CNTs)的吸波材料,并考察了碳纳米管含量对包覆后样品磁性能及吸波性能的影响.经TEM、XRD验证锶铁氧体成功地包覆在碳纳米管表面;ALVSM图中可以看出6%CNTs-SrFe11.5O19的磁性能最佳,矫顽力(Hc)为5916.13Oe.而经网络分析仪测定,5% CNTs-S...     

Growth of aligned carbon nanotubes on ALD-Al2O3 coated silicon and quartz substrates

The smooth surface of the amorphous Al₂O₃ film on either silicon or quartz, coated by atomic layer deposition (ALD), was changed to rough surface by annealing in either air or hydrogen at high temperature (745°C) due to the formation of nanosized pinholes and micrometre pimples during the crystallisation of the amorphous Al₂O₃. The rough surface makes the growth of long carbon nanotubes (CNTs) by chemical vapour deposition impossible. Nevertheless, we were able to develop new catalyst recipes for successful growth of vertically aligned CNTs on ALD-Al₂O₃ coated silicon and quartz substrates. The lengths of the CNTs reached 90?µm on silicon substrates and 180?µm on quartz substrates. Furthermore, it is observed that the adhesion of CNTs on silicon substrates is much stronger than that on quartz substrates.     

Employing Al buffer layer with Al droplets-distributed surface to obtain high-quality and stress-free GaN epitaxial films on Si substrates

Al buffer layers with Al droplets-distributed surface have been employed to grow high-quality and stress-free GaN epitaxial films on Si substrates. The Al droplets are proved to efficiently improve the quality of as-grown GaN. On the one hand, they can act as nucleation seeds to facilitate the epitaxial growth, improving the crystalline quality and surface morphology of as-grown GaN epitaxial films. On the other hand, they also can compensate the huge compressive stress produced by Al buffer layer during the cooling process, achieving stress-free film. The density and volume of Al droplets greatly impact the properties of as-grown GaN epitaxial films. The GaN epitaxial film grown on the Al buffer layer with many small Al droplets uniformly distributed on it shows the best crystalline quality with the full-width at half maximum (FWHM) of GaN(0002) and GaN(10–12) as 0.5° and 0.7°, respectively, and flat surface with the smallest surface root-mean-square roughness of 3.8 nm. In addition, it also exhibits relatively better photoelectric properties with an FWHM of near band gap emission peak of 18 nm, carrier concentration of 2.0 × 10¹⁷ cm^?3, and mobility of 137.1 cm²/Vs. This work has revealed the advantages of Al buffer layer and the important effects of buffer layer surface on achieving high-quality GaN by PLD, which is of significance for various applications of GaN-based devices.     

Nanocrystalline Si formation in the a-Si/Al system on polyimide and silicon dioxide substrates

Polysilicon (poly-Si) films fabricated on flexible substrates are of considerable interest because of their potential application in flexible displays. In this study, an 800 nm layer of amorphous silicon (a-Si), followed by a 20 nm layer of aluminum (Al), were deposited on polyimide/silicon and silicon dioxide/silicon (SiO₂/Si) substrates. Samples on polyimide were rapid thermal annealed at 900 °C for 20 s, while those on SiO₂/Si were vacuum annealed at temperatures between 200 and 600 °C for 1 h. Film properties were analyzed using Rutherford backscattering spectrometry, cross-section transmission electron microscopy, and X-ray diffraction. Silicon films containing nanocrystallites and pores were obtained, with a pore formation activation energy (E_A) of 0.59 eV. A short-range self-diffusion model is proposed for the formation of Si crystallites in cases where the solid-solubility limit for Si dissolution into Al has not been reached.     

CNTs含量对CNTs/Al微观组织及力学性能的影响

为增加碳纳米管(CNTs)在铝基体中的分散性,利用机械球磨-真空热压烧结工艺制备碳纳米管/铝(CNTs/Al)复合材料,采用扫描电子显微镜(SEM)、电子万能试验机和万能摩擦磨损实验机,研究了CNTs质量分数对CNTs/Al复合材料微观组织、力学性能及摩擦磨损性能的影响.结果表明:CNTs经超声波预先分散后分散性增加;当CNTs质量分数为2.0%时,复合材料中CNTs与Al粉之间表现出较好的相容性;随着CNTs含量进一步增加,CNTs团聚现象严重;热压烧结温度600℃时,随着CNTs添加量的增加,铝基复合材料的屈服强度和抗拉强度呈现出明显的先增大后降低的趋势,同时,CNTs/Al复合材料的摩擦因数和磨损率随CNTs含量的增大先减小后增加;CNTs质量分数为2.0%时,复合材料的屈服强度最大值为116 MPa,抗拉强度最大值为245 MPa,与纯Al基体相比,分别提高了78%和1.9倍.2.0%CNTs/Al复合材料可获得较好的摩擦磨损性能,其摩擦系数和磨损率呈现平缓趋势,复合材料的磨痕最浅.     

浮动催化CVD法CNTs膜及CNTs膜/环氧复合材料拉伸特性

针对浮动催化化学气相沉积(CVD)法制备的碳纳米管(CNTs)膜,首先采用红外光谱表征分析了包覆在CNTs表面的无定形物质的组成,然后分别采用热处理和酸洗处理方法,考察了CNTs膜中无定形物和残留Fe催化剂对CNTs膜拉伸取向行为的影响。结果表明:采用CVD法制备的CNTs膜中CNTs表面无定形物为含氧或烷烃、烯烃类低聚物,可通过350℃有氧热处理基本去除。该CNTs膜的牵伸取向重排行为受组成影响显著,CNTs表面的低聚物可增强CNTs的管间黏结作用,Fe催化剂颗粒成为CNTs网络结构的交联结点,两者均有利于提高CNTs的取向程度和聚并成束的尺寸,进而提高CNTs膜的拉伸稳定性和断裂韧性。牵伸取向后CNTs膜与环氧树脂溶液的浸润性提高,其CNTs膜/环氧复合材料的拉伸强度和模量达到1228MPa和94.5GPa,相比初始无规CNTs膜/环氧复合材料的分别提高了337%和729%。      

石墨表面镀Si对石墨/Al复合材料热物理性能的影响

研究了石墨粒径及表面镀Si处理对石墨/Al复合材料热物理性能的影响。结果表明:在盐浴过程中石墨表面形成了SiC层,这不仅增强了石墨-Si/Al复合材料的界面结合力,而且抑制了Al4C3相的产生。随着石墨鳞片体积分数从50%增加到70%,复合材料X-Y方向的热导率从492 W/(m·K)增加到654 W/(m·K),而且体积分数为50%的镀Si石墨/Al复合材料抗弯强度达到了81 MPa,相比未镀覆的提高了53%,是理想的定向导热电子封装材料。随着石墨粒径从500μm减小到150μm,石墨-Si/Al复合材料X-Y面方向的热导率由654 W/(m·K)降低到445 W/(m·K),但Z方向的热导率和复合材料抗弯强度变化不明显。