V2O5熔化成膜法制备VO2薄膜

发展了一种新的VO2薄膜制备方法—V2O5熔化成膜法，其基本步骤为：基片预处理—涂粉—熔化成膜—真空退火—VO2薄膜。采用XRD和XPS等手段，对所得薄膜的物相组成与价态进行了分析，同时对薄膜进行了电阻随温度变化的测试。结果表明：通过该方法获得的薄膜，其主要成分是VO2，电阻突变达到4个数量级，相变温度为67．5℃。     

退火升温速率对VO2薄膜相变性能的影响

采用溶胶-凝胶法在云母(001)衬底表面制备氧化钒薄膜,然后通过高温退火获得VO2多晶膜.利用SEM、FTIR等手段,分析不同退火升温速率条件下所制备薄膜的微观形貌、光学性能和热致相变特性.结果表明:在退火升温速率为8 ℃/min时,所制备的VO2薄膜具有最优异的热致相变特性,相变温度为65 ℃,滞后温宽为10 ℃.     

不同衬底上VO2薄膜的微观结构和光学性能研究

以云母(001)晶面和玻璃片为衬底,采用溶胶-凝胶法在其表面制VO2薄膜.利用XRD,AFM,FTIR等手段分析了不同衬底上薄膜的微观结构和光学性能.结果表明,云母表面VO22薄膜常温下呈单一的(011)取向,而玻璃表面VO2薄膜呈现(100)和(011)2种取向,单一(011)晶体取向的OV2薄膜表现出更好的光学开关性能.还分析了VO2薄膜的晶体取向对其光学性能的影响.     

VO2(A)型薄膜表面形貌与相变性能的相关性

以高纯五氧化二钒（V2O5）粉末(纯度≥99.99%)为原料,采用真空蒸发——还原工艺制备出VO2(A)型薄膜(A表示发生热致相变的薄膜)。讨论退火温度对VO2(A)型薄膜表面形貌的影响,并进一步研究表面形貌与薄膜光电性质的相关性。结果显示：当退火温度从500 ℃升高到540 ℃,VO2(A)型薄膜中层状特征减弱并消失,山峰状颗粒出现并增大,当退火温度继续升高,VO2(A)型薄膜中山峰状颗粒是先减小再增大,但是其尺寸趋于一致,约为50 nm;随着 VO2(A)型薄膜形貌的改变,相变温度点、数量级、热滞回线宽度等相变性能参数也会改变;VO2(A)型薄膜相变温度点降低,其在所测波段的透过率会降低,但只有在中红外波段,薄膜在相变前后透过率的改变量与电阻变化的数量级有关。     

共溅射氧化法制备掺钼VO_2及其相变特性

采用共溅射氧化法,在普通玻璃衬底上室温直流溅射沉积钒钼金属薄膜,再在大气环境下经热氧化处理获得掺钼VO2薄膜。通过XRD、SEM、热致相变电学特性等分析,研究制备工艺及掺杂改性对掺钼VO2薄膜的微结构、形貌、热滞回线和相变温度的影响。实验与分析结果表明,与相同厚度的纯VO2薄膜相比,钼掺杂显著改变了VO2薄膜的表面形貌特征,掺钼VO2薄膜呈多晶态且沿VO2(002)择优取向生长,结晶性和取向性明显提高,薄膜的相变温度降低至38℃,热滞回线宽度收窄约至8℃。低温共溅射氧化法制备的掺钼VO2薄膜的热阻效应明显,薄膜的金属-半导体相变特性良好。     

磁控溅射制备SiC薄膜及其高温抗氧化性

用射频磁控溅射法在单晶Si(100)基片上制备了SiC薄膜.将制备的薄膜分别在800、900和1000℃空气气氛中退火120 min.用X射线衍射仪和傅里叶变换红外光谱仪测试了薄膜的结构,用X射线光电子能谱仪测试了薄膜元素的组成和状态,用场发射扫描电子显微镜测试了薄膜表面的形貌.结果表明:经800℃空气退火后,薄膜表面生成了一层SiO2保护层,阻止了内部SiC薄膜的继续氧化,因此SiC薄膜在800℃具有较好的高温抗氧化性;随着退火温度的升高,SiC薄膜被进一步氧化,经1000℃空气退火后,薄膜已大部分转变为SiO2.     

The oxidation and resistance of tantalum-nitride thin films

The oxidation of reactively-sputtered, tantalum—nitride thin films has been studied between 473 and 773 K in air. Films with thicknesses that correspond to sheet resistances of 43, 75, and 150 / were evaluated in this study. X-ray diffraction revealed that the films and the oxidation products were amorphous. The oxidation products were characterized with AES and XPS. The oxidation process was monitored by measuring the change in sheet resistance with time. Sheet resistance measurements were performed with a four-point probe. The oxidation kinetics can be represented by the equation R/R ⁿ =kt. R/R is sheet resistance change in %, t is time, and k is the rate constant. The oxidation kinetics, for the thickest film, were parabolic above about 598 K, and approximately quartic below this temperature. The 75 / films deviated from parabolic kinetics below 603 K, and approached approximate cubic kinetics at 498 K. However, the data were forced to fit parabolic kinetics with good correlation. For the thinnest film, no deviation from parabolic kinetics was observed. The rate constants obeyed the Arrhenius relation. An activation energy of 147 kJ/mole (1.52eV) was calculated, for the thickest film, during parabolic kinetics. This value is approximately equal to the activation energy obtained during quartic kinetics. A model that explains the deviation from parabolic to quartic oxidation kinetics at lower temperatures is presented. In this model, the change in resistance as a function of time was due to simultaneous change in film resistivity, as a result of oxygen dissolution into the film, and oxide-scale growth. The temperature at which this deviation occurs should be a function of film thickness.     

超细VO_2粉末的制备及其可逆相变的原位表征

采用氧化还原法,在N2保护气氛中,通过程序控温,用草酸还原V2O5制备VO2超细粉末,重点考察原料配比对还原产物物相纯度的影响。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)及X射线能量色散谱仪(EDS)分析产物的相组成和微观形貌,通过同步热分析(STA)和原位XRD研究VO2粉体的热致可逆相变特性。结果表明:V2O5和草酸以1:1.2~1.4的摩尔比混合,可制得较纯的单斜晶系VO2超细粉末,颗粒呈近球形,平均晶粒度约为50 nm。低温为M相(单斜晶系,P21/c),升温时可转化为R相(正方晶系,P42/mnm),升温相变点为68.1℃,降温相变点为60.2℃,滞后7.9℃。具有良好的热致可逆循环相变稳定性,M/R相多次循环转换的DSC热滞回线呈现很好的重现性。     

Growth of HT-LiCoO2 thin films on Pt-metalized silicon substrates

Layered LiCoO2 (HT-LiCoO2) films were grown on Pt-metalized silicon (PMS) substrates and polished bulk nickel (PBN) substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [001] preferential orientated triangular shaped grains with the average grain size less than 100nm. Electrochemical measurements show that the highly [001] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45 μA·h·cm-2μm-1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5C.     

Infrared transition properties of vanadium dioxide thin films across semiconductor-metal transition

Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray dif- fraction (XRD), atom force microscopy (AFM), and Fourier transform infrared spectrum (FTIR) were employed to measure the crystalline structure, surface morphology, and infrared opdcal transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO<,2>, with preferred orientation of (011). The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80℃. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same tempera- ture across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect.     

二氧化钒纳米点阵的制备及其红外光学特性研究

为了得到相变温度低且变色性能优越的光学材料,使其能够广泛应用于智能窗领域,对周期结构VO2纳米点阵的相变和光学特性展开了研究。用修正的Sellmeier色散模型结合二维点阵周期结构的等效折射率计算了VO2纳米点阵在不同占空比下的反射率和透射率。利用多孔氧化铝模板掩膜溅射法,先在玻璃上制备钒金属纳米点阵,再经热氧化工艺制备出VO2纳米点阵,测试其表面形貌、组分结构、红外反射和透射谱线。结果表明,占空比为0.83的纳米点阵其相变温度有效降低至43℃,在1700 nm处透射率改变量达到29%,表现出良好的变色特性,且透射率整体高于VO2薄膜。说明通过制备较佳占空比的纳米点阵可以有效降低材料的相变温度,提升材料的热致变色性能。     

Phase change induced degradation of amorphous vanadium oxide cathode thin film during charge-discharge

Amorphous vanadium oxide (V₂O₅) is a very good candidate as material for cathode thin film since it has a relatively high capacity. In addition, the room temperature deposition process is valuable in V₂O₅ thin film fabrication. Due to these advantages, much effort to grow amorphous V₂O₅ thin film has been made. In this research, we successfully grew amorphous V₂O₅ thin film using room temperature sputtering. Based on a Li/LiPON/V₂O₅ full cell structure, charge-discharge performances were measured according to cycling number. Even though the full cell structure showed an average capacity of 15 μAh/cm² over more than 500 cycles, a capacity fade was shown after a few cycles. Many reports revealed that the phase change of V₂O₅ from amorphous to crystalline made this kind of capacity fade. In order to investigate this phenomenon, high-resolution transmission electron microscopy (HRTEM) was employed. The as-deposited V₂O₅ thin film consisted of a homogeneous amorphous without any grain-boundary and/or polycrystalline island. However, the microcrystalline V₂O₅ phase was randomly distributed in the amorphous V₂O₅ thin film matrix after 450 cycles by cross sectional TEM (XTEM). That is, some amorphous phase in the V₂O₅ thin film matrix changed to the crystalline phase. This crystalline phase strongly prevented the extraction of Li ions during the charge process, which induced the irreversible diffusion of Li ions from cathode to anode. From this result, a high efficiency thin film battery based on amorphous V₂O₅ can be fabricated by preventing amorphous-crystal phase transformation during cycling. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

Formation of crystalline Al-Ti-O thin films and their properties

The article reports on the effect of addition of Ti into Al₂O₃ films with Ti on their structure, mechanical properties and oxidation resistance. The main aim of the investigation was to prepare crystalline Al-Ti-O films at substrate temperatures T_s ≤ 500 °C. The films with three different compositions (41, 43 and 67 mol% Al₂O₃) were reactively sputtered from a composed Al/Ti target and their properties were characterized using X-ray diffraction (XRD), X-ray fluorescent spectroscopy (XRF), microhardness testing, and thermogravimetric analysis (TGA). It was found that (1) the addition of Ti stimulates crystallization of Al-Ti-O films at lower substrate temperatures, (2) Al-Ti-O films with a nanocrystalline cubic γ-Al₂O₃ structure, hardness of 25 GPa and zero oxidation in a flowing air up to ∼ 1050 °C can be prepared already at low substrate temperature of 200 °C, and (3) the crystallinity of Al-Ti-O films produced at a given temperature improves with the increasing amount of Ti. The last finding is in a good agreement with the binary phase diagram of the TiO₂-Al₂O₃ system.