真空还原制备的VO_2热致相变薄膜光学性质研究

本文对不同衬底制备的VO2 薄膜进行了表面形貌测试 ,对其红外透射光谱和Raman光谱进行了研究 ,并进行 370nm -90 0nm波段的光透射测试以及 90 0nm波长的热滞回线特性测试 ,表明所制备VO2 薄膜具有优良的热致相变光学特性 ,薄膜为纳米结构 ,并且结晶状态不同的薄膜其Raman谱位置有明显改变 ,室温时的红外光谱表现出较好的红外振动特性。讨论了薄膜结晶状态对Raman位移的影响以及VO2 薄膜的红外光谱     

利用制备参数的改变调整VO2薄膜的电阻温度系数

利用真空还原方法,通过合理控制时间和真空退火温度,制备出具有优良热致相变特性的VO2薄膜,并对不同真空还原时间、真空退火温度和衬底条件下制备的VO2薄膜结构和半导体相的电阻温度系数进行了研究。结果表明,不同制备参数对所得薄膜的结构的结构和价态有显著影响,从而对VO2的电阻温度系数产生较大调整。     

γ射线辐照引起的VO2薄膜结构和相变光学特性变化

利用剂量为35kGy-3500kGy的Co^60γ源辐照VO2薄膜,对辐照后薄膜进行XRD和激光Raman光谱测试。结果表明,较低剂量γ辐照后VO2薄膜聘较显著的晶态变差现象,而高剂量γ辐照则在薄膜中产生退火效应,使薄膜晶态较好。由此引起VO2薄膜的热致相变的光学特性、特征Raman峰的强度和位置随γ辐照剂量的增加而出现变化。根据γ射线与物质相互作用原理对γ辐照引起的以上效应进行了讨论。     

制备过程中对VO2薄膜热致相变光电性能的控制

本文利用真空还原Ｖ２Ｏ５的方法制备出优质对ＶＯ２薄膜;研究了不同真空还原时间ＶＯ２薄膜热致相变过程中光电性能的影响;利用ＸＰＳ、ＸＲＤ对薄膜的化学状态和结晶状态进行了研究。制备的薄膜高／低 电阻变化最大达到三个数量级,９００ｎｍ处的光学透过率在相变前后改变了４０％左右,热致相变性能优良。讨论了不同的真空还原时间下ＶＯ２薄膜热滞回线的宽度、相变温度点以及高低温光透射性能。最后给出了最佳真空还原时间。     

VO2/TiO2复合薄膜的结构和红外光学性质研究

采用溶胶凝胶法在白云母沿（001）方向的解理表面制备VO2/TiO2热致相变复合薄膜。利用X射线衍射仪（XRD）,X射线光电子能谱仪（XPS）,原子力显微镜（AFM）等手段分析了薄膜的微观结构和表面形貌,通过原位傅里叶变换红外光谱（in-situ FTIR）分析复合薄膜在不同温度下的红外透过率,研究其热致相变特性。结果表明,复合薄膜在云母解理面表面呈VO2（011）/TiO2（101）取向生长,表面致密平整。复合薄膜在金属-半导体相变前后表现出优异的光学开关效应,相变过程中的红外光（波长为4 m）透过率变化（Tr）为75.5%;相变过程陡然,透过率变化率（-dTr/dT）达15.7%/℃,滞回温宽减小到8 ℃。     

二氧化钒薄膜制备及其热致变发射率特性研究

通过溶胶-凝胶和真空热处理工艺在石英基底上制备了二氧化钒薄膜,对制备出的薄膜进行了X射线衍射及X射线光电子能谱分析,结果表明所制备出的薄膜价态单一,纯度较高,薄膜为多晶态,晶粒尺寸约为27 nm.利用红外热像仪拍摄了薄膜在不同温度下的红外热图并计算了发射率,结果表明二氧化钒薄膜7.5～14 μm波段发射率在相变时发生突变,突变量可达0.6,具有优异的热致变发射率性能,在红外自适应伪装等领域应用前景广阔.     

云母表面不同厚度VO2薄膜的红外光学特性

以天然白云母的解理面为基底,采用无机溶胶-凝胶法在其表面制备不同厚度的VO2薄膜,并研究了厚度对VO2薄膜的微观结构和红外光学特性的影响.利用SEM、XRD等手段分析了薄膜的表面形貌和晶体结构,利用原位FTlR分析了VO2薄膜半导体-金属相变特性.结果表明,云母表面VO2薄膜室温下具有(011)择优生长取向,随着厚度增...     

铁电薄膜光学性质的研究

本文对铁电薄膜的光学性质的研究进展进行了详细的总结。与人们对铁电薄膜的电学性质的研究相比,人们对光学性质的研究较少。由于铁电薄及其无定形薄膜都具有许多优良的电学性质,因此对它们的光学性质研究也很有必要。光学手段具有非破坏性,通过这种手段可以获得薄膜的光学常数折射率和消光系数,从而进一步获得它们的禁带宽度。中红外透射可以表征铁电薄膜内部结构的相变过程。通过远红外手段,可以研究薄膜的内部微观机制,如晶格振动等。最后,阐述了铁电薄膜及其无定形薄膜光学性质研究的发展方向。     

制备过程中对VO_2薄膜热致相变光电性能的控制

本文利用真空还原V2 O5的方法制备出优质对VO2 薄膜 ;研究了不同真空还原时间VO2 薄膜热致相变过程中光电性能的影响 ;利用XPS、XRD对薄膜的化学状态和结晶状态进行了研究。制备的薄膜高 /低温电阻变化最大达到三个数量级 ,90 0nm处的光学透过率在相变前后改变了 40 %左右 ,热致相变性能优良。讨论了不同的真空还原时间下VO2 薄膜热滞回线的宽度、相变温度点以及高低温光透射性能。最后给出了最佳真空还原时间。     

Structural properties of V2O5 thin films prepared by vacuum evaporation

Vanadium pentoxide (V₂O₅) films were deposited on glass substrates by vacuum evaporation technique at various deposition temperatures (T_s) viz., 300, 473, 573, 623 and 673 K. The structural and microstructural properties of the films are analyzed using XRD and Raman scattering measurements. X-ray characterization revealed the films deposited at T_s473 K are amorphous and the film deposited at T_s573 K are polycrystalline with orthorhombic symmetry. The corrected lattice constant values are determined from Nelson-Riely plots. The lattice constants “a” and “c” are found to decrease with increase in the deposition temperature, which may be attributed to the increase in non-stoichiometry. Change in the preferred orientation is observed for films deposited at substrate temperatures 623 K which is likely to be governed by the recrystallization process. Various structural parameters such as lattice constants, grain size, and microstrain and dislocation density are determined and the influence of deposition temperature on the structural parameters are discussed.     

Optical properties of ZnO thin films prepared by sol-gel process

The present study focused on ZnO thin films fabricated by sol-gel process and spin coated onto Si (1 0 0) and quartz substrates. ZnO thin films have a hexagonal würtzite structure with a grain diameter about 50 nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, two transitions were observed by PL. One near to the prohibited energy band in ultraviolet (UV) region and the other centered at 640 nm, characteristic of the electronic defects in the band-gap. The spectrum at 6 K is dominated by donor-bound exciton lines and donor-acceptor pair transition. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of high-quality thin films.     

用热蒸发法制备的Cu2ZnSnS4 薄膜的光电性能

在室温下用真空热蒸发法在玻璃基片上制备Sn/Cu/ZnS 前躯体膜层,然后对其在550C 下在硫气氛中硫化3小时以制得Cu₂ZnSnS₄ (CZTS) 多晶薄膜。对该薄膜进行X射线衍射（XRD）、能量色散X射线光谱（EDX）、紫外可见近红外分光光度计、霍尔测量系统和3D光学显微镜等分析测试。实验结果表明,当[Cu]/([Zn] [Sn]) =0.83和[Zn]/[Sn] =1.15时,该CZTS薄膜在光子能量范围在1.5 - 3.5 eV 时其吸收系数大于4.010₄cm_-1 ,直接带隙为1.47 eV。其载流子浓度、电阻率和迁移率分别为7.9710₁₆ cm_-3, 6.06 Ω.cm, 12.9 cm₂/(V.s), 导电类型为p型。因此,所制备出的CZTS 薄膜适合作为太阳电池的吸收层材料。     

Post deposition UV-induced O2 annealing of HfO2 thin films

UV-assisted annealing processes for thin oxide films is an alternative to conventional thermal annealing and has shown many advantages such as low annealing temperature, reducing annealing time and easy to control. We report in this work the deposition of ultra-thin HfO₂ films on silicon substrate by two CVD techniques, namely thermal CVD and photo-induced CVD using 222 nm excimer lamps at 400 °C. As-deposited films of around 10 nm in thickness with refractive indices from 1.72 to 1.80 were grown. The deposition rate measured by ellipsometry was found to be about 2 nm/min by UV-CVD, while the deposition rate by thermal CVD is 20% less than that by UV-CVD. XRD showed that the as-deposited HfO₂ films were amorphous. This work focuses on the effect of post deposition UV annealing in oxygen on the structural, optical and electrical properties of the HfO₂ films at low temperature (400 °C). Investigation of the interfacial layer by FTIR revealed that thickness of the interfacial SiO₂ layer slightly increases with the UV-annealing time and UV annealing can convert sub-oxides at the interface into stoichiometric SiO₂, leading to improved interfacial qualities. The permittivity ranges in 8–16, are lower than theoretical values. However, the post deposition UV O₂ annealing results in an improvement in effective breakdown field and calculated permittivity, and a reduction in leakage current density for the HfO₂ films.     

Electrical properties of vacuum annealed La2O3 thin films grown by E-beam evaporation

In this article, the conduction mechanisms of metal-oxide-semiconductor with vacuum annealed Lanthana (La₂O₃) oxide film are investigated. Lanthana films with thicknesses of 3.5, 4.7, and 11 nm were deposited by E-beam evaporation on n-Si (100), and annealed at various temperatures (300-500 °C) in ultra-high vacuum (10⁻¹⁰-10⁻⁹ Torr) for 90 min. From the measurement of spectroscopic ellipsometry, it is found that film thickness is increased with annealing temperature, which would be cause of flat-band voltage shift (ΔV_FB) due to the growth of interfacial layer. From the capacitance measurement, it is found that ΔV_FB of the film is reduced by post-deposition anneal (PDA) compared to that of as-deposited film, but increase again at high temperature annealing, especially in the case of thin film (3.5 nm). From the applied voltage and temperature dependence of the leakage current of the film, with different gate electrode materials (Ag, Al, and Pt), it is shown that the leakage currents are associated with ohmic and Poole-Frenkel (P-F) conductions when flat-band voltage (V_FB) is less than zero, and ohmic and Space-Charge-Limited Current (SCLC) conductions when V_FB is greater than zero. The dielectric constants obtained from P-F conduction for Al gate electrode case is found to be 11.6, which is consistent with the C-V result 11.9. Barrier height of trap potential well is found to be 0.24 eV from P-F conduction. Based on SCLC theory, leakage currents of 3.5 and 11 nm films with different PDA temperatures are explained in terms of oxide trap density.     

Photo-CVD process for ultra thin SiO2 films

In this paper we first report the use of very low deposition rate photo-induced chemical vapor deposition process, (below 0.05 nm/min). This photo-CVD process is adequate to grow very thin and ultra thin layers of SiO₂. Details on the design of the reaction chamber, reactive gases and process parameters to obtain the desired deposition regime are presented. Dependence of deposition rate on pressure in the chamber and gas flow ratio is discussed. Deposited layers were characterized using I–V and C–V techniques.     

Structural properties of fluorinated SiO2 thin films

Fluorinated SiO₂ (SiOF) films, prepared by plasma enhanced chemical vapour deposition from SiH₄, N₂O and CF₄ precursors, have been analysed by infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to extract chemical and structural information. Notwithstanding XPS reveals that fluorine concentrations are quite low (less than 4 at.%), the analysis of the Si–O–Si vibration modes in the IR spectra indicates that CF₄ addition involves a deeper modification of the film structure, than the simple formation of Si–F bonds. In particular, by increasing the F concentration in the oxides, the stretching frequency of the Si–O–Si bonds increases, while the bending frequency decreases. On the basis of the central force model, both observations are consistent with the occurrence of a Si–O–Si bond angle relaxation phenomenon, the importance of which increases with the fluorine concentration in the films.     

Electrical properties of thin Ta2O5 films obtained by thermal oxidation of Ta on Si

Tantalum pentoxide films (13–260 nm) on p-type Si have been prepared by thermal oxidation at 673–873 K of rf sputtered Ta films and have been studied using Al–Ta₂O₅–Si capacitors. Both dielectric constant and refractive index were found to depend on the thickness of the Ta₂O₅ layers. Layers with a dielectric constant of 25–32 were obtained. A decreasing trend in the leakage current was found upon increasing oxidation temperature from 673 to 873 K. Leakage current density of (10⁻⁸ to 3×10⁻⁷) A cm⁻² at 1 MV cm⁻¹ effective field was achieved.     

Leakage current reduction in chemical-vapor-depositedTa2O5 films by rapid thermal annealing in N2O

This study aims to improve the electrical characteristics and reliability of low-pressure chemical vapor deposited (LPCVD) Ta₂ O₅, films by developing a new post-deposition single-step annealing technique. Experimental results indicate that excited oxygen atoms generated by N₂O decomposition can effectively repair the oxygen vacancies in the as-deposited CVD Ta₂ O₅ film, thereby resulting in a remarkable reduction of the film's leakage current. Two other post-deposition annealing conditions are compared: rapid thermal O₂ annealing and furnace dry-O₂ annealing. The comparison reveals that RTN₂O annealing has the lowest leakage current, superior thermal stability of electrical characteristics and the best time-dependent dielectric breakdown (TDDB) reliability