Optical properties of Langmuir-Blodgett polydiacetylene thin films

The colour phase transition of Langmuir-Blodgett polydiacetylene (LB PDA) films is investigated as a function of annealing temperature. A new reversible colour change is observed for a short annealing time. Such a reversible property has not previously been reported in LB PDA films. The X-ray diffraction patterns show that the reversible property is closely related to the layer structure of the LB films. Furthermore, the ratio of the line intensities of the Raman peaks due to C≡C and C=C stretch modes changes with the annealing temperature. The colour phase transition of the LB PDA films is correlated with this ratio. Such phase transitions have also been observed in laser-annealed points of LB PDA films. From these results, a new optical device based on LB PDA films is proposed. Furthermore, the electrical properties of ion-irradiated LB PDA films are briefly reported.     

Annealing and recrystallization of amorphous ZnO thin films deposited under cryogenic conditions by pulsed laser deposition

This article deals with the annealing of amorphous ZnO thin films prepared by pulsed laser deposition (PLD) under cryogenic conditions. The substrate holder was cooled by liquid nitrogen. X-ray diffraction analysis evidenced that as-deposited films had amorphous structures: analysis by scanning electron microscopy (SEM) revealed their fine grained surface and inner structure. Annealing at temperatures in the range of 200-800 °C resulted in a transition in the thin film crystal structure from amorphous to polycrystalline. Various properties of the ZnO films were found depending on the recrystallization temperature. In depth investigations employing SEM, X-ray diffraction, atomic force microscopy and secondary ion mass spectroscopy provided comparisons of the recrystallizations of undoped ZnO thin films during the phase transition processes from amorphous to hexagonal wurtzite structures.     

Microstructural changes of Pt/Ti bilayer during annealing in different atmospheres — an XRD study

The high temperature behaviour of Pt/Ti base electrode bilayers is crucial for the deposition of ferro-electric thin films on top of such metal films. Therefore the microstructural development during annealing has to be considered. These parameters are studied by X-ray diffraction (XRD). Comparing the microstructure before and after thermal treatment significant differences could be found. Pt₃Ti compound formation was observed in all coatings. The stress in the Pt phase changes from compressive to tensile during annealing. In contradiction the stress in the Pt₃Ti phase is compressive after thermal treatment. From measurements of the total reflected signal an amount of TiO₂ on the surface of the oxygen treated film could be found. A model based on diffusion of Ti along grain boundaries and considering thermodynamic aspects of stress development is predicted to describe the microstructural changes during annealing.     

Patterning polymer metal precursors for high temperature superconducting Bi-Sr-Ca-Cu-O-films

Bi-Sr-Ca-Cu-O HTSC thin films were prepared from polymer metal precursors in a special annealing procedure. The precursor films can be patterned before the annealing process in which the superconducting phase is generated. We have investigated the patterning of precursor films by UV radiation, and the thermal degradation process by thermogravimetry and mass spectroscopy. The HTSC films were characterized by X-ray diffraction and electrical resistivity measurements.     

Effect of heat treatment on characteristics of nanocrystalline ZnO films by electron beam evaporation

Zinc oxide thin films have been grown on glass substrate at room temperature by electron beam evaporation and then were annealed in annealing pressure 600 mbar at different temperatures ranging from 250 to 550 °C for 30 min. Electrical, optical and structural properties of thin films such as electrical resistivity, optical transmittance, band gap and grain size have been obtained as a function of annealing temperature. X-ray diffraction has shown that the maximum intensity peak corresponds to the (002) predominant orientation for ZnO films annealed at various temperatures. The full width at half maximum, decreases after annealing treatment which proves the crystal quality improvement. Scanning electron microscopy images show that the grain size becomes larger by increasing annealing temperature and this result agrees with the X-ray diffraction analysis.     

Structural change of Langmuir-Blodgett film of tetra-neopentoxy phthalocyanine zinc during heat treatment

Langmuir-Blodgett (LB) films of tetra-neopentaxy phthalocyanine zinc (TNPPcZn) were prepared and annealed at a selected temperature. Their optical spectra and optical constants were measured and the structural changes of the films were studied by X-ray diffraction. The arrangement of molecules in the TNPPcZn LB film is changed from disorder to order due to increase of the dimer when the films are annealed at the temperature range of 363 to 433 K. When the annealing temperature is increased further from 433 K to the 573 K, the film undergoes a reorganization in which the orientation of phthalocyanine rings are transformed formed from perpendicular to the substrate surface into parallel to the substrate surface, because the dimers are destroyed owing to the segregation of the neopentoxy and the monomers are recovered.     

多晶硅薄膜的铝诱导晶化法制备及其晶粒的择优取向特性

采用铝诱导非晶硅薄膜晶化技术制备了多晶硅薄膜,并研究了多晶硅的成核和生长特性。非晶硅薄膜采用等离子体增强化学气相沉积法制备,其表面沉积铝薄膜后经不同温度的氮氛围退火处理。结果表明,退火后的硅薄膜层与铝层发生置换,所生长的多晶硅颗粒的平均尺寸约为150nm。X射线衍射分析结果揭示,薄膜的晶向显著依赖于退火温度,较低温度下,铝诱导晶化速率较慢,薄膜的优化晶向与非晶硅薄膜中团簇的初始原子排列趋势紧密相关。而较高温度下,铝诱导晶化促使多晶硅(111)择优成核及随后的固相生长。     

Effect of temperature on microstructure and electrical properties of TaSi2 thin films grown on Si substrates

Tantalum silicide (TaSi₂) thin films were deposited on n-type silicon single crystal substrates using a dual electron-gun system and with Ta and Si targets. The thicknesses of TaSi₂ thin films considered in this study are in the range 200-500 nm, respectively. The TaSi₂/Si samples were annealed at temperature 1173 K for 2 h in a vacuum of 10⁻⁸ mbar. The structure of the tantalum silicide thin films was investigated by X-ray diffraction (XRD). X-ray diffraction results show changes in the structure of TaSi₂ thin films from amorphous to crystalline after annealing. According to XRD analysis, a complete conversion to single-phase disilicide TaSi₂ was achieved from a sample composition of Ta:Si = 1:2. DC conductivity was measured for the TaSi₂ thin films in the temperature range 300-900 K before and after annealing. It has been observed that the DC conductivity and activation energy was affected by changing the TaSi₂ film thickness and by annealing. The experimental results indicate that, the conduction phenomena of the investigated sample proceeded via two distinct mechanisms. The first one in the low-temperature range T < 500 K can be described by thermally-assisted tunneling of the carriers in the localized states near the band edge. The value of the pre-exponential factor before and after annealing is less than 10⁴ Ω⁻¹ cm⁻¹. The other process appears in the high temperature region T > 500 K, where thermally activated conduction occurs through the extended states. Here the value of the pre-exponential factor before and after annealing is larger than 10⁴ Ω⁻¹ cm⁻¹. The conductivity is greater in the crystalline phase than in the amorphous phase. The activation energy ΔE for our films before and after annealing is increased with increasing film thickness.     

VOx/TiOx/Ti多层薄膜的制备工艺与内耗研究

用磁控反应溅射法在玻璃和镅片衬底上制备Vox/TiOx/Ti多层薄膜.用X射线衍射(XRD)、QJ31单臂电桥、薄膜内耗仪等测试了薄膜的晶体结构、电阻、内耗.分别进行了薄膜的制备工艺与内耗研究.测试分析结果表明:试样的晶体结构、电阻-温度曲线、杨氏模量的突变均表明多层薄膜在66℃左右发生相变.样品的电阻温度系数为-4.35%/℃.并且真空退火有利于二氧化钒相生成.     

Effect of annealing on the electrical and optical properties of electron beam evaporated ZnO thin films

Zinc oxide thin films have been grown on (100)-oriented silicon substrate at a temperature of 100 °C by reactive e-beam evaporation. Structural, electrical and optical characteristics have been compared before and after annealing in air by measurements of X-ray diffraction, real and imaginary parts of the dielectric coefficient, refractive index and electrical resistivity. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented with a full width at half maximum (FWMH) lower than 0.5°. The electrical resistivity increases from 10⁻² Ω cm to reach a value about 10⁹ Ω cm after annealing at 750 °C. The FWHM decreases after annealing treatment, which proves the crystal quality improvement. Ellipsometer measurements show the improvement of the refractive index and the real dielectric coefficient after annealing treatment at 750 °C of the ZnO films evaporated by electron beam. Atomic force microscopy shows that the surfaces of the electron beam evaporated ZnO are relatively smooth. Finally, a comparative study on structural and optical properties of the electron beam evaporated ZnO and the rf magnetron deposited one is discussed.     

LaNi5合金膜退火后的表面结构和氢敏特性

通过在空气中退火来改善由磁控溅射方法制备的LaNi_5合金膜的表面结构,使其具有在室温下吸放氢的能力。借助原子力显微镜、X射线衍射和X射线光电子能谱,分析了LaNi_5合金膜退火前后的形貌、结构和表层成分。结果表明:在空气中退火后,LaNi_5合金膜比表面积增加,并在其表层形成了La_2O_3-Ni的表层结构。氢敏测试结果显示,在空气中退火的样品不需要在高压纯氢中活化,在室温下即对氢气响应,说明该合金膜可以作为氢气传感器的敏感层。     

铜薄膜微结构的X射线衍射线形分析

首先采用真空蒸镀法制备了不同厚度的铜薄膜,并对薄膜进行了退火处理;然后用X射线衍射仪测定铜薄膜的衍射谱,最后采用线形分析法对衍射谱进行计算,得到了不同厚度铜薄膜退火前后的晶粒尺寸和微应变。结果表明:真空蒸镀铜薄膜晶粒尺寸随薄膜厚度的增加而增大,微应变随薄膜厚度的增加而减小;退火处理后薄膜晶粒明显长大,薄膜微应变在退火处理后明显减小。     

X-ray and Magnetoresistance Measurements of Electrodeposited Cu-Co Granular Films

Granular CoxCu1-x alloy films were prepared by electrodeposition at room temperature directly onto semiconducting Si substrate. X-ray diffraction (XRD) revealed that the as-deposited films formed single phase metastable fcc alloy structure. The fcc lattice parameter αwas found to decrease linearly with increasing Co concentration x in the studied range. The giant magnetoresistance (GMR) of the films was improved after annealing. Pure Co fcc diffraction peaks were observed in the diffractogram of the annealed sample, indicating phase separation occurred upon annealing. The optimal annealing temperature was 450℃. The maximum of magnetoresistance (MR) ratio 8.21% was obtained for the Co20Cu80 thin film after annealing at 450℃for 1 h. The saturation field decreased upon annealing in the MR curves of Co20Cu80 film.     

Structural characterization of BDN-SOH LB films using small angle XRD and Fourier transform IR spectroscopy

We investigated the structure of BDN(bis(4-diethylaminodithiobenzil) Nickel)-SOH(Stearyl alcohol) Langmuir-Blodgett films using small angle X-ray diffraction and polarized FTIR spectroscopy. The results show that the microcrystal domains formed on the surface of LB film resemble a well-laminated periodic structure with a molecular spacing of 2.56 nm. Meanwhile, the tilted angles of the molecules of SOH and BDN are about 30°, referring to the normal direction of the sample surface, as determined by our XRD and FTIR studies.     

Solar-light photoamperometric and photocatalytic properties of quasi-transparent TiO2 nanoporous thin films

Transparent photocatalytic surfaces are of ever increasing importance for many applications on self-cleaning windows and tiles in everyday applications. Here, we report the formation and photocatalytic testing of a quasi-transparent thin and nanoporous titania films deposited on glass plates. Sputtered Ti thin films were anodized in fluoride-ion-containing neutral electrolytes to form optically semitransparent nanoporous films, which transformed to be completely transparent after thermal annealing. The nanoporous films were studied at different stages, such as before and after anodization, as well as after thermal annealing using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis and Raman spectroscopy. It was observed that anodization at 20 V of high-temperature deposited titanium films resulted in regular nanopore films with pore diameters of 30 nm. Structural investigations on the transparent nanopore arrays reveal the presence of anatase phase TiO(2) even after annealing at 500 °C, which was confirmed by XRD and Raman spectroscopy measurements. The solar-light induced photocatalytic decomposition of stearic acid and photoconductivity characteristics of these nanoporous thin films are also presented.     

Annealing effects on the structural properties of IrO2 thin films

We have demonstrated the structural and morphological changes of iridium oxide (IrO₂) films by the thermal annealing process. We have characterized the samples by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The Ir-related XRD peaks predominantly appeared after the thermal annealing at 750-1000 °C. SEM images revealed that the films became quite uneven in thickness by annealing at 750 °C, whereas island-like structures were found to agglomerate on substrate surfaces by annealing at 1000 °C. From EDX and XRD analysis, we suggested that the agglomerated structures mainly consisted of Ir phase.     

Thin films of liquid crystal fumarates and a related acrylate

Five fumarate esters and one acrylate ester have been synthesized and their properties examined. Four of them can be deposited as multilayers by evaporation in vacuo, and three of this group behave as thermotropic smectic liquid crystals. We have attempted to stabilize the homeotropic smectic phase by polymerizing the film using UV light. In two cases we have been successful and have produced films which are resistant to prolonged heating in THF. We infer that these materials are both polymerized and cross linked. They retain their regular layer structure after polymerization, a behaviour which we have demonstrated by X-ray diffraction. We have also attempted to form Langmuir-Blodgett multilayers with these compounds and in four cases have been successful.     

Infrared spectroscopic characterization of orientation and order of thin oligothiophene films

Thin films (2–100 nm) of oligothiophenes (ST, 6T) were prepared on semiconductors (ZnSe, Si/SiO₂) by Knudsen evaporation. The orientation and order of these films were determined by FTIR spectroscopy. The dichroism of the (C=C) and (C-H)-stretching vibration demonstrates, that the films are highly orientated with a fixed tilt angle to the surface normal. This tilt angle y can be calculated from the dichroitic ratio of the polarized spectra. The order of these films was derived from the factor group splitting of the γ-C-H-out-of-plane mode. Vapor deposition on a substrate at 380 K results in a crystalline phase. A liquid crystal phase was obtained by evaporating on substrates at room temperature (300 K). In 30–100 nm films of 6T two different liquid crystalline phases were observed. By annealing 5T films the liquid crystal phase changes into the crystalline phase. After annealing 6T only the smectic phase was obtained. The intensity ratios of the factor group splitted bands give the herringbone angle τ.     

Influence of annealing on thermoelectric properties of bismuth telluride films grown via radio frequency magnetron sputtering

Bismuth telluride films were prepared via radio frequency magnetron sputtering. Mixed powders with different composition were used as sputtering targets. Influence of the annealing temperature on surface topography, crystal structure and thermoelectric properties of the films has been investigated. It was found that the grain size increased and the surface roughness decreased with a rising annealing temperature. X-ray diffraction analysis revealed an improved crystallization after the annealing, and that crystal planes perpendicular to c-axis became prominent. High temperature treatments resulted in a decrease of Seebeck coefficient and an increase of electrical conductivity. The highest power factor was obtained after being annealed at 300 °C.     

磁控溅射法制备CIGS薄膜太阳能电池的工艺及性能研究

采用磁控溅射方法直接溅射铜铟镓硒(CIGS)靶材,制备得到了用于太阳能电池吸收层的CIGS薄膜,然后在Se气氛中对该CIGS薄膜进行退火处理。采用扫描电镜、X射线衍射、Raman、XRF、Hall等方法观察和分析了退火的主要工艺参数对薄膜表面形貌、组织结构、成分以及电学性能的影响,并制备了CIGS太阳能电池。结果表明,采用磁控溅射CIGS靶材+Se气氛中退火处理的方法,可以制备得到成分均匀、电学性能优良、单一黄铜矿相的CIGS薄膜;退火温度和退火时间是影响退火后薄膜质量的主要因素。退火温度低于350℃时,退火效果不明显。退火温度在400℃,退火时间达120 min时,薄膜完成再结晶过程,并制得单一黄铜矿相的CIGS薄膜;退火过程存在Cu-Se二次相的析出和消融,同时具有为薄膜补Se的作用。本文采用该方法制备出的CIGS太阳能电池的最高转换效率为7.69%。