Oxygen interaction with CdS based gas sensors by varying different preparation parameters

The interaction of oxygen gas atmosphere with CdS films prepared by spray pyrolysis is studied. Spray time and deposition temperature are taken as variable parameters. The prepared film structure is characterized by XRD to elucidate the film crystallinity nature and size. Both thickness and crystallite size of the CdS films decrease as the deposition temperature increases from 340 to 490 °C at constant deposition time. The opposite trend was observed when the films are deposited at different deposition times and constant deposition temperature. The films are exposed to different concentrations of oxygen and the thinner CdS films show higher sensitivity and a shorter response time than the thicker films. The results obtained are promising to use the prepared films for detecting oxygen.     

介质保护膜制备参数对AC PDP放电特性的影响

以ＭｇＯ为例,对ＡＣ　ＰＤＰ中电子束蒸发介质保护膜制备的工艺参数,如成膜时基板温度、沉积速率、成膜后的热处理条件等对ＡＣＰＤＰ工作特性的影响进行了系统的研究和分析,讨论了保护膜成分、结构、形貌等对发射特性和ＡＣＰＤＰ工作特性的影响,探讨了成膜的最佳工艺,并根据在放电过程中,由离子轰击产生的 ＭｇＯ膜表面特性的变化和假设氧对 ＭｇＯ膜表面特性的作用,对观测到的放电特性对 ＡＣＰＤＰ板各种制造工艺参数的依赖性进行了解释。     

Effect of CdCl2 annealing treatment on thin CdS films prepared by chemical bath deposition

In order to study the CdS recrystallization mechanism, a comparative study was carried out on thin films prepared by chemical bath deposition. The CdS films were annealed in air with or without a CdCl₂ coating layer. In-situ Raman spectra obtained during the annealing showed that both the air- and the CdCl₂-annealing did not cause rearrangement of the neighboring atoms in the CdS clusters below ~ 300 °C. CdS thin film was partially oxidated to CdO and CdSO₄ on the cluster surface when annealed in air. The oxides and the sulfur stoichiometric deficiency prevented the clusters to coalesce at higher temperatures. Coating thin CdS film with a thin CdCl₂ layer protected it from oxidation during annealing in air and promoted formation of Cl_S and V_Cd point defects in CdS. The anti-oxidation was attributed to the incorporation of a significant amount of Cl into CdS to form the Cl_S, which prevented the oxygen in-diffusion and chemical bonding during the annealing. The anti-oxidation at the CdS nano-crystalline surface and the point defects formed in the CdS promoted coalescence of the neighboring clusters without the need of long-range redistribution of the atoms. Large CdS grains with good crystalline quality formed through recrystallization during the CdCl₂ heat treatment, which provided the solid basis for the subsequent CdTe growth and high efficient CdS/CdTe solar cell fabrication.     

Chemical bath deposition of CdS thin films and their partial conversion to CdO on annealing

CdS thin films prepared by chemical bath deposition technique are characterized using X-ray diffraction, optical absorption spectrometry and scanning electron microscopy. The results of the annealing studies on the films in flowing argon and air atmospheres are also presented in this paper. The resistivity has drastically reduced on annealing in flowing air which is attributed to the partial conversion of CdS to CdO phase.     

Structure and Electrical Properties of NdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thin Films by Laser Ablation at Low Oxygen Partial Pressure

A deposition process for NdBa₂Cu₃O _y thin films by laser ablation at decreased deposition temperature was developed using substitution of oxygen with argon in the chamber during deposition. A low deposition rate is the crucial factor to obtain high-quality NBCO films. The Nd/Ba cation disorder in the film can be suppressed by an increase of the deposition temperature or by a decrease of the oxygen partial pressure during deposition. The presence of Nd/Ba disorder during deposition stimulates the introduction of oxygen into the growing film. A simple model is proposed for estimation of oxygen contents in the film using structural parameters measured with XRD techniques. Studies of the post-deposition annealing process showed ordering of the Nd/Ba sub-lattice and intense oxygen in- and out-diffusion. The temperature of the post-deposition annealing step should be chosen low enough (～400 °C) to avoid oxygen diffusion out of the NBCO film.     

Effect of thermal annealing on the cathodoluminescence of evaporated CdS films

Cathodoluminescence (CL) of evaporated undoped CdS films was investigated before and after thermal annealing in air and in vacuum at 300 °C for several hours. Pure CdS single crystals were studied for comparison. CL spectra were obtained at room temperature using the electron microprobe technique. The two well-known (green and red) CL bands of pure CdS were observed for all samples. Annealing of the films in air decreased the green luminescence while vacuum annealing led to its increase. The red luminescence increased under both annealing conditions. The results were explained in terms of radiative transitions attributed mainly to native defects and their complexes. The role of oxygen and residual impurities on the CL of thin films was discussed. A modulation of the CL spectra was obtained in thin films owing to optical interference.     

连续离子层吸附与反应法(SILAR)生长ZnO多晶薄膜的研究

采用连续离子层吸附与反应法(SILAR),以锌氨络离子([Zn(NH₃)₄]²⁺)为前驱体溶液,在玻璃衬底上沉积了ZnO薄膜,以XRD和SEM等手段分析了薄膜的晶体结构和表面、断面形貌,考察了空气气氛下的退火过程对ZnO薄膜晶体结构与微观形貌的影响,并初步探讨了以SILAR方法沉积ZnO薄膜的机理.结果表明,经200次SILAR沉积循环,所得ZnO薄膜为红锌矿结构的多晶薄膜,沿<002>方向择优生长;薄膜表面致密、光滑均匀,厚度约800nm.退火处理使ZnO薄膜氧缺位减少,晶粒沿c轴取向增强;随退火温度升高,锌间隙原子增加;500℃退火时,ZnO薄膜发生再结晶.减小前驱体溶液的[NH₃·H₂O]/[Zn²⁺]比率可提高ZnO薄膜生长速率.     

An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV-Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm-19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.     

Nucleation and growth characteristics of spray- pyrolyzed CdS thin films

The nucleation, growth and microstructure of CdS films deposited by spray pyrolysis processing (SPP) was investigated. Comparisons of experimental data on films deposited by SPP were made with existing theories of deposition. Droplet impingement, surface pyrolysis and the incorporation of impurity phases were identified as the major mechanisms of film growth.     

薄膜太阳电池缓冲层硫化镉的制备

采用操作简单的化学水浴法(CBD)在普通载玻片上制备了太阳能电池用缓冲层硫化镉薄膜。通过改变反应温度、溶液p H值和退火温度等实验条件,探讨了硫化镉薄膜的最佳制备工艺条件,并利用X射线衍射仪、紫外-可见-分光光度计和电化学工作站对生成的薄膜样品进行了表征。结果表明,制备均匀性好、致密、覆盖度好的硫化镉薄膜的最佳实验条件如下:反应温度为70℃,溶液p H值为10,且后续在350℃温度下进行热处理1 h。此条件下得到的硫化隔薄膜的可见光透过率较高,具有明显的光电导现象;通过计算,最优实验条件下获得薄膜的禁带宽度为2.3 5 e V,与理论值2.42 e V很接近。     

Formation of Photosensitive Films by High Temperature Sintering

Photosensitive ZnCdS:CdS structure was formed by screen printing of ZnS and CdCl2 powders followed by sintering at high temperatures. The sintering of the film at high temperatures resulted in the formation of ZnCdS (ZCS) nanoparticles in a CdS matrix by an ion interchange reaction followed by a solid state reaction. It was observed that the film composition depends on the sintering atmosphere (air in the present case). The photosensitivity of the film depends on parameters such as film composition, sintering atmosphere and sintering temperature. Influence of these parameters on the dark and photocurrent characteristics of ZCS:CdS structure is explained by taking into consideration the presence of deep acceptor centers related to Cd and Zn vacancies and shallow donor levels due to S vacancies in the films.     

Effect of indium diffusion on characteristics of CdS films and nCdS/pSi heterojunctions

Diffusion of indium in In/nCdS/glass and In/nCdS/pSi structures at 350–550 °C in vacuum 1.33 × 10⁻¹ Pa and its effect on structural, electrical, optical and photovoltaic characteristics of nCdS films, fabricated by spray pyrolysis technique and nCdS/pSi heterojunctions have been investigated. The indium-doped and undoped CdS films were characterized by X-ray diffraction (XRD), electrical and optical measurements. The concentration profiles of indium and the components of CdS films (Cd and S) in In/nCdS/pSi structures were studied using the energy dispersive X-ray fluorescence (EDXRF) analysis. The thermal annealing of In/nCdS/pSi structures is accompanied by the diffusion penetration of In through CdS film into Si substrate. At the same time, the Cd and S atoms from CdS film diffuse into Si substrate. The diffusion doping of CdS film by indium did not change the polycrystalline hexagonal structure and the energy band gap of CdS films and increased the electron concentration from 1.4 × 10¹³ to 1.3 × 10¹⁶ cm⁻³. The photovoltaic parameters and spectral responsivity of In-doped nCdS(In)/pSi(In) cells were higher than those for nCdS/pSi cells and reached the maximum values after the thermal annealing at 450 °C. The improvement of the photovoltaic parameters of nCdS(In)/pSi(In) photocells was discussed on the base of the changes introduced in the energy band diagram of nCdS/pSi heterojunction due to the indium diffusion.     

Structure and composition of bismuth ferrite films grown by spray pyrolysis of iron and bismuth methacrylate solutions

Bismuth ferrite films on single-crystal lanthanum aluminate substrates have been grown for the first time through spray pyrolysis of iron and bismuth methacrylate solutions. The film growth process comprises two steps: liquid-phase and crystalline (including pyrolysis). In the liquid-phase step, we analyzed the elemental composition and surface morphology of the coatings as functions of substrate temperature. In the pyrolytic and high-temperature steps, we analyzed the elemental composition and crystal structure of the films as functions of substrate and annealing temperatures. Conditions were established for the growth of partially oriented films.     

Characterization and photovoltaic device application of dip-coated and rapid thermal annealed CdS films

The structure, composition, electronic and optical properties of dip-coated CdS in the as-deposited condition and following rapid thermal annealing have been investigated. It has been shown that oxygen incorporated in the CdS film can be leached out following rapid thermal annealing. Strongly oriented CdS films with resistivity = 0.16 cm and free electron concentration = 2.65 × 10¹⁷ cm^–3 have been grown. Thin film heterojunction devices fabricated by non-aqueous electrodeposition of CdTe on a glass-ITO-CdS cathode have been shown to exhibit good rectification behaviour and photovoltaic activity.     

Annealing effects on the chemical deposited CdS films and the electrical properties of CdS/CdTe solar cells

CdS layers grown by chemical bath deposition (CBD) are annealed in the oxygen and argon-hydrogen atmosphere respectively. It has been found that the open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen before the deposition of CdTe by close spaced sublimation (CSS), while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Electronic properties of the CdS films are investigated using X-ray photo-electron spectroscopy (XPS), which indicates that the Fermi level is shifting closer to the conduction band after annealing in the oxygen and consequently a higher open circuit voltage of the solar cell can be obtained.     

Solution precursor plasma deposition of nanostructured CdS thin films

Cadmium sulfide (CdS) films are used in solar cells, sensors and microelectronics. A variety of techniques, such as vapor based techniques, wet chemical methods and spray pyrolysis are frequently employed to develop adherent CdS films. In the present study, rapid deposition of CdS thin films via plasma spray route using a solution precursor was investigated, for the first time. Solution precursor comprising cadmium chloride, thiourea and distilled water was fed into a DC plasma jet via an axial atomizer to create ultrafine droplets for instantaneous and accelerated thermal decomposition in the plasma plume. The resulting molten/semi-molten ultrafine/nanoparticles of CdS eventually propel toward the substrate to form continuous CdS films. The chemistry of the solution precursor was found to be critical in plasma pyrolysis to control the stoichiometry and composition of the films. X-ray diffraction studies confirmed hexagonal α-CdS structure. Surface morphology and microstructures were investigated to compare with other synthesis techniques in terms of process mechanism and structural features. Transmission electron microscopy studies revealed nanostructures in the atomized particulates. Optical measurements indicated a decreasing transmittance in the visible light with increasing the film thickness and band gap was calculated to be ～2.5 eV. The electrical resistivity of the films (0.243 ± 0.188 × 10⁵ Ω cm) was comparable with the literature values. These nanostructured polycrystalline CdS films could be useful in sensing and solar applications.     

Growth and characterization of high resistivity c-axis oriented ZnO films on different substrates by RF magnetron sputtering for MEMS applications

In the present work, we report the deposition of high resistivity c-axis oriented ZnO films by RF magnetron sputtering. The deposition parameters such as RF power, target-to-substrate spacing, substrate temperature, and sputtering gas composition affect the crystallographic properties of ZnO films, which were evaluated using XRD analysis. The self-heating of the substrate in plasma during film deposition was investigated and we report that highly “c-axis oriented” ZnO thin films can be prepared on different substrates without any external heating under optimized deposition parameters. The post-deposition annealing of the film at 900 °C for 1 h in air ambient increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). Bond formation of ZnO was confirmed by FTIR analysis. Grains distribution and surface roughness have been analyzed using SEM and AFM. The DC resistivity of the films prepared under different deposition conditions was measured using MIS/MIM structures and was found to be in the range of 10¹¹–10¹² Ω cm at low electric field of 10⁴ V/cm. The ZnO film of 1 μm thickness has transmittance of over 85% in the visible region. Applications of these films in MEMS devices are discussed.     

氧化锌镓薄膜的制备技术和研究现状

介绍了制备GZO薄膜的各种方法,如磁控溅射法、化学气相沉积法、溶胶-凝胶法、脉冲激光沉积法、喷雾热解法;阐述了这些方法的镀膜原理,并比较了各种工艺的优缺点。综述了GZO薄膜在单层膜领域、复合多层膜领域有机物基底上镀膜领域和薄膜后续退火处理领域的研究现状。提出了产业化过程中需要解决的问题:①制备高密度、高溅射稳定性和导电性优良的靶材;②完善现有镀膜工艺条件;③制备符合不同生产要求的薄膜。     

射频溅射Y-ZrO_2薄膜的研究

采用射频磁控溅射法制成含钇的二氧化锆薄膜,借助背散射分析(RBS)、透射电子显微镜(TEM)和X光衍射(XRD)方法研究了薄膜的化学剂量比、微观结构和相结构。同时研究了微观结构与机械性能(显微硬度、韧性、抗磨损性)之间的关系,以及退火对相稳定性的影响。     

Electrical conductivity and optical properties of thin carbon films grown from ethanol vapor

Transparent, ultrathin carbon films have been grown through the pyrolysis of ethanol vapor at a reduced pressure on copper substrates at temperatures from 600 to 950°C. The electrical conductivity of the films increases with deposition temperature. Depending on deposition temperature, ethanol vapor pyrolysis may follow different mechanisms and the carbon deposition process has different key features, which influence the properties of the films. In the range 600–750°C, ethanol vapor pyrolysis is a catalytic process, which results in selective growth of a thin carbon film with an optical transmittance of ∼95% only on the copper surface. At higher temperatures, carbon deposition is nonselective, and the resultant films are darker. The carbon deposition mechanism is discussed in relation to the ethanol vapor pyrolysis temperature. The present results suggest that carbon deposition from ethanol vapor is a promising approach to producing transparent, conductive carbon films.