Investigations on structural, vibrational, morphological and optical properties of CdS and CdS/Co films by ultrasonic spray pyrolysis

CdS and CdS/Co films have been deposited on glass substrates by an ultrasonic spray pyrolysis method. The effects of Co incorporation on the structural, optical, morphological, elemental and vibrational properties of these films were investigated. XRD analysis confirmed the hexagonal wurtzite structure of all films and had no impurity phase. While CdS film has (0 0 2) as the preferred orientation, CdS/Co films have (1 1 0) as the preferred orientation. The direct optical band gap was found to decrease from 2.42 to 2.39 eV by Co incorporation. The decrease of the direct energy gaps by increasing Co contents is mainly due to the sp-d exchange interaction between the localized d-electrons of Co²⁺ ions and band electrons of CdS. After the optical investigations, it was seen that the transmittance of CdS films decreased by Co content. The Raman measurements revealed two peaks corresponding to the 1LO and 2LO modes of hexagonal CdS. The vibrational modes of Cd-S were obtained in the wavenumber range (590-715 cm⁻¹) using Fourier transform infrared spectroscopy (FTIR). The elemental analysis of the film was done by energy dispersive X-ray spectrometry.     

Study on the ferromagnetism in Co and N doped ZnO thin films

Present investigation reports the structural, optical and magnetic properties of co-doping of Co and N ions in ZnO samples, prepared by two distinct methods. In the first method, samples are synthesized by Sol–gel technique in which the Co and N are co-doped simultaneously during the growth process itself. In the second case, N ions are implanted in the Co doped ZnO thin films grown by Pulsed Laser Deposition (PLD). Structural studies showed that the nitrogen implantation on Co doped ZnO samples developed compressive stress in the films. X-ray photoelectron spectroscopy confirmed the doping of Co and N in ZnO matrix. In the Resonant Raman scattering multiple LO phonons up to fifth order are observed in the (Co, N) co-doped ZnO. Photoluminescence spectra showed that there is reduction in the bandgap due to the presence of Co in the lattice and also the presence of Zn vacancies in the films. All samples showed ferromagnetic behavior at room temperature. The magnetic moment observed in the implanted films is found to be varied with the different dosages of the implanted N ions. First principle calculations have been carried out to study the possible magnetic interaction in the co-doped system. Present study shows that the ferromagnetic interaction is due to the hybridization between N 2p and Co 3d states in the (Co, N) co-doped ZnO and is very sensitive to the geometrical configurations of dopants and the vacancy in the ZnO host lattice.     

带隙可调的Al，Mg掺杂ZnO薄膜的制备

利用射频磁控溅射（RF-MS）方法,固定Al₂O₃掺杂量2 wt%,Mg掺杂量分别为1 wt%,3 wt%和5 wt%,在玻璃基底上制备了Al掺杂和Al,Mg共掺杂的ZnO薄膜,在500 ℃空气中退火2 h后,测量并比较了它们的光学和电学性质．结果表明,Al,Mg共掺杂的ZnO薄膜结晶质量良好,具有ZnO纤锌矿结构,具有较强的（002）面衍射峰,表明薄膜晶体沿c轴优先生长;与Al掺杂ZnO薄膜相比蓝端光透射率增加,1 wt%和3 wt% Mg掺杂薄 关键词： 射频磁控溅射 ZnO薄膜 Al Mg共掺杂     

Cesium doped and undoped ZnO nanocrystalline thin films: a comparative study of structural and micro‐Raman investigation of optical phonons

Undoped and cesium‐doped zinc oxide (ZnO) thin films have been deposited on sapphire substrate (0001) using the sol–gel method. Films were preheated at 300 °C for 10 min and annealed at 600 and 800 °C for 1 h. The grown thin films were confirmed to be of wurtzite structure using X‐ray diffraction. Surface morphology of the films was analyzed using scanning electron microscopy. The photoluminescence (PL) spectra of ZnO showed a strong ultraviolet (UV) emission band located at 3.263 eV and a very weak visible emission associated with deep‐level defects. Cesium incorporation induced a blue shift of the optical band gap and quenching of the near‐band‐edge PL for nanocrystalline thin film at room temperatures because of the band‐filling effect of free carriers. A shift of about 10–15 cm⁻¹ is observed for the first‐order longitudinal‐optical (LO) phonon Raman peak of the nanocrystals when compared to the LO phonon peak of bulk ZnO. The UV resonant Raman excitation at RT shows multiphonon LO modes up to fifth order. Copyright © 2010 John Wiley & Sons, Ltd.     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Microstructure,optical and structural characterization of Cd0.98Fe0.02S thin films co-doped with Zn by chemical bath deposition method

Fe-doped CdS (Cd_0.98Fe_0.02S) and Fe, Zn co-doped CdS (Cd_0.98−xZn_xFe_0.02S (x=0.02, 0.04, and 0.06)) thin films have been successfully deposited on glass substrate by chemical bath deposition technique using aqueous ammonia solution at pH = 9.5. Phase purity of the samples having cubic structure with (111) as the preferential orientation was confirmed by X-ray diffraction technique. Shift of X-ray diffraction peak position towards higher angle side and decrease of lattice parameters, volume and crystallite size confirmed the proper incorporation of Zn into Cd–Fe–S except Zn=6%. The compositional analysis (EDX) showed that Cd, Fe, Zn and S are present in the films. The enhanced band gap and higher transmittance observed in Cd_0.94Zn_0.04Fe_0.02S films are the effective way to use solar energy and enhance its photocatalytic activity under visible light. The enhanced green band emission than blue band by Zn-doping evidenced the existence of higher defect states.     

Na-Mg共掺杂ZnO薄膜的结构和光学性质

利用溶胶-凝胶法,在普通载玻片上使用旋转涂膜技术制备了具有c轴择优取向生长的Na-Mg共掺杂的ZnO薄膜。用XRD、SEM、光致发光(PL)及透射光谱对薄膜样品进行了表征。结果表明:Na-Mg共掺杂有利于ZnO薄膜的c轴择优取向生长,并且随着Na+掺杂浓度的增加,晶粒尺寸先增大后减小;通过比较不同掺杂浓度ZnO薄膜的PL谱,推测发光峰值位于380nm的紫外发射与ZnO的自由激子复合有关;发现掺入Mg的确能使ZnO禁带宽度增大,掺杂组分为Na0.04Mg0.2Zn0.76O时,其PL谱只有一个很强的紫光发射峰,其近带边紫外光发射强度较未掺杂的ZnO增强了近10倍,极大地提高了薄膜紫外发光性能;并且随Na+浓度增加薄膜透光性减弱。     

溶胶—凝胶法制备CdS微晶掺杂TiO2／SiO2薄膜及其非线性光学特性

采用溶胶－凝胶方法在普通的载玻片上制备了ＣｄＳ微晶掺杂的ＴｉＯ２／ＳｉＯ２复合薄膜。用正硅酸乙酯、钛酸丁酯、醋酸镉作原料，比较了两种硫化剂：硫尿和硫代乙酰氨的硫化作用。Ｘ射线衍射谱和拉曼光谱揭示了ＣｄＳ微晶镶嵌在ＴｉＯ２／ＳｉＯ２薄膜的玻璃网络中。不同热处理温度、不同热处理时间的吸收光谱表明薄膜中存在着量子尺寸效应。采用Ｚ扫描技术测量了薄膜的非线性吸收及非线性折射率ｎ２＝－４．６７×１０－７ｅｓｕ。     

Synthesis and characterization of the Pd/InVO4-TiO2 co-doped thin films with visible light photocatalytic activities

Novel Pd/InVO₄-TiO₂ thin films with visible light photocatalytic activity were synthesized from the Pd and InVO₂ co-doped TiO₂ sol via sol-gel method. The photocatalytic activities of Pd/InVO₄-TiO₂ thin films were investigated based on the oxidative decomposition of methyl orange in aqueous solution. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy (UV-vis). The results indicate that the Pd/InVO₄-TiO₂ thin films are compact, uniform and consist of sphere nanoparticles with diameters about 80-100 nm. The UV-vis spectra show that the Pd/InVO₄-TiO₂ thin films extend the light absorption spectrum toward the visible region. XPS results reveal that doped Pd exist in the form of metallic palladium. The photocatalytic experiments demonstrate that Pd doping can effectively enhance the photocatalytic activities of InVO₄-TiO₂ thin films in decomposition of aqueous methyl orange under visible light irradiation. It has been confirmed that Pd/InVO₄-TiO₂ thin films could be excited by visible light (E < 3.2 eV) due to the existence of the Pd and InVO₄ doped in the films.     

Co,Sn共掺ZnO薄膜结构与光致发光的研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co,Sn掺杂ZnO系列薄膜.通过金相显微镜和X射线衍射(XRD)研究了Co与Sn掺杂对薄膜的表面形貌和微结构的影响.XRD结果表明,所有ZnO薄膜样品都存在(002)择优取向,特别Sn单掺ZnO薄膜的c轴择优取向最为显著,而且晶粒尺寸最大.XPS测试表明样品中Co和Sn的价态分别为2+和4+,证实Co²⁺,Sn⁴⁺进入了ZnO的晶格.室温光致发光谱(PL)显示在所有的样品中都有较强的蓝光双峰发射和较弱的绿光发 关键词： ZnO薄膜 溶胶-凝胶 掺杂 光致发光     

Fabrication of Mg-doped ZnO thin films by laser ablation of Zn:Mg target

Mg-doped ZnO thin films were fabricated by laser ablation of Zn:Mg targets consisting of Mg metallic strips and Zn disk in oxygen atmosphere with a goal to facilitate convenient control of Mg contents in the films. The characteristics of the deposited films were examined by analyzing their photoluminescence (PL), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) spectra. Mg contents as analyzed by XPS indicate that the target composition is fairly transferred to the deposited films. The wurtzite structure of ZnO was conserved even for the highly doped ZnO films and there was no Mg- or MgO-related XRD peaks. With increase in the Mg content, the bandgap and PL peak energy shifted to blue and the Stokes shift became larger.     

Influence of post-deposition annealing on the structural,optical and electrical properties of Li and Mg co-doped ZnO thin films deposited by sol–gel technique

Lithium (Li) and magnesium (Mg) co-doped zinc oxide (ZnO) thin films were deposited by sol–gel method using spin coating technique. The films were deposited on glass substrates and annealed at different temperatures. The effects of annealing temperature on the structural, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), Ultraviolet–Visible absorption spectra (UV–VIS), photoluminescence spectra (PL), X-ray photo electron spectroscopy (XPS) and Hall measurements. XRD patterns indicated that the deposited films had a polycrystalline hexagonal wurtzite structure with preferred (0 0 0 2) orientation. All films were found to exhibit a good transparency in the visible range. Analysis of the absorption edge revealed that the optical band gap energies of the films annealed at different temperatures varies between 3.49 eV and 3.69 eV. Room temperature PL spectra of the deposited films annealed at various temperatures consist of a near band edge emission and visible emission due to the electronic defects, which are related to deep level emissions, such as oxide antisite (O_Zn), interstitial zinc (Zn_i), interstitial oxygen (O_i) and zinc vacancy (V_Zn) which are generated during annealing process. The influence of annealing temperature on the chemical state of the dopants in the film was analysed by XPS spectra. Ion beam analysis (Rutherford back scattering) experiments were performed to evaluate the content of Li and Mg in the films. Hall measurements confirmed the p-type nature of the deposited films.     

Photoluminescence studies on nanostructured cadmium sulfide thin films prepared by chemical bath deposition method and annealed at different temperatures

Nanostructured cadmium sulfide (CdS) thin films have been prepared by chemical bath deposition (CBD) method and after post deposition annealing of the thin films at different temperatures, photoluminescence (PL) property has been studied. The effects of various photoexcitation wavelengths on the PL behaviour of different annealed films of CdS were studied by recording the PL spectra. The intensity of PL, the profile of the PL spectra and the effects of photoexcitation wavelength depend drastically on the temperature of the post deposition annealing of the thin films. The XRD patterns of the films show the presence of both the hexagonal and cubic phases (mixed phases). The emission peak arises from the surface defects of the CdS nanocrystalline thin films. Significant modification in the surface morphology of the CdS films upon annealing has been observed from the FESEM images. The morphology of the thin films is expected to influence the PL behaviour of the CdS thin films. The quantum size effect and size dependant PL have been observed.     

微量Mg掺杂ZnO薄膜的光致发光光谱和带隙变化机理研究

利用射频磁控溅射(RF-MS)法在450℃玻璃基底上制备了Mg掺杂量分别为0.81at%,2.43at%和4.05at%的ZnO薄膜,对其微观结构、室温光致发光光谱(PL)、光学和电学性质进行了研究.结果发现,微量Mg掺杂ZnO薄膜晶体具有六方纤锌矿结构并保持高结晶质量;掺杂0.81at%和2.43at%Mg的ZnO薄膜室温PL谱中近带边发射(NBE)峰的短波方向出现了高能发射带与NBE峰同时存在;随着Mg掺杂量增加至4.05at%,这个高能发射带逐步将NBE峰掩盖.推测在Mg掺杂ZnO薄膜中,Mg2+替代Zn2+附近核外电子的能量增大并产生了一个高能级.而未被Mg2+替代的Zn2+周围的核外电子能量状态不变,带间能级依然存在,随着Mg掺杂量的增加处于高能级的电子数目逐步增加并占绝对优势.因此,ZnO薄膜随着Mg掺杂量增加薄膜禁带宽度增大,这是由于Mg掺杂后周围电子能量增大与Burstein-Moss效应共同作用的结果.另外,薄膜在可见光区域的平均透射率均大于85%,随着Mg掺杂量的增加,薄膜禁带宽度增大并在3.36—3.52eV内变化;Mg掺杂量为0.81at%,2.43at%和4.05at%时,薄膜电阻率分别为2.2×10-3,3.4×10-3和8.1×10-3Ω.cm.     

Co与Cu掺杂ZnO薄膜的制备与光致发光研究

采用溶胶-凝胶旋涂法在玻璃衬底上制备了Co, Cu单掺杂及Co,Cu共掺杂ZnO薄膜.用金相显微镜观察了Co与Cu掺杂对ZnO薄膜形貌的影响.X射线衍射（XRD）研究揭示所有ZnO薄膜样品都存在（002）择优取向,在Cu单掺的ZnO薄膜中晶粒尺寸最大.对所有样品的室温光致发光测量都观察到较强的蓝光双峰发射和较弱的绿光发射,其中长波长的蓝光峰和绿光峰都能够通过掺杂进行控制.对不同掺杂源的ZnO薄膜发光性能进行了分析,认为蓝光峰来源于电子由导带底到锌空位能级的跃迁及锌填隙到价带顶的跃迁,绿光峰是由于掺杂造成的 关键词： ZnO薄膜 溶胶-凝胶 Co Cu掺杂 光致发光     

Quenching of surface traps in Mn doped ZnO thin films for enhanced optical transparency

The structural and photoluminescence analyses were performed on un-doped and Mn doped ZnO thin films grown on Si (1 0 0) substrate by pulsed laser deposition (PLD) and annealed at different post-deposition temperatures (500-800 °C). X-ray diffraction (XRD), employed to study the structural properties, showed an improved crystallinity at elevated temperatures with a consistent decrease in the lattice parameter ‘c’. The peak broadening in XRD spectra and the presence of Mn 2p3/2 peak at ∼640 eV in X-ray Photoelectron Spectroscopic (XPS) spectra of the doped thin films confirmed the successful incorporation of Mn in ZnO host matrix. Extended near band edge emission (NBE) spectra indicated the reduction in the concentration of the intrinsic surface traps in comparison to the doped ones resulting in improved optical transparency. Reduced deep level emission (DLE) spectra in doped thin films with declined PL ratio validated the quenching of the intrinsic surface traps thereby improving the optical transparency and the band gap, essential for optoelectronic and spintronic applications. Furthermore, the formation and uniform distribution of nano-sized grains with improved surface features of Mn-doped ZnO thin films were observed in Field Emission Scanning Electron Microscopy (FESEM) images.     

Microstructural, optical and photocatalytic properties of CdS doped TiO2 thin films

CdS doped TiO₂ thin films (with CdS content=0, 3, 6, 9 and 12 at%) were grown on glass substrates. The X-ray diffraction analysis revealed that the films are polycrystalline of monoclinic TiO₂ structure. The microstructure parameters of the films such as crystallite size (D_ν) and microstrain (e) are calculated. Both the crystallites size and the microstrain are decreased with increasing CdS content. The optical constants have been determined in terms of Murmann's exact equations. The refractive index and extinction coefficient are increased with increasing CdS content. The optical band gap is calculated in the strong absorption region. The possible optical transition in these films is found to be an allowed direct transition. The values of E_g^opt are found to decrease as the CdS content increased. The films with 3 at% CdS content have better decomposition efficiency than undoped TiO₂. The films with 6 at% and 9 at% CdS content have decomposition efficiency comparable to that of undoped TiO₂, although they have lower band gap. The CdS doped TiO₂ could have a better impact on the decomposing of organic wastes.     

Fe,Ni掺杂CdS的电子结构和光学性质

基于密度泛函理论（DFT）的第一性原理研究了Fe,Ni单掺杂和（Fe,Ni）共掺杂CdS的能带结构、电子态密度分布、介电常数和光学吸收系数,分析了掺杂后电子结构和光学性质的变化.计算结果表明:掺杂体系的CdS晶格常量均减少,能带宽度减小,介电函数虚部ε₂（ω）都在0.53 eV左右出现了一个新峰,吸收光谱发生明显的红移,它们均在1.35 eV处出现较强吸收峰.     

Effect of iodine doping on the electrical transport mechanism in plasma polymerized 2,6-diethylaniline thin films

The current density–voltage characteristics of pure and iodine doped plasma polymerized 2,6-diethylaniline (PPDEA) thin films of different thicknesses ranging from 150 to 450 nm with aluminum (Al)/PPDEA/Al structure have been investigated at room temperature. The direct current electrical conductivity has showed a higher value due to iodine doping of PPDEA thin film. In contrast to pure PPDEA thin films where the most probable conduction mechanism is electrode limited Schottky type, Poole–Frenkel (PF) conduction mechanism is found to be operative in iodine doped PPDEA thin films. The PF conduction mechanism in iodine doped PPDEA thin films may have generated due to the charge transfer complex formation through donor type monomer and acceptor type iodine. The presence of charge transfer complex is confirmed by a new absorption shoulder/peak in ultraviolet–visible spectrum of iodine doped PPDEA thin film.     

Effect of strain on the structural and optical properties of Cu-N co-doped ZnO thin films

Polycrystalline ZnO thin films co-doped with Cu and N have been obtained by chemical bath deposition. Introduction of Cu and N causes the change of strained stress in ZnO films, which subsequently affects the structural and optical properties. The dependence of structural and optical properties of the ZnO films on lattice strained stress is investigated by XRD measurement, SEM, PL spectrum, optical reflection and Raman spectrum. The result of photoluminescence of Cu-N co-doped ZnO films indicates that the UV emission peaks shift slightly towards higher energy side with decrease in tensile strain and vise versa. The blue-shift of the absorption edge and up-shift of E2 (high) mode of the films can be observed in the optical reflection and Raman spectra.