Optical properties of zinc peroxide and zinc oxide multilayer nanohybrid films

Zinc peroxide and zinc oxide nanoparticles were prepared and self-assembled hybrid nanolayers were built up using layer-by-layer (LbL) technique on the surface of glass substrate using the layer silicate hectorite and an anionic polyelectrolyte, sodium polystyrene sulfonate (PSS). Light absorption, interference and morphological properties of the hybrid films were studied to determine their thickness and refractive index. The influence of layer silicates and polymers on the self-organizing properties of ZnO₂ and ZnO nanoparticles was examined. X-ray diffraction revealed that ZnO₂ powders decomposed to ZnO (zincite phase) at relatively low temperatures (less than 200 °C). The optical thickness of the films ranged from 190 to 750 nm and increased linearly with the number of layers. Band gap energies of the ZnO₂/hectorite films were independent from the layer thickness and were larger than that of pure ZnO₂ nanodispersion. Decomposition of ZnO₂ to ZnO and O₂ at 400 °C resulted in the decrease of the band gap energy from 3.75 to 3.3 eV. Concomitantly, the refractive index increased in correlation with the formation of the zincite ZnO phase. In contrast, the band gap energies of the ZnO₂/PSS hybrid films decreased with the thickness of the nanohybrid layers. We ascribe this phenomenon to the steric stabilization of primary ZnO₂ particles present in the confined space between adjacent layers of hectorite sheets.     

Effect of the laser fluence on structural and optical characterization of thin CdS films synthesized by femtosecond pulsed laser deposition

CdS thin films have been grown on Si(1 1 1) and quartz substrates using femtosecond pulsed laser deposition. X-ray diffraction, atomic force microscopy, photoluminescence measurement, and optical transmission spectroscopy were used to characterize the structure and optical properties of the deposited CdS thin films. The influence of the laser fluence (laser incident energy in the range 0.5–1.5 mJ/pulse) on the structural and optical characterizations of CdS thin films has been studied. The results indicate that the structure and optical properties of the CdS thin films can be improved as increasing the per pulse output energy of the femtosecond laser to 1.2 mJ. But when the per pulse output energy of the femtosecond laser is further increased to 1.5 mJ, which leads to the degradation of the structure and optical properties of the CdS thin films.     

Effect of precursors on structure, optical and electrical properties of chemically deposited nanocrystalline ZnO thin films

Nanocrystalline ZnO thin films were chemically deposited on glass substrates using two different precursors namely, zinc sulphate and zinc nitrate. XRD studies confirm that the films are polycrystalline zinc oxide having hexagonal wurtzite structure with crystallite size in the range 25-33 nm. The surface morphology of film prepared using zinc sulphate exhibits agglomeration of small grains throughout the surface with no visible holes or faulty zones, while the film prepared using zinc nitrate shows a porous structure consisting of grains with different sizes separated by empty spaces. The film prepared using zinc sulphate shows higher reflectance due to its larger refractive index which is related to the packing density of grains in the film. Further, the film prepared using zinc sulphate is found to have normal dispersion for the wavelength range 550-750 nm, whereas the film prepared using zinc nitrate has normal dispersion for the wavelength range 450-750 nm. The direct optical band gaps in the two films are estimated to be 3.01 eV and 3.00 eV, respectively. The change in film resistance with temperature has been explained on the basis of two competing processes, viz. thermal excitation of electrons and atmospheric oxygen adsorption, occurring simultaneously. The activation energies of the films in two different regions indicate the presence of two energy levels - one deep and one shallow near the bottom of the conduction band in the bandgap.     

Physical properties of ZnO thin films deposited by spray pyrolysis technique

Thin films of ZnO have been prepared on glass substrates at different thicknesses by spray pyrolysis technique using 0.2 M aqueous solution of zinc acetate. X-ray diffraction reveals that the films are polycrystalline in nature having hexagonal wurtzite type crystal structure. The resistivity at room temperature is of the order 10⁻² Ω cm and decreased as the temperature increased. Films are highly transparent in the visible region. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, E_g, has been reported for the films. A shift from E_g = 3.21 eV to 3.31 eV has been observed for deposited films.     

Influence of aging time of the starting solution on the physical properties of fluorine doped zinc oxide films deposited by a simplified spray pyrolysis technique

Fluorine doped zinc oxide (FZO) films were fabricated from fresh and aged (4, 8, 12 and 16 days) starting solutions using a simplified and low cost spray pyrolysis technique. The X-ray diffraction study showed that the preferential orientation is along the (0 0 2) plane for all the films irrespective of the age of the solution. The crystallite size calculated using the Scherrer’s formula is comparatively smaller only for the film prepared from the starting solution having aging time 4 days which may be due to the efficient incorporation of fluorine atoms into the ZnO lattice. This phenomenon is confirmed by the minimum resistivity value (3.14 × 10⁻² Ω cm) obtained in this particular case. The visible transmittance and the optical band gap values are found to be in the range of 63–83% and 3.20–3.31 eV, respectively. The optical transmittance is found to decrease gradually as the aging time of the solution increases and the optical band gap is found to be slightly higher in the case of the film prepared from the fourth day solution. The scanning electron microscopy results depicted that the microstructure of ZnO:F films are largely influenced by the aging of the starting solution.     

Effect of substrate temperature and oxygen partial pressure on microstructure and optical properties of pulsed laser deposited yttrium oxide thin films

Yttrium oxide thin films were deposited on Si (1 1 1) and quartz substrates by pulsed laser deposition technique at different substrate temperature and oxygen partial pressure. XRD analysis shows that crystallite size of the yttrium oxide thin films increases as the substrate temperature increases from 300 to 873 K. However the films deposited at constant substrate temperature with variable oxygen partial pressure show opposite effect on the crystallite size. Band gap energies determined from UV-visible spectroscopy indicated higher values than that of the reported bulk value.     

Deposition of zinc oxide thin films by reactive pulsed laser ablation

Thin films of zinc oxide have been deposited by reactive pulsed laser ablation of Zn and ZnO targets in presence of a radio frequency (RF) generated oxygen plasma. The gaseous species have been deposited at several substrate temperatures, using the on-axis configuration, on Si (1 0 0). Thin films have been characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and infrared spectroscopy. A comparison among conventional PLD and reactive RF plasma-assisted PLD has been performed.     

Influence of sputter-etching of substrate on the microstructural and optical properties of ZnO films deposited by RF magnetron sputtering

ZnO films were prepared using radio frequency magnetron sputtering on Si(1 1 1) substrates that were sputter-etched for different times ranging from 10 to 30 min. As the sputter-etching time of the substrate increases, both the size of ZnO grains and the root-mean-square (RMS) roughness decrease while the thickness of the ZnO films shows no obvious change. Meanwhile, the crystallinity and c-axis orientation are improved by increasing the sputter-etching time of the substrate. The major peaks at 99 and 438 cm⁻¹ are observed in Raman spectra of all prepared films and are identified as E₂(low) and E₂(high) modes, respectively. The Raman peak at 583 cm⁻¹ appears only in the films whose substrates were sputter-etched for 20 min and is assigned to E₁(LO) mode. Typical ZnO infrared vibration peak located at 410 cm⁻¹ is found in all FTIR spectra and is attributed to E₁(TO) phonon mode. The shoulder at about 382 cm⁻¹ appearing in the films whose substrates were sputter-etched for shorter time (10-20 min) originates from A₁(TO) phonon mode. The results of photoluminescence (PL) spectra reveal that the optical band gap (Eg) of the ZnO films increases from 3.10 eV to 3.23 eV with the increase of the sputter-etching time of the substrate.     

Structure and optical properties of nanostructured zinc oxide films with different growth temperatures

ZnO films were prepared by pulsed laser deposition (PLD) on glass substrate with temperature ranging from room temperature (RT) to 500 °C. All the films formed the hexagonal wurtzite structure and showed the c-axis (0 0 2) preferred orientation. The films deposited at 200 °C showed the narrowest full width at half maximum of both X-ray diffraction (XRD) and rocking curve, largest height grain size, smallest macrostress and least point defects. Meanwhile, it was found that the films deposited at 350 °C displayed the most intense diffraction peak in XRD and a strong UV emission while it showed the most intense defect-related green emission, fastest growth rate and larger macrostress. In addition, the cross section images showed all films grew with a columnar form along (0 0 2) orientation.     

Growth and characterization of pulsed laser deposited ZnO thin films

One of the most important and promising materials from metal oxides is ZnO with specific properties for near UV emission and absorption optical devices. The properties of ZnO thin films strongly depend on the deposition method. Among them, pulsed laser deposition (PLD) plays an important role for preparing various kinds of ZnO films, e.g. doped, undoped, monocrystalline, and polycrystalline. Different approaches — ablation of sintered ZnO pellets or pure metallic Zn as target material are described. This contribution is comparing properties of ZnO thin films deposited from pure Zn target in oxygen atmosphere and those deposited from sintered ZnO target. There is a close connection between final thin film properties and PLD conditions. The surface properties of differently grown ZnO thin films are measured by secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, different approaches — ablation of sintered ZnO pellet or pure metallic Zn as target materials are described. The main results characterize typical properties of ZnO films versus technological parameters are presented. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Effect of solvent volume on the physical properties of undoped and fluorine doped tin oxide films deposited using a low-cost spray technique

Undoped and fluorine doped tin oxide films were deposited from starting solutions having different values of solvent volume (10-50 ml) by employing a low cost and simplified spray technique using perfume atomizer. X-ray diffraction studies showed that there was a change in the preferential orientation from (2 1 1) plane to (1 1 0) plane as the volume of the solvent was increased. The sheet resistance (R_sh) of undoped SnO₂ film was found to be minimum (13.58 KΩ/□) when the solvent volume was lesser (10 ml) and there was a sharp increase in R_sh for higher values of solvent volume. Interestingly, it was observed that while the R_sh increases sharply with the increase in solvent volume for undoped SnO₂ films, it decreases gradually in the case of fluorine doped SnO₂ films. The quantitative analysis of EDAX confirmed that the electrical resistivity of the sprayed tin oxide film was mainly governed by the number of oxygen vacancies and the interstitial incorporation of Sn atoms which in turn was governed by the impinging flux on the hot substrate. The films were found to have good optical characteristics suitable for opto-electronic devices.     

Preparation and properties of zinc blende and orthorhombic SnS films by chemical bath deposition

SnS (stannous sulfide) films were prepared by chemical bath deposition in which a novel chelating reagent ammonium citrate was used. The film has a zinc blende structure or an orthorhombic structure which is determined by the pH value and the temperature of the deposition solution. The reason for this result is considered to be that SnS films prepared under different conditions have different deposition mechanisms (ion-by-ion mechanism for the zinc blende structured SnS and hydroxide cluster mechanism for the orthorhombic structured SnS). The prepared SnS films are homogeneous and well adhered. SEM images show that the SnS films with different structures have different surface morphologies. Electrical test shows that the resistivity of the films is as low as 420 Ω cm and 3300 Ω cm for orthorhombic and zinc blende SnS films, respectively, which are much lower than the ever reported values. Persistent photoconductivity (PPC) phenomena are observed for both the films with zinc blende and orthorhombic structures by photo-current responses measurement. The optical bandgaps of the SnS films are determined to be 1.75 eV and 1.15 eV for zinc blende structure and orthorhombic structure, respectively.     

Effect of some preparative parameters on optical properties of spray deposited iridium oxide thin films

Optical properties of iridium oxide films fabricated by the spray pyrolysis technique (SPT) have been investigated. The transmission and reflection spectra of the sprayed films were measured by using a double-beam spectrophotometer in the wavelength range from 200 to 2500 nm. Influences of the preparative parameters; namely, substrate temperature (350-500 °C) and solution molarity (0.005-0.03 M), on the optical characteristics were examined. The solution molarity of the iridium chloride solution was varied so as to prepare iridium oxide thin films with thicknesses ranging from 160 to 325 nm. Some important characteristics of optical absorption, such as optical dispersion energies, the dielectric constant, the ratio of the number of charge carriers to the effective mass, the single oscillator wavelength, and the average value of the oscillator strength, were evaluated. The value of the refractive index was found to depend on the chemical composition as well as the degree of stoichiometry of IrO₂. The values obtained for the high frequency dielectric constant through two procedures are in the range of 2.8-3.9 and 3.3-4.6 over the relevant ranges of the substrate temperature and solution molarity, respectively. Analysis of the energy dispersion curve of the absorption coefficient indicated a direct optical transition with the bandgap energy ranging between 2.61 and 2.51 eV when the substrate temperature increases from 350 to 500 °C.     

Effect of [Zn]/[S] ratios on the properties of chemical bath deposited zinc sulfide thin films

ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80 °C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of [Zn]/[S] on formation and properties of ZnS thin films has been investigated. The ratio of [Zn]/[S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV-vis spectroscopic analysis. ZnS films were obtained with the [Zn]/[S] ratio ranged from1:1 to 1:6. In the cases of [Zn]/[S] ratio ≥ 3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the [S]/[Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80-90%) in the visible region and the band gap is found to be in the range of 3.65-3.74 eV. The result is useful to further develop the CBD ZnS technology.     

衬底温度对PLD制备的Mo薄膜结构及表面形貌的影响

运用脉冲激光沉积(PLD)技术在Si(100)基片上沉积了金属Mo薄膜。在激光重复频率2 Hz,能量密度5.2 J/cm2,本底真空10－6 Pa的条件下,研究Mo薄膜的结构和表面形貌,讨论了衬底温度对薄膜形貌与结构的影响。原子力显微镜(AFM)图像和X射线小角衍射(XRD)分析表明,薄膜表面平整、光滑,均方根粗糙度小于2 nm。沉积温度对Mo薄膜结构和表面形貌影响较大,在373~573 K范围内随着温度升高,薄膜粗糙度变小,结晶程度变好。     

脉冲激光沉积(PLD)法生长高质量ZnO薄膜及其发光性能

采用脉冲激光沉积(PLD)法在单晶Si(100)衬底上生长ZnO薄膜,以X射线衍射(XRD)、原子力显微镜(AFM)和透射电镜(TEM)等手段分析了所得ZnO薄膜的晶体结构和微观形貌。优化工艺(700℃,20Pa)下生长的ZnO薄膜呈c轴高度择优取向,柱状晶垂直衬底表面生长,结构致密均匀。室温光致发光(PL)谱分析结果表明,随着薄膜生长时O₂分压的增大,近带边紫外发光峰与深能级发光峰之比显著增强,表明薄膜的结晶性能和化学计量比都有了很大的改善。O₂分压为20Pa时所生长的ZnO薄膜具有较理想的化学计量比和较高的光学质量。     

Fe纳米颗粒嵌埋对类金刚石薄膜结构及电学性能的影响

 采用脉冲激光气相沉积方法制备了不同Fe嵌埋浓度的Fe: DLC多层纳米复合薄膜。用X射线光电子能谱仪(XPS)对薄膜的组成成分进行分析。利用透射电子显微镜（TEM）、拉曼光谱、电流-电压曲线研究Fe纳米颗粒嵌埋对薄膜的微观结构及电学性能的影响。XPS和TEM表明,Fe纳米颗粒周期性地均匀地嵌埋在碳薄膜中。拉曼光谱表明薄膜中的C为典型的类金刚石结构,Fe纳米颗粒促进芳香环式结构的形成,薄膜结构的有序度提高。电流 电压曲线表明,Fe纳米颗粒的嵌埋导致薄膜的室温电导率增加。     

Characteristics of ZnO-Cu-ZnO multilayer films on copper layer properties

ZnO/Cu/ZnO multilayers on glass with different copper layer thickness were prepared by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Cu. Different optimization procedure were used for good transparent conductive film. Several analytical tools such as spectrophotometer, scanning electron microscope (SEM), four point probes were used to explore the causes of the changes in electrical and optical properties. The sheet resistance of the structure was severely influenced by the deposition condition of both top ZnO and intermediate Cu layer. Effect of substrate temperature and annealing treatment on ZnO and Cu layer was analyzed. A sheet resistance of 10 Ω/sq and transmittance over 85% at 580 nm wavelength was achieved and could be reproduced by controlling the preparation process parameter. The results of an optimization condition of both oxide layers and metallic Cu layers are illustrated.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

激光功率密度对类金刚石膜结构性能的影响

采用大功率高重复频率准分子激光溅射热解石墨靶制备了类金刚石膜，研究了激光功率密度对膜的结构和性能的影响，分析了膜的紫外可见透过谱及膜的带隙结构、Raman谱和电子衍射图，结果表明随着激光功率密度由10⁸W／cm²提高至10¹⁰ W／cm²，膜的结构也由无定形非晶结构转变为纳米晶金刚石结构，膜 中的sp³键舍量及各项性能均有提高. 关键词： 激光功率密度 类金刚石膜 性能 结构