Structural and optical properties of CdTe-nanocrystals thin films grown by chemical synthesis

By mans of a chemical synthesis technique stoichiometric CdTe-nanocrystals thin films were prepared on glass substrates at 70 °C. First, Cd(OH)₂ films were deposited on glass substrates, then these films were immersed in a growing solution prepared by dissolution of Te in hydroxymethane sulfinic acid to obtain CdTe. The structural analysis indicates that CdTe thin films have a zinc-blende structure. The average nanocrystal size was 19.4 nm and the thickness of the films 170 nm. The Raman characterization shows the presence of the longitudinal optical mode and their second order mode, which indicates a good crystalline quality. The optical transmittance was less than 5% in the visible region (400–700 nm). The compositional characterization indicates that CdTe films grew with Te excess.     

Structural, electrical and optical properties of ZnO thin films deposited by sol-gel method

Thin films of intrinsic and Al-doped ZnO were prepared by the sol-gel technique associated with spin coating onto glass substrates. Zinc acetate dehydrate, ethanol and monoethanolamine were used as a starting material, solvent and stabiliser, respectively. Structural, electrical and optical characterizations of the films have been carried out. All films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction 〈0 0 2〉. The four-points technique was used to characterize thin films electrically. All films exhibit a transmittance above 80-90% along the visible range up to 650 nm and a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge 3.3 eV. Intense UV photoluminescence is observed for undoped and 1% Al-doped ZnO films.     

ZnO薄膜的结构特征及光学性能评价

利用金属有机物化学气相沉积(MOCVD)方法在Al2O3(0001)衬底上生长ZnO薄膜,通过改变衬底温度及生长舱压力,得到了各种不同表面形貌的ZnO薄膜.扫描电镜(SEM)用来对样品的形貌进行观察,当衬底温度及生长舱压力分别为400℃,40Pa和450℃,8Pa时,得到了纳米管及纳米墙结构.利用X射线衍射谱(XRD)、透射光谱及光致发光谱对样品的结构及光学性能进行评价.实验结果证明对于较高的生长温度和较低的生长舱压力所生长的样品具有较好的结晶质量.     

制备工艺对ZnO薄膜的结构与光学性质的影响

利用射频磁控反应溅射技术生长出具有高度晶面(0002)取向的ZnO外延薄膜。通过AFM、XRD、吸收光谱和荧光光谱等测试手段,分别研究分析了不同衬底、不同溅射气氛和退火对ZnO薄膜结构及光学性质的影响。研究表明,在200℃低温生长的硅基ZnO薄膜具有几百纳米的氧化锌准六角结构外形;当氧氩比为4:1(质量流量比)时,吸收谱激子峰最佳;退火后,激子峰(363 nm)加强,同时出现了402 nm的本征氧空位紫光发射。     

Structural and optical properties of thin In2O3 films produced by autowave oxidation

Cubic-phase In₂O₃ films are produced by the autowave oxidation reaction. Electron microscopy and photoelectron spectroscopy of the atomic profiles show that the samples are homogeneous over the entire area and throughout the thickness, with the typical grain size being 20–40 nm. The optical and electrical properties are studied for In₂O₃ films fabricated at different pressures in the vacuum chamber. In the wave-length range from 400 to 1100 nm, the transparency of the films was higher than 85%; the resistivity of the films was 1.8 × 10^?2 Ω cm.     

Structural, electrical and optical properties of zinc oxide produced by oxidation of zinc thin films

We have investigated the effects of oxidation temperature on the physical properties of polycrystalline zinc oxide thin films. Zinc thin films are oxidized at different temperatures in air. We have found that increasing the oxidation temperature deteriorates the preferred c-axis orientation. Also, increasing the oxidation temperature enlarges the crystal size and increases the number of needle-shaped crystals on the surface of the ZnO samples. By increasing the oxidation temperature, more than zinc melting point, tensile stresses start to build up in the films. Also by increasing temperature, sheet resistance of the films decreases, while photoluminescence intensity ratio (green to orange) increases. Increasing the oxidation temperature reduces the transparency of the films, too. It is proposed that either an increase in the number of oxygen vacancies or a decrease in the volume of grain boundaries, is responsible for the observed behavior of the films at higher oxidation temperatures.     

Structural and optical properties of nanocrystalline lead sulfide thin films prepared by microwave-assisted chemical bath deposition

Nanocrystalline PbS thin films have been successfully deposited on glass substrate from lead nitrate (Pb²⁺ ions) and thiourea (S^2? ions) precursors using MACB technique. The effects of molar concentration (0.02, 0.05, 0.075 and 0.1 M) on the structure and microstructure evolution were studied using X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy. The optical properties were investigated using UV–vis spectrophotometer. Crystal size values obtained from XRD were compared with these calculated using atomic force microscopy (AFM). The values of optical band gaps were found to decrease as the ion source molar concentration increase.     

Structural and optical properties of copper enriched ZnSe thin films prepared by closed space sublimation technique

Thin films of Zn_1?xCu_xSe (0.00≤x≤0.20) have been prepared by the closed space sublimation technique. Various structural and optical properties have been investigated through X-ray diffraction (XRD), atomic force microscopy (AFM), spectrophotometry, spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR). The effect of Cu concentration has been observed on the physical properties of Zn_1?xCu_xSe films for varying concentrations of copper. X-ray diffraction patterns show that the films are polycrystalline having preferential orientation along the (111) plane. Full width at half maximum (FWHM) values obtained by XRD show that FWHM decreases up to 10% copper concentration while an opposite trend has been observed beyond this concentration. RMS values calculated by AFM shows that the deposited films have smooth morphology; crystallinity improves with increasing Cu concentration and optimum results are shown with 10% Cu concentration. Various optical parameters i.e. absorption coefficient (α), extinction coefficient (k), reflectance (R), refractive index (n), optical conductivity (σ_op) and electrical conductivity (σ_el) have been determined using transmission spectra at different copper concentrations. From the reflection spectra it is observed that reflectance increases with the increase of copper concentration. The band gap energy has been determined using k spectra at various copper concentrations through spectroscopic ellipsometry. It is found that the band gap energy of the films decreases with the increase of copper concentration while dielectric constant increases. FTIR analysis revealed that the characteristic ZnSe bond stretching–vibrating mode occurs at 670.8 cm^?1.     

ZnO薄膜的结构与光学性能研究

采用sol-gel法在石英衬底上制备了ZnO薄膜,通过改变溶胶浓度、涂敷层数及退火温度,研究了ZnO薄膜的形貌、结构性能及光学性能。结果表明,薄膜具有六方纤锌矿结构,表面均匀致密,晶粒大小在25～35nm之间,Zn含量为0.8mol/L的溶胶经旋涂并在500℃下退火1h后可获得最高的可见光透射率,平均透射率约为94%。获得的ZnO薄膜的光学带隙在3.27～3.29eV之间。     

Facile deposition of ZnO:Cu films: Structural and optical characterization

Sol–gel technology has been applied for preparation of ZnO:Cu films. The proposed facile approach allows obtaining a wide variety of copper doped zinc oxide systems, revealing different structural and optical behaviors. The work presents structural and optical studies depending on Cu concentration and thermal treatments in the range of 500–800 °C. The structural analysis is performed by X-Ray diffraction (XRD). It reveals that small Cu addition enhances the film crystallization. Increasing copper concentration results in deterioration of ZnO:Cu crystallization. XRD study manifests no Cu oxide phases in ZnO:Cu film structure for lower Cu additions. For a specific higher copper concentration, an appearance of a small fraction of copper oxide is detected. Vibrational properties have been characterized by FTIR spectroscopy. The effect of the copper introduction into ZnO reveals a slight change of optical properties compared to ZnO films for certain Cu ratios. ZnO:Cu films with higher copper contents manifest different optical behaviors with very high transparency in spectral visible range.     

Structure and optical properties of SiN x : H films with Si nanoclusters produced by low-frequency plasma-enhanced chemical vapor deposition

The SiN _x : H films with compositions differently deviating from the stoichiometric proportion are produced by low-frequency plasma-enhanced chemical vapor deposition at the temperatures 100 and 380°C. Deviations from the stoichiometric composition are varied by varying the ratio between the ammonia and monosilane fluxes from 0.5 to 5. The films are studied by ellipsometry, Raman spectroscopy, infrared absorption spectroscopy, and luminescence measurements. In the SiN _x : H films (x < 4/3), amorphous silicon clusters were found. According to estimations, only a small fraction of excess silicon coalesces into clusters, and an increase in the substrate temperature stimulates clustering. It is found that, with increasing the content of excess silicon in the films, the photoluminescence peak shifts to longer wavelengths.     

Structural and optical properties of the polycrystalline ZnO films synthesized via oxidative annealing of ZnSe/YSZ heterostructures

We synthesized polycrystalline ZnO films via oxidative annealing of ZnSe/yttria-stabilized zirconia (YSZ) heterostructures and investigated the influence of the processing conditions on their structural and optical properties. While ZnO films synthesized using low-temperature annealing (500-600 °C) did not show any preferential orientation, highly textured films were obtained at high temperatures (700-800 °C). In addition, we demonstrated that prolonged high-temperature annealing (3 h at 800 °C) effectively eliminated point defects, as was evident from the increased band edge to deep-level emission intensity ratio.     

Sol-gel-derived ZnO/Cu/ZnO multilayer thin films and their optical and electrical properties

Sol-gel preparation of transparent conducting ZnO/Cu/ZnO multilayer thin films has been investigated. CuO thin films were deposited on glass substrates via a dip-coating method. The CuO thin films were further subjected to reductive annealing in hydrogen to form highly conductive Cu thin films with sheet resistances as low as 10 Ω/□. ZnO/Cu/ZnO multilayers were successfully prepared in a similar way by reducing ZnO/CuO/ZnO. The sheet resistance of the ZnO/Cu/ZnO multilayer thin films is about 10 kΩ/□, which is much higher than that of the pure Cu thin films. The formation of large discrete Cu crystallites in the multilayers explains the poor electrical conductivity of the sol-gel-derived ZnO/Cu/ZnO multilayers.     

Structural,optical and dielectric properties of HfSiO films prepared by co-evaporation method

HfSiO dielectric films were prepared on Si substrate by the co-evaporation method. The chemical composition, crystalline temperature, optical and electrical properties of the compound film were investigated. X-ray photoelectron spectroscopy analysis illustrated that the atom ratio of Hf to Si was about 4:1 and Hf–Si–O bonds appeared in the film. The X-ray diffraction analysis revealed that the crystalline temperature of the film was higher than 850 °C. Optical measurements showed that the refractive index was 1.82 at 550 nm wavelengths and the optical band gap was about 5.88 eV. Electrical measurements demonstrated that the dielectric constant and a fixed charge density were 18.1 and 1.95×10¹² cm⁻² respectively. In addition, an improved leakage current of 7.81 μA/cm² at the gate bias of −3 V was achieved for the annealed HfSiO film.     

Modification of electrical and optical properties of ZnO films under ultraviolet irradiation

The effect of ultraviolet radiation of polycrystalline zinc oxide films (with a thickness of 200 nm) on their resistivity, transparency, and luminescence in the visible and violet spectral regions is studied. It is shown that, under irradiation of the films in air and vacuum, the conductivity, transmittance, and edge luminescence intensity increase with characteristic times of about 100 min. It is established that the corresponding processes controlled by desorption of oxygen atoms and molecules from the surface of nanocrytals in the ZnO films are reversible.     

Dependence of electrical and optical properties of ZnO films on substrate temperature

ZnO films were prepared by filtered cathodic vacuum arc technique with Zn target at different substrate temperatures. The crystallinity is enhanced with increasing substrate temperature and preferably oriented at (1 0 3) direction when the substrate temperature is higher than 230°C. The PL emission corresponding to the exciton transition at 3.37 eV can be observed at room temperature, which indicates that high-quality films have been obtained by this technique. The Hall mobility, which increases with substrate temperature, is dominated by grain boundary scattering.     

Effect of deposition time on optical and luminescence properties of ZnS thin films prepared by photo assisted chemical deposition technique

Photo assisted chemical deposition method (PCD) is a new procedure for the deposition of compound semiconducting materials which is less explored. In this method the deposition is carried out with the irradiation of UV light on the reaction bath. PCD scores advantages for its low cost, use of flexible substrates and capability of large area deposition compared to other chemical methods like chemical bath deposition (CBD), electro chemical deposition (ECD), etc. Zinc sulfide films have been deposited on glass substrate by aqueous alkaline solution comprised of zinc nitrate, hydrazine hydrate, ammonium nitrate, ammonia and thiourea. The samples were prepared under UV illumination for different durations and characterized. The thickness of the samples increases with the deposition time. XRD patterns revealed the crystalline nature of samples with more number of dips. Optical study showed a low absorbance and constant transparency throughout the visible region disclosing the stiochiometric nature of the film. Obtained band gap energies were in good agreement with the theoretical value. Photoluminescence spectra showed two blue emission bands around 450 and 470 nm, and the intensity was found to depend on the thickness of the films.     

ZnO:Ag薄膜的制备及其光学性能研究

采用蒸镀与氧化二步法,以高纯混合金属Zn:Ag作蒸发源,在石英衬底上沉积Zn:Ag金属薄膜,经不同热氧化处理生长Ag掺杂ZnO薄膜。结果显示,以Ag含量为质量分数3%的蒸发源沉积的Zn:Ag薄膜经500℃氧化后,生成的ZnO:Ag薄膜在380 nm附近出现很强的近带边紫外发光峰,在438~470 nm附近出现较弱的深能级缺陷发光峰,该薄膜在360 nm有接近垂直的吸收边,其载流子浓度为1.810×1021cm–3,表现出p型导电特性和较好的光学质量。     

Structural,optical and photocatalytic properties of ZnO nanoparticles modified with Cu

ZnO and ZnO modified with Cu nanoparticles have been prepared by a simple forced hydrolysis method. The concentration of Cu incorporated in ZnO ranged from 1% to 5% by atomic weight, and the influence of Cu concentration on the physical properties of ZnO and the relation to the photocatalytic performance has been investigated. The prepared ZnO and ZnO:Cu samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and UV–vis transmittance spectroscopy. The results show that the ZnO nanomaterial was crystalline with the hexagonal wurtzite structure, with the preferential orientation of the grains along the (101) plane. The average grain size for samples with 1–5% Cu was in the range of 11–29 nm. The ZnO nanoparticles annealed at 420 °C showed an increased photocatalytic activity for the decomposition of methylene blue.     

Structural and optical properties of CdS/PEO nanocomposite solid films

In this paper solution mixing and casting of Cd(NO₃)₂·4H₂O and poly(ethylene oxide) (PEO) at different molar ratios (1:100–1:600) followed by hydrogen sulfide treatment were employed to fabricate solid films of cadmium sulfide (CdS)/polyethylene oxide (PEO) nanocomposites. The nanocomposites were found to exhibit uniform distribution of CdS nanoparticles in the polymer matrix without any additional capping agent. Systematic investigations on the role of PEO on the optical properties of CdS are presented. The optical properties of the composites examined by UV–vis absorption spectroscopy show that the band gap of CdS nanoparticles increases from 2.45 eV to 2.54 eV with decreasing concentration of CdS in PEO films. X-ray diffraction pattern shows the broadening in shape of the PEO peaks which is induced by the CdS particles in PEO matrix. The CdS particle sizes ranging from 10 to 20 nm are clearly seen in a transmission electron microscope (TEM). The X-ray photoelectron spectroscopic studies (XPS) also confirm the presence of CdS in PEO. Fourier transform infrared spectroscopy studies using attenuated total reflectance (FTIR-ATR) indicate the influence of Cd²⁺ ion on C–O–C stretching in PEO and confirm the presence of CdS nanoparticles within PEO. Photoluminescence spectroscopy (PL) shows the broad emission due to the presence of surface trapped carrier states.