Effects of 1064 nm laser on the structural and optical properties of nanostructured TiO2 thin film

TiO₂ thin film has been widely used as photoelectrode in dye-sensitized solar cells. It can also be used in quantum dot synthesized solar cells. Study of its effects in different spectrum of light is important for its use in solar cells. We have reported effects of 1064 nm laser on the surface morphology, structural and optical properties of nanostructured TiO₂ thin film deposited on glass substrates using sol-gel spin coating technique. Q-Switched Nd:YAG pulsed laser at various power densities is used in this study. Surface morphology of the film is investigated using X-ray diffraction (XRD) and atomic force microscopy technique. The XRD pattern of as deposited TiO₂ thin film is amorphous and after laser exposure it became TiO₂ anatase structure. Atomic force microscopy of the crystalline TiO₂ thin film shows that the grain size increases by increasing laser power density. The calculations of the band gap are carried out from UV/Visible spectroscopy measurements with JASCO spectrometer. For laser power density of 25 MW/cm² there is an increase in the transmission and it decreases at the value of 38 MW/cm² and band gap decreases with increasing laser power density. Photoluminescence spectra of the crystalline TiO₂ thin film indicate two broad peaks in the range of 415 and 463 nm, one for band gap peak (415 nm) and other for oxygen defect during film deposition process.     

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     

Laser radiation effects on optical and structural properties of nanostructure CdSe thin film

Cadmium selenide (CdSe) thin films were deposited on a glass substrate using the thermal evaporation method at room temperature. The changes in the optical properties (optical band gap and absorption coefficient) after irradiation by TEA N₂ laser at different energies were measured in the wavelength range 190–800 nm using a spectrophotometer. It was found that the optical band gap is decreased after irradiating the thin films. The samples were characterized using X-ray diffraction (XRD), and the grain size of the CdSe thin film was calculated from XRD data, which was found to be 41.47 nm as-deposited. It was also found that grain size increases with laser exposure. The samples were characterized using a scanning electron microscope and it was found that big clusters were formed after irradiation by TEA N₂ laser.     

Molecular dynamics and experimental studies on deposition mechanisms of ion beam sputtering

Molecular dynamics (MD) simulation and experimental methods are used to study the deposition mechanism of ionic beam sputtering (IBS), including the effects of incident energy, incident angle and deposition temperature on the growth process of nickel nanofilms. According to the simulation, the results showed that increasing the temperature of substrate decreases the surface roughness, average grain size and density. Increasing the incident angle increases the surface roughness and the average grain size of thin film, while decreasing its density. In addition, increasing the incident energy decreases the surface roughness and the average grain size of thin film, while increasing its density. For the cases of simulation, with the substrate temperature of 500 K, normal incident angle and 14.6 × 10⁻¹⁷ J are appropriate, in order to obtain a smoother surface, a small grain size and a higher density of thin film. From the experimental results, the surface roughness of thin film deposited on the substrates of Si(1 0 0) and indium tin oxide (ITO) decreases with the increasing sputtering power, while the thickness of thin film shows an approximately linear increase with the increase of sputtering power.     

Thickness dependent surface microstructure evolution of bismuth thin film prepared by molecular beam deposition method

The evolution of surface microstructure on bismuth thin film deposited by molecular beam deposition method is investigated. Morphological, topographical, structural, and electrical property changes of the film with various thicknesses are studied by means of AFM, XRD, XRR, and 4-point probe. Drastic change of surface grain in shape, which transforms from round shape to polyhedral shape, is detected around 13–18 nm film thickness. Abrupt horizontal profile change of surface grain is verified with power spectral density (PSD) function. At this threshold thickness, the film shows very low roughness value and surface area ratio. Then both increase steeply as the film thickness surpasses the thickness. As the bismuth film is deposited thicker, it has textured structure and high roughness on surface. With increment of the thickness, the electrical sheet resistance of the films is significantly decreased. We explain this surface microstructure evolution on the bismuth film with the evolutionary selection model.     

Thermal analysis of magneto-optical thin films under laser irradiation

A two-dimensional finite-difference method was applied to study the thermal behavior of thin films irradiated by a pulsed Gaussian laser beam. In particular, the method was applied to rare-earth/transition-metal alloyed films for magneto-optic recording. The effects of film parameters (thermal conductivity, specific heat, absorption coefficient, and film thickness) and laser parameters (output power and pulse duration) on healing and cooling behavior were investigated extensively. The temperature profile of a film was sensitively dependent on these parameters. The results might be used to predict the recorded bit size and to optimize the laser parameters. For a given energy density of the laser beam, a large output power with a short pulse width was desirable for effective heating of a film. Heating by radial thermal diffusion became important with increasing thermal conductivity of a film. Therefore, to achieve high storage density, a film must have low thermal conductivity.     

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。     

Compatibility and optoelectronic of ZnSe nano crystalline thin film

We report the room temperature synthesis of zinc selenide (ZnSe) nano crystalline thin film on quartz by using a relatively simple and low cost closed space sublimation process (CSSP). The compatibility of the prepared thin films for optoelectronic applications was assessed by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), Raman spectroscopy, photoluminescence, and Fourier transform infrared spectroscopy (FT-IR). The XRD confirmed that the films were polycrystalline with the preferential orientation along the (111) plane corresponding to the cubic phase (2θ = 27.28 ). The AFM indicated that the ZnSe film presented a smooth and compact morphology with RMS roughness 19.86 nm. The longitudinal optical phonon modes were observed at 247 cm 1 and 490 cm 1 attributed to the cubic structured ZnSe. The Zn-Se stretching band was confirmed by the FT-IR. The microstructure and compositional analysis was made with the SEM. The grain size, dislocation density, and strain calculated were co-related. All these properties manifested a good quality, high stability, finely adhesive, and closely packed structured ZnSe thin film for optoelectronic applications.     

Modification of polycrystalline SnO2 and ZnO under the action of a high-power ion beam of nanosecond duration

The modification of polycrystalline oxides (SnO₂ and ZnO) under the action of a nanosecond high-power ion beam (HPIB) with current densities of 50–150 A/cm², which is accompanied by melting of initial particles of the surface layer, is investigated. It is established that submicron-sized particles of tetragonal SnO whose average size is 210 nm are formed on the SnO₂ surface irradiated by an ion beam with a current density of 150 A/cm². These particles have pronounced crystallographic faceting. When ZnO is irradiated by HPIBs with different current densities, a thin Zn film is formed in the sintered surface layer. Possible mechanisms of the observed conversions are discussed.     

Synthesis and characterization of nanostructured (Pb1− x Sr x )TiO3 thin films by a modified chemical route

The coating solutions of nanostructured (Pb_{1– x} Sr _x )TiO₃ (PST) thin films have been prepared by the sol–gel combined metallo-organic decomposition method. The coating solutions were deposited on Pt/Ti/SiO₂/Si substrates using a spin-coating technique with spinning speed of 4300 rpm and annealed at 650°C. The effect of Sr content in reducing the grain size and tetragonal distortion of PST films has been studied. The optimum conditions for crystalline phase formation in the films have been analyzed by thermogravimetric, differential thermal analysis and Fourier transform infrared spectroscopy. The phase and microstructure of the films were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD pattern shows that the PST thin films are crystallized into tetragonal structures without any impurity phase and the distortion ratio reduces with increasing Sr concentration. The AFM results indicate an increase in grain size with increasing annealing temperature of the film and reduction in grain size with increasing Sr concentration.     

Evaluation of probe lasers employed in optical diagnostics for phase transformation of thin films during excimer laser crystallization

The stability and reliability of probe laser is an important factor affecting the inspection of the phase transformation process of Si thin films during excimer laser crystallization using in-situ time-resolved optical measurements. The changes in 2D intensity profile, peak power density, and beam wander of the commonly used helium–neon (He–Ne) and diode laser are investigated experimentally. It is found that the peak power density of He–Ne laser is higher than that of diode laser, while the total power of He–Ne laser is lower than that of diode laser. Although the instability in the peak power density of He–Ne laser will increase with increasing the operation time, the beam stability of He–Ne laser is better than that of diode laser. For long-time operation (>24 h) of optical measurements, the diode laser is a good candidate of probe laser. Conversely, the diode laser is suitable for the short-time operation (<24 h) of optical measurements because the beam-wander is higher than that of He–Ne laser.     

Investigation of transmittance property of Palladium thin films fabricated by pulsed laser deposition with polarization using single layer model

In this paper the structure, morphology and optical properties of Pd thin films deposited on glass substrate by pulse laser deposition technique at two different substrate temperatures have been investigated. The fabricated films were characterized by various methods such as XRD, AFM, and UV-vis-NIR spectroscopy. The influence of surface roughness and angle of incidence with p polarization was investigated experimentally by optical property of palladium (Pd) thin films of two different thicknesses and rms roughness from transmission measurement in the visible spectral range. It has been shown that the experimental transmittance spectra agree well with their theoretical values for absorbing Pd thin film. The transmittance of thin film increases with increase in incident angle for the same sample.     

Influence of nitrogen and magnesium doping on the properties of ZnO films

Undoped ZnO and doped ZnO films were deposited on the MgO(111) substrates using oxygen plasma-assisted molecular beam expitaxy. The orientations of the grown ZnO thin film were investigated by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction(XRD). The film roughness was measured by atomic force microscopy, which was correlated with the grain sizes determined by XRD. Synchrotron-based x-ray absorption spectroscopy was performed to study the doping effect on the electronic properties of the ZnO films, compared with density functional theory calculations.It is found that, nitrogen doping would hinder the growth of thin film, and generate the NOdefect, while magnesium doping promotes the quality of nitrogen-doped ZnO films, inhibiting(N_2)Oproduction and increasing nitrogen content.     

On the structural and optical properties investigation of annealed Zn nanorods in the oxygen flux

Zn nano rods were produced on glass substrates using oblique angle deposition method at different deposition angles. For oxidation, the samples were placed in a furnace under oxygen flux. AFM and FESEM images were used to morphology analysis of the structures. The results showed that with increasing the angle of deposition, the grain size decreases and the porosity of the structures increases. XRD pattern and XPS depth profile analysis were used to crystallography and oxide thickness investigations, respectively. The XRD results confirmed oxide phase formation, and the XPS results analyzed the oxide layer thickness. The result showed that as the deposition angle of the nanorods increases, the thickness of the oxide layer increases. The reason for the increase in the thickness of the oxide layer with increasing deposition angle was investigated and attributed to the increase in the porosity of the thin films. The optical spectra of the structures for p polarized light at 10° incident light angle were obtained using single beam spectrophotometer in the 300 nm to 1000 nm wavelengths. The results showed that the formed structures although annealed in oxygen flux, tend to behave like metal. To calculate the optical constant of the structures, the reverse homogenization theory was used and the void fraction and complex refractive index of the structures were obtained. Finally, by calculating permittivity and optical conductivity of the structures, their changes with the deposition angle were investigated.     

Growth and structure of Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 thin films prepared by pulsed laser deposition technique

Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5TiO₃ (BNKLT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition (PLD) technique. The films prepared were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effects of the processing parameters, such as oxygen pressure, substrate temperature and laser power, on the crystal structure, surface morphology, roughness and deposition rates of the thin films were investigated. It was found that the substrate temperature of 600 °C and oxygen pressure of 30 Pa are the optimized technical parameters for the growth of textured film, and all the thin films prepared have granular structure, homogeneous grain size and smooth surfaces.     

High Reflection Ge_(0.45)Te_(0.55) Recording Films

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Analysis of laser induced thermal mechanical relationship of HfO_2/SiO_2 high reflective optical thin film at 1064 nm

A numerical model is developed for the calculation of transient temperature field of thin film coating induced by a long-pulsed high power laser beam. The electric field intensity distribution of HfO2/Si02 high reflective （HR） film is investigated to calculate the thermal field of the film. The thermal-mechanical relationships are discussed to predict the laser damage area of optical thin film under long pulse high energy laser irradiation.     

原子力显微镜对TeOx薄膜中短波长静态记录点结构的分析

以真空蒸镀法在K9基底上制备了TeOx单层薄膜,采用特定的定位方法,使用原子力显微镜对不同记录功率下薄膜中短滤长静态记录点（514．5nm)的结构进行了分析。实验结果表明薄膜具有良好的记录灵敏性,在记录功率1．5mW时就可产生较高的反射率对比度,记录点具有明显的凹陷和凸起结构,随着记录功率的提高,凹陷和凸起增强,记录点增大。记录点的形态结构和记录前后反射率对比度是直接相关的。研究揭示了原子力显微镜在提高薄膜存储特性如信噪比,存储密度等方面的分析功能。     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

Effect of substrate temperature on structural, optical and electrical properties of pulsed laser ablated nanostructured indium oxide films

Nanocrystalline indium oxide (INO) films are deposited in a back ground oxygen pressure at 0.02 mbar on quartz substrates at different substrate temperatures (T_s) ranging from 300 to 573 K using pulsed laser deposition technique. The films are characterized using GIXRD, XPS, AFM and UV-visible spectroscopy to study the effect of substrate temperature on the structural and optical properties of films. The XRD patterns suggest that the films deposited at room temperature are amorphous in nature and the crystalline nature of the films increases with increase in substrate temperature. Films prepared at T_s ≥ 473 K are polycrystalline in nature (cubic phase). Crystalline grain size calculation based on Debye Scherrer formula indicates that the particle size enhances with the increase in substrate temperature. Lattice constant of the films are calculated from the XRD data. XPS studies suggest that all the INO films consist of both crystalline and amorphous phases. XPS results show an increase in oxygen content with increase in substrate temperature and reveals that the films deposited at higher substrate temperatures exhibit better stoichiometry. The thickness measurements using interferometric techniques show that the film thickness decreases with increase in substrate temperature. Analysis of the optical transmittance data of the films shows a blue shift in the values of optical band gap energy for the films compared to that of the bulk material owing to the quantum confinement effect due to the presence of quantum dots in the films. Refractive index and porosity of the films are also investigated. Room temperature DC electrical measurements shows that the INO films investigated are having relatively high electrical resistivity in the range of 0.80-1.90 Ωm. Low temperature electrical conductivity measurements in the temperature range of 50-300 K for the film deposited at 300 K give a linear Arrhenius plot suggesting thermally activated conduction. Surface morphology studies of the films using AFM reveal the formation of nanostructured indium oxide thin films.