Irradiation effects in MgF2 coatings on Si and GaAs substrates

Heavy-particle irradiation effects have been investigated as a potential method for inducing ion-beam mixing and thereby improving the adhesion between a thin-film MgF₂ anti-reflection coating and substrates with optical or electro-optical applications. The nature of the ion-beam-induced alterations of MgF₂ films deposited on Si or GaAs substrates and subsequently irradiated with 210 keV Xe⁺ ions was studied using Rutherford backscattering and scanning electron microscopy. The results are compared with those obtained in previous studies of MgF₂ films deposited on LiF substrates.     

Auger-free luminescence of the BaF2:Sr, BaF2:MgF2 and CsBr:LiBr crystals under excitation of VUV photons and high-energy electrons

The emission spectrum, the time dependence of the luminescence, the excitation spectrum and the reflectance spectrum have been measured for the pure BaF₂ crystal, the BaF₂:Sr crystals with Sr⁺⁺ concentrations of 2 and 5 mol%, the BaF₂:MgF₂ crystal with a mole mixing ratio of 1:2, and the pure CsBr crystal and the CsBr:LiBr crystal with a mole mixing ratio of 1:1. The measurements have been made by using synchrotron orbital radiation and high-energy electrons produced by gamma-rays. It is shown that the BaF₂, the BaF₂:Sr and the BaF₂:MgF₂ crystals have the Auger-free luminescence having decay times around 0.90 ns. The slow and fast luminescence components of the BaF₂ crystal are suppressed by introduction Sr⁺⁺ and Mg⁺⁺ ions. It is, however, clearly seen that the suppression of the slow component is more effectively occurring than that of the fast component, especially in the BaF₂:MgF₂ crystal. By analyzing the Auger-free luminescence spectrum, it is shown that the valence band widths are 2.7 ± 0.3 eV, 2.7 ± 0.3 eV and 4.2 ± 0.3 eV and the band-gap energies are 11.1 ± 0.3 eV, 11.1 ± 0.4 eV and 11.9 ± 0.4 eV for BaF₂, BaF₂:Sr and BaF₂:MgF₂ crystals, respectively. The introduction of LiBr into CsBr has resulted in a significant enhancement in the luminescence intensity, attaining 40 times larger intensity than that of CsBr crystal at room temperature, due to the suppression of the non-radiative relaxation of the outer-most core holes due to the absorption induced by the Urbach effect. The observations of the increases in the band gap-energy, the exciton energy and the decay time of the CsBr:LiBr crystal compared with those of the CsBr crystal support the argument given in the present study regarding the suppression of the Urbach effect in the CsBr:LiBr crystal. The decay times observed are 0.20 ± 0.05 ns and 0.90 ± 0.06 ns for CsBr and CsBr:LiBr crystals, respectively.     

High-resolution and analytical transmission electron microscopy of epitaxial YBa2Cu3O7−x thin films and YBa2Cu3O7/PrBa2Cu3O7 superlattices

Transmission electron microscopy (TEM) studies of epitaxial YBa₂Cu₃O_7−x thin films and YBa₂Cu₃O₇/PrBa₂Cu₃O₇ superlattices are summarized. High-resolution imaging of cross-sections and plan views and energy-dispersive X-ray microanalysis and electron energy loss spectroscopy in the transmission electron microscope were the methods applied. In the first section results on YBa₂Cu₃O_7−x thin films With varying oxygen stoichiometry deposited onto SrTiO₃ are discussed. Then, YBa₂Cu₃O₇/PrBa₂Cu₃O₇ superlattices deposited onto SrTiO₃ and MgO are investigated. Finally, an interface analysis of high-quality YBa₂Cu₃O_7−x thin films deposited onto sapphire with yttrium-stabilized zirconia buffer layers is presented.     

Photochemical synthesis and characterization of Bi2S3 nanofibers

Bismuth sulfide (Bi₂S₃) nanofibers have been successfully prepared by a photochemical method from an aqueous solution of bismuth nitrate (Bi(NO₃)₃) and thioacetamide (TAA) in the presence of complexing agents of nitrilotriacetic acid (NTA) at room temperature. It was found that the irradiation time, the pH of the solution, and the species of complexing agents play important roles in the morphology control of the bismuth sulfate (Bi₂S₃) nanomaterials. The nanofibers were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectra (XPS), and UV-Visible absorption spectra (UV-Vis). Probable mechanisms for the photochemical formation of Bi₂S₃ nanofibers in aqueous solutions are proposed. The photochemical method is a convenient approach for controlling the shape for other metal sulfide semiconductor nanocrystals.     

Line-focus acoustic microscopy measurements ofNb2O5/MgO and BaTiO3/LaAlO3thin-film/substrate configurations

Line-focus acoustic microscopy has been used to measure the phase velocities of surface acoustic waves on bare MgO and bare LaAlO₃ , and on Nb₂O₅/MgO and BaTiO₃/LaAlO₃ thin-film/substrate configurations. The thin films are polycrystalline materials. The substrates are anisotropic single-crystals. The measured angular variation of the surface acoustic wave velocities has been used to determine the elastic constants of MgO substrate and Nb₂O₅ thin-film. It has been assumed that the Nb₂O₅ films may be considered as essentially isotropic. The measurements for LaAlO₃ and BaTiO₃/LaAlO₃ show anomalies which are attributed to twinning in the LaAlO₃ substrate     

Microstructure and composition of MgF2 optical coatings grown on Si substrate by PVD and IBS processes

MgF₂ is a current material for the optical applications in the UV and deep UV range. Nevertheless, modern applications still require improvement of the optical and structural quality of the deposited layers. In the present work, the composition and microstructure of MgF₂ single layers grown on Si [100] substrate by physical vapour deposition (PVD) and ion beam sputtering (IBS) processes, were analyzed and compared. Experiments were carried out using X-ray photoelectron spectroscopy (XPS) in depth profile, grazing angle X-ray diffraction (XRD) and transmission electron microscopy (TEM). Both layers exhibited a good stoichiometry and a low level of contamination. The sample grown by IBS revealed a more homogeneous and regular columnar microstructure than the other one.     

Preparation and antibacterial behavior of Fe-doped nanostructured TiO2 thin films

Fe³⁺-doped nanostructured TiO₂ thin films with antibacterial activity were prepared on soda–lime–silica glass slides by using sol–gel technology. Water containing Escherichia coli K-12 with TiO₂ thin films in was exposed to low intensity fluorescent light and antibacterial efficiency was evaluated with spread plate techniques. The films are porous and have anatase phase. Iron ions increased luminous energy utilization as the absorption edge of the Fe³⁺-doped film has a red shift compared to that of the pure TiO₂ film in the UV–VIS absorption spectrum. The bacterial removal efficiency reached 95% at the optimum concentration of iron ion (about 0.5% (mol)) after 120 min irradiation. The antibacterial behavior of the doped TiO₂ films was explicitly observed using scanning electron microscopy and cell wall damage was found.     

Deposition and photoluminescence of sol–gel derived Tb:Zn2SiO4 films on SiO2/Si

Tb³⁺ doped Zn₂SiO₄ films have been deposited on SiO₂ buffered Si wafers by sol–gel method. The structures of these films have been investigated with X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results revealed that these films were composed of nanometer-size grains with a Willemite structure and had smooth surfaces. Photoluminescence measurements of the films showed a strong emission from ⁵D₄ to ⁷F₅ at 544 nm. The blue emission from ⁵D₃–⁷F_j was depressed because of cross-relaxation effect. The decay kinetics of the ⁵D₄–⁷F₅ green emission was studied and a best fitting was obtained by a double exponential function. The lifetime of the excited ⁵D₄ state is estimated to be 5.2 ms.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

Sputtered Ta2O5 antireflection coatings for silicon solar cells

Ta₂O₅ thin films were deposited onto monocrystalline silicon surfaces by magnetron reactive sputtering. When the Ta₂O₅ films are employed as antireflection coatings, the reflectance of the original silicon surface diminishes from about 30% to approximately 3%. At the same time, a very low absorption coefficient (less than 10³ cm^-1) for the Ta₂O₅ films below their fundamental absorption edge (hv < 4.2 eV) is obtained from reflectance and transmittance spectra of Ta₂O₅ deposited onto quartz substrates. Finally, the technique of reactive sputtering is considered from the point of view of preparing antireflection coatings for solar cells.     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

Investigation on the cross sensitivity of NO2 sensors based on In2O3 thin films prepared by sol-gel and vacuum thermal evaporation

In₂O₃ thin films have been prepared from commercially available pure In₂O₃ powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In₂O_3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In₂O₃ (HVTE) and nearly stoichiometric In₂O_3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO₂ gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO₂ the calculated sensitivities (S=R_g/R_a) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In₂O₃ films to CO and CH₄. Negligible H₂O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl₂ and 10 ppm NO. Only 1000 ppm C₂H₅OH has resulted to have a significant cross to the NO₂ response.     

铁电相BiFeO3对多铁复合薄膜CoFe2O4-BiFeO3铁磁性能的影响

为了研究铁电相BiFeO₃对复合薄膜磁性能的影响,在LaNiO₃ (LNO)缓冲层的Si (100)衬底上旋涂制备了含有0、6、9、10层等不同厚度BiFeO₃的层状CoFe₂O₄-BiFeO₃ (CFO-BFO) 多铁复合薄膜。采用XRD、SEM以及TEM对其结构和形貌进行了表征,采用振动样品磁强计测量磁性,研究了不同厚度BFO对复合薄膜磁性的影响。结果表明: CFO和BFO在异质结构薄膜中共存。缓冲层LNO和铁磁相CFO薄膜具有精细微观结构及明显界面。铁电相BFO的厚度对CFO-BFO复合薄膜的磁性能产生了很大影响。在含有不同层数铁电相BFO的复合薄膜中,含有9层BFO复合薄膜的饱和磁化强度最大,达到了230 emu·cm^-3,相比无铁电相BFO的薄膜,饱和磁化强度提高了18.6%。初步讨论认为: 随着铁电相BFO厚度的增加,CFO与BFO之间的应力传导引起了复合薄膜饱和磁化强度的提高。     

Density, thickness and interface roughness of SiO2, TiO2 and Ta2O5 films on BK-7 glasses analyzed by x-ray reflection

BK-7 glass with high surface quality and thin oxidic films (SiO₂, TiO₂, Ta₂O₅) deposited by ion plating (IP) and reactive evaporation (RE) on BK-7 glass have been characterized by means of X-ray reflectivity. The quantities determined with great precision are the film thickness, the film density and the interface roughness. It turned out that the IP films are more dense and smoother than the corresponding RE films. The ion-plated layers have a thin surface layer on top of the oxide which is reduced in density, whereas for the RE films there is an intermediate layer with an enhanced density between the glass substrate and the oxide.     

Grain dependence of ferroelectric domain switching on SrBi2Ta2O9 thin films observed by Kelvin probe force microscope

We have studied grain-shape dependence of Kelvin probe force microscopy of SrBi₂Ta₂O₉ thin films on epitaxial La_0.5Sr_0.5CoO₃/LaAlO₃ substrates. By changing the growth condition in pulsed laser deposition, we have grown the SrBi₂Ta₂O₉ thin films with various grain shapes. The shape and the orientation of SrBi₂Ta₂O₉ the thin films with various growth conditions have been analyzed by X-ray diffraction and scanning electron microscope. The large number of the long rectangular grains was observed accompanied with relatively larger (220) peaks than other peaks. From the Kelvin probe force microscope study, it has been observed that the long rectangular grains showed characteristics of easy ferroelectric domain switching at a low writing bias and weaker influence of surface charges.     

Electrochemical deposition and oxidation of CuFe2 alloy: a new method to deposit CuFe2O4 thin films at room temperature

The objective of this research work is to develop an electrochemical process to deposit polycrystalline copper iron oxide (CuFe₂O₄) films on different conducting substrates at room temperature (27°C). Cathodic Electrodeposition of CuFe₂ was carried out on various conducting substrates in galvanostatic mode. The composition of alloy was determined using atomic absorption spectroscopy (AAS) technique. The electrodeposited CuFe₂ alloy films were electrochemically oxidized (anodized) in aqueous KOH electrolyte at room temperature. The structural studies of oxide films were carried out using X-ray diffraction and IR absorption techniques. For surface morphological studies, optical microscopy and scanning electron microscopy (SEM) techniques were used.     

氟化镁基底上HfO2中间层对Al2O3薄膜微观组织和力学性能的影响

采用电子束蒸镀技术在氟化镁基底上制备了单层Al₂O₃薄膜和含有HfO₂中间层的HfO₂/Al₂O₃双层薄膜。在空气中对所制备的薄膜进行1 h 600℃的退火处理。通过掠入角X射线衍射仪(GIXRD)、场发射扫描电镜(FE-SEM)、傅里叶变换红外光谱仪(FTIR)、纳米压痕和划痕法对薄膜的微观结构、红外透过率和力学性能进行了表征。结果表明: 退火处理后HfO₂/Al₂O₃双层薄膜中形成了一层树枝状的新层, 这种新层的硬度大于17.5 GPa。这种高硬度的新层能够保护氟化镁基底不被划伤。从GIXRD图谱中只能找到单斜相HfO₂的衍射峰, 而Al₂O₃薄膜仍然保持非晶态。从这些结果中可以推断出HfO₂从非晶态向单斜相的转变促进了这种树枝状新层的产生, 也正是这种新层提高了保护薄膜的力学性能。     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

WO3/TiO2复合薄膜的制备及其电致变色性能

使用水热法在掺氟SnO₂涂覆的导电玻璃（FTO）基板上生长TiO₂纳米线,随后在TiO₂纳米线上采用水热法生长WO₃纳米线,制备出WO₃/TiO₂复合薄膜。通过循环伏安法（CV）、计时电流法（CA）、计时电量法（CC）等电化学测试技术研究了WO₃/TiO₂复合薄膜的电致变色性能;采用紫外分光光度计对薄膜的着色﹑漂白状态的响应时间进行测试。通过以上测试,计算得到了薄膜的循环稳定性﹑光调制﹑着色效率和切换时间（Y和X）等参数。结果显示WO₃/TiO₂复合薄膜的电致变色性明显提高,其中WO₃/TiO₂复合薄膜可逆性增加了6%,着色效率提高了40.96 cm2/C。