Structural properties of the titanium dioxide thin films grown by atomic layer deposition at various numbers of reaction cycles

A dependence of structural properties of TiO₂ films grown on both Si- and Ti-substrates by atomic layer deposition (ALD) at the temperature range of 250-300 °C from titanium ethoxide and water on the number of reaction cycles N was investigated using Fourier-transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). TiO₂ films grown on both Si- and Ti-substrates revealed amorphous structure at low values of N < 400. However, an increase of N up to values 400-3600 resulted in the growth of polycrystalline TiO₂ with structure of anatase on both types of substrates and according to XRD-measurements the sizes of crystallites rose with the increase of N. The maximum anatase crystallite size for TiO₂ grown on Ti-substrate was found to be on ∼35% lower in comparing with that for TiO₂ grown on Si-substrate. A use of titanium methoxide as a Ti precursor with the ligand size smaller than in case of titanium ethoxide allowed to observe an influence of the ligand size on both the growth per cycle and structural properties of TiO₂. The average growth per cycle of TiO₂ deposited from titanium methoxide and water (0.052 ± 0.01 nm/cycle) was essentially higher than that for TiO₂ grown from titanium ethoxide and water (0.043 ± 0.01 nm/cycle). Ligands of smaller sizes were found to promote the higher crystallinity of TiO₂ in comparison with the case of using the titanium precursor with ligands of bigger sizes.     

Photocatalytic properties of TiO2 thin films obtained by glancing angle deposition

Titanium dioxide (TiO₂) thin films with different nanostructures such as nano-particles and separated vertical columns were grown by glancing angle deposition (GLAD) in an electron beam evaporation system. The photocatalytic properties of grown TiO₂ films with different deposition angles and different annealing temperatures were evaluated by following decomposition of methyl orange under ultraviolet (UV) light irradiation. The results suggest that increased surface area due to the GLAD process could improve the photocatalytic properties of TiO₂ films.     

Influence of glucose on the structural and optical properties of ZnO thin films prepared by sol-gel method

In this work, ZnO thin films were prepared by sol-gel method on glass substrates followed by calcinations at 500 °C for an hour. The effect of glucose on the structure and optical properties of the films was studied. The structural characteristics of the samples were analyzed by X-ray diffractometer (XRD) and atomic force microscope (AFM). The optical properties were studied by a UV-visible spectrophotometer. The results show that some of the prepared ZnO thin films have a high preferential oriented c-axis orientation with compact hexagonal wurtzite structure due to a proper amount of glucose introducing. After introducing the glucose additive in ZnO colloids, the intensity of (002) peak, the transmittance, and the optical band gap of the ZnO thin films increases because of the enhanced ZnO crystallization. On the contrary, the absorbance, the film thickness, and the surface root-mean-square (RMS) roughness of the ZnO thin films decreases. The glucose additive could not only improve the surface RMS roughness and microstructure of ZnO thin films, but also enhance the transmittance and the energy band gap more easily.     

Nanocrystalline formation and optical properties of germanium thin films prepared by physical vapor deposition

Amorphous and nanocrystalline germanium thin films were prepared on glass substrates by physical vapor deposition (PVD). The influence of thermal annealing on the characteristics of the Ge thin films has been investigated. X-ray diffraction (XRD) and SEM show amorphous structure of films deposited at room temperature. After thermal annealing, the crystallinity was improved when the annealing temperature increases. The Ge thin films annealed at different temperatures in air were nanocrystalline, having the face-centered cubic structure with preferred orientation along the 〈1 1 1〉 direction. The nanostructural parameters have been evaluated by using a single-order Voigt profile analysis. Moreover, the analysis of the optical transmission and reflection behavior was carried out. The values of direct and indirect band gap energies for amorphous and nanocrystalline phases are 0.86±0.02, 0.65±0.02 and 0.79±0.02, 0.61±0.02 eV, respectively. In addition, the complex optical functions for the wavelength range 600-2200 nm are reported. The refractive index of the nanocrystalline phase drops from 4.80±0.03 to 2.04±0.02, and amorphous phase changes from 5.18±0.03 to 2.42±0.02 for the whole wavelength range. The dielectric functions ε₁ and ε₂ of the deposited films were recorded as a function of wavelength within the range from 600 to 2200 nm.     

Spectroscopic study of an atmospheric pressure plasma generated for the deposition of titanium dioxide thin films

TiO₂ thin films are applied in various domains, e.g. air or water purification, self-cleaning surfaces etc. The deposition of titanium dioxide at industrial scale remains challenging. Atmospheric pressure plasma chemical vapor deposition methods are currently developed to provide an easy and viable method for deposition at industrial scale. Even though those methods lead to promising applicative coatings their formation mechanisms remain poorly investigated. In order to investigate the effect of the plasma parameters, i.e. plasma power and introduction of oxygen, on the plasma chemistry, optical emission spectroscopy (OES) is employed to monitor the various species present in the discharge. X-ray Photoelectron Spectroscopy (XPS) analyses of the deposited thin films are carried out and show that by either decreasing the plasma power or introducing oxygen the carbon impurities in the layer can be reduced. By comparing OES and XPS data, the ratio of carbon containing species (CH and C₂) to oxygen, i.e. I_CH/I_O or I_C2/I_O, in the discharge is shown to be related to the carbon/oxygen composition ratio in the layer.     

脉冲偏压电弧离子镀TiO2薄膜的力学与光学性能

用脉冲偏压电弧离子镀技术在玻璃基片上制备均匀透明的TiO₂薄膜.利用X射线衍射仪、原子力显微镜、扫描电子显微镜、紫外-可见透射光谱仪和纳米压痕仪等手段,对不同脉冲负偏压下合成薄膜的相结构、微观结构、表面形貌、力学和光学性能进行表征.结果表明，沉积态薄膜为非晶态.脉冲负偏压对薄膜性能有明显的影响.随偏压的增加，薄膜厚度、硬度和弹性模量均先增大后减小，前者峰值出现在100—200 V负偏压范围，后两者则在250—350V范围.300 V负偏压时薄膜硬度最高，薄膜达到原子级表面光滑度，均方 关键词： 2薄膜')" href="#">TiO₂薄膜 脉冲偏压电弧离子镀 硬度 折射率     

Photoluminescence properties of Eu-doped ZnO films grown by sputtering-assisted metalorganic chemical vapor deposition

Photoluminescence (PL) properties of Eu-doped ZnO (ZnO:Eu) grown by a sputtering-assisted metalorganic chemical vapor deposition technique were investigated. In PL measurements at 300 K, the samples annealed at 600 °C for 30 min showed clear red-emission lines due to the intra-4f shell transition of ⁵D₀→⁷F_J (J=0–4) in Eu³⁺. In photoluminescence excitation (PLE) spectra, the PL was observed under the high-energy excitation above the band-gap energy of ZnO (indirect excitation) and the low-energy excitation resonant to the energy levels of ⁷F₀–⁵D₃ and ⁷F₀–⁵D₂ transitions in Eu³⁺ (direct excitation). The PL lifetime under the indirect excitation was shorter than that under the direct excitations. These PL properties revealed that the energy transfer from ZnO host to Eu³⁺ was accompanied under indirect excitation.     

直接观测乙醇分子在TiO2(110)面的光催化过程

利用扫描隧道显微镜研究了在低温(80 K)下乙醇分子在TiO₂(110)面的光解离过程．在这种温度下,大部分乙醇分子都以分子吸附的形式吸附在表面五配位钛位．在紫外光照射之后,乙醇发生了光解离,两种不同的产物特征被探测到．使用针尖操控技术对其中一种产物特征进行了详细的分析,成功了解了它的构成,中间一个五配位钛位吸附的乙醛分子加上位于左右两个不同氧列的羟基构成了这种产物．接着实施了多次光照实验来进一步研究乙醇两种光解离产物特征之间的联系．     

Tailoring titanium dioxide by silver particles for photocatalysis

Titanium dioxide-silver (TiO₂–Ag) composites are synthesized by using the hydrothermal method with different weight ratios for photocatalyst applications. With the introduction of Ag, the composites exhibited absorbance in visible region, and the bandgap also decreased by 0.45 eV. The TiO₂–Ag composite with 5:7 ratio shows the best photocatalytic degradation of methylene blue, the highest photocurrent response, and the lowest electrochemical impedance, thus exhibiting the best photocatalytic performance. The introduction of Ag into TiO₂ retards the recombination time of the photo-generated electrons and holes as well as increases the charge transfer rate at interfaces of the composites.     

Raman-spectroscopy study of PbTiO3 thin films grown on Si substrates by metalorganic chemical vapor deposition

Raman spectra have been investigated in PbTiO₃ thin films grown on Si by metalorganic chemical vapor deposition. A large grazing-angle scattering technique was taken to measure the temperature dependence of Raman spectra below room temperature. All Raman modes in the thin films are assigned and compared with those in the bulk single crystal, a newA ₁(TO) soft mode at 104 cm^–1 was recorded which satisfies the Curie-Weiss relation ² =A(T _c –T). Intensities of theA ₁(1TO) andE(1TO) modes were anomalously strengthened with increasing temperature. Raman modes for the thin films exhibit remarkable frequency downshift and upshift which is related to the effect of internal stress.     

Investigation of BiFeO3 Multiferroic thin films prepared by metalloorganic chemical vapor deposition

BiFeO₃ thin oriented films are grown on SrTiO₃(001) and ZrO₂(Y₂O₃)(001) substrates by metalloorganic chemical vapor deposition (MOCVD) in the temperature range T= 500–800°C. Iron dipivaloylmethanate Fe(thd)₃ and triphenylbismuth Bi(C₆H₅)₃ are used as volatile precursors. It is shown that the high thermal stability of Bi(C₆H₅)₃ leads to significant deviations of the Bi: Fe ratio in the film from their ratio in the precursor flow. An increase in the residence time of the precursor flow in the reactor makes this ratio close to unity. The film-substrate epitaxial relations are determined. It is found that the film orientation on the ZrO₂(Y₂O₃)(001) substrate changes with increasing temperature. Optical second harmonic generation (SHG) measurements show the presence of ferroelectric ordering in the films. A significant decrease in the Curie temperature due to epitaxial stress is found. At the same time, the magnetization noticeably increases as compared to a BiFeO₃ single crystal.     

Physical properties of ZnS thin films prepared by chemical bath deposition

Zinc sulphide thin films are deposited on SnO₂/glass using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the structure of the films; the surface composition of the films is studied by Auger electrons spectroscopy, the work function and the photovoltage are investigated by the Kelvin method. Using these techniques, we specify the effect of pH solution and heat treatment in vacuum at 500 °C. The cubic structure corresponding to the (1 1 1) planes of β-ZnS is obtained for pH equal to 10. The work function (Φ_material − Φ_probe) for ZnS deposited at pH 10 is equal to −152 meV. Annealing at 500 °C increases Φ_m (by about 43 meV) and induces the formation of a negative surface barrier. In all cases, Auger spectra indicate that the surface composition of zinc sulphide thin films exhibits the presence of the constituent elements Zn and S as well as C and O as impurity elements.     

Structural and magnetic properties of thin epitaxial Fe films on (1 1 0) GaAs prepared by metalorganic chemical vapor deposition

Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (T_s) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at T_s between 200°C and 330°C were single crystals. Amorphous films were observed at T_s below 200°C and it was not possible to deposit films at T_s above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at T_s above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at T_s between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.     

Formation of the ferroelectric domains in epitaxial PbTiO3 thin films grown by metalorganic chemical vapor deposition

3 thin films have been prepared by metalorganic chemical vapor deposition under reduced pressure. The formation of ferroelectric domains in films grown on SrTiO₃ and LaAlO₃ substrates was investigated by synchrotron radiation and Rutherford backscattering spectroscopy. Single-domain (3000-Å thick) and multi-domain (4500-Å thick) PbTiO₃ films were produced on SrTiO₃. For multi-domain PbTiO₃ film, the c-domain presented epitaxial structure with its c-axis perpendicular to the substrate surface, while a-domains aligned four-fold symmetrically with c-domains by 2.79^° off the c-axis of c-domains. In the film, the measured lattice constants (a, b and c) of the a- and c-domains were different from each other, indicating that the films suffered a modulated strain during domain formation. In contrast, both the a and c domains of films on LaAlO₃ were alternatively aligned on substrate with the a-axis of the a-domain and the c-axis of c-domains perpendicular to the substrate surface. Two-dimensional distribution of these domains is proposed and the formation of these kinds of domains is discussed. The surface morphology and phase transition process of single and multi domain PbTiO₃ film on SrTiO₃ were studied by atomic force microscope (AFM) and high temperature X-ray diffraction, respectively. Received: 15 August 1996/Accepted: 21 January 1997     

Structure, electrical and optical properties of TiNx films by atmospheric pressure chemical vapor deposition

Titanium nitride (TiN_x) films with various nitride compositions (x) were prepared on glass substrates by atmospheric pressure chemical vapor deposition using TiCl₄ and NH₃ as precursors. The structural, compositional, electrical and optical properties of the films were studied and the results were discussed with respect to nitride composition. The results showed a linear relationship between the lattice constant and the nitride composition. Resistivity of the films was minimized near x = 1. All the TiN_x films exhibited a transmission band with a peak value of about 15% in the visible region (400-700 nm). As the wavelength increased to transition point (λ_T-R), the reflectance of the obtained films presented a sharp increase and then reached a high value of about 50% near 2000 nm. Moreover, the red-shift of transmission band and the transition wavelength (λ_T-R) with increasing the nitride composition were also discussed.     

Photocatalytic hydroxyapatite/titanium dioxide multilayer thin film deposited onto glass using an rf magnetron sputtering technique

Hydroxyapatite (HA)/titanium dioxide (TiO₂) thin film was deposited on glass using a radio frequency magnetron sputtering. X-ray diffraction (XRD), Fourier-transform infrared spectrometry, ultraviolet-visible spectroscopy and measurement of its photocatalytic activity by the decomposition of formaldehyde gas and the bacterial survival test of Escherichia coli (E. coli) cells were applied to characterize the film. After heat treatment (at 500 °C), XRD analysis of the HA/TiO₂ film showed a crystalline TiO₂ crystal structure with anatase phase. The transmittance of the HA/TiO₂ film decreased after the heat treatment, however, the average transmittance remained at 87% in the visible light range.In the decomposition of formaldehyde gas, the HA/TiO₂ film showed a higher decomposition rate than either the TiO₂ or the HA film alone. However, in the bacterial survival test, survival of cells on the HA/TiO₂ film was higher than that on the TiO₂ film, which indicates the HA/TiO₂ film has a lower bactericidal effect than the TiO₂ film alone.     

Effect of Er doping on optical band gap energy of TiO2 thin films prepared by spin coating

In order to evaluate the effect of Er doping in the range of 0–1.0 mol% on optical indirect band gap energy (E_g) of the film, the Er-doped TiO₂ (Er-TiO₂) thin films were spin-coated onto fluorine-doped SnO₂ coated (FTO) glasses. Glancing angle X-ray diffraction (GAXRD) results indicated that the films whose thickness was 550 nm consisted of pure anatase and FTO substrate. The anatase (101) TiO₂ peaks became broader and weaker with the rise in Er content. The apparent crystallite size decreased from 12 nm to 10 nm with increasing the amount of Er from 0 mol% to 1.0 mol%. UV–vis spectrophotometry showed that the values of E_g decreased from 3.25 eV to 2.81 eV with the increase of Er doping from 0 to 0.7 mol%, but changed to 2.89 eV when Er content was 1.0 mol%. The reduction in E_g might be attributed to electron and/or hole trapping at the donor and acceptor levels in the TiO₂ band structure.     

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.     

等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

利用感应耦合等离子体增强化学气相沉积法以Ar，He，N₂和B₂H₆为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析，发现B₂H₆完全被电离而N₂只是部分被电离.H₂和过量的N₂在等离子体中生成大量中性的H原子和活化的N^*₂，它们与表面的相互作用严重地阻碍了立方 关键词： 立方氮化硼薄膜 等离子体 质谱     

Nanoparticulate cerium dioxide and cerium dioxide-titanium dioxide composite thin films on glass by aerosol assisted chemical vapour deposition

Two series of composite thin films were deposited on glass by aerosol assisted chemical vapour deposition (AACVD)—nanoparticulate cerium dioxide and nanoparticulate cerium dioxide embedded in a titanium dioxide matrix. The films were analysed by a range of techniques including UV-visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive analysis by X-rays. The AACVD prepared films showed the functional properties of photocatalysis and super-hydrophilicity. The CeO₂ nanoparticle thin films displaying photocatalysis and photo-induced hydrophilicity almost comparable to that of anatase titania.