Structural and electrochromic properties of TiO2 thin films prepared by metallorganic chemical vapor deposition

Titanium dioxide thin films were deposited by Metallorganic Chemical Vapor Deposition at substrate temperatures ranging from 250 °C to 450 °C over soda lime glass and indium tin oxide coated glass substrates. X-ray diffraction studies show that films have a crystalline anatase structure at all the deposition temperatures. Particle size decreases and texture changes with the increase in substrate temperature. X-ray photoelectron spectroscopy confirms the appearance of a new well resolved state in the core level of Ti 2p spectrum shifted by 1.16 eV to lower binding energy due to the reduction of Ti^+ 4 to Ti^+ 3 upon litheation. Chronoamperometery, cyclic voltammetery and in situ UV-Vis spectrophotometeric studies were carried out on the prepared samples. Particle size and crystallinity control the electrochromic performance. The 350 °C film shows the highest ion storage capacity and the highest optical modulation along with an appreciable band gap broadening.     

Preparation of Al-Cu-Fe thin films by vapor deposition technique from a single source

In this paper, we report the formation of stable icosahedral Al-Cu-Fe quasicrystalline thin films by thermal vapor deposition techniques (indirect heating and e-beam heating) from a single source. Deposition of these films by a single-source indirect heating method, in the stable icosahedral phase, is reported for the first time. A direct comparison between the two different heating methods has been made. The final compositions of the prepared films with desired properties were found to be Al_62.9Cu_24.6Fe_12.5 (indirect heating method) and Al_63.1Cu_24.5Fe_12.4 (e-beam method), respectively. The resistivities of the films prepared by both methods were ∼2000 μΩ cm at room temperature and ∼4000 μΩ cm at 10 K.     

Manganese oxide thin films prepared by pulsed laser deposition for thin film microbatteries

Manganese oxide thin films with various oxidation states (MnO, Mn₃O₄ and Mn₂O₃) have been prepared by pulsed laser deposition using a Mn target at different oxygen partial pressures. The structural and morphological features of the as-deposited thin films are characterized by X-ray diffraction, Raman, field emission scanning electron microscopy (FESEM). The oxidation states of Mn in different thin films are investigated by X-ray photoelectron spectroscopy for both Mn 2p and 3s levels. It is found that the structure, surface morphology, and Mn oxidation state of the thin films can be tuned by oxygen partial pressure during the deposition. As anode for thin film lithium-ion microbatteries, the Mn₃O₄ thin film electrode exhibits the largest reversible capacity up to 800 mAh g⁻¹ with good cycling stability and excellent rate capability. The promising electrochemical performance of the Mn₃O₄ thin film electrode indicates the potential application of Mn₃O₄ thin film anode in all solid-state thin film microbatteries.     

Effects of sol aging on mesoporous silica thin films organization

Cetyltrimethylammonium bromide (CTAB) templated mesoporous silica thin films were deposited on glass slides by evaporation-induced self-assembly (EISA) process using a dip-coating method. The effects of sol aging on the mesophase structure of the thin films organization were investigated. Identification of the structures was accomplished by coupling X-ray diffraction (XRD) and transmission electron microscope (TEM) investigations, and corresponding sol was characterized by ²⁹Si solution state nuclear magnetic resonance (²⁹Si NMR) and UV-Vis spectrophotometer for studying the mesophase structure evolution. Results indicate that sol aging has great effects on the mesophase structure of the films organization, which includes degree of order and phase transformation of mesoporous silica thin films. To obtain a better understanding of the effects of sol aging on the mesophase structure, the theories of apparent mass fractal dimension and charge density matching were introduced to explain the self-assembly process.     

蒸发诱导自组装仿生合成高有序度三维六方介孔氧化硅薄膜

借鉴自然界生物矿化的形成机理,利用蒸发诱导自组装(EISA)的方法,以十六烷基三甲基溴化铵(CTAB)为结构导向剂,正硅酸乙酯(TEOS)为硅源,通过浸渍提拉在普通玻璃片上制备出高有序度、三维六方结构的介孔氧化硅薄膜,通过XRD、TEM、低温N2吸附/脱附等方法对薄膜进行了表征,并初步讨论了形成三维六方结构的机理.     

Phase composition of mixed ZnS-EuS thin films grown by metal organic chemical vapor deposition

The phase composition of the mixed ZnS-EuS films deposited from volatile dithiocarbamates has been studied using differential dissolution technique (chemical method of the phase analysis) and electron microscopy. Phase composition was found to depend on the Eu content in the films, that in turn depends on a flow density ratio of the Eu and Zn volatile precursors. A single-phase solid solution, Zn_0.998Eu_≤0.002S, was observed only for films with Eu content≤1 mol%, other films were found to be two-phase. For films with the Eu content between 2 and 16% and above 80%, impurity phases, EuS and ZnS, respectively, were detected by differential dissolution technique. They evolved as low-sized sulfide precipitates encapsulated in an organic coat. No impurity phases in the films of the same Eu content were noticed by X-ray technique and Raman spectroscopy. For the films with the Eu content between 16 and 80%, sulfide phases, ZnS and EuS, were found to be free from any organic coat, and structural methods as with differential dissolution technique were also capable of observing the phases. Conditions are given to prepare Eu doped ZnS films of good quality by MOCVD technique.     

Gold nanoparticles incorporated mesoporous silica thin films of varied gold contents and their well-tuned third-order optical nonlinearities

Gold nanoparticles (NPs) incorporated mesoporous silica thin films (MSTFs) of varied gold contents from 4.64 to 29.15 wt.% were synthesized through a refined chemical modification to the mesopore surface using different amounts of silane with amino end group. The microstructures of the composite thin films were characterized and the off-resonant third-order optical nonlinearities of the composite thin films were investigated by Z-scan technique at 1064 nm. The resultant composite thin films showed increased third-order optical nonlinear susceptibility (χ⁽³⁾) from 4.26 × 10⁻¹¹ to 9.24 × 10⁻¹⁰ esu at increased gold contents. The dependence of χ⁽³⁾ on gold content have been discussed, which can be described by an exponent function y = y₀ + Ae^−x/t when the gold contents of the composite thin films were below 30 wt.%.     

Poly-crystalline silicon thin films prepared by plasma-assisted hot-wire chemical vapor deposition

A combination of hot-wire chemical vapor deposition (HWCVD) and RF plasma, referred to as plasma-assisted HWCVD (P-HWCVD) was used to prepare poly-crystalline silicon (poly-Si) thin films. The effects of the plasma on the film properties were studied by varying the RF power (P_w) from 0 to 40 W. The results indicate that, compared with that of HWCVD samples, the film crystalline fraction (X_c) is enhanced at low P_w assistance, whereas it decreases at higher P_w. The uniformity of the film thickness is considerably improved by introducing plasma. It is also found that the porosity of the film, indirectly detected from infrared spectra, is much reduced. Auger analysis of the tantalum filament used in the P-HWCVD process shows much lower silicon contamination than that in HWCVD.     

Synthesis and characterization of mesoporous silica thin films as a catalyst support on a titanium substrate

Mesoporous silica films with a thickness of 500-900 nm were synthesized on a titanium substrate by the evaporation-induced self-assembly method (with 900-1200 rpm for 90 s) using cetyltrimethylammonium bromide (CTAB) as structure-directing agent and tetraethyl orthosilicate as the silica source. Prior to coating deposition, the titanium substrate was oxidized to increase the surface roughness up to 500 nm and to produce a thin titania layer. Just before the synthesis, the titania layer was made super hydrophilic by an UV treatment for 2 h to provide a better adhesion of the silica film to the substrate. Films with hexagonal and cubic mesostructures with a uniform pore size of 2.8 nm and a surface area of 1080 m²/g were obtained and characterized by different methods. An alternative approach for surfactant removal by gradual heating up to 250 °C in vacuum was applied. Complete removal of CTAB from the as-synthesized silica films was confirmed by infrared spectroscopy.     

Effect of HCl addition on the crystalline fraction in silicon thin films prepared by hot-wire chemical vapor deposition

In an effort to increase the crystalline fraction of silicon films directly deposited on a glass substrate by hot-wire chemical vapor deposition, the effect of HCl addition was studied. The silicon film was deposited on a glass substrate at 320 °C under a reactor pressure of 1333 Pa at the wire temperature of 1600 °C with 10%SiH₄–90%He at a fixed flow rate 100 standard cubic centimeter per minute (sccm) and HCl varied at 0, 10, 16 and 28 sccm. With increasing HCl, the crystalline fraction of silicon was increased as revealed by Raman spectra but the growth rate was decreased.     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.     

Low-temperature growth and orientational control in RuO2 thin films by metal-organic chemical vapor deposition

For growth temperatures in the range of 275°C to 425°C, highly conductive RuO₂ thin films with either (110)- or (101)-textured orientations have been grown by metal-organic chemical vapor deposition (MOCVD) on both SiO₂/Si(001) and Pt/Ti/SiO₂/Si(001) substrates. Both the growth temperature and growth rate were used to control the type and degree of orientational texture of the RuO₂ films. In the upper part of this growth temperature range ( 350°C) and at a low growth rate (< 3.0 nm/min.), the RuO₂ films favored a (110)-textured orientation. In contrast, at the lower part of this growth temperature range ( 300°C) and at a high growth rate (> 3.0 nm/min.), the RuO₂ films favored a (101)-textured orientation. In contrast, higher growth temperatures (> 425°C) always produced randomly-oriented polycrystalline films. For either of these low-temperature growth processes, the films produced were crack-free, well-adhered to the substrates, and had smooth, specular surfaces. Atomic force microscopy showed that the films had a dense microstructure with an average grain size of 50–80 nm and a rms. surface roughness of 3–10 nm. Four-probe electrical transport measurements showed that the films were highly conductive with resistivities of 34–40 μΩ-cm (at 25°C).     

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.     

ITO thin films prepared by a microwave heating

ITO thin films were prepared by irradiating 2.45 GHz of microwave with an output power of 700 W using a commercial kitchen microwave oven. A substrate temperature went up and down rapidly between 100 and 650 °C in a minute by a dielectric loss of SnO₂ layer pre-deposited on a glass substrate. We found that the electrical and optical properties of films were affected by the atmosphere in a microwave irradiation, while the sintering was completed within a few minutes. Although the electrical resistivity was not reduced below 5.0 × 10^− 4 Ω·cm in this study, the results lead to the possibility of a practical rapid synthesis of ITO transparent conducting oxide films.     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Some physical properties of Sn-doped CdO thin films prepared by chemical bath deposition

Undoped and Sn-doped CdO thin films were prepared by the chemical bath deposition method by means of a procedure that improves the deposition efficiency. All as-grown films were crystallized in the cubic structure of cadmium peroxide (CdO₂) and transformed into CdO with a cubic structure after an annealing process. The as-grown films have a high resistivity (> 10⁶ Ω cm) and an optical bandgap around 3.6 eV. Undoped CdO displays an optical bandgap around 2.32–2.54 eV and has an electrical conductivity of 8 × 10^− 4 Ω cm. The Sn incorporation into CdO produces a blue shift in the optical bandgap (from 2.55 to 2.84 eV) and a decrease in the electrical conductivity.The deposition procedure described here gives colloid-free surface thin films as indicated by the surface morphology analysis.     

Structure, morphology and magnetic properties of Fe-B-Si-Nb glassy alloy thin film prepared by a pulsed laser deposition method

With the aim of applying to a soft magnetic underlayer of the double-layered perpendicular magnetic recording media, an Fe_74.9B_17.5Si_2.5Nb_5.1 alloy thin film was fabricated on Si substrate by a pulsed laser deposition method. The Fe-based alloy thin film of 200 nm in thickness was confirmed as a glassy structure. The thermal properties of the thin film have similar features to those for the melt-spun glassy alloy ribbon. The glassy alloy thin film exhibits good soft magnetic properties, i.e., high B_s of 1.2 T and in-plane low H_c of 134 A/m. The Fe-B-Si-Nb glassy alloy thin film is expected to be suitable for the soft magnetic underlayer material in the double-layered perpendicular magnetic recording media.     

Annealing effect of thermal spike in MgO thin film prepared by cathodic vacuum arc deposition

MgO films were prepared by using pulsed cathodic vacuum arc deposition technique. The substrate bias voltage was in the range of −150 to −750 V. Film structure was investigated by X-ray diffraction (XRD). The annealing effect of thermal spike produced by the impacting of energetic ions was analyzed. The calculated results showed that the lifetime of a thermal spike generated by an energetic ion with the energy of 150 eV was less than one picosecond and it was sufficient to allow Mg²⁺ or O^2- to move one bond length to satisfy the intrinsic stress relief in the affected volume. The MgO(200) lattice spacings of the films deposited at different bias voltages were all larger than the ideal value of 2.1056 Å. As the bias amplitude increased the lattice spacing decreased, which indicated that the compressive stress in the film was partially relieved with increasing impacting ion energy. The stress relief also could be reflected from the film orientation with bias voltage. The biaxial elastic modulus for MgO(100), MgO(110) and MgO(111) planes were calculated and they were M₍₁₀₀₎ = 199 GPa, M₍₁₁₀₎ = 335 GPa and M₍₁₁₁₎ = 340 GPa, respectively. The M values indicated that the preferred orientation will be MgO(200) due to the minimum energy configuration when the lattice strain was large. It was confirmed by the XRD results in our experiments.     

Nanocone SiGe antireflective thin films fabricated by ultrahigh-vacuum chemical vapor deposition with in situ annealing

In this study, we fabricated nanocone-presenting SiGe antireflection layers using only ultrahigh-vacuum chemical vapor deposition. In situ thermal annealing was adopted to cause SiGe clustering, yielding a characteristic nanocone array on the SiGe surface. Atomic force microscopy indicated that the SiGe nanocones had uniform height and distribution. Spectrophotometric measurements revealed that annealing at 900 °C yielded SiGe thin films possessing superior antireflective properties relative to those of the as-grown SiGe sample. We attribute this decrease in reflectance to the presence of the nanostructured cones. Prior to heat treatment, the mean reflectance of ultraviolet rays (wavelength < 400 nm) of the SiGe thin film was ca. 61.7%; it reduced significantly to less than 28.5% when the SiGe thin film was annealed at 900 °C. Thus, the drop in reflectance of the SiGe thin film after thermal treatment exceeded 33%.     

Electrical characteristics of mixed Zr-Si oxide thin films prepared by ion beam induced chemical vapor deposition at room temperature

Mixed Zr-Si oxide thin films have been prepared at room temperature by ion beam decomposition of organometallic volatile precursors. The films were flat and amorphous. They did not present phase segregation of the pure single oxides. A significant amount of impurities (-C-, -CH_x, -OH, and other radicals coming from partially decomposed precursors) remained incorporated in the films after the deposition process. This effect is minimized if the Ar content in the O₂/Ar bombarding gas is maximized. Static permittivity and breakdown electrical field of the films were determined by capacitance-voltage and current-voltage electrical measurements. It is found that the static permittivity increases non-linearly from ~ 4 for pure SiO₂ to ~ 15 for pure ZrO₂. Most of the dielectric failures in the films were due to extrinsic breakdown failures. The maximum breakdown electrical field decreases from ~ 10.5 MV/cm for pure SiO₂ to ~ 45 MV/cm for pure ZrO₂. These characteristics are justified by high impurity content of the thin films. In addition, the analysis of the conduction mechanisms in the formed dielectrics is consistent to Schottky and Poole-Frenkel emission for low and high electric fields applied, respectively.