Effects of nitridation durations on the synthesis of wurtzite GaN thin films by spin coating method

In this paper, the effects of nitridation durations on the structural, surface morphologies and lattice vibrational properties of gallium nitride (GaN) thin films grown via spin coating method were reported. X-ray diffraction (XRD) results revealed that all the deposited GaN thin films have wurtzite structure and with GaN(002) preferred orientation. In addition, the crystallinity of the GaN thin films increases with increasing of nitridation durations from 15 to 75 min while it degrades at 105 min. Field-emission scanning electron microscopy observations showed that GaN thin films with hexagon grains were formed at nitridation duration of 45 and 75 min, whereas rose-like microstructures were formed at nitridation duration of 105 min. P-polarized infrared reflectance measurements demonstrated that the reststrahlen feature of GaN thin films gradually increases from 15 to 75 min and diminished at 105 min, which is consistent with the XRD results. Finally, all the results revealed that the duration of 75 min was the most efficient time for the nitridation process.     

Synthesis of thin dense titania films via an aqueous solution-gel method

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti⁴⁺ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15–20 nm grains. At higher crystallization temperatures (600, 650°C) also larger particles (40–70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450°C. Crystallization temperatures equal to or higher than 600 °C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness (≤1.1 nm) measured by AFM.     

Deposition of Silicon Carbide Thin Films from 1,1-Dimethyl-1-Silacyclobutane

1,1-Dimethyl-1-silacyclobutane was used as a single-source precursor to deposit SiC thin films on Si(100) and Si(111) by low-pressure chemical vapor deposition (LPCVD). Polycrystalline β-SiC thin films were grown at temperatures 1100 and 1200°C. At temperatures between 950 and 1100°C, amorphous thin films of silicon carbide were obtained. The films were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED).     

Influence of substrate chemistry and the network homogeneity of ultra‐thin cross‐linked polymer films cured at their surface on the main relaxations temperatures probing by microthermal analysis

Thin 200‐nm epoxy–amine mixtures were cured on silicon wafers with different surface chemistry to quantify the effect of the chemistry on the glass transition temperature evolution in ultra‐thin thermosetting films. Two surface treatments were investigated: the first one only consisted in the activation of the silanols groups at the silicon surface, whereas the second one consisted in the grafting 3‐aminopropyltrimethoxysilane (APTMS) monolayer on the silicon wafers. The epoxy films were deposited on these chemistry modified wafers by spin coating a toluene solution of DGEBA–amine mixture at stoichiometric ratio. The same cure processing was used for both samples. Thin films were analysed not only using microthermal and thermomechanical analysis to determine the relaxation transitions temperatures of these films but also using FTIR in infrared reflection absorption spectroscopy mode to determine the curing rate of these networks. It was found that all these thin films showed two different glass transitions, the first one at 96 °C and was independent of the surface treatments, whereas the second one increasing from 142 °C for the oxidised wafers surface to 167 °C for the aminosilane grafted on the silicon wafer. The substrate chemistry extent on the film network structure, the interfacial bonds and interactions are discussed. This work also illustrates the interest in using microthermal analysis to obtain relevant temperature glass transition of thin film at sub‐micrometre scale, strongly dependant of local structure and chemistry composition. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and effect of post-deposition thermal annealing on morphological and optical properties of ZnO thin film

Zinc oxide thin films have been deposited on glass substrates by the chemical bath deposition method; a surfactant, cetyltrimethylammonium bromide (CTAB); was used as capping agent. The films were annealed at two different temperatures: 200 and 300 °C. The structural features were investigated by X-ray diffraction analysis which exhibited hexagonal wurtzite structures along with c-axis orientations. Crystallite size was estimated and found to be around 33–41 nm. The effect of post-deposition thermal annealing on the morphological and optical properties has been investigated by scanning electron microscopy and photoluminescence spectra at room temperature. The band gap energies of uncapped and CTAB-capped ZnO films were found to be 3.28 and 3.48 eV, respectively.     

Structure and voltage tunable dielectric properties of sol–gel derived Bi1.5MgNb1.5O7 thin films

Bi_1.5MgNb_1.5O₇ (BMN) thin films were fabricated on Au/Ti/SiO₂/Si(100) substrates using a sol?Cgel spin coating process. Thermo decomposition of the BMN precursor gel was discussed. The structures, morphologies, dielectric properties and voltage tunable dielectric properties were investigated. The deposited films showed a cubic pyrochlore structure after annealing at 550?°C or higher temperatures. With the annealing temperature increased from 500 to 800?°C, the root-mean-square surface roughness of the films increased from 0.6 to 6.8?nm. Additional phase, MgNb₂O₆, emerged after annealing at 800?°C due to the volatilization of Bi element. The dielectric properties and tunability of the films were annealing temperature dependent. BMN thin films annealed at 750?°C had a high dielectric constant of 135 and low dielectric loss of 0.002 at 1?MHz. The high tunability of 31.3?% and figure of merit of 156.5 were obtained under an applied electric field of 1?MV/cm at room temperature.     

Synthesis of crystallized TaON and Ta3N5 by nitridation of Ta2O5 thin films grown by pulsed laser deposition

TaON and Ta₃N₅ thin films of different thicknesses were prepared by pulsed laser deposition of tantalum oxide followed by ex situ thermal nitridation under ammonia. The nitridation was carried out in flowing gas in the 600–800 °C temperature range. The dependence of tantalum oxynitride and nitride crystalline phases formation on nitridation reaction parameters was investigated. Structural and microstructural characteristics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM).     

Role of reaction atmosphere in preparation of potassium tantalate through sol–gel method

Potassium tantalate (KT) thin films and powders of both K₂Ta₂O₆ (KT pyrochlore) and KTaO₃ (KT perovskite) structures were prepared by means of chemical solution deposition method using Si(111) with ZnO and MgO buffer layers as a substrate. The influence of reaction atmosphere on reaction pathway and phase composition for both KT powders, and KT thin films has been studied mainly by means of powder diffraction and infrared spectroscopy. When an oxygen flow instead of static air atmosphere has been used the process of pyrolysis in oxygen runs over much narrower temperature interval (200–300 °C), relatively to air atmosphere (200–600 °C) and almost no (in case of powders), or no (in case of thin films) pyrochlore intermediate phase has been detected in comparison with treatment in air, where the pyrochlore phase is stable at temperatures 500–600 °C (powders). KT perovskite phase starts to crystallize at temperatures 50° and 150 °C lower compared to air atmosphere in case of powders and thin films, respectively. Microstructure formed by near-columnar grains and small grains of equiaxed shape was observed in films treated in oxygen and air atmosphere, respectively.     

Structural and electrochemical studies of annealed LiNiVO4 thin films

We prepared stoichiometric lithium nickel vanadate amorphous thin films by using r.f. magnetron sputtering under controlled oxygen partial pressure. The amorphous films were heated at various temperatures, 300–600 °C, for 8 h. The as‐deposited and annealed thin films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analysis, Auger electron spectroscopy, X‐ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochemical behavior of the various films was studied by the galvanostatic method. The cells were tested in a liquid electrolyte at room temperature, with lithium metal used as the counter and reference electrode. The best electrochemical storage value was obtained with the thin film annealed at 300 °C, which showed superior capacity and small capacity loss during cycling. Copyright © 2007 John Wiley & Sons, Ltd.     

Highly transparent solution processed In-Ga-Zn oxide thin films and thin film transistors

Highly transparent In-Ga-Zn oxide (IGZO) thin films were fabricated by spin coating using acetate- and chlorate-based precursors, and thin film transistors (TFTs) were further fabricated employing these IGZO films as the active channel layer. The impact of the post-annealing temperature on the physical properties of IGZO films and performance of IGZO TFTs were investigated. Compared to the nitrate-based IGZO precursor, the chlorate-based precursor increases the phase change temperature of IGZO thin films. The IGZO films changed from amorphous to nanocrystalline phase in an annealing temperature range of 600–700 °C. The transparency is more than 90% in the visible region for IGZO films annealed with temperatures higher than 600 °C. With the increase of post-annealing temperature, the carrier concentration of IGZO film decreases, while the sheet resistance increases firstly and then saturates. The bottom-gate TFT with IGZO channel annealed at 600 °C in oxygen showed the best performance, which was operated in n-type enhancement mode with a field effect mobility of 1.30 cm²/V s, a threshold voltage of 10 V, and a drain current on/off ratio of 2.5 × 10⁴.     

Influence of surfactant and annealing temperature on optical properties of sol–gel derived nano-crystalline TiO2 thin films

Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO₂ thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO₂ films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO₂ films was estimated by Tauc's method at different annealing temperature.     

The effect of heat treatment in the reducing atmosphere on the physical properties of TiO2 thin films prepared by sol–gel method

Multilayered nanostructured TiO₂ thin films were prepared by sol–gel and dipping deposition on quartz substrate followed by thermal treatment under reducing atmosphere (20 %H₂–80 %Ar). Heat treatment at progressively higher temperatures caused structural, morphological, and optical changes, which were investigated by X-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy, and UV–Vis spectroscopy. The conductivities of the thin films were also measured by 4-point probe method. The XRD results showed that the calcined TiO₂ thin films consist of single anatase phase which was completely transformed into rutile phase after heat treatment at 1,000 °C. The grains of films grew by intra-agglomerate densification after heat treatment at higher temperatures. The root mean square roughness of the samples was found to be in the range of 0.58–3.36 nm. The partially reduced TiO₂ samples have red-shifted transmittance bands due to new energy band formed by oxygen vacancies. The electrical conductivity of the films was also enhanced after heat treatment in reducing atmosphere.     

Preparation and characterization of crack-free sol–gel based SiO2–TiO2 hybrid nanoparticle film

Owing to the diverse potential applications of hybrid silica–titania thin films, the synthesis and characterization of these films have been carried out with a special focus on application as a medium index layer for multilayered functional coatings. For synthesis, tetraethylorthosilicate and titanium tetraisopropoxide were chosen as precursors for the formation of silica-titania hybrid thin films/nano-composites through an in situ sol–gel process. These films were sequentially obtained on Cu substrate utilizing spin coating. The hybrids were characterized by field emission scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, atomic force microscopy and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscope morphology displayed a smooth, densified and crack- free layer of silica-titania hybrid nanoparticles in the range of 20–71 nm after calcinations at low temperature of 300ºC for 1 h. X-ray diffraction pattern confirms the phases of titania with higher crystallinity and phase transformation at low temperature. The prepared films were uniform with low 8.852 nm RMS value. The stoichiometry of films was confirmed by EDX results. The FTIR spectroscopy indicated the establishment of heterogeneous chemical bonding between the Ti and Si surfaces through oxygen.     

Structural and optical properties of Na doped ZnO nanocrystalline thin films synthesized using sol–gel spin coating technique

Sodium (Na) doped Zinc oxide (ZnO) thin films have been deposited on a glass substrate by the sol–gel spin coating method. Effect of doping with various percentages of Na at a particular annealing temperature of 500 °C is studied. The samples were characterized by X-ray diffraction (XRD), micro-photoluminescence, Raman and Polarized Raman spectroscopy. The X-ray diffraction and micro-Raman spectroscopy confirmed the presence of Na substitution in zinc oxide and the wurtzite structure of the lattice is retained. An enhancement of resonant Raman scattering processes as well as longitudinal optical phonon overtones up to the fifth order were observed in the micro Raman spectra. The similar values of depolarization ratios obtained from Polarized Raman studies recommend no change in the symmetry. Photoluminescence showed a strong emission peak in the near UV at 3.2 eV and negligible visible emission.     

Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

The properties of sol–gel derived ZrO₂ thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO₂ thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO₂ coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO₂ coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO₂ coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO₂ thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm² (1,064 nm, 10 ns) and 14.6 J/cm² (1,064 nm, 10 ns) are obtained for ZrO₂ coating and ZrO₂/SiO₂ multilayer coatings respectively.     

Oxidation and nitridation of niobium films by rapid thermal processing

The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200 and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination of the Nb films from the substrates was observed.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterisation and properties of magnetron sputtered nanoscale bi‐layered Ni/Ti thin films and effect of annealing

Single‐bi‐layer of Ni–Ti thin film was deposited using DC and RF magnetron sputtering technique by layer‐wise deposition of Ni and Ti on Si(100) substrate in the order of Ni as the bottom layer and Ti as the top layer. The deposition of these amorphous as‐deposited thin films was followed by annealing at 300 °C, 400 °C, 500 °C, and 600 °C temperature with 1‐h annealing time for each to achieve crystalline thin films. This paper describes the fabrication processes and the novel characterization techniques of the as‐deposited as well as the annealed thin films. Microstructures were analysed using FESEM and HRTEM. Nano‐indentation and AFM were carried out to characterize the mechanical properties and surface profiles of the films. It was found that, for the annealing temperatures of 300 °C to 600 °C, the increase in annealing temperature resulted in gradual increase in atomic‐cluster coarsening with improved ad‐atom mobility. Phase analyses, performed by GIXRD, showed the development of silicide phases and intermetallic compounds. Cross‐sectional micrographs exhibited the inter‐diffusion between the two‐layer constituents, especially at higher temperatures, which resulted either in amorphization or in crystallization after annealing at temperatures above 400 °C. Copyright © 2015 John Wiley & Sons, Ltd.     

Spun films of perylene diimide derivative for the detection of organic vapors with host–guest principle

The optical characterization and chemical vapor sensing properties of 1,7-dibromo-N,N′-(bicyclohexyl)-3,4:9,10-perylene diimide thin film against to organic vapors were discussed in this study by using spin coating, UV–Vis spectroscopy, atomic force microscopy, surface plasmon resonance (SPR) and Quartz Crystal Microbalance (QCM) techniques. The perylene diimide thin films were fabricated with a refractive index values from 1.55 to 1.60 and thicknesses in the range between 15.80 and 26.32 nm using different spin speeds from 1000 to 5000 rpm. In this study, perylene diimide thin film sensor was exposed to dichloromethane, chloroform, carbon tetrachloride, tetrahydrofuran and ethyl acetate vapors by using both SPR and QCM techniques. Also, the swelling behaviors of the perylene diimide thin films prepared at different spin speeds were investigated with respect to dichloromethane vapor at the room temperature by using SPR data. Diffusion coefficients were found to be 11.34?×?10^?17 (1000 rpm), 2.56?×?10^?17 (3000 rpm) and 0.38?×?10^?17 cm² s^?1 (5000 rpm) for dichloromethane vapor by using the Fick’s law of diffusion. It might be proposed that perylene diimide thin film optical chemical sensor element has a good sensitivity and selectivity for the dichloromethane vapor at room temperature.     

Effect of Li- and Ta-doping on the ferroelectric properties of Na0.5K0.5NbO3 thin films prepared by a chelate route

The effects of lithium and tantalum doping on the properties of Na_0.5K_0.5NbO₃ (NKN) thin films were investigated. The films were fabricated by an optimized chelate route which offers the advantage of a simple and rapid solution synthesis. The optimization was achieved by investigating the effects of alkaline volatilization loss on film properties. In this way, undoped NKN thin films fabricated by this conventional method exhibited good ferroelectric properties (P_r ~ 8 μC/cm², and E_c ~ 55 kV/cm for films annealed at 650 °C). The developed chelate route was then used to grow Li (5 %) and Ta (10 %) substituted thin films. Such structures allowed us to compare the effect of these dopant cations on phase formation, microstructure and ferroelectric properties. We show that both modifications produced a remarkable improvement on the ferroelectricity of the films. While the undoped material exhibited large leakage components in films annealed at 600 °C, films modified with Li or Ta presented well saturated ferroelectric hysteresis loops, indicating that those ions have a significant influence on the conducting process. The remnant polarizations of the Ta-doped films are greater than those of the Li-doped samples. This feature is however reversed for films annealed at low temperature (600 °C) due to the presence of a non-ferroelectric secondary phase in the Ta-doped composition.