Well-crystallized Thin Films Research Articles

Microstructural, ferroelectric and photoluminescence properties of Er3+-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 thin films

Er3+-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 (xEr-BCTZ, x = 0, 0.005, 0.01) ferroelectric-luminescent thin films were prepared by the chemical solution deposition method. The effects of annealing temperature on microstructures of the samples were examined. Fine, uniform and well-crystallized thin films with pure perovskite structure were obtained through annealing at 750 °C. And the number of pores reduce with denser microstructure by increasing the Er3+ content. Additionally, ferroelectric and photoluminescence (PL) properties of xEr-BCTZ thin films were studied. Owing to dense microstructure and few defects, high remanent polarization and strongest up-conversion PL intensity were obtained at x = 0.01. The result of X-ray photoelectron spectroscopy confirms the existence of oxygen-related defects in the films, which can partly deteriorate the ferroelectricity and PL intensity. This work can guide other multifunctional lead-free ferroelectric-luminescent thin films for micro-optoelectronic applications.

Iron molybdate thin films prepared by sputtering and their electrochemical behavior in Li batteries

With the aim of developing 3V all-solid-state lithium microbatteries, Fe2(MoO4)3 thin films were prepared by radiofrequency magnetron sputtering from a home-made Fe2(MoO4)3 target using optimized sputtering conditions. In addition to elemental analyses, Mössbauer spectroscopy and XPS analyses, showing that Mo6+ and Fe3+ are the main detected species, confirmed the stoichiometric character of the films. Post-deposition annealing was necessary to form well-crystallized thin films. The best electrochemical performance was obtained with those annealed at 500 °C which were able to deliver a stable reversible capacity close to the theoretical one, i.e. 2 Li+ per Fe2(MoO4)3 formula unit. The corresponding voltage curve displays a plateau with a low hysteresis located at 3.0 V/Li+/Li and related to the Fe2(MoO4)3 – Li2Fe2(MoO4)3 two-phase system. Therefore, it was demonstrated for the first time the possible use of Fe2(MoO4)3 thin films as positive electrodes for 3 V lithium microbatteries.

Lithium-rich manganese oxide spinel thin films as 3 V electrode for lithium batteries

Thin film positive electrodes of lithium-rich manganese oxide spinels were prepared by radiofrequency magnetron sputtering from a LiMn2O4 ceramic target at a total pressure close to 2Pa. Post-annealing treatments were necessary to get well-crystallized thin films displaying interesting electrochemical performances. Raman spectrum exhibiting several well-defined bands between 296 and 635cm−1 is typical for the lithium-rich spinel. Based on ICP, RBS and XRD analyses, the thin films composition is close to Li1.2Mn1.8O4. The latter is also in accordance with a Mn3+/Mn4+ ratio close to 0.1 deduced from XPS measurements. Best electrochemical performance (capacity value, cycling life) between 2V and 3.5V vs Li+/Li was obtained for thin films annealed at 600°C. A volumetric capacity of 52μAhcm−2μm−1 (close to about 90% of the theoretical value) was obtained at the first cycle at a C/100 regime. Contrary to most studies carried out on spinel thin films cycled in the 3V range, no appreciable degradation of the discharge capacity was observed after few tens of cycles at room temperature, highlighting the beneficial effect of substituting 20% of Mn ions by Li ions and the presence of microvoids in thin films that limits the effect of strain generated from volume variation during the Li insertion/deinsertion process.

Rhodium thin film-carbon nanotube nanostructures: Synthesis, characterization and electron transfer properties

Rh thin films have been synthesized onto carbon nanotubes by pulsed laser deposition under vacuum and under 266Pa of helium background pressure. Field emission scanning electron microscopy revealed two types of Rh films: (i) Rh film fabricated under vacuum was smooth and of closed structure and (ii) Rh prepared at 266Pa of He was porous. Transmission electron microscopy showed that the smooth Rh film was made of highly interconnected particles of 2nm diameter, whereas the porous film had a morphology of particles arranged into columns with particles having an average diameter of 5nm. In addition, using high resolution transmission electron microscopy images, the Rh film thickness could be estimated to be about 20nm. X-ray diffraction pattern showed well-crystallized thin films with a (111) intense orientation. X-ray photoelectron spectroscopy confirmed the presence of metallic Rh at the surface of the carbon nanotubes. Preliminary evaluation of the electron transfer properties showed that porous Rh-carbon nanotubes exhibited reduced oxophilicity than smooth Rh. In addition, the porous Rh film offered larger electrochemical stability window between the onset of hydrogen adsorption and Rh oxide formation. Such interesting properties have important implications in many electroanalytical applications.

Characterization of CuInS2 thin films prepared by aerosol jet deposition

CuInS2 thin films were prepared using an aerosol jet deposition (AJD) technique with an aqueous solution of CuCl2, InCl3 and thiourea on a heated glass substrate. X-ray diffraction patterns showed that well-crystallized thin films with a preferential (112) orientation could be deposited at 400°C and [Cu]/[In] molar ratio of 1.2. Field emission scanning electron microscopy revealed well-crystallized grains in the films produced at high temperature of 400°C. In addition, energy dispersive X-ray spectroscopy confirmed that excess Cu and S were required to achieve well-crystallized CuInS2 films. As the [Cu]/[In] molar ratio increased from 0.8 to 1.4, the highest intensity of the (112) orientation and better crystallization were obtained at a [Cu]/[In] ratio of 1.2. The [Cu]/[In] ratios in the film were always higher than those in the precursor solution. All the CuInS2 thin films turned out to be p-type and had a band gap of 1.4eV. The depth profiles of Cu, In and S in the CuInS2 thin films deposited at the optimal [Cu]/[In] and [S]/[In] ratios of 1.2 and 3, respectively, were relatively constant throughout the films. Overall, the CuInS2 thin films deposited using the AJD method have well grown grains with good crystallinity.

Fabrication of ZnO thin films by femtosecond pulsed laser deposition

The growth of ZnO thin films on sapphire substrate using the femtosecond PLD technique is reported. The effect of substrate temperature and oxygen pressure on the structural properties of the films was studied. Highly c-axis oriented ZnO films can be grown on sapphire substrates under vacuum conditions using the femtosecond PLD process. There is an optimum substrate temperature for the pulsed laser deposition of ZnO film that enhances the thermodynamic stability and allows the formation of well-crystallized thin films. The crystal quality of the films can be further improved by increasing the deposition time and introducing oxygen during the pulsed laser deposition process.

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO2) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.

Electrical properties of ferroelectric YMnO3 films deposited on n-type Si(111) substrates

YMnO3 thin films were grown on an n-type Si substrate by nebulized spray pyrolysis in the metal–ferroelectric–semiconductor (MFS) configuration. The capacitance–voltage characteristics of the film in the MFS structure exhibit hysteretic behaviour consistent with the polarization charge switching direction, with the memory window decreasing with increase in temperature. The density of the interface states decreases with increasing annealing temperature. Mapping of the silicon energy band gap with the interface states has been carried out. The leakage current, measured in the accumulation region, is lower in well-crystallized thin films and obeys a space-charge limited conduction mechanism. The calculated activation energy from the dc leakage current characteristics of the Arrhenius plot reveals that the activation energy corresponds to oxygen vacancy motion.

Ultra-thin Cr 2O 3 well-crystallized films for high transmittance APSM in ArF line

Ultra-thin Cr 2O 3 well-crystallized thin films are deposited on UV grade fused silica substrates and Si wafers by using r.f. reactive unbalanced magnetron sputtering from a Cr metal target in an atmosphere of Ar and O 2 at 350 °C. The optical constants of such thin films were found to be a sensitive function of oxygen-to-argon flow rate ratio. At the ratio of 0.2, a Cr 2O 3 well-crystallized thin film with appropriate refractive index and extinction coefficient at a wavelength of 365 nm can be used as attenuated phase-shifting mask (APSM) blank as well as being good for inspection. The simulated thickness range of a Cr 2O 3 well-crystallized thin film was found to be between 28.2 and 30.3 nm. This meets the optical requirements for high transmittance APSM (HT-APSM) with a transmittance of 18–20% at 193 nm for the pattern fabrication and with transmittance less than 50% at 365 nm for the mask inspection. One such Cr 2O 3 well-crystallized thin film that satisfies the optical requirements was fabricated.

Sol-gel derived Ba(Mg1/3Ta2/3)O3 thin films: Preparation and structure

Ba(Mg1/3Ta2/3)O3 thin films were prepared by a sol-gel process involving the reaction of barium isopropoxide, tantalum ethoxide, and magnesium acetate in 2-methoxyethanol and subsequently hydrolysis, spin-coating, and heat treatment. Transmission electron microscopy, x-ray diffraction, and Raman spectroscopy were used for the characterization of the thin films. It was shown that the thin films tend to crystallize with small grains sized below 100 nm. Crystalline phase with cubic (disordered) perovskite structure was formed in the samples annealed at a very low temperature (below 500 °C), and well-crystallized thin films were obtained at 700 °C. Although disordered perovskite is dominant in the thin films annealed below 1000 °C, a low volume fraction of 1 : 2 ordering domains was found in the samples and grows with an increase of annealing temperature.