Phase evolution and Sn-substitution in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films prepared on a Pt/Ti/SiO₂/Si(100) substrate by pulsed laser deposition were studied with focusing on the effects of different processing conditions and Sn substitution on phase evolvement and surface microstructure. Major experimental parameters include substrate temperature up to 770 °C and working oxygen pressure of 50–250 mTorr. LiMn₂O₄ thin films became highly crystallized with increased grain sizes as the substrate temperature increased. Second phases such as LiMnO₂ and Li₂Mn₂O₄ were found at the temperature of 300 and 770 °C, respectively. As an optimum condition, films grown at 450 °C showed a homogeneous spinel phase with well-defined crystallinity and smooth surface. A high pressure of oxygen tended to promote crystallization and grain growth. Working pressure did not affect significantly the phase formation of the thin films except that unexpected LiMn₃O₄ phase formed at the lowest oxygen pressure of 50 mTorr. Tin-substituted thin films showed lower Mn–O stretching vibrations, which suggests that more Li-ions can be inserted into vacant octahedral sites of the spinel structure.     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

Effects of Substrate Bias on the Diamond Nanostructure by Reactive Ion Etching

Abstract

Dense and uniform diamond nanocone arrays on titanium substrate were constructed by using bias-assisted reactive ion etching (RIE) of diamond films in a microwave plasma chemical vapor deposition (MPCVD) system. A hydrogen/argon mixture was employed as work gas with ratio of 3/1. The formation of nanocone structure was generated the lengthways physical bombardment/sputtering by argon ions, and selective chemical reaction of graphite and disordered carbons by hydrogen atoms and ions. The structure, size, and density depended on the substrate bias. The surface morphology of diamond film and nanostructures were characterized by field emission scanning electron microscope (FESME), and the composition of diamond film and nanostructures were characterized by Raman spectra. The Stopping and Range of Trons in Matter (SRIM) software was used to simulate the bombardment effect of the diamond film on different Ar⁺ ion incident angles during the etching process. The experimental results showed substrate bias at ?180?V and ?210?V was beneficial to the formation of high density, small size and sharp nanocones, meanwhile larger bias contributed to the formation of large size nanocones. Besides, as-prepared nanocones still maintained significant diamond phase.     

Filament-assisted pulsed laser deposition of epitaxial PbZrxTi1−xO3 films: Morphological and electrical characterization

Abstract

A modification of the conventional pulsed laser deposition technique was employed, whereby a low energy electron emitting filament was placed between the target and the substrate (-20 V filament/substrate bias) in order to produce reactive species (O_2- and O_?) during deposition. Using this modification, epitaxial thin films of PbZr_xTi_1?xO3 (PZT, 0 ≤ × ≤ 0.6) were prepared in situ on virgin (100) MgO and (100) Pt/(100) MgO substrates at a substrate temperature of 550°C and in an oxygen ambient (0.3 Torr). The topography of films prepared without a filament on virgin MgO were porous and composed of grains of about 1000 Å in diameter. As the emission current was increased from 0 to 400 μA, the grain size decreased to less than 100 Å with a concomitant decrease in the porosity. The nucleation of crystallites of other orientations was observed at emission currents greater than about 500 μA. Trilayer structures (Pt/PZT/Pt/<100>MgO) were fabricated for electrical measurements. Non-filament-assisted PZT cells usually failed because of a high probability of conductive paths through the PZT layer. Filament-assisted films were much less prone to this problem. Typical remanent polarizations and coercive fields were 15–20 μC/cm² and 30–50 kV/cm, respectively.     

Grain growth kinetics of LiMn2O4 nanocrystals during calcining process

ABSTRACT

LiMn₂O₄ nanocrystal was synthesized by coprecipitation using Mn(CH₃COO)₂ and LiOH as raw materials. Samples were characterized by thermo gravimetric/differential scanning calorimetry, X-ray diffraction and transmission electron microscope. Effort of calcination temperatures (600, 650, 700, 750 and 800°C) on grain size of LiMn₂O₄ was discussed. Results indicated that temperature had positive correlation with grain size. Grain growth kinetics of LiMn₂O₄ nanocrystal was simulated with a conventional model and an isothermal model. Simulation results indicated that the isothermal model was suitable to fit with data, implying the important roles of diffusion and surface reaction.     

Mathematical model of sapphire micromachining by CVD diamond coating tool

Abstract

A CVD diamond coating tool with prismatic crystal structure was prepared by hot filament chemical vapor deposition (HFCVD) method to improve sapphire’s lapping efficiency. The full plastic removal model of Sapphire (0001) plane is established based on the extended domain removal theory of hard and brittle materials such as sapphires. This model is used to analyze the effect of parameters such as prismatic particle’s size of the CVD diamond coating, lapping rate, lapping pressure, and material properties on the removal rate during the lapping process, and to predict the material removal rate, which lays the foundation for the high-efficiency micromachining of sapphire.     

Synthesis and Characterization of Nanostructured BSTO Thin-Films for Microwave Applications

Nanophase synthesis of ferroelectric thin-films of Ba_0.6Sr_0.4TiO₃ (BSTO) was studied systematically for applications in tunable microwave components. Synthesis of nanostructured BSTO was performed using a pulsed-laser deposition system with real-time in-situ process control. The main research goal was to utilize the pulsed laser deposition parameters to control the grain growth for low microwave loss nanostructured BSTO thin-films on crystalline substrates such as LaAlO₃. These parameters include the energy density of the laser pulses, wavelength, oxygen partial pressure, distance between the target and the substrate, and the substrate temperature. The nanostructural characterization was performed using XRD, SEM and AFM. Microwave characterization was done using coplanar waveguide lines to characterize the frequency dependent dielectric properties (?_r and tan δ). BSTO films were grown at the same measured temperature and energy density but in different oxygen ambient pressures from 19 mTorr through 300 mTorr. Using contact mode AFM, the grain size was found to decrease as the oxygen ambient pressure was reduced from 150 mTorr to 38 mTorr. The growth process changed when the pressure was increased above 150 mTorr. Nanocluster structures rather than nanoparticles were found at 225 mTorr. Average grain sizes less than 100 nm were obtained to oxygen pressures below 75 mTorr. The XRD spectra indicate the highly crystalline nature of the film. Microwave measurements, performed between 9–18 GHz, suggest the nano-structured BSTO thin-films on LaAlO₃ (LAO) substrates are highly tunable (up to 25%).     

Atomic-scale microstructures of SrBi2Ta2O9 (SBT) ferroelectric thin films prepared by MOD and PLD for ferams applications

Abstract

In this work, the microstructural defects in SrBi₂Ta₂O₉ (SBT) ferroelectric thin films were investigated at the atomic-scale by high-resolution transmission electron microscopy (HRTEM). A stacking fault with an extra inserted Bi-O plane normal to the c-axis was observed in SBT film with 10mol% excess bismuth prepared by metalorganic deposition. Edge dislocations with an average space about 3nm were observed at the small misorientation angle (8.2°) tilt grain boundary of SBT film with (001)-orientation prepared by pulsed laser deposition. The Burgers vector b for the edge dislocation was determined to be 1/2[110]α₀, where α₀ is the parameter of SBT unit cell. Chemical compositions of grains and grain boundaries in SBT films annealed in forming gas at 450°C and 500°C for 60 minutes were analyzed by using energy dispersive spectra at the nano-scale. Effects of the microstructural defects and microchemistry of the grain boundaries on the leakage current of SBT films are briefly discussed.     

Fabrication of AMO4 (A = Ba, Sr, Ca M = Mo, W) films on M substrate by solution reaction assisted ball rotation

An alkaline earth molybdates and tungstates, such as AMoO₄ and AWO₄, films have been successfully fabricated on the respective metal substrate in AOH (A = Ba, Sr, Ca) solutions by a ball rotation-assisted solution reaction at room temperature. This film consists the polyhedral crystals of AMO₄ with an average grain size of 8 μm. The dissolution of substrate surface was mainly controlled by the concentration of H₂O₂ oxidizing agent and ball rotation to form MO₄ ^{2 −} in the solution. AMO₄ was deposited on the substrate by the reaction between MO₄ ^{2 −} and A^{2 +} ions without any high energy or high temperature treatment. Also, the mass transport of alkaline earth ions on to the solid/solution interface was improved as a result of the vigorous solution agitation by the ball rotation. Therefore, the deposition rate of the AMO₄ films was accelerated by the ball rotation. A decrease in the grain size of the film was observed incase of an excessive ball rotation.     

Investigation of the Effects of Acid Content and Annealing on the Properties of Nanostructured TiO2 Sol

Abstract

Titanium dioxide (TiO₂) sol was prepared using tetrabutyl titanate as a precursor via an acid catalyzed sol-gel process. Investigation of the effects of acid content and annealing on the properties of nanostructured TiO₂ materials. The influence of acid content on the sol density, viscosity, stability and particle size were studied and based on the kinematic viscosity data, Gibbs energies of activation for viscous flow (ΔG*) were also calculated. Furthermore, the prepared samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and ultraviolet-visible (UV-Vis) spectrophotometer. The results showed that the increase of acid content nearly had no obvious influence on the chemical structure of TiO₂ sol. With the increase of annealing temperature, titanium dioxide changes from amorphous phase to crystalline phase, anatase coexists with rutile at 600?°C, sample absorbance increases, and the edge of UV-Vis spectra shows red shift. Ti-O-Ti bond is the main structure of TiO₂ sol, and the formed TiO₂ molecule has linear structure.     

Electrical characterizations of MgTiO3 thin films grown on Si

Abstract

We have analyzed MgTiO₃ thin films grown on the Si substrate with/without SiO₂ using pulsed laser deposition (PLD). We find that MgTiO₃ thin films start to crystallize at 600°C, causing electrical instabilities in the MIS capacitors above this temperature. Detailed analysis by XRD technique reveals that structural differences of MgTiO₃ thin films were not obvious below 600°C, whereas the electrical characteristics changes as a function of deposition temperature and the presence of thermally grown SiO₂. We observe that the decrease of deposition temperature results in the increase of leakage current and anomalous positive charge (APC) density. These drawbacks were effectively suppressed by growing 100A SiO₂ layer on the Si substrate prior to the deposition of MgTiO₃ thin films.     

Polycrystalline SrBi2Ta0.8Nb1.2O9 thin films

Abstract

The growth, microstructure and micro-Raman properties of SrBi₂Tao_0.8Nb_1.2O₉ (SBTN) thin films deposited on Si(100) substrates using pulsed laser deposition (PLD) technique were studied at various substrate temperatures. Films were characterized using X-ray diffraction(XRD), atomic force microscopy(AFM), energy dispersive X-ray analysis (EDAX) and micro-Raman studies. AFM studies indicated that the average grain size of the films increased between 0.08 μm to 0.1 μm with the increasing growth temperatures. Micro-Raman studies of SBTN films revealed the fact that shifting of Raman modes corresponds to the BO₆ (where B' Ta/Nb) octahedral symmetry, to higher frequencies, is in accordance with the different masses of the B site atoms and the force constants involved due to Nb doping at Ta sites.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

INFLUENCE OF DEPOSITION TEMPERATURE AND N2 FLOW RATE ON HIGH QUALITY ZNO THIN FILM DEPOSITED ON SiO2/SI SUBSTRATE BY ULTRASONIC SPRAY PYROLYSIS

ABSTRACT

ZnO thin films were prepared on SiO₂/Si substrate by ultrasonic spray pyrolysis (USP) method using the aqueous solution of zinc acetate dehydrate. X-ray diffraction (XRD) and atomic force microscopy (AFM) were employed to analyze the crystalline and microscopic structure of the films. The properties of ZnO films were investigated with respect to deposition temperature (T_s) and N₂ flow rate (f). The results show that ZnO thin films exhibit hexagonal wurtzite structure and the highly preferential orientation along c-axis under T_s = 320°C and f = 5 L/min deposition condition.     

Characterization of MOCVD Pt electrode for ferroelectric thin films

Abstract

Platinum thin films were deposited by low pressure chemical vapor deposition (LPMOCVD) on SiO₂/Si and (Ba, Sr)TiO₃/Pt/SiO₂/Si substrates using Pt-hexafluoroacetylacetonate at various deposition temperatures. The shiny mirror-like Pt thin films of a high electrical conductivity were obtained, when the deposition temperature is between 325°C and 350°C, whereas above 375°C Pt thin films showed rough surface as well as poor adhesion property to oxide substrate. Pt thin films had a good step coverage of 90%. The results indicate that LPMOCVD Pt thin films can be applied for the top electrode of high dielectric thin film, which is thought to be one of the best candidate materials for a capacitor of ULSI DRAM.     

Investigation of the effects of milling ceramic targets on the optical and electrical properties of BST thin films deposited by RF sputtering

Abstract

The RF sputtering method was utilized to deposit thin films of Ba_1-xSr_xTiO₃ (BST). The targets utilized in these experiments were prepared from ceramic powders with different particle size. The goal of this work is to examine whether the particle size distribution of the target can affect the properties of the thin films fabricated by the sputtering method. The Atomic Force Microscope (AFM) was used to examine the grain size in the thin films. The composition of the thin films and the bulk materials were examined by Fourier Transform Infrared (FTIR) spectroscopy. The dielectric properties of the thin films were measured and compared to its bulk counterparts. It was found that on lattice matched electrodes of SrRuO₃ on LaAlO₃ substrates, the thin films deposited from ceramic targets manufactured from ball-milled powders had finer grain size than those deposited from targets made from unmilled powders. However, this phenomenon was not observed in the case of polycrystalline films deposited on platinized silicon wafers.     

Influence of the growth temperature on the epitaxial quality of PbTiO3 films deposited in-situ by sputtering

Abstract

Thin films of lead titanate were prepared in-situ on SrTiO₃ substrates using radio-frequency magnetron sputter deposition. The epitaxial quality of the films has been studied as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range [550°C, 600°C]. The films deposited in the equilibrium zone have a high degree of c-axis oriented epitaxial crystalline structure as shown by X-ray diffraction in the 2θ/θ, θ, and ? scans configuration as well as by electron channeling pattern. The optimum conditions for growing epitaxial PbTiO₃ layers were determined. The crystallinity of films deposited at 550°C is suprior to those deposited at 600°C. The PbTiO₃ films grown at 550°C have a rocking curve full width at half maximum (FWHM) of 0.2°; Normaski optical and atomic force microscopy show that the surface is apparently free of grain boundaries and very smooth. The refractive index of these films has been evaluated from transmission spectra; it is very close to the bulk material value.     

Preparation and Performance of Li4Ti5O12 by Sol-Gel Method

Abstract

In This paper, butyl titanate and LiOH·H₂O was used as titanium source and lithium source respectively. Li₄Ti₅O₁₂ as battery negative material was prepared by sol-gel method. The effects of chelating agent (triethanolamine), raw material ratio, calcination temperature and calcination time on Li₄Ti₅O₁₂ products were studied by single factor method. The experimental results show that The optimum synthetic conditions are as follows: the spinel Li₄Ti₅O₁₂ with pure phase, uniform grain size, 100–200?nm particle size and no obvious agglomeration can be prepared under the conditions of molar ratio of lithium to titanium is 0.9–1.0, the calcination temperature can be 730–750?°C at 8?h. After assembled into CR2016 button cell, the first charge-discharge capacity of CR2016 button cell can reach 169 mAh/g at 0.1?C rate, which is very close to the theoretical value of 175 mAh/g.     

Preparation of PbTiO3 thin films by laser ablation

Abstract

PbTiO₃ thin films have been deposited on Si or Pt substrates by laser ablation method using ArF excimer or YAG laser. Species evaporated in the vacuum have been studied by mass analysis, and the measured Pb and Ti are not oxidized. Spacial distributions of the deposition rates on the substrate have been studied as a parameter of laser fluence. The excimer laser gives better films than the YAG. Perovskite films have been obtained at substrate temperature ～ 400 °C and appropriate ambient O₂ gas pressure.     

Based on the Study on Preparation and Properties of Co(II) and La3+-Doped TiO2 Electrochromic Film

Abstract

In order to improve the optical properties and coloration effect. Co(II) and La³⁺ doped TiO₂ thin films were synthesized via a sol–gel, by using butyl titanate as precursor on the surface of ITO conductive glass substrate. Several techniques were used to characterize produces. Adopting the Sol-gel technology, [CH₃(CH₂)₃O]₄Ti, La₂O₃, CoC_l2?6H₂O as the precursor, the composite membranes with different molar ratio of Ti, Ti/La, Ti/Co to be prepared on the ITO glass substrate, the optimum technological parameters for preparation of the base material of the electro-induced discoloration glass are determined. The structure and surface morphology optical and electrochromic properties of Co(II) and La³⁺-doped TiO₂ films were examined with X-ray diffraction (XRD) analysis, energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometer (UV-vis) DTA-TG analysis. It was found that:

1. The sintering temperature coating number, [CH₃(CH₂)₃O]₄Ti content of the TiO₂ film sample, and the doping category are the main factors that affect the structure and properties of the membrane based material;

2. Using two alcohol amine as chelating agent can effectively inhibit the formation of Ti (OH)₄ precipitation;

3. The properties of the TiO₂ glass film prepared by La₂O₃ and CoCl₂·6H₂O are fine;

4. Materials based on the preparation of a radiochromic film transmittance, high cyclic reversibility, cyclic voltammetry characteristics significantly, the results of the study for the electric induced radiochromic film-based material development and application provide a theoretical and experimental basis.