Amorphous BaTiO3 Thin Films Research Articles

Optical characteristics and luminescence of amorphous BaTiO3 thin films doped with Eu3+

Sol-gel spin coated BaTiO3:Eu3+ thin films on fused silica substrate were thermally annealed between 400°C and 800°C. The multilayer films were doped with Eu3+ which was limited to 10 mol % doping concentration. Standard physical and optical characterizations were performed in addition to excitation-emission and UVPL spectroscopy. The films were amorphous at temperatures below 600°C and exhibited stronger luminescence at 613.0 nm (5D0 → 7F2) than crystalline films. Optical energy band-gap ranged from 3.825 eV (crystalline) to 4.325 eV (amorphous) and the amorphous films’ CIE showed excellent red coordinates whilst red/orange (R/O) asymmetry ratio shows tailored emission color is possible.

Crystallization behavior of amorphous BaTiO3 thin films

The crystallization behavior of amorphous barium titanate (BaTiO3) thin films was studied as a function of annealing temperature from 500 to 1000 °C. Quantitative phase analysis by grazing incidence X-ray diffractometry revealed that the metastable hexagonal phase preferentially nucleates at lower temperatures with a transition to stable cubic nuclei at higher temperatures. The predominance of the metastable hexagonal-phase nucleation at lower temperatures suggests that it has the lowest nucleation barrier, in accordance with the Ostwald’s step rule. To help induce the nucleation of the cubic phase at lower temperatures, we explored the effects of electric fields on the crystallization behavior and found that direct-current fields moderately enhanced the cubic phase fraction in the 500–700 °C temperature range. Although the nucleation barrier of the cubic phase in the presence of an electric should be lowered more significantly with respect to that of the hexagonal phase because of the former’s higher relative permittivity, the effect arising from the change in volume free energy should only become significant at electric field strengths in the range of MV cm−1, an order of magnitude higher than the experimentally accessible fields in the present study. This suggests alternative, perhaps interface-mediated, mechanisms by which the electric field modifies the nucleation behavior of BaTiO3.

Copper-nanoparticle-dispersed amorphous BaTiO3 thin films as hole-trapping centers: enhanced photocatalytic activity and stability.

Nobel metal (Au and Ag) nanoparticles are often used in semiconductor photocatalysis to enhance the photocatalytic activity, while inexpensive Cu attracts less attention due to its easy oxidization. Herein, an elaborate study was conducted using Cu-nanoparticle-dispersed amorphous BaTiO3 films as photocatalysts. Photocatalytic and photoelectrochemical measurements demonstrated that the degradation efficiency and photocurrent density of the nanocomposite films are approximately 3.5 and 10 times as high as the pristine BaTiO3 film, respectively, which can be ascribed to a synergetic effect of the surface plasmon resonance and interband excitation. In addition, a good stability was also demonstrated by cyclic tests for the degradation of rhodamine B, which may be due to the amorphous nature of the BaTiO3 matrix providing hole-trapping centers. The high photocatalytic stability suggests that Cu is a promising alternative metal to replace Au and Ag for the development of cost-effective photocatalysts. Our work demonstrates a simple and promising strategy for improving the photostability of Cu nanomaterials and may provide a useful guideline for designing Cu-based composite materials toward various photocatalytic applications such as water pollution treatment.

Space charge limited transient currents and oxygen vacancy mobility in amorphous BaTiO3 thin films

Time-dependent transient currents were studied at elevated temperatures (200–220°C) in amorphous barium titanate thin film capacitors. Current transients display a peak whose time position varies with applied voltage and temperature. The response is analyzed through space charge limited current transient theories. Extracted drift mobilities are in the 10−11–10−12cm2V−1s−1 range and show an activation energy of 1eV. The phenomena are associated with oxygen vacancies migration in BaTiO3.

Preparation and optical properties of gold nanoparticles embedded in barium titanate thin films

High amount of gold nanoparticles was successfully incorporated into amorphous BaTiO3 thin films by sol-gel process. Thiourea was applied to prevent Au ions from being reduced and aggregating as the effective stabilization agents. These films exhibited unique surface plasma resonance red-shifting and particular changes of surface plasma resonance intensity with the increase of heat-treating temperature, which could be attributed to the influence of BaTiO3 ferroelectric domains. The films also exhibited superfast nonlinear optical response and larger third-order nonlinear susceptibility χ(3), which was attributed to hot electron contribution.

Iron nanoparticles in amorphous BaTiO3 thin films with large third-order optical nonlinearity

Composite thin films comprising nanometer-size iron particles embedded in an amorphous BaTiO3 matrix (Fe/BTO) were fabricated by alternate pulsed-laser deposition from pure metallic Fe and ceramic BaTiO3 targets. The distribution of Fe nanoparticles in BTO matrix was observed using high-resolution transmission electron microscope. X-ray photoelectron spectroscopy was used to check the Fe chemical bond state for the deposited films. Optical absorption spectra showed no significant surface plasma resonance peak in the wavelength range of 330–800 nm. The nonlinear optical properties of the Fe/BTO films were determined using the Z-scan method at the wavelength of 532 nm with laser duration of 10 ns. The real and imaginary parts of the third-order nonlinear susceptibility χ(3) were determined to be 7.18×10−7 esu and −8.60×10−8 esu, respectively. The results show that Fe/BTO composite thin films have great potential in designing nonlinear optical devices.

Electrical Properties of Sol-Gel Processed Amorphous BaTiO3 Thin Films

BaTiO3 thin films were prepared on single crystal silicon (1 0 0) and platinum substrates by sol-gel technique. Amorphous films with thickness uniformity were obtained by spinning the solution at 3000 rpm for 30 s and by post-deposition annealing at 400°C. The films exhibited good dielectric and insulating properties. The dielectric constant and dissipation factor at a frequency of 100 kHz were 17 and 0.20, respectively, for 1400 A thick film on platinum substrate (MIM). The corresponding values were 16 and 0.015 for films on Si (MIS). Dielectric properties were also studied as functions of frequency and voltage. The C-V curve for MIS structure exhibited a hysteresis. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 2.10 × 1011 cm−2 and total oxide charge density was about 4.28 × 1011 cm−2. I-V measurements were performed on films of different thicknesses. The leakage current densities at 5 V for the films having thicknesses 1400 and 2800 A were 0.86 and 0.11 μA/cm2 respectively. The conduction mechanism is found to be Poole-Frenkel and Schottky mechanisms at low and high fields, respectively.

Electrical and Optical Properties of Amorphous BaTiO3 Thin Films Grown by Metalorganic Chemical Vapor Deposition on Indium Tin Oxide-Coated Glass

In order to fabricate insulating films for a full-color thin-film electroluminescent display, an amorphous BaTiO3 thin film was deposited on an indium tin oxide-coated soda lime glass substrate at a low substrate temperature by metalorganic chemical vapor deposition with use of Ba(tmhd)2, Ti(OC3H7)4 and N2O. Scanning electron microscopy of the tilted surface of the as-grown BaTiO3 film showed a surface morphology of granular-like micrograins without defects such as pinholes and clusters. The thickness of the as-deposited film was approximately 1400 Å as confirmed by cross-sectional transmission electron microscopy. The formation of an interface film between the as-grown film and the indium tin oxide was not observed. Room-temperature frequency dependence of capacitance and dissipation factor was clearly indicated those typically exhibited by the amorphous BaTiO3 capacitor deposited on the conducting substrates having a metal-insulator-metal (MIM) structure. Optical transmittance measurements showed that the amorphous BaTiO3 film deposited at 400°C on the indium tin oxide-coated glass substrate has the transparency of about 80% in the visible wavelength range. Furthermore, the value of the optical band gap was approximately 4.71 eV. These results indicate that the amorphous BaTiO3 thin film grown on the indium tin oxide-coated glass can be used for thin-film flat panel electroluminescent display applications.

Preparation of amorphous BaTiO3 thin films on indium tin oxide-coated soda lime glass by metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition of BaTiO3 thin films on indium tin oxide–coated soda lime glass substrate in the temperature range between 400 and 550 °C was investigated to produce an insulating layer with high breakdown voltage and a smooth surface for electroluminescence display. In order to prevent the diffusion of sodium ions toward the indium tin oxide layer and BaTiO3 insulating layer, the deposition temperature should not be higher than 500 °C. X-ray diffraction patterns showed that the BaTiO3 thin film deposited at 400 °C was amorphous. The stoichiometry of the films was identified by Auger electron spectroscopy. Scanning electron microscopy results suggested that BaTiO3 thin films deposited at 400 °C had smooth surfaces without defects such as pinholes and clusters, but surface flatness decreased at the deposition temperature of 550 °C. The dielectric constant was 12.9. The breakdown voltage determined from current–voltage measurements was as large as 2×106 V/cm.

Deposition of Dielectric Thin Films by Atomic Layer Epitaxy and Their Application for Electroluminescence Displays

AbstractVarious dielectric thin films have been studied for electroluminescence display (ELD) application to improve dielectric constant and breakdown voltage. In this work, amorphous BaTiO3 thin films were deposited on indium tin oxide (ITO) - coated glass substrates by atomic layer epitaxy (ALE) using metalorganic precursors. Influences of deposition conditions on microstructure, interface characteristics and dielectric properties are investigated. It was possible to obtain dielectric films with good dielectric properties and textured, flat surface microstructure without defects due to the improvement of qualities of the grown films. These results were examined by XRD, SEM and AES analysis.

Densification induced dielectric properties change in amorphous BaTiO3 thin films

The properties of amorphous BaTiO3 thin films deposited on Si substrates were studied as functions of annealing temperature. The film thickness decreased monotonically as the annealing temperature increased up to 600 °C. This reduction is believed to correlate with the densification process observed in the amorphous films during annealing. After the 500 °C annealing, a partial crystallization process was observed. It was also found that the dielectric constant and the index of refraction of the film showed significant changes as the annealing temperature increased from 400 to 500 °C. Correlations between the film density, index of refraction, and the dielectric constant are discussed. A severe reaction at the interface between the film and Si substrate was observed in the 750 °C annealed sample.

Direct observation of BaTiO3 microcrystallites in thin amorphous BaTiO3 films

Well separated BaTiO3 microcrystallites were observed by transmission electron microscopy (TEM) in rapidly annealed, amorphous BaTiO3 thin films. The crystallization temperature for amorphous BaTiO3 is between 400 °C and 500 °C.

High charge storage in amorphous BaTiO3 thin films

A high charge storage density was achieved in BaTiO3 thin films on Si substrates prepared by a reactive partially ionized beam deposition technique and rapid thermal annealing (RTA) treatment. The films, being deposited at a low substrate temperature, were amorphous. The films were then annealed by using RTA in N2 ambient at 500 °C for 1 min. After the annealing the relative dielectric constant of the films was 20 and the thickness of the films was 310 Å. The charge storage density of the films was calculated to be as high as 5.6 μC/cm2 at 10 V. The leakage current density was on the order of 10−7 A/cm2 at an applied electric field of l MV/cm. The potential application of this film in high density memory is discussed.

Structural and electrical properties of rf-sputtered amorphous barium titanate thin films

Structural and electrical properties of rf-sputtered amorphous BaTiO3 thin films grown on water-cooled substrates have been investigated. The dielectric and electrical properties have been studied for films grown under varying sputtering gas composition (Ar+O2 gas mixtures) as a function of film thickness, frequency, and temperature. As-grown films were amorphous in nature and highly transparent. Post-deposition annealing had no discernible effect either on film structure or dielectric properties, and there was no evidence of ferroelectricity. Films sputtered in pure argon showed a dielectric constant ε′∼12 with little dependence on frequency (0.1–100 kHz) over the temperature range 0–75 °C. The dielectric properties were a function of film thickness and the percentage of oxygen in the sputtering gas during growth. The thickness-dependent dielectric properties of amorphous BaTiO3 thin films on conducting glass substrates could be satisfactorily explained by a model based on the existence of electrode barriers. The high breakdown voltage (106 V/cm), charge storage capacity (3.1 μC/cm2), and frequency- and temperature-dependent dielectric properties of a-BaTiO3 films sputtered in pure argon show promise for application as insulating layers in thin-film electroluminescent display devices.