Amorphous Fused Silica Substrates Research Articles

Black carbon-doped TiO2 films: Synthesis, characterization and photocatalysis

Black colour TiO2 films were synthesized on amorphous fused silica substrates by DC magnetron sputtering technique with carbon powders placed at the working magnetron surface. Comprehensive sample analysis by X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy showed that the rutile/anatase heterostructure TiO2 films were successfully formed. Moreover, observation of OTiC bonds confirmed that TiO2 phase was doped by carbon additives. Scanning electron microscopy, atomic force microscopy and X-ray diffraction were used to identify the effect of deposition time and TiO2 film thickness on the surface morphology, roughness and crystallite size. Results of electron spin resonance showed that oxygen vacancies were generated on the surface with trapped unpaired electrons. Optical analysis by UV–vis light spectrophotometer showed that TiO2 films with carbon additives improve its capability to absorb visible light. Accordingly, methylene blue bleaching experiments under UVA and visible light irradiation showed that black colour TiO2 films are capable to decompose methylene blue solution at both UVA and visible light irradiation.

Zr-substituted Ba0.6Sr0.4TiO3 ferroelectric thin films grown by pulsed laser deposition (PLD) at different laser fluence

ABSTRACTZr-substituted Ba0.6Sr0.4TiO3 ((Ba0.6Sr0.4)(Ti0.8 Zr0.2)O3) - BSZT) thin films are deposited by using Pulsed Laser Deposition method with different fluence at optimized conditions on amorphous fused silica substrates. The X-ray diffraction (XRD) pattern of the films confirms the formation of cubic phase. Raman studies are performed to understand vibrational modes present in the films. The optical band gap of deposited BSZT thin films were calculated from the transmittance measurements. Microwave dielectric properties of the thin films deposited at 2 J/cm2 were measured. These results show BSZT thin films are useful in tunable microwave devices.

Effect of rapid thermal annealing on polycrystalline InGaN thin films deposited on fused silica substrates

In this work, we report on the effects of Rapid Thermal Annealing (RTA) on the structural, electrical and optical properties of polycrystalline InGaN thin films deposited on amorphous fused silica substrates by molecular beam deposition. Films with 20%, 35% and 50% indium content were grown and subjected to post-deposition RTA treatments. Annealing promoted crystallization in the case of the film with 0.5 InN mole fraction while in the lower indium content cases no apparent effect on the improvement of crystallinity was observed. For RTA temperature above 550°C, film resistivity was reduced by at least two orders of magnitude due to annealing-induced increased carrier concentration. The optical properties of the films were systematically studied by variable angle spectroscopic ellipsometry. In the highest indium content films, a monotonic optical band gap widening was observed upon annealing, explained by the Burstein–Moss effect. In contrast, photoluminescence peak position was not affected by the resulting Fermi level changes. This is attributed to the different mechanisms between optical absorption and emission in such highly doped semiconductors.

Optical, ferroelectric, and piezoresponse force microscopy studies of pulsed laser deposited Aurivillius Bi5FeTi3O15 thin films

Bi5FeTi3O15 (BFTO) based Aurivillius ferroelectric thin films were fabricated on strontium ruthanate coated amorphous fused silica substrates using pulsed laser deposition technique. Optical, ferroelectric, and piezoresponse properties of these thin films were investigated. The estimated refractive index (n) and extinction coefficient (k) for these films were in the range from 2.40 to 2.59 and 0.012 to 0.19, respectively. The bandgap of the BFTO thin layers was estimated to be 2.88 eV. Domain switching and hysteresis loops of BFTO films were studied utilizing piezoresponse force microscopy (PFM). The measured apparent polarization (Pr) and coercive field (Ec) for the samples were 20 μC/cm2 and 250 kV/cm, respectively. The amplitude and phase hysteresis curves obtained from PFM characterization reveal that these films can be switched below 5 V. These results suggest that BFTO in thin film form is a promising material for photo ferroelectric and optoelectronic devices applications.

Photovoltaic properties of Aurivillius phase Bi5FeTi3O15thin films grown by pulsed laser deposition

We report a remarkable photovoltaic effect in pulsed laser deposited multiferroic aurivillius phase Bi5FeTi3O15 (BFTO) thin films sandwiched between ZnO:Al transparent conductive oxide top electrode and SrRuO3 bottom electrode fabricated on amorphous fused silica substrates. The structural and micro structural properties of these films were analysed by X-ray diffraction and atomic force microscopy techniques. The films were showing a photo sensitive ferroelectric behaviour with a notable apparent polarization in the range of 10–15 μC/cm2. These films also exhibited a switchable photo-response and this parameter was observed to be sensitive to polarisation field and the polarization direction. The device shows a large ON/OFF photo current ratio with an open circuit voltage of 0.14 V. The photo response at zero bias of this BFTO based heterostructures showed rapid increase to a saturation value of 6 μA at zero bias.

Variation In Mechanical Properties With Substrate Temperature Of SbTi Thin Film Deposited By RF Sputtering Technique

Nanoindentation technique has been used to determine the mechanical properties of bismuth layered structure ferroelectric thin films, which have been shown to be promising for MEMS based devices used in sensing, actuation and energy harvesting, especially at elevated temperatures. SBTi (SrBi4Ti4O15) is a promising layered ferroelectric material and thin films of this composition are deposited on amorphous fused silica substrates by rf sputtering technique varying the substrate temperature from 600–725 o C. The crystal structure and surface morphology of SBTi thin films are characterized by X-ray diffraction and atomic force microscopy. Depth- sensing nanoindentation system is used to measure the mechanical characteristics of SBTi thin films. Nanoindentation measurements reveal that the Young’s modulus and hardness of SBTi thin films are related with grain size and crystal orientation which in turn depend on substrate temperature. The increase in mechanical properties with grain size is observed, indicating the reverse Hall-Petch effect. Furthermore, hardness and Young’s modulus of the (119) oriented films were higher than those of (0010) oriented films. The tribological properties of these films are confirmed by performing the scratch tests on the same films.

Nanomechanical and microwave dielectric properties of SrBi4Ti4O15 thin films sputtered on amorphous substrates by rf sputtering

SBTi (SrBi4Ti4O15) thin films were prepared on amorphous fused silica substrates by rf magnetron sputtering technique and crystallized in a microwave oven and conventional furnace. The difference in crystalline perfection was observed for both conventional and microwave annealed films. Nanoindentation and nanoscratch test were preformed to extract the mechanical properties of the films. Microwave annealed films exhibited higher hardness (6.2 GPa), Young’s modulus (103 GPa) and low friction coefficient than conventional annealed films. Microwave dielectric properties are measured at 10 and 20 GHz using spilt post dielectric resonator technique. Microwave annealed films have shown good microwave dielectric properties even at high temperatures by controlling the Bi volatization.

Sputter-deposited polycrystalline tantalum-doped SnO2 layers

In this study, tin oxide (SnO2) thin films doped with 1 cation percent tantalum were deposited on amorphous fused silica substrates by RF-magnetron sputter deposition. Electrical and optical properties were subsequently measured and analyzed as a function of deposition temperature (300 to 700°C) and oxygen ratio in the process gas (0 to 50%). In situ photoelectron spectroscopy was used to determine tantalum incorporation, sample stoichiometry, valence band electronic structure and Fermi level position. Samples were analyzed with respect to their optical and electrical characteristics by spectral transmittance and Hall measurement. Electrical resistivity reached values as low as 1.7×10−3Ωcm with a charge carrier density of 3.3×1020cm−3 and a mobility of 12cm2V−1s−1. Electrical transport properties were related to structural properties as determined by atomic force microscopy, scanning electron microscopy and X-ray diffraction. It was found that electrical properties are a strong function of substrate temperature, mainly due to a reduced charge carrier density for deposition temperatures below 700°C. This is thought to be caused by an intrinsic compensation mechanism which has not yet been identified.

Structural and luminescent characteristics of pulsed laser deposited Eu3+-doped Y2O3 thin films

Thin films of Eu-doped Y2O3 were deposited using the pulsed laser ablation technique on amorphous fused silica substrates. The effect of oxygen partial pressure (pO2) and substrate temperature on the structural and optical characteristics of the deposited films were investigated. All the deposited films were crystalline, showing preferred orientation along the (111) plane, irrespective of oxygen partial pressure and substrate temperature. The film deposited at 0.005 mbar pO2 exhibited better crystallinity with minimum FWHM at a substrate temperature of 600°C. All the films deposited at various substrate temperatures and different partial pressure (at 600°C) exhibited a red luminescence peak at 615 nm corresponding to the 5D0–7F1 transition in Eu3+. Photoluminescence excitation spectra exhibited two bands, one corresponding to band to band excitation (212 nm) of the host and the other to charge transfer band excitation (245 nm). A microstructure analysis revealed that surface roughness of the as-deposited films increases with increase in oxygen partial pressure.

Effects of aluminum doping and substrate temperature on zinc oxide thin films grown by pulsed laser deposition

Aluminum-doped zinc oxide (AZO) thin films have been deposited on amorphous fused silica substrates by pulsed laser ablation of a Zn:Al metallic targets. We varied the film growth condition such as the substrate temperature and Al concentrations. The films were deposited at substrate temperatures ranging from 20 to 600°C with oxygen partial pressure of 1 torr. The characteristics of the deposited films were examined by analyzing their photoluminescence (PL), X-ray diffraction (XRD), and UV–visible spectra. It is observed that the optical bandgap energy of the deposited films increased with the increase of Al concentration and substrate temperature. Besides, the PL peak energy shifted to blue and the Stokes shift became larger as the Al content increased.

Laser Ablation of a ZnO:P2O5Target under the Presence of a Transverse Magnetic Field

*, and Zn* neutrals in the presence of magnetic field turn out to be considerably different from those without magnetic field. The characteristics of the deposited films grown on amorphous fused silica substrates by pulsed laser deposition (PLD) are examined by analyzing their photoluminescence (PL), X-ray diffraction (XRD), and UV-visible spectra.

Growth-Temperature-Controlled Optical Properties of Textured Mg x Zn1−x O Thin Films

Pulsed laser deposition was used to grow magnesium zinc oxide thin films on amorphous fused silica substrates at several temperatures between room temperature and 750°C. In this study, the effect of growth temperature on the optical properties of textured Mg x Zn1−x O thin films was examined. The optical properties of the films were measured using absorption and photoluminescence spectrometry. Absorption spectra revealed that the bandgap values of textured Mg x Zn1−x O thin films were enhanced in films grown at higher temperatures. The absorption spectra near the absorption edge were fitted using the Urbach equation in order to investigate the effects of growth temperature on exponential band tail and bandgap. The photoluminescence spectra were measured for magnesium zinc oxide thin films deposited at 250°C, 350°C, 450°C, 550°C, and 650°C. The film grown at 350°C provided the highest excitonic peak intensity. On the other hand, the film grown at 250°C exhibited the lowest excitonic peak intensity. The excitonic peak intensity was considerably reduced in magnesium zinc oxide thin films grown at temperatures greater than 350°C. The ability to perform substrate-temperature-dependent bandgap engineering of Mg x Zn1−x O will enable use of this material in next-generation optical and optoelectronic devices.

Ambient Oxygen Effects on the Growth of ZnO Thin Filmsby Pulsed Laser Deposition

ZnO thin films were prepared by pulsed laser deposition on amorphous fused silica substrates at different ambient <TEX>$O_2$</TEX> pressures varying from 0.5 to 500 mTorr, to observe the effect of ambient gas on their crystalline structure, morphology and optical properties. Results of X-ray diffraction, scanning electron microscopy, atomic force microscopy and photoluminescence studies showed that crystallinity, surface features and optical properties of the films significantly depended on the oxygen background pressure during growth. A low oxygen pressure (0.5 mTorr) seems to be suitable for the growth of highly c-axis oriented and smoother films possessing a superior luminescent property. The films grown at the higher <TEX>$O_2$</TEX> pressures (50-500 mTorr) were found to have many defects probably due to an excessive incorporation of oxygen into ZnO lattice. We speculate that the film crystallinity could be affected by the kinetics of atomic arrangement during deposition at the higher oxygen pressures.

Ultraviolet-illumination-enhanced photoluminescence effect in zinc oxide thin films

We report an enhancement effect of ultraviolet illumination on the photoluminescence intensities of zinc oxide thin films. Large-grain ⟨0001⟩-textured zinc oxide thin films were deposited on amorphous-fused silica substrates using pulsed laser deposition. We found that the intensities of excitonic emission and green-band emission increased with ultraviolet light exposure time until a maximum value was achieved. We attribute this ultraviolet radiation enhancement effect to oxygen desorption on the surface of the zinc oxide thin film. We have proposed a phenomenological model to explain this interesting photoluminescence behavior.

Ga-doped ZnO single-crystal nanotips grown on fused silica by metalorganic chemical vapor deposition

In situ Ga-doped ZnO nanotips were grown on amorphous fused silica substrates using metalorganic chemical vapor deposition. Structural, optical, and electrical properties of as-grown ZnO nanotips are investigated. Despite the amorphous nature of fused silica substrates, Ga-doped ZnO nanotips are found to be single crystalline and oriented along the c-axis. Photoluminescence (PL) spectra of Ga-doped ZnO nanotips are dominated by near-band-edge emission with negligible deep-level emission. The increase in PL intensity from Ga doping has been attributed to the increase of Ga donor-related impurity emission. Current–voltage characteristics of the ZnO nanotips are measured by conductive-tip atomic force microscopy, which shows the conductivity enhancement due to Ga doping.

Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films

A semiconductor laser whose cavities are “self-formed” due to strong optical scattering in highly disordered gain media is demonstrated. The lasers are made of zinc oxide polycrystalline films grown on amorphous fused silica substrates. Lasing occurs at an ultraviolet wavelength of ∼380 nm under optical pumping. Actual images of the microscopic laser cavities formed by multiple scattering have been captured. These results suggest the possibility of using disordered semiconductor microstructures as alternative sources of coherent light emission.

”Mirrorless” UV lasers in ZnO polycrystalline films and powder

AbstractWe report the first observation of ultraviolet lasing in ZnO powder and ZnO polycrystalline films grown on amorphous fused silica substrates. In the absence of any fabricated mirrors, laser action occurs in the closed loops formed by multiple optical scattering of light.

Morphology and Microstructure of (111) Crystalline CeO2 Films Grown on Amorphous SiO2 Substrates by Pulsed-Laser Ablation

AbstractThe surface morphology and microstructure of (lll)-oriented CeO2 thin films, grown on amorphous fused silica (S1O2) substrates by low-energy-ion-beam assisted pulsed laser ablation, have been studied by atomic force microscopy (AFM) and x-ray diffraction (XRD). These CeO2 films are aligned with respect to a single in-plane axis despite being deposited on an amorphous substrate. There is a honeycomb-like growth morphology to the films and island-growth can be observed in thicker films. These islands, inside of which are high density of honeycomb-like clusters, are separated by a void network with ∼700nm width. However, on the surface of the thinnest film (∼3nm), only very small clusters (diameter &lt;60nm) appear, and the boundaries of the void network are undefined, which implies that the film is just beginning to coalesce into clusters (grains). The combined AFM images and XRD pattern suggest these clusters probably are the initial seeds for the subsequent island growth. Based on these results, the growth mechanism of oriented CeO2 films on amorphous fused silica substrates is discussed.

Pulsed Laser Deposition of NbNx (0 ≤ x ≤ 1.4) Thin Films

ABSTRACTThe structure, morphology, and electrical properties of pulsed laser deposited NbNx (0 ≤ x ≤ 1.4) thin films have been investigated. Films were deposited from Nb metal targets on oriented MgO (100) and amorphous fused silica substrates as a function of substrate temperature and ambient pressure. A reducing atmosphere (N2 with 10% H2) was used to prevent oxide formation. At elevated temperatures, the N/Nb ratios of films deposited on MgO, as determined from Rutherford Backscattering Spectroscopy, increased from 0 −1.4 as the ambient pressure was varied from vacuum to 200 mTorr, respectively. NbNx films (x=l) were deposited at 600 °C and 60 mTorr. Both the structure and electrical properties of the deposited films varied strongly with the substrate type. On fused silica, NbN films were poorly crystalline with low critical temperatures (Tc ∼ 8 – 11 K) and low critical currents (Jc (4.2 K) ∼ 2 MA/cm2), whereas on MgO the NbN films were oriented and had better transport properties (Tc ∼ 16.4 K and Jc (4.2 K) = 7.1 MA/cm2).

Effects of oxygen partial pressure on lead content of PLZT thin films produced by excimer laser deposition

Excimer laser ablation has been used to produce thin films of lanthanum-modified lead zirconate titanate (PLZT), or Pb 1− x La x ( Zr 1− y Ti y ) 1− x/4 O 3. PLZT is an interesting class of materials since it has a wide range of compositionally dependent electro-optical properties and strong non-linear optical characteristics. PLZT thin films of 7/0/100, 28/0/100 and 0/0/100 compositions have been deposited onto crystalline Si〈100〉 and amorphous fused silica substrates. Effects of oxygen backfill pressure on the Pb:(Ti + La) ratios were investigated. The results indicate that controlling the oxygen backfill pressure during laser deposition strongly influences the stoichiometry and crystal structure of PLZT thin films.