Pulsed Laser Ablation Technique Research Articles

Luminescence from Surfactant-Free ZnO Quantum Dots Prepared by Laser Ablation in Liquid

Highly transparent, luminescent and biocompatible ZnO quantum dots were prepared in water, methanol, and ethanol usingliquid-phase pulsed laser ablation technique without using any surfactant. Transmission electron microscopy analysis confirmedthe formation of good crystalline ZnO quantum dots with a uniform size distribution of 7 nm. The emission wavelength could bevaried by varying the native defect chemistry of ZnO quantum dots and the laser fluence. Highly luminescent nontoxic ZnOquantum dots have exciting application potential as florescent probes in biomedical applications.© 2007 The Electrochemical Society. DOI: 10.1149/1.2820767 All rights reserved.Manuscript submitted September 4, 2007; revised manuscript received November 6, 2007.Available electronically December 17, 2007.

Ion and photon emission from laser-generated titanium-plasma

Titanium-plasma was obtained by nanosecond pulsed laser ablation technique. A Nd:Yag laser was employed to irradiate titanium in vacuum. The ion emission from plasma was on-line monitored by an electrostatic ion energy analyzer which permitted to measure the ion kinetic energy and charge state. The visible photon emission was monitored by an optical spectrometer. The ion energy, charge state and angular distributions, the temperature and density of the non-equilibrium plasma were investigated. The temperature gradient of the plasma plume was evaluated and discussed.

Thermo-optical studies of NaNbO3 thin films

Thermo-optical studies of sodium niobate NaNbO3 (NN) thin films, deposited by the pulsed laser ablation technique on Si/SrRuO3 substrates, were performed by spectroscopic ellipsometry in the temperature range 300-550°C. Optical constants at the room temperature were measured in the spectral range 250-1000 nm. Substantial changes in the refractive index temperature behaviour (taken at λ = 300 nm) were found at temperatures 370, 445, 503, 520, and 532°C, where the first and the last temperatures are the phase transitions P → R and S → T1, respectively. Other temperatures (445, 503, and 520°C) are suggested as the points of some local structural changes in the NN film.

XRD and HRTEM Study of Zirconia Nanoparticles Synthesized by Laser Ablation

To investigate doping-free zirconia, pulsed laser ablation technique was applied to synthesize pure zirconia nanoparticles. Various experimental parameters were investigated by means of microscopic, spectroscopic and diffractmetric techniques to reveal morphology and production yield. It is successful to form cubic and monoclinic phases at nanometer-scale fine particles. The cubic phase has relatively small lattice parameters than the stabilized zirconia.

Antiferroelectriclike polarization behavior in compositionally varying (1−x) Pb(Mg1∕3Nb2∕3)O3–(x) PbTiO3 multilayers

Compositionally varying multilayers of (1−x) Pb(Mg1∕3N2∕3)O3–(x) PbTiO3 were fabricated using pulsed laser ablation technique. An antiferroelectriclike polarization hysteresis was observed in these relaxor based multilayer systems. The competition among the intrinsic ferroelectric coupling in the relaxor ferroelectrics and the antiferroelectric coupling among the dipoles at the interface gives rise to an antiferroelectriclike polarization behavior. An increment in the coercive field and the applied field corresponding to the polarization flipping at low temperatures, provide further insight on the competition among the long-range ferroelectric interaction and the interfacial interaction in the polarization behavior of these relaxor multilayers.

Structural and optical characterization of Ba0.8Sr0.2TiO3 PLD deposited films

Structural and optical properties of Ba0.8Sr0.2TiO3(BST) ferroelectric thin films, deposited by the pulsed laser ablation (PLD) technique on Si/SiO2/Ti/Pt, Si/SrRuO3 and Si substrates, were performed by X-ray diffraction, micro Raman, atomic force microscopy (AFM), and optical reflectometry measurements. Temperature dependences of the Raman spectrum, and room temperature refractive and extinction indices, and surface roughness were evaluated.

Preparation and characterization of nanostructured NiO thin films by reactive-pulsed laser ablation technique

Nanostructured nickel oxide (NiO) thin films were prepared using pulsed laser ablation technique on heated quartz substrates under an oxygen partial pressure of 2×10 −3 mbar. X-ray diffraction (XRD) studies indicate enhancement in growth along (1 1 1) and (2 0 0) crystal planes with increase of substrate temperature. The atomic force microscopic (AFM) studies indicate a self-assembly of NiO nanocrystals having size ∼84 nm, with a uniform height profile along the assembly for films prepared at a substrate temperature of 673 K. Formation of arrays of confined two-dimensional NiO layers in the films prepared at a substrate temperature of 473 K is also reported. The optical band gap and electrical resistivity of the films synthesized under different deposition conditions are also discussed.

${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ Films With ${\rm BaZrO}_{3}$ Inclusions for Strong-Pinning in Superconducting Films on Single Crystal Substrate

The addition of artificially induced defects improves the pinning efficiency of magnetic flux vortices in YBa2Cu3O7-delta (YBCO) films. In YBCO films by pulsed laser ablation (PLD) technique this goal can be pursued by the introduction of epitaxial second phase nanoinclusions in the YBCO matrix. In the present work, the effect of BaZrO3 (BZO) inclusions in stoichiometric YBCO films on transport properties has been studied. Composite targets obtained by addition of BZO powder in molar percents ranging from 2.5 to 7 mol.% have been prepared with BZO mean grain size of about 1 mum. Structural and morphological characterizations of the films obtained by PLD from these targets have been carried out through X-ray diffractometry and Scanning Electron Microscopy (SEM) analysis. Dc electrical transport measurements at 77 K have revealed a better magnetic field retention of the critical current density, Jc, being at 3 T the 14.6% and the 16.4% of the zero field values for YBCO-BZO 5% and 7%, respectively. The complex surface impedance has been measured by means of a dielectric resonator at a high microwave frequency (50 GHz). In order to identify the potentially strong pinning induced by the inclusions, the field-dependent complex resistivity has been determined as a function of temperature in a moderate magnetic field (B < 1T). Very high depinning frequency are estimated in YBCO films with BZO inclusions indicating extremely high vortex pinning and steep potential wells.

High Power SOFC using LaGaO3 Based Oxide Electrolyte Film Prepared on Porous Metal Substrate

SOFC single cell was fabricated on the porous metal substrate which is prepared by thermal reduction method. After reduction of the NiO-Fe3O4 mixed oxide at 873K for 5h, it was found that the porous metal substrate is successfully obtained. Thus obtained metal porous substrate has 30 % in porosity and ca. 15cc/min for H2 permeation rate, which is enough permeation rate for hydrogen. Pulsed laser ablation techniques were used for the preparation of LSGM film on top of thus obtained porous metal. In order to prevent the reaction between Ni and LSGM, thin film of SDC was deposited between Ni-Fe substrate and LSGM electrolyte. Sm0.5Sr0.5CoO3 is applied by the screen printing techniques. Thus obtained SOFC shows the almost theoretical OCV and the maximum power density is achieved a value of 1.6 and 0.5 W/cm2 at 973 and 773 K, respectively.

Growth of self-assembled ZnO nanoleaf from aqueous solution by pulsed laserablation

Zinc oxide ‘nanoleaf’ structures have been synthesized at room temperature and pressureusing the novel technique of pulsed laser ablation (Nd:YAG 532 nm) of a zinc target in anaqueous solution of sodium dodecyl sulfate (SDS). Transmission electron microscopy(TEM), selected area electron diffraction (SAED), high-resolution transmission electronmicroscopy (HRTEM), photoluminescence spectroscopy and UV–visible spectroscopy wereused to study the morphology, nanostructure and optical properties of these ZnOnanostructures. The growth mechanism appears to involve an increase of the structuralcomplexity from zero-dimensional nanoparticles to one-dimensional nanorods, and thenbroadening of these into two-dimensional ‘nanoleaf’ structures. Variations are discussedin terms of differences in the concentration of SDS and the laser ablation time.

High energy oxygen ion induced modifications in lead based perovskite thin films

The lead based ferroelectric PbZr 0.53Ti 0.47O 3 (PZT), (Pb 0.90La 0.10)TiO 3 (PLT10) and (Pb 0.80La 0.20)TiO 3 (PLT20) thin films, prepared by pulsed laser ablation technique, were studied for their response to the 70 MeV oxygen ion irradiation. The dielectric analysis, capacitance–voltage ( C– V) and DC leakage current measurements were performed before and after the irradiation to high-energy oxygen ions. The irradiation produced considerable changes in the dielectric, C– V, leakage characteristics and induced some amount of amorphization. The PZT films showed partial recrystallization after a thermal annealing at 400 °C for 10 min. The phase transition temperature [ T c] of PLT20 increased from 115 °C to 120 °C. The DC conductivity measurements showed a shift in the onset of non-linear conduction region. The current density decreased by two orders of magnitude after irradiation. After annealing the irradiated films at a temperature of 400 °C for 10 min, the films partially regained the dielectric and electrical properties. The results are discussed in terms of the irradiation-induced amorphization, the pinning of the ferroelectric domains by trapped charges and the thermal annealing of the defects generated during the irradiation.

A Rapid Flow Mixer with 11-μs Mixing Time Microfabricated by a Pulsed-Laser Ablation Technique: Observation of a Barrier-Limited Collapse in Cytochrome c Folding

Proteins with more than ∼100 residues usually demonstrate a rapid and significant collapse as the earliest event in their folding dynamics; however, the limit in the time resolution of available experimental methods precluded us from conducting a detailed analysis of the event. To investigate the collapse in a real time, a new rapid flow mixer was developed by using a femtosecond laser ablation technique, which achieved a mixing time of 11 μs. By using the developed mixer, the collapse dynamics of cytochrome c, initiated by pH jumps after the solution mixing, was investigated. The time domain within 100 μs, which was previously unobservable, was clearly resolved and demonstrated that the process can be approximated by a single-exponential process. The results support the presence of a single kinetic barrier in the initial collapse of cytochrome c.

Pulsed laser deposition of anatase and rutile TiO 2 thin films

The investigation deals with the preparation of both anatase and rutile thin films from a sintered rutile target of TiO 2 by pulsed laser ablation technique. Microstructural characterization of the sintered target was carried out using X-ray diffraction and AC impedance spectroscopy. Thin films of titania were deposited on (111) Si substrates at 673 K in the laser energy range 200–600 mJ/pulse at two different conditions: (i) deposition at 3.5 × 10 − 5 mbar of oxygen, and (ii) deposition at an oxygen partial pressure of 0.1 mbar. The influence of laser energy and oxygen addition on the film growth has been studied. X-ray diffraction analysis of the films indicated that the films are single phasic and nano crystalline. Titania films deposited in the energy range 200–600 mJ/pulse at a base pressure of 5 × 10 − 5 mbar are rutile with particle sizes in the range 5–10 nm, whereas the films formed at the oxygen partial pressure 0.1 mbar are anatase with particle sizes in the range 10–24 nm. In addition, at higher energies, a significant amount of particulates of titania are found on the surface of the films. The change in the microstructural features of the films as a function of laser energy and oxygen addition is discussed in relation with the interaction of the ablated species with the background gas.

Nanostructured mesoporous nickel oxide thin films

Nanostructured nickel oxide thin films were prepared by the pulsed laser ablationtechnique. The effects of annealing on the structural, morphological, electrical and opticalproperties are discussed. Phase imaging was used to examine the surface contaminants,adhesion and hardness and height imaging to evaluate the height profile of the films.Morphological investigations using atomic force microscopy and scanning electronmicroscopy indicate a strong influence of the annealing process on the surfaceroughness and particle size. A self-assembly of nanocrystals agglomerating togetherto form an island-like structure is observed in films annealed at 773 K. X-raydiffraction and x-ray photoelectron spectroscopy investigations indicate the presence ofNi2O3 in the as-deposited films. A transformation to cubic NiO with growth along (111) and (200)planes with increase of annealing temperature is also observed.

Leakage current behavior in pulsed laser deposited Ba(Zr0.05Ti0.95)O3 thin films

Barium zirconium titanate [Ba(Zr0.05Ti0.95)O3, BZT] thin films were prepared by pulsed laser ablation technique and dc leakage current conduction behavior was extensively studied. The dc leakage behavior study is essential, as it leads to degradation of the data storage devices. The current-voltage (I-V) of the thin films showed an Ohmic behavior for the electric field strength lower than 7.5MV∕m. Nonlinearity in the current density-voltage (J-V) behavior has been observed at an electric field above 7.5MV∕m. Different conduction mechanisms have been thought to be responsible for the overall I-V characteristics of BZT thin films. The J-V behavior of BZT thin films was found to follow Lampert’s theory of space charge limited conduction similar to what is observed in an insulator with charge trapping moiety. The Ohmic and trap filled limited regions have been explicitly observed in the J-V curves, where the saturation prevailed after a voltage of 6.5V referring the onset of a trap-free square region. Two different activation energy values of 1.155 and 0.325eV corresponding to two different regions have been observed in the Arrhenius plot, which was attributed to two different types of trap levels present in the film, namely, deep and shallow traps.

UV assisted oxidation and nitridation of hafnia based thin films for alternate gate dielectric applications

The synergistic effects of NH 3 ambient and ultraviolet illumination on the dielectric properties of hafnia based gate dielectrics are reported in this paper. The films were processed at relatively low temperatures (∼400 °C) by pulsed laser ablation and UV oxidation technique. UV illumination and the NH 3 ambient created a thin and a denser interfacial layer (at the film–Si interface) comprised of Hf Si O N bonding. As a result of the interfacial layer modification, a leakage current density lower than 10 −4 A/cm 2 and a dielectric constant of ∼21.7 were extracted from the best samples processed in NH 3 and under UV illumination. The nitrogen doped HfO 2 also exhibited a thinner interfacial layer (∼12 Å) in comparison to the films processed without NH 3 ambient.

Dielectric, impedance and ferroelectric characteristics of c-oriented bismuth vanadate films grown by pulsed laser deposition

Ferroelectric bismuth vandante, Bi 2VO 5.5 (BVO) thin films with layered perovskite structure were deposited by pulsed excimer laser ablation technique on (1 1 1) Pt/TiO 2/SiO 2/Si substrates. The polarization hysteresis ( P versus E) studies on the BVO thin films at 300 K confirmed the remnant polarization ( P r) and coercive field ( E c) to be 5.6 μC/cm 2 and 113 kV/cm, respectively. The same was corroborated via the capacitance–voltage measurements. The dielectric response and conduction mechanism of BVO thin films under small ac fields were analyzed using impendence spectroscopy. A strong low frequency dielectric dispersion (LFDD) was found to exist in these films, which was ascribed to the presence of the ionized space charge carriers such as oxygen ion vacancies and interfacial polarization. The room temperature dielectric constant and the loss ( D) at 100 kHz were 233 and 0.07, respectively. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.85 eV. The frequency characteristics of BVO thin films under study showed universal dynamic response that was proposed by Jonscher for the systems associated with quasi-free charges.

Microstructural evolution and metastable phase formation in laser ablation-deposited films of Fe-rich Fe–Ge intermetallic compounds

Thin films of Fe-rich Fe–18 at% Ge and Fe–25 at% Ge were deposited by a pulsed laser ablation technique on single crystal NaCl substrates at room temperature to study phase evolution using transmission electron microscopy. As-deposited films contain nano-scale clusters embedded in a featureless matrix. Quadrupole mass spectrometric observations of the laser-ablated plume show the presence of charged clusters. During in situ heating of the films, the fine-scale clusters grow and profuse crystallization to a bcc FeGe solid solution occurs. For Fe–25 at% Ge thin film, crystallized bcc grains undergo two ordering transitions, viz. bcc → B2 → DO3, during subsequent cooling to room temperature. However, in the case of Fe–18 at% Ge thin film, crystallization leads to formation of the disordered bcc phase. Growth morphologies of the crystals formed during heat treatment indicate faceted growth form, which has been explained by using Jackson's interface model.

Ultra fine carbon nitride nanocrystals synthesized by laser ablation in liquid solution

Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR) were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure of the nanoparticles are consistent with the theoretical calculations for a-C3N4. After 2 h ablation the particles had a size distribution � 8–12 nm, whereas after 5 h ablation the particles had grown into nanorod-like structures with a crystalline C3N4 tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure.

Growth of diamond nanocrystals by pulsed laser ablation of graphite in liquid

Nanocrystalline diamond has been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation (Nd:YAG, 532 nm) of a graphite target in water. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and laser Raman spectroscopy have been used to characterise the nanocrystals and to confirm that they are diamond. Time-averaged optical emission spectroscopy showed the presence of H, C and O atoms in the ablation plume. Imaging of the light emitted from the plume showed that H atoms were formed in two regions, in the liquid above the graphite surface, and also in the air just above the water surface. The results are consistent with the idea that atomic H is a necessary requirement for the growth of diamond via this method.