Pulsed Laser Deposition Growth Research Articles

The power ofin situpulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high-energy diffraction with the in situ synchrotron high-resolution X-ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target-substrate separation distance. Ba0.5Sr0.5TiO3 grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X-ray reflectivity, in situ two-dimensional reciprocal space mapping of symmetric X-ray diffraction and acquisition of time-resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two-dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba0.5Sr0.5TiO3 grown on MgO could be determined from the acquisition of time-resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.

Ultrabroadband near-infrared luminescence and efficient energy transfer in Bi and Bi/Ho co-doped thin films

Ultrabroadband near-infrared luminescence in the 1.0–2.4 μm range has been observed in bismuth (Bi)-doped oxyfluoride germanate thin films prepared by pulsed laser deposition (PLD). The emission peak position shows a red-shift with decreasing oxygen pressure during PLD growth. Systematic investigation reveals that the origin of the luminescence could be ascribed to Bi clusters. With the sensitization of Bi near-infrared active centers, enhanced broadband ∼2 μm luminescence of Ho3+ is realized in Bi/Ho co-doped films, and a high energy transfer efficiency is obtained. These results may provide promise to realize planar waveguide lasers in the near-infrared region for integrated optics.

Magnetic anisotropy in Fe films epitaxied by thermal deposition and pulse laser deposition on GaAs(001)

The in-plane magnetic anisotropy of Fe films fabricated with thermal deposition (TD) and pulse laser deposition (PLD) techniques on GaAs(001) substrate was studied quantitatively. The volume anisotropy in TD Fe film is attributed to the constant strain anisotropy, supported by reflection high-energy electron diffraction analysis. The PLD growth was found to deeply influence the interface anisotropy at Fe/GaAs interface even through a 30 ML Fe TD underlayer. The volume anisotropy was found to exist in TD Fe film even grown on top of a PLD film. Our study indicates that the uniaxial magnetic anisotropy in Fe/GaAs(001) system can be controlled by a combination of TD and PLD growth.

Epitaxial growth of 2 inch diameter homogeneous AlN single-crystalline films by pulsed laser deposition

2 inch diameter homogeneous AlN films are epitaxially grown on sapphire substrates by pulsed laser deposition (PLD). By optimizing laser rastering and PLD growth conditions, the 2 inch diameter single-crystalline AlN films exhibit excellent thickness uniformity with root-mean-square (RMS) inhomogeneity less than 4.5% and very smooth surface with RMS roughness less than 1.53 nm. There is a maximum of 1.5 nm thick interfacial layer, if there is any, existing between the as-grown AlN and the pre-nitrided sapphire substrate, and the as-grown AlN films are almost fully relaxed only with a 0.26% in-plane compressive strain. The achievement of high-quality large-scale AlN films with uniform thickness and atomically abrupt interface is of great interest for the commercial development of AlN-based devices, particularly acoustic filters where abrupt heterointerfaces with substrates and flat surfaces for AlN films are highly desired.

Homogeneous epitaxial growth of AlN single-crystalline films on 2 inch-diameter Si (111) substrates by pulsed laser deposition

Homogeneous and crack-free AlN films have been epitaxially grown on 2 inch Si (111) substrates by pulsed laser deposition (PLD). By optimising the laser rastering and PLD growth conditions, the 2 inch-diameter single-crystalline AlN films exhibit excellent thickness uniformity with a root-mean-square (RMS) inhomogeneity of less than 3.6% and a very smooth surface with a RMS roughness of 1.4 nm. There is a 1.5 nm-thick interfacial layer between the as-grown AlN films and Si substrates, which is confirmed by HRTEM and a GIXR simulation, and the as-grown AlN films are almost fully relaxed with only 0.3% in-plane tensile strain. The achievement of high-quality and crack-free AlN films with a uniform thickness and abrupt interface on 2 inch Si (111) substrates is of great interest for AlN-based devices, particularly acoustic filters, where abrupt heterointerfaces with the substrates and flat surfaces of AlN films are highly desired.

Growth processes of lithium titanate thin films deposited by using pulsed laser deposition

We have investigated the pulsed laser deposition (PLD) growth processes of spinel lithium titanates based on the preparation of Li4Ti5O12 and LiTi2O4 from a Li4Ti5O12 target. The Li/Ti atomic ratio of the species arriving at substrate during the deposition was only ∼0.5. The LiTi2O4 epitaxial thin films fabricated on MgAl2O4 (111) substrate exhibited high conductivity at room temperature (∼3.0 × 103 Ω−1 cm−1) and a superconducting transition temperature of ∼12 K. These values are the highest reported for epitaxial thin films. Our results demonstrate the importance of the target composition, providing further insights into the Li-containing metal oxide deposition processes using PLD.

Low power flexible organic thin film transistors with amorphous Ba0.7Sr0.3TiO3 gate dielectric grown by pulsed laser deposition at low temperature

We deposited amorphous Ba0.7Sr0.3TiO3 (BST) on silicon and plastic substrate under 110°C by pulsed laser deposition (PLD) and use it as the dielectric of the organic transistor. Depends on the thickness of BST layer, the highest mobility of the devices can achieve 1.24cm2V−1s−1 and 1.01cm2V−1s−1 on the silicon and polyethylene naphthalate (PEN) substrate, respectively. We also studied the upward and downward bending tests on the transistors and the dielectric thin films. We found that the BST dielectric pentacene transistor can maintain the mobility at 0.5cm2V−1s−1 or higher while the bending radius is around 3mm in both upward and downward bending. Our finding demonstrates the potential application of PLD growth high-k dielectric in the large area organic electronics devices.

Control of Catalytic Activity Via Porosity, Chemical Composition, and Morphology of Nanostructured Porous Manganese Oxide Materials

AbstractThis review concerns a summary of synthesis, characterization, and applications of octahedral molecular sieve (OMS) materials. These OMS systems have been the focus of our research program for over 20 years. This review primarily covers the past 10 years with an emphasis on the most recent developments in this area. Some current areas of concern include the systematic synthesis of well ordered materials, control of particle sizes, generation of nano‐size particles, and development of new synthetic methods like pulse laser deposition and epitaxial growth of oxidic materials. Applications include use of OMS in environmental catalysis, adsorption, clean energy materials, activation of the Greenhouse gas carbon dioxide, and selective oxidations. OMS catalysts are outstanding selective oxidation catalysts and can also drive total oxidations. The highly selective of OMS systems may be related to redox cycling and redox catalysis.

Self-organization of SrRu03 nanowires on ordered oxide surface terminations

Abstract

Monte Carlo simulation of the subsurface growth mode during pulsed laser deposition

The pulsed laser deposition (PLD) growth of aluminum (Al) metal in the presence of noble background gases is studied using a Monte Carlo model constructed on the basis of srim 2010 calculations. It is shown that Al ions are deposited with a high kinetic energy of about 100 eV. These high kinetic incident energies lead to the implantation of ions into the existing film and resputtering from its surface. The consequent film growth is in the subsurface or subplantation growth mode, in which the material does not grow on top of the already deposited film. It is proved that by considering the role of resputtering, which is neglected in other theoretical models of PLD, experimentally observed deviations from the stoichiometric growth of multicomponent materials and dips in thickness profiles of elemental materials at the film center can be explained. The calculated implantation depths are also consistent with the reported measured ones. Taking into account the role of sputtering yield in calculating the deposition rate of the material, and evaluating the mean number of produced vacancies inside the growing film, two different approaches are proposed for the optimal growth of materials in PLD. To obtain high quality thin films, one should use a noble gas that ensures higher mass ratios (the ratio of the ablated ion to the gas atomic masses) at higher pressures; however, to achieve the highest growth speeds, higher mass ratios at lower pressures are recommended.

Imposed layer-by-layer growth of ZnO on GaN/sapphire substrates using pulsed laser interval deposition

The oxide semiconductor ZnO is of high interest for electrooptical applications due to its direct and wide band gap in the UV region. We present our results on pulsed laser deposition growth of ZnO on GaN-buffered Al 2O 3 substrates. Using in-situ reflection high energy electron diffraction, intensity oscillations were recorded and used to apply the technique of interval deposition. A significant improvement of structural thin film quality was achieved due to the expansion of the high quality from the first layers to the whole film thickness.

Pulsed laser deposition growth of FeSb 2 films for thermoelectric applications

FeSb 2 films were produced in a low-pressure Ar environment by pulsed laser deposition at 355 nm. The influence of growth parameters such as substrate temperature, Ar pressure and deposition time on the growth of FeSb 2 films was studied. Nearly phase-pure FeSb 2 films with thicknesses of 100–400 nm were produced at 425 °C with an Ar pressure of 1.5–2 Pa. Thermal transport and Hall measurements were performed to explore the thermoelectric transport properties of the FeSb 2 films. A maximum thermopower of ∼120 μVK −1 at 40 K was obtained. In general it is highly important to understand the growth properties of FeSb 2 films if they are to eventually reach thermoelectric applications at cryogenic temperatures.

Investigation of the effect of different oxygen partial pressure to LaAlO 3 thin film properties and resistive switching characteristics

The pulsed laser deposition and growth of a high-k dielectric lanthanum aluminate LaAlO 3 (LAO) thin film on indium tin oxide/glass substrate at different oxygen partial pressure was studied. Based on the pulsed laser deposition growth mechanism, we explain how a difference in the oxygen partial pressure influences the surface roughness, formation of an interfacial layer, and the transparent resistive switching characteristics of LAO thin films. The micro-structure and oxygen concentration difference inside LAO thin films may be the main reason for the difference in electrical and resistive switching properties. Films grown at higher oxygen partial pressure displayed more reliable resistive switching performance, due to the formation of the interfacial layer and a lower concentration of oxygen vacancies. The interfacial layer serves as a good oxygen reservoir and the involvement of more oxygen ions ensures the switching reliability. The migration of oxygen ions between the interfacial layer and the LAO film under applied bias may be the switching mechanism.

Scaling in film growth by pulsed laser deposition and modulated beam deposition

The scalings in film growth by pulsed laser deposition (PLD) and modulated beam deposition (MBD) were investigated by Monte Carlo simulations. In PLD, an atomic pulse beam with a period t(0) were deposited instantaneously on a substrate, whereas in MBD, adatoms were deposited during a short time interval t(1) (0≤t(1)≤t(0)) within each period. If t(1)=0, MBD will be identical to PLD and, if t(1)=t(0), MBD will become usual molecular beam epitaxy (MBE). Specifically, logarithmic scaling was investigated for the nucleation density reported for PLD, and the scaling of island density was studied regarding the growth for 0<t(1)<t(0) in MBD. It was found that the logarithmic scaling held for the nucleation density when growing islands were fractal-like but the quality of data collapsing became worse when islands were compact by adatom diffusion along the edges of islands. A crossover behavior from PLD growth to MBE growth was observed as t(1) increased. The phase diagram was also presented.

Fabrication and Magnetic Properties of fcc-Co Nanorods Embedded in Epitaxial Thin Films of Anatase TiO2 As a Transparent Matrix

Nanocomposite thin films consisting of Co nanorods and an anatase TiO2 matrix were successfully prepared by pulsed laser deposition (PLD). Co nanorods with diameters of 9−6 nm and heights of 10−22 nm were homogeneously dispersed in the matrix as a result of phase separation during PLD growth. Magnetization measurements confirmed ferromagnetic signals comparable to those expected for Co metal, suggesting that because of the high oxygen affinity of Ti, oxidation of Co nanorods did not occur. The obtained nanocomposite films were highly transparent in the visible-light region and had a ferromagnetic Faraday ellipticity of 1.9 × 104 deg cm−1 at 3.5 eV.

Growth and characterization of polycrystalline Ge 1− xC x by reactive pulsed laser deposition

Polycrystalline thin films of Ge–C were grown on Si (1 1 1) substrates by means of reactive pulsed laser deposition with methane pressure of 100 mTorr. Effect substrate temperature, T s, on C incorporation to substitutional sites ( x) in Ge 1− x C x was investigated systematically by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyzes. The substrate temperatures were ranging from 250 to 400 °C. The substitutional C composition x in the films by XRD were estimated using the Vegard's linear law. The maximum value of x calculated by XRD was 0.032 for T s of 350 °C. The position of the C 1s peak at 283.4 eV in the XPS spectrum confirmed the germanium–carbon alloys. XRD measurements indicated that x increased with T s from 250 °C to 350 °C. At T s = 400 °C, the estimation of x was lowered. However, the C content calculated by XPS analyzes increased with T s being more these values than substitutional C composition x. XPS and XRD analyzes demonstrate that the remaining C atoms are incorporated to interstitial sites. The use of the T s plays important roles in the incorporation of substitutional C and in restraining C-cluster formation in the reactive pulsed laser deposition growth of Ge–C/Si.

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm2/V s. By using the ZnO thin film grown by two-step PLD and a HfO2 high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×106 and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.

Thermal stability of SrTiO3/SiO2/Si Interfaces at Intermediate Oxygen Pressures

The thermal stability of epitaxial SrTiO3 thin films grown by molecular-beam epitaxy on Si (001) has been studied using x-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and thermodynamic calculations. Our studies focus on the stability of the SrTiO3/Si structures under the conditions typically employed in the pulse laser deposition (PLD) growth of complex metal oxide heteroepitaxy on Si. We observe additional Bragg peaks in thermally treated SrTiO3 buffered Si structures, corresponding to possibly TiSi2 and/or SrSiO3, reaction products which are consistent with the reaction schemes we propose. In addition, OM and SEM reveal microstructures that are not readily accounted for solely by the solid state reactions as put forth by previous workers but can be reasonably explained by our proposed reaction schemes. Using our observations and thermodynamic analysis, we argue that reactions involving the gaseous species SiO(g), the reactivity of which has not been previously considered in this system, are important. We attribute the onset of degradation of the SrTiO3 film at high temperatures, to the circular void forming reaction Si(s)+SiO2(s)→2SiO(g) at the interface and suggest that the reactions considered by previous workers involving all solid state reactants occurs only at the conclusion of degradation. Our results points to the need for keeping the PLD temperature as low as possible to minimize the production of reactive SiO(g) in avoiding the deleterious reactions.

Self‐organized growth of ZnO‐based nano‐ and microstructures

AbstractZnO‐based nano‐ and micro‐structures with controlled orientation, size, and lateral density were grown by specially designed two‐step pulsed laser deposition and direct carbothermal growth, respectively. Different substrate orientations and nucleation layers allow well‐defined tuning of growth direction and lateral arrangement of the wires. As a result, axial MgZnOZnO nano quantum dots and homogeneous radial nano core‐shell quantum well structures are demonstrated. Donor and acceptor doping of nano‐ and microwires influence considerably both electrical characteristics as well as morphology including branching. Field effect transistors with n‐ and p‐type wire channel and nanowire p–n junctions seem to prove a reproducible p‐type conductivity of phosphorous‐doped ZnO wires. Single ZnO wire (309 nm thick, 3.99 µm high) grown on pyramidal base with controlled lateral density by tuning the ZnO template layer in a two‐step PLD process. magnified image

Characteristic properties of Y2SiO5:Ce thin films grown with PLD

Three different gases (nitrogen (N2), oxygen (O2) and argon (Ar)) were used as background gases during the growth of pulsed laser deposition (PLD) Y2SiO5:Ce thin films. A Krypton fluoride laser (KrF), 248 nm was used for the PLD of the films on silicon (Si) (1 0 0) substrates. The effect of the background gases on the surface morphology, crystal growth and luminescent properties were investigated. All the experimental parameters, the gas pressure (455 mT), the substrate temperature (600 °C), the pulse frequency (8 Hz), the number of pulses (4000) and the laser fluence (1.6±0.2) J/cm2 were kept constant. The only parameter that was changed during the deposition was the ambient gas species. The surface morphology and average particle sizes were monitored with scanning electron microscopy (SEM) and atomic force microscopy (AFM). X-ray diffraction (XRD) and Auger electron spectroscopy (AES) were used to determine the crystal structure and composition, respectively. Cathodo- (CL) and photoluminescence (PL) were used to measure the luminescent intensities for the different phosphor thin films. The nature of the particles, ablated on the substrate, is related to the collisions between the ejected particles and the ambient gas particles. The CL and PL intensities also depend on the particle sizes. A 144 h (coulomb dose of 1.4×104 C cm−2) electron degradation study on the thin films ablated in the Ar gas environment resulted in a decrease in the main CL intensity peak at 440 nm and to the development of a new very broad luminescent peak spectra ranging from 400 to 850 nm due to the growth of a SiO2 layer on the surface.