Pulsed Laser Deposition Conditions Research Articles

Atom Probe Tomography of the LiFePO4-Electrolyte Interface Enabled by Thin Film Electrodes

Atom probe tomography (APT) can yield three-dimensional tomographic images at atomic-scale resolution and low-AMU elements such as Li are readily observed, making it a powerful tool for exploring battery materials interfaces. However, it is difficult to prepare APT specimen tips containing the interface of interest starting with typical particle-based battery electrodes. Here we demonstrate a methodology for reliable APT imaging of battery interfaces in which a thin film electrode geometry is used to provide well-controlled planar interfaces that are ideal for APT sample preparation and imaging. LiFePO4 (LFP) thin film electrodes, synthesized using pulsed laser deposition (PLD), were studied as an example system, with standard Li-salt electrolytes. For the results to be applicable to conventional particulate electrodes, it is important to obtain representative thin film structure and electrochemical characteristics. Thus, the effects of PLD conditions including substrate temperature, substrate crystallinity, target composition, and deposition time (number of laser pulses) on the thin film’s crystallographic texture, morphology, and electrochemical performance were studied. Optimized LFP film showed good crystallinity with low-C-rate capacity of ∼90 mAh g−1. Initial APT three-dimensional imaging of the LFP/electrolyte interface shows an ∼10 nm cathode-electrolyte interphase layer that is enriched in F and Li.

A DFT-based kinetic Monte Carlo simulation of multiphase oxide-metal thin film growth

Functional thin films of nanoscale metal pillars in oxide or nitride matrices known as vertically aligned nanocomposite (VAN) have gained much interest owing to their unique strain-coupled and highly anisotropic properties. So far, the deposition of these films has been explored mostly experimentally. In this work, a density functional theory (DFT)-based kinetic Monte Carlo simulation model using Bortz–Kalos–Lebowitz algorithm was developed to understand the growth of VAN films deposited by pulsed laser technique on mismatching substrates. The model has been parameterized and applied to understand the kinetics of growth thin films consisting of Au pillars in CeO2 matrix deposited on SrTiO3 substrates. The effects of pulsed laser deposition (PLD) conditions including the pulse frequency, deposition flux, and substrate temperature were explored. The simulations indicate that the Au pillar size and shape exhibit significant dependence on the PLD conditions. Namely, increasing the temperature increases the average pillar size and lowers the pillar density, and vice versa. In addition, the simulations revealed that increasing the deposition rate results in lowering the average pillar size and increasing the density. Particularly, the DFT results suggest that Au pillar size can be tuned during the initial growth of the first monolayer due to the significantly low activation barrier. Our analysis showed that the relationship between the average pillar size and pillar density is influenced by the kinetics. Furthermore, autocorrelation analysis showed that pillars self-organize in quasi-ordered patterns at certain windows of the deposition conditions, which is attributed to the complex nature of the chemical interactions in the system, the kinetics, and the deposition parameters.

Bi doped LaOCl and LaOF thin films grown by pulsed laser deposition

Thin films of Bi3+ doped LaOCl and LaOF phosphors prepared via the pulsed laser deposition (PLD) technique in vacuum and different argon (Ar) pressures were compared in order to assess their luminescence properties. All peaks of the X-ray diffraction patterns of the films were consistent with the tetragonal structure of the LaOCl and LaOF, but in the case of LaOF the signal was weaker and not all peaks were present, suggesting some preferred orientation. Photoluminescence measurements revealed that the films exhibited emission around 344 nm for LaOCl:Bi and 518 nm for LaOF:Bi under excitations of 266 nm and 263 nm, respectively. The luminescence from the LaOF:Bi sample was less intense compared to the LaOCl:Bi sample prepared under the same conditions, which was also the case for the powder samples. The amount of ablated material present on the substrate was much less for LaOF:Bi compared to LaOCl:Bi, which is attributed to the greater bandgap and hence weaker absorption of the laser pulses for LaOF:Bi. Therefore phosphors based on LaOCl as the host material were found to be preferable over LaOF under the PLD conditions used in this study.

Designing Multidimensional and Interconnected Multi-Element Nanostructures by Exsolution-Self-Assembly in a Complex Concentrated Oxide

Complex concentrated oxides (CCOs) are an emerging material class that includes high-entropy oxide (HEOs) and entropy-stabilized oxides (ESOs), whose unprecedented properties stem from disorder-induced distributions in electronic structure and chemistry caused by stabilizing many-cation (typically > 5) solid solutions [1-2]. Integrating these materials into composites with nanoscale tunability will enable tailored (multi)functionality beyond what is possible in a single phase [3]. Here, we demonstrate a novel, highly extensible approach, exsolution self-assembly (ESA), to realize CCO-based nanocomposite thin films with intricate multi-element nanostructures [4]. Using pulsed-laser deposition (PLD), we selectively reduce cations in a 6-cation model perovskite CCO, inducing defect-interaction-driven exsolution and simultaneous self-assembly of metal nanorods and metal-oxide core-shell nanoparticles, depending on film growth conditions. ESA using a CCO precursor enables novel multielement composite morphologies with finely tuned sub-phase chemical composition that are not possible by conventional exsolution or self-assembly independently. By mapping the distribution of distinct sub-phase structure and chemistry with sub-nanoscale electron microscopy and atom probes, we show that Ellingham's model of cation reducibility predicts nanostructure chemical composition while mass transport via extended defects governs local morphology formation. Importantly for various applications, the electronic conductivity of our nanocomposites exceeds 0.1 S/cm at room temperature, with transport correlated to nanostructure formation primarily through B-site cation mixed valency and site occupancy in the CCO matrix.A correlated analysis using aberration-corrected scanning transmission electron microscopy (STEM) imaging, energy dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), geometric phase analysis (GPA) strain mapping, atom probe tomography (APT) with 3D mass spectrometry, and X-ray photoemission spectroscopy (XPS) was performed to elucidate the fundamental nanostructure formation mechanisms underlying the highly tailorable synthesis approach. We show that the method achieves uniform bulk exsolution with short process time and is manipulated by tuning readily accessible PLD conditions. Detailed characterization resolved the impact of increasing oxygen vacancy concentration and varying cation reducibility on nanostructure self-assembly. For example, metal nanorods grow from the bottom of the thin film to the top surface, with growth restricted by compressive stress exerted by the matrix in the in-plane direction. Metal-oxide core-shell nanoparticles embedded in the matrix form via seed growth effect triggered by metal nanoparticle formation followed by subsequent reduction of additional mobile cations. This work demonstrates a route towards vast morphological tunability and compositional complexity through nanocomposite design of CCO thin films. Given CCOs’ vast combinatorial space, ESA is expected to be highly extensible via application to novel compositions and crystal structures, with the understanding presented here enabling one to take advantage of chemical complexity in a rational way.

Impact of Calcium Doping of YBa2Cu3O7-δ Multilayer Thin Films on the Flux Pinning Landscape at 65–5 K, 0–9 T for Various Applications

An important research goal in the applications of high temperature superconductor YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) thin films is increasing both the critical current density and also the isotropic nature of the film. YBCO is inherently anisotropic due to its layered perovskite structure. The critical current density of YBCO thin films is enhanced by increasing the flux pinning sites in the film by the addition of insulating nano-phase materials, such as BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BZO) nanorods, which are also anisotropic in nature. Using a multilayer pulsed laser deposition technique has been shown to produce films with inclusions that are more isotropic in nature. However, the defective BZO nanorod interface, resulting from its lattice mismatch with YBCO, prevents obtaining optimum pinning force. This research explores the effect of Ca doped YBCO space layers in the multilayer composite film, on the BZO nanorod/YBCO interface, over a wide range of conditions of 65–5 K and 0– 9T that are suitable for various applications. The interplay of combining these three variables: BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> addition to YBCO, multilayer film growth resulting from varying pulsed laser deposition conditions, and employing calcium doped YBCO space layers, and the resulting impact on film microstructures and superconducting properties, will be presented.

Terahertz emission enhancement of GaAs-based photoconductive antennas via the nanodecoration of their surface by means of pulsed-laser-deposition of gold nanoparticles

We report a systematic study of free-space terahertz (THz) emission from photoconductive antennas (PCAs) nanodecorated with gold nanoparticles (Au-NPs) deposited by using the pulsed laser deposition (PLD) technique. H-shaped dipole micro-structured PCAs fabricated on semi-insulating GaAs substrates were decorated under various PLD conditions. Thus, by increasing the number of laser ablation pulses (NLP) of the Au target, both the average size of Au-NPs and the surface loading of PCAs increase. Compared with non-decorated PCAs, those decorated with Au-NPs exhibit significant enhancement in the radiated THz pulse amplitude. A maximum enhancement of ∼2.3 was achieved at NLP = 1250. Under this optimal NLP condition, not only is the average Au-NP size (of ∼15 nm) favorable for light absorption via localized surface plasmons, but also the inter-distance between NPs, the light reflectance, and facilitated transport of photocarriers, all combine to yield a stronger THz field emission. For higher NLP (≥2000), NPs coalesce and tend to form continuous film NPs, which not only significantly limits the light scattering toward the GaAs underlying substrate, but also electrically shorts the PCA. Finally, the Au-NP decoration of GaAs PCAs was also found to improve their overall thermal conductivity, making them much more thermally stable than their non-decorated counterparts.

Control of self-organization of drop-casted Nafion film for improving proton conduction in a polymer-electrolyte-membrane fuel cell to raise its output power density

A simple drop-cast method to directly deposit Nafion polymer electrolyte membrane (PEM) on nanostructured thin-film catalyst layer composed of stacked Pt nanoparticles prepared by pulsed laser deposition (PLD) was demonstrated. Through optimization of solvent composition and drying temperature of Nafion solution to control self-organization of Nafion, a uniform PEM with better bulk and interface microstructures could be produced, leading to a significant improvement in the output current density of a PEM fuel cell over that using reference commercial PEMs. The formation of facile proton conduction pathways in the bulk Nafion membrane resulted in a 35% reduction in ohmic resistance compared to that with the commercial membrane. Moreover, the infiltration of Nafion in the catalyst layer formed suitable proton transport network to render more catalyst nanoparticles effective and thus lower charge-transfer resistance. With the optimized PLD, drop-cast, and hot-pressing conditions, the current density of PEMFCs using drop-casted PEM reached 1902 mA cm−2 at 0.6 V at 2 atm H2 and O2 pressures with a cathode Pt loading of 100 μg cm−2, corresponding to a power density of 1.14 W cm−2 and a cathode mass-specific power density of 11.4 kW g−1.

Thermodynamics as a Driving Factor of LiCoO2 Grain Growth on Nanocrystalline Ta-LLZO Thin Films for All-Solid-State Batteries.

All-solid-state batteries primarily focus on macrocrystalline solid electrolyte/cathode interfaces, and little is explored on the growth and stability of nanograined Li-garnet and cathode ones. In this work, a thin (∼500 nm) film of LiCoO2 (LCO) has been grown on top of the polycrystalline layer of Ta-doped Li7La3Zr2O12 (Ta-LLZO) solid electrolyte using the pulsed laser deposition (PLD) technique. Scanning transmission electron microscopy, electron diffraction, and electron tomography demonstrated that the LCO film is formed by columnar elements with the shape of inverted cones. The film appears to be highly textured, with the (003) LCO crystal planes parallel to the LCO/Ta-LLZO interface and with internal pores shaped by the {104} and {102} planes. According to density functional theory (DFT) calculations, this specific microstructure is governed by a competition between free energies of the corresponding crystal planes, which in turn depends on the oxygen and lithium chemical potentials during the deposition, indicating that thermodynamics plays an important role in the resulting LCO microstructure even under nonequilibrium PLD conditions. Based on the thermodynamic estimates, the experimental conditions within the LCO stability domain are proposed for the preferential {104} LCO orientation, which is considered favorable for enhanced Li diffusion in the positive electrode layers of all-solid-state batteries.

Nano-electrical conductivity guided optimization of pulsed laser deposited ZnO electron transporting layer for efficient perovskite solar cell

ZnO films are deposited on optically transparent electrodes (OTE) by Pulsed Laser Deposition (PLD) and those are utilized as the electron transporting layer (ETL) of perovskite solar cells (PSC). PLD conditions are tuned to optimize the ZnO films in order to achieve an efficient device. Along nanostructure, nano-electrical conducting characteristics of the ETL films, which are measured by conducting atomic force microscopy (c-AFM), are found to be the guiding factor in determining the photovoltaic properties of the devices.

Utilizing TiO2 amorphous precursors for polymorph selection: An in situ TEM study of phase formation and kinetics

AbstractSelective synthesis of metastable polymorphs requires a fundamental understanding of the complex energy landscapes in which these phases form. Recently, the development of in situ high temperature and controlled atmosphere transmission electron microscopy has enabled the direct observation of nucleation, growth, and phase transformations with near atomic resolution. In this work, we directly observe the crystallization behavior of amorphous TiO2 thin films grown under different pulsed laser deposition conditions and quantify the mechanisms behind metastable crystalline polymorph stabilization. Films deposited at 10 mTorr chamber oxygen pressure crystallize into nanocrystalline Anatase at 325°C, whereas films deposited at 2 mTorr crystallize into significantly larger needle‐like grains of Brookite and Anatase at 270°C. Increasing film deposition rate by a factor of 4 results in a 10× increase in the crystalline growth front velocity as well as a decrease in crystallization temperature from 270°C to 225°C. Engineering the amorphous precursor state through deposition conditions therefore provides routes to microstructure control and the accessibility of higher energy metastable phases.

Development of Metal Supported Cells Using BaZrO3-Based Proton Conducting Ceramics

Proton Conducting Ceramics (PCCs) enable a variety of potential applications, such as hydration or dehydration of chemicals in addition to fuel cells and electrolysers. Here we demonstrate the development of PCCs in the third-generation architecture, i.e. porous Metal Supported (MS) cells, performed in the project DAICHI based on the expertize of MS-solid oxide cells in the European project EVOLVE. Engineering the electrode and electrolyte coating process on a porous ITM metal substrate, (La,Sr)MnO3 electrode and intermediate electrolyte layers were successfully fabricated to reduce the pore size from a few tens of µm (MS) to below hundred nm. A few µm-thick BaZrO3-based electrolyte layer was coated on the top of nano-porous intermediate layer by Pulsed Laser Deposition (PLD). The results demonstrated dense and crack-free MS-PCC cells obtained under optimal PLD conditions and with the entire processing below 1000°C.

Selection of pulsed laser deposition conditions for preparation of perfect thin-film MoSx hydrogen evolution catalysts

The influence of pulsed laser deposition conditions in the geometry “off-axis” on the catalytic properties of MoSx films in the hydrogen evolution reaction is investigated. For the deposition of MoSx films from MoS2 target, pulsed laser radiation from the IR and UV wavelength ranges was used. The angle of incidence of the laser-induced plume on the surface of the substrate in a buffer gas was varied to check the influence of large in-size Mo-enriched particles. The efficiency of the catalyst was estimated from the results of the turnover frequency (TOF) measurement, which made it possible to minimize the influence of the “loading” of the catalyst on its characteristics. The effects of the chemical composition, local structure, and properties of the catalyst–substrate interface on the efficiency of the hydrogen evolution reaction are analysed. The regime of pulsed laser deposition of more effective thin-film MoSx catalysts is determined.

High optical quality cellulose thin films grown from raw natural cotton by pulsed laser deposition

Raw natural cotton harvested in the fields of Thessaly, Central Greece, was used to grow high optical quality, highly durable cellulose thin films by pulsed laser deposition, using 193 nm ArF laser pulses. Standard pulsed laser deposition conditions at room temperature were applied and raw, unprocessed, natural cotton targets were used. The semi-crystalline cellulose of natural cotton converts to very durable solid films that are fully transparent in the visible wavelength range and exhibit amorphous structure. Thin film quality and surface morphology are parametrically investigated and show a strong dependence on laser fluence. Films deposited at the lowest fluence levels ~ 5 mJ/cm2 on target, close to the observed ablation threshold, exhibit roughness of ~ 1.7 nm rms. The high optical quality of the grown biocompatible cellulose materials proves the unique capacities of laser deposition and processing methods and promise novel biophotonics and other interdisciplinary applications for the health and safety of the citizen.

Characterisation of AlN nano thin films prepared by PLD

ABSTRACTAluminium nitride (AlN) nano thin films have been prepared by pulsed laser deposition (PLD) in this paper. The microstructure and grain size of the nano thin films were characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the PLD conditions such as laser fluence, ambient pressure and substrate temperature influence the thickness, morphology and grain size of the nano thin films obviously, i.e. the surface of the nano thin films becomes rough while the grain size increases with increasing the laser fluence, ambient pressure and substrate temperature. In addition, there exists a preferred orientation growth in the thin films.

Development of Long-Length BMO-Doped REBCO Coated Conductors by Hot-Wall PLD Process

Fujikura Ltd., Chiba, Japan, has developed stable and high-throughput production techniques for REBCO coated conductors (CC) by using large-area ion-beam-assisted-deposition (IBAD), and hot-wall type pulsed-laser-deposition (PLD). Recently, we have been attempting to dope BaMO 3 (BMO, M: Zr or Hf) to REBCO layer in order to enhance in-field critical current density (J c ). In the course of optimizing deposition conditions of PLD for BaHfO 3 doped EuBCO films on IBAD templates, “high J c condition” and “high growth rate condition” were found. For samples prepared under these conditions, the magnetic field angle dependence of I c and REBCO thickness dependence were investigated. Finally, we succeeded in fabricating a 300-m-long CC with uniform I c distribution at the high-growth-rate condition. The longitudinal I c homogeneity (defined as standard deviation divided by average) at 77 K evaluated by magnetization method was 2.6%, which is comparable to nondoped conductors. Transport in-field I c for the both end points were 1756 and 1786 A/cm at 30 K, 2 T, respectively.

Toward a comprehensive UV laser ablation modeling of multicomponent materials—A non-equilibrium investigation on titanium carbide

Titanium carbide (TiC) coatings of great quality can be produced using nanosecond pulsed laser deposition (PLD). Because the deposition rate and the transfer of the target stoichiometry depend strongly on the laser-target/laser-plasma interaction as well as the composition of the laser induced plume, investigating the ruling fundamental mechanisms behind the material ablation and the plasma evolution in the background environment under PLD conditions is essential. This work, which extends previous investigations dedicated to the study of nanosecond laser ablation of pure target materials, is a first step toward a comprehensive non-equilibrium model of multicomponent ones. A laser-material interaction model coupled to a laser-plasma interaction one is presented. A UV 20 ns KrF (248 nm) laser pulse is considered. Ablation depths, plasma ignition thresholds, and shielding rates have been calculated for a wide range of laser beam fluences. A comparison of TiC behavior with pure titanium material under the same conditions is made. Plasma characteristics such as temperature and composition have been investigated. An overall correlation between the various results is presented.

Studying Pulsed Laser Deposition conditions for Ni/C-based multi-layers

Nickel carbon based multi-layers are a viable route towards future hard X-ray and soft γ-ray focusing telescopes. Here, we study the Pulsed Laser Deposition growth conditions of such bilayers by Reflective High Energy Electron Diffraction, X-ray Reflectivity and Diffraction, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and cross-sectional Transmission Electron Microscopy analysis, with emphasis on optimization of process pressure and substrate temperature during growth. The thin multi-layers are grown on a treated SiO substrate resulting in Ni and C layers with surface roughnesses (RMS) of ≤0.2 nm. Small droplets resulting during melting of the targets surface increase the roughness, however, and cannot be avoided. The sequential process at temperatures beyond 300 °C results into intermixing between the two layers, being destructive for the reflectivity of the multi-layer.

Imaging pulsed laser deposition oxide growth by in situ atomic force microscopy.

To visualize the topography of thin oxide films during growth, thereby enabling to study its growth behavior quasi real-time, we have designed and integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD) vacuum setup. The AFM scanner and PLD target are integrated in a single support frame, combined with a fast sample transfer method, such that in situ microscopy can be utilized after subsequent deposition pulses. The in situ microscope can be operated from room temperature up to 700 °C and at (process) pressures ranging from the vacuum base pressure of 10-6 mbar up to 1 mbar, typical PLD conditions for the growth of oxide films. The performance of this instrument is demonstrated by resolving unit cell height surface steps and surface topography under typical oxide PLD growth conditions.

Enhanced electrocatalytic nitrate reduction by preferentially-oriented (100) PtRh and PtIr alloys: the hidden treasures of the ‘miscibility gap’

Bimetallic alloys of Pt and Rh or Ir were prepared with pulsed laser deposition (PLD) on a well-ordered MgO(100) substrate, leading to epitaxial growth along the [001] plane, as confirmed by surface analysis techniques. The out-of-equilibrium conditions of PLD allowed the exploration of a range of compositions for which phase separation would instead be expected. The electrochemistry of a series of PtRh and PtIr (100) alloys was investigated in 0.5M H2SO4, showing a surprisingly intense electrocatalytic activity towards the reduction of nitrate for a Pt content of 21–42%. These alloys feature a lower reaction overpotential with respect to Rh and Ir while outperforming the pure metals in terms of reduction current. A detailed analysis of the voltammetric features with respect to alloy composition highlighted a correlation between hydrogen desorption and nitrate reduction activity. In addition, an optimal potential range for nitrate reduction, common to PtRh and PtIr alloys, was observed, corresponding to the potential window in which nitrate adsorption coincides with fast reduction of the key reaction intermediate NOads.

Pulsed laser-deposited nanocrystalline GdB6 thin films on W and Re as field emitters

Gadolinium hexaboride (GdB6) nanocrystalline thin films were grown on tungsten (W), rhenium (Re) tips and foil substrates using optimized pulsed laser deposition (PLD) technique. The X-ray diffraction analysis reveals formation of pure, crystalline cubic phase of GdB6 on W and Re substrates, under the prevailing PLD conditions. The field emission (FE) studies of GdB6/W and GdB6/Re emitters were performed in a planar diode configuration at the base pressure ~10−8 mbar. The GdB6/W and GdB6/Re tip emitters deliver high emission current densities of ~1.4 and 0.811 mA/cm2 at an applied field of ~6.0 and 7.0 V/µm, respectively. The Fowler–Nordheim (F–N) plots were found to be nearly linear showing metallic nature of the emitters. The noticeably high values of field enhancement factor (β) estimated using the slopes of the F–N plots indicate that the PLD GdB6 coating on W and Re substrates comprises of high-aspect-ratio nanostructures. Interestingly, the GdB6/W and GdB6/Re planar emitters exhibit excellent current stability at the preset values over a long-term operation, as compared to the tip emitters. Furthermore, the values of workfunction of the GdB6/W and GdB6/Re emitters, experimentally measured using ultraviolet photoelectron spectroscopy, are found to be same, ~1.6 ± 0.1 eV. Despite possessing same workfunction value, the FE characteristics of the GdB6/W emitter are markedly different from that of GdB6/Re emitter, which can be attributed to the growth of GdB6 films on W and Re substrates.