Pulsed Laser Deposition Target Research Articles

Dopant compensation in component-dependent self-doped Cs2SnI6 thin films grown with PLD at room temperature

Tetravalent tin (Sn4+)-based inorganic perovskite semiconductors like Cs2SnI6 are expected to replace lead-based perovskite counterparts due to advantages such as structural stability and environmental friendliness. In this paper, we reported the dopant compensation effect in the component-dependent self-doped (111)-oriented Cs2SnI6 thin films grown with pulsed laser deposition (PLD) at room temperature. The films were grown on (100)-SrTiO3 (STO) substrates at room temperature by PLD. Hall results of the Cs2SnI6 films with different components realizing by controlling the ratio of SnI4/CsI in the targets demonstrate a clear change of conductivity type from N-type to P-type, while the carrier concentration decreases from 1018 to 1013 and accordingly the film resistivity increases significantly from 3.8 to 2506 Ω cm. The defect-related optical fingerprints of Cs2SnI6 films were also investigated with temperature-dependent photoluminescence spectroscopy. At low temperatures of 10 K, the Cs2SnI6 films exhibit donor-bound (D0X) and donor-acceptor pair (DAP) emission, respectively, due to the self-doping effect. These results indicate that controlling the composition of the PLD target is a powerful way to tune the electrical properties of Cs2SnI6 films for possible applications in solar cells or X-ray detectors.

Deposition of Sn-Zr-Se precursor by thermal evaporation and PLD for the synthesis of SnZrSe3 thin films

Background ABX3 (X=Se, S) chalcogenides are an emerging class of materials for sustainable photovoltaics. Among ABX3 materials, BaZrS3 has gained the highest community interest. BaZrS3 is the wide bandgap absorber (> 1.7 eV) and therefore is intended for application as a top sub-cell in multijunction devices. However, narrow band gap ABX3 compounds have drawn little attention although this could potentially open the path for fabrication of multijunction solar cells based entirely on ABX3 materials. SnZrSe3 is a narrow bandgap semiconductor with an absorption edge located at around 1.0 eV, but there are no reports on the formation of SnZrSe3 thin films thus far. In this work, therefore, we aim to obtain SnZrSe3 thin films by sublimation methods. Methods Thermal evaporation and pulsed laser deposition (PLD) techniques were used to deposit Sn-Zr-Se precursor films. SnZrSe3 powder was synthesized and used as a source material for evaporation and PLD target preparation. Precursor films were deposited by PLD from single-phase and binary selenide targets. Results We found that using SnZrSe3 powder, only SnSe films were deposited under various conditions by thermal evaporation. Precursor films obtained by PLD from single-phase targets were amorphous and comprised SnSe2 and a-Se phases whereas using binary targets crystalline SnSe and a-Se were detected. Thermogravimetric analysis revealed that SnZrSe3 was thermally stable up to 450 °C and afterwards decomposed into SnSe, Se and ZrSe2-x. Conclusions Using methods described in this work, we were not able to achieve congruent sublimation of SnZrSe3 because of the following reasons: (i) upon energetic excitation, SnZrSe3 decomposes into compounds with very different vapour pressure; (ii) inability to substitute O with Se due to very high chemical affinity of Zr and O. Direct sublimation methods are challenging for formation of SnZrSe3 thin films and other techniques, such as co-evaporation should be explored.

Epitaxial growth of pure Sr3Al2O6 sacrificial layer for high quality freestanding single-crystalline oxide membranes

The water-soluble cubic Sr3Al2O6 has recently boosted the study of freestanding single-crystalline oxide membranes with extraordinary mechanical, ferroelectric, piezoelectric, or ferromagnetic properties for flexible electronics. Secondary phases usually exist in ceramic target due to complexity of SrO-Al2O3 binary solution. Therefore, pure Sr3Al2O6 epitaxial thin film is critical for obtaining high-quality freestanding single-crystalline oxide membranes. In this study, we prepare phase-pure Sr3Al2O6 thin films from both phase-pure and phase-impure targets as pulsed laser deposition targets and fabricate SrTiO3(001)/Sr3Al2O6/SrRuO3 heterostructures to obtain freestanding single-crystalline SrRuO3 membranes. The phase of the sacrificial layer is very sensitive to the laser energy density, and a secondary phase appears when it is below 1.5 J/cm2 and disappears under a higher laser energy density. Similar behavior is observed again when using a stoichiometric but phase-impure Sr3Al2O6 ceramic target. Such a secondary phase is identified to be SrAl2O4, and its appearance accompanies a Sr/Al gradient in the sacrificial layer, possibly due to the film growth kinetics. The freestanding SrRuO3 membranes crack easily during transferring when such secondary phase appears in the heterostructure while eliminating it facilitates crack-free membranes. This study brings insight into the growth of phase-pure Sr3Al2O6 films to prepare high-quality freestanding single-crystalline oxide membranes.

Pulsed-laser deposition and photocatalytic activity of pure rutile and anatase TiO2 films: Impact of single-phased target and deposition conditions

Titanium dioxide is a technologically interesting material in many applicative fields that, however, exhibits critical aspects in terms of phase purity and synthesis/growth conditions.The presented work deals with the deposition, in vacuum, of single-phase rutile and anatase titania films by excimer laser ablation (λ = 248 nm) of anatase and rutile targets. Post-deposition thermal treatment at 450 °C in air was applied to drive the crystalline evolution of the as-deposited films, limit oxygen desorption and avoid changes in the polymorph phase.Unlike the typical use of oxygen as a background gas and Ti target in pulsed laser deposition of TiO2, our setting vacuum background atmosphere not only allows to relate the final phase of the film directly to the target phase but also to rule out phase transitions and mixed-phase, by the interplay between post-growth temperature and limited oxygen desorption. Herein, we study and discuss how the ablation process impacts on and determines film composition and morphology. The discussed influence of the target phase on the optical, morphological and photocatalysis properties of the titania films points out good performances of our samples and the importance to tune deposition to obtain the titania polymorph phase more suitable for specific applications.

Pathway to tailor the phase composition, microstructure and mechanical properties of pulsed laser deposited cobalt-substituted calcium phosphate coatings on titanium

Dense calcium phosphate-based ceramics were fabricated to be used as targets for pulsed laser deposition (PLD). Nanostructured cobalt-substituted hydroxyapatite (Co:HAP) was used as a starting powder. To vary phase composition and microstructure of targets, two sintering approaches were applied, conventional (CS) and two-step sintering (TSS). The obtained results show that in both cases biphasic calcium phosphate (BCP) ceramics (targets) were prepared, with slightly different HAP-to-β–TCP amount ratio and a significantly different microstructure. While the CS method yielded fully dense ceramics with an average grain size of 1.3 μm, the ceramics prepared by TSS had a density of 98.5%, with a predominant grain size below 100 nm. (Ca + Co)P coatings were prepared by PLD of (Ca + Co)P targets. The temperature of the Ti substrate was adjusted to be 25 and 500 °C. The results show that the phase composition of (Ca + Co)P coatings depended on the phase composition of targets as well as on the temperature of the Ti substrate. The coating prepared at 25 °C using CS target consisted of three calcium phosphate phases, HAP, β–TCP and α–TCP; when the TSS target was used, the coating was biphasic, containing HAP and β–TCP. When the substrate was heated to 500 °C, regardless of whether the CS or the TSS target was used, the deposited coatings were composed of HAP and α–TCP. Due to different phase compositions, the (Ca + Co)P coatings deposited at 25 °C showed an improved hardness compared to those deposited at 500 °C. The obtained results confirmed that the phase composition, morphology and mechanical properties of 0.3 μm thick (Ca + Co)P coatings on a Ti substrate can be tailored by employing (Ca + Co)P targets with different microstructures, and also by varying the temperature of the Ti substrate during deposition experiments.

PREPARATION AND BIOLOGICAL EVALUATION OF PLD-BASED FORSTERITE–HYDROXYAPATITE NANOCOMPOSITE COATING ON STAINLESS STEEL 316L

The present work deals with the fabrication of forsterite–hydroxyapatite (FS–HA) hybrid coatings on stainless-steel 316L using the pulsed laser deposition (PLD) technique. The stainless steel (SS 316L) as a metallic implant is widely used in hard tissue applications. The XRD studies have confirmed the crystalline behavior of synthesized FS powder with an average crystallite size of 54[Formula: see text]nm. The synthesized FS powder was mixed in different compositions (10, 20, 30[Formula: see text]wt.%) into HA for preparing PLD targets (pellets). The XRD of the prepared pellets by UTM has confirmed both phases of FS and HA. The Scanning Electron Microscopy (SEM) of the coated samples depicted the successful deposition of composite powders on the substrates (SS 316[Formula: see text]L). The Ellipsometer was used to investigate the thickness of different substrates and it was found as 243, 251, 255, and 257[Formula: see text]nm for CP1, CP2, CP3, and CP4, respectively. The bioactivity of the coated substrates with different compositions (pure HA, 10%, 20%, 30%, and pure FS) was investigated by immersing the samples in simulated body fluid (SBF) for 14[Formula: see text]days. The same samples were then characterized by SEM which confirms the apatite layer formation that reflects the bioactivity. The addition of FS powder into HA will stimulate the apatite formation which enhances the bioactivity. The Raman Spectroscopy of coated samples reveals the successful deposition of different compositions of FS–HA nanocomposite. The peaks of Raman spectroscopy were corresponding to the XRD results of the pellets (different compositions of FS–HA). The antimicrobial activity of different compositions of FS–HA against Escherichia coli (E. coli) bacteria also showed a significant zone of inhibition. The bioactivity and antimicrobial behavior of FS–HA along with successful deposition by PLD have shown better potential applications for biomedical implant coating.

Effect of Target Morphology on Morphological, Optical and Electrical Properties of FTO Thin Film Deposited by Pulsed Laser Deposition for MAPbBr3 Perovskite Solar Cell

Three targets for pulsed laser deposition (PLD), having different morphology were used to deposit FTO thin film on three glass substrates to fabricate three FTO/SnO2/perovskite/spiro-OMeTAD/Silver perovskite solar cells. 5000 pulses of KrF excimer laser (348 nm, 50 Hz, 10 ns), having 1.2J energy were used to ablate FTO targets. Absorption, transmittance, resistivity, charge mobility and bandgap of deposited FTO thin film were observed to be dependent on target morphology. SEM micrographs of FTO layer reviled significant changes in smoothness and compactness of the thin films due to change in target morphology. Random three dimensional structures of FTO are observed on FTO layer by AFM. These random structures played very important role in improvement of solar cell performance. Maximum efficiency of 12.5% was achieved for proposed FTO/SnO2/perovskite/spiro-OMeTAD/Silver solar cell.

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

Structural properties of rhombohedral α‐(AlxGa1−x)2O3 thin films grown by two combinatorial pulsed laser deposition (PLD) techniques are investigated for the entire composition range. One α‐(AlxGa1−x)2O3 thin film is deposited on a 2 inch in diameter large a‐plane sapphire substrate using the continuous composition spread (CCS) PLD technique to fabricate a thin film with varying Al content ranging between x = 0.13 and x = 0.84. Laterally homogeneous α‐(AlxGa1−x)2O3 thin films exhibiting discrete Al contents are fabricated using radially segmented PLD targets on (11.0) Al2O3. Independent of the PLD technique, for x ≈ 0.55, a change from relaxed to pseudomorphic growth is observed as confirmed by the evolution of in‐ and out‐of‐plane lattice constants. The crystal structure is studied depending on the cation composition by X‐ray diffraction confirming the fabrication of epitaxial, corundum‐structured thin films.

Epitaxial κ-(AlxGa1−x)2O3 thin films and heterostructures grown by tin-assisted VCCS-PLD

The structural, surface, and optical properties of phase-pure κ-(AlxGa1−x)2O3 thin films on c-sapphire and STO(111):Nb substrates as well as on MgO(111) and κ-Ga2O3 templates are reported as a function of alloy composition for x < 0.4. The thin films were grown by tin-assisted pulsed laser deposition (PLD). For the variation of the Al-content, we utilized radially segmented PLD targets that enable the deposition of a thin film material library by discrete composition screening. Growth on κ-Ga2O3 (001) thin film templates enhanced the phase pure growth window remarkably up to x = 0.65. The crystallization of the κ-phase was verified by X-ray diffraction 2θ-ω-scans for all samples. Both in- and out-of-plane lattice constants in dependence on the Al-content follow a linear relationship according to Vegard’s law over the complete composition range. Atomic force microscope measurements confirm smooth surfaces (Rq ≈ 1.4 nm) for all investigated Al-contents. Furthermore, bandgap tuning from 4.9 eV to 5.8 eV is demonstrated and a linear increase in the bandgap with increasing Al-content was observed.

Enhanced flux pinning isotropy by tuned nanosized defect network in superconducting YBa2Cu3O6+x films

Striving to improve the critical current density Jc of superconducting YBa2Cu3O6+x (YBCO) thin films via enhanced vortex pinning, the interplay between film growth mechanisms and the formation of nanosized defects, both natural and artificial, is systematically studied in undoped and BaZrO3 (BZO)-doped YBCO thin films. The films were grown via pulsed laser deposition (PLD), varying the crystal grain size of the targets in addition to the dopant content. The microstructure of the PLD target has been observed to have a great impact on that of the deposited thin films, including the formation of vortex pinning centers, which has direct implications on the superconducting performance, especially on the isotropy of flux pinning properties. Based on experimentally measured angular dependencies of Jc, coupled with a molecular dynamics (MD) simulation of flux pinning in the YBCO films, we present a quantitative model of how the splay and fragmentation of BZO nanorods artifically introduced into the YBCO film matrix explain the majority of the observed critical current anisotropy.

Fabrication and Characterization of Thin Film SrCo0.8Nb0.1Ta0.1O3-Δ By Pulsed Laser Deposition

High working temperature(≥800 °C) of solid oxide fuel cell(SOFC) causes high cost of balance of plant, long start up time, and low durability. To overcome these barriers, lowering the working temperature of SOFC is one of the most attractive ways and such strategy has been researched through the fabrication of thin electrolyte and developing new perovskite cathode material. Recently, mixed ionic electronic conducting(MIEC) cathode material, SrCo0.8Nb0.1Ta0.1O3-δ (SCNT), has been developed by Li et al. and the SOFC with the cathode showed high performance(1.22W/cm2) at low working temperature (500 °C) with 14µm thick gadolinia doped ceria(GDC) electrolyte[1]. To apply SCNT to SOFC with thin electrolyte(≤1µm), the cathode must be fabricated on the electrolyte without high temperature sintering process(≥1000 °C) because of the weak mechanical strength of thin electrolyte. In this work, pulsed laser deposition(PLD) method was employed for the fabrication of thin film SCNT. PLD has been used widely for perovskite material deposition because of its high preservability of stoichiometric ratio of its original target material. However, the deposition temperature of PLD has a great influence on both physical and chemical structure of the film which means oxygen reaction activity(ORR) of the film also varies as temperature changes. Therefore, thin film SCNT was deposited by PLD at various temperature condition in this work to see the diversity of thin film characteristic for understanding the feasibility of application of SCNT to thin film SOFC (TF-SOFC). Powder and PLD target of SCNT were both prepared by the method Li et al. used, solid state reactive sintering(SSRS). The film was firstly deposited on Si wafer at various temperature (room temp, 500, 600, 700 °C) by PLD. Field emission scanning electron microscope (FE-SEM) and focused ion beam-SEM (FIB-SEM) were used to see the nano-structure of the film and deposition rate. 75mTorr of oxygen atmosphere was enough to make the structure of thin film deposited at room temperature very porous but dense film was observed at the temperature higher than 500 °C. The atomic ratio and crystallinity of each film were identified by X-ray spectroscopy(XPS) and X-ray diffraction(XRD) respectively. Through the understanding the physical and chemical variation of PLD deposited SCNT at different temperature condition, the best PLD deposition condition of SCNT for TF-SOFC was derived. Acknowledgment This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2012M3A6A7054855) References [1] M. Li et al., “A niobium and tantalum co-doped perovskite cathode for solid oxide fuel cells operating below 500 °c,” Nat. Commun., vol. 8, no. 5, pp. 1–9, 2017.

Effect of Ceramic-Target Crystallinity on Metal-to-Insulator Transition of Epitaxial Rare-Earth Nickelate Films Grown by Pulsed Laser Deposition

We demonstrate the effect of the crystallinity of ceramic targets on the electronic properties of LaNiO3 (001) thin films epitaxially grown by pulsed laser deposition (PLD). We prepared two kinds of LaNiO3 targets with different crystallinity by manipulating calcination temperature (i.e., 300 and 1000 °C) in the solid state reaction for ceramic synthesis. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) experiments of the as-sintered LaNiO3 ceramic targets clearly show that the LaNiO3 target sintered after high-temperature (1000 °C, high crystallinity) calcination is more oxidized to Ni3+ with better crystallinity than the LaNiO3 target sintered after low-temperature (300 °C, poor crystallinity) calcination. Using these two LaNiO3 ceramics as PLD targets, we fabricated epitaxial LaNiO3/LaAlO3 (001) thin-film heterostructures to examine how target crystallinity affects the physical properties of LaNiO3 films. Intriguingly, the electri...

Comparison Study of the Flux Pinning Enhancement of YBa2Cu3O7−δ Thin Films With BaHfO3 + Y2O3 Single- and Mixed-Phase Additions

Incorporating nano-scale insulating phases to YBa2Cu3O7−δ (YBCO) superconductor thin films enhances flux pinning by combining different pinning mechanisms, which in turn increases the current density. This research explores the effects of addition of the non-reactive phases of barium hafnate (BHO) and yttrium oxide Y2O3. Pulsed laser deposition (PLD) produces thin films on SrTiO3 (STO) substrates at various deposition temperatures ranging from 790 °C to 840 °C. PLD target compositions vary the volume percent of BHO from 2 to 6 vol% while maintaining 3 vol% Y2O3 and the remaining vol% YBCO. Examining the microstructure through SEM, TEM, and XRD analyses provides insight into the impact of the additions of BHO and Y2O3 on the YBCO thin films’ magnetic and transport current densities measured with an applied field parallel to the c and ab directions, and on the films’ critical temperature measurements. The Y2O3 additions decrease the variability in the current density between the c and ab directions, which is an important aspect to consider in applications, such as for HTS wires for motors.

Combinatorial Material Science and Strain Engineering Enabled by Pulsed Laser Deposition Using Radially Segmented Targets.

Vertical composition gradients of ternary alloy thin films find applications in numerous device structures. Up to now such gradients along the growth direction have not been realized by standard pulsed laser deposition (PLD) systems. In this study, we propose an approach based on a single elliptically segmented PLD target suited for the epitaxial growth of vertically graded layers. The composition of the thin films can be varied by a simple adjustment of the position of the PLD laser spot on the target surface. We demonstrate this principle for the Mg xZn1- xO alloy system. Such vertically composition-graded Mg xZn1- xO thin films exhibit high optical quality and a well-defined Mg-content for each layer. No signs of interdiffusion of Mg-atoms between the layers have been found. Further, this method is capable to deposit homogeneous thin films with any desired, well-defined cation composition having the same high optical and structural quality as films grown by conventional PLD.

Tuning Fe concentration in epitaxial gallium ferrite thin films for room temperature multiferroic properties

Stoichiometric gallium ferrite (GFO) is a promising single-phase multiferroic material at room temperature. Nevertheless, simultaneous magnetism and ferroelectricity in a single GFO at room temperature has not been demonstrated yet. In this work, single-phase GFO thin films with different amount of excessive Fe have been successfully grown using a dual target pulsed laser deposition (PLD) process, and the magnetic transition temperature is found to be above room temperature with excessive Fe distributed among the available cation sites of GFO unit cell. Ferroelectricity of GFO films have been confirmed by second harmonic generation (SHG), polarization hysteresis, pyroelectric reversal, and piezoresponse force microscopy (PFM), and magnetoelectric (ME) coupling has been demonstrated by increase in piezoresponse induced via external magnetic field applied in-plane, all measured at room temperature. From the data, it is theorized that the magnetic properties of GFO originate from the superexchange interaction mediated via the Fe1-O-Fe2 bond, and an additional Fe1-O-Fe* bond can form from excess Fe atoms. Under a magnetic field applied along c axis, the magnetic moment of Fe2 and Fe* increase while that of Fe1 decreases, and these changes in magnetic moment result in larger distortion of Fe2 and Fe* octahedrons along the b-axis, and thus enhanced polarization and piezoresponse. This series of studies thus confirm single-phase GFO with excessive Fe as a multiferroic material at room temperature with ME coupling, paving way for its potential functional applications in microelectronic and spintronic devices.

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.

Development of Ultra-Thin Opaque White Hydroxyapatite Sheet for Restoration of Enamel and Aesthetic Treatments of Teeth

In cosmetic dentistry, bleaching and laminate veneer methods are common treatments to improve the appearance of teeth. However, there are limitations to these treatments, as they damage the enamel which are not capable of recovering naturally. In this study, novel hydroxyapatite (HAp) sheets, which enable both enamel restoration and aesthetic treatments, were developed. Results indicated that the lower range of the sintering temperatures, of the pulsed laser deposition targets, produced lighter shades of amorphous Calcium phosphate (ACP) sheets. Subsequently, the post-annealing process of the sheets induced crystallization processes of the ACP sheets, to form HAp sheets, and improved the shade rank of the sheet. The shade rank of the developed sheet (6.8 ± 0.2) was almost comparable to the average shade rank of the teeth of Japanese people, within a range of 6.5 to 7.0.

Tuning chemical potential in the dirac cone by compositional engineering

To realize fully topological transport for any device applications it is essential to tune the chemical potential in the bulk gap of the Dirac cone. Bi2Se3 (BS) and Bi2Te3 (BT) thin films do not show in general topological transport as the chemical potential doesn’t lie entirely in the bulk gap. We report the successful formation of bulk insulating ternary topological insulators Bi2Se2Te (BST) by double target pulsed laser deposition technique. The films were deposited with sequential ablation of separate BS and BT targets. From the X-ray diffraction analysis and temperature dependent resistivity, we were able to conclude that the as-grown thin films have ordered chalcogen layers and the chemical potential in these thin films lie in the bulk gap. We have been able to achieve this fully topological transport in our sample grown by this technique. Our Magnetotransport data exhibits pronounced two-dimensional weak-antilocalization behavior (WAL) at low temperatures. It was possible to tune the chemical potential at will in the gap by depositing thin films through pulsed laser deposition technique using this simple and cost effective double target approach to grow quaternary TI thin films.

3D hierarchical nanostructures of iron oxides coatings prepared by pulsed laser deposition for photocatalytic water purification

3D hierarchical nanostructured hematite (α-Fe2O3) coatings containing various shapes were developed by pulsed laser deposition (PLD). A cold pressed, homogeneous mixture of Fe and H3BO3 (Fe+H3BO3) was used as a target in PLD to deposit the coatings in O2 atmosphere. Phase explosion phenomenon provided by laser ablation on the target, allowed to form rough, porous and embedded metallic Fe particulates coating with H3BO3 as background on a glass substrate. Subsequent thermal annealing of the as deposited Fe+H3BO3 coating at 600°C, led to formation of crystalline, hierarchical 3D nanostructured features with nanowires, nanorods, and nanosheets grown from the spherical particulates. Characterization by XRD, Micro-Raman, XPS, SEM and KPM analysis provided information on the systematic phase and morphology transformation from metallic Fe to hierarchical Iron oxide. Stress-induced phase segregation and stress release process during thermal annealing are suggested as the growth mechanism for the nanostructures. Photocatalytic activity measurements were studied with the coating in presence of Methylene Blue dye through Photo-Fenton process. To understand the effect of precursors, morphology, and synthesis technique (physical and chemical), similar hematite nanostructures were also prepared by thermal annealing of as deposited metallic Fe coating, hematite nanoparticles assembled coating by PLD, and by hydrothermal chemical method respectively. All these coatings showed less photocatalytic activity as compared to the hematite coating obtained from thermal annealing of Fe+H3BO3 sample. A series of various parameters such as effect of H2O2 concentration, effect of pH, water medium and recyclability tests for 10 times were performed, and all revealed promising results in terms of enhanced activity and high mechanical stability of the coatings. Presence of various 3D hierarchical nanostructures, high aspect ratio, more exposed active sites, increased interactions between catalyst surface and reactant dye molecules, and enhanced charge carrier separation, with immobilized stable coating form developed by PLD contributed to achieve the enhanced and stable photocatalytic activity.

Plasma plume dynamics, rebound, and recoating of the ablation target in pulsed laser deposition

The effects of the type of background gas and pressure on the spatial distributions of plume species have been investigated by time and space resolved imaging in vacuum, 1 × 10−2 mbar and 1 × 10−1 mbar O2 and Ar. The ablation of La0.4Ca0.6MnO3 in vacuum shows dissimilar arrival times for the different neutral species and a backscattering of the impinging species from the substrate. At 1 × 10−2 mbar, a species-dependent plume splitting appears and preferential scattering of the lighter elements is detected generating a cation off-stoichiometry along the plume axis. In addition at 1 × 10−1 mbar the plume expansion in this relatively high pressure traps a portion of the background gas against the substrate holder, thereby creating a transient high local pressure with remarkable effects once the plume reaches the substrate. In an Ar background, a rebound wave is seen, which travels backwards and recoats/contaminates the target with a different composition than the original target. In O2, in addition to the rebound, a long-lived volume of excited species is created, which consists mainly of LaO I. The rebound has important effects on the film composition and is background gas dependent. The same effects are also detected during Ag ablation and are probably valid for most target materials.