Laser Deposition Of Films Research Articles

Atomic Structure and Dynamics of Unusual and Wide‐Gap Phase‐Change Chalcogenides: A GeTe2 Case

Brain‐inspired computing, reconfigurable optical metamaterials, photonic tensor cores, and many other advanced applications require next‐generation phase change materials (PCMs) with better energy efficiency and a wider thermal and spectral range for reliable operations. Germanium ditelluride (GeTe2), with higher thermal stability and a larger bandgap compared to current benchmark PCMs, appears promising for THz metasurfaces and the controlled crystallization of atomically thin 2D materials. Using high‐energy X‐ray diffraction supported by first‐principles simulation, we investigate the atomic structure in semiconducting pulsed laser deposition films and metallic high‐temperature liquids. The results suggest that the structural and chemical metastability of GeTe2, leading to disproportionation into GeTe and Te, is related to high internal pressure during a semiconductor‐metal transition, presumably occurring in the supercooled melt. Similar phenomena are expected for canonical GeS2 and GeSe2 under high temperatures and pressures.This article is protected by copyright. All rights reserved.

Vertically Aligned Nanocomposite Thin Films Incorporating 3D-Architectures for Micro-Battery Applications

Vertically aligned nanocomposite (VAN) thin films have shown strong potential in oxide nanoionics but are yet to be explored in detail in solid-state battery systems [1,2]. VANs, typically grown by pulsed laser deposition (PLD), are chessboard-like structures comprised of pillars of one phase embedded in a matrix the second phase. They form by solid-state thermodynamic self-assembly, allowing the spontaneous formation of interdigitated battery components in a single deposition without additional processing steps such as etching. Their 3D architectures are attractive because they may allow enhancements in capacity, current and power densities [3]. Furthermore, VAN films grow with a preferential orientation, allowing for selective growth of the optimum crystallographic orientation for high performance by altering the substrate phase and/or orientation. Also, owing to their large interfacial surface areas, VAN could serve as models to study interfaces and solid-electrolyte interphase formation during cycling due to their high interfacial surface areas.In this poster, first we present highly crystalline and epitaxial vertically aligned nanocomposite PLD films comprised of a LixLa0.32±0.05(Nb0.7±0.1Ti0.32±0.05)O3±δ-Ti0.8±0.1Nb0.17±0.03O2±δ-anatase (LL(Nb,Ti)O-(Ti,Nb)O2) electrolyte/anode system, the first anode VAN battery system reported (Figure 1) [4]. This system exhibits an order of magnitude increased Li+ ionic conductivity over that in bulk Li3xLa1/3-xNbO3 (LLNO) and is comparable with the best available Li3xLa2/3-xTiO3 (LLTO) pulsed laser deposition films. Then, we will highlight the considerations and challenges that VANs pose, and how to overcome them [5]. Finally, we will also present our recently submitted work on VAN based cathodes [6]. Our carefully selected materials combination exhibits remarkable high-rate performance, achieving discharge capacities > 70 mAh g-1 up to ~200 C with clear redox behavior of the cathode-of-choice. The enhanced electrochemical performance is enabled by the 3D VAN architecture. Interestingly, we elucidate the relationship between pillar morphology and electrochemical performance, namely there is an optimum size and orientation of cathodic nanopillars such that high discharge capacity under high-rate regimes is possible. These works open up the possibility of incorporating VAN films into an all solid-state battery, either as electrodes or electrolytes, by the pairing of suitable materials.

Decoding the Atomic Structure of Ga2Te5 Pulsed Laser Deposition Films for Memory Applications Using Diffraction and First-Principles Simulations.

Neuromorphic computing, reconfigurable optical metamaterials that are operational over a wide spectral range, holographic and nonvolatile displays of extremely high resolution, integrated smart photonics, and many other applications need next-generation phase-change materials (PCMs) with better energy efficiency and wider temperature and spectral ranges to increase reliability compared to current flagship PCMs, such as Ge2Sb2Te5 or doped Sb2Te. Gallium tellurides are favorable compounds to achieve the necessary requirements because of their higher melting and crystallization temperatures, combined with low switching power and fast switching rate. Ga2Te3 and non-stoichiometric alloys appear to be atypical PCMs; they are characterized by regular tetrahedral structures and the absence of metavalent bonding. The sp3 gallium hybridization in cubic and amorphous Ga2Te3 is also different from conventional p-bonding in flagship PCMs, raising questions about its phase-change mechanism. Furthermore, gallium tellurides exhibit a number of unexpected and highly unusual phenomena, such as nanotectonic compression and viscosity anomalies just above their melting points. Using high-energy X-ray diffraction, supported by first-principles simulations, we will elucidate the atomic structure of amorphous Ga2Te5 PLD films, compare it with the crystal structure of tetragonal gallium pentatelluride, and investigate the electrical, optical, and thermal properties of these two materials to assess their potential for memory applications, among others.

Study of hydroxyapatite in bones and in laser-deposited films for biomedical applications

Hydroxyapatite (HAp) present in bones has been studied and characterized using different physical analyses. Optical and scanning electron microscopies (SEM), Energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), attenuated total reflectance (ATR) – Fourier transform infrared (FTIR) spectroscopy have been employed. Particular attention has been given to the sample preparation as well to the lyophilization processes of bones, which can be employed for different applications. Pulse laser irradiation has been employed to deposit biocompatible thin HAp films in vacuum on Ti substrates. The prepared biocompatible substrates, which can be employed for metallic load prostheses, have been compared with the bone surface.

Transient Mesoscopic Immiscibility, Viscosity Anomaly, and High Internal Pressure at the Semiconductor–Metal Transition in Liquid Ga2Te3

Gallium tellurides appear to be promising phase-change materials (PCMs) of the next generation for brain-inspired computing and reconfigurable optical metasurfaces. They are different from the benchmark PCMs because of sp3 gallium hybridization in both cubic Ga2Te3 and amorphous pulsed laser deposition (PLD) films. Liquid Ga2Te3 also shows a viscosity η(T) anomaly just above melting when η(T) first increases and only then starts decreasing. We used high-energy X-ray diffraction to observe a transient mesoscopic immiscibility that suggested dense metallic liquid droplets in a semiconducting melt. The η(T) shape was consistent with this finding. A vanishing first sharp diffraction peak that also shifts to a higher Q indicates a high internal pressure in the metallic melt, which produces a remarkable asymmetry of the Ga-Te nearest neighbor distances and is reminiscent of high-pressure rhombohedral Ga2Te3. The observed phenomena provide a realistic scenario for a fast, multilevel SET-RESET response, which also unravels similar trends in the purported density-driven liquid polyamorphism of water, phosphorus, sulfur, and other materials.

Lithium-based vertically aligned nanocomposite films incorporating LixLa0.32(Nb0.7Ti0.32)O3 electrolyte with high Li+ ion conductivity

Vertically aligned nanocomposite (VAN) thin films have shown strong potential in oxide nanoionics but are yet to be explored in detail in solid-state battery systems. Their 3D architectures are attractive because they may allow enhancements in capacity, current, and power densities. In addition, owing to their large interfacial surface areas, the VAN could serve as models to study interfaces and solid-electrolyte interphase formation. Here, we have deposited highly crystalline and epitaxial vertically aligned nanocomposite films composed of a LixLa0.32±0.05(Nb0.7±0.1Ti0.32±0.05)O3±δ-Ti0.8±0.1Nb0.17±0.03O2±δ-anatase [herein referred to as LL(Nb, Ti)O-(Ti, Nb)O2] electrolyte/anode system, the first anode VAN battery system reported. This system has an order of magnitude increased Li+ ionic conductivity over that in bulk Li3xLa1/3−xNbO3 and is comparable with the best available Li3xLa2/3−xTiO3 pulsed laser deposition films. Furthermore, the ionic conducting/electrically insulating LL(Nb, Ti)O and electrically conducting (Ti, Nb)O2 phases are a prerequisite for an interdigitated electrolyte/anode system. This work opens up the possibility of incorporating VAN films into an all solid-state battery, either as electrodes or electrolytes, by the pairing of suitable materials.

Decrease of Surface Recombination in Single-Crystalline Silicon by Means of Pulse Laser Film Deposition with Silicon Quantum Points

Decrease of Surface Recombination in Single-Crystalline Silicon by Means of Pulse Laser Film Deposition with Silicon Quantum Points

Pulsed Laser Deposition Films Based on CdSe-Doped Zinc Aluminophosphate Glass

A composite material with applications in optoelectronics has been investigated. Pulsed laser deposition CdSe-doped glass film was prepared by the combinatorial deposition from two targets, namely pure CdSe and glass belonging to the 20Li2O-10Al2O3-7BaO-2La2O3-2ZnO-59P2O5 system. Exciton peaks in the Vis domain, related to electron–hole pairs transitions from the valence band to the conduction band, were revealed in the optical absorption spectra of the CdSe-doped film. CdSe quantum dots (QDs) band gap energy depends on the CdSe quantum confinement effect. CdSe-doped film photoluminescence exhibits peaks in the red domain assigned to CdSe transitions from the excited state to the ground state. The size of CdSe nanoclusters, determined from x-ray diffraction is correlated with scanning electron microscopy–energy dispersive x-ray spectroscopy and atomic force microscopy results. Vibration modes specific both to CdSe QDs and to the vitreous network have been evidenced by Fourier transform infrared and Raman spectroscopy.

Multilevel reflectance switching of ultrathin phase-change films

Several design techniques for engineering the visible optical and near-infrared response of a thin film are explored. These designs require optically active and absorbing materials and should be easily grown on a large scale. Switchable chalcogenide phase-change material heterostructures with three active layers are grown here using pulsed laser deposition. Both Fabry–Perot and strong interference principles are explored to tune the reflectance. Robust multilevel switching is demonstrated for both principles using dynamic ellipsometry, and measured reflectance profiles agree well with simulations. We find, however, that switching the bottom layer of a three-layer device does not yield a significant change in reflectance, indicating a maximum in accessible levels. The pulsed laser deposition films grown show promise for optical display applications, with three shown reflectance levels.

Pulsed laser deposition films from a Ba2FeMoO6 target onto SrTiO3[001]: Chemical and magnetic inhomogeneity.

Pulsed laser deposition films from Ba2FeMoO6 (BFMO) targets onto SrTiO3[001] (STO) substrates have been reported previously to have non-zero magnetism at 300 K, a majority of magnetic ordering at 240 K that is less than the 370 K ordering temperature of polycrystalline BFMO, and suppressed saturation magnetization compared to polycrystalline BFMO. To interrogate these previously reported observations of BFMO on STO, we have used a combination of x-ray diffraction, atomic force microscopy, x-ray and neutron reflectivity, and x-ray photoelectron spectroscopy that shows inhomogeneities. The present results show off-stoichiometry on the A-site by incorporation of Sr from the substrate and on the B-site to have %Fe/%Mo > 1 by evolution of BaMoO4. There is an enhanced ordering temperature and magnetic response nearer to the SrTiO3 interface compared to the air interface. Depth dependent strain and microstructure are needed to explain the magnetic response. Holistic considerations and implications are also discussed.

Studies on piezo coefficients of PLD and sol-gel grown PZT thin film for devices

The effect of electrical (DC) contact poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsed laser-deposited PZT thin films has been investigated as a function of the poling field, temperature and time. The remnant polarization and piezoelectric coefficient are found to increase with and saturate at dc-poling field of 100- 300 kV/cm, temperature of 100–120 °C and poling time of 10–20 min. as compared with un-poled PZT thin films. The P-E hysteresis loops of poled PLD grown PZT films shows sharper switching behaviour as compared to imbalanced loop in sol-gel grown films. An improvement of piezoelectric and ferroelectric properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel PZT thin films.

Avalanche solar blind photodetectors with high responsivity based on MgO/MgZnO heterostructures

High responsivity is important for solar blind detection because solar blind signals are generally weak. In this work, we achieved a high responsivity of 48 A/W at 262 nm via Au/MgO/MgZnO/MgO/Au structured photodetectors at a 10 V bias. Wurtzite Mg0.55Zn0.45O films with a band gap of 4.57 eV were grown on c-plane sapphire by pulse laser deposition and MgO films were deposited on MgZnO films as barrier layers to induce ionization impact for avalanche gain. The photodetectors achieved a rejection ratio (R262-nm/R350-nm) of over 103 and a cut-off wavelength of 273 nm. The time-resolved response measurement showed a response time of 453 μs. The devices performed good stability without degeneration of responsivity under repeating illumination. The high performance of the photodetector implied a wide potential for solar blind application.

Three-Dimensional Bicontinuous Nanocomposite from a Self-Assembled Block Copolymer for a High-Capacity All-Solid-State Lithium Battery Cathode

Safe secondary batteries with high energy densities and high power densities will be necessary if pure-electric and hybrid vehicles are to become more widespread, and all-solid-state lithium-ion batteries (LiBs) are among the most promising options. Much research has focused on the development of cathode materials with solid Li electrolytes, including composites fabricated from calcined microparticles, laser-deposited film systems, and materials with three-dimensional structures. However, because utilization of a high percentage of the active cathode material requires an electrode with a high electrolyte content, achieving high active-material-utilization rates in electrodes with high active-material contents (and thus relatively low electrolyte contents) has been challenging. Herein, we describe the self-assembled block copolymer-templated synthesis of a three-dimensional bicontinuous nanocomposite electrode material consisting of LiCoO2 as the active cathode material and Li7La3Zr2O12 as the solid Li ele...

Ion-beam-induced ferromagnetism in Mn-doped PrFeO3 thin films grown on Si (100)

The present study shows that the ion beam irradiation induces room-temperature ferromagnetic ordering in pulsed laser-deposited Mn-doped PrFeO3 thin films on Si (100) apart from change in the morphological, structural and electrical properties. Dense electronic excitation produced by high-energy 120 MeV Ag9+ ion irradiation causes change in surface roughness, crystallinity and strain. It is also evident that these excitations induce the magnetic ordering in this system. The observed modifications are due to the large electronic energy deposited by swift heavy ions irradiation. The appearance of ferromagnetism at 300 K in these samples after irradiation may be attributed to the canting of the antiferromagnetically ordered spins due to the structural distortion.

Magnetic and electronic structure of the film-stabilized Mott insulator BaCrO3

We have synthesized and characterized laser-deposited film samples of perovskite BaCrO${}_{3}$, a missing member of the perovskite-chromate family. The BaCrO${}_{3}$ films have a substantially larger lattice constant than other chromates, are insulating, and exhibit weak ferromagnetism. Employing first-principles density functional theory calculations, we attribute such weak ferromagnetism to a canted $C$-type antiferromagnetic spin order. Additionally, comparison with the other sister compounds CaCrO${}_{3}$ and SrCrO${}_{3}$ suggests an anomalous Mott transition where magnetism is independent of whether the compound is metallic or insulating.

In situ X-ray studies of film cathodes for solid oxide fuel cells

Synchrotron-based X-ray techniques have been used to study in situ the structural and chemical changes of film cathodes during half-cell operations. The X-ray techniques used include X-ray reflectivity (XR), total-reflection X-ray fluorescence (TXRF), high-resolution diffraction (HRD), ultra-small angle X-ray scattering (USAXS). The epitaxial thin film model cathodes for XR, TXRF, and HRD measurements are made by pulse laser deposition and porous film cathodes for USAX measurements are made by screen printing technique. The experimental results reviewed here include A-site and B-site segregations, lattice expansion, oxidation-state changes during cell operations and liquid-phase infiltration and coarsening of cathode to electrolyte backbone.

Pulsed laser deposition film of a donor–acceptor–donor polymer as possible active layer in devices

A molecule having a ketone group between two thiophene groups was synthesized. Presence of alternating electron donating and accepting moieties gives this material a donor-acceptor-donor (DAD) architecture. PolyDAD was synthesized from DAD monomer by oxidative polymerization. Device quality films of polyDAD were fabricated using pulsed laser deposition technique. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectra (FTIR) data of both as synthesized and film indicate the material does not degrade during ablation. Optical band gap was determined to be about 1.45 eV. Four orders of magnitude increase in conductivity was observed from as synthesized to pulsed laser deposition (PLD) fabricated film of polyDAD. Annealing of polyDAD films increase conductivity, indicating better ordering of the molecules upon heating. Rectifying devices were fabricated from polyDAD, and preliminary results are discussed.

Dramatic mobility enhancements in doped SrTiO3 thin films by defect management

We report bulk-quality n-type SrTiO3 (n-SrTiO3) thin films fabricated by pulsed laser deposition, with electron mobility as high as 6600 cm2 V−1 s−1 at 2 K and carrier density as low as 2.0×1018 cm−3 (∼0.02 at. %), far exceeding previous pulsed laser deposition films. This result stems from precise strontium and oxygen vacancy defect chemistry management, providing a general approach for defect control in complex oxide heteroepitaxy.

Magnetotransport properties of high quality Co:ZnO and Mn:ZnO single crystal pulsed laser deposition films: Pitfalls associated with magnetotransport on high resistivity materials

The electrical resistivity values for a series of pure and doped (Co, Mn, Al) ZnO epitaxial films grown by pulsed laser deposition were measured with equipment designed for determining the direct current resistivity of high resistance samples. Room-temperature resistances ranging from 7 x 10(1) to 4 x 10(8) Omega/sq were measured on vacuum-reduced cobalt-doped ZnO, (Al,Co) co-doped ZnO, pure cobalt-doped ZnO, Mn-doped ZnO, and undoped ZnO. Using a four-point collinear geometry with gold spring-loaded contacts, resistivities were measured from 295 to 5 K for resistances of < approximately 10(12) Omega/sq. In addition, magnetoresistance and Hall effect were measured as a function of temperature for select samples. Throughout the investigation, samples were also measured on commercially available instrumentation with good agreement. The challenges of transport measurements on high resistivity samples are discussed, along with some offered solutions to those challenges.

All chemical YBa2Cu3O7 superconducting multilayers: Critical role of CeO2 cap layer flatness

New advances toward microstructural improvement of epitaxial CeO2 films grown by chemical solution deposition and their use as buffer layers for YBa2Cu3O7 (YBCO) films are presented. We demonstrate that the degree of epitaxy and the fraction of (001) atomically flat surface area are controlled by the incorporation of tetravalent (Zr4+) or trivalent (Gd3+) cations into the ceria lattice. The degree of epitaxy has been investigated by means of Rutherford backscattering spectroscopy-channeling and reflection high-energy electron diffraction, and a new methodology is also presented to quantify the fraction of (001) atomically flat area from atomic force microscopy images. Results are further correlated with the superconducting properties, microstructure, and texture of YBCO films grown by the trifluoroacetate route. A comparison with pulsed laser deposition and YBCO films grown on the same ceria layers is also presented. This growth procedure has allowed us to obtain all chemical multilayer films with controlled microstructure and critical current densities above 4 MA cm−2 at 77 K.