Synthesis and in-depth structure determination of a novel metastable high-pressure CrTe phase.

This study reports the synthesis and crystal structure determination of a novel CrTe phase using various experimental and theoretical methods. The average stoichiometry and local phase separation of this quenched high-pressure phase were characterized by synchrotron powder X-ray diffraction and total scattering. Several structural models were obtained using simulated annealing, but all suffered from an imperfect Rietveld refinement, especially at higher diffraction angles.

Boosting Thermoelectric Performance of Bi Te Material by Microstructure Engineering.

Due to the intrinsic contradiction of electrical conductivity and Seebeck coefficient in thermoelectric materials, the enhancement for the power factor (PF) is limited. Since the PF decides the output power, strategies to the enhancement of PF are of paramount importance. In this work, Bi Te /Sb and Bi Te /W multilayer films are proposed to enhance the thermoelectric properties.

All-optical nonvolatile optical modulator for in-fiber operation.

The control of information is a defining feature of the information age, and the optical modulator likewise has a crucial role in optical networks. The transmission, processing, and storage of data have demanded low energy consumption and high speed for photonic systems, promoting the development of electro-optic modulators to all-optical modulators. Although these all-optical modulation methods eliminate the photoelectric conversion, the disadvantage of volatile materials requiring continuous power supply when processing and retaining data in new materials-based devices increase energy consumption.

Energetic Electron-Assisted Synthesis of Tailored Magnetite (FeO) and Maghemite (γ-FeO) Nanoparticles: Structure and Magnetic Properties.

Iron oxide nanoparticles with a mean size of approximately 5 nm were synthesized by irradiating micro-emulsions containing iron salts with energetic electrons. The properties of the nanoparticles were investigated using scanning electron microscopy, high-resolution transmission electron microscopy, selective area diffraction and vibrating sample magnetometry. It was found that formation of superparamagnetic nanoparticles begins at a dose of 50 kGy, though these particles show low crystallinity, and a higher portion is amorphous.

Growth of Highly c-Axis Oriented AlScN Films on Commercial Substrates.

In this work, we present a method for growing highly -axis oriented aluminum scandium nitride (AlScN) thin films on (100) silicon (Si), silicon dioxide (SiO) and epitaxial polysilicon (poly-Si) substrates using a substrate independent approach. The presented method offers great advantages in applications such as piezoelectric thin-film-based surface acoustic wave devices where a metallic seed layer cannot be used. The approach relies on a thin AlN layer to establish a wurtzite nucleation layer for the growth of -AlScN films.

Exploding and weeping ceramics.

The systematic tuning of crystal lattice parameters to achieve improved kinematic compatibility between different phases is a broadly effective strategy for improving the reversibility, and lowering the hysteresis, of solid-solid phase transformations. (Kinematic compatibility refers to the fitting together of the phases.) Here we present an apparently paradoxical example in which tuning to near perfect kinematic compatibility results in an unusually high degree of irreversibility.

Strongly enhanced and tunable photovoltaic effect in ferroelectric-paraelectric superlattices.

Ever since the first observation of a photovoltaic effect in ferroelectric BaTiO, studies have been devoted to analyze this effect, but only a few attempted to engineer an enhancement. In conjunction, the steep progress in thin-film fabrication has opened up a plethora of previously unexplored avenues to tune and enhance material properties via growth in the form of superlattices. In this work, we present a strategy wherein sandwiching a ferroelectric BaTiO in between paraelectric SrTiO and CaTiO in a superlattice form results in a strong and tunable enhancement in photocurrent.

Nanocomposites with Three-Dimensional Architecture and Impact on Photovoltaic Effect.

We demonstrate the synthesis of self-assembled three-dimensional nanocomposite thin films consisting of NiO nanocolumns in an layered Aurivillius phase matrix. The structures were grown on single-crystal SrTiO substrates via pulsed laser deposition (PLD) with single ceramic (PbTiO)(BiNiNbO) targets. The nanocolumns, which are about 10 nm in diameter each, extend over the entire film thickness of up to 225 nm.

"Stickier"-Surface SbTe Templates Enable Fast Memory Switching of Phase Change Material GeSbTe with Growth-Dominated Crystallization.

Ge-Sb-Te (GST)-based phase-change memory (PCM) excels in the switching performance but remains insufficient of the operating speed to replace cache memory (the fastest memory in a computer). In this work, a novel approach using SbTe templates is proposed to boost the crystallization speed of GST by five times faster. This is because such a GST/SbTe heterostructure changes the crystallizing mode of GST from the nucleation-dominated to the faster growth-dominated one, as confirmed by high-resolution transmission electron microscopy, which captures the interface-induced epitaxial growth of GST on SbTe templates in devices.

Structural Transitions in GeSbTe Phase Change Memory Thin Films Induced by Nanosecond UV Optical Pulses.

Ge-Sb-Te-based phase change memory alloys have recently attracted a lot of attention due to their promising applications in the fields of photonics, non-volatile data storage, and neuromorphic computing. Of particular interest is the understanding of the structural changes and underlying mechanisms induced by short optical pulses. This work reports on structural changes induced by single nanosecond UV laser pulses in amorphous and epitaxial GeSbTe (GST) thin films.

Direct Measurement of Crystal Growth Velocity in Epitaxial Phase-Change Material Thin Films.

Central to the use of Ge-Sb-Te based phase-change materials for data storage applications is their crystallization capability since it determines memory writing time. Although being intensively studied to identify intrinsic limits and develop strategies to enhance memory performance, the crystallization process in these materials is still not fully explored. Therefore, this study focuses on the determination of crystal growth dynamics in an epitaxial phase-change material thin film model system offering the advantage of high crystalline quality and application-relevant sizing.

In situ observations of the reversible vacancy ordering process in van der Waals-bonded Ge-Sb-Te thin films and GeTe-SbTe superlattices.

Chalcogenide-based thin films are employed in data storage and memory technology whereas van der Waals-bonded layered chalcogenide heterostructures are considered to be a main contender for memory devices with low power consumption. The reduction of switching energy is due to the lowering of entropic losses governed by the restricted motion of atoms in one dimension within the crystalline states. The investigations of switching mechanisms in such superlattices have recently attracted much attention and the proposed models are still under debate.

Ultrafast interfacial transformation from 2D- to 3D-bonded structures in layered Ge-Sb-Te thin films and heterostructures.

Two-dimensional van-der-Waals-bonded chalcogenide heterostructures have recently received a lot of attention due to promising applications in the fields of photonics, plasmonics and data storage. Of particular interest is the interfacial switching process inherent in these structures, which is assumed to occur locally at the van-der-Waals interfaces and thus represents an intracrystalline transition. However, detailed experimental studies on the underlying mechanism are still lacking.

Shortening Nucleation Time to Enable Ultrafast Phase Transition in ZnSbTe Pseudo-Binary Alloy.

ZnSbTe thin films have been deposited by magnetron co-sputtering of ZnTe and SbTe targets. The microstructure, phase-change speed, optical cycling stability, and crystallization kinetics have been investigated during thermal annealing and laser irradiation. The thermal-annealed and laser-irradiated films give a clear evidence of the coexistence of trigonal SbTe and cubic ZnTe phases, which are homogeneously distributed in a single alloy as confirmed by advanced scanning transmission electron microscopy.

Ion Beam Assisted Deposition of Thin Epitaxial GaN Films.

The assistance of thin film deposition with low-energy ion bombardment influences their final properties significantly. Especially, the application of so-called hyperthermal ions (energy <100 eV) is capable to modify the characteristics of the growing film without generating a large number of irradiation induced defects. The nitrogen ion beam assisted molecular beam epitaxy (ion energy <25 eV) is used to deposit GaN thin films on (0001)-oriented 6H-SiC substrates at 700 °C.

Crystallization of Ge2Sb2Te5 thin films by nano- and femtosecond single laser pulse irradiation.

The amorphous to crystalline phase transformation of Ge2Sb2Te5 (GST) films by UV nanosecond (ns) and femtosecond (fs) single laser pulse irradiation at the same wavelength is compared. Detailed structural information about the phase transformation is collected by x-ray diffraction and high resolution transmission electron microscopy (TEM). The threshold fluences to induce crystallization are determined for both pulse lengths.

Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures.

Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution.

High quality reduced graphene oxide flakes by fast kinetically controlled and clean indirect UV-induced radical reduction.

This work highlights a surprisingly simple and kinetically controlled highly efficient indirect method for the production of high quality reduced graphene oxide (rGO) flakes via UV irradiation of aqueous dispersions of graphene oxide (GO), in which the GO is not excited directly. While the direct photoexcitation of aqueous GO (when GO is the only light-absorbing component) takes several hours of reaction time at ambient temperature (4 h) leading only to a partial GO reduction, the addition of small amounts of isopropanol and acetone (2% and 1%) leads to a dramatically shortened reaction time by more than two orders of magnitude (2 min) and a very efficient and soft reduction of graphene oxide. This method avoids the formation of non-volatile species and in turn contamination of the produced rGO and it is based on the highly efficient generation of reducing carbon centered isopropanol radicals via the reaction of triplet acetone with isopropanol.

Water-Soluble Phosphine Capable of Dissolving Elemental Gold: The Missing Link between 1,3,5-Triaza-7-phosphaadamantane (PTA) and Verkade's Ephemeral Ligand.

We herein describe a tricyclic phosphine with previously unreported tris(homoadamantane) cage architecture. That water-soluble, air- and thermally stable ligand, 1,4,7-triaza-9-phosphatricyclo[5.3.

An aberration-corrected STEM study of structural defects in epitaxial GaN thin films grown by ion beam assisted MBE.

Ion-beam assisted molecular-beam epitaxy was used for direct growth of epitaxial GaN thin films on super-polished 6H-SiC(0001) substrates. The GaN films with different film thicknesses were studied using reflection high energy electron diffraction, X-ray diffraction, cathodoluminescence and primarily aberration-corrected scanning transmission electron microscopy techniques. Special attention was devoted to the microstructural characterization of GaN thin films and the GaN-SiC interface on the atomic scale.

Mechanistic aspects of the radiation-chemical reduction of graphene oxide to graphene-like materials.

Purpose: The aim of the work was to investigate mechanistic details of the preparation of graphene-like materials (GLM) via reduction of graphene oxide (GO) in aqueous dispersions by electron beam (EB) generated reducing free radicals.

Materials And Methods: A 10 MeV linear accelerator was employed to irradiate aqueous GO dispersions at ambient temperatures. The kinetics of GO reduction was followed using UV-Vis spectroscopy.

Defect chemistry of oxide nanomaterials with high surface area: ordered mesoporous thin films of the oxygen storage catalyst CeO2-ZrO2.

Herein we report the electrical transport properties of a series of ordered mesoporous ceria-zirconia (CexZr1-xO2, referred to as mp-CZO) thin films with both a cubic structure of (17±2) nm diameter pores and nanocrystalline walls. Samples over the whole range of composition, including bare CeO2 and ZrO2, were fabricated by templating strategies using the large diblock copolymer KLE as the structure-directing agent. Both the nanoscale structure and the chemical composition of the mesoporous materials were analyzed by a combination of scanning and transmission electron microscopy, grazing incidence small-angle X-ray scattering, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry.

The influence of carbon content on the structure and properties of MoS(x)C(y) photocatalysts for light-driven hydrogen generation.

Carbon containing nano-sized molybdenum sulfide composites (MoS(x)C(y)) obtained by thermal decomposition reactions of (R(4)N)(2)MoS(4) (R = -H (C(0)), -CH(3) (C(1)), -C(3)H(7) (C(3)), and -C(6)H(13) (C(6))) show promising performance in visible-light driven photocatalytic hydrogen generation.

Aerographite: ultra lightweight, flexible nanowall, carbon microtube material with outstanding mechanical performance.

An ultra lightweight carbon microtube material called Aerographite is synthesized by a novel single-step chemical vapor deposition synthesis based on ZnO networks, which is presently the lightest known material with a density smaller than μg/cm(3). Despite its low density, the hierarchical design leads to remarkable mechanical, electrical, and optical properties. The first experiments with Aerographite electrodes confirm its applicability.

Structure and dynamics of the fast lithium ion conductor "Li7La3Zr2O12".

The solid lithium-ion electrolyte "Li(7)La(3)Zr(2)O(12)" (LLZO) with a garnet-type structure has been prepared in the cubic and tetragonal modification following conventional ceramic syntheses routes. Without aluminium doping tetragonal LLZO was obtained, which shows a two orders of magnitude lower room temperature conductivity than the cubic modification. Small concentrations of Al in the order of 1 wt% were sufficient to stabilize the cubic phase, which is known as a fast lithium-ion conductor.