Fundamental Material Properties Research Articles

Circular photogalvanic effect

The spin and valley degree of freedom are a novel way to extend the functionalities of spintronic and valleytronic devices. A traditional, room-temperature way of examining the spin polarization generates the photocurrent whose magnitude and polarity depend on chirality of induced optical excitation. The circularly polarized photovoltaic effect is a kind of second-order nonlinear photoelectric response, which means that the photocurrent generated varies with the polarization angle of circularly polarized light. The generation of photocurrent depends on many factors such as spin, valley polarization, symmetry and Berry curvature, so it can reveal the fundamental physical properties of materials. In this review, we discuss the main mechanisms of circularly polarized photovoltaic effect in different material systems, including circularly polarized optical current caused by symmetry breakdown of Rashba spin-orbit coupling in semiconductor heterojunction, the electron momentum selection caused by Berry curvature and Pauli blocking in topological Weyl semimetals, and the valley polarization current generated by circularly polarized light in TMDC. Additionally, the recent progress of applications of circular photogalvanic effect is also presented.

Raman Scattering under Strong Vibration-Cavity Coupling

Strong cavity coupling can have profound effects on fundamental material properties. In this work, we examine the Raman scattering response of a poly(methyl methacrylate) (PMMA) carbonyl band under...

Recent Advances and Challenges in Halide Perovskite Crystals in Optoelectronic Devices from Solar Cells to Other Applications

Organic-inorganic hybrid perovskite materials have attracted tremendous attention as a key material in various optoelectronic devices. Distinctive optoelectronic properties, such as a tunable energy band position, long carrier diffusion lengths, and high charge carrier mobility, have allowed rapid progress in various perovskite-based optoelectronic devices (solar cells, photodetectors, light emitting diodes (LEDs), and lasers). Interestingly, the developments of each field are based on different characteristics of perovskite materials which are suitable for their own applications. In this review, we provide the fundamental properties of perovskite materials and categorize the usages in various optoelectronic applications. In addition, the prerequisite factors for those applications are suggested to understand the recent progress of perovskite-based optoelectronic devices and the challenges that need to be solved for commercialization.

Widths of imbricate thrust blocks and the strength of the front of accretionary wedges and fold-and-thrust belts

Besides the large-scale wedge shape itself, the most prominent structural feature of accretionary wedges and fold-and-thrust belts is the common pattern of imbricate thrust faults. This study illuminates the fundamental mechanical processes and material properties controlling the width of the crustal blocks bounded by major thrusts using analytical solutions of stress as well as two-dimensional finite-difference models. The numerical models predict that the initial width w0 of a thrust block is set when that block first forms at the very front of the wedge. The width is found to subsequently decreases approximately in proportion to the mean horizontal strain needed for an ideally triangular-shaped Coulomb wedge with a critical taper. Block width is proportional to the thickness H of the incoming, accreting sediment. A key quantity that influences the normalized initial block width w0/H is the distance L forward of the frontal thrust needed for the net horizontal force from shear on the base of the incoming sediment to balance the net force on the frontal thrust. It is within this distance where stress in the incoming sediment is substantially elevated and thus where the new frontal thrust forms. Results show that L/H and, correspondingly, w0/H increase with increasing sediment friction angle ϕ, cohesive strength C0 and pore-fluid pressure ratio λ, and decrease with increasing basal friction angle ϕb and basal dip β. Normalized width is sensitive to ϕ and relatively insensitive to ϕb and λ. Results for submarine and subaerial wedges follow the same scaling law. The scaling law relates the observables, w0/H and β, to the material properties, ϕ, ϕb, λ, and therefore provides a theoretical relation that can be used independent of, or together with critical Coulomb wedge theory (CWT) to constrain these properties.

Volume, strength, and stiffness characteristics of expandable foam grout

An expandable foam grout (EFG) is developed to fill underground cavities. The objective of this study is to evaluate the volume, strength, and stiffness of the EFG during curing using various testing methods. Flow, expansion, and unconfined compressive tests are conducted to investigate the fundamental material properties of the EFG. X-ray computed tomography is performed to verify the pore distribution of the EFG. Elastic waves and electrical resistivity are monitored to estimate the stiffness and strength characteristics of the EFG. The results show that EFG has high flowability, expanding within four hours depending on the temperature. The X-ray computed tomography images indicate a heterogeneous pore distribution in the EFG. A series of relationships between static and dynamic properties based on the elastic wave velocities and electrical resistivity are established. Furthermore, elastic wave measurement and electrical resistivity monitoring may be useful for estimating the volume, strength, and stiffness characteristics during curing.

New method enables multifunctional measurement of elastic moduli and internal frictions

Elastic moduli and internal frictions are fundamental properties of solid materials, and they are usually fairly sensitive to temperature, microstructure, deformation, and external fields. Measurement of elastic moduli and internal frictions is very important and useful in both academics and engineering. In this work, we first briefly reviewed the measurement methods of elastic moduli and internal frictions over the past 100 years and the related applications. Next, a promising measurement method called modified piezoelectric ultrasonic composite oscillator technique (M-PUCOT) was presented which can measure Young's modulus, shear modulus, and the related internal frictions accurately and quickly. Then, some typical measurement results using M-PUCOT on metals and phase transition materials were presented from room temperature up to 500 °C. The M-PUCOT measurement on rocks after different levels of compression was also conducted to predict the damage before fracture. The perspective and challenge of the M-PUCOT method as the indicator of heat treatment, mechanical fatigue, and early damage of metals and ceramics were further presented and discussed. It is expected that, in the near future, the measurement of elastic moduli and internal friction will be as convenient as that of electric conductivity, permittivity, etc. and can turn to be a multi-functional tool for many advanced applications.

InAsSb-Based Infrared Photodetectors: Thirty Years Later On

In 1989, one author of this paper (A.R.) published the very first review paper on InAsSb infrared detectors. During the last thirty years, many scientific breakthroughs and technological advances for InAsSb-based photodetectors have been made. Progress in advanced epitaxial methods contributed considerably to the InAsSb improvement. Current efforts are directed towards the photodetector’s cut-off wavelength extension beyond lattice-available and lattice-strained binary substrates. It is suspected that further improvement of metamorphic buffers for epitaxial layers will lead to lower-cost InAsSb-based focal plane arrays on large-area alternative substrates like GaAs and silicon. Most photodetector reports in the last decade are devoted to the heterostructure and barrier architectures operating in high operating temperature conditions. In the paper, at first InAsSb growth methods are briefly described. Next, the fundamental material properties are reviewed, stressing electrical and optical aspects limiting the photodetector performance. The last part of the paper highlights new ideas in design of InAsSb-based bulk and superlattice infrared detectors and focal plane arrays. Their performance is compared with the state-of-the-art infrared detector technologies.

Evaluating the ratio of electron and hole mobilities from a single bulk sample using Photo-Seebeck effect

When a semiconductor is under photoexcitation, the voltage response to a temperature gradient is the photo-Seebeck effect. Here we study this effect, focusing on the contribution from transport of photo-excited carriers. We demonstrate that by combining photo-Seebeck with photoconductivity measurements, one can determine the ratio between electron and hole mobilities, and hence both of them when one is known. This is found for the case of defect-free samples, where no detail on the absorbance, carrier lifetime or recombination is necessary. Our method reported here does not require chemical doping, which could introduce defects and is often not feasible. It applies to both thin film and bulk samples. Experiment-wise, photo-Seebeck effect is relatively easy to implement, or added to existing systems. In a broader context, for semiconductors with significant influence from defects, our result suggests that the photo-Seebeck behavior can still be understood. In this case another photo-transport property is necessary, in order to identify the mobilities of carriers and information regarding the defects. This framework integrates the information from photoexcitation and thermal gradients to provide a general method to determine fundamental electronic properties of materials.

Topological materials by molecular beam epitaxy

Topology appears across condensed matter physics to describe a wide array of phenomena which could alter, augment, or fundamentally change the functionality of many technologies. Linking the basic science of topological materials to applications requires producing high-quality thin films. This will enable combining dissimilar materials while utilizing dimensionality, symmetry, and strain to create or control the electronic phase, as well as platforms to fabricate novel devices. Yet, one of the longstanding challenges in the field remains understanding and controlling the basic material properties of epitaxial thin films. The aim of this Perspective article is to discuss how understanding the fundamental properties of topological materials grown by molecular beam epitaxy (MBE) is key to deepening the knowledge of the basic physics, while developing a new generation of topological devices. A focus will be on the MBE growth of intrinsic materials, creation, and control of superconducting and magnetic topological phases. Addressing these questions in the coming decade will undoubtedly uncover many surprises as new materials are discovered and their growth as high-quality thin films is refined.

Cation Distributions and Magnetic Properties of Ferrispinel MgFeMnO4.

The crystal structure and magnetic properties of the cubic spinel MgFeMnO4 were studied by using a series of in-house techniques along with large-scale neutron diffraction and muon spin rotation spectroscopy in the temperature range between 1.5 and 500 K. The detailed crystal structure is successfully refined by using a cubic spinel structure described by the space group Fd3̅m. Cations within tetrahedral A and octahedral B sites of the spinel were found to be in a disordered state. The extracted fractional site occupancies confirm the presence of antisite defects, which are of importance for the electrochemical performance of MgFeMnO4 and related battery materials. Neutron diffraction and muon spin spectroscopy reveal a ferrimagnetic order below TC = 394.2 K, having a collinear spin arrangement with antiparallel spins at the A and B sites, respectively. Our findings provide new and improved understanding of the fundamental properties of the ferrispinel materials and of their potential applications within future spintronics and battery devices.

Subcompartmentalization and Pseudo-Division of Model Protocells.

Membrane enclosed intracellular compartments have been exclusively associated with the eukaryotes, represented by the highly compartmentalized last eukaryotic common ancestor. Recent evidence showing the presence of membranous compartments with specific functions in archaea and bacteria makes it conceivable that the last universal common ancestor and its hypothetical precursor, the protocell, may have exhibited compartmentalization. To the authors' knowledge, there are no experimental studies yet that have tested this hypothesis. They report on an autonomous subcompartmentalization mechanism for protocells which results in the transformation of initial subcompartments to daughter protocells. The process is solely determined by the fundamental materials properties and interfacial events, and does not require biological machinery or chemical energy supply. In the light of the authors' findings, it is proposed that similar events may have taken place under early Earth conditions, leading to the development of compartmentalized cells and potentially, primitive division.

Second-nearest-neighbor modified embedded-atom method interatomic potential for V-M (M = Cu, Mo, Ti) binary systems

Interatomic potentials for V-M (M = Cu, Mo, Ti) binary systems have been developed within the framework of the second-nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The potentials reproduce a wide range of fundamental material properties such as thermodynamic and structural properties of compound and solution phases in reasonable agreement with experimental data or CALPHAD and first-principles calculations. The reasonable reproduction of material properties implies that the potentials can be combined with those of V-H and M-H systems for a permeability study of hydrogen in vanadium alloys or can be extended for further development of V-containing ternary system potentials.

How Good is “Good Enough?” Major Element Chemical Analyses of Planetary Basalts by Spacecraft Instruments

Abstract Bulk chemical composition is a fundamental property of a planetary material, rock or regolith, and can be used to constrain the properties and history of a material, and by extension its parent body, including its potential for habitability. Here, we investigate how uncertainties in bulk major element analyses can affect inferences derived from those analyses, including rock classification by total-alkalis–silica (TAS); Chemical Index of Alteration (CIA); a tectonic discriminant for magma genesis; and the inferred mantle pressure and temperature of a basaltic magma’s origin. Uncertainties for actual spacecraft instruments (Mars Exploration Rover and Mars Science Laboratory (MER/MSL), Alpha Proton X-Ray Spectroscopy (APXS), and Mars Science Laboratory: Laser-Induced Breakdown Spectroscopy (MSL LIBS)) and a suggested uncertainty level for analyses on Venus (Venus Exploration Targets (VExT) Workshop) are higher than those of standard Earth-based analyses (e.g., by inductively coupled plasma optical emission spectrometry (ICPOES)). We propagate the uncertainties from each analysis type to the derived parameters, both implicitly and via boot-strap (Monte Carlo) methods. Our calculations show that the uncertainties of APXS and VExT are greater than those for ICPOES, but they still allow useful inferences about rock type and history. Our results show that the uncertainties of MSL LIBS analyses are significantly larger than the other techniques, and can provide only limited constraints on rock types or histories. Any instruments chosen for future mission must have uncertainties of the chemical analyses small enough to meet the mission’s overall scientific objectives.

Multiple Pseudo-Plastic Appearance of the Dynamic Fracture in Quasi-Brittle Materials.

Understanding and simulating the dynamic response of quasi-brittle materials still remains as one of the most challenging issues in structural engineering. This paper presents the damage propagation material model (DAMP) developed in order to obtain reliable results for use in structural engineering practice. A brief overview focuses on the differences between fracture mechanics studies, and engineering material modelling is presented to highlight possible guideline improvements. An experimental dynamic test performed on ultra-high-performance concrete specimens was used to obtain evidence of the physical behaviour of brittle materials with respect to specimen size variations and, consequently, to verify the reliability of the material equations proposed. Two widely used material models (RHT and M72R3), as representatives of the classical brittle material models for structural purposes, and the proposed material model are compared. Here, we show how: (i) the multiple structural strength of brittle materials arises from the damage propagation process, (ii) there is no contradiction between fracture mechanics and the engineering approach once the velocity of damage propagation is chosen as fundamental material property and (iii) classical dynamic material models are intrinsically not objective with related loss of predictive capability. Finally, the original material model equation and the experimental strategy, dedicated to its extended verification, will be shown in order to increase the design predictiveness in the dynamic range considering structure and specimen size variations. The dynamic stress increasing factor (DIF), experimentally observed and widely recognised in literature as a fundamental concept for quasi-brittle material modelling, has been reviewed and decomposed in its geometrical and material dependencies. The new material model defines its DIF starting from the physical quantities of the damage propagation velocity applied to the test case boundary conditions. The resultant material model predictiveness results improved greatly, demonstrating its ability to model several dynamic events considering size and dynamic load variations with a unique material property set without showing contradictions between numerical and experimental approaches.

The Photo‐Hall Effect in High‐Mobility Organic Semiconductors

AbstractHigh‐mobility crystalline organic semiconductors are important for applications in advanced organic electronics and photonics. Photogeneration and transport of mobile photocarriers in these materials, although very important, remain underexplored. The photo‐Hall effect can be used to address the fundamental charge transport properties of these functional molecular materials, without the need for fabricating complex transistor devices or chemical doping. Here, a photo‐Hall effect is demonstrated in organic semiconductors, using a benchmark molecular system rubrene as an experimental platform. It is shown that this technique can be used to directly measure the charge carrier mobility and photocarrier density, decouple the surface and bulk transport phenomena, and thus significantly deepen the understanding of the mechanism of photoconductivity in these high‐performance molecular materials.

Using Fundamental Material Properties to Predict the Moisture Susceptibility of the Asphalt Binder: Polarizability and a Moisture-Induced Shear-Thinning Index.

Many biomodifiers have recently been introduced to the asphalt industry to improve the performance of asphalt mixtures, rejuvenate aged asphalt, and/or partially replace asphalt binder. It is critical to screen these biomodifiers for their susceptibility to moisture damage before they are used in construction. This study develops a computational approach and a laboratory technique to predict the moisture susceptibility of modifiers used in asphalt binder mixtures. The computational approach uses the "polarizability" factor, which is one of the conceptual descriptors in density functional theory. Polarizability is indicative of the formation of instantaneous dipoles that are oriented in the applied field. A lower polarizability indicates a lower propensity of the chemical species to interact with other species in their chemical environment. The laboratory method defines a moisture-induced shear-thinning index. Moisture-induced shear-thinning measures the loss of interfacial bonds between the asphalt binder and siliceous surfaces due to water exposure. Both proposed indicators are used to evaluate and compare biomodifiers from four sources: waste vegetable oil, swine manure, algae, and a co-liquefied blend of swine manure and algae. In a comparative study, waste vegetable oil with a high content of long-chain alkanes and fatty acids showed the highest polarizability and the highest moisture-induced shear-thinning index, indicating the highest susceptibility to moisture damage. In contrast, the chemical composition of the biomodifier produced from the co-liquefaction of swine manure and algae showed the lowest polarizability and the lowest moisture-induced shear-thinning index, indicating the highest resistance to moisture damage.

Magnetism and ion diffusion in honeycomb layered oxide {hbox {K}_2hbox {Ni}_2hbox {TeO}_6}

In the quest for developing novel and efficient batteries, a great interest has been raised for sustainable K-based honeycomb layer oxide materials, both for their application in energy devices as well as for their fundamental material properties. A key issue in the realization of efficient batteries based on such compounds, is to understand the K-ion diffusion mechanism. However, investigation of potassium-ion (K^+) dynamics in materials using e.g. NMR and related techniques has so far been very challenging, due to its inherently weak nuclear magnetic moment, in contrast to other alkali ions such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic ratio, make the muon spin rotation and relaxation (mu ^+SR) technique ideal for probing ions dynamics in these types of energy materials. Here we present a study of the low-temperature magnetic properties as well as K^+ dynamics in honeycomb layered oxide material {hbox {K}_2hbox {Ni}_2hbox {TeO}_6} using mainly the mu ^+SR technique. Our low-temperature mu ^+SR results together with complementary magnetic susceptibility measurements find an antiferromagnetic transition at T_{mathrm{N}}approx 27 K. Further {mu}^{+}SR studies performed at higher temperatures reveal that potassium ions (K^+) become mobile above 200 K and the activation energy for the diffusion process is obtained as E_{mathrm{a}}=121 (13) meV. This is the first time that K^+ dynamics in potassium-based battery materials has been measured using mu ^+SR. Assisted by high-resolution neutron diffraction, the temperature dependence of the K-ion self diffusion constant is also extracted. Finally our results also reveal that K-ion diffusion occurs predominantly at the surface of the powder particles. This opens future possibilities for potentially improving ion diffusion as well as K-ion battery device performance using nano-structuring and surface coatings of the particles.

Lifetime assessment of functional components in the ESS target environment during beam energy ramp up

The Target Station at the European Spallation Source (ESS) is designed to convert high power proton beam to high brightness neutron beams, for studying fundamental properties of materials. Upon commissioning of the ‘beam on target’ planned in 2022, the ESS linac will deliver lower energy proton beam than the design value of 2 GeV, for neutron production. The beam energy will then be gradually ramped up, with the sequential commissioning of the downstream part of the superconducting cryomodules. During neutron production, the beam intercepting devices and moderators are exposed to intense flux of primary and secondary particles, suffering from radiation induced structural degradation. The extent of the radiation damage depends on the energy and intensity of the impinging protons. Currently, the lifetime criteria determined for these components are based on the 2 GeV beam energy. To secure availability and reliability of the neutron production during the beam energy ramp-up phase, the radiation damage rates in these components should be reassessed and the lifetime criteria be adjusted. In this paper, we present the lifetime criteria for the beam intercepting devices and moderators for different beam energies, to serve for the planning of the maintenance and replacement schedule during the proton energy ramp-up phase.

An Overview of Photoconductivity in Zn-based Nanomaterials

Photoconductivity is a phenomenon in which the electrical conductivity of a material increases upon exposure to light. Zn-based nanomaterials, including ZnO and ZnS nanoparticles, nanowires, and nanorods, have gained considerable attention in recent years due to their unique photoconductive properties. Photoconductivity is a fundamental property of materials that refers to the increase in electrical conductivity upon absorption of light. This paper provides an overview of photoconductivity in Zn-based nanomaterials, including the mechanisms of photoconductivity, and the factors affecting it, such as size, morphology, and doping, and highlights the prospects of zinc-based nanomaterials in optoelectronics.

Picosecond multilevel resistive switching in tantalum oxide thin films

The increasing demand for high-density data storage leads to an increasing interest in novel memory concepts with high scalability and the opportunity of storing multiple bits in one cell. A promising candidate is the redox-based resistive switch repositing the information in form of different resistance states. For reliable programming, the underlying physical parameters need to be understood. We reveal that the programmable resistance states are linked to internal series resistances and the fundamental nonlinear switching kinetics. The switching kinetics of hbox {Ta}_2 hbox {O}_5-based cells was investigated in a wide range over 15 orders of magnitude from 10^5 s to 250 ps. The capacitive charging time of our device limits the direct observation of the set time below 770 ps, however, we found indication for an intrinsic switching speed of 10 ps at a stimulus of 3 V. On all time scales, multi-bit data storage capabilities were demonstrated. The elucidated link between fundamental material properties and multi-bit data storage paves the way for designing resistive switches for memory and neuromorphic applications.