Properties Of Related Materials Research Articles

(Invited) Epitaxial Lift-Off of GaN and Related Materials for Device Applications

The unique material and transport properties of GaN and related III-N materials have led to their importance in both optoelectronic and RF/microwave power amplification applications, as well as to their promise for emerging applications including power control and conversion, harsh-environment and radiation-resistant sensing and signal processing, and biomedical applications. The use of epitaxial lift-off with III-N materials provides an approach that can improve the electrical and thermal performance of electronic and optoelectronic devices, while at the same time reducing cost and dramatically reducing device size and weight. However, in contrast to other III-V material systems, epitaxial lift-off of III-N materials is challenging due to the lack of high-selectivity, high-etch-rate wet etches in this material system. As an alternative, we have explored the use of band gap selective photoelectrochemical (PEC) wet etching to perform epitaxial lift-off of GaN-based materials and devices. By combining the use of a thin pseudomorphic InGaN release layer and KOH electrolyte with high-intensity filtered ultraviolet illumination tuned to generate electron-hole pairs only in the InGaN release layer (and not in the surrounding GaN material), sufficient selectivity and etch rate have been achieved to allow epitaxial lift-off of large-area films [1]. This process has been demonstrated to improve the electrical and thermal performance of Schottky diodes on non-native substrates [2, 3] and high-voltage, high-power pn junctions grown on low-dislocation-density bulk GaN substrates [4-6] without compromising material quality, while also resulting in ultra-thin devices with total thicknesses below 15 µm. The devices show no evidence of additional defects or recombination centers as a result of either the inclusion of the pseudomorphic InGaN release layer in the epitaxial layer structure or the epitaxial lift-off fabrication processing steps. In addition to device performance, device cost can be improved both through potential re-use of the substrate after lift-off [7] and reduction in die size due to improved thermal performance [8]. While demonstrated for power electronics applications, the ability to form high-quality, high-performance III-N based devices in an ultra-thin, flexible form factor may be an enabling technology for additional applications in flexible electronics, displays, wearable electronics, RF/microwave communication systems, and other fields.

Coordination Dynamics and Thermal Stability with Aminal Metallogels and Liquids

In this article, we review a dynamic covalent gel system developed as a high temperature well construction fluid. The key gel/fluid phase changes and related materials properties are addressable via the constitutional and coordination dynamics of the equilibrium and non-equilibrium molecular species comprising the material. The interplay between these species and external stimuli leads to material adaptability. Specifically, the introduction of metal ions into a non-equilibrium hemiaminal gel reverts this phase into a non-equilibrium liquid. When heated, this liquid transforms itself catalytically into the thermodynamically favoured closed-ring polyhexahydrotriazine (PHT) gel product. The temperature stability of different PHT gel formulations is evaluated as a function of the inclusion of various salts. It is possible to revert this thermodynamic PHT gel back into a liquid. This pH dependent transformation depends on the R groups linking the hexahydrotriazines (HTs) to one another. While polyethylene glycol (PEG) based PHT gels revert to liquids with water and mild protonation conditions, in comparison, polypropylene glycol (PPG) based gels require stronger acid conditions with heat, or a different more nucleophilically driven ring-opening mechanism by, for example, phosphines. The covalent dynamic chemistry in this chemical system gives way to many possible applications in addition to the high temperature solution-gelation (sol-gels) for which it has been primarily designed.

Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling

Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties. Exploration of these phenomena is theoretically demanding, as polaritons exist at the intersection between quantum optics, solid state physics, and quantum chemistry. Fortunately, nanoscale polaritons can be realized in small plasmon-molecule systems, enabling treatment with ab initio methods. Here, we show that time-dependent density-functional theory calculations access the physics of nanoscale plasmon-molecule hybrids and predict vacuum Rabi splitting. By considering a system comprising a few-hundred-atom aluminum nanoparticle interacting with benzene molecules, we show that cavity quantum electrodynamics holds down to resonators of a few cubic nanometers in size, yielding a single-molecule coupling strength exceeding 200 meV due to a massive vacuum field of 4.5 V · nm−1. In a broader perspective, ab initio methods enable parameter-free in-depth studies of polaritonic systems for emerging applications.

Enhanced luminescence in Tb3+-doped glass-ceramic scintillators containing LiYF4 nanocrystals

Tb3+ ions single-doped transparent oxyfluoride glass-ceramics (GC) containing LiYF4 nanocrystals were prepared via a conventional high-temperature melt quenching way and subsequent further thermal-treatment. The microstructure and related luminescent properties of the composite materials were studied in detail. It was confirmed by XRD and TEM techniques that the precipitated particles in the glass phase of the GC590-4h sample were LiYF4 nanocrystals having a size of approximately 26 nm. Compared to the PG sample, the luminescence intensity of the GCs at 378 nm light excitation was significantly enhanced and the corresponding lifetime was prolonged. This is because the Tb3+ ions are preferentially enriched in the precipitated low-phonon-energy LiYF4 nanocrystals, which can effectively induce the reduction of non-radiative transitions. It is worth noting that the emission intensity of Tb3+ single-doped GCs containing LiYF4 nanocrystals at 545 nm (5D4→7F5) is also greatly improved (under X-ray excitation). The obtained results indicate that Tb3+ single-doped LiYF4 GC may have the potential to be a novel scintillator applied to X-ray detection for the slow event.

Direct observation of the f–c hybridization in the ordered uranium films on W(110)**Project supported by the National Natural Science Foundation of China (Grant No. 11874330), Science Challenge Project, China (Grant No. TZ2016004), and the National Key Research and Development Program of China (Grant No. 2017YFA0303104).

A key issue in metallic uranium and its related actinide compounds is the character of the f electrons, whether it is localized or itinerant. Here we grew well ordered uranium films on a W(110) substrate. The surface topography was investigated by scanning tunneling microscopy. The Fermi surface and band structure of the grown films were studied by angle-resolved photoemission spectroscopy. Large spectral weight can be observed around the Fermi level, which mainly comes from the f states. Additionally, we provided direct evidence that the f bands hybridize with the conduction bands in the uranium ordered films, which is different from previously reported mechanism of the direct f–f interaction. We propose that the above two mechanisms both exist in this system by manifesting themselves in different momentum spaces. Our results give a comprehensive study of the ordered uranium films and may throw new light on the study of the 5f-electron character and physical properties of metallic uranium and other related actinide materials.

Multiphonon anharmonicity of MgO

The anharmonic lattice dynamics of MgO has been studied at ambient conditions and at high temperatures by infrared spectroscopy and inelastic x-ray scattering measurements combined with density functional perturbation theory calculations. The agreement between the measured phonon energies and widths with ab initio calculated values provides a direct and pertinent test of the validity of advanced theoretical methods. Long observed anharmonic features in the infrared reflectivity find a clear explanation in terms of well-defined multiphonon scattering processes and lattice dynamics peculiarities, also responsible for a significant and sharp reduction of the longitudinal optical phonon lifetime at critical finite wave vectors. Our work highlights the importance of multiphonon scattering processes on the collective dynamics and related material properties.

Analysis of cold compaction for Fe-C, Fe-C-Cu powder design based on constitutive relation and artificial neural networks

The constitutive relations for Fe-C and Fe-C-Cu powder compactions were investigated with the three consitituents: i) powder design parameters, ii) material related properties, and iii) final compaction properties. With the concept of materials informatics, this approach enables to predict the final compaction properties depending on the material conditions. The correlations between powder design parameters (particle size, graphite content, lubricant content, particle size distribution, copper content) and material related properties (ρTap, γ, a, b, n) in Shima-Oyane model were characterized by the compaction experiments and artificial neural network (ANN) model. The ANN model was developed to predict the effect of powder design parameters on the material related properties. The average mean absolute percentage error of predicted material related properties was 2.194%. The final properties (green density, density gradient, effective stress, hydrostatic stress, effective strain, volumetric strain) were calculated by the compaction simulation based on the experimental and predicted material related properties.

Remarkable wettability of highly dispersive rGO ink on multiple substrates independent of deposition techniques

Numerous methods are available for obtaining reduced graphene oxide (rGO), however, the agglomeration of rGO flakes is a major challenge for different applications. Incorporation of additives (as anti-agglomerating chemicals) along with reducing agents modifies the chemical properties of graphene oxide and related carbon materials. Intrinsically, reduced graphene oxide (rGOH) synthesized via hydrazine (reducing agent) agglomerates and exhibits a hydrophobic nature that limits its surface application necessitating the use of surface treatments. The present article describes a process for the formulation of graphene oxide that results in a highly dispersive ink of rGOA using hydrazine as reducing agent and a water based additive composed cationic surfactants (e.g. Hexadecyltrimethylammonium bromide or benzisothiazoline) and anionic surfactants (e.g. Dioctyl sulfosuccinate sodium salt or methylisothiazolinone). The constituent chemicals of the dispersing agent assist in three ways: (i) allow rGO flakes to exist in a highly dispersive form, (ii) act as binder via cross linking with the carboxylic groups, and (iii) enhance the wettability of the rGO ink on a variety of substrates including glass, SiO2, PDMS etc, without any surface treatment, independent of applying techniques say spin coating, dip coating, doctor blade, etc. Thus, the proposed chemical recipe is an attractive procedure to obtain rGOA ink with high wettability owing to its simplicity, low cost and eco-friendly nature.

Tensile strength performance with determination of the Poisson‘s ratio of additively manufactured AlSi10Mg samples

AbstractAdditive manufacturing of metals is a key technology and an emerging industrial sector enabling the manufacture of highly specialized and advanced components. It's outstanding advantages are the geometric flexibility and the elimination of tools compared to conventional manufacturing techniques. However, multiple directional dependencies lead to an anisotropic material behaviour, rendering the material description more complicated. Samples used for this study were fabricated from the age‐hardenable alloy AlSi10Mg, focusing on fluctuating material properties in relation to differing built orientations. In addition, the effect of thermal post treatment was considered. Comprehensive tensile tests employing a lateral strain sensor were performed, in order to determine the transverse contraction during loading and to quantify directional dependencies. The Young's modulus varied between 66 GPa and 68 GPa, however the Poisson's ratio ranged between 0.31 and 0.39. Investigations on the fractured faces by means of scanning electron microscopy investigations were also part of this study.

A new method for an old topic: Efficient and reliable estimation of material bulk modulus

Bulk modulus is a key material property which provides fundamentals on the chemical bonding nature of a material as well as for deriving other related material properties, such as Young’s modulus and Grüneinsen constant. Traditional numerical methods of estimating bulk modulus often involve layers of approximations and cost considerably. In this work, we propose a novel and efficient numerical framework to estimate bulk modulus using the ab initio calculated data. Based on the generalized polynomial chaos expansion (gPC) method, our approach does not impose any physical priori and is mathematically rigorous and versatile. We have demonstrated the reliability and efficiency of the proposed method by estimating the bulk modulus of Ti3SiC2 and Sb2Te3 with comparison to conventional methods.

Effects of Hydroforming Process on Fatigue Life of Reinforced S-Shaped Bellows

Reinforced s-shaped bellows, which can withstand high pressure, is a kind of typical reinforced metal bellows. The reinforced s-shaped bellows mainly uses the hydroforming process, and the forming process is a severe plastic deformation process. The hydroforming process and its effects on the fatigue life of reinforced s-shaped bellows were discussed in the present study. Different levels of plastic strain and wall thickness thinning were detected in the hydroforming process. The maximum plastic strain can reached 32%, while the maximum wall thickness thinning ratio is 20%, which occurs on the wave peak. Mechanical characteristics of reinforced s-shaped bellows were discussed considering the effects of hydroforming process. The maximum stress appears on the upper and lower ends, which is the weak part of the structure. Fatigue life of the reinforced s-shaped bellows was analyzed based on the modified Manson-Coffin method. Mechanical properties of related materials, which can be more accurate consideration the effects of hydroforming process, were tested under the pre-plastic deformation. Fatigue life analysis of reinforced s-shaped bellows was carried out and the effects of hydroforming process were discussed. The hydroforming process will lead to a decline in fatigue life, which needs to be considered well in the structural design and analysis. Keywords: Reinforced s-shaped bellows, Hydroforming process, Fatigue life, Mechanical characteristics.

PROPOSAL FOR A EUROPEAN METROLOGY NETWORK ON BIOLOGICAL IONISING RADIATION EFFECTS.

Progress in the field of ionising radiation (IR) metrology achieved in the BioQuaRT project raised the question to what extent radiobiological investigations would benefit from metrological support of the applied methodologies. A panel of experts from the medical field, fundamental research and radiation protection attended a workshop at Physikalisch-Technische Bundesanstalt to consult on metrology needs related to biological radiation effects. The panel identified a number of metrological needs including the further development of experimental and computational techniques for micro- and nanodosimetry, together with the determination of related fundamental material properties and the establishment of rigorous uncertainty budgets. In addition to this, a call to develop a metrology support for assisting quality assurance of radiobiology experiments was expressed. Conclusions from the workshop were presented at several international conferences for further discussion with the scientific community and stakeholder groups that led to an initiative within the metrology community to establish a European Metrology Network on biological effects of IR.

Poly(urethane-acrylate) aerogels from the isocyanurate trimer of isophorone diisocyanate

Poly(urethane acrylate) aerogels were synthesized from radical polymerization of a dendritic monomer having an isocyanurate-based rigid/aliphatic core, urethane linkages and nine terminal acrylate groups. The rigidity of the core comes from the triisocyanate, an isophorone diisocyanate trimer (IPDI). The material properties of those aerogels were compared to the properties of related literature materials derived from triisocyanates with flexible/aliphatic or rigid/aromatic cores, bearing (a) three, or (b) nine terminal acrylate groups. Data support that material properties such as the primary particle size and the BET surface areas are determined mainly by the degree of crosslinking (i.e., the monomer multifunctionality), while the molecular rigidity vs flexibility of the triisocyanate core plays only a secondary role. Addition of ethylene glycol dimethacrylate (EG) in the sol as a chain extender increased the hydrophilicity of the aerogels and their ability to absorb water.

Dielectric relaxation and electrical properties of Bi2.5Nd0.5Nb1.5Fe0.5O9 ceramics

Abstract Aurivillius single-phase Bi2.5Nd0.5Nb1.5Fe0.5O9 (BNNF) ceramics was synthesized via solid state mixed oxide sintering method. Electrical properties of the samples were intensely studied in a wide range of temperature (25 °C–650 °C). Dielectric behaviors were investigated by dielectric and impedance spectroscopies in the range (40 Hz−10 MHz) of frequency. Single dielectric relaxation was observed due to the grains contribution. The phase transition temperature (TC) was noticed at ∼270 °C. Kinetic analysis of dielectric data was used to understand the possible relaxation-conduction behaviors in the ceramics. Above ∼250 °C, relaxation and conduction of the ceramics was assigned to the motion of ionized oxygen vacancies. The Aurivillius ceramics has promising industrial applications in dielectric capacitors and piezoelectric transducers due to low leakage below ∼200 °C. The results could be valuable for designing and/or modifying properties of BNNF related materials.

Multi-scale fracture analysis of fibre-reinforced composites

Fibre reinforced composite (FRC) have been widely used in engineering applications for the purpose of strengthening or lightening of the structures. Many modern applications such as aircraft structures, automotive components, ships, yacht, and infrastructures etc. are fabricated by FRC materials. Since the FRC is the homogenized mixture of fibre and resin (matrix). The structural performance of the FRC materials depends on the fibre arrangement in the matrix, as well as FRC constituents. Therefore, an accurate prediction of structural response of this material needs prior information of micro to macro-level material properties. This paper presents a multi-scale numerical approach to predict the fracture response of fibre reinforced composites. At the micro-level, analysis of representative volume element (RVE) using DIGIMAT software has been presented to describe the microstructure related material properties. In this analysis, fibre is described as a linear elastic material while the matrix phase is modelled by an exponential linear law. The unknown constitutive relationship at the macro-scale has been obtained by DIGIMAT-FE analysis. Further, the macro-scale constitutive relation is used to predict fracture behaviour of FRC. Virtual crack closure technique (VCCT) of Finite Element Method has been implemented to study fracture parameters of FRC. All presented computational results are obtained by DIGIMAT-FE analysis and ABAQUS software. In order to check the robustness and accuracy of the presented approach, few benchmark problems were solved at the multi-scale level and compared with the reference results. In addition, edge crack and centre crack problems were solved by the multi-scale approach to analyse the fracture response of FRC.

Collective Strong Light-Matter Coupling in Hierarchical Microcavity-Plasmon-Exciton Systems.

Polaritons are compositional light-matter quasiparticles that arise as a result of strong coupling between the vacuum field of a resonant optical cavity and electronic excitations in quantum emitters. Reaching such a regime is often hard, as it requires materials possessing high oscillator strengths to interact with the relevant optical mode. Two-dimensional transition metal dichalcogenides (TMDCs) have recently emerged as promising candidates for realization of strong coupling regime at room temperature. However, these materials typically provide coupling strengths in the range of 10-40 meV, which may be insufficient for reaching strong coupling with low quality factor resonators. Here, we demonstrate a universal scheme that allows a straightforward realization of strong coupling with 2D materials and beyond. By intermixing plasmonic excitations in nanoparticle arrays with excitons in a WS2 monolayer inside a resonant metallic microcavity, we fabricate a hierarchical system with the collective microcavity-plasmon-exciton Rabi splitting exceeding ∼500 meV at room temperature. Photoluminescence measurements of the coupled systems show dominant emission from the lower polariton branch, indicating the participation of excitons in the coupling process. Strong coupling has been recently suggested to affect numerous optical- and material-related properties including chemical reactivity, exciton transport, and optical nonlinearities. With the universal scheme presented here, strong coupling across a wide spectral range is within easy reach and therefore exploration of these exciting phenomena can be further pursued in a much broader class of materials.

Wave propagation and pattern formation in two-dimensional hexagonally-packed granular crystals under various configurations

We study wave propagation in two-dimensional granular crystals under the Hertzian contact law consisting of hexagonal packings of spheres under various basin geometries including hexagonal, triangular, and circular basins which can be tiled with hexagons. We find that the basin geometry will influence wave reflection at the boundaries, as expected, and also may result in bottlenecks forming. While exterior strikers the size of a single sphere have been considered in the literature, it is also possible to consider strikers which impact multiple spheres along a boundary, or to have multiple sides being struck simultaneously. It is also possible to consider obstructions or even strikers in the interior of the hexagonally packed granular crystal, as previously considered in the case of square packings, resulting in the basin geometry no longer forming a convex set. We consider various configurations of either boundary or interior strikers. We shall also consider the case where a granular crystal is composed of two separate crystals of differing material, with a single interface between the two distinct materials. Depending on the relative material properties of each type of sphere, this can result in a trapping of most of the wave energy within one of the two regions. While repeated reflections from the boundaries will cause the systems we study to fall into disorder for large time, there are a number of interesting wave structures and patters that emerge as transients at intermediate timescales.

Simulation of crack propagation in prestressed concrete sleepers by fracture mechanics

Abstract Mode I crack propagation in prestressed concrete sleepers B70 is simulated by a fracture mechanics approach. The plastic damage model, which takes the non-linear behavior of concrete into account, is utilized to calculate crack length and crack mouth opening displacement (CMOD). Numerical data from prestressed concrete sleepers B70 under three-point bending load are compared with those of the proposed fracture mechanics model. In this study, fracture mechanics parameters of prestressed concrete sleepers are investigated. Sleepers with the length of initiation crack of 5 to 45 mm (with 10 mm steps) and the width of initiation crack of 2 to 8 mm (with 2 mm steps) are analyzed. Sleeper cracks are created in the notch and both of its sides. These analyses confirm that the structural behavior of prestressed concrete sleepers can be predicted by a simple fracture mechanics model provided that the related material properties like KIC, crack length and CMOD, are known.

Photoacoustic response of a transmission photoacoustic configuration for two-layer samples with thermal memory

In this paper, the models of surface temperature variations have been derived. Based on these models, photoacoustic (PA) response has been commented for transmission PA setup configurations of two-layer optically transparent samples, including the impact of finite heat propagation velocity through both layers (thermal memory) and the existence of volume absorption in both layers. By analyzing the derived model it has been shown that many parameters influence the photoacoustic response. Based on the derived model, some approximations have been discussed in order to enable the development of more accurate inverse solutions of photoacoustic problem, and the estimation of optical, thermal and other related physical properties of versatile materials. By using specific two-layer structure that consist of aluminum sample coated with layer of color dye, used in some photoacoustic experimental investigations, the influence of thermal memory properties of either the sample or the coating has been discussed.

Quenching of Infrared-Active Optical Phonons in Nanolayers of Crystalline Materials by Graphene Surface Plasmons

Optical phonons are fundamental excitations in many solid-state materials and have crucial influences on numerous material properties. Therefore, achieving extrinsic control of optical phonon properties, such as the phonon frequency, lifetime and population, may lead to new ways of tailoring various material properties relevant to key technological applications. Here, we experimentally demonstrate that infrared-active optical phonons in thin (tens of nm) layers of crystalline materials such as III–V semiconductors can be significantly quenched by a monolayer graphene. The optical phonon quenching effect is attributed to the ultrafast decay of optical phonons into resonant graphene surface plasmons at a rate which is significantly higher than the intrinsic decay rate of optical phonons due to lattice anharmonicity. Our results point to a new approach to engineering optical phonon properties and potentially other related material properties. Such an approach can be applied to a wide range of materials with ...