High Internal Energy Research Articles

Role of mechanical stress localizations on the radiation hardness of AlGaN/GaN high electron mobility transistors

Abstract Multi-material, multi-layered systems such as AlGaN/GaN high electron mobility transistor (HEMTs) contain residual mechanical stresses that arise from sharp contrasts in device geometry and materials parameters. These stresses, which can be either tensile or compressive, are difficult to detect and eliminate because of their highly localized nature. We propose that their high stored internal energy make potential sites for defect nucleation sites under radiation, particularly if their locations coincide with the electrically sensitive regions of a transistor. In this study, we validate this hypothesis with molecular dynamic simulation and experiments exposing both pristine and annealed HEMTS to 2.8 MeV Au+3 irradiation. Our unique annealing process uses mechanical momentum of electrons, also known as the electron wind force (EWF) to mitigate the residual stress at room temperature. High-resolution transmission electron microscopy (TEM) and cathodoluminescence spectra reveal the reduction of point defects and dislocations near the two-dimensional electron gas region of EWF-treated devices compared to pristine devices. The EWF-treated HEMTs showed relatively higher resilience with approximately 10% less degradation of drain saturation current and ON-resistance and 5% less degradation of peak transconductance. Both mobility and carrier concentration of the EWF-treated devices were less impacted compared to the pristine devices. Our results suggest that the lower density of nanoscale stress localization contributed to the improved radiation tolerance of the EWF-treated devices. Intriguingly, the EWF is found to modulate the defect distribution by moving the defects to electrically less sensitive regions in the form of dislocation networks, which act as sinks for the radiation induced defects and this assisted faster dynamic annealing.

Numerical investigation on the impact resistance of ceramic-based composite structure with hybrid architecture

As known, ceramics possess desirable strength, hardness and low density, which have been extensively applied in engineering fields. However, the inherent brittleness makes the ceramics present poor toughness and consequently impact resistance as well. In recent decades, some ingenious architectures of biomaterials employed to improve the mechanical properties of brittle bulk materials, such as laminate and brick-mud, have become increasingly popular. Here, in order to further enhance the impact resistance of ceramics, a kind of hybrid ceramic-based composite structure is designed according to the gradient feature in dactyl club of mantis shrimp. The impact resistance performances of bulk, laminate, brick-mud and hybrid structures are investigated by finite element simulation. The results show that the hybrid structure can effectively avoid catastrophic failure, thereby having large scope of deformation area to store energy. Moreover, the damage mass of impactor for the hybrid plate is the largest due to the beginning hard collision between impactor and target plate and long cumulative damaging time of impactor. As a result, with the highest internal energy and eroding kinetic energy of impactor simultaneously, the hybrid structure dissipates the most energy of impactor. Further, under extreme working conditions of oblique and high velocity impact, the hybrid structure still exhibits optical impact resistance performance.

Novel self-healing glass-like CexOY film on a Flash-PEO coated AZ31B Mg alloy

The aim of this work is to develop a glass-like CexOy coating to seal the pores of a Flash-PEO coated AZ31B Mg alloy and simultaneously provide smart self-healing corrosion protection. The cerium sol was synthesized using cerium acetate as main precursor by sol-gel method. SEM micrographs revealed that upon cerium sol deposition, the pores of the oxide coating were effectively sealed, resulting in a double-layer coating system and thereby in a big reservoir of cerium ions (Ce3+/Ce4+). The glassy character of the cerium coating, confirmed by X-Ray diffraction, implies that cerium exists in Ce3+ and Ce4+ ionic states enclosed in a high internal energy structure which facilitate the diffusion of cerium ions to active cathodic zone. Electrochemical Impedance Spectroscopy (EIS), X-Ray Diffraction (XRD), and Raman spectroscopy were used to explore the active corrosion protection of the CexOy sol-gel coating. The corrosion inhibition mechanism involves the migration of cerium ions and the precipitation of insoluble-crystalline cerium compounds (CeO2). The coating demonstrated self-healing properties, presenting a promising alternative to traditional chrome conversion coatings (CCC).

Internal Energy Dependence of the Pyrrole Dimer Cation Structures Formed in a Supersonic Plasma Expansion: Charge-Resonance and Hydrogen-Bonded Isomers.

The structures of the pyrrole dimer cation (Py2+) formed in an electron-ionization-driven supersonic plasma expansion of Py seeded in Ar or N2 are probed as a function of its internal energy by infrared photodissociation (IRPD) spectroscopy in a tandem mass spectrometer. The IRPD spectra recorded in the CH and NH stretch ranges are analyzed by dispersion-corrected density functional theory (DFT) calculations at the B3LYP-D3/aug-cc-pVTZ level. The spectra of the cold Ar/N2-tagged Py2+ clusters, Py2+Ln (n = 1-5 for Ar, n = 1 for N2), indicate the exclusive formation of the most stable antiparallel π-stacked Py2+ structure under cold conditions, which is stabilized by charge-resonance interaction. The bare Py2+ dimers produced in the ion source have higher internal energy, and the observation of additional transitions in their IRPD spectra suggests a minor population of less stable hydrogen-bonded isomers composed of heterocyclic Py/Py+ structures formed after intramolecular H atom transfer and ring opening. These intermolecular isomers differ from the chemically bonded structures proposed earlier in the analysis of IRPD spectra of Py2+ generated by VUV ionization of neutral Pyn clusters.

Layered High-Entropy Metallic Glasses for Photothermal CO2 Methanation.

High entropy alloys and metallic glasses, as two typical metastable nanomaterials, have attracted tremendous interest in energy conversion catalysis due to their high reactivity in nonequilibrium states. Herein, a novel nanomaterial, layered high entropy metallic glass (HEMG), in a higher energy state than low-entropy alloys and its crystalline counterpart due to both the disordered elemental and structural arrangements, is synthesized. Specifically, the MnNiZrRuCe HEMG exhibits highly enhanced photothermal catalytic activity and long-term stability. An unprecedented CO2 methanation rate of 489mmol g-1 h-1 at 330°C is achieved, which is, to the authors' knowledge, the highest photothermal CO2 methanation rate in flow reactors. The remarkable activity originates from the abundant free volume and high internal energy state of HEMG, which lead to the extraordinary heterolytic H2 dissociation capacity. The high-entropy effect also ensures the excellent stability of HEMG for up to 450 h. This work not only provides a new perspective on the catalytic mechanism of HEMG, but also sheds light on the great catalytic potential in future carbon-negative industry.

The Unimolecular Chemistry of Methyl Chloroformate Ions and Neutrals: A Story of Near-Threshold Decomposition.

The near-threshold dissociation of ionized and neutral methyl chloroformate (CH3COOCl, MCF) was explored with imaging photoelectron photoion coincidence spectroscopy. The threshold photoelectron spectrum (TPES) for MCF was acquired for the first time; the large geometry changes upon ionization of MCF result in a broad, poorly defined TPES. Franck-Condon simulations are consistent with an adiabatic ionization energy (IE) of 10.90 ± 0.05 eV. Ionized MCF dissociates by chlorine atom loss at a measured 0 K appearance energy (AE) of 11.30 ± 0.01 eV. Together with the above IE, this AE suggests a reaction barrier of 0.40 ± 0.05 eV, consistent with the SVECV-f12 computational result of 0.41 eV. At higher internal energies, the loss of CH3O• becomes competitive due to its lower entropy of activation. Pyrolysis of neutral MCF formed the anticipated major products CH3Cl + CO2 (R1) and the minor products HCl + CO + CH2O (R2). The thermal decomposition products were identified by their photoion mass-selected threshold photoelectron spectrum (ms-TPES). Possible reaction pathways were explored computationally to confirm the dominant ones: R1 proceeds by a concerted Cl atom migration via a four-membered transition state in agreement with the mechanism proposed in the literature. R2 is a two-step reaction first yielding 2-oxiranone by HCl loss, which then decomposes to CH2O and CO. Kinetic modeling of the neutral decomposition could simulate the observed reactions only if the vibrational temperature of the MCF was assumed not to cool in the expansion.

Synthetic molecular spectra modeling for determining rotational, vibrational, and excitation temperatures of low-pressure nitrogen plasma

Nitrogen plasma is highly sought after in industries due to its unique properties, including high chemical reactivity and internal energy, which enhance process efficiency. However, a detailed understanding of thermal characteristics of nitrogen plasma is required to control nitrogen plasma properties and produce desirable reactants. Therefore, in this work, we proposed an advanced numerical simulation by clustering synthetic spectra of three molecular band systems (i.e., N2 B-A, N2 C-B, and N2+ B-X). Through this method, rotational, vibrational, and excitation temperatures of excited species in inductively coupled nitrogen plasmas (5 mTorr, 50 W − 900 W) were determined. Results revealed that rotational and vibrational temperatures increased at various input power with an inflection point at around 250 W. However, the excitation temperature decreased with input power below 250 W but increased with input power above 250 W. We also found that energy states were not in thermal equilibrium and that vibrational temperature and excitation temperature were reciprocally related. Finally, correlations between dissociation, ionization, and excitation temperature were discussed by examining N I and N2+ intensities as a function of input power.

Improved continuous precipitation kinetics and tensile properties of extruded AZ80 alloy through {10–12} twin formation

This study investigates the effect of {10–12} deformation twins on the continuous precipitation behavior of an extruded Mg–8.0Al–0.5Zn–0.2Mn (AZ80) alloy during aging. The extruded AZ80 alloy is compressed along the transverse direction to introduce {10–12} twins, followed by an aging treatment at 300 °C. The extruded material exhibits a twin-free microstructure with low internal strain energy, whereas the pre-twinned material possesses abundant {10–12} twins and has high internal strain energy. The aging results reveal that the peak-aging time of the pre-twinned material (1 h) is one-eighth of that of the extruded material (8 h). Although Mg17Al12 continuous precipitates (CPs) are observed in both the peak-aged materials, these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging time. The CPs size in the peak-aged materials increases in the following order: twinned region in the pre-twinned material (0.47 µm) < residual matrix region in the pre-twinned material (1.71 µm) < matrix region in the extruded material (2.55 µm). Moreover, the CPs number density in the twinned region of the pre-twinned material is approximately 11 times higher than that in the matrix region of the extruded material. The peak-aged pre-twinned material exhibits significantly higher tensile strength and ductility than the peak-aged extruded material. These results demonstrate that the formation of {10–12} twins in the extruded AZ80 alloy substantially accelerates the static precipitation of CPs during aging at 300 °C and improves the tensile properties of the peak-aged material.

Chaotic dynamics in refraction galactic billiards

We prove the presence of topological chaos at high internal energies for a new class of mechanical refraction billiards coming from Celestial Mechanics. Given an open and bounded domain with smooth boundary, a central mass generates a Keplerian potential in it, while, in , a harmonic oscillator-type potential acts. At the interface, Snell’s law of refraction holds. The chaoticity result is obtained by imposing progressive assumptions on the domain, arriving to geometric conditions which holds generically in . The workflow starts with the existence of a symbolic dynamics and ends with the proof of topological chaos. Intermediate results will be the analytic non-integrability and the presence of multiple heteroclinic connections between different equilibrium saddle points. This work can be considered as the final step of the investigation carried on in De Blasi and Terracini (2022 Nonlinear Anal. 218 112766; 2023 Discrete Contin. Dyn. Syst. 43 1269–318).

Effects of intermediate annealing time on texture evolution during multi-pass cold-shear-straining of an Al–Mg–Si–Cu alloy

This study examines the effects of different intermediate annealing times during multi-pass cold-torsion tests on the microstructure in alloys of aluminum, magnesium, silicon, and copper (Al–Mg–Si–Cu). The mean flow stress, when the intermediate annealing time is shorter, increases until sufficient internal strain accumulates and then decreases rapidly. In contrast, the mean flow stress decreases continuously when the IA time is longer. X-ray line profile analysis revealed a rapid decrease in mean flow stress because of the high stored internal energy represented by the dislocation density. In addition, a short annealing time allows the B component to form in the initial stage of multi-pass torsion, and a random texture distribution occurs as the multi-pass torsion stage progresses. In contrast, a long annealing time can dissipate the texture distribution in a low-pass stage (low strain) and decreases the overall deformation resistance, despite the much stronger texture intensity in a high-strain area. Finally, the B texture component is consumed by the A component in the initial stages of the multi-pass cold torsion test. This is attributed to the different orientation relationships of the shear plane in the A and B components, which caused deviations in dislocation density.

Microstructural and Texture Evolution of Pearlite-Drawn Wires for Flexible Marine Pipelines: Investigating the Effect of Heat Treatments on Mechanical Properties

Flexible pipelines connect offshore platforms to subsea production systems due to their high flexibility, applicability, and recycling. Flexible armor layers in flexible pipelines are constructed using the parallel helical wrapping of several rectangular wires. The complex stress modes to which pipelines are subjected provide complex failure modes that are mostly unpredictable, requiring expensive pipeline integrity verification methods. This work investigates texture and microstructure evolution in pearlite-drawn wires due to different heat treatments. The material was subjected to annealing and isothermal heat treatments to obtain changes in its microstructure and texture. The changes were characterized using SEM, XRD, and EBSD techniques. Samples were subjected to tensile testing to evaluate their mechanical properties. This work revealed that annealing and isothermal treatments mainly modify the material microstructure, whereas annealing provides a material with grains with ease of deformation. In contrast, isothermal treatment provides grain growth with high internal energy and more deformation resistance. Annealing increases the intensity of all texture components, while isothermal treatment reduces intensity. These findings provide insights into the relationship between material properties and heat treatments, which can be used to optimize the design and performance of flexible pipelines, thereby reducing the need for expensive integrity verification methods.

Direct chemical dynamics simulations of CN- + CH3I bimolecular nucleophilic substitution reaction.

Bimolecular nucleophilic substitution reactions have been studied for more than a century. Experimental and theoretical investigations of these reactions are extensively going on due to their wide applicability and the discovery of new features of these reactions. The CN- + CH3I nucleophilic substitution reaction can result in two isomeric products (NCCH3/CNCH3 + I-) because the incoming nucleophile has two reactive centers. Velocity map imaging experiments of this reaction have been reported and dominant direct rebound dynamics and high internal energy excitation of the reaction products were found in the experiments. However, it was not possible to directly obtain the isomer branching ratios from the experimental data and statistical ratios were predicted based on a numerical simulation. In the present work, direct chemical dynamics simulations of this reaction were performed using density functional theory and semi-empirical potential energy surfaces. Reactivity was low at all collision energies and direct rebound dynamics was observed in a major fraction of trajectories in agreement with experiments. However, the branching ratios computed from the trajectories were different from the previously reported estimates. Product energy distributions and scattering angles were computed and detailed atomic level reaction mechanisms are presented.

Effects of pre-strain and aging treatments on the mechanical property and corrosion resistance of the spray formed ultra-high strength Al-Zn-Mg-Cu alloy

Mechanical property and corrosion resistance are essential performances in ultra-high strength Al-Zn-Mg-Cu alloys for the aerospace and weapon industries. In this study, the pre-strain and aging treatments were used to enhance such performances of the spray formed ultra-high strength Al-Zn-Mg-Cu alloy. After 2% pre-strain with peak aging (PA) and retrogression and re-aging (RRA) treatments, the ultimate tensile strength, yield strength, and elongation can reach to 774 MPa, 735 MPa, 10.7% and 774 MPa, 747 MPa, 9.4%, respectively. The coarser precipitates of the samples with 4% pre-strain can lead to the slight lower strength compared with the samples with 2% pre-strain. The proper combination of pre-strain and aging treatments can also effectively enhance the stress corrosion resistance of the studied alloy by the following reasons. First, the higher strain concentration degree and dislocation density introduced by pre-strain treatments have high internal energy and provide more stored energy for the growth of the passive film. Second, the spacing of grain boundary precipitates under double aging (DA) and RRA states is larger than that under PA state. The width of uniform precipitation free zone (PFZ) with 2% pre-strain is larger than that with 4% pre-strain. Third, after pre-strain treatments, the cracks perpendicular to the deformation direction can be produced in Al 7 Cu 2 Fe phase, which further breaks up such particles. According to the results of Kelvin probe microscopy, the Al 7 Cu 2 Fe phase with smaller dimension can obtain the lower difference of potential to Al matrix. • The strength and corrosion resistance of the alloy were enhanced by pre-strain. • The pre-strain produced cracks in Al 7 Cu 2 Fe particles and further broke up them. • The pre-strain improved the strain concentration degree and dislocation density. • The effect of precipitation free zone and precipitate is better under 2% strain. • The improvement mechanism of pre-strain treatment was revealed.

Bending-deformation-induced inhomogeneous aging behavior and accelerated precipitation kinetics of extruded AZ80 alloy

In this study, the effects of bending deformation on the precipitation behavior of an extruded AZ80 alloy are investigated by subjecting a plate of the alloy to three-point bending and subsequent aging at 200 °C. In the upper region of the bent specimen (denoted as CZ), numerous {10−12} extension twins are formed. In the lower region of the bent specimen (denoted as TZ), small quantities of {10−12} extension twins, {10−11} contraction twins, and {10−11}–{10−12} double twins are formed, and most of the bending deformation is accommodated by dislocation slip. In the central region of the bent specimen (denoted as NZ), few twins are formed, and the microstructural characteristics of this region are almost identical to those of the initial material. When the bent specimen is aged, the peak-aging time of the CZ and TZ (8 h) is 60% shorter than that of the NZ (20 h), which is attributed to the accelerated precipitation caused by the abundant twins in and high internal strain energy of the CZ and TZ. In the CZ, nucleation and growth of continuous Mg 17 Al 12 precipitates (CPs) occur rapidly, especially inside the {10−12} twins, and this accelerated CP formation inhibits the formation of discontinuous Mg 17 Al 12 precipitates (DPs). Because of the high internal strain energy of the TZ, promoted formation of CPs occurs in the early stage of aging, which, in turn, suppresses the formation of DPs. In contrast, the NZ, because of its low internal strain energy and insufficient twins, exhibits slower CP formation behavior and has a considerably larger amount of DPs than the CZ and TZ. Although the bending deformation before aging induces inhomogeneous precipitation behaviors, the prebending deformation shortens the overall peak-aging time of the material and increases its peak hardness. • An extruded AZ80 alloy plate is subjected to bending and subsequent aging. • The bent plate has an inhomogeneous microstructure and internal strain energy. • Its upper and lower regions show a faster aging rate than its central region. • Continuous and discontinuous precipitation behaviors are different in each region. • Bending deformation shortens the peak-aging time and improves the peak hardness.

Parametric study of the ceramic roller hearth kiln combustion chamber with pre-heated air from the kiln flue gases

The energy demand for the heating process of ceramic tiles is very high and plays a significant role in environmental pollution with a higher rate of release of CO2. The energy consumption of ceramic tiles can be optimized with an efficient or complete combustion possibility with less fuel input. This is achieved with the optimum design of the burner and its combustion air. In this research, an attempt has been made to optimize the combustion process of the ceramic kiln section with the utilization of waste heat recovery from the exhaust gases released from the kiln section. This exhaust air consists of high internal energy; hence, its effect has been studied with different temperature and pressure inlet conditions to optimize the combustion process. The whole project has been executed numerically by considering the cross-sectional domain of the kiln module. It is equipped with two burners on either side of the domain and accomplishes combustion of natural gas. The internal flow physics with chemical reaction has been analyzed by solving the Reynolds averaged Navier-Stokes equations, energy, and species transport conservation equations. From the analysis of different operating conditions of the kiln, it is found that the reaction rate increases with an increase in pre-heated air temperature, which is heated by the kiln exhaust gases. The desired operating temperature of 1100–1300 °C of the kiln has been achieved even with decreased fuel intake of 0.02 g/s by considering the increased waste heat recovery from the kiln flue gases. Among the different working conditions, case-4 is the optimum operating condition for reducing the fuel usage of 103.67 kg per day without compromising the desired output.

On-the-fly investigation of XUV excited large molecular ions using a high harmonic generation light source

We present experiments where extreme ultraviolet femtosecond light pulses are used to photoexcite large molecular ions at high internal energy. This is done by combining an electrospray ionization source and a mass spectrometer with a pulsed light source based on high harmonic generation. This allows one to study the interaction between high energy photons and mass selected ions in conditions that are accessible on large-scale facilities. We show that even without an ion trapping device, systems as large as a protein can be studied. We observe light induced dissociative ionization and proton migration in model systems such as reserpine, insulin and cytochrome c. These results offer new perspectives to perform time-resolved experiments with ultrashort pulses at the heart of the emerging field of attosecond chemistry.

Nonoxidative Coupling of Methane over Ceria-Supported Single-Atom Pt Catalysts in DBD Plasma.

Plasma-catalytic direct nonoxidative coupling of methane (NCM) into C2 hydrocarbons was investigated over ceria-supported atomically dispersed Pt (Pt/CeO2-SAC) and nanoparticle Pt (Pt/CeO2-NP) catalysts in dielectric barrier discharge (DBD) plasma. Nonthermal plasma facilitated C-H bond dissociation in CH4 at low temperatures (<150 °C) and atmospheric pressure. The presence of Pt/CeO2 catalysts in plasma further enhanced CH4 conversion and C2 hydrocarbon selectivity by enabling the conversion of vibrationally excited methane species with high internal energy on active Pt sites. Noticeably, the Pt/CeO2-SAC catalyst displayed a more remarkable performance, with a CH4 conversion of 39% and a C2 selectivity of 54% at 54 W. The enhanced CH4 conversion was attributed to abundant coordinatively unsaturated Pt sites in Pt/CeO2-SAC, which were more active for C-H bond scission. Meanwhile, isolated Pt atoms in Pt/CeO2-SAC promoted C2 hydrocarbon formation by hindering the unselective formation of coke from deep dehydrogenation of CHx• intermediates and higher hydrocarbons from oligomerization reactions.

An assessment of the tropospherically accessible photo-initiated ground state chemistry of organic carbonyls

Abstract. Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a test set of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2 loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implications for global H2 production, and tautomerisation has implications for the atmospheric production of organic acids.

Effect of the selected parameters in idealizing material failures under tensile loads: Benchmarks for damage analysis on thin-walled structures

Abstract The development of the global economy has led to a rise in ship traffic. As a result, the risk of accidents, such as collisions between ships and grounding, has also increased. Different failure criteria to capture these accidents have been introduced by researchers. Therefore, the purpose of this study was to determine the essential distinction between these failure criteria. The simulations suggest that failure criteria based on the maximum stress result in a slightly higher rupture strain value, greater crack propagation, and higher internal energy than those based on the maximum strain. Furthermore, using a larger mesh size compared with the size of the test specimen appears to greatly affect the validity of the simulation results.

Pressure-sensitive Ce3+ photoluminescence in LiCaY5(BO3)6: high internal quantum yields and energy transfer to Tb3+

LiCa(Y0.99Ce0.01)5(BO3)6 has a high IQY of 51%, which can be enhanced to 89% by co-doping 20% Tb3+. The maximal wavelength of Ce3+ PL emission is highly sensitive to the applied pressure, which exhibits a linear red-shift (∼43 nm) up to 20.1 GPa.