Lattice Resistance Research Articles

Impact of self-heating on geometric variations in nano-ribbon FET: Analog/RF perspective

In recent technology, Nano Ribbon FET (NR-FET) is an emerging device due to its enhanced effective width than other FET devices. In this paper, the electrical parameters including self-heating effect (SHE) for NRFET is presented. The drain current (ID), transconductance (gm), transconductance generation factor (TGF = gm/ID), and cut-off frequency (fc) are highlighted in NRFET with/without considering SHE. It is observed that various electrical parameters are degraded by significant amount in the presence of SHE for NR-FET. The gm is changed from 1.45 to 0.725 mS in presence of SHE, whereas, fc is reduced to 2.47 THz from 4.5 THz in presence of SHE for NRFET. Further, the effect of variation in width and height of ribbon in NRFET on e-density, drain current, and transconductance are reported with/without including SHE. Result reveals that with increased width/height, the performance of NRFET is enhanced and this is further degraded with including SHE. Finally, the important parameters like lattice temperature and thermal resistance (Rth) are calculated for NRFET. The calculated lattice temperature and Rth are 375.2 K and 1.534 K/μWatt, respectively.

Short-range ordering mechanics in FCC materials

Short-range order (SRO) has a crucial impact on the mechanical strength of metallic alloys. Recent atomistic investigations defined an average SRO and attempted to correlate it with the yield strength. We propose that the local change in SRO upon slip advance must dictate the strengthening, and we elaborate the methodology to establish the “SRO change” on a slip plane considering the Wigner-Seitz cell. The model captures the variation of lattice resistance (Critical Resolved Shear Stress; CRSS) in the crystal as the SRO changes depending on the probability of neighboring atoms. The methodology was applied to Ni-V binary alloys for a wide range of compositions and stacking fault widths. Dislocation core widths were determined as a function of SRO and energy parameters (unstable and intrinsic stacking fault energies; γus, γisf). The complex variation of CRSS with compositional variations shows good agreement with limited experimental results. The compositions corresponding to the transition from partial to full dislocations at higher vanadium contents are found depending on the SRO and the intrinsic energy levels.

Electrical properties, microstructure, and thermal conductivity of hot-pressed CaO-doped AlN ceramics

AlN ceramics exhibit good physical and chemical properties and are ideal materials for the dielectric layer of electrostatic chucks. However, they cannot generate a strong J−R-type electrostatic adsorption force because of their high resistivity. Therefore, adding other substances is necessary to regulate the electrical properties and enable their application. In this study, AlN ceramics were prepared using hot-pressed sintering with 0.2 wt% CaO as an additive at a sintering temperature range of 1700–1900 °C. The effects of CaO doping on the phase composition, microstructure, electrical properties, and thermal conductivity of the AlN ceramics were systematically investigated. The addition of CaO not only enhanced the sintering process of the AlN ceramics, but also significantly reduced the electrical resistivity and increased the thermal conductivity. The relative density of CaO-doped AlN ceramics reached 98.88 % at 1700 °C, with a thermal conductivity of 81.51 W m−1•K−1. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and AC impedance spectroscopy were used to analyse the impurities and defects in the AlN ceramics. The lattice parameters and fitting grain resistance indicated that the CaO-doped AlN presented a higher lattice oxygen concentration, increasing the concentration of Al vacancies and electrons. Moreover, the level of dissolved oxygen could be controlled by altering the sintering temperature, resulting in AlN ceramics with electrical resistivity ranging from 8.1 × 106 to 1.7 × 1012 Ω cm. Further research was conducted to investigate the effect of the electrical resistivity of AlN ceramics on the J−R-type electrostatic adsorption force, and it was found that AlN ceramics with a specific resistivity of 109 Ω cm exhibited the highest electrostatic adsorption of 351.7 g/cm2.

The effect of atomic hydrogen on the behavior of a single dislocation of 〈111〉{112} in bcc tungsten: Atomistic study

Tungsten (W) has been widely studied and spotlighted as a plasma-facing material (PFM) in the extreme environment of nuclear fusion due to its excellent physical properties. It is important to investigate the effect of hydrogen on the material behavior of tungsten as it was used in the hydrogen-rich fusion environment. Solute hardening is a typical phenomenon and it is traditionally understood by dragging or pinning effect when hydrogen atoms act like solute atoms that impede dislocation motion. On the other hand, there were several experimental studies reporting softening associated with enhanced dislocation activity, either by easy nucleation or increased mobility, or both. In order to better understand how the effect of hydrogen on mechanical behavior of W, the authors conducted molecular dynamics simulations on dislocation mobility with different dislocation types, hydrogen concentrations, stress, and temperature. At high concentration of 1 at.%, H atoms are often strongly clustered around a dislocation core and produce a super-pinning effect in that both edge and screw started to move at a stress far beyond Peierls stress. This critical stress reduces with temperature increase, and thermally assisted kink or jog formation helps a dislocation escape from the H-cloud trapping. At a low concentration of 0.01-0.1 at.% or a high concentration of 1 at.% without super-pinning, hydrogen dragging barely appeared with a screw dislocation, and the intrinsic lattice resistance dominated the motion of a screw. For an edge dislocation under the same condition, an appreciable reduction in mobility was observed with the increase of H concentration at a low temperature of 300 K and this change in mobility becomes inconspicuous for higher temperatures. In conclusion, this study predicts the hardening of W at a high H concentration of 1 at.% due to dislocation trapping at the H cluster.

Rare-earth cerates with a high coefficient of thermal expansion and excellent CMAS corrosion resistance obtained through high-entropy designing

As the demand for aero-engines with a high thrust-to-weight ratio has increased, the comprehensive performance requirements for thermal barrier coatings (TBCs) have become extremely challenging. Among them, the indicator that measures the service life of TBCs not only requires a high coefficient of thermal expansion (CTE) but also strong resistance to molten calcium-magnesium-aluminum-silicate (CMAS) corrosion. In this study, we used the solid-state method to prepare (La0.2Nd0.2Sm0.2Eu0.2Lu0.2)2Ce2O7 (5RLC), (La0.25Nd0.25Sm0.25Eu0.25)2Ce2O7 (4RLC), and Sm2Ce2O7 (SC) by sintering at 1700 °C for 10 h. By regulating the average radius and the variation of rare-earth ions through high-entropy designing, the lattice structure, micromorphology, element composition, CTE, and resistance to CMAS corrosion were systematically studied. The results showed that the bulk samples had defective fluorite structures, dense microstructures, and a uniform distribution of elements. At 1400 °C, the CTEs of 5RLC and 4RLC were 12.14 × 10−6 K−1 and 12.45 × 10−6 K−1, respectively. After 20 h of CMAS corrosion at 1300 °C, the thickness of the product layers was only 9.73 μm and 10.80 μm for 5RLC and 4RLC, respectively. In this study, we combined the high coefficient of thermal expansion and excellent CMAS corrosion resistance of 5RLC and 4RLC and found that they can maintain a good service life.

Strengthening effects of Al element on strength and impact toughness in titanium alloy

Pure Ti and binary Ti–6Al alloy have been employed as the investigated targets of our research. The strengthening effects of Al element on strength and impact toughness in titanium alloy were systematically investigated. The experimental results indicated that the addition of Al element significantly improved the tensile strength while deteriorating the plasticity and impact toughness. Analysis of deformation mechanisms indicated that addition of Al element strongly inhibited the dislocation movement and deformation twinning in titanium alloy. The theoretical results demonstrated that the dissolution of Al atoms reset the atomic bond configurations and electronic structures of the α-Ti lattice. Therefore, the lattice resistance to dislocation nucleation and dislocation gliding was significantly improved which led to the strong strengthening effect of Al element in α-Ti. The lattice resistance to the shearing atomic motion of deformation twinning was also improved due to the dissolution of Al atoms. Moreover, the strengthening of Al element was revealed at the electronic level by employing the empirical electron theory (EET) of solids and molecules. The strengthening effects of Al element in titanium was also quantitatively evaluated according to the valence electron structure (VES) parameters. A prediction model for the tensile strength of α-type Ti-xAl alloys was proposed based on the quantitative strengthening of Al element. The high accuracy of the prediction model for strength of Ti-xAl alloy was verified by the average error (3.58%) between the computational strength and experimental results.

Analytical flow equation for irradiated low-alloy steels established by multiscale modeling

In this paper, we show how results of multiscale modeling can be condensed to establish a simple analytical flow equation for irradiated low-alloy steels. The flow equation accounts for temperature, strain rate, the initial and irradiation microstructure. Starting from a complete set of constitutive equations describing crystal plasticity of irradiated ferritique steels, simple assumptions and approximations are used to integrate the equations over the homogenized polycrystal. The final flow equation incorporates the lattice friction resistance, the Hall-Petch effect, the forest strengthening and irradiation hardening. Every component is established by multiscale modeling at lower scales. Irradiation hardening is attributed to solute clusters. Their size and density are determined in experiment, their shear resistance computed by atomistic simulations and their contribution to the flow stress assessed using dislocation dynamics simulations. The formation of solute clusters is found to increase the flow stress and the strain hardening modulus. Irradiation hardening decreases with temperature and with the yield stress of the unirradiated material. Predictions of the tensile curves and irradiation hardening are compared with many experimental results. A special section is dedicated to the interpretation of irradiation hardening measured in a surveillance program.

Engineering Heat Transport Across Epitaxial Lattice-Mismatched van der Waals Heterointerfaces.

Artificially engineered 2D materials offer unique physical properties for thermal management, surpassing naturally occurring materials. Here, using van der Waals epitaxy, we demonstrate the ability to engineer extremely insulating thermal metamaterials based on atomically thin lattice-mismatched Bi2Se3/MoSe2 superlattices and graphene/PdSe2 heterostructures with exceptional thermal resistances (70-202 m2 K/GW) and ultralow cross-plane thermal conductivities (0.012-0.07 W/mK) at room temperature, comparable to those of amorphous materials. Experimental data obtained using frequency-domain thermoreflectance and low-frequency Raman spectroscopy, supported by tight-binding phonon calculations, reveal the impact of lattice mismatch, phonon-interface scattering, size effects, temperature, and interface thermal resistance on cross-plane heat dissipation, uncovering different thermal transport regimes and the dominant role of long-wavelength phonons. Our findings provide essential insights into emerging synthesis and thermal characterization methods and valuable guidance for the development of large-area heteroepitaxial van der Waals films of dissimilar materials with tailored thermal transport characteristics.

Atomistic determination of Peierls barriers of dislocation glide in nickel

The Peierls barrier measures the lattice resistance to dislocation glide in crystalline solids. We use the nudged elastic band (NEB) method to calculate the Peierls barriers for screw and edge dislocation glide in a face-centered cubic (FCC) metal of Ni. The minimum energy paths (MEPs) across single or sequential Peierls barriers are determined under shear loading. The NEB results show the decreasing Peierls barrier with increasing shear stress, giving the Peierls stress at which the Peierls barrier vanishes. The effects of boundary condition and system size on Peierls barriers are studied by comparing strain- and stress-controlled NEB results. Furthermore, the free-end NEB methods are applied to determine MEPs with improved computational efficiency. The NEB results are also used to evaluate the energetic driving force of dislocation glide, which is consistent with that determined from the Peach-Koehler force. The accuracy of the present NEB results based on an empirical interatomic potential is assessed by comparison with a machine-learning potential. This work demonstrates the robust and efficient quantification of Peierls barriers to dislocation glide in an FCC metal, and it lays a solid foundation for the atomistic determination of Peierls barriers in compositionally complex alloys with the FCC structure in future studies.

Achieving high strength and ductility in high-entropy alloys via spinodal decomposition-induced compositional heterogeneity

The compositional heterogeneity in high-entropy alloys (HEAs) has been reported to be an inherent entity, which significantly alters the mechanical properties of materials by tuning the variation of lattice resistance for dislocation motion. However, since the body-centered cubic (BCC) structure is not close-packed, the change of lattice resistance is less sensitive to the normal concentration wave compared to that in face-centered cubic (FCC) structured materials. In this work, we selected a refractory bcc HEAs TiZrNbTa for the matrix and added a small amount of Al to facilitate the special spinodal decomposition structure. In particular, (TiZrNbTa)98.5Al1.5 displayed a typical basket-weave fabric morphology of spinodal decomposition structure with a characteristic periodicity of ∼8 nm and had an optimal combination of strength and ductility (the yield strength of 1123 ± 9 MPa and ductility of ∼20.7% ± 0.6%). It was determined that by doing in situ TEM mechanical testing, the plastic deformation was dominated by the formation and operation of dislocation loops which provided both edge and screw components of dislocations. The synergetic effect of the remarkable chemical heterogeneity created by the spinodal decomposition and the spreading lattice distortion in high entropy alloys is quite effective in tuning the mobility of different types of dislocations and facilitates dislocation interactions, enabling the combination of high strength and ductility.

Investigation of Electro-Thermal Performance for TreeFET from the Perspective of Structure Parameters

In this work, the electro-thermal properties of TreeFET, which combines vertically stacked nanosheet (NS) and fin-shaped interbridge (IB) channels, are investigated in terms of interbridge width (WIB), nanosheet space (SNS) and nanosheet width (WNS) by TCAD simulation. Electrical characteristics such as electron density distributions, on/off-state current (ION, IOFF), subthreshold swing (SS) and self-heating effects (SHE) such as lattice temperature and thermal resistance (Rth) are systematically studied to optimize the performance of TreeFET. The result shows that a smaller WIB mitigates the short-channel effects and increases the electron concentration in NS channels but increases thermal resistance. A larger SNS increases the on-state current while compensating for the gate drive loss and mitigating the thermal coupling effect between NS channels but results in longer conduction paths of carriers and heat, which hinders further improvements. Moreover, a suitable WNS is required to lessen the decline of gate controllability induced by IB channels. Hence, suitable geometry parameters should be selected to achieve a compromise between thermal and electrical performance.

Reaction of a crystal lattice of metallic materials to long-term storage in elastic-stressed state

The resistance of the crystal lattice of 08ps structural steel, AD1 aluminum grade and M1 copper grade to long-term action (9 years) of elastic stresses at different levels of static loads was studied by the X-ray diffraction method. It has been established that the annual ambient temperature variation from -50°С in winter to +35°С in summer in the period from 2013 to 2022 does not cause significant changes in the characteristics of the diffraction line profiles of the studied materials. The characteristics of the diffraction line profiles obtained in the winter period of observations indicate a slight decrease in instrumental errors due to the experiment design conditions. A systematic change in the resistance of the studied materials crystal lattice to the action of elastic stresses at values of σ > 0.5 σ0,2 was found. The stepwise process of the occurrence of elementary acts of the crystal lattice reaction in the local zone of X-ray reflection is revealed. This gradation experimentally substantiates the value of the minimum safety factor of materials used in strength calculations of structures.

Role of lattice resistance in the shock dynamics of fcc-structured high entropy alloy

The shock response of high entropy alloys (HEAs) would be important for their performance under extreme conditions. However, it is still difficult to obtain the shock response data at the atomic scale over the wide range of loading conditions. Here, the shock compression response of fcc-structured modeled HEAs and pure metals with different degrees of lattice resistance and stacking fault energy has been studied using the molecular dynamics simulations in the terms of the Hugoniot stress, atomic structure, and dislocation density. The results show that the HEA with low lattice resistance exhibits a significantly low shock compression strength in comparison with pure metal. In contrast to pure metal, Shockley partial dislocations and stacking faults with high density were found in HEA with low lattice resistance. Interestingly, during the shock wave propagation in HEA with high lattice resistance to dislocation glide, the crystalline to amorphous phase transformation has been observed to occur behind the shock front. The high lattice resistance slows down the movement of dislocations in HEA, and then promotes the amorphization process. This trend gives an effective toughening mechanism in shock loading of HEAs. In addition, the microstructure-based physical model suggests the obvious effect of lattice resistance on the working hardening of the HEAs after shock compression. It indicates that the lattice resistance of intrinsic chemically disordered structures dominates the rate of dislocation generation and the shock compression strength. The current study provides an important atomic insight for understanding the dynamic mechanical behaviors of HEAs. • Shock compression response of HEAs and pure metals was studied. • HEA with low lattice resistance exhibit low strength in comparison to pure metals. • Amorphization occurred behind the shock front of HEA with high lattice resistance.

Bending and punching characteristics of aluminum sheets using the quasi-continuum method.

The nano-punching characteristics of single-crystalline aluminum are investigated using the quasi-continuum (QC) method. Four variables (i.e., crystal orientation, workpiece thickness, clearance between the punch and the substrate, and the taper angle of punch) are used to explore their effect during the nano-punching process. The shear stress distribution is used to express the punching effect on the punch and on both sides of the substrates. Besides, fracture strength, residual flash, and the atomic displacement vector are observed and discussed regarding the behaviors of the nano-punching process under various conditions. Based on the results, the Al workpiece with the X[111]Y[-110] orientation presents less lattice resistance during the punching process. Besides, the thickness of the workpiece has a significant effect on the punching quality. Workpieces with thickness values of 5 and 10 Å are more suitable for punching, due to stable loading and unloading stress-displacement curves and less residual flash on the cutting surfaces of these workpieces. In contrast, the effect of clearance has less impact on the punching behaviors of thinner workpieces. However, for thicker workpieces (i.e., 15 and 20 Å), a larger clearance will likely cause more residual flash. Furthermore, the taper angle of the punch should not be larger than 10°, otherwise, it might damage the workpiece and the substrate.

Carbon monoxide-sensing of SnS nanoflakes induced by the electron-trapped polaron upon the substituted-lithium

Two-dimensional (2D) SnS with wrinkled lattice and strong oxidation resistance exhibits malleable talents and great potential for gas-sensing applications. But it suffers the inherent disadvantage of low sensitivity towards weakly polarized gases like CO. Herein, inspired by the unique atomic real polarization and orbital penetration of lithium, a distinct polarized configuration of 2D Li-substituted SnS is proposed for achieving a moderate CO adsorption-desorption dynamics at room temperature. The 2D nanoflakes of Li-SnS, synthesized via one-step solvothermal method, reveal highly sensitive and selective performances towards trace CO as low as 2 ppm at RT. Conducting with first-principles calculations, the substitutional doping of Li in SnS crystal is unveiled as the knob to modulate the electronic state of SnS. The enhanced electron-deficiency states and the local vibration modes of Li atoms, urge the coupling of electrons and longitudinal-optical phonons to form a polaron on each Li site. These polarons serve as efficient electron traps, and synergize with anharmonic local vibrations of Li atoms to form energy state fluctuation, promoting CO adsorption-desorption dynamics and carrier transport for the SnS system. This work provides novel perspectives for understanding the structure-electrical configurations of 2D materials and the microscopic mechanism of gas adsorption.

The influence of stress levels on the creep behavior of Ti–42Al–6Nb–0.05Y2O3 alloy

The paper studied the creep behavior of Ti–42Al–6Nb–0.05Y2O3 alloy. Short-term creep tests were performed at the temperature range of 750–900 °C and the stress range of 100–300 MPa. The results reveal that the stress exponent varies from 1.85 to 5.01 when the creep stress increases from 100 to 300 MPa at 850 °C. Interface sliding and dislocation climb are the main creep mechanisms at 100 and 300 MPa, respectively. Formation of intergranular cracks is the major cause of the failure above 150 MPa. Instead, under 100 MPa, nucleation of cracks along lamellar interfaces plays a dominant role in the rupture. There is a critical temperature at which the apparent activation energy (Qc) increases suddenly. For the lamellar alloy, the increase of Qc has a close association with the dislocation movement in minority α2 laths. Below the activation energy transition temperature (AETT), the deformation of α2 phase is mainly governed by a→ type dislocations. Whereas above the AETT, the activation of 2c→+a→ type dislocations plays a dominant role. Moreover, the AETT at 300 MPa is determined to be 800–850 °C, whereas that at 100 MPa is 850–900 °C. There is an increase of AETT with the decrease of creep stress. At the low stress (100 MPa), the AETT depends on lattice resistance rather than long-range internal stress, since the flow stress may be less than Peierls-Nabarro force for slipping of 2c→+a→ type dislocations, resulting in a high AETT.

Characteristics and mechanism in ultrasonic vibration-assisted deformation of Ni-based superalloy thin-walled sheet by quasi-in-situ EBSD

Ultrasonic vibration-assisted (UVA) forming is expected to be an effective way to improve the forming ability of Ni-based superalloy thin-walled sheet. However, the deformation characteristics and mechanism of this material under ultrasonic field keep unclear. To this end, experiments of UVA tension followed by quasi-in-situ EBSD were conducted. The tensile mechanical properties under different amplitudes were investigated, and the quasi-in-situ microstructure evolutions of the feature areas on non-UVA/UVA tensile specimens were compared. Experimental results show that ultrasonic vibration reduces the stress response, but the fracture may occur in advance under excessive ultrasonic amplitude. During the UVA deformation, the easy-to-deform grains with initial orientation close to<101>along the tensile direction rotate to<111>and<001>orientations, which then have a tendency to rotate back to<101>orientation in subsequent deformation. In addition, low-angle grain boundaries and dislocation density are also promoted. Based on the experimental results, a new perspective of the acoustic softening mechanism considering grain rotation and dislocation slip was proposed. The ultrasonic vibration facilitates grain rotation to coordinate plastic deformation. Meanwhile, the superposition of the ultrasonic field intensifies the atomic inherent vibration. The lattice resistance required for dislocation slip decreases accordingly. • Excessive ultrasonic amplitude reduces the flow stress and accelerates the microcracks growth of Ni-based superalloy. • Direct observation of microstructure evolution during ultrasonic vibration-assisted tension by quasi-in-situ EBSD. • A new perspective of acoustic softening mechanism considering grain rotation and dislocation slip.

Creep Rheology of Antigorite: Experiments at Subduction Zone Conditions

AbstractNovel fluid medium pressure cells were used to deform antigorite under constant stress creep conditions at low temperature, low strain rate (10−9 − 10−4 1/s), and high pressure (1 GPa) in a Griggs‐type apparatus. Antigorite cores were deformed at constant temperatures between 75°C and 550°C, by applying 8–12 stress‐strain steps per temperature. The microstructures of deformed samples share features documented in previous work (e.g., shear microcracks), and highlight the importance of basal shear and kinks to antigorite plasticity. Rheological data were fit with a low temperature plasticity law, consistent with a deformation mechanism involving large lattice resistance. When applied at geologic stresses and strain rates, the extrapolated viscosity agrees well with predictions based on subduction zone thermal models.

Intrinsic freedom of dislocation structures and Peierls stress oscillation

When the continuous translation symmetry breaks, a continuous mode splits into two distinct discrete modes with different energies. Based on the fully discrete Peierls model, it is found that stability of such discrete modes for dislocations can be tuned by the stacking fault energy of a slip system. As the stacking fault energy changes continuously, the stable dislocation structure transforms periodically and the Peierls stress varies oscillatorily. Furthermore, at the transformation point, the lattice resistance nearly vanishes and thus the dislocation can almost move freely.

Physical mechanism interpretation of polycrystalline metals’ yield strength via a data-driven method: A novel Hall–Petch relationship

The Hall–Petch relationship σy=σ0+kyd−0.5 is widely used to describe the relationship between yield strength and grain size of polycrystalline metals, and the material constants σ0 and ky fitted by experimental data are interpreted as lattice friction resistance and coefficient of grain boundary resistance, respectively. The frequent deviations from the Hall–Petch relationship between σy and d in coarser or finer grains, as well as the physical essence of σ0 and ky, have always been the focus of material scientists. In this study, intrinsic factors of the fitted constants σ0 and ky in the traditional Hall–Petch relationship are mined via a data-driven machine learning method, which reveals that the key physical quantities affecting σ0 are valence electron distance (S), cohesive energy (W), and coefficient of linear thermal expansion (lt); meanwhile, the key physical quantities affecting ky are grain boundary interface energy (γ), Young's modulus (E) and coefficient of linear thermal expansion (lt). Then, a novel Hall–Petch model σy=79W/(S3lt)+1.2γE/ltd−0.5 with satisfying prediction accuracy is constructed by symbolic regression methods. There is no experimental fitting constant term in the novel model, which can directly predict the yield strength of polycrystalline metals by key physical quantities. The novel Hall–Petch model has an excellent generalization ability and can be extended to the correlation calculation between the composition, grain structure and mechanical properties of single-phase alloys, which provides a theoretical method for the trans-scale calculation of metallic materials.