Effect Of Compressive Strain Research Articles

Effect of regulating compressive strains on thermal transport of silicon-based amorphous silica thin films and interfacial thermal resistance

To investigate the modulation of compressive strains on the thermal transport of silica thin films, a test method is proposed. A more accurate and anti-interference thermal conductivity test system was built, and the thermal-induced compressive strain was regulated by the external tensile stress setup. The microstructure and composition of sample were analyzed, and regulation law of compressive strains on the thermal conductivity of silica thin films was obtained. The effect of compressive strains on the thermal conduction of amorphous silica and interfacial thermal resistance was analyzed based on molecular dynamics simulation. The thermal conductivity calculation result is consistent with the change trend of the test result. The interfacial thermal resistance is small and the strain effect can be ignored.

Comparison of Auger Coefficients in Type I and Type II Quantum Well Midwave Infrared Lasers

We perform a detailed comparison of 2D Auger coefficients in narrow-gap type-I and type-II quantum wells (T1QWs and T2QWs), and the relative effects of Auger non-radiative decay on midwave infrared lasers employing both types of gain media. Comparison is also made to 3D Auger coefficients in bulk mid-IR materials, by defining a “normalization length” that accounts for the spatial extent of the electron and hole wavefunctions in the quantum wells. The comparisons confirm that Auger recombination in both types of QW is substantially suppressed relative to bulk, due primarily to the effects of compressive strain on the valence subband dispersions. We find that the 2D Auger coefficients in T1QWs remain substantially lower than those in T2QWs out to wavelengths beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5~\mu \text{m}$ </tex-math></inline-formula> . However, this does not necessarily imply a lower lasing threshold because a substantial fraction of the holes injected into T1QWs occupy lower subbands that do not contribute gain, so more must be injected to reach the lasing threshold. When all of the relevant considerations are combined, the thresholds for the best T1QW and T2QW lasers cross over near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda ~\approx ~3.0~\mu \text{m}$ </tex-math></inline-formula> . Other characteristics governing the relative T1QW and T2QW laser performances above threshold, such as maximum output power and wallplug efficiency, are also considered.

Molecular dynamics simulation of compression induced phase transformation in Cu1Ni3 alloy

The phase transformation mechanism and transformation path of Cu-Ni alloys is very important to study for their applications in excellent electrical properties and chemical catalysis. In this paper, the effect of compressive strain on the transformation path and mechanism of Cu1Ni3 alloy is studied by molecular dynamics simulations. The simulation results reveal that the transformation path of alloys is from Fcc-Bcc-Hcp phase to other phase (amorphous state). The simulations not only revealed the processes of atomic displacements and pair correlation function during the transformation, but also elucidated the underlying mechanism of the transformation at the atomic level. The mechanism of phase transformation could be the lattice reconstruction caused by lattice sliding and stretching. The simulation results provide a clear landscape on the transformation mechanism, facilitating our comprehensive understanding on the phase transition in the Cu-Ni system.

On the optical properties and dynamical and mechanical stability of 1T PdSSe, PdSTe, and PdSeTe monolayers under biaxial strain

In this work, the effects of compressive and tensile biaxial strain, applied to monolayered 1T Pd Janus PdSSe, PdSTe, and PdSeTe structures are investigated. For tensile strengths larger than 4%, the valence band maxima no longer occur at the high symmetry Γ point; this phenomenon is accompanied by the emergence of a quasi-direct bandgap, where Dirac-like cones develop for large enough strain. A semiconductor-semimetal phase transition takes place for compressive strain strengths of −8%, −4%, and −2% in PdSSe, PdSTe, and PdSeTe respectively. Phonon dispersion calculations show that the Janus structures, subject to tensile strains, are dynamically stable; yet under compressive strains, they are only stable for values not exceeding −6% in PdSSe, −4% in PdSTe, and −2% in PdSeTe. All structures are mechanically stable except for PdSTe under a 14% tensile strain, registering negative in-plane stiffness constants of −9.36 and −7.62 N/m along the x and y directions respectively. Optical absorption/emission within the infrared region is possible when the materials are exclusively subject to tensile strain. Once the Pd Janus structures are synthesized, the results presented here can serve as a guide for the fabrication of optoelectronic devices of optimal performance.

Band gap opening and surface morphology of monolayer graphene induced by single ion impacts of argon monomer and dimer ions

Craters have been observed upon irradiation by single ion impacts of Ar monomer and Ar dimer ions with 35 keV/atom in monolayer graphene on copper at a fluence of 1 × 1012 atoms/cm2. The observed craters at the ion impacts are in the underlying copper substrate, which pull down the graphene layer conformally towards them, introducing disorder into graphene. The number density of craters per atom produced by Ar-monomers is higher than that of Ar-dimer ions. In the ion impact region, disorder is high, and graphene is metallic in both Ar-monomer and dimer irradiation. In the ion impact region of dimer irradiated graphene, local density of states is higher and there is a shift in Dirac point position by +0.07 eV and a bandgap opening of 0.25 eV in the ordered region ∼15 nm away from the ion impact. Microscopic ripples in graphene are not observed in the case of monomer irradiation while they are present in the case of dimer irradiation with a reduced wavelength. Isotropic compressive strain is introduced by the ion impacts and it is larger for Ar-dimer irradiation. The combined effects of compressive strain along with breaking the equivalence between A and B sublattice of graphene is attributed to the opening of the band gap in graphene.

Indirect light absorption model for highly strained silicon infrared sensors

The optical properties of silicon can be greatly tuned by applying strain and opening new perspectives, particularly in applications where infrared is key. In this work, we use a recent model for the indirect light absorption of silicon and include the effects of tensile and compressive uniaxial strains. The model is based on material properties such as the bandgap, the conduction and valence band density-of-states effective masses, and the phonon frequencies, which are obtained from first principles including strain up to ±2% along the [110] and [111] directions. We show that the limit of absorption can increase from 1.14 (1.09) to 1.35 μm (0.92 eV) under 2% strain and that the absorption increases by a factor of 55 for the zero-strain cutoff wavelength of 1.14 μm when a 2% compressive strain is applied in the [110] direction. We demonstrate that this effect is mainly due to the impact of strain on the electronic bandgaps of silicon, directly followed by the valence band density-of-states effective mass.

Strain tuning of the Curie temperature and valley polarization in two dimensional ferromagnetic WSe2/CrSnSe3 heterostructure

Magnetic proximity effect can be used to tailor the magnetic ground state and valley polarization in the monolayer of transition metal dichalcogenides. Thus, we explore the effect of biaxial tensile and compressive strain on valley polarization in the WSe2/CrSnSe3 heterostructures with different stacking orders systematically. The indirect band gaps in the two most stable stackings; hollow (0.27 eV) and top (0.33 eV) were further enhanced to 0.35 eV under tensile strain while suppressed to almost 0.13 eV under compressive strain. The heterostructures had a FM ground state with a total magnetic moment per unit cell of 6 μ B in pristine as well as strained structures. In hollow stacking and compressively strained structures, we obtained a perpendicular magnetocrystalline anisotropy, while the top stacking and tensile strain structures had small in-plane anisotropy. An enhancement was found in Curie temperature from 73 K in pristine to 128 K in a 6% tensile strained structure. The valley splittings found in pristine hollow (4 meV) and top (9 meV) stacked heterostructures were further enhanced to 29 meV and 22 meV at 5% compressive strain respectively. This enhancement was attributed to the increased spatial dependence of the charge density along K+ and K− directions of the Brillouin zone, which give rise to the different local dipolar fields at these valleys. Our results suggest that strain could be an effective way to control or tune the valley splitting in WSe2/CrSnSe3 heterostructures.

Enhancement of thermoelectric performance of CH3NH3PbI3 through strain driven topological phase transition and doping

The effects of compressive strain, doping and temperature on the thermoelectric properties of CH3NH3PbI3 have been investigated by employing first principles based calculations and semi-classical Boltzmann theory. CH3NH3PbI3 displays a topological phase transition under 9.9% external compressive strain. Thermoelectric studies reveal that application of strain enhances the Seebeck coefficient for electron and hole-doped regions. This increment is attributed to the strain induced band inversion and modifications in the electronic density of states at the topological transition point. The strain driven topological phase transition produces a ZT value of 0.89 for hole-doped CH3NH3PbI3 at 800 K.

Kinetics for the Slip Motion of Ripple Dislocations on Gold-Coated Poly(dimethylsiloxane)

Understanding the evolution of the defects in surface patterns is of practical importance to improve the performance and structural durability of the pattern-based micro- and nanodevices. In this work, we investigate the effects of temperature, compressive strain, and relative direction of the compression to the prestretch on the slip motion of ripple dislocations formed on the surface of gold-coated poly(dimethylsiloxane) films. Applying compression in the direction parallel to the direction of prestretch cannot cause the slip motion of the ripple dislocations. The initial velocity of the slip motion of the ripple dislocations increases with the increases in temperature and compressive strain. The temperature dependence of the ratios of the configuration force to the viscous coefficient and the viscous coefficient to the effective mass of the ripple dislocations follows the Arrhenius equation.

Effect of LaNiO3 interlayer on electrical properties of Pb(Zr0.52Ti0.48)O3/LaNiO3/Pb(Zr0.52Ti0.48)O3 composite films

In this study, Pb(Zr0.52Ti0.48)O3/LaNiO3/Pb(Zr0.52Ti0.48)O3 (PZT/LNO/PZT) composite films with different LNO thicknesses were prepared by a sol-gel method. The influences of LNO interlayer on crystalline structure, microstructure and electrical properties of PZT/LNO/PZT composite films were studied. The results show that the perovskite grains of the upper PZT layer grow along the epitaxy of the LNO interlayer when the LNO layer is inserted into the composite films. Due to the in-plane compressive strain effect in the upper PZT layer and the reduced leakage current caused by the accumulated space charges at the PZT/LNO interface, an obvious enhancement of electrical properties is observed in PZT/LNO/PZT composite films. The PZT/LNO/PZT composite film with the 140-nm-thick-LNO layer possesses the best remnant polarization and dielectric constant, which are 43.3 μC cm−2 and 1841, respectively. The preparation of ferroelectric composite film with a ferroelectric/metallic oxide/ferroelectric structure provides a promising way for improving the electrical properties of ferroelectric materials.

Effect of pre-mechanical compression on free water removal, drying collapses and associated internal voids of oil palm wood

To prevent defects caused by drying collapse, transverse pre-mechanical compression with lateral restraint of green oil palm wood (OPW) before kiln-drying was performed. OPW specimens were divided according to specific gravity into low density (LD 0.22 ± 0.05) and medium-density (MD 0.33 ± 0.02) groups. Effects of compressive strain (0–0.65) and strain rate (0.01–1.0/min) on moisture removal and wood recovery after the compression and on collapse and internal void formations after kiln-drying were investigated. Results indicate that pre-mechanical compression linearly removes moisture out of wood and linearly generates permanent thickness strain that is independent of the strain rate used. The pre-compression reduces the true cross-sectional strain in the kiln-dried LD OPW and MD OPW and the internal voids caused by drying collapse in the LD OPW. The collapse-induced voids, not observed in all kiln-dried MD OPW, disappear when compressive strain > 0.45 is applied to the LD OPW. Microstructural examination reveals that directional folding of parenchyma cells caused by the compression reduces intercellular micro-voids randomly generated during drying by the non-directional collapse of parenchyma cells caused by capillary force. However, above the compressive strains of 0.35 and 0.25 in the LD OPW and MD OPW, interfacial micro-cracks, generated at the boundaries between the parenchyma cells and the fiber bundles, link to form shear bands at the angle of approximately 30–40° to the compression axis. After kiln-drying, these shear bands expand into shear-induced voids. Finally, mechanical properties of the kiln-dried LD OPW pre-compressed at a 0.45 strain without collapse-induced voids are comparable to those that have been air-dried.

Compressive and Tensile Deformations Alter ATP Hydrolysis and Phosphate Release Rates in Actin Filaments.

Actin filament networks in eukaryotic cells are constantly remodeled through nucleotide state controlled interactions with actin binding proteins, leading to macroscopic structures such as bundled filaments, branched filaments, and so on. The nucleotide (ATP) hydrolysis, phosphate release, and polymerization/depolymerization reactions that lead to the formation of these structures are correlated with the conformational fluctuations of the actin subunits at the molecular scale. The resulting structures generate and experience varying levels of force and impart cells with several functionalities such as their ability to move, divide, transport cargo, etc. Models that explicitly connect the structure to reactions are essential to elucidate a fundamental level of understanding of these processes. In this regard, a bottom-up Ultra-Coarse-Grained (UCG) model of actin filaments that can simulate ATP hydrolysis, inorganic phosphate release (Pi), and depolymerization reactions is presented in this work. In this model, actin subunits are represented using coarse-grained particles that evolve in time and undergo reactions depending on the conformations sampled. The reactions are represented through state transitions, with each state represented by a unique effective coarse-grained potential. Effects of compressive and tensile strains on the rates of reactions are then analyzed. Compressive strains tend to unflatten the actin subunits, reduce the rate of ATP hydrolysis, and increase the Pi release rate. On the other hand, tensile strain flattens subunits, increases the rate of ATP hydrolysis, and decrease the Pi release rate. Incorporating these predictions into a Markov State Model highlighted that strains alter the steady-state distribution of subunits with ADPPi and ADP nucleotide, thus identifying possible additional factors underlying the cooperative binding of regulatory proteins to actin filaments.

Elucidation of durability of carbon-supported PdIr alloy catalyst by experimental and theoretical approaches in polymer electrolyte membrane fuel cell

PdIr nanoparticles supported on carbon support are synthesized and their oxygen reduction reaction (ORR) activity and durability in a half cell or membrane-electrode assembly (MEA) configuration for polymer electrolyte membrane fuel cell are examined. A synergistic effect of the combination of Pd possessing the effective ORR catalytic activity and Ir as one of the most stable elements in acidic media leads to a decrease in particle size, a higher particle dispersion, and a better ORR activity than Pd monometallic catalysts. It is expected that PdIr alloys would form phase-separated nanoalloys that have Pd-rich surface owing to the higher surface energy of Ir. The addition of Ir to Pd in PdIr/C increases the metallic Pd portion. Meanwhile, the Pd5Ir/C is the most durable compared to Pd/C and Pt/C over 3000h of MEA operation. The ORR activity of PdIr alloy is expected to increase by reducing the oxygen binding energy of Pd in the presence of Ir from the first-principle calculation, and each contribution of compressive strain and ligand effects is quantified. The cohesive energy and the kinetic segregation energy are also calculated to support the improved stability of PdIr compared to Pd and Pt in the ORR condition.

Electronic, optical, and thermoelectric properties of perovskite BaTiO3 compound under the effect of compressive strain

The theoretical effects of compressive strain on electronic, optical and thermoelectric properties for the cubic and tetragonal phases of BTO perovskite-type crystal have been investigated using Density Functional Theory (DFT). It was found that the compressive strain influences on the nature of the forbidden band of the cubic and tetragonal phases of BTO because by applying −2.3% or more of compressive strain, BTO becomes a semiconductor with a direct forbidden gap which eliminate the additional interaction in the CB which is a quite remarkable for photovoltaic devices. Furthermore, the values of forbidden gap width increase with increasing the percentage of compressive strain which shows the piezoelectric property of BTO. Moreover, the optical properties show that the pure and compressed BTO compounds are good materials for optical applications in both visible and UV spectrum. Additionally, the mobility of the holes grows with the compressive strain, which leads to increase the thermal and electrical conductivity of BTO.

PdCoNi alloy nanoparticles decorated, nitrogen-doped carbon nanotubes for highly active and durable oxygen reduction electrocatalysis

Alloying Pd with transition metals is an effective strategy to enhance its catalytic activity toward oxygen reduction reaction (ORR). However, these catalysts always suffer from poor durability due to metal leaching during ORR. Herein, the catalyst of PdCoNi alloy nanoparticles supported on nitrogen-doped carbon nanotubes (PdCoNi/NCNTs) is prepared via one-pot solvothermal method and subsequent calcination. Introducing Co and Ni into Pd lattice not only boosts the catalytic activity, but also promotes the stability of the catalyst. As a result, the PdCoNi/NCNTs catalyst achieves a half-wave potential of 0.907 V and a specific activity of 3.78 mA/cm2 at 0.9 V vs. RHE, with 10 mV positive shift and 17.2 times enhancement over the commercial Pt/C catalyst in alkaline solution. Meanwhile, PdCoNi/NCNTs show much improved durability, with only 5 mV shift in the half-wave potential after 10,000 cycles, remarkably superior to those of PdCo/NCNTs, PdNi/NCNTs, and Pd/NCNTs. Valence band photoemission spectral analysis and theoretical calculations indicate that the existence of Co and Ni can tune the electronic structure of Pd by compressive strain effect and coordination effect, facilitating the activation of O2 and stabilizing the alloy elements, thus delivering a desired ORR activity and stability. Meanwhile, the high stability and intrinsic catalytic activity of NCNTs is also beneficial to ORR. Furthermore, PdCoNi/NCNTs also exhibit high performance as the air cathode catalysts in lithium-air battery.

Computational characterization of thermal and mechanical properties of single and bilayer germanene nanoribbon

Two-dimensional germanene has provided a cornucopia of new functionalities in the field of nanotechnology owing to its remarkable electronic and thermoelectric attributes. The robust spin–orbit coupling and high carrier mobility give rise to many salient features including non-trivial topological properties, quantum spin-Hall state near room temperature, and topological superconductivity, rendering it an excellent contender for valleytronics, spintronics, and quantum computation. As such, an in-depth characterization of thermal and mechanical properties of germanene is crucial for its practical implication and efficient operation, which remains elusive. Here, we employed equilibrium molecular dynamics simulations utilizing Stillinger Weber potential to reveal the mechanical strength, melting temperature, and phonon thermal conductivity (PTC) of single-layer germanene nanoribbon (SLGeNR) and bilayer germanene nanoribbon (BiLGeNR). Effects of temperature, biaxial tensile and compressive strain, monovacancy defects, length and width of the nanoribbon on the PTC have been rigorously investigated. It has been found that PTC of SLGeNR could be substantially reduced by BiLGeNR. Our simulation results suggest that PTC of SLGeNR demonstrates an inverse relation with temperature, biaxial compressive strain, and monovacancy defects while biaxial tensile strain, length and width of the nanoribbon increases the PTC of SLGeNR significantly. To understand the PTC more profoundly, phonon density of state (PDOS) profiles have been studied. The BiLGeNR demonstrates more tensile strength as well as melting temperature compared to SLGeNR. This study offers a comprehensive guideline for engineering the TC as well as discloses important mechanical and melting characteristics of the SLGeNR and BiLGeNR for a wide range of applications in flexible nano-electronics and thermoelectric nanodevices.

Achievements in Pt nanoalloy oxygen reduction reaction catalysts: strain engineering, stability and atom utilization efficiency.

The Pt nanoalloy surfaces often show unique electronic and physicochemical properties that are distinct from those of their parent metals, which provide significant room for manipulating their oxygen reduction reaction (ORR) behaviour. In this Feature Article, we present the progress of our recent research and that of other groups in Pt nanoalloy catalysts for ORR from three aspects, namely, strain engineering, stability and atom utilization efficiency. Some new insights into Pt surface strain engineering will be firstly introduced, with a focus on discussing the effect of compressive and tensile strain on the chemisorption properties. Secondly, the design concepts and synthetic methodologies to intensify the inherent stability of Pt nanoalloys will be summarized. Then, the exciting research push in developing nanostructured alloys with high atom utilization efficiency of Pt will be presented. Finally, a brief illumination of challenges and future developing perspectives of Pt nanoalloy catalysts will be provided.

Rhombohedral Ordered Intermetallic Nanocatalyst Boosts the Oxygen Reduction Reaction

Low platinum-group-metal (PGM) ordered intermetallic catalysts have been considered one of the most promising candidates for catalyzing the oxygen reduction reaction (ORR) in fuel cells, but achieving the desired performances in terms of activity, durability, and cost is still a grand challenge for the fuel cell research field. While the cubic- and tetragonal-ordered (L12 and L10 phases) low-PGM nanocatalysts have been investigated extensively and have shown considerably improved durability and activity toward the ORR, so far, little is known about rhombohedral ordered L11 catalysts. We report the synthesis of an L11-ordered PtCu catalyst for the ORR. We demonstrate that by applying nitrogen (N) doping through a thermal treatment in an NH3 gas, the activity and stability of the N-doped, rhombohedral ordered PtCu catalyst can be further enhanced, and the ORR mass and specific activities achieve nearly 5-fold and 4-fold enhancement in acidic media, respectively, relative to those of commercial Pt/C. In situ synchrotron X-ray absorption and pair-distribution-function measurements reveal that both the formation of the ordered intermetallic structure and N-doping synergistically improve the corrosion resistance of the PtCu catalyst by lowering the Cu diffusivity and introduce a compressive strain effect regulating the adsorption of oxygenated species on the Pt surface, thus accounting for the improved ORR kinetics.

Effect of Compressive Strain of Brake Pads on Brake Noise

Brake noise, a principal component of vehicle noise, is among the most critical measures of vehicle quality. The perceived quality of cars can be improved by reducing brake noise; therefore, vehicle manufacturers are extensively investigating the influencing factors, generating mechanism, and solutions of brake noise. Compressive strain is one of the most influential performance parameters of a brake pad and can be adjusted by regulating the material elastic modulus and by modifying the shape of the brake lining. In this study, the compressive strain of a brake pad was adjusted through four methods, and the noise characteristics of brake pads with different elastic modulus, section outlines, lining widths, and chamfers were studied through finite element analysis and the complex-eigenvalue method. The effects of compressive strain of a brake pad on brake noise were examined, and an optimized brake-pad scheme was developed. A dynamometer test conducted to validate the effectiveness of the optimized scheme confirmed a clear alleviation in brake noise.

High‐Quality AlN Template Prepared by Face‐to‐Face Annealing of Sputtered AlN on Sapphire

This study comprehensively investigates the properties of metalorganic vapor phase epitaxy (MOVPE)‐grown AlN films on high‐quality face‐to‐face annealed sputtered AlN (FFA Sp‐AlN) templates on sapphire substrates, which are highly important to control the surface morphology for various applications, such as UV light‐emitting diodes and laser diodes. The conditions of thermal cleaning and AlN growth by MOVPE are investigated to remove numerous small islands on as‐annealed FFA Sp‐AlN. Subsequent to thermal cleaning in H2 + NH3 at 1300 °C, MOVPE growth is performed with varying NH3 flow rate and growth temperature (Tg) under a constant pressure and group‐III flow rate. An atomically flat surface with an atomic step‐and‐terrace structure is obtained at a growth rate of ≈1.0 μm h−1 and a Tg of 1300 °C. Transmission electron microscopy images and secondary‐ion mass spectrometry reveal low dislocation densities and impurity concentrations. Finally, the effects of compressive strain in FFA Sp‐AlN on the lattice constant and curvature of the MOVPE‐grown AlN film on FFA Sp‐AlN are investigated. The compressive strain of the AlN film, which is carried over from FFA Sp‐AlN, can prevent crack formation but leads to a large wafer curvature after cooling down from the Tg.