Intrinsic Strain Research Articles

Tubular/helical architecture construction based on rolled-up AlN nanomembranes and resonance as optical microcavity

Aluminum nitride (AlN) has attracted a great amount of interest due to the fact that these group III–V semiconductors present direct band gap behavior and are compatible with current micro-electro-mechanical systems. In this work, three dimensional (3D) AlN architectures including tubes and helices were constructed by rolling up AlN nanomembranes grown on a silicon-on-insulator wafer via magnetron sputtering. The properties of the AlN membrane were characterized through transmission electron microscopy and X-ray diffraction. The thickness of AlN nanomembranes could be tuned via the RIE thinning method, and thus micro-tubes with different diameters were fabricated. The intrinsic strain in AlN membranes was investigated via micro-Raman spectroscopy, which agrees well with theory prediction. Whispering gallery mode was observed in AlN tubular optical microcavity in photoluminescence spectrum. A postprocess involving atomic layer deposition and R6G immersion were employed on as-fabricated AlN tubes to promote the Q-factor. The AlN tubular micro-resonators could offer a novel design route for Si-based integrated light sources. In addition, the rolled-up technology paves a new way for AlN 3D structure fabrication, which is promising for AlN application in MEMS and photonics fields.

New approaches for achieving more perfect transition metal oxide thin films

This perspective considers the enormous promise of epitaxial functional transition metal oxide thin films for future applications in low power electronic and energy applications since they offer wide-ranging and highly tunable functionalities and multifunctionalities, unrivaled among other classes of materials. It also considers the great challenges that must be overcome for transition metal oxide thin films to meet what is needed in the application domain. These challenges arise from the presence of intrinsic defects and strain effects, which lead to extrinsic defects. Current conventional thin film deposition routes often cannot deliver the required perfection and performance. Since there is a strong link between the physical properties, defects and strain, routes to achieving more perfect materials need to be studied. Several emerging methods and modifications of current methods are presented and discussed. The reasons these methods better address the perfection challenge are considered and evaluated.

Intrinsic-strain-induced curling of free-standing two-dimensional Janus MoSSe quantum dots

Motivated by the fascinating properties of both two-dimensional transition metal dichalcogenide quantum dots (TMD QDs) and Janus TMD monolayers, we theoretically explore the equilibrium structures of free-standing Janus MoSSe QDs in which atomic asymmetry of chalcogen is introduced. Two distinct types of spontaneous curling are observed by molecular dynamics simulations, and the curling behavior depends on the size of QD. The bowl-like (tube-like) curling occurs in relatively small (large) MoSSe QDs with different shapes (hexagon and triangle) and edge types (zigzag and armchair). The transition between these two curling types occurs at the sizes of around 10 nm and 13 nm for hexagonal and triangular shapes, respectively. By applying equivalent misfit strains into two adjacent sublayers, finite element analysis reproduces similar curling behavior. This confirms the relaxation of intrinsic strain in Janus structure acting as the predominant driving force of spontaneous curling. In addition, the curvatures of Janus TMD QDs increase from MoSSe to MoSeTe to MoSTe, indicating the positive correlation between the curling and misfit.

Stress variations in space and time within the mantle section of an oceanic transform zone: Evidence for the seismic cycle

AbstractThe Bogota Peninsula shear zone in New Caledonia (southwest Pacific Ocean) is the exhumed mantle section of an oceanic transform zone. Ductile fabrics in this zone formed at temperatures >820 °C, and differential stresses estimated from microstructures vary spatially and temporally. Along a transform-perpendicular transect, stresses increase toward the high-strain areas. We attribute this stress gradient to an increase in strain rate caused by imposed rather than intrinsic strain localization. Temporal stress variations are indicated by the formation of fine-grained microdeformation zones (MDZs) that truncate and offset coarser grains. We interpret the MDZs to result from zones of brittle deformation caused by earthquake fracture propagation downward in the upper mantle, which are in turn overprinted by ductile deformation at stresses 2–6 times higher (22–81 MPa) than their surrounding steady-state fabrics. We interpret the spatial and temporal variations in microstructures and stresses as reflecting different stages of the seismic cycle in oceanic lithosphere.

Uncovering the internal structure of five-fold twinned nanowires through 3D electron diffraction mapping**Project supported by the National Natural Science Foundation of China (Grant Nos. 51201015 and U1532262).

Five-fold twinned nanostructures are intrinsically strained or relaxed by extended defects to satisfy the space-filling requirement. Although both of metallic and semiconductor five-fold twinned nanostructures show inhomogeneity in their cross-sectional strain distribution, the evident strain concentration at twin boundaries in the semiconductor systems has been found in contrast to the metallic systems. Naturally, a problem is raised how the chemical bonding characteristics of various five-fold twinned nanosystems affects their strain-relieving defect structures. Here using three-dimensional (3D) electron diffraction mapping methodology, the intrinsic strain and the strain-relieving defects in a pentagonal Ag nanowire and a star-shaped boron carbide nanowire, both of them have basically equal radial twin-plane width about 30 nm, are non-destructively characterized. The non-uniform strain and defect distribution between the five single crystalline segments are found in both of the five-fold twinned nanowires. Diffraction intensity fine structure analysis for the boron carbide five-fold twinned nanowire indicates the presence of high-density of planar defects which are responsible for the accommodation of the intrinsic angular excess. However, for the Ag five-fold twinned nanowire, the star-disclination strain field is still present, although is partially relieved by the formation of localized stacking fault layers accompanied by partial dislocations. Energetic analysis suggests that the variety in the strain-relaxation ways for the two types of five-fold twinned nanowires could be ascribed to the large difference in shear modulus between the soft noble metal Ag and the superhard covalent compound boron carbide.

120 MeV Ni10+ swift heavy ions irradiation on CdSe nanocrystals induces cubic to hexagonal phase transformation - A study of microstructural modification

In the present work, chemically synthesized cadmium selenide (CdSe) nanocrystals, which have a cubic lattice structure as per X-ray diffraction (XRD) analysis, has been irradiated with 120 MeV Ni10+ swift heavy ions (SHI) for the study of their structural modification. A significant change in the lattice structure has been found with different ion fluence of 120 MeV Ni10+ irradiation, which may be due to the high electronic energy loss of SHI. AFM analysis also shows changes in morphological properties with ion irradiation. The evolution of lattice structure with different fluence has been studied using double ion impact model. Further, SHI induced cubic to hexagonal transformation effect the microstructural parameters such as intrinsic strain, dislocation density of CdSe nanocrystals. SHI induced microstructural modifications have also been studied with the help of Variance model.

On-demand production of hydrogen by reacting porous silicon nanowires with water

On-demand hydrogen generation is desired for fuel cells, energy storage, and clean energy applications. Silicon nanowires (SiNWs) and nanoparticles (SiNPs) have been reported to generate hydrogen by reacting with water, but these processes usually require external assistance, such as light, electricity or catalysts. Herein, we demonstrate that a porous SiNWs array, which is fabricated via the metal-assisted anodic etching (MAAE) method, reacts with water under ambient and dark conditions without any energy inputs. The reaction between the SiNWs and water generates hydrogen at a rate that is about ten times faster than the reported rates of other Si nanostructures. Two possible sources of enhancement are discussed: SiNWs maintain their high specific surface area as they don’t agglomerate, and the intrinsic strain of the nanowires promotes the reactivity. Moreover, the porous SiNWs array is portable, reusable, and environmentally friendly, yielding a promising route to produce hydrogen in a distributed manner.

Effects of strain on various properties and applications on one-dimensional nano-/microstructures

Strain is an unavoidable feature of the nanostructures grown by different synthesizing techniques due to several factors like lattice mismatching with substrate, different growth parameters, etc. Part of strain could be released by post-growth treatment such as annealing, detaching sample from substrate and giving further strain. Researchers have worked on minimizing the intrinsic strain for better performances of grown nanostructures and enhancing the stability. But about four decades ago, strain engineering has taken another level of research interest as strain modifies the nanostructures mechanical, electronic and optical properties. Those modifications are beneficial for novel flexible device applications. Thus, nowadays, research related to strain on both one- and two-dimensional nanostructures has boost up for exploring new features, thereby paving the way for future stretchable novel devices. In this article, we first concentrate on the investigations of various strain-related effects on the properties of one-dimensional nanostructures and its advantages. Finally, we discuss the challenges and future opportunities on strain-induced effects.

How Can Si/Ge Core/Shell Nanowires Outperform Their Pure Material Counterparts?

Si/Ge core/shell nanowires have been demonstrated to be a promising candidate for the next-generation transistor channel. The tunable electron and hole transport paths improve their mobilities significantly. Here, we comparatively investigate the electronic properties of the Si-core-Ge-shell and Ge-core-Si-shell nanowires and their pure material counterparts using the first-principles method. The effects of core/shell ratio, atom number, and cross-sectional shape are studied. The Si-core-Ge-shell nanowires show excellent transport path separation and small carrier effective mass properties when the core/shell ratios exceed 0.5. For smaller ratios, the energies of the off- $\Gamma $ valleys in the Ge shells are lowered and become the conduction band minimum (CBM) because of the intrinsic strains along the radial direction, enlarging the electron effective masses significantly. To restrain this effect, the uniaxial strain engineering is adopted and the best performance is exhibited when 2%–3% tensile strains are applied. In the Ge-core-Si-shell nanowires, both electrons and holes are easily confined to the core region. Compared with the Si-core-Ge-shell nanowires, their energy gaps and electron effective masses are smaller and larger, indicating poor transportability. The above discoveries are further validated by changing the cross-sectional shapes of the nanowires and device performance simulations, confirming that the Si-core-Ge-shell nanowires can outperform their pure material counterparts in high-speed transistor designs.

Fine‐Tuning Intrinsic Strain in Penta‐Twinned Pt–Cu–Mn Nanoframes Boosts Oxygen Reduction Catalysis

AbstractTuning the intrinsic strain of Pt‐based nanomaterials has shown great promise for improving the oxygen reduction reaction (ORR) performance. Herein, reported is a tunable surface strain in penta‐twinned ternary Pt–Cu–Mn nanoframes (NFs). Pt–Cu–Mn ultrafine NFs (UNFs) exhibit ≈1.5% compressive strain compared to Pt–Cu–Mn pentagonal NFs (PNFs) and show the superior activity toward ORR in an alkaline environment. Specifically, the specific and mass activity of Pt–Cu–Mn UNFs are 3.38 mA cm−2 and 1.45 A mg−1, respectively, which is 1.45 and 1.71 times higher than that of Pt–Cu–Mn PNFs, demonstrating that compressive strain in NFs structure can effectively enhance the catalytic activity of ORR. Impressively, Pt–Cu–Mn UNFs exhibit 8.67 and 9.67 times enhanced specific and mass activity compared with commercial Pt/C. Theoretical calculations reveal that compression on the surface of Pt–Cu–Mn UNFs can weaken the bonding strengths and adsorption of oxygen‐containing intermediates, resulting in an optimal condition for ORR.

Excellent temperature stability with giant electrostrain in Bi0.5Na0.5TiO3-based ceramics

In this work, we report a giant strain (0.42%) in lead-free ceramics of (1–x) (0.79Bi0.5Na0.5TiO3–0.20 Bi0.5K0.5TiO3–0.01NaNbO3)–xSrTiO3 with x=0.03. Most importantly, ultra-high temperature stability was simultaneously achieved under this giant strain with the variation less than 10% in the range of 20 °C and 140 °C. Systematic temperature dependent Raman spectra measurements and Ginzburg–Landau–Devonshire thermodynamic theory analysis revealed that the intrinsic lattice strain and electric field induced relaxor-ferroelectric phase transition provide reverse strain response with the increase of temperature, jointly conducive to the ultra-high temperature stability of strain property. These materials are extremely competitive in practical application of actuators.

Serine protease autotransporters of Enterobacteriaceae (SPATEs) are largely distributed among Escherichia coli isolated from the bloodstream.

Extraintestinal pathogenic Escherichia coli (ExPEC) is the major cause of Gram-negative-related sepsis. Bacterial survival in the bloodstream is mediated by a variety of virulence traits, including those mediating immune system evasion. Serine protease autotransporters of Enterobacteriaceae (SPATE) constitute a superfamily of virulence factors that can cause tissue damage and cleavage of molecules of the complement system, which is a key feature for the establishment of infection in the bloodstream. In this study, we analyzed 278 E. coli strains isolated from human bacteremia from inpatients of both genders, different ages, and clinical conditions. These strains were screened for the presence of SPATE-encoding genes as well as for phylogenetic classification and intrinsic virulence of ExPEC. SPATE-encoding genes were detected in 61.2% of the strains and most of these strains (44.6%) presented distinct SPATE-encoding gene profiles. sat was the most frequent gene among the entire collection, found in 34.2%, followed by vat (28.4%), pic (8.3%), and tsh (4.7%). Although in low frequencies, espC (0.7%), eatA (1.1%), and espI (1.1%) were detected and are being reported for the first time in extraintestinal isolates. The presence of SPATE-encoding genes was positively associated to phylogroup B2 and intrinsic virulent strains. These findings suggest that SPATEs are highly prevalent and involved in diverse steps of the pathogenesis of bacteremia caused by E. coli.

Detachment of epitaxial graphene from SiC substrate by XUV laser radiation

The thermal decomposition on silicon carbide (SiC) is one of the most used growth techniques for fabrication of epitaxial graphene. However, it significantly diminishes graphene’s otherwise exceptional carrier mobility. Reduction of the substrate influence is therefore essential for keeping conductivity at high levels. Here we present a novel technique where a sample with epitaxial graphene grown on SiC was exposed to intense 21.2 nm radiation. A sub-nanosecond pulse at low fluence in an interval 0.4–0.7 J/cm2 was used to break covalent sp3 bonds between the SiC substrate and buffer (the first graphene layer) which remains, except for release of its intrinsic strain, almost unaffected. A detailed analysis of the irradiated area examined by several microscopic and spectroscopic methods such as white-light interferometry and micro-Raman spectroscopy shows a clear evidence of a graphene layer detached from the substrate. Higher fluences induce damage to SiC substrate which expands due to the amorphization process. Damage thresholds were obtained by an advanced method of ablative imprints and compared with those calculated by the hybrid code XTANT.

Synthesis and Characterization of Indium Tin Oxide with Neem Extract for Antioxidant Applications

Indium tin oxide was prepared by using simple co precipitation method with Neem extract as reducing agent and it was characterized by using X-ray diffractometer, with the applications of antioxidant effect, the prepared sample was directly calcined at 400ºC and then characterized. Morphological studies were analyzed by using Transmission Electron Microscopy and Selective area diffraction pattern. The crystal sizes were calculated and it value is nearly 12 nm. Here, Williamson-Hall (W–H) have been used to investigate the particle size and the intrinsic strain from the XRD peak broadening analysis.

Au icosahedrons as efficient electrocatalyst for glucose-based biofuel cells by strain engineering

Strain engineering has proven to be a powerful method in tailoring the surface electronic structure and the catalytic properties of nanomaterials. Here, we develope a green and effective strategy for synthesis of Au icosahedron and report systematic studies Au nanocrystals (including cubes, octahedrons, and icosahedrons) with similar nanosizes as efficient electrocatalyst for glucose-based biofuel cells. Our results demonstrate that the penta-twinned Au icosahedron catalyst shows a maximum specific activity in glucose electrooxidation with 2.5 mA cm−2 current density, which is over 3 times higher than the Au octahedron catalyst. The microstructures of Au icosahedron confirm that such enhanced electrocatalytic activity could be ascribed to the intrinsic surface strain.

Structural Core-Shell beyond Chemical Homogeneity in Non-Stoichiometric Cu5FeS4 Nano-Icosahedrons: An in Situ Heating TEM Study.

Thermal stability of core-shell structured nanoparticles is of vital importance to their practical applications at elevated temperature. Understanding the evolution of chemical distribution and the crystal structure of core-shell nanostructures with temperature variation at the nanoscale will open the route for practical applications and property enhancement of nanoparticles through proper design of new nanomaterials. In this study, core-shell non-stoichiometric Cu5FeS4 icosahedral nanoparticles were investigated by in situ heating transmission electron microscopy. Compared to the high structural and compositional stability at room temperature, the interdiffusion of Cu and Fe atoms became significant, ending up with disappearance of chemical difference in the core and shell over 300 °C. In contrast, different crystal structures of the core and shell were preserved even after heating at 350 °C, indicating the high structural stability. The inconsistency between chemical composition and crystal structure should be ascribed to the interaction between the intrinsic strain existing in the icosahedrons and various structures of this material system. In other words, the geometrically intrinsic strain of the nano-icosahedrons is helpful to modulate/maintain the core-shell structure. These findings open new opportunities for revealing the thermal stability of core-shell nanostructures for various applications and are helpful for the controllable design of new core-shell nanostructures.

Lewis Base Catalysis Based on Homoconjugate Addition: Rearrangement of Electron-Deficient Cyclopropanes and Their Derivatives

Cyclopropane is one of the most reactive functionalities owing to its intrinsic ring strain. Transition-metal catalysis and Lewis acid catalysis have been extensively used in ring openings of cyclopropanes; however, Lewis base-catalyzed activation of cyclopropanes remains largely unexplored. Upon nucleophilic attack with Lewis bases, cyclopropanes undergo ring cleavage in a manner known as homoconjugate addition to form zwitterionic intermediates, which have significant potential for reaction development but have garnered little attention. Here, we present a brief overview of this area, with an emphasis on our recent efforts on Lewis base-catalyzed rearrangement reactions of electron-deficient cyclopropanes using the homoconjugate addition process.1 Introduction2 DABCO-Catalyzed Cloke–Wilson Rearrangement of Cyclopropyl Ketones3 Hydroxylamine-Mediated Tandem Cloke–Wilson/Boulton–­Katritzky Reaction of Cyclopropyl Ketones4 Phosphine-Catalyzed Rearrangement of Vinylcyclopropyl Ketones To Form Cycloheptenones5 Phosphine-Catalyzed Rearrangement of Alkylidenecyclopropyl Ketones To Form Polysubstituted Furans and Dienones6 Conclusion and Outlook

A High‐Performing, Visible‐Light‐Driven Actuating Material Responsive to Ultralow Light Intensities

AbstractLight‐driven actuating materials are highly desirable for miniaturized, untethered devices and microrobots. However, current light actuators require high light intensity or the use of UV or IR light to operate, which greatly increase the cost and difficulty for real‐life applications. Here, a significant visible (vis)‐light‐driven actuation effect in cobalt oxides/hydroxides (C–O–H), inducible at low intensities from ≈3 mW cm−2 (≈0.03 sun), is reported. In the form of bilayered films, the actuators can curl into loops at 70–180 ms per loop, corresponding to a high intrinsic strain of more than 1% at strain rate 0.6% s−1, and actuating stress exceeding 60 MPa, at ≈50 mW cm−2 (≈0.5 sun). Linear actuators made from actuating hinges of C–O–H can weightlift objects ≈200 times heavier than the active material. A chemo‐mechanics model describes the actuation well, showing that the mechanism is light‐induced volume shrinkage assisted by diffusion, and C–O–H exhibits outperforming chemical driving force per unit light‐intensity stimulation.

Intrinsic cardiovascular strain and wave imaging using rapid frame rate imaging

Intrinsic cardiovascular strain and wave imaging using rapid frame rate imaging

Unusual Sonochemical Assembly between Carbon Allotropes for High Strain-Tolerant Conductive Nanocomposites.

Facile methods toward strain-tolerant graphene-based electronic components remain scarce. Although being frequently used to disperse low-dimensional carbonaceous materials, ultrasonication (US) has never been reliable for fabricating stretchable carbonaceous nanocomposite (SCNC). Inspired by the unusual sonochemical assembly between graphene oxide (GO) and carbon nanotube (CNT), we verified the roots-like GO–CNT covalent bonding, rather than just π–π conjugation, was formed during US. In addition, the shockwave-induced collision in the binary-component system enables a burst of fragmentation at the early stage, spatially homogeneous hybridization, and time-dependent restoration of graphitic domains. All of the above are distinct from extensive fragmentation of a conventional single-component system and π–π conjugative assembly. The optimized SCNC exhibits conductivity comparable to reduced monolayer GO and outperforms π–π assemblies in retaining electrical conductance at a strain of 160%—among one of the best reported stretchable conductors. Raman analysis and mechanics simulation confirm the dominant role of counterweighing between the intrinsic and external strains on the mechano-response and durability of SCNC. This work suggests the guideline of creating multiple-component sonochemical systems for various functional nanocomposites.