Structural evolution of low-dimensional metal oxide semiconductors under external stress

Metal oxide semiconductors(MOSs) are attractive candidates as functional parts and connections in nanodevices.Upon spatial dimensionality reduction, the ubiquitous strain encountered in physical reality may result in structural instability and thus degrade the performance of MOS. Hence, the basic insight into the structural evolutions of low-dimensional MOS is a prerequisite for extensive applications, which unfortunately remains largely unexplored. Herein, we review the recent progress regarding the mechanical deformation mechanisms in MOSs, such as CuO and ZnO nanowires(NWs). We report the phase transformation of CuO NWs resulting from oxygen vacancy migration under compressive stress and the tensile strain-induced phase transition in ZnO NWs. Moreover, the influence of electron beam irradiation on interpreting the mechanical behaviors is discussed.

Boron quantum dots all-optical modulator based on efficient photothermal effect

All-optical devices without external electronic components have drawn extraordinary attentions in all-optical communication.In this work,boron quantum dots(BQDs)were synthesized by a facile liquid-phase exfoliation method.The as-prepared BQDs showed good structural homogeneity and crystallinity,broadband optical absorption as well as excellent photothermal properties.Femtosecond-resolved transient absorption further revealed the short carrier relaxation time of BQDs.Inspired by the outstanding photothermal properties and ultrafast carrier dynamic of BQDs,we fabricated BQDsbased all-optical modulator.The phase shift with a slope efficiency of 0.032π/m W and response time of 0.97 ms can be achieved.The modulator was used in laser resonance cavity to achieve all-optical actively Q-switched laser operation with control repetition rate.This prototypical BQDs-based all-optical modulator shows a great potential to be applied in all-optical information processing and communication.

Study of structure-property relationship of semiconductor nanomaterials by off-axis electron holography

As the scaling down of semiconductor devices, it would be necessary to discover the structure-property relationship of semiconductor nanomaterials at nanometer scale. In this review, the quantitative characterization technique off-axis electron holography is introduced in details, followed by its applications in various semiconductor nanomaterials including group IV, compound and two-dimensional semiconductor nanostructures in static states as well as under various stimuli. The advantages and disadvantages of off-axis electron holography in material analysis are discussed, the challenges facing in-situ electron holographic study of semiconductor devices at working conditions are presented, and all the possible influencing factors need to be considered to achieve the final goal of fulfilling quantitative characterization of the structure-property relationship of semiconductor devices at their working conditions.

Atomistic origin of high grain boundary resistance in solid electrolyte lanthanum lithium titanate

Lanthanum lithium titanate is one of the promising electrolytes for solid-state lithium-ion batteries due to its high bulk ionic conductivity up to∼10^(−3) S/cm.However,the practical application of this material has been bottlenecked by high grain boundary(GB)resistance,while the underlying mechanism is still under debate.Here we report a comprehensive study with direct evidence to reveal the origin of high GB resistance in La_(2/3)–xLi_(3x)TiO_(3)(LLTO).Atomic-scale observations via advanced scanning transmission electron microscopy show that the GBs are uniformly subject to subsurface segregation of La atoms to compensate for the excess surface charges.The La segregation leads to an abrupt decrease of charge carrier concentration neighboring GBs and hence is supposed to have deleterious effect on GB conductivity.The findings suggest a novel mechanism of space-charge-induced cation segregation,which shed lights on the intrinsic origin of low GB ionic conductivity in LLTO.

Atomistic insight into ordered defect superstructures at novel grain boundaries in CuO nanosheets: From structures to electronic properties

Determining atomistic structures of grain boundaries (GBs) is essential to understand structure--property interplay in oxides.Here,different GB superstructures in CuO nanosheets,including (111) and (114) twinning boundaries (TBs) and (002)/(223) GB,are investigated.Unlike the lower-energy stoichiometric (111) TB,both experimental and first-principles investigations reveal a severe segregation of Cu and O vacancies and a nonstoichiometric property at (114) TB,which may facilitate ionic transportation and provide space for elemental segregation.More importantly,the calculated electronic structures have shown the increased conductivity as well as the unanticipated magnetism in both (114) TB and (002)/(223) GB.These findings could contribute to the race towards the property-directing structural design by GB engineering.

Effects of twin orientation and twin boundary spacing on the plastic deformation behaviors in Ni nanowires

Spreading twins throughout nano metals has been proved to effectively mediate the mechanical behaviors in face-centered-cubic(fcc)metals.However,the experimental investigation concerning the roles of twin boundary(TB)during deformation is rarely reported.Here,with the joint efforts of in-situ nanomechani-cal testing and theoretical studies,we provide a systematic investigation regarding the effects of TB orien-tation(θ,the angle between tensile loading direction and the normal of TB)and spacing on deformation mechanisms in Ni nanowires(NWs).As compared with single-crystalline counterparts,it is found that nano-twinned(nt)NWs withθ∼0°exhibit limited ductility,whereas TB can serve as an effective block-age to the dislocation propagation.In contrast,in nt NWs withθ∼20°and 55°,TB migration/detwinning induced by TB-dislocation reaction or partial dislocation movement dominates the plasticity,which con-tributes to enhanced NW ductility.Regarding nt NWs withθ∼90°,dislocations are found to be able to transmit through the TBs,suggesting the limited effect of TB on the NW stretchability.Furthermore,de-creasing TB spacing(λ)can facilitate the detwinning process and thus greatly enhance the ductility of NW withθ∼55°.This study uncovers the distinct roles that TB can play during mechanical deforma-tions in fcc NWs and provides an atomistic view into the direct linkage between macroscopic mechanical properties and microscopic deformation modes.

Strong size effect on deformation twin-me diate d plasticity in body-centered-cubic iron

Deformation twinning serves as an important mode of plastic dissipation processes in nanoscale body-centered cubic(BCC)metals,but its origin and spatio-temporal features are mysterious.Here,applying in situ tensile experiments,we report a strong size effect on mediating the twinning behaviors and twin boundary(TB)-dislocation interaction mechanisms in BCC iron(Fe)nanowires(NWs).There exists a critical diameter(d)of∼2.5 nm,above which the deformation twinning rather than dislocation slip dominates the plasticity.Unlike the traditional reflection TBs,the intermediate isosceles TBs are consis-tently observed as mediated by the 1/12<111>partial dislocations.Moreover,we uncover two distinct TB-related deformation mechanisms,including twin variant re-orientation and TB cracking for NWs with d<17 nm and d>17 nm,respectively.Further molecular dynamics and statics simulations provide the basic underlying mechanisms for size-dependent plasticity,which have been largely overlooked in previous experimental investigations.Our findings highlight the importance of grain size in mediating the deformation behaviors in Fe,serving as possible guidance for exploring single-crystalline and poly-crystalline Fe-based materials(e.g.steel)with optimized mechanical performance.

Coordinatively unsaturated single Co atoms immobilized on C_(2)N for efficient oxygen reduction reaction

Developing cost-effective and high-efficiency oxygen reduction reaction(ORR)catalysts is imperative for promoting the substantial progress of fuel cells and metal-air batteries.The coordination and geometric engineering of single-atom catalysts(SACs)occurred the promising approach to overcome the thermodynamics and kinetics problems in high-efficiency electrocatalysis.Herein,we rationally constructed atomically dispersed Co atoms on porous N-enriched graphene material C_(2)N(CoSA-C2N)for efficient oxygen reduction reaction(ORR).Systematic characterizations demonstrated the active sites for CoSA-C2N is as identified as coordinatively unsaturated Co-N_(2)moiety,which exhibits ORR intrinsic activity.Structurally,the porous N-enriched graphene framework in C_(2)N could effectively increase the accessibility to the active sites and promote mass transfer rate,contributing to improved ORR kinetics.Consequently,CoSA-C_(2)N exhibited superior ORR performance in both acidic and alkaline conditions as well as impressive long-term durability.The coordination and geometric engineering of SACs will provide a novel approach to advanced catalysts for energy related applications.

3D Porous MXene Aerogel through Gas Foaming for Multifunctional PressureSensor

The development of smart wearable electronic devices puts forward higher requirements for future flexible electronics. The design of highly sensitive and high-performance flexible pressure sensors plays an important role in promoting the development of flexible electronic devices. Recently, MXenes with excellent properties have shown great potential in the field of flexible electronics. However, the easy-stacking inclination of nanomaterials limits the development of their excellent properties and the performance improvement of related pressure sensors. Traditional methods for constructing 3D porous structures have the disadvantages of complexity, long period, and difficulty of scalability. Here, the gas foaming strategy is adopted to rapidly construct 3D porous MXene aerogels. Combining the excellent surface properties of MXenes with the porous structure of aerogel, the prepared MXene aerogels are successfully used in high-performance multifunctional flexible pressure sensors with high sensitivity (306 kPa^(-1)), wide detection range (2.3 Pa to 87.3 kPa), fast response time (35 ms), and ultrastability (>20,000 cycles), as well as self-healing, waterproof, cold-resistant, and heat-resistant capabilities. MXene aerogel pressure sensors show great potential in harsh environment detection, behavior monitoring, equipment recovery, pressure array identification, remote monitoring, and human-computer interaction applications.

Universal time delay in static spherically symmetric spacetimes for null and timelike signals

A perturbative method of computing the total travel time of both null and lightlike rays in arbitrary static spherically symmetric spacetimes in the weak field limit is proposed.The resultant total time takes a quasi-series form of the impact parameter.The coefficient of this series at a certain order n is shown to be determined by the asymptotic expansion of the metric functions to the order n+1.For the leading order(s),the time delay,as well as the difference between the time delays of two types of relativistic signals,is shown to take a universal form for all SSS spacetimes.This universal form depends on the mass M and a post-Newtonian parameter γ of the spacetime.The analytical result is numerically verified using the central black hole of galaxy M87 as the gravitational lensing center.

Phase engineering of Mo-V oxides molecular sieves for zinc-ion batteries

With the ever-increasing demands of grid-scale energy storage,aqueous zinc-ion batteries(ZIBs)have garnered increasing attention around the world.However,limited Zn^(2+)host materials have hindered the commercialization of ZIBs.Hence,Mo-V oxides with different phase structures(orth-,tri-,and tetra-MoVO)were precisely constructed to develop phase-dependent Mo-V oxide cathodes for Zn^(2+)storage in ZIBs.The open frameworks and varied tunnel structures formed a favorable alternative for achieving suitable Zn^(2+)diffusion kinetics.With optimized phase engineering,the high specific capacity of approximately 400 mA h g^(−1) and excellent cyclic stability of 1000 cycles were achieved with orth-MoVO as the cathode.The large amount of six-and seven-member rings in the orth-MoVO phase,which allow for alternative Zn^(2+)insertion,play a vital role in hosting Zn^(2+)ions reversibly.The proposed phase engineering strategy provides a new approach toward cathode design in ZIBs.

Study of the growth mechanism of a self‑assembled and ordered multi‑dimensional heterojunction at atomic resolution

Multi-dimensional heterojunction materials have attracted much attention due to their intriguing properties,such as high efciency,wide band gap regulation,low dimensional limitation,versatility and scalability.To further improve the performance of materials,researchers have combined materials with various dimensions using a wide variety of techniques.However,research on growth mechanism of such composite materials is still lacking.In this paper,the growth mechanism of multidimensional heterojunction composite material is studied using quasi-two-dimensional(quasi-2D)antimonene and quasione-dimensional(quasi-1D)antimony sulfde as examples.These are synthesized by a simple thermal injection method.It is observed that the consequent nanorods are oriented along six-fold symmetric directions on the nanoplate,forming ordered quasi-1D/quasi-2D heterostructures.Comprehensive transmission electron microscopy(TEM)characterizations confrm the chemical information and reveal orientational relationship between Sb2S3 nanorods and the Sb nanoplate as substrate.Further density functional theory calculations indicate that interfacial binding energy is the primary deciding factor for the self-assembly of ordered structures.These details may fll the gaps in the research on multi-dimensional composite materials with ordered structures,and promote their future versatile applications.