Orientation Dependence of Electromechanical Characteristics of Defect-free InAs Nanowires

Advancements and Challenges in the Integration of Indium Arsenide and Van der Waals Heterostructures

The strategic integration of low-dimensional InAs-based materials and emerging van der Waals systems is advancing in various scientific fields, including electronics, optics, and magnetics. With their unique properties, these InAs-based van der Waals materials and devices promise further miniaturization of semiconductor devices in line with Moore's Law. However, progress in this area lags behind other 2D materials like graphene and boron nitride. Challenges include synthesizing pure crystalline phase InAs nanostructures and single-atomic-layer 2D InAs films, both vital for advanced van der Waals heterostructures. Also, diverse surface state effects on InAs-based van der Waals devices complicate their performance evaluation. This review discusses the experimental advances in the van der Waals epitaxy of InAs-based materials and the working principles of InAs-based van der Waals devices. Theoretical achievements in understanding and guiding the design of InAs-based van der Waals systems are highlighted. Focusing on advancing novel selective area growth and remote epitaxy, exploring multi-functional applications, and incorporating deep learning into first-principles calculations are proposed. These initiatives aim to overcome existing bottlenecks and accelerate transformative advancements in integrating InAs and van der Waals heterostructures.

Non-〈111〉-oriented semiconductor nanowires: growth, properties, and applications

In recent years, non-〈111〉-oriented semiconductor nanowires have attracted increasing interest in terms of fundamental research and promising applications due to their outstanding crystal quality and distinctive physical properties. Here, a comprehensive overview of recent advances in the study of non-〈111〉-oriented semiconductor nanowires is presented. We start by introducing various growth techniques for obtaining nanowires with certain orientations, for which the growth energetics and kinetics are discussed. Attention is then given to the physical properties of non-〈111〉 nanowires, as predicted by theoretical calculations or demonstrated experimentally. After that, we review the advantages and challenges of non-〈111〉 nanowires as building blocks for electronic and optoelectronic devices. Finally, we discuss the possible challenges and opportunities in the research field of non-〈111〉 semiconductor nanowires.

Electromechanical conversion efficiency of GaN NWs: critical influence of the NW stiffness, the Schottky nano-contact and the surface charge effects

The piezoelectric nanowires (NWs) are considered as promising nanomaterials to develop high-efficient piezoelectric generators. Establishing the relationship between their characteristics and their piezoelectric conversion properties is now essential to further improve the devices. However, due to their nanoscale dimensions, the NWs are characterized by new properties that are challenging to investigate. Here, we use an advanced nano-characterization tool derived from AFM to quantify the piezo-conversion properties of NWs axially compressed with a well-controlled applied force. This unique technique allows to establish the direct relation between the output signal generation and the NW stiffness and to quantify the electromechanical coupling coefficient of GaN NWs, which can reach up to 43.4%. We highlight that this coefficient is affected by the formation of the Schottky nano-contact harvesting the piezo-generated energy, and is extremely sensitive to the surface charge effects, strongly pronounced in sub-100 nm wide GaN NWs. These results constitute a new building block in the improvement of NW-based nanogenerator devices.

Microscopic Understanding of the Growth and Structural Evolution of Narrow Bandgap III-V Nanostructures

III–V group nanomaterials with a narrow bandgap have been demonstrated to be promising building blocks in future electronic and optoelectronic devices. Thus, revealing the underlying structural evolutions under various external stimuli is quite necessary. To present a clear view about the structure–property relationship of III–V nanowires (NWs), this review mainly focuses on key procedures involved in the synthesis, fabrication, and application of III–V materials-based devices. We summarized the influence of synthesis methods on the nanostructures (NWs, nanodots and nanosheets) and presented the role of catalyst/droplet on their synthesis process through in situ techniques. To provide valuable guidance for device design, we further summarize the influence of structural parameters (phase, defects and orientation) on their electrical, optical, mechanical and electromechanical properties. Moreover, the dissolution and contact formation processes under heat, electric field and ionic water environments are further demonstrated at the atomic level for the evaluation of structural stability of III–V NWs. Finally, the promising applications of III–V materials in the energy-storage field are introduced.

Investigations on the Electrochemical and Mechanical Properties of Sb2 O3 Nanobelts by In Situ Transmission Electron Microscopy

Sb₂ O₃ shows great promise as a high-capacity anode material for sodium-ion batteries (SIBs) due to the combined mechanisms of intercalation, conversion, and alloying. In this work, the electrochemical performance and mechanical property of Sb₂ O₃ nanobelts during sodiation/desodiation are revealed by constructing nanoscale solid-state SIBs in a high-resolution transmission electron microscopy. It is found that the Sb₂ O₃ nanobelt exhibits an ultrahigh sodiation speed of ≈13.5 nm s^-1 and experiences a three-step sodiation reaction including the intercalation reaction to form Na_x Sb₂ O₃ , the conversion reaction to form Sb, and the alloying reaction to form NaSb. The alloying reaction is found to be reversible, while the conversion reaction is partially reversible. The Sb₂ O₃ nanobelt shows anisotropic expansion and the orientation of the Sb₂ O₃ nanobelt has great influence on the expansion ratio. It is found that the existence of a {010} plane with large d-spacing in the nanobelt leads to a surprisingly small expansion ratio (≈5%). The morphology of the Sb₂ O₃ nanobelt is well maintained during multiple electrochemical cycles. In situ bending experiments suggest that the sodiated Sb₂ O₃ nanobelts show improved toughness and flexibility compared to pristine Sb₂ O₃ nanobelts. These fundamental studies provide insight into the rational design of anode materials with improved electrochemical and mechanical performance in SIBs.

Piezoresistivity of InAsP Nanowires: Role of Crystal Phases and Phosphorus Atoms in Strain-Induced Channel Conductances

Strong piezoresistivity of InAsP nanowires is rationalized with atomistic simulations coupled to Density Functional Theory. With a focal interest in the case of the As(75%)-P(25%) alloy, the role of crystal phases and phosphorus atoms in strain-driven carrier conductance is discussed with a direct comparison to nanowires of a single crystal phase and a binary (InAs) alloy. Our analysis of electronic structures presents solid evidences that the strong electron conductance and its sensitivity to external tensile stress are due to the phosphorous atoms in a Wurtzite phase, and the effect of a Zincblende phase is not remarkable. With several solid connections to recent experimental studies, this work can serve as a sound framework for understanding of the unique piezoresistive characteristics of InAsP nanowires.

Control of Conductivity of InxGa1-xAs Nanowires by Applied Tension and Surface States

The electronic properties of semiconductor AIIIBV nanowires (NWs) due to their high surface/volume ratio can be effectively controlled by NW strain and surface electronic states. We study the effect of applied tension on the conductivity of wurtzite In_xGa_1-xAs (x ∼ 0.8) NWs. Experimentally, conductive atomic force microscopy is used to measure the I-V curves of vertically standing NWs covered by native oxide. To apply tension, the microscope probe touching the NW side is shifted laterally to produce a tensile strain in the NW. The NW strain significantly increases the forward current in the measured I-V curves. When the strain reaches 4%, the I-V curve becomes almost linear, and the forward current increases by 3 orders of magnitude. In the latter case, the tensile strain is supposed to shift the conduction band minima below the Fermi level, whose position, in turn, is fixed by surface states. Consequently, the surface conductivity channel appears. The observed effects confirm that the excess surface arsenic is responsible for the Fermi level pinning at oxidized surfaces of III-As NWs.

In Situ TEM Observation of Crystal Structure Transformation in InAs Nanowires on Atomic Scale

In situ transmission electron microscopy investigation of structural transformation in III-V nanowires is essential for providing direct insight into the structural stability of III-V nanowires under elevated temperature. In this study, through in situ heating investigation in a transmission electron microscope, the detailed structural transformation of InAs nanowires from wurtzite structure to zinc-blende structure at the catalyst/nanowire interface is witnessed on the atomic level. Through detailed structural and dynamic analysis, it was found that the nucleation site of each new layer of InAs and catalyst surface energy play a decisive role in the growth of the zinc-blende structure. This study provides new insights into the growth mechanism of zinc-blende-structured III-V nanowires.

Strain Mapping and Raman Spectroscopy of Bent GaP and GaAs Nanowires

Strain engineering of nanowires (NWs) has been recognized as a powerful strategy for tuning the optical and electronic properties of nanoscale semiconductors. Therefore, the characterization of the strains with nanometer-scale spatial resolution is of great importance for various promising applications. In the present work, we synthesized single-crystalline zinc blende phase GaP and GaAs NWs using the chemical vapor transport method and visualized their bending strains (up to 3%) with high precision using the nanobeam electron diffraction technique. The strain mapping at all crystallographic axes revealed that (i) maximum strain exists along the growth direction ([111]) with the tensile and compressive strains at the outer and inner parts, respectively; (ii) the opposite strains appeared along the perpendicular direction ([2̅11]); and (iii) the tensile strain was larger than the coexisting compressive strain at all axes. The Raman spectrum collected for individual bent NWs showed the peak broadening and red shift of the transverse optical modes that were well-correlated with the strain maps. These results are consistent with the larger mechanical modulus of GaP than that of GaAs. Our work provides new insight into the bending strain of III-V semiconductors, which is of paramount importance in the performance of flexible or bendable electronics.

1D Piezoelectric Material Based Nanogenerators: Methods, Materials and Property Optimization

Due to the enhanced piezoelectric properties, excellent mechanical properties and tunable electric properties, one-dimensional (1D) piezoelectric materials have shown their promising applications in nanogenerators (NG), sensors, actuators, electronic devices etc. To present a clear view about 1D piezoelectric materials, this review mainly focuses on the characterization and optimization of the piezoelectric properties of 1D nanomaterials, including semiconducting nanowires (NWs) with wurtzite and/or zinc blend phases, perovskite NWs and 1D polymers. Specifically, the piezoelectric coefficients, performance of single NW-based NG and structure-dependent electromechanical properties of 1D nanostructured materials can be respectively investigated through piezoresponse force microscopy, atomic force microscopy and the in-situ scanning/transmission electron microcopy. Along with the introduction of the mechanism and piezoelectric properties of 1D semiconductor, perovskite materials and polymers, their performance improvement strategies are summarized from the view of microstructures, including size-effect, crystal structure, orientation and defects. Finally, the extension of 1D piezoelectric materials in field effect transistors and optoelectronic devices are simply introduced.

Bent Polytypic ZnSe and CdSe Nanowires Probed by Photoluminescence

Nanowires (NWs) have witnessed tremendous development over the past two decades owing to their varying potential applications. Semiconductor NWs often contain stacking faults due to the presence of coexisting phases, which frequently hampers their use. Herein, it is investigated how stacking faults affect the optical properties of bent ZnSe and CdSe NWs, which are synthesized using the vapor transport method. Polytypic zinc blende-wurtzite structures are produced for both these NWs by altering the growth conditions. The NWs are bent by the mechanical buckling of poly(dimethylsilioxane), and micro-photoluminescence (PL) spectra were then collected for individual NWs with various bending strains (0-2%). The PL measurements show peak broadening and red shifts of the near-band-edge emission as the bending strain increases, indicating that the bandgap decreases with increasing the bending strain. Remarkably, the bandgap decrease is more significant for the polytypic NWs than for the single phase NWs. This work provides insights into flexible electronic devices of 1D nanostructures by engineering the polytypic structures.

Indium-Arsenic Molecules with an In≡As Triple Bond: A Theoretical Approach

The effect of substitution on the potential energy surfaces of RIn≡AsR (R = F, OH, H, CH3, and SiH3 and R' = SiMe(SitBu3)2, SiiPrDis2, and N-heterocyclic carbene (NHC)) is determined using density functional theory calculations (M06-2X/Def2-TZVP, B3PW91/Def2-TZVP, and B3LYP/LANL2DZ+dp). The computational studies demonstrate that all of the triply bonded RIn≡AsR species prefer to adopt a bent geometry, which is consistent with the valence electron model. The theoretical studies show that RIn≡AsR molecules that have smaller substituents are kinetically unstable with respect to their intramolecular rearrangements. However, triply bonded R'In≡AsR' species that have bulkier substituents (R' = SiMe(SitBu3)2, SiiPrDis2, and NHC) occupy minima on the singlet potential energy surface, and they are both kinetically and thermodynamically stable. That is, the electronic and steric effects of bulky substituents play an important role in making molecules that feature an In≡As triple bond viable as a synthetic target. Moreover, two valence bond models are used to interpret the bonding character of the In≡As triple bond. One is model [A], which is best represented as . This interprets the bonding conditions for RIn≡AsR molecules that feature small ligands. The other is model [B], which is best represented as . This explains the bonding character of RIn≡PAsR molecules that feature large substituents.

Piezoresistive effect of n-type 〈111〉-oriented Si nanowires under large tension/compression

Small-scale samples enable us to understand changes in physical properties under larger strain due to their higher tolerance to deformation. In this study, the piezoresistive character of n-type 〈111〉-oriented Si nanowires under large strain was measured during tensile and compressive deformations. The Si nanowires were directly cut from the wafer using top-down technology and deformed while capturing their electrical properties inside a transmission electron microscope. The experimental results show that both tensile and compressive deformation enhanced their electrical transport properties. The piezoresistance coefficient is of the same order of magnitude as its bulk counterpart, but half as large, which may be attributed to a larger strain magnitude. We also studied the circulatory characteristics and influence of electron beam radiation. This study provided new physical insights into piezoresistive effects under large strain.

Study on fracture behavior of individual InAs nanowires using an electron-beam-drilled notch

The mechanical properties and fracture behavior of individual InAs nanowires (NWs) were investigated under uniaxial tensile loading in a transmission electron microscope.

Electromechanical Properties and Spontaneous Response of the Current in InAsP Nanowires

The electromechanical properties of ternary InAsP nanowires (NWs) were investigated by applying a uniaxial tensile strain in a transmission electron microscope (TEM). The electromechanical properties in our examined InAsP NWs were governed by the piezoresistive effect. We found that the electronic transport of the InAsP NWs is dominated by space-charge-limited transport, with a I ∞ V² relation. Upon increasing the tensile strain, the electrical current in the NWs increases linearly, and the piezoresistance gradually decreases nonlinearly. By analyzing the space-charge-limited I-V curves, we show that the electromechanical response is due to a mobility that increases with strain. Finally, we use dynamical measurements to establish an upper limit on the time scale for the electromechanical response.