Topological crystalline insulator tin telluride (SnTe) provides a rich playground to examine interactions of correlated electronic states, such as ferroelectricity, topological surface states, and superconductivity. Making SnTe into nanowires further induces novel electronic states due to one-dimensional (1D) confinement effects. Thus, for transport measurements, SnTe nanowires must be made narrow in their diameters to ensure the 1D confinement and phase coherence of the topological surface electrons. This study reports a facile growth method to produce narrow SnTe nanowires with a high yield using alloy nanoparticles as growth catalysts. The average diameter of the SnTe nanowires grown using the alloy nanoparticles is 85 nm, nearly a factor of three reduction from the previous average diameter of 240 nm using gold nanoparticles as growth catalysts. Transport measurements reveal the effect of the nanowire diameter on the residual resistance ratio and magnetoresistance. Particularly, the ferroelectric transition temperature for SnTe is observed to change systematically with the nanowire diameter. In situ cryogenic cooling of narrow SnTe nanowires in a transmission electron microscope directly reveals the cubic to rhombohedral structural transition, which is associated with the ferroelectric transition. Thus, these narrow SnTe nanowires represent a model system to study electronic states arising from the 1D confinement, such as 1D topological superconductivity as well as a potential multi-band superconductivity.
SnTe topological crystalline insulator nanowires have been grown by molecular beam epitaxy on graphene/SiC substrates. The nanowires have cubic rock-salt structure, they grow along [001] crystallographic direction and have four sidewalls consisting of {100} crystal planes known to host metallic surface states with Dirac dispersion. Thorough high resolution transmission electron microscopy investigations show that the nanowires grow on graphene in the van der Walls epitaxy mode induced when the catalyzing Au nanoparticle mixes with Sn delivered from SnTe flux, providing liquid Au-Sn alloy. The …
The recent discovery of excellent thermoelectric properties and topological surface states in SnTe-based compounds has attracted extensive attention in various research areas. Indium doped SnTe is of particular interest because, depending on the doping level, it can either generate resonant states in the bulk valence band leading to enhanced thermoelectric properties, or induce superconductivity that coexists with topological states. Here we report on the vapor deposition of In-doped SnTe nanowires and the study of their surface oxidation and thermoelectric properties. The nanowire growth is a…
In this work, ZnO nanowire arrays decorated with titanium nitride (TiN) nanoparticles as surface enhanced Raman scattering (SERS) substrates is demonstrated. ZnO nanowires were grown by hydrothermal synthesis while ~100 nm TiN nanoparticles were obtained by grinding commercial powders for several hours. They were then decorated on the ZnO nanowire arrays using acetone as the medium. Scanning electron microscopy confirmed the presence of TiN nanoparticles on the ZnO nanowires. TiN nanoparticles exhibited localized surface plasmon resonances at 430, 520 and 600 nm. SERS experiments using Nile Bl…
Bimetallic nanoalloys such as nanoparticles and nanowires are attracting significant attention due to their vast potential applications such as in catalysis and nanoelectronics. Notably, Pd-Pt nanoparticles/nanowires are being widely recognized as catalysts and hydrogen sensors. Compared to unary systems, alloys present more structural complexity with various compositional configurations. Therefore, it is important to understand energetically preferred atomic structures of bimetallic nanoalloys. In this study, we performed a series of simulated annealing Monte Carlo simulations to predict the …
A new class of materials, Topological Crystalline Insulators (TCIs) have been shown to possess exotic surface state properties that are protected by mirror symmetry. These surface features can be enhanced if the surface-area-to-volume ratio of the material increases, or the signal arising from the bulk of the material can be suppressed. We report the experimental procedures to obtain high quality crystal boules of the TCI, SnTe, from which nanowires and microcrystals can be produced by the vapour-liquid-solid (VLS) technique. Detailed characterisation measurements of the bulk crystals as well …
A simple and most promising oxide-assisted catalyst-free method is used to prepare silicon nitride nanowires that give rise to high yield in a short time. After a brief analysis of the state of the art, we reveal the crucial role played by the oxygen partial pressure: when oxygen partial pressure is slightly below the threshold of passive oxidation, a high yield inhibiting the formation of any silica layer covering the nanowires occurs and thanks to the synthesis temperature one can control nanowire dimensions.
SnTe is a topological crystalline insulator that possesses spin-polarized, Dirac-dispersive surface states protected by crystal symmetry. Multiple surface states exist on the {100}, {110}, and {111} surfaces of SnTe, with the band structure of surface states depending on the mirror symmetry of a particular surface. Thus, to access surface states selectively, it is critical to control the morphology of SnTe such that only desired crystallographic surfaces are present. Here, we grow SnTe nanostructures using vapor-liquid-solid and vapor-solid growth mechanisms. Previously, SnTe nanowires and nan…
While most of the experimental studies are dealing with partially oxidized metallic nanosolids, their behaviour is not well understood theoretically. To this end we utilized molecular dynamics simulation and charge-optimized many-body potential to probe melting of Cu nanoparticles and nanowires with and without a monolayer of Cu$_2$O as a shell. It is shown that partially oxidized nanosolids present a different melting behaviour than the widely accepted picture of melting, and especially different than surface melting. (i) For both types of nanosolids we observed inward diffusion of $\sim$40\%…
The role of the sublimation of the compound and of the evaporation of the constituents from the gold nanoparticle during the growth of semiconductor nanowires is exemplified with CdTe-ZnTe heterostructures. Operating close to the upper temperature limit strongly reduces the amount of Cd present in the gold nanoparticle and the density of adatoms on the nanowire sidewalls. As a result, the growth rate is small and strongly temperature dependent, but a good control of the growth conditions allows the incorporation of quantum dots in nanowires with sharp interfaces and adjustable shape, and it mi…
The near field scanning optical microscopy (NSOM) is not only a tool for imaging of sub-diffraction limited objects but also a prominent characteristic tool for understanding the intrinsic properties of the nanostructures. In order to understand the light-matter interactions in the near field regime using NSOM technique with an excitation of 532 nm (2.33 eV), we selected an isolated single semiconducting AlGaN nanowire (NW) of diameter ~120 nm grown via vapor liquid solid (VLS) mechanism along with metallic Au nanoparticle (NP) catalyst. The role of electronic transitions from different native…
We investigate the full and half-shells of Pb(1-x)Sn(x)Te topological crystalline insulator deposited by molecular beam epitaxy on the sidewalls of wurtzite GaAs nanowires (NWs). Due to the distinct orientation of the IV-VI shell with respect to the III-V core the lattice mismatch along the nanowire axis is less than 4%. The Pb(1-x)Sn(x)Te solid solution is chosen due to the topological crystalline insulator properties for some critical concentrations of Sn (x >= 0.4). The IV-VI shells are grown with different compositions spanning from binary SnTe, through Pb(1-x)Sn(x)Te with decreasing x val…
A kinetic Monte Carlo approach is applied to study physical mechanisms responsible for the breakup of nanowires with the diamond cubic crystal structure into a chain of nanoparticles discovered in preceding experiments on Silicon nanowires. We show that this process is based on the well-known mechanism of roughening transition, which specifically manifests itself in quasi-one-dimensional systems/nanowires with a pronounced anisotropy of the surface energy density. Depending on the temperature and orientation of the nanowire relative to its internal crystal structure, the wavelengths of substan…
A kinetic Monte Carlo approach is applied to studying shape instability of nanowires that results in their breaking up into chains of nanoparticles. Our approach can be used to explore dynamical features of the process that correspond to experimental findings, but that cannot be interpreted by continuum mechanisms reminiscent of the description of the Plateau-Rayleigh instability in liquid jets. For example, we observe long-lived dumbbell-type fragments and other typical non-liquid-jet characteristics of the process, as well as confirm the observed lattice-orientation dependence of the breakup…
Confining two dimensional Dirac fermions on the surface of topological insulators has remained an outstanding conceptual challenge. Here we show that Dirac fermion confinement is achievable in topological crystalline insulators (TCI), which host multiple surface Dirac cones depending on the surface termination and the symmetries it preserves. This confinement is most dramatically reflected in the flux dependence of these Dirac states in the nanowire geometry, where different facets connect to form a closed surface. Using SnTe as a case study, we show how wires with all four facets of the <100>…
Growth of mono-dispersed AlGaN nanowires of ternary wurtzite phase is reported using chemical vapour deposition technique in the vapour-liquid-solid process. The role of distribution of Au catalyst nanoparticles on the size and the shape of AlGaN nanowires are discussed. These variations in the morphology of the nanowires are understood invoking Ostwald ripening of Au catalyst nanoparticles at high temperature followed by the effect of single and multi-prong growth mechanism. Energy-filtered transmission electron microscopy is used as an evidence for the presence of Al in the as-prepared sampl…
The controllable handling of an arbitrary single particle of matter with sub-100 nanometer (nm) dimensions is an essential but unsolved scientific challenge. We demonstrate nanoparticle-seeded glancing angle deposition using 10-100 nm diameter nanoparticle seeds (Er2O3, Fe@C, and Fe). The products are nanoparticle-nanowire heterostructures composed of arbitrary nanoscale tips attached to micron-length nanowire handles. Optical micromanipulation of the micron-scale handles enables concurrent manipulation of the attached nanoscale particles of matter.
General approach for consideration of primary ferroic (ferroelectric, ferromagnetic, ferroelastic) nanoparticles phase transitions was proposed in phenomenological theory framework. The surface stress, order parameter gradient, striction as well as depolarization and demagnetization effects were included into the free energy. The strong intrinsic surface stress under the curved nanoparticle surface was shown to play the important role in the shift of transition temperature (if any) up to the appearance of new ordered phase absent in the bulk ferroic. The approximate analytical expression for t…
The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles with N2 in the 1200-1440 C temperature range is reported. The nitridation conditions are such that the reaction with nitrogen is favoured by the presence of silicon oxide in the particles and by the active oxidation of silicon without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on the amount of silicon particles used in the experiments and that, in general, the reaction slows down for greater amounts. This trend is explained by particle stacking, which restricts the exchange of gases between th…
Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter be…
We report a simple and versatile waterborne synthesis of magnetic nanowires following the innovative concept of electrostatic "desalting transition". Highly persistent superparamagnetic nanowires are generated from the controlled assembly of oppositely charged nanoparticles and commercially available polyelectrolytes. The wires have diameters around 200 nm and lengths comprised between 1 μm and 1/2 mm, with either positive or negative charges on their surface. Beyond, we show that this soft-chemistry assembly approach is a general phenomenon independent of the feature of the macromolecular bui…
It is demonstrated by the current work controlled one-to-one synthesis of Ge nanowires (GeNWs) with ~100% yield from Au seed particles. The optimum GeNW growth conditions are found to be size dependent. For < 50 nm Au seeds, under-growth, one-to-one growth and over-growth can occur depending on the growth conditions. Growth of large GeNWs appears to be diffusion limited. These results should have generic implications to the synthesis of other types of nanowires via vapor-liquid-solid (VLS) processes. Patterning and positioning of individual Au nanoparticles are achieved by lithographic pattern…
InAs nanowires have been actively explored as the channel material for high performance transistors owing to their high electron mobility and ease of ohmic metal contact formation. The catalytic growth of non-epitaxial InAs nanowires, however, has often relied on the use of Au colloids which is non-CMOS compatible. Here, we demonstrate the successful synthesis of high yield of crystalline InAs nanowires with high yield and tunable diameters by using Ni nanoparticles as the catalyst material on amorphous SiO2 substrates. The nanowires show superb electrical properties with field-effect electron…
In this work we present how the optical properties of ZnSe nanowires are modified by the presence of Ag nanoparticles on the sidewalls of the ZnSe nanowires. In particular we show that the low-temperature luminescence of the ZnSe nanowires changes its shape, enhancing the phonon-replicas of impurity related recombination and affecting rise and decay times of the transient absorption bleaching at room temperatures, with an increase of the former and a decrease of the latter. In contrast, the deposition of Au NPs on the ZnSe nanowires does not change the optical properties of the sample. We sugg…
X-ray diffraction experiments were performed on MnO confined in mesoporous silica SBA-15 and MCM-41 matrices with different channel diameters. The measured patterns were analyzed by profile analysis and compared to numerical simulations of the diffraction from confined nanoparticles. From the lineshape and the specific shift of the diffraction reflections it was shown that the embedded objects form ribbon-like structures in the SBA-15 matrices with channels diameters of 47-87 Å, and nanowire-like structures in the MCM-41 matrices with channels diameters of 24-35 Å. In the latter case the confi…
A novel method for measuring the surface coverage of randomly distributed cylindrical nanoparticles such as nanorods and nanowires, using atomic force microscopy (AFM), is presented. The method offers several advantages over existing techniques such as particle beam and x-ray diffraction spectroscopy. These include, subnanometer vertical and lateral resolution, non destructive interaction with the sample surface allowing repeated measurements, user-friendly setup and ambient operating conditions. The method relies on the use of a statistical model to describe the variations of the nanoparticle…
Part of developing new strategies for fabrications of nanowire structures involves in many cases the aid of metal nanoparticles (NPs). It is highly beneficial if one can define both diameter and position of the initial NPs and make well-defined nanowire arrays. This sets additional requirement on the NPs with respect to being able to withstand a pre-growth annealing process (i.e. de- oxidation of the III-V semiconductor surface) in an epitaxy system. Recently, it has been demonstrated that Ag may be an alternative to using Au NPs as seeds for particle-seeded nanowire fabrication. This work bri…
Pentagonal nanowires from topological crystalline insulators: a platform for intrinsic core-shell nanowires and higher-order topology
International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所磁顶国际研究中心）；Institute for Advanced Study, Shenzhen University（深圳大学高等研究院）；Consiglio Nazionale delle Ricerche (CNR-SPIN), Unitá di Ricerca presso Terzi c/o Universitá “G. D’Annunzio”（意大利国家研究委员会（CNR-SPIN）第泽齐研究单元/阿布鲁佐大学）
Till now the nanoscale focussing and imaging in the sub-diffraction limit is achieved mainly with the help of plasmonic field enhancement assisted with noble metal nanoparticles. Using far field imaging technique, we have recorded polarized spectroscopic photoluminescence (PL) imaging of a single AlGaN nanowire (NW) of diameter ~ 100 nm using confinement of polarized light. The nanowires on the substrate have a nematic ordering. It is found that the PL from a single NW is influenced by the proximity to other NWs with the PL intensity scaling as 1/(lxd), where l and d are the NW length and the …
Eutectic related reaction is a special chemical/physical reaction involving multiple phases, solid and liquid. Visualization of phase reaction of composite nanomaterials with high spatial and temporal resolution provides a key understanding of alloy growth with important industrial applications. However, it has been a rather challenging task. Here we report the direct imaging and control of the phase reaction dynamics of a single, as-grown free-standing gallium arsenide nanowire encapped with a gold nanoparticle, free from environmental confinement or disturbance, using four-dimensional electr…
Nano1D: An accurate Computer Vision software for analysis and segmentation of low-dimensional nanostructures
Institute of Technology, University of Tartu（塔尔图大学技术研究所）；Institute of Physics, University of Tartu（塔尔图大学物理研究所）；Institute of Solid State Physics, University of Latvia（拉脱维亚大学固体物理研究所）
This work presents the synthesis of SiC nanowires floating in a gas stream through the vapour-liquid-solid (VLS) mechanism using an aerosol of catalyst nanoparticles. These conditions lead to ultrafast growth at 8.5 μm/s (maximum of 50 μm/s), which is up to 3 orders of magnitude above conventional substrate-based chemical vapour deposition. The high aspect ratio of the nanowires (up to 2200) favours their entanglement and the formation of freestanding network materials consisting entirely of SiCNWs. The floating catalyst chemical vapour deposition growth process is rationalised through in-situ…
CdS nanotubes with wall thickness comparable to excitonic diameter of the bulk material are synthesized by a chemical route. A change in experimental conditions result in formation of nanowires, and well-separated nanoparticles. The diameter and wall thickness of nanotubes measured to be 14.4 $\pm$ 6.1 and 4.7 $\pm$ 2.2 nm, respectively. A large number of CdS nanocrystallites having wurzite structure constitute these nanotubes. These nanotubes show high energy shifting of optical absorption and photoluminescence peak positions, compared to its bulk value, due to quantum confinement effect. It …
