The tremendous interest in nanoscale structures such as quantum dots (zero-dimension) and wires (quasi-one-dimension) stems from their size-dependent properties. One-dimensional (1D) semiconductor nanostructures are of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. For 1D semiconductor nanomaterials to have wide practical application, however, several areas require further development. In particular, the fabrication of desired 1D nanomaterials with tailored atomic structures and their assembly into functional devices are still major challenges for nanotechnologists. In this review, we focus on the status of research on the formation of nanowire structures via highly anisotropic growth of nanocrystals of semiconductor and metal oxide materials with an emphasis on the structural characterization of the nucleation, initial growth, defects and interface structures, as well as on theoretical analyses of nanocrystal formation, reactivity and stability. We review various methods used and mechanisms involved to generate 1D nanostructures from different material systems through self-organized growth techniques including vapor–liquid–solid growth, oxide-assisted chemical vapor deposition (without a metal catalyst), laser ablation, thermal evaporation, metal-catalyzed molecular beam epitaxy, chemical beam epitaxy and hydrothermal reaction. 1D nanostructures grown by these technologies have been observed to exhibit unusual growth phenomena and unexpected properties, e.g., diameter-dependent and temperature-dependent growth directions, structural transformation by enhanced photothermal effects and phase transformation induced by the point contact reaction in ultra-thin semiconductor nanowires. Recent progress in controlling growth directions, defects, interface structures, structural transformation, contacts and hetero-junctions in 1D nanostructures is addressed. Also reviewed are the quantitative explorations and predictions of some challenging 1D nanostructures and descriptions of the growth mechanisms of 1D nanostructures, based on the energetic, dynamic and kinetic behaviors of the building block nanostructures and their surfaces and/or interfaces.

Growth of nanowires

A first-principles investigation of the electronic properties of boron nitride nanoribbons (BNNRs) having either armchair or zigzag shaped edges passivated by hydrogen with widths up to 10 nm is presented. Band gaps of armchair BNNRs exhibit family dependent oscillations as the width increases and, for ribbons wider than 3 nm, converge to a constant value that is 0.02 eV smaller than the bulk band gap of a boron nitride sheet owing to the existence of very weak edge states. The band gap of zigzag BNNRs monotonically decreases and converges to a gap that is 0.7 eV smaller than the bulk gap due to the presence of strong edge states. When a transverse electric field is applied, the band gaps of armchair BNNRs decrease monotonically with the field strength. For the zigzag BNNRs, however, the band gaps and the carrier effective masses either increase or decrease depending on the direction and the strength of the field.

/pdf/energy-gaps-and-stark-effects-in-boron-nitride-nanoribbons-ks761kghpx.pdf

Energy gaps and Stark effects in boron nitride nanoribbons

Using density functional theory (DFT), we have investigated the structural and electronic properties of a prototype ZnO (6,0) zigzag single-walled nanotube (SWNT) with and without oxygen vacancy (VO), as well as its potential application as a sensor for gas molecules O2, H2, CO, NH3, and NO2. The DFT calculation shows that the defect-free ZnO (6,0) SWNT is semiconducting with a direct band gap larger than that of bulk ZnO. By introducing the VO defects, localized impurity states are induced above the valence band maximum while the Fermi level is lifted. As such, the defect-containing ZnO (6,0) SWNT becomes an n-type semiconductor. On the sidewall of a defect-free ZnO (6,0) SWNT, O2 and H2 molecules are physisorbed while CO, NH3, and NO2 are molecularly chemisorbed. With the VO defects, the binding interaction between gas molecules and the ZnO nanotube becomes stronger. The electron-donor molecules (CO and NH3) tend to enhance the concentration of major carriers (electrons), whereas the electron-acceptor m...

Adsorption of O2, H2, CO, NH3, and NO2 on ZnO Nanotube: A Density Functional Theory Study

Thin Friction The rubbing motion between two surfaces is always hindered by friction, which is caused by continuous contacting and attraction between the surfaces. These interactions may only occur over a distance of a few nanometers, but what happens when the interacting materials are only that thick? Lee et al. (p. 76; see the Perspective by Müser and Shakhvorostov) explored the frictional properties of a silicon tip in contact with four atomically thin quasi–two dimensional materials with different electrical properties. For all the materials, the friction was seen to increase as the thickness of the film decreased, both for flakes supported by substrates and for regions placed above holes that formed freely suspended membranes. Placing graphene on mica, to which it strongly adheres, suppressed this trend. For these thin, weakly adhered films, out-of-plane buckling is likely to dominate the frictional response, which leads to this universal behavior. A universal trend is observed for the friction properties of thin films on weakly adhering substrates. Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS2), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS2 exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length–dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets’ increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.

Frictional Characteristics of Atomically-Thin Sheets

We have performed a comparative density functional theory study on adsorption of hydrogen peroxide (H2O2) on the boron nitride and silicon carbide nanotubes (BNNT and SiCNT) in terms of energetic, geometric, and electronic properties. It has been found that the molecule is chemically adsorbed on both of the tubes so that its interaction with SiCNT (adsorption energy ∼−0.97 eV) is much stronger than that with BNNT (adsorption energy ∼−0.47 eV). The H2O2 adsorption on BNNT slightly decreases its work function, increasing the field electron emission from the BNNT surface while it may not affect that of the SiCNT. In addition, the adsorption process may increase the electrical conductivity of SiCNT while does not affect that of the BNNT, significantly. We believe that the SiCNT may be a potential candidate for detection of H2O2.

H2O2 adsorption on the BN and SiC nanotubes: A DFT study

The structural and electronic properties of armchair and zigzag models of single-wall ZnO nanotubes have been investigated by performing semiempirical molecular orbital self-consistent field calculations at the level of AM1 method within the RHF formulation. It has been found that these structures are stable and endothermic. The armchair model has zero net dipole moment, whereas the zigzag model has nonzero net dipole moment. The interfrontier molecular energy gap of these systems are different; the gap of armchair model is about 0.2 eV, whereas the gap of zigzag model is about 4.4 eV. Armchair ZnO nanotubes seem to be conductors, however zigzag ZnO nanotubes seem to be semiconductors.

Structural and electronic properties of single-wall ZnO nanotubes

Energetics and structural properties of carbon and oxygen doped hexagonal boron nitride sheets have been investigated by performing density functional theory calculations. Substitutional doping model has been considered in the neutral charge state. C and O atoms replaced either B or N site in the system as impurities. A systematic study has been performed to see the effect of cell size on the calculated quantities, such as formation energy, relaxation energy, charge and bond length. It has been found that substitution of O atom on the N site in the hexagonal BN sheet is more favorable.

Energetics and structural properties of carbon and oxygen doped hexagonal boron nitride sheets

Thermodynamics of small platinum clusters

Structural properties and energetics of silicon and phosphorus doped hexagonal boron nitride sheets were investigated by performing density functional theory calculations. The dopant atoms were substituted in a neutral charge state at either the B or the N site in the system as an impurity. All the systems under consideration were fully optimized. A systematic study was performed to see the eect of cell size on the calculated quantities, such as bond length, charge transfer, and defect formation energies. It was found that both silicon and phosphorus atom substitutions cause the bond lengths to increase with respect to the pristine sheets. Si atom replaced on the N site yields relatively large charge transfer from Si to the lattice. Substitutions of Si at the B site and of P at the N site are exothermic processes, while for the other cases the processes are endothermic.

https://journals.tubitak.gov.tr/physics/issues/fiz-14-38-3/fiz-38-3-5-1406-17.pdf

A study on Si and P doped h-BN sheets: DFT calculations

Using an empirical potential energy function parametrized for each of the Ni, Cu, Pd, Pt, and Pb systems, minimum-energy structures of Nin, Cun, Pdn, Ptn, and Pbn (n=3–13) microclusters have been determined by performing molecular-dynamics simulations. The structural and energetic features of the obtained microclusters have been investigated.

Hatice Kökten

Papers

Structural and electronic properties of single-wall ZnO nanotubes

Energetics and structural properties of carbon and oxygen doped hexagonal boron nitride sheets

Thermodynamics of small platinum clusters

A study on Si and P doped h-BN sheets: DFT calculations

ON THE STRUCTURAL AND ENERGETIC FEATURES OF SMALL METAL CLUSTERS: Nin, Cun, Pdn, Ptn, AND Pbn; n=3–13