Growth Of Quantum Wires Research Articles

Synthesis Strategy of Metal Oxide Quantum Wires via a Nanoparticle-Induced Graphene Oxide Rolling Procedure.

The efficient synthesis of quantum materials is becoming a research hotspot as it determines their successful application in the fields of biomedicine, illumination, energy, sensors, information, and communication. Among the quantum materials, it is still a challenge to synthesize quantum wires (QWs) with surfactants due to the inevitable radial growth of QWs in the soft template method. In this paper, amphipathic graphene oxide (GO) was adopted as a macromolecular surfactant to limit the radial growth instead of the commonly used surfactant. GO could roll up under its electrostatic interaction with a cuprous oxide (Cu2O) quantum dot (QD) and then form a tubular template for the growth of the Cu2O QW, which was named herein as the nanoparticle-induced graphene oxide rolling (NIGOR) procedure. The NIGOR procedure was confirmed by the molecular dynamics results by simulating systems consisting of GO and Cu2O nanoparticles. An intermediate with a necklace morphology corresponding to the simulation result was also observed experimentally during the formation of the QW. Meanwhile, the formation mechanism of the QW was demonstrated rationally. Furthermore, increasing the dosage of the reactant, reaction time, and temperature altered the diameter of the QW from 2 to 4 nm and also changed the morphology of the final products from a QD to a QW and then to a bundle of QWs. This was attributed to the aggregation of materials for the lowest surface energy in the system. Additionally, the universality of NIGOR was manifested via the synthesis of other metal oxides as well. The NIGOR strategy provided an alternative, convenient, and mass production method for synthesizing QWs.

Role of Precursor-Conversion Chemistry in the Crystal-Phase Control of Catalytically Grown Colloidal Semiconductor Quantum Wires.

Crystal-phase control is one of the most challenging problems in nanowire growth. We demonstrate that, in the solution-phase catalyzed growth of colloidal cadmium telluride (CdTe) quantum wires (QWs), the crystal phase can be controlled by manipulating the reaction chemistry of the Cd precursors and tri-n-octylphosphine telluride (TOPTe) to favor the production of either a CdTe solute or Te, which consequently determines the composition and (liquid or solid) state of the BixCdyTez catalyst nanoparticles. Growth of single-phase (e.g., wurtzite) QWs is achieved only from solid catalysts (y ≪ z) that enable the solution-solid-solid growth of the QWs, whereas the liquid catalysts (y ≈ z) fulfill the solution-liquid-solid growth of the polytypic QWs. Factors that affect the precursor-conversion chemistry are systematically accounted for, which are correlated with a kinetic study of the composition and state of the catalyst nanoparticles to understand the mechanism. This work reveals the role of the precursor-reaction chemistry in the crystal-phase control of catalytically grown colloidal QWs, opening the possibility of growing phase-pure QWs of other compositions.

Solution–Liquid–Solid Growth of Semiconductor Quantum-Wire Films

We report the growth of cadmium-selenide (CdSe) quantum-wire (QW) films on a variety of substrates by the solution-liquid-solid (SLS) method. Our SLS syntheses employ size-controlled, near-monodisperse bismuth (Bi) nanoparticles (NPs) as the catalysts for QW growth, which offers several advantages over Bi NPs thermally generated from thin Bi films, including mean QW diameter control, narrow diameter distributions, small diameters in the quantum-confinement regime, and control of the QW density on the substrates. The Bi NPs are deposited on the substrates via drop casting of a Bi-NP solution and subsequently annealed in a reducing atmosphere, a key step to ensure firm attachment of the Bi NPs onto the substrates and maintenance of their catalytic activity for the QW-film growth. The QW growth density is proportional to the Bi-NP coating density, which is determined by the concentration of the Bi-NP deposition solution. Lower concentrations are used for small Bi NPs to reduce their high tendency for agglomeration and to achieve control over mean QW diameter and to produce narrow diameter distributions. Spectroscopic evidence of quantum confinement is provided. Related films of InP, InAs, and PbSe QWs are also described.

Preparation of stair-step grooves by wet etching of AlAs/GaAs heterostructures and MOCVD growth of QWR

The possibility of preparing stair-step V- or U-grooves into a GaAs/AlAs heterostructure by isotropic and anisotropic wet chemical etching was studied. Several patterned structures with well-defined (100) planes of stairs were overgrown by MOCVD with the aim to realize quantum wires (QWRs) due to the selectivity of growth on these planes. This approach should allow for adjusting lateral and vertical dimensions independently as well as for a simple regulation of the density of QWRs. Samples were subsequently characterized by photoluminescence (PL), and it was supposed that the observed red shift could result from the presence of the QWRs.

Computer simulation of the growth of heterostructure systems

We have investigated the growth of heterostructures with high lattice mismatch and the growth of quantum wires on the top of ridges and through shadowing masks. Simulations are performed within a Monte Carlo scheme using tetrahedral lattice structure of semiconductor materials. It is shown that results of different simulations present similarities that we attribute to the primary role of kinetic effects as the driving force during epitaxial growth. The formation of 3D islands showing (111) facets, or (111) side walls when depositing through a shadowing mask, has been observed. The facets are of better quality than the top (001) surface because of the higher mobility of atoms on these facets.

Calculated absorption and photoluminescence spectra for quantum wires grown in a 'V' groove

The growth of quantum wires within a 'V' groove etched in a substrate is a recognized method of fabricating an active region confined in two dimensions for use in optoelectronic devices. The authors have approximated the 'crescent shaped' wire obtained using such a process by a rectangular cross section and have calculated the absorption and photoluminescence spectra of such a structure. They have used a GaAs-Al0.35Ga0.65As quantum wire of typical dimensions 100*(150-250)AA for their calculations and have included dimensional fluctuations. By varying the size of the largest confinement direction between 150 and 250 AA, the authors have determined that the differences in the absorption and photoluminescence spectra at different light polarizations are such that they can use these techniques to monitor the wire's dimensions.

Formation of laterally propagating supersteps of InP/InGaAs on vicinal wafers

We propose and demonstrate a technique for artifically bunching the atomic steps on a vicinal substrate to form supersteps of almost arbitrary height. The process involves the etching of a grating of parallel grooves on the surface of a vicinal substrate followed by epitaxial growth that fills the grooves. Steps of height proportional to the period of the grating and the substrate misorientation angle are formed. The technique is demonstrated on a macroscopic scale for the InP/InGaAs material system using chloride transport vapor levitation epitaxy, resulting in InGaAs wire-like structures confined both horizontally and vertically by InP. The growth of quantum wires and laterally periodic superlattices should be possible using this technique with proper scaling of parameters.