Defective Nanostructures Research Articles

Nanoscale Removal Processing by a Twin-Cylinder Tool

A major problem for the implementation of microelectroremoval is the cost and the design of the tool electrode. An effective nanoscale processing for yield improvement was developed using microelectroremoval and a designed twin-cylinder tool as a precision reclamation retrieval system to remove the defective indium tin oxide (ITO) thin-film nanostructures from the optical PET surfaces of digital paper. By establishing a recycling process using the ultra-precise removal of nanostructures, the optoelectronic semiconductor industry can effectively recycle defective products, minimizing both production costs and pollution. In the current experiment, small thickness of the anode, combined with enough electric power and provided a larger discharge space, and better removal effect. A large diameter of the cylinder acthode accompanied by a small gap-width between the cathode and the workpiece, takes less time to do the same amount of ITO removal. A higher rate of removal of the defective ITO nanostructures corresponds to high temperature, a large electrolyte flow rate with a high rotational speed of the electrodes. A faster feed rate of color filters combined with a higher electric current produces a fast removal rate. A small edge angle of the anode also provides higher current density, which is advantageous for ITO removal.

Selective nucleation induced by defect nanostructures: A way to control cobalt disilicide precipitation during ion implantation

In this paper, we show a way to control cobalt disilicide precipitation during Co ion implantation at high temperatures (650 °C) by affecting radiation defects involved in precipitate nucleation and growth. We demonstrate that the relative shares of different precipitate types nucleated by implantation are strongly affected by defect microstructures deliberately created in investigated samples prior to cobalt implantation. Especially interesting is the effect of a dense ensemble of extremely small (1-3 nm) cavities, which promotes the formation of a relatively uniform layer of coherent cobalt disilicide precipitates with a narrow size distribution. In order to better understand the mechanism of the microstructural influence on the precipitate nucleation modes during Co implantation, we investigate the disilicide precipitation using different implantation setups and compare the results with those for cavity-free Si specimens implanted in similar conditions.

Tailoring atomic structure to control the electronic transport in zigzag graphene nanoribbon

We have performed ab initio density functional theory calculation to study the electronic transport properties of the tailored zigzag-edged graphene nanoribbon (ZGNR) with particular electronic transport channels. Our results demonstrated that tailoring the atomic structure had significantly influenced the electronic transport of the defective nanostructures, and could lead to the metal-semiconducting transition when sufficient atoms are tailored. The asymmetric I–V characteristics as a result of symmetry breaking have been exhibited, which indicates the route to utilize GNR as a basic component for novel nanoelectronics.

Computational study of the thermal conductivity in defective carbon nanostructures

We use non-equilibrium molecular dynamics simulations to study the adverse role of defects including isotopic impurities on the thermal conductivity of carbon nanotubes, graphene and graphene nanoribbons. We find that even in structurally perfect nanotubes and graphene, isotopic impurities reduce thermal conductivity by up to one half by decreasing the phonon mean free path. An even larger thermal conductivity reduction, with the same physical origin, occurs in presence of structural defects including vacancies and edges in narrow graphene nanoribbons. Our calculations reconcile results of former studies, which differed by up to an order of magnitude, by identifying limitations of various computational approaches.

Controllable tuning of the electronic transport in pre-designed graphene nanoribbon

We make use of ab initio density functional theory calculation to explore the electronic and transport properties of zigzag-edged graphene nanoribbon (ZGNR) with peculiar designed electronic transport channels by tailoring the atomic configuration of the nanostructure. Tailoring the atomic structure has significant influences on the electronic transport of the defective nanostructure, and eventually the metal-semiconducting transition are identified with the increasing number of missing atoms. Our results demonstrate that pre-designed graphene nanoribbon by selective tailoring with high precision is expected to be served as the basic component for nanoelectronic device.

Modulation of electric behavior by position-dependent substitutional impurity in zigzag-edged graphene nanoribbon

We investigate the electronic properties of symmetric zigzag-edged graphene nanoribbon (ZGNR) in the presence of nitrogen (N) substitutional doping by ab initio density functional theory. The transformation energies indicate that the impurity prefers to distribute near the edges. With N-doping moving from edge to center, the electronic transport properties are mainly governed by holes and carriers, respectively. The charge transfer induced by substitutional doping is analyzed in detail and the influences of doping on the electronic transport properties of the defective nanostructure have been discussed. Our results suggest that ZGNRs’ transport properties can be tuned via tailoring the atomic structures in terms of selective doping profiles, which would be helpful for designing graphene nanoribbon (GNR)-based nanoelectronic devices in future.

Chromium and tantalum oxide nanocoatings prepared by filtered cathodic arc deposition for corrosion protection of carbon steel

Combined analysis by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), polarization curves and Electrochemical Impedance Spectroscopy (EIS) of the relation between chemical architecture of thin (10 and 50nm) chromium and tantalum oxide coatings grown by filtered cathodic arc deposition (FCAD) on carbon steel and their corrosion protection properties is reported. Pre-etching in the deposition process allows reducing the substrate native oxide layer to traces of iron oxide. A carbidic interlayer is then formed by reaction between the first deposited metallic particles and the residual carbon surface contamination of the alloy. The bulk coatings mostly consist of Cr2O3 or Ta2O5 with no in-depth variation of the stoichiometry. Surface and bulk of the coatings are contaminated by hydroxyl and organic groups. The 50nm coating has a relatively large porosity assigned to a columnar growth preventing good sealing at grain boundaries. The duplex structure (Ta/Ta–C) of the carbidic interlayer promotes a less defective growth of tantalum oxide than the single Cr–C interlayer for chromium oxide, thereby improving the sealing properties. The dielectric constants suggest poor insulating properties in line with a defective and porous nanostructure of the coatings. No dissolution was observed for both oxide nanocoatings in neutral 0.2M NaCl. Penetration of the electrolyte and access to the interface with the carbon steel surface cause the dissolution of the Cr–C interlayer, but not that of the Ta/Ta–C interlayer, and a more rapid initiation of localized corrosion.

Molecular dynamics study of configuration and stability of vacancy clusters in fcc Ag

Vacancies may agglomerate to form vacancy Frank loops of different shapes, as observed by transmission electron microscopy in quenched and irradiated fcc metals. The dynamics for the dissociation of vacancy Frank loops and the subsequent evolution of defect nanostructures were explored by means of the molecular dynamics method and displayed by the local crystalline order method. Frank loops of different initial shapes were found to transform to a variety of defect nanostructures: triangle to stacking fault tetrahedra, equilateral hexagon to quasi-heptahedron, and scalene hexagon to various intermediate structures depending on the length of the short side. The formation energies for vacancy Frank loops of different geometries are introduced to categorize various final configurations. Crystallographic analysis and elasticity calculations were performed to elucidate the transform mechanisms in fcc Ag.

In-process characterization tool for optically produced sub-100-nm structures

In this paper an in-process measurement tool based on coherent laser light scattering by sub-100-nm structures is presented. Laser beams of high fluence are used for fabricating three-dimensional nanostructures in the sub-100-nm range for different applications and measurement of these nanostructures is vital during manufacturing for quality control, defect analysis, calibration measurements, etc. However, present offline measurement techniques such as atomic force microscopy and scanning electron microscopy prove to be too slow and, in some cases, also destructive. It is shown that by measuring the scattered laser light distribution of nanostructures such as zinc-oxide nanograss, it is possible to distinguish between defect-free and defective nanostructures. This allows for fast, contactless and nondestructive measurements of nanostructures. Using discrete dipole approximation (DDA) to simulate the scattered laser light distribution of modeled zinc-oxide nanograss and also CCD optical measurements of commercial grade nanograss, a correlation between the two sets of measurements strongly supports the concept of a tool capable of providing measurements of sub-100-nm nanostructures in a running manufacturing process.

Optical assistance in thin film microelectro-removal for touch-panel displays

Abstract Achieving a low yield of In2O3SnO2 thin film nanostructures during the production of optoelectronic semiconductors is easy. A newly designed optical assistance module uses excimer irradiation in the deep ultraviolet to assist in the micro electro-removal process in a nano-scale recovery process for flexible display panels. The method effectively removes defective In2O3SnO2 nanostructures from the surface of the optical PET-film (PET) of e-paper and allows the substrate to be returned to the production line. This study uses 172-nm excimer light to promote the efficient removal of In2O3SnO2 nanostructures by the etching process. The excimer irradiation enhances the removal of the In2O3SnO2 thin film which is easily broken into nano-particles and removed from the PET substrate quickly and cleanly. The time required for the etching process using excimer irradiation is shorter when compared to the time taken without irradiation under similar processing conditions. It was also shown that excimer irradiation is absolutely necessary to promote the etching effect with the designed tool to efficiently strip away the In2O3SnO2 nanostructures.

INTERSTELLAR ANALOGS FROM DEFECTIVE CARBON NANOSTRUCTURES ACCOUNT FOR INTERSTELLAR EXTINCTION

Because interstellar dust is closely related to the evolution of matter in the galactic environment and many other astrophysical phenomena, the laboratory synthesis of interstellar dust analogs has received significant attention over the past decade. To simulate the ultraviolet (UV) interstellar extinction feature at 217.5 nm originating from carbonaceous interstellar dust, many reports focused on the UV absorption properties of laboratory-synthesized interstellar dust analogs. However, no general relation has been established between UV interstellar extinction and artificial interstellar dust analogs. Here, we show that defective carbon nanostructures prepared by high-energy collisions exhibit a UV absorption feature at 220 nm which we suggest accounts for the UV interstellar extinction at 217.5 nm. The morphology of some carbon nanostructures is similar to that of nanocarbons discovered in the Allende meteorite. The similarity between the absorption feature of the defective carbon nanostructures and UV interstellar extinction indicates a strong correlation between the defective carbon nanostructures and interstellar dust.

An effective microsystem by design of a twin-plate tool for precision removal

The low yield of ITO thin film deposition is an important factor in semiconductor production. An effective microsystem with economic viability that uses micro electroremoval as a reclaim process was developed to remove the defective ITO nanostructure coatings from the optical PET surfaces of digital paper. By establishing the reclaim process using the ultra-precise removal of the nanostructure coatings, the optoelectronic semiconductor industry can effectively reclaim defective products, minimizing both production costs and pollution. In the current experiment, a large twin-plate cathode with a small gap-width between the cathode and the workpiece takes less time for the same amount of ITO removal. A small end radius of the cathode combines with enough electric power to drive fast machining. Pulsed direct current can improve the effect of dreg discharge, and it is advantageous to associate the workpiece with the fast feed rate. However, this improvement can increase the current rating. A high rotational speed of the electrodes, a higher temperature, or a large flow rate of the electrolyte corresponds to a higher removal rate for the ITO nanostructure. The micro electroremoval requires only a short period of time to remove the ITO thin film coatings easily and cleanly.

HTSC cuprate films doped with nanoparticles and their electrodynamics, determined by Abrikosov vortices

This paper presents the results of a comprehensive study of the relationship of the structural and electrodynamic characteristics of quasi-single-crystal films of the HTSC cuprate YBa2Cu3O7−δ (YBCO) with various concentrations (several mass percent) of nanosize inclusions of the perovskitelike phase of BaZrO3 (BZO). High-resolution electron microscopy is used to investigate the nanostructure of the fabricated films and to determine the main types of defects that cause strong pinning of Abrikosov vortices and, accordingly, large critical current densities. The results of theoretically modelling the genesis of the defect nanostructure that appears in such films and its influence on the critical current are presented. The magnetic and transport properties of HTSC films made from YBCO(BZO) have been experimentally studied. The temperature, magnetic-field, and magnetic-orientation dependences of the critical current density of the test films are found. The results of an experimental investigation of the high-frequency properties of YBZO(BZO) films—the surface microwave impedance of the films in the linear and nonlinear regimes—are also given. The experimental results are discussed, and the influence of the nanostructure of the impurity phase on the electrodynamic characteristics of the HTSC films is analyzed.

Defects-enhanced flexoelectricity in nanostructures

Recent studies show that low dimensional nanostructures may exhibit nonlocal electromechanical effects such as flexoelectricity. Despite the recent progress in nanostructure growth techniques imperfections such as defects are practically unavoidable. These imperfections may enhance flexoelectric effects. Therefore, the main goal of this paper is to analyze the effects of these imperfections on linear electromechanical properties and on flexoelectricity. The constitutive relations for the adiabatically insulated reversible system are derived from the total differential of the general thermodynamic Gibbs potential. The mechanical and electrical balance equations coupled through the constitutive equations are then solved with finite element method for the defective nanostructures. We focus in our study on GaN-based nanostructures which are important in electronic and optoelectronic applications. They exhibit higher magnitudes of electric field compared to other semiconductors in similar contexts. Our results are presented for GaN quantum dots embedded in an AlN matrix.

Bulge-Form Tool Design in the Precise Reclamation of a Digital Paper Display Surface

The low yield of indium tin oxide (ITO) thin-film deposition is an important factor in optoelectronic semiconductor production. An effective reclamation process was developed that uses ultrasonic electroetching and a designed bulge-form tool to remove the defective ITO nanostructure from the optical polyethyleneterephthalate (PET) surfaces of digital paper. In the current experiment, the assistance of ultrasonics was found to be more effective than pulsed current, requiring no increase in electric power. The large length of the bulge-form tool’s cathode, with a small gap width between the cathode and the workpiece, requires less time to do the same amount of ITO etching. The small end radius of the cathode, combined with enough electric power, results in very fast etching. Additionally, electric power, when combined with a fast feed rate, provides highly effective etching. A higher rate of removal of the defective ITO nanostructure corresponds to high temperature, a large electrolyte flow rate, or a high rotational speed of the electrodes. Importantly, ultrasonic electroetching with the designed bulge-form tool requires only a short period of time to remove the ITO’s thin-film coatings easily and cleanly.

Defect Clustering and Nanostructure Formation in PbTe-based Bulk Thermoelectrics

AbstractIn recent years, LAST-m (AgPbmSbTem+2) and related materials have emerged as potential high performance high temperature thermoelectrics. One example is LAST-18. When optimally doped, this compound has thermoelectric figure of merit ZT=1.7 at 700K. This large ZT is most likely due to the low lattice thermal conductivity, caused by phonon scattering from nanostructures. These nanostructures involve clustering and ordering of Ag, Sb, and Pb ions. The origin of these nanostructures has been studied using Monte Carlo (MC) simulation of an ionic model and ab initio studies of pair interaction energies. Effects of these substitutions on the band structure near the gap and their implications on transport properties are briefly discussed.

Positron annihilation studies of defects and interfaces in ZnS nanostructures of different crystalline and morphological features

Nanostructures of ZnS, both particles and rods, were synthesized through solvothermal processes and characterized by x-ray diffraction and high resolution transmission electron microscopy. Positron lifetime and Doppler broadening measurements were made to study the features related to the defect nanostructures present in the samples. The nanocrystalline grain surfaces and interfaces, which trapped significant fractions of positrons, gradually disappeared during grain growth, as indicated by the decreasing fraction of orthopositronium atoms. The crystal vacancies present within the grains also trapped positrons. These vacancies further agglomerated into clusters during the thermal treatment given to effect grain growth. The positron lifetime was remarkably large at extremely small grain sizes (approximately 1.5 nm) and this was attributed to the occurrence of quantum confinement effects, as verified through optical absorption measurements. Positron lifetimes in ZnS nanorods increased with increasing content of cubic phase in the samples and this observation is assigned to the annihilation of positrons in sites with increased cubic unit cell volume. The Doppler broadened spectra also indicated qualitative changes consistent with these observations.

A computational study on nanocrystalline SnO 2: Adsorption of CO and O 2 onto defective nanograins

This work presents a study of the adsorption properties of defective nanostructures. The calculations have quantum mechanical detail and are based on a semi-empirical Hamiltonian, which is applied to the evaluation of both the electronic structure and of the conductance. The material considered in this study, i.e. SnO 2, has a widespread use as gas sensor and oxygen vacancies are known to act as active catalytic sites for the adsorption of small molecules. In the following calculations crystalline SnO 2 nanograins, with a size and shape comparable with the experimental ones, have been considered. The grains lattice, which has the rutile structure of the bulk material, includes oxygen vacancies and the adsorbed system is generated by depositing a gaseous molecule, either CO or O 2, above an atom on the grain surface. The calculations show that the presence of the defects enhances the grain cohesion and favors adsorption. The conductance has a functional relationship with the structure and the defective state of the nanograins and its dependence on these quantities parallels the one of the binding energy.

Increase in Upturn Power Dissipation of Surge Suppressors Due to Highly Defective Nanostructure of Zinc Oxide

Nanodefects are probable root causes for the observed high power dissipation of ZnO‐based surge suppression devices (SSDs). In this work, nanodefects are introduced by overgrinding ZnO for 100 hours via wet milling. Using FESEM, ZnO nanostructures are found to contain fine cracks, chipped‐off surfaces and nanofragments. For the defective ZnO, the zinc relative atomic % (EDS analysis) is observed to be much larger accompanied by higher oxygen vacancy concentration as revealed by PL green emission. Average particle size drops from 0.24 µm to 0.19 µm and specific surface area increases from 4.72 m2/g to 5.67 m2/g. Fabricated SSDs with defective ZnO exhibits higher power dissipation and bigger grain resistivity. A model is proposed to provide a correlation between nanodefects and power dissipation.

Defects in nanocrystalline SnO $\mathsf{_{2}}$ studied by Tight Binding

In this work we present a study of the properties of defective nanostructures. The material chosen to this purpose, i.e. SnO2, has practical applications and many of them rely on the spontaneous formation of vacancies. Therefore, crystalline grains with shape and size comparable to the experimental ones have been considered. According to the bulk properties, the grains lattice has the rutile structure and may also include vacancy defects. The calculations describe the effects of the structural grain parameters, i.e. size and shape, as well as of the defect type, on the grain cohesion and are based on a Tight Binding method. The comparison with Density Functional calculations, also carried out in the course of this study, illustrates the limits of both methods when used for these complex structures.