Defects In Nanostructures Research Articles

Influence of the precursor anion on the photoluminescence properties of ZnO.

ZnO nanorod arrays were synthesized by hydrothermal method with two different zinc salts as precursors: zinc acetate and zinc nitrate. Different anions in solution distinctly influence the intrinsic defects in ZnO nanostructures, resulting in different photoluminescence properties. The defects induced by precursors were systematically studied by photoluminescence spectroscopy, X-ray photoelectron spectrometer and electron paramagnetic resonance. The results show that zinc acetate precursor mainly introduces zinc vacancy to the lattice while ZnO nanorods obtained from zinc nitrate contain more interstitial oxygen.

Pt Nanoparticle Sintering and Redispersion on a Heterogeneous Nanostructured Support

Understanding how nanostructure and atomic-scale defects of the support affect metal catalyst nanoparticle sintering is of crucial importance to minimize thermal deactivation, as well as to understand the origin of widely observed but still unexplained phenomena, such as transient multimodal particle size distributions and nanoparticle redispersion. To shed light on these issues, we present a generic experimental approach that relies on nanofabrication to introduce controlled structural heterogeneity in a chemically homogeneous model catalyst support. This is achieved by fabricating arrays of nanocone structures separated by flat areas, where both are homogeneously sputter-coated with a thin amorphous alumina layer. Using ex situ aberration-corrected scanning transmission electron microscopy (STEM) to analyze Pt model catalyst nanoparticles on such nanostructured supports prior and after exposure to 4% O2 in Ar carrier gas at 600 °C, we find that the initial particle size distributions and their time evol...

Domain morphology, boundaries, and topological defects in biophotonic gyroid nanostructures of butterfly wing scales.

Many organisms in nature have evolved sophisticated cellular mechanisms to produce photonic nanostructures and, in recent years, diverse crystalline symmetries have been identified and related to macroscopic optical properties. However, because we know little about the distributions of domain sizes, the orientations of photonic crystals, and the nature of defects in these structures, we are unable to make the connection between the nanostructure and its development and functionality. We report on nondestructive studies of the morphology of chitinous photonic crystals in butterfly wing scales. Using spatially and angularly resolved x-ray diffraction, we find that the domains are highly oriented with respect to the whole scale, indicating growth from scale boundaries. X-ray coherent diffractive imaging reveals two types of crystalline domain interfaces: abrupt changes between domains emerging from distinct nucleation sites and smooth transitions with edge dislocations presumably resulting from internal stresses during nanostructure development. Our study of the scale structure reveals new aspects of photonic crystal growth in butterfly wings and shows their similarity to block copolymer materials. It opens new avenues to exploration of fundamental processes underlying the growth of biological photonic nanostructures in a variety of species.

Photoactivation of Luminescent Centers in Single SiO2 Nanoparticles

Photobleaching of fluorophores is one of the key problems in fluorescence microscopy. Overcoming the limitation of the maximum number of photons, which can be detected from a single emitter, would allow one to enhance the signal-to-noise ratio and thus the temporal and spatial resolution in fluorescence imaging. It would be a breakthrough for many applications of fluorescence spectroscopy, which are unachievable up to now. So far, the only approach for diminishing the effect of photobleaching has been to enhance the photostability of an emitter. Here, we present a fundamentally new solution for increasing the number of photons emitted by a fluorophore. We show that, by exposing a single SiO2 nanoparticle to UV illumination, one can create new luminescent centers within this particle. By analogy with nanodiamonds, SiO2 nanoparticles can possess luminescent defects in their regular SiO2 structure. However, due to the much weaker chemical bonds, it is possible to generate new defects in SiO2 nanostructures using UV light. This allows for the reactivation of the nanoparticle's fluorescence after its photobleaching.

Engineering Single Defects in Silicon Carbide Bulk, Nanostructures and Devices

We will review recent demonstrations of single photon emission in different silicon carbide (SiC) polytypes, in both bulk and nano-structured form. Due to well established doping, and micro- and nanofabrication procedures deep defects photoluminescence (PL) can be electrically excited and incorporated in SiC nanomaterials. Finally we will report on preliminary results to incorporate near infrared defects in SiC nanoparticles.

Line defects in boron nitride nanostructures: A first-principles study

Abstract Using first-principles calculations we have explored the structural reconstruction of a special type of line defect (LD), formed as the result of a defective growth of a given monolayer (ML) or nanoribbon (NR). More specifically, we have studied the presence of tetragonal rings at boron nitride monolayers (BNMLs) and zigzag boron nitride nanoribbons (ZBNNRs). Different reconstruction processes are observed forming different types of LD depending on the nature of the atoms into the grain boundary between two BN domains as well as the structures type. The structural, magnetic, energetic, and electronic properties of the reconstructed BNMLs and ZBNNRs are calculated. These structures show a wide range of electronic structures going from semiconducting to semimetallic and metallic.

Tuning the work function of randomly oriented ZnO nanostructures by capping with faceted Au nanostructure and oxygen defects: enhanced field emission experiments and DFT studies

The lowering of the work function (Φ) can lead to a better field emission (FE) behavior at lower threshold fields. We report on enhanced FE from randomly oriented and faceted Au-capped ZnO hetero-nanostructures (HNs) having more oxygen defects. Large-area arrays of non-aligned, faceted Au-capped ZnO HNs, such as nanowires (NWs) and triangular nanoflakes (TNFs) are grown using the chemical vapor deposition (CVD) method. Enhanced FE properties from the TNF sample resulted in a turn-on field as low as 0.52 V μm−1 at a current density of 0.1 mA cm−2 and a field enhancement factor (β) as high as ≈5.16 × 105. Under similar experimental conditions, drawing the same current density from an NW specimen needs a higher turn-on field (0.86 V μm−1) and to exhibit nearly four times less field enhancement factor compared to the TNFs samples. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) measurements confirm the presence of more oxygen defects in the TNF samples compared to the NW samples. Kelvin probe force microscopy (KPFM) measurements show the average local work function to be 4.70 ± 0.1 eV for the TNF sample, which is ≈ 0.34 eV lower than the NW sample. Using density functional theory (DFT) calculations, the estimated Φ values are found to be 4.98 eV for ZnO(0001), 4.17 eV for Au(001)/ZnO(0001) and 3.91 eV for Au(001)/Ovac-ZnO(0001) surfaces. The DFT results are qualitatively in agreement with our experimental results. The presence of Au nanostructures on top of O-deficient and sharp-tipped TNFs results in enhanced FE performance following their reduced tunneling barrier via pinning of effective Φ.

Local defects in the nanostructure of the membrane of erythrocytes upon ionizing radiation of blood

The purpose of the study is to investigate local topological defects in the erythrocyte membranes resulting from the ultraviolet (UV) radiation of blood in vitro. Biological effects in the erythrocytes after exposure to UV radiation at a wavelength of 254 nm are equivalent to those after γ radiation. It has been shown that oxidative processes developing in a suspension upon UV radiation result in the disruption of the nanostructure of the membranes of erythrocytes. In the experiments, typical topological defects in the membrane nanostructure were observed. The parameters of the defects differed from the characteristics of the nanostructure of the control cell membrane without irradiation. The characteristic dimensions of the topological defects are commensurate with the size of the spectrin matrix. As a result of the exposure to the UV radiation, polymorphism of the erythrocytes was observed.

Characterizing nanotube–polymer interaction using molecular dynamics simulation

Theoretical characterization of the interaction between Carbon nanotube (CNT) and surrounding polymer is presented in this article using molecular dynamics simulation. Firstly, isolated non-defected and defected CNTs are simulated. The reduction level in Young’s modulus of CNT is analyzed due to the induced vacancy defects in CNT nanostructure. Then, embedded CNT in polymer is simulated focusing on the CNT and polymer interaction. The effect of chemical functionalization on mechanical properties of nanocomposites is discussed at micro level. Stochastic analysis is conducted treating numbers of established covalent bonds between CNT and polymer and their positions as random parameters. Young’s modulus of the interphase region as an intermediate phase between CNT and polymer for continuum modeling is extracted. It is revealed that increasing numbers of transverse covalent bonds between CNT and polymer, Young’s modulus of the nanocomposites decreases arisen from induced vacancy defects in CNT. Although functionalization can improve the interfacial shear strength between CNT and polymer, it has a disadvantage in reducing Young’s modulus of the interphase region leading to weak stress transferring from resin to CNT.

Lifetimes of photogenerated electrons on a GaAs surface affected by nanostructural defects

The recombination dynamics of photogenerated carriers on temporal and spatial scales of 100 fs and 100 nm, respectively, on an inhomogeneous GaAs surface with structural defects was investigated using time-resolved photoemission electron microscopy with femtosecond laser pulses. The observed photocarrier lifetimes (τ) ranged from subpicoseconds to picoseconds at isolated structural defects and were inversely proportional to the photoemission intensity at each defect. We concluded that τ corresponds to the carrier trapping time to midgap defect states and estimated the density of the midgap states at each defect on the basis of the relation between τ and the photoemission intensity.

The pronounced role of impurity phases in the optical properties of Mn catalyzed ZnS nanostructures

We report the effect of Mn self-doping in Mn catalyzed ZnS nanostructures grown via vapor liquid solid mechanism, which also resulted in the formation of additional impurity minority phases like ZnO and MnO2. The synthesized ZnS nanostructures were subsequently annealed in the range of 500 °C – 700 °C in an inert environment to remove impurity phases and enhance the incorporation of dopant. Room temperature photoluminescence showed strong defect assisted luminescence. It was observed that green emission due to intrinsic defects of ZnS nanostructures was reduced in magnitude and Mn related orange/red luminescence increased in magnitude in nanostructures annealed at high temperature. The presence of impurity phases led to the observation of surface optical and interface phonon modes as observed in the Raman spectroscopy. Dielectric continuum and phonon confinement models were employed to determine the correlation lengths of the optical phonon modes.

Intrinsic defect formation in peptide self-assembly

In contrast to extensively studied defects in traditional materials, we report here a systematic investigation of the formation mechanism of intrinsic defects in self-assembled peptide nanostructures. The Monte Carlo simulations with our simplified dynamic hierarchical model revealed that the symmetry breaking of layer bending mode at the two ends during morphological transformation is responsible for intrinsic defect formation, whose microscopic origin is the mismatch between layer stacking along the side-chain direction and layer growth along the hydrogen bond direction. Moreover, defect formation does not affect the chirality of the self-assembled structure, which is determined by the initial steps of the peptide self-assembly process.

Characteristic investigation of scanning surface plasmon microscopy for nucleotide functionalized nanoarray.

A calculation based on surface plasmon coupling condition and Maxwell-Garnett equation was performed for predicting the coupling angle shift and thin film thickness in scanning surface plasmon microscopy (SSPM). The refractive index sensitivity and lateral resolution of an SSPM system was also investigated. The limit of detection of angle shift was 0.01°, the limit of quantification of angle shift was 0.03°, and the sensitivity was around 0.12° shift per nm ZnO film when the film thickness was less than 22.6 nm. Two partially connected Au nano-discs with a center-to-center distance of 1.1 μm could be identified as two peaks. The system was applied to image nanostructure defects and a virus-probe functionalized nanoarray. We expect the potential application in nanobiosensors with further optimization in the future.

Nanostructural Defects and Critical Current Densities in High-Quality <inline-formula> <tex-math notation="TeX">$\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{CaCu}_{2}\hbox{O}_{8+{\rm X}} $</tex-math></inline-formula> Epitaxial Thin Films Prepared by MOCVD

Nanostructural defects were investigated by transmission electron microscopy in c-axis-oriented epitaxial Bi 2 Sr 2 CaCu 2 O 8+X (Bi2212) thin films with high T c (R = 0) ≥ 83 K and high transport critical current density ofJ c >10 10 A/m 2 at 10 K. We observed misfit dislocations at twin boundaries, dislocations associated with stacking faults parallel to the a-b plane, and antiphase boundaries. We compared the magnetic-field dependent J c values at various temperatures in two Bi2212 films. About 110-nm-thick film A showed lower J c than ~280-nm-thick film B at low temperatures (≤ 20 K) or in low magnetic fields (≤ 0.1 T). However, the J c of film B decreased more rapidly in high magnetic fields, leading to a crossover of the two J c -B curves at temperatures of 30 K and above. This is probably because film B contained a higher density of antiphase boundaries, which caused stronger pinning and higher J c values at low temperatures but may have caused enhanced thermally activated motion of pancake vortices that eventually resulted in lower Jc values in high magnetic fields at moderate temperatures.

The effect of point defects and nanoparticles on thermal conductivity of magnesium silicide

We compute thermal conductivity (κ) of magnesium silicide (Mg2Si) with point defects and nanoparticles through molecular dynamics simulation. To describe an alloy with complex defect structures, the extended modified embedded atom method is utilized in this simulation study. The calculated phonon dispersion and κ of pristine Mg2Si are in close agreement with first-principles calculations and experimental results. We compared the effect of intrinsic point defects and nanoparticles on heat transfer in Mg2Si at the same stoichiometry. We find that point defects could be more effective than nanoparticles to reduce κ. The geometric size effect is also investigated for Mg and Si nanoparticles. Smaller Mg nanoparticles can significantly reduce κ. However, Si nanoparticles demonstrate little size effect on κ. Our simulation results show that phonon transport in Mg2Si has more contribution from strain scattering than mass defect scattering. These findings can provide guidance for experiments to more effectively engineer bulk Mg2Si with nanostructured defects for thermoelectric applications.

Microscopic Damage of Tungsten and Molybdenum Exposed to Low-Energy Helium Ions**supported by the National Magnetic Confinement Fusion Program of China (No. 2011GB108011), National Natural Science Foundation of China (No. 11405023) and the Scientific Research Fund of Liaoning Provincial Education Department (No. L2014539) and the Fundamental Research Funds for the Central Universities of China (No. DC201502080410)

Polycrystalline tungsten (W) and molybdenum (Mo) materials both non-annealed and annealed at temperatures of 800-1750°C have been irradiated with low-energy (220 eV), high-flux (∼1021 ions/m2 ·s) He+ at an irradiation temperature of 600°C and at a dose of 1.0×1025 ions/m2. This non-destructive conductive atomic force microscopy technique provides direct observation and comparison of surface swellings with growth of nanoscale defects in the irradiated materials. A coral-like surface structure and nanostructured defects were formed in W when irradiated at a He+ dose of 1.0×1025 ions/m2. Increasing the annealing temperature resulted in an increase in the size of nanostructured defects and serious surface damage of W. Compared to W, Mo suffered much less surface damage after being irradiated at various He+ doses.

Enhanced charge recombination due to surfaces and twin defects in GaAs nanostructures

Power conversion efficiency of gallium arsenide (GaAs) nanowire (NW) solar cells is severely limited by enhanced charge recombination (CR) at sidewall surfaces, but its atomistic mechanisms are not well understood. In addition, GaAs NWs usually contain a high density of twin defects that form a twin superlattice, but its effects on CR dynamics are largely unknown. Here, quantum molecular dynamics (QMD) simulations reveal the existence of an intrinsic type-II heterostructure at the (110) GaAs surface. Nonadiabatic quantum molecular dynamics (NAQMD) simulations show that the resulting staggered band alignment causes a photoexcited electron in the bulk to rapidly transfer to the surface. We have found orders-of-magnitude enhancement of the CR rate at the surface compared with the bulk value. Furthermore, QMD and NAQMD simulations show unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective CR centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying CR processes.

Defect‐induced effects in nanomaterials

Abstract“Crystals are like people, it is the defects in them which tend to make them interesting!” said Cambridge Professor Sir Colin Humphrey once upon a time. Today, this statement still rings true. Defects govern the properties of nanostructures to the same or even to a greater extent as they do in bulk solids. Any surface or interface is already a perturbation of an ideal solid, and the role of interfaces increases with decreasing dimensionality of objects. However, the research field of defects in nanostructures extends much farther, encompassing doping, diffusion, radiation effects, phase transitions – virtually all fields of solid‐state science and technology. A burst of research activity in two‐dimensional materials has been brought about by the isolation of graphene from bulk graphite in 2004 by Geim and Novoselov (Nobel prize in Physics 2010). The invention of efficient blue light‐emitting diodes crowned with the very recent Nobel prize in Physics awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura goes hand‐in‐hand with the defect engineering in semiconductors.The first EMRS symposium on defects in nanomaterials was held during the 2012 Fall meeting in Warsaw, and the success of the event was a motivation to organize a follow‐up symposium during the 2014 Spring Meeting in Lille. The Symposium E entitled “Defect‐induced effects in nanomaterials” attracted even more participants from all over the world, and this volume includes 36 papers based on presentations from the five days of oral and poster sessions, from May 26 to 30.The program of the symposium comprised 15 invited and 47 oral talks, as well as 98 poster presentations. The presenters came from 44 countries located on five continents: Africa, North and South America, Asia, Australia, and Europe. The following topics have been covered:– Swift heavy ion irradiation as the means to tailor nanomaterials;– Effects of grain boundaries and interfaces on diffusion and transport processes in nanomaterials;– Electronic structure of defects in nanostructures; consequences for carrier transport, magnetism, optical and electronic properties, as well as device parameters;– Creation, evolution and properties of radiation defects in nanosize materials and heterostructures; the role of interfaces, nonstoichiometry, strain and adjacent layers;– Defects in two‐dimensional materials;– Use of defects as microprobes;– Multiscale computer modeling of defect creation in nanomaterials;– Novel technological processes of micro‐, nano‐ and optoelectronics using defects and radiation effects in nanostructures.The latest achievements in theory and experiment as well as technological applications have been presented and discussed by academic and industrial researchers.We are deeply grateful to all participants who, through their valuable contributions, friendly and open discussions, turned the symposium into an exciting event. We also greatly acknowledge the financial and administrative support of the E‐MRS Headquarters which allowed the organization of the symposium. Last but not least, our thank goes to Wiley‐VCH that took over the publication of the symposium proceedings. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of in-plane and bridging oxygen vacancies of SnO2 nanostructures on CH4 sensing at low operating temperatures

Role of “O” defects in sensing pollutant with nanostructured SnO2 is not well understood, especially at low temperatures. SnO2 nanoparticles were grown by soft chemistry route followed by subsequent annealing treatment under specific conditions. Nanowires were grown by chemical vapor deposition technique. A systematic photoluminescence (PL) investigation of “O” defects in SnO2 nanostructures revealed a strong correlation between shallow donors created by the in-plane and the bridging “O” vacancies and gas sensing at low temperatures. These SnO2 nanostructures detected methane (CH4), a reducing and green house gas at a low temperature of 50 °C. Response of CH4 was found to be strongly dependent on surface defect in comparison to surface to volume ratio. Control over “O” vacancies during the synthesis of SnO2 nanomaterials, as supported by X-ray photoelectron spectroscopy and subsequent elucidation for low temperature sensing are demonstrated.

Substrate Effect on Growth Behaviour of Well-Aligned ZnO Nanorods Using an Aqueous Solution Method

The substrate effects on the morphology and photoluminescence (PL) properties of ZnO nanorods synthesized by a low temperature solution method has been investigated. ZnO seed layers on the substrates were prepared by radio-frequency sputtering. ZnO nanorods have been characterized by PL spectra and field emission scanning electron microscopy (FESEM). FESEM results showed that the nanorods grown on the polyethylene terephthalate (PET) substrate had the most uniform size and the highest coverage density compared with the Si and glass substrates. PL measurements showed that the ZnO nanorods grown on the Si substrate had the best performance that may be attributed to higher crystallization and the low density of defects in the ZnO nanostructures. These findings have shown that the morphology and PL of ZnO nanorods strongly depend on the substrate.