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The appropriate procedure for analyzing experimental data of defects in metals is discussed. The following two diverse procedures have been proposed earlier: either in terms of single vacancy formation with temperature dependent enthalpy and entropy, or by assuming coexistence of vacancies and divacancies with temperature-independent parameters. Using aspects of thermodynamics of the defect formation processes in solids, we show that the former procedure leads to self-consistent parameters.

We investigate the effect of vacancy defect reconstruction on electron transport properties in a (4, 0) zigzag and (5, 5) armchair silicon-carbide nanotubes (SiCNTs) by applying self consistent non-equilibrium Green's function formalism in combination with the density-functional theory to a two probe molecular junction constructed from SiCNTs. The geometry optimization results show that single vacancies and di-vacancies in SiCNTs have different reconstructions. A single vacancy when optimized, reconstructs into a 5-1DB configuration in both zigzag and armchair SiCNTs, and a di-vacancy reconstructs into a 5-8-5 configuration in zigzag and into a 5-2DB configuration in armchair SiCNTs. Analysis of frontier molecular orbitals (FMO) and transmission spectrum show that the vacancy defect increases the band gap of (4, 0) metallic SiCNT and decreases the band gap of (5, 5) semiconducting SiCNT. Bias voltage dependent current characteristic show reduction in overall current in metallic SiCNT and an increase in overall current in semiconducting SiCNT.

The defect centers in TlGaSSe single crystals have been investigated by performing thermoluminescence (TL) measurements with various heating rates between 0.5 K/s and 1.0 K/s in the temperature range of 10–180 K. The TL spectra, with peak maximum temperatures at 39 K and 131 K, revealed the existences of two defect levels. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of two defect centers. The experimental results also showed that the trapping process was dominated by second-order kinetics for the trap related with low temperature peak while the general order (mixed order) kinetics was dominant for the trap donated to high temperature peak. Furthermore, heating rate dependences and traps distributions were studied for two defect centers separately. Thermal quenching effect dominates the behavior of these defects as the heating rate is increased. Also, quasi-continuous distributions were established with the increase of the activation energies from 16 meV to 27 meV and from 97 meV to 146 meV for the traps associated with the peaks observed at low and high temperatures, respectively.

In this paper, α-Mn₂O₃ thin films were fabricated by plasma-assisted molecular beam epitaxy on SrTiO₃ and Nb:SrTiO₃, respectively. The grown samples showed room temperature ferromagnetism (RFM) properties. All the experimental results manifested that the RFM properties in undoped thin films were induced by oxygen vacancies formed during the growth process. Even more, the ferromagnetism of thin films grown on Nb:SrTiO₃ were enhanced, and these results confirmed the fact that oxygen vacancies induced ferromagnetism. That is to say, more oxygen vacancies result the more unpaired electrons induced prominent abnormal spin causing ferromagnetism.

Here, we investigate the following key prediction of a thermodynamical model that interrelates the defect parameters with the bulk elastic and expansivity data: for various defect processes in a given matrix material, a proportionality exists between defect entropies and enthalpies. The investigation is focused on BaF₂ for which ab initio calculations within density functional theory and the generalized-gradient approximation have been recently made as far as the formation and migration of intrinsic defects are concerned, as well as for the elastic constants. Four defect processes have been studied in BaF₂: anion Frenkel formation, fluorine vacancy migration, fluorine interstitial motion and electrical relaxation associated with a single tetravalent uranium. For these processes, the entropies and enthalpies vary by almost two orders of magnitude and reveal a proportionality between them. We find that this proportionality is solely governed by the bulk elasticity and expansivity data, which conforms to the aforementioned thermodynamical model.

We, at the ab initio level, simulated the rearrangement magnitudes of the adjacent neighboring ions, surrounding the (100) surface F-center in ABO₃ perovskite matrixes. They are noticeably greater than the respective ionic shift magnitudes of the adjacent neighboring ions surrounding the bulk F-center. In ABO₃ perovskites, the electron charge is noticeably better bounded on the inside of the bulk oxygen vacancy, as interior the respective (100) surface vacancy. The oxygen vacancy formation energy, located on the (100) surface of ABO₃ perovskites, as a rule, is smaller as in the bulk. This slight energy distinction encourages the oxygen vacancy segregation from the ABO₃ perovskite bulk to their (100) surfaces. The ABO₃ complex oxide (100) surface F-center generated defect levels are positioned nearer to the (100) surface CB bottom than the bulk F-center generated respective defect levels. In contrary, the BaF₂, SrF₂ and CaF₂, both, surface and bulk F-center charges are well localized inside the fluorine vacancy. The ionic rearrangement magnitudes of the adjacent neighboring ions, surrounding the surface and bulk F-centers in BaF₂, SrF₂ and CaF₂ matrixes, are much smaller regarding the respective situation in ABO₃ perovskites.

Nitrogen (N) is an important impurity in silicon (Si), which associates with impurities as well as with other defects to form defect complexes. The knowledge of the properties and behavior of defect structures containing carbon (C), N and oxygen (O) is important for the Si–based electronic technology. Here, we employ density functional theory (DFT) calculations to investigate the association of nitrogen with carbon and oxygen defects to form the C_iN and C_iNO_i defects. We provide evidence of the formation of these defects and additional details of their structure, their density of states (DOS) and Bader charges. Therefore, C_iN and C_iNO_i defects are now well characterized.

Nonpotential effects in nonlinear evolution of Marangoni convection patterns are investigated analytically and numerically. Three manifestations of nonpotential effects are considered: (i) spatial modulations of hexagonal patterns; (ii) interaction between a short-scale hexagonal pattern and a long-scale slow deformational (Goldstone) mode; (iii) generation of the mean flow by the free-surface deformation in a large-scale Marangoni convection with poorly conducting boundaries. Nonpotential effects are shown to cause various secondary instabilities leading to skewed hexagonal structures, coexisting u- and d-hexagons, oscillating hexagonal patterns, spatially irregular cellular patterns, etc.

Nonstoichiometry could cause many point defects and limit the application of KTP crystal. Nonstoichiometry in KTP and Nb:KTP crystals by high-temperature solution method were studied by laser-ablation inductively coupled plasma mass spectometry (LA-ICP-MS) and X-ray photoelectron spectroscopy (XPS). The formation of high potassium and Ti${}^{3+}$ centers in KTP and Nb:KTP crystals was analyzed. The effect of niobium on nonstoichiometry in Nb:KTP crystal was discussed. The results showed that high potassium, low phosphate, and low oxygen existed in KTP and Nb:KTP crystal samples. Low phosphate and low oxygen in crystal samples resulted from phosphate volatilization, which could be inhibited by the increase of niobium content. Meanwhile, Ti${}^{3+}$ centers in crystal samples were original and formed during crystal growth, and were generated with high potassium simultaneously.

In this paper we report on the preparation of nanobrushes of ZnO on quartz substrate by a direct atmosphere evaporation method using Zn metal flakes. Activated charcoal was used as a catalyst that facilitated the formation of nanobrushes in which the brush stem was about 15–20 μm in length and the bristles (100–200 nm thick) were made up of nanofibrous ZnO whose tips were 10–15 nm in width and were angled in some cases. These aligned nanobrushes can find potential applications as nanopower generators and high aspect ratio AFM probes by virtue of the piezoelectric property of ZnO. This technique is simple for realizing aligned ZnO nanobrushes with metallic Zn as the source material.

This research demonstrates the capability of controlled, focused ion beam (FIB)–assisted tailoring of morphologies in both multiwall carbon nanotubes (CNTs) and Y junction nonlinear CNT systems through defect engineering. We have shown that a 30 keV FIB Ga⁺ ion beam at low ion milling currents of 1 pA can be used to partially reduce the CNT diameter, to provide electrical conduction bottleneck morphologies for linear CNTs, and to introduce both additive and subractive defects at Y junction locations of Y-CNT samples. Our aim is for this work to provide motivation for additional research to determine the effects of ion-beam-induced changes in modulating the physical and chemical properties of nanotubes.

Nanocrystalline ZnO particles substituted with different concentrations (0–30%) of Mn were synthesized by using a modified ceramic route and characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction and energy dispersive X-ray analysis methods. Positron lifetime and coincidence Doppler broadening measurements were used as probes to identify the vacancy-type defects present in them and monitor the changes while doping. The predominant positron trapping center in the undoped ZnO is identified as the trivacancy-type cluster V_Zn+O+Zn, which is negatively charged, and it transformed to the neutral divacancy V_Zn+O on doping with Mn²⁺ ions. The intensity of the defect-specific positron lifetime component got reduced initially indicating partial occupancy of the vacancies by the doped cations but then recovered on further doping due to the additional Zn vacancies created as a result of the increasing strain introduced by the Mn ions of larger radius. The creation of a new phase ZnMn₂O₄ thereafter changed the course of variation of the annihilation parameters, as the positrons got increasingly trapped in the vacancies at the tetrahedral and octahedral sites of the spinel nanomanganite.

We report room temperature ferromagnetism (RTFM) in nanocrystalline Zn_1-xCu_xO(0.03 ≤ x ≤ 0.07) materials synthesized by autocombustion technique. The average particle sizes are in the range of 60 nm. The saturation magnetization and coercivity of 7% Cu-doped ZnO is enhanced significantly in comparison to 3% and 5% Cu-doped ZnO. There is not much variation in the optical band gap due to Cu doping, thus suggesting the uniform distribution of Cu in the ZnO matrix. Micro-Raman and photoluminescence analysis predict the presence of clusters of oxygen vacancies in Cu-doped system which improves with the increase in Cu concentration. This study provides further evidence that oxygen vacancies play an important role in the enhancement of room temperature ferromagnetic property in Cu-doped ZnO.

Spherical Bi₂S₃ nanoparticles (NPs) were prepared by a facile in situ thermal sulfuration method. Different Bi₂S₃ samples were obtained by controlling the sulfuration time. The products were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), Raman and Fourier-transform infrared (FT-IR) methods. The optical properties were examined by UV-visible-near-infrared (UV-Vis–NIR) and photoluminescence (PL) techniques. The results show that the phase of the products after sulfuration is pure and the spherical shape of Bi NPs has been successfully transmitted to Bi₂S₃ samples. The light absorption edges exhibit red shift to 1060 nm while the light emission displays blue shift to 868 nm, compared with the energy bandgap of bulk Bi₂S₃. The reason for the special optical properties of Bi₂S₃ NPs by this in situ sulfuration route is considered to associate with the defects and quantum size effect of NPs.

Molecular dynamics (MD) is a technique of atomistic simulation which has facilitated scientific discovery of interactions among particles since its advent in the late 1950s. Its merit lies in incorporating statistical mechanics to allow for examination of varying atomic configurations at finite temperatures. Its contributions to materials science from modeling pure metal properties to designing nanowires is also remarkable. This review paper focuses on the progress of MD in understanding the behavior of iron — in pure metal form, in alloys, and in composite nanomaterials. It also discusses the interatomic potentials and the integration algorithms used for simulating iron in the literature. Furthermore, it reveals the current progress of MD in simulating iron by exhibiting some results in the literature. Finally, the review paper briefly mentions the development of the hardware and software tools for such large-scale computations.

A novel lead zinc titanate tungsten oxide (PbZn${}_{1∕3}$Ti${}_{1∕3}$W${}_{1∕3}$O${}_3)$ single perovskite was synthesized employing a cost-effective solid-state reaction technique. A phase transition occurs from tetragonal (P4mm) to monoclinic (C2/m) after substituting zinc (Zn) and tungsten (W) into the B-site of the pure lead titanate. The average crystallite size and micro-lattice strain are 66.2nm and 0.159%, respectively, calculated by the Williamson–Hall method. The grains are uniformly distributed through well-defined grain boundaries and the average grain size is about 17.8$\mu$m analyzed from the SEM micrograph. Raman spectrum suggests the presence of all constituent elements in the sample. The UV–Visible study suggests that the sample is suitable for photovoltaic applications because of high bandgap energy $E_g=4.17$eV. The dielectric study confirms the negative temperature coefficient resistance (NTCR) behavior of the sample. The activation energy increases from 13.9meV to 142meV with a rise of temperature suggesting that ac conductivity is thermally activated. The thermally activated relaxation process was managed by immobile charge carriers at low temperatures while defects and oxygen vacancies at higher temperatures. The presence of the asymmetrical curves in modulus plots confirms the non-Debye-type behavior. Both Nyquist and Cole–Cole semi-circular arcs confirm the semiconductor nature of the sample.