The authors report on the generation of localized defects on single-walled carbon nanotubes by means of a hydrogen electron cyclotron resonance plasma. The defects have been investigated using scanning tunneling microscopy (STM) and show an apparent topographic height in the STM of 1–3 ... (Read more)

We present a combined experimental and computational study of the (110) cross-sectional surface of Mn δ-doped GaAs samples. We focus our study on three different selected Mn defect configurations not previously studied in detail, namely surface interstitial Mn, isolated and in pairs, and... (Read more)

Recent work has suggested that prior determinations of diffusion mechanism and point defect thermodynamics in silicon have been affected by nonequilibrium effects stemming from uncontrolled adsorption-induced suppression of a pathway for defect creation at the surface. Through silicon self-diffusion... (Read more)

We use ab initio methods to calculate the magnetic properties of vacancies in a graphitic boron nitride sheet (g-BN). By applying a full spin-polarized description to the system, we demonstrate that the nitrogen vacancy (V_N) or the boron vacancy (V_B)... (Read more)

Understanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first-principles molecular dynamics, we perform a systematic study of the nonequilibrium processes of radiation damage in... (Read more)

The rearrangement of silicon dangling bonds induced by pulsed laser heating of monohydride-covered Si(001) surfaces has been studied by means of scanning tunneling microscopy (STM). The initial configurations, which were created by laser-induced thermal desorption, consist of isolated pairs of... (Read more)

The effect of HF etching of the silicon oxide shell covering the surface of Si nanocrystals (NCs) on the subsequent room-temperature atmospheric oxidation of Si-NCs has been investigated by means of photoluminescence measurements, Fourier transform infrared spectroscopy, and electron paramagnetic... (Read more)

In this paper we describe the use of electron backscatter diffraction (EBSD) mapping and electron channeling contrast imaging—in the scanning electron microscope—to study tilt, atomic steps and dislocations in epitaxial GaN thin films. We show results from a series of GaN thin films of... (Read more)

Detailed studies of mechanisms for hydrogen dissociative adsorption and diffusion on pure and nitrogen-doped (8, 0) carbon nanotubes are carried out using the first-principles density functional theory method. (1) For pure carbon nanotubes, we have identified the energetically most favorable... (Read more)

In a recent experiment, Derycke et al. have made the exciting observation that H₂ molecules readily adsorb dissociatively on the c(4×2) but not on the 3×2 surface of SiC(001) at room temperature. To unravel this spectacular reactivity difference, we have investigated a... (Read more)

We have studied the structure and spectroscopic properties of the paramagnetic nonbridging oxygen hole center and of the Egamma^[prime]" align="middle"> center at the hydroxylated silica surfaces using density functional theory and an embedded-cluster model. To investigate the... (Read more)

Plastic relaxation of carbon nanotubes under tension and at high temperature is described in terms of dislocation theory and with atomistic computer simulations. It is shown how the glide of pentagon-heptagon defects and a particular type of their pseudoclimb, with the atoms directly breaking out of... (Read more)

The doping characteristics and carrier transport in a GaAs p-n junction were visualized with a ~10 nm spatial resolution, using light-modulated scanning tunneling spectroscopy. The dynamics of minority carriers under operating conditions, such as recombination, diffusion, and electric... (Read more)

We report an ab initio study of the electronic properties of surface dangling-bond (SDB) states in hydrogen-terminated Si and Ge nanowires with diameters between 1 and 2 nm, Ge/Si nanowire heterostructures, and Si and Ge (111) surfaces. We find that the charge transition levels ε(+/-)... (Read more)

A random telegraph signal appears at a smaller absolute gate bias for a larger absolute drain-source bias in a carbon nanotube transistor. Its mechanism is attributed to a defect located in the drain side of the Schottky barrier carbon nanotube transistor with Ti/Au as contact material. Furthermore,... (Read more)

In this work, we present a detailed cathodoluminescence characterization of GaInNAs quantum wells grown on GaAs(111)B. As-grown and annealed InGaAs and GaInNAs quantum wells were maeasured and compared by spatially resolved cathodoluminescence at different photon energies. In the case of... (Read more)

By direct observation using ultrahigh vacuum conducting atomic force microscopy, it is found that a local leakage path in HfO₂/GeO_x stacks created by an electrical stress with a positive tip bias annihilates after applying a reverse tip bias. The creation and... (Read more)

Crystal qualities of Si/SiGe/Si-on-insulator structures with different SiGe thicknesses were evaluated by photoluminescence (PL). The wafers were annealed at different temperatures with a ramping rate of 5 °C/min. Free exciton PL peaks were clearly observed for the as-grown wafers and decreased... (Read more)

Hydrogenated amorphous silicon carbide (a-SiC:H) films have been deposited using magnetron sputtering technique. An integrated investigation of the effect of vacuum annealing temperature on photoluminescence properties and paramagnetic defects and its correlation with structural... (Read more)

Systematic slow positron implantation spectroscopy (SPIS) and atomic force microscopy studies of various 6H-SiC samples are presented to clarify the role of conductivity type, crystal quality, ion implantation (B⁺,Al⁺, and N⁺), and annealing (1.650 °C) in... (Read more)

The discovery of ferromagnetism in Mn-doped GaAs1 has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices2, 3, 4. A major hurdle for realistic applications of Ga_1-XMn_XAs, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized5. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn–Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga_1-XMn_XAs structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples. (Read more)

The dynamics of multivacancy defects in a graphene layer is investigated by tight-binding molecular dynamics simulations and by first principles calculation. The simulations show that four single vacancies in the graphene layer first coalesce into two double vacancies, each consisting of a... (Read more)

Progressive implantation of hydrogen atoms into graphite is modeled by first-principles density functional theory. The maximum H/C ratio was found at 53%, which is in good agreement with experimental results. The hydrogen trapping energy varies from −0.7 eV at very low concentrations to a... (Read more)

In the same way that gases react with surfaces from above, solid-state point defects such as interstitial atoms can react from below. Little attention has been paid to this form of surface chemistry. Recent bulk self-diffusion measurements near the Si(100) surface have quantified Si interstitial... (Read more)

We present a detailed analysis of the fundamental atomic-scale processes that determine the surface smoothness of hydrogenated amorphous silicon (a-Si:H) thin films. The analysis is based on a synergistic combination of molecular-dynamics (MD) simulations of radical precursor migration on surfaces... (Read more)

NaAlH₄ and LiBH₄ are potential candidate materials for mobile hydrogen storage applications, yet they have the drawback of being highly stable and desorbing hydrogen only at elevated temperatures. In this letter, ab initio density functional theory calculations reveal... (Read more)

Adsorption of gold atoms and clusters (N=6) on a graphite (0001) surface with defects has been studied using density functional theory. In addition to perfect graphite (0001), three types of surface defects have been considered: a surface vacancy (hole), a pyridinelike defect comprising three... (Read more)

Two-dimensional electron systems fabricated from a single layer of P-donors have been lithographically confined to nanometer scale in lateral directions. The electronic transport of such quasi-one-dimensional systems with and without a perpendicular magnetic field was characterized at cryogenic... (Read more)

Hydrogen reactions with silicon substrates is an established technique for the study and control of surface morphology. Here, we report the results of first-principles calculations on the trapping and depassivation reactions involving excess hydrogen (x-H) at a fully H-passivated Si(111) surface. We find that x-H atoms can depassivate Si-H bonds with a small barrier of 0.8 eV, or they can get trapped in very stable configurations that comprise of a dihydride and a vicinal Si-H bond. Desorption of H₂ molecules from these complexes has an activation energy of 1.68 eV, which can account for pertinent experimental data. We discuss also the effect of strain on the possibility of altering the x-H surface profile. (Read more)

The basic properties of point defects, such as local geometries, positions of charge-transfer levels, and formation energies, have been calculated using density-functional theory, both in the bulk and on the (110) surface of InP, InAs, and InSb. Based on these results we discuss the electronic... (Read more)

An entire family of nano-scale trenches, ridges, and steps has been observed experimentally on AsH₃-exposed Si(100). Some of these line structures have been observed previously, but their structures have remained a mystery. Theoretical modeling shows that they are all based upon the same... (Read more)

Based on first-principles calculations, we studied the generation behavior of P_b centers at SiO₂/Si interfaces, especially for P_b1 centers, under oxidation of Si(100) surfaces. P_b1 centers were found to be formed... (Read more)

We propose a new method for calculating optical defect levels and thermodynamic charge-transition levels of point defects in semiconductors, which includes quasiparticle corrections to the Kohn-Sham eigenvalues of density-functional theory. Its applicability is demonstrated for anion vacancies at... (Read more)

It has been experimentally observed that a bridging oxygen vacancy on the rutile TiO₂(110) surface introduces localized Ti³⁺ 3d¹ states about 1 eV below the conduction band which are not removed upon dissociation of a water molecule and formation of a pair of... (Read more)

By analyzing atomic force microscopy images, we derive a continuum equation that quantitatively explains the roughening at the Si(001)-SiO₂ interface during thermal oxidation at the temperature at 1200 °C in an Ar atmosphere containing a small fraction of O₂. We also show... (Read more)

The structures of comet defects in a 4H–SiC homoepitaxially grown film are investigated by deep-ultraviolet micro-Raman spectroscopy. Spatial distribution of the 4H- and 3C–SiC is clearly distinguished both from the intensities of the folded longitudinal acoustic phonon mode and the peak... (Read more)

We investigate the Si-rich 3×3 to Si-terminated × phase transition of the 6H-SiC(0001) surface by atom-resolved scanning tunneling microscopy. We find a 2×2-R30° reconstruction, coexisting with few 3×3 domains. While a high-quality 3×3 surface preparation is... (Read more)

Anodic etching of SiC yields a highly monodisperse distribution of nanometer dimension porous structures which extend to a significant depth. Cathodoluminescence (CL) studies of the porous layers yield luminescence peaks in the UV region, above the band gap energy of bulk SiC. Higher etching current... (Read more)

We report the formation processes of interface dangling bonds (P_b centers) during initial oxidation of a clean Si(111) surface using an ultrahigh-vacuum electron-spin-resonance technique. At the oxidation of one or two Si layer(s), the P_b center... (Read more)

Dry oxidation kinetics of the Si(001) surface has been investigated using reflectance difference oscillation to resolve atomic-scale phenomena. The activation energy for oxidation has been found to increase as the oxide-Si interface moves in the depth direction, reaching the value for bulk... (Read more)

We present first-principle calculations on the initial stages of SiC homoepitaxial growth on the –SiC(111)–(×) surface. We show that the nonstoichiometric reconstruction plays a relevant role in favoring the attainment of high-quality films. The motivation is twofold: On one hand, we... (Read more)

Some paramagnetic superoxide ions detectable by electron paramagnetic resonance (EPR) can be generated on Au/ZnO catalyst by oxygen adsorption at room temperature as well as at 553 K. In both the cases, the O2− ions are present on the catalyst surface. The disappearance of the O2−... (Read more)

We prepared ZnO ultrafine particles (UFPs) by thermal decomposition of the precursor zinc carbonate hydroxide. The surface properties of the as-prepared particles were studied using TEM, XRD, BET, SPS, EPR, IR, and XPS. The surface contains active species such as oxygen deficiencies and hydroxyl... (Read more)

The interaction of atomic hydrogen with a-Si:H films was studied by means of in situ ESR during H plasma treatment. H diffuses into the a-Si:H film and creates additional Si dangling bonds (∼10¹³ cm ^-2). We observed a high diffusion coefficient (>10^-10  cm... (Read more)

The mixed MoO3–ZnO catalyst was expected to reveal the new function as a catalyst. The catalyst was characterized by XRD, ESR, XANES and so on. We found that the MoO3–ZnO catalyst was effective for isomerization and metathesis of 1-butene. The defects with the anion vacancy were formed... (Read more)

The method of doping trivalent metal ions into a copper-based catalyst for methanol synthesis is effective in modifying the surface structure of the catalyst. The promotion effect and its relation to catalytic activity for hydrogenation of CO to methanol after doping with trivalent metal ions such... (Read more)

The spectroscopic properties, structure and interconversions of optically active oxygen-deficiency-related point defects in vitreous silica are reviewed. These defects, the E′-centers (oxygen vacancies with a trapped hole or 3-fold-coordinated silicons), different variants of diamagnetic... (Read more)

The preparation of ZnO microcrystallites using a microemulsion method and their electron spin resonance (ESR) properties are reported for the first time. It was found that the ZnO microcrystallite exhibits an ESR signal at room temperature, in contrast to that of bulk ZnO. The results confirmed that... (Read more)

In situ electron-spin-resonance (ESR) measurements of film growth of hydrogenated amorphous silicon (a-Si:H) using a remote hydrogen plasma technique have been performed. The Si dangling-bond signal in a-Si:H during and after deposition has been detected, in addition to the... (Read more)

Microwave-Hall-effect (MHE) and electrical conductivity measurement techniques can now be used to obtain absolute values of the electrical properties of semiconductor powders under different controlled conditions. A commercial ESR spectrometer was modified to conduct MHE experiments and a network... (Read more)

A detailed atomistic understanding of charge transfer reactions between semiconductor surfaces and adsorbing particles is essential for designing gas sensors or metal-oxide catalysts.This will be demonstrated in a discussion of thermodynamically or kinetically controlled solid/gas interactions at... (Read more)

Investigations are reported on the reaction of oxygen with electrostatic neutral ZnO–100-surfaces studied by means of AES, LEED, EPR, thermal desorption spectroscopy, and isotopic exchange as well as changes in the surface conductivity and work function. Geometric and electronic structures of... (Read more)

The activities and ESR spectra of zinc oxide catalysts for hydrogenation of ethylene at 150 °C have been studied. No catalytic activity was observed for silica- or alumina-supported ZnO at surface coverages below 2–3 nominal monolayers. The ESR signal at g = 1.958 from the zinc oxide was... (Read more)

Photoinduced O^– ions or V-type centers have been detected in ZnO following ultraviolet irradiation at –196°C. The EPR spectrum of the ions is characterized by g=2.021 and g = 2.0026. The concentration of O^– was greatly... (Read more)

The method was applied to the investigation of adsorption of oxygen on the transition metal oxides MnO, FeO, CoO, Cu2O, and their solid solutions in the diamagnetic matrices ZnO and MgO. It has been found that in the case of pure oxides and their solid solutions at high magnetic metal ion... (Read more)

A brief description of the dc and rf diode sputtering unit is first presented. The study of properties of the films is reviewed taking into consideration two main parameters, oxygen partial pressure and substrate temperature. Reflection electron diffraction and x-ray diffraction studies show that... (Read more)

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The effect of the electron transfer process between the bulk and surface of ZnO upon oxygen sorption was investigated by measuring the changes of the following ESR parameters: the spin densities of the g = 1.96 and g ~ 2.0 signals, the intensity of a Mn2+ reference sample, and the crystal current of... (Read more)

An electron spin resonance study of the surface interaction of zinc oxide with oxygen, oxides of nitrogen (NO2, NO and N2O) and chlorine was made. Characteristic spectra obtained following adsorption of NO2 and NO were analyzed and attributed to rigidly adsorbed neutral molecules. Confirmation of... (Read more)

An ESR study of the interaction of nitrobenzene with nonstoichiometric ZnO surfaces was made. A 3-line spectrum with g values 1.9840, 2.0055 and 2.0225 was observed and was identified as due to nitrobenzene anion radicals strongly held to the surface. An unidentified signal at g = 2.0050 was left... (Read more)

The effects of the conditions of preparation of ZnO---Cr2O3 catalysts on their ESR spectra have been investigated by means of a Q-band spectrometer. The linewidths of oxides prepared by a low-temperature decomposition of the respective hydroxides in nitrogen flow are large and exhibit concentration... (Read more)

EPR measurements have been made on aligned cleavage faces of Si, prepared and studied in high vacuum (<10^-9 Torr). The signal, observable after accumulation, is a single line at g=2.0055 with width 6 G, similar to that from vacuum-crushed powders. It is unaffected by oxygen exposures... (Read more)

An approach is described for investigating the nature of sorbed oxygen species on a semiconductor catalyst surface and for determining their relative reactivities in a heterogeneous oxidation reaction. Experimental information as to the types of oxygen species on ZnO with presorbed oxygen, ZnO... (Read more)

ESR measurements were combined with determinations of the amount of oxygen adsorbed or desorbed on ZnO in order to investigate the relationship between the solid state electronic properties of a semiconductor catalyst and the amounts and the nature of the adsorbed oxygen species. (Read more)