Types Of Structural Defects Research Articles

Suppressing Twin Formation in Bi2Se3 Thin Films

The microstructure of Bi2Se3 topological‐insulator thin films grown by molecular beam epitaxy on InP(111)A and InP(111)B substrates that have different surface roughnesses has been studied in detail using X‐ray diffraction, X‐ray reflectivity, atomic force microscopy and probe‐corrected scanning transmission electron microscopy. The use of a rough Fe‐doped InP(111)B substrate results in complete suppression of twin formation in the Bi2Se3 thin films and a perfect interface between the films and their substrates. The only type of structural defect that persists in the twin‐free films is an antiphase domain boundary, which is associated with variations in substrate height. We also show that the substrate surface termination influences which family of twin domains dominates.

Formation of Copper Impurity-Defect Complexes and Their Impact on Electrical Properties of Silicon

Nature and types of structural defects in the p-type silicon doped with copper are determined by the methods of infrared microscopy and measuring of the specific resistivity, concentration, and lifetime (τ) of charge carriers. It is found that the value of τ is increased and stabilized due to the formation of a trap level associated with the “copper-oxygen” complex [Cu-O] in silicon. It is shown that the copper atoms migrate from a saturated dislocation to the volume of lightly doped silicon during slow cooling after high-temperature diffusion, which is associated with the decomposition of the Si–Cu solid solution.

Roles of Different Forms of Lipopolysaccharides in Ralstonia solanacearum Pathogenesis

Lipopolysaccharides (LPS) are critical components for the fitness of most gram-negative bacteria. Ralstonia solanacearum causes a deadly wilting disease in many crops; however, the pathogenic roles of different forms of LPS and their pathways of biogenesis remain unknown. By screening for phage-resistant mutants of R. solanacearum Pss4, whose genome sequence is unavailable, mutants with various types of structural defects in LPS were isolated. Pathogenesis assays of the mutants revealed that production of rough LPS (R-LPS), which does not contain O-polysaccharides, was sufficient to cause necrosis on Nicotiana benthamiana and induce the hypersensitive response on N. tabacum. However, biosynthesis of smooth LPS (S-LPS), which contains O-polysaccharides, was required for bacterial proliferation at infection sites on N. benthamiana leaves and for proliferation and causing wilt on tomato. Complementation tests confirmed the involvement of the previously unidentified cluster RSc2201 to RSc2204 in the formation of R. solanacearum S-LPS. With these data and the availability of the annotated genomic sequence of strain GMI1000, certain loci involved in key steps of R. solanacearum LPS biosynthesis were identified. The strategy of this work could be useful for similar studies in other bacteria without available genome sequences.

Effect of Cooling Rate on Magnetic Properties, Size and Type of Structural Defects in the Volume of Bulk Amorphous Fe36Co36B19Si5Nn4 Alloy in the Form of Rods of Various Diameters

Abstract This paper presents the results of microstructure and magnetic properties analysis for bulk amorphous samples of Fe36Co36B19Si5Nb4 alloy in the form of rods of 1 mm, 2 mm, and 3 mm diameters in the as-cast state, produced using the method of injecting liquid alloy into cooled copper mold. The main purpose of the research was to examine the effect of solidification speed of the liquid material into amorphous state on the shape of initial magnetization curve as well as to determine the type and size of structural defects occurring in the volume of the material. In order to achieve these objectives, the magnetization measurements were carried out, which according to H. Kronmüller’s theory on magnetization behavior near the area called reaching the ferromagnetic saturation, allow to determine the type, size, and surface density of structural defects occurring in the volume of the sample. The analysis of reduced magnetization curves indicates that solidification speed of the liquid alloy into the amorphous state is the main determining factor for the shape of initial magnetization curve and for the type and size of structural defects formed in the sample, which affects such magnetic parameters as: coercive field (HC) or saturation magnetization (MS).

The origin of white luminescence from silicon oxycarbide thin films

Silicon oxycarbide (SiCxOy) is a promising material for achieving strong room-temperature white luminescence. The present work investigated the mechanisms for light emission in the visible/ultraviolet range (1.5–4.0 eV) from chemical vapor deposited amorphous SiCxOythin films, using a combination of optical characterizations and electron paramagnetic resonance(EPR) measurements. Photoluminescence(PL) and EPR studies of samples, with and without post-deposition passivation in an oxygen and forming gas (H2 5 at. % and N2 95 at. %) ambient, ruled out typical structural defects in oxides, e.g., Si-related neutral oxygen vacancies or non-bridging oxygen hole centers, as the dominant mechanism for white luminescence from SiCxOy. The observed intense white luminescence (red, green, and blue emission) is believed to arise from the generation of photo-carriers by optical absorption through C-Si-O related electronic transitions,and the recombination of such carriers between bands and/or at band tail states. This assertion is based on the realization that the PL intensity dramatically increased at an excitation energy coinciding with the E04 band gaps of the material, as well as by the observed correlation between the Si-O-C bond density and the PLintensity. An additional mechanism for the existence of a blue component of the white emission is also discussed.

Scanning tunneling microscopic and spectroscopic studies on a crystalline silica monolayer epitaxially formed on hexagonal SiC(0001¯) surfaces

An epitaxial silicon-oxide monolayer of chemical composition of Si2O3 (the Si2O3 layer) formed on hexagonal SiC(0001¯) surfaces has been observed by scanning tunneling microscopy (STM). Filled- and empty-state STM images with atomic resolution support the previously reported model. Typical structural defects in the Si2O3 layer are found to be missing SiOn (n = 1, 2, 3) molecules. The band gap of the Si2O3 layer obtained by point tunneling spectroscopy is 5.5±0.5 eV, exhibiting considerable narrowing from that of bulk SiO2, 8.9 eV. It is proposed that the Si2O3 layer is suitable as a relevant interface material for formation of SiC-based metal-oxide-semiconductor devices.

Competing Striped Structures in La2CuO4+y

High temperature superconductivity emerges in unique materials, like cuprates, that belong to the class of heterostructures at atomic limit, made of a superlattice of superconducting atomic layers intercalated by spacer layers. The physical properties of a strongly correlated electronic system, emerge from the competition between different phases with a resulting inhomogeneity from nanoscale to micron scale. Here, we focus on the spatial arrangements of two types of structural defects in the cuprate La2CuO4+y : (i) the local lattice distortions in the CuO2 active layers and (ii) the lattice distortions around the charged chemical dopants in the spacer layers. We use a new advanced microscopy method: scanning nano X-ray diffraction (nXRD). We show here that local lattice distortions form incommensurate nanoscale ripples spatially anticorrelated with puddles of self-organized chemical dopants in the spacer layers.

Regression Analysis for Transport Electron Scattering Caused by Structural Defects in InSb Quantum Wells: Application of Matthiessen's Formula

The graphical representation and numerical interpretation of the results obtained by a regression analysis for Matthiessen's formula have been investigated for the electron scattering due to micro-twins (MTs) and threading dislocations (TDs) in InSb quantum wells (QWs) at room temperature. By plotting the reciprocal of the total mobility vs the summation of the linear terms due to MTs and TDs, a two-dimensional graphical representation that clearly exhibits the “goodness of fit” of the regression analysis was depicted. The usefulness of numerical indexes, “effective defect density” and “equivalent defect scattering”, was discussed: “effective defect density” made it possible to evaluate the electron scattering in InSb QWs by using one type of structural defects, either MTs or TDs. “Equivalent defect scattering” enables one to intuitively grasp the difference in magnitude of electron scattering between MTs and TDs in InSb QWs.

ChemInform Abstract: Photonic Crystals Based on Opals and Inverse Opals: Synthesis and Structural Features

AbstractReview: 253 refs.

Optical quality improvement of rare-earth doped silica layers by CO2 laser irradiation

We investigate different types of structural defects in 20–30μm thick Yb/Al-codoped fused silica layers on a pure fused silica substrate, and show that all types of structural defects can be treated in a single laser heat treatment. Laser-induced processes of defect elimination include diffusion of micro-voids, amorphization of crystallites and roughness reduction via surface-tension-driven mass flow. The physical mechanisms for defect elimination are analyzed in terms of onset temperature and typical time of elimination. Results of such treatment include complete amorphization, reduction of surface roughness by an order of magnitude to about 15nm, and a remarkable improvement of more than an order of magnitude in optical cross-transmittance. The treatment thus provides a possible route for producing lasers and high-power integrated optics components using silica-on-silica technology.

Electron scattering by structural defects in InSb quantum wells: Analysis with simplified Mayadas-Shatzkes equation

The scattering of transport electrons in InSb quantum wells (QWs) caused by two types of structural defects, micro-twins (MTs) and threading dislocations (TDs), has been investigated at room temperature. The electron scattering due to a MT is explained by its energy barrier with a height of ∼0.087 eV or its reflection with a coefficient of ∼0.33. The electric charge of a TD is 1.7 × 10−10 C/m along the [001] direction which is perpendicular to the InSb QWs examined in this study, under the assumption that the electron scattering due to a TD is fully attributed to its electric field. The electron scattering efficiency of one TD line in InSb QWs is equivalent to that of MT plates with a total length of 75 nm. In the course of this study, a mathematical simplification was made for Mayadas-Shatzkes equation which is one of the most frequently used equations to analyze carrier scattering due to a planar defect.

The transformation balance between two types of structural defects in silica glass in ion-irradiation processes

Structural modification in silica glass irradiated by Au ions was investigated by ultraviolet (UV), photoluminescence and Raman spectrum at the energies from 0.5 to 8 MeV with a fluence of 5 × 10 13 cm − 2 . In this transit energy region, both nuclear energy loss and electronic energy loss are not negligible. It was found that both the formation of irradiation-induced intrinsic defects and structural transformation from irregular large ring structure (LRS) to small three- and four-member ring structures (SRS) are dominated by the nuclear energy loss. Furthermore, unlike the case of irradiation with β, γ or proton, the concentration of non-bridging oxygen hole center is much enhanced followed with a distinct peak appearing at 5.05 eV in the UV absorption spectra that is attributed to divalent Si. The results suggest that the structural modification in silica glass in the transit energy region is dominated by nuclear energy loss. A mutual transformation balance model among irradiation-induced intrinsic defects, LRS and SRS is established to interpret the identical variation tendencies of intrinsic defects and structural transformation with ion energy.

Influence of Solidification Speed on Quality and Quantity of Structural Defects in Fe<sub>61</sub>Co<sub>10</sub>Zr<sub>2.5</sub>Hf<sub>2.5</sub>Y<sub>2</sub>W<sub>2</sub>B<sub>20</sub> Amorphous Alloy

The microstructure of Fe61Co10Zr2,5Hf2,5Nb2W2B20 amorphous alloy in the form of ribbons obtained by classical melt spinning and plates obtained by an induction suction method were investigated using X-ray diffraction. The type of structural defects were studied by analysis of the magnetization characteristics near ferromagnetic saturation of the sample. It was shown that the presence of structural defects is strongly correlated with sample thickness and production process. It was shown that ribbons with cooling rate between 105-106 K/s have point type defects, wires obtained with lower cooling rate between 101-102 K/s, have linear type defect (quasi-dislocation dipoles). crystallization.

Defect Formation in Ga-Catalyzed Silicon Nanowires

The synthesis of silicon nanowires by Ga-assisted plasma enhanced chemical vapor deposition (PECVD) has been recently demonstrated. In the present work, we study in detail the structural characteristics of the synthesized nanowires. High resolution transmission electron microscopy (HRTEM) analysis reveals the existence of various types of structural defects, which can be classified mainly according to the orientation into axial twins, lateral twins, and transverse twins. We compare our results with previous studies of Si nanowires synthesized with other catalyst metals. Understanding both the origin and the effects of the observed defects is important for technological applications. The presence of twinned domains changes locally the structure of the material. As a consequence, one should find a different local density of states and band gap, which should result in a variation of the carrier transport and optical properties of the nanowires.

Harmonic wavelet-based data filtering for enhanced machine defect identification

A filter construction technique is presented for enhanced defect identification in rotary machine systems. Based on the generalized harmonic wavelet transform, a series of sub-frequency band wavelet coefficients are constructed by choosing different harmonic wavelet parameter pairs. The energy and entropy associated with each sub-frequency band are then calculated. The filtered signal is obtained by choosing the wavelet coefficients whose corresponding sub-frequency band has the maximum energy-to-entropy ratio. Experimental studies using rolling bearings that contain different types of structural defects have confirmed that the developed new technique enables high signal-to-noise ratio for effective machine defect identification.

Mg doping and its effect on the semipolar GaN(112¯2) growth kinetics

We report the effect of Mg doping on the growth kinetics of semipolar GaN(112¯2) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(112¯2). We observe an enhancement of Mg incorporation in GaN(112¯2) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

Computer simulation of the theoretical contrast of various types of structure defects with noise factors

We present computer simulation results for the images of various types of structural defects in 6H-SiC and Si single crystals with taking into account noise factors (background heterogeneity and contrast graininess). If we know the parameters used to simulate the image, we can increase the reliability of defect identification and location in the single crystal’s bulk and find the quantitative and qualitative characteristics of defects by comparing the experimental and theoretical noise contrast.

Structural features of the KH2PO4: Cr single crystal

The precision X-ray structural investigation of KH2PO4 (KDP) crystal samples from different growth sectors of a single crystal containing chromium impurities is performed. It is demonstrated that the structure of the sample from the prismatic growth sector is more perfect than the structure of the sample from the pyramidal growth sector. The impurity trapping can lead to the formation of at least four different types of structural defects on the face of the pyramid, whereas only two of them can be formed on the face of the prism. A comparison with the relevant data for the “pure” KDP crystal shows that the number of defects and their character are approximately identical for all samples. The analysis of the IR spectra indicates that nitrate ions are contained in the samples from both growth sectors. Moreover, structurally bound water molecules and OH groups are revealed in the sample from the prismatic sector.

Interfacial superconductivity in bilayer and multilayer IV–VI semiconductor heterostructures

A comprehensive investigation and comparison of the superconducting properties of bilayer and multilayer epitaxial heterostructures of IV–VI semiconductors exhibiting superconductivity at critical temperatures Tc⩽6.5K is carried out. The superconductivity of these systems is due to inversion of the bands in the narrow-gap semiconductors on account of the nonuniform stresses created by the grids of misfit dislocations arising at the interfaces during the epitaxial growth. It is found that Tc and the character of the superconducting transition of bilayer PbTe∕PbS heterostructures depend on the thickness d of the semiconductor layers and are directly related to the quality of the grids of misfit dislocations at the interfaces (the number and type of structural defects in the grids). Substantial differences in the behavior of bilayer sandwiches and superlattices are found. The minimum thickness d at which superconductivity appears is several times larger for bilayer than for multilayer systems. The upper critical magnetic fields Hc2 of the bilayer systems are more anisotropic. For superlattices 3D behavior is observed in the temperature region close to Tc, and with decreasing temperature a 3D–2D crossover occurs. For the bilayer structures 2D behavior starts immediately from Tc, and a 2D–1D crossover is observed, with the sharp divergence of Hc2 that is characteristic of superconducting nets.

Maternal Congenital Cardiac Disease

To evaluate contemporary perinatal and cardiac outcomes of pregnancies in women with major structural congenital heart disease. Obstetric, neonatal, and cardiac outcomes were abstracted retrospectively from medical records of all women with congenital cardiac disease delivering at our institution from 2000-2007 and compared by type of structural defect. Predictors of adverse cardiac or obstetric events were identified. Over the 7-year study period, 74 deliveries occurred in 69 women with congenital heart disease, median age 28 years. There were three right-obstructive defects, 14 left-obstructive defects, four right-regurgitant defects, 19 conotruncal defects, 19 shunts, and four miscellaneous lesions. There were 21 adverse cardiac events in 15 pregnancies (20.2%); these were defined as maternal death, congestive heart failure, myocardial infarction, stroke, the need for urgent cardiac intervention, or arrhythmia requiring treatment. There were 44 adverse obstetric events in 34 pregnancies (45.9%), defined as preterm delivery, stillbirth, preeclampsia, small for gestational age, or neonatal intensive care unit admission. Patients with shunt morphology were more likely to experience adverse obstetric and cardiac outcomes. Pregnancy in women with underlying major congenital heart defects poses increased risks to both mother and fetus. Nonetheless, favorable maternal and neonatal outcomes occur in the majority of patients.