Application of Channeling to Defect Studies in Crystals

1980 ◽  
Vol 2 ◽  
Author(s):  
W. K. Chu
Keyword(s):  
Defect Density ◽  
Bond Distance ◽  
Crystal Defects ◽  
Structural Defects ◽  
Substitutional Impurity ◽  
Structure Information ◽  
Surface And Interface ◽  
Impurity Atoms ◽  
Light Ions ◽  
Fast Light

ABSTRACTChanneling of fast, light ions in crystals has been widely used as a tool for studying crystal defects. Backscattering yield measurement on ions incident along major axial or planar crystalline directions provides information on the depth distribution of the structural defects in the first few microns. The channeling technique in defect detection is not as sensitive as Transmission Electron Spectroscopy, nor is it accurate in measuring the absolute numbers of defect density. Channeling measurements can give only an indication of the degree of lattice disorder. It is possible to distinguish one type of defect from another by carefully studying the energy dependence of the dechanneling. The dechanneling interpretation is not always unique, and in practice it is difficult to obtain structure information through that method. Despite these negative qualities, channeling is an attractive and unique method in certain defect studies. For example, it is sensitive for studying the lattice location of impurity atoms at substitutional or interstitial sites. Clustering of substitutional impurity atoms will show a displacement of the impurity atoms from lattice sites due to the change of bond distance. Channeling is sensitive for measuring impurity displacement as small as 0.1A°. This has been demonstrated in the study of arsenic clustering formation in Si. Interfacial relaxation and contraction in a multi-layered structure made by molecular beam epitaxy has been detected by dechanneling along various axial directions. Channeling study on surface and interface structures has developed over the past few years. In this paper, I will use examples to illustrate the unique features of the channeling technique and its application to defect studies in single crystals.

Defect studies in crystals by means of channeling

1968 ◽  
Vol 46 (6) ◽  
pp. 653-662 ◽  
Author(s):  
E. Bøgh
Keyword(s):  
Nuclear Reactions ◽  
Depth Resolution ◽  
Atomic Layer ◽  
Orientation Dependence ◽  
Crystal Defects ◽  
Structural Defects ◽  
Experimental Conditions ◽  
Light Ions ◽  
Set Up ◽  
Fast Light

Channeling of fast, light ions (e.g. protons and α particles) in crystals containing displaced atoms is discussed on the basis of Lindhard's theory, with the particular purpose of applying channeling as a tool for studying crystal defects. Measurements of the orientation dependence of the yield of close-encounter processes, such as nuclear reactions and wide-angle elastic scattering, can provide information about the depth distribution of structural defects in the first few microns beneath the surface of a single crystal. The relation between the yield and defect concentration is derived. This relation has led to a new double-alignment technique that combines channeling and blocking, and increases considerably the sensitivity for detecting structural defects.Scattering yield measurements in tungsten and silicon crystals covered with amorphous oxide layers of accurately known thickness are used to verify the results of the theoretical discussion. Double alignment is demonstrated. Criteria for selecting the optimal experimental conditions are set up. The sensitivity of the method for detecting lattice disorder corresponds to the displacement of ~1014–1015 atoms per cm2 (i.e. less than one atomic layer); the depth resolution with which, for example, radiation damage may be determined is ~50 Å.

Characterization of Defects and Interfaces by the Ion Channeling Technique

1984 ◽  
Vol 41 ◽  
Author(s):  
W. K. Chu ◽  
S. T. Picraux
Keyword(s):  
Ion Beam ◽  
Strain Analysis ◽  
Crystal Defects ◽  
Interfacial Structure ◽  
Heteroepitaxial Growth ◽  
Ion Channeling ◽  
Light Ions ◽  
Recent Developments ◽  
Fast Light

AbstractChanneling of fast, light ions in crystals has been widely used as a tool for studying crystal defects. This subject has been reviewed earlier at MRS-1980. During MRS-1980, principles of ion channeling, and examples of channeling analysis on bulk defects and surface structures, lattice location of impurities, and clustering phenomena were given. In this review, we give a brief overview of defect studies by the channeling technique and then elaborate on recent developments in channeling analysis of interfacial structure. The ion beam channeling technique permits characterization of heteroepitaxial growth starting at monolayer coverages and allows quantitative measurement of the lattice strain in heteroepitaxial layers. The strain analysis has been developed for multilayer structures and, for example, the tetragonal distortions of strained-layer superlattices can be determined for lattice mismatches as low as 0.2% corresponding to lattice distortions of 0.01Å.

Electronic modes in carbon nanotubes with single and double impurity sites

2017 ◽  
Vol 31 (29) ◽  
pp. 1750220
Author(s):  
P. G. Komorowski ◽  
M. G. Cottam
Keyword(s):  
Carbon Nanotubes ◽  
Nearest Neighbor ◽  
Tight Binding ◽  
Longitudinal Axis ◽  
Binding Model ◽  
Substitutional Impurity ◽  
Impurity Atoms ◽  
Spatial Configurations ◽  
Impurity Sites ◽  
Walled Carbon Nanotubes

A theoretical study of isolated and doubly-clustered impurities is presented for the electronic excitations in a carbon nanotube lattice. Using a matrix operator formalism and a tight-binding model where the interactions between atoms take place via nearest-neighbor hopping, the properties of the excitations are deduced. A geometry consisting of long, single-walled carbon nanotubes is assumed with the defects introduced in the form of substitutional impurity atoms, giving rise to the localized electronic modes of the nanotube as well as the propagating modes of the pure (host) material. The impurities are assumed to be in a low concentration, having the form of either a single, isolated defect or a small cluster of two defects close together. A tridiagonal matrix technique is employed within a Green’s function formalism to obtain the properties of the discrete modes of the system, including their frequencies and localization. The numerical examples show a dependence on the nanotube diameters and on the relative spatial configurations of the impurities. The results contrast with the previous studies of line impurities since there is no translational symmetry along the longitudinal axis of the nanotubes in the present case.

Low Temperature Boronizing of Surface Nanostructured Ni-Cr-Mo Steel Using SMAT

2015 ◽  
Vol 830-831 ◽  
pp. 663-666 ◽  
Author(s):  
G. Sreejith ◽  
Teotia Sunny ◽  
J.N. Sahu ◽  
Chandrabalan Sasikumar
Keyword(s):  
Low Temperature ◽  
Defect Density ◽  
Thermochemical Treatment ◽  
Optical Microscope ◽  
Crystal Defects ◽  
Surface Mechanical Attrition Treatment ◽  
Metallic Surface ◽  
Hardness Tester ◽  
Nano Crystalline ◽  
Nanocrystalline Structures

Boronizing is a surface thermochemical treatment in which boron atoms are made to diffuse into a metallic surface at high temperatures. A nano-crystalline surface with larger defect density assists in enhancing the diffusion rate even at low temperatures. In the present work Ni-Cr-Mo steel is subjected to a surface mechanical attrition treatment (SMAT) to activate the surface with nanocrystalline structures and crystal defects. Subsequently the samples were boronized at low temperature regime (400°C - 600°C) for 5 hours using a pack boronizing technique. The microstructure, chemical analysis and hardness of borided layers were investigated using optical microscope, SEM – EDX and Microvicker’s Hardness Tester. The SMAT treated samples showed severe plastic deformation of the surface, nano-structured grains (10-30 nm) and larger defect density illustrating mechanically activated surface for diffusion. The boronizing had clearly demonstrated the diffusion of boron even at 400°C. The thickness of diffused layer was found to be about 20 µm at 400°C and 50 µm at 600°C for SMAT samples while the untreated samples showed practically no diffusion at 400°C and 12 µm at 600°C. The SEM-EDX results had confirmed the presence of boron at the diffused layer; however the hardness was found to be low. A maximum of 650 HV0.3was achieved by low temperature boronizing of SMAT treated samples.

Stress and Dopant Activation in Solid Phase Crystalized Si Films

1999 ◽  
Vol 558 ◽  
Author(s):  
A. Kaan Kalkan ◽  
Stephen J. Fonash
Keyword(s):  
Tensile Stress ◽  
Defect Density ◽  
Solid Phase ◽  
Structural Defects ◽  
Raman Shift ◽  
Solid Phase Crystallization ◽  
Dopant Activation ◽  
Defect Creation ◽  
Si Films ◽  
High Level

ABSTRACTDefect creation mechanisms during solid phase crystallization (SPC) of Si thin films were investigated with PECVD amorphous precursor samples produced with various deposition temperatures and thicknesses. These precursor films were implanted with dopant and then crystallized to obtain both SPC and dopant activation. The doping efficiency was found to decrease with the tensile stress level as measured by Raman shift. The stress shows a decrease as the precursor deposition temperature and thickness are lowered. Furthermore, a lower level of stress is induced by rapid thermal annealing when the annealing temperature is high enough to soften the glass substrate on which the films were deposited. We show that by control of stress during the SPC step, intragrain defect density can be lowered and electronic quality of the resulting polycrystalline Si films can be improved. Based on these observations, we propose the following tentative model to explain the defect creation: during SPC, tensile stress evolution is considered to result from the volumetric contraction of Si film when it transforms from the amorphous to crystalline phase. This contraction is retarded by the substrate, which imposes a tensile stress on the film. A high level of stress leads to formation of structural defects inside the grains of the resulting polycrystalline material. These defects trap carriers or complex with the dopant reducing doping efficiency.

TEM and SEM Studies of MOCVD-Grown GaP on Si

1985 ◽  
Vol 62 ◽  
Author(s):  
M. M. Ai-Jassim ◽  
J. M. Olson ◽  
K. M. Jones
Keyword(s):  
Defect Density ◽  
Growth Parameters ◽  
Three Dimensional ◽  
Chemical Vapor ◽  
Structural Defects ◽  
Organic Chemical ◽  
Cross Sectional ◽  
Plan View ◽  
Si Substrates ◽  
Antiphase Domains

ABSTRACTGaP and GaP/GaAsP epitaxial layers have been grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). These layers were characterized by SEM and TEM plan-view and cross-sectional examination. At growth temperatures ranging from 600° C to 800° C, the initial stages of growth were dominated by three-dimensional nucleation. TEM studies showed that at high temperatures the nuclei were generally misoriented with respect to each other yielding, upon coalescence, polycrystalline layers. The growth of single-crystal layers was achieved by nucleating a 30–50 nm layer of GaP at 500° C, followed by annealing and continued growth at 750 ° C. The defect density in these structures was investigated as a function of various growth parameters and substrate conditions. A high density of structural defects was generated at the Si/GaP interface. The use of 2° off (100) Si substrates resulted in GaP layers free of antiphase domains. These results and their implications are discussed.

Structural Defects and Critical Electric Field in 3C-SiC

2006 ◽  
Vol 527-529 ◽  
pp. 431-434 ◽  
Author(s):  
Michael A. Capano ◽  
A.R. Smith ◽  
Byeung C. Kim ◽  
E.P. Kvam ◽  
S. Tsoi ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Electric Field ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Chemical Vapor ◽  
Structural Defects ◽  
X Ray ◽  
Transmission Electron ◽  
Current Voltage ◽  
P Type

3C-SiC p-type epilayers were grown to thicknesses of 1.5, 3, 6 and 10 μm on 2.5° off-axis Si(001) substrates by chemical vapor deposition (CVD). Silane and propane were used as precursors. Structural analysis of epilayers was performed using transmission electron microscopy (TEM), high-resolution x-ray diffractometry (HRXRD), and Raman spectroscopy. TEM showed defect densities (stacking faults, twins and dislocations) decreasing with increasing distance from the SiC/Si interface as the lattice mismatch stress is relaxed. This observation was corroborated by a monotonic decrease in HRXRD peak width (FWHM) from 780 arcsecs (1.5 μm thick epilayer) to 350 arcsecs (10 μm thick epilayer). Significant further reduction in x-ray FWHM is possible because the minimum FWHM detected is greater than the theoretical FWHM for SiC (about 12 arcsecs). Raman spectroscopy also indicates that the residual biaxial in-plane strain decreases with increasing epilayer thickness initially, but becomes essentially constant between 6 and 10 μm. Structural defect density shows the most significant reduction in the first 2 μm of growth. Phosphorus implantation was used to generate n+/p junctions for the measurement of the critical electric field in 3C-SiC. Based on current-voltage analyses, the critical electric field in p-type 3C-SiC with a doping of 2x1017 cm-3 is 1.3x106 V/cm.

scholarly journals Graphene: One Material, Many Possibilities—Application Difficulties in Biological Systems

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Marta Skoda ◽  
Ilona Dudek ◽  
Anna Jarosz ◽  
Dariusz Szukiewicz
Keyword(s):  
Cell Imaging ◽  
Defect Density ◽  
Biological Systems ◽  
Basic Element ◽  
Structural Defects ◽  
Pristine Graphene ◽  
Biological Impact ◽  
Cytotoxic Effects ◽  
Flat Membrane

Energetic technologies, nanoelectronics, biomedicine including gene therapy, cell imaging or tissue engineering are only few from all possible applications for graphene, the thinnest known carbon configuration and a basic element for other more complicated, better discovered and widely used nanostructures such as graphite, fullerenes and carbon nanotubes. The number of researches concerning graphene applications is rising every day which proves the great interest in its unique structure and properties. Ideal pristine graphene sheet presents a flat membrane of unlimited size with no imperfections while in practice we get different flakes with irregular edges and structural defects which influence the reactivity. Nanomaterials from graphene family differ in size, shape, layer number, lateral dimension, surface chemistry and defect density causing the existence of graphene samples with various influence on biological systems. Whether graphene induces cellular stress and activates apoptosis, or on the contrary facilitates growth and differentiation of the cells depends on its structure, chemical modifications and the growth process. A certain number of in vitro studies has indicated cytotoxic effects of graphene while the other show that it is safe. The diversity of the samples and methods of the production make it impossible to establish clearly the biological impact of graphene.

scholarly journals Simultaneous X-ray radiography and diffraction topography imaging applied to silicon for defect analysis during melting and crystallization

2019 ◽  
Vol 52 (6) ◽  
pp. 1312-1320 ◽  
Author(s):  
Maike Becker ◽  
Gabrielle Regula ◽  
Guillaume Reinhart ◽  
Elodie Boller ◽  
Jean-Paul Valade ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Grain Boundaries ◽  
Growth Process ◽  
Defect Formation ◽  
Simultaneous Recording ◽  
European Synchrotron Radiation Facility ◽  
Crystal Defects ◽  
Structural Defects ◽  
X Ray

One of the key issues to be resolved to improve the performance of silicon solar cells is to reduce crystalline defect formation and propagation during the growth-process fabrication step. For this purpose, the generation of structural defects such as grain boundaries and dislocations in silicon must be understood and characterized. Here, in situ X-ray diffraction imaging, historically named topography, is combined with radiography imaging to analyse the development of crystal defects before, during and after crystallization. Two individual indirect detector systems are implemented to record simultaneously the crystal structure (topographs) and the solid–liquid morphology evolution (radiographs) at high temperature. This allows for a complete synchronization of the images and for an increased image acquisition rate compared with previous studies that used X-ray sensitive films to record the topographs. The experiments are performed with X-ray synchrotron radiation at beamline ID19 at the European Synchrotron Radiation Facility. In situ observations of the heating, melting, solidification and holding stages of silicon samples are presented, to demonstrate that with the upgraded setup detailed investigations of time-dependent phenomena are now possible. The motion of dislocations is recorded throughout the experiment, so that their interaction with grain boundaries and their multiplication through the activation of Frank–Read sources can be observed. Moreover, the capability to record with two camera-based detectors allows for the study of the relationship between strain distribution, twinning and nucleation events. In conclusion, the simultaneous recording of topographs and radiographs has great potential for further detailed investigations of the interaction and generation of grains and defects that influence the growth process and the final crystalline structure in silicon and other crystalline materials.

Ion-beam-assisted deposition of nonhydrogenated a-Si:C films

1996 ◽  
Vol 74 (3-4) ◽  
pp. 97-101
Author(s):  
C. D. Tucker ◽  
D. E. Brodie
Keyword(s):  
Electron Cyclotron Resonance ◽  
Defect Density ◽  
Ion Beam ◽  
High Vacuum ◽  
Argon Plasma ◽  
Localized States ◽  
Structural Defects ◽  
Electrical Characteristics ◽  
Ion Beam Assisted Deposition ◽  
Ultra High Purity

Amorphous silicon carbide (a-Si:C) films were prepared by low-energy ion-beam-assisted deposition (IBAD) in an attempt to remove structural defects in the "lattice" and improve the electrical characteristics of the film. The ion beam was generated by electron cyclotron resonance from an ultra-high-purity argon plasma. The deposition environment was first evacuated to a very high vacuum to eliminate all but trace amounts of water vapour and other gases so that improvements in the electrical and (or) structural properties of the film would be attributable to the influence of the densification by ion bombardment and not to contaminants. The IBAD process does improve the film characteristics by reducing the density of localized states at the Fermi level and the porosity of the film. However, even though these films have the best electrical characteristics obtained thus far for these kind of films, none of them exhibited device quality and none were observed to be photoconducting. A large density (≈1 at.%) of implanted argon atoms may be limiting the reduction in the defect density that might otherwise be achievable.

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