Interaction of two substitutional impurity atoms in an hcp crystal

2010 ◽  
Vol 36 (4) ◽  
pp. 360-362 ◽  
Author(s):  
V. I. Belan ◽  
A. I. Landau
Keyword(s):  
Substitutional Impurity ◽  
Impurity Atoms

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.

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.

Ab initio study of substitutional impurity atoms in 4H-SiC

2008 ◽  
Vol 104 (12) ◽  
pp. 123702 ◽  
Author(s):  
Masanori Miyata ◽  
Yoshitsune Higashiguchi ◽  
Yoshinori Hayafuji
Keyword(s):  
Ab Initio ◽  
Ab Initio Study ◽  
Substitutional Impurity ◽  
Impurity Atoms

Localization of magnetic and electronic excitations in nanotubes with line defects

2015 ◽  
Vol 29 (12) ◽  
pp. 1550074 ◽  
Author(s):  
P. G. Komorowski ◽  
M. G. Cottam
Keyword(s):  
Nearest Neighbor ◽  
Tight Binding ◽  
Square Lattice ◽  
Wave Number ◽  
Electronic Excitations ◽  
Binding Model ◽  
Substitutional Impurity ◽  
Impurity Atoms ◽  
Line Defects ◽  
Spectral Intensities

A matrix Green's function formalism is employed to study the excitations in long nanotubes where the dynamics are governed by nearest-neighbor interactions between atoms. Examples of the excitations, which can be characterized in terms of the tube circumference and a one-dimensional wave number along the length, include ferromagnetic spin waves in a Heisenberg exchange model and electronic modes in a tight-binding model with hopping. It is assumed that the system is a single-walled nanotube of negligible thickness and that the atoms are arranged on a simple square lattice. Defects in the form of substitutional impurity atoms are introduced to study localized modes as well as the propagating modes of the pure (host) material. The impurities have the form of one or more line defects parallel to the nanotube axis. The derived Green's functions provide a description of the frequencies of the discrete modes of the system and their spectral intensities. Numerical examples are presented for different mode types (magnetic and electronic), nanotube diameters and arrangements of impurity lines.

Diffusion of ion implanted indium and silver in ZnO crystals

2012 ◽  
Vol 1394 ◽  
Author(s):  
Faisal Yaqoob ◽  
Mengbing Huang
Keyword(s):  
Activation Energy ◽  
Total Dose ◽  
Gas Flow ◽  
Defect Formation ◽  
Activation Energies ◽  
Substitutional Impurity ◽  
Impurity Atoms ◽  
And Migration ◽  
Diffusion Activation ◽  
Ion Implanted

ABSTRACTWe report on diffusion behavior for ion implanted indium and silver atoms in ZnO crystals. Both In and Ag ions were implanted at room temperature at 7-10° relative to c-axis to avoid channeling effects during implantation. In ions were implanted at four different energies (40, 100, 200, and 350 keV, respectively) and doses (4.20×1013, 6.70×1013, 8.10×1013 and 3.10×1014 /cm2, respectively), resulting in a total dose of 5 ×1014 /cm2. For another set of ZnO samples, Ag ions were implanted at energies 30, 75, 150, and 350 keV at doses 3.3×1013, 4.2×1013, 8.3×1013 and 3.4×1014 /cm2, respectively, to reach a total dose of 5×1014 /cm2. Both In and Ag implants resulted in a uniform concentration profile of the implanted dopants from surface to depth ~ 150 nm. The samples were annealed for 30 minutes at temperatures between 850-1050 °C in an oxygen gas flow. The distributions of In and Ag atoms, either aligned or nonaligned along the crystalline directions, were measured by Rutherford backscattering combined with ion channeling. The diffusivities for nonaligned (interstitial) and aligned (substitutional) dopants atoms were determined to vary with annealing temperature via the Arrhenius relationship. The diffusion activation energies (Ea) along the <10-11> direction for substitutional impurity atoms were lower than those for interstitial dopants atoms e.g., in the case of In, Ea ~ 1.52 eV for <10-11> aligned In atoms and Ea ~ 2.61 eV for interstitial In atoms between <10-11> atomic rows and in the case of Ag, Ea ~ 1.77 eV for the interstitial Ag atoms between the <10-11> atomic rows and 1.11 eV for <10-11> aligned Ag atoms. The diffusion activation energies showed a different trend for the two dopants as measured along the <0001> crystalline direction. For Ag implanted in ZnO, the activation energy of Ea ~ 0.91 eV for the aligned Ag atoms along <0001> direction and Ea ~ 1.55 eV were found for the interstitial Ag atoms, whereas in the case of In along the <0001> direction, the interstitial In was found to migrate with a higher activation energy (Ea ~ 1.78 eV) than the substitutional In (Ea ~1.42 eV). These results will be compared with first-principle calculations for understanding the energetics of defect formation and migration in both n- and p-type doping cases.

Diffusion mechanism in cutting Ni-based alloy containing γ′ phase (Ni3Al) with CBN tool based on MD simulation

2021 ◽  
pp. 095440542110024
Author(s):  
YiHang Fan ◽  
WenYuan Wang ◽  
ZhaoPeng Hao
Keyword(s):  
Impurity Atom ◽  
Md Simulation ◽  
Diffusion Mechanism ◽  
Interstitial Impurity ◽  
Diffusion Activation Energy ◽  
Temperature Oxidation ◽  
Substitutional Impurity ◽  
Impurity Atoms ◽  
Cbn Tool ◽  
Cutting Model

Ni-based alloys are widely used in aerospace because of their high strength and high temperature oxidation resistance. CBN tool is suitable for precision machining of Ni-based alloy. Diffusion wear is an important wear form of CBN tool in the process of cutting Ni-based alloy. Therefore, it is of great significance to study the diffusion phenomenon in the process of cutting Ni-based alloy with CBN tool. In this paper, the cutting model of Ni-based alloy containing γ′ phase (Ni3Al) with CBN tool is established based on the molecular dynamics (MD) simulation method. The self diffusion activation energy of all kinds of atoms in the workpiece and the formation energy of several point defects in the tool are calculated, so as to study in depth the atom diffusion mechanism according to the simulation results. The results show that the atoms in the crystal boundary of the workpiece are the most easily diffused, followed by the atoms in the phase boundary, and the atoms in the lattice are the most difficult to diffuse. When the workpiece atoms diffuse into the tool, it is easier to diffuse into the tool grain boundary than to form interstitial impurity atoms or displacement impurity atoms. It is more difficult to form the substitutional impurity atom than to form the interstitial impurity atom.

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