Diffusion Of Intrinsic Defects Research Articles

Defect‐Induced Effects in Nanomaterials

Defect‐Induced Effects in Nanomaterials

Formation and Diffusion of Intrinsic Point Defects in Bulk and Monolayer MoS 2 : First‐Principles Study

The formation and diffusion of intrinsic defects in bulk and monolayer MoS2 are studied. For the first time, the formation energy of a split sulfur and molybdenum Frenkel pair in bulk (6.56 and 12.6 eV) and monolayer (3.95 and 12.1 eV) MoS2 is determined without using chemical potential. For the intrinsic defects, a complete calculation of the diffusion coefficient (pre-exponential factor and activation barrier) is performed and the effect of the defect charge state on the diffusion coefficient is studied.

Diffusion model of intrinsic defects in lead zirconate titanate films on heat treatment in air

A one-dimensional model describing the diffusion of intrinsic defects in lead zirconate titanate (LZT) films of nonstoichiometric composition during their high-temperature treatment is proposed. The model includes the diffusion of vacancies by lead and oxygen, the formation and decay of their associates, interaction with extensive defects (dislocations in LZT films and the near-surface layer), interstitial inclusions, and LZT film contact with air leading to lead oxide evaporation from LZT film and its saturation by oxygen. The dependences of LZT film composition on the temperature and time of treatment are calculated. The possibility the concentration’s oversaturation by lead in a near-surface layer of LZT film, which can lead to the release of lead oxide, is shown.

Characterization of oxygen and titanium diffusion at the anatase TiO2(001) surface

The diffusion of intrinsic defects in a single crystal anatase TiO2(001) film was explored by isotopic labeling and static secondary ion mass spectrometry. Using both 46Ti and 18O as isotopic labels, we show that the anatase surface responds to redox imbalances by diffusion of both Ti and O into the bulk under vacuum reduction and (at least) Ti from the bulk to the surface during oxidation. The diffusion of Ti between the bulk and surface in anatase TiO2(001) closely resembles what was observed in the literature for the rutile TiO2(110) surface, however the latter is not known to have oxygen diffusion between the bulk and surface under typical ultrahigh vacuum conditions. We speculate that the open lattice of the anatase bulk structure may facilitate independent diffusion of both point defects (Ti interstitials and O vacancies) or concerted diffusion of “TiO” subunits.

Anomalous Diffusion of Intrinsic Defects in K+ Implanted ZnO using Li as Tracer

ABSTRACTPotassium (K) ions have been implanted in hydrothermally grown ZnO to a dose of 1 × 1015 cm-2, followed by isochronal annealing in a tube furnace (30min) and by rapid thermal annealing (30s) on two separate samples. For annealing temperatures below 700°C, only a minor redistribution of Li is observed behind the projected range of the K+ ions. At temperatures between 700 and 750°C, however, both annealing treatments show a wide region behind the implantation peak which is depleted of Li, and this depletion is used as a tracer to monitor diffusion of intrinsic defects like the Zn interstitial. The results are interpreted as Zn interstitials being released from the implanted region in a burst at temperatures above ∼700°C, followed by rapid migration, replacement of Li on Zn site through the kick-out mechanism, and migration of Li away from the active region.

Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory

Using periodic density functional theory, we calculate the structure and migration energies of fluorine vacancies and interstitials in the bulk and at the stoichiometric bulk-truncated surface of three alkali-earth fluorides: ${\text{CaF}}_{2}$, ${\text{SrF}}_{2}$, and ${\text{BaF}}_{2}$. We then study the adsorption of water and hydrogen, in both molecular and dissociated form, at the ideal surface, and at neutral and charged vacancies in the surface and subsurface layers. The results demonstrate that in nearly all cases molecular adsorption is strongly favored. For the most probable configurations on the surfaces, we also studied the migration paths and barriers, and found that water is highly mobile on the surface, even when adsorbed at defects. In general, ${\text{CaF}}_{2}$ and ${\text{SrF}}_{2}$ show similar behavior with respect to water, while adsorption energies and migration barriers for ${\text{BaF}}_{2}$ are smaller. Finally, we discuss our results in the context of recent experimental Atomic Force Microscopy studies on ${\text{CaF}}_{2}$ and compare to calculations on other insulating surfaces.

The unusual influence of intrinsic defects on the diffusion of Ag and Cu in CdTe

The diffusion of Ag and Cu in CdTe was investigated using the radiotracers 111Ag and 67Cu. The diffusion properties are similar for both dopants and are essentially determined by diffusion of intrinsic defects in the crystal. Both dopants show up interstitial fractions which are incorporated substitutionally if Cd vacancies are present. The resulting unusual diffusion profiles map the actual distribution of the intrinsic defects and indicate the chemical self diffusion in CdTe.

Ab initiostudy of the migration of intrinsic defects in3C−SiC

The diffusion of intrinsic defects in 3C-SiC is studied using an ab initio method based on density functional theory. The vacancies are shown to migrate on their own sublattice. The carbon split-interstitials and the two relevant silicon interstitials, namely the tetrahedrally carbon-coordinated interstitial and the <110>-oriented split-interstitial, are found to be by far more mobile than the vacancies. The metastability of the silicon vacancy, which transforms into a vacancy-antisite complex in p-type and compensated material, kinetically suppresses its contribution to diffusion processes. The role of interstitials and vacancies in the self-diffusion is analyzed. Consequences for the dopant diffusion are qualitatively discussed. Our analysis emphasizes the relevance of mechanisms based on silicon and carbon interstitials.

Diffusion of intrinsic defects in dielectric and semiconductor crystals with impurities

This paper reports on the results of detailed theoretical investigations into the diffusion of intrinsic defects in impurity crystals doped with mixed-valence ions. The special case of diffusion stimulated by variations in the redox properties of the atmosphere at the crystal boundary during high-temperature annealing is analyzed. The major consideration is given to the following fundamental problems: (i) the dynamics of valence transitions and the structure of the chemical reaction zone, (ii) the possibility of determining the type of chemical reaction at the crystal-atmosphere interface and the type of diffusing defects, (iii) the effect of dilatation mechanical stresses arising in the reaction zone on the reaction-zone structure and on the dynamics of diffusion processes, and (iv) the determination of the diffusion parameters of intrinsic defects and the constants of their interaction with impurity centers.