113 research outputs found
Reaction rate theory with account of the crystal anharmonicity
Reaction rate theory in solids is modified taking into account intrinsic
localized modes or discrete breathers (DBs) that can appear in crystals with
sufficient anharmonicity resulting in violation of Arrhenius law. Large
amplitude oscillations of atoms about their equilibrium positions in the
lattice cause local potentials of alternating sign, which are described in
terms of time-periodic modulations of the potential barriers for chemical
reactions taking place in the vicinity of DBs. The reaction rate averaged over
large macroscopic volumes and times including a lot of DBs is increased by a
factor that depends on the DB statistics. The breather statistics in thermal
equilibrium and in thermal spikes in solids under irradiation with swift
particles is considered, and the corresponding reaction rate amplification
factors are derived.Comment: 17 pages, 12 figure
Fracture surfaces of tungsten wires used in fiber-reinforced plasma facing components: Effect of potassium doping and high temperature annealing
A new mechanism for radiation damage processes in alkali halides
We present a theory of radiation damage formation in alkali halides based on a new mechanism of dislocation climb, which involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface of halogen bubbles. Voids can ignite a back reaction between the radiolytic products resulting in decomposition of the irradiated material
The origin of defects induced in ultra-pure germanium by Electron Beam Deposition
The creation of point defects in the crystal lattices of various
semiconductors by subthreshold events has been reported on by a number of
groups. These observations have been made in great detail using sensitive
electrical techniques but there is still much that needs to be clarified.
Experiments using Ge and Si were performed that demonstrate that energetic
particles, the products of collisions in the electron beam, were responsible
for the majority of electron-beam deposition (EBD) induced defects in a
two-step energy transfer process. Lowering the number of collisions of these
energetic particles with the semiconductor during metal deposition was
accomplished using a combination of static shields and superior vacuum
resulting in devices with defect concentrations lower than cm, the measurement limit of our deep level transient
spectroscopy (DLTS) system. High energy electrons and photons that samples are
typically exposed to were not influenced by the shields as most of these
particles originate at the metal target thus eliminating these particles as
possible damage causing agents. It remains unclear how packets of energy that
can sometimes be as small of 2eV travel up to a m into the material while
still retaining enough energy, that is, in the order of 1eV, to cause changes
in the crystal. The manipulation of this defect causing phenomenon may hold the
key to developing defect free material for future applications.Comment: 18 pages, 9 figure
The influence of carbon impurities on the formation of loops in tungsten irradiated with self-ions
The microstructure changes taking place in W under irradiation are governed by many factors, amongst which C impurities and their interactions with self-interstitial atoms (SIA). In this work, we specifically study this effect by conducting a dedicated 2-MeV self-ions irradiation experiment, at room temperature. Samples were irradiated up to 0.02, 0.15 and 1.2 dpa. Transmission electron microscopy (TEM) expectedly revealed a large density of SIA loops at all these doses. Surprisingly, however, the loop number density increased in a non-monotonous manner with the received dose. Performing chemical analysis with secondary ion spectroscopy measurements (SIMS), we find that our samples were likely contaminated by C injection during the irradiation. Employing an object kinetic Monte Carlo (OKMC) model for microstructure evolution, we demonstrate that the C injection is the likely factor explaining the evolution of loops number density. Our findings highlight the importance of the well-known issue of C injection during ion irradiation experiments, and demonstrate how OKMC models can help to rationalize this effect.Peer reviewe
Plastic deformation in advanced tungsten-based alloys for fusion applications studied by mechanical testing and TEM
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