Effect of prior structural defects in quartz fiber lightguides on defect formation by γ radiation

Atomic Energy ◽  
2008 ◽  
Vol 104 (1) ◽  
pp. 33-37 ◽  
Author(s):  
N. Akchurin ◽  
M. Kh. Ashurov ◽  
M. I. Baidzhanov ◽  
Zh. D. Ibragimov ◽  
I. R. Rustamov ◽  
...  
Author(s):  
Ottorino Ori ◽  
Franco Cataldo ◽  
Mihai V. Putz

Recent advances in graphene studies deal with the influence of structural defects on graphene chemical, electrical, magnetic and mechanical properties. Here the complex mechanisms leading to the formation of clusters of vacancies in 2D honeycomb HD lattices are described by a pure topological point of view, aiming to correlate the variation of specific topological invariants, sensible to vacancy concentration, to the structural evolution of the defective networks driven by the topo-thermodynamical Gibbs free energy. Interesting predictions on defect formation mechanisms add details on the topological mechanisms featured by the graphenic structures with defects. Future roles of bondonic particles in defective HD materials are also envisaged.


Crystals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 555 ◽  
Author(s):  
Hadjer Ouaddah ◽  
Maike Becker ◽  
Thècle Riberi-Béridot ◽  
Maria Tsoutsouva ◽  
Vasiliki Stamelou ◽  
...  

To control the final grain structure and the density of structural crystalline defects in silicon (Si) ingots is still a main issue for Si used in photovoltaic solar cells. It concerns both innovative and conventional fabrication processes. Due to the dynamic essence of the phenomena and to the coupling of mechanisms at different scales, the post-mortem study of the solidified ingots gives limited results. In the past years, we developed an original system named GaTSBI for Growth at high Temperature observed by Synchrotron Beam Imaging, to investigate in situ the mechanisms involved during solidification. X-ray radiography and X-ray Bragg diffraction imaging (topography) are combined and implemented together with the running of a high temperature (up to 2073 K) solidification furnace. The experiments are conducted at the European Synchrotron Radiation Facility (ESRF). Both imaging techniques provide in situ and real time information during growth on the morphology and kinetics of the solid/liquid (S/L) interface, as well as on the deformation of the crystal structure and on the dynamics of structural defects including dislocations. Essential features of twinning, grain nucleation, competition, strain building, and dislocations during Si solidification are characterized and allow a deeper understanding of the fundamental mechanisms of its growth.


1990 ◽  
Vol 202 ◽  
Author(s):  
Tri-Rung Yew ◽  
Rafael Reif

ABSTRACTThis paper investigates the defect formation at the epi/substrate interface and epitaxial layers due to an improper in–situ Ar or Ar/H2 plasma cleaning at 500–800 °C Deposition process was carried out immediately after the in–situ cleaning process by ultralow pressure chemical vapor deposition process (ULPCVD) from SiH4/H2. Characteristics of the defects and their relationship with damage or impurity contaminations at the interface are presented. Finally, an optimum cleaning condition which ensures high quality epitaxial growth is addressed.


2005 ◽  
Vol 20 (12) ◽  
pp. 3368-3373 ◽  
Author(s):  
S.A. Curran ◽  
J.A. Talla ◽  
D. Zhang ◽  
D.L. Carroll

We systematically introduced defects onto the body of multi-walled carbon nanotubes through an acid treatment, and the evolution of these defects was examined by Raman spectroscopy using different excitation wavelengths. The D and D′ modes are most prominent and responsive to defect formation caused by acid treatment and exhibit dispersive behavior upon changing the excitation wavelengths as expected from the double resonance Raman (DRR) mechanism. Several weaker Raman resonances including D″ and L1 (L2) + D′ modes were also observed at the lower excitation wavelengths (633 and 785 nm). In addition, specific structural defects including the typical pentagon-heptagon structure (Stone–Wales defects) were identified by Raman spectroscopy. In a closer analysis we also observed Haeckelite structures, specifically Ag mode response in R5,7 and O5,6,7.


Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1402
Author(s):  
Jiaona Zou ◽  
Alex Fauler ◽  
Alexander S. Senchenkov ◽  
Nikolai N. Kolesnikov ◽  
Lutz Kirste ◽  
...  

Structural defects and compositional uniformity remain the major problems affecting the performance of (Cd, Zn)Te (CZT) based detector devices. Understanding the mechanism of growth and defect formation is therefore fundamental to improving the crystal quality. In this frame, space experiments for the growth of CZT by the Travelling Heater Method (THM) under microgravity are scheduled. A detailed ground-based program was performed to determine experimental parameters and three CZT crystals were grown by the THM. The structural defects, compositional homogeneity and resistivity of these ground-based crystals were investigated. A ZnTe content variation was observed at the growth interface and a high degree of stress associated with extensive dislocation networks was induced, which propagated into the grown crystal region according to the birefringence and X-ray White Beam Topography (XWBT) results. By adjusting the growth parameters, the ZnTe variations and the resulting stress were efficiently reduced. In addition, it was revealed that large inclusions and grain boundaries can generate a high degree of stress, leading to the formation of dislocation slip bands and subgrain boundaries. The dominant defects, including grain boundaries, dislocation networks and cracks in the interior of crystals, led to the resistivity variation in the crystals. The bulk resistivity of the as-grown crystals ranged from 109 Ωcm to 1010 Ωcm.


2021 ◽  
Vol 22 (3) ◽  
pp. 437-443
Author(s):  
Yu.V. Pavlovskyy ◽  
O.V. Berbets ◽  
P.G. Lytovchenko

The influence of growth impurities (oxygen and carbon) on the thermalsdefect formation in silicon single crystals has been studied. Annealing was carried out in the temperature range 700-1100°C in steps of 50°C for 5 hours at each temperature. The magnetic, micromechanical and structural properties of annealed silicon single crystals have been experimentally studied. The distribution of defects formed at different annealing temperatures has been studied. The correlation between changes of magnetic susceptibility, microhardness and rearrangement of structural defects in crystals after their heat treatment is revealed. Concentrations and sizes of magnetically ordered clusters are estimated. Interpretation of the obtained experimental results is offered.


2019 ◽  
Vol 52 (6) ◽  
pp. 1312-1320 ◽  
Author(s):  
Maike Becker ◽  
Gabrielle Regula ◽  
Guillaume Reinhart ◽  
Elodie Boller ◽  
Jean-Paul Valade ◽  
...  

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.


1998 ◽  
Vol 510 ◽  
Author(s):  
Noboru Ohtani ◽  
Jun Takahashi ◽  
Masakazu Katsuno ◽  
Hirokatsu Yashiro ◽  
Masatoshi Kanaya

AbstractThe defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the <0001> c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation


Author(s):  
Yimei Zhu ◽  
H. Zhang ◽  
Z.X. Cai ◽  
R.C. Budhani ◽  
D.O. Welch ◽  
...  

We studied the the structure and properties of high Tc superconductors using heavy ions. While irradiation of YBa2Cu3O7-δ (hereafter denoted as 123) with 300 MeV Au+24 and 276 MeV Ag+21 ions produces columns of amorphous tracks along the ion trajectories, such defects are only created occasionally during irradiation with 236 MeV Cu+18, and are not induced with 182 MeV Si+13. A comprehensive electron microscopy study of defect formation in Bi2Sr2Ca2Cu3Ox, and in oxygen-reduced and ozone-treated 123, shows that the degree of radiation damage (the size and the shape of the defect) by the heavy ions depends on: (a) the rate at which ions lose their energy in the target; (b) crystallographic orientations with respect to the incident ion-beam (Fig.1); (c) thermal conductivity and chemical state (eg. oxygen concentration of 123) of the sample, and (d) the extent of pre-existing defects in the crystal. Calculation and simulation of the strain contrast surrounding the amorphous column using two-beam dynamical theory agree well with the observations and suggest that the reduced hole density observed in the crystal near the amorphous region is mainly due to lattice distortion.


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