scholarly journals Evolution of Defects in CVD-W Irradiated by H/He Neutral Beam Using Positron Annihilation Spectroscopy

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 211
Author(s):  
Xuefen Tian ◽  
Xiang Liu ◽  
Min Gong ◽  
Weidi He ◽  
Xinge Fu ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Fusion Energy ◽  
Positron Beam ◽  
Surface Damage ◽  
Neutral Beam ◽  
Beam Irradiation ◽  
Type Defect ◽  
Damage Layer ◽  
S Parameters ◽  
Vacancy Type Defect

One of the key problems for the application of nuclear fusion energy is to select the suitable plasma facing materials (PFMs). Among the W-based materials, CVD-W exhibits some unique advantages. In order to estimate the performance of CVD-W under the fusion environment, the vacancy-type defects and their evolution are investigated by the Doppler-broadening slow positron beam analysis (DB-SPBA) combined with SEM (scanning electron microscope). There are two kinds of neutral beam irradiation, the pure H neutral beam and the H + 6 at.% He neutral beam irradiation, which are performed at the neutral beam facility GLADIS (IPP, Germany). The surface temperatures of CVD-W irradiated by H (H + 6 at.% He) are 850 and 1000 (700 and 800 °C). By comparing the samples under different conditions, the defect evolution of CVD-W is obtained. As for the pure H neutral beam irradiated samples, the DB-SPBA results demonstrate that the CVD-W sample at the surface temperature of 1000 °C, compared to the 850 °C sample, shows a decrease in S parameters, which is due to the reduction of vacancy-type defect concentration. The defect damage layer in 1000 °C sample is narrower than that of 850 °C sample and the defect type tends to be consistent in 1000 °C sample. The SEM results suggest that the surface damage of the 1000 °C sample was recovered to some extent. As for the H + 6 at.% He neutral beam irradiated samples, compared with the CVD-W sample at the surface temperature of 700 °C, the 800 °C sample shows an increased S parameters, which can be attributed to the volume increase of vacancy-type defect. The defect damage layer in the 800 °C sample is wider than that of the 700 °C sample. Both the H + 6 at.% He irradiated samples show complex defect types. The surface of the 800 °C sample exhibits more dense pinhole damage structures compared to that of the 700 °C sample.

scholarly journals Vacancy type defect formation in irradiated α-iron investigated by positron beam Doppler broadening technique

2014 ◽  
Vol 505 ◽  
pp. 012018 ◽  
Author(s):  
C W He ◽  
K Dawi ◽  
C Platteau ◽  
M F Barthe ◽  
P Desgardin ◽  
...  
Keyword(s):  
Defect Formation ◽  
Positron Beam ◽  
Doppler Broadening ◽  
Type Defect ◽  
Vacancy Type Defect

scholarly journals Low Energy, Low Angle, Large Area Ion Polishing for Improved EBSD Indexing

2009 ◽  
Vol 17 (3) ◽  
pp. 30-35
Author(s):  
S.D. Walck ◽  
J.R. Porter ◽  
H-W. Yang ◽  
S.S. Dheda
Keyword(s):  
Current Density ◽  
Surface Defects ◽  
Incident Angle ◽  
Surface Damage ◽  
Beam Current ◽  
Mechanical Polishing ◽  
Beam Current Density ◽  
Large Area ◽  
Electron Backscattered Diffraction ◽  
Damage Layer

Good sample preparation is essential for acquiring successful electron backscattered diffraction (EBSD) patterns in the SEM. Mechanical polishing to obtain the required surface quality with minimal sub-surface defects and deformation that does not interfere with the quality of the diffraction data is, more often than not, an art form. Special polishing techniques, such as low force lapping fixtures, electrochemical-mechanical polishing, and vibratory polishing, have been used to minimize the sub-surface damage, but have not eliminated it. Ion polishing has been used to reduce the damage layer further. However, the commercially available ion systems suffer several drawbacks, including: 1) small area treatment (≤ 1 cm) 2) decreasing beam current density with accelerating voltages, and 3) the inability to process non-conducting samples. Barna and Pecz have shown that at 3 keV with an incident angle of 5° relative to the surface, approximately 25 nm of ion damage occurs in Si and GaAs, but at 250 eV, there is less than 1 nm of amorphization of the surface. They also showed that a glancing angle across the surface is essential for removing topographic features. The ion guns that have been available for ion polishing and ion etching of SEM samples typically cannot operate effectively below 3 keV because of the low current density.

scholarly journals Study of Microvoids in High-Rate a-Si:H Using Positron Annihilation

1997 ◽  
Vol 467 ◽  
Author(s):  
X. Zou ◽  
D. P. Webb ◽  
S. H. Lin ◽  
Y. W. Lam ◽  
Y. C. Chan ◽  
...  
Keyword(s):  
Thin Films ◽  
Positron Annihilation ◽  
Surface Region ◽  
Positron Beam ◽  
High Rate ◽  
Doppler Broadening ◽  
Slow Positron ◽  
Depth Profiles ◽  
Vacancy Type Defect ◽  
Low Rate

ABSTRACTIn this paper, we have carried out the positron annihilation measurement on high-rate and low-rate a-Si:H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. We have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.

Comparison of diffraction methods for measurement of surface damage in superalloys

2006 ◽  
Vol 21 (7) ◽  
pp. 1775-1781 ◽  
Author(s):  
L.N. Brewer ◽  
M.A. Othon ◽  
Y. Gao ◽  
B.T. Hazel ◽  
W.H. Buttrill ◽  
...  
Keyword(s):  
Surface Damage ◽  
High Energy ◽  
Machining Process ◽  
X Ray Diffraction ◽  
X Ray ◽  
Damage Layer ◽  
Potential Source ◽  
Machining Operations ◽  
Electron Back Scattered Diffraction ◽  
Super Alloy

Surface damage from machining operations is a potential source of failure in metallic components. The ability to quantitatively characterize the depth and extent of the damage layer is critical to controlling the machining process. Electron back scattered diffraction and synchrotron high energy x-ray diffraction were applied to the measurement of machining surface damage in a Ni-based super alloy. Both techniques clearly showed a plastic deformation profile below the surface as a function of the machining conditions used. Using the average intragrain misorientation parameter, the electron back scattered diffraction was able to quantify the amount of surface damage from one surface treatment to another. In addition, the x-ray diffraction measurements were able to simultaneously measure the elastic strain as a function of depth from the surface.

Modulation of the Dielectric Properties of CaCu3Ti4O12 System with Gd-Substitution

2017 ◽  
Vol 373 ◽  
pp. 213-216 ◽  
Author(s):  
Zhen Ping Chen ◽  
Hui Fang He ◽  
Tao Li ◽  
Hai Yang Dai ◽  
Zhi Quan Chen
Keyword(s):  
Grain Size ◽  
Dielectric Properties ◽  
Positron Annihilation ◽  
Defect Concentration ◽  
Doping Content ◽  
Type Defect ◽  
Vacancy Type Defect

To specify the effects of modulating mechanism of Gd substitution on the dielectric properties for Ca1-xGdxCu3Ti4O12 system, the XRD, SEM and positron positron annihilation technique have been implemented. The results display that both grain size and vacancy-type defect concentration play important roles in controlling the dielectric properties of CaCu3Ti4O12. The dielectric properties are improved by adding an appropriate amount of Gd additives (x=0.01) but weakened by higher Gd doping content since this is closely related to the grain size and concentration of vacancy-type defect in the samples.

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