Study Of Defect Clusters Research Articles

STUDY OF FORMATION OF DEFECTS/DEFECT CLUSTERS IN NICKEL NANOWIRES

In this paper, formation of defects/defect clusters in nickel nanowires (Ni-NWs) due to interaction of a 60 kilo-electron-volt (keV) beam of proton (H[Formula: see text] ions is studied. Ni-NWs are exposed to various fluencies of H[Formula: see text] ions ranging between [Formula: see text] and [Formula: see text][Formula: see text]ions/cm2. The analysis of pristine and H[Formula: see text] ion-irradiated Ni-NWs samples is mainly done using transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. Stopping range of ions in matter (SRIM) simulation software is employed to verify the production of defect clusters in Ni-NWs theoretically. Furthermore, insight of creation of defects in Ni-NWs due to interaction of low energy H[Formula: see text] ions in keV range is made using the theory of collision cascade effect. The study of defect clusters induced in Ni-NWs under H[Formula: see text] ions beam irradiation is essential for application of Ni-NW-based nanodevices in harsh environment containing plenty of H[Formula: see text] ions such as for use in spacecraft equipped for space missions.

Classification of clusters in collision cascades

The structure of defect clusters formed in a displacement cascade plays a significant role in the micro-structural evolution during irradiation. Molecular dynamics simulations have been widely used to study collision cascades and subsequent clustering of defects. We present a novel method to pattern match and classify defect clusters. A cluster is characterized by the geometrical and topological histograms of its angles and distances which can then be used as similarity metrics. The technique is demonstrated by matching similar clusters for different cluster shapes like ring, crowdions etc. in a database of cascade damage configurations in Fe and W at different energies. We further use graph based dimensionality reduction techniques and unsupervised machine learning on the features of all the clusters present in the database to find classes of clusters. The classification successfully separates out many already known categories of clusters such as crowdions, planar crowdion pairs, rings and perpendicular crowdions. The dimensionality and size of different classes provides a broad categorization of classes. The distribution of different classes of shapes among cascades of different elements and energies shows the exclusivity of shapes to elements and energies. We discuss the key points and computational efficiency of the algorithms along with the various prominent results of their application. We discuss the motivation for using machine learning and statistics for the problems and compare different techniques. The algorithms along with the supporting analysis and visualizations give an unsupervised approach for classification and study of defect clusters in cascades. The distribution of cluster shapes and structures along with the shape properties like diffusivity, stability, etc. can be used as input to higher scale models in a multi-scale radiation damage study.

Analysis of Amorphous Matrices Induced in Nickel Nanowires Due to Kilo-Electron-Volt H+ Ions Beam Irradiation for Application in Spacecrafts

This report is based on study of defect clusters or amorphous matrices induced in nickel nanowires (Ni-NWs) due to interaction of a beam of ~ 60 KeV hydrogen (H+) ions. Ni-NWs are exposed to various fluencies of hydrogen (H+) ions ranging between ~ 1014 ions/cm2 to 1017 ions/cm2. The analysis of pristine and hydrogen (H+) ions irradiated Ni-NWs samples has been mainly done using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. SRIM (stopping range of ions in matter) simulation is performed to corroborate the production of defect clusters/amorphous matrices in Ni-NWs theoretically. Moreover, basic insight of defect creation in Ni-NWs due to interaction of low energy in kilo-electron-volt (KeV) range hydrogen (H+) ions has been built using collision cascade theory. The purpose of this analysis is to explore the possibility of application of Ni-NWs based future nanodevices in environment containing plenty of hydrogen (H+) ions such as for use in spacecrafts employed for upper space missions.

The use of exafs in the study of defect clusters in doped CaF2

Abstract The results of a study of the local structural environment of dopant ions in CaF2 using the EXAFS technique are reported and compared with data for the same systems obtained from neutron diffraction and computer simulation studies. It is shown that the local structure surrounding the dopant ion is different for Er-doped and La-doped CaF2. The observed fine-structure is compatible with an octahedral cluster of dopant ions and fluoride interstitials, in the case of Er-doped CaF2, and an interstitial-dopant dimer which has captured an additional fluoride interstitial, in the case of La-doped CaF2.