Heteroepitaxial Self Assembling Noble Metal Nanoparticles in Monocrystalline Silicon

Embedding metal nanoparticles in crystalline silicon possesses numerous possible applications to fabricate optoelectronic switches, increase efficiency of radiation detectors, decrease the thickness of monocrystalline silicon solar panels and investigate fundamental properties. Noble metal nanoparticles made of gold or silver are grown in cavities in monocrystalline silicon formed by helium ion implantation and high temperature annealing at depth greater than 500 nm from the surface. Metals are introduced into the system by low energy ion implantation or physical vapor deposited thin film on the surface, and diffused into cavities by heat treatment. Nanoparticles nucleate on the inner surface of cavities heteroepitaxially and form face centered cubic crystal structure in the case of silver. Excessive heat treatment causes metal to be emitted from nanoparticles into bulk after trapping and nanoparticle formation. Helium ion implantation, annealing and diffusion heat treatment conditions have been optimized so that residual crystalline damage, point defects and dislocations, is reduced in monocrystalline silicon substrate

EXPLORING CORRELATIVE MICROSCOPY METHODOLOGIES FOR ENHANCED IMAGING AND ANALYSIS WITH HELIUM ION MICROSCOPE

Correlative microscopy plays a vital role in scientific research and material analysis by offering a valuable solution to integrate diverse imaging techniques, resulting in a comprehensive understanding of complex samples. Combining Secondary Electron (SE), Scanning Transmission Ion Microscopy (STIM), and Secondary Ion Mass Spectrometry (SIMS) in one apparatus using a He+/Ne+ ion beam, we can establish meaningful connections between the morphology, crystal structure, and chemistry of a given sample on a nanometre scale. This approach delves deep into the complexities of material characteristics such as semiconductors, biological processes, etc. However, one of these three correlative approaches, STIM, has potential applications that still need to be studied and compared to similar existing methods. Before delving into STIM imaging, we initiated our study by examining ion-induced damage effects before and during imaging on the sample. For this aim we performed preliminary experiments related to Ga+ and He+ ion irradiation on thin lamellae of silicon and aluminium. Depending on the experimental conditions, we investigated the top and bottom surface morphologies, as well as a structural transformation from crystalline to amorphous material. Subsequently, to understand STIM applications, we compared STIM imaging with existing comparable imaging techniques such as Transmission Kikuchi Diffraction (TKD), Backscattered Electrons (BSE), and SE. Additionally, we expanded the capabilities of STIM imaging by conducting Time of Flight (ToF) measurements using a separate apparatus to explore the potential for complementary studies within the STIM technique. Towards the conclusion of our research, we focused on the materials science applications of ion beam microscopy techniques namely SE, SIMS and STIM techniques. Our initial focus was on studying dopant profiling by analysing SE-generated contrast with a helium ion beam. In the subsequent stage of our correlative approach, we established connections between SIMS, SE imaging, and other techniques to investigate perovskite solar cell materials. In the final segment of our correlative approach, we attempted to correlate STIM with SIMS. While this endeavour had limited success, it did provide valuable insights in that direction.R-AGR-3444 - PRIDE17/12246511 PACE_Common (01/03/2019 - 31/08/2025) - DALE Philli

Fundamentals of Ion-Solid Interaction: A Compact Introduction

Abstrac

Ion-induced damage in alkali halide crystals

An investigation has been made of radiation damage in alkali halide crystals induced by heavy bombardment of 1 MeV helium ions. The channeling technique has been employed and three processes have been monitored simultaneously to explain the apparent reduction of damage at high doses, and to attempt to relate dechanneling processes to the types of defects that are created. A discussion of the basic channeling parameters is given, followed by a description of the common defects known to exist in alkali halides. An outline of the Pooley mechanism for the creation of F-centres, and the subsequent fate of these and their complementary interstitial defects, is presented. The experimental apparatus designed for the study of the emission of particles and photons, resulting from the bombardment is described together with the computerized data collection equipment. The importance of adequate monitoring techniques for the detection and recording systems is stressed

Embrittlement induced by the synergistic effects of radiation damage and helium in structural steels

Ferritic/martensitic steels are candidate materials for fusion reactor structural components, liquid metal containers of spallation neutron sources, and accelerator driven systems, with good radiation resistance and thermo-mechanical properties. However, embrittlement resulting from the combined effects of radiation induced displacement damage (measured in dpa = displacement per atom) and transmutation products, especially helium gas, is one of the key issues. Four different steels were selected for mechanical and microstructural studies to understand the mechanisms of embrittlement induced by the combined effects of displacement damage and helium after irradiation in SINQ, the Swiss spallation source. The irradiations conditions were in the range: 10.7 ¿ 20.4 dpa with 850-1750 appm He at 160-300 °C. The evolution of the mechanical properties after irradiation was investigated by tensile and hardness tests. Radiation-induced defect clusters and helium bubbles were quantified by transmission electron microscopy (TEM). Emphasis was put on the deformation mechanisms under the different observed fracture mode, (ductile, quasi-cleavage and intergranular), whose occurrence depends on the irradiation conditions (dpa, He content and irradiation temperature). The tensile stress-strain curves and the scanning electron microscopy images of fracture surfaces showed distinct fracture mechanisms under different irradiation and test conditions. The tensile tests showed a yielding stress increase and loss of ductility of irradiated specimens. Hardness was measured on the specimens before tensile testing. The hardness results demonstrated an increasing trend with irradiation dose and helium content. TEM observations were done for all irradiated fractured specimens. Small defect clusters were observed in the 12.3 dpa specimen, but large defect clusters with loop-shape were very few. In the specimens of 17.2, 17.7 and 20.4 dpa, many large dislocation loops were detected besides small clusters. In addition, helium bubbles were observed in all specimens. The average size of defect clusters increased from 4.2 nm to 11.8 nm with dose increasing from 12.3 dpa to 20.4 dpa, whereas the number density did not change significantly. Meanwhile, the average size of visible helium bubbles increased from 1.03 nm to 1.93 nm. The microstructures in deformed area of irradiated specimens were observed and defect free channels with {110} and {112} slip planes were found in some specimens, indicating plastic flow localization. The average width of the channels is about 100 nm. Regarding the brittle samples, the TEM-lamella were extracted directly below intergranular fracture surfaces or cleavage surfaces by focused ion beam. Strikingly, deformation twinning was observed as the main feature in three irradiated specimens at high dose. Only twins with {112} planes were observed in all of these samples. The average thickness of twins is about 34 nm. Twins started from a fracture surface became gradually thinner with distance away from the fracture surface and stopped in the matrix finally. Features such as twin-precipitates interaction, twin-grain boundary and/or lath boundary interaction were observed. Twinning bands were seen to be arrested by grain boundaries or large precipitates, but could penetrate martensitic lath boundaries. Unlike the case of defect free channels, inside twins small defect-clusters, dislocation loops and dense small helium bubbles were observed

Material characterization and modification using helium ion microscopy: various examples

This thesis describes several approaches for material characterization using helium ion microscopy (HIM). Furthermore, it also demonstrates a possibility for in-situ observation and investigation of material modification and defect creation. This has been done using He+ ions with an energy of several tens of keV. The influence of a sub-nanometer He+ ion beam on different classes of materials, such as metals, semiconductors and insulators, was studied in the current work

Ion beam modification of strontium titanate and highly oriented pyrolytic graphite

Doping and structural modification affects such important characteristics as conductivity, catalytic activity, luminescent and magnetic properties of modern materials. Ion beam implantation is a conventional doping method which combines a low processing temperature with convenient control of concentration and distribution of dopant and irradiation damage. In this study, the ion beam implantation method was used to modify strontium titanate (STO) and highly oriented pyrolytic graphite (HOPG). Both materials have immense potential for applications in different areas of modern technology, including gas sensing, catalysis, electronics and spintronics. Fe-implanted STO and N- and O-implanted HOPG were examined with complementary experimental techniques, including Particle Induced X-ray Emission (PIXE), Rutherford Backscattering (RBS), X-ray Absorption Near Edge Structure (XANES) and X-ray Photoemission (XPS). Magnetic properties were analyzed with Superconducting quantum interference device (SQUID) magnetometry. Irradiation with ion beams modifies structure and increases the surface reactivity of STO and HOPG. XPS reveals an increase of O and C content on STO surface due to reactions with gases from the ambient atmosphere with the surface defects. XANES analysis detects the formation of carbonyl and other functional groups as well as amorphization with formation of sp3 carbon species on the ion irradiated HOPG surfaces. Iron irradiation and post-implantation annealing in O2 at 350°C cause unexpected loss of Sr at the surface area of STO due to formation of lower density SrCO3 and Sr(OH)2 phases and possible SrO desorption. The STO single crystals exhibit weak ferromagnetic moments prior to implantation. The maximum saturation moment is obtained after our highest implantation dose of 2x1016 Fe atom/cm2, which could be correlated with the metallic Fe0 phases in addition to the presence of O/Ti vacancies. The annealing in oxygen atmosphere partially heals implantation damages and changes the oxidation state of the implanted iron from metallic Fe0 to Fe2+/Fe3+ oxide, accompanied by a loss of the ferromagnetic response. Iron oxide phases with Fe2+ and Fe3+ states corresponding to this regime are identified and their structures are confirmed by calculations using the Real Space Multiple Scattering program (FEFF9). Magnetic moments of the N-and O-implanted HOPG samples are correlated well with transition metal impurities

Charakterisierung der Strahlenschäden in Wolfram

Tungsten as plasma-facing material of a future fusion reactor will be subjected to high-flux neutron irradiation. The defect creation and its influence on hydrogen retention in tungsten irradiated with different ions were investigated. The microstructure and hydrogen retention was studied with transmission electron microscopy, positron annihilation spectroscopy, nuclear reaction analysis and thermal desorption spectroscopy. It was found that the displacement damage and hydrogen retention in tungsten irradiated by medium to heavy ions (Si, Fe, Cu, W) is very similar.Wolfram als plasmabelastetes Material eines zukünftigen Fusionsreaktors wird hohen Neutronenflüssen ausgesetzt. Strahlenschäden und deren Einfluss auf die Wasserstoffrückhaltung wurde in ionengeschädigtem Wolfram untersucht. Die Mikrostruktur und die Wasserstoffrückhaltung wurde mit Transmissionselektronenmikroskopie, Positronannihilationsspektroskopie, Kernreaktionanalyse und Desorptionsspektroskopie untersucht. Die Mikrostruktur und Wasserstoffrückhaltung ist sehr ähnlich in Wolfram, dass mit mittelschweren bis schweren Ionen (Si, Fe, Cu, W) geschädigt wurde