GaAs a model system to study the role of electron–phonon coupling on ionization stimulated damage recovery

International audienceAbstract The latent ion tracks observed in various materials after swift heavy ion (SHI) irradiation is often explained in the framework of thermal spike model (TSM). Dominantly, SHIs deposit most of their energy via intense ionization leading to a very high density of localized electronic excitations. The energy transfer from electrons to lattice, within a time of electronic cooling ∼100 fs, is governed by the ‘electron-phonon coupling’ parameter g . In this work, GaAs is used as a model system for studying ionization-stimulated damage recovery. Controlled damage is introduced using 300 KeV Ar ion irradiation, followed by successive irradiation using 100 MeV Ag ions at ∼80 K by varying the fluence (ions cm −2 ). The TSM is utilized to explain the observed recovery. Using the previously published value of g = 3.2 × 10 12 W cm −3 K −1 for GaAs, the existing thermal spike code resulted in melting and quick quenching within ∼10 ps, suggesting the formation of SHI-induced tracks. However, experimental observations do not support the formation of tracks in pristine GaAs. Multiple simulation runs, for different g values, predict that for no melting in GaAs, g should be ⩽ 1.4 × 10 12 W cm −3 K −1 . Finally, the 3D version of the TSM is used to simulate the temperature profiles after an impact of SHI irradiation on an amorphous nano-zone embedded in a crystalline GaAs matrix. Simulations predict that the thermal spike in this zone is confined, indicating melt-flow at the crystalline-amorphous interface that can promote recovery. This lattice recovery is further supported by both RBS/C and TEM results

GaAs a model system to study the role of electron–phonon coupling on ionization stimulated damage recovery

International audienceAbstract The latent ion tracks observed in various materials after swift heavy ion (SHI) irradiation is often explained in the framework of thermal spike model (TSM). Dominantly, SHIs deposit most of their energy via intense ionization leading to a very high density of localized electronic excitations. The energy transfer from electrons to lattice, within a time of electronic cooling ∼100 fs, is governed by the ‘electron-phonon coupling’ parameter g . In this work, GaAs is used as a model system for studying ionization-stimulated damage recovery. Controlled damage is introduced using 300 KeV Ar ion irradiation, followed by successive irradiation using 100 MeV Ag ions at ∼80 K by varying the fluence (ions cm −2 ). The TSM is utilized to explain the observed recovery. Using the previously published value of g = 3.2 × 10 12 W cm −3 K −1 for GaAs, the existing thermal spike code resulted in melting and quick quenching within ∼10 ps, suggesting the formation of SHI-induced tracks. However, experimental observations do not support the formation of tracks in pristine GaAs. Multiple simulation runs, for different g values, predict that for no melting in GaAs, g should be ⩽ 1.4 × 10 12 W cm −3 K −1 . Finally, the 3D version of the TSM is used to simulate the temperature profiles after an impact of SHI irradiation on an amorphous nano-zone embedded in a crystalline GaAs matrix. Simulations predict that the thermal spike in this zone is confined, indicating melt-flow at the crystalline-amorphous interface that can promote recovery. This lattice recovery is further supported by both RBS/C and TEM results

Recovery of ion-damaged 4H-SiC under thermal and ion beam-induced ultrafast thermal spike-assisted annealing

International audienceThe recovery effect of isochronal thermal annealing and inelastic energy deposited during 100 MeV Ag swift heavy ion (SHI) irradiation is demonstrated in the case of 4H-SiC pre-damaged by elastic energy deposition of 300 keV Ar ion. The Ar-induced fractional disorder follows a nonlinear two-step damage build-up. The fractional disorder level of 0.3 displacements per atom (dpa) is established as the threshold above which the lattice rapidly enters the amorphous phase, characterized by the presence of highly photo-absorbing defects. The SHI-induced recovery suggests that the damage annealing, in the pre-damaged region (∼350 nm) where the Se for 100 MeV Ag is almost constant (∼16.21 keV/nm), is more pronounced than the damage creation by SHI. This allows the disorder values to saturate at a lower value than the present initial disorder. Furthermore, the thermal effect due to SHI irradiation of an amorphous nano-zone embedded in a crystalline host matrix has been evaluated using the 3D implementation of the thermal spike. The recovery process by SHI is ascribed to the thermal spike-induced atomic movements resulting from the melting and the resolidification of the crystalline–amorphous interface

Monitoring of the recovery of ion-damaged 4H-SiC with in situ synchrotron X-ray diffraction as a tool for strain-engineering

International audienceIn situ thermal annealing (673-1273 K) during X-ray diffraction synchrotron measurements was performed to monitor the strain level as a proxy to follow the recovery of 300 keV Ar ion irradiated 4H-SiC single crystals. Results show that, when exposed to Ar ions at a fluence of 6.7 $\times$ 10$^{14}$ ions/cm$^2$ (0.7 dpa), the material suffers a maximum strain of 12$\%$ that reduces to 2$\%$ after the final anneal at 1273 K. In the same time, the disorder derived from the XRD data also demonstrates a thermal recovery of the crystalline structure. Hence, this work presents ion irradiation as a means to induce specific crystalline order and depth-controlled strain states within a few 100 s of nm window in 4H-SiC.[graphic not available: see fulltext][graphic not available: see fulltext

Investigating the thermal stability of ultra-small Ag, Au and AuAg alloy nanoparticles embedded in a silica matrix

Thermal growth kinetics of embedded bimetallic (AuAg/SiO$_2$) nanoparticles are explored and compared with their monometallic (Au/SiO$_2$ and Ag/SiO$_2$) counterparts, as their practical applicability demands stability and uniformity. The plasmonic properties of these nanoparticles (NPs) significantly improve when their size falls in the ultra-small region (diameter < 10 nm), owing to their large active surface area. Interestingly, the bimetallic NPs exhibit better optical properties and structural stability as compared to their monometallic counterparts. This calls for a thorough understanding of the nucleation and temperature-dependent growth to ensure size stability against thermal coarsening that most bimetallic NPs completely lack. Herein, the atom beam sputtered AuAg NPs are systematically analysed over a wide range of annealing temperatures (ATs), and the results are compared with those of Au and Ag NPs. The X-ray photoelectron spectroscopy spectra and other experimental results confirm the formation of AuAg alloy NPs inside the silica matrix. Furthermore, techniques like transmission electron microscopy and grazing-incidence small-/wide-angle X-ray scattering were used to explore the temperature-dependent structural and morphological stability of the NPs. Our results show that the deposited AuAg NPs retain their spherical shape and remain as an alloy for the entire range of ATs. When the AT increases from 25 °C to 800 °C, the size of the NPs also increases from 3.5 to 4.8 nm; beyond that, their size grows substantially to 13.6 nm at 900 °C. We observed that the NPs remain in the ultra-small size range (∼5 nm) until an AT of 800 °C. Beyond that Ostwald ripening is ascribed to be the major cause of particle growth, resulting in an active surface area loss. Based on the outcomes, a three-step nucleation and growth mechanism is proposed

A Combinatorial Study Investigating the Growth of Ultrasmall Embedded Silver Nanoparticles upon Thermal Annealing

Ultrasmall nanoparticles (NPs) with a high active surface areaare essential for optoelectronic and photovoltaic applications. However, thestructural stability and sustainability of these ultrasmall NPs at highertemperatures remain a critical problem. Here, we have synthesized thenanocomposites (NCs) of Ag NPs inside the silica matrix using the atombeam co-sputtering technique. The post-deposition growth of the embeddedAg NPs is systematically investigated at a wide range of annealingtemperatures (ATs). A novel, fast, and effective procedure, correlating theexperimental (UV−vis absorption results) and theoretical (quantummechanical modeling, QMM) results, is used to estimate the size of NPs.The QMM-based simulation, employed for this work, is found to be moreaccurate in reproducing the absorption spectra over the classical/modifiedDrude model, which fails to predict the expected shift in the LSPR forultrasmall NPs. Unlike the classical Drude model, the QMM incorporates theintraband transition of the conduction band electrons to calculate the effective dielectric function of metallic NCs, which is the majorcontribution of LSPR shifts for ultrasmall NPs. In this framework, a direct comparison is made between experimentally andtheoretically observed LSPR peak positions, and it is observed that the size of NPs grows from 3 to 18 nm as AT increases fromroom temperature to 900 °C. Further, in situ grazing-incidence small- & wide-angle X-ray scattering and transmission electronmicroscopy measurements are employed to comprehend the growth of Ag NPs and validate the UV + QMM results. Wedemonstrate that, unlike chemically grown NPs, the embedded Ag NPs ensure greater stability in size and remain in an ultrasmallregime up to 800 °C, and beyond this temperature, the size of NPs increases exponentially due to dominant Ostwald ripening.Finally, a three-stage mechanism is discussed to understand the process of nucleation and growth of the silica-embedded Ag NPs