Structural properties of embedded Ge nanoparticles modified by swift heavy-ion irradiation

Abstract

Silica-embedded Ge nanoparticles (NPs) of different sizes irradiated with swift heavy ions (SHIs) at a given energy may reportedly elongate along the incident ion direction, perpendicular to it, or not at all. Here, for a given NP size distribution, we have investigated the SHI energy dependence of the elongation process. Higher-energy irradiation generally yielded elongation along the ion track (as previously observed), but for lower-energy irradiation, elongation both parallel and perpendicular to the ion direction was observed. We demonstrate that NP size and electronic energy loss together govern the elongation process, reinforcing the proposed model where elongation perpendicular to the ion direction is only expected for Ge NPs bigger than the mean ion track diameter in silica. Here, a wide fluence range is also probed, enabling us to follow in more detail the transition from spherical unirradiated Ge NPs to Ge NPs elongated either parallel or perpendicular to the ion beam. X-ray absorption spectroscopy (XAS) measurements are utilized for the quantification of crystalline, amorphous, and oxidized environments around Ge atoms. Combining such results with transmission electron microscopy (TEM) observations shows the Ge NPs are rendered amorphous prior to elongation, potentially via a melt-and-quench process. Thereafter, stronger electron-phonon coupling in amorphous Ge compared to crystalline Ge may potentially influence the elongation process. The Ge NP amorphization occurs at lower fluences for higher irradiation energies, indicating electronic energy loss-and not ballistic effects-governs the amorphization. Subsequent to amorphization and elongation, TEM and XAS results also show the NPs gradually intermix with SiO 2 and dissolve within the matrix as the irradiation fluence increases. We discuss the impact of such results in the ion beam tailoring of Ge NPs for technological applications.

Plasmonic Nanoparticles in Dielectrics Synthesized by Ion Beams: Optical Properties and Photonic Applications

“…It is believed that the realization of elongation requires several basic conditions as follows: the high enough energy (hundreds of MeV) and proper fluence (≈10 13 ions cm −2 ) of implanted ions to form the ion tracks in the dielectrics; the larger diameter of NPs than the width of tracks (usually larger than 10 nm); and the suitable dielectrics. [ 90–102 ] It should be noted that the size condition of NPs for elongation is still under debate; and some experimental and theoretical studies on smaller NPs for effective elongation have been reported. [ 81 ] In this way, the NP–dielectrics systems can be well designed with tunable physical properties by optimizing the parameters during ion beam processing.…”

Ion–solid interactions at the extremes of electronic energy loss: Examples for amorphous semiconductors and embedded nanostructures

“…Araujo et al [40] examined the shape transformation in greater detail. While Schmidt et al utilised sputtering to form different layers of NPs of uniform size (as shown in Fig.…”

“…10), Araujo et al utilised ion implantation to produce a broad NP size distribution. An advantage of the latter is that spherical, oblate and prolate NPs can be viewed in a single XTEM image and size threshold(s) can be better quantified relative to an image with only three different NP [40]. The ion fluences required for the NP crystalline-to-amorphous phase transformation and NP dissolution both decreased as the ion energy increased, demonstrating electronic energy loss was responsible for the two processes.…”

Modification of semiconductor or metal nanoparticle lattices in amorphous alumina by MeV heavy ions

“…Previous studies of crystalline Ge NPs embedded in silica have shown that SHIs can modify them in different ways. Depending on the SHI electronic stopping power (S e ), ion fluence and initial NP size, Ge NPs can elongate along the incident ion direction, elongate perpendicular to it or stay unchanged [6,7]. It is important to mention that in the most of the studied cases authors have used SHI having S e values exceeding S e values of ions used in the present work and NPs were embedded in amorphous silica matrix.…”