A review of matter transformation induced in crystalline inorganic insulators by swift heavy ions is presented. The emphasis is made on new results obtained for amorphizable materials such as Gd3Ga5O12, GeS, and LiNbO3 and for non-amorphizable crystals such as SnO2, LiF and CaF2. Assuming that latent tracks result from a transient thermal process, a quantitative development of a thermal spike is proposed. The only free parameter is the electron–lattice interaction mean free path λ. With this parameter it is possible to quantitatively describe track radii, whatever the bonding character of the crystal is, in a wide range of ion velocities assuming two specific criteria: tracks may result from a rapid quenching of a cylinder of matter in which the energy deposited on the lattice has overcome either the energy necessary to reach a quasi-molten phase in the case of amorphizable materials or the cohesion energy in the case of non-amorphizable materials. The evolution of the λ parameter versus the band gap energy of the considered insulator will be presented. On the basis of this discussion some predictions are developed.

Transient thermal processes in heavy ion irradiation of crystalline inorganic insulators

Radiation damage in nanostructured materials

Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subjects. The current status of the research field is discussed and examples of superior performance and competitive advantage of plasma processes and techniques are given. These examples are selected to represent a range of applications of two major types of plasmas suitable for nanoscale synthesis and processing, namely thermally non-equilibrium and thermal plasmas. Major concepts and terminology used in the field are introduced. The paper also pinpoints the major challenges facing plasma-aided nanofabrication and identifies some emerging topics for future research.

http://iopscience.iop.org/article/10.1088/0022-3727/40/8/S01/pdf

Plasma-aided nanofabrication: where is the cutting edge?

Spherical metallic nanoparticles have been formed in ${\mathrm{SiO}}_{2}$ layers by 160-keV implantation of Co ions at a fluence of ${10}^{17}$ ions ${\mathrm{cm}}^{\ensuremath{-}2}.$ The implanted samples were next irradiated with $200\ensuremath{-}\mathrm{MeV}{}^{127}\mathrm{I}$ at fluences ranging from ${10}^{11}$ to ${10}^{14}$ ions ${\mathrm{cm}}^{\ensuremath{-}2}$ at room temperature. Modifications of nanoparticle size and shape were observed by transmission-electron microscopy and have been characterized by magnetic measurements at 295 and 5 K. For ${}^{127}\mathrm{I}$ fluences below ${10}^{12}$ ions ${\mathrm{cm}}^{\ensuremath{-}2},$ the nanoparticles grow in size but remain spherical. For higher fluences an anisotropic growth occurs, with elongation and the preferential easy axis seen along the incident-beam direction. The nanoparticle's growth and deformations are attributed to thermal spike effects.

Anisotropy of Co nanoparticles induced by swift heavy ions

Nanocrystalline silicon carbide (SiC) thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (Td) ranging from 80 to 575 °C and different gas flow ratios (GFRs). While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of Td, GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope (HRTEM), micro-Raman, Fourier transform infrared (FTIR) and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300 °C. The degree of crystallization increases with increasing Td and the crystalline fraction (fc) is 65%±2.2% at 575 °C. The fc is the highest for the films deposited with hydrogen d...

Low temperature deposition of nanocrystalline silicon carbide films by plasma enhanced chemical vapor deposition and their structural and optical characterization

Silicon carbide thin films have been deposited by reactive magnetron sputtering in a pure hydrogen plasma at substrate temperatures, Ts, ranging between 100 and 600 °C. The infrared (IR) absorption spectra and the transmission electron microscopy observations reveal an onset of crystallization at Ts as low as 300 °C. The crystalline fraction increases with Ts and reaches a value of about 60% for Ts=600 °C. Both refractive index n and room temperature dark conductivity σd(RT) show quite consistent behaviors with the structural evolution of the layers. Thus n increases from 1.9 to 2.4 and σd(RT) improves by six orders of magnitude when Ts is raised from 100 to 600 °C.

Low temperature deposition of nanocrystalline silicon carbide thin films

A nanometric powder of tin oxide (SnO2) has been irradiated with lead ions. The same grains have been observed by Transmission Electron Microscopy (TEM) before and after irradiation at a fluence of 5×1012 Pb cm−2. The shape of largest grains strongly changes while the smallest ones disappear. This phenomenon has been explained by using the thermal spike model. It appears that the irradiation induces an increase of the internal pressure in the grains leading to their explosion. In the smallest grains, the calculated maximal temperatures exceed the boiling point so that these grains disappear.

Nanometric size effects on irradiation of tin oxide powder

Tin oxide nanometric powders have been irradiated with several swift heavy ions (Ar, Cd, Ta, Pb and U) and observed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Except for Ar ions, cylindrical tracks are visible at low fluences. The mean track radius is all the more important since the electronic stopping power S e is high. Furthermore, the high S e irradiating ions (Pb, Ta and U) create cylindrical holes while, in the case of Cdion irradiations, the track cores remain crystallized with a difference of contrast from the surrounding crystal. In this case, simulations of HREM images allow us to assert that an amount of matter is lost in Cd track cores. Assuming that the observed latent tracks result from a thermal process, the thermal spike model gives a good description of the observed effects in the high-S e regime. Cylindrical holes correspond to a local area where the maximum temperature reached along the ion path exceeds the boiling point. Concernin...

Behaviour of a nanometric SnO2 powder under swift heavy-ion irradiation: From sputtering to splitting

Tin oxide nanometric powders have been irradiated with swift heavy ions (Ar, Cd, Ta, Pb and U) and observed by high resolution electron microscopy (HREM). Except for Ar ions, cylindrical tracks are visible. The mean track radius is all the more important since the electronic stopping power S e is high. Furthermore, the high- S e ions (Ta, Pb and U) create cylindrical holes, while in the case of Cd irradiations, a crystal-like contrast remains in the core track. Cylindrical holes correspond to a local zone where the maximum temperature calculated using the thermal spike model exceeds the boiling point. For Cd ion irradiations, a sputtering process is investigated.

Irradiation of a tin oxide nanometric powder with swift heavy ions

The irradiation effects induced by swift heavy ions are now widely described in `bulk' materials. It is shown here that the behaviour of matter under irradiation depends on its crystalline state in the sense that a given material is all the more sensitive to swift heavy ion irradiations as the mean crystallite size L is small. The present paper relates the experimental results obtained in yttrium oxide from `in situ' X-ray diffraction measurements. Three kinds of sample have been irradiated: sintered samples (L = 1μm), non-ground powders (L = 45 nm) and ground powders (L = 28 nm). A cubic to monoclinic phase transformation appears if the electronic energy loss of the incident particle is higher than a threshold. The comparison between the different kinds of samples reveals that this phase transformation is all the easier as the mean crystallite size of the target is weak.

A. Berthelot

Papers

Low temperature deposition of nanocrystalline silicon carbide thin films

Nanometric size effects on irradiation of tin oxide powder

Behaviour of a nanometric SnO2 powder under swift heavy-ion irradiation: From sputtering to splitting

Irradiation of a tin oxide nanometric powder with swift heavy ions

Influence of the crystallite size on the phase transformation of yttria irradiated with swift heavy ions