Nanoscale density variations induced by high energy heavy ions in amorphous silicon nitride and silicon dioxide

Abstract

The cylindrical nanoscale density variations resulting from the interaction of 185 MeV and 2.2 GeV Au ions with 1.0 μm thick amorphous SiN :H and SiO :H layers are determined using small angle x-ray scattering measurements. The resulting density profiles resembles an under-dense core surrounded by an over-dense shell with a smooth transition between the two regions, consistent with molecular-dynamics simulations. For amorphous SiN :H, the density variations show a radius of 4.2 nm with a relative density change three times larger than the value determined for amorphous SiO :H, with a radius of 5.5 nm. Complementary infrared spectroscopy measurements exhibit a damage cross-section comparable to the core dimensions. The morphology of the density variations results from freezing in the local viscous flow arising from the non-uniform temperature profile in the radial direction of the ion path. The concomitant drop in viscosity mediated by the thermal conductivity appears to be the main driving force rather than the presence of a density anomaly.

Unravelling the secrets of the resistance of GaN to strongly ionising radiation

“…The use of equilibrium thermodynamic quantities to describe a process far from equilibrium must be taken with some care. Yet, the excellent agreement between experimental and theoretical results presented here and previously for other semiconductors and insulators 12,39,40 suggests that the simplicity and low computational costs offset the small deviations that may arise due to nonequilibrium physics. However, it is important to note that the TTM does not take into consideration the structural dynamics of the crystal hence hiding compelling phenomena such as phase transitions or defect dynamics.…”

Etched ion tracks in amorphous SiO2 characterized by small angle x-ray scattering: influence of ion energy and etching conditions

“…Several theoretical studies have dealt with these issues by using a combination of numerical analysis and molecular dynamics simulations [20][21][22]. However, although the thermal spike model is a simple model, when used in conjunction with molecular dynamics simulation, it can yield valuable results that agree well with experiments [23,24].…”

“…Although polymer etched ion track membranes have been commercially produced for many years and many studies on their fabrication and characterisation have been conducted, the transition into commercial applications for nanopores fabricated in SiO 2 and Si 3 N 4 by the ion track etching method has been less successful, despite the fact that the mechanisms for track formation are well understood [19,23,27,28]. Reliable and reproducible production of pores in these materials is highly desirable since they exhibit mechanical, chemical and thermal stability under a wide range of conditions, including those used to fabricate semiconductor devices.…”

Vaporlike phase of amorphous SiO2 is not a prerequisite for the core/shell ion tracks or ion shaping

“…Therefore, the V-M model is excluded. The C/S tracks are formed in SiO 2 without vaporization, probably due to the inhomogeneous radial temperature profile in a molten track [15]. The ion shaping of NPs is induced through mass transport via underdense cores of the tracks, in correlation with the recovery process of the silica matrix after emitting a pressure wave.…”

“…Consequently, we need to detect and calculate fine structures in the subnanometer region. It should be noted that Mota-Santiago et al recently have proposed another mechanism for the C/S track formation without vaporization [15]; inhomogeneous temperature distribution along the radial direction that generates the C/S tracks.…”