The density and pressure of helium nano-bubbles encapsulated in silicon

Abstract

The 1 s 2 → 1 s 2 p ( 1 P ) excitation in compressed helium atoms in either the bulk material or encapsulated in a bubble is shifted to energies higher than in the free atom. For bulk helium, energy shifts predicted from non-empirical electronic structure computations are in excellent agreement with experimentally determined values. However, there are significant discrepancies both between the results of experiments on different bubbles and between these and the well established descriptions of the bulk. A critique is presented of previous analyses of earlier scanning transmission electron microscope measurements that are untrustworthy because the density dependence of the electron impact excitation cross section was neglected. Experimental electron energy loss data from an earlier study of helium encapsulated in silicon are reanalysed and it is shown that the properties of the helium in these bubbles do not differ significantly from those in the bulk, thereby enabling the densities in the bubbles to be determined. These enable bubble pressures to be deduced from a well established experimentally derived equation of state. It is shown that the errors of up to 80% in the incorrectly determined densities are greatly magnified in the predicted pressures which can be too large by factors of over seven.

Synergistic Effect of He for the Fabrication of Ne and Ar Gas-Charged Silicon Thin Films as Solid Targets for Spectroscopic Studies

“…This behavior for the He 1s→2p transition has been associated with the short-range Pauli pseudo-repulsion of the 2p-electron wave function with the ground-state orbital of neighboring atoms [ 59 , 60 ]. This effect has also been measured at the microscopic scale by monitoring individual bubbles in a transmission electron microscope using STEM–EELS [ 24 , 27 , 61 ]. For the case of gaseous Ne, the K-shell excitation has also been previously investigated through EELS using small-angle inelastic scattering of 2.5 keV electrons [ 62 ].…”

“…An exhaustive microstructural characterization also showed that gas content and nanobubble size and shape are finely tunable [ 17 , 24 , 25 ]. Due to the high density and pressure of He trapped in the nanobubbles [ 24 , 25 , 26 , 27 ], the He-charged Si films have been proposed as “solid targets” for nuclear reaction studies in our previous works [ 28 , 29 , 30 , 31 , 32 , 33 ].…”

Synergistic Effect of He for the Fabrication of Ne and Ar Gas-Charged Silicon Thin Films as Solid Targets for Spectroscopic Studies

“…This behavior for the He 1s→2p transition has been associated to the short-range Pauli pseudo-repulsion of the 2p-electron wave function with the ground-state orbital of neighboring atoms [58,59]. This effect has also been measured at the microscopic scale monitoring individual bubbles in a transmission electron microscope by STEM-EELS [24,27,60]. For the case of gaseous Ne, the K-shell excitation has been also previously investigated by EELS spectroscopy using small-angle inelastic scattering of 2.5 keV electrons [61].…”

“…An exhaustive microstructural characterization also showed that gas content and nanobubbles size and shape are finely tunable [17,24,25]. Due to the high density and pressure of He trapped in the nanobubbles [24][25][26][27], the He-charged Si films have been proposed as "solid-targets" for nuclear reaction studies in our previous works [28][29][30][31][32][33].…”