Anisotropy of electronic stopping power in graphite

Abstract

The rate of energy transfer from ion projectiles onto the electrons of a solid target is hard to determine experimentally in the velocity regime between the adiabatic limit and the Bragg peak. First-principles simulations have lately offered relevant new insights and quantitative information for prototypical homogeneous materials. Here we study the influence of structural anisotropy on electronic stopping power with time-dependent density functional theory simulations of a hydrogen projectile in graphite. The projectile travelled at a range of angles and impact parameters for velocities between 0.1 and 1.4 a.u., and the electronic stopping power was calculated for each simulation. After validation with average experimental data, the anisotropic crystal structure was found to have a strong influence on the stopping power, with a difference between simulations parallel and perpendicular to the graphite plane of up to 25%, more anisotropic than expected based on previous work. The velocity dependence at low velocity displays clear linear behaviour in general, except for projectiles travelling perpendicular to graphitic layers, for which a threshold-like behaviour is obtained. For projectiles travelling along graphitic planes metallic behaviour is observed with a change of slope when the projectile velocity reaches the Fermi velocity of the electrons.

Siesta: Recent developments and applications

“…95 The difference of sign between protons and antiprotons produces a significant difference in the stopping power (rate of energy excitation) beyond the linear-response paradigm (the Barkas effect), and the insulating character of the target makes it inaccessible to the jellium paradigm. The success stimulated further studies along this line [77][78][79][80] using improved versions of TD-DFT in SIESTA, as described here. Fig.…”

“…75, this algorithm can be shown not to be entirely consistent with the connection represented by the D matrix defined above. Nevertheless, the discrepancies due to the mentioned inconsistency have been shown to be small in a series of studies using this formalism [77][78][79][80] , at least for low atomic velocities. The practical benefit of separating the two procedures is to perform the change of basis only when necessary, allowing for many electronic steps per atomic motion step, if the nuclei are still significantly slower than electrons, for instance.…”

“…These terms are well known, 86 and their geometrical meaning in terms of the relevant curvature 75 will appear in Ref. 87. They are being tested and should be incorporated shortly to a visible branch in the open source repository, to be later merged into the trunk, and further incorporated into SIESTA releases.…”

Ab initio electronic stopping power for protons in Ga 0.5 In 0.5 P/GaAs/Ge triple-junction solar cells for space applications

“…Others have highlighted the different contributions of semicore electrons in channelling versus off-channelling conditions [ 35 ]. Local enhancement and reduction of the ESP for specific channels and velocity-dependent deviations from an ideal channelling trajectory were also reported [ 31 ], as well as the influence of a strongly anisotropic crystal structure on the stopping power [ 36 ].…”

First-principles simulation of light-ion microscopy of graphene

“…Computational modeling of electron dynamics during ion irradiation of materials offers opportunities to accurately predict optimal beam and detector parameters for nondestructive imaging of 2D materials. Many studies have demonstrated the ability of first-principles calculations to predict accurate energy deposition rates for ions traversing bulk materials [23][24][25][26][27][28][29]. However, projec-tile charge may not fully equilibrate within a thin target [30][31][32], fundamentally altering the response of these materials to ion irradiation.…”