Charge Exchange and Energy Loss of Slow Highly Charged Ions in 1 nm Thick Carbon Nanomembranes

Abstract

Experimental charge exchange and energy loss data for the transmission of slow highly charged Xe ions through ultra-thin polymeric carbon membranes are presented. Surprisingly, two distinct exit charge state distributions accompanied by charge exchange dependent energy losses are observed. The energy loss for ions exhibiting large charge loss shows a quadratic dependency on the incident charge state indicating that equilibrium stopping force values do not apply in this case. Additional angle resolved transmission measurements point on a significant contribution of elastic energy loss. The observations show that regimes of different impact parameters can be separated and thus a particle's energy deposition in an ultra-thin solid target may not be described in terms of an averaged energy loss per unit length. Modern approaches in ion and electron irradiation of solids such as nano-structuring of thin films or even structuring of free-standing monolayers such as graphene [1][2][3] or MoS 2 [4, 5] rely on models for structural and electronic defect formation. Most important for processes during ion-solid interaction is the amount of deposited energy and its dissipation channels [6]. We show that the energy loss and charge exchange of ions in very thin films, such as 2D-materials, show significant differences to solids with reduced thickness. The understanding of these differences is not only of importance for ion beam analysis of 2D-materials but in particular for manipulating and tailoring their properties. [7]. To probe interaction processes in very thin target materials slow highly charged ions (HCI) are ideal tools due to their energy deposition confinement to shallow surface regions. Besides the well known near-surface potential energy deposition [8,9] also an expected increased pre-equilibrium kinetic energy loss (stopping force) [10] is confined to a few nm at the surface. In the conventional description of both contributions to the stopping force, i.e. nuclear and electronic stopping, the charge state of an ion is identified with its equilibrium charge state by Bohr's stripping criterion [11,12]. The equilibrium charge state by Bohr is given as Q eq = Z 1/3 v/v 0 and describes the (average) charge state of an ion passing through a solid at a given velocity v (v 0 : Bohr's velocity, Z: nuclear charge of the ion). The charge state Q of slow highly charged ions is much higher than the equilibrium charge state Q eq (Q eq Q < ∼ Z). Therefore, the interaction of HCI with surfaces may not be described in terms of an equilibrium charge state dependent stopping force. Furthermore, due to the localization of the energy deposition slow HCI can be used as an efficient tool for surface nano-structuring [13][14][15][16][17][18][19][20][21][22][23][24] and tuning of the electrical properties of materials [25], as well as a probe for surface energy deposition processes [26,27]. Recently, it has been shown that slow HCI can create pores in 1 nm thick carbon nanomembranes (CNM) [28,29] mainly by deposition of their potential ...

Highly charged ion induced nanostructures at surfaces by strong electronic excitations

“…Direct transmission measurements of HCI through 1 nm thick carbon nanomembranes showed [16] that the charge exchange is bimodal, namely one part of the ions stabilize only very few electrons during transmission and therefore deposit almost no potential energy in the target material. The other part of the ions neutralizes almost completely during transmission and deposits correspondingly a large fraction of its potential energy.…”

“…(3) charge exchange and energy loss measurements are necessary [15,16], whereas determining the right side requires knowledge about the total secondary electron yield N e [17,18] and electron energy distribution E e;i [9,19] as well as yield and energy distribution of emitted X-rays. The term E surf =exc is accessible by calorimetric measurements in experiments and can eventually be extracted from simulations [9,20].…”

Response of GaN to energetic ion irradiation: conditions for ion track formation

“…For HCI it is not possible to calculate the electronic energy loss using the SRIM code [26], but a recent study indicates that the energy loss of such a projectile can be up to 10% of its kinetic energy when passing through 1 nm thin membrane [43]. Neuchatel, Switzerland) with cantilever resonance frequencies around 300 kHz.…”

Ibc - Ion Beam Center

“…Slow, highly-charged ions (HCI), on the other hand, are special in that they carry additionally a high amount of potential energy -the stored ionization energy -which is released and deposited into the electronic system of the materials surface (Gruber et al, 2016;Wilhelm et al, 2014). The electronic excitation by the potential energy of HCIs induces nanostructures on surfaces, in thin-lms, or 2D materials by single ion impacts.…”