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

Experimental charge exchange and energy loss data for the transmission of slow highly charged Xe ions through ultrathin 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 ultrathin solid target may not be described in terms of an averaged energy loss per unit length.

Figure 1

Spectrum of a $1050\mathrm{eV}/\mathrm{amu}$ ${\mathrm{Xe}}^{30+}$beam transmitted through a 1 nm thick carbon nanomembrane. All charge states below $Q=30$ (but larger than $Q=4$) are visible, whereas two distinct distributions can be observed. The high exit charge state distribution is magnified in the inset.

Figure 2

Transmission spectra of a 46.8 keV ($363\mathrm{eV}/\mathrm{amu}$) ${\mathrm{Xe}}^{25+}$ beam for different transmission angles of 0° (green), 2° (red), and 4° (black). High exit charge states are only observable under 0° (see double logarithmic inset). Due to the lower beam energy, the lowest observable exit charge state is $Q_{\text{exit}}=2$.

Figure 3

Energy loss of 40 keV ions as a function of the charge loss $\mathrm{\Delta }Q$ (a) and of the incident charge state $Q_{\text{in}}$ (b), respectively. In (b) the energy loss is shown only for ions with exit charge state $Q_{\text{exit}}=2$ (red) and for ions with a charge loss of $\mathrm{\Delta }Q=1$ (green) (maximum and minimum $\mathrm{\Delta }Q$). The red curve is a polynomial fit of second order to the obtained data ($\mathrm{\Delta }E(Q_{\text{in}})=3.7\mathrm{eV}·Q_{\text{in}}^2+264\mathrm{eV}$). The dotted line shows the result from a TRIM simulation (see text).

Figure 4

Normalized intensity of exit charge states for different incident charge states from $Q_{\text{in}}=10$ (black) to $Q_{\text{in}}=30$ (purple) at $E_{\text{kin}}=40\mathrm{keV}$ ($310\mathrm{eV}/\mathrm{amu}$).

Figure 5

Integrated normalized intensity (see text) as a function of the incident charge state for $E_{\text{kin}}=40\mathrm{keV}$ ($310\mathrm{eV}/\mathrm{amu}$). The dotted line is drawn to guide the eye.