Electron emission and energy loss in grazing collisions of protons with insulator surfaces

Electron emission from LiF, KCl, and KI crystal surfaces during grazing collisions of swift protons is studied using a first-order distorted-wave formalism. Owing to the localized character of the electronic structure of these surfaces, we propose a model that allows us to describe the process as a sequence of atomic transitions from different target ions. Experimental results are presented for electron emission from LiF and KI and energy loss from KI surfaces. Calculations show reasonable agreement with these experimental data. The role played by the charge of the incident particle is also investigated.

Figure 1

Sketch of the coordinate system.

Figure 2

Pulse height distributions of the amplified SBD signal for coincident (full circles) and noncoincident (open circles) detection with $100\mathrm{keV}$ ${\mathrm{H}}^0$ projectiles specularly reflected from a LiF(001) surface under ${\Phi }_{\mathit{in}}=0.57°$.

Figure 3

${\mathrm{H}}^0$ fraction as a function of the distance of the projectile to the KCl(001) surface for incidence of $100\mathrm{keV}$ (a) protons; (b) neutral hydrogen atoms.

Figure 4

Electron emission yields for grazing protons colliding with LiF(001) surfaces, as a function of the incidence angle, measured with respect to the surface plane. Three different impact energies are considered: (a) 100; (b) 200; (c) $300\mathrm{keV}$. Full dots, present experimental data; solid lines, theoretical values derived as explained in the text.

Figure 5

Similar to Fig. 4 for $100\mathrm{keV}$ protons impinging on (a) KCl(001) and (b) KI(001) surfaces.

Figure 6

Energy loss for grazing scattering of $100\mathrm{keV}$ protons from insulator surfaces, as a function of the incidence angle. The target surfaces are (a) LiF(001), (b) KCl(001), and (c) KI(001). Solid lines, theoretical results; full dots, present experimental data.

Figure 7

Energy loss for grazing scattering of ${\mathrm{H}}^0$ from KI(001) surfaces, as a function of the impact energy. Full dots, present experimental data; solid line, theoretical results for proton impact.