On the energy spectra of secondary ions emitted from silicon and graphite single crystals
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On the Energy Spectra of Secondary Ions Emitted from Silicon and Graphite Single Crystals V. V. Khvostov, I. K. Khrustachev, K. F. Minnebaev*, E. Yu. Zykova, I. P. Ivanenko, and V. E. Yurasova** Department of Physics, Moscow State University, Moscow, 119991 Russia *email: [email protected] **email: [email protected] Received August 13, 2013
Abstract—Secondary ion emission from silicon and graphite single crystals bombarded by argon ions with energies E0 varied from 1 to 10 keV at various angles of incidence α has been studied. The evolution of the energy spectra of C+ and Si+ secondary ions has been traced in which the positions of maxima (Emax) shift toward higher secondaryion energies E1 with increasing polar emission angle θ (measured from the normal to the sample surface). The opposite trend has been observed for ions emitted from single crystals heated to several hundred degrees Centigrade; the Emax values initially remain unchanged and then shift toward lower energies E1 with increasing angle θ. It is established that the magnitude and position of a peak in the energy spectrum of secondary C+ ions is virtually independent of E0, angle α, and the surface relief of the sample (in the E0 and α intervals studied). Unusual oscillating energy distributions are discussed, which have been observed for secondary ions emitted from silicon (111) and layered graphite (0001) faces. Numerical simula tions of secondary ion sputtering and charge exchange have been performed. A comparison of the measured and calculated data for graphite crystals has shown that C+ ions are formed as a result of charge exchange between secondary ions and bombarding Ar+ ions, which takes place both outside and inside the target. This substantially differs from the ion sputtering process in metals and must be taken into account when analyzing secondary ion emission mechanisms and in practical applications of secondaryion mass spectrometry. DOI: 10.1134/S1063776114020113
1. INTRODUCTION Investigation of the energy spectra of secondary ions is important for understanding the mechanisms of sec ondary ion emission (SIE) and for practical applications of this process. A large body of data has been gained con cerning the laws of SIE and the methods for the theoret ical description of this phenomenon [1–7]. However, a number of relationships involved in SIE remain insuffi ciently studied. Moreover, some experimental data have still not been explained by the existing theories. In addition to purely basic interest, investigations of the SIE process and specific features of the energy dis tribution of secondary ions are of considerable practical significance for the development of secondaryion mass spectrometry (SIMS), which is one of the most sensitive methods for analyzing solid surfaces [8–11]. The devel opment of SIMS techniques and the creation of SIE theory require detailed experimental data, in particular, on the angular and energy distributions of secondary ions and on the influence of the surface relief of a t
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