Negative ion yield and sputter yield variations for Cs⁺ bombardment of Si with O₂ gas flooding

Abstract

We have investigated whether negative secondary ion yields from Cs + sputtered silicon might be improved by simultaneous O 2 gas flooding, which lowers the sputter yield of the silicon, and thus, might increase the cesium content at the surface. The composition at the sputtered surface is derived from quantitative measurements of the ratios of O/Si and Cs/Si in the total emitted flux using the recently developed oxygen 18 method [1] and sputter yield measurements, respectively (with X Si + X Cs + X O = 1). The silicon sputter yield, Y, is lowered by adsorbed oxygen by as much as a factor of 2.7 and is found to scale almost linearly with the silicon atom fraction X Si at the surface, resulting in the cesium atom fraction X Cs at the surface remaining nearly constant during oxygen flooding. We find that oxidation of the cesiated silicon surface influences differently the useful ion yields (ions detected/atom sputtered) of various elements. The yields of B − and Cs − are enhanced by factors of 3 and 34, respectively, the yield of O − remains roughly constant, and yields of other elements (As − , Cl − , P − , Sb − , Si − ) are lowered by a factor of 2 or 3.

Implementation of Nanoscale Secondary‐Ion Mass Spectrometry Analyses: Application to Ni‐Based Superalloys

“…Despite a low transmission (<3%), chemical maps at the nanoscale were obtained, where y 0 III precipitates with a size < 30 nm were detected and imaged. This high lateral resolution was obtained without degrading the high mass resolution of 4500 routinely obtained on 28 Si. Localized chemical analyses of specific features at the grain boundaries and on segregated areas are also reported.…”

“…Thus, the duty cycle is a factor to be applied to the transmission of maximum 1 (100%). In our measurements, a mass range of 0À125 μ was used, which gives a duty cycle of 14% for 28 Si. Depending on the mass of the secondary-ion and the mass range selected, the duty cycle varies between a few percent and just over 30% from small masses (<150 μ).…”

“…In contrast, halogens and oxygen improve positive ionization. [14,22,[26][27][28] As the secondary ionization yield is commonly too low for many elements to form an image at a nanometer scale, a GIS was integrated on the NanoSpace to inject Oxygen. The results with Cs will be shown in a further work.…”

“…An example of line profile with 25 nm resolution on a γ 0 II is given in Figure 6a. In addition, thanks to the secondary-ion beam pulsation (instead of the primary pulsation of conventional TOFÀSIMS), a mass resolution of at least 4500 was routinely obtained on 28 Si (Figure 6b). The mass resolution is defined as the mass divided by the FWHM of its peak.…”