Time-of-flight secondary ion mass spectrometry of insulators with pulsed charge compensation by low-energy electrons

Abstract

A new charge compensation system for time-of-flight (TOF) secondary ion mass spectrometry is described. A pulsed low-energy electron source (10 eV) in combination with a pulsed extraction voltage of the TOF analyzer allows low-energy electrons to reach the target in the relatively long period of time between two excitation pulses. Low-energy electrons allow self-adjusting of the surface potential. Sample damages by these electrons are not detectable. Effects due to electron stimulated desorption are suppressed by pulsing the anode of the electron source. Compensation is possible for the accumulation of positive as well as negative spectra. With this experimental arrangement we investigated a variety of insulating materials (e.g., thick polymer films, glasses, ceramics). In all cases we found stable and reproducible spectra, even of insulators with extremely low conductivity.

Static SIMS studies of the oxides and hydroxides of aluminium

“…Mass resolution was typically between 3000 and 5000 at mass 28. Instrumental conditions varied only in the optimisation of charge compensation, based on the pulsed electron method of Hagenhoff et al 14 Charge compensation is a significant problem for these samples, especially the massive α‐alumina sample, and the specific analytical conditions employed for each sample were largely dictated by the need for achieving optimal stability and intensity with respect to charging. Apart from the flake of α‐alumina cleaved from a sapphire disc, powdered samples were mounted by pressing onto an indium foil, while the metal foils were directly clamped to the sample holder.…”

Static secondary ion mass spectrometry (S-SIMS) Part 1: methodology and structural interpretation

“…Although low energy electrons striking the sample give structurally useful secondary ions by the``electron stimulated desorption'' (ESD) process, it is crucial that no electrons are¯ooded when the extraction voltage is on, since it would result in a keV-electron sputtering of the surface (Lub et al, 1988). Hagenhoff et al (1989) have elaborated a technique based on the low duty-cycle TOF system: after each primary pulse the extraction voltage is removed and 10 eV electrons from a pulsed source impinge on the sample. Briggs et al (1990) followed a similar approach, but claimed that it is only necessary to hit the sample with electrons once every ten or more cycles.…”

Dual beam depth profiling of organic materials: assessment of capabilities and limitations

“…Switching on the analysis beam without the Ar sputtering leads to the typical exponential decay of the signal as expected for the Bi 3 + cluster beam due to the generation of subsurface damage. The cross section is approximately σ D = 35 nm 2 . If both beams sputter simultaneously, a part of the subsurface damage will be removed by the Ar sputtering.…”

“…In addition, it is compatible with charge compensation by low-energy electrons for the analysis of insulators. [2] In the following years, the technique was optimized for shallow depth profiling with high-depth resolution using low-energy oxygen or cesium sputter beams. Today, this dynamic SIMS mode is widely applied in most modern ToF-SIMS instruments for the characterization of thin inorganic films with thicknesses from nanometers to several microns.…”