AVS 46th International Symposium
    Applied Surface Science Division Tuesday Sessions
       Session AS-TuP

Paper AS-TuP16
Optimizing Signal Intensities in REELM and SAM Microscopies: A Comparision of Instruments Operated in Fixed-Analyzer-Transmission (FAT) and Fixed-Retard-Ratio (FRR) Modes

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: E. Paparazzo, Consiglio Nazionale delle Ricerche, Italy
Authors: E. Paparazzo, Consiglio Nazionale delle Ricerche, Italy
L. Moretto, Consiglio Nazionale delle Ricerche, Italy
S.A. Lea, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
Correspondent: Click to Email
Signal intensity is the main factor for chemical contrast in reflected electron energy loss microscopy (REELM) and scanning Auger microscopy (SAM) images of surfaces. We report here on REELM and SAM signal intensities measured as a function of the primary beam energy (Ep) for two Auger microprobes: one operated in the fixed analyzer transmission (FAT) mode (Cameca 'Nanoscan 50', Rome), the other in the fixed retard ratio (FRR) mode (PHI '680 Auger Nanoprobe', Richland). The aim of this work is to quantitatively determine the extent to which each type of microprobe affects the relative intensities of REELM and SAM signals. To accomplish this task we conducted a comparative analysis in the two laboratories using atomically-clean Al metal as a sample. We measured the intensity ratio between the first bulk plasmon signal and the Auger Al LVV signal (KE ~ 70 eV) as a function of Ep, which was chosen at several values within the range 200-2000 eV. We found that for both the FAT and FRR microprobe this ratio decreases by a factor ~ 10 upon increasing Ep from 200 to 2000 eV. These findings are discussed in light of both the energy resolution and response function associated with the FAT and FRR operation modes in the KE range considered, and they are used to account for the chemical contrast of REELM and SAM images acquired in the two microprobes at differing Ep's. We show that our work can help devise an optimal compromise between chemical contrast, surface-specificity and chemical speciation in both REELM and SAM imaging, whether the two methods are performed in FAT or FRR Auger microprobes.