Compositional analysis in the nano-regime： A SIMS perspective

A serious problem in secondary ion mass spectrometry (SIMS) analysis is its "matrix effect" that hinders the quantification of a certain species in a sample and consequently, appropriate corrective measures are taken to calibrate the secondary ion currents into respective concentrations for accurate compositional analysis. Use of "calibration standards" is necessary for this purpose. Detection of molecular MCsn+ ions (M-element to be analyzed, n=1, 2, 3,....) under Cs+ ion bombardment is a possible mean to minimize such matrix effect, enabling one to quantify without the need of calibration standards. Our recent studies on MCsn+ molecular ions aim towards the understanding of their formation mechanisms, which are important to know their effects on SIMS quantification.In-depth quantitative analysis is a major strength of SIMS for which 'depth resolution' is of significant relevance. The optimal choice of the impact parameters during SIMS analyses can play an effective role in obtaining data with ultra-high depth resolution. SIMS is possible at depth resolution in the nm or even sub-nm range, with quantifiable data obtained from the top monolayer onwards into the material. With optimized experimental conditions, like extremely low beam current (down to ～10 nA), and low bombarding energy (below 1 keV), ultra-high depth resolution SIMS has enabled interfacial composition analysis of ultra-thin films, quantum wells, heterostructures, etc. and complex low-dimensional structures with high precision and repeatability.