Characterization of Individual Nano-Objects by Secondary Ion Mass Spectrometry

Abstract

We present secondary ion mass spectrometry (SIMS) data obtained from the bombardment of a novel nanomaterial with a suite of projectiles: Au1+, Au3+, Au9+, and Au400(4+). These are the first experiments where free-standing nano-objects were bombarded with kiloelectronvolt projectiles of atomic to nanoparticle size (Au400(4+)). The objects are aluminum monohydrate nanowhiskers, identified as crystalline boehmite (AlOOH) using X-ray diffraction. The nanoalumina is bonded to a microglass fiber that serves as a scaffold. The largest projectile, Au400(4+), has a diameter of approximately 2 nm, comparable to the nominal diameter of the nanowhiskers. There are notable differences in secondary ion (SI) response from sample volumes too small for full projectile energy deposition. The whisker spectra are dominated by small clusters--the most abundant species being AlO- and AlO2-. Bulk samples have larger yields for AlO2- than AlO-, whereas this trend is reversed in the whisker samples. Bulk samples give similar abundances of large SI cluster families [(Al2O3)(n)AlO2]- and [(Al2O3)(n)OH]-, whereas the whisker samples give an order of magnitude lower yield of these SIs. Given the nature of our experiments, i.e., the event-by-event bombardment/detection mode, we are uniquely able to obtain information from SIs emitted from single-projectile impacts. As such, effective yields were calculated in order to determine quantitative differences between the nano-objects and bulk samples.