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.

Probing chemical homogeneity within single cluster impact sites

“…There are contributions from both carbon and hydrocarbon peaks from the polystyrene spheres as well as from aluminum oxides from the underlying whisker substrate. The notable abundances of Al − and AlO − have been previously observed for whiskers and are attributed to sample‐size dependent secondary ion emission from volumes too small for full projectile energy deposition 1. Carbon based clusters of C n H − and C n − are abundant and observable up to n = 22.…”

“…We refer here to experiments run as a sequence of single massive projectile impacts with individual collection of the corresponding secondary ion, SI, emission. Suitable projectiles for this mode of operation include C 60 , Au 400 with impact energies > 300 eV/atom 1–4. The ejecta from one impact originated from a surface volume of ∼10 3 nm 3 3, 5.…”

“…However, a confined volume does not allow full dissipation of the energy carried by the projectile. As a consequence, the SIMS signature will reflect the physical and chemical characteristics of the nano‐object and those of its environment 1, 4. The limits where physical segregations of distinct topography may be resolved remain to be explored.…”

Nanodomain analysis with cluster‐SIMS: application to the characterization of macromolecular brush architecture

“…Further, the DBT films show SI emissions of carbon‐based clusters, C n − and C n H − , (1 ≤ n ≤ 16). For odd numbers of n , ion clusters of C n − predominate over the C n H − type; the reverse holds for clusters with even numbers of n. …”

Inorganic mass spectrometry as a tool for characterisation at the nanoscale

“…SIMS and SNMS allow depth profile analysis with a depth resolution in the low-nanometre range of hard coatings [93], atmospheric aerosol particles (with aerodynamic diameters on the order of 25-200 nm) [94], nano-objects (nanowhiskers consist of fibres of about 2-nm diameter) [95] and nanoscale multilayers [96][97][98][99][100]. Figure 5 shows the depth profiles obtained by SNMS for a triple-layer system used for gas sensor microdevices (Fig.…”