The study of the interaction of hypervelocity nano-particles with a 2D material and ultra-thin targets (single layer graphene, multi-layer graphene, and amorphous carbon foils) has been performed using mass selected gold nano-particles produced from a liquid metal ion source. During these impacts, a large number of atoms are ejected from the graphene, corresponding to a hole of ∼60 nm(2). Additionally, for the first time, secondary ions have been observed simultaneously in both the transmission and reflection direction (with respect to the path of the projectile) from a 2D target. The ejected area is much larger than that predicted by molecular dynamic simulations and a large ionization rate is observed. The mass distribution and characteristics of the emitted secondary ions are presented and offer an insight into the process to produce the large hole observed in the graphene.

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Abstract. Secondary ion mass spectrometry, SIMS, is a method of choice for the characterization of nanoparticles, NPs. For NPs with large surface-to-volume ratios, heterogeneity is a concern. Assays should thus be on individual nano-objects rather than an ensemble of NPs; however, this may be difficult or impossible. This limitation can be side-stepped by probing a large number of dispersed NPs one-by-one and recording the emission from each NP separately. A large collection of NPs will likely contain subsets of like-NPs. The experimental approach is to disperse the NPs and hit an individual NP with a single massive cluster (e.g., C-60, Au-400). At impact energies of~1keV/atom, they generate notable secondary ion (SI) emission. Examination of small NPs (≤20nm in diameter) shows that the SI emission is sizedependent and impacts are not all equivalent. Accurate identification of the type of impact is key for qualitative assays of core or outer shell composition. For quantitative assays, the concept of effective impacts is introduced. Selection of co-emitted ejecta combined with rejection (anticoincidence) of substrate ions allows refining chemical information within the projectile interaction volume. Last, to maximize the SI signal, small NPs (≤5nm in diameter) can be examined in the transmission mode where the SI yields are enhanced~10-fold over those in the (conventional) reflection direction. Future endeavors should focus on schemes acquiring SIs, electrons, and photons concurrently.

Secondary ion mass spectrometry (SIMS) applied in the event-by-event bombardment/detection mode is uniquely suited for the characterization of individual nano-objects. In this approach, nano-objects are examined one-by-one, allowing for the detection of variations in composition. The validity of the analysis depends upon the ability to physically isolate the nano-objects on a chemically inert support. This requirement can be realized by deposition of the nano-objects on a Nano-Assisted Laser Desorption/Ionization (NALDI™) plate. The featured nanostructured surface provides a support where nano-objects can be isolated if the deposition is performed at a proper concentration. We demonstrate the characterization of individual nano-objects on a NALDI™ plate for two different types of nanometric bacteriophages: Qβ and M13. Scanning electron microscope (SEM) images verified that the integrity of the phages is preserved on the NALDI™ substrate. Mass spectrometric data show secondary ions from the phages are identified and resolved from those from the underlying substrate.

The uniqueness of nanoparticles, NPs, due to their functionalities not present in bulk size is well documented. A nuanced understanding of their functionalities depends on their accurate characterization. Generally the analysis is done on an ensemble of NPs. However, there is likely some variation in the NP population and ensemble averaging can limit insight into the relationships between size, composition, and chemical reactivity of NPs. This is especially the case for very small NPs where minor changes in size, shape, or composition can significantly affect chemical reactivity. We have developed an innovative methodology for analyzing individual NPs, in particular objects of 2-50 nm in size.Our approach is based on an innovative Secondary Ion Mass Spectrometry, SIMS, technique where NPs dispersed on a substrate are probed one by one. They are bombarded with a sequence of individual "nanoprojectiles", specifically 4 400 Au  (a NP of ~2 nm in diameter). The impact of a single nanoprojectile at hypervelocity ~30 km/s) generates abundant ion emission from an area of ~10 nm in diameter. The ejecta from each impact are mass-analyzed and recorded individually. This approach avoids problems due to ensemble averaging. From the pool of individual NP records (typically ~1M) we extract subsets of data from alike NPs; specifically we can identify molecules co-located within ~10 nm.The instrument used for the investigation of discrete nano-objects is a custom-built secondary ion mass spectrometer comprised of a Au-liquid metal ion source (Au-LMIS) used to generate a variety of gold clusters as projectiles. A specific cluster can be mass-selected by a Wien filter installed on a 120 kV platform. Clusters are steered by a series of deflectors to the suspended target, biased at ±10 kV, giving a total kinetic energy of 110-130 qkeV. Collimators and pulser plates in the pathway of the primary ions reduces the dose to a sequence of individual projectiles of ~1000 projectiles per second to meet the requirements of an event-by-event bombardment/detection mode. Sputtered ions and electrons are extracted from the impact area by 90% transmission grids maintained at ground. Electrons or protons are turned using a magnetic field to a microchannel plate (MCP) detector that triggers the timing of the time of flight measurement. Secondary ions proceed to an 8 anode detector which stops the timing measurement.An isolated nano-object constitutes a finite system where the energy imparted by the projectile cannot be dissipated as in a semi-infinite solid. As a consequence sputter and ion yields are size-dependent 1 . The same holds for electron emission 2 . The case of the secondary ions is illustrated with ejecta from gold NPs where the yields are increased twofold for 15 and 20 nm NPs over that from bulk gold. Gold NPs with a diameter of 50 nm produce secondary ion yields similar to that of the bulk case, while smaller gold NPs (2-10 nm) show a reduction from the bulk emission yields 3 . Another study showed that the nature of the ejecta may ...