Mass spectrometric analysis of the dissociation of argon cluster ions in collision with several kinds of metal

Large Molecular Cluster Formation from Liquid Materials and Its Application to ToF-SIMS

Since molecular cluster ion beams are expected to have various chemical effects, they are promising candidates for improving the secondary ion yield of Tof-SIMS. However, in order to clarify the effect and its mechanism, it is necessary to generate molecular cluster ion beams with various chemical properties and systematically examine it. In this study, we have established a method to stably form various molecular cluster ion beams from relatively small amounts of liquid materials for a long time by the bubbling method. Furthermore, we applied the cluster ion beams of water, methanol, methane, and benzene to the primary beam of SIMS and compared the molecular ion yields of aspartic acid. The effect of enhancing the yields of [M+H]+ ion of aspartic acid was found to be the largest for the water cluster and small for the methane and benzene clusters. These results indicate that the chemical effect contributes to the desorption/ionization process of organic molecules by the molecular cluster ion beam.

Large cluster ions: soft local probes and tools for organic and bio surfaces

Ionised cluster beams have been produced and employed for thin film deposition and surface processing for half a century. In the last two decades, kiloelectronvolt cluster ions have also proved to be outstanding for surface characterisation by secondary ion mass spectrometry (SIMS), because their sputter and ion yields are enhanced in a non-linear fashion with respect to monoatomic projectiles, with a resulting step change of sensitivity for analysis and imaging. In particular, large gas cluster ion beams, or GCIB, have now become a reference in organic surface and thin film analysis using SIMS and X-ray photoelectron spectroscopy (XPS). The reason is that they induce soft molecular desorption and offer the opportunity to conduct damageless depth-profiling and 3D molecular imaging of the most sensitive organic electronics and biological samples, with a nanoscale depth resolution. In line with these recent developments, the present review focuses on rather weakly-bound, light-element cluster ions, such as noble or other gas clusters, and water or alcohol nanodroplets (excluding clusters made of metals, inorganic salts or ionic liquids) and their interaction with surfaces (essentially, but not exclusively, organic). The scope of this article encompasses three aspects. The first one is the fundamentals of large cluster impacts with surfaces, using the wealth of information provided by molecular dynamics simulations and experimental observations. The second focus is on recent applications of large cluster ion beams in surface characterisation, including mass spectrometric analysis and 2D localisation of large molecules, molecular depth-profiling and 3D molecular imaging. Finally, the perspective explores cutting edge developments, involving (i) new types of clusters with a chemistry designed to enhance performance for mass spectrometry imaging, (ii) the use of cluster fragment ion backscattering to locally retrieve physical surface properties and (iii) the fabrication of new biosurface and thin film architectures, where large cluster ion beams are used as tools to transfer biomolecules in vacuo from a target reservoir to any collector substrate.

Temperature Dependence of Arn+ Cluster Backscattering from Polymer Surfaces: a New Method to Determine the Surface Glass Transition Temperature

In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to study the intensity variations of the backscattered Ar_n⁺ clusters as a function of temperature for several amorphous polymer surfaces (polyolefins, polystyrene, and polymethyl methacrylate). For all these investigated polymers, our results show a transition of the ratio Ar₂⁺/(Ar₂⁺ + Ar₃⁺) when the temperature is scanned from -120 °C to +125 °C (the exact limits depend on the studied polymer). This transition generally spans over a few tens of degrees and the temperature of the inflection point of each curve is always lower than the bulk glass transition temperature (T_g) reported for the considered polymer. Due to the surface sensitivity of the cluster backscattering process (several nanometers), the presented analysis could provide a new method to specifically evaluate a surface transition temperature of polymers, with the same lateral resolution as the gas cluster beam. Graphical abstract ᅟ.