Cluster-Induced Desorption/Ionization of Polystyrene: Desorption Mechanism and Effect of Polymer Chain Length on Desorption Probability

Abstract

Soft cluster-induced desorption/ionization of polystyrene oligomers was investigated with respect to application in mass spectrometry. Clear peak progressions corresponding to intact polystyrene molecules were observed in the mass spectra, and no fragmentation was detected; efficient desorption was deduced from quartz crystal microbalance measurements. Molecular dynamics (MD) simulations of the process revealed that even in the case of the nonpolar polystyrene molecules cluster-induced desorption proceeds via dissolvation in the polar clusters. Experimentally, a significantly lower desorption efficiency was observed for polystyrene molecules with larger chain length. Taking into account MD simulations and further experiments with mixed samples consisting of long- and short-chain polystyrene oligomers, the reduced desorption efficiency for longer chain polystyrene molecules was attributed to a stronger entanglement of the larger polystyrene molecules.

Soft Deposition of Organic Molecules Based on Cluster-Induced Desorption for the Investigation of On-Surface and Surface-Mediated Reactions

“…In this application of DINeC, the molecules are softly desorbed from a bulk sample by the SO 2 clusters and deposited directly onto a substrate that is placed opposite to the target (Figure a). The soft desorption of the molecules relies on a dissolution-based mechanism: ,, the impacting clusters do not only provide the energy for desorption but also serve as a transient matrix in which the desorbing molecules are dissolved. − As a result, the effective desorption barrier is reduced which enables soft desorption with low-energy clusters. − As most of the SO 2 molecules are evaporating from the desorbed molecules after cluster-surface impact and desorption, , the bare molecules can be then deposited on a target of choice; as only a minority of the desorbed molecules are ionized, mainly neutral molecules are deposited. Based on the results for DINeC-MS, the DINeC-Depo method can be applied to a broad variety of molecules, e.g., lipids, peptides, proteins, dyes, polymers, and ionic liquids. ,− The coverage of the deposited layers ranges from isolated molecules in the submonolayer regime (Figure b) to films of the thickness of several monolayers.…”

“…The soft desorption of the molecules relies on a dissolution-based mechanism: 15 , 18 , 19 the impacting clusters do not only provide the energy for desorption but also serve as a transient matrix in which the desorbing molecules are dissolved. 18 − 20 As a result, the effective desorption barrier is reduced which enables soft desorption with low-energy clusters. 15 − 17 As most of the SO 2 molecules are evaporating from the desorbed molecules after cluster-surface impact and desorption, 15 , 20 the bare molecules can be then deposited on a target of choice; as only a minority of the desorbed molecules are ionized, 21 mainly neutral molecules are deposited.…”

“… 18 − 20 As a result, the effective desorption barrier is reduced which enables soft desorption with low-energy clusters. 15 − 17 As most of the SO 2 molecules are evaporating from the desorbed molecules after cluster-surface impact and desorption, 15 , 20 the bare molecules can be then deposited on a target of choice; as only a minority of the desorbed molecules are ionized, 21 mainly neutral molecules are deposited. Based on the results for DINeC-MS, the DINeC-Depo method can be applied to a broad variety of molecules, e.g., lipids, peptides, proteins, dyes, polymers, and ionic liquids.…”

“…Based on the results for DINeC-MS, the DINeC-Depo method can be applied to a broad variety of molecules, e.g., lipids, peptides, proteins, dyes, polymers, and ionic liquids. 20 , 22 − 25 The coverage of the deposited layers ranges from isolated molecules in the submonolayer regime ( Figure 1 b) to films of the thickness of several monolayers. The sample composition was controlled by changing the target material during the deposition process ( Figure 1 c).…”