In Situ Reactivity and TOF-SIMS Analysis of Surfaces Prepared by Soft and Reactive Landing of Mass-Selected Ions

Abstract

An instrument has been designed and constructed that enables in situ reactivity and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis of surfaces prepared or modified through soft and reactive landing of mass-selected polyatomic cations and anions. The apparatus employs an electrospray ion source coupled to a high transmission electrodynamic ion funnel, two focusing collision quadrupoles, a large 19 mm diameter quadrupole mass filter, and a quadrupole bender that deflects the ion beam, thereby preventing neutral contaminants from impinging on the deposition surface. The ion soft landing apparatus is coupled to a commercial TOF-SIMS instrument permitting the introduction of surfaces into vacuum and SIMS analysis before and after ion deposition without breaking vacuum. To facilitate a comparison of the current TOF-SIMS instrument with the in situ Fourier transform ion cyclotron resonance (FTICR-SIMS) deposition apparatus constructed previously, dications of the cyclic peptide Gramicidin S (GS) and the photoactive organonometallic complex ruthenium tris-bipyridine (Ru(bpy)(3)) were soft-landed onto fluorinated self-assembled monolayer (FSAM) on gold surfaces. In both cases, similarities and differences were observed in the secondary ion mass spectra, with the TOF-SIMS results, in general, characterized by greater sensitivity, larger dynamic range, less fragmentation, and fewer in-plume reactions than the corresponding FTICR-SIMS spectra. The charge reduction kinetics of both the doubly and singly protonated GS cations on the FSAM surface were also examined as was the influence of the primary gallium ion (Ga(+)) flux on the efficiency of these processes. In addition, we demonstrate that the new instrument enables detailed studies of the reactivity of catalytically active species immobilized by soft and reactive landing toward gaseous reagents.

IonCCD™ for Direct Position-Sensitive Charged-Particle Detection: from Electrons and keV Ions to Hyperthermal Biomolecular Ions

“…The experimental setup is described in detail elsewhere [32]. The ions were then injected into a miniature MH-MS with a 200 μm wide slit plate (object slit).…”

“…At this low resolution, the large fragments originating from peptide loss of water (-18 u) and ammonia (-17 u) with half mass separation due to the doubly charged nature of the ions are convoluted with the parent ions, resulting in a broad tail at the lower mass side. The somewhat bimodal nature of the ion energy exiting the collisional quadrupole [32] can also affect the mass resolution as the low energy component would contribute to a signal tail at low mass side. Note that the peak separation in Figure 7 can be used to determine the doubly protonated ion energy, which is calculated back to be about 2 x 70 V=140 V. This value is in accordance with the voltage bias of the CQ (120 V) with the most ion energy contribution coming from the region between the latter voltage and the conductance limit biased at 20 V.…”

Characterization of the Ion Beam Focusing in a Mass Spectrometer Using an IonCCD™ Detector

“…Characterization of the ion beam focusing was performed within a recently constructed custom-built ion deposition instrument described in detail elsewhere [17] and shown schematically in Figure 1. Briefly, doubly charged ruthenium tris(bipyridine) cations Ru(bpy) 3 2+ were generated by electrospray ionization (ESI) at ambient pressure.…”

<em>In Situ</em> SIMS and IR Spectroscopy of Well-defined Surfaces Prepared by Soft Landing of Mass-selected Ions

“…To date, a multitude of techniques have been applied for this purpose including secondary ion mass spectrometry (SIMS) 19,[97][98][99][100] , temperature programmed desorption and reaction 50,52 , laser desorption and ionization 101 , pulsed molecular beam reaction 102 , infrared spectroscopy (FTIR and Raman) 98,103,104 , surface enhanced Raman spectroscopy 103,105 , cavity ringdown spectroscopy 106 , xray photoelectron spectroscopy 35,107 , scanning tunneling microscopy 33,[108][109][110][111] , atomic force microscopy [112][113][114] , and transmission electron microscopy 39 . However, to most accurately characterize surfaces prepared or modified by ion soft landing, it is crucial that the analysis be performed in situ without exposure of the substrate to the environment in the laboratory.…”