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

Summary

Soft landing of mass-selected ions onto surfaces is a powerful approach for the highly-controlled preparation of novel materials. Coupled with analysis by in situ secondary ion mass spectrometry (SIMS) and infrared reflection absorption spectroscopy (IRRAS), soft landing provides unprecedented insights into the interactions of well-defined species with surfaces.

Abstract

Soft landing of mass-selected ions onto surfaces is a powerful approach for the highly-controlled preparation of materials that are inaccessible using conventional synthesis techniques. Coupling soft landing with in situ characterization using secondary ion mass spectrometry (SIMS) and infrared reflection absorption spectroscopy (IRRAS) enables analysis of well-defined surfaces under clean vacuum conditions. The capabilities of three soft-landing instruments constructed in our laboratory are illustrated for the representative system of surface-bound organometallics prepared by soft landing of mass-selected ruthenium tris(bipyridine) dications, [Ru(bpy)₃]²⁺ (bpy = bipyridine), onto carboxylic acid terminated self-assembled monolayer surfaces on gold (COOH-SAMs). In situ time-of-flight (TOF)-SIMS provides insight into the reactivity of the soft-landed ions. In addition, the kinetics of charge reduction, neutralization and desorption occurring on the COOH-SAM both during and after ion soft landing are studied using in situ Fourier transform ion cyclotron resonance (FT-ICR)-SIMS measurements. In situ IRRAS experiments provide insight into how the structure of organic ligands surrounding metal centers is perturbed through immobilization of organometallic ions on COOH-SAM surfaces by soft landing. Collectively, the three instruments provide complementary information about the chemical composition, reactivity and structure of well-defined species supported on surfaces.

Introduction

Soft landing of mass-selected ions onto surfaces remains a subject of current research interest due to the demonstrated capabilities of the technique for the highly-controlled preparation of novel materials^1-6. Recent efforts have indicated potential future applications of soft landing of mass-selected ions in the preparation of peptide and protein arrays for use in high-throughput biological screening^7,8, separation of proteins and conformational enrichment of peptides^9-12, covalent attachment of peptides to surfaces^9,10,13,14, chiral enrichment of organic compounds¹⁵, electrochemical characterization of specific....

Protocol

1. Preparation of COOH-SAM Surfaces on Gold for Soft Landing of Mass-selected Ions

1. Obtain flat gold substrates on silicon (Si) or mica backing materials. Alternatively, prepare gold films on Si or mica surfaces according to procedures described in the literature^118,119. Note: Use surfaces that have the following specifications: 1 cm² or circular and 5 mm in diameter, 525 µm thick Si layer, 50 Å thick Ti adhesion layer, 1,000 Å Au layer.
2. Place fresh gold-on-silicon surfaces into glass scintillation vials and immerse in pure (non-denatured) ethanol.
3. Place scintillation vials containing gold ....

Results

1. Investigating the Reactivity of Ru(bpy)₃²⁺ on COOH-SAMs Using In Situ TOF-SIMS

Soft landing of mass-selected organometallic ions onto functionalized SAMs is first illustrated using in situ TOF-SIMS to provide maximum sensitivity toward detection of adducts formed between the deposited ions and the individual molecules in the monolayers as well as any products of chemical reactions following exposure of the surfaces to reactive gases. The doubly charged .......

Discussion

Soft landing of mass-selected ions is generally conducted employing unique custom-built instrumentation that exists in several laboratories around the world that are specially equipped for these experiments. Modifications are constantly being made to these instruments to facilitate the ionization of a wider array of compounds, to achieve larger ion currents and shorter deposition times, to multiplex soft landing and thereby achieve simultaneous deposition of several species at different locations on the surface, and to a.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Gold on Silicon Substrates 1 cm2	Platypus Technologies	Au.1000.SL1custom
Gold on Silicon Substrates 4.8 mm diameter circular	SPI Supplies	4176GSW-AB
Glass Scintillation Vials	Fisher Scientific	03-337-14
Non-denatured Ethanol	Sigma-Aldrich	459836-1L
Ultraviolet Cleaner	Boekel Scientific
16-Mercaptohexadecanoic Acid	Sigma-Aldrich	448303-5G
Hydrochloric Acid	Sigma-Aldrich	320331-500ML
Aluminum Foil	Sigma-Aldrich	Z185140-1EA
Metal Forceps/Tweezers	Wiha	49185
Nitrile Gloves	Fisher Scientific	S66383
Tris(2,2′-bipyridine)dichlororuthenium(II) hexahydrate	Sigma-Aldrich	224758-1G
Methanol	Sigma-Aldrich	322415-1L
1 ml Gas Tight Glass Syringe	Hamilton
Syringe Pump	KD Scientific	100
360 μm ID Fused Silica Capillary	Polymicro Technologies	TSP075375
High Resistance Electrometer	Keithley	6517A
Commercial TOF-SIMS Instrument	Physical Electronics	TRIFT
Ultra High Purity Oxygen	Matheson	G1979175
Research Purity Ethylene	Matheson	G2250178
Cesium Ion Source	Heat Wave Labs	101502
Commercial FTIR Spectrometer	Bruker	Vertex 70