Fast and versatile ambient surface analysis by plasma-assisted desorption/ionisation mass spectrometry

Abstract

Introduction Surfaces play a crucial role in a wide range of applications, hence have been the subject of intense study since the very early days of chemical analysis. With increasing knowledge and manufacturing capabilities, the need for ever more detailed surface analytical information has grown rapidly over the years. Whilst vibrational spectroscopies, in particular, have yielded crucial information in a wide range of settings, the very nature of these techniques does limit the information available. Mass spectrometry on the other hand has the capability to yield exquisitely detailed datasets, but has traditionally been significantly less convenient in actual applications. After initial use, predominantly for inorganic and materials science applications and with Alfred Benninghoven (Germany) and David Briggs (UK) among the main protagonists, advances in liquid metal ion guns and time-offlight analysers enabled secondary ion mass spectrometry (SIMS) to become a powerful technique for the analysis of organic materials. A step-change in sensitivity revolutionised the use of SIMS in the latter part of the last century and allowed researchers to acquire detailed mass spectra from damageprone organic materials without significantly altering the surface chemistry under investigation. Moreover, surface mass spectra containing information on large molecules can be generated from very small surface areas, especially since the introduction of cluster primary ion sources, allowing micron-scale image generation with an enormous wealth of information, in the form of a high mass-range and -resolution spectrum for each image pixel. These developments opened up entire new fields of analysis and time-of-flight SIMS (ToF-SIMS) has since been applied highly successfully in a seemingly endless range of applications from medical implants and cell biology to astrochemistry, art history and archaeology.1 Whilst much exquisite research has been and continues to be published using SIMS, a crucial restriction is the requirement for samples to be in a vacuum environment. This necessitates samples sensitive to vacuum to be especially prepared to negate any adverse effects. Moreover, sample throughput is restricted by pump-down times and sample size and geometry are limited to