Development of Multiplexed ToF-SIMS Instrumentation

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful and widely used method for surface chemical analysis. The technique involves bombarding a sample with a high energy primary ion beam and detecting the chemistry of the molecular secondary ions that are ejected. The research group at the University of Manchester has over 30 years acquired an internationally-leading reputation for the development and analytical application of the ToF-SIMS technique. In recent years the development of novel primary ion beams such as C60 and massive gas clusters (e.g. Ar2000) has extended the range of chemistry that can be detected and allowed in-depth and 3D molecular analysis beyond the surface region. This has greatly accelerated the uptake of the technique in academic and industrial labs, to measure complex molecular systems such as biological cells and advanced materials and devices, and to make advances in healthcare diagnostics and manufacturing.

Conventionally, ToF-SIMS measurements rely on signal averaging (SA) over multiple experimental cycles to maximise the signal-to-noise ratio and resulting sensitivity. Each cycle consists of a short (nanosecond) primary ion pulse, followed by the measurement of the flight time (up to 0.2 milliseconds) of secondary ions, ejected from the sample, to a detector to determine their mass-to-charge (m/z) ratio. The m/z ratio in turn provides information about the chemistry of the detected ions and therefore of the sample. In this configuration the system waits for all secondary ions in each cycle to reach the detector before beginning the next cycle - the data is inherently sparse. The resulting poor duty cycle limited by the flight time of the largest m/z ion leads to inefficient (<0.1%) primary ion usage and long experimental measurements. In producing a pixel-by-pixel chemical image of the sample surface very many (~1 million) experimental cycles are used to gain the required sensitivity, often taking several hours of experiment time. Extending the analysis to the sub-surface region (depth-profiling or 3D imaging) requires many times longer or involves a different methodology whereby only a small fraction of the sample is analysed and potentially important information is lost. Here we present a multiplexing methodology in which multiple secondary ion packets are measured simultaneously. This allows much more efficient (up to 50%) usage of the primary beam for signal generation and ensures that the summed mass spectra more rapidly converge to a sensitive and accurate measurement. This represents a completely new paradigm for ToF-SIMS.

The development of the necessary hardware (ion optics and electronics), computer control and data processing software is an adventurous task for which we have put together a multidisciplinary academic and industrial team, uniquely positioned to meet this challenge. The result will be greatly improved signal-to-noise and therefore greater sensitivity in shorter experiments. This will increase the throughput and analytical power of the ToF-SIMS technique and extend the range of complex samples that can be analysed. Benefits of improved analytical power will impact on many sectors using this technology including advanced manufacturing and healthcare.

The EPSRC Analytical Sciences Review (May 2015) emphasised the importance of Analytical Sciences as a 'critical enabler of research and innovation in the UK', 'vastly interdisciplinary, affecting science, society and the economy'. This proposal builds on previous EPSRC/industry funded groundbreaking ion beam research to allow significant efficiency gains in their application in basic and applied research and in industry.

Society. Polyatomic ToF-SIMS, pioneered by the Manchester group has resulted in greatly enhanced analysis protocols, rapidly and widely adopted across many sectors including pharmaceuticals, organic electronics and healthcare technology to develop new products and knowledge to enhance quality of life. Expected impact includes the more effective ToF-SIMS determination of drug distributions in pharmaceutical products, organic multilayer structures in flat screen displays and solar energy devices and in molecular pathology to deliver stratified medicine. The general public will benefit from the educational and outreach activities which the researchers will continue to contribute to.

Knowledge. Developments in analytical science and allied disciplines including sensor design and signal processing have potential for great impact across many subjects. This project will develop enhanced capability for the surface and in-depth chemical analysis of complex samples. The ability to determine lateral resolution below the 1 micron level and in-depth resolution on the 10 nm level will enable new understanding of the structure-function relationships in biological and technological materials and devices. The UK analytical science, microfab and digital signal processing research communities will be further strengthened, gain increased international visibility and will benefit from early engagement.

People. The multidisciplinary interaction across analytical science, instrumentation, electronics and digital signal processing will provide training and develop associated interdisciplinary skills in academic researchers and hosted students working in this stimulating environment. Close industrial engagement will foster entrepreneurship and innovation skills. The project will help ensure that the Manchester SIMS group maintains its internationally-leading reputation for innovation in instrumentation development. As evidenced through our previous collaboration with UK SME in technology development for surface analytical instrumentation, the research will help secure employment and growth in this sector.

Economy. The proposal will further increase uptake of polyatomic ToF-SIMS analysis across many sectors including semiconductors, biotechnology, automotive and pharmaceuticals to develop new products, and in emerging areas including nanoscience and advanced manufacturing by providing access to molecular depth-profiling through a cost-effective, high-throughput methodology. This will accelerate the development of new products and stimulate economic growth. The instrumentation developed will provided added stimulus to the international competitiveness of the UK surface analysis instrumentation manufacturing base, which has already benefited from our introduction of C60 ion beams which have been widely adopted for molecular sputtering and ToF-SIMS analysis. By providing a route for their more successful implementation into the majority of existing ToF-SIMS instruments (estimated ~400 worldwide), the market for polyatomic primary ion beams will expand further through the success of this project. Engagement with our UK SME industrial partner will secure further competitive advantage in the worldwide instrumentation market and ensure research directions are relevant to trends in application demands e.g. in emerging industries. IP generation from the design and implementation of the novel multiplex ToF-SIMS technique will provide new opportunities for UK-based patent applications and licensing opportunities.