John C. Vickerman

Surface Analysis– The Principal Techniques

List of Contributors. Preface. 1 Introduction ( John C. Vickerman). 1.1 How do we Define the Surface? 1.2 How Many Atoms in a Surface? 1.3 Information Required. 1.4 Surface Sensitivity. 1.5 Radiation Effects - Surface Damage. 1.6 Complexity of the Data. 2 Auger Electron Spectroscopy ( Hans Jorg Mathieu). 2.1 Introduction. 2.2 Principle of the Auger Process. 2.3 Instrumentation. 2.4 Quantitative Analysis. 2.5 Depth Profile Analysis. 2.6 Summary. References. Problems. 3 Electron Spectroscopy for Chemical Analysis ( Buddy D. Ratner and David G. Castner). 3.1 Overview. 3.2 X-ray Interaction with Matter, the Photoelectron Effect and Photoemission from Solids. 3.3 Binding Energy and the Chemical Shift. 3.4 Inelastic Mean Free Path and Sampling Depth. 3.5 Quantification. 3.6 Spectral Features. 3.7 Instrumentation. 3.8 Spectral Quality. 3.9 Depth Profiling. 3.10 X-Y Mapping and Imaging. 3.11 Chemical Derivatization. 3.12 Valence Band. 3.13 Perspectives. 3.14 Conclusions. Acknowledgements. References. Problems. 4 Molecular Surface Mass Spectrometry by SIMS ( John C. Vickerman). 4.1 Introduction. 4.2 Basic Concepts. 4.3 Experimental Requirements. 4.4 Secondary Ion Formation. 4.5 Modes of Analysis. 4.6 Ionization of the Sputtered Neutrals. 4.7 Ambient Methods of Desorption Mass Spectrometry. References. Problems. 5 Dynamic SIMS ( David McPhail and Mark Dowsett). 5.1 Fundamentals and Attributes. 5.2 Areas and Methods of Application. 5.3 Quantification of Data. 5.4 Novel Approaches. 5.5 Instrumentation. 5.6 Conclusions. References. Problems. 6 Low-Energy Ion Scattering and Rutherford Backscattering ( Edmund Taglauer). 6.1 Introduction. 6.2 Physical Basis. 6.3 Rutherford Backscattering. 6.4 Low-Energy Ion Scattering. Acknowledgement. References. Problems. Key Facts. 7 Vibrational Spectroscopy from Surfaces ( Martyn E. Pemble and Peter Gardner). 7.1 Introduction. 7.2 Infrared Spectroscopy from Surfaces. 7.3 Electron Energy Loss Spectroscopy (EELS). 7.4 The Group Theory of Surface Vibrations. 7.5 Laser Raman Spectroscopy from Surfaces. 7.6 Inelastic Neutron Scattering (INS). 7.7 Sum-Frequency Generation Methods. References. Problems. 8 Surface Structure Determination by Interference Techniques ( Christopher A. Lucas). 8.1 Introduction. 8.2 Electron Diffraction Techniques. 8.3 X-ray Techniques. 8.4 Photoelectron Diffraction. References. 9 Scanning Probe Microscopy ( Graham J. Leggett). 9.1 Introduction. 9.2 Scanning Tunnelling Microscopy. 9.3 Atomic Force Microscopy. 9.4 Scanning Near-Field Optical Microscopy. 9.5 Other Scanning Probe Microscopy Techniques. 9.6 Lithography Using Probe Microscopy Methods. 9.7 Conclusions. References. Problems. 10 The Application of Multivariate Data Analysis Techniques in Surface Analysis ( Joanna L.S. Lee and Ian S. Gilmore). 10.1 Introduction. 10.2 Basic Concepts. 10.3 Factor Analysis for Identification. 10.4 Regression Methods for Quantification. 10.5 Methods for Classification. 10.6 Summary and Conclusion. Acknowledgements. References. Problems. Appendix 1 Vacuum Technology for Applied Surface Science ( Rod Wilson). A1.1 Introduction: Gases and Vapours. A1.2 The Pressure Regions of Vacuum Technology and their Characteristics. A1.3 Production of a Vacuum. A1.4 Measurement of Low Pressures. Acknowledgement. References. Appendix 2 Units, Fundamental Physical Constants and Conversions. A2.1 Base Units of the SI. A2.2 Fundamental Physical Constants. A2.3 Other Units and Conversions to SI. References. Index.

A New Dynamic in Mass Spectral Imaging of Single Biological Cells

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has unique capabilities in the area of high-resolution mass spectrometric imaging of biological samples. The technique offers parallel detection of native and non-native molecules at physiological concentrations with potentially submicrometer spatial resolution. Recent advances in SIMS technology have been focused on generating new ion sources that can in turn be used to eject more intact molecular and biological characteristic species from a sample. The introduction of polyatomic ion beams, particularly C60, for TOF-SIMS analysis has created a whole new application of molecular depth profiling and 3D molecular imaging. However, such analyses, particularly at high lateral resolution, are severely hampered by the accompanying mass spectrometry associated with current TOF-SIMS instruments. Hence, we have developed an instrument that overcomes many of the drawbacks of current TOF-SIMS spectrometers by removing the need to pulse the primary ion beam. The instrument samples the secondary ions using a buncher that feeds into a specially designed time-of-flight analyzer. We have validated this new instrumental concept by analyzing a number of biological samples generating 2D and 3D images showing molecular localization on a subcellular scale, over a practical time frame, while maintaining high mass resolution. We also demonstrate large area mapping and the MS/MS capability of the instrument.

Handbook of static secondary ion mass spectrometry (SIMS) : Wiley, Chichester, 1989 (ISBN 0-471-91627-7). 156 pp. Price £ 125.00

Part 1 Static secondary ion mass spectrometry for surface chemical characterization: the SIMS phenomenon the experimental parameters the SIMS experiment experimental procedures used in acquisition of spectra. Part 2 Library of spectra. Part 3 Case studies: static SIMS in surface science cleaning of semiconductor materials SIMS imaging of the mechanism of oxide growth the use of MS/MS techniques in materials analysis SIMS imaging of semiconductor devices. (Part contents).

Development and experimental application of a gold liquid metal ion source

Abstract A liquid metal ion source (LMIS) based upon a gold/germanium eutectic has been developed. The LMIS emits a variety of ions including monatomic gold and gold clusters. Gold ions have been utilised for SIMS analysis of the polypeptide gramicidin and the polymer poly(ethylene-terepthalate) (PET). It has been found that monatomic gold (Au + ) increases secondary ion yields up to a factor of four compared to gallium, for both gramicidin and PET. The Au 3 + cluster produces a strong non-linear increase in yield over monatomic gold, for both gramicidin and PET. This effect is greatest at high mass, the yield for the gramicidin molecular ion increasing by a factor of over 60. No evidence has been found to suggest increased fragmentation as a result of cluster ion bombardment. The LMIS also exhibits good static SIMS imaging capacity.

TOF-SIMS with Argon Gas Cluster Ion Beams: A Comparison with C60+

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an established technique for the characterization of solid sample surfaces. The introduction of polyatomic ion beams, such as C(60), has provided the associated ability to perform molecular depth-profiling and 3D molecular imaging. However, not all samples perform equally under C(60) bombardment, and it is probably naïve to think that there will be an ion beam that will be applicable in all situations. It is therefore important to explore the potential of other candidates. A systematic study of the suitability of argon gas cluster ion beams (Ar-GCIBs) of general composition Ar(n)(+), where n = 60-3000, as primary particles in TOF-SIMS analysis has been performed. We have assessed the potential of the Ar-GCIBs for molecular depth-profiling in terms of damage accumulation and sputter rate and also as analysis beams where spectral quality and secondary ion yields are considered. We present results with direct comparison with C(60) ions on the same sample in the same instrument on polymer, polymer additive, and biomolecular samples, including lipids and small peptides. Large argon clusters show reduced damage accumulation compared with C(60) with an approximately constant sputter rate as a function of Ar cluster size. Further, on some samples, large argon clusters produce changes in the mass spectra indicative of a more gentle ejection mechanism. However, there also appears to be a reduction in the ionization of secondary species as the size of the Ar cluster increases.

Applications of Fourier transform infrared microspectroscopy in studies of benign prostate and prostate cancer. A pilot study.

Fourier transform infrared (FTIR) microspectroscopy has been applied to a study of prostate cancer cell lines derived from different metastatic sites and to tissue from benign prostate and Gleason‐graded malignant prostate tissue. Paraffin‐embedded tissue samples were analysed by FTIR, after mounting onto a BaF2 plate and subsequent removal of wax using Citroclear followed by acetone. Cell lines were analysed as aliquots of cell suspension held between two BaF2 plates. It was found that the ratio of peak areas at 1030 and 1080 cm−1, corresponding to the glycogen and phosphate vibrations respectively, suggests a potential method for the differentiation of benign from malignant cells. The use of this ratio in association with FTIR spectral imaging provides a basis for estimating areas of malignant tissue within defined regions of a specimen. Initial chemometric treatment of FTIR spectra, using the linear discriminant algorithm, demonstrates a promising method for the classification of benign and malignant tissue and the separation of Gleason‐graded CaP spectra. Using the principle component analysis, this study has achieved for the first time the separation of FTIR spectra of prostate cancer cell lines derived from different metastatic sites. Copyright

Performance characteristics of a chemical imaging time-of-flight mass spectrometer.

A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a liquid metal ion gun, medium energy resolution reflectron mass analyzer, liquid nitrogen cooled sample stage, preparation chamber and dual stage entry port. Unique features include compatibility with laser postionization experiments, large field of view, cryogenic sample handling capability and high incident ion beam current. Instrument performance is illustrated by the characterization of scanning electron microscopy grids, silver and functionalized polystyrene beads and the postionization of an organic overlayer on a gold substrate.

DEVELOPMENTS IN MOLECULAR SIMS DEPTH PROFILING AND 3D IMAGING OF BIOLOGICAL SYSTEMS USING POLYATOMIC PRIMARY IONS

In principle mass spectral imaging has enormous potential for discovery applications in biology. The chemical specificity of mass spectrometry combined with spatial analysis capabilities of liquid metal cluster beams and the high yields of polyatomic ion beams should present unprecedented ability to spatially locate molecular chemistry in the 100 nm range. However, although metal cluster ion beams have greatly increased yields in the m/z range up to 1000, they still have to be operated under the static limit and even in most favorable cases maximum yields for molecular species from 1 µm pixels are frequently below 20 counts. However, some very impressive molecular imaging analysis has been accomplished under these conditions. Nevertheless although molecular ions of lipids have been detected and correlation with biology is obtained, signal levels are such that lateral resolution must be sacrificed to provide a sufficient signal to image. To obtain useful spatial resolution detection below 1 µm is almost impossible. Too few ions are generated! The review shows that the application of polyatomic primary ions with their low damage cross-sections offers hope of a new approach to molecular SIMS imaging by accessing voxels rather than pixels to thereby increase the dynamic signal range in 2D imaging and to extend the analysis to depth profiling and 3D imaging. Recent data on cells and tissue analysis suggest that there is, in consequence, the prospect that a wider chemistry might be accessible within a sub-micron area and as a function of depth. However, these advances are compromised by the pulsed nature of current ToF-SIMS instruments. The duty cycle is very low and results in excessive analysis times, and maximum mass resolution is incompatible with maximum spatial resolution. New instrumental directions are described that enable a dc primary beam to be used that promises to be able to take full advantage of all the capabilities of the polyatomic ion beam. Some new data are presented that suggest that the aspirations for these new instruments will be realized. However, although prospects are good, the review highlights the continuing challenges presented by the low ionization efficiency and the complications that arise from matrix effects.

Model studies on bimetallic CuRu catalysts: III. Adsorption of carbon monoxide

Abstract The adsorption of CO on Cu-covered Ru(0001) surfaces prepared at different temperatures was studied in UHV between 150 and 350 K by means of LEED, thermal desorption spectroscopy (TDS), and work function change (Δϑ) measurements. Cu deposition at 540 K leads to statistically distributed nuclei which grow to three-dimensional clusters, deposition at 1080 K gives a more dispersed and strictly two-dimensional Cu atom distribution. The amount of strongly chemisorbed CO is greatly reduced by the presence of Cu, and the results indicate the clear operation of an ensemble effect with 3 Ru atoms participating in binding 1 CO molecule. A small ligand effect accounts for the slight reduction of the CO binding energy observed over the bimetallic surfaces. At ~ 150 K adsorption temperature, there is evidence that isolated copper atoms are capable of forming complexes of the kind Cu(CO) 2 ; in addition various low-energy Cu Ru “mixed” sites become populated by CO. Moreover, the proximity of Ru atoms enables Cu atoms on top to adsorb CO more efficiently in that the well-known CO back-donation mechanism is allowed for by a transfer of charge from Ru to Cu atoms. The importance of the ensemble effect with respect to the adsorption mechanism (i.e., dissociative or nondissociative) is compared and discussed in view of recent adsorption studies on bimetallic Ru Cu surfaces.

Secondary Ion Mass Spectrometry: Characterizing Complex Samples in Two and Three Dimensions

■ CONTENTS Application of NanoSIMS to the Study of Complex Organic Systems 612 Molecular SIMS in the Static Regime 614 Molecular SIMS beyond the Static Regime 619 3D Reconstruction 619 Instrument Developments 620 Organic Depth Profile Challenges: Contribution of GCIBs 622 MD Simulations Providing Insights into Cluster and Polyatomic Mechanisms 624 Molecular SIMS: The Challenges 627 Sample Preparation 627 Matrix Effect 628 Secondary Ion Yields 631 Data Interpretation 633 Whither Molecular SIMS? 635 Author Information 636 Corresponding Author 636 Present Address 636 Notes 636 Biographies 636 Acknowledgments 636 References 636