Surfaces, studies SIMS

The application of heterogeneous catalysis plays a key role in technological processes. Engineering of the catalytic activities requires the study of the complex chemistry between absorbate and the catalyst at the surface. Static SIMS has been used to determine the surface composition and properties of solid catalysts before and after the catalytic actions by several groups.138-140 In addition, the dissociation kinetics of NO on Rh (111) surfaces have been studied by temperature programmed static SIMS.139... 

Other examples of SIMS for surface analyses are studies of CU2S-CdS solar-cell samples (101) and the study of chemisorbed species on inorganic substrates such as methanol on Cu (100) and titania (102). De Pauw s studies of such adsorbed systems may prove to be valuable in determining the mechanism of catalytic reactions on surfaces (103). Winograd and co-workers (104-6) have studied chemisorption on metal surfaces, using SIMS. In a related study (107), Unger et al. have used molecular SIMS to study the reactions of thiophene on a silver surface. They observed the self-hydrogenation of thiophene on the sur-... 

Interactions of Ion Beams with Organic Surfaces Studied by XPS, UPS, and SIMS... 

Fig. 1. Experimental techniques available for surface studies. SEM = Scanning electron microscopy (all modes) AES = Auger electron spectroscopy LEED = low energy electron diffraction RHEED = reflection high energy electron diffraction ESD = electron stimulated desorption X(U)PS = X-ray (UV) photoelectron spectroscopy ELS = electron loss spectroscopy RBS = Rutherford back scattering LEIS = low energy ion scattering SIMS = secondary ion mass spectrometry INS = ion neutralization spectroscopy.

Mass-spectrometry principles and techniques have been employed in other kinds of surface studies in which sample atoms are sputtered by interaction with a laser beam or by RF glow discharges. These approaches are more highly specialized, but it should be clear that mass spectrometry is an important tool in surface chemistry. The student should compare SIMS and ISS with other surface analytical techniques such as ESCA, Auger spectroscopy, electron microprobe, and low-energy electron diffraction (see Chaps. 14 and 15). 

Weng LT, Poleunis C, Bertrand P, Carlier V, Sclavons M, Franquinet P, Legras R, Sizing removal and functionalization of the carbon fiber surface studied by combined ToF SIMS and XPS, J Adhesion Sci Technol, 9, 859-871, 1995. 

Briggs, D., Hearn, M.J. and Ratner, B.D. (1984) Analysis of polvmcr surfaces by SIMS. 4. A study of some... 

Some examples of these applications include studies on p-hydroxybenzoic acid-6-hydroxy-2-naphthoic acid copolyester-based adhesives [269] and further miscellaneous studies on adhesion [270, 271]. West [272] has characterised medical polymers using XPS and ToF-SIMS. These two techniques have also been used to characterise carbon black surfaces [273] and carbon fibres [274]. Other workers have reviewed various aspects of the application of ToF-SIMS to polymer surface studies [237, 275-277] (See also Section 3.11.1). 

This Chapter mainly deals with the big four surface analysis techniques (XPS, AES, SIMS, ISS). For spatially resolved surface analytical methodologies, cfr. Chps. 3 and 5. Various surface analysis methods provide images of elements and other information (cfr. Chp. 5.9). Eor surface studies by means of IR spectroscopies, cfr. Chp. 1. 

Literature reports on interfaces are mainly limited to metallic solids while little is known on ceramic materials, which are mainly ionic solids of nonstoichiometric compounds. The reason for the scarcity of literature reports on ceramic interfaces results from the substantial experimental difficulties in studies of these compounds. Even the most advanced surface-sensitive techniques have experimental limitations in the surface studies of materials. Most of these techniques are based on ion and electron spectroscopy, such as XPS, SIMS, LEED, AFM, and LETS, and are still not adequate to characterize the complex nature of compounds. Namely, these surface techniques require an ultra-high vacuum and therefore may not be applied to determine surface properties during the processing of materials which takes place at elevated temperatures and under controlled gas phase composition. Consequently, the resultant experimental data allow one to derive only an approximate picture of the interface layer of compounds. 

J. W. Rabalais, Interaction of ion beams with organic surfaces studied by XPS, UPS, and SIMS, in Photon, Electron, and Ion Probes of Polymer Structure and Properties (D. W. Dwight, T. J. Fabish and H. R. Thomas, eds.), ACS Symposium Series 162, American Chemical Society, Washington, DC, 1981, pp. 237-246. 

Studies to determine the nature of intermediate species have been made on a variety of transition metals, and especially on Pt, with emphasis on the Pt(lll) surface. Techniques such as TPD (temperature-programmed desorption), SIMS, NEXAFS (see Table VIII-1) and RAIRS (reflection absorption infrared spectroscopy) have been used, as well as all kinds of isotopic labeling (see Refs. 286 and 289). On Pt(III) the surface is covered with C2H3, ethylidyne, tightly bound to a three-fold hollow site, see Fig. XVIII-25, and Ref. 290. A current mechanism is that of the figure, in which ethylidyne acts as a kind of surface catalyst, allowing surface H atoms to add to a second, perhaps physically adsorbed layer of ethylene this is, in effect, a kind of Eley-Rideal mechanism. 

This assumes that the gas-solid exchange kinetics at the interface is rapid. When this process affects the exchange kinetics significantly dieii analysis of concentrations layer by layer in die diffused sample is necessaty. This can be done by the use of SIMS (secondary ion mass spectrometry) and the equation used by Kihier, Steele and co-workers for this diffusion study employs a surface exchange component. 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

With diblock copolymers, similar behavior is also observed. One component is enriched at the surface and depending on miscibility and composition a surface-induced ordered lamellar structure normal to the surface may be formed. Recent investigations include poly (urethanes) [111], poly(methoxy poly (ethyleneglycol) methacrylate)/PS [112] and PS/PMMA [113, 114]. In particular the last case has been extensively studied by various techniques including XPS, SIMS, NR and optical interferometry. PS is enriched at the surface depending on blockcopolymer composition and temperature. A well ordered lamellar structure normal to the surface is found under favourable conditions. Another example is shown in Fig. 6 where the enrichment of poly(paramethylstyrene), PMS(H), in a thin film of a di-... 

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