Quantitative Surface Analysis Techniques

Kawamura et al. [220] have reported the simultaneous determination method for 53 polymer additives in PE for food packaging. All additives were identified and quantified by GC-MS. Quantitative analysis of Irganox PS802 by LC-APCI-MS has been reported [221]. Yu et al [213] described the quantification of the PP additives NC-4, Naugard-XL, 1-octadecanol and Irganox 1076 by means of LC-APCI -MS authentic reference standards were needed. pSFC-APCI-MS can be used for quantitative analysis of a wide range of polymer additives [222]. 

Principles and Characteristics As polymer surfaces (top 10 A) and microscopic phases ( 60 /xm) influence many of today s critical technologies, their detailed quantitative characterisation is crucial. However, the spatially resolved chemical analysis of polymer surfaces and microscopic phases has historically been difficult to obtain. It is clearly the ultimate objective of surface analysis to give a quantitative description of the 

DSIMS Only with standards of very similar composition n.d. 

Quantification of data from XPS or AES is complex. There appears to be no one single satisfactory method of quantification which gives reliable results in all cases. Also, the ultimate resolutions and sensitivities of the techniques are not yet totally clear. In the first-principles method the emitted intensities 

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A specific problem consequent upon these inhomogeneous samples arises in the quantification of XPS results, which requires the assumption that the depth probed by XPS has a homogeneous composition. While XPS is a surface-sensitive technique, only ca 30% of the total intensity arises from the top atomic layer which may contain adsorbates and promoter films. The deeper layers, which may be of variable composition in catalyst samples, contribute the other 70% of spectral intensity in a section of ca 2 nm in thickness. Furthermore, very little information can be obtained from the inner surfaces of the pore system of an activated catalyst. It has therefore generally been assumed that the inner surface of the catalyst can be considered to be similar to the outer surface. These assumptions limit the significance of quantitative surface analysis techniques when applied to heterogeneous porous solids and do not allow clear conclusions to be drawn, as can be done in the case of single-crystal samples. 

In other articles in this section, a method of analysis is described called Secondary Ion Mass Spectrometry (SIMS), in which material is sputtered from a surface using an ion beam and the minor components that are ejected as positive or negative ions are analyzed by a mass spectrometer. Over the past few years, methods that post-ion-ize the major neutral components ejected from surfaces under ion-beam or laser bombardment have been introduced because of the improved quantitative aspects obtainable by analyzing the major ejected channel. These techniques include SALI, Sputter-Initiated Resonance Ionization Spectroscopy (SIRIS), and Sputtered Neutral Mass Spectrometry (SNMS) or electron-gas post-ionization. Post-ionization techniques for surface analysis have received widespread interest because of their increased sensitivity, compared to more traditional surface analysis techniques, such as X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES), and their more reliable quantitation, compared to SIMS. 

Such features make SIMS a powerful technique for surface analysis. However, SIMS as a surface analysis technique has not yet reached a mature stage because it is still under development in both theoretical and experimental aspects. This lack of maturity is attributed to the complicated nature of secondary ion yield from a solid surface. Complexity of ion yield means that SIMS is less likely to be used for quantitative analysis because the intensity of secondary ions is not a simple function of chemical concentrations at the solid surface. SIMS can be either destructive or non-destructive to the surface being analyzed. The destructive type is called dynamic SIMS it is particularly useful for depth profiling of chemistry. The nondestructive type is called static SIMS. Both types of SIMS instruments are widely used for surface chemical examination. 

AES is primarily a surface elemental analysis technique. It is used to identify the elemental composition of solid surfaces, and can be used to quantify surface components, although quantitative analysis is not straightforward. AES is a true surface analysis technique, because the low-energy Auger electrons can only escape from the first few (three to five) atomic layers or from depths of 0.2-2.0 nm. 

Only exposed atoms on the surface, that is, the top monolayer of atoms, contributes to the signal in ISS. It is therefore the most surface sensitive of the surface analysis techniques. ISS is one technique that provides isotopic information on surface atoms. ISS can be used to determine all elements with an atomic number greater than that of the bombarding ion. The elemental and isotopic compositions of the surface can be determined both qualitatively and quantitatively. Sensitivity is about 1% of a monolayer for most elements. 

In most Materials Characterization experiments the sample is subjected to some kind of radiation electromagnetic, acoustic, thermal, or particles (electrons, ions, neutrons, etc.). The surface analysis techniques usually require a high vacuum. As aresult of interactions between the solid (or liquid) and the incoming radiation abeam of a similar (or a different) nature will emerge from the sample. Measurement of the physical and/or chemical attributes of this emerging radiation will yield qualitative, and often quantitative, information about the composition and the properties of the material being probed. 

Cox and co-workers [179] analysed PS/polyvinyl methyl ether blends by coincidence counting ToF mass spectrometry. This technique gave information on the chemical and spatial relationships between secondary ions. Thompson [180] carried out a quantitative surface analysis of organic polymer blends (e.g., miscible polycarbonate/PS blends) using ToF-SIMS. Lin and co-workers [181] used supersonic beam/multiphoton ionisation/ToF mass spectrometry to analyse photoablation products resulting from styrene-containing polymers snch as styrene-bntadiene, ABS, and PS foams. Photoablation products were examined by snpersonic beam spectrometry and the results were compared with those obtained by thermal decomposition. 

LEIS has grown to become a mature surface analysis technique. In contrast to other surface analysis techniques (XPS, AES, etc.) LEIS only observes the outermost atomic layer and thus is able to provide information that is very difficult to obtain otherwise. LEIS allows non-destructive and quantitative measurements on all kinds of material, including very sensitive polymer layers. However, LEIS finds most application for inorganic systems. The application of LEIS to polymeric surface analysis remains to a large extent underdeveloped. Various specific areas can be described ... 

The understanding of material properties on a local level implies knowledge of the chemistry and, hence, of the molecules present. Therefore the molec ular specificity of LMMS is a major advantage in comparison with most micro- and surface analysis techniques, which characterize relative elemental abundances, bonds present or functional groups. Quantitation in LMMS is difficult because adequate... 

X-ray photoelectron spectroscopy (XPS), which is a very sensitive surface analysis technique, has also been used to characterize UHMWPE/HA. By measuring the energies of electrons emitted from an X-ray irradiated surface, XPS can provide qualitative and quantitative information on the elemental composition and chemical state of the surface with a sampling depth between 20-lOOA [103]. XPS can identify all elements (except H and He) at concentration >0.1 atomic % and identify organic groups via... 

XPS (X-ray Photoelectron Spectroscopy) or ESCA (Electron Spectroscopy for Chemical Analysis) as a surface analysis technique has been most widely used due to its high information content, flexibility in addressing a wide variety of samples, and sound theoretical basis since mid-1960s. Over the past few decades, XPS has been developed into the key snrface characterization method which combines surface sensitivity with the abihty to quantitatively obtain both elemental and chemical state information. Nowadays it is known that XPS is a very important analytical tool in the area of thin films. XPS analysis gives rise to useful information such as composition, chemical state, and thickness, etc., of thin film. 

It is often the case that complementary surface analysis techniques such as SIMS and XPS can be used together in order to successfully solve a failure or characterisation problem. In such cases, XPS would be used to generate quantitative information, whilst SIMS would provide qualitative clues with respect to the chemistry. An example of this is where XPS has successfully detected and quantified silicon on a surface which is not responding well to bonding with an adhesive, but the chemical form that the silicon is in is not readily apparent, i.e., it could be silica, silicate or silicone. Analysis of the same surface by static SIMS enables the mass spectmm of the sputtered top layer fragments to be determined and ihe presence of m/e ions at 43,73 and 147 confirm that a polydimethyl siloxane is present. 

Batts and Paul [101b] used time-of-flight secondary-ion mass spectrometry (ToF-SIMS) to investigate the competitive adsorption of a cationic fluorinated surfactant (FC-134) at the gelatin-air interface. ToF-SIMS is a very sensitive surface analysis technique. In the static mode, the sampling depth of ToF-SIMS is only one to two monolayers. However, the ToF-SIMS data are difficult to interpret in quantitative terms and experimental conditions must be carefully controlled. Batts and Paul used positive secondary-ion spectra only, although negative-ion spectra may have been used as well. 

Chemical analysis of the metal can serve various purposes. For the determination of the metal-alloy composition, a variety of techniques has been used. In the past, wet-chemical analysis was often employed, but the significant size of the sample needed was a primary drawback. Nondestmctive, energy-dispersive x-ray fluorescence spectrometry is often used when no high precision is needed. However, this technique only allows a surface analysis, and significant surface phenomena such as preferential enrichments and depletions, which often occur in objects having a burial history, can cause serious errors. For more precise quantitative analyses samples have to be removed from below the surface to be analyzed by means of atomic absorption (82), spectrographic techniques (78,83), etc. 

Within the last 5—10 years PIXE, using protons and helium ions, has matured into a well-developed analysis technique with a variety of modes of operation. PIXE can provide quantitative, nondestructive, and fast analysis of essentially all elements. It is an ideal complement to other techniques (e.g., Rutherford backscattering) that are based on the spectroscopy of particles emitted during the interaction of MeV ion beams with the surface regions of materials, because... 

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