Surface Analyses

Surface science is an invisible yet exceedingly important branch of physics and organic chemistry that studies the behavior and characteristics of molecules at or near the surface or interface. The interface can be between solids, liquids, gases, and combinations of these states. Sophisticated apparatus have been developed to identify and quantify surfaces and interfaces. Polymer surfaces are of special interest in industrial and biological applications examples of the latter include dental implants and body part prosthetic devices. Modification of surfaces of these devices allows formation of controlled interfaces to achieve characteristics such as bondability and compatibility. 

In analyzing surface effects of ultra fine polymer particles, we calculated the surface area and volume using Connolly s contact-reentrant method [231-233]. The contact-reentrant surface (molecular surface) uses a rigid hard sphere with a spherical probe that can trace molecular shape while in contact with the van der Waals surface. The van der Waals surface treats a CH2 bead as a rigid hard sphere equal to the van der Waals radii. The union of the spheres is considered the volume. Connolly s method provides a smooth surface by patching the space between the probe radius and the probed molecule. For our surface area and volume calculations, the van der Waals radius for the PE particles is set at 1.89 C for CH2 beads and the probe radius at 1.4 C to mimic the H2O molecule. Using the molecular surface, we also computed the fractal dimension D to determine roughness of the surface.. The value of D can be calculated by 

Images of the surface were recorded for increasing irradiation times by atomic force microscopy (AFM). Initially, the surface was flat and only some hill-like 

The experimental results showed that, during the first 20 h of irradiation, the photochemical behavior of the blend may be related to that of PVME. To understand better the results of the surface analysis and to try to explain the phase separation phenomenon, a correlation should be made with PVME results. The IR analysis of the photooxidation of PVME homopolymer showed that during the first 5-6 h of irradiation an important increase in a band at 3290 cm-1 was observed [4]. This band has been attributed to tertiary hydroperoxides. For prolonged irradiations, the hydroperoxide absorption band decreased. The decomposition of hydroperoxides yields acetates  

The decomposition of hydroperoxides also produces a chain ketone and methanol  

By AFM analysis, it was shown that the modifications of the surface aspect can be characterized as a function of the irradiation time using the roughness parameters. A correlation between the modifications of the surface and the modifications of the chemical structure of the macromolecules resulting from irradiation showed that the degradation of the surface depends essentially on the decomposition of the hydroperoxides. 

The first step of the mechanism of photooxidation of PS is the abstraction of a hydrogen atom on the tertiary carbon of the macromolecule structure, which 

The term surface analysis is used to mean the characterization of the chemical and physical properties of the surface layer of solid materials. The surface layer of a solid usually differs in chemical composition and in physical properties from the bulk solid material. A common example is the thin layer of oxide that forms on the surface of many metals such as aluminum upon contact of the surface with oxygen in air. The thickness of the surface layer that can be studied depends on the instrumental method. This layer may vary from one atom deep, an atomic monolayer, to 100-1000 nm deep, depending on the technique used. Surface analysis has become increasingly important because our understanding of the behavior of materials has grown. The nature of the surface layer often controls important material behavior, such as resistance to corrosion. The various surface analysis methods reveal the elements present, the distribution of the elements, and sometimes the chemical forms of the elements in a surface layer. Chemical speciation is possible when multiple siuface techniques are used to study a sample. 

Spectroscopic surface analysis techniques are based on bombarding the surface of a sample with a beam of X-rays, particles, electrons, or other species. The bombardment of the surface by this primary beam results in the emission or ejection of X-rays, electrons, particles, and the like from the sample surface. This emitted beam is the secondary beam. The nature of the secondary beam is what provides us with information about the surface. A number of techniques have been developed for surface analysis but only the most common will be discussed in this chapter. The names of these spectroscopic techniques and the primary and secondary beams used for each technique are listed in Table 14.1. These techniques are frequently quite different in physical approach, but all provide information about solid surfaces. Applications of these surface analysis techniques are presented in Tables 14.2 and 14.3. 

The student should be aware that there is another class of surface analysis instruments based on analytical microscopy, including scanning electron microscopy, 

Abbreviated name Full name Primary beam Secondary beam 

XPS Electron spectroscopy for chemical analysis, X-ray photoelectron spectroscopy X-rays Electrons 

The student should be aware that there is another class of surface analysis instruments based on analytical microscopy, including scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and scanning tunneling microscopy. A discussion of these microscopy techniques is beyond the scope of this chapter. Most industrial materials characterization laboratories will have some combination of electron spectroscopy. X-ray analysis, surface mass spectrometry, and analytical microscopy instrumentation available, depending on the needs of the industry. 

Abbreviated Name Full Name Primary Beam Secondary Beam 

What one considers included in surface properties depends on what one considers the surface. (We are not in this chapter considering specific coatings per se that may be applied to achieve a particular effect or property). For adhesion 

Comprehensive Analytical Chemistry, Volume 53 ISSN 0166-526X, DOI 10.1016/S0166-526X(08)00416-9 

Surface (Table 7.3) as well as bulk analysis (Table 7.2) shows that the metal powders produced by this reduction technique are quite complex materials containing considerable amounts of carbon, hydrogen, and oxygen. The ESCA results are summarized in Table 7.3. 

Metal halide Lithium Metal halide Lithium 

BET surface area measurements were carried out on the activated Ni powder and were found to have a specific surface area of 32.7 m /g. Bulk analysis was performed on Ni powders, and the results are shown in Table 7.2. 

The BET analysis on the activated Ni clearly shows the high surface area of these materials. The bulk analysis data indicate the very complex nature of these materials. All samples contained considerable carbon and hydrogen. It is not clear at this point whether this is due to trapped solvent molecules or degradation products from the solvent. Klabunde has demonstrated that 

The origin of the high reactivity of these metals is thus still open to much speculation. Part of this reactivity certainly comes from the high surface area and small particle size. Also, before any manipulations, this surface area must be relatively free of passivation oxide coatings. It is also possible that the adsorbed hydroxide ions, alkoxide anions, and possibly halide anions may be adsorbed on the surfaces and reduce the work function of the metal. This would enhance the metal s ability to transfer an electron to the organic substrate in the initial step of these oxidative addition reactions. 

A variation of the LORIA test uses new technology to evaluate the surface quality of Class A automotive body panels, eliminating subjective visual methods. It uses a low-intensity visible laser to detect surface deviations and imperfections. The beam is projected and scanned across the area, reflected on screen and captured by a high-resolution video camera. There is no contact with the surface, no stylus and no damage. 

Low-angle scanning allows study of flat or curved surfaces. During analysis, the scanning process is utilized more than 20 times across the part data is stored by computer and mathematically reduced by special software to a quantified surface quality number, called Ashland Index . 

The FTIR spectra were recorded with a Nexus instrument (Nicolet, USA) using the ATR (attenuated total reflectance, 45° angle of incidence) technique with a diamond or a Ge cell ( Golden Gate, Specac, Kent, UK). The IR signal comes from a near-surface layer of the polymer film. The information depth de- 

For exact XPS quantification of the functional groups, derivatizations were performed using trifluoroacetic anhydride (TFAA) [62, 63] or m-trifluoromethylphe-nyl isocyanate (TMPl) for the OH groups, pentafluorobenzaldehyde (PFBA) or 

As the use of aqueous base in the development step has been mandated, the wettability of resist films is very important and therefore water contact angles of polymer and resist films are measured often. The contact angle measurement can provide important information about surface segregation of blend films. 

Total internal reflection fluorescence spectroscopic measurements have been carried out on pyrene-doped PHOST thin films, in which pyrene serves as a fluorescence probe to study inhomogeneous distribution of small molecules and hydrophobicity of the interface layer [497]. 

Some instrumental methods have been used for the investigation of sulphide mineral-thio-collector system such as infi-a-red (IR) spectroscopy (Mielezarski and Yoon, 1989 Leppinen, 1990 Persson et al., 1991 Laajalehto et al, 1993) and X-ray photoelectron spectroscopy (XPS) (Pillai et al., 1983 Page and Hazell, 1989 Grano et al, 1990 Laajalehto et al, 1991). These surface sensitive spectroscopic techniques can be applied for the direct determination of the surface composition at the conditions related to flotation. 

In order to characterize the adsorption species on mineral surface, DDTC is oxidized into the dimmer by adding definite H2O2 into the DDTC solution, which then is extracted by cyclohexane to determine its UV spectrum. As seen from the UV spectrum in Fig. 4.33, there are three UV absorbance peaks at 230 nm, 261 nm, 280 nm respectively. The maximum absorbance peak is at 230 nm, the next peak is at 260 nm, and the weak peak is at 280 nm. The peak at 230 nm can serve as a characteristic absorbance peak, and the peak at 260nm results from absorbance overlapping of diethyl dithiocarbamate and its dimmer. 

The UV spectra of the cyclohexane solution extracted from jamesonite acted by DDTC solution, shown in Fig. 4.34, indicates that the adsorption of diethyl dithiocarbamate on the surface of jamesonite is almost the same at pH = 4 and 7, but decreases with the increasing of pH in the base solution. Because the UV spectra in Fig. 4.33 and Fig. 4.34 are similar with peaks at 230 mn and 260 nm, it indicates that the hydrophobic species on jamesonite should be the mixture of diethyl dithiocarbamate and its dimmer. 

After ethyl xanthate interacts with marmatite, the UV spectra of the hydrophobic species on marmatite surface extracted by cyclohexane are shown in Fig. 4.37. There are three UV peaks, lying in 228 nm, 263 nm and 286 nm respectively. It is 

From the flotation results in Fig. 4.21 and the voltammogram in Fig. 4.22, it is derived that the hydrophobic entity of collector on marmatite is mainly of disulphide of xanthate and dithiocarbamate, which is further confirmed by the above UV analysis. However, the UV analysis also suggested the coexistence of collector salts. We propose that the initial oxidation products of xanthate and dithiocarbamate on marmatite should be mainly of disulphide. At higher potential, the adsorbed disulphide may be decomposed and react with surface zinc species to form some parts of collector salts as in the following reactions  

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As on previous occasions, the reader is reminded that no very extensive coverage of the literature is possible in a textbook such as this one and that the emphasis is primarily on principles and their illustration. Several monographs are available for more detailed information (see General References). Useful reviews are on future directions and anunonia synthesis [2], surface analysis [3], surface mechanisms [4], dynamics of surface reactions [5], single-crystal versus actual catalysts [6], oscillatory kinetics [7], fractals [8], surface electrochemistry [9], particle size effects [10], and supported metals [11, 12]. 

Fig. XVin-3. AFM image of DNA strands on mica. Lower figure image obtained in the contact mode under water. The contrast shown covers height variations in the range of 0-2 nm. Upper figure observed profile along the line A-A of the lower figure. (From S. N. Magnov and M.-H. Whangbo, Surface Analysis with STM and AFM, VCH, New Yoric, 1996.)...

Because surface science employs a multitude of teclmiques, it is necessary that any worker in the field be acquainted with at least the basic principles underlying tlie most popular ones. These will be briefly described here. For a more detailed discussion of the physics underlymg the major surface analysis teclmiques, see the appropriate chapter m this encyclopedia, or [49]. 

With the exception of the scanning probe microscopies, most surface analysis teclmiques involve scattering of one type or another, as illustrated in figure A1.7.11. A particle is incident onto a surface, and its interaction with the surface either causes a change to the particles energy and/or trajectory, or the interaction induces the emission of a secondary particle(s). The particles that interact with the surface can be electrons, ions, photons or even heat. An analysis of the mass, energy and/or trajectory of the emitted particles, or the dependence of the emitted particle yield on a property of the incident particles, is used to infer infomiation about the surface. Although these probes are indirect, they do provide reliable infomiation about the surface composition and structure. 

Energetic particles interacting can also modify the structure and/or stimulate chemical processes on a surface. Absorbed particles excite electronic and/or vibrational (phonon) states in the near-surface region. Some surface scientists investigate the fiindamental details of particle-surface interactions, while others are concerned about monitormg the changes to the surface induced by such interactions. Because of the importance of these interactions, the physics involved in both surface analysis and surface modification are discussed in this section. 

Photoelectron spectroscopy provides a direct measure of the filled density of states of a solid. The kinetic energy distribution of the electrons that are emitted via the photoelectric effect when a sample is exposed to a monocluomatic ultraviolet (UV) or x-ray beam yields a photoelectron spectrum. Photoelectron spectroscopy not only provides the atomic composition, but also infonnation conceming the chemical enviromnent of the atoms in the near-surface region. Thus, it is probably the most popular and usefiil surface analysis teclmique. There are a number of fonus of photoelectron spectroscopy in conuuon use. 

Scaiming probe microscopies have become the most conspicuous surface analysis tecimiques since their invention in the mid-1980s and the awarding of the 1986 Nobel Prize in Physics [71, 72]- The basic idea behind these tecimiques is to move an extremely fine tip close to a surface and to monitor a signal as a fiinction of the tip s position above the surface. The tip is moved with the use of piezoelectric materials, which can control the position of a tip to a sub-Angstrom accuracy, while a signal is measured that is indicative of the surface topography. These tecimiques are described in detail in section BI.20. 

Lykke K R and Kay B D 1990 State-to-state inelastic and reactive molecular beam scattering from surfaces Laser Photoionization and Desorption Surface Analysis Techniquesvo 1208, ed N S Nogar (Bellingham, WA SPIE) p 1218... 

The importance of low pressures has already been stressed as a criterion for surface science studies. However, it is also a limitation because real-world phenomena do not occur in a controlled vacuum. Instead, they occur at atmospheric pressures or higher, often at elevated temperatures, and in conditions of humidity or even contamination. Hence, a major tlmist in surface science has been to modify existmg techniques and equipment to pemiit detailed surface analysis under conditions that are less than ideal. The scamiing tunnelling microscope (STM) is a recent addition to the surface science arsenal and has the capability of providing atomic-scale infomiation at ambient pressures and elevated temperatures. Incredible insight into the nature of surface reactions has been achieved by means of the STM and other in situ teclmiques. 

Figure A3.10.il Side view of a combined high-pressnre cell and UFIV surface analysis system [37].

Campbell R A and Goodman D W 1992 A new design for a multitechnique ultrahigh vacuum surface analysis chamber with high-pressure capabilities Rev. Sc/. Instrum. 63 172... 

Riviere J C 1990 Practical Surface Analysis 2nd edn, vol 1, ed D Briggs and M P Seah (Chiohester Wiley) Briggs D 1990 Practical Surface Analysis 2nd edn, vol 2, ed D Briggs and M P Seah (Chiohester Wiley)... 

Sharma A and Khatri R K 1995 Surface analysis optical spectroscopy Encyciopedia of Anaiyticai Science ed A Townshend (London Academic) 8 4958-65... 

Czanderna A Wand Flercules D M (ed) 1991 Ion Spectroscopies for Surface Analysis (New York Plenum)... 

Grizzi O, Shi M, Bu H, and Rabalais J W 1990 Time-of-flight scattering and recoiling spectrometer (TOF-SARS) for surface analysis Rev. Sc/. Instrum. 61 740-52... 

Taglauer E 1997 Low-energy Ion scattering and Rutherford backscattering Surface Analysis The Principal Techniques ed J C VIckerman (Chichester Wiley) pp 215-66... 

Briggs D and Seah M P (eds) 1983 Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy (New York Wiley)... 

It is difficult to observe tliese surface processes directly in CVD and MOCVD apparatus because tliey operate at pressures incompatible witli most teclmiques for surface analysis. Consequently, most fundamental studies have selected one or more of tliese steps for examination by molecular beam scattering, or in simplified model reactors from which samples can be transferred into UHV surface spectrometers witliout air exposure. Reference [4] describes many such studies. Additional tliemes and examples, illustrating botli progress achieved and remaining questions, are presented in section C2.18.4. 

Briggs, D. (Ed.) (1994) Practical Surface Analysis Auger and X-ray Photoelectron Spectroscopy, John Wiley, Chichester. 

Table 1. Overview of Common Surface Analysis Techniques...

Imaging of Surfaces—Analysis of Surface Morphology. Several important techniques can help answer the question what does the surface look like This question is often the first one to be posed ia the characterization of a new surface or iaterface. Physical imaging of the surface is necessary to distinguish the relevant features important for understanding the whole surface and is essential for accurate iaterpretation of data from other surface analysis techniques which might later be appHed to a more limited region of the surface or iaterface. 

Analysis of Surface Elemental Composition. A very important class of surface analysis methods derives from the desire to understand what elements reside at the surface or in the near-surface region of a material. The most common techniques used for deterrnination of elemental composition are the electron spectroscopies in which electrons or x-rays are used to stimulate either electron or x-ray emission from the atoms in the surface (or near-surface region) of the sample. These electrons or x-rays are emitted with energies characteristic of the energy levels of the atoms from which they came, and therefore, contain elemental information about the surface. Only the most important electron spectroscopies will be discussed here, although an array of techniques based on either the excitation of surfaces with or the collection of electrons from the surface have been developed for the elucidation of specific information about surfaces and interfaces. 

Xps was first successfully implemented for surface analysis by K. Siegbahn in the early 1950s. Much of the development of this approach for studyiag surfaces was subsequendy developed by this same group (20), and Siegbahn was awarded the Nobel Prize ia physics ia 1981 for these efforts. 

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. 

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