Surface enhanced infrared difference

Ataka, K., and Heberle, J. (2003) Electrochemically induced surface-enhanced infrared difference absorption (SEIDA) spectroscopy of a protein monolayer. Journal of the American Chemical Society, 125, 4986 987. 

SEIDAS Surface enhanced infrared difference absorption spectroscopy... 

There are different paths to achieving surface specificity. One can exploit optical susceptibilities and resonances that are nonzero only at the surface or only for the molecular species of interest adsorbed on the surface. Examples include the use of second-order nonlinear mixing processes such as second harmonic generation7-9 for which the nonlinear susceptibility tensor is nonzero only where inversion symmetry is broken. Spectroscopic techniques with very high selectivity for molecular resonances such as surface-enhanced infrared or Raman spectroscopy10-12 may also be used. 

Fig. 1. (a) A chemical structure of a 2.5th generation carboxylic acid-terminated poly(amido amine) (PAMAM) dendrimer. (b) Transmission surface enhanced infrared absorption spectra (SEIRAS) of dendrimer adlayers prepared at 30 min adsorption from aqueous solutions (0.01 wt.%) of a dendrimer at different pHs. Numerical values are pHs of the solutions, (c) Adsorption-desorption profiles as a function of time at different pHs and adlayer thicknesses at adsorption and desorption equilibrium as a function of pH for aqueous solutions (0.1 wt.%) of the dendrimer. The symbols, j and J, in the top figure denote start of adsorption and desorption, respectively. In the bottom figure, filled circle and opened square denote adlayer thicknesses at adsorption and desorption equilibrium, respectively. The dark tie denotes the calculated dendrimer size width. A solid curve is drawn to be visual, (d) Schematic illustration of dendrimers adsorbed at different pHs. Reprinted with permission from Ref. [69], 2006, American Scientific Publishers. 

The tremendous advances that have occurred in the spectroscopic analysis of the electrode/electrolyte interface have begun to provide a fundamental understanding of the elementary processes and the influence of process conditions. Surface-sensitive spectroscopic and microscopic analyses such as surface-enhanced Raman scattering (SERS) [1], potential-difference infrared spectroscopy (PDIRS) [2], surface-enhanced infrared spectroscopy (SEIRS) [3], sum frequency generation (SFG) [4], and scanning tunneling microscopy (STM) [5,6] have enabled the direct observation of potential-dependent changes in molecular structure [2,7] chemisorption [8,9], reactivity [10], and surface reconstruction [11]. 

We note that surface-enhanced infrared absorption can also be used for near-field probing of chemical constitution with a local resolution of less than 100 nm (Knoll and Kellmann 1999). In fact, fortunately one finds in many different cases, surface enhancement effects caused by the scanning tip, which should allow one to use a variety of traditionally far-field spectroscopies in the near-field regime. 

Some characteristics of, and comparisons between, surface-enhanced Raman spectroscopy (SERS) and infrared reflection-absorption spectroscopy (IRRAS) for examining reactive as well as stable electrochemical adsorbates are illustrated by means of selected recent results from our laboratory. The differences in vibrational selection rules for surface Raman and infrared spectroscopy are discussed for the case of azide adsorbed on silver, and used to distinguish between "flat" and "end-on" surface orientations. Vibrational band intensity-coverage relationships are briefly considered for some other systems that are unlikely to involve coverage-induced reorientation. 

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

The mechanism of C02 reduction to methane at Cu electrodes has been proposed by various groups [72-74], most of which involved the splitting of adsorbed CO followed by the hydrogenation of surface C atoms. When DeWulf et al. used X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy to study the reaction [72], they observed surface-bound carbenes (Cu CH2) as an intermediate in the system. Likewise, others used both in situ infrared (IR) reflection absorption spectroscopy and surface-enhanced Raman spectroscopy to observe the initial product of C02 reduction on Cu [74]. Typically, two different linearly bound CO species were identified and attributed to adsorption on either surface defect sites or terraces. 

LPSIRS Linear Potential Sweep Infra-Red Spectroscopy SPAIRS Single Potential Alteration Infra-Red Spectroscopy PDIRS Potential Difference Infrared Spectroscopy EMIRS Electrochemically Modulated Infra-Red Spectroscopy SERS Surface Enhanced Raman Scattering (Surface Enhanced Raman Spectroscopy)... 

This chapter has been organized by considering several aspects. An introduction concerning the relevance of the electronic properties and applications of the azamacrocycles related to surface phenomena as well as the general aspects and characteristics of the vibrational techniques, instruments and surfaces normally used in the study of the adsorbate-surface interaction. The vibrational enhanced Raman and infrared surface spectroscopies, along with the reflection-absorption infrared spectroscopy to the study of the interaction of several azamacrocycles with different metal surfaces are discussed. The analysis of the most recent publications concerning data on bands assignment, normal coordinate analysis, surface-enhanced Raman and infrared spectroscopies, reflection-absorption infrared spectra and theoretical calculations on models of the adsorbate-substrate interaction is performed. Finally, new trends about modified metal surfaces for surface-enhanced vibrational studies of new macrocycles and different molecular systems are commented. 

In the normal-incident transmission measurements of LB films deposited on transparent substrates, the electric vector of the infrared beam is parallel to the film surface (Figure 5A). Therefore, only absorption bands which have the transition moments parallel to the film surface can be detected by this method. On the other hand, in the above-mentioned RA measurements, in which the p-polarized infrared beam is incident upon the LB film prepared on Ag-evaporated substrates at a large angle of incidence, we have a strong electric field perpendicular to the film surface as shown in Figure 5B. Therefore, in this case, only absorption bands which have the transition moments perpendicular to the film surface can be detected with a large intensity enhancement. Thus, if the molecules are highly oriented in the LB films, the peak intensities of particular bands should be different between the transmission and RA spectra. 

The differently produced conductive polymer structures described above all have enhanced conductivity, which can be employed in microelectronics [44] and as sensors using immobilized enzymes [46, 47[. Martin and coworkers used polarized infrared absorption spectroscopy to access the alignment of the polymer fibers on the outer surface of the nanotubes [48[. The study showed that the enhancement of the conductivity is due to the alignment of the polymer fibers on the outer surface of the tubes. 

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