Crystal surface reflectivity

Ichimiya A, Ohno Y and Horio Y 1997 Structural analysis of crystal surfaces by reflection high energy electron diffraction Surf. Rev. Left 4 501-11... 

Attenuated total reflection (ATR), also called internal reflection, is based on the phenomenon of total internal reflection. In ATR the infrared beam is directed into an infrared-transmitting crystal so that it strikes the crystal surface at less than the critical angle and undergoes total internal reflection. 

The combination of SXRD and X-ray reflectivity is a very powerful technique for the study of adlayers on single-crystal surfaces. An interesting example is the work of Wang et al. (1998) on the adsorption of T1 and Br on Au(l 11) from 1 mM TlBr in O.IMHCIO4. 

Bhzanac BB, Arenz M, Ross PN, Markovic NM. 2004b. Surface electrochemistry of CO on reconstructed gold single crystal surfaces studied by infrared reflection absorption spectroscopy and rotating disk electrode. J Am Chem Soc 126 10130-10141. 

Reflection-Absorption IR spectroscopy (RAIRS) where the linearly polarized IR beam is specularly reflected from the front face of a highly reflective sample, such as a metal single crystal surface (Figure 3.1(a)). This is also sometimes referred to as IRAS (IR reflection absorption). The IR beam comes in at grazing angle (i.e. almost parallel to the surface), and although absorption bands in RAIRS have intensities that are some two orders of magnitude weaker than in transmission studies on... 

Figure 3.7. In-situ reflection-absorption infrared (RAIRS) spectra as a function of catalyst temperature from a Pd(lll) single-crystal surface in the presence of a NO + CO gas mixture (240mbar, Pco/Pno = 1-5) [66]. The data clearly show the appearance of an isocyanate-related band at 2256 cm-1 at temperatures above 500 K. In-situ spectroscopic experiments such as these have proven indispensable to detect and identify key reaction intermediates for the catalytic reduction of NO on metal surfaces. (Figure provided by Professor Goodman and reproduced with permission from the American Chemical Society, Copyright 2003).

Carbon monoxide on metals forms the best-studied adsorption system in vibrational spectroscopy. The strong dipole associated with the C-O bond makes this molecule a particularly easy one to study. Moreover, the C-0 stretch frequency is very informative about the direct environment of the molecule. The metal-carbon bond, however, falling at frequencies between 300 and 500 cm1, is more difficult to measure with infrared spectroscopy. First, its detection requires special optical parts made of Csl, but even with suitable equipment the peak may be invisible because of absorption by the catalyst support. In reflection experiments on single crystal surfaces the metal-carbon peak is difficult to obtain because of the low sensitivity of RAIRS at low frequencies [12,13], EELS, on the other hand, has no difficulty in detecting the metal-carbon bond, as we shall see later on. 

Summarizing, infrared spectroscopy measures, in principle, force constants of chemical bonds. It is a powerful tool in the identification of adsorbed species and their bonding mode. Infrared spectroscopy is an in situ technique, which is applicable in transmission or diffuse reflection mode on real catalysts, and in reflection-absorption mode on single crystal surfaces. Sum frequency generation is a speciality... 

Hydrogen adsorption and oxidation of formic acid show a pronounced dependence on the structure of single crystal surfaces. The influence of the terrace and step orientation and step density is reflected in both reactions on step surfaces. The multiple states of hydrogen adsorption can be correlated with the nature of adsorption sites. 

An advantage of the constant composition technique is that relatively large extents of growth and enhanced crystallinity can be achieved at low supersaturations. Improved crystallinity of the particles during crystallization is reflected in lower specific surface areas of the solid phases x-ray powder diffractograms of the solid phases removed from the crystallization cell also show increases in sharpness. Experiments in which crystal growth was allowed to proceed until five or six times the amount of... 

The number of units in an MQW will be much more limited than the number of atomic planes sampled by the X-ray beam in a standard reflection. The intensity will be low, but also the MQW will behave as a thin crystal —the reciprocal lattice points will be extended into rods perpendicular to the crystal surface. This will broaden the reflection, and thus the width of each satellite peak is determined by the number of units in the MQW. It has even been possible, by... 

Laser irradiation onto the insulating (EDO)2PF6 crystal induces a phase transition to the highly conductive state within a few picoseconds [162, 180]. The crystal surface was excited by laser irradiation with a pulse width of 0.12 ps. The excitation photon energy (1.55 eV) was nearly resonant to the CT band at 11.1 x 10 cm (1.37 eV), directly reflecting the excitation of the charge ordered state. 

---