Laser Studies of Surface Chemical Reactions

Abstract

Currently lasers are being applied to study a very broad range of problems in surface chemistry and surface physics. In many of these areas the introduction of laser probes complements or duplicates more conventional or traditional instrumentation. For instance, surface-enhanced [6.1,2] or unenhanced [6.3] Raman scattering provides the same type of vibrational structure information of surface adsorbates as obtained through reflection absorption infrared and electron energy loss spectroscopies [6.4]. The pulsed laser atom probe is receiving attention as a potential technique for characterizing surface composition and depth profiling [6.5], but does not yet significantly extend the temporal or spatial resolution available from the more traditional atom probe techniques [6.6]. In several specialized research areas laser-induced desorption, sputtering and multiphonon ionization are replacing conventional mass spectrometer ionization sources, but result in chemical speciation data comparable to conventional mass spectrometer [6.7] sources. There are many specific and important areas of surface chemistry/physics where the spatial resolution and high power densities available with lasers present the potential for real scientific advancement [6.8,9]. One obvious such area is semiconductor device fabrication [6.10]. Alternatively, lasers provide the capability to distinguish between reactive (or product species) of the same chemical identity but which occur with differing amounts or types of internal excitation due to competing reaction pathways. This potential for detailed, quantum-state specific information about surface chemical processes opens the door to exploring and, hopefully, unraveling the complex dynamical interplay in chemical processes occurring at the gas-solid interface.