Surface chemistry laser-induced

The recent development of high T superconductors opens a whole new realm of possible chemistry involving supercondcting solids and surfaces. It had always been assumed that a perfect conductor did not exist, but now comes a special kind of perfect conductor available at temperatures readily accessible to chemists. An example of new chemistry is laser-induced chemical vapor deposition, where a laser could be used to "write" an insulating layer or a "normal" conducting layer on top of a superconductor, or even to write a superconductor on a semiconducting substrate. 

Recent advances in ultrasensitive instrumentation have allowed the detection of individual atoms and molecules in solids [174, 175], on surfaces [176, 177], and in the condensed phase [178, 179] using laser-induced fluorescence. In particular, single molecule detection in the condensed phase enables scientists to explore new frontiers in many scientific disciplines, such as chemistry, molecular biology, molecular medicine and nanostructure materials. There are several optical methods to study single molecules, the principles and application of which have been reviewed by Nie and Zare [180]. These methods are listed in Tab. 6.12. 

Carbenes are prominent in synthetic and polymer chemistry as well as in interstellar and atmospheric chemistry [2-5]. The great interest stems largely from the chemical differences between singlet and triplet carbenes, particularly in their reactivity and rich spectroscopy and photochemistry. The latter were recentiy discussed and summarized in a review by Kable et al. [6]. Laser-induced fluorescence (LIE) studies in particular have yielded a wealth of structural and spectroscopic data as well as useful information on the nature of the potential energy surface of the excited A state, such as barriers to dissociation and... 

Good examples that illustrate direct photon adsorption for an adsorbate are the photodissociation of Mo(Co)g on Cu(lll) and Ag(lll). Here, the wavelength dependence of photodissociation is nearly the same as that in the gas phase. Direct absorption can also mediate charge-transfer surface reactions. Dissociative electron attachment of adsorbates is an important process in surface chemistry induced by laser excitation this will be the topic of Section 27.2. 

Sharma S, Lucey P, Ghosh M et al (2003) Stand-off Raman spectroscopic detection of minerals on planetary surfaces. Spectrochim Acta A 59 2391-2407 Singh J, Thakur S (2007) Laser-induced breakdown spectroscopy. Elsevier, Amsterdam Smith E, Dent G (2005) Modem Raman spectroscopy a practical approach. Wiley, Hoboken Steinfeld J, Wormhoudt J (1998) Explosives detection a challenge for physical chemistry. Ann Rev Phys Chem 49 203-232... 

The occurrence of proton transfer, i.e., of proper Bronsted acidity, is usually revealed by IR spectroscopy, because the vibrational modes of protonated and non-protonated species are remarkably different. This topic, now a standard tool in surface chemistry, is dealt with in detail in other chapters of the present volume, and will not be treated here (cf. also Volmne IV, Chapter 1 of the present series Molecular Sieves - Science and Technology ). A variant of the IR method is the use of quinoline instead of pyridine, which allows the distinction between protonated and non-protonated species by the use of laser-induced fluorescence [32]. 

The objective of the following sub-sections is to exemplify the synergetic effect of the combined processing by laser-induced siuface roughening and subsequent UV-induced modification of surface chemistry and simi-marizes experimental results from earlier studies of the authors. The first example (sub-section 13.3.1) concerns the increase of water repellence of... 

This is illustrated in the context of data recorded on the p-aramid (Kevlar ) fabrics, which are summarized in Table 13.4. The first observation is that, again, extremely high water repellence is achieved by the combined process of laser-induced surface roughening and subsequent UV-induced modification of surface chemistry. The photo-chemical modification used... 

An ultrafast laser can excite the surface electrons and these can induce chemistry as well as desorption prior to their being rapidly ( 1 ps) thermalized with the phonons (Bonn et ai, 1999). The electronic mechanism for laser-induced desorp-tion(Gomer, 1983 Gadzuk, 1988 Avouris and Walkup, 1989) is through the temporary formation of the negative ion of the adsorbate. The ion is pnlled sttongly toward the surface while its equiUbrium distance tends to increase. Shortly thereafter the charge is returned to the surface and a vibrationally excited neutral is ejected. 

A great deal of effort has been invested in recent years in the study of the surface chemistry of Uthiated carbon anodes in Li battery electrol)de solutions. Fortunately, the basic surface reactions of a large variety of nonaqueous Li salt solutions on Li, Li-C, and noble metal electrodes polarized cathodically are very similar. The tools for the study of the surface chemistry of these systems included XPS [53], AES [54], FTIR [55], Raman [56], EDAX [57], and, recently, SIMS-TOF [58], The study of the surface chemistry of the composite electrodes used in Li-ion batteries is difficult. Hence, a previous study of the surface chemistry developed on noble metal and Li electrodes in the solutions of interest may be very helpful. It should be emphasized that the use of XPS, AES, Raman (laser beam needed), and SIMS-TOF may lead to changes in the surface species during the measurements due to further surface reactions induced by X-rays, laser beams, or bombardment by ions. 

Inasawa, S., Sugiyama, M. and Yamaguchi, Y. (2005) Laser-induced shape transformation of gpld nanopartides below the melting point the effect of surface melting. The Journal of Physical Chemistry B, 109, 3104—11. 

R. D. Levine As emphasized by the speakers on femtosecond pumping schemes, an important point is that the initial excitation is localized within the Franck-Condon regime. The question is whether the sheer localization can be used to advantage to induce laser-selective chemistry (K. L. Kompa and R. D. Levine, Acc. Chem. Res. 27, 91 (1994)]. As we understand better the topography of potential-energy surfaces for polyatomic molecules, it may be possible to launch the system with such initial conditions that it will, of its own accord, proceed to cross a particular transition state and so exit toward a particular set of products. 

Lasers also have many research applications outside of chemistry. They can be modulated (turned on or off, or changed in frequency) in tens of femtoseconds, and this means that they can transmit many bits of information in a very short time. Intense laser beams can cut metal or human tissue with high precision. They can even generate high pressures (photons have momentum, so bouncing light off a surface exerts a pressure, just as bouncing gas molecules off a surface exerted pressure), and this is used to induce nuclear fusion. 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

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