Thermal desorption studies

This article discusses why one would choose nonresonant multiphoton ionization for mass spectrometry of solid surfaces. Examples are given for depth profiling by this method along with thermal desorption studies. 

Chemisorption of simple diatomic molecules has usually been the object of thermal desorption studies. Recently, there has been a growing interest in the application of this method to the investigation of surface phenomena produced by more complex molecules which yield either fragment desorption products or catalytically formed species (35, 46a 46h). Also, physisorp-... 

Jachimowski TA, Meng B, Johnson DP, Weinherg WH. 1995. Thermal desorption studies of high-coverage hydrogen overlayers on Ru(OOl) created with gas-phase atomic hydrogen. J Vac Sci Technol A 13 1564. 

Figure 2.10 Experimental set-up for thermal desorption studies in ultrahigh vacuum. The heat dissipated in the tantalum wires resistively heats the crystal the temperature is measured by a thermocouple spot-welded to the back of the crystal. Desorption of gases is followed with a mass spectrometer...

Formic acid decomposes generally on metal surfaces to carbon dioxide and hydrogen. A thermal desorption study on Cu(l 10) showed that the reaction... 

Thermal desorption studies of preadsorbed oxygen on a number of transition metal oxides have been carried out by Iwamoto (170) and others who observed several desorption peaks for each oxide. In this type of work, reliable assignment of the desorption peaks to particular oxygen species is only possible when parallel spectroscopic studies are carried out. This is difficult for many of these oxides where only material of low specific surface area is available. 

Studies by Teplyakov et al. provided the experimental evidence for the formation of the Diels-Alder reaction product at the Si(100)-2 x 1 surface [239,240]. A combination of surface-sensitive techniques was applied to make the assignment, including surface infrared (vibrational) spectroscopy, thermal desorption studies, and synchrotron-based X-ray absorption spectroscopy. Vibrational spectroscopy in particular provides a molecular fingerprint and is useful in identifying bonding and structure in the adsorbed molecules. An analysis of the vibrational spectra of adsorbed butadiene on Si(100)-2 x 1 in which several isotopic forms of butadiene (i.e., some of the H atoms were substituted with D atoms) were compared showed that the majority of butadiene molecules formed the Diels-Alder reaction product at the surface. Very good agreement was also found between the experimental vibrational spectra obtained by Teplyakov et al. [239,240] and frequencies calculated for the Diels-Alder surface adduct by Konecny and Doren [237,238]. 

The greater amount of retention observed with acetylene than with ethylene has been ascribed to the ability of the former to polymerise extensively. The existence of surface polymers following acetylene adsorption on alumina- and silica-supported platinum [60], evaporated palladium films [154] and silica-supported rhodium [67] has been demonstrated by thermal desorption studies. 

Slater Type Orbital using 3 primitive Gaussians Two Configuration Self-Consistent Field Thermal Desorption Study... 

Thermal desorption studies have indicated that, as with massive gold, adsorbed carbon monoxide desorbs from small gold particles below room temperature. Thus, with model AU/AI2O3 there were two desorption... 

Our studies of olefin and acetylene chemisorption states on platinum surfaces is presently incomplete. Ethylene and acetylene chemisorption on platinum (111) are complicated by the apparent presence of more than one chemisorption state (indicated by thermal desorption studies). When C2HH and C2D1, are chemisorbed on Pt(lll), the small fraction of ethylene thermally desorbed as ethylene comprises nearly a statistical mixture of all possible molecules. Thus we see here reversible C-H (and C-D) bond breaking on this flat platinum surface. In an analogous experiment with C2H2 and C2D2> only a small extent of H-D exchange was observed for the small fraction of acetylene molecules that reversibly desorb from this surface (11). 

Thermal desorption studies revealed for Li-, Na, and K-borohydrides the formation of alkali hydride as decomposition products above 430 °C. While Mg-, Sc, and Zr-borohydrides decompose through the formation of intermediate phases and/or borides, Zn(BH4)2 decomposes directly to elemental Zn [5]. 

HUg] in C.(1996) New Applications of Aerosol Phoioemission Characterization of Wood Combustion Particles and Time Resolved Thermal Desorption Studies,... 

Davis S, Zaera F, Gordon BE, Somoijai GA (1985) Radiotracer and thermal desorption studies of dehydrogenation and atmospheric hydrogenation of organic fragments obtained from [ C]ethylene chemisorbed over Pt(lll) surfaces. J Catal 92 240... 

The type of soil also plays an important role in determining how readily contaminants will desorb when treated with thermal desorption. Studies conducted on harbor sediment indicate organic contaminants exhibit preferential sorption to coal and coal-derived particles over sand, silt, and clays. Researchers found that while coal/wood derived particles only accounted for 5%i of particles in the test soil, 62% of total PAHs were sorbed to these particles. Successive extractions were conducted and revealed that only 8%i of the PAHs sorbed to the coal/wood-derived... 

Thermal desorption studies have the attraction of comparatively simple experimentation, but face severe problems in the evaluation of unambiguous, unique rate parameters from the measurements. The subject has been reviewed several times recently (see, for example, refs. 57—61), particularly in relation to gas—metal systems, so here we will concentrate on its specific applications to semiconductors, where it has been used almost exclusively to study metal absorbate-isemiconductor surface interactions. Since this topic provides the subject matter for Sect. 5, we will limit the discussion in this section to the basic experimental approach and available methods of data analysis. We will leave to Sect. 5 the critical appraisal of the validity of these methods as applied to solid adsorbates, and the interaction models which have been postulated. 

S.M. Davis, F. Zaera, B.E. Gordon, and G.A. Somoijai. Radiotracer and Thermal Desorption Studies of Dehydrogenation and Atmospheric Hydrogenation of Organic Fragments Obtained from l C]Ethylene Chemisorbed over Pt(l 11) Surfaces. J. Catal. 92 240 (1985). 

Evidence for the formation of these species was obtained from X-ray and thermal desorption studies of the solid phases in the UC -amine systems (I. Kalnins and G. Gibson, 7, Inorg. Nucl. Chem., 1958, 7, 55). ... 

---