Laser-induced thermal desorption

J.L. Brand, A.A. Deckert, and S.M. George, Surface diffusion of hydrogen on sulfur-covered Ru(001) surfaces studied using laser-induced thermal desorption, Surf. Sci. 194, 457-474 (1988). 

Laser-Induced Thermal Desorption with Fourier Transform Mass Spectrometric Detection... 

During the last year we have built an FTMS instrument specifically designed for laser-induced thermal desorption from single-crystal surfaces. Figure 5 is a perspective drawing of the Instrument. The chamber is pumped by a 150 1/s ion pump and has a base pressure of 2.0 X 10- torr. Gases are Introduced through sapphire-sealed leak valves from a diffusion pumped gas manifold. 

The term 1 or h indicates low or high coverage of adsorbed ethene, as inferred from ethene exposures.h TPD, temperature-programmed desorption LITD, laser-induced thermal desorption 1 FT-MS, Fourier-transform mass spectrometry SIMS, secondary-ion mass spectrometry MS, mass spectrometry T-NEXAFS, transient near-edge X-ray absorption fine structure spectroscopy RAIRS, reflection-absorption infrared spectroscopy. d Data for perdeut-erio species.1 Estimated value. 

Fig. 15. Adsorbed ethene decomposition data (laser-induced thermal desorption mass 27 against time) and ethylidyne formation data (IR signal against time) for selected coverages and reaction temperatures. [Reprinted from Ref. 386, Surf. Sci. 301, W. Erley, Y. Li, D. P. Lang, and J. C. Hemminger, p. 177. Copyright 1994 with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.]...

Experimentally, information about the adsorption and desorption rates is obtained with the help of programmed desorption. One procedure is flash desorption A surface is instantaneously heated up (normally in vacuum) and we measure the temporal desorption of material, for instance with a mass spectrometer. Heating is usually done with a laser pulse (PLID, pulsed laser induced thermal desorption). 

J. L. Brand and S. M. George, Effects of laser-pulse characteristics and thermal desorption parameters on laser-induced thermal desorption, Surf. Sci. 167, 341-362 (1986). 

In the 1980 s a versatile technique based on laser-induced thermal desorption (LITD) was introduced for the investigation of surface diffusion phenomena [30]. LITD is conceptionally straightforward. A specific homogeneous concentration of adsorbates is established on a surface. 

Laser-induced thermal desorption experiments indicate that the desorption of deuterium from a Si (111) surface has Arrhenius parameters of 1015 2 s-1 and 247 kJ mol-1. Calculate the length of time required to desorb deuterium from a surface initially covered with 0.8 ML to a coverage of 0.2 ML at 720 K. 

As a result, the desorption of hep hollow species is considered to be due to laser-induced thermal desorption. These results are caused by a high laser fluence and the specimen temperature Ts being close to the thermal desorption temperature as compared with the temperature jump in the experiment of Buntin et al. [6]. The laser-induced specimen temperature jump AT is estimated from the laser fluence used to be 110 K at Ts = 117 K, while in the experiment of Fukutani et al. [8], the corresponding figures are a laser fluence <3 mJ/cm2, AT < 20 K and Ts = 80 K. Under these circumstances, desorption of NO is expected to be by the non-thermal process. 

Inoue Y, Kojima 1, Moriki S, Yasumori 1 (1976) Template effects in paUadiiun catalysis. In Proceedings of the sixth international congress on catalysis, vol 1, p 139 Abdelrehim IM, Caldwell TE, Land DP (1996) Coverage effects on the kinetics of benzene formation from acetylene on Pd(lll) A laser-induced thermal desorption Fourier transform mass spectrometry investigation. J Phys Chem 100 10265... 

Abdelrehim IM, Thornburg NA, Sloan JT, CaldweU TE, Land DP (1995) Kinetics and mechanism of benzene formation from acetylene on Pd(lll) studied by laser-induced thermal-desorption Fouiier-transform mass-spectrometry. J Am Chem Soc 117 9509... 

Land, D.P., Tai, T.-L., Lindquist, J.M., Hemminger, J.C. and Mclver, R.T. (1987). Characterization of multilayer thin films by laser-induced thermal desorption mass spectrometry. Anal. Chem. 59, 2924-2927. 

Adsorbed atoms and molecules can also diffuse across terraces from one adsorption site to another [33]. On a perfect terrace, adatom diffusion could be considered as a random walk between adsorption sites, with a diffusivity that depends on the barrier height between neighbouring sites and the surface temperature [29]. The diffusion of adsorbates has been studied with FIM [14], STM [M, 35] and laser-induced thermal desorption [36]. 

George S M, DeSantolo A M and Hall R B 1985 Surface diffusion of hydrogen on Ni(IOO) studied using laser-induced thermal desorption Surf. Scl. 159 L425... 

The technique in question is called laser-induced thermal desorption. This technique is used to study diffusion in systems where a local concentration gradient would be difficult to prepare. The method is straightforward ... 

Finally, as concerns Pt(lll), the reaction of co-adsorbed ethene-d4 and hydrogen has been studied using a combination of laser-induced thermal desorption, mass-spectrometry and RAIRS exchange occurred above 215 K with an activation energy of 46 kJ mol this being below the point at which conversion to... 

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