Desorption electron stimulated

FIGU RE 4.7. The Antoniewicz model for electron-stimulated desorption (ESD) of neutral particles [39]. 

An interesting extension of the ESD technique was achieved by measuring the angular distribution of desorbing particles 

ESDIAD from PF3 adsorbed on a Ni(l 11) surface at 85K exhibited a sixfold s)rmmetric F pattern, as sketched in Fig. 4.8a [44]. Molecular adsorption at atop sites through the lone pair of P was concluded with PF bonds directed toward the nearest-neighbor Ni atoms in agreement with previous TPD and UPS experiments [45]. Prolonged exposure to the electron beam changed the F+ ESDIAD pattern to that reproduced in Fig. 4.8b that was attributed to transformation into a mixed PF2 + PF overlayer. 

FIGURE 4.8. Electron-Stimulated desorption angular distribution (ESDIAD) data from PF3 adsorbed on a Ni(l 11) surface [44]. (a) Unperturbed PF3 adlayer. (b) After electron induced fragmentation into PF2 and PF species. 

Coupling between different modes was revealed with acetylene adsorbed on Cu(l 00) [51]. Excitation of the C—H stretch 

Samples that can be studied include metals, highly ionic oxides, alkali-metal halide solids and semiconductors among others, usually with an adsorbed layer of gas or other atom/molecule. 

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ESDIAD Electron-stimulated desorption ion angular distribution [150-152] A LEED-like pattern of ejected ions is observed Orientation of adsorbed species... 

The nature of reaction products and also the orientation of adsorbed species can be studied by atomic beam methods such as electron-stimulated desorption (ESD) [49,30], photon-stimulated desoiption (PDS) [51], and ESD ion angular distribution ESDIAD [51-54]. (Note Fig. VIII-13). There are molecular beam scattering experiments such... 

An electron or photon incident on a surface can induce an electroiuc excitation. When the electroiuc excitation decays, an ion or neutral particle can be emitted from the surface as a result of the excitation. Such processes are known as desorption induced by electroiuc transitions (DIET) [82]. The specific teclmiques are known as electron-stimulated desorption (ESD) and photon-stimulated desorption (PSD), depending on the method of excitation. 

Ramsier R D and Yates J T Jr 1991 Electron-stimulated desorption principles and applications Surf. Sc/. Rep. 12 243... 

EID = electron impact desorption ESCA = electron spectroscopy for chemical analysis ESD = electron-stimulated desorption ... 

ESDIAD Electron-stimulated desorption ion angular distribution IPES Inverse photoemission spectroscopy... 

Electron Stimulated Desorption (ESD) and ESD Ion Angular Distribution (ESDIAD)... 

The most common ions observed as a result of electron-stimulated desorption are atomic (e. g., H, 0, E ), but molecular ions such as OH", CO", H20, and 02" can also be found in significant quantities after adsorption of H2O, CO, CO2, etc. Substrate metallic ions have never been observed, which means that ESD is not applicable to surface compositional analysis of solid materials. The most important application of ESD in the angularly resolved form ESDIAD is in determining the structure and mode of adsorption of adsorbed species. This is because the ejection of positive ions in ESD is not isotropic. Instead the ions are desorbed along specific directions only, characterized by the orientation of the molecular bonds that are broken by electron excitation. 

An Auger Electron Spectroscopic and Electron-Stimulated Desorption Study... 

Electron spin resonance (esr), 22 132 for lignin characterization, 15 10 Electron-stimulated desorption-ion angular distribution (ESDIAD), 24 74 Electron transfer (ET), 9 376-381, 388 mechanisms of, 13 444 rate constant for, 13 447 Electron-transfer dynamics, in... 

The observations of complex dynamics associated with electron-stimulated desorption or desorption driven by resonant excitation to repulsive electronic states are not unexpected. Their similarity to the dynamics observed in the visible and near-infrared LID illustrate the need for a closer investigation of the physical relaxation mechanisms of low energy electron/hole pairs in metals. When the time frame for reaction has been compressed to that of the 10 s laser pulse, many thermal processes will not effectively compete with the effects of transient low energy electrons or nonthermal phonons. It is these relaxation channels which might both play an important role in the physical or chemical processes driven by laser irradiation of surfaces, and provide dramatic insight into subtle details of molecule-surface dynamics. 

Figure 2 Schematic overview of an apparatus suitable for measurements of the electron-stimulated desorption of anions from vacuum deposited films. (From Ref. 26.)...

Anion Desorption Measurements. Reactive scattering by DEA fragment ions in condensed media was first noted in the form of OH electron-stimulated desorption (ESD) yields from O2 embedded in multilayer alkane films [246] and subsequently for aniline physisorbed on top of O2 solids [215]. The anion produced following DEA to N2O has also been observed to react with other N2O molecules within an Ar/N20 matrix to generate a desorbed yield of NO and NO2, among other products. Part of the H2 ESD yield observed from multilayer films of H2O, at incident electron energies below 10 eV, has also been attributed to proton abstraction by fragments produced by DEA, viz., -I- H20 H30 ... 

Electron-Stimulated Desorption from Water ice Fiims... 

Anion Electron-Stimulated Desorption from Thin Films of Deoxyribose Analogs... 

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