Electron-Stimulated-Desorption Ion Angular Distributions of Negative Ions

Abstract

We report the first measurements of the electron-stimulated-desorption ion-angular-distributions of negative ions from surfaces. The angular distributions of F ~ ions for electron-stimulated desorption of PF3, NF3, and (CF3>2CO on Ru(0001) depend on the molecular geometry and the state of the adsorbed species. The structural information obtained from these negative-ion studies complements that from similar positive-ion studies.

Effects of electron irradiation on structure and bonding of SF6 on Ru(0001)

“…2,b), suggesting that several SF x species with S-F bonds in off normal directions could be contributing to the six F + beams. It is most interesting that these fragments tend to be ordered on the surface (we observe a hexagon instead of a «halo»), in a manner very similar to the results obtained during irradiation-induced decomposition of PF 3 molecules adsorbed on Ru(0001) [27,28]. Based upon theoretical equilibrium structures of SF x (x = 1-6) [29] and simple bonding symmetry considerations similar to those for domains of PF 2 [12], it is possible that the hexagon originates, for example, from 3 domains of SF 4 species, or bridge-bonded SF 2 species, azimuthally rotated by 120°as shown in Fig.…”

“…This suggests that low coverages of SF 6 have a higher dissociation rate than higher coverages. In concluding this part of the discussion, we note that there is previous evidence from ESD studies of PF 3 and (CF 3 ) 2 CO to support the contention that negative ion desorption arises mainly from molecularly-intact adsorbates, while positive ion desorption can be dominated also by dissociative fragments, when they are present [27]. We suggest that the temporary-negative-ion states formed during DEA of molecules such as SF 6 , etc., are more weakly coupled to the surface than similar states associated with more strongly chemisorbed fragments.…”

“…Electron-stimulated mobility of adsorbed species at low temperatures is well known [27,28]. However, the differences between F + and F -ESDIAD patterns during electron irradiation strongly suggest that electron bombardment causes dissociation of the adsorbed molecular SF 6 , rather than ordering of the adsorbed layer, and that F -ions escape from undissociated SF 6 molecules.…”

The influence of preadsorbed K on the adsorption of PF3 on Ru(0001) studied by soft x-ray photoelectron spectroscopy

“…This work is a part of a series of experiments focusing on the adsorption of PF 3 and the coadsorption of PF 3 and K on Ru(0001).4,7, [13][14][15][16] Those results that are relevant to the present study are reviewed here. It has been shown, through thermal desorption spectroscopy (TDS), photoelectron spectroscopy, and electron-stimulated desorption ion angular distributions (ESDIAD), that PF 3 adsorbs molecularly on clean Ru(OOOl) via a Ru-P bond with the P-F bonds pointing away from the surface.…”

Linear and Nonlinear Spectroscopy with the Tunable AC Scanning Tunneling Microscope

“…Adsorbed PF 3 on a number of qt metal surfaces is known from ESDIAD measurements to have a bound (hindered) to free rotor transition as the temperature is increased [30][31][32]. Jn NMR experiments, benzene has been shown to rotate on Ft particles which are predominantly textured Pt4 111) [33,34].…”