Electrostatic fields above individual atoms

Catalytic reactions on platinum nanofacets: bridging the size and complexity gap

“…The field effect on the binding strength of adsorbed species results from the additional charge transfer caused by a field-induced redistribution of the electronic charge at the surface: the ''positive'' field applied in FIM reduces the electronic density outside the geometric surface plane as compared to the fieldfree case [43]. The changes in the binding energies of the molecular adsorption states of O 2 and CO on Pt, shift the adsorption/desorption equilibria of the molecular O 2 species and of CO.…”

“…The hydrogen oxidation on Pt was visualised by FIM and FEM for first time in the former group of Block in Berlin [22,52,58,59] later the FIAES was also applied [60,61]. The imaging process in FIM is governed mainly by the ionisation potential I of the impinging molecule (field ionisation) or by the appearance energy A if the molecule is adsorbed (field desorption), the lower these values the higher (exponentially) the field ion rate is [62]. In this context it seems, by comparing the educts (I O2 = 12.1 eV, I H2 = 15.4 eV) and the product (I H2O = 12.6 eV) that the oxygen field ionisation rate should prevail.…”

Field Ion and Field Desorption Microscopy: Surface Chemistry Applications

“…The main strength of the FIAES is the ability to obtain locally the binding energy of adsorbed (or field-adsorbed) atoms or molecules on chosen surface sites by the direct measuring of appearance energy of corresponding field ions. 84 This has allowed, for example, measurements of the local electric fields above the individual surface atoms from the binding energies of the field-adsorbed noble gas atoms 13,14 and of the binding energies of CO and O 2 molecules on various metal surfaces. [22][23][24][25] The probe-hole analysis of field ions allows also the chemical identification of single surface atoms by the atom probe field ion microscope (APFIM), developed by Mü ller et al 3,85 Since that time, this technique, commonly called AP, has evolved to a 3-D atom probe tomography (APT), which allows 3-D reconstructions of the sample on an atomic scale and is not dependent on the probehole analysis anymore.…”

“…A version of this technique, pulsed field desorption mass spectrometry, which combines a FIM with the time- of-flight analysis of surface species, field-desorbed as ions, offers a unique method to study the reaction intermediates or products, which can be sampled far below the temperatures that would normally be required for their unassisted thermal desorption. 82,83 Progress in methods for measurements of energy distributions of field ions has led to the development of the field ion appearance energy spectroscopy (FIAES [13][14][15] ). The main strength of the FIAES is the ability to obtain locally the binding energy of adsorbed (or field-adsorbed) atoms or molecules on chosen surface sites by the direct measuring of appearance energy of corresponding field ions.…”

Hydrogen Oxidation on Stepped Rh Surfaces: µm-Scale versus Nanoscale

“…In fact, a principal difference originates from the field direction: in FIM the tip is positively charged, so that the spatial electron density distribution near the tip surface might be field-modified: the field-free spatial electron density distribution is shifted towards the bulk, depleting the near-surface region [39,40]. Such a field-modified electron density influences, of course, the interaction of adsorbed molecules with the catalyst surface, as was demonstrated hysteresis loop and the phase diagram in Fig.…”