High-resolution Energy Loss Spectra Research Articles

An electron energy loss spectrometer designed for studies of electronic energy losses and spin waves in the large momentum regime

Based on 143° electrostatic deflectors we have realized a new spectrometer for electron energy loss spectroscopy which is particularly suitable for studies on surface spin waves and other low energy electronic energy losses. Contrary to previous designs high resolution is maintained even for diffuse inelastic scattering due to a specific management of the angular aberrations in combination with an angle aperture. The performance of the instrument is demonstrated with high resolution energy loss spectra of surface spin waves on a cobalt film deposited on the Cu(100) surface.

An angle-resolved mass-spectrometric study of non-dissociating excited states of CS +2 formed in 5 keV collisions of CS +2 with rare-gas targets

High-resolution energy-loss spectra were obtained for 5 keV CS + 2 ions scattered through selected angles within the range 0–0.52° following collisions with rare-gas target atoms. Excitation to CS + 2 ( A ) and CS + 2 ( B ) electronic states was clearly observed for all of the five targets used and relative differential cross-sections constructed for each process. From these, integrated cross-sections and most-probable centre-of-mass frame scatter angles, Θ c, were determined. The former increase across the series He to Xe whilst the latter decrease, both trends suggesting that collisions occur with increasingly larger values of impact parameter across this series. The most-probable scatter angles, θ c, in the laboratory frame were largest for a neon target and least for helium and also increase with increasing endothermicity of reaction. If such values (typically 0.1–0.3°) represent lower limits for the θ c values associated with excitation to dissociating states of CS + 2, then collisional scattering will not be negligible in relation to fragmentation scattering in CID experiments involving this molecular ion.

On the formation of CH2+ions

The results of high resolution energy loss spectra of CH2+ product ions formed in 3 keV single charge stripping collisions of CH+ ions with Kr are compared with recent ab initio calculations of potential energy functions of 2 Pi and 2 Sigma states of the doubly charged molecular ion.

Vibrational populations of N2(B3Πg) and CO(a3Π) produced by He+impact on N2(X) and CO(X) in the 200-1000 eV energy range

High-resolution energy loss spectra (ELS) for the production of N2(B3 Pi g) and CO(a3 Pi ) in collisions of He+ on N2(X1 Sigma g+) and CO(X1 Sigma +) have been obtained in the 200 eV 500 eV, the authors invoke in the case of CO long-range charge dipole interactions that perturb the entrance channel prior to (and/or the exit channel after) the electronic transition. For E<500 eV the deviations from FC distributions in both the N2 and CO cases are tentatively attributed to perturbations caused by near-resonant charge exchange channels.

Relationship between vibrational states of O-Ni systems and their superficial structure on (100) face of nickel single crystal

High resolution energy loss spectra of 4 eV electrons reflected in the specular direction from Ni(100) surface clean or covered by the ordered structures obtained in the different stages of the metal oxidation, are analysed with reference to LEED patterns. At room temperature, the successive p(2 × 2) and c(2 × 2) structures associated with the chemisorption of oxygen have been observed without modification of the energy loss spectra, in respect of the clean nickel surface. Surface phonons are known to occur in the case of the c(2 × 2)S ordered layer and their absence in the case of Ni-O corresponding system is discussed. After short exposures to oxygen between 200 to 500° C, the surface exhibits a so called “intermediate oxide”. It is identified by its hexagonal unit mesh (∼5 Å) with two equivalent orientations along the [100] and [110] directions of the substrate and its vibrational spectra characterized by a loss peak at − 112.5 meV (± 2.5 meV). Subsequent exposures to oxygen lead to the formation of the (100) face of NiO (in epitaxy on the Ni(100) face) accurately identified by its LEED pattern. The obtained typical multiple loss spectra with spacing 67.5 meV (± 15 meV) reveal a scattering of low energy electrons by long wavelength optical phonons associated to the oxide. The characteristic energy loss (67.5 meV) is in relative good agreement with the energy of the Fuchs-Kliewer surface phonon calculated from the optical constants of the nickel oxide.

Phononenspektroskopie von Ammoniumchlorid und Ammoniumbromid mit keV-Elektronen

The high resolution energy loss spectrum of NH4Cl in the spectral region of internal lattice vibration has been reinvestigated. In order to assure the assignement made, the spectra of the deuterated ammonium halides ND4Cl and ND4Br has been studied too. The structure of the films, which were investigated, was checked by electron-diffraction and by electron microscopy. The deuterated films show the shift of energy losses towards lower energy losses as expected. Unshifted losses are assigned to partially deuterated material. Two types of spectra are observed for NH4Cl depending on the size of the crystals and presumably on the perfectnes of the lattice. Unlike the external vibrations, which are strongly influenced by surface effects, at least for the strongest bands good agreement is found with the absorption measurement concerning the positions of the peaks.