Raman scattering of MnOx?CeOx composite catalysts: structural aspects and laser‐heating effects

Composite MnO_x CeO_x catalysts (Mn_at: Ce_at = 1) synthesized via the redox and coprecipitation routes were comparatively characterized by micro‐Raman spectroscopy using a laser irradiation power ranging between 0.6 and 4.2 mW. A quasi‐molecular dispersion of the oxide species determines a major and irreversible structural rearrangement of the redox MnO_x CeO_x system because of severe heating effects for laser power in excess of 0.6 mW. The X‐ray diffraction data of samples calcined in the range of 673 1273 K confirm that the micro‐Raman characterization of the composite MnO_x CeO_x systems requires an adequate minimization of the irradiation power to prevent the strong sintering and restructuring phenomena due to laser‐heating effects. Copyright © 2011 John Wiley & Sons, Ltd.     

Angle of incidence effects in a molecular solid

We investigate the influence of the angle of incidence on the sputter yield when bombarding molecular solid, benzene, with C₆₀. Our simulations show that at normal incidence, essentially all of the projectile energy is deposited into the substrate within ∼2.5 nm of the surface. However, at 75° incident angle, only 35% of the projectile energy is deposited within a depth of less than 1.5 nm of the surface while 65% of the projectile energy is reflected. Therefore, important aspects of the collision process which are dependent upon energy deposition, such as sputter yield, ejection depth, and molecule dissociation, may change as the incident angle changes.     

Transverse spin correlations in a random anisotropy system: Amorphous ErCo2

We provide a coherent interpretation of early small angle scattering experiments performed by some of us on amorphous ErCo₂ [9]. At low temperature the zero field transverse spin-spin correlation function is found to fit a simple exponential for large length scales (l >l_c), supporting the lower critical dimensionality d_c=4. For shorter length scales (l<l_c) the correlation function is of the Ornstein-Zernike type. These results are physically understood in terms of the breaking of ferromagnetism into Imry and Ma domains.A further physical interpretation leads us to consider the localization of ferromagnetic spin waves within Imry and Ma domains in zero field, and their delocalization by application of an external field.     

Structure sensitive factors in molecular cluster formation by ion bombardment of single crystal surfaces

The dynamics of molecular cluster formation from a solid bombarded by a 600 eV Ar⁺ ion have been studied classically by computer simulation. The dimers and trimers are found to establish their identity as clusters within interaction range of the solid, but not by a direct ejection of a bound molecule. The Cu₂/Cu and Cu₃/Cu ratios are found to be strongly dependent on crystal orientation. The (111) face is 2–3 times more likely to produce multimers than the (100) face. We find 9 trimers from (111) but none from (110). The relationship between cluster composition and the original arrangement of those atoms on the surface is presented in detail. We find that each multimer forms from atoms that originate within a roughly circular region of area ～70 Ų or less. This region is not necessarily centered on the ion impact point. A consequence of this observation is that dimers can consist of atoms that were several Ångströms apart on the surface but that most trimers contain at least one nearest neighbor pair of atoms. The calculated energy distribution for the dimers matches well with similar experimental studies.     

Aortic elastin fluorescence afterin vivo labeling with Congo red

Congo red (CR) is an azo dye which not only preferentially binds to elastin, an extracellular matrix protein found in the media of arterial vessel walls, but also fluoresces when it binds to this protein. Protein solubilization data following laser irradiation of elastin:CR suspensions determined that the amount of elastin solubilized by laser irradiation increased with the increase in CR. The saturation point of CR to elastin was attained when 400 g CR was added to 20 mg elastin suspension. When 20 ml of a 5% CR solution in 5% dextrose was administered intravenously, the CR was absorbed in levels sufficient to produce fluorescence of the main arteries in rabbits. Layers of tissue both in the media of the vessels and at the endothelial/intimal interface were clearly differentiated. Therefore, the elastin:CR complex appears to be an ideal system in which the elastin fluorescence could aid in distinguishing between normal and diseased tissue in certain pathological conditions, such as atherosclerosis and some types of breast tumors.     

Etude de la structure magnetique et de la transition de typr “spin-flop” de Rb2FeF5

The nature of the magnetic interactions in the chain compound Rb₂FeF₅ has been investigated using neutron diffraction and magnetic measurements under high applied fields. Rb₂FeF₅ orders antiferromagnetically at T_N = 8.0 ± 0.5 K; the magnetic structure is of the A_Z + G_X mode and the moment of the Fe³⁺ ion extrapoled to 0K is 3.5 ± 0.2 μ_B, this low value being due to zero-point spin reduction. Within a chain the Fe³⁺ ions are antiferromagnetically coupled with an exchange constant of J/k = ?8.8 K. A spin-flop behavior has been observed and interpreted on the basis of the molecular field theory. The critical field was found to be H_C = 65 kOe at 1.7 K.     

Exact calculations of p-polarized electromagnetic fields incident on grating surfaces: Surface polariton resonances

Exact calculations of the interaction of p-polarized light from grating surfaces are presented by using the theory of Toigo, Marvin, Celli and Hill. New features for the scattered field are found for light resonating with surface plasmon polaritons; the reflectivity present maxima for large amplitude gratings. The electromagnetic field is calculated on a fine grid near the grating. We find enhancements of the order of 200 to 300 for the square of the field that could partly explain SERS.