Narrow Results

The growth and structure of ultrathin Rh films on Fe(100) are studied by grazing scattering of 50 keV He projectiles, incident along "random" and low index surface lattice directions. Oscillations in the specular intensity for scattered ions indicate initial layer-by-layer growth, followed by multilayer growth on top of the two-monolayer film. Growth temperatures below about 400 K result in a persistent though rough layer growth up to higher coverages. From distinct maxima in the target current as a function of the azimuthal incidence angle, we deduce that growth is epitaxial and pseudomorphic.

The ion-driven mechanism in hydrogen permeation is substantially modified when iron is coated with palladium. A detailed knowledge of the electronic structure at the metal–metal interfaces is a prerequisite for understanding the process of H permeation. We have selected two low-Miller-index surfaces as a simple model for the interface. The system under consideration has 148 metallic atoms forming an Fe–Pd cluster distributed in six metallic layers.

We have investigated the interaction of atomic hydrogen with the Fe(110)–Pd(100) interface using the semiempirical atom superposition and electron delocalization (ASED-MO) method. The changes in the electronic structures, density of states (DOS) and crystal overlap orbital population (COOP) in two different Fe–Pd interfaces were compared with the bulk ground states of both metals.

The interfacial Fe–Pd distance results in about 1.74 Å, whereas for the Fe–Pd first neighbors distance it is about 1.85 Å. An important conclusion is that the metal–metal bonds at the interface are stronger than those bonds in the pure metal bulk. A favorable metal adhesion is observed, as revealed by the energetic stabilization of the composite metal system.

H is stabilized near the FePd interface and stopped at the first Pd layer. A H–metal bond is developed with both Fe and Pd atoms while Fe–Pd bonding at the interface remains unaltered.

The Fe–C–H interaction near defects in iron structures was studied using qualitative structure calculations in the framework of the atom superposition and electron delocalization molecular orbital. Calculations were performed using three Fe clusters to simulate an edge dislocation, a divacancy; both in bcc iron and a stacking fault in an fcc iron structure. In all cases, the most stable location for C atom inside the clusters was determined. Therefore, H atom was approximated to a minimum energy region where the C atom resides. The total energy of the cluster decreases when the C atom is located near the defects zone. In addition, the presence of C in the defects zone makes no favorable H accumulation. The C acts as an expeller of H in a way that reduces the hydrogen Fe–Fe bonds weakening.

We have investigated the adsorption sites and the electronic structure correlated with the magnetic properties of ultrathin Fe films on W(110) system using spin-polarized calculations within the density-functional approach with generalized gradient approximation by the pseudopotential plane-wave code. For one Fe monolayer (ML) on W(110) system the Fe atoms prefer to bind on the bridge adsorption sites of the W(110) surface, with an inward relaxation of $-$12.68%. The top and diagonal bridge sites investigated are energetically less favorable. We have shown that intermixing between Fe and W is unlikely: the surface ordered Fe–W alloy is unstable against the 1-ML Fe on W(110). While the control of oxygen element is known to be an important key to a perfect growth of Fe on W(110), its possible contamination is checked. Performing spin polarized calculations with the optimized geometry, the induced magnetic moments on W subsurface are obtained: the W atoms are always antiferromagnetically coupled to the Fe atoms, one exception being the case of the antiferromagnetic Fe surface where, due to frustration, the induced polarization on the W atoms is zero. The bridge site is the lower adsorption energy one for O₂ molecular bonding perpendicular to the surface. In the case of O₂ bonding parallel and oblique to the surface, it is always dissociated into two O atoms on Fe/W(110) surface through geometry optimization, for all considered sites.

In order to decrease the decomposition temperature of SiC, 12nm Fe thin film is applied on SiC substrates as a catalyst layer using electron beam (e-beam) deposition. To investigate the mechanism of Fe-treated SiC decomposition, local Fe regions are formed through dewetting of the catalyst layer by hydrogen annealing. The results show that Fe decreases the decomposition temperature of SiC effectively and increases the kinetics of the graphitization. Studies showed that depending on the amount of Fe, crumpled and ordered graphene films can be synthesized simultaneously on SiC by using this method.