Ultrathin Ce 2 O 3 layers have been grown on Si(111) by reactive metal deposition in an oxygen background and characterized by x-ray standing waves, x-ray diffraction, x-ray photoelectron spectroscopy, and low-energy electron diffraction to elucidate and quantify both atomic structure and chemical composition. It is demonstrated that highly ordered, mostly B-oriented, epitaxial ceria films can be achieved by preadsorption of a monolayer of atomic chlorine, effectively passivating the substrate and thereby suppressing cerium silicate and silicon oxide formation at the interface.

A grand challenge in designing polymeric materials is to tune their properties by macromolecular engineering. In this context, one of the drawbacks that often limits broader applications under high temperature conditions is their poor thermal conductivity κ. Using molecular dynamics simulations, we establish a structure-property relationship in hydrogen bonded polymer blends for possible improvement of κ. For this purpose, we investigate two experimentally relevant hydrogen bonded systems− one system consists of short poly(N-acryloyl piperidine) (PAP) blended with longer chains of poly(acrylic acid) (PAA) and the second system is a mixture of PAA and short poly(acrylamide) (PAM) chains. Simulation results show that PAA-PAP blends are at the onset of phase separation over the full range of PAP monomer mole fraction φPAP, which intensifies even more for φPAP > 0.3. While PAA and PAP interact with preferential hydrogen bonding, phase separation is triggered by the dominant van der Waals attraction between the hydrophobic side groups of PAP. However, if PAP is replaced with PAM, which has a similar chemical structure as PAP without the hydrophobic side group, PAA-PAM blends show much improved solubility. Better solubility is due to the preferential hydrogen bonding between PAA and PAM. As a result, PAM oligomers act as cross-linking bridges between PAA chains resulting in a three dimensional highly cross-linked network. While κ for PAA-PAP blends remain almost invariant with φPAP, PAA-PAM systems show improved κ with increasing PAM concentration and also with respect to PAA-PAP blends. Consistent with the theoretical prediction for the thermal transport of amorphous polymers, we show that κ is proportional to the materials stiffness, i.e., the bulk modulus K and sound velocity v of PAA-PAM blends. However, no functional dependence between κ and K (or v) is observed for the immiscible PAA-PAP blends.

Iron oxide monolayers are grown on Ag(0 0 1) via reactive molecular beam epitaxy (metal deposition in oxygen atmosphere). The monolayer shows FeO stoichiometry as concluded from x-ray photoemission spectra. Both low energy electron diffraction as well as scanning tunneling microscopy demonstrate that the FeO layer has a quasi-hexagonal (1 1 1) structure although deposited on a surface with square symmetry. Compared to bulk values, the FeO(1 1 1) monolayer is unidirectionally expanded by 3.4% in [Formula: see text] directions while bulk values are maintained in [Formula: see text] directions. In [Formula: see text] directions, this lattice mismatch between FeO(1 1 1) monolayer and Ag(0 0 1) causes a commensurate undulation of the FeO monolayer where 18 atomic rows of the FeO(1 1 1) monolayer match 17 atomic rows of the Ag(0 0 1) substrate. In [Formula: see text] directions, however, the FeO(1 1 1) monolayer has an incommensurate structure.

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A well-ordered Fe film epitaxially grown on Ag(001) has been applied to different post deposition treatments of oxidation and post oxidation annealing. The structure of the film and its surface has been investigated by x-ray diffraction and low energy electron diffraction, while x-ray photoelectron spectroscopy is used to determine the film stoichiometry. A first oxidation step at moderate temperature leads to a badly ordered Fe2O3 film. The structure of the film is improved by additional annealing at increased temperature. Finally, a well-ordered Fe3O4 film is obtained with well developed magnetic properties as proved by vector magneto optical Kerr effect experiments.