Integration of graphene with Si microelectronics is very appealing by offering a potentially broad range of new functionalities. New materials to be integrated with the Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etching and electrochemical delamination methods with respect to residual submonolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection X-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10(13) atoms/cm(2). These metal impurities appear to be partially mobile upon thermal treatment, as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics, these results reveal that further progress in synthesis, handling, and cleaning of graphene is required to advance electronic and optoelectronic applications.

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

The vibrational and electronic properties of amorphous and well-ordered alumina formed on Ni3Al(100) were investigated using high-resolution electron energy loss spectroscopy. The structure of well-ordered alumina was analyzed by low-energy electron diffraction. The amorphous Al2O3 films are prepared by adsorption of O2 at room temperature, while the well-ordered Al2O3 are obtained by direct oxidation of Ni3Al at 1150 K. The band gap energy is ∼3.2 and ∼4.3 eV for amorphous alumina and well-ordered alumina thin films respectively. The lowering of the band gap with respect to the bulk value of Al2O3 is associated with defect-induced states located in the band gap.

Integration of functional oxides on Si substrates could open a pathway to integrate diverse devices on Si-based technology. Oxygen vacancies (Vo(··)) can strongly affect solid state properties of oxides, including the room temperature ferromagnetism (RTFM) in diluted magnetic oxides. Here, we report a systematical study on the RTFM of oxygen vacancy engineered (by Pr(3+) doping) CeO2 epitaxial thin films on Si substrates. High quality, mixed single crystalline Ce1-xPrxO2-δ (x = 0-1) solid solution films were obtained. The Ce ions in CeO2 with a fluorite structure show a Ce(4+)-dominant valence state in all films. The local crystal structures of the films were analyzed in detail. Pr doping creates both Vo(··) and PrO8-complex defects in CeO2 and their relative concentrations vary with the Pr-doping level. The RTFM properties of the films reveal a strong dependence on the relative Vo(··) concentration. The RTFM in the films initially increases with higher Pr-doping levels due to the increase of the F(+) center (Vo(··) with one occupied electron) concentration and completely disappears when x > 0.2, where the magnetic polaron concentration is considered to decline below the percolation threshold, thus long-range FM order can no longer be established. We thus demonstrate the possibility to directly grow RTFM Pr-doped CeO2 films on Si substrates, which can be an interesting candidate for potential magneto-optic or spintronic device applications.