Nowadays, ultrathin films play a fundamental role in modern material science and technology. Recently, several theoretical and experimental works [1-3] have been indicated that the magnetic properties of Pd ultrathin films could be controlled by structural parameters of the film, and much work has been done to study induced magnetic properties of ultrathin Pd films grown on different substrates. For the epitaxy of Pd monolayers on Ru(0001)[4] and on C(0001)[5], it was not clear if Pd grows in an hcp or fcc structure and a detailed surface structure determination was not available for these systems. In this study, Pd films with thicknesses ranging from sub-monolayer up to approximately 15 ML were grown on a Ru(0001) single crystal substrate and on a high oriented graphite under UHV conditions, and the electronic structure, surface crystallography an magnetism were investigated by multiple (experimental and theoretical) techniques: x-ray photoelectron spectroscopy and diffraction (XPS and XPD) using conventional MgKα and synchrotron radiation sources, low- and high-energy electron diffraction (LEED and RHEED),Squid and magneto-optical Kerr effect measurements, and density-functional theory (DFT) calculations. The electronic structure, surface crystallography and magnetism of the Pd films are discussed in details.
References:
[1]T. Shinohara, T. Sato, and T. Taniyama, Phys. Rev. Lett. 91, 197201 (2003).
[2]E. Häuger and K. Osuch, Phys. Rev. B 72, 085432 (2005).
[3]J. Walter, Advanced Materials 12, 31 (2000).
[4]E. de Biasi,A. de Siervo, F. Garcia, F. Vicentin, R. Landers, M. Knobel, "Pd ultrathin film growth on C(0001):Does it show magnetic behavior?", J. Elect. Spect. and Rel. Phen. (in press 2007).
[5]A. de Siervo, E. de Biasi, F. Garcia, R. Landers, M.D. Martins, W.A. Macedo, " The magnetic properties, surface and electronic structure of Pd ultrathin films on Ru(0001)" (Submitted to Phy. Rev. B 2007).
Acknowledgments:
The authors are pleased to thank LNLS staff for their technical support, especially P.T. Fonseca for his help during the measurements in the SGM beamline. We are in debit with M. L. Viana and E. A. Soares (UFMG) that permit the use of their GA algorithm. This work received financial support from FAPESP and CNPq. |