Volume 118, Issue 23, 15 June 2003
Index of content:
Polarized total-reflection x-ray absorption fine structure for self-assembled monolayer of zinc porphyrin at air–water interface118(2003); http://dx.doi.org/10.1063/1.1580095View Description Hide Description
A new x-rayabsorption fine structure (XAFS) method is applied to the air–solution interface. Under the total reflection condition, the XAFS method becomes surface sensitive, enabling the self-assembledmonolayer of a metal complex at the solution surface to analyze in situ. Furthermore the introduction of two types of linearly polarized x rays allows us to determine the selective orientation of a planar metal complex at the surface. We obtain spectra for a square planar complex, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato zinc(II) (ZnTPPC) adsorbed on the aqueous solution surface forming a monolayer with two polarized x rays and compared them with spectra of the same compound in a bulk solution and in solid powder. The polarized XAFS spectra exhibit different features leading to the unambiguous conclusion that the plane of the ZnTPPC molecule is oriented parallel to the air–water interface and that there is no coordination to the axial sites of the zinc atom.
118(2003); http://dx.doi.org/10.1063/1.1580800View Description Hide Description
Unique occurrence of magnetism is shown, in which magnetism appears ex nihilo, when organic molecules are self-assembled as monolayers on gold substrate. The molecules as well as the substrate, when they stand alone, are diamagnetic. Using a superconducting quantum interference device type magnetometer we obtained direct evidence that close-packed organized thio-organic films adsorbed on gold substrates possess magnetic properties at room temperature. The films studied show very high specific magnetization, up to many tens Bohr magnetons per adsorbed molecule, with a very small hysteresis. It is highly anisotropic and shows almost no temperature dependence. The magnetism observed is related to charge transfer between the organic layer and the metal substrate. Yet, the uniqueness here is that many spins are polarized per adsorbed molecules. The magnetic effect is related to the two dimensional organization of the organic molecules on the metal substrate which might explain the high anisotropy.