Papers by Georgeta Salvan
The Journal of Physical Chemistry B, 2009
Ni nanoparticles with a size distribution from 2 to 6 nm, embedded in various organic matrices, w... more Ni nanoparticles with a size distribution from 2 to 6 nm, embedded in various organic matrices, were fabricated in ultrahigh vacuum. For this purpose metal free and Ni phthalocyanine, fullerene C(60), and pentacene were coevaporated with Ni. When coevaporated, Ni and H(2)Pc react, leading to the formation of NiPc and Ni nanoparticles. The molecular structure of the matrix was found to have negligible effect on the size of the nanoparticles but to influence the magnetic anisotropy of the nanoparticles: Ni nanoparticles formed in the buckyball matrix have a cubic symmetry, while nanoparticles formed in matrices consisting of planar molecules exhibit a uniaxial symmetry. After exposure to atmosphere, photoelectron spectroscopy investigations demonstrate the presence of metallic Ni nanoparticles accompanied by Ni oxide and the existence of a charge transfer from the organic matrix to the particles in all investigated systems. The oxidized Ni nanoparticles exhibit a larger magnetic anisotropy compared to the freshly prepared particles which show superparamagnetic properties above 17 K. Moreover, photoelectron spectroscopy was used to probe the oxidation process of the Ni nanoparticles in different organic matrices. It could thus be shown that a matrix consisting of spherical molecules like C(60) prevent the particles much better from oxidation compared to matrices of flat molecules.
Raman spectroscopy was used to characterize the structural order in thin organic films of 3, 4, 9... more Raman spectroscopy was used to characterize the structural order in thin organic films of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA). Films of the same average thickness were grown by organic molecular beam deposition on hydrogen-passivated p-type silicon ...
In this work the interface formation between cytosine and hydrogen-passivated Si(1 1 1) substrate... more In this work the interface formation between cytosine and hydrogen-passivated Si(1 1 1) substrates, the growth of cytosine layers as well as the interface between a metal (In or Ag) and the cytosine layers are studied. Cytosine was thermally evaporated by organic molecular beam deposition (OMBD) onto H-passivated Si(1 1 1) substrates under ultra-high vacuum conditions. Metal deposition on monolayers ($0.4 nm) of cytosine leads to an enhancement of the Raman signal via the surface-enhanced Raman scattering (SERS) effect. The interaction with metals is found to be very different due to the large difference in the ionisation potential of Ag and In (IP Ag ¼ 7.58 eV, IP In ¼ 5.78 eV). The signal enhancement arises mainly from contributions due to molecule-metal charge transfer. Density functional theory calculations were employed for modelling the interaction of metal atoms with cytosine. Computational approaches were carried out on silver-cytosine and indium-cytosine complexes using the B3LYP density functional with the LANL2DZ basis set. #
Scientific reports, 2015
Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials whe... more Ferromagnetism can occur in wide-band gap semiconductors as well as in carbon-based materials when specific defects are introduced. It is thus desirable to establish a direct relation between the defects and the resulting ferromagnetism. Here, we contribute to revealing the origin of defect-induced ferromagnetism using SiC as a prototypical example. We show that the long-range ferromagnetic coupling can be attributed to the p electrons of the nearest-neighbor carbon atoms around the VSiVC divacancies. Thus, the ferromagnetism is traced down to its microscopic electronic origin.
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Papers by Georgeta Salvan