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ELECTRONIC STRUCTURE AND MAGNETISM OF DILUTED MAGNETIC SEMICONDUCTORS AND OXIDES

 

This research project is focused on the Mn-Ge system, a diluted magnetic semiconductor which has shown promising magnetic properties for applications in the field of spin-electronics [1]. In spite of its properties, the early stages of growth of the epitaxial layers are largely unexplored and a combination of growth temperature, layer thickness and post growth treatments can provide a rich scenario determined by the interplay of magnetism and electronic properties [2,3].

Aim of the project is to draw the phase diagram of this system by combining state-of-the-art electron spectroscopies, including band mapping with angle-resolved photoemission spectroscopy and magnetic circular dichroism with X-rays.

The experimental activity will be carried out both in the Surface Science and spectroscopy Lab of the Catholic University and at the ELETTRA synchrotron radiation facility.

 

In the last few years, we have also started a research activity on the electronic properties of diluted magnetic oxides [4],  mainly based on the TiO2-rutile host system. This activity involves the growth by r.f.sputtering of thin films doped with transition metals, N and C, and the experimental study of their electronic and magnetic properties [5-8].  Ab-initio calculations of the electronic structure of doped-TiO2, accounting for the effects of dopants, defects, and oxygen vacancies is  becoming a standard tool in our activity, and represents one of expanding fields of our investigations.

 

[1] F.X. Xiu, et al. NATURE MATERIALS 9, 337 (2010)

[2] L. Sangaletti, et al. , PHYSICAL REVIEW B 75, 153311 (2007)

[3] A. Verdini, PHYSICAL REVIEW B 77, 075405 (2008)

[4] M. Venkatesan et al. Nature 430, 630 (2004)

[5] L. Sangaletti, et al. J. Phys. Cond. Matter 18, 7643 (2006)

[6] L. Sangaletti, et al., PHYSICAL REVIEW B 78, 075210 (2008)

[7] L. Sangaletti et al. PHYSICAL REVIEW B 80, 033201 (2009)

[8] G. Drera, et al. APPLIED PHYSICS LETTERS 97, 012506 (2010)

 

GROWTH, ELECTRONIC STRUCTURE, AND FUNCTIONAL PROPERTIES OF EUMELANIN THIN FILMS AND RELATED INTERFACES

 

Eumelanin has recently attracted the attention of research groups involved in the study of functional organic materials, with the goal to identify proper bio-organic materials for applications in the optic, electronic and catalysis fields [1]. For example, its strong absorbance and semiconducting characteristics render melanin a possible candidate for application in dye sensitised (organic)

solar cells. Despite extensive experimental and theoretical studies conducted on both natural and synthetic melanins, the structure, composition and aggregation behaviour of this class of pigments remain unknown. This is part due to the fact that melanins are difficult molecules to study, because they strongly polymerize in disordered aggregates and are virtually insoluble in the most

common solvents.

Only recently, by using soft X-ray spectroscopies for the analysis of eumelanin aggregates, we have been able to measure for the first time the density of states of both occupied and unoccupied electronic levels and we have shown to which extent the calculated electronic structure of single monomers catches the main features of solid state aggregates [2]. The research activity is being carried out in collaboration with Andrea Goldoni (Elettra, Trieste) and with the ALOISA beamline staff at ELETTRA (IOM-CNR, Trieste), as well as with the support of theoretical calculations of Ralph Gebauer and collaborators at ICTP.

On the basis of these studies, a research project has started with the aim to study effects of doping on the electronic properties of eumelanin thin films grown on several substrates, including 3d transition metal oxides and semiconductors [3,4].

The project has a prevalent experimental character, based on photo-electron spectroscopies with conventional and synchrotron radiation sources. An important part of the activity is also devoted to the optimization of thin film deposition, which includes electropolimerization

and spin coating techniques.

 

[1] J.P. Bothma et al. ADVANCED MATERIALS 20, 3539 (2008)

[2] L. Sangaletti et al. J. Phys. Chem. B, 111 (2007)

[3] L. Sangaletti, et al., PHYSICAL REVIEW B, 80 174203 (2009)

[4] P. Borghetti, et al. LANGMUIR, 26, 19007 (2010)

 
 

 

 

 

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