Induced magnetism in transition metal intercalated graphitic systems

We investigate the structure, chemical bonding, electronic properties, and magnetic behavior of a three-dimensional graphitic network in aba and aaa stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu). Using density functional theory, we find induced spin-polarization of the C atoms both when the graphene sheets are aba stacked (forming graphite) and aaa stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe, and Co turns out to vary from 1.38 {\mu}B to 4.10 {\mu}B, whereas intercalation of Ni and Cu does not lead to a magnetic state. The selective induction of spin-polarization can be utilized in spintronic and nanoelectronic applications.Comment: 13 pages, 3 figures, 1 tabl

Cu2Se and Cu Nanocrystals as Local Sources of Copper in Thermally Activated in Situ Cation Exchange

Among the different synthesis approaches to colloidal nanocrystals, a recently developed toolkit is represented by cation exchange reactions, where the use of template nanocrystals gives access to materials that would be hardly attainable via direct synthesis. Besides, postsynthetic treatments, such as thermally activated solid-state reactions, represent a further flourishing route to promote finely controlled cation exchange. Here, we report that, upon in situ heating in a transmission electron microscope, Cu2Se or Cu nanocrystals deposited on an amorphous solid substrate undergo partial loss of Cu atoms, which are then engaged in local cation exchange reactions with Cu “acceptor” phases represented by rod- and wire-shaped CdSe nanocrystals. This thermal treatment slowly transforms the initial CdSe nanocrystals into Cu2−xSe nanocrystals, through the complete sublimation of Cd and the partial sublimation of Se atoms. Both Cu “donor” and “acceptor” particles were not always in direct contact with each other; hence, the gradual transfer of Cu species from Cu2Se or metallic Cu to CdSe nanocrystals was mediated by the substrate and depended on the distance between the donor and acceptor nanostructures. Differently from what happens in the comparably faster cation exchange reactions performed in liquid solution, this study shows that slow cation exchange reactions can be performed at the solid state and helps to shed light on the intermediate steps involved in such reactions

Suplementacija s antioksidansima i serumski lipidi kod bolesnika s Graves-ovom bolesti: Učinak na LDL-kolesterol

The effect of supplementation with a fixed combination of antioxidants (beta-carotene, selenium, vitamins C and E) on serum lipids was monitored in patients with newly detected Graves\u27 disease. Measurements were made prior to the commencement of therapy and after 30 and 60 days. Patients were randomized into two groups. Test group comprised patients who received antioxidant supplementation in addition to methimazole, while patients treated with methimazole only were in the control group. The concentration of total and HDL-cholesterol increased significantly in test and control groups (p < 0.05) but these groups did not differ significantly. Concentration of LDL-cholesterol increased significantly in the test group only (p < 0.005) and was significantly different from the control group 60 days after the commencing the therapy (p < 0.005). Significant increase in the LDL-cholesterol concentration in the test group requires further investigations.U ovom istraživanju promatran je učinak suplementacije fiksnom kombinacijom antioksidansa (beta-karoten, selen, vitamin C i E) na koncentracije serumskih lipida, u odnosu na brzinu postizanja eutiroze. Mjerenja su obavljena u bolesnika s novo otkrivenom Graves-ovom bolešću liječenih metimazolom (tiamazolom) prije početka terapije, te nakon 30 i 60 dana. Bolesnici su bili randomizirani u dvije skupine. Test skupinu sačinjavali su bolesnici koji su dodatno uzimali antioksidanse, a kontrolnu skupinu bolesnici koji su uzimali samo metimazol (tiamazol). Koncentracije ukupnog i HDL-kolesterola u serumu rasle su tijekom terapije kod bolesnika iz obje skupine (p < 0,05) no, nisu se međusobno značajno razlikovale 60 dana nakon početka terapije. Kod bolesnika test skupine, koncentracija LDL-kolesterola se značajno povećala (p < 0,005) i bila je značajno različita od one u kontrolnoj skupini (p < 0,005), 60 dana nakon početka liječenja. Rezultati ovog istraživanja ukazuju da suplementacija s ovom kombinacijom antioksidansa nema značajnog utjecaja na promjene koncentracije serumskih lipida kod bolesnika s Graves-ovom bolešću 60 dana nakon početka terapije, s izuzetkom LDL-kolesterola. Zbog značajnog porasta koncentracije LDL-kolesterola kod bolesnika s Graves-ovom bolešću, koji su dodatno uzimali antioksidanse, potrebna su daljnja istraživanja u cilju pojašnjenja opisanih promjena

Role of the electronegativity for the interface properties of non-polar heterostructures

Density functional theory is used to investigate the interfaces in the non-polar ATiO3/SrTiO3 (A=Pb, Ca, Ba) heterostructures. All TiO2-terminated interfaces show an insulating behavior. By reduction of the O content in the AO, SrO, and TiO2 layers, metallic interface states develop, due to the occupation of the Ti 3d orbitals. For PbTiO3/SrTiO3, the Pb 6p states cross the Fermi energy. O vacancy formation energies depend strictly on the electronegativity and the effective volume of the A ion, while the main characteristics of the interface electronic states are maintained

Ge-intercalated graphene: The origin of the p-type to n-type transition

Recently huge interest has been focussed on Ge-intercalated graphene. In order to address the effect of Ge on the electronic structure, we study Ge-intercalated free-standing C6 and C8 bilayer graphene, bulk C6Ge and C8Ge, as well as Ge-intercalated graphene on a SiC(0001) substrate, by density functional theory. In the presence of SiC(0001), there are three ways to obtain n-type graphene: i) intercalation between C layers; ii) intercalation at the interface to the substrate in combination with Ge deposition on the surface; and iii) cluster intercalation. All other configurations under study result in p-type states irrespective of the Ge coverage. We explain the origin of the different doping states and establish the conditions under which a transition occurs

K-intercalated carbon systems: Effects of dimensionality and substrate

Density functional theory is employed to investigate the electronic properties of K-intercalated carbon systems. Young's modulus indicates that the intercalation increases the intrinsic stiffness. For K-intercalated bilayer graphene on SiC(0001) the Dirac cone is maintained, whereas a trilayer configuration exhibits a small splitting at the Dirac point. Interestingly, in contrast to many other intercalated carbon systems, the presence of the SiC(0001) substrate does not suppress but rather enhances the charge carrier density. Reasonably high values are found for all systems, the highest carrier density for the bilayer. The band structure and electron-phonon coupling of free-standing K-intercalated bilayer graphene points to a high probability for superconductivity in this system