Helena Pardo | University of the Republic (UdelaR). Faculty of Chemistry (original) (raw)
Address: Montevideo, Departamento de Montevideo, Uruguay
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Papers by Helena Pardo
Physical Review B, 2008
We present an ab initio density functional theory study of the magnetic moments that arise in gra... more We present an ab initio density functional theory study of the magnetic moments that arise in graphite by creating single carbon vacancies in a three-dimensional ͑3D͒ graphite network using full potential, all electron, spin polarized electronic structure calculations. In previous reports, the appearance of magnetic moments was explained in a two-dimensional graphene sheet just through the existence of the vacancies itself ͓Carbon-Based Magnetism, edited by F.
The Journal of Physical Chemistry C, 2010
We present an ab initio study on the structural and electronic distortions of modified graphene b... more We present an ab initio study on the structural and electronic distortions of modified graphene by creation of vacancies, inclusion of boron atoms, and the coexistence of both, by means of thermodynamics and band structure calculations. In the case of coexistence of boron atoms and vacancy, the modified graphene presents spin polarization only when B atoms locate far from vacancy. Thus, when a boron atom fills single-and di-vacancies, it suppresses the spin polarization of the charge density. In particular when B atoms fill a di-vacancy a new type of rearrangement occurs, where a stable BC 4 unit is formed 2 inducing important out of plane distortions to graphene. All these findings suggest that new chemical modifications to graphene and new type of vacancies can be used for interesting applications such as sensor and chemical labeling.
Physical Review B, 2005
In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained ... more In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained by a chemical route previously described. This magnetic graphite has been obtained by a vapor reaction consisting of a controlled etching on the graphite structure. By magnetic force microscopy we have verified that its magnetic properties are related to the topographic defects introduced in the pristine material. Also, the magnetic properties have been verified through magnetization measurements as a function of temperature and applied magnetic field. At low temperatures ͑2 K͒ the saturation magnetization reaches a value of 0.58 emu/ g, leading to a defect concentration of 1250 ppm. The system is highly irreversible due to the inhomogeneity of the distribution of defects in the material. Two transition temperatures are detected, T c1 = 115͑5͒ K and T c2 = 315͑5͒ K. These transitions could be associated to the weak coupling between ferromagnetic regions related to defects and to the ferromagnetism inside the defect regions.
European Journal of Organic Chemistry, 2009
New 1, 8-dioxooctahydroxanthenes with substituents in the 2-, 3-, and 9-positions were obtained b... more New 1, 8-dioxooctahydroxanthenes with substituents in the 2-, 3-, and 9-positions were obtained by cyclization with iodine from tandem Michael/Michael adducts. The X-ray molecular structure of the methyl 2-(1, 8-dioxo-2, 3, 4, 5, 6, 7, 8, 9-octahydro-1H-xanthen-9 ...
Physical Review B, 2008
We present an ab initio density functional theory study of the magnetic moments that arise in gra... more We present an ab initio density functional theory study of the magnetic moments that arise in graphite by creating single carbon vacancies in a three-dimensional ͑3D͒ graphite network using full potential, all electron, spin polarized electronic structure calculations. In previous reports, the appearance of magnetic moments was explained in a two-dimensional graphene sheet just through the existence of the vacancies itself ͓Carbon-Based Magnetism, edited by F.
The Journal of Physical Chemistry C, 2010
We present an ab initio study on the structural and electronic distortions of modified graphene b... more We present an ab initio study on the structural and electronic distortions of modified graphene by creation of vacancies, inclusion of boron atoms, and the coexistence of both, by means of thermodynamics and band structure calculations. In the case of coexistence of boron atoms and vacancy, the modified graphene presents spin polarization only when B atoms locate far from vacancy. Thus, when a boron atom fills single-and di-vacancies, it suppresses the spin polarization of the charge density. In particular when B atoms fill a di-vacancy a new type of rearrangement occurs, where a stable BC 4 unit is formed 2 inducing important out of plane distortions to graphene. All these findings suggest that new chemical modifications to graphene and new type of vacancies can be used for interesting applications such as sensor and chemical labeling.
Physical Review B, 2005
In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained ... more In this paper we report on the magnetic properties of pure bulk ferromagnetic graphite, obtained by a chemical route previously described. This magnetic graphite has been obtained by a vapor reaction consisting of a controlled etching on the graphite structure. By magnetic force microscopy we have verified that its magnetic properties are related to the topographic defects introduced in the pristine material. Also, the magnetic properties have been verified through magnetization measurements as a function of temperature and applied magnetic field. At low temperatures ͑2 K͒ the saturation magnetization reaches a value of 0.58 emu/ g, leading to a defect concentration of 1250 ppm. The system is highly irreversible due to the inhomogeneity of the distribution of defects in the material. Two transition temperatures are detected, T c1 = 115͑5͒ K and T c2 = 315͑5͒ K. These transitions could be associated to the weak coupling between ferromagnetic regions related to defects and to the ferromagnetism inside the defect regions.
European Journal of Organic Chemistry, 2009
New 1, 8-dioxooctahydroxanthenes with substituents in the 2-, 3-, and 9-positions were obtained b... more New 1, 8-dioxooctahydroxanthenes with substituents in the 2-, 3-, and 9-positions were obtained by cyclization with iodine from tandem Michael/Michael adducts. The X-ray molecular structure of the methyl 2-(1, 8-dioxo-2, 3, 4, 5, 6, 7, 8, 9-octahydro-1H-xanthen-9 ...