Papers by Emilye Rosas Landa
We created 4 p-Si models and 4 p-Si:H models all with 50% porosity. The models contain 32, 108, 2... more We created 4 p-Si models and 4 p-Si:H models all with 50% porosity. The models contain 32, 108, 256 and 500 silicon atoms with a pore parallel to one of the simulational cell axes and a regular cross-section. We obtained the densities of states of our models by means of ab initio computational methods. We wrote a code to simulate the emission spectra of our structures considering particular excitations an decay conditions. After comparing the simulated spectra with the experimental results, we observe that the position of the maximum of the emission spectra might be related with the size of the silicon backbone for the p-Si models as the quantum confinement models say and with the hydrogen concentration for the p-Si:H structures. We conclude that the quantum confinement model can be used to explain the emission of the p-Si structures but, in the case of the p-Si:H models it is necessary to consider others theories.
Journal of Nanostructure in Chemistry, 2013
The morphology of porous silicon (p-Si) depends on several parameters such as the doping type and... more The morphology of porous silicon (p-Si) depends on several parameters such as the doping type and the carriers’ concentration of the crystalline silicon substrate. The electrolytes used in the p-Si fabrication also have an important role. The final structure determines if p-Si is luminescent or suitable for photonic applications. Experimental results on p-Si produced by electrochemical etching show that although the carriers are greatly reduced by the etching process, boron atoms remain in the bulk. The study of p-type porous silicon nanostructures by means of an ab initio computational simulation might help to understand how boron atoms influence the p-Si final structure. Here, we report electronic and topological properties of ten p-type porous silicon structures as an extension of our previous paper on p-type crystalline silicon. Our results suggest that the boron atoms can not remain bonded on the porous surface but do so in the bulk. The presence of impurities changes the bond ...
Journal of Non-Crystalline Solids, 2008
We report ab initio molecular dynamic simulations of several supercells of crystalline porous sil... more We report ab initio molecular dynamic simulations of several supercells of crystalline porous silicon, that are first relaxed and then analyzed by their radial distribution functions (RDF). The porosities vary from 10% to 80% of the total volume of the supercell. The interatomic distance is determined by the position of the first peak of the RDF. We manipulated a maximum of 500 atoms of silicon and a minimum of 32. The interatomic distance of the model with a porosity of 10% was 2.35 Å , for those models with porosity from 11% to 50% was 2.45 Å and finally, 2.55 Å for those with a porosity greater than 50%. If the supercell backbone structure is small compared with the void of the supercell, then the interatomic distance between the silicon atoms run out of the crystalline value. Our results agree with experiment.
Journal of Non-Crystalline Solids, 2006
Porous carbon is considered a promising material to store hydrogen. It can be visualized as a def... more Porous carbon is considered a promising material to store hydrogen. It can be visualized as a defective relaxed sample and therefore some of the methods we have developed to deal with porous silicon are presently applied to this material. Porous atomic structures with 50% porosity that, due to the size of the supercells fall within the regime of nanoporous carbon, are generated using our procedure. Two pure nanoporous samples of densities 1.75 g/cm 3 and 1.31 g/cm 3 were hydrogenated, relaxed and their total energy obtained. The hydrogenated samples were first stripped of the hydrogen atoms and their total energy obtained. Then the original samples were stripped of the carbon atoms and the total energy calculated. From these values the average energy per hydrogen atom was then deduced. We compare our results to CH bond energies; conclusions are drawn.
Journal of Non-Crystalline Solids, 2004
Porous silicon has been studied extensively due to the interesting luminous properties that it di... more Porous silicon has been studied extensively due to the interesting luminous properties that it displays. However, amorphous porous silicon, ap-Si, is an elusive material difficult to produce and study. Since ap-Si can be visualized as highly defective a-Si we have applied our new thermal process, based on an ab initio molecular dynamics method that uses the Harris functional, to generate samples of ap-Si with 50% porosity starting with a cubic periodic supercell of 216 atoms, from which a porous cell was carved out. The randomizing process was done using a 7.5 fs time step and after the various structures were obtained, their optical gaps were determined. We find that the gaps increase monotonically with the randomness of the structure from 0.004 to 0.580 eV.
Silicon nanoparticles are widely used in the medical area and until now they have not manifested ... more Silicon nanoparticles are widely used in the medical area and until now they have not manifested toxicological effects in humans beings. In order to understand the physical properties that determine their low-toxicity, we perform ab initio computational simulations of silicon nanoclusters, pure, p-doped and hollow structured. The topological and electronic properties obtained pointed out to the number of dangling bonds and electronic density as fundamental parameters to locate active sites and directly related to toxicity, besides the size and surface chemistry of the silicon nanoparticle.
Solid State Communications, 2012
Porous silicon ðpÀSiÞ morphology depends on several parameters of the crystalline silicon substra... more Porous silicon ðpÀSiÞ morphology depends on several parameters of the crystalline silicon substrate such as doping type and carriers concentration. Experimental results on ðpÀSiÞ show that although in the porous samples carriers are greatly reduced, boron atoms remain in the bulk. The study of p-type silicon crystals substrates by means of ab initio computational simulations will help to understand how boron atoms behave during the electrochemical reaction of porous silicon ðpÀSiÞ fabrication. Here we studied the properties of p-types crystalline silicon models analyzed using the ABINIT code. We constructed 4 silicon crystal models with a maximum of 216 atoms by simulation cell. The optimized geometries and some electronic properties were obtained. We observed that around the boron impurity the crystal lattice is deformed because of the bonding length SiÀB. The total energy increases with the number of boron atoms by simulation cell. The relative electronic densities indicated that the charge contributions to the dangling bond, produced by the presence of the boron impurity, are mainly distributed around its first silicon neighbors.
Solid State Communications, 2012
Porous silicon ðpÀSiÞ morphology depends on several parameters of the crystalline silicon substra... more Porous silicon ðpÀSiÞ morphology depends on several parameters of the crystalline silicon substrate such as doping type and carriers concentration. Experimental results on ðpÀSiÞ show that although in the porous samples carriers are greatly reduced, boron atoms remain in the bulk. The study of p-type silicon crystals substrates by means of ab initio computational simulations will help to understand how boron atoms behave during the electrochemical reaction of porous silicon ðpÀSiÞ fabrication. Here we studied the properties of p-types crystalline silicon models analyzed using the ABINIT code. We constructed 4 silicon crystal models with a maximum of 216 atoms by simulation cell. The optimized geometries and some electronic properties were obtained. We observed that around the boron impurity the crystal lattice is deformed because of the bonding length SiÀB. The total energy increases with the number of boron atoms by simulation cell. The relative electronic densities indicated that the charge contributions to the dangling bond, produced by the presence of the boron impurity, are mainly distributed around its first silicon neighbors.
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Papers by Emilye Rosas Landa