Papers by Kevin Sebastián Sanchez
Biomolecules, 2019
Antimicrobial peptides (AMPs) are effector molecules of the innate immune system and have been is... more Antimicrobial peptides (AMPs) are effector molecules of the innate immune system and have been isolated from multiple organisms. Their antimicrobial properties are due to the fact that they interact mainly with the anionic membrane of the microorganisms, permeabilizing it and releasing the cytoplasmic content. Alyteserin 1c (+2), an AMP isolated from Alytes obstetricans and its more cationic and hydrophilic analogue (+5) were synthesized using the solid phase method, in order to study the interaction with model membranes by calorimetric and spectroscopic assays. Differential scanning calorimetry (DSC) showed that both peptides had a strong effect when the membrane contained phosphatidylcholine (PC) alone or was mixed with phosphatidylglycerol (PG), increasing membrane fluidization. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to study the secondary structure of the peptide. Peptide +2 exhibited a transition from β-sheet/turns to β-sheet/α-...
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
Results of quantum calculations in M-doped chalcopyrite Cu 4 MGa 3 S8 (with M=Ti, V, Cr or Mn) ar... more Results of quantum calculations in M-doped chalcopyrite Cu 4 MGa 3 S8 (with M=Ti, V, Cr or Mn) are evaluated. The purpose of this work is the quest of a compound which possesses an isolated narrow partiallyfilled electronic band sited into the host semiconductor bandgap. The aforementioned material could be useful for designing novel solar cells with very high efficiency. Density Functional Theory calculations in the spinpolarized GGA approach have been carried out in all cases for obtain band dispersion diagrams and densities of electronic states. For the systems having Cr and Ti as dopants, where the results reveal promising features, an advanced DFT+U formalism has been used to ascertain their properties with higher certainty. Finally, after having reasoned that Cu^iGasSs has the desired features, a prediction of its energetic feasibility has been formulated.
2008 Conference on Optoelectronic and Microelectronic Materials and Devices, 2008
An ab-initio study of novel photovoltaic materials with enhanced optoelectronic properties is pre... more An ab-initio study of novel photovoltaic materials with enhanced optoelectronic properties is presented in this contribution. Predictions of absorption coefficients agree completely with the characterization of the first experimental samples grown in the laboratory. Compounds selected for the study are derived from chalcogenide semiconductors in which several atoms are substituted by transition elements. These atoms modify the electronic band structure in such a way that a new narrow band appears inside the parent semiconductor band-gap. Partial occupation of this band enables that additional carriers could be obtained from absorption of photons with energy lower than that of the band-gap, thus enhancing the photovoltaic conversion properties of the material. It was estimated than a photovoltaic solar cell designed from this novel concept could reach a thermodynamic efficiency of 63.2% compared to 43.1% corresponding to the thermodynamic efficiency limit of conventional semiconductor based solar cells. Results show a significant enhancement of the absorption coefficient respecting to the corresponding parent semiconductor in the main emission region of the solar spectrum. For some of the theoretically proposed compounds, optoelectronic properties of recently synthesized samples have been obtained experimentally. Comparison of experimental absorption measurements with results of the calculations presented here shows a very good agreement.
Thin Solid Films, 2007
Electronic structure calculations are carried out for CuGaSi partially substituted with Ti, V, C-... more Electronic structure calculations are carried out for CuGaSi partially substituted with Ti, V, C-r or Mn to ascertain if some of these systems could provide an intermediate band material able to give a high efficiency photovoltaic cell. Trends in electronic level positions are analyzed and more accurate advanced theory levels (exact exchange or Hubbard-type methods) are used in some cases. The Ti-substituted system seems more likely to yield an intermediate band material with the desired properties, and furthermore seems realizable from the thermodynamic point of view, while those with Cr and Mn might give half-metal structures with applications in spintronics.
Thin Solid Films, 2009
We present the structural and electronic characterization of n-doped (Aluminium or Indium) ZnO an... more We present the structural and electronic characterization of n-doped (Aluminium or Indium) ZnO and the effect of the doping on the calculated photoelectron spectroscopy (PES) spectra. The fully-relaxed calculations have been made using the density functional theory, including a Hubbard correlation term that increases the Zn-3d states binding energy, and which matches the experimental values. The effect of Oxygen vacancies is also included in our study. Our results show that the new Al or In-donor levels appearing in the conduction band hybridize with the Oxygen-2p states and help decrease the resistivity of these doped systems as was found experimentally. The calculated PES spectra show a small enhancement in the intensity close to the chemical potential as a result of these new Al or In levels.
Journal of Solar Energy Engineering, 2007
Recent work has proposed that enhanced efficiency can be achieved in photovoltaic cells through i... more Recent work has proposed that enhanced efficiency can be achieved in photovoltaic cells through implementation of the intermediate band (IB) concept in which a narrow band inserted within the band gap of a semiconductor is used to make the combined absorption of two sub-band gap energy photons lead to the generation of current at the higher voltage corresponding to the full band gap. Trying to tell which materials could have the IB properties necessary for this, quantum calculations within density functional theory at the generalized gradient approximation level have been carried out in this work for chalcopyrite-type copper gallium sulphide structures where gallium is partially substituted by transition metal atoms (Ti, V, Cr, Mn), as these materials are presumed to be candidates for developing the IB electronic structure able to realize this concept. The computed electronic structures characterized by density-of-state curves and band dispersion diagrams, show transition metal-indu...
Uploads
Papers by Kevin Sebastián Sanchez