We have recently developed a procedure to amorphize structures of some semiconducting elements st... more We have recently developed a procedure to amorphize structures of some semiconducting elements starting from cubic supercells. This procedure includes the use of an ab initio computer code based on the Harris functional, 64 or 216 atoms in the originally crystalline supercells, and a thermal procedure that heats the samples to just below their corresponding melting temperature. Here we report the use of non-cubic supercells: the graphitic hexagonal (72 atoms) and rhombohedral (108 atoms) supercells, both with a density q ¼ 2:239 g/cm 3 . The rhombohedral form is metastable whereas the hexagonal form is stable. We find that the radial distribution functions as well as the atomic topologies are similar in both cases, indicating that the symmetry of the initial crystalline structure does not affect the final amorphized samples.
Nanoparticles are the cornerstone of nanotechnology. Their crystal structure and relation to shap... more Nanoparticles are the cornerstone of nanotechnology. Their crystal structure and relation to shape are still open problems despite a lot of advances in the field. The classical theory of nanoparticle stability predicts that for sizes <1.5-2 nm the icosahedral structure should be the most stable, then between around 2-5 nm, the decahedral shape should be the most stable. Beyond that, face-centered-cubic (FCC) structures will be the predominant phase. However, in the experimental side, icosahedral (I h ) and decahedral (D h ) particles can be observed much beyond the 5 nm limit. In fact, it is possible to find I h and D h particles even in the mesoscopic range. Conversely, it is possible to find FCC particles with a size <1.5 nm. In this paper we review a number of the mechanisms proposed in the literature that allow the stabilization of nanoparticles. Some of the mechanisms are very interrelated and it becomes difficult to distinguish between them. Fig. 1 Schematic representation, showing the crystal faces of a) calcite (trigonal) and b) sodium chlorate (regular).
In this work we present a theoretical model for the structural evolution and energy stability for... more In this work we present a theoretical model for the structural evolution and energy stability for metal nanoparticles from the small (1-2 nm) to the big (˜50 nm) size ranges. We have found that the appearances of structural lattice defects as well as surface reconstructions are important factors that highly influence the growth process. A simple assembly model for a path transformation for metal nanoparticles is presented and compare with experimental evidence.
A quantum-dot (QD) is a nanoscale structure consisting of one or more semiconducting materials in... more A quantum-dot (QD) is a nanoscale structure consisting of one or more semiconducting materials in which the motion of fundamental charge carriers is confined in all spatial dimensions. Core/shell quantum-dots (CSQDs) are a variety of QD consisting of two sections: An ellipsoidal core is manufactured from one material, and a shell of a second material is added around this. QDs have been the subject of great scientific and technological interest, with promising applications that include display devices, biological tagging materials, photovoltaics, and lasers. In this work, the electronic structure of bimetallic CSQDs (size < 2 nm) is analyzed by using Density-Functional Theory (DFT), with the end of correlate their electronic properties with their potential applications. We select the Au/Ag, Au/Pd and Au/Pt systems because of the experimental studies reported on these systems.
Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of ... more Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of research. Its advances and applications will result in technical capabilities that will allow the development of novel nanomaterials with applications that will revolutionize the industry in many areas. In this work we present the structural evolution and energy stability results for silver nanoparticles from the small (1-2 nm) to the big (50 nm) size ranges. We have found that the appearances of structural lattice defects are important factors that influence the growth process. A simple assembly model for a path transformation for silver nanoparticles is presented and compared with experimental evidence.
Au/Ag nanoparticles which absorb radiation near the infrared zone have been synthesized with the ... more Au/Ag nanoparticles which absorb radiation near the infrared zone have been synthesized with the expectation that they will be employed in photothermal cancer diagnosis and treatment. The material exhibited two main morphologies, triangular shapes and nanostars, which in both cases presented two extra very bright peaks ending in a triangular face in a plane parallel to the electron beam direction. The particles have been characterized by weak beam dark field (WBDF) transmission electron microscopy, STEM-HAADF, SEM, and the composition was confirmed by point EDX analysis. HRTEM was used to analyze the defects observed in the microstructure.
We have recently developed a procedure to amorphize structures of some semiconducting elements st... more We have recently developed a procedure to amorphize structures of some semiconducting elements starting from cubic supercells. This procedure includes the use of an ab initio computer code based on the Harris functional, 64 or 216 atoms in the originally crystalline supercells, and a thermal procedure that heats the samples to just below their corresponding melting temperature. Here we report the use of non-cubic supercells: the graphitic hexagonal (72 atoms) and rhombohedral (108 atoms) supercells, both with a density q ¼ 2:239 g/cm 3 . The rhombohedral form is metastable whereas the hexagonal form is stable. We find that the radial distribution functions as well as the atomic topologies are similar in both cases, indicating that the symmetry of the initial crystalline structure does not affect the final amorphized samples.
Nanoparticles are the cornerstone of nanotechnology. Their crystal structure and relation to shap... more Nanoparticles are the cornerstone of nanotechnology. Their crystal structure and relation to shape are still open problems despite a lot of advances in the field. The classical theory of nanoparticle stability predicts that for sizes <1.5-2 nm the icosahedral structure should be the most stable, then between around 2-5 nm, the decahedral shape should be the most stable. Beyond that, face-centered-cubic (FCC) structures will be the predominant phase. However, in the experimental side, icosahedral (I h ) and decahedral (D h ) particles can be observed much beyond the 5 nm limit. In fact, it is possible to find I h and D h particles even in the mesoscopic range. Conversely, it is possible to find FCC particles with a size <1.5 nm. In this paper we review a number of the mechanisms proposed in the literature that allow the stabilization of nanoparticles. Some of the mechanisms are very interrelated and it becomes difficult to distinguish between them. Fig. 1 Schematic representation, showing the crystal faces of a) calcite (trigonal) and b) sodium chlorate (regular).
In this work we present a theoretical model for the structural evolution and energy stability for... more In this work we present a theoretical model for the structural evolution and energy stability for metal nanoparticles from the small (1-2 nm) to the big (˜50 nm) size ranges. We have found that the appearances of structural lattice defects as well as surface reconstructions are important factors that highly influence the growth process. A simple assembly model for a path transformation for metal nanoparticles is presented and compare with experimental evidence.
A quantum-dot (QD) is a nanoscale structure consisting of one or more semiconducting materials in... more A quantum-dot (QD) is a nanoscale structure consisting of one or more semiconducting materials in which the motion of fundamental charge carriers is confined in all spatial dimensions. Core/shell quantum-dots (CSQDs) are a variety of QD consisting of two sections: An ellipsoidal core is manufactured from one material, and a shell of a second material is added around this. QDs have been the subject of great scientific and technological interest, with promising applications that include display devices, biological tagging materials, photovoltaics, and lasers. In this work, the electronic structure of bimetallic CSQDs (size < 2 nm) is analyzed by using Density-Functional Theory (DFT), with the end of correlate their electronic properties with their potential applications. We select the Au/Ag, Au/Pd and Au/Pt systems because of the experimental studies reported on these systems.
Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of ... more Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of research. Its advances and applications will result in technical capabilities that will allow the development of novel nanomaterials with applications that will revolutionize the industry in many areas. In this work we present the structural evolution and energy stability results for silver nanoparticles from the small (1-2 nm) to the big (50 nm) size ranges. We have found that the appearances of structural lattice defects are important factors that influence the growth process. A simple assembly model for a path transformation for silver nanoparticles is presented and compared with experimental evidence.
Au/Ag nanoparticles which absorb radiation near the infrared zone have been synthesized with the ... more Au/Ag nanoparticles which absorb radiation near the infrared zone have been synthesized with the expectation that they will be employed in photothermal cancer diagnosis and treatment. The material exhibited two main morphologies, triangular shapes and nanostars, which in both cases presented two extra very bright peaks ending in a triangular face in a plane parallel to the electron beam direction. The particles have been characterized by weak beam dark field (WBDF) transmission electron microscopy, STEM-HAADF, SEM, and the composition was confirmed by point EDX analysis. HRTEM was used to analyze the defects observed in the microstructure.
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Papers by Hector Barron