Papers by José Luis Rodríguez-López
2 Abstract: We present a study of a system composed of a scanning tunneling microscope (STM) tip ... more 2 Abstract: We present a study of a system composed of a scanning tunneling microscope (STM) tip coupled to an absorbed impurity on a host surface using the functional renormalization group (FRG). We include the effect of the STM tip as a correction to the self-energy in addition to the usual contribution of the host surface in the wide band limit. We calculate the differential conductance curves at two dif- ferent lateral distances from the quantum impurity and find good qualitative agree- ment with STM experiments where the differential conductance curves evolve from an antiresonance to a Lorentzian shape.
Journal of Physics and Chemistry of Solids, 2019
MRS Proceedings, 2012
ABSTRACTIn this work we present the bases to perform investigation on the effects on the morpholo... more ABSTRACTIn this work we present the bases to perform investigation on the effects on the morphology and size of nanostructures of silver, owed to the modification of synthesis factors in a polyol process such as temperature, concentration, time of reaction, injection speed and time of injection. It is claimed that control over Ag nanostructures shape could be improved and significant information about the synthesis process can be obtained. The design of experiments was done aimed to obtain useful information about how to yield as much as possible specific structures of interest.
Inorganic Chemistry, 2013
Pure Ca2Ba3(PO4)3Cl and rare earth ion (Eu(2+)/Ce(3+)/Dy(3+)/Tb(3+)) doped Ca2Ba3(PO4)3Cl phospho... more Pure Ca2Ba3(PO4)3Cl and rare earth ion (Eu(2+)/Ce(3+)/Dy(3+)/Tb(3+)) doped Ca2Ba3(PO4)3Cl phosphors with the apatite structure have been prepared via a Pechini-type sol-gel process. X-ray diffraction (XRD) and structure refinement, photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, absolute quantum yield, as well as lifetimes were utilized to characterize samples. Under UV light excitation, the undoped Ca2Ba3(PO4)3Cl sample shows broad band photoluminescence centered near 480 nm after being reduced due to the defect structure. Eu(2+) and Ce(3+) ion doped Ca2Ba3(PO4)3Cl samples also show broad 5d → 4f transitions with cyan and blue colors and higher quantum yields (72% for Ca2Ba3(PO4)3Cl:0.04Eu(2+); 67% for Ca2Ba3(PO4)3Cl:0.016Ce(3+)). For Dy(3+) and Tb(3+) doped Ca2Ba3(PO4)3Cl samples, they give strong line emissions coming from 4f → 4f transitions. Moreover, the Ce(3+) ion can transfer its energy to the Tb(3+) ion in the Ca2Ba3(PO4)3Cl host, and the energy transfer mechanism has been demonstrated to be a resonant type, via a dipole-quadrupole interaction. However, under the low voltage electron beam excitation, Tb(3+) ion doped Ca2Ba3(PO4)3Cl samples present different luminescence properties compared with their PL spectra, which is ascribed to the different excitation mechanism. On the basis of the good PL and CL properties of the Ca2Ba3(PO4)3Cl:A (A = Ce(3+)/Eu(2+)/Tb(3+)/Dy(3+)), Ca2Ba3(PO4)3Cl might be promising for application in solid state lighting and field-emission displays.
Physical Review Letters, 2004
We report on energetic surface reconstruction phenomena observed on bimetallic nanoparticle syste... more We report on energetic surface reconstruction phenomena observed on bimetallic nanoparticle systems of AuPd and AuCu, similar to a resolidification effect observed during the cooling process in lead clusters. These binary alloy nanoparticles show the fivefold edges truncated, resulting in f100g facets on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence so far. We demonstrate experimentally as well as by computational simulations that this new eutectic structure is favored in such nanoalloy systems.
2018 XIV International Engineering Congress (CONIIN), 2018
Mesoporous silica-based nanomaterials have been considered as potential carriers for drug deliver... more Mesoporous silica-based nanomaterials have been considered as potential carriers for drug delivery applications. Their main advantages are: i) tunable pore size, ii) high surface area, iii) functional surface chemistry and iv) biocompatibility. The internal and external domains of mesoporous silica allow encapsulating a wide variety of drugs and functionalizing its surface with specific molecules in the perspective of targeting medicine. In this work, we synthetized and characterized the silica-based mesostructures known as SBA-15 and MSF. We highlighted their pore size distribution, functional surface chemistry and loading capacity using valproic acid as probe. We observed that the SBA-15 sample has an average pore size of about 6 nm, while the modified MSF sample has an average pore size of 13 nm. These are encouraging results demonstrating that the use of swelling agents allows increasing the pore size distribution and thus the applicability of MSF as drug carries. The surface functionalization, using liposomes, was successfully achieved. This last may play a key role in the presence of living cells, enhancing the uptake. The more efficient material was the MSF, which encapsulated a higher VPA amount. Hence, the loading capacity was found pore size dependent. This work is the proof-of-concept of the use of MSF as biocompatible and effective drug delivery system.
Journal of Photochemistry and Photobiology A: Chemistry, 2019
ZnO/p-MnO nanocomposites with different percentages of manganese (0.5%, 1.1%, and 2.25%) with a s... more ZnO/p-MnO nanocomposites with different percentages of manganese (0.5%, 1.1%, and 2.25%) with a semiconducting junction were prepared. Changes in Flat band potential (E fb) for ZnO due the different amounts of MnO was observed, meanwhile same donor density (N d) was held in all materials. From chronoamperometric experiments under on-off illuminated conditions a transient time constant (τ), related to the electron transport in the electrodes were calculated, where higher values are observed in materials with high amounts of MnO. Photodegradation studies of anthracene in an ethanol:water (1:1, pH 12) solution were performed, showing that anthraquinone is the main product with no photodegrading of ethanol. The results suggest that the junction n-ZnO/p-MnO and materials with high transient time constant (τ), enhance the photocatalytic degradation. The best photocatalytic performance for the photodegradation of anthracene was obtained with the nanocomposite n-ZnO /p-MnO (Mn=2.25%) .
ACS Applied Bio Materials, 2019
New Journal of Chemistry, 2018
We report a facile approach to synthesise small Au–Ag alloyed nanoparticles using a new cali[8]ar... more We report a facile approach to synthesise small Au–Ag alloyed nanoparticles using a new cali[8]arene derivative as a stabiliser.
ECS Transactions, 2021
In this work we present a comparison of the properties of three tin selenide (SnSe) thin films sy... more In this work we present a comparison of the properties of three tin selenide (SnSe) thin films synthesized by electrodeposition under air or nitrogen atmosphere. The films were synthesized at -0.7 V, -0.8 V, and -0.9 V vs. Ag/AgCl using a fluorine doped tin oxide conductive glass as working electrode, a silver chloride electrode as reference electrode, and a platinum mesh as counter electrode. After the electrodeposition, films were heated at 55°C for 30 minutes in air atmosphere. Films without and with thermal treatment were characterized by UV-Visible Spectroscopy, Atomic Force Microscopy, and Raman Spectroscopy. Analyzing the results, it was found that the optimal conditions for the electrodeposition were at -0.8 V vs Ag/AgCl. Band gap values were in the range from 1.2 to 1.5 eV. Raman spectroscopy revealed characteristic vibrational modes of SnSe and SnSe2 materials. The analysis by Atomic Force Microscopy revealed grain size of 100-700 nm.
Molecules, 2021
Silver and gold nanoparticles were synthesized under environmentally-friendly reaction conditions... more Silver and gold nanoparticles were synthesized under environmentally-friendly reaction conditions by using a biodegradable copolymer and water as a solvent. The triblock copolymer Pluronic P103 was utilized as a stabilizing agent or soft template to produce Ag and Au nanoparticles (NPs) of different sizes. Moreover, in the synthesis of Au NPs, the polymer acted as a reducing agent, decreasing the number of reagents used and consequently the residues produced, hence, rendering the procedure less complicated. It was observed that as the concentration of the polymer increased, the size of the metallic NPs augmented as well. However, AgNPs and AuNPs prepared with 1 and 10 wt% Pluronic P103, respectively, showed a significant decrease in particle size due to the presence of polymeric soft templates. The hybrid materials (metal/polymer) were characterized by UV-Vis spectroscopy, DLS, and TEM. The pre-synthesized nanoparticles were employed to decorate anatase-TiO2, and the composites were...
To theoretically study the physicochemical properties of nanowires, it is necessary to build the ... more To theoretically study the physicochemical properties of nanowires, it is necessary to build the corresponding atomic geometrical models. Here we present the geometrical characteristics of nanowires with fcc, hcp, and polycrystalline structures. We consider fcc and hcp wires grown along the (111) andz axis directions, respectively, with various diameters and lengths. In addition, since staking faults in these systems are very common, we analyze also the case of nanowires formed by stacked pieces having different crystalline structures and orientations, a fact that leads to the formation of several internal interfaces. By performing simulations of transmission electron microscopy (TEM) images and diffraction patterns of the nanowires considered here, we reveal how sensitive are the calculated images to the defocus condition as well as to the orientation of the wire with respect to the incident beam, a result that must be taken into account in order to better understand the measured d...
Photothermal tumor ablation might be carried out with multibranched gold nanoparticles (MBAuNPs) ... more Photothermal tumor ablation might be carried out with multibranched gold nanoparticles (MBAuNPs) having maximum absorbance (Amax) in the infrared region and functionalized with ligands that would bind them to the target tumor markers. However, in nanomedicine applications, the nanostructures must reach their target tissues to be effective, but the corona of serum proteins they instantaneously acquire when administered by intravenous injection may affect their activity; for this reason, we decided to analyze the effect that exposing MBAuNPs to bovine serum albumin (BSA) and human serum (HS) have on their protein corona and physical properties. The synthesized spherical Au seeds stoichiometrically generate pinata-like MBAuNPs of 8–20 peaks potentially useful for photothermal tumor ablation since they induce hyperthermia of more than 4 °C in phantom gels mimicking the skin irradiated with an 808 nm laser at 0.75 W/cm2. The calculated surface area of MBAuNPs ranges from 24 984 nm2 to 40...
Catalysis Communications, 2016
Abstract The incorporation of Er 3+ ions in the CaTiO 3 structure provides an enhanced H 2 photop... more Abstract The incorporation of Er 3+ ions in the CaTiO 3 structure provides an enhanced H 2 photoproduction due to the formation of long-lived charge-carriers in the semiconductor. Nitroblue tetrazolium reaction, photoluminescence and time resolved microwave conductivity techniques were used to investigate the generation of the superoxide species and the lifetime of the charge-carriers. The improved photoactivity has been explained in terms of the dopant agent, finding that phenomena such as a higher concentration of the superoxide radicals, a more efficient separation of the photogenerated charge-carriers, and a slower recombination process take place in the Er 3 + doped CaTiO 3 compared to the undoped CaTiO 3 .
The Journal of Physical Chemistry C, 2016
Ag and CuO nanoparticles (NPs) synthesized on the surface of commercial TiO2 (P25) by radiolytic ... more Ag and CuO nanoparticles (NPs) synthesized on the surface of commercial TiO2 (P25) by radiolytic reduction were characterized by diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). In the case of modification with silver and copper, results from HAADF-STEM, EDS, XPS, and XAS show that Ag@CuO nanoparticles (large silver cores decorated with small clusters of CuO) were obtained on TiO2–P25. The photocatalytic properties of bare and modified TiO2–P25 were studied for phenol photodegradation and for acetic acid oxidation under UV and visible irradiation. The mechanisms involved in photocatalysis were studied by time-resolved microwave conductivity (TRMC) and action spectra (AS). The electronic properties of the surface-modified TiO2–P25 were studied by TRMC to follow the cha...
ACS Nano, 2016
The alloy Au−Ag system is an important noble bimetallic phase, both historically (as "Electrum") ... more The alloy Au−Ag system is an important noble bimetallic phase, both historically (as "Electrum") and now especially in nanotechnology, as it is applied in catalysis and nanomedicine. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. Using a regular solution model within a nanothermodynamic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. Besides an overall shift downward, there is a "tilting" effect on the solidus−liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. Finally, the optical properties of Au−Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment.
Physical Review B, 2002
We report a systematic study of the structural and magnetic properties of free-standing rhodium c... more We report a systematic study of the structural and magnetic properties of free-standing rhodium clusters (Rh N , 4рNр26). The geometrical structures of the global minima and lowest energy isomers were obtained with a semiempirical Gupta potential and employing a global evolutive search algorithm. The spin-polarized electronic structure and related magnetic properties of these geometries were calculated by solving selfconsistently a spd tight-binding Hamiltonian. We determined the possible coexistence of different isomers and found that inclusion does not, in general, change significantly the magnetic moments obtained for the global minima structures. Results are compared with the experiment and with other theoretical calculations available in the literature.
Applied Computational Materials Modeling
Modern research in the field of small metallic systems has confirmed that many nanoparticles take... more Modern research in the field of small metallic systems has confirmed that many nanoparticles take Platonic and Archimedean solids related shapes. A Platonic solid looks the same from any vertex, and intuitively they appear as good candidates for atomic equilibrium shapes. A good example is the icosahedral (I h) particle that only shows {111} facets that produce a more rounded structure. Indeed, many studies report the I h as the most stable particle at the size range r ≤ 20 Å for noble gases and for some metals. In this chapter, we discuss the structure and shape of mono-and bimetallic nanoparticles in the size range from 1-300 nm. First, AuPd nanoparticles (1-2 nm) that show dodecahedral atomic growth packing. Next, in the range of 2-5 nm, we discuss a surface reconstruction phenomenon observed also on AuPd and AuCu nanoparticles. These binary alloy nanoparticles show the fivefold edges truncated, resulting in {100} facets on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence in the literature before. Next, we review a monometallic system (≈ 5 nm) that we termed the decmon. Finally, we present icosahedrally derived star gold nanocrystals (100-300 nm) which resemble the great stellated dodechaedron, a Kepler-Poisont solid. We conclude that the shape or morphology of some mono-and bimetallic particles evolves with size following the sequence from atoms to the Platonic solids. As the size increases, they tend to adopt Archimedean related shapes and then beyond the Archimedean (Kepler-Poisont) solids, up to the bulk structure of solids.
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Papers by José Luis Rodríguez-López