Francisco Javier González holds a courtesy appointed professorship at the Physics department of the University of Central Florida. Dr. González is a member of the Mexican National Research System (SNI) Level 3 (highest level) and is the 2012 recipient of the Mexican National Research Award from the Mexican Academy of Sciences, which is the highest Mexican award for scientists under 40 years old. His areas of expertise are biophotonics and non-invasive medical diagnosis, areas in which he has contributed with 150 journal publications, which have been cited over 2000 times (h-index: 32). Dr. González has also published 2 Book Chapters, presented 80 papers at conferences and has 7 patents granted or pending in the US, Mexico and Spain. Dr. González is Senior Member of IEEE, OSA and SPIE and Member of the Mexican Academy of Sciences. Supervisors: Glenn Boreman
In this work, the bolometric parameters of Sierpinski fractal antenna-coupled SWCNT semi-metallic... more In this work, the bolometric parameters of Sierpinski fractal antenna-coupled SWCNT semi-metallic films are obtained by thermoelectric characterization, this in order to find out the performance as bolometer. The method was based on an experimental setup considering a line-of-sight wireless link between two identical planar fractal antennas, infrared thermography, and electrical resistance measurements. The experimental setup considered the antennas resonant frequencies. Both the transmitting and receiving antenna were third-iteration Sierpinski fractal dipoles designed to work at UHF frequencies. Films made either of cracked or uncracked SWCNT films were each separately coupled to the receiving fractal antenna. Measurements showed that the receiving antenna that was impinged with radiation at UHF frequencies coming from the transmitting antenna, experienced as it was expected an induction of electric current, the induced current flowed through the film producing a temperature chang...
A nanoparticle’s shape and size determine its optical properties. Nanorods are nanoparticles that... more A nanoparticle’s shape and size determine its optical properties. Nanorods are nanoparticles that have double absorption bands associated to surface plasmon oscillations along their two main axes. In this work, we analize the optical response of gold nanorods with numerical simulations and spectral absorption measurements to evaluate their local field enhancement—which is key for surface-enhanced Raman spectroscopic (SERS) applications. Our experimental results are in good agreement with finite element method (FEM) simulations for the spectral optical absorption of the nanoparticles. We also observed a strong dependence of the optical properties of gold nanorods on their geometrical dimension and shape. Our numerical simulations helped us reveal the importance of the nanorods’ morphology generated during the synthesis stage in the evaluation of absorption and local field enhancement. The application of these gold nanorods in surface-enhancement Raman spectroscopy is analyzed numeric...
In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The ... more In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers.
Thermoelectric (TE) thin films have promise for harvesting electrical energy from waste heat. We ... more Thermoelectric (TE) thin films have promise for harvesting electrical energy from waste heat. We demonstrate TE materials and thermocouples deposited by aqueous spray deposition on glass. The n-type material was CdO doped with Mn and Sn. Two p-type materials were investigated, namely PbS with co-growth of CdS and doped with Na and Na2CoO4. Seebeck coefficients, resistivity, and power generation for thermocouples were characterized.
In this paper, we report a fast and easy method to detect histamine dihydrochloride using gold na... more In this paper, we report a fast and easy method to detect histamine dihydrochloride using gold nanostars in colloidal aqueous solution as a highly active SERS platform with potential applications in biomedicine and food science. This colloid was characterized with SEM and UV–Vis spectroscopy. Also, numerical calculations were performed to estimate the plasmonic resonance and electric field amplification of the gold nanoparticles to compare the difference between nanospheres and nanostars. Finally, aqueous solutions of histamine dihydrochloride were prepared in a wide range of concentrations and the colloid was added to carry out SERS. We found SERS amplified the Raman signal of histamine by an enhancement factor of 1 . 0 × 10 7 , demonstrating the capability of the method to detect low concentrations of this amine molecule.
8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 2013
ABSTRACT Optical antennas serve as light detectors in the infrared when coupled to transducers. D... more ABSTRACT Optical antennas serve as light detectors in the infrared when coupled to transducers. Distributed bolometers have been proposed and positively demostrated to produce an electric signal when light is inciding on it. These devices can be easily fabricated using only one e-beam lithography step. However, the choice of the material used to fabricate the antennas is of great importance to enhance the performance of these devices. In this contribution we present an optimized distributed bolometer. The auxiliary elmentes analyzed to provide the maximum possible response. This analysis is made using a multiphysics approach taking into account the electromagnetic and thermal domains.
ABSTRACT Optical antennas and passive resonant structures, as frequency selective surfaces, confi... more ABSTRACT Optical antennas and passive resonant structures, as frequency selective surfaces, configure a new kind of optical systems that can be classified as belonging to the resonant optics area. Typical antenna-coupled detectors using microbolometers as transducers have included materials with the largest temperature coefficient of resistance (TCR) value. These materials are located at the feed point of the antenna where the electric current is the largest and the Joule effect dissipates the best. At the same time, the signal delivered to the external circuit is also depending on the resistivity value. This two-material configuration requires al least two e-beam fabrication steps. Although the resistivity values of metals changes substantially, the actual range of TCR values for most of metals is quite narrow. In this contribution we analyze how the choice of the material involved in the fabrication of resonant structures may enhance the bolometric effect. This analysis is made taking into account the electromagnetic interaction of light with the resonant element. The generated heat changes temperature and this variation produces the signal. Finite element package Comsol has been used to properly simulate the situation and predict the effect of changing the fabrication to an unique material, simplifying the manufacturing. Besides, the performance of the structure is depending on the used material.
Optical antennas have been proposed as an alternative option for solar energy harvesting. In this... more Optical antennas have been proposed as an alternative option for solar energy harvesting. In this work the power conversion efficiency of broadband antennas, log-periodic, square-spiral, and archimedian-spiral antennas, coupled to Metal-Insulator-Metal and Esaki rectifying diodes has been obtained from both theoretical and numerical simulation perspectives. The results show efficiencies in the order of 10(-6) to 10(-9) for these rectifying mechanisms, which is very low for practical solar energy harvesting applications. This is mainly caused by the poor performance of diodes at the given frequencies and also due to the antenna-diode impedance mismatch. If only losses due to antenna-diode impedance mismatch are considered an efficiency of about 10(-3) would be obtained. In order to make optical antennas useful for solar energy harvesting new rectification devices or a different harvesting mechanism should be used.
Optical nanoantennas made of two metals are proposed to produce a Seebeck voltage proportional to... more Optical nanoantennas made of two metals are proposed to produce a Seebeck voltage proportional to the Stokes parameters of a light beam. The analysis is made using simulations in the electromagnetic and thermal domains. Each Stokes parameter is independently obtained from a dedicated nanoantenna configuration. S1 and S2 rely on the combination of two orthogonal dipoles. S3 is given by arranging two Archimedian spirals with opposite orientations. The analysis also includes an evaluation of the error associated with the Seebeck voltage, and the crosstalk between Stokes parameters. The results could lead to the conception of polarization sensors having a receiving area smaller than 10λ(2). We illustrate these findings with a design of a polarimetric pixel.
ABSTRACT The Raman effect consists of a shift in photon energy due to inelastic collisions of pho... more ABSTRACT The Raman effect consists of a shift in photon energy due to inelastic collisions of photons with molecules. These wavelength shifts are unique for each molecule, and they provide a fingerprint of the molecular structure of the sample that can be used to identify the material that is being analyzed, providing a noninvasive method to detect substances with clinical relevance. In the particular case of detecting filaggrin, Raman spectroscopy has been used successfully to characterize this molecule, and measurements have been successfully correlated to filaggrin-related diseases. In this chapter, the basic theory behind Raman spectroscopy is presented along with the instrumentation needed to perform Raman spectroscopy in a clinical setting and some of the recent work on using Raman spectroscopy to detect filaggrin-related skin conditions.
ABSTRACT Nanoantennas coupled to nanobolometers have been used as detectors of optical radiation.... more ABSTRACT Nanoantennas coupled to nanobolometers have been used as detectors of optical radiation. They are typically manufactured using two different materials: one for the nano-antenna and another for the nanobolometer. However, those metals used to fabricate nano-antennas also present a bolometric response. Therefore, antenna-coupled detectors using the bolometric effect distributed along the device were compared with the results previously reported for nanobolometers coupled with dipole antennas in the infrared regime. We modeled the relevant physical mechanisms and also simulated the simple case of a dipole antenna using a multi-physics computational tool. The simulation results were compared with experimental results. The advantage in performance when using a dedicated material to enhance the bolo-metric effect, is balanced with the easiness of the fabrication of resonant structures involving only one material where the bolometric effect is distributed along the device.
This Letter shows the effect of the geometrical and material properties of lead lines and connect... more This Letter shows the effect of the geometrical and material properties of lead lines and connections on the robustness and reliability of optical antennas working as distributed bolometers. We analyze the operational limits of the biasing voltage using a mutiphysics finite element method. We demonstrate that, after evaluating the effect of the electromagnetic irradiance falling on the device, biasing voltage is the main limiting factor to maintain operative titanium optical antennas. Results have been experimentally verified by finding the biasing values needed to destroy optical antennas working as distributed bolometers. Structural damage has been identified from scanning electron microscopy images.
In this work, the bolometric parameters of Sierpinski fractal antenna-coupled SWCNT semi-metallic... more In this work, the bolometric parameters of Sierpinski fractal antenna-coupled SWCNT semi-metallic films are obtained by thermoelectric characterization, this in order to find out the performance as bolometer. The method was based on an experimental setup considering a line-of-sight wireless link between two identical planar fractal antennas, infrared thermography, and electrical resistance measurements. The experimental setup considered the antennas resonant frequencies. Both the transmitting and receiving antenna were third-iteration Sierpinski fractal dipoles designed to work at UHF frequencies. Films made either of cracked or uncracked SWCNT films were each separately coupled to the receiving fractal antenna. Measurements showed that the receiving antenna that was impinged with radiation at UHF frequencies coming from the transmitting antenna, experienced as it was expected an induction of electric current, the induced current flowed through the film producing a temperature chang...
A nanoparticle’s shape and size determine its optical properties. Nanorods are nanoparticles that... more A nanoparticle’s shape and size determine its optical properties. Nanorods are nanoparticles that have double absorption bands associated to surface plasmon oscillations along their two main axes. In this work, we analize the optical response of gold nanorods with numerical simulations and spectral absorption measurements to evaluate their local field enhancement—which is key for surface-enhanced Raman spectroscopic (SERS) applications. Our experimental results are in good agreement with finite element method (FEM) simulations for the spectral optical absorption of the nanoparticles. We also observed a strong dependence of the optical properties of gold nanorods on their geometrical dimension and shape. Our numerical simulations helped us reveal the importance of the nanorods’ morphology generated during the synthesis stage in the evaluation of absorption and local field enhancement. The application of these gold nanorods in surface-enhancement Raman spectroscopy is analyzed numeric...
In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The ... more In this article nickel interdigital capacitors were fabricated on top of silicon substrates. The capacitance of the interdigital capacitor was optimized by coating the electrodes with a 60 nm layer of HfO2. An analytical solution of the capacitance was compared to electromagnetic simulations using COMSOL and with experimental measurements. Results show that modeling interdigital capacitors using Finite Element Method software such as COMSOL is effective in the design and electrical characterization of these transducers.
Thermoelectric (TE) thin films have promise for harvesting electrical energy from waste heat. We ... more Thermoelectric (TE) thin films have promise for harvesting electrical energy from waste heat. We demonstrate TE materials and thermocouples deposited by aqueous spray deposition on glass. The n-type material was CdO doped with Mn and Sn. Two p-type materials were investigated, namely PbS with co-growth of CdS and doped with Na and Na2CoO4. Seebeck coefficients, resistivity, and power generation for thermocouples were characterized.
In this paper, we report a fast and easy method to detect histamine dihydrochloride using gold na... more In this paper, we report a fast and easy method to detect histamine dihydrochloride using gold nanostars in colloidal aqueous solution as a highly active SERS platform with potential applications in biomedicine and food science. This colloid was characterized with SEM and UV–Vis spectroscopy. Also, numerical calculations were performed to estimate the plasmonic resonance and electric field amplification of the gold nanoparticles to compare the difference between nanospheres and nanostars. Finally, aqueous solutions of histamine dihydrochloride were prepared in a wide range of concentrations and the colloid was added to carry out SERS. We found SERS amplified the Raman signal of histamine by an enhancement factor of 1 . 0 × 10 7 , demonstrating the capability of the method to detect low concentrations of this amine molecule.
8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 2013
ABSTRACT Optical antennas serve as light detectors in the infrared when coupled to transducers. D... more ABSTRACT Optical antennas serve as light detectors in the infrared when coupled to transducers. Distributed bolometers have been proposed and positively demostrated to produce an electric signal when light is inciding on it. These devices can be easily fabricated using only one e-beam lithography step. However, the choice of the material used to fabricate the antennas is of great importance to enhance the performance of these devices. In this contribution we present an optimized distributed bolometer. The auxiliary elmentes analyzed to provide the maximum possible response. This analysis is made using a multiphysics approach taking into account the electromagnetic and thermal domains.
ABSTRACT Optical antennas and passive resonant structures, as frequency selective surfaces, confi... more ABSTRACT Optical antennas and passive resonant structures, as frequency selective surfaces, configure a new kind of optical systems that can be classified as belonging to the resonant optics area. Typical antenna-coupled detectors using microbolometers as transducers have included materials with the largest temperature coefficient of resistance (TCR) value. These materials are located at the feed point of the antenna where the electric current is the largest and the Joule effect dissipates the best. At the same time, the signal delivered to the external circuit is also depending on the resistivity value. This two-material configuration requires al least two e-beam fabrication steps. Although the resistivity values of metals changes substantially, the actual range of TCR values for most of metals is quite narrow. In this contribution we analyze how the choice of the material involved in the fabrication of resonant structures may enhance the bolometric effect. This analysis is made taking into account the electromagnetic interaction of light with the resonant element. The generated heat changes temperature and this variation produces the signal. Finite element package Comsol has been used to properly simulate the situation and predict the effect of changing the fabrication to an unique material, simplifying the manufacturing. Besides, the performance of the structure is depending on the used material.
Optical antennas have been proposed as an alternative option for solar energy harvesting. In this... more Optical antennas have been proposed as an alternative option for solar energy harvesting. In this work the power conversion efficiency of broadband antennas, log-periodic, square-spiral, and archimedian-spiral antennas, coupled to Metal-Insulator-Metal and Esaki rectifying diodes has been obtained from both theoretical and numerical simulation perspectives. The results show efficiencies in the order of 10(-6) to 10(-9) for these rectifying mechanisms, which is very low for practical solar energy harvesting applications. This is mainly caused by the poor performance of diodes at the given frequencies and also due to the antenna-diode impedance mismatch. If only losses due to antenna-diode impedance mismatch are considered an efficiency of about 10(-3) would be obtained. In order to make optical antennas useful for solar energy harvesting new rectification devices or a different harvesting mechanism should be used.
Optical nanoantennas made of two metals are proposed to produce a Seebeck voltage proportional to... more Optical nanoantennas made of two metals are proposed to produce a Seebeck voltage proportional to the Stokes parameters of a light beam. The analysis is made using simulations in the electromagnetic and thermal domains. Each Stokes parameter is independently obtained from a dedicated nanoantenna configuration. S1 and S2 rely on the combination of two orthogonal dipoles. S3 is given by arranging two Archimedian spirals with opposite orientations. The analysis also includes an evaluation of the error associated with the Seebeck voltage, and the crosstalk between Stokes parameters. The results could lead to the conception of polarization sensors having a receiving area smaller than 10λ(2). We illustrate these findings with a design of a polarimetric pixel.
ABSTRACT The Raman effect consists of a shift in photon energy due to inelastic collisions of pho... more ABSTRACT The Raman effect consists of a shift in photon energy due to inelastic collisions of photons with molecules. These wavelength shifts are unique for each molecule, and they provide a fingerprint of the molecular structure of the sample that can be used to identify the material that is being analyzed, providing a noninvasive method to detect substances with clinical relevance. In the particular case of detecting filaggrin, Raman spectroscopy has been used successfully to characterize this molecule, and measurements have been successfully correlated to filaggrin-related diseases. In this chapter, the basic theory behind Raman spectroscopy is presented along with the instrumentation needed to perform Raman spectroscopy in a clinical setting and some of the recent work on using Raman spectroscopy to detect filaggrin-related skin conditions.
ABSTRACT Nanoantennas coupled to nanobolometers have been used as detectors of optical radiation.... more ABSTRACT Nanoantennas coupled to nanobolometers have been used as detectors of optical radiation. They are typically manufactured using two different materials: one for the nano-antenna and another for the nanobolometer. However, those metals used to fabricate nano-antennas also present a bolometric response. Therefore, antenna-coupled detectors using the bolometric effect distributed along the device were compared with the results previously reported for nanobolometers coupled with dipole antennas in the infrared regime. We modeled the relevant physical mechanisms and also simulated the simple case of a dipole antenna using a multi-physics computational tool. The simulation results were compared with experimental results. The advantage in performance when using a dedicated material to enhance the bolo-metric effect, is balanced with the easiness of the fabrication of resonant structures involving only one material where the bolometric effect is distributed along the device.
This Letter shows the effect of the geometrical and material properties of lead lines and connect... more This Letter shows the effect of the geometrical and material properties of lead lines and connections on the robustness and reliability of optical antennas working as distributed bolometers. We analyze the operational limits of the biasing voltage using a mutiphysics finite element method. We demonstrate that, after evaluating the effect of the electromagnetic irradiance falling on the device, biasing voltage is the main limiting factor to maintain operative titanium optical antennas. Results have been experimentally verified by finding the biasing values needed to destroy optical antennas working as distributed bolometers. Structural damage has been identified from scanning electron microscopy images.
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Papers by Javier Gonzalez