Articles de revista
http://hdl.handle.net/2117/2413
Sun, 26 Feb 2017 10:26:43 GMT2017-02-26T10:26:43ZEffects of photon reabsorption phenomena in confocal micro-photoluminescence measurements in crystalline silicon
http://hdl.handle.net/2117/101546
Effects of photon reabsorption phenomena in confocal micro-photoluminescence measurements in crystalline silicon
Roige, Abel; Alvarez, J.; Jaffre, A.; Desrues, T.; Martín García, Isidro; Alcubilla González, Ramón; Kleider, J.P.
Confocal micro-photoluminescence (PL) spectroscopy has become a powerful characterization technique for studying novel photovoltaic (PV) materials and structures at the micrometer level. In this work, we present a comprehensive study about the effects and implications of photon reabsorption phenomena on confocal micro-PL measurements in crystalline silicon (c-Si), the workhorse material of the PV industry. First, supported by theoretical calculations, we show that the level of reabsorption is intrinsically linked to the selected experimental parameters, i.e., focusing lens, pinhole aperture, and excitation wavelength, as they define the spatial extension of the confocal detection volume, and therefore, the effective photon traveling distance before collection. Second, we also show that certain sample properties such as the reflectance and/or the surface recombination velocity can also have a relevant impact on reabsorption. Due to the direct relationship between the reabsorption level and the spectral line shape of the resulting PL emission signal, reabsorption phenomena play a paramount role in certain types of micro-PL measurements. This is demonstrated by means of two practical and current examples studied using confocal PL, namely, the estimation of doping densities in c-Si and the study of back-surface and/or back-contacted Si devices such as interdigitated back contact solar cells, where reabsorption processes should be taken into account for the proper interpretation and quantification of the obtained PL data.
Fri, 24 Feb 2017 13:32:47 GMThttp://hdl.handle.net/2117/1015462017-02-24T13:32:47ZRoige, AbelAlvarez, J.Jaffre, A.Desrues, T.Martín García, IsidroAlcubilla González, RamónKleider, J.P.Confocal micro-photoluminescence (PL) spectroscopy has become a powerful characterization technique for studying novel photovoltaic (PV) materials and structures at the micrometer level. In this work, we present a comprehensive study about the effects and implications of photon reabsorption phenomena on confocal micro-PL measurements in crystalline silicon (c-Si), the workhorse material of the PV industry. First, supported by theoretical calculations, we show that the level of reabsorption is intrinsically linked to the selected experimental parameters, i.e., focusing lens, pinhole aperture, and excitation wavelength, as they define the spatial extension of the confocal detection volume, and therefore, the effective photon traveling distance before collection. Second, we also show that certain sample properties such as the reflectance and/or the surface recombination velocity can also have a relevant impact on reabsorption. Due to the direct relationship between the reabsorption level and the spectral line shape of the resulting PL emission signal, reabsorption phenomena play a paramount role in certain types of micro-PL measurements. This is demonstrated by means of two practical and current examples studied using confocal PL, namely, the estimation of doping densities in c-Si and the study of back-surface and/or back-contacted Si devices such as interdigitated back contact solar cells, where reabsorption processes should be taken into account for the proper interpretation and quantification of the obtained PL data.Circuit modeling of a MEMS varactor including dielectric charging dynamics
http://hdl.handle.net/2117/100953
Circuit modeling of a MEMS varactor including dielectric charging dynamics
Giounanlis, Panagiotis; Andrade Miceli, Dennis; Gorreta Mariné, Sergio; Pons Nin, Joan; Domínguez Pumar, Manuel; Blokhina, Elena
Electrical models for MEMS varactors including the effect of dielectric charging dynamics are not available in commercial circuit simulators. In this paper a circuit model using lumped ideal elements available in the Cadence libraries and a basic Verilog-A model, has been implemented. The model has been used to simulate the dielectric charging in function of time and its effects over the MEMS capacitance value.
Tue, 14 Feb 2017 10:00:51 GMThttp://hdl.handle.net/2117/1009532017-02-14T10:00:51ZGiounanlis, PanagiotisAndrade Miceli, DennisGorreta Mariné, SergioPons Nin, JoanDomínguez Pumar, ManuelBlokhina, ElenaElectrical models for MEMS varactors including the effect of dielectric charging dynamics are not available in commercial circuit simulators. In this paper a circuit model using lumped ideal elements available in the Cadence libraries and a basic Verilog-A model, has been implemented. The model has been used to simulate the dielectric charging in function of time and its effects over the MEMS capacitance value.Charge trapping control in MOS capacitors
http://hdl.handle.net/2117/100877
Charge trapping control in MOS capacitors
Domínguez Pumar, Manuel; Bheesayagari, Chenna Reddy; Gorreta Mariné, Sergio; López Rodríguez, Gema; Martín García, Isidro; Blokhina, Elena; Pons Nin, Joan
This paper presents an active control of C-V characteristic for MOS capacitors based on Sliding Mode control and sigma-delta-modulation. The capacitance of the device at a certain voltage is measured periodically and adequate voltage excitations are generated by a feedback loop to place the C-V curve at the desired target position. Experimental results are presented for a n-type c-Si MOS capacitor made with silicon dioxide. It is shown that with this approach it is possible to shift horizontally the C-V curve to the desired operation point. A physical analysis is also presented to explain how the C-V horizontal displacements can be linked to charge trapping in the bulk of the oxide and/or in the silicon-oxide interface. Finally, design criteria are provided for tuning the main parameters of the sliding mode controller.
Mon, 13 Feb 2017 09:10:13 GMThttp://hdl.handle.net/2117/1008772017-02-13T09:10:13ZDomínguez Pumar, ManuelBheesayagari, Chenna ReddyGorreta Mariné, SergioLópez Rodríguez, GemaMartín García, IsidroBlokhina, ElenaPons Nin, JoanThis paper presents an active control of C-V characteristic for MOS capacitors based on Sliding Mode control and sigma-delta-modulation. The capacitance of the device at a certain voltage is measured periodically and adequate voltage excitations are generated by a feedback loop to place the C-V curve at the desired target position. Experimental results are presented for a n-type c-Si MOS capacitor made with silicon dioxide. It is shown that with this approach it is possible to shift horizontally the C-V curve to the desired operation point. A physical analysis is also presented to explain how the C-V horizontal displacements can be linked to charge trapping in the bulk of the oxide and/or in the silicon-oxide interface. Finally, design criteria are provided for tuning the main parameters of the sliding mode controller.A CubeSAT payload for in-situ monitoring of pentacene degradation due to atomic oxygen etching in LEO
http://hdl.handle.net/2117/100363
A CubeSAT payload for in-situ monitoring of pentacene degradation due to atomic oxygen etching in LEO
Gorreta Mariné, Sergio; Pons Nin, Joan; López Rodríguez, Gema; Figueras, Eduard; Jové Casulleras, Roger; Araguz López, Carles; Via Ortega, Pol; Camps Carmona, Adriano José; Domínguez Pumar, Manuel
This paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.
Tue, 31 Jan 2017 10:54:21 GMThttp://hdl.handle.net/2117/1003632017-01-31T10:54:21ZGorreta Mariné, SergioPons Nin, JoanLópez Rodríguez, GemaFigueras, EduardJové Casulleras, RogerAraguz López, CarlesVia Ortega, PolCamps Carmona, Adriano JoséDomínguez Pumar, ManuelThis paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.Study of resonant modes in a 700 nm pitch macroporous silicon photonic crystal
http://hdl.handle.net/2117/99959
Study of resonant modes in a 700 nm pitch macroporous silicon photonic crystal
Cardador Maza, David; Vega Bru, Didac; Segura García, Daniel; Rodríguez Martínez, Ángel
In this study the modes produced by a defect inserted in a macroporous silicon (MP) photonic crystal (PC) have been studied theoretical and experimentally. In particular, the transmitted and reflected spectra have been analyzed for variations in the defect’s length and width. The performed simulations show that the resonant frequency is more easily adjusted for the fabricated samples by length tuning rather than width. The optimum resonance peak results when centered in the PC bandgap. The changes in the defect geometry result in small variations of the optical response of the PC. The resonance frequency is most sensitive to length variations, while the mode linewidth shows greater change with the defect width variation. Several MPS photonic crystals were fabricated by the electrochemical etching (EE) process with optical response in the range of 5.8 µm to 6.5 µm. Results of the characterization are in good agreement with simulations. Further samples were fabricated consisting of ordered modulated pores with a pitch of 700 nm. This allowed to reduce the vertical periodicity and therefore to have the optical response in the range of 4.4 µm to 4.8 µm. To our knowledge, modes working in this range of wavelengths have not been previously reported in 3-d MPS structures. Experimental results match with simulations, showing a linear relationship between the defect’s length and working frequency inside the bandgap. We demonstrate the possibility of tailoring the resonance peak in both ranges of wavelengths, where the principal absorption lines of different gases in the mid infrared are placed. This makes these structures very promising for their application to compact gas sensors.
Tue, 24 Jan 2017 15:08:33 GMThttp://hdl.handle.net/2117/999592017-01-24T15:08:33ZCardador Maza, DavidVega Bru, DidacSegura García, DanielRodríguez Martínez, ÁngelIn this study the modes produced by a defect inserted in a macroporous silicon (MP) photonic crystal (PC) have been studied theoretical and experimentally. In particular, the transmitted and reflected spectra have been analyzed for variations in the defect’s length and width. The performed simulations show that the resonant frequency is more easily adjusted for the fabricated samples by length tuning rather than width. The optimum resonance peak results when centered in the PC bandgap. The changes in the defect geometry result in small variations of the optical response of the PC. The resonance frequency is most sensitive to length variations, while the mode linewidth shows greater change with the defect width variation. Several MPS photonic crystals were fabricated by the electrochemical etching (EE) process with optical response in the range of 5.8 µm to 6.5 µm. Results of the characterization are in good agreement with simulations. Further samples were fabricated consisting of ordered modulated pores with a pitch of 700 nm. This allowed to reduce the vertical periodicity and therefore to have the optical response in the range of 4.4 µm to 4.8 µm. To our knowledge, modes working in this range of wavelengths have not been previously reported in 3-d MPS structures. Experimental results match with simulations, showing a linear relationship between the defect’s length and working frequency inside the bandgap. We demonstrate the possibility of tailoring the resonance peak in both ranges of wavelengths, where the principal absorption lines of different gases in the mid infrared are placed. This makes these structures very promising for their application to compact gas sensors.In situ size sorting in CVD synthesis of Si microspheres
http://hdl.handle.net/2117/99527
In situ size sorting in CVD synthesis of Si microspheres
Garin Escriva, Moises; Fenollosa Esteve, Roberto; Kowalski, Lukasz
Silicon microspheres produced in gas-phase by hot-wall CVD offer unique quality in terms of sphericity, surface smoothness, and size. However, the spheres produced are polydisperse in size, which typically range from 0.5¿µm to 5¿µm. In this work we show through experiments and calculations that thermophoretic forces arising from strong temperature gradients inside the reactor volume effectively sort the particles in size along the reactor. These temperature gradients are shown to be produced by a convective gas flow. The results prove that it is possible to select the particle size by collecting them in a particular reactor region, opening new possibilities towards the production by CVD of size-controlled high-quality silicon microspheres.
Tue, 17 Jan 2017 17:14:53 GMThttp://hdl.handle.net/2117/995272017-01-17T17:14:53ZGarin Escriva, MoisesFenollosa Esteve, RobertoKowalski, LukaszSilicon microspheres produced in gas-phase by hot-wall CVD offer unique quality in terms of sphericity, surface smoothness, and size. However, the spheres produced are polydisperse in size, which typically range from 0.5¿µm to 5¿µm. In this work we show through experiments and calculations that thermophoretic forces arising from strong temperature gradients inside the reactor volume effectively sort the particles in size along the reactor. These temperature gradients are shown to be produced by a convective gas flow. The results prove that it is possible to select the particle size by collecting them in a particular reactor region, opening new possibilities towards the production by CVD of size-controlled high-quality silicon microspheres.Characterization of dielectric charging in MEMS using Diffusive Representation
http://hdl.handle.net/2117/99524
Characterization of dielectric charging in MEMS using Diffusive Representation
Atienza García, María Teresa; Gorreta Mariné, Sergio; Pons Nin, Joan; Domínguez Pumar, Manuel
Tue, 17 Jan 2017 17:02:38 GMThttp://hdl.handle.net/2117/995242017-01-17T17:02:38ZAtienza García, María TeresaGorreta Mariné, SergioPons Nin, JoanDomínguez Pumar, ManuelIntermittent chaos for ergodic light trapping in a photonic fiber plate
http://hdl.handle.net/2117/99203
Intermittent chaos for ergodic light trapping in a photonic fiber plate
Mariano, Marina; Kozyreff, Gregory; Gerling Sarabia, Luis Guillermo; Romero Gómez, Pablo; Puigdollers i González, Joaquim; Bravo Abad, Jorge; Martorell, Jordi
Extracting the light trapped in a waveguide, or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction, is essential for optimal energetic performance in illumination, display or light harvesting devices. Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate. Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory, leading to an optically ergodic system. We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces, light absorption is greatly enhanced. Confirming this, we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.
Fri, 13 Jan 2017 10:11:06 GMThttp://hdl.handle.net/2117/992032017-01-13T10:11:06ZMariano, MarinaKozyreff, GregoryGerling Sarabia, Luis GuillermoRomero Gómez, PabloPuigdollers i González, JoaquimBravo Abad, JorgeMartorell, JordiExtracting the light trapped in a waveguide, or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction, is essential for optimal energetic performance in illumination, display or light harvesting devices. Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate. Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory, leading to an optically ergodic system. We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces, light absorption is greatly enhanced. Confirming this, we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.Analysis and synthesis of textures through the inference of Boolean functions
http://hdl.handle.net/2117/97955
Analysis and synthesis of textures through the inference of Boolean functions
Domínguez Pumar, Manuel; Torres Urgell, Lluís
This work deals with Boolean functions of non-linear and linear basis. The Boolean random functions of non-linear basis were proposed by Serra (1988,1989). These functions are generated through a Poisson point process upon which a family of independent functions, called germ functions, are installed. This process of installation consists in taking the Sup (supremum), point to point, of the result of placing the germ functions upon the points of the Poisson process. Boolean functions of linear basis, which are defined and proposed in this paper, are generated in the same manner as the non-linear functions but with a modified installation process. Instead of taking the Sup point to point, the sum point to point is defined. So the process is then equivalent to the convolution of a Poisson train of deltas with a random pulse. The aim of this paper is to analyse textures through these two models, in order to infere their genetics through a given realisation of the process, i.e., to analyse the complete statistics of the germ functions and the density of the associated Poisson process in order to characterise a given texture. Experiments and results are provided which prove that the real textures can be understood as realisations of Boolean random functions (of linear and non-linear basis), and that it has been possible to infere the genetics of unidimensional Boolean random functions of linear basis with the algorithm proposed here. It has also been possible to do it with non-linear Boolean functions but only by imposing two restrictive conditions on the genetics of the realisation.
Fri, 09 Dec 2016 15:57:51 GMThttp://hdl.handle.net/2117/979552016-12-09T15:57:51ZDomínguez Pumar, ManuelTorres Urgell, LluísThis work deals with Boolean functions of non-linear and linear basis. The Boolean random functions of non-linear basis were proposed by Serra (1988,1989). These functions are generated through a Poisson point process upon which a family of independent functions, called germ functions, are installed. This process of installation consists in taking the Sup (supremum), point to point, of the result of placing the germ functions upon the points of the Poisson process. Boolean functions of linear basis, which are defined and proposed in this paper, are generated in the same manner as the non-linear functions but with a modified installation process. Instead of taking the Sup point to point, the sum point to point is defined. So the process is then equivalent to the convolution of a Poisson train of deltas with a random pulse. The aim of this paper is to analyse textures through these two models, in order to infere their genetics through a given realisation of the process, i.e., to analyse the complete statistics of the germ functions and the density of the associated Poisson process in order to characterise a given texture. Experiments and results are provided which prove that the real textures can be understood as realisations of Boolean random functions (of linear and non-linear basis), and that it has been possible to infere the genetics of unidimensional Boolean random functions of linear basis with the algorithm proposed here. It has also been possible to do it with non-linear Boolean functions but only by imposing two restrictive conditions on the genetics of the realisation.Mechanical properties of Al2O3 inverse opals by means of nanoindentation
http://hdl.handle.net/2117/91314
Mechanical properties of Al2O3 inverse opals by means of nanoindentation
Roa Rovira, Joan Josep; Coll Valentí, Arnau; Bermejo, Sandra; Jiménez Piqué, Emilio; Alcubilla González, Ramón; Castañer Muñoz, Luis María; Llanes Pitarch, Luis Miguel
In order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them
Wed, 02 Nov 2016 08:45:14 GMThttp://hdl.handle.net/2117/913142016-11-02T08:45:14ZRoa Rovira, Joan JosepColl Valentí, ArnauBermejo, SandraJiménez Piqué, EmilioAlcubilla González, RamónCastañer Muñoz, Luis MaríaLlanes Pitarch, Luis MiguelIn order to understand the mechanical behaviour of Al2O3 inverse opals, nanoindentation techniques have been implemented in material layers with three different microstructures, in terms of hollow or polystyrene spheres, with Al2O3 shells of distinct wall thickness. Different indenter tip geometries as well as contact loading conditions have been used, in order to induce different stress field and fracture events to the layers. Field emission scanning electron microscopy and focused ion beam have been employed to understand accommodation of plastic deformation induced during the indentation process. Results show that materials with polystyrene spheres exhibit higher hardness and modulus under sharp indentation, and cracking resistance under spherical indentation. Furthermore, deformation is discerned to be mainly governed by the rotation of the microspheres. In the case of the inverse opals made of hollow spheres, the main deformation mechanisms activated under indentation are the rearrangement and densification of them