Sensitivity Comparison of a Self-Standing Porous Silicon Membrane Under Flow-Through and Flow-Over Conditions

An optical sensor based on a self-standing porous silicon (PS) membrane is presented. The sensor was created by electrochemically etching a heavily doped p-type silicon wafer with an organic electrolyte that contained dimethylformamide. After fabrication, a high-current density close to electropolishing was applied in order to allow the detachment from the substrate using a lift-off method. The PS membrane was integrated in a microfluidic cell for sensing purposes, and reflectance spectra were continuously obtained while the target substance was flowed. A comparison of the bulk sensitivity is achieved when flowing through and over the pores is reported. During the experiments, a maximum sensitivity of 770 nm/RIU measured at 1700 nm was achieved. Experimental sensitivity values are in good agreement with the theoretical calculations performed when flowing through the PS membrane, it means that the highest possible sensitivity of that sensor was achieved. In contrast, a drop in the sensitivity of around 25% was observed when flowing over the PS membrane

Thermo-Optic Coefficient of Porous Silicon in the Infrared Region and Oxidation Process at Low Temperatures

In this work, a porous silicon nanostructure has been fabricated by electrochemical means and used as a thermal sensor. The thermo-optic effect in the near infrared region has been experimentally studied based on spectroscopy measurements. Values of the thermo-optic coefficient between 3.2 and 7.9·10^{-5} K^{-1} have been obtained, depending on the porosity, reaching a maximum thermal sensitivity of 91 ± 3 pm/°C during the experiments carried out with the fabricated samples. Additionally, the oxidation process of the sensor at temperatures below 500 K has been studied, showing that the growth of the silicon oxide was dependent on the characteristics of the porous layers. Based on the experimental results, a mathematical model was developed to estimate the evolution of the oxidation process as a function of porosity and thickness

Macropore Formation and Pore Morphology Characterization of Heavily Doped p-Type Porous Silicon

Tuning the pore diameter of porous silicon films is essential for some applications such as biosensing, where the pore size can be used for filtering analytes or to control the biofunctionalization of its walls. However, macropore (>50nm) formation on p-type silicon is not yet fully controlled due to its strong dependence on resistivity. Electrochemical etching of heavily doped p-type silicon usually forms micropores (<5nm), but it has been found that bigger sizes can be achieved by adding an organic solvent to the electrolyte. In this work, we compare the results obtained when adding dimethylformamide (DMF) and dimethylsulfoxide (DMSO) to the electrolyte as well as the effect of a post-treatment of the sample with potasium hydroxide (KOH) and sodium hydroxide (NaOH) for macropore formation in p-type silicon with resistivities between 0.001 and 10Ω·cm, achieving pore sizes from 5 to 100nm

Thermal Simulation of Rolled Concrete Dams: Influence of the Hydration Model and the Environmental Actions on the Thermal Field

Mathematical models for the simulation of the thermal evolution of roller-compacted concrete (RCC) dams during construction constitute an important tool for preventing excessive temperature rise, which may lead to cracking and losses of functionality. Here, we present a framework for the simulation of the thermal process. We define the boundary conditions of the problem using a careful description that incorporates the main heat exchange mechanisms. We adopt both a non-adiabatic and an adiabatic heat generation model for the simulation of the cement hydration. Our numerical framework lets us study the effect of the adopted heat generation model on the thermal field. Moreover, we study the influence of the weather conditions on the evolution of the hydration, and on the starting date of construction. Our simulations have shown that the hydration model has an important influence over the temperature field during the construction and the heat generation rate. Moreover, the hydration process and the temperature evolution are driven by the weather conditions. Once the next lift is cast, its thermal insulation effect makes the hydration take place under quasi-adiabatic conditions. As expected, dams built in cold months are prone to dissipate more heat than those built in warm seasons

Optical sensors based on polymeric nanofibers layers created by electrospinning

Porous materials have become ideal candidates for the creation of optical sensors that are able to reach extremely high sensitivities, due to both the possibility to infiltrate the target substances on them and to their large surface-to-volume ratio. In this work, we present a new alternative for the creation of porous optical sensors based on the use of polymeric nanofibers (NFs) layers fabricated by electrospinning. Polyamide 6 (PA6) NFs layers with average diameters lower than 30 nm and high porosities have been used for the creation of Fabry-Pérot optical sensing structures, which have shown an experimental sensitivity up to 1060 nm/RIU (refractive index unit). This high sensitivity, together with the low production cost and the possibility to be manufactured over large areas, make NFs-based structures a very promising candidate for the development of low-cost and high performance optical sensors

Experimental study of the sensitivity of a porous silicon ring resonator sensor using continuous in-flow measurements

A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization

Manganese Defective Clustering: Influence on the Spectroscopic Features of Ceria-Based Nanomaterials

The influence of manganese modification on the spectroscopic features of manganese-doped CeO2 systems synthesized by the microwave-assisted hydrothermal route and their correlation with the presence of O defective structures were verified, focusing on their interaction with poisonous atmospheres. Raman and electron paramagnetic resonance studies confirmed the presence of defective clusters formed by dipoles and/or quadrupoles. The number of paramagnetic species was found to be inversely proportional to the doping concentration, resulting in an increase in the Mn2+ signal, likely due to the reduction of Mn3+ species after the interaction with CO. X-ray photoelectron spectroscopy data showed the pure system with 33% of its cerium species in the Ce3+ configuration, with an abrupt decrease to 19%, after the first modification with Mn, suggesting that 14% of the Ce3+ species are donating one electron to the Mn2+ ions, thus becoming nonparamagnetic Ce4+ species. On the contrary, 58% of the manganese species remain in the Mn2+ configuration with five unpaired electrons, corroborating the paramagnetic feature of the samples seen in the electron paramagnetic resonance study

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory

The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies $E>E_{th}=5.5\times 10^{19}$ eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at $E>E_{th}$ are heavy nuclei with charge $Z$, the proton component of the sources should lead to excesses in the same regions at energies $E/Z$. We here report the lack of anisotropies in these directions at energies above $E_{th}/Z$ (for illustrative values of $Z=6,\ 13,\ 26$). If the anisotropies above $E_{th}$ are due to nuclei with charge $Z$, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies

Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluoresence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to author list and references in v