Study of resonant modes in a 700 nm pitch macroporous silicon photonic crystal

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.Postprint (author's final draft

Surface and bulk carbonate formation in calcium oxide during CO2 capture

The Engineering and Physical Sciences Research Council (EPSRC) is gratefully acknowledged for a Doctoral Training Grant for G.A.M. (EP/K0502960/1). Mr. C. McRitchie (Surface Chemistry and Catalysis Group, University of Aberdeen) is thanked for useful discussion.Peer reviewedPostprintPostprin

Transmission and thermal emission in the NO2 and CO absorption lines using macroporous silicon photonic crystals with 700 Nm pitch

Postprint (author's final draft

Zeta potential of a natural clayey sandstone saturated with carbonated NaCl solutions at supercritical CO2 conditions

The zeta potential is a measure of electric potential at the mineral-electrolyte interfaces. The zeta potential of natural sandstones depends on mineralogy, electrolyte pH, concentration, composition, amount of dissolved CO2, and temperature. We report for the first time the zeta potential measured on clayey sandstone comprising quartz, kaolinite, illite, albite and microcline saturated with NaCl solutions at supercritical CO2 conditions. Our results demonstrate that zeta potentials in clayey sandstone samples at supercritical CO2 conditions are significantly different from similar measurements conducted under ambient conditions and from those obtained with clean sandstones. Supercritical CO2 zeta potential remains negative but is influenced by clays and feldspars due to their significant presence and exposure to large pores, which yields less negative zeta potential compared to quartz, under identical conditions. Our results have significant implications to natural subsurface systems such as CO2 geo-sequestration sites, aquifers, geothermal sources and hydrocarbon reservoirs

Enhanced geometries of macroporous silicon photonic crystals for optical gas sensing applications

A macroporous silicon photonic crystal is designed and optimized theoretically for its use in gas sensing applications and IR optical filters. Light impinges perpendicularly onto the sample surface (vertical propagation) so a three-dimensional (3d) structure is used. For gas sensing, a sharp resonance is desired in order to isolate an absorption line of the gas of interest. The high Q-factors needed mandate the use of a plane defect inside the PhC to give rise to a resonant mode inside the bandgap tuned to the gas absorption line. Furthermore to allow gas passage through the device, an open membrane is required. This can affect the mechanical resilience. To improve the strength of the photonic crystal the pores are extended after the “active” 3d part. The number of modulations, and the extension length have been optimized to obtain the largest Q-factor with reasonable transmitted power. These proposed structures have been experimentally performed, probing an enhancement of almost an order of magnitude in the Q-factor in respect with the basic case. Simulations considering CO2 have been performed showing that the proposed structures are promising as precise optical gas sensors.Peer ReviewedPostprint (author's final draft

Speeds of sound for (CH4 + He) mixtures from p = (0.5 to 20) MPa at T = (273.16 to 375) K

Acknowledgements The authors want to thank for the support to Ministerio de Economía, Industria y Competitividad project ENE2017-88474-R and Junta de Castilla y León project VA280P18.Peer reviewedPostprin

Impact of the absorption in transmittance and reflectance on macroporous silicon photonic crystals

The characteristics of reflection and transmission peaks in the spectra of photonic crystals have been studied theoretically and the results compared to measurements performed in fabricated samples. The aim of this work is to investigate the relation between material losses and the effective Q factors that can be obtained in photonic crystals made with it. Photonic crystals have been designed with defects of periodicity to introduce states in the band gap that give place to reflectance and transmittance peaks at adjustable specific wavelengths. The fabricated structures are described together with their reflection and transmission spectra. The influence of losses in the material in these spectra is evaluated.Postprint (published version

Heat capacities of different amine aqueous solutions at pressures up to 25 MPa for CO2 capture

Producción CientíficaA high-pressure flow calorimeter is used to determine isobaric heat capacities for aqueous solutions of some amines such as MEA, DEA TEA, DMAE, MDEA, PZ from T = (293.15 to 353.15) K and up to 25 MPa. The experimental device can measure heat capacities with an estimated total uncertainty better than 1% for a coverage factor k = 2. The isobaric heat capacity values are analysed in conjunction with their temperature and pressure dependencies. Furthermore, empirical equations are proposed to fit isobaric heat capacities as functions of temperature and pressure for given conditions, for this kind of mixtures, obtaining standard deviations within the uncertainty of the measurements. Finally, DMAE shows the highest value of heat capacity and TEA the lowest value, when they are compared at the same conditions of temperature, pressure and composition.Junta de Castilla y León - EU-FEDER (VA280P18 y CLU-2019-04)Fellowship “Beatriz Galindo Senior” (BEAGAL18/00259

Speeds of sound for (CH4 + He) mixtures from p = (0.5 to 20) MPa at T = (273.16 to 375) K

Producción CientíficaThis work aims to provide accurate and wide-ranging experimental new speed of sound data w(p,T) of two binary (CH4 + He) mixtures at a nominal helium content of 5 % and 10 % at pressures p = (0.5 up to 20) MPa and temperatures T = (273.16, 300, 325, 350 and 375) K. For this purpose, the most accurate technique for determining speed of sound in gas phase has been used: the spherical acoustic resonator. Speed of sound is determined with an overall relative expanded (k = 2) uncertainty of 230 parts in 106 and compared to reference models for multicomponent natural gas-like mixtures: AGA8-DC92 and GERG-2008 equations of state. Relative deviations of experimental data from model estimations are outside the experimental uncertainty limit, although all points are mostly within the AGA uncertainty of 0.2 % and GERG uncertainty of 0.5 % and worsen as the helium content increases. Absolute average deviations are better than 0.45 % for GERG and below 0.14 % for AGA models in (0.95 CH4 + 0.05 He) mixture and below 0.83 % for GERG and within 0.22 % for AGA equations in (0.90 CH4 + 0.10 He) mixture.Junta de Castilla y León (project VA280P18)Ministerio de Economía, Industria y Competitividad (project ENE2017-88474-R

Cation Dependent Carbonate Speciation and the Effect of Water

A Doctoral Training Grant (EP/K0502960/1) for G.A.M. from the Engineering and Physical Sciences Research Council (EPSRC) is gratefully acknowledged. The Erasmus programme is thanked for supporting a study visit for R.W. to Turin.Peer reviewedPostprintPostprin