Liquids Analysis with Optofluidic Bragg Microcavities

Abstract

Porous Bragg microcavities formed by stacking a series of porous nanocolumnar layers with alternate low (SiO2) and high (TiO2) refractive index materials have been prepared by physical vapor deposition at glancing angles (GLAD). By strictly controlling the porosity and refractive index of the individual films, as well as the relative orientation of the nanocolumns from one layer to the next, very porous and nondispersive high optical quality microcavities have been manufactured. These photonic structures have been implemented into responsive devices to characterize liquids, mixtures of liquids, or solutions flowing through them. The large displacements observed in the optical spectral features (Bragg reflector gap and resonant peak) of the photonic structures have been quantitatively correlated by optical modeling with the refractive index of the circulating liquids. Experiments carried out with different glucose and NaCl solutions and mixtures of water plus glycerol illustrate the potentialities of these materials to serve as optofluidic devices to determine the concentration of solutions or the proportion of two phases in a liquid mixture.

Nanoindentation and scratch resistance of multilayered TiO2-SiO2coatings with different nanocolumnar structures deposited by PV-OAD

“…This figure clearly shows that hardness and elastic modulus depend on the deposition angle, a result that agrees with previous results for TiO 2 PV-OAD coatings [19,21]. Common features of PV-OAD thin films, including the TiO 2 -SiO 2 multilayers studied here, are that both the tilting angle of nanocolumns and the void space increase with the deposition angle (c.f., Figure 1) [2,3,6,7]. This is also the case for multilayer coatings as can be evidenced in the FESEM micrographs of the slanted microstructure in Figure 1, where an increase in the tilting angle of nanocolumns from about 30º to 45º can be appreciated when examining the micrographs of the 70º and 85º samples, respectively.…”

“…The thickness of each single layer was adjusted at approximately 85 nm. Details about the deposition procedure and conditions can be found elsewhere [7]. While performing the deposition, the substrate was mantained fixed or azimuthally turned by 180º or 90º when passing from one layer to the next.…”

“…These nanocolumnar structures can be prepared in a wide range of architectures changing the zenithal angle of evaporation and rotationally moving the substrate during deposition [4,5]). In our group, TiO 2 -SiO 2 multilayer nanocolumnar systems behaving as 1D photonic crystals or Bragg microcavities have been used for liquid sensing applications [6,7]. Applications as polarized light emitters, selective transmitters or humidity sensors have been reported by others [8,9,10].…”

Nanocolumnar growth of thin films deposited at oblique angles: Beyond the tangent rule

“…[1][2][3] This anisotropy combined with their high open porosity [4][5][6][7] are essential for other applications such as Bragg reflectors with tunable optical response, 8 templates for nanocomposite films, [9][10][11][12] broad band antireflection coatings, 13,14 optical microresonators, 15 light emitting diodes, 16 photovoltaic cells, 17 advanced plasmon photocatalysis, 18,19 microfluidic sensors, 20 transparent conductive electrodes 21 and many others. In this technique, a given material is sublimated in a vacuum reactor, either thermally or assisted by an electron beam, yielding vapor species that follow straight trajectories in a "line of sight" configuration with respect to the substrate, and giving rise to thin films with well-defined tilted nanocolumnar structures.…”

1D photonic defect structures based on colloidal porous frameworks: Reverse pore engineering and vapor sorption

“…To this solution, deionized water (0.43 mL) and 0.5 M HCl (0.02 mL) were added consecutively under stirring and the clear mixture was kept stirring at RT until further use. In an alternative route, the SiO 2 sol suspension was obtained by mixing Si(OEt) 4 , ethanol and 0.1 M HCl (without the addition of water) in volume ratios of 1:10:1 or 2:10:2.…”