Enhanced Resonator Sensitivity with Nanostructured Porous Silica Coatings

Abstract

We present a strategy to increase the sensitivity of resonators to the presence of specific molecules in the gas phase, measured by the change in resonant frequency as the partial pressure of the molecule changes. We used quartz crystals as the resonators and coated them with three different thin films (<1 microm thick) of porous silica: silica xerogel, silica templated by an ordered hexagonal phase of surfactant micelles, and silica templated by an isotropic L3 phase surfactant micellar system. We compared the sensitivity of coated resonators to the presence of water vapor. The crystals coated with hexagonal phase-templated silica displayed a sensitivity enhancement up to 100-fold compared to an uncoated quartz crystal in the low-pressure regime where adsorption played a dominant role. L3 phase-templated silica displayed the highest sensitivity (up to a 4000-fold increase) in the high partial pressure regimes where capillary condensation was the main accumulation mechanism. Three parameters differentiate the contributions of these coatings to the sensitivity of the underlying resonator: (i) specific surface area per unit mass of the coating, (ii) accessibility of the surfaces to a target molecule, and (iii) distribution in the characteristic radii of curvature of internal surfaces, as measured by capillary condensation.

The Stability of L3 Sponge Phase in Acidic Solutions

“…We attributed these inconsistencies in the synthesis of the L 3 -templated silica to be due to (1) the L 3 template used in the preparation of these gels was not prepared in the L 3 phase domain and/or (2) addition of TMOS to synthesize the silica gel was possibly pushing the system out of the L 3 phase field. Our experimental observations supported the former since we noted that some solutions appeared turbid and showed optical birefringence under cross-polarizer optics, contrary to the low viscosity, optically clear solution expected of an L 3 phase, despite using a hexanol/CpCl·H 2 O ratio (h/c) of 1.15 consistent with the previously published phase diagram. , Further, samples that were characterized to have the L 3 structure went on to generate L 3 -templated silica gels, as determined by small-angle X-ray scattering (SAXS). , …”

Electrochemical Performance of Graphene as Effected by Electrode Porosity and Graphene Functionalization

“…The curves show a typical shape (type IV) [38,49] that is commonly observed in the literature [36,48]. At low benzene partial pressures (p/p sat <~0.35), the mass accumulation (with increasing p) and reduction (with decreasing p) isotherms are due to gas adsorption and desorption and can be analyzed by the Brunauer-Emmett-Teller (BET) equation [39,50]. The specific BET surface areas of the films dried from ethanol and DI-water suspensions are about 350 and 150 m 2 /g, respectively.…”

“…At larger partial pressures, the mass accumulation increases strongly, and upon subsequent reduction of p a hysteresis is observed during mass reduction. Both observations are typical for condensation and evaporation inside a porous network [38,39]. The hysteresis associated with mass accumulation and reduction is more pronounced for the FGS film made by the evaporation of ethanol suspension, indicating a larger fraction of mesopores [38,39,51] in this material as compared to the DI-water-based film.…”

“…The porosity and surface area of the films deposited from ethanol-and water-based suspensions were analyzed by measuring mass accumulation/reduction isotherms of benzene on graphene coatings, as a function of partial pressure of benzene in the gas phase [36][37][38] measured by a quartz crystal microbalance (QCM) technique [39,40]. The electrode coating procedure described above was applied to gold coated QCMs which were placed in a homemade gas flow cell.…”

Surface area enhancement of microcantilevers by femto-second laser irradiation

“…Various methods have been reported up to date. 5,6 However, these methods typically require multiple complicated micro-fabrication steps. Here, we report a single-step process to enhance the surface area of a microcantilever sensor.…”