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L A Pinnaduwage

Publications and source records attributed to L A Pinnaduwage.

6 recordsLinked to original sources
PubMed2005

Photochemical hydrosilylation of 11-undecenyltriethylammonium bromide with hydrogen-terminated Si surfaces for the development of robust microcantilever sensors for Cr(VI).

We report a novel approach to the design and development of microcantilever sensors in which photochemical hydrosilylation is used to modify the microcantilever surface. This process enables individual microcantilevers in multicantilever array chips to be modified separately by focusing the activating UV light sequentially on each particular cantilever. Photochemical hydrosilylation of 11-undecenyltriethylammonium bromide with hydrogen-terminated silicon microcantilever surfaces was carried out to yield a robust quaternary ammonium terminated organic monolayer suitable for chromate detection. The surface functionalities retain their affinity toward Cr(VI), and the organic monolayer is dense enough to generate significant surface stress upon subsequent adsorption of chromate ions from aqueous solutions.

Letter↗
PubMed2004

Adsorption of trinitrotoluene on uncoated silicon microcantilever surfaces.

We measured the adsorption characteristics of trinitrotoluene (TNT) on piezoresistive silicon microcantilever surfaces under ambient air using a well-characterized TNT vapor generator. This allowed us to quantify the adsorption parameters and to estimate the sticking coefficient. The sticking coefficient initially increases with TNT exposure time and then levels off around 0.3. Atomic force microscopy images of silicon surfaces exposed to TNT revealed "island" formation of the adsorbate on the silicon surface. At low exposure times, mainly the number density of islands increased with exposure time; at longer exposure times, the size (in particular, height) of the islands grew, corresponding to the higher sticking coefficients. These observations can be qualitatively explained via the difference between TNT-surface and TNT-TNT interactions mediated by water molecules.

Adsorption↗
PubMed2004

Desorption characteristics of uncoated silicon microcantilever surfaces for explosive and common nonexplosive vapors.

We measured the desorption of explosive trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1,3,5-triazine (RDX) vapors from piezoresistive silicon microcantilevers under ambient air. Depending on the amount of vapor loaded on the cantilever, TNT desorption took a few minutes to tens of minutes (for nanogram quantities). On the other hand, no significant loss of PETN or RDX was observed after many hours. We also measured desorption of common "nonexplosive" compounds (water, acetone, and ethyl alcohol) and observed that desorption was too fast to be measured. There is a good correlation between the desorption time and the melting point (or the vapor pressure) of a particular substance. In principle, this method can be used to measure desorption rates of various substances from cantilever surfaces.

Journal Article↗
PubMed2002

Micromechanical measurement of active sites on silicon nitride using surface free energy variation.

We have investigated chemical reactions between adsorbed water and active sites on a silicon nitride surface as a function of temperature and relative humidity using microcantilevers. Effects that might produce a change in the response of the microcantilever, such as a mass adsorption, surface tension of the adsorbed water, and changes in thermal conductivity, were systematically investigated. It is shown that the judicious choice of experimental conditions could make these effects essentially inconsequential in comparison with the instrument response produced by the change in free surface energy of the microcantilever due to the chemical reactions. Using this method, the variation in free surface energy when changing from dry to high humidity conditions was found and the number of active sites that reacted was estimated. This method may be extended to other problems for use in determining surface free energy change and thus the density of reactant sites under different conditions of interest.

Journal Article↗
PubMedDate not supplied

Adsorption-desorption characteristics of explosive vapors investigated with microcantilevers.

Understanding the kinetics of adsorption and desorption of explosive vapors such as TNT from surfaces is important in the design of sensors. We report for the first time, the adsorption-desorption characteristics of TNT from a Si-microcantilever exposed to vapors of TNT. It was observed that TNT readily sticks to the exposed Si surface with the adsorption kinetics showing an initial exponential behavior followed by roughly linear kinetics. It was also observed that for cantilever temperatures close to room temperature, TNT desorbs spontaneously from the surface with decaying exponential kinetics. Based on the known equilibrium partial vapor pressures of TNT, the "effective" sticking coefficient for the silicon oxide surface at room temperature under the experimental conditions was calculated to be about 0.02. This information can be very useful in the design of sensors and that of vapor-delivery systems.

Journal Article↗