BS in Materials Engineering
Materials Engineering Department
A microfluidic reactor for synthesizing cadmium selenide (CdSe) quantum dots (QDs) was synthesized out of silicon and Pyrex glass. Microfabrication techniques were used to etch the channels into the silicon wafer. Holes were wet-drilled into Pyrex glass using a diamond-tip drill bit. The Pyrex wafer was aligned to the etched silicon wafer and both were anodically bonded to complete the microfluidic reactor. Conditions for anodic bonding were created by exposing the stacked substrates to 300V at ~350oC under 5.46N of force. Bulk CdSe solution was mixed at room temperature and treated as a single injection. The syringe containing bulk CdSe solution was interfaced to the microfluidic reactor by using Polydimethylsiloxane (PDMS) as a ferrule. Tygoprene® and stainless-steel tubing transported the bulk CdSe solution in and the QDs out of the microfluidic reactor. The microfluidic reactor was placed on a hot plate at 225oC, creating conditions for the QD chemical reaction to occur within the etched channels. The CdSe solution was injected into the channels by a syringe pump at a constant injection rate of 20mL/hr. This pump rate allowed for nucleation and growth of the QDs to occur during laminar flow through the microfluidic channels. Pressure was the most significant constraint; therefore, QD residence time was controlled by varying the length of the channels while keeping the pump rate (pressure) constant. The QD fluorescence Full-Width-Half-Max is directly proportional to their size distribution. Shorter channel lengths (2.5 cm) synthesize smaller QDs than longer lengths (12.5 cm). On a single microfluidic device, an array of various channel lengths was developed that can synthesize an array of QDs with discrete spectral profiles.