|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||N7, Olefin Metathesis Reaction on GaN (0001) Surfaces
||Matthew Makowski, Dmitry Zemlyanov, Albena Ivanisevic
|On-Site Speaker (Planned)
An essential step towards designing new and versatile biosensors is to validate new methodologies for the attachment of biomolecules to the surface. Gallium nitride (GaN) offers a number of promising properties for novel microfabricated sensors. A surface modification scheme was characterized using X-ray Photoelectron Spectroscopy (XPS) to adapt GaN for use in biosensors. Wafers of undoped GaN (0001) on sapphire were etched in boiling 2 M KOH for 5 minutes to remove the oxide layer. The exposed gallium atoms on the surface were covalently bound to hydrogen through a hydrogen plasma treatment. The wafers were subsequently passivated with chlorine in a solution of phosphorus pentachloride and benzoyl peroxide in chlorobenzene at 90°C for 30 minutes. An alkene termination on the surface was then achieved in 2 M allylmagnesium chloride in tetrahydrofuran at 55°C for 30 minutes. The surfaces were next primed for olefin metathesis by 13.8 mM first generation Grubbs catalyst in dichloromethane at 35°C for 30 minutes. The first run of the scheme resulted in the binding of an amine group by olefin metathesis through 0.5 M allylamine in dichloromethane at 35°C for 30 minutes. The second run consisted of 0.5 M 7-bromo-1-heptene in dicholoromethane at 35°C for 2 hours. The bromine served as a label for XPS to verify the binding of the hydrocarbon to the surface. A microfluidic chip composed of polyetheretherketone was constructed and implemented for the alkene termination, Grubbs priming and olefin metathesis reactions. This resulted in a decrease in reagent volumes and wafer handling. Following each surface termination step, XPS analysis identified the chemical species at the surface. The absence of a shoulder on the Ga 2p peak for the chlorine-terminated and bromine-terminated samples indicates that no substantial oxidation of the surface occurred following the passivation with chlorine and throughout the duration of the scheme. The Cl 2p spectrum is composed of a pair of doublet peaks. Gallium to chlorine bonds produced the doublet with the greater binding energy. The peak within the C 1s spectrum at 280.9 eV signifies the presence of the ruthenium within the Grubbs catalyst following the priming of the surfaces with the olefin metathesis catalyst. The single Br 3d peak indicates the presence of bromine on the GaN surface following the linkage of 7-bromo-1-heptene via olefin metathesis. The final bromine surface coverage was 4.0% of a monolayer. The demonstrated scheme is greatly versatile due to the Grubbs catalyst allowing for a wide variety of alkene-terminated molecules to covalently bind to the GaN surface via olefin metathesis. Future applications of this scheme toward the development of novel biosensors include the binding of peptides, proteins, or antibodies to GaN electronic devices.