The research objective of this award is to develop a versatile method to engineer the surface properties of gallium nitride (GaN), a semiconductor material used for the fabrication of different microelectronic devices. The work will start by utilizing a Grubb?s catalyst previously used in polymer synthesis. The Grubb?s catalyst will enable to modify the surface with a variety of different functional groups using an olefin cross metathesis reaction. The availability of a general route to place different chemical functionalities on the surface is essential for the development of (bio)sensors. The work progresses from the development of the catalysis reaction on the GaN surface to the optimization of all the reaction conditions so that several classes of biomolecules can be anchored on the GaN surface while still retaining their recognition properties and specificity. Deliverables of this award will include an empirical model for selectivity of olefin cross metathesis on GaN. The model will be derived by performing a set of surface characterization tests in order to quantify chemical, morphological and mechanical properties of the modified GaN. If successful, the results of this research will increase the understanding of the possible ways to enhance the properties of GaN. The knowledge can be used to design new types of devices and interfaces that utilize a more robust and functional GaN. For example, GaN based transistor devices can benefit from high chemical stability and be used in more reliable and label free biosensor schemes if desired chemical groups are present on surfaces. Undergraduate and graduate students, as well as underrepresented minorities such as women majoring in engineering will be engaged with the research efforts as well as an outreach program with local middle school students. Through the outreach activities associated with this work, the students will be to educate the audience on their research efforts, to convey the excitement of their scientific investigation, to portray a positive image of their research and to provide role models for the younger attendants (middle and high school students).
The work investigated a method of direct covalent modification of the GaN surface that will allow for a thin molecular layer between the GaN and the sensing environment, provide chemical passivation, and supply a variety of chemical functional groups on the surface. This functionalization method involves olefin cross-metathesis chemistry. In olefin metathesis, C-C bonds are formed as a result of alkenes interchanging alkylidene functional groups through a transition metal-catalyzed reaction. The ruthenium-based olefin metathesis catalysts are stable in various solvents, work with a variety of functional groups, and are optimized for diverse applications. Several studies have demonstrated the use of these catalysts to functionalize silicon surfaces through olefin metathesis. Olefin metathesis is an ideal route for GaN surface functionalization due to its versatility in binding a variety of biological molecules. Exposure to hydrogen plasma terminated the surfaces with hydrogen atoms. Chlorine termination was achieved with phosphorus pentachloride in chlorobenzene with crystals of benzoyl peroxide as a radical initiator. The purpose of the hydrogen and chlorine termination steps are to passivate semiconductor surfaces by inhibiting reaction of the surfaces with the atmosphere before functionalizing the surface with organic molecules. The chlorine termination also activated the surface for the subsequent Grignard reaction that was used to terminate the GaN surfaces with an alkene functional group with a solution of allylmagnesium chloride in tetrahydrofuran. The alkene termination step was necessary for the use of olefin cross-metathesis to bind an alkene terminated organic molecule to the surface. The surface was first primed with Grubbs first generation catalyst, a ruthenium-based olefin metathesis catalyst, and the desired alkene-terminated molecule was then bound to the surface. The modified GaN was used to demonstrate that peptides can bind to the surface and that these surfaces can be utilized in aqueous solutions. In summary, the work demonstrated that olefin cross-metathesis on GaN provides a versatile approach for binding a variety of biomolecules. Graduate and undergraduate students were trained and successfully published in peer reviewed publications.
