Functionalization of MgZnO nanorod films and characterization by FTIR microscopic imaging

Metal organic chemical vapor deposition grown films consisting of MgxZn1-xO (4% < x < 5%) nanorod arrays (MgZnOnano) were functionalized with 11-azidoundecanoic acid (1). The MgZnOnano was used instead of pure ZnO to take advantage of the etching resistance of the MgZnOnano during the binding and subsequent sensing device fabrication processes of sensor devices, while the low Mg composition level ensures that selected ZnO properties useful for sensors development, such as piezoelectricity, are retained. Compound 1 was bound to the MgZnOnano surface through the carboxylic acid group, leaving the azido group available for click chemistry and as a convenient infrared spectroscopy (IR) probe. The progress of the functionalization with 1 was characterized by FTIR microscopic imaging as a function of binding time, solvents employed, and MgZnOnano morphology. Binding of 1 was most stable in solutions of 3-methoxypropionitrile (MPN), a non-protic polar solvent. This occurred first in μm-scale islands, then expanded to form a rather uniform layer after 22 h. Binding in alcohols resulted in less homogenous coverage, but the 1/MgZnOnano films prepared from MPN were stable upon treatment with alcohols at room temperature. The binding behavior was significantly dependent on the surface morphology of MgZnOnano.