Modification of the Surface Properties of AlxGa1–xN Substrateswith Gradient Aluminum Composition Using Wet Chemical Treatments

摘要

The surface properties of biomolecular gradients are widely known to be important for controlling cell dynamics, but there is a lack of platforms for studying them in vitro using inorganic materials. The changes in various surface properties of an AlxGa1–xN film (0.173 ≤ x ≤ 0.220) with gradient aluminum content were quantified to demonstrate the ability to modify interfacial characteristics. Four wet chemical treatments were used to modify the surface of the film: (i) oxide passivation by hydrogen peroxide, (ii) two-step functionalization with a carboxylic acid following hydrogen peroxide pretreatment, (iii) phosphoric acid etch, and (iv) in situ functionalization with a phosphonic acid in phosphoric acid. The characterization confirmed changes in the topography, nanostructures, and hydrophobicity after chemical treatment. Additionally, X-ray photoelectron spectroscopy was used to confirm that the chemical composition of the surfaces, in particular, Ga2O3 and Al2O3 content, was dependent on both the chemical treatment and the Al content of the gradient. Spectroscopic evaluation showed red shifts in strain-sensitiveRaman peaks as the Al content gradually increased, but the same peaksblue-shifted after chemical treatment. Kelvin probe force microscopymeasurements demonstrated that one can modify the surface charge usingthe chemical treatments. There were no predictable or controllablesurface charge trends because of the spontaneous oxide-based nanostructuredformations of the bulk material that varied based on treatment andwere defect-dependent. The reported methodology and characterizationcan be utilized in future interfacial studies that rely on water-basedwet chemical functionalization of inorganic materials.