Atomic Layer Deposition of TiO2 to Bond Free-Standing Nanoporous Alumina Templates to Gold-Coated Substrates as Planar Optical Waveguide Sensors

We demonstrate a method to intimately bond a free-standing nanoporous anodic aluminum oxide (AAO) template onto a piece of gold-coated high reflective index glass (LaSFN9) substrate by an atomic layer deposition (ALD) technique. The capability of ALD as nanoglue is well demonstrated by the optical waveguide behavior of the bonded sample. We monitored the optical behavior before and after ALD of TiO2 with no exciting waveguide modes in the sample before ALD. Quantitative analysis of the ALD TiO2 thickness layer using the Fresnel calculation is in good agreement with the expected growth rate of the ALD setup. The subangstrom sensitivity of the waveguide sensor for bio- or chemical sensing is demonstrated with bovine serum albumin (BSA) adsorption/desorption processes at various pH values. Furthermore, a layer-by-layer polyelectrolyte multilayer deposition is performed to distinguish processes that occurred inside and outside the nanopores. This novel function of ALD as nanoglue finds a wide range of applications in areas such as bonding or adhering nanostructures to various substrates.