Selective-area ALD for positively and negatively charged layers into the ion-beam track-etched conical pores in polyethylene terephthalate

This paper presents the strategy of selective-area growing of a positively-charged layer of Al2O3 and the negatively-charged layer of HfO2 on ion beam track-etched polyethylene terephthalate (PET) nanotubes through the thermal atomic layer deposition (T-ALD) technique. We used the self-assembled monolayer of octadecyl trichlorosilane (OTS-SAMs) on the surface to serve as a passivation layer and then selectively deposited the Al2O3 and HfO2 in the nanotubes. The influence of the dipping time of the substrates in the OTS solution and the experimental conditions on the roughness and the thickness of the OTS monolayer have been investigated. X-ray photoelectron spectroscopy (XPS) was used to analyze the composition of the ALD Al2O3 and HfO2 films. Atomic force microscope (AFM) and scanning electron microscope (SEM) were employed to study the morphologies before and after the ALD of Al2O3 and HfO2. The I-V characteristics of the film confirmed the surface charge polarities in the nanotubes, i.e. the positively-charged Al2O3 and negatively-charged HfO2, in the electrically-neutral solution. The results will aid surface modification and functionalization of PET by nanotubes.