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Self-assembly of organic molecules within oxide nanostructures

Subject Area Physical Chemistry of Solids and Surfaces, Material Characterisation
Coating and Surface Technology
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 410554859
 
Final Report Year 2024

Final Report Abstract

Nanoporous oxides find application in areas ranging from bioactive coatings to high surface area electrodes. For enhancement of the functionality, the nanostructure can be modified with organic self-assembled monolayers or filled with functional components. This project addresses current challenges in loading and especially in the characterization of such interlaced organic-inorganic nanoarchitectures. Several analytical approaches based on time-of-flight secondary ion mass spectrometry (ToF-SIMS) were compared to achieve artefact-less chemical maps of the depth distribution of organic molecules within metal oxide nanostructures. ToF-SIMS can provide chemical information about the material composition, in mapping the obtainable resolution is ~200 nm, while in depth profiling a depth resolution down to 1 nm is achievable. Regular depth profiling in a dual beam approach yielded surprisingly clear information about the location of the organics, push-on effects were observed but minimal. However, the depth information is restricted to small characteristic fragments, especially such containing heteroatoms, and thus may yield ambiguous information in the case of multicomponent systems. Two other approaches were followed, cross section mapping (CSM) and SIMS mapping of the inclined slope of a focused ion-beam cut (FIB&SIMS). While CSM, in which an ion milled cross section of the hybrid nanoarchitecture is analyzed in SIMS mapping, yields data that can be interpreted easily, the technique is only applicable to thicker layers, due to the resolution limit of the ToF-SIMS. In a FIB’n’SIMS approach we were able to produce a very shallow inclined slope, virtually stretching out the cross-section, and, thus, leading to a well resolved chemical image of the organic depth distribution within the nanoarchitecture. Nanostructures of ZrO2 and NiO were in the focus of this project. A library of anodization parameters for ZrO2 nanotubes and NiO nanosponge with varying diameters and thickness produced without HF etching treatments was established. Structurally modulated “bottleneck” ZrO2 nanotubes were developed to control the release kinetics of loaded compounds from the nanoarchitecture. Heterogeneous molecule depth distributions were obtained by combining different modification methods, e.g., filling by immersion and modifying the openings of the pores by microcontact printing and led to a drug release system that reacts to external stimulus. The transfer of such readily modified nanoarchitectures to non-anodizable surfaces, e.g., drug release coatings on ceramic implants or encapsulated dye-sensitized solar cells on concrete, was additionally investigated to produce sophisticated surface functionality. It was, furthermore, observed that no generally valid filling protocol for all oxide nanoarchitectures is applicable, the infiltration depends on the chemical composition of both organic compound and oxide and can be tuned by chemically altering the oxide nanostructure.

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