Chemical Infiltration during Atomic Layer Deposition: Metalation of Porphyrins as Model Substrates

Abstract

Atomic layer deposition (ALD) is a gas-phase deposition process based on successive self-terminating gas-solid reactions. During the process, the template substrate is exposed to precursor molecules from the gas phase, which ideally promotes adsorption of a monolayer on the surface. After purging the excess precursor and subsequent exposure to a second gaseous precursor, reaction on the surface of the substrate leads to formation of a layer of the desired material. The layer thickness is controlled by the number of the reaction cycles. Owing to the precise thickness control and broad range of operating temperatures, ALD has recently been used for coating various structures, including thermally and chemically sensitive organic and biological macromolecules. [1][2][3] Much work has also been performed to develop new precursors and new processes to increase the versatility of ALD. For example, a number of studies have been devoted to the investigation of the interface chemistry during the deposition process to achieve better control over the deposition rate and the area selectivity of the deposition. Several reviews about ALD have been recently published. [4][5][6] To date, only little attention has been paid to the chemical interactions between the precursors and the substrate underneath the macroscopic interface formed during the ALD process. It is essential to understand such interactions, particularly as an increasing number of organic soft materials are being used in ALD processes to fulfill various tasks: for example, as masks for area-selective deposition, [1] scaffolds for hybrid material fabrication, [7] or templates for the fabrication of nanostructures.[8] Such materials normally contain various functional groups that are potentially reactive with ALD precursors. Precursors can diffuse through polymer layers during the ALD process, but the chemical interactions between the precursors and the substrate during the diffusion process has only been proposed. [3,9] Herein, we use J-aggregate nanostructures composed of meso-tetra(p-phenylsulfonato)porphyrin (TSPP) or meso-tetraphenylporphyrin (H 2 TPP) as model substrates for standard metal oxide ALD, and show for the first time that the precursor can infiltrate the substrate at the molecular level and induce site-specific metalation. Self-assembly of protonated TSPP molecules into J-aggregate nanotapes occurs through electrostatic interactions between the negatively charged sulfonato groups and positively charged pyrrole amine groups, [10] which are also potential active sites for interactions with ALD precursors. Moreover, the protonated and deprotonated monomer and the J-aggregate of TSPP have distinct light absorption profiles, [11] which provides a convenient method for analysis. Specifically, we show that processing the J-aggregates with standard ZnO-ALD results in infiltration of the metal precursor diethylzinc into the TSPP J-aggregates and induces metalation of TSPP molecules with zinc(II) ions. Formation of the metalloporphyrins was confirmed by UV/Vis...

SCIP: a new simultaneous vapor phase coating and infiltration process for tougher and UV-resistant polymer fibers

“…This is in-line with the observations from the ngerprint area where Al is more efficiently binding to C]O than Zn, which on the other hand has a stronger affinity to N-H than Al. 27 Thus, in agreement with the conclusions extracted from the mechanical data, the alumina processes are more strongly degrading the polymer chains, while covalent cross-linking of the Kevlar chains is more pronounced in the SCIP sample, which is further conrmed with X-ray diffraction (Fig. 4C).…”

In vacuo interfacial tetrapyrrole metallation

“…42 Such metallation or demetallation reactions are not restricted to silver surfaces, but are also reported for more complex supports as sodium hectorate 43 or metal oxides grown via atomic layer deposition and thus play a considerable role in chemistry, organic photovoltaics, nanoscience and materials engineering. 44,45 Beyond metallation reactions, demetallation and transmetallation processes are well documented in solution and utilized to rank metallotetrapyrroles regarding their stability. 46 Interestingly, the exploration of analogous procedures on surfaces is just in its infancy.…”

Mesoscale Integration in Titania/J‐Aggregate Hybrid Nanofibers

“…[19][20][21][22][23][24] In each case, the underlying structural motif is based on a "spread deck of cards" conformation or "staircase" arrangement of porphyrin monomers that gives rise to stacked supramolecular arrays with an average diameter of 1.7-2 nm, and which subsequently self-organize into higher-order J-aggregate superstructures to produce nanorods, nanotapes, or nanotubes with typical widths and lengths of 20-30 nm and several micrometers, respectively. [22,23] Significantly, recent studies have exploited anisotropic TPPS nanoparticles as template-directing agents to produce electrically conducting core-shell J-aggregate/polymer nanotubes, [25,26] metal nanowires, [27,28] optically responsive silica-coated J-aggregate nanotapes, [29] zinc-metalated nanotapes, [30] and J-aggregate nanotubes encased within ultrathin inorganic oxide layers of Al 2 O 3 or TiO 2 .[30] Whilst the above examples clearly highlight the versatility of integrating 20-30 nm-wide rods and tapes of TPPS into nanocomposite objects, transcription or encasement of the individual 1.7 nm-thick filaments of the primary J-aggregate stacked superstructure to produce functional hybrid nanomaterials with high spatial resolution remains unexplored. Herein, we describe a facile procedure for producing titania/ J-aggregate nanorods and nanotapes that comprise an internally ordered hybrid mesostructure of co-aligned columnar arrays of [H 4 TPPS] 2À ions in which individual stacks of the porphyrin molecules are encased with oligomers of hydrolyzed/condensed titanium(IV) hydroxy/oxo species.…”