Plasma assisted deposition of single and multistacked TiO₂ hierarchical nanotube photoanodes

Abstract

We present herein an evolved methodology for the growth of nanocrystalline hierarchical nanotubes combining physical vapor deposition of organic nanowires (ONWs) and plasma enhanced chemical vacuum deposition of anatase TiO 2 layers. The ONWs act as vacuum removable 1D and 3D templates, occurring the whole process at temperatures ranging from RT to 250 ºC. As result, a high density of hierarchical nanotubes with tunable diameter, length and tailored walls microstructures are formed on a variety of processable substrates as metal and metal oxides films or nanoparticles including transparent conductive oxides. The reiteration of the process leads to the development of an unprecedented 3D nanoarchitecture formed by stacking layers of hierarchical TiO 2 nanotubes. As a proof of concept, we present the superior performance of the 3D nanoarchitecture as photoanode within an excitonic solar cell with efficiencies as high as 4.69% for nominal thickness of the anatase layer below 2.75 um. Mechanical stability and straightforward implementation in devices are at the same time demonstrated. The process is extendable to other functional oxides fabricated by plasma-assisted methods with readily applications in energy harvesting and storage, catalysis and nanosensing.

Supported Porous Nanostructures Developed by Plasma Processing of Metal Phthalocyanines and Porphyrins

“…In this section, we will show the extension of the results above to a soft-template method for the fabrication of core@shell nanowires and nanotubes. Such a method has been developed during the last years for the synthesis of supported and on-device nanowires and nanotubes with applications as superhydrophobic and antifreezing surfaces, nanoscale waveguides, nanosensors, excitonic solar cell photoelectrodes, and piezoelectric nanogenerators (Borras et al, 2009;Macias-Montero et al, 2013Filippin et al, 2017bFilippin et al, , 2019Alcaire et al, 2019b). Scheme 2 presents the main steps for the fabrication of these hierarchical nanostructures.…”

“…Metal and metal oxide thin films and nanoparticles deposited on a substrate as well as polymeric and organic surfaces have been demonstrated as suitable nucleation centers for the formation of small-molecule organic nanowires. In our previous articles (Borras et al, 2008(Borras et al, , 2009(Borras et al, , 2010Macias-Montero et al, 2013Filippin et al, 2017bFilippin et al, , 2019Alcaire et al, 2019b) we have optimized the process for Au, Ag, ITO, ZnO, TiO 2 , SiO 2 , PDMS, and organic substrates (Step i) and molecules as metal -porphyrins, -phthalocyanines and perylenes working as the nanowires building blocks (Step ii). Scheme 2 right shows SEM images of the different steps during the formation of the core@shell nanowires.…”

“…Nevertheless, the organic core can be easily removed by annealing at mild temperatures during the formation of the shell or in a post-processing step as it is shown in the STEM micrograph in Figure 6d. The removal of the organic core leaves square or rectangular inner tubes with extremely flat walls (Filippin et al, 2017b;Macias-Montero et al, 2017). In addition, in concordance with the results regarding the thin film counterparts, once the hybrid core@shell nanowires are formed, we can apply the soft-plasma etching post-processing SCHEME 2 | Steps for the formation process of the hierarchical core@shell nanostructures (left) and SEM micrographs characteristic of every step (right): (i) Deposition of metal nanoparticles or oxide thin film as nucleation centres.…”

Hierarchical Nanostructures of Titanium Dioxide: Synthesis and Applications

“…Flipin et al [76] grew hierarchical TiO 2 nanotubes by plasma-enhanced chemical vapor deposition technique. Porphyrins and phthalocyanines were used as cost-effective precursor molecules.…”

One-reactor plasma assisted fabrication of ZnO@TiO 2 multishell nanotubes: assessing the impact of a full coverage on the photovoltaic performance

“…In a recent work, we addressed the fabrication of ZnO nanotubes by an all-vacuum template procedure 1 . The protocol involves 3 basic steps: (i) growth of single crystal organic nanowires (ONWs) by Physical Vapor Deposition (OPVD) 2 acting as supported 1D templates; (ii) formation of a metal oxide shell by Plasma Enhanced Chemical Vapor Deposition (PECVD) 3 , 4 and, (iii) sublimation of the organic template to yield metal oxide nanotubes. We aim herein to extend the potential of the developed protocol for the fabrication of multishell ZnO@TiO 2 nanotubes.…”