Vacuum template synthesis of multifunctional nanotubes with tailored nanostructured walls

Abstract

A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a post-annealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensor.

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

“…12,36−39 In this article, we take advantage of a recently developed method consisting of the alignment of the ONWs driven by electrostatic interaction with the plasma-sheath electric field. 19,21,28 The protocol involves the formation of an inorganic shell that acts as a scaffold that maintains the vertical orientation of the ONWs once the plasma is switched off. In practice, the FePcCl and FePc ONWs reach vertical alignment by growing by PECVD 40 a SiO 2 conformal shell.…”

“…For this, Si(100) wafers and fused silica slides were coated in three ways: (a) with Al by thermal evaporation in high vacuum, (b) with Cu by oblique angle deposition (OAD), 44 and (c) with a thin layer of mesoporous TiO 2 deposited by PECVD. 21 These methods yielded nanostructured films or nanoparticles with mean size in the range of 100 nm when the thickness was settled below the percolation limit. These systems served as nucleation centers for the preferential condensation of the molecule.…”

“…A conformal SiO 2 shell was formed by plasma-enhanced chemical vapor deposition (PECVD), using a microwave (2.45 MHz) ERC reactor in a downstream configuration keeping the substrates at room temperature. 19,21 The precursor (chlorotrimethylsilane, Sigma-Aldrich) was introduced into the chamber through a heated dosing line using a mass flow controller. The microwave plasma source (SLAN, Plasma Consult GmbH) was coupled to the reaction chamber and separated from it by a grounded grid located 10 cm above the sample holder and operated at 600 W. The working gas was 1 × 10 −2 mbar of 100% O 2 .…”

“…A detailed characterization applying high resolution transmission electron microscopy (HREM), selected area electron diffraction (SAED), scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray absorption spectroscopy (XANES/EXAFS), and X-ray photoemission spectroscopy (XPS) is aimed at a thorough elucidation of the structure and composition of the ONWs. In addition, following a protocol recently developed, 19,21,28 we show the vertical alignment of the as-grown FePc and FePcCl ONWs after deposition of a conformal SiO 2 shell by plasma enhanced chemical vapor deposition (PECVD). Both the effect of the Fe(III) cation presence along the NWs structure and their vertical alignment will be addressed regarding their magnetic properties.…”

Plasma assisted deposition of single and multistacked TiO2 hierarchical nanotube photoanodes

“…Scheme 1 and Figure 1 gather the different vacuum and plasma deposition and processing steps involved in the formation of anatase hierarchical nanotubes (HNTs 16,20 In order to provide the formation of crystalline TiO 2 we have applied the conditions reported for the formation of anatase thin films by PECVD. 19 It is important to address that the temperature required for the formation of the anatase layer (250 ºC) is close to the sublimation temperature of the H 2 PC small-molecule.…”