Precise Synthesis and Thin Film Self-Assembly of PLLA-b-PS Bottlebrush Block Copolymers

The ability of bottlebrush block copolymers (BBCPs) to self-assemble into ordered large periodic structures could greatly expand the scope of photonic and membrane technologies. In this paper, we describe a two-step synthesis of poly(l-lactide)-b-polystyrene (PLLA-b-PS) BBCPs and their rapid thin-film self-assembly. PLLA chains were grown from exo-5-norbornene-2-methanol via ring-opening polymerization (ROP) of l-lactide to produce norbornene-terminated PLLA. Norbonene-terminated PS was prepared using anionic polymerization followed by a termination reaction with exo-5-norbornene-2-carbonyl chloride. PLLA-b-PS BBCPs were prepared from these two norbornenyl macromonomers by a one-pot sequential ring opening metathesis polymerization (ROMP). PLLA-b-PS BBCPs thin-films exhibited cylindrical and lamellar morphologies depending on the relative block volume fractions, with domain sizes of 46–58 nm and periodicities of 70–102 nm. Additionally, nanoporous templates were produced by the selective etching of PLLA blocks from ordered structures. The findings described in this work provide further insight into the controlled synthesis of BBCPs leading to various possible morphologies for applications requiring large periodicities. Moreover, the rapid thin film patterning strategy demonstrated (>5 min) highlights the advantages of using PLLA-b-PS BBCP materials beyond their linear BCP analogues in terms of both dimensions achievable and reduced processing time.

In Situ Scanning X-Ray Diffraction Reveals Strain Variations in Electrochemically Grown Nanowires

<p><a>Templated electrochemical growth in nanoporous alumina can be used to fabricate nanowires with applications in magnetic storage devices, hydrogen sensors, and electrocatalysis. It is known that nanowires, grown in such templates, are strained. The strain in nanoscale materials can influence their performance in applications such as catalysts and electronic devices. However, it is not well established how the nanoporous template affects the lattice strain in the nanowires and how this develops during the growth process due to the lack of non-destructive <i>in situ </i>studies with spatial resolution. Here we have measured the strain and grain size of palladium nanowires in nanoporous templates during the growth process. For this we performed <i>in situ</i> scanning x-ray diffraction with a submicron focused x-ray beam. We found that there is a tensile strain in the nanowires and that it is more pronounced along the growth direction than in the confined direction of the templates. The tensile strain measured <i>in situ</i> is higher than previous <i>ex situ </i>reports, possibly due to hydrogen absorption during the growth. With the spatial information made possible with the focused synchrotron x-ray beam we could observe local variations in strain as a function of height. A region of local strain variation is found near the bottom of the nanowires where growth is initiated in branches at the pore bottoms. Knowledge of how nanoporous templates influence the strain of the nanowires may allow for atomic scale tailoring of the catalytic activity of such nanowires or minimizing strain to optimize electronic device performance. </a></p>

In Situ Scanning X-Ray Diffraction Reveals Strain Variations in Electrochemically Grown Nanowires

<p><a>Templated electrochemical growth in nanoporous alumina can be used to fabricate nanowires with applications in magnetic storage devices, hydrogen sensors, and electrocatalysis. It is known that nanowires, grown in such templates, are strained. The strain in nanoscale materials can influence their performance in applications such as catalysts and electronic devices. However, it is not well established how the nanoporous template affects the lattice strain in the nanowires and how this develops during the growth process due to the lack of non-destructive <i>in situ </i>studies with spatial resolution. Here we have measured the strain and grain size of palladium nanowires in nanoporous templates during the growth process. For this we performed <i>in situ</i> scanning x-ray diffraction with a submicron focused x-ray beam. We found that there is a tensile strain in the nanowires and that it is more pronounced along the growth direction than in the confined direction of the templates. The tensile strain measured <i>in situ</i> is higher than previous <i>ex situ </i>reports, possibly due to hydrogen absorption during the growth. With the spatial information made possible with the focused synchrotron x-ray beam we could observe local variations in strain as a function of height. A region of local strain variation is found near the bottom of the nanowires where growth is initiated in branches at the pore bottoms. Knowledge of how nanoporous templates influence the strain of the nanowires may allow for atomic scale tailoring of the catalytic activity of such nanowires or minimizing strain to optimize electronic device performance. </a></p>

Sensing Ability of Ferroelectric Oxide Nanowires Grown in Templates of Nanopores

Nanowires of ferroelectric potassium niobate were grown by filling nanoporous templates of both side opened anodic aluminum oxide (AAO) through radiofrequency vacuum sputtering for multisensor fabrication. The precise geometrical ordering of the AAO matrix led to well defined single axis oriented wire-shaped material inside the pores. The sensing abilities of the samples were studied and analyzed in terms of piezoelectric and pyroelectric response and the results were compared for different length of the nanopores (nanotubes)—1.3 µm, 6.3 µm and 10 µm. Based on scanning electronic microscopy, elemental and microstructural analyses, as well as electrical measurements at bending and heating, the overall sensing performance of the devices was estimated. It was found that the produced membrane type elements, consisting potassium niobate grown in AAO template exhibited excellent piezoelectric response due to the increased specific area as compared to non-structured films, and could be further enhanced with the nanowires length. The piezoelectric voltage increased linearly with 16 mV per micrometer of nanowire’s length. At the same time the pyroelectric voltage was found to be less sensitive to the nanowires length, changing its value at 400 nV/µm. This paper provides a simple and low-cost approach for nanostructuring ferroelectric oxides with multisensing application, and serves as a base for further optimization of template based nanostructured devices.

Progress in Nanoporous Templates: Beyond Anodic Aluminum Oxide and Towards Functional Complex Materials

Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry.