Davor Copic

There is a need for direct-write patterning alternatives to support trends in low-volume and late-stage manufacturing of devices and integrating sensors directly to existing products or formed materials. This is particularly challenging when trying to take advantage of the sensing properties linked to vertically aligned carbon nanotube forests. The catalyst layer thickness is a critical parameter when growing these forests by chemical vapor deposition, as it determines the size of catalyst nano-islands that form and act as seeds for nanotube growth. Physical vapor deposition is a standard technique for catalyst deposition, with photolithography used across the literature to pattern layers of catalyst and enable device design. However, wide-area direct-write techniques face a major barrier in reliably controlling layer thickness to the nanoscale precision required. In this paper, we combine deposition of iron oxide nanoparticles by the direct-write technique of inkjet printing with material removal by laser ablation to deliver both patterning and fine control of the layer thickness. First, we show that there is an optimum printed layer thickness to ensure a good quality forest growth and second that laser ablation can be used to enhance, reduce, or stop this growth. Detailed analysis of the catalyst with AFM, sXRD, and electron microscopy shows that these controls stem from their influence over nano-island formation of the catalyst at the start of the CVD process. Finally, we demonstrate the potential for applications by fabricating a simple gas sensor with this hybrid approach.

A challenge is to integrate Cu with carbon nanotubes (CNTs) and form a free‐standing composite wire. This is achieved by first making a CNT filament using high concentration (20 g L⁻¹ ) CNT dispersion, an acid‐free wet spinning process and then by replacing the polymer with copper using heat based polymer decomposition and periodic pulse reverse electroplating. It is demonstrated that indeed the specific conductivity and the current‐carrying capability (or ampacity) are increased manifold. The multiwalled CNT (MWCNT)/Cu composite wires developed in this paper have electrical conductivity σ ≈ 5.5 × 10 5 S cm⁻¹. These MWCNT/Cu wires are 2/3rd the weight of bulk Cu wires. Their specific electrical conductivity is σ_ρ ≈ 9.38 ×10 4 S cm² g⁻¹ which is 45% higher than International Annealed Copper Standard Cu. These composite wires have an ampacity of A ≈ 20 × 10⁵ and 4 × 10⁵ A cm⁻² for 1.5 and 17 mm gauge length wires, respectively, which is four to six times higher than pure Cu depending on the wire lengths. MWCNTs volume percentage in the MWCNT/Cu wire is about 40%.

Advances in the synthesis and assembly of nanomaterials offer a unique opportunity to purposefully design nanoparticle structures for a specific applications. Here 3D carbon nanotube structures are coated with BiVO₄ for solar water splitting.

Controlling the arrangement and interface of nanoparticles is essential to achieve good transfer of charge, heat, or mechanical load. This is particularly challenging in systems requiring hybrid nanoparticle mixtures such as combinations of organic and inorganic materials. This work presents a process to coat vertically aligned carbon nanotube (CNT) forests with metal oxide nanoparticles using microwave‐assisted hydrothermal synthesis. Hydrothermal processes normally damage delicate CNT forests, which is addressed here by a combination of lithographic patterning, transfer printing, and reduction of the synthesis time. This process is applied for the fabrication of structured Li‐ion battery (LIB) electrodes where the aligned CNTs provide a straight electron transport path through the electrode and the hydrothermal coating process is used to coat the CNTs with conversion anode materials for LIBs. These nanoparticles are anchored on the surface of the CNTs and batteries fabricated following this process show a fourfold longer cyclability. Finally, this process is used to create thick electrodes (350 µm) with a gravimetric capacity of over 900 mAh g⁻¹.

Microfluidic diffusional sizing is combined with synchrotron radiation circular dichroism to resolve the secondary structure of protein mixtures.

Carbon nanotube (CNT)‐based filters have the potential to revolutionize water treatment because of their high capacity and fast kinetics in sorption of organic, inorganic, and biological pollutants. To date, CNT filters either rely on CNTs dispersed in liquids, which are difficult to recover and cause safety concerns, or on CNT buckypaper, which offers high efficiency, but suffers from an intrinsic trade‐off between filter permeability and capacity. Here, a new approach is presented that bypasses this trade‐off and achieves buckypaper‐like efficiency combined with filter‐column‐like permeability and capacity. For this, CNTs are first assembled into porous microspheres and then are packed into microfluidic column filters. These microcolumns exhibit large flow‐through filtration efficiencies, while maintaining membrane permeabilities an order of magnitude larger then CNT buckypaper and specific permeabilities double that of activated carbon for similar flowrates (232 000 L m⁻² h⁻¹ bar⁻¹, 1.23 × 10⁻¹² m²). Moreover, in a test to remove sodium dodecyl sulfate (SDS) from water, these microstructured CNT columns outperform activated carbon columns. This improved filtration efficiency and permeability is an important step toward a broader implementation of CNT‐based filtration devices.

Electrogenic cells such as cardiomyocytes and neurons rely mainly on electrical signals for intercellular communication. Microelectrode arrays (MEAs) have been developed for long‐term recording of cell signals and stimulation of electrogenic cells under low‐cell‐stress conditions, providing new insights in the behavior of electrogenic cells and the operation of the brain. To date, MEAs are relying on flat or needle‐shaped electrode surfaces, mainly due to limitations in the lithographic processes. This paper relies on a previously reported elasto‐capillary aggregation process to create 3D carbon nanotube (CNT) MEAs. This study shows that CNTs aggregate in well‐shaped structures of similar size as cardiomyocytes are particularly interesting for MEA applications. This is because i) CNT microwells of the right diameter preferentially trap individual cardiomyocytes, which facilitates single cell recording without the need for clamping cells or signal deconvolution, and ii) once the cells are trapped inside of the CNT wells, this 3D CNT structure is used as an electrode surrounding the cell, which increases the cell–electrode contact area. As a result, this study finds that the recorded output voltages increase significantly (more than 200%). This fabrication process paves the way for future study of complex interactions between electrogenic cells and 3D recording electrodes.

Access to clean water is fundamental to maintain the basic standards of public health. The World Bank is estimating over a billion individuals lacking access to potable water, causing millions of deaths annually. Only few point-of-use technologies are available providing efficient removal of pollutants and pathogens. Hence there is a critical need to develop low-cost, sustainable and highly effective filtration technologies essential for undeveloped countries lacking water treatment infrastructures. Since the Middle Ages, people have been using charcoal to filter water because of its exceptional ability to adsorb contaminants. With the advent of nanotechnology, new forms of carbon have been discovered (i.e. carbon nanotubes, CNTs), which have demonstrated impressive sorption capacities, and more spectacularly, have found to be able to efficiently remove viruses and bacteria from water. Unfortunately, methods need to be developed to organize CNTs into highly structured and well-understood materials for safe and efficient implementation in filtration devices. Herein we report an unprecedented sequential engineering of the architecture of CNT materials by combining emulsification methods with colloidal self-assembly. This approach allows preparation of well-defined spherical CNT supraparticles, which upon assembly, give rise to a filter whose porosity and density can be precisely engineered, allowing full exploitation of the impressive decontaminating action of CNTs.

An advanced battery architecture composed of 3D carbon nanotube (CNT) current collectors is used to mitigate stresses in flexible batteries. On Page 6705, C. George, M. De Volder, and co-workers describe the fabrication process and characteristics of this new generation of ultraflexible batteries, which show high rate and cyclablility. These batteries may find applications in the powering of flexible displays and logics.

The flexible batteries that are needed to power flexible circuits and displays remain challenging, despite considerable progress in the fabrication of such devices. Here, it is shown that flexible batteries can be fabricated using arrays of carbon nanotube microstructures, which decouple stress from the energy-storage material. It is found that this battery architecture imparts exceptional flexibility (radius ≈ 300 μm), high rate (20 A g⁻¹), and excellent cycling stability.