Additive Manufacturing of Electrically Conductive Multi-Layered Nanocopper in an Air Environment.

The additive manufacturing (AM) of functional copper (Cu) parts is a major goal for many industries, from aerospace to automotive to electronics, because Cu has a high thermal and electrical conductivity as well as being ~10× cheaper than silver. Previous studies on AM of Cu have concentrated mainly on high-energy manufacturing processes such as Laser Powder Bed Fusion, Electron Beam Melting, and Binder Jetting. These processes all require high-temperature heat treatment in an oxygen-free environment. This paper shows an AM route to multi-layered microparts from novel nanoparticle (NP) Cu feedstocks, performed in an air environment, employing a low-power (<10 W) laser sintering process. Cu NP ink was deposited using two mechanisms, inkjet printing, and bar coating, followed by low-power laser exposure to induce particle consolidation. Initial parts were manufactured to a height of approximately 100 µm, which was achieved by multi-layer printing of 15 (bar-coated) to 300 (inkjetted) layers. There was no evidence of oxidised copper in the sintered material, but they were found to be low-density, porous structures. Nonetheless, electrical resistivity of ~28 × 10-8 Ω m was achieved. Overall, the aim of this study is to offer foundational knowledge for upscaling the process to additively manufacture Cu 3D parts of significant size via sequential nanometal ink deposition and low-power laser processing.

Low-voltage 2D materials-based printed field-effect transistors for integrated digital and analog electronics on paper.

Paper is the ideal substrate for the development of flexible and environmentally sustainable ubiquitous electronic systems, which, combined with two-dimensional materials, could be exploited in many Internet-of-Things applications, ranging from wearable electronics to smart packaging. Here we report high-performance MoS2 field-effect transistors on paper fabricated with a "channel array" approach, combining the advantages of two large-area techniques: chemical vapor deposition and inkjet-printing. The first allows the pre-deposition of a pattern of MoS2; the second, the printing of dielectric layers, contacts, and connections to complete transistors and circuits fabrication. Average ION/IOFF of 8 × 103 (up to 5 × 104) and mobility of 5.5 cm2 V-1 s-1 (up to 26 cm2 V-1 s-1) are obtained. Fully functional integrated circuits of digital and analog building blocks, such as logic gates and current mirrors, are demonstrated, highlighting the potential of this approach for ubiquitous electronics on paper.

Graphene oxide nanosheets modulate spinal glutamatergic transmission and modify locomotor behaviour in an in vivo zebrafish model.

Graphene oxide (GO), an oxidised form of graphene, is widely used for biomedical applications, due to its dispersibility in water and simple surface chemistry tunability. In particular, small (less than 500 nm in lateral dimension) and thin (1-3 carbon monolayers) graphene oxide nanosheets (s-GO) have been shown to selectively inhibit glutamatergic transmission in neuronal cultures in vitro and in brain explants obtained from animals injected with the nanomaterial. This raises the exciting prospect that s-GO can be developed as a platform for novel nervous system therapeutics. It has not yet been investigated whether the interference of the nanomaterial with neurotransmission may have a downstream outcome in modulation of behaviour depending specifically on the activation of those synapses. To address this problem we use early stage zebrafish as an in vivo model to study the impact of s-GO on nervous system function. Microinjection of s-GO into the embryonic zebrafish spinal cord selectively reduces the excitatory synaptic transmission of the spinal network, monitored in vivo through patch clamp recordings, without affecting spinal cell survival. This effect is accompanied by a perturbation in the swimming activity of larvae, which is the locomotor behaviour generated by the neuronal network of the spinal cord. Such results indicate that the impact of s-GO on glutamate based neuronal transmission is preserved in vivo and can induce changes in animal behaviour. These findings pave the way for use of s-GO as a modulator of nervous system function.

Raman Fingerprints of Graphene Produced by Anodic Electrochemical Exfoliation.

Electrochemical exfoliation is one of the most promising methods for scalable production of graphene. However, limited understanding of its Raman spectrum as well as lack of measurement standards for graphene strongly limit its industrial applications. In this work, we show a systematic study of the Raman spectrum of electrochemically exfoliated graphene, produced using different electrolytes and types of solvents in varying amounts. We demonstrate that no information on the thickness can be extracted from the shape of the 2D peak as this type of graphene is defective. Furthermore, the number of defects and the uniformity of the samples strongly depend on the experimental conditions, including postprocessing. Under specific conditions, the formation of short conductive trans-polyacetylene chains has been observed. Our Raman analysis provides guidance for the community on how to get information on defects coming from electrolyte, temperature, and other experimental conditions, by making Raman spectroscopy a powerful metrology tool.

Inkjet-printed graphene Hall mobility measurements and low-frequency noise characterization.

We report room temperature Hall mobility measurements, low temperature magnetoresistance analysis and low-frequency noise characterization of inkjet-printed graphene films on fused quartz and SiO2/Si substrates. We found that thermal annealing in vacuum at 450 °C is a necessary step in order to stabilize the Hall voltage across the devices, allowing their electrical characterization. The printed films present a minimum sheet resistance of 23.3 Ω sq-1 after annealing, and are n-type doped, with carrier concentrations in the low 1020 cm-3 range. The charge carrier mobility is found to increase with increasing film thickness, reaching a maximum value of 33 cm2 V-1 s-1 for a 480 nm-thick film printed on SiO2/Si. Low-frequency noise characterization shows a 1/f noise behavior and a Hooge parameter in the range of 0.1-1. These results represent the first in-depth electrical and noise characterization of transport in inkjet-printed graphene films, able to provide physical insights on the mechanisms at play.

Flexible, Print-in-Place 1D-2D Thin-Film Transistors Using Aerosol Jet Printing.

Semiconducting carbon nanotubes (CNTs) printed into thin films offer high electrical performance, significant mechanical stability, and compatibility with low-temperature processing. Yet, the implementation of low-temperature printed devices, such as CNT thin-film transistors (CNT-TFTs), has been hindered by relatively high process temperature requirements imposed by other device layers-dielectrics and contacts. In this work, we overcome temperature constraints and demonstrate 1D-2D thin-film transistors (1D-2D TFTs) in a low-temperature (maximum exposure ≤80 °C) full print-in-place process (i.e., no substrate removal from printer throughout the entire process) using an aerosol jet printer. Semiconducting 1D CNT channels are used with a 2D hexagonal boron nitride (h-BN) gate dielectric and traces of silver nanowires as the conductive electrodes, all deposited using the same printer. The aerosol jet-printed 2D h-BN films were realized via proper ink formulation, such as utilizing the binder hydroxypropyl methylcellulose, which suppresses redispersion between adjacent printed layers. In addition to an ON/OFF current ratio up to 3.5 × 105, channel mobility up to 10.7 cm2·V-1·s-1, and low gate hysteresis, 1D-2D TFTs exhibit extraordinary mechanical stability under bending due to the nanoscale network structure of each layer, with minimal changes in performance after 1000 bending test cycles at 2.1% strain. It is also confirmed that none of the device layers require high-temperature treatment to realize optimal performance. These findings provide an attractive approach toward a cost-effective, direct-write realization of electronics.

All-2D Material Inkjet-Printed Capacitors: Toward Fully Printed Integrated Circuits.

A well-defined insulating layer is of primary importance in the fabrication of passive ( e.g., capacitors) and active ( e.g., transistors) components in integrated circuits. One of the most widely known two-dimensional (2D) dielectric materials is hexagonal boron nitride (hBN). Solution-based techniques are cost-effective and allow simple methods to be used for device fabrication. In particular, inkjet printing is a low-cost, noncontact approach, which also allows for device design flexibility, produces no material wastage, and offers compatibility with almost any surface of interest, including flexible substrates. In this work, we use water-based and biocompatible graphene and hBN inks to fabricate all-2D material and inkjet-printed capacitors. We demonstrate an areal capacitance of 2.0 ± 0.3 nF cm-2 for a dielectric thickness of ∼3 µm and negligible leakage currents, averaged across more than 100 devices. This gives rise to a derived dielectric constant of 6.1 ± 1.7. The inkjet printed hBN dielectric has a breakdown field of 1.9 ± 0.3 MV cm-1. Fully printed capacitors with sub-micrometer hBN layer thicknesses have also been demonstrated. The capacitors are then exploited in two fully printed demonstrators: a resistor-capacitor (RC) low-pass filter and a graphene-based field effect transistor.