A simple process for the fabrication of large-area CVD graphene based devices via selective in situ functionalization and patterning

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.We report a novel approach for the fabrication of micro- and nano-scale graphene devices via the in-situ plasma functionalization and in-situ lithographic patterning of large-area graphene directly on CVD catalytic metal (Cu) substrates. This enables us to create graphene-based devices in their entirety prior to any transfer processes, simplifying very significantly the device fabrication process and potentially opening up the route to the use of a wider range of target substrates. We demonstrate the capabilities of our technique via the fabrication of a flexible, transparent, graphene/graphene oxide humidity sensor that outperforms a conventional commercial sensor.This work was carried out under the auspices of the EU FP7 project CareRAMM. This project received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 309980. The authors are grateful for helpful discussions with all CareRAMM partners, particularly Prof A. Ferrari and Ms A. Ott at the University of Cambridge, and Dr A. Sebastian and Dr W. Koelmans at IBM Research Zurich. We also gratefully acknowledge the assistance of the National EPSRC XPS User’s Service (NEXUS) at Newcastle University, UK (an EPSRC Mid-Range Facility) in carrying out the XPS measurements and the assistance of Prof S. Russo at the University of Exeter in carrying out humidity sensing measurements. A.M.A. would also like to thank Dr E. Alexeev for useful ideas for this Letter and pleasurable discussions of the result

Humidity‐Controlled Ultralow Power Layer‐by‐Layer Thinning, Nanopatterning and Bandgap Engineering of MoTe2

This is the final version. Available on open access from Wiley via the DOI in this recordA highly effective laser thinning method is demonstrated to accurately control the thickness of MoTe2 layers. By utilizing the humidity present in the ambient atmosphere, multilayered MoTe2 films can be uniformly thinned all the way down to monolayer with layer-by-layer precision using an ultralow laser power density of 0.2 mW µm−2. Localized bandgap engineering is also performed in MoTe2, by creating regions with different bandgaps on the same film, enabling the formation of lateral homojunctions with sub-200 nm spatial resolution. Field-effect transistors fabricated from these thinned layers exhibit significantly improved electrical properties with an order of magnitude increase in on/off current ratios, along with enhancements in on-current and field-effect mobility values. Thinned devices also exhibit the fastest photoresponse (45 µs) for an MoTe2-based visible photodetector reported to date, along with a high photoresponsivity. A highly sensitive monolayer MoTe2 photodetector is also reported. These results demonstrate the efficiency of the presented thinning approach in producing high-quality MoTe2 films for electronic and optoelectronic applications.Office of Naval Research GlobalEngineering and Physical Sciences Research Council (EPSRC)Defence Science and Technology Laborator

Photoconductivity of Few-Layer MoTe2

This is the final version of the paper. Available from metaconferences.org via the URL in this record.A photoconductivity study of few-layer MoTe2 in a field effect transistor (FET) configuration was performed to find the photoresponsivity and photocurrent response of the material. The mechanisms for MoTe2 with no applied gate voltage were found to be dominated by the photovoltaic effect, showing its potential for use in solar cells. Due to the band gap of MoTe2 being 1.1 eV, MoTe2 is a suitable photodetector for optical wavelengths and potentially the near infrared

Multilevel ultrafast flexible nanoscale nonvolatile hybrid graphene oxide-titanium oxide memories

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Graphene oxide (GO) resistive memories offer the promise of low-cost environmentally sustainable fabrication, high mechanical flexibility and high optical transparency, making them ideally suited to future flexible and transparent electronics applications. However, the dimensional and temporal scalability of GO memories, i.e., how small they can be made and how fast they can be switched, is an area that has received scant attention. Moreover, a plethora of GO resistive switching characteristics and mechanisms has been reported in the literature, sometimes leading to a confusing and conflicting picture. Consequently, the potential for graphene oxide to deliver high-performance memories operating on nanometer length and nanosecond time scales is currently unknown. Here we address such shortcomings, presenting not only the smallest (50 nm), fastest (sub-5 ns), thinnest (8 nm) GO-based memory devices produced to date, but also demonstrate that our approach provides easily accessible multilevel (4-level, 2-bit per cell) storage capabilities along with excellent endurance and retention performance-all on both rigid and flexible substrates. Via comprehensive experimental characterizations backed-up by detailed atomistic simulations, we also show that the resistive switching mechanism in our Pt/GO/Ti/Pt devices is driven by redox reactions in the interfacial region between the top (Ti) electrode and the GO layer.This work was carried out under the auspices of the EU FP7 project CareRAMM. This project received funding from the European Union Seventh Framework Programme (FP7/2007- 2013) under grant agreement no. 309980. The authors are grateful for helpful discussions with all CareRAMM partners, particularly Prof. Andrea Ferrari and Ms. Anna Ott at the University of Cambridge, and Drs. Abu Sebastian and Wabe Koelmans at IBM Research Zurich. We also gratefully acknowledge the assistance of the National EPSRC XPS User’s Service (NEXUS) at Newcastle University, U.K. (an EPSRC Mid-Range Facility) in carrying out the XPS measurement

A nonvolatile phase-change metamaterial color display

This is the final version. Available from Wiley via the DOI in this record.Chalcogenide phase-change materials, which exhibit a marked difference in their electrical and optical properties when in their amorphous and crystalline phases and can be switched between these phases quickly and repeatedly, are traditionally exploited to deliver nonvolatile data storage in the form of rewritable optical disks and electrical phase-change memories. However, exciting new potential applications are now emerging in areas such as integrated phase-change photonics, phase-change optical metamaterials/metasurfaces, and optoelectronic displays. Here, ideas from these last two fields are fused together to deliver a novel concept, namely a switchable phase-change metamaterial/metasurface resonant absorber having nonvolatile color generating capabilities. With the phase-change layer, here GeTe, in the crystalline phase, the resonant absorber can be tuned to selectively absorb the red, green, and blue spectral bands of the visible spectrum, so generating vivid cyan, magenta, and yellow pixels. When the phase-change layer is switched into the amorphous phase, the resonant absorption is suppressed and a flat, pseudowhite reflectance results. Thus, a route to the potential development is opened-up of nonvolatile, phase-change metamaterial color displays and color electronic signage.Engineering and Physical Sciences Research Council (EPSRC

Phase-change metadevices for the dynamic and reconfigurable control of light

This is the author accepted manuscript. The final version is available from Optical Society of America via the DOI in this recordNovel Optical Materials and Applications 2018, 2–5 July 2018, Zurich, SwitzerlandThe combination of chalcogenide phase-change materials with optical metamaterial arrays is exploited to create new forms of dynamic, tuneable and reconfigurable photonic devices including perfect absorbers, modulators, beam steerers and filters.CDW and VKN acknowledge ONRG funding (#N62909-16-1-2174). CDW, AMA, Y-YA, VKN acknowledge EPSRC funding EP/M015130/1 & EP/M015173/1. CrdeG, SG-CC, EG and LT the EPSRC CDT in Metamaterials (EP/L015331/1). LT acknowledges support from QinetiQ. MLG acknowledges EPSRC funding EP/M009033/1

Temperature Evolution in Nanoscale Carbon-Based Memory Devices Due to Local Joule Heating

© 2002-2012 IEEE. Tetrahedral amorphous (ta-C) carbon-based memory devices have recently gained traction due to their good scalability and promising properties like nanosecond switching speeds. However, cycling endurance is still a key challenge. In this paper, we present a model that takes local fluctuations in sp 2 and sp 3 content into account when describing the conductivity of ta-C memory devices. We present a detailed study of the conductivity of ta-C memory devices ranging from ohmic behavior at low electric fields to dielectric breakdown. The study consists of pulsed switching experiments and device-scale simulations, which allows us for the first time to provide insights into the local temperature distribution at the onset of memory switching

Carbon-Based Resistive Memories

Carbon-based nonvolatile resistive memories are an emerging technology. Switching endurance remains a challenge in carbon memories based on tetrahedral amorphous carbon (ta-C). One way to counter this is by oxygenation to increase the repeatability of reversible switching. Here, we overview the current status of carbon memories. We then present a comparative study of oxygen-free and oxygenated carbon-based memory devices, combining experiments and molecular dynamics (MD) simulations

The effect of nitrogen implantation on resistive switching of tetrahedral amorphous carbon films

© 2018 Elsevier B.V. We report the effect of nitrogen implantation on the resistance switching of tetrahedral amorphous carbon (ta-C) films. Both unimplanted and implanted films show resistive switching, with a characteristic threshold voltage required to switch the films from the high-resistance to the low-resistance state. The switching voltages for the unimplanted films are between 7 and 10 V for ta-C films of thickness 15 to 40 nm. These are significantly reduced upon implantation by up to 60% when using an implantation dose ~3 × 1015 cm−2. We attribute this to increased sp2 bonding and clustering in the implanted films. This demonstrates the importance of sp2 clustering for resistive-switching in sp3-rich ta-C films