Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals

© The Author(s) 2017. A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes

Corrigendum: Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals.

Nature Communications 8: Article number: 14482; published: 17 February 2017; Updated: 22 March 2017 The original version of this Article contained a typographical error in the spelling of the author Omid Kavehei, which was incorrectly given as Omid Kevehei. This has now been corrected in both the PDF and HTML versions of the Article.</jats:p

Reverse Hall-Petch effect in ultra nanocrystalline diamond

We present atomistic simulations for the mechanical response of ultra nanocrystalline diamond, a polycrystalline form of diamond with grain diameters of the order of a few nm. We consider fully three-dimensional model structures, having several grains of random sizes and orientations, and employ state-of-the-art Monte Carlo simulations. We calculate structural properties, elastic constants and the hardness of the material; our results compare well with experimental observations for this material. Moreover, we verify that this material becomes softer at small grain sizes, in analogy to the observed reversal of the Hall-Petch effect in various nanocrystalline metals. The effect is attributed to the large concentration of grain boundary atoms at smaller grain sizes. Our analysis yields scaling relations for the elastic constants as a function of the average grain size.Comment: Proceedings of the IUTAM Symposium on Modelling Nanomaterials and Nanosystems, Aalborg, Denmark, May 19-22 2008; to be published in the IUTAM Bookseries by Springe

Aluminum-Ion-Intercalation Supercapacitors with Ultrahigh Areal Capacitance and Highly Enhanced Cycling Stability: Power Supply for Flexible Electrochromic Devices

Electrochemical capacitor systems based on Al ions can offer the possibilities of low cost and high safety, together with a three-electron redox-mechanism-based high capacity, and thus are expected to provide a feasible solution to meet ever-increasing energy demands. Here, highly efficient Al-ion intercalation into W18O49 nanowires (W18O49NWs) with wide lattice spacing and layered single-crystal structure for electrochemical storage is demonstrated. Moreover, a freestanding composite film with a hierarchical porous structure is prepared through vacuum-assisted filtration of a mixed dispersion containing W18O49NWs and single-walled carbon nanotubes. The as-prepared composite electrode exhibits extremely high areal capacitances of 1.11–2.92 F cm−2 and 459 F cm−3 at 2 mA cm−2, enhanced electrochemical stability in the Al3+ electrolyte, as well as excellent mechanical properties. An Al-ion-based, flexible, asymmetric electrochemical capacitor is assembled that displays a high volumetric energy density of 19.0 mWh cm−3 at a high power density of 295 mW cm−3. Finally, the Al-ion-based asymmetric supercapacitor is used as the power source for poly(3-hexylthiophene)-based electrochromic devices, demonstrating their promising capability in flexible electronic devices

Calligraphy-inspired brush written foldable supercapacitors

Chinese brush, made of a bundle of animal hairs in a quasi-parallel arrangement, is an effective tool that can be used to continuously place low-viscosity ink onto different substrates with high ink mass loading. Here, we demonstrate a highly effective approach to coat graphene onto rough and even crumpled substrates by using a Chinese brush. By combining forces including Laplace pressure differential, asymmetric retention and gravity, the low-viscosity graphene oxide ink can be sufficiently transferred onto different substrates through the brush hairs in a controlled manner. The as-prepared graphene films are used as electrodes for all-solid-state foldable supercapacitors. Using series and/or parallel connections, the energy storage performance of the foldable all-solid-state supercapacitors can be tailored to provide different output voltages and currents. The voltage of the three series connected devices with gel electrolyte can be extended to 2.4 V. A parallel connected foldable all-solid-state supercapacitor exhibits promising electrochemical performance, such as high areal capacitance of 258.6 mF cm−2, good energy density of 23.1 μW h cm−2 and power density of 0.2 mW cm−2. This work offers an alternative method of GO ink transfer, graphene film production and the fabrication of flexible electronics

Characterization of aniline tetramer by MALDI TOF mass spectrometry upon oxidative and reductive cycling

By combining electrochemical experiments with mass spectrometric analysis, it is found that using short chain oligomers to improve the cycling stability of conducting polymers in supercapacitors is still problematic. Cycling tests via cyclic voltammetry over a potential window of 0 to 1.0 V or 0 to 1.2 V in a two-electrode device configuration resulted in solid-state electropolymerization and chain scission. Electropolymerization of the aniline tetramer to generate long chain oligomers is shown to be possible despite the suggested decrease in reactivity and increase in intermediate stability with longer oligomers. Because aniline oligomers are more stable towards reductive cycling when compared to oxidative cycling, future conducting polymer/oligomer-based pseudocapacitors should consider using an asymmetric electrode configuration

Case-based postgraduate programmes : a survey of general dental practitioners' postgraduate education activity and demand for extended modular postgraduate programmes.

The aim of this paper is to assess the level of involvement of general dental practitioners in postgraduate education and training, identify their speciality interests, preferred format of course presentation and assess the potential demand for modular postgraduate programmes. A questionnaire analysis of a one in three random sample of general dental practitioners on Health Authority lists in the North West of England and North Wales was designed and carried out. Out of a random sample of 799, 552 GDPs completed an anonymous questionnaire in 1998 which investigated their current postgraduate activity, the areas of specialist interest and their interest in extended modular postgraduate education courses with associated summative assessment. Fifty three percent of respondents attended more than four postgraduate sessions per year of whom the majority (59%) were in the 35-44 year old age group. 79% identified Section 63 courses as their first preference and 63% preferred mixed didactic and 'hands on' courses. Seventy five percent of respondents expressed an interest in attending modular programmes which might lead to a postgraduate qualification. In conclusion, an enthusiasm to attend existing postgraduate courses was identified but a demand was also perceived for courses of longer duration possibly leading to additional postgraduate qualifications