Arseny Alexeev

Multilevel Ultrafast Flexible Nanoscale Nonvolatile Hybrid Graphene Oxide–Titanium Oxide Memories

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.

Electric dipole moment oscillations in Aharonov-Bohm quantum rings

Magneto-oscillations of the electric dipole moment are predicted and analyzed for a single-electron nanoscale ring pierced by a magnetic flux (an Aharonov-Bohm ring) and subjected to an electric field in the ring’s plane. These oscillations are accompanied by periodic changes in the selection rules for interlevel optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation.

Aharonov-Bohm quantum rings in high-Q microcavities

A single-mode microcavity with an embedded Aharonov-Bohm quantum ring, which is pierced by a magnetic flux and subjected to a lateral electric field, is studied theoretically. It is shown that external electric and magnetic fieldsprovideadditionalmeansofcontroloftheemissionspectrumofthesystem.Inparticular,whenthemagnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quantum, a small change in the lateral electricfield allows tuning of the energy levels of the quantum ring into resonance with the microcavity mode providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are calculated for several combinations of the applied magnetic and electric fields.

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

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 results

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.

New routes to the functionalization patterning and manufacture of graphene-based materials for biomedical applications

Graphene-based materials are being widely explored for a range of biomedical applications, from targeted drug delivery to biosensing, bioimaging and use for antibacterial treatments, to name but a few. In many such applications, it is not graphene itself that is used as the active agent, but one of its chemically functionalized forms. The type of chemical species used for functionalization will play a key role in determining the utility of any graphene-based device in any particular biomedical application, because this determines to a large part its physical, chemical, electrical and optical interactions. However, other factors will also be important in determining the eventual uptake of graphene-based biomedical technologies, in particular the ease and cost of manufacture of proposed device and system designs. In this work, we describe three novel routes for the chemical functionalization of graphene using oxygen, iron chloride and fluorine. We also introduce novel in situ methods for controlling and patterning such functionalization on the micro- and nanoscales. Our approaches are readily transferable to large-scale manufacturing, potentially paving the way for the eventual cost-effective production of functionalized graphene-based materials, devices and systems for a range of important biomedical applications.

Joule heating effects in nanoscale carbon-based memory devices

One of the emerging candidates to bridge the gap between fast but volatile DRAM and non-volatile but slow storage devices is tetrahedral amorphous carbon (ta-C) based memory [1]-[3]. This offers a very good scalability, data retention and sub-5ns switching [2], [3]. Amorphous carbon memory devices can be electrically and optically switched from a high resistance state (HRS) to a low resistance state (LRS) [4]. The electrical conduction in the LRS is thought to be through sp2 clusters that form a conductive filament [4].

Two-phonon scattering in graphene in the quantum Hall regime

One of the most distinctive features of graphene is its huge inter-Landau-level splitting in experimentally attainable magnetic fields which results in the room-temperature quantum Hall effect. In this paper we calculate the longitudinal conductivity induced by two-phonon scattering in graphene in a quantizing magnetic field at elevated temperatures. It is concluded that the purely phonon-induced scattering, negligible for conventional semiconductor heterostructures under quantum Hall conditions, becomes comparable to the disorder-induced contribution to the dissipative conductivity of graphene in the quantum Hall regime.