Room temperature manipulation of long lifetime spins in metallic-like carbon nanospheres

The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin–lattice and spin–spin relaxation times of electrons. Minimizing the effects of spin–orbit coupling and the local magnetic contributions of neighbouring atoms on spin–lattice and spin–spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin–lattice and spin–spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid- state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temperature

A quantum electronic device

This disclosure relates to quantum electronic devices for storing qubits. In particular, this disclosure relates to a quantum electronic device comprising a carbon nanosphere adapted to store a qubit represented by an electron spin and a control and readout device to set the qubit and read the qubit stored on the carbon nanosphere. Qubits stored on carbon nanospheres have a long electron spin lifetime at room temperature. This disclosure further relates to a method for quantum computing. The method comprises storing a qubit represented by an electron spin on a carbon nanosphere, performing a quantum operation on the qubit to generate a resulting qubit and reading the resulting qubit from the nanosphere. There is further provided a spintronic device comprising multiple carbon nanospheres adapted to provide a qubit represented by an electron spin in that carbon nanosphere and a control device to facilitate interaction between the qubits to perform a quantum operation

Spin lifetime of itinerant electrons in chemically synthesized graphene multi-layers

A chemically synthesized graphitic material where the structural coherence between the layers is missing approximates very well the assembly of graphene sheets. Our multi-frequency (9.4-420 GHz) electron spin resonance (ESR) study clearly identifies itinerant and localized electrons below 50 K. The metallic signal ascribed to the conduction electrons in graphene is characterized by a remarkably long spin lifetime of 65 ns. Above this temperature incoherent in-plane and inter-plane scattering give a motionally narrowed single line at g = 2.0044. (C) 2014 Elsevier Ltd. All rights reserved

Electron spin lifetime in chemically synthesized graphene sheets

Graphene is theoretically expected to be a highly suitable material for spintronic and quantum computation applications. Current experimental reports assign surprisingly low spin lifetimes to graphene and related carbon structures. Recently, we showed a solvothermal synthesis method that can be employed to produce a high-purity sample, which approximates very well the assembly of graphene sheets. Using the contactless spectroscopic technique of electron spin resonance (ESR), we were able to identify in this graphene material the ESR of both conduction electrons and localized spins [Nafradi et al., Carbon 74, 346-351 (2014)]. Here, we show the temperature dependent evolution of the ESR of these two spin species. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Electron Spin Dynamics of Two-Dimensional Layered Materials

The growing library of two-dimensional layered materials is providing researchers with a wealth of opportunity to explore and tune physical phenomena at the nanoscale. Here, we review the experimental and theoretical state-of-art concerning the electron spin dynamics in graphene, silicene, phosphorene, transition metal dichalcogenides, covalent heterostructures of organic molecules and topological materials. The spin transport, chemical and defect induced magnetic moments, and the effect of spin-orbit coupling and spin relaxation, are also discussed in relation to the field of spintronics

A Conductive Crosslinked Graphene/Cytochrome C Networks for The Electrochemical and Biosensing Study

The direct electrochemistry of catalytically active cytochrome C (Cyt c) adsorbed together with a 3-dimensional network of chemically synthesized graphene on glassy carbon electrode has been readily obtained in aqueous phosphate buffer. Direct electrical communication between the redox center of Cyt c and the modified graphene-based electrode was established. The modified electrode was employed as a high-performance hydrogen peroxide (H2O2) biosensor. The Cyt c present in modified electrode exhibited a pair of quasi-reversible redox peaks with a midpoint potential of −0.380 and −0.2 V, cathodic and anodic, respectively. Investigations into the electrocatalytic activity of the modified electrode upon hydrogen peroxide exposure revealed a rapid amperometric response (5 s). Under optimized conditions, the linear range of response to H2O2 concentration ranged from 5 × 10−7 to 2 × 10−4 M with a detection limit of 2 × 10−7 M at a signal-to-noise ratio of 3. The stability, reproducibility, and selectivity of the proposed biosensor are discussed in relation to the morphology and composition of the modified electrode

Novel chemical pathways to carbon nanostructures: Graphene and Fullerenes

Graphene, carbon onions, and multi-walled carbon nanotubes have been chemically synthesised through a variety of novel pathways. Graphene was synthesised in gram-scale quantities by a bottom-up wet chemical approach involving a solvothermal process. Purification methods of the chemically synthesised graphene were investigated along with the physical properties of the material. High surface areas and long range anti-ferromagnetic behaviour was identified in the synthesised graphene. The graphene was incorporated into superconducting magnesium boride, and nano-sized silicon particles in battery devices. The graphene based composite materials showed enhanced properties to that of the parent materials.Gram-scale quantities of carbon onions were obtained by a simple combustion method involving a polyaromatic hydrocarbon. The synthesis provided insights into the formation of carbon nanostructures. Carbon onion coatings on glass were found to be superhydrophobic. Solvothermal conditions were used to synthesise very large multi-walled carbon nanotubes. Through a set of interdependent reactions involving lithium metal and polytetrafluoroethylene, it was shown that the formation of carbon nanotubes could be controlled. Under ambient pressures, multi-walled carbon nanotubes were also synthesised by the reaction of sodium metal and carbon tetrachloride

Adsorption and desorption characteristics of 3-dimensional networks of fused graphene

Here we explore the exceptional structural characteristics of a set of graphene-related materials prepared by a wet chemical approach. We present a comprehensive study of the effects of morphology, sonication, temperature, probe species, and stacking behaviour on the measurement of graphene surface area. Nitrogen gas was used in the solid state gas adsorption measurements and methylene blue dye for adsorption measurements on aqueous dispersions of graphene. The surface area values obtained are among the highest reported for synthetic graphenes: 1700 m²g⁻¹ in aqueous dispersions and 612 m²g⁻¹ in the solid state. Microscopy revealed the graphene used in the study was present in large part as free sheets and electron diffraction confirmed the successful synthesis of high quality graphene with a regular C-C bond length of 1.41 ± 0.02 Å.6 page(s

Strong Interplay between the Electron Spin Lifetime in Chemically Synthesized Graphene Multilayers and Surface-Bound Oxygen

The electron spin lifetime in an assembly of chemically synthesized graphene sheets was found to be extremely sensitive to oxygen. Introducing small concentrations of physisorbed O-2 onto the graphene surface reduced the exceptionally long 140 ns electron spin lifetime by an order of magnitude. This effect was completely reversible: Removing the O-2 by using a dynamic vacuum restored the spin lifetime. The presence of covalently bound oxygen also decreased the electron spin lifetime in graphene, although to a far lesser extent compared to physisorbed O-2. The conduction electrons in graphene were found to play a significant role by counter-balancing the spin depolarization caused by oxygen molecules. Our results highlight the importance of chemical environment control and device packing in practical graphene-based spintronic applications

Carborane functionalization of the aromatic network in chemically-synthesized graphene

The conjugated aromatic system of graphene was used to trap the reactive, boron-rich 1,2-carborane cluster. Functionalization of the graphene surface was confirmed by solid-state MAS 11B NMR spectroscopy and quantified by X-ray photoelectron spectroscopy. This work represents the first confirmed example of direct functionalization of a graphene lattice with carboranes.University of Sydney, Australian Research Council (ARC