10 research outputs found
Conductivity crossover in nano-crystalline diamond films: Realization of a disordered superlattice-like structure
We present the electrical transport characteristics of a batch of
nano-crystalline diamond films of varying nitrogen concentrations and explain
the conduction mechanism by the disordered quasi-superlattice model applied to
semiconductor heterostructures. Synthesized by the hot filament chemical vapour
deposition technique, the degree of structural disorder in the films, confirmed
from Raman spectroscopy, is found to be controllable, resulting in the
transition of conduction mechanism from localized and activated to the metallic
conduction regime. Hence through high field magneto-resistance measurements at
low temperatures we firmly establish a conductivity crossover from hopping to
3D weak localization. The long electronic dephasing time and its weak
temperature dependence suggest the possibility for diamond-based high-speed
device applications
Theoretical model of structure-dependent conductance crossover in disordered carbon
We analyze the effects of sp^2/sp^3 bond-aspect ratio on the transport
properties of amorphous carbon quasi-1D structures where structural disorder
varies in a very non-linear manner with the effective bandgap. Using a
tight-binding approach the calculated electron transmission showed a high
probability over a wide region around the Fermi-level for sp^2-rich carbon and
also distinct peaks close to the band edges for sp^3-rich carbon structures.
This model shows a sharp rise of the structure resistance with the increase of
sp^3C % followed by saturation in the wide bandgap regime for carbon
superlattice-like structures and suggests the tuneable characteristic time of
carbon-based devices.Comment: 6 pages, 6 figure
Tuning the reduction of graphene oxide nanoflakes differently affects neuronal networks in the zebrafish
The increasing engineering of biomedical devices and the design of drug-delivery platforms enriched by graphene-based components demand careful investigations of the impact of graphene-related materials (GRMs) on the nervous system. In addition, the enhanced diffusion of GRM-based products and technologies that might favor the dispersion in the environment of GRMs nanoparticles urgently requires the potential neurotoxicity of these compounds to be addressed. One of the challenges in providing definite evidence supporting the harmful or safe use of GRMs is addressing the variety of this family of materials, with GRMs differing for size and chemistry. Such a diversity impairs reaching a unique and predictive picture of the effects of GRMs on the nervous system. Here, by exploiting the thermal reduction of graphene oxide nanoflakes (GO) to generate materials with different oxygen/carbon ratios, we used a high-throughput analysis of early-stage zebrafish locomotor behavior to investigate if modifications of a specific GRM chemical property influenced how these nanomaterials affect vertebrate sensory-motor neurophysiology—exposing zebrafish to GO downregulated their swimming performance. Conversely, reduced GO (rGO) treatments boosted locomotor activity. We concluded that the tuning of single GRM chemical properties is sufficient to produce differential effects on nervous system physiology, likely interfering with different signaling pathways
Public money creation to maintain fundamental human rights during the COVID-19 pandemic
As governments around the world respond to the COVID-19 pandemic with a range of policies aimed at mitigating the economic fallout, we argue that low- and middle-income countries (LMICs) should prioritize public money creation over foreign borrowing. Experience shows that the cost of servicing foreign debt diverts resources from public services and can undermine fundamental economic, social and cultural rights, such as the rights to clean water, sanitation, basic education and health care. Moreover, the conditions attached to any subsequent debt restructuring can make matters worse.https://www.hhrjournal.orghj2020Economic