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Bucharest, Romania

Dragoman M.,IMT Bucharest
Proceedings of the Romanian Academy Series A - Mathematics Physics Technical Sciences Information Science | Year: 2014

The aim of this paper is to show that simple devices based on graphene monolayer devices are able to detect electromagnetic fields in an amazing large spectrum ranging from microwaves up to far IR. Source


Eremia S.A.V.,Romanian National Institute for Research and Development for Biological Sciences | Vasilescu I.,Romanian National Institute for Research and Development for Biological Sciences | Radoi A.,IMT Bucharest | Litescu S.-C.,Romanian National Institute for Research and Development for Biological Sciences | Radu G.-L.,Romanian National Institute for Research and Development for Biological Sciences
Talanta | Year: 2013

A disposable amperometric biosensor was developed for the detection of total polyphenolic compounds from tea infusions. The biosensor was designed by modifying the surface of a carbon screen-printed electrode with platinum nanoparticles and reduced graphene oxide, followed by the laccase drop-casting and stabilization in neutralised 1% Nafion solution. The obtained biosensor was investigated by scanning electron microscopy and electrochemical techniques. It was observed that platinum nanoparticles-reduced graphene oxide composite had synergistic effects on the electron transfer and increased the electroactive surface area of the carbon screen-printed electrode. The constructed analytical tool showed a good linearity in the range 0.2-2 μM for caffeic acid and a limit of detection of 0.09 μM. The value of Michaelis-Menten apparent constant was calculated from the electrochemical version of Lineweaver-Burk equation to be 2.75 μM. This disposable laccase biosensor could be a valuable tool for the estimation of total polyphenolic content from tea infusions. © 2013 Elsevier B.V. All rights reserved. Source


Dragoman M.,IMT Bucharest
Romanian Reports in Physics | Year: 2013

I will present my recent research concerning electronic devices on graphene. Graphene was discovered few years ago, and its amazing physical properties have ignited the hopes to reach THz frequencies with a single electronic device. So, high speed devices challenging Moore's law have emerged in the last years, opening the era of "beyond Moore law". Source


Dragoman D.,University of Bucharest | Dragoman M.,IMT Bucharest
Journal of Applied Physics | Year: 2010

The paper shows that there is no Hartman effect due to Klein paradox for electrons traversing electrostatic barriers in graphene. In addition, the quantum dwell time in such single-and double-barrier structures can be modulated by an applied gate voltage. © 2010 American Institute of Physics. Source


Obreja V.V.N.,IMT Bucharest
AIP Conference Proceedings | Year: 2014

The electrode material is a key component for supercapacitor cell performance. As it is known, performance comparison of commercial available batteries and supercapacitors reveals significantly lower energy storage capability for supercapacitor devices. The energy density of commercial supercapacitor cells is limited to 10 Wh/kg whereas that of common lead acid batteries reaches 35-40 Wh/kg. For lithium ion batteries a value higher than 100 Wh/kg is easily available. Nevertheless, supercapacitors also known as ultracapacitors or electrochemical capacitors have other advantages in comparison with batteries. As a consequence, many efforts have been made in the last years to increase the storage energy density of electrochemical capacitors. A lot of results from published work (research and review papers, patents and reports) are available at this time. The purpose of this review is a presentation of the progress to date for the use of new materials and approaches for supercapacitor electrodes, with focus on the energy storage capability for practical applications. Many reported results refer to nanostructured carbon based materials and the related composites, used for the manufacture of experimental electrodes. A specific capacitance and a specific energy are seldom revealed as the main result of the performed investigation. Thus for nanoprous (activated) carbon based electrodes a specific capacitance up to 200-220 F/g is mentioned for organic electrolyte, whereas for aqueous electrolyte, the value is limited to 400-500 F/g. Significant contribution to specific capacitance is possible from fast faradaic reactions at the electrode-electrolyte interface in addition to the electric double layer effect. The corresponding energy density is limited to 30-50 Wh/kg for organic electrolyte and to 12-17 Wh/kg for aqueous electrolyte. However such performance indicators are given only for the carbon material used in electrodes. For a supercapacitor cell, where two electrodes and also other materials for cell assembling and packaging are used, the above mentioned values have to be divided by a factor higher than four. As a consequence, the specific energy of a prototype cell, hardly could exceed 10 Wh/kg because of difficulties with the existing manufacturing technology. Graphene based materials and carbon nanotubes and different composites have been used in many experiments reported in the last years. Nevertheless in spite of the outstanding properties of these materials, significant increase of the specific capacitance or of the specific energy in comparison with activated or nanoporous carbon is not achieved. Use of redox materials as metal oxides or conducting polymers in combination with different nanostructured carbon materials (nanocomposite electrodes) has been found to contribute to further increase of the specific capacitance or of the specific energy. Nevertheless, few results are reported for practical cells with such materials. Many results are reported only for a three electrode system and significant difference is possible when the electrode is used in a practical supercapacitor cell. Further improvement in the electrode manufacture and more experiments with supercapacitor cells with the known electrochemical storage materials are required. Device prototypes and commercial products with an energy density towards 15-20 Wh/kg could be realized. These may be a milestone for further supercapacitor device research and development, to narrow the storage energy gap between batteries and supercapacitors. © 2014 AIP Publishing LLC. Source

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