Bucharest, Romania
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Kusko C.,IMT Bucharest
Proceedings of the International Semiconductor Conference, CAS | Year: 2012

In this work we have numerically investigated by employing the finite difference time domain (FDTD) method the coupling between two metal-dielectric-metal (MDM) plasmonic waveguides supporting symmetric forward propagating fundamental modes, one of them presenting a Kerr non-linearity. A coupling analysis is performed in order to investigate the all - optical switching properties of this directional coupler. This analysis was performed for optimization of this coupler in terms of length, modal characteristics of the waveguides as well as the input power. © 2012 IEEE.

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.

Radoi A.,IMT Bucharest | Dragoman M.,IMT Bucharest | Dragoman D.,University of Bucharest
Applied Physics Letters | Year: 2011

Memristors are passive nanoelectronics devices with applications in memories and switches which, although not containing magnetic components, have as distinct signature a hysteresis loop in the current-voltage dependence. Even if the prototype material for memristors is a binary oxide, we demonstrate that such devices can be easily implemented using carbon nanotubes decorated with metallic nanoislands, where the hysteretic action is a result of the thermionic emission of electrons trapped in the gold nanoislands. © 2011 American Institute of Physics.

Sajin G.I.,IMT Bucharest
Progress in Electromagnetics Research Letters | Year: 2011

The paper deals with a method to measure the unknown impedance of metamaterial antenna made in Composite Right/Left- Handed (CRLH) Co Planar Wavegiude (CPW) technique for the millimeter wave frequency domain. The method uses a measurement setup made of a high frequency vector network analyzer (VNA) and an on-wafer characterization equipment. The measurement procedure consists in placing the probe-tip of the on-wafer equipment and to move it along the feedline of the antenna radiating structure until the minimum values of the return loss is reached. Using the facilities of the on-wafer equipment (micrometric screws to move the probe-tips) and knowing the geometrical dimensions of the antenna structure, the dimension and the position of an equivalent open-circuit matching stub are obtained. Then, using relationships derived from the transmission lines theory, real and imaginary parts of the unknown antenna impedance are computed.

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.

Dragoman M.,IMT Bucharest | Dinescu A.,IMT Bucharest | Dragoman D.,University of Bucharest
Nanotechnology | Year: 2014

Negative differential resistance (NDR) with a room temperature peak-to-valley ratio of 8 was observed in a graphene-based ballistic field-effect transistor (FET) with an oblique top gate. Graphene FETs with a top gate inclination angle of 45° and a drain-source distance of 400 nm were fabricated on a chip cut from a 4-inch graphene wafer grown by chemical vapor deposition (CVD). Of the 60 measured devices, NDR was observed only in the regions where the CVD graphene displayed a Raman signature of defectless monolayers. In other specific positions on the wafer, where graphene quality was not high enough, and the Raman signature indicated the presence of defects, the ballistic character of transport was lost and the graphene FETs displayed nonlinear drain-voltage dependences tuned by the top-gate and back-gate voltage. © 2014 IOP Publishing Ltd.

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.

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".

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.

Dragoman D.,University of Bucharest | Dragoman M.,IMT Bucharest
Applied Physics Letters | Year: 2014

We show that reversible two- and three-input logic gates, such as the universal Toffoli gate, can be implemented with three tilted gate electrodes patterned on a monolayer graphene flake. These reversible gates are based on the unique properties of ballistic charge carriers in graphene, which induce bandgaps in transmission for properly chosen potential barriers. The enhanced architectures for reversible logic gate implementation proposed in this paper offer a remarkable design simplification compared to standard approaches based on field-effect transistor circuits, as well as potential high-frequency operation. © 2014 AIP Publishing LLC.

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