Daniela Dragoman

Terahertz fields and applications

Abstract Terahertz signals were until recently an almost unexplored area of research due to the difficulties in generation and detection of electromagnetic fields at these wavelengths. Neither optical nor microwave techniques are directly applicable in the terahertz range since optical wavelengths are too short and microwave wavelengths are too long compared to terahertz field wavelengths. The development of ultrafast optical techniques, the manufacturing of semi-insulating semiconductors with very short lifetimes and of band-engineered heterostructures, as well as the micromachining techniques and nanotechnology have boosted the terahertz fields as a new area of research in quantum electronics with many important applications. The paper reviews the most recent results in THz fields and is focused on the physical principles of terahertz generators and receivers, underlining the link between terahertz devices and modern technologies such as micromachining and nanotechnology.

Giant thermoelectric effect in graphene

The paper predicts a giant thermoelectric coefficient in a nanostructure consisting of metallic electrodes periodically patterned over graphene, which is deposited on a silicon dioxide substrate. The Seebeck coefficient in this device attains 30mV∕K, this value being among the largest reported ever. The calculations are based on a transfer matrix approach that takes a particular form for graphene-based devices. The results are important for future nanogenerators with applications in the area of sensors, energy harvesting, and scavenging.

Terahertz antenna based on graphene

We have investigated several configurations of antennas based on graphene. We show that patterned metallic dipole antennas or arrays of dipole antennas deposited on graphene highly benefit from the reversible high-resistivity-to-low-resistivity transition in graphene, tuned by a gate voltage. The radiation pattern and the efficiency of such antennas are changed via the gate voltage applied on graphene.

Quantum-classical analogies

1 Introduction.- 2 Analogies Between Ballistic Electrons and Electromagnetic Waves.- 3 Electron/Electromagnetic Multiple Scattering and Localization.- 4 Acoustic Analogies for Quantum Mechanics.- 5 Optical Analogs for Multilevel Quantum Systems.- 6 Particle Optics.- 7 Quantum/Classical Nonlinear Phenomena.- 8 Quantum/Classical Phase Space Analogies.- 9 Analogies Between Quantum and Classical Computing.- 10 Other Quantum/Classical Analogies.- References.

Negative differential resistance of electrons in graphene barrier

The graphene is a native two-dimensional crystal material consisting of a single sheet of carbon atoms. In this unique one-atom-thick material, the electron transport is ballistic and is described by a quantum relativisticlike Dirac equation rather than by the Schrodinger equation. As a result, a graphene barrier behaves very differently compared to a common semiconductor barrier. The authors show that a single graphene barrier acts as a switch with a very high on-off ratio and displays a significant differential negative resistance, which promotes graphene as a key material in nanoelectronics.

Optical analogue of a type II semiconductor heterostructure

A succession of directional couplers, which differ only through their refractive index distribution, is shown to be the optical analog of type II semiconductor heterostructures. The design of such a dielectric structure with the same transmission characteristic of the electric field propagating through it as the electron wave function in a type II heterostructure is discussed. An example of the design procedure is also given.

Microwave propagation in graphene

We report on measurements and modeling of microwave propagation in graphene. In deep contrast with carbon nanotubes, which display very high impedances in the microwave range, planar waveguides patterned directly on graphene display a 50 Ω impedance, which is tuned slightly by an applied dc. The high values of kinetic impedance in carbon nanotubes were not observed in graphene.

Graphene for Microwaves

Graphene nanoelectronics is an emerging area of research. The 2010 Nobel Prize for physics was awarded to A. Geim and K. Novoselov for the discovery of graphene and its unexpected physical properties, paving the way for many new applications in the area of nanoelectronics, nanooptics, and solid state physics. The most-studied microwave device is the graphene transistor, which, in only three years, has reached a cutoff frequency of 100 GHz. As consequence of this impressive development, the prediction that a 0.5-1 THz graphene FET transistor will soon be demonstrated is quite realistic. Moreover, graphene multipliers and other microwave graphene devices are expected to follow the graphene FET development dynamics and reach 100 GHz in few years.

Writing simple RF electronic devices on paper with carbon nanotube ink

This paper shows that we can print on paper simple high-frequency electronic devices such as resistances, capacitances or inductances, with values that can be changed in a controllable manner by an applied dc voltage. This tunability is achieved with the help of an ink containing functionalized carbon nanotubes and water. After the water is evaporated from the paper, the nanotubes remain steadily imprinted on paper, showing a semiconducting behavior and tunable electrical properties.

Optical analogue structures to mesoscopic devices

Abstract Optical analogues of several mesoscopic structures are presented. Classical or quantum optical analogies are found for tunnelling mesoscopic devices in the electron ballistic regime, for quantum interference devices, quantum wells with nonlinear effects, and for the electron spin operator. Mesoscopic set-ups analogous to optical set-ups for classical optical experiments, interaction-free imaging and quantum computing are also presented.