Scaling down the minimum feature size of integrated circuits is pushing the operation of field effect transistors into a ballistic regime, where electron inertia and plasma wave effects start playing a dominant role. In this paper, we review detection and generation of sub-terahertz and terahertz radiation by plasma waves. Both resonant and non-resonant detection has been demonstrated in Si,-based, III-V based, and AlGaN/GaN field effect transistors, and the results are in reasonable agreement with theory. These devices expect to find applications for terahertz detection at high operating frequencies. Weak tunable terahertz emission has been observed at cryogenic temperatures but the plasma wave mechanism still needs to be explored to be proven responsible for this emission. Further improvements are expected by using field effect transistor arrays both for terahertz detection and emission.

We report on our study of the effects of external magnetic field on the intersubband optical transitions in quantum cascade systems. We address the properties of two types of cascade structures: terahertz quantum cascade lasers and quantum dot infrared photodetectors. In both cases we study the optical properties of active regions of the systems: optical emission in the case of quantum cascade lasers and optical absorption in the case of photodetectors. The new features and new peaks in the optical spectra appear in the tilted magnetic field for quantum cascade lasers and in the parallel magnetic field for quantum dot photodetectors. In the relation to the possible spintronic application of cascade structures we study interplay of spin-orbit and magnetic field effects in cascade systems. If spin-orbit coupling is strong enough then at finite parallel magnetic field the optical emission spectra of quantum cascade lasers have two-peak structure.

Designing nanoscale devices presents a number of unique challenges. As device features shrink, the computational demands of the simulations necessary to accurately model them increase significantly. This is a result of not only the increasing level of detail in the device design itself, but also the need to use more accurate models. The approximations that are generally made when dealing with larger devices break down as feature sizes decrease. This can be seen in the optics field when contrasting the complexity of physical optics models with those requiring a rigorous solution to Maxwell's equations. This added complexity leads to more demanding calculations, stressing computational resources and driving research to overcome these limitations. There are traditionally two means of improving simulation times as model complexity grows beyond available computational resources: modifying the underlying algorithms to maintain sufficient precision while reducing overall computations and increasing the power of the computational system. In this paper, we explore the latter. Recent advances in commodity hardware technologies, particularly field-programmable gate arrays (FPGAs) and graphics processing units (GPUs), have allowed the creation of desktop-style devices capable of outperforming PC clusters. We will describe the key hardware technologies required to build such a device and then discuss their application to the modeling and simulation of nanophotonic devices. We have found that FPGAs and GPUs can be used to significantly reduce simulation times and allow for the solution of much large problems.

We formulate and justify several proposals utilizing the unique electronic properties of different types of carbon nanotubes in a broad range of applications to THz optoelectronics, including THz generation by hot electrons in quasi-metallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse electric field, and THz radiation detection by armchair nanotubes in strong magnetic fields.

A carbon nanotube is a one-dimensional molecular wire. In this paper, we discuss some of the properties of carbon nanotubes as microwave and mm-wave antennas. We also discuss some of the conceptual issues involved with understanding the interaction of microwaves with one-dimensional quantum wires. While we focus on simple dipole antennas, our discussion applies generally to the interaction of microwaves with nano-materials, including nanotube arrays and composites.

The Leontovich-Levin equation for optical scattering by an achiral carbon nanotube (CNT) of finite length is formulated, based on a quantum-mechanical microscopic model of the conductivity. Application over a wide frequency range from the terahertz to the ultraviolet is possible. The CNT polarizability scalar in the low-frequency regime and the scattering pattern in the regime of optical interband transitions as well as in the vicinity of plasmon resonance are calculated. Geometric resonances of strongly retarded surface waves emerge, and can be used for the qualitative interpretation of experimentally observed features in the optical response characteristics of CNT-based composite mediums. The potential of isolated CNTs as optical nanoantennas of both the receiving and the transmitting types is established.

In the first part of the present contribution, we will report on transport calculations of nanoscaled devices based on Carbon Nanotubes obtained via self-consistent density-functional method coupled with non-equilibrium Green's function approaches. In particular, density functional tight-binding techniques are very promising due to their intrinsic efficiency. This scheme allows treatment of systems comprising a large number of atoms and enables the computation of the current flowing between two or more contacts in a fully self-consistent manner with the open boundary conditions that naturally arise in transport problems. We will give a description of this methodology and application to field effect transistor based on Carbon nanotubes. The advances in manufacturing technology are allowing new opportunities even for vacuum electron devices producing radio-frequency radiation. Modern micro and nano-technologies can overcome the typical severe limitations of vacuum tube devices. As an example, Carbon Nanotubes used as cold emitters in micron-scaled triodes allow for frequency generation up to THz region. The purpose of the second part of this contribution will be a description of the modelling of Carbon Nanotube based vacuum devices such as triodes. We will present the calculation of important figures of merit and possible realizations.

We present theoretical study of carbon nanotubes as novel transport channels for electrons and molecules using atomistic simulation. For electronic transport, we present self-consistent tight-binding study of the electronic and transport properties of semiconducting carbon nanotubes in contact with metal electrodes at different contact geometries. We analyze the Schottky barrier effect at the metal-nanotube interface by examining the electrostatics, the band line up and the conductance of the metal-nanotube wire-metal junction as a function of the nanotube channel length. For molecular transport, we analyze the dynamics of rigid and semi-flexible molecules spontaneously inserted into the nanotubes as engineered flow channels in aqueous environment. We show that in the absence of water solvation, the van der Waals interaction between the molecule and the nanotube wall can induce a rapid spontaneous encapsulation of the molecule inside the nanotube channel. The encapsulation process is strongly impeded for nanotube dissolved in water due to the competition between the van der Waals, hydrophobic and hydrogen bonding interactions in the nanotube/water/molecule complex.

Symmetry based calculations of the polarized optical absorption in single-wall MoS₂ nanotubes are presented. Optical conductivity tensor for the individual tubes, using line group symmetry implemented POLSym code and DFTB-calculated Slater type orbital functions and Hamiltonian/overlap matrix elements as input data is numerically evaluated. This minimal, full symmetry implementing algorithm enabled calculations of the optical response functions very efficiently and addressing the large diameter tubes and highly chiral tubes (which have huge number of atoms within a unit cell) as well. The absorption spectra dependence on the diameter and chiral angle of the nanotubes is investigated. The results obtained are related to the previously reported measured spectra.

The optical dichroism which appears in the nanotube-DNA hybrid is studied within a phenomenological approach. Naturally non-chiral nanotubes may acquire a chiral optical response when wrapped by the DNA helix. The hybrids of the DNA and the metallic nanotubes are discussed in conjunction with the possible gap opening and the subsequent arising of a pair of van Hove singularities close to the Fermi point. Polarized light absorption experiments are proposed to find the predicted effect.

The literature is alive with papers devoted to the design of metamaterials and there appears to be a particular desire to create photonic applications that will operate at THz frequencies and above. At one level the modelling of suitable artificial molecules is straightforward but nevertheless the approximations involved need to be able to inspire confidence for optical frequency operation. This presentation will set out a modelling activity that is known to be satisfactory only over certain frequency ranges. Split-ring and omega particles will be specifically investigated and the possibilities discovered will be related to the current experimental expertise. The detailed manner in which the constitutive relations can be controlled and the novel way in which an envelope equation emerges for even the most complex structure is exposed. The transmission and reflection properties of nano-structured materials will be discussed within a magneto-optic environment. Simulations of sub-wavelength transmission through holes in metallic and magneto-optic screens will be discussed using finite-difference time-domain (FDTD) methods. Modelling the interaction of light beams with metamaterials is developed, again using FDTD techniques, and it is shown that special care needs to be taken with structures that have sharp external edges. Finally, a summary of the problems surrounding efficient computations will be shown and some discussion of the role of genetic algorithms in metamaterial design will be featured.

We investigate the group velocity of electromagnetic signals in compositionally graded films consisting of nonspherical particles. The theory is first based on generalized effective medium approximation to obtain the local dielectric function tensor in a x slice. Then, the effective dielectric tensor of the graded film is directly determined, and the group velocities for ordinary and extraordinary waves in the film are derived. It is found that the group velocity is dependent on the graded profile and the particles' shape. For a power-law graded profile f(x) = ax^m, increasing m results in the decreased extraordinary group velocity. Such a decreased tendency becomes significant when the incident angle increases. Moreover, enhanced or decreased group velocity may be achieved when the geometric shape of particles is non-spherical. In detail, oblate particles with large depolarization factor L results in large velocity enhancement and prolate one with small L leads to decreased velocity for normal incidence. Therefore, the non-spherical shape and graded profile play crucial roles in determining the magnitude of the group velocity in compositionally graded film.

Under certain circumstances, the magnitude of the group velocity in a homogenized composite material (HCM) can exceed that of the group velocity in its constituent materials. An enhancement in the magnitude of group velocity in isotropic as well as anisotropic dielectric HCMs is predicted by the application of the Bruggeman formalism for the homogenization of two constituent dielectric materials, one of which is characterized by a relatively large permittivity and relatively small frequency-dispersion as compared with the other constituent material. Group-velocity enhancement is sensitively dependent upon the shape and orientation of the constituent particles.

We propose an approach to far field optical imaging below the diffraction limit, based on dielectric metamaterials with strong anisotropy. As opposed to the "superlens" that relies on negative index materials, our method allows image magnification and is robust with respect to material losses.

In a material with large magneto-optical susceptibility, due to the Inverse Faraday Effect, circularly polarized optical pulses induce a pulsed magnetic flux. Alternatively, sufficiently intense optical pulses can induce a pulsed magnetic flux by means of ultrafast demagnetization of a metallic thin film or multilayer with a perpendicular magnetic anisotropy. The time varying magnetic flux may induce a transient electro-motive force and electric current in a conducting loop on the surface of the illuminated material. The latter current induces a transient magnetic field that can be used in various nanomagnetic processes. The magnetic field pulses due to the transient current appear to be too short for use in the magnetic field or spin-current induced precessional switching of magnetization. However, our calculations suggest that the magnetic field could lead to ultrafast switching of a nanomagnet overlaid on the surface of the conductor and demagnetized by the same optical pulse. In the case of photo-magnetic pulses due to the Inverse Faraday Effect, the switching direction could be controlled by the helicity of the optical pulse. We also demonstrate that the proposed device, which we call a Faraday Magneto-Optical Transformer, could be used as a Terahertz emitter.

A plane-wave complex photonic bandstructure approach is used to calculate the pass bands as a function of rod diameter for a system consisting of circular metallic rods in a 2-D square lattice. In addition, FDTD calculations are employed to calculate the transmission properties of a finite 6-layer structure of the same form. The results of the two methods are compared and found to be consistent. The effective plasma frequency, the lowest frequency at which propagation can occur in the infinite lattice, is extracted from the bandstructure calculations, and is in the region of 1 THz for the 200 μm period structures considered. The results for the effective plasma frequency are compared to those predicted by several analytic models.

The evolution of the field of nanotechnology has propelled humankind to the brink of an impending revolution, which will fundamentally impact every aspect of human life. While theory and experimentation are indeed critical to this future, simulation will play a key role in the shape of this future. To this end, the field of nanotechnology has required significant advances in the way cyberinfrastructure is utilized to derive scientific progress. To sustain and indeed fuel growth in nanotechnology requires a new generation of scientists, currently in middle and high schools and in colleges and universities, trained to think and perform across disciplinary barriers. The task of reaching these students and to capture their imagination requires a fundamental and systematic approach, that is positioned at the convergence point of nanotechnology, pedagogy, and cyberinfrastructure. The Network for Computational Nanotechnology (NCN), through its nanoHUB.org website, is leading a new charge in bridging nanotechnology discovery and learning. In this paper, we will use the nanoHUB.org as a case study to highlight how the nanoscale vision is impacting teaching and learning at various levels.

Advances in microscopy and optical lenses have opened a 'window to nature' that allows us to see how the building blocks of our world interact at the atomic level. This scale of science encompasses all the sciences and demands collaboration between physics, chemistry, biology, engineering and information technology, as wells as the talents of simulation and modeling software technicians. Career paths are expanding exponentially with each passing year of new discoveries but guidance counselors at the high school level are still uninformed about the nano scale of science. They need to be included in the teacher training sessions in order to advise students on the subjects required to enter a university and excel in the integrated fields of science and math. All future STEM careers will require an expanded knowledge base in the various applications of nanotechnology for manufacturing. Foreign students are much better prepared for entry into the university level of learning as they are required to master three mathematic and three science courses per year throughout the high school curriculum while United States National Standards only require one math and one science course per year throughout high school.

The application of nanotechnology has enormous potential to greatly influence the world in which we live. The major challenge is to incorporate nanotechnology into our understanding of what it means to be scientifically literate. This is even more vital for that segment of our population that will move into the scientific and technical workforce in 5 to 10 years. This pilot program is developing course materials to be incorporated into existing high school science subjects as part of K12 Nanoeducation.

In 2004 two groups have reported observation of the strong coupling regime in 3D microcavities with single quantum dots (QD). We present the quantum theory of non-linear emission of photons by such structures. We derive the exciton creation operator which coincides with a Fermi one for QDs smaller than the exciton Bohr radius and with Bose one for very large QDs. In intermediate size dots excitonic statistics is in between the Fermi and Bose ones. Consequently, the non-linear optical spectra change from the Mollow triplet in the fermionic case to the Rabi doublet in the bosonic case. We predict appearance of a characteristic multiplet structure of the non-linear emission in the intermediate regime.

We observe an anomalous exciton lifetime in columnar InAs/GaAs quantum rods by using the time-resolved differential reflectivity (TRDR) technique. At low excitation density, the decay time of the TRDR signal show a clear excitonic type of behavior. At increased excitation, a resonant radiative lifetime develops, which seems to be dependent on the excited QD density being resonant with the probe laser spectrum. We interpret the resonance behavior as due to electromagnetic coupling between the excited QDs resonant with the probe laser.

The properties of localised dipole emitters in the form of a quantum dot or a colour centre embedded in a crystal environment can be drastically modified by a change in the composition, size and shape of the environment in which the emitter is embedded. Thanks to recent advances in material deposition techniques and lithography, as well as the advances in detection techniques and optical manipulation, experimental work is now capable of revealing a new range of physical phenomena when the typical dimensions are of the order of an optical dipole transition wavelength and below. These advances have arisen at a time of a heightened research effort devoted to the important goal of identifying a qubit and a suitable environment that forms the basis for a scalable hardware architecture for the practical realisation of quantum information processing. A physical system that we have recently put forward as a candidate for such a purpose involves localised emitters in the form of quantum dots or colour centres embedded in a nanocrystal. This suggestion became more persuasive following the success of experiments which, for the first time, were able to demonstrate quantum cryptography using a nitrogen vacancy in a diamond nanocrystal as a single-photon source. It has, however, been realised that a more versatile scenario could be achieved by making use of the interplay between dielectric cavity confinement and dipole orientation. Besides position dependence the main properties exhibit strong dipole orientational dependece suggesting that the system is a possible candidate as a qubit for a scalable hardward architecture for quantum information processing. Cavity confinement can control processes since it can lead to the enhancement and the complete suppression of the de-excitation process, with further control provided by the manipulation of the dipole orientation by optical means. This article is concerned with the modelling of quantum processes for quantum systems localised in artificially fabricated structures made of high conductivity metals and dielectric cavities. The essential features of cavity field confinement in this context are presented and the effects on de-excitation rates are assessed.

Dendrimers are synthetic, highly branched polymers with an unusually high density of chromophores. As a result of their extremely high absorption cross-sections for visible light, they represent some of the most promising new materials for energy harvesting. Although the signature of the bonding structure in dendrimers is an essentially fractal geometry, the three-dimensional molecular folding of most higher generation materials results in a chromophore layout that is more obviously akin to concentric spherical shells. The number of chromophores in each shell is a simple function of the distance from the central core. The energy of throughput optical radiation, on capture by any of the chromophores, passes by a multi-step but highly efficient process to the photoactive core. Modeling this crucial migration process presents a number of challenges. It is far from a simple diffusive random walk; each step is subject to an intricate interplay of geometric and spectroscopic features. In this report, the first results of a new approach to the theory is described, developed and adapted from an adjacency matrix formulation. It is shown how this method offers not only kinetic information but also insights into the typical number of steps and the patterns of internal energy flow.

Electron energy structure and optical response functions of semiconducting conjugated polymers, Poly-Phenylene- Vinylenes (PPV) are studied by first principle modeling based on the density functional theory (DFT). Equilibrium atomic geometries are obtained through total energy minimization. Electron energy structure and optical properties are calculated using generalized gradient approximation method with ab initio pseudopotentials. Predicted data are compared with measured optical absorption spectra of PPV. Dominant contribution of the optical excitations related to the delocalized π-electrons within the PPV chains is demonstrated by comparative analysis of experimental and theoretical data. Optical absorption spectra of acceptor type PPV chains show substantial blue shift with respect to the donor type of the PPV polymer. Comparison between calculated and measured optical spectra demonstrates that the shift could be attributed to the structural deformations of the benzene rings of the host PPV unit due to the interaction with the atoms of the derivative groups.

In this article the rates of electron scattering via phonons in the single-wall armchair carbon nanotubes were calculated within the approximation of tight-binding atoms and graphene zone folding.

Basic mechanisms of the interaction of electron beam tavelling through a carbon nanotube with electromagnetic wave, resulting in the radiative instability and generation of stimulated radiation, are considered. The effect of the surface electromagnetic wave slow-down in CNT (c/v > 100) [Slepyan et al., Phys. Rev. B 60, 17136, 1999] is exploited to synchronize the wave and the beam and thus to realize the Cherenkov radiation mechanism. Alternative mechanism of the electron beam instability is proposed based on the undulator emission arising due to the interband transitions of electrons moving in nanotube. The dispersion equations of the electron beam instability and threshold conditions for the stimulated radiation are derived and studied. The analysis of the threshold conditions estimates the possibility of the stimulated emission by electron beam as realistic and attainable at present-day experimental technique.

The parametrization scheme for carbon nanotubes (CNTs), helical parametrization, has been developed, where the crystalline structure of non-zigzag (n₁, n₂) CNTs is described as a set of n₂ double helices, and the electron energy spectrum of the CNTs consists of n₂ different helicoidal branches. The parametrization scheme is shown to be natural and more convenient for analyzing the electromagnetic response properties of chiral CNTs. Bloch equations for the density matrix have been obtained and adapted for the helical parametrization that allows studying the interaction between chiral CNTs and electromagnetic fields with arbitrary polarization and spatial structure. As an example, the spectra of high-order harmonics in chiral CNTs have been evaluated from the Bloch equations.

We computed three measures each of the durations and average speeds of ultrashort optical pulsed plane waves transmitted through linear and nonlinear chiral sculptured thin films (STFs). The durations tended in general to decrease with increasing carrier wavelength (save for an exception involving the circular Bragg phenomenon), while average speeds tended to increase under the same conditions. Durations tended to increase with increasing nonlinearity displayed by the chiral STF, while average speeds tended to decrease. The results quantify some aspects of ultrashort optical pulse shaping by chiral STFs, which heretofore had only been studied qualitatively.

Spectral and localization properties of electromagnetic wave propagation in fractal nanostructures have been reviewed and summarized. Quarter-wave binary multilayer structures have been chosen as a simplest model that would allow to isolate effects pertaining to the geometrical organization of the structure. Intra- and inter-generation scaling relations have been obtained and compared to those known for quasiperiodic structures. Localization patterns have been shown to have an intermediate form between extended and localized eigenstates.