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We study charge transport in a source-channel-drain system with a time-varying applied gate potential acting on the channel. We calculate both the current flowing from the source into channel and out of the channel into the drain. The current is expressed in terms of nonequilibrium Green’s functions. These nonequilibrium Green’s functions can be determined from the steady-state Green’s functions and the equilibrium Green’s functions of the free leads. We find that the application of the gate potential can induce current to flow even when there is no source-drain bias potential. However, the direction of the current from the source and the current to the drain are opposite, thereby resulting in no net current flowing within the channel. When a source-drain bias potential is present, the net current flowing to the source and drain can either be attenuated or amplified depending on the sign of the applied gate potential. We also find that the response of the system to a dynamically changing gate potential is not instantaneous, i.e., a relaxation time has to pass before the current settles into a steady value. In particular, when the gate potential is in the form of a step function, the current first overshoots to a maximum value, oscillates and then settles down to a steady-state value.

The effect of iron atom junction on transport characteristics of carbon–silicon mixed chain has been studied from an ab initio study. At zero bias, the Fe(CSi)${}_n$ system appears to be the decrease of the conductance as the number of the Si–C pairs in the chain increases (n changes). When n$>$ 5, the conductance tends to zero. These changes are independent of the transferring charge of the system, depending on the coupling of the electrodes and the central region. Under bias, the higher the bias voltage, the bigger the transmission coefficient of the system, and the transmission peak moves closer to the Fermi level. The I–V curves of Fe(CSi)₂ and Fe (CSi)₃ are linear, showing the behavior of metal resistance.

The transport properties of gold clusters with eight and nine atoms between gold electrodes are investigated by using non-equilibrium Green’s function method combined with density functional theory. Negative differential resistance effect is found both in Au₈ and Au₉. From a new respect, the mechanism for the negative differential resistance effect is explored through calculating the number of electrons of the atoms in the clusters at different bias voltages. When Au₉ takes vertical orientation, it is found that the voltage can change the coupling strength of the sandwiched system. When the value of the voltage is small, the current increases with decreasing of the cluster-electrode separation. But when the voltage increases to a certain value, the current decreases with decreasing of the cluster-electrode separation. When Au₉ takes parallel orientation, different from other electronic transport systems, it is found that the transport behaviors for Au₉ are not sensitive to the cluster-electrode separation, showing that this configuration has a better transport stability over the changes in distance, which may provide some new clues for developing future electron device.

Single-walled carbon nanotubes (SWNTs) are grown by thermal chemical vapor deposition at 900°C using methane. Application of an electric field (0.4 V/μm) in situ during the growth process results in directed growth of SWNTs on a horizontal plane bridging a distance as long as 25 μm. This approach is useful in the fabrication of nanotube based transistors.

Terahertz (THz) electroluminescence was produced by three different types of sources: intersubband transitions in silicon germanium quantum wells, resonant state transitions in boron-doped strained silicon germanium layers, and hydrogenic transitions from dopant atoms in silicon. The devices were grown by molecular beam epitaxy, fabricated by dry etching, and characterized by infrared spectroscopy. The absorption of THz was observed in silicon germanium quantum wells at energies corresponding to heavy hole and light hole intersubband transitions. These results suggest that SiGe nanotechnology is attractive for THz device applications.

The fabrication of nanodevices and nanosystems having dimensions smaller than 100 nm requires the ability to produce, control, manipulate, and modify structures at the nanometer scale. Physical and chemical nanolithography techniques have been demonstrated to be promising because of the low cost and high throughput. Although the physical and chemical nanolithography techniques can pattern small features on single chips or across an entire wafer, there are considerable challenges when dealing with complex nanostructures, alignment and multilevel stacks. In this paper, the problems are reviewed and potential solutions suggested.

In this paper, we discuss the role of material parameters and external field effects on a thin film topological insulator(TI) in the context of quantum phase transition (QPT). First, we consider an in-plane tilted magnetic field and determine the band structure of the surface states as a function of the tilt angle. We show that the presence of either a hybridization term or hexagonal warping or a combination of both leads to a semi-metal to insulator phase transition which is facilitated by their ${𝒫}{𝒯}$ symmetry breaking character. We then note that while the introduction of an electric field does not allow for this QPT since it does not break ${𝒫}{𝒯}$ symmetry, it can be used in conjunction with a tunneling element to reach a phase transition efficiently. The corresponding critical point is then nontrivially dependent on the electric field, which is pointed out here. Then, we demonstrate that including a hexagonal warping term leads to an immediate ${𝒫}{𝒯}$ symmetry violating QPT.

Carbon is one of the elements most abundant in nature. It is essential for living organisms, and as an element occurs with several morphologies. Nowadays, carbon is encountered widely in our daily lives in its various forms and compounds, such as graphite, diamond, hydrocarbons, fibers, soot, oil, complex molecules, etc. However, in the last decade, carbon science and technology has enlarged its scope following the discovery of fullerenes (carbon nanocages) and the identification of carbon nanotubes (rolled graphene sheets). These novel nanostructures possess physico-chemical properties different to those of bulk graphite and diamond. It is expected that numerous technological applications will arise using such fascinating structures. This account summarizes the most relevant achievements regarding the production, properties and applications of nanoscale carbon structures. It is believed that nanocarbons will be crucial for the development of emerging technologies in the following years.

Casimir energies and forces have been calculated in various configurations and boundary conditions. The calculations indicated that the Casimir energy might change its sign depending not only on the boundary conditions but also on geometry and topology of the configuration. With the development of nanotechnology, it is known that repulsive Casimir force is very important in nanodevices. In this paper, we review some research results on repulsive Casimir force, and discuss whether it could be realizable theoretically and experimentally.