Narrow Results

The effect of incoherent pumping field on absorption spectrum and population inversion in a four-level quantum dot nanostructure are investigated. It is found that with incoherent pumping field the probe field absorption can be converted to probe field gain. Also, it is found that with combine effect of incoherent pumping field and electron tunneling the lasing can be obtained in the absence or presence of population inversion.

Graphene single electron transistor (SET) as a coulomb blockade (CB) device operates based on the quantum mechanical effect. Its desired current is achieved by overcoming the CB energy that depends on the total capacitance of SET. Therefore, small size of graphene quantum capacitance is suitable for SET structure because it plays a dominant role in the total capacitance. In this paper, the density of state (DOS) model of graphene SET is suggested because of its important effect on many physical properties. Furthermore, carrier concentration as a key factor in quantum capacitance is modeled. Finally, the quantum capacitance of graphene SET based on the fundamental parameters is modeled and compared to the experimental data, so an acceptable agreement between them is reported. As a result, silicon SET can be replaced with graphene SET because of its lower quantum capacitance and also higher operation speed than the silicon one.

Electron tunneling in small-area junctions has been treated. It is found that at the appropriate set of barrier parameters and electronic characteristics of the electrodes, the quantization of the lateral wave vector component manifests itself in the differential tunneling conductance as quite noticeable singularities. The dependance of the second derivative of the tunnel current versus the bias voltage calculated for the perfectly smooth quantized electrode should contain distinct periodic dips. It is shown that for real not perfectly smooth electrodes the resonance structure caused by the commensurate states may be observed.

In this paper, we study the localization of an electron in a binary quantum system formed by a pair of quantum dots (QDs). The traditional theoretical consideration of such systems is limited to the symmetrical case when QDs in such double quantum dot (DQD) are assumed identical in all respects. In this paper, we model the effects of breaking QD similarities in a DQD by studying two-dimensional (2D) DQDs as a double quantum well (DQW). This is done by solving the Schrödinger equation, with parameters chosen to describe an InAs/GaAs heterostructure. We calculate the energy spectrum of the electron confinement and the spectral distribution of localized/delocalized spatial states. Both symmetric and asymmetric QW shapes are considered and their effects are compared. The effects of symmetry breaking are explained within the framework of the two-level system theory. We delineate the QW weak and strong coupling cases in DQW. In particular, we show that the coherence in ideal DQW is unstable in the case of a weak QW coupling. Within the framework of the proposed approach, a charge qubit realized on a DQD is discussed and, as an example, a qubit based on an almost ideal DQD is proposed.

The electric-field behavior of the resonance features in the photoelectric characteristics of InAs/GaAs heterostructures is studied. We discuss the emission mechanism of the charge carriers excited from InAs quantum dots into the GaAs matrix. It was shown that at the temperature of liquid nitrogen the photocurrent in a strong transverse electric field is only determined by the effect of electron tunneling through the barrier formed at the quantum-dot interfaces. Comparison of the experimental curves with the quasi-classical expression for the tunneling current component and analysis of the potential structure allowed us to specify some parameters of investigated heterostructures. Analysis of the electric-field dependences of the photocurrent-tunneling component revealed resonance peculiarities connected with the local defect states in the vicinity of InAs/GaAs interface.

Transmission coefficient and field emission current in a silicon vacuum nanostructure with a pyramidal cathode were calculated as a function of applied voltage, size of the cathode and distance between the anode and cathode by the phase function method. The field emission current density in the range of 1–10 A/cm² was found to be achieved by varying the distance between the anode and cathode in the range of 15–25nm and the applied voltage in the range of 1.2–2.3V.

This short note covers some of my favorite scientific accomplishments of Britton Chance.

The quest for more energy remains vital to energy sustainability. In the wake of several adverse consequences of indiscriminate combustion of fossil fuel, there is an urgency to exploit our natural environment for ecologically benign alternatives. This search led to S. anisatum dye being investigated for its prospective application in dye-sensitized solar cells. Phytochemical screening revealed the presence of phenols, flavonoids, tannins, glycosides, terpenoids and protein, presenting a wide repertoire of chromophore selection for charge transport. UV/VIS spectroscopy showed that S.anisatum dye exhibits multiple peak absorbances of radiation within the near ultraviolet and the visible region of the electromagnetic spectrum of light. The consequent adsorption of its chromophores into titanium structure, amplitude of interatomic vibrations of the novel structures formed in S. anisatum dye were subject of our investigation. The outcome shows TiO₂/S.anisatum dye interface reveals the impact of orientation on output photovoltaic performance of S.anisatum dye-sensitized solar cells with a short circuit current of 0.07 mA, open circuit voltage of 68.8 mV, fill factor value of 0.84 and the output efficiency was 0.027 % using KBr electrolyte. This is a comparatively good result considering previous records of dye-sensitized solar cell photovoltaic performance. The significance of these results was re-analyzed from molecular perspective with the aid of scanning electron microscopy (SEM). A need to boost the efficiency necessitated the interpretation of SEM micrographs using Gwwydion software program. These presented possible areas for charge transport within the electron shells of S.anisatum dye nanocomposite, and regions where tunneling occurred providing a much needed insight for future studies. Consequently, this study was expanded to accommodate the influence of bandgap on electron occupancy in S.anisatum shells. This elucidation captures the molecular dynamics of charge transport versus tunneling, consequent upon output performance of dyesensitized solar cell technology explained with quantum principles. The application of this work is particularly relevant in modelling, photovoltaic simulations and building energy efficient models.