Narrow Results

The effects of the vascular disrupting agent AVE8062 on tumor and normal tissue samples were investigated by particle-induced X-ray emission (PIXE) analysis using quantum dots (QDs). We investigated fibrosarcoma tumors in mice, and used kidney tissue as a control. Non-targeted QDs were used to characterize the tissue regions where blood flow is interrupted by AVE8062. We found that the concentration of the QDs in the tumors and kidneys exposed to AVE8062 was lower than that of the control group. Sub-millimeter PIXE analysis (with a beam size of 0.5 $\times$ 0.5 mm²) was used to investigate the spatial distribution of QDs in the tissue samples. We found that the QDs were accumulated in localized regions of the kidney section of the AVE8062-treated group whereas the QDs were uniformly distributed in the control kidney. This suggests that AVE8062 caused blood flow interruption not only in the tumor samples but also in the normal blood vessels in the kidneys.

Quantum Dots (QD) provide unique opportunities to extend all the basic properties of heterostructure lasers and move further their applications. Practical fabrication of QD lasers became possible when techniques for self-organized growth allowed fabrication of dense and uniform arrays of narrow-gap nanodomains, coherently inserted in a semiconductor crystal matrix. Using of InAs QD lasers enabled significant improvement of device performance and extension of the spectral range on GaAs substrates to mainstream telecom wavelengths. Continuous wave 1.3 μm room-temperature output power of ~300 mW single mode for edge-emitters and of 1.2 mW multimode for vertical-cavity surface-emitting lasers are realized. Long operation lifetimes are manifested. The breakthrough become possible both due to development of self-organized growth and defect-reduction techniques in QD technology.

We present calculations of the acoustic phonon spectra for a variety of quantum dots and consider the cases where the quantum dots are both free-standing and embedded in a selection of different matrix materials — including semiconductors, plastic, and water. These results go beyond previous calculations for free-standing quantum dots and demonstrate that the matrix material can have a large effect on the acoustic phonon spectrum and consequently on a variety of phonon-assisted transitions in quantum-dot heterostructures.

The technology progress and increasing high density demand have driven the nonvolatile memory devices into nanometer scale region. There is an urgent need of new materials to address the high programming voltage and current leakage problems in the current flash memory devices. As one of the most important nanomaterials with excellent mechanical and electronic properties, carbon nanotube has been explored for various nonvolatile memory applications. While earlier proposals of "bucky shuttle" memories and nanoelectromechanical memories remain as concepts due to fabrication difficulty, recent studies have experimentally demonstrated various prototypes of nonvolatile memory cells based on nanotube field-effect-transistor and discrete charge storage bits, which include nano-floating gate memory cells using metal nanocrystals, oxide-nitride-oxide memory stack, and more simpler trap-in-oxide memory devices. Despite of the very limited research results, distinct advantages of high charging efficiency at low operation voltage has been demonstrated. Single-electron charging effect has been observed in the nanotube memory device with quantum dot floating gates. The good memory performance even with primitive memory cells is attributed to the excellent electrostatic coupling of the unique one-dimensional nanotube channel with the floating gate and the control gate, which gives extraordinary charge sensibility and high current injection efficiency. Further improvement is expected on the retention time at room temperature and programming speed if the most advanced fabrication technology were used to make the nanotube based memory cells.

We have observed that Terahertz (THz) irradiation to a carbon nanotube quantum dot (CNT-QD) leads to the generation of an excess current in the Coulomb blockade regime. It was found that this THz detected signal survives even when the incident THz wave is extremely weak (~1 fW). This means that the CNT-QD could works as a highly sensitive THz detector.

This paper presents quantum dot channel (QDC) Field Effect Transistors (FETs) which are configured as nonvolatile memories (NVMs) by incorporating cladded GeO_x-Ge quantum dots in the floating gates as well as the transport channels. The current flow and the threshold characteristics were significantly improved when the gate dielectric was changed from silicon dioxide (SiO₂) to hafnium aluminum oxide (HfAlO₂), and the control dielectric was changed from silicon nitride (Si₃N₄) to hafnium aluminum oxide (HfAlO₂). The device operations are explained by carrier transport in narrow energy mini-bands which are manifested in a quantum dot transport channel.

Quantum Dot (QD) Optical Modulators can provide high speed modulation in low cost indirect bandgap materials. Si based optical modulators can be realized with the inclusion of self-assembled Ge QDs to provide low cost, high speed CMOS compatible optical devices. In this paper, we present the optical characterization of a novel Ge-QD Si-SiO2 based waveguide for use in as an optical modulator. Optical performance figures of merit are investigated including insertion loss (IL) measurements, and Wavelength dependent loss (WDL). We present a multimode waveguide fabricated with conventional CMOS processing. The waveguide provides 4.43dB/cm loss and individual discrete absorption regimes corresponding to the unique minibands produced by superlattice properties of the self-assembled Ge QDs in the IR regime. Absorption properties of the Ge QDs are demonstrated and verified against the QD superlattice bandgap model. Analysis and simulation is presented to qualitatively compare the QD bandgap energies with the reported optical properties. The QD functionalized structure demonstrates the fundamental optical principles of a QD waveguide, setting the foundation for a active modulation testing of this QD based optical modulator.

This paper describes the recent advances in device designs and optical transmission applications of semiconductor optical amplifiers (SOA). The device advances described are quantum-dot-based SOA and photonic-integrated circuits using SOA. The use of nonlinear properties of SOAs in high-speed optical transmission is discussed.

Studying the transport characteristics of carriers in quantum dot (QD) film provides theory support for the structure design and performance improvement of QD film device. However, time of flight experiment can only test the global optoelectric current signal brought by the carrier transport, and cannot analyze the carrier transport in the transport layer. Here, the hopping transport model of photogenerated carriers in QD films was established to study the expansion and drift movement of carriers in the PDE module of COMSOL. According to the material properties of the actual QD films, the carrier transport in single-size QD films was studied.

We study the analogue of the Aharonov–Bohm effect for bound states for a neutral particle with a permanent magnetic dipole moment interacting with an external field. We consider a neutral particle confined to moving between two coaxial cylinders and show the dependence of the energy levels on the Aharonov-Casher quantum flux. Moreover, we show that the same flux dependence of the bound states can be found when the neutral particle is confined to a one-dimensional quantum ring and a quantum dot, and we also calculate the persistent currents in each case.

We start by investigating the arising of a spin-orbit coupling and a Darwin-type term that stem from Lorentz symmetry breaking effects in the CPT-odd sector of the Standard Model Extension. Then, we establish a possible scenario of the violation of the Lorentz symmetry that gives rise to a linear confining potential and an effective electric field in which determines the spin-orbit coupling for a neutral particle analogous to the Rashba coupling [E. I. Rashba, Sov. Phys. Solid State2, 1109 (1960)]. Finally, we confine the neutral particle to a quantum dot [W.-C. Tan and J. C. Inkson, Semicond. Sci. Technol.11, 1635 (1996)] and analyze the influence of the linear confining potential and the spin-orbit coupling on the spectrum of energy.

We investigate the Fano line shape in electron transport through a quantum dot in presence of dephasing. The dephasing effect is introduced by the Büttiker model. We derive a generalized Fano formula for the conductance that includes the components of the standard Fano line shape and the Breit–Wigner line shape. According to this formula the Fano parameter |q| decreases when the dephasing strength increases by increasing the temperature. The increase of the half width of the resonance peak by increasing the temperature measured by Zacharia et al. [Phys. Rev.B64, 155311 (2001)] which is more rapid than expected from the ordinary theories is possibly attributed to the dephasing.

The thermal noise of DC Josephson current in the superconducting leads coupled with a quantum dot system is investigated, and the general thermal current noise formula is derived in the presence of Zeeman field. The resonant structure versus gate voltage and Zeeman energy are displayed. Novel structures associated with the bound state and normal energy state are obtained. As the temperature is low, the Andreev reflection plays an important role in thermal noise and this provides new channels for electron to tunnel. However, if the temperature is high enough, the thermal noise due to Andreev reflection is trivial compared with the normal transport one. The thermal noise versus phase difference is also given to exhibit the temperature dependence. The Fano factor versus phase is much larger than 1 if the temperature is nonzero.

We find an analytical expression for the conductance of a single electron transistor in the regime when temperature, level spacing and charging energy of a grain are all of the same order. We consider the model of equidistant energy levels in a grain in the sequential tunneling approximation. In the case of spinless electrons, our theory describes transport through a dot in the quantum Hall regime. In the case of spin-½ electrons, we analyze the line shape of a peak, shift in the position of the peak's maximum as a function of temperature and the values of the conductance in the odd and even valleys.

Using a realistic model of an Aharonov-Bohm ring with a quantum dot in one arm and a control gate in the other, we demonstrate phase persistence in the Fano and Aharonov-Bohm effects as has been observed in experiments. The Fano effects in the conductance is examined by changing the states in the Aharonov-Bohm ring by the control gate.

Small numbers N<5 of two-dimensional Coulomb-interacting electrons trapped in a parabolic potential placed in a perpendicular magnetic field are investigated. The reduced wave function of this system, which is obtained by fixing the positions of N-1 electrons, exhibits strong correlations between the electrons and the zeros. These zeros are often called vortices. An exact-diagonalization scheme is used to obtain the wave functions and the results are compared with results obtained from the recently proposed rotating electron molecule (REM) theory. We find that the vortices gather around the fixed electrons and repel each other, which is to a much lesser extend so for the REM results.

Polaronic shifts of the donor binding energies in an electric field in a quantum well are presented here. The properties of a polaron in a quantum well are investigated within the second-order perturbation theory. GaAs/Ga_1-xAl_xAs quantum well is chosen as an example to calculate the polaron energy. Since this system is a weak polar material, the electron-lattice coupling constant is small so this effect is considered by second-order perturbation theory. The polaronic effects are suppressed when an electric field is coupled. The diamagnetic susceptibility is also calculated and the results are compared with the results obtained using other approximation methods.

On the basis of the finite element approach, we systematically investigated the strain field distribution of conical-shaped InAs/GaAs self-organized quantum dot using the two-dimensional axis-symmetric model. The normal strain, the hydrostatic strain and the biaxial strain components along the center axis path of the quantum dots are analyzed. The dependence of these strain components on volume, height-over-base ratio and cap layer (covered by cap layer or uncovered quantum dot) is investigated for the quantum grown on the (001) substrate. The dependence of the carriers' confining potentials on the three circumstances discussed above is also calculated in the framework of eight-band k·p theory. The numerical results are in good agreement with the experimental data of published literature.

We investigate a two sub-rings mesoscopic system embedded with one quantum dot in common. Owing to the screening cloud of the two sub-rings, the change of the magnetic flux and the number of lattice sites in one sub-ring influence the persistent current not only in itself but also in another. Kondo-assisted (suppressed) tunneling appears in the two sub-rings system constructed by even (odd) number of lattice sites.

We introduce a general analysis method, which allows us to simulate the operation of high-performance molecular nano-devices and to design the expected function of a wide range of devices in nano-scale size. The method is based on the use of a resonant tunneling phenomenon, admitting strong electron correlation in a quantum dot with degenerated states. Three examples of the application of this method are given: Coulomb repulsion, uncorrelated resonant tunneling, and electron-phonon interaction. It is shown that there is a good agreement with experimental data in all three cases.