Size dependence of the polarizability and Haynes rule for an exciton bound to an ionized donor in a single spherical quantum dot

International audienceWe study the effect of an external electric field on an exciton bound to an ionized donor (D+, X) confined in a spherical quantum dot using a perturbative-variational method where the wave function and energy are developed in series of powers of the electric field strength. After testing this new approach in the determination of the band gap for some semiconductor materials, we generalize it to the case of (D+, X) in the presence of the electric field and for several materials ZnO, PbSe, and InAs, with significant values of the mass ratio. Three interesting results can be deduced: First, we show that the present method allows to determine the ground state energy in the presence of a weak electric field in a simple way (E = E-0 - alpha f(2)) using the energy without electric field E-0 and the polarizability a. The second point is that our theoretical predictions show that the polarizability of (D+, X) varies proportionally to R-3.5 and follows an ordering alpha(D0) < alpha(X) < alpha((D+, X)). The last point to highlight is that the Haynes rule remains valid even in the presence of a weak electric field

Simulating the Effect of Modulated Tool-Path Chip Breaking On Surface Texture and Chip Length

One method for creating broken chips in turning processes involves oscillating the cutting tool in the feed direction utilizing the CNC machine axes. The University of North Carolina at Charlotte and the Y-12 National Security Complex have developed and are refining a method to reliably control surface finish and chip length based on a particular machine&#x27;s dynamic performance. Using computer simulations it is possible to combine the motion of the machine axes with the geometry of the cutting tool to predict the surface characteristics and map the surface texture for a wide range of oscillation parameters. These data allow the selection of oscillation parameters to simultaneously ensure broken chips and acceptable surface characteristics. This paper describes the machine dynamic testing and characterization activities as well as the computational method used for evaluating and predicting chip length and surface texture

Simultaneous effects of dielectric mismatch and electric field on the electronic properties in Si nanodots

By using the finite element method within the effective mass approximation, the effects of both dielectric confinement and electric field on the shallow-donor binding energy and polarizability in spherical Si quantum dots are investigated. It is found that: (i) the ground state binding energy is significantly increased by the dielectric mismatch at the dot interface, (ii) in the freestanding nanodot the competition between the electric field, polarization charges induced at interfaces and impurity position determines the symmetry of the electron probability distribution; (iii) the donor polarizability decreases with electric field strength and this effect is more pronounced for large dielectric mismatches. Therefore, the electronic properties of the nanocrystals could be tuned by proper tailoring of the surrounding medium dielectric constant as well as by varying the electric field. The normalized binding energy of an on-center hydrogenic donor is also been estimated and the results are in good agreement with the previous reported values

Stark shift and dissociation process of an ionized donor bound exciton in spherical quantum dots

The effect of an electric field on the ground state energy of an exciton bound to an ionized donor (D+, X) was studied in CdSe spherical quantum dots where quantum confinement is described by an infinitly deep potential. Calculations have been performed in the framework of the effective mass approximation using a variational method by choosing an appropriate sixty-terms wave function taking into account different interparticles correlations and symetry distorsion induced by the electric field. It appears that the Stark shift is significant even for low fields and depends strongly of spherical dot sizes. The competition between the confinement effect and the Stark effect is discussed as function of the spherical dot size and the applied electric field strength. The (D+, X) Stark shift is estimated and its behavior is discussed as a function of the dot radius and electric field strength. The electron and hole average distances have also been calculated and the role of the ionized donor in the excitonic dissociation is established

Robust nonparametric estimation of the intensity function of point data

Cross-validation, Earthquake data, Kernel regression, Local polynomial, M-type estimation, Recursive algorithms, San Francisco bay,