Zhijing Hu

Asymmetric polarization induced by strong electric field on spherical semiconducting particles

A spherical conductive particle immersed in a uniform electric field acquires a charge distribution that displays odd symmetry with respect to the equatorial plane perpendicular to the applied field, while the internal field exhibits even symmetry. This configuration in symmetry is preserved in metal particles for a large intensity applied field, owing to the abundance in electrons. In extrinsic semiconductor particles, this symmetry is not maintained when the applied field approaches high intensity (∼104 V/cm for a dopant concentration of 1017 cm−3) as a result of depletion of mobile charge carriers (electrons or holes) in one of the hemispheres. While the mobile charges are able to congregate close to the surface on one side of the particle, the exposed dopant ions on the opposite side are unable to migrate, resulting in the broken symmetry when the applied field reaches a certain intensity.

Electric polarizability of a conductive nanoparticle and its equivalent circuit representation

Dispersion effects and power dissipation by a conductive nanoparticle are revealed by its frequency dependent polarizability, which collectively represents the response of the charge species within the particle to an applied field when the particle diameter is small compared to the wavelength in the embedding medium. Plasmonic interactions in nanoparticles are impetus to a variety of novel device and waveguiding structures realized over frequencies ranging from terahertz to visible optical region. Based on the consideration of the physical process of charge polarization and the frequency dependence of the electric polarizability, equivalent circuits for semiconductor and metal nanoparticles have been developed to facilitate the analysis of aggregates of nanoparticles and composite structures by network theory and effective medium theory.

Application of wireless technology to retailing at drive-through facilities

A voiceless ordering system for the drive-through facility of the fast-food industry has been proposed and implemented. To be integrated with the existing audio-based system, tracking of the customers position in the ordering queue needs to be automated by proper sensing devices while the information contents of the order are being transmitted to the order taking register. These are accomplished by Bluetooth sensor function and Wi-Fi application on the mobile device respectively. Descriptions of the system architecture and user interface are presented. The implemented system can be adapted to other retailing functions such as grocery purchase and pharmacy transactions.

Pedagogical construction of a green's function from physical consideration

By invoking an elementary problem in electrostatics, the Greens function for the Poissons equation in one dimension is obtained from physical principles. Simple in mathematical form, the physical implications of the function can readily be drawn from its graphical appearance, while the consequence of the singular nature of the source that gives rise to the electric field and the corresponding potential function can readily be recognized. Relation of the Greens function for bounded domain to that in infinite space can be seen by receding the boundary to infinity. A series representation of the function can be obtained by augmenting it to form a periodic function, followed by series expansion of the latter. The discussion borne out by this development can provide an early exposure to the concept of the Greens function that brings forth physical insight. Knowledge of ordinary differential equation and Fourier series is sufficient to comprehend the discussion.

Symmetry and symmetry breaking in a class of solutions of the Poisson-Boltzmann equation

Symmetry in the charge distribution and internal field in an extrinsic semiconductor sphere immersed in an originally uniform electric field ceases to be sustained at high field intensities. Governed by the Poisson-Boltzmann equation, these distribution functions are studied for their field dependence and implications on the polarizabilities of a sphere and a pair of spheres made of semiconductor. The potential of the nonlinear response in the polarization for realization of new devices in the Terahertz frequency range are discussed.

Terahertz space-charge interactions in a semiconductor nanoplate

To properly account for space-charge effects, transport models can be employed in the analysis of charge motions within semiconductor nanostructures. In this paper, we present the analysis and computations of internal charge and field distributions in a semiconductor nanoplate. Analytical and numerical simulation results reveal space-charge waves excited in the plate as the bulk plasma frequency is approached, which is in the terahertz band. A lumped equivalent circuit is developed to characterize the dispersion properties and to facilitate the consideration of more complex structures based on aggregates of nanoplates for potential circuit and waveguide applications in the terahertz frequency range.