Under construction
Toroidal systems draw much interest in different fields of physics. In photonics, the development of optical resonators with a toroidal shape has enabled to reach ultra-high values of the Q factor. These resonators are on the scale of micrometers. In the nanometer range, toroidal nanoantenna in silver or in gold have led to many interesting applications as improvement of solar-cell efficiency, biosensing and detection of particles. Fullerene nanotoroids have been observed. Their shape, size, and remarkable properties point to the possibility of innovative applications.
This page web is devoted to the description of the activity of the SPIN research group on the physics of nanotoroids.
A first subject of research is devoted to the study of polar phonon modes in tori made of ionic semiconductors such as GaAs, ZnO, ... . Besides phonons present in the bulk of crystals, there exist surface phonons in nanotoroids. In polar semiconductors, these phonons produce an electric field which extend outside the torus. The results of calculations in the framework of the continuum dielectric approximation are presented in the preprint below. The left figures show a snapshot of the electric potential map for different torus size and dfferent phonon modes.
This page web is devoted to the description of the activity of the SPIN research group on the physics of nanotoroids.
A first subject of research is devoted to the study of polar phonon modes in tori made of ionic semiconductors such as GaAs, ZnO, ... . Besides phonons present in the bulk of crystals, there exist surface phonons in nanotoroids. In polar semiconductors, these phonons produce an electric field which extend outside the torus. The results of calculations in the framework of the continuum dielectric approximation are presented in the preprint below. The left figures show a snapshot of the electric potential map for different torus size and dfferent phonon modes.
Figure caption.
Preprint:
Polar interface phonons in ionic toroidal systems
Authors: N.D. Nguyen, R. Evrard, SPIN
Michael A. Stroscio, Department of Physics, University of Illinois at Chicago, IL, USA.
Michael A. Stroscio, Department of Physics, University of Illinois at Chicago, IL, USA.
Abstract: We use the dielectric continuum model to obtain the polar (Fuchs-Kliewer like) interface vibration modes of toroids made of ionic materials either embedded in a different material or in vacuum, with applications to nanotoroids specially in mind. We report the frequencies of these modes and describe the electric potential they produce. We establish the quantum-mechanical Hamiltonian appropriate for their interaction with electric charges. We show that the interaction between an ion lying at the torus center and these polar vibration modes leads to an important attractive energy, which can reach 1 eV in the case of materials ionic enough and toroids with a narrow free space about the axis.
Full text in pdf: tor_phon2col.pdf
Helmholtz equation in tori
The description of many properties of nanoscopic systems in the framework of a continuous-medium approximation requires the solution of the Helmholtz equation. This is the case of the bulk-like acoustic phonons and the confined optical phonons, of the electron and hole states within the band-mass approximation. In collaboration with Prof. M. A. Stroscio of the University of Chicago, the SPIN research group has developed a numerical procedure of obtaining the eigenvalues and eigenfunctions of the Helmholtz equation inside tori.