Nanoscale-Enhanced Processes in a Quantum Dot Structures

Nanocrystal quantum dots are a new form of matter that can be considered as "artificial atoms." They have linear discrete absorption spectra ( atoms) and photoluminescence tunable over a wide range, from the far IR to the deep UV. Nanocrystal size is the only parameter that governs optical transition energies. On the other hand, we can move them around and form quantum dot molecules and threedimensional ordered arrays of these atoms. In addition, very strong confinement of carriers enhances nonlinear optical and magnetic properties of nanocrystals and allows the creation of new materials with very unusual properties.

Considerable progress has been made in recent years both in chemical synthesis and physical understanding of colloidal nanostructures, including much critical theoretical work on optical and transport properties of nanocrystals, nanorods, and nanowires at the NRL Nanoscience Institute. A theory that takes into account the effect of the surface on the nanocrystal energy spectra has been developed. This allows one to predict and describe the size dependence of the optical gap opening in HgTe, InSb, and other narrow-gap semiconductor nanocrystals [1], which shows the capability of making HgTe nanocrystal quantum dot lasers working at 1.6 µm (a wavelength that ropagates through atmosphere without absorption and scattering and is eye safe).

We have also predicted a giant splitting of the electron-spin levels in single Mn-iondoped nanocrystals that exists in a zero external magnetic field. This enables one to use these nanocrystals as a nonlinear voltage control spin-filter that allows one to reach 98% polarized electron spin current at room temperature [2].

Recently, we have demonstrated that optical properties of strongly anisotropic colloidal particles, such as nanorods, are controlled by the spectra of one-dimensional excitons. The large binding energy and the short radiative decay time of these excitons predicted theoretically show clearly that nanorods should be much more efficient (40 times) than nanocrystals for the optical labeling of biological molecules, which can be used for nanocrystal-based ultrasensitive detection of toxic biological agents or explosives.

1. "The Electronic Structure of Semiconductoranocrystals," Annual Review of Material Science 30, 475-521 (2000).
2. "Paramagnetic Ion-doped Nanocrystal as a Voltage-controlled Spin Filter," Phys. Rev Lett. 87, 206601 (2002); A US patent IEB approved (case no. 83, 185) was filed at the NRL.

Contact the Principal Investigator, Alexander Efros, for more information