Colloidal versus epitaxial quantum confined systems: the influence of a surface on optoelectronic properties of nanomaterials

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In the blooming field of nanotechnology, we are still in the infancy of tool development at this small scale. The interaction of these tools with the environment surrounding them, including complex molecules which can be bigger than the tool itself (!), is not well understood. The tools we are interested in are crystalline semiconductor particles so small that one could fit more than ten thousands of them on the edge of a piece of paper. These nanometer-sized particles are called quantum dots to underline that their behaviour is governed by the laws of quantum mechanics. In this sense, they behave like artificial atoms for which we can engineer the properties eventually leading to entirely new materials. However compared to the natural atoms, we don't have the equivalent of a periodic table of elements to guide us on how the quantum dots interact together and with other molecules. To probe this interaction, we will use the light emitted by the quantum dots. The color (wavelength) of this light is one of the properties we can engineer simply by changing the quantum dot size. The emitted light also blink on and off randomly when the quantum dots are synthesized and kept in a liquid, but these fluctuations interestingly do not occur when the quantum dots are grown in a semiconductor solid. With the light intensity and wavelength, the statistics of this blinking constitute a third parameter to investigate the collective interaction dynamics of the atoms inside and outside the quantum dots. Three types of quantum dot samples will be probed through their emitted light: one where the quantum dots are on a semiconductor surface, one where the quantum dots will be buried just below the semiconductor surface within range of quantum interactions and one where the quantum dots are embedded in conductive polymers. With this last sample, we will be able to give energy to the quantum dots by passing current through the conductive polymer device whereas the other samples receive energy via excitation with a laser. Research on quantum dots in this organic polymer device will contribute to the development of a whole new generation of transparent, flexible, light-weight and even printable technologies from solar cells to light emitting devices.