Erik C. Scher

SHAPE CONTROL OF CDSE NANOCRYSTALS

Nanometre-size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties that depend sensitively on both size and shape, and are of both fundamental and technological interest. In contrast to the syntheses of zero-dimensional systems, existing preparations of one-dimensional systems often yield networks of tubes or rods which are difficult to separate. And, in the case of optically active II–VI and III–V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects. Thus, except for some metal nanocrystals, there are no methods of preparation that yield soluble and monodisperse particles that are quantum-confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II–VI and III–V nanocrystals by injection of precursor molecules into a hot surfactant. Here we demonstrate that control of the growth kinetics of the II–VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod-like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments and as chromophores in light-emitting diodes.

Shape control and applications of nanocrystals

Inorganic nanocrystals with well–defined shapes are important for understanding basic size–dependent scaling laws, and may be useful in a wide range of applications. Methods for controlling the shapes of inorganic nanocrystals are evolving rapidly. This paper will focus on how we currently control the shape of nanocrystals and this will be illustrated using CdSe and Co nanocrystals as examples for semiconductors and for metals. These materials show a more pronounced variation of fundamental properties with aspect ratio. However, to take advantage of these shape–dependent properties in possible applications, several challenges need to be overcome. Issues such as alignment, high quantum yield and photostability and precise control of three–dimensional structures need to be addressed. These challenges, as well as several potential applications, will be described briefly.

Shape Control of Colloidal Semiconductor Nanocrystals

Shape control of inorganic nanocrystals is important for understanding basic size- and shape-dependent scaling laws, and may be useful in a wide range of applications. Methods for controlling the shapes of inorganic nanocrystals are evolving rapidly. This paper will focus on how we currently control the shape of semiconductor nanocrystals using CdSe as example.