In the size range between 1 and 100 nm, materials can present properties that are fundamentally different from those found in single molecules or macroscopic samples. These new properties that are in many cases due to surface or size confinement effects are in the focus of nanoscience and nanotechnology. This highly interdisciplinary field is gradually gaining shape at the intersection of classical disciplines like physics, chemistry, biology and materials science. No matter how many unrealistic expectations we may see associated with nanotechnology and its impact on our daily life, there are many aspects of the emerging nanoscale science that are truly exciting both for experimentalists and theorists.

Among the many research targets that have been identified recently, the interest in fabricating (synthesizing) nanoscopic objects from different classes of materials has attracted particular attention. This is a prerequisite to gain insight into the nanoscopic physical properties that can be fundamentally different from bulk samples and are often highly sensitive to exact size and shape.

Nanometer scale

Colloidal quantum dots (QDs) are nano-sized crystals of semiconductor materials. The motion of charge carriers becomes more restricted as the QD size reduces (quantum confinement). As a result, the smaller QDs have a larger bandgap and discrete energy levels. The optical absorption and emission spectra of QDs can be tuned across the visible by varying their size, as shown in this photograph of CdTe QD colloids ranging from 2.5 to 5 nm. Courtesy of Prof. Andrey L. Rogach

A well known example is the change in the optoelectronic properties of small clusters of semiconductor materials with sizes that are smaller than the radius of an exciton. Another one is the optical resonances found in nano-sized samples of nobel metals, e.g. gold colloids, that give rise to very characteristic spectral properties. Materials like those have spurred a considerable effort in developing the experimental and theoretical tools needed to address the complex interplay between structure, size and optoelectronic properties at the nanoscale.

The more we learn how to synthesize, and thus to finely tune the composition, size and shape of such small particles, the more we are fascinated by the novel fundamental phenomena at this length scale and their technological implications. A particularly exciting aspect of research with nanoparticles is the possibility to combine such small objects made of different materials in three dimensional arrangements in order to produce hybrid aggregates or nanostructures with even a wider spectrum of physical properties.

In the Applied nanoPhysics Group we investigate the properties and explore novel applications of such nanosystems.