Nanocrystals

NaonPlat. — Three vials of CdSe quantum dots dispersed in a liquid. The nanocrystals have average diameters (left to right) of 2.6, 3.4, and 5.2 nanometers. The particles are exposed to ultraviolet light, causing them to fluoresce green, orange, and red colors.

The optical properties of semiconductors change when their size is reduced to the nanometer scale. This effect (known as quantum confinement) can be exploited to enhance the performance of semiconductors. The most studied example is quantum dots, nanoscale crystallites that are roughly spherical in shape. They are exploited in commercial flat-panel televisions because their color varies with nanocrystal diameter (see figure above). However, many other shapes, including nanocubes, nanoplatelets, nanowires, etc., can also be prepared. In all cases, the nanocrystals can exhibit size-tunable optical properties in the nanometer regime.

However, because the behavior of nanocrystals is so strongly size dependent, samples should be uniform to yield homogeneous properties. Unfortunately, all real samples exhibit distributions in size and shape that reduce their performance. At OMEL, we are currently investigating two classes of semiconductor nanocrystals^1,2 that have potential to yield “perfect” samples that are uniform in size and shape: semiconductor nanoplatelets and "magic-sized" nanocrystals.

Riedinger, Ott, Mule, Mazzotti, Knüsel, Kress, Prins, Erwin, & Norris. An Intrinsic Growth Instability in Isotropic Materials Leads to Quasi-Two-Dimensional Nanoplatelets. Nature Materials 16, 743 (2017). (external page Link)
Pun, Mazzotti, Mule, & Norris. Understanding Discrete Growth in Semiconductor Nanocrystals: Nanoplatelets and Magic-Sized Clusters. Accounts of Chemical Research 54, 1545 (2021). (external page Link)