Single Review on past events

In his research Tuhin Shuvra Basu is interested in the smallest particles we can synthesize today: nanocrystals. In his presentation on “Size matters: Glimpses of some experiments with silicon nanocrystal” he explained some basics of Nanoscience and Nanotechnology as well as his research on silicon nanocrystals. 

The term Nanotechnology was coined independently by Professor Norio Taniguchi in 1974 and was explored in much more depth by Dr. K. Eric Drexler in 1986. The technology opens the door to the new field of molecular manufacturing. Tuhin Basu is convinced that what the electronic revolution did for manipulating data, nanotechnological revolution can do for manipulating matter and juggling atoms like bits. But what is so unique of the nanostructured material? One key aspect is the vast increment of the surface area to volume ratio. Materials reduced to nanoscale often show sudden changes in properties, so called quantum size effects, e.g. opaque copper becomes transparent, semiconductors like silicon can become conducting and emit light, platinum which is inert in the bulk scale behaves like a catalyst.                                                                                                                                                       

The physicist presented two approaches how to make nanomaterials: 1. Start with a bulk material and then break it into smaller pieces using mechanical, chemical or other forms of energy (top down approach); 2. Building things by combining smaller components, as opposed to carving them out of larger ones (bottom up approach). According to the physicist the quality of bottom up nanomaterial is better than the top down one.

Silicon is almost the most important element for nanoelectronics as it has many near ideal properties: “Its conductivity can be tuned over a very wide range – essentially from insulating to metal-like – simply by adjusting the concentration of dopant atoms in crystal.  It has the advantage of a naturally forming oxide with excellent insulating and passivating properties. Combined with sophisticated lithographic techniques, these properties make it possible to sculpt very fine and numerous electrical paths and switches into a silicon crystal. And finally silicon is the second most abundant material on the earth’s crust and thereby creates the pathway for devices.”

To increase the functionality of any modern electronic device like computers  we need to increase the level of integration of the electronic components in single electronic chip ,eventually it will increase the length and will decrease the cross section of metallic interconnects of those components. The usual consequence is an unmanageable heat into the electronic device. One of the key solutions can be in replacing an electron by a photon for communication. In this regard nanostructured silicon, which shows room temperature photoluminescence, may have potential application as integrating them in an existing system is usually easier. It is possible to tune the bandgap of those nanocrystals in order to achieve desired photon energy (depending on the application) by so called bandgap engineering by changing the dimension of the nanocrystal easily.

Tuhin Basu´s aim is to measure the properties of silicon one by one rather than an ensemble by employing scanning tunneling microscopy. Usually charging energy of silicon nanocrystals is appreciably high and they exhibit pronounced single-electron-tunneling effects. By tunneling spectroscopy the conduction and the valence band states and their degeneracy can be separately probed. Measurements on the single object level show interesting results. It provides an estimation of the excitonic bandgap of individual silicon nanocrystal . Additionally the study shows the band-structure and exciton dynamics of silicon nanoparticles on a single particle level at extremely low temperature (300 mK). These studies will enhance the general understanding of these nanocrystals and hence pave the way to apply them in photonic communication.