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Nanoscience and Nanotechnology: A Perspective from the Very Small

Por: | 12 de mayo de 2014


By Stefano Zacchini, University of Bologna

As a chemist, I have had to deal with the very small since the beginning of my studies. Although I started my research career as a molecular chemist at the University of Bologna, my interest has moved towards the tiny realm of nanoscience and nanotechnology. In particular, I focus on the possibility of shedding light into this nanoworld using the knowledge and experimental experience of large molecular metal clusters gained by chemists through the years. In fact, these clusters are “large” only in an atomic sense — some are so small that they can only be found at the very end of the nanoscale.

A nanometre (nm) is one thousand millionth of a metre. To put this into perspective, a typical human hair is about 80,000 nm across. In comparison, the molecular clusters that occupy my research are about 40,000 times smaller — just 2 nm across. In common with nanoscience researchers around the world, the phenomena we study occur on a tiny scale of 1 to 100 nm. At these sizes, physics, chemistry, material science, biology, medicine, electronics and engineering collide.

We all are familiar with the miniaturisation of electronics over recent decades. Modern microelectronics provide computational power at levels undreamed of just a few years ago. Today, nanotechnologists work on the next level of miniaturisation — the design, characterisation, production and application of structures and devices at the nanoscale. Indeed, some applications from nanoscience are already in use today. The development of nanoelectronics may herald the next revolution in the development of computers.

From another viewpoint, nanosized objects are not new at all — chemists have made use of them for a long time. For instance, the catalytic converters in the exhausts of our cars contain nanoparticles — just a few nanometres across — of noble metals dispersed on a ceramic support. Similar highly dispersed metal nanoparticles are used as catalysts in industrial processes for the production of chemicals and for the abatement of pollutants.

Nanomaterial usage goes back much further than these industrial applications. Gold and silver nanoparticles feature in stained glasses —for instance, in the spectacular Lycurgus Cup, a Roman glass beaker that shows different colours as it is held up to the light, and the colourful windows created in cathedrals by medieval craftsman. The natural world also contains many nanoscale structures, ranging from milk to the sophisticated nanosized and nanostructured proteins produced in the cells of living organisms.

Only recently have advanced tools been developed that allow us to investigate and manipulate matter at the nanoscale. Thus, what we can call the “nanotech revolution” is mainly about our increased awareness of the nanoworld. Despite huge advancements, full comprehension and control of the phenomena occurring in the nanoscale regime is still lacking.

In order to fill this gap, a more rigorous approach is needed — looking at nanoscience from the perspective of the very small. For this purpose, our research group is developing a molecular approach toward nanoscience in general and metal nanoparticles in particular. This would help to fill the existing gap between molecular chemistry and nanochemistry, shedding some light on the fascinating but still relatively obscure area of transitions between the molecular domain, the nanosized and colloidal regime and the macroscopic world.

The main contribution our studies can give to nanoscience and nanotechnology is related to the complete characterisation and control of the molecules we are dealing with. Large molecular metal clusters, which are molecules or molecular ions composed of an inner metal core shielded and stabilised by a shell of inert components, can be prepared and fully characterised at the atomic level. These clusters are ideal for study thanks to their perfectly defined composition and exact structural, physical and chemical details. Improved understanding of these molecular metal clusters can be applied to other metal nanoparticles having a shell made of organic molecules, which are less well-defined and harder to study. Also, new insights might help in clarifying many of the misunderstandings and false ideas now present in nanoscience.

Large molecular metal clusters trespass into the nanodomain in terms of size. As the dimensions of the cluster increase, electronic and magnetic properties develop. For instance, some of our metal clusters act as electron sinks, in the sense that they can reversibly accept and release electrons at well-defined potentials. Moreover, we have recently demonstrated the insurgence of magnetic properties in molecular clusters, making them candidates for use as superparamagnetic quantum dots and nanomagnets. These clusters have great practical potential if they can be exploited to manufacture nanosized devices for data storage.

Other tailored clusters might have appropriate properties for the assembly of nanowires or more complex structures. For instance, columnar clusters are valuable precursors for the preparation of continuous molecular conductor wires, which can be used to connect electrical devices of different length scales, coupling the nanoscopic and macroscopic worlds.

The thermal decomposition of molecularly defined metal clusters can lead to the formation of metal nanoparticles of completely pre-determined dimensions and composition, as we have clearly demonstrated in recent studies. This might enable improvements in the design of heterogeneous catalysts to be used in industrial processes and for pollutant abatement. In addition, magnetic nanoparticles of controlled size and properties are interesting for biomedical applications. Finally, soluble metal clusters can be exploited as printable metals for nano-printing and patterning with metal wires.

In conclusion, molecular metal clusters can have a substantial impact in nanoscience and nanotechnology, both by helping a better understanding of the chemical and physical phenomena occurring in the nanoworld, and as building-blocks and/or precursors of nanostructured materials to be used in electronics, catalysis and medicine. All these aspects are now under investigation by our group in Bologna.

Stefano Zacchini
University of Bologna

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