Electronic properties of supracrystals of Au nanocrystals: influence of thickness and nanocrystallinity

P Yang¹, I Arfaoui¹, T Cren², N Goubet¹ and M P Pileni¹*

¹Laboratoire des Matériaux Mésoscopiques et Nanométriques (LM2N), Université Pierre et Marie Curie, and CNRS UMR 7070, 4 Place Jussieu, 75005 Paris, France

²Institut des Nanosciences de Paris (INSP), Université Pierre et Marie Curie, and CNRS UMR 7588, 4 Place Jussieu, 75005 Paris, France

I worked on the electronic properties of the gold nanocrystals (NCs) and supracrystals (SCs). I also simulated the optical properties of the metal nanocrystals and their self-organization using the discrete dipole approximation method (DDA). Actually, I am working on the atom and the molecule manipulation and the electron transport in the nano-objects using the scanning tunneling microscopy/ spectroscopy (STM/STS) and spin polarized (SP) STM/STS at low temperature (LT) under ultra-high vacuum (UHV).

Well-defined superlattices of colloidal nanocrystals, called supracrystals, are expected to have interesting physical properties. While the electronic properties of thin supracrystals were extensively studied in planar configuration, few are known about the electron transport through micrometer-thick supracrystals. Here, we investigated the electronic properties of supracrystals made of Au nanocrystals with diameters of 5, 6, 7 and 8 nm using scanning tunneling microscopy/spectroscopy at low temperature. The current-voltage characteristics show power-law dependences with exponents varying strongly with supracrystal thickness from 30 nm to a few microns. The crystallinity of these nanocrystals, called nanocrystallinity, is exclusively single domain for 5 nm nanocrystals and a mixture of single and polycrystalline phase for 6, 7 and 8 nm nanocrystals. We observed that the supracrystals made of 5 nm nanocrystals have a different behavior than the supracrystals made of 6, 7 and 8 nm nanocrystals and might be related to the nanocrystallinity. These results help to better understand the electron transport mechanism in such miniscule structure built from a bottom up approach.