KPFM Visualization of the Schottky Barrier at the Interface Between Gold Nanoparticles and Silicon—Application to Biomolecular Electronics

Schottky barrier appears when a metal and a semi-conductor (SC), with different work function, (metal one being larger) are in contact¹. Determination of this Schottky barrier height (SBH) is well known for an ideal plan-plan interface². However, when dealing with nanostructures, such as metallic nanoparticles in contact with a semiconducting surface, this barrier is hardly predictable because the nanoparticles are already significantly charged when their size is small, which profoundly modifies their apparent work function³^,⁴. Moreover their work function also depends on their diameters⁴^,⁵. Yet predicting the presence of a Schottky barrier and the Schottky barrier height (SBH) in case of nanoparticle has become an important topic (e.g. for hot electron in photocatalysis)^6-8. Here, gold nanoparticles (AuNPs) of 50 nm are deposited on an APTES functionalized n-doped silicon substrate. The sample surface is probed by Kelvin Probe Force Microscopy (KPFM) which allows measuring the local work function through the contact potential difference (CPD) simultaneously with the topography. This technic allows to investigate the charge transfer effects at the nanoscale. SEM and Dark-Field Microscopy characterization are also performed. KPFM measurements reveals a surprising ring-shaped pattern around the nanoparticles. We discuss how this pattern correspond to a potential barrier of 30 mV with a SBH calculated at 300 mV. The value of the SBH is strongly reduced compared to an ideal plan-plan metal/SC junction (SBH = 930 mV). The reasons of this reduction are discussed and a qualitative model is proposed. Gold nanoparticles are objects studied since a long time and widely used in nanoelectronics devices. Our study using the KPFM can act as case study for other unknow metal nanoparticles once deposited on doped silicon. We use this approach for our study on ferritin. Ferritin is a biomaterial (protein) that is formed by the self-assembly of 24 monomers (amino-acid chains) in a 12 nm nanocage that contains an iron core (with up to 4800Fe). Ferritin nanocages have already been used in different electronics devices⁹. Here, ferritins are deposited on doped silicon and characterized by KPFM. Results show also ring-shaped potential around the nanocages.<br/><br/><b>References: </b><br/>¹ Sze and Ng, <i>Physics of Semiconductor Devices</i>, 1981<br/>² R. T. Tung and L. Kronik <i>Physical Review B</i>, 2021, <b>103,</b> 03530<br/>³ S. Stehlik, T. Petit, H.A. Girard, A. Kromka, J.C. Arnault, B. Rezek <i>Langmuir</i>, 2013, <b>29,</b> 1634-41<br/>⁴Y. Zhang, O. Pluchery, L. Caillard, A.F. Lamic-Humblot, S. Casale, Y.J. Chabal and M. Salmeron, <i>Nano Letters, 2015, </i><b>15</b>, 51-5<br/>⁵ D. M. Wood, <i>Physical Review Letters</i>, 1981, <b>46</b>, 749<br/>⁶ E. Kazuma and T. Tatsuma, <i>Advanced Materials Interfaces</i>, 2014, <b>1</b> 1400066<br/>⁷ S. Wang, Y. Gao, and S. Miao, <i>J. Amer. Chem. Soc.</i>, 2017, <b>139,</b> 11771-8<br/>⁸ Y. Gao, W. Nie, Q. Zhu, X. Wang, S. Wang, F. Fan, and C.Li, Angewandte<i> Chemie International Edition</i>, 2020, <b>59,</b> 18218-23<br/>⁹ K. S. Kumar, R. R. Pasula, S. Lim, and C.A. Nijhuis, Adv. Mater., 2016, 28, 1824–1830