High resolution nc-AFM and KPFM imaging of dipolar molecule assemblies on Si(111):B by stiff- probe non-contact AFM at low-temperature

Oral, sans d'actesInternational audienceWe studied by non-contact AFM (nc-AFM) the formation of molecular self-assemblies on the passivated surface of boron-doped Silicon B-Si(111)-(√3×√3)R30. The investigated molecules (1-(4’cyanophenyl)-2,5-bis(decyloxy)-4-(4’-iodophenyl)benzene) possess aliphatic chains attached to a triphenyl core ended with two possible different terminations (either iodine or cyano group). The use of a passivated semiconductor substrate enables creating regular and extended structures without significant change in electronic properties of molecules [1]. Scanning tunneling microscopy and nc-AFM imaging have been performed using a low-temperature (AFM/STM (JT AFM/STM,SPECS) operated at T=4K with high stiffness Kolibri sensors (k=540 kN/m, f0=1 MHz). The growth of a periodic molecular network is observed, formed by parallel lines made by molecule aromatic cores and interdigitated aliphatic chains placed between adjacent rows. We obtain submolecular resolution in the constant height ∆f images without intentional tip functionalization, but only by conditioning the tip on the Si surface [2]. Kelvin Probe Force Microscopy (KPFM) images of single molecules and molecular assemblies with sub-elementary charge sensitivity [3] and submolecular resolution will be shown. They attest of the dipolar character of asymmetric molecules and are consistent with the formation of dipole-driven molecular arrays