Study of amino-ended dendrons adsorbed onto carbon by Kelvin probe force microscopy

VERÓNICA BRUNETTI; ELIANA D. FARIAS; MARIO C.G. PASSEGGI (JR); MARTIN E. ZOLOFF-MICHOFF; THILO GLATZEL

La Falda, Córdoba

Congreso; V Congreso Argentino de Microscopía; 2018

Dendrimers are synthetic organic molecules that have attracted great attention due to their very particular physical structure and chemical properties. Their monomeric units are designed in such a way that the number of terminal groups grow geometrically. Dendrons, the wedged-shaped sections of a dendrimer, are monodisperse and maintain the desired dendritic effect with costeffective synthesis [1].Surface modification using dendrons is a simple synthetic methodology that offers significant advantages over other polymers to tailor the surface properties. For example, it offers control over the hydrophobic or hydrophilic character of the surfaces, it enhances the biocompatibility as well as the intelligent response to external stimulation [2]. In recent years, Kelvin Probe Force Microscopy (KPFM) has emerged as a versatile and robust tool to study the electrical properties of an important variety of nanomaterials. This technique offers valuable information such as mapping the local surface potential of nanostructured materials at surfaces and interfaces. At the same time, KPFM allows the correlation of structural and electronic properties that are crucial issues for technological and scientific studies. The physical meaning of the measured surface potential is strictly related to the sample and its electrical properties. In the case of metallic samples, the measured surface potential is the work function difference between the tip and the sample. Instead, for thin films (TF´s), it measures an effective work function that is the sum of that of the substrate and the dipole moment of the TF [3,4].It is interesting to point out that the work function depends on intrinsic properties of the surface arrangement such as its conformation, the crystalline orientation of the surface, the chain lengths of its organic body, but also on extrinsic variables such as the density and packing of the chemisorbed or physisorbed molecules [5]. In this work, we study changes on the work function of carbon attributed to the adsorbates different molecular orientation. For this purpose, amino-ended dendrons were adsorbed onto highly oriented pyrolytic graphite (HOPG). Changes on the work function were measured by KPFM considering the contact potential difference (CPD) between the AFM tip and the sample. In addition, topographical and DFT studies were achieved to analyze the influence of molecular orientation and packing conditions of the adsorbates on the modified HOPG work function.