[en] We report on local measurements of the surface potential and quantum capacitance in single layer graphene as well as multilayers thereof as a function of the carrier density by using frequency-modulated Kelvin probe force microscopy. We find excellent agreement to tight-binding calculations reported for graphene monolayers and extract the minimum quantum capacitance from density sweeps at room temperature. The surface potential of graphene multilayers is found to depend linearly on the carrier density, which suggests treating them as two-dimensional electron gases. In addition, we demonstrate that the simultaneously detected second harmonic of the Kelvin modulation, proportional to |∂²C/∂z²|, is directly sensitive to local changes in the quantum capacitance of graphene.

[en] Organic field effect transistors (OFETs) with a gate ''electrode'' that is made out of a ferroelectric (FE) have become a field of intense research. Non-volatile memory functionality is expected due to the strong and remanent electric field arising from bound surface charges at the FE/molecular interface. In order to achieve excellent electric transport properties, a high degree of intermolecular ordering is inevitable. In our approach, lead zirconate titanate (PZT) is used as material of choice for the design of an ultra-thin ferroelectric gate electrode in a Ferroelectric-OFET. The focus of the present work lays on the growth process of the molecularly thin organic conduction layer, based on α,ω-dicyano-β,β*-dibutylquaterthiophene (DCNDBQT). Film formation is effectively promoted through specifically designed, bifunctional self-assembling molecules (CNBTPA: 5-cyano-2-(butyl-4-phosphonic acid)-3-butylthiophene) which act as template layer. We report on nc-AFM and KPFM investigation of the template layer's structural and electronic properties.

[en] Surface layer (SL) proteins are self-assembling nanosized arrays which can be recrystallized in solution or on surfaces. In this paper, we investigate the metallization, contact potential difference and conductivity of in vitro recrystallized mSbsC-eGFP tube-like assemblies for possible applications in nanobiotechnology. Treatment of mSbsC-eGFP tube-like structures with 150 mM Pt salt solution resulted in the formation of metallized SL assemblies decorated with Pt nanoparticles ( > 3 nm) which were closely packed and aggregated into metal clusters. Kelvin probe force microscopy (KPFM) measurements revealed that metallized and unmetallized SL templates showed different surface potential behaviours, demonstrating that the metal coating changes the electrostatic surface characteristics of SL assemblies. In situ conductivity measurements showed that unmetallized SL assemblies were not conductive. Metallized samples showed linear I-V dependence between - 1 and + 1 V with a conductivity of ∼ 10³ S m^-1.