SPM Aarhus 150 HT

A new design of a noncontact atomic force microscope (AFM) is introduced in this paper, based on a piezoelectric oscillator sensor (PEOS) for ambient and liquid environments. Because of the recent development of quartz technology, the PEOS sensor operates independently from conventional laser alignments. The sensor is based on the length extension resonator, which has high force sensitivity and can deliver high resolution AFM images in ultrahigh vacuum. The oscillator design was tested in different gas compositions and liquids to determine its oscillation stability. The scan performance was investigated in both air and liquid on the topography of an inorganic hard material, graphite. The usability of PEOS for soft organic materials was further proven by imaging biological samples of DNA origami.

Graphene‐metal interfaces have been the subject of surface science since the beginning of 1960s when the studies of the catalytic properties of the metallic surfaces with low‐energy electron diffraction methods were started. After discovery of the unique transport properties of graphene defined by its electronic structure, i.e. the linear dispersion of the electronic states E(k) in the vicinity of the Fermi level, many applications of graphene were proposed and recently realised. These findings renew the interest in graphene on metals as it was realised that synthesis of graphene on metals with its further transfer on insulating or polymer support is the most perspective way to move this technology from lab to industry. Recent applications of scanning probe microscopy and spectroscopy methods to graphene‐ metal systems, from complete layers to nanostructures, shed light on the mechanism of interaction at the interface between graphene and metal that defines the electronic properties of the system and its transport properties (see the Feature Article by Dedkov et al. on pp. 451–468). Besides, fascinating quantum phenomena inherent in graphene nano‐objects open a door for the application of graphene in future nanotechnology.

The graphene moiré structures on 4d and 5d metals, as they demonstrate both long (moiré) and short (atomic) scale ordered structures, are the ideal systems for the application of scanning probe methods. Taking graphene–Ir(111) as an example, we present the complex studies of this graphene–metal moiré–structure system by means of 3D scanning tunnelling and atomic force microscopy/spectroscopy as well as Kelvin-probe force microscopy. The results clearly demonstrate variation of the moiré and atomic scale contrast as a function of the bias voltage as well as the distance between the scanning probe and the sample, allowing one to discriminate between topographic and electronic contributions in the imaging of a graphene layer on metals. The presented results are compared with the state-of-the-art density functional theory calculations demonstrating excellent agreement between theoretical and experimental data.

Realization of graphene moiré superstructures on the surface of 4d and 5d transition metals offers templates with periodically modulated electron density, which is responsible for a number of fascinating effects, including the formation of quantum dots and the site selective adsorption of organic molecules or metal clusters on graphene. Here, applying the combination of scanning probe microscopy/spectroscopy and the density functional theory calculations, we gain a profound insight into the electronic and topographic contributions to the imaging contrast of the epitaxial graphene/Ir(111) system. We show directly that in STM imaging the electronic contribution is prevailing compared to the topographic one. In the force microscopy and spectroscopy experiments we observe a variation of the interaction strength between the tip and high-symmetry places within the graphene moiré supercell, which determine the adsorption sites for molecules or metal clusters on graphene/Ir(111).

The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.

Nanostructured Nb-doped SrTiO3(001) surfaces were investigated with STM, and the surface patterns for observed nanostructures were assigned. Sequential C60 deposition onto these nanostructured templates reveals distinct growth modes, including discrete small C60 islands on the c(4 × 2) reconstruction surface, parallel one-dimensional C60 chains on (6 × 2) dilines, C60 double chains on (8 × 2) trilines, epitaxial C60 close packed adlayers over (11 × 2) tetralines, and two-dimensional ordered C60 dimer arrays on (7 × 6) waffles. These structural diversities mainly stem from the relatively strong adsorbate−substrate interactions as well as the surface topography demands. The nanostructured oxide surfaces as templates thus have great potential in molecular nanoarchitecture.