This article deals with the analysis of the relationship between the pull-off force measured by atomic force microscopy and the dimensions of water bridge condensed between a hydrophilic silicon oxide tip and a silicon oxide surface under ambient conditions. Our experiments have shown that the pull-off force increases linearly with the radius of the tip and nonmonotonically with the relative humidity (RH). The latter dependence generally consists of an initial constant part changing to a convex-concave-like increase of the pull-off force and finally followed by a concave-like decrease of this force. The reproducibility tests have demonstrated that the precision limits have to be taken into account for comparing these measurements carried out under atmospheric conditions. The results were fitted by a classical thermodynamic model based on water-bridge envelope calculations using the numerical solution of the Kelvin equation in the form of axisymmetric differential equations and consequent calculation of adhesive forces. To describe the measured data more precisely, a decrease of the water surface tension for low RH was incorporated into the calculation. Such a decrease can be expected as a consequence of the high surface curvature in the nanometer-sized water bridge between the tip and the surface.

Synthesis of graphene by chemical vapor deposition is a promising route for manufacturing large-scale high-quality graphene for electronic applications. The quality of the employed substrates plays a crucial role, since the surface roughness and defects alter the graphene growth and cause difficulties in the subsequent graphene transfer. Here, we report on ultrasmooth high-purity copper foils prepared by sputter deposition of Cu thin film on a SiO2/Si template, and the subsequent peeling off of the metallic layer from the template. The surface displays a low level of oxidation and contamination, and the roughness of the foil surface is generally defined by the template, and was below 0.6 nm even on a large scale. The roughness and grain size increase occurred during both the annealing of the foils, and catalytic growth of graphene from methane (≈1000 °C), but on the large scale still remained far below the roughness typical for commercial foils. The micro-Raman spectroscopy and transport measurements proved the high quality of graphene grown on such foils, and the room temperature mobility of the graphene grown on the template stripped foil was three times higher compared to that of one grown on the commercial copper foil. The presented high-quality copper foils are expected to provide large-area substrates for the production of graphene suitable for electronic applications.

This paper deals with the analysis of the influence of humidity on the process of local anodic oxidation carried out by atomic force microscope ͑AFM͒ on GaAs ͑100͒ surfaces. Recent experiments have shown that the height and half width of oxide nanolines do not increase monotonously with relative humidity, but for lower relative humidities ͑Ͻ50%͒ the lines comparable in size to those prepared at 90% were obtained. However, their height and width along the lines revealed significant variations. To better understand these phenomena, the AFM force-distance spectroscopy measurements together with computer simulations of an electric-field distribution and water bridge formation between the tip and the substrate at different relative humidities were carried out. Our experiments on AFM force-distance spectroscopy have not proved an enhanced water condensation between the tip and the surface at lower humidities. However, the simulations of the electric field in the vicinity of the tip at the early stages of the oxidation process at low relative humidities showed an increase in the average intensity in the oxide layer promoting the diffusion of oxidizing species toward the substrate and, hence, the formation of oxide lines under these conditions. Finally, our simulations on water bridge variations along the tip track showed that at lower humidities there are higher relative standard deviations in the size of the water bridge while the tip is being moved along the surface. This indicates why the oxide lines showed a bigger variability in size.