M. Guggisberg

Site-specific friction force spectroscopy

The two‐dimensional histogram technique is used to determine the loading dependence of friction on terrace and step sites of NaCl(001). An extended adhesion model is used to analyze the data. Both Hertz and JKR theory are incorporated for the elastic deformation. Depending on the model, shear strengths of 100–190 MPa are found at the terrace region. Increased shear strength values of 500–1800 MPa are found at the step edges that are interpreted in terms of the increased energy barriers at the steps, known as Schwoebel barriers.

Ultrathin films of NaCl on Cu(111) : a LEED and dynamic force microscopy study

Ultrathin films of NaCl on Cu(111) have been studied with low-energy electron diffraction (LEED) and Dynamic force microscopy (DFM). The orientation and the lattice constant of the films are revealed by LEED while DFM allows a real space view on their growth modes. The ability of the DFM to image local mechanical surface properties is demonstrated at a substrate step which is covered by a continuous NaCl film.

Ferroelectric domain characterisation and manipulation : A challenge for scanning probe microscopy

Domain writing and reading on the nanometer scale is addressed with scanning force microscopy (SFM) Compared to other scanning probe methods, SFM provides broad possibilities for the on-line data controlling. i.e. three-dimensional mapping of polarisation distribution, differentiation between polarisation and topography, nanoscale domain switching of domains with a 60 nm diameter, recording of nanoscale hysteresis loops, phase transition mapping. domain wall imaging with 9 nm resolution, atomic resolution of ferroelectric surfaces, etc. All these issues are reported in this paper. The challenging result of such a concerted investigation is the possibility of using SFM for nanoscale domain writing and reading with nanometer resolution. Fig. 1 illustrates such an example where line shaped c - domains are purposely written into a ferroelectric Barium-Titanate single crystal with a 400 nm line-width. With this figure we highly appreciate and honour the work of Bob Newnham passing our best nano-wishes for his future.

Nanotribology: an UHV-SFM study on thin films of C60 and AgBr

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on C60 and AgBr thin films deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. A novel experimental approach is presented where local friction coefficients are determined: the lateral (frictional) forces are measured as a function of normal load, controlled by an external ramp generator. The local friction coefficient can be extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.15 +/- 0.02, 0.33 +/- 0.07 and > 0.03 were found between probing SiOx tip and C60, AgBr and NaCl, respectively. The two-dimensional histogram reveals significant details about the force regime of wear-less friction and the initial stage of wear on these thin films.

Carbon nanotubes as tips in non-contact SFM

Abstract The demand for sharp and stable tips suggests the use of carbon nanotubes as probing tips in scanning force microscopy. Here, we report a comparison of the long-range forces of conventional tips and nanotube tips, topographical images of various surfaces, such as Cu(111), Si(111)7×7 and NaCl(100), as well as images of a bundle of multiwalled nanotubes, which was deposited by severe tip crashing. It is found that the long-range forces of carbon nanotube probing tips are reduced and that they are more resistant to wear than conventional silicon tips

Phase variation experiments in non-contact dynamic force microscopy using phase locked loop techniques

This work presents constant amplitude Dynamic Force microscopy (DFM) measurements under ultra-high vacuum conditions performed with home-built digital electronics based on the principle of phase locked loop (PLL) techniques. In DFM so-called topography is often measured in constant frequency shift (Delta f) mode. This study describes the influence of phase shifts on constant af imaging. Therefore, phase variation experiments were acquired, leading to information about the cantilever resonance behaviour close to the surface. As sample, an evaporated thin film of NaCl on a Cu(111) substrate was chosen in order to obtain a heterogeneous system with clean Cu and NaCl areas. The atomic structure of both materials was resolved, which is the first time true atomic resolution was obtained on a metal. Large apparent topography variations are observed on this heterogeneous sample when changing the phase between the excitation and oscillation of the cantilever end. Such artefacts can be explained by comparison with phase variation experiments

Surface morphology, chemical contrast, and ferroelectric domains in TGS bulk single crystals differentiated with UHV non-contact force microscopy

Ferroelectric bulk single crystals of tri-glycine sulphate (TGS) have been investigated in ultra-high vacuum (UHV) using dynamic force microscopy (DFM) in the non-contact (nc) mode. Bath chemical contrast from different sub-unit cell cleavage steps, and ferroelectric domains were differentiated by recording the variation in interaction force affecting the excitation amplitude A(exc) applied to the piezo shaker in constant amplitude DFM. No chemical difference was found for steps measuring half the unit cell height b, in contrast to b/4-steps where sulphate ions change the local short-range chemical forces. By varying the bias voltage applied to the TGS counter electrode, the sign of bound surface charge within each ferroelectric domain was determined. Domain walls separating regions with antiparallel polarisation vectors are resolved down to a 9 nm domain wall width. Furthermore, we achieved atomic resolution with nc-DFM on cleaved TGS samples indicating the monoclinic unit cell at the ferroelectric sample surface with a = 1.0 +/- 0.05 nm, c = 0.55 +/- 0.05 nm, and beta = 107 +/- 3 degrees.

Aspects of dynamic force microscopy on NaCl/Cu(111): resolution, tip–sample interactions and cantilever oscillation characteristics

Ultrathin films of NaCl on Cu(111) have been studied using a dynamic force microscope. We present images with atomic resolution at step sites on the NaCl films, Force spectroscopy measurements of the tip-sample interaction on NaCl-covered areas and the Cu substrate are analysed with respect to electrostatic, van der Waals and short-range contributions, The interaction contrast between NaCl and Cu is shown to be reflected in the oscillation characteristics of the cantilever, First results of a resonance analysis with the help of a novel digital oscillation control system are presented.

An Interdisciplinary Virtual Laboratory on Nanoscience

The Swiss Virtual Campus project ”Virtual Nanoscience Laboratory” realises a virtual laboratory for the booming field of Nanoscience. Nanoscience laboratories are expensive and only major companies and organizations sponsored by research programmes can aord their usage. With a concept of distance education, complex and sensible experimental equipment can be shared through the Internet. Three main topics are realized in the framework of a virtual laboratory: user management, communication and co-operation, and the control of virtual experiments. The basic architecture is based on a multitiered client-server model. Each nanoscience experiment is implemented as a stand-alone web-service.

Using higher flexural modes in non-contact force microscopy

The oscillation characteristics of higher flexural modes of a rectangular microfabricated silicon cantilever have been studied in ultra-high vacuum (UHV) for a free cantilever and for a typical situation in non-contact force microscopy. The results are discussed with respect to the use of such modes in dynamic force microscopy (DFM) and local dissipation measurements.