Search

Thermally grown surface oxide layers dominate the single-asperity tribological behavior of a Zr60Cu30Al10glass. Increase in oxidation time leads to an increased contribution of shearing and a corresponding decreased contribution of ploughing to friction. This change in the dominating friction and wear mechanism results in an overall minor decrease of the friction coefficient of oxidized surfaces compared to the metallic glass sample with native surface oxide. Our results demonstrate the importance of creating a stable oxide layer for practical applications of metallic glasses in micro-devices involving sliding contact.

The surface displacement technique is used to measure the temperature and frequency dependence of the periodic expansion of a CaF2-surface subject to a modulated focused beam of 1keV electrons. Theoretical models are presented for a prediction of the observed phenomena based on thermal transport and defect lifetime effects. The use of such investigations for the study of thermal and non-thermal transport phenomena in alkaline-earth halides is discussed.

In comparison of a Pt57.5Cu14.7Ni5.3P22.5metallic glass with a Pt(111) single crystal we find that wearless friction is determined by chemistry through bond formation alloying, while wear is determined by structure through plasticity mechanisms. In the wearless regime, friction is affected by the chemical composition of the counter body and involves the formation of a liquid-like neck and interfacial alloying. The wear behavior of Pt-based metallic surfaces is determined by their structural properties and corresponding mechanisms for plastic deformation. In the case of Pt(111) wear occurs by dislocation-mediated homogeneous plastic deformation. In contrast the wear of Pt57.5Cu14.7Ni5.3P22.5metallic glass occurs through localized plastic deformation in shear bands that merge together in a single shear zone above a critical load and corresponds to the shear softening of metallic glasses. These results open a new route in the control of friction and wear of metals and are relevant for the development of self-lubricated and wear-resistant mechanical devices.

The role of thermal activation for a nanoasperity sliding on a flat surface with low speed is discussed. If the asperity slides in a vacuum, thermal vibrations may excite slipping from an equilibrium position to the next one along the sliding path. This effect is reduced if the velocity increases and leads to a logarithmic increase of friction with the sliding velocity. This is not always the case in a humid environment, where the formation of capillaries between tip and surface acts as an obstacle for thermally activated jumps. Depending on the wettability of the surface, different behaviors are observed. Copyright © 2006 John Wiley & Sons, Ltd.

Atomic friction studies have been performed by means of a friction force microscope (FFM) in ultrahigh vacuum, where well-defined surfaces can be prepared. A home-built FFM allows us to study lateral forces as low as 0.05 nN using rectangular silicon cantilevers. Furthermore, comparison with dissipation measurements performed in non-contact mode are possible. Recent experimental results are presented and discussed in the framework of a one-dimensional Tomlinson model which includes thermal activation. Atomic-scale stick–slip processes on a metallic surface could be repeatedly measured on Cu(111), while the Cu(100) surface was distorted by the tip during the scanning process. A logarithmic velocity dependence of atomic friction has been measured on Cu(111) and NaCl(100) for low scanning velocities. The dissipation found in stick–slip measurements is compared to the power loss detected in dynamic non-contact measurement.

AbstractWe have studied cleavage faces of NaCl crystals containing (OCN)−molecules with a scanning force microscope in ultra-high vacuum. The dopant content in the crystals was determined using infrared spectroscopy. The molecular impurities appear as nm-sized elevations in the scanning force micrographs. Their position at cleavage steps is discussed in terms of both diffusion and step formation during cleavage. Although the atomic periodicity of the NaCl lattice is imaged, high-resolution investigations of impurities are limited by a convolution between the tip apex and the elongated molecules sticking out of the surface.

The local contact potential difference (CPD) between different linear alkanethiols self-assembled as monolayers on Au substrates was investigated with Kelvin probe force microscopy (KPFM). Our results demonstrate that KPFM simultaneously provides information on the sample topography and its contact potential down to a lateral resolution of 100 nm. The reported CPD measurements allow the distinction between regions in the monolayer comprising thiol molecules with chemically different terminal head groups down to a resolution of 3 meV. Furthermore, the CPD values measured in monolayers having one type of functionality vary with the chain length of the molecules in the film, which is consistent with a dipole-layer model. Variations in the length of the alkyl chain reveal a linear dependence as a function of the (−CH2−) units in the chain, with an increase in the CPD potential of 14.1 ± 3.1 mV per (−CH2−) unit.

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. Copyright © 1999 John Wiley & Sons, Ltd.

We operate dynamic force microscopy (DFM) in non-contact mode under ultrahigh vacuum conditions in order to differentiate local chemical inhomogeneities from ferroelectric domains in bulk single crystals of triglycine sulphate (TGS). Individual layers of both mixed glycine and sulphate, and pure glycine ions are resolved resulting in a lateral material contrast of 5 nm and a sub-unit cell vertical contrast. The clue information is deduced when analysing the excitation amplitude Aexc applied to the piezo shaker in constant amplitude DFM which is strongly affected either by the short-range chemical force or the longer range electrostatic contribution. The latter arises from the bound surface charge within individual ferroelectric domains and results in a long-range tip–sample interaction. From variation of the bias voltage applied to the TGS counter electrode we deduce the sign of the bound surface charge within each ferroelectric domain. Hence, domain walls that separate regions of antiparallel polarization are resolved down to a 9 nm domain wall width. Copyright © 1999 John Wiley & Sons, Ltd.

The local contact potential difference (CPD) of different self-assembled n-alkanethiol monolayers on Au substrates has been measured using Kelvin probe force microscopy (KPFM). Our results demonstrate that KPFM can be used to obtain topography and CPD information simultaneously. The measured CPDs show a clear chemical contrast, allowing us to distinguish between thiol molecules with different terminal groups. The CPD values of the same terminal group are found to vary with chain length, which is explained in the context of the dipole layer model. Copyright © 1999 John Wiley & Sons, Ltd.

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. Copyright © 1999 John Wiley & Sons, Ltd.

Electron irradiation of CaF2 with 2 keV electrons causes metallization of the surface and near surface layers by the formation of colloids. Colloids on the surface are significantly larger than those in the bulk indicating a higher mobility of defects on the surface. Optical spectroscopy on extinction bands of bulk colloids reveals Ostwald ripening as the driving force for aggregation, while scanning force microscopy results suggest that similar processes dominate the early stages of surface colloid formation.

In this contribution we report on the metallization of (111)-surfaces of CaF2single crystals as a result of low energy electron irradiation. An in-situ control of the spatial distribution of the metal coverage was obtained by rapidly scanning a low intensity electron beam across the irradiated area and monitoring the STE luminescence radiation. Metallized spots are identified by a reduced luminescence intensity. Surface stoichiometry was tested by XPS-microscopy. The spatially resolved observation of line intensities as well as line shifts revealed an effective metallization and oxidation of the surface. Using atomic force microscopy we found evidence for a 3-dimensional island-like formation of Ca aggregates with a size up to 12 μm diameter. Results for cluster formation in the center of the irradiating beam are compared to those from outer regions. The size distribution of the aggregates reproduces the different levels of electron dosage across the beam profile.

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.

Not Available

The usually employed chemical methods for the determination of the content of active substances in high-percent products of trichlorphone and dichlorvos are discussed and the behaviour of these substances and also of tribuphone is examined with regard to their ability of cleaving off chlorine and to the saponification of ester-groups in the presence of alkali or acid on different conditions. According to the results the WHO method for trichlorphone is also suitable for the determination of tribuphone in pure and technical products. Subsequently, the influence of chlorine containing impurities and foreign substances on the determination of tribuphone and trichlorphone in technical products is investigated and it is shown that only very few substances interfere or are co-determined. The confidence level of the average value of double determinations amounts to about ±1% abs. for both the active substances. A detailed working procedure is described for the determination of tribuphone and trichlorphone.

No Abstract.

Abstract: The contact mechanics of a fibrillar micro-fabricated surface structure made of poly(dimethyl siloxane) (PDMS) is studied. The attachment and detachment of individual fibrils to and from a spherical indenter upon approach and retraction are detected as jumps in force and stiffness. A quantitative model describes the stiffness values by taking into account the deformation of the fibrils and the backing layer. The results emphasize the importance of long-range interactions in the contact mechanics of elastic materials and confirm some of the important concepts underlying the development of fibrillar adhesive materials. [Copyright &y& Elsevier]