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The scaling-index method (SIM) is a novel tool for image processing in scanning-probe microscopy. Originating from the theory of complex systems, the SIM can be used in order to extract structural information from arbitrary data sets. This method can readily be applied to the analysis of digital atomic-force microscopy (AFM) images. Especially for biomedical diagnostics, where genetic material is investigated by various microscopic methods, a reliable image segmentation based on the SIM algorithm is helpful. As a first application, AFM-images of GTG-banded human metaphase chromosomes (with G bands obtained by Trypsin using Giemsa) are compared with micrographs from conventional light microscopy by means of a scaling-index analysis. While the grey-level distributions of the optical and the AFM-images are largely different from each other, the scaling-index images are remarkably similar. Using this method, a fingerprint of an image can be produced which helps in the classification and interpretation of the measured data.

Atomic force microscopy (AFM) allows direct measurement of local elastic sample properties by force spectroscopy. The AFM tip indents into a soft sample and the resulting relation between loading force and indentation is used to determine the elastic properties of the sample. In order to calculate the indentation an analytical expression for the sensor response vs. z -piezo displacement based on the Hertz model of mechanical contact is derived. This model is fitted to data obtained on a silica aerogel sample using a least-squares method. The aerogel powder particles were analysed individually for their surface structure and elastic behaviour. Prior to the indentation experiments, the aerogel surface was characterised by AFM in the tapping mode. The results were validated by the comparison of data obtained by using two types of cantilevers of very different stiffnesses (spring constant k =0.2 and 54 N/m) and by assessing the reversibility of the indentation process. Tip indentations smaller than 200 nm were usually reversible, whereas indentations of 2000 nm caused irreversibilities.

A porous silicon (PS) based tip has been developed as a small light emitting probe for scanning near field optical microscopy (SNOM). Another possible application is photoresist patterning on the micrometer and nanometer scale, where dimensions ∼ 100 nm are required for extending conventional lithographic processes. In principal light emission can be excited optically in fluorescence as well as electrically by an applied bias voltage. We show the mechanical fabrication of a luminescent probe at the apex of a conventional STM tip and its use to record initial NFO images of micron-sized test structures. The sensor has been characterized by life time measurements and shows its stability over more than thousand minutes. Its quantum efficiency has been measured to range from 0.025 to 0.14 depending on the excitation photon rate and is found to increase with small size of the particles. The emission power with the present set-up is 7 × 10 −11 W at 630 nm under an Ar + laser (488) nm excitation at room temperature. Additionally high frequency plasma etching has been used to fabricate conventional Si atomic force microscopy (AFM) cantilevers with a PS luminescent tip which can be used simultaneously for AFM and SNOM measurements. We present design studies for the fabrication of integrated tips suitable for simultaneous AFM, STM and SNOM measurements.

In many prokaryotic cells (eubacteria and archaebacteria) the outermost cell envelope component is composed of a regularly structured protein surface layer (S-layer). The two-dimensional S-layer from Bacillus coagulans E38-66 and Bacillus sphaericus CCM2177 has been investigated by SFM at molecular resolution under physiological conditions (i.e., in buffer solution). We find the E38-66 S-layer lattice to be oblique with lattice parameters of a = 9–10 nm, b = 7–8 nm and γ = 80°–90° (E38-66). The CCM2177 lattice is square with a = 12–14 nm, in good agreement with TEM data. We have used the unique possibility of the SFM to study the kinematics of biological processes and have performed experiments on the adhesion of polyclonal antibodies to the recrystallized E38-66 protein layer on a time scale of about two to ten seconds per image frame. This represents a first step in directly visualizing molecular recognition reactions.

We show that domain walls on graphite are very likely to mimic features of extended macromolecules like DNA strands, when imaged with an STM. We explain with a simple model how different translational periods along a grain boundary originated from different relative orientations of the graphite lattice at the domain wall. We show how simple geometrical analysis of the images can be used to distinguish true macromolecular features from artifacts.

We have calculated the thermal noise of a v-shaped AFM cantilever (Microlever, Type E, Thermomicroscopes) by means of a finite element analysis. The modal shapes of the first 10 eigenmodes are displayed as well as the numerical constants, which are needed for the calibration using the thermal noise method. In the first eigenmode, values for the thermomechanical noise of the z-displacement at 22°C temperature of 〈u 1 2 〉 =0.627 A / c cant and the photodiode signal (normal-force) of 〈S 1 2 〉 =0.558 A / c cant were obtained. The results also indicate a systematic deviation of the spectral density of the thermomechanical noise of v-shaped cantilevers as compared to rectangular beam-shaped cantilevers.