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Prof. Ivo W. Rangelow


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Scanning probe microscopy

Scanning probe microscopy, being a main area of nano technology, provides imaging methods and tools for capturing basic phenomenons and for product characterization. High resolution probes in the form of cantilever arrays allow for reliable topographical, physical and chemical analysis on the nanometer scale. Calibration proves the high performance of the piezoresistive cantilever system with nanometer resolution.
The goal of the relatively time consuming development of the cantilever array technology is to provide commercial systems that combine highest precision, stability and metrological flexibility.

Our department deals with the realization of piezoresistive cantilever arrays for atomic force microscopy (AFM), a branch of the wide field of scanning probe microscopy (SPM), and for related applications (see sensor technology). Sensors for SPM are very fascinating micro systems from a physical point of view, because by combining physics and technology they can provide a novel nanoscopic insight into material properties. SPM doesn't only open new horizons for fundamental research, but also gives a chance for utilizing formerly unused effects by developing novel sensors and sensor arrays. Microscopic cantilevers can effectively capture physical, biological and chemical quantities and interactions by translating them into a mechanical reaction (bending) and finally into electronically utilizable signals.

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SPM sensors

We are busy with the realization of self actuated piezo resistive sensors for scanning probe microscopy.

We are convinced that this technology will play a key role in the future of fast scanning probe microscopy and will be decisive in analytics and synthesis of nanostructures in all fields of nano technology and of strategic importance for real time bio diagnostics.

Our piezo resistive sensors are based on modern microfabrication techniques and well-established CMOS processes.  We have further optimized the piezo resistive detection principle and employ wheatstone bridge configurations consisting of four piezo resistors, which can yield a vertical resolution (“z-resolution”) of 0.1 nm.

The elegance of this concept relies on the use of that detection principle and differently functionalized tips or cantilever surfaces.

Thus the detection of subtle interactions (mechanical, electrical, thermal, biological or chemical) within smallest space, the so-called “nano-space” is enabled. The specific functionalized SPM-tip constitutes a nano-space with exceptional properties.

This measurement system is much more compact than conventional techniques methods based on optical methods, as used in AFM sensor technology.

In case of non-contact scanning probe microcopy a thermal operated bimorph (bimetal) actuator was integrated in the cantilever, which enables parallel measurements as well as high eigenmodes.  The scanning probe microscope can operate in all known AFM modes.

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Fast AFM

A serious disadvantage of scanning probe microscopy is the low speed of acquisition of individual AFM images. Depending on magnification and type of sample, images with resolutions within the nanometer scale can take from 5 minutes up to 30 minutes each.  The size of the sample is limited by the limits of the scanning range of conventional AFMs .  Therefore the use of AFMs is limited to static samples, whose physical, chemical or biological properties don’t alter under examination.

In scanning probe microscopy, the acquisition rate of images depends on fast three-dimensional movement of the cantilever with its scanning tip, a high precision control of the positioning system, and a high speed of data processing.

The cantilever shall be as small and soft as possible. The resonance frequencies then will be in the range of some MHz and the stiffness in the range of a few µN/m.

 The data acquisition rate can be significantly limited by the inertia of the AFM positioning system. In the department of Univ.-Prof. Dr.-Ing. habil. Ivo W. Rangelow innovative and dynamic positioning systems are developed to overcome these problems. These activities take place in frame of the SFB 622 research program. A fast and dynamic nano positioning device for small range of motions together with nano tools and tips developed in our department shall enable real-time analysis with nanometer resolution at a precise position. These innovations are based on new techniques in mechatronics, control engineering, and electronics (FPGA).

Poster "Dynamische Nanopositionierung"
AFM-Video 128x128, 40 lines/s

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Translation: B. Volland, A. Reum
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