Karl-Heinz Franke

White light interferometry in combination with a nanopositioning and nanomeasuring machine (NPMM)

This article presents white light interferometry as a new application for the nanopositioning and nanomeasuring machine (NPMM). The NPMM was developed under the leadership of the Institute of Process Measurement and Sensor Technology at the Technische Universität Ilmenau (Germany) and allows highly exact dimensional and traceable positioning with a resolution of 0.1 nm within a volume of 25 mm x 25 mm x 5 mm. An application of white light interferometry was developed on the basis of these features which can utilize the devices very high precision and large effective range, which enables the stitching of partitioned results without overlapping measurements and expensive matching methods. In order to extract height data from the interferograms, a robust, precise and fast method using matched filters in the frequency domain has been put into practice. The filter templates are calculated according to a model function or are directly sampled from the light source power spectrum, which has been previously analyzed once. Thus, light sources with different spectral forms can be used.

GPU vs FPGA: Example Application on White Light Interferometry

High performance image processing applications area challenging field when targeting embedded processing. Field programmable gate arrays (FPGA) receive a growing interest as implementation platforms, but these solutions have to compete with the state of the art in image processing, which is codefined by graphics processing units (GPU). This paper provides a case study which analyzes the potential of embedded or hybrid implementation on FPGA and GPU for image stack processing in a white light interferometry (WLI) application.

Navigation in a Large Measurement Volume by Using AFM Technology as a Sensor System in the NPMMNavigation in einem großen Messvolumen in der Nanopositionier- und Mess-Maschine (NPMM) mittels AFM-Technologie

Abstract This article discusses methods to measure samples up to 25×25 mm2 using the NPMM [1] as an atomic force microscope (AFM) [2]. An entire scan at full resolution (10 nm) and 10 μm/s scan speed would take about 200 years. Therefore, overview scans with the AFM can be done to reduce the scan time, but these scans can induce aliasing artifacts due to sub-sampling. This paper gives a solution to that problem. The AFM camera is used for approximate orientation in the scan field. From an automatic optical area scan stitching software creates an overview image of about 2.6 GPixel with 0.5 μm resolution. The GEOtiff standard [3] is introduced to enable orientation in such big images. This format includes positioning information in the image and is used to solve the nano-orientation problem. This article further presents routines to create an overview image and a segmentation routine to detect structure domains. Since a combination of an AFM and optical scanning leads to higher positioning performance, both measurements are merged.

Kelvin probe force microscopy: measurement data reconstruction

The Kelvin Probe Force Microscopy (KPFM) is a method to detect the surface potential of micro- and nanostructured samples using a common Scanning Probe Microscope (SPM). The electrostatic force has a very long range compared to other surface forces. By using SPM systems the KPFM measurements are performed in the noncontact region at surface distances greater than 10 nm. In contrast to topography measurement, the measured data is blurred. The KPFM signal can be described as a convolution of an effective surface potential and a microscope intrinsic point spread function, which allows the restoration of the measured data by deconvolution. This paper deals with methods to deconvolute the measured KPFM data with the objective to increase the lateral resolution. An analytical and a practical way of obtaining the point spread function of the microscope was compared. In contrast to other papers a modern DoF-restricted deconvolution algorithm is applied to the measured data. The new method was demonstrated on a nanoscale test stripe pattern for lateral resolution and calibration of length scales (BAM-L200) made by German Federal Istitute for Materials Research and Testing.

Freiheitsgradregularisierte Entfaltung von Messdaten aus AFM-Sondermodi DoF-Restricted Deconvolution of Measured Data from AFM Special Modes

Zusammenfassung Seit geraumer Zeit werden durch Forschergruppen an verschiedenen Stellen Anstrengungen unternommen, bildhafte Messdaten von Rasterkraftmikroskopen (AFM) mit dem aus der Bildverarbeitung verfügbaren Methodenrepertoire zu verbessern. Im Fall der Potenzialmessung nach der Kelvin-Methode (KFM) bieten sich aufgrund der linearen Zusammenhänge bei der Datenentstehung sehr gute Voraussetzungen, um die prinzipbedingt geringere laterale Auflösung der KFM-Messdaten durch Entfaltung zu erhöhen. Im Beitrag wird in diesem Zusammenhang ein adaptives freiheitsgradbeschränktes Bildmodell zur Verfahrensregularisierung vorgestellt. Derartige Modelle wurden von den Autoren bereits erfolgreich im Bereich der Restauration astronomischer Himmelsüberwachungsaufnahmen eingesetzt.

Speeding up powerful state-of-the-art restoration methods with modern graphics processors

One important aspect of digital image processing is the removal of glitches from the measured data, particularly from observations of physical phenomenons. We propose an approach which realises valid results that have nearly no restoration artefacts. It is based on a further developed state of the art regularisation principle - the restriction of the degrees of freedom of the solution-describing model. The key idea is to use parameterised image elements instead of single pixels which are determined jointly in a bayesian estimation. However, the long duration of a restoration using such an approach is a problem in many applications. This article presents a technique how to speed up this method and reduce the runtime using the example of restoration of kelvin probe force microscopy-data.