Working Group of the Expert Committee Materialography
Quantitative 3D-Microscopy of Surfaces

Optical surface measuring devices record topographies quickly and without contact, which is why they are becoming increasingly popular in the industry, for example. But how accurate are the characteristic values derived from them, and how can measurement artifacts be reliably detected at all? This Working Group provides a forum for experienced and new users from a wide range of disciplines and brings them together with metrologists as well as manufacturers of microscopic 3D measuring instruments ranging from interference and confocal microscopes to focus variation, stereo image pair analysis, and projection methods. The focus is on the wide range of diverse practical requirements of users, current developments in metrology, new types of standards, application-specific calibration procedures, and guideline and standardization efforts in the relevant committees of VDI/VDE-GMA, VDA, DIN, and ISO. The Working Group aims to facilitate an uncomplicated exchange between users, equipment manufacturers, and experts from metrology and standardization through open workshops, mostly at the "Physikalisch-Technische Bundesanstalt" (PTB), to exploit the potential of these measurement methods and to deepen the understanding of their safe application.

Development of microscopic topography measurement - opportunities and challenges
 

The Working Group Quantitative 3D Microscopy of Surfaces looks back on several decades of continuous activity and successful work. Initially led for many years by Edeltraut Materna-Morris (KIT, Karlsruhe), several dozen interested parties have since met at regular intervals in various event formats to exchange their experiences in the field of topography measurement and assessment using various microscopic techniques.
Optical surface metrology has developed rapidly over these decades. Although the physical and technical fundamentals of, for example, the various interference and confocal microscopy methods as well as the focus variation method have been known for many decades, they have only found broader application since powerful processors have made it possible to convert the measured data into a 3D topography within (fractions of) a second and to display it graphically. As a result, these non-contact measurements are not only fast, but can also be automated and thus used efficiently, especially for industry.

In the early days of the Working Group, the focus was on stereo image pair analysis and projection methods, in some cases still with manual evaluation, primarily for defect analysis in materials science laboratories. Nowadays, most of the contributions deal with the applications of inferential and confocal microscopy in many industrial sectors (e.g. vehicle and plant construction, optics, electronics) and scientific disciplines (in addition to materials science, also bio/medicine, archaeology, etc.). As a result, the user community has become more diverse and heterogeneous. Especially for industrial process control, the reliability of the measurement methods is crucial; questions about calibration, traceability, and uncertainty come to the fore. Besides, these methods often show measurement artifacts in the 3D representations, which can distort the result of roughness and form measurements - and are often not visible at first glance. Consequently, strategies for device characterization are required that allow the device to be qualified for specific measurement tasks.

A close exchange between users, instrument developers, and metrologists


When E. Materna-Morris retired, the leadership of the Working Group was therefore offered to colleagues at the "Physikalisch-Technische Bundesanstalt" (PTB) in Braunschweig, to achieve closer interaction with metrology, the development of standards, and guideline and standardization committees. In this way, the users of optical topography measurement methods participating in the Working Group can become more quickly familiar with newly developed calibration methods and learn how to better characterize their devices and examine their suitability for specific measurement tasks. Conversely, the metrologists and those active in the guideline/standardization committees benefit directly from the reports of the users from their everyday metrological practice and can incorporate their complex experiences and suggestions into their work, to develop both standards and guidelines and norms better in the future to meet the needs of the users. The new ISO 25178 series of standards for areal texture measurement and the VDI 2655 guideline sheets play a major role here.

This direct feedback characterizes the current Working Group. This makes it possible to jointly discuss requests from the broad user community and new requirements arising, for example, from current metrological challenges in industry or other research disciplines, to outline possible approaches to solutions and to initiate better networking in the form of joint projects or standardization/guideline initiatives. This close exchange will be complemented by technical presentations and expertise from some Central European-based equipment manufacturers and software developers.

Beyond optical surface measurement techniques, developments in scanning probe microscopy (SPM, especially AFM) and 3D techniques in electron microscopy (SEM), as well as stylus instruments, are also included in the context of topography measurement and texture determination across many orders of magnitude.

Regular open workshops
 

Since 2015, the Working Group together with the PTB has organized an open workshop about every two years, at which the above-mentioned topics are dealt with - sometimes with a current focus. Participants have the opportunity to present their work in the form of (short) talks or posters, whereby open, tricky questions are also welcome to stimulate discussion. A lot of space is given to informal discussions in a relaxed atmosphere.

On the sidelines or independently of the workshop, there is the opportunity to exchange critical samples and to measure with various measuring instruments at the partners, which will be reported at the following workshop. (Prototype) standards are also passed around for testing in various laboratories. Besides, image processing and evaluation strategies are also compared.

Workshops have resulted in joint work in smaller groups, often in conjunction with committees in the VDI/VDE-GMA (FA 3.40, 3.41, 3.64) or in the context of third-party funded projects. Currently, the Joint Research Project (JRP) i04 "TraceOptic" within the European Metrology Programme for Innovation and Research (EMPIR) with an expected duration of 2021-2024 should be mentioned in particular, in which some workshop participants are also involved as partners or stakeholders. This research project addresses many questions that are dealt with in this Working Group. A close exchange up to joint events is planned.

The Working Group welcomes further interested parties!

Goals

  • Regular open workshops (approx. every 2 years at PTB)
    Users, instrument manufacturers, metrologists.

  • Better understanding of measuring instruments, avoidance of measurement artifacts.

  • Testing of prototype standards, measurements on critical samples.

  • Practical and efficient application of the ISO 25178 series of standards - how to measure, evaluate and document in compliance with the standards.

  • Comparison of evaluation software and strategies for determining e.g. surface roughness parameters.

  • Cutting edge measurement/evaluation, tip shape determination
    (Co-initiated by the VDI/VDE GMA 3.64, which develops guidelines for this purpose).

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