Visible nanocosmos | XYZ system for Atomic Force Microscopy, AFM

2020/10 | For the atomic force microscopic examination of particularly large glass samples, Nanosurf and Steinmeyer Mechatronik have developed a high-precision,
extremely rigid XYZ system.

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Visible nanocosmos

In the early 1980s, physicists Gerd Binnig and Heinrich Rohrer developed the scanning tunneling microscope (STM) - laying the foundation for scanning probe microscopy (SPM). The way it works can easily be compared to that of a record player: Similar to aLike a needle on a record, a probe scans the surface of a sample and collects information about its properties. Scanning probe microscopy makes use of interactions between the probe and the sample, thus enabling resolutions up to the subatomic level. The results are highly accurate images of the smallest structures, which can be obtained using optical or electron-optical methodssuch as light or scanning electron microscopes. This opened up completely new possibilities for the analysis, research and processing of surfaces - the triumphal march of nanoscience and nanotechnologytook its course.In 1986, the two scientists were awarded the Nobel Prize in Physics for their invention. In the same year, Gerd Binning, Calvin Quate and Christoph Gerber developed the atomic force microscope (AFM), which - in contrast to the scanning tunneling microscope - can also be used to study non-conducting materials. The AFM makes use of the atomic forces that occur between the probe and the sample.The AFM exploits the atomic forces (including Van der Waals and capillary forces) that occur between the probe and the sample, and is the most widely used type of SPM today, thanks to its many applications in disciplines as diverse as materials science, semiconductors, and medical technology, to name just a few.

 

Proven on Earth and Mars alike

One of the leading manufacturers is the Swiss high-tech company Nanosurf. The Swiss company specializes in the development of scanning probe microscopes and offers compact AFMs and STMs, state-of-the-art atomic force microscope systems for scientific applications, as well as individual solutions for specific requirements. Around the globe, customers from industry as well as research & education appreciate the innovative approach, the modularity as well as the easy handling of the products. In 2007, an AFM from Nanosurf was also on board NASA's "Phoenix" space probe to Mars, helping to search for life on the red planet. It goes without saying that this was not an "off the off the shelf" model. Understanding the requirements, responding to them and developing an exactly fitting solution - that is one of Nanosurf's strengths. Nanosurf was also involved in the development of two customer-specific solutions for the investigation of particularly large glass subtrates.
large glass subtrates, the creativity of the Swiss engineers was also in demand. The large stone stages required for this purpose, which move and hold Nanosurf's AFM, were built by Steinmeyer Mechatronik.

 

From Dresden to the whole world

For more than 145 years, the name Steinmeyer Mechatronik has stood for quality and precision. In addition to standard products, the development of individual special projects in particular is one of the core competencies of the Dresden-based specialists for high-precision positioning systems. Together with the customer, the company develops innovative concepts perfectly tailored to the respective application. It is precisely this problem-solving competence that Nanosurf particularly appreciates about the Saxons. particularly appreciates. "With Steinmeyer Mechatronik, we have a competent partner at our side whose flexibility and wealth of ideas enable us to realize even highly complex custom products," says Nanosurf marketing manager Dr. Björn Pietzak. Another plus point is that the Dresden-based company also handles the logistics. When the positioning stages is ready, the Nanosurf engineers come to Steinmeyer Mechatronik, jointly install the AFM and perform the necessary tests on site. From Dresden, the finished system is then sent directly to the customer. "This is a great advantage for us," Dr. Pietzak tells us. "Because we wouldn't even be able to get such large stages as in this case through the door. That's why Steinmeyer Mechatronik always comes into play for us when the samples are particularly large and heavy."

 

Served up

After all, the larger of the two stages has dimensions of 1.45 m x 2.2 m and weighs 2.25 tons. Samples up to 54 cm wide, 1.5 m long and 21 cm high can be examined. The maximum sample weight is 500 kg. Since the specimen is firmly fixed on the platform, the XYZ system scores points for compactness and manages travel distances of 55 cm, 1.55 m and 5 cm. A belt drive and a stepper motor provide the movement and achieve speeds of up to 30 mm/s. In contrast, its smaller brother appears almost slender, although it also has impressive dimensions. With a size of 53 x 59 cm and a height of 47 cm, it is also extremely compact. The XYZ stage has travel ranges of 15 x 27.5 cm on the horizontal plane and 5 cm in the vertical plane and holds samples with a maximum size of 25 x 70 x 17.5 cm.By comparison, a "normal" AFM sample is typically 1 x 1 cm and 1 mm high. The system is driven by a spindle and a stepper motor. The 130 kg stage can hold samples with a maximum weight of 150 kg. Both gantry systems are made of heavy granite to withstand the large weight of the specimens. Above a u-shaped sample platform is a movable crosshead that holds Nanosurf's atomic force microscope. This allows the AFM's measuring instrument - the so-called cantilever, an elastic leaf spring with a nanoscopically small tip at the end - to be precisely aligned and moved to any point within the U-shape. When the cantilever traverses the surface relief of a sample, the attractive and repulsive forces occurring between the cantilever and the sample cause the leaf spring to deflect. This is detected and recorded with the aid of a laser beam. Thus results in a highly accurate image. A resolution of 1 µm and a positioning accuracy of +-5 µm, as provided by the two motorized XYZ systems, are essential for this.

 

The power lies in the silence

The special feature of the design: The crossbeam moves on specially developed air bearings. It virtually floats on an air gap approx. 5 µm thick and thus operates practically contactless and wear-free. This guarantees a very long service life.

A further advantage is that extreme rigidity can be achieved with the aid of the air bearings. As soon as the measuring head is brought into position, the air is released from the bearings and the system is fixed by its internal preload. The entire mass of the transverse axis then also rests directly on the base granite, ensuring maximum stability. "This is enormously important. Because when the AFM is stationary, it must not
no longer be allowed to move. After all, differences in height of one nanometer or less are to be
be measured reproducibly," explains Dr. Pietzak. "For this, the AFM must be atomically stable. If it were to oscillate - even if it were only a few nanometers - the measurement results would be unusable." In the case of the large stage, moreover, six feet were mounted under the granite as extra vibration dampers to further protect the system from building vibrations. This extraordinary rigidity was not an everyday occurrence for Steinmeyer Mechatronik either. "We ourselves would not have had the opportunity to prove whether our stages even met the required high stiffness requirements," reports Reinhard Weihmann of Steinmeyer Mechatronik. But thanks to the intensive cooperation with Nanosurf and the joint years of experience with such heavyweights, the Dresden-based positioning specialists solved this challenge with flying colors.