Scientific instrumentation

Atomic Force Microscope - from Lab to Fab - via Space

The development of an instrument for a specific experiment is very often the first step for exploiting new scientific knowledge and bringing it closer to industrial applications. Fundamental engineering research addresses the hurdles that must be overcome in order to make new insight usable for a larger community. This can be nicely illustrated by the example of the atomic force microscope [AFM]. The instrument was invented in 1986 [1] in the search of a tool that allows imaging insulating surfaces with atomic resolution, comparable to the earlier scanning tunnelling microscope [STM]. At that time, both instruments, the STM and the AFM, were “homebuilt” by the scientists who wanted to use them. But soon start-up companies began building and selling instruments for other scientists who did not have the capacity, knowledge or interest to construct it themselves. Through a close interaction with these expert-costumers, the instruments were constantly improved, which finally opened new applications fields where non-specialists carry out operations.

Figure 1. AFM image of Martian Dust particles, recorded during the Phoenix Mission on Mars. The image was scanned from top to bottom and shows an area of 16.5µm x 19.8µm. Shortly before the middle of the image, one of the platy particles was dislodged due to the interaction with the AFM tip.

From an instrumentation point of view, one of the most demanding applications on that path was the development of an instrument for planetary science [1] and space research [2]. These instruments needed to be extremely robust and operated in an autonomous mode. Having successfully demonstrated AFM measurements on Mars, see Figure 1, under such special circumstances made the instrument fit for the next challenge: applications in a production line. During the European FP 7 project aim4np [3] we demonstrated such a concept, where innovative sensors, actuators and control technology were combined in a mechatronic solution. This allowed establishing a stiff, virtual link between the instrument and the workpiece while the AFM was mounted on and positioned by a robot. Therefore, the vibrations, which are typical for such an environment, were no longer hindering nanometre-resolution measurements. Figure 2 shows a model of the instrument that was mounted to a robotic arm and successfully operated in an environment that mimicked the vibration of a production line. Future applications could be found, for example, in the production of flat-panel displays, high-precision injection moulding, or role-to-role imprinting of nanopatterns on foils etc.

Figure 2. Mock-up of the aim4np instrument. The black bracket is just to support the model, as it is not mounted to a robot on this image. The instrument on the left hand side is a white light interferometer which allows larger scale measurements. The AFM is mounted at the bottom side of the instrument. The cylindrical features at the bottom are the lenses of the three vertical sensors. The horizontal sensors are contained in a rectangular box like the one on the right side of the image where the cables are leading to.

Microfabricated Tensile Tester - a Tool for Mechanically Probing 2D Materials

Graphene and other 2D materials are well-known for their attractive electronic characteristics. However, they show also interesting mechanical properties, which were investigated by e.g. atomic force microscope based indentation techniques [5], or by bending a substrate onto which the 2D materials were transferred, and which allowed straining the 2D material [6]. Inspired by earlier work of the group of H. Espinoza, [7] we developed a MEMS tensile tester shown in Figure 3, which allowed straining graphene while measuring at the same time the applied force and investigating the changes in the Raman spectrum. Straining graphene to more 10% was demonstrated using this device [8].This technique is currently further developed such that we can study the changes of interaction of 2D material with surrounding gasses as function of the applied strain.

Figure 3. (a) Micro-Tensile tester with a thermal actuator (on the left) and load cell. The thermal actuator is indicated in red and the shuttles are highlighted in blue [reproduced with permission from H. H. Pérez Garza et al, Nano Lett., 2014, 14 (7), 4107; Copyright 2014 American Chemical Society.]