Part 2 of the series "Under lock and key at Münster University": the vacuum machine at the Institute of Physics is used to investigate spin phenomena
The yellow stickers can already be seen from a distance: "Laser beam", "High voltage - danger to life", "No unauthorized access". The locked door with the warning notices is located at the end of a long, dark corridor on the fourth floor of the Institute of Physics at the University of Münster. In the lab is a vacuum machine. What looks to laypeople like a huge monster is for Prof. Markus Donath’s research group the means to investigate the spin, the intrinsic angular momentum, of electrons.
"There is only one such apparatus in the world. We use it to fathom the secrets of spin phenomena for new electronic components", explains Markus Donath. Using state-of-the-art spectroscopic methods, physicists at Münster University study the surfaces of various materials such as ferromagnets and graphene-like layered materials. There is no way around nanophysics if in the future we want to build data memories for computers in a more energy efficient way, for example, or increase their data density and speed of data processing. Besides the electron charge, the scientists also want to use the electron spin as an information carrier for a more efficient electronics. And for that they need the vacuum machine.
"This work often requires a great deal of patience"
The machine consists of four chambers and 19 pumps. Several ladders from DIY stores hang under the ceiling, and serve as cable ducts for water hoses for cooling or for the numerous power cables. A stainless steel beer barrel serves as a vacuum reservoir. Inside the machine there is ultra-low pressure that is as low as in space. The pumps run without interruption during the measurement series. There is a constant humming and droning in the room. "Such an apparatus is never finished. We keep replacing parts. We also rebuild the machine and are always developing it further", says Markus Donath. The fundamental parts were purchased in 2002 and then upgraded individually. Numerous parts have been specially made in the precision mechanics workshop of the Institute of Physics.
The glass door with the yellow warning stickers and an opaque curtain behind it is for several reasons always locked. First, invisible laser light is used, which is dangerous for the eyes. Second, electric high voltage poses a danger to life. Third, the laboratory contains ultra-cold gases such as nitrogen, which can cause injury if used incorrectly. And, finally, vibrations when a person enters the room can influence the measurements. The instrument settings for a series of experiments must also not be changed. These are the reasons that the vacuum machine is under lock and key.
For the various measurement series, the material samples to be examined are first cleaned and sorted atom by atom, since the researchers require ultra-pure conditions to create small structures. The samples are moved from one chamber to the other by means of long rods serving as gripper arms. The next step is to check the material. For this purpose, the surface is scanned at the atomic level with an ultra-pointed needle. At the heart of the vacuum apparatus is the ingenious investigation of the properties of electrons and their spin that is carried out by Münster’s nanophysicists. The duration of a measurement series varies between several weeks and one year, depending on the research question. Four to six BA and MA students, as well as PhD students, can all work on the vacuum machine at the same time.
"This work often requires a great deal of patience and you have to be able to persevere in the meantime. But so far everything has always worked out in the end", says PhD student Philipp Eickholt. "The vacuum apparatus provides good results and is versatile. As scientists, we want to understand things exactly and therefore ensure that measurement uncertainties are as small as possible", adds Markus Donath. By analyzing and manipulating the electron spin in materials for future spin electronics applications, Markus Donath and his team put a new spin on nanophysics.