When we step on a bathroom scale, the force we exert on the scale is measured. The precision scale at TU Wien is based on a completely different principle: it is a quartz crystal microbalance. In this process, a crystal is set into vibration. If its mass changes, the crystal’s oscillation frequency also changes, and this can be measured with astonishing precision—to nine significant figures, meaning with an accuracy of approximately one in a billion.
At TU Wien, this extremely precise microbalance is used to study the bombardment of surfaces with ions. The ions can knock individual atoms out of the surface—a process that is crucial in materials research and nuclear fusion. To understand such minute material losses, one must push the limits of what is measurable. These limits have now been examined in greater detail by a team at TU Wien in collaboration with partners at Uppsala University. The study revealed that a high-energy ion beam affects not only the material under investigation—but also the measuring instrument itself. The results were published in the journal Applied Surface Science.
During the measurements conducted as part of the study using a quartz crystal microbalance, the researchers could not simply read a single measurement result, as one would with a bathroom scale. “The system reacts in a highly complex manner, and several different effects emerge on different time scales that overlap with one another,” explains Martina Fellinger of TU Wien, the study’s lead author.
When the ion beam strikes the crystal, it acts like a tiny, point-like heat source. “The local heating generates mechanical stresses in the crystal,” says Fellinger. “And it is precisely these stresses that alter the resonance frequency.” Particularly noteworthy: The effect depends heavily on exactly where the beam strikes the crystal. “Small changes in position can significantly alter the signal,” says Fellinger. On a timescale of minutes, another effect is also important: The entire crystal heats up slowly, which also changes the resonance frequency.
The actual change in mass that one would like to detect with the quartz crystal microbalance, however, would be a permanent effect: When atoms are removed from the surface, the vibrating mass decreases, causing the resonance frequency to increase. Yet the study shows that even a persistent frequency signal is not automatically pure mass information. It can also arise from changes in the quartz itself, such as radiation damage.
The superposition of all these effects means that it is impossible to draw a clear line between the balance and the object being measured. The balance itself changes as a result of the measurement—and only by taking this into account can one obtain accurate results. In their research, the team was able to physically explain and quantify the individual effects. This is particularly essential for future applications of this measurement methodology.
Precise measurements of mass changes are important, for example, to optimize material ablation in future fusion reactors or to understand surface erosion on planets and moons in space. The corresponding experiments have been intensively studied for years at TU Wien in the group led by Prof. Friedrich Aumayr, where Martina Fellinger is conducting her dissertation. In the long term, the combination of quartz microbalances with high-energy ion beams for material analysis opens up new possibilities: for example, material losses and chemical changes could be investigated simultaneously in the future. The study makes it clear: when measuring with extreme precision, one is not only measuring the object—but also the physics of the measuring device itself.
Applied Surface Science
Experimental study
Not applicable
Response of a quartz crystal microbalance to a localized heat source: The case of MeV ion irradiation
2-Jun-2026