Not long ago, a single nanometer displacement was seen as one of the hardest measurements to achieve, as well as one of the most difficult distances within which to precisely control movement. But now, Mad City Labs has demonstrated the capability to repeatably achieve a one-picometer movement with a piezo nanopositioner — 1/1,000 of a nanometer — and that PicoQ® sensors offer a low enough noise floor to accurately resolve that movement.
While not every experiment requires a device capable of taking a single picometer step, many applications require high precision. Prominent examples include atomic force microscopy and large baseline measurements, such as gravity wave detection and astronomical interferometry.
These disparate examples demonstrate the challenges of active feedback control mechanisms. Astronomical interferometry requires the ability to make small displacements that translate to large motion over long distances. For atomic force microscopy, the length scale is extremely small, meaning the feedback displacement is also extremely small. In both cases, the fundamental requirement is the ability to control a very small displacement. Before now, no one had demonstrated the ability to control movement at the single picometer level.
The ability to achieve such high precision for a positioning device is largely dictated by the position sensor — in this case, Mad City Labs’ PicoQ® sensor. Achieving high precision with repeatability is only possible with closed loop feedback, meaning the sensor value is fed back into the control system to maintain a position. The position noise level must be exceptionally low so the stage can maintain that change in distances of a single picometer.
Moving One Picometer vs. Measuring One Picometer of Movement
Mad City Labs knew our PicoQ® sensor technology could resolve one picometer if system noise was kept low enough. The fundamental question was, could we actually control movement at a small enough distance?
In Fig. 1, we show the fundamental noise floor of a customized Nano-METZ nanopositioning system. We can only hope to control a one-picometer movement if we can resolve it from the measured noise floor. We demonstrate this by measuring the sensor output. An input signal of known amplitude and frequency is used to move the stage. With the instrumentation calibrated using our normal methods, we command a peak-to-peak signal of 10 pm. Therefore, on the sensor output, we should read the same value, depicted in Fig. 1 as the central sharp peak.
Fig. 1 — Position noise of a customized Nano-METZ nanopositioning system.
With the ability to command stage movements in one-picometer increments, and having established that the noise floor was below a single picometer, we moved to the larger challenge of controlling and resolving displacement at the picometer level. This can be demonstrated by firstly commanding stage movements of a known value, and then measuring the sensor for a real-time assessment of displacement.
The data shown in Fig. 2 was acquired by commanding the stage to move in a five-picometer step, then a two-picometer step, and finally a single picometer step. The command converter has a resolution of 20 bits, but the sensor measurement utilizes a 24-bit resolution converter. We can then resolve the individual command steps since the sensor measurement is at a higher resolution than the command value. The jagged plateaus represent a combination of remaining noise in the system and conversion noise in the sensor measurement.
Fig. 2 — Nanopositioner displacements (peaks L-R) of 5 picometers, 2 picometers, and 1 picometer. Data acquired using a customized Nano-METZ with 1.05 μm total range of motion.
Fig. 2 clearly shows it is possible not only to command displacements at the single picometer level, but also to precisely control and resolve those displacements. A critical element of this demonstration is that it was performed in ambient conditions, without a specially designed room or customized software. It can be accomplished by anyone with a combination of low sensor noise, low-noise electronics, and a high-resolution interface.
Maximize Collaboration to Maximize Results
A Mad City Labs nanopositioning system with PicoQ® sensors has been able to resolve and control a single picometer step. This has not been demonstrated previously and it opens opportunities for high resolution metrology, measurement and microscopy.
It is important, however, to realize that the positioner is often just one element of a larger instrument. While positioner performance provides a minimum baseline, other factors will almost certainly affect the final achievable resolution and control.
For this reason, Mad City Labs encourages collaboration with us before purchasing any of our products. Using such an approach, the customer can understand any potential limitations of our devices, and we can better understand the scope of their problem and their desired outcome. For customers who are operating at the frontiers of their discipline, this is a valuable way to analyze proposed designs and maximize the chances of successful outcomes.
Pushing Extreme Metrology’s Limits
The capabilities of our nanopositioners, which incorporate PicoQ® sensors, are fully utilized in our atomic force microscopy (AFM) products. AFM applications are particularly sensitive to noise, which can limit the data being acquired. The extremely low noise and high-resolution control of our positioners is the backbone of our high performance AFM products, such as the MadAFM™. However, these same positioner attributes also will ease experiments in long baseline interferometry, wherein such a device might be used as part of an active feedback loop over extreme distances. Maximizing sensitivity and minimizing noise at one end of the experiment has a profound effect on results gleaned at the other end.
But research is always evolving, pushing the limits of what can be measured, tested, and investigated. So, what doors does this motion system open? Likely, both new and existing applications: it may take some time for new applications and experiments to get to the point where they need this level of control. Still, now that the tools exist, can we repeat other experiments, but investigate more deeply? To learn more, contact the author and visit www.madcitylabs.com.
Resources
https://www.photonicsonline.com/doc/building-active-feedback-control-methods-at-the-nanoscale-0001
https://www.photonicsonline.com/doc/confirming-picometer-performance-of-nanopositioning-systems-0001
https://www.photonicsonline.com/doc/extreme-metrology-big-science-requires-a-nano-perspective-0001
https://www.photonicsonline.com/doc/understand-noise-at-the-sub-nanometer-scale-0001
By Shannon Ghorbani, Mad City Labs Inc.
About the Author
Shannon Ghorbani is a member of the Technical Sales team at Mad City Labs. He obtained a B.S. in Physics and Astronomy from the University of Wisconsin – Madison. Shannon has been a part of the Mad City Labs team for over 16 years, focusing on wide-ranging applications of extreme metrology, scanning probe microscopy, optical microscopy, and more. He may be contacted at
About Mad City Labs
Mad City Labs designs and manufactures a complete product line of high-precision piezo nanopositioners, micropositioners, atomic force microscopes, and single molecule microscopes. We provide innovative instrument solutions from the micro- to pico-scale for leading industrial partners and academic researchers.