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A breakthrough in Atomic Force Microscopy

Scientists at the Indian Institute of Science, Bangalore, have developed a way to efficiently replace and then reuse the “tips” of an Atomic Force Microscope, thus making it more versatile and time saving.

An Atomic Force Microscope (AFM) is a device used to image objects at nanometre scale, a billionth of a meter. Conventional methods of shining visible light and magnifying the reflected light does not work on these objects, as the size of the objects are often smaller than the wavelength of the smallest visible light wave. The AFM instead uses an atomically sharp tip permanently attached to a cantilever to image the objects. The imaging is done by scanning the object, similar to a blind person touching or feeling an object to get a sense of its size and shape. The AFM’s utilities, however, aren’t just limited to imaging objects. It can also function as a device for manipulation of objects at the nanoscale and is an indispensible tool in metrology, the science of measurement.

One of the drawbacks of this otherwise versatile tool is wear out of AFM tips when it is repeatedly used for scanning. Such worn out tips have to be replaced. “Conventional AFM probes have its tip integrated with the cantilever. And once the tip has seen some wear, the entire probe is replaced. The new probe then has to be recalibrated for sensitivity, which is often a lengthy and time consuming activity. This process is more elaborate, expensive and difficult to automate in case of AFM probes with integrated actuation or sensing”, says R. Sri Muthu Mrinalini, a member of the research team. The orientation of the tip also plays an important role, especially while scanning three dimensional (3D) surfaces. Conventionally, different tips, oriented in different directions, are used to scan the 3D object. These scans are then stitched to form a complete image of the object. Having to replace the probe after scanning in each direction not only increases the time of imaging, but also affects the accuracy of the image obtained.

Now, Ms. R. Sri Muthu Mrinalini and Dr. G. R. Jayanth of the Department of Instrumentation and Applied Physics at IISc have devised a system to efficiently replace and then re-use only the tips of the AFM probe. Since the tips alone are replaced during the scanning process, and the rest of the probe is left intact, the new system consumes lesser time for tip-replacement and is more cost effective. The proposed new system can change the tip in less than a minute. Further, images of 3D objects obtained using the new system can potentially be more precise. 

The new system employs a liquid meniscus-based microgripper at the end of the AFM cantilever, to pick up a new tip, grip it during imaging and subsequently drop it off after its use. Once the tip is dropped off, the used tips are stored in a tip holder while new tips are supplied by a tip supply station. The team was able to successfully design a prototype based on this new design. They were able to show that the tips did not suffer any damage during its pick up and storage. The performance of the re-used tips was also found to be satisfactory as the image obtained using them did not contain any glitches or artifacts. Since the cantilever is not changed, its sensitivity need not be recalibrated, which is conducive to save time. Ms. Mrinalini goes on to say “currently we are working on a way to automate this process of changing the tip, which would further improve the efficiency and throughput of the AFM.”

The AFM is one of the most important modern tools devised for imaging, metrology and manipulation of nanometer sized objects. This research improves the functioning of this already resourceful device.

About the authors:

Ms. R. Sri Muthu Mrinalini is a PhD student working with Dr. G. R. Jayanth at the Department of Instrumentation and Applied Physics at IISc.

Contact: mrinalini@iap.iisc.ernet.in

Dr. G. R. Jayanth is an Assistant Professor at the Department of Instrumentation and Applied Physics at IISc.

Contact:jayanth@isu.iisc.ernet.in

About the paper:

The paper titled ‘A system for replacement and re-use of Tips in Atomic Force Microscopy’ was published in IEEE/ASME Transaction on Mechatronics journal. A link to the abstract of the paper is provided below.

http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7437501

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