Getting Close to Nanostructures
Both methods have their own advantages and drawbacks, and are used for their own particular tasks; all in all, they complement each other well. Mikhail Zhukov, a graduate of the Chair of Nanotechnologies and Materials Science explains that one of the unique benefits of probe microscopes are that you can work with biological specimens in their native (live) state, while cutting their surface and manipulating nano-objects right on the spot. For instance, when using the electron microscope, the specimen has to be conducting electricity, thus it becomes impossible to work on a live specimen – it dies soon after the conductive coating (Au, C, Pt, etc.) is applied. Zhukov’s work at ITMO University has to do with the development of new types of sensor probes, which should improve their resolving power and increase the application of scanning probe microscopy.
“In traditional optical microscopy, we look at the specimen, in electron microscopy we bombard it with electrons and study the response. Probe microscopy is about “feeling” the surface of the specimen with a special tip (probe), that gives information about its surface and characteristics (adhesive strength, Young’s modulus, charge distribution, magnetic fields, current-voltage characteristics, etc.). That is why this type of microscopy can be applied in different fields of science”, adds Mr. Zhukov.
In addition to imaging of surface topology, scanning probe microscopy can be used for nanolithography, for assessing the object’s rigidity, the elasticity of its structure, its adhesive strength, the presence of electromagnetic forces and so on. Different types of probes are used for different purposes, as the probe’s geometry and purposes affect the possibility and quality of imaging. For instance, when working with structures with a complex surface it’s better to use long sharp probes that offer higher precision; more stable probes are used in nanolithography.
“My work mostly focuses on the development of new types of sensor probes. For example, I am working on probes with nanowhisker structures. A regular probe is conic or pyramidal in shape, and it can’t reach into deep narrow irregularities should they be present on the object’s surface – which decreases the accuracy of the data. A nanowhisker has a continuous crosswise size – and a really small one at that, so it can easily reach into pores and canals in the object. There are also probes with scalpels, which are used for precise nanolithography, for cutting the surface of biological objects and precise nanoparticle manipulation, as well as other projects”, says the postgraduate student.
Mr. Zhukov adds that his inventions have a large range of applications. For instance, he’s been using probes with nanowhiskers in medical research – for studying membranes in cellular structures under different conditions, and nanosurgery. They’ve also proved useful in high-resolution imaging of living objects – bacteria and cells – in a liquid medium. In nanoelectronics, these probes were used for studying the emitting surface of photon-emitting diodes covered with nanorods – a regular probe could not reach between them. They were also used for high-precision imaging of magnetic fields and in creation of small diffraction gratings.
Scanning probe microscopy has many advantages and possible applications; still, it has 2 major drawbacks: a slow scanning process and the presence of artifacts on the generated image.
“The artifacts – i.e. things on the image that aren’t actually there – can be caused by defects in incorrect settings in the prob. And it’s quite possible that you won’t even understand that it’s an artifact and mistake it for an irregularity of the surface. That’s why we are set on removing artifacts by developing new probes as well as using specific software during postprocessing. It’s really important to be careful about it so as not to distort the signal. In a way, this is similar to editing regular photographs – with the exception of it being done in three dimensions. Thus, as you erase noise from the image, you might as well delete an essential signal and lose some of the data as well”, explains Mikhail Dzukov.
The prototypes developed by Mikhail have been presented at various competitions. In 2015, Mikhail Dzukov became the winner of the Presidential scholarship, the postgraduate student of the year, the winner of the Committee of Science and Higher Education award, etc.