Atomic force microscopes use powerful technology that operates on the same principle as a miniature turntable. A tiny cantilever with a nanometric tip is used to pass over a sample and trace its relief, atom by atom. The tip’s miniscule up and down movements are recorded by a sensor to determine the sample’s topography. Nanometric scale sensors that are able to improve the performance of atomic force microscopes have been printed by EPFL researchers.
The nanosensors have miniaturized the microscopes’ detection component by up to 100 times. This enhances the detection speed and sensitivity and may well be the basis for the next generation of atomic force microscopes. EPFL recently demonstrated the sensors in a real-world application for the first time.
Georg Fantner, the lab’s director, explained that detection is sped up, sensitivity is increased and inertia is reduced by miniaturizing the cantilever. This improves the performance of atomic force microscopes. The researchers at EPFL’s Laboratory for Bio- and Nano-Instrumentation accomplished this by furnishing the cantilever with a 5-nanometer thick sensor made with a nanoscale 3-D printing technique. The result is that the size of the cantilever is reduced by 100 times.
The deformation of the sensor positioned at the fixed end of the cantilever measures the nanometric tip’s up and down movements.
As the team had to detect movement that is smaller than an atom, this presented a unique challenge that had to be overcome. Collaborating with Michael Huth’s lab at Goethe Universität at Frankfurt am Main, they prototyped a sensor constructed from highly conductive platinum nanoparticles that is surrounded by an insulating carbon matrix. The carbon would normally isolates the electrons, but at the nano-scale, a quantum effect comes into play. Some electrons travel from one nanoparticle to the next by jumping through the insulating material.
The nanoparticles move further away from each other when the shape of the sensor changes. This results in less electrons jumping between them. The changes in the current is measured and this reveals the deformation of the sensor and, by inference, the composition of the sample.
Finding a way to manufacture the sensors in nanoscale dimensions while at the same time controlling their structure and, by extension, their properties, was the researchers’ real feat.
Maja Dukic, the article’s lead author explained that a precursor gas containing platinum and carbon atoms was distributed over a substrate in a vacuum. An electron beam is then applied. This forces the platinum atoms to gather to form nanoparticles. The carbon atoms naturally form a matrix around them. To build sensors with any thickness and shape they want, this process is repeated.
It has been proven that the sensors can be built using this method and that they work on existing infrastructures. The new technique can now be used for broader applications, ranging from ABS sensors for cars, biosensors and touch sensors on flexible membranes in artificial skin and prosthetics.