The atomic force microscope was placed on a chip

Vladimir Korolev, N+1

The principle of operation of the atomic force microscope.
PZT is a piezoelectric scanner that moves a sample (Wikimedia Commons).

Engineers from the University of Texas and the University of Newcastle (Australia) have developed an atomic force microscope that fits completely on a small chip. Microelectromechanical systems are used as active elements in it. The authors note that the "silicon on insulator" approach was used to assemble the system – its scalability can help significantly reduce the cost of devices. Study Michael G. Ruppert et al. On-Chip Dynamic Mode Atomic Force Microscopy: A Silicon-on-Insulator MEMS Approach published in Journal of Electromechanical Systems.

Photo of an atomic force microscope on a chip.
The width of the image covers eight millimeters. The cantilever is in the center.
(Here and below are drawings from an article in the Journal of Electromechanical Systems).

An atomic force microscope is a device that studies the surface of a sample by "feeling". One of its main parts is a cantilever, a very sharp needle located on a special beam. The radius of the needle tip can reach one nanometer. When the needle approaches the surface, intermolecular forces begin to act on it, which leads to deflection of the beam. By this deflection, the relative height of two adjacent sample points can be determined. To measure this value, a laser is shone on the beam – it plays the role of an optical arm and any change in its position in space also changes where the laser beam is reflected (its position on the photodiode).

The resolution of the microscope is determined by how accurately it can bring the needle to the desired points. In the best installations, this accuracy is much smaller than the size of an atom – this allows you to feel and determine the shape of the electron shell of individual atoms. As a rule, piezoelectric motors are used for this purpose – ceramic tubes that lengthen under the action of applied voltage. In general, atomic force microscopes turn out to be very complex and expensive systems.

The authors of the new work proposed to change the operating scheme of the device and miniaturize the microscope. Scientists have proposed using silicon MEMS devices manufactured using the "silicon on insulator" technology as a basis. This technology is compatible with mass production and uses photolithographic techniques.

The device created by the authors consists of the same basic parts as the "large" probe microscopes. In the role of piezoelectric motors, electrostatic actuators act in it: pairs of conductive combs attracted to each other under the action of applied voltage. Two pairs of such actuators provide a needle positioning error of only 16 nanometers. To swing the needle itself, required for scanning in tapping mode ("tapping" of the sample), a thin layer of piezoelectric on the beam of the cantilever is used. It was also used to analyze the mechanical state of the beam (oscillation amplitude, etc.) and estimate the height of the surface. The engineers managed to successfully use the created microscope to analyze the surface.

Appearance of the microscope

The authors note that microelectromechanical actuators make it possible to use not only standard trajectories (line-by-line scanning) for scanning the surface, but also more complex ones, for example, spirals or Lissajous figures. This can increase the speed of scanning samples.

Atomic force microscopy is actively used in materials science, medicine and many other technical disciplines. For example, with its help, scientists have learned how to diagnose cancer, assemble molecules by manipulating single atoms, draw electrical circuits on graphene and control lasers. Thanks to the atomic force microscope located on board the Rosetta spacecraft, physicists learned about the structure of comet dust.

Portal "Eternal youth" http://vechnayamolodost.ru  17.02.2017