Applied nanotechnology, from nanometrology to nanolithography
Nano-measures and interferometers
The displacement measures based on the single-crystal material with a reverse piezoelectric effect change their size directly proportional to the control voltage. Depending on the direction of the electric field and crystallographic orientation of the single crystal axes, the surface can move in different planes. Thus allowing the professionals of NANO-ATTO Metria to create horizontal and vertical measures to calibrate the probe and electron microscopes, and other measuring and process equipment.
For the production of displacement measures the company uses single crystals produced in Russia. Electrodes are deposited on single crystals, and then calibration is performed, packaging and checking the stability of characteristics in time. The latter should not exceed 1–2%, that is the statistical measurement error. The life of the measures is not defined as the first standards manufactured more than 5 years ago are still stable. However, it is recommended to check measures every few years.
To measure the displacement of the reference surface of measures, optical interferometers based on the Russian-made semiconductor lasers were designed. Stabilisation of the laser radiation by the Bragg and cesium cells provided a decrease in the relative frequency instability to 10-8. According to the laboratory staff, the minimum displacement, which can be measured with interferometers, is 3 pm. NANO-ATTO Metria produces several types of interferometers, which can be used for various purposes.
Displacement measures are compact and equipped with an electronic control unit developed by the company; it can generate pulses of a pre-determined shape.
A potential project involving interferometers was the creation of a near-field scanning optical microscope for reflection measurements. "Overcoming the diffraction limit and optical measurements with nanometer resolution represent a concept that has been in place for many decades, but only devices for transmission measurements are presented on the market", says a leading engineer at NANO-ATTO Metria Alexander Dykov. In the device prototype the drive and control system of the FemtoScan scanning probe microscope produced by the Advanced Technologies Center is used. Currently, the resolution of 60 nm is achieved, and efforts to improve it are being taken. In particular, the urgent task is to improve the probe.
Also based on the prototype of the scanning near-field optical microscope the so-called "nano-tweezers" are being developed which allow to manipulate nanoscale objects. The idea is to apply the electrode to the tip of the probe in order to capture the object with an electric field. This contactless technology is well suited for working with nanoparticles of various nature including biological items.
In the 1990s, the Delta Research Institute conducted research into surface modification and creation of nanoscale structures on films using nanolithography. As the Research Institute was closed, the project was run by the NANO-ATTO Metria.
The process unit, a lithograph based on the scanning tunnelling microscope modified for high-voltage (tens of volts) and aggressive environment. The machine generates electrical pulses, and gas-phase deposition with the generation of a given structure on a substrate take place in the processing atmosphere. Disposable probes of tungsten wire with an etched tip are made in the company’s laboratory. Resolution depends on the sharpness of the probe needle and can reach 3 nm. Items of the smallest sizes can be obtained on the carbon films. Through years of research, optimal substrate materials, gas mixtures and process modes were selected.
The developed compact unit is provided with a vacuum system but the process does not require high vacuum, and can be implemented at normal pressure in the gas atmosphere. The technology is safe for humans, and it does not require the use of any hazardous chemicals. According to the chief process engineer Andrey Shavykin, in order to improve the speed, it is possible to create an independent system to control several tens of parallel probes.
The resulting structures can be used in the production of data storage devices, nanoelectronics and photonics. Thus, the resolution of up to 3 nm provides a high recording density, while when using carbon media data can be stored for centuries. In the field of nanoelectronics it is challenging to create new classes of devices, for example, based on quantum effects. Manufacture of optical elements is also quite a promising area.
Currently, some experiments to transfer material to the surface from the tip of the probe are in progress. This technique may find application in the manufacture of nanoelectronic devices as well as in 3D-printing.
Now, not all the projects of the NANO-ATTO Metria, which we have briefly described in this publication, are close to the stage of commercial products but they are implemented by the people focusing on the final outcome, which is an essential pre-condition for success.