created a device to study the properties of quantum materials, which combined several scientific instruments. It
allows to study the surface of materials using atomic force
and scanning tunneling microscopes, and investigate the phenomena occurring during the flow of current through the material in the presence of a magnetic field at ultralow temperatures down to 10 millikelvin. New tool
superior in precision of the previous development of ten times, said the article,
published in the journal Review of Scientific Instruments.
Despite the fact that the macroscopic
properties of matter originate on the micro level, they are usually described
the laws of classical physics, as quantum effects are negligible at
large scale and therefore ignored. However, there is a class of materials in which quantum effects play a prominent
role on the macro level. These materials are called quantum, and their typical representatives, such as graphene, consists of a single
or several thin layers with a thickness of one atom. In the study of such
structures it is often important to correlate the measurement of macroscopic properties
microscopic characteristics that it is much easier to do if measurements are performed in the same conditions within a single device.
Physics under the leadership of Joseph
Svenka and Johannes (Johannes
of the U.S. National Institute of standards and technology created an experimental
apparatus for the study of quantum materials, capable of performing measurements of this kind. It combines the capabilities of scanning probe microscopy:
atomic force and scanning tunneling microscopes designed for
the study of surface materials at scales down to the size of individual atoms, to measure the effects
magnetotransport — phenomena related to the influence of the magnetic field on the flow
the current in the substance.
Atomic force (AFM) and scanning tunneling microscopes (STM) study of surface properties of the material at the nano-scale, with a probe-needle. While STM
used to study conductive materials, as the basis of his
work is a measurement of the tunneling current between the surface and “floating” above it on
the height of several angstroms needle probe. While the AFM, in which the forces
the interaction between the probe and surface are registered by the deflection of the cantilever — console at the end of which is fixed nanogl can be applied to nonconductive
materials. The new device both modes are implemented using one
universal quartz sensor, similar in appearance to a tuning fork, one of the teeth which is rigidly fixed, and the second is a measuring needle.
For the study of the phenomena associated with magnetotransport, the sample is mounted on a special contact pad, and then
when enabled, the external magnetic field of known value (up to 15 Tesla), it is applied current, and
electrical characteristics are measured in different points.
During measurement, all
system tools and the study material are in ultra-high vacuum
at very low temperature inside the refrigerator dissolution — cryogenic
device for cooling which is a mixture of the isotopes helium-3 and
helium-4. Value of operating temperature is 10 millikelvin. With such
temperature minimizes the random quantum fluctuations of particles and the
the noise is reduced.
To reduce radio frequency interference, the researchers applied the system inside the cryostat filter, consisting of a mixture of metal powder and epoxy
resin, and developed a new system of signal amplifiers operating at cryogenic temperatures. All this allowed to increase the sensitivity almost ten times in comparison
with other known tools, approaching the maximum possible limit under the working
temperature. So during the calibration tests, scientists have been assessed for resolution in the regime of tunneling spectroscopy at least eight microelectronic at the operating temperature of 10 millikelvin.
In the wordsof the head of
group Joseph Stroscio, other scientists will be able to use the scheme of the new device
to modify existing tools that will save them from having
buy new equipment for research. In addition, in the future, the researchers plan
to expand the list of possibilities, for example adding a module for observing electron paramagnetic resonance.
Previously we toldhow
scientists from two research groups created cryoelectron microscopes, which allow for measurements with a resolution of 1.2 angstroms, and the creation of the device for future gravitational detectors, which is able at room temperature to suppress to 15 percent of quantum noise in light beam