Hydrogen-based quantum microscope visualizes minute changes in atoms

Physicists from the University of California, Irvine placed two bonded hydrogen atoms between a silver

probe of a scanning tunneling microscope (STM)and the test sample, consisting of a flat copper surface with small islands of copper nitride. Using laser pulses lasting trillionths of a second at cryogenic temperatures in the ultra-high vacuum of the device, scientists were able to excite a hydrogen molecule and record changes in its quantum states. This allowed the STM to form “still” images of the sample at the atomic scale.

The researchers note that the hydrogen moleculeis an example of a two-tier system. Its orientation shifts between two positions: up and down and slightly tilted horizontally. Using a laser pulse, scientists force the system to cycle from the ground state to the excited state, which leads to a superposition of the two states. The duration of cyclic oscillations is vanishingly small - only a few tens of picoseconds. By measuring this "decoherence time" and cyclic periods, the scientists were able to see how the hydrogen molecule interacts with its environment.

Source: University of California, Irvine

Space between STM tip and sampleis only 0.6 nm. The microscope assembled by the authors of the work detects the smallest electrical currents flowing in this space and obtains spectroscopic readings confirming the presence of a hydrogen molecule and elements of the sample. 

“The hydrogen molecule has become part of the quantummicroscope in the sense that wherever the microscope scanned, hydrogen was between the needle and the sample, says Wilson Ho, head of the study. “This is an extremely sensitive probe, allowing us to see deviations down to 0.1 angstroms. With this resolution, we saw how the charge distribution on the sample changes.”

High detail based on quantumThe coherence of hydrogen, according to physicists, can be very useful in scientific research and in the development of catalysts, the functioning of which often depends on surface defects on the scale of individual atoms.

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