student in physics & astronomy Wilson Ho, Bren Professor of physics & astronomy and chemistry Yunpeng Xia, Ph.D. Student in physics & astronomy and Likun Wang and Ph.D. “The hydrogen molecule became part of the quantum microscope in the sense that wherever the microscope scanned, the hydrogen was there in between the tip and the sample,” said Ho. At this resolution, we could see how the charge distributions change on the sample.” “It makes for an extremely sensitive probe, allowing us to see variations down to 0.1 angstrom.
The space between the STM tip and the sample is almost unimaginably small, about six angstroms or 0.6 nanometers. The STM that Ho and his team assembled is equipped to detect minute electrical current flowing in this space and produce spectroscopic readings proving the presence of the hydrogen molecule and sample elements. Ho said this experiment represents the first demonstration of a chemically sensitive spectroscopy based on terahertz-induced rectification current through a single molecule. The ability to characterize materials at this level of detail based on hydrogen’s quantum coherence can be of great use in the science and engineering of catalysts, since their functioning often depends on surface imperfections at the scale of single atoms, according to Ho. “As long as hydrogen can be adsorbed onto a material, in principle, you can use hydrogen as a sensor to characterize the material itself through observations of their electrostatic field distribution,” said study lead author Likun Wang, UCI graduate student in physics & astronomy. Joining Ho and Wang on this project, which was supported by the U.S. Department of Energy Office of Basic Energy Sciences, was Yunpeng Xia, UCI graduate student in physics & astronomy. Reference: “Atomic-scale quantum sensing based on the ultrafast coherence of an H 2 molecule in an STM cavity” by Likun Wang, Yunpeng Xia and W. Ho, 21 April 2022, Science.The phenomenon of electrical oscillations in the case of a d-c discharge in hydrogen in tho region of the positive v-i characteristic has been investigated for the pressure range 40 to 200 microns, discharge voltages 0.6 to 11.2 kv, and discharge currents 0.1 to 2.5 ma. Coherent oscillations were observed in the frequency range 40 to 100 kc/sec which were accompanied by three or four frequency groups in the range 170 to 2,300 kc/sec. The existence of a common cut-off current for all these frequencies has been shown which is found to depend on the pressure in such a manner that it has a maximum value for p = 60 to 90 microns. The frequencies of the oscillations show a significant dependence on i and p and are independent of the circuit parameters. The frequencies have a minimum value for p = 60 to 90 microns. The lower frequencies show only an insignificant variation with i whereas in the highest frequency group there is a very rapid rise of frequency with current. The amplitude of the oscillations is determined by i and p and shows a maximum for some value of i and p = 60 to 90 microns.
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