Rohma Khan (CUNY City College of New York, CUNY Graduate Center, United States)
Bluesky: @gbalavoi.bsky.social
Abstract: Characterization of nanoscale confinement of liquids via quantum sensing can overcome the sensitivity, spatial, and temporal limitations of other measurement techniques, allowing deeper understanding of dynamics central to areas spanning geophysics, tribology, catalysis, polymer science, and biology. Using shallow nitrogen vacancy (NV) centers as our quantum sensors we probe the molecular dynamics of water molecules confined within engineered ~5-nm-tall channels formed by a hexagonal boron nitride (hBN) structure on the diamond surface. Our resultant NV-enabled nuclear magnetic resonance spectra of confined water protons reveal a reduced H2O self-diffusivity, orders of magnitude lower than that in bulk water. Correlation measurements show us long lasting nuclear spin coherences, indicative of molecular dynamics intermediate between bulk water and ice. Molecular dynamics modeling indicate cluster formations may arise from accumulation of surface charge and carrier injection into the fluid under laser illumination. Our next step is the extension of these experiments to variable temperatures with preliminary findings showing narrowing of our NV NMR Spectra as we approach freezing point.
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Hi Rohma,
Excellent presentation. From the perspective of an organic chemist, I am curious if you could use the same system to detect protons in other solvents, such as organic solvents instead of water. Would you expect to observe different proton frequencies depending on the chemical structure of the solvents, and achieve NV-enabled H NMR? Thanks! -
Hello Yunfan Qiu,
Thank you for your question!
We can use the same system to detect protons in other solvents, in my colleague’s case he is able to detect protons in fluorinated oil. We have also tried this with PEG. In our system we would not be able to observe different proton frequencies depending on the chemical structure of the solvents, but others have with a slightly modified setup. Here is the citation for them Glenn, D., Bucher, D., Lee, J. et al. High-resolution magnetic resonance spectroscopy using a solid-state spin sensor. Nature 555, 351–354 (2018). https://doi.org/10.1038/nature25781
One of the key points in our system is that we work with statistical polarization but to see the chemical shifts we need thermally polarized nuclear spins. Please let me know if you have any further questions, thanks!
Rohma
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Hi Rohma, interesting presentation! I am wondering if there are good ways to optimize this technique without substantially changing the result. I am thinking of two ways:
1) Optimizing the diamond properties (e.g. number of NV centers, closeness of NV centers to the surface, size of the diamond, etc.)
2) Implementing Dynamic Nuclear Polarization via organic radicals being placed in the solvent and microwaves being shined onto the water to enhance the NV-NMR signal
I am curious about your thoughts on these two and whether you already know ways the diamond could be optimized or how compatible DNP could be with your methodology (would the radicals interfere too much with the end result?)
Thank you!
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