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Dynamic nuclear polarization

Dynamic nuclear polarization (DNP) results from transferring spin polarization from electrons to nuclei, thereby aligning the nuclear spins to the extent that electron spins are aligned. Note that the alignment of electron spins at a given magnetic field and temperature is described by the Boltzmann distribution under the thermal equilibrium.[1][2][3] It is also possible that those electrons are aligned to a higher degree of order by other preparations of electron spin order such as: chemical reactions (leading to chemical-induced DNP, CIDNP), optical pumping and spin injection. DNP is considered one of several techniques for hyperpolarization. DNP can also be induced using unpaired electrons produced by radiation damage in solids.[4][5]

When electron spin polarization deviates from its thermal equilibrium value, polarization transfers between electrons and nuclei can occur spontaneously through electron-nuclear cross relaxation or spin-state mixing among electrons and nuclei. For example, the polarization transfer is spontaneous after a homolysis chemical reaction. On the other hand, when the electron spin system is in a thermal equilibrium, the polarization transfer requires continuous microwave irradiation at a frequency close to the corresponding electron paramagnetic resonance (EPR) frequency. In particular, mechanisms for the microwave-driven DNP processes are categorized into the Overhauser effect (OE), the solid-effect (SE), the cross-effect (CE) and thermal-mixing (TM).

The first DNP experiments were performed in the early 1950s at low magnetic fields[6][7] but until recently the technique was of limited applicability for high-frequency, high-field NMR spectroscopy, because of the lack of microwave (or terahertz) sources operating at the appropriate frequency. Today such sources are available as turn-key instruments, making DNP a valuable and indispensable method especially in the field of structure determination by high-resolution solid-state NMR spectroscopy.[8][9][10]

  1. ^ Goldman, Maurice (1970). Spin Temperature and Nuclear Magnetic Resonance in Solids. Oxford University Press. ISBN 978-0-19-851251-6.
  2. ^ A. Abragam; M. Goldman (1976). "Principles of Dynamic Nuclear Polarization". Reports on Progress in Physics. 41 (3): 395–467. Bibcode:1978RPPh...41..395A. doi:10.1088/0034-4885/41/3/002. S2CID 250855406.
  3. ^ J. Puebla; E.A. Chekhovich; M. Hopkinson; P. Senellart; A. Lemaitre; M.S. Skolnick; A.I. Tartakovskii (2013). "Dynamic nuclear polarization in InGaAs/GaAs and GaAs/AlGaAs quantum dots under non-resonant ultra-low power optical excitation". Phys. Rev. B. 88 (4): 9. arXiv:1306.0469. Bibcode:2013PhRvB..88d5306P. doi:10.1103/PhysRevB.88.045306. S2CID 76658845.
  4. ^ Solem, J. C.; Rebka Jr., G. A. (1968). "EPR of atoms and radicals in radiation-damaged H2 and HD". Physical Review Letters. 21 (1): 19. Bibcode:1968PhRvL..21...19S. doi:10.1103/PhysRevLett.21.19.
  5. ^ Solem, J. C. (1974). "Dynamic polarization of protons and deuterons in solid deuterium hydride". Nuclear Instruments and Methods. 117 (2): 477–485. Bibcode:1974NucIM.117..477S. doi:10.1016/0029-554X(74)90294-8.
  6. ^ T.R. Carver; C.P. Slichter (1953). "Polarization of Nuclear Spins in Metals". Physical Review. 92 (1): 212–213. Bibcode:1953PhRv...92..212C. doi:10.1103/PhysRev.92.212.2.
  7. ^ T.R. Carver; C.P. Slichter (1956). "Experimental Verification of the Overhauser Nuclear Polarization Effect". Physical Review. 102 (4): 975–980. Bibcode:1956PhRv..102..975C. doi:10.1103/PhysRev.102.975.
  8. ^ T. Maly; G.T. Debelouchina; V.S. Bajaj; K.-N. Hu; C.G. Joo; M.L. Mak-Jurkauskas; J.R. Sirigiri; P.C.A. van der Wel; J. Herzfeld; R.J. Temkin; R.G. Griffin (2008). "Dynamic Nuclear Polarization at High Magnetic Fields". The Journal of Chemical Physics. 128 (5): 052211–19. Bibcode:2008JChPh.128e2211M. doi:10.1063/1.2833582. PMC 2770872. PMID 18266416.
  9. ^ A.B. Barnes; G. De Paëpe; P.C.A. van der Wel; K.-N. Hu; C.G. Joo; V.S. Bajaj; M.L. Mak-Jurkauskas; J.R. Sirigiri; J. Herzfeld; R.J. Temkin; R.G. Griffin (2008). "High-Field Dynamic Nuclear Polarization for Solid and Solution Biological NMR". Applied Magnetic Resonance. 34 (3–4): 237–263. doi:10.1007/s00723-008-0129-1. PMC 2634864. PMID 19194532.
  10. ^ Akbey, U.; Linden, A. H. & Oschkinat, H. (May 2012). "High-Temperature Dynamic Nuclear Polarization Enhanced Magic-Angle-Spinning NMR". Appl. Magn. Reson. 43 (1–2): 81–90. doi:10.1007/s00723-012-0357-2. ISSN 0937-9347. S2CID 254087348.

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