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Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Electron nuclear double resonance (ENDOR) Gavin W Morley, Department.

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Presentation on theme: "Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Electron nuclear double resonance (ENDOR) Gavin W Morley, Department."— Presentation transcript:

1 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Electron nuclear double resonance (ENDOR) Gavin W Morley, Department of Physics, University of Warwick

2 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Electron nuclear double resonance (ENDOR) Overview -Why do ENDOR? -Continuous-wave ENDOR -Pulsed ENDOR with: -Selective pulses -Non-selective pulses

3 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Electron nuclear double resonance (ENDOR) -Why do ENDOR? -More sensitive than NMR -“EPR-detected NMR” (electron has a larger magnetic moment, flips faster and can be detected more sensitively) -NMR may be impossible due to nearby electron spin -Higher resolution than EPR -Extra selection rules

4 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 George Feher (born 1924) Photo from AIP Emilio Segre Visual Archives Image by Manuel Vögtli (UCL) Birth of ENDOR

5 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 EPR-detected NMR: how? Electron nuclear double resonance (ENDOR)

6 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Energy of a spin system Magnetic field, B Photons reflected S = ½ I = ½ I z = ½ I z = -½ Magnetic field, B Electron paramagnetic resonance

7 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Energy of a spin system Magnetic field, B Photons reflected I z = ½ I z = -½ Magnetic field, B Electron paramagnetic resonance S = ½ I = ½ You need to record an EPR spectrum before trying ENDOR

8 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Energy of a spin system Magnetic field, B Photons reflected I z = ½ I z = -½ Magnetic field, B ENDOR RF in S = ½ I = ½

9 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Microwave photons reflected RF frequency Two ENDOR transition frequencies For isotropic A “Weak coupling” Microwave photons reflected RF frequency “Strong coupling”

10 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Energy of a spin system Magnetic field, B Photons reflected I z = ½ I z = -½ Electron paramagnetic resonance Magnetic field, B

11 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Energy of a spin system Magnetic field, B Electron paramagnetic resonance

12 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 B 0 is static magnetic field B 1 is EPR magnetic field B 2 is NMR magnetic field EPR-detected NMR: how? Electron nuclear double resonance (ENDOR)

13 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 B 0 is static magnetic field B 1 is EPR magnetic field B 2 is NMR magnetic field EPR-detected NMR: how? Electron nuclear double resonance (ENDOR)

14 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 B 0 is static magnetic field B 1 is EPR magnetic field B 2 is NMR magnetic field EPR-detected NMR: how? Electron nuclear double resonance (ENDOR)

15 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 B 0 is static magnetic field B 1 is EPR magnetic field B 2 is NMR magnetic field EPR-detected NMR: how? Electron nuclear double resonance (ENDOR)

16 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 EPR-detected NMR Continuous Wave ENDOR George Feher Photo from AIP Emilio Segre Visual Archives Image by Manuel Vögtli (UCL)

17 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR

18 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR

19 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR CW ENDOR is the desaturation of a saturated EPR transition by providing an extra T 1e relaxation route via NMR

20 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR Hale & Mieher, Phys Rev (1969) (following Feher, Phys Rev 114, 1219 (1959)) ν NMR (MHz) CW ENDOR is the desaturation of a saturated EPR transition by providing an extra T 1e relaxation route via NMR (use FM and lock-in)

21 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR ν NMR (MHz) Image by Manuel Vögtli (UCL) B Koiller, R B Capaz, X Hu and S Das Sarma, PRB 70, (2004) Hale & Mieher, Phys Rev (1969) (following Feher, Phys Rev 114, 1219 (1959))

22 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR ν NMR (MHz) CW ENDOR effect is typically a few % of the EPR signal Hale & Mieher, Phys Rev (1969) (following Feher, Phys Rev 114, 1219 (1959))

23 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Continuous Wave ENDOR George Feher Photo from UCSD Advantage of CW ENDOR: Observe sharpest ENDOR resonances Disadvantage of CW ENDOR: CW ENDOR line intensity depends on a delicate balance between relaxation rate and excitation power. Jack Freed did the relaxation theory for this for molecules in solution. This is compared with experiments in solution in: Plato, Lubitz & Mobius, J Phys Chem 85, 1202 (1981)

24 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Pulsed ENDOR Use a π pulse for nuclei, but there are two main pulse sequences for electrons: 1.Davies ENDOR: π pulse then echo readout with all selective (long) pulses. 2.Mims ENDOR uses a stimulated echo with non-selective (short) pulses

25 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Roy Davies, Royal Holloway, University of London π π π/2π/2 RF: MW: As with CW ENDOR, sweep RF frequency to get a spectrum. Use long, selective MW pulses to burn a hole  smaller signal. However, there are no “blind spots” which is an advantage over Mims ENDOR. π

26 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Rotating frame

27 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Rotating frame

28 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Spin echo In rotating frame

29 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Spin echo In rotating frame

30 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Product operator notation: Electron-nuclear two-spin order, 2S z I z

31 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR RF pulse duration is an important parameter to set

32 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Echo height RF frequency Davies ENDOR efficiency, F Davies = 50%

33 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Product operator notation: Electron-nuclear two-spin order, 2S z I z Start again…

34 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Off-resonance RF does nothing

35 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Echo height RF frequency

36 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Product operator notation: Electron-nuclear two-spin order, 2S z I z Start again again…

37 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR

38 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Echo height RF frequency Davies ENDOR efficiency, F Davies = 50%

39 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Davies ENDOR Davies ENDOR disadvantage: selective pulses on electron spins mean many spins are ignored if the resonance is inhomogeneously broadened

40 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Mims ENDOR ττ π RF: sweep RF frequency MW: Non-selective (short) MW pulses excite more spins  bigger signal. However, ENDOR efficiency, F Mims = ¼ (1 – cos (A τ )) so there are “blind spots” with no signal for some τ

41 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Mims ENDOR

42 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Beware Mims ENDOR blind spots ENDOR efficiency, F Mims = ¼ (1 – cos (A τ )) C Gemperle & A Schweiger, Chem Rev 91, 1481 (1991)

43 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Beware short RF pulses in pulsed ENDOR C Gemperle & A Schweiger, Chem Rev 91, 1481 (1991) This problem is avoided by “time-domain pulsed ENDOR”, instead of the standard frequency domain experiments.

44 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Beware short RF pulses with frequency-domain pulsed ENDOR C Gemperle & A Schweiger, Chem Rev 91, 1481 (1991)

45 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Beware short microwave pulses with Davies ENDOR C Gemperle & A Schweiger, Chem Rev 91, 1481 (1991)

46 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 ENDOR – orientation dependence at high magnetic field M Rohrer, F MacMillan, T F Prisner, A T Gardiner, K Möbius & W Lubitz, J Phys Chem B 102, 4648 (1998)

47 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 ENDOR – orientation dependence at high magnetic field M Rohrer, F MacMillan, T F Prisner, A T Gardiner, K Möbius & W Lubitz, J Phys Chem B 102, 4648 (1998) duroquinone

48 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 ENDOR for Quantum Information Processing We can control electronic qubits fast, but nuclear qubits have longer coherence times

49 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 Pulsed ENDOR For more details including TRIPLE (ENDOR with two RF frequencies) see: Schweiger & Jeschke, Principles of pulse electron paramagnetic resonance, OUP 2001 C Gemperle & A Schweiger, Chem Rev 91, 1481 (1991)

50 Introduction to ENDOR, Gavin W Morley, iMR CDT Advanced Workshop, 10 th April 2013 ENDOR conclusions -ENDOR is much more sensitive than NMR and has much higher resolution than EPR -Continuous-wave ENDOR for very sharp resonances -Pulsed ENDOR with: -Selective pulses (Davies) -Non-selective pulses (Mims)


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