Designing broadband pulsed dynamic nuclear polarization sequences in static solids.

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Dynamic nuclear polarization (DNP) enhances nuclear magnetic resonance (NMR) sensitivity.
• Microwave (MW) irradiation facilitates polarization transfer from electrons to nuclei.
• Arbitrary waveform generators enable advanced DNP pulse sequence design.

Purpose of the Study:

• To develop novel broadband DNP pulse sequences using single-spin vector effective Hamiltonian theory.
• To introduce adiabatic XiX-DNP and broadband excitation by amplitude modulation (BEAM)-DNP experiments.
• To enhance the robustness and versatility of DNP techniques.

Main Methods:

• Application of single-spin vector effective Hamiltonian theory for pulse sequence design.
• Development and implementation of adiabatic XiX-DNP and BEAM-DNP pulse sequences.
• Experimental validation using trityl radicals in static solids at 0.35 T and 80 K.

Main Results:

• The adiabatic BEAM-DNP sequence achieved a ¹H enhancement factor of approximately 360.
• This enhancement surpasses ramped-amplitude NOVEL (nuclear spin orientation via electron spin locking) under similar conditions.
• BEAM-DNP experiments demonstrated a bandwidth of ~50 MHz, three times the ¹H Larmor frequency.

Conclusions:

• Novel DNP pulse sequences based on effective Hamiltonian theory offer significant improvements.
• Adiabatic BEAM-DNP provides superior ¹H enhancement compared to existing methods.
• The theoretical framework supports the development of new pulsed DNP sequences for broader applications.