Natural-abundance ¹³C dynamic nuclear polarization experiments on chemical vapor deposited diamond film

Abstract

13C cross-polarization (CP) and direct-polarization (DP) spectra of an 83 mg sample of a chemical vapor deposited (CVD) diamond film (combined from 12 separate depositions) have been obtained via dynamic nuclear polarization (DNP) combined with magic-angle spinning (MAS). With DNP, the presence of unpaired electron spins in the sample, measured to be 2 × 1018 spins/g, provides a way to enhance the 13C or the “residual” 1H signal by irradiating the sample with microwaves at or near the electron spin resonance (ESR) Larmor frequency; the interactions between the unpaired electrons and protons or 13C spins lead to a transfer of polarization from the electron spin system to the 1H and/or 13C spin systems. No signal for sp2 hybridized carbons could be observed. The DNP-CP-MAS spectrum, obtained in an experiment in which the DNP-enhanced proton polarization is in turn transferred via CP to the 13C spin system, differs significantly from the DNP-DP-MAS spectrum, in which the 13C spins are directly enhanced.

13C NMR Investigations of Spin–Lattice Relaxation in 99%13C-Enriched Diamonds

“…One of Semiconducting diamond Natural 4 hours (5) the most interesting features in the 99% 13 C-enriched diaDiamond film Natural 70 s (6) Diamond film 50% 17 s (6) mond is that the enhanced atomic mass means a reduced Diamond film 100% 8 s (6) lattice parameter (21), which leads to slightly enhanced elas-CVD diamond film Natural 55 s (7) tic constants (24) (elastic moduli deduced from the Brillouin CVD diamond film Natural 1000 s (8) shifts experienced by inelastically scattered monochromatic CVD diamond film 14% 22 s (8) radiation are approximately 0.5% higher than the correDifferent CVD diamond films 22% 1-20 s (9) sponding values for a natural diamond). The conclusion from this result is that such a diamond is the hardest material known.…”

“…By using the DNP (dynamic nuclear polarization) NMR experiment the same t 1/2 magnetization This paper represents a full investigation of the 13 C spinlattice relaxation mechanism in single crystal 99% 13 C-enrecovery behavior has been found in natural and synthetic diamonds, as well as in 13 C natural abundant and 14% 13 C-riched diamonds. The experimental behavior of 13 C spinlattice relaxation times as a function of crystal orientation, enriched diamond films (3,4,7,8).…”

“…In 13 C-enriched diamonds with low impulonger relaxation times. This leads to a distribution of relaxrity concentration the dipole-dipole interactions between ation rates over the sample resulting in a nonexponential neighboring 13 C nuclei will accelerate relaxation in comparispin-lattice relaxation, which can be fitted to a stretched son to natural 13 C abundance diamonds with low impurity exponent (7, 14,15). A distribution of relaxation rates over concentration.…”

Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

“…It indicates that the sp2-bonded carbon is absent or, if present, is below the detection limit of our instrument. The DNP enhancement factor E is one of the characteristics in the DNP experiment defined as E = (P~-~o)/Pt0, where Pt and P~0 ate nuclear polarization at thermal equilibrium with and without microwave irradiation, respectively [9]. Another normal ~3C NMR signal without DNP enhancement was measured, recorded b.y accumulations (number of scans, 256).…”

Study of synthetic diamonds by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

“…The value of x indicates that the precession of 13C relaxation in synthetic diamond is almost the complete spin diffusion limit. The 13C spin-lattice relaxation time of DSY-2 is shorter than that of natural diamond [10], but is longer than that of diamond film [16,17]. It may be the influence of Fe-Co catalyst inclusion or the existence of spin diffusion.…”