We use microwave-induced dynamic nuclear polarization (DNP) of the substitutional nitrogen defects (P1 centers) in diamond to hyperpolarize bulk 13 C nuclei in both single crystal and powder samples at room temperature at 3.34 T. The large (>100-fold) enhancements demonstrated correspond to a greater than 10 000-fold improvement in terms of signal averaging of the 1% abundant 13 C spins. The DNP was performed using low-power solid state sources under static (nonspinning) conditions. The DNP spectrum (DNP enhancement as a function of microwave frequency) of diamond powder shows features that broadly correlate with the EPR spectrum. A well-defined negative Overhauser peak and two solid effect peaks are observed for the central ( m I = 0) manifold of the 14 N spins. Previous low temperature measurements in diamond had measured a positive Overhauser enhancement in this manifold. Frequency-chirped millimeter-wave excitation of the electron spins is seen to significantly improve the enhancements for the two outer nuclear spin manifolds ( m I = ±1) and to blur some of the sharper features associated with the central manifold. The outer lines are best fit using a combination of the cross effect and the truncated cross effect, which is known to mimic features of an Overhauser effect. Similar features are also observed in experiments on single crystal samples. The observation of all of these mechanisms in a single material system under the same experimental conditions is likely due to the significant heterogeneity of the high pressure, high temperature (HPHT) type Ib diamond samples used. Large room temperature DNP enhancements at fields above a few tesla enable spectroscopic studies with better chemical shift resolution under ambient conditions.
Nanodiamond (ND) hosting nitrogen-vacancy (NV) centers is a promising platform for quantum sensing applications. Sensitivity of the applications using NV centers in NDs is often limited due to presence of paramagnetic impurity contents near the ND surface. Here, we investigate near-surface paramagnetic impurities in NDs. Using high-frequency (HF) electron paramagnetic resonance spectroscopy, the near-surface
Nanodiamonds (NDs) hosting nitrogen-vacancy (NV) centers are promising for applications of quantum sensing. Long spin relaxation times (T1 and T2) are critical for high sensitivity in quantum applications. It has been shown that fluctuations of magnetic fields due to surface spins strongly influence T1 and T2 in NDs. However, their relaxation mechanisms have yet to be fully understood. In this paper, we investigate the relation between surface spins and T1 and T2 of single-substitutional nitrogen impurity (P1) centers in NDs. The P1 centers located typically in the vicinity of NV centers are a great model system to study the spin relaxation processes of the NV centers. By employing high-frequency electron paramagnetic resonance spectroscopy, we verify that air annealing removes surface spins efficiently and significantly reduces their contribution to T1.
Polyaromatic dye molecules employed in photovoltaic and electronic applications are often processed in organic solvents. The aggregation of these dyes is key to their applications, but a fundamental molecular understanding of how the solvent environment controls the stacking of polyaromatics is unclear. This study reports initial results from Monte Carlo simulations of how various acene molecule dimers stack when they are dissolved in different solvents. Free energies computed using full dispersion interactions versus those with sterics only suggest that solvent entropy alone accounts for the majority of the stacking free energy in solvents with compact molecular geometries such as carbon tetrachloride. However, in contrast with carbon tetrachloride, we also observe significant variations in the stacking free energies of naphthalene, anthracene, and tetracene across other solvents such as toluene and cyclohexane. The weak attractive dispersion interactions between the acene solutes and planar and near-planar solvent molecules enable them to intercalate between the acene monomers, inducing extra stability beyond what solvent entropic driving force alone could predict. In all three solvents studied (carbon tetrachloride, cyclohexane, toluene) the solvent environment helps facilitate stacking of all three acenes studied (naphthalene, anthracene, tetracene), inducing a significant stabilization free energy between −4 and −8 kcal/mol. Extensive free energy umbrella sampling along the other orthogonal directions allows us to accurately calculate the dimerization equilibrium constants of all three acenes, which vary over several orders of magnitude in a way that depends intricately on the solvent they are in. Given the prevalence of solution-based processing techniques for organic electronic and photonic devices, these results provide useful insights into the critical role that solvent structure and characteristics play in the solution-based aggregation of organic dyes.
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