Fig. 3.

Hyperpolarized ${}^{29}\mathrm{Si}$ polarization buildup curves for (a) 20 nm and (b) $2\mu \mathrm{m}$ silicon particles. Silicon microparticles provide $\sim 25\times$ more ${}^{29}\mathrm{Si}$ NMR signal than the nanoscale particles, but take significantly longer to reach steady-state polarization. Insets: example NMR spectra at relevant time points [(a) 60 min and (b) 330 min]. Data were collected in real time during DNP process and using on-board NMR system and a pulse/acquire sequence ($100\mu \mathrm{s}$ pulse duration; 24.4 MHz). All data were normalized to sample mass.