{'fraction_non_alphanumeric': 0.025078369905956112, 'fraction_numerical': 0.003134796238244514, 'mean_word_length': 6.174157303370786, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Quantitative Chemical Mapping of Anisotropic Molecular Distributions on Gold Nanorods

The ability to characterize and quantify anisotropic distributions of organic molecules at nanoparticle interfaces is a longstanding challenge in the realization and design of functional coatings, monodisperse synthesis, and colloidal assembly [1]. Here, we show that by using electron energy loss spectroscopy (EELS) spectral imaging on graphene substrates in an aberration-corrected scanning transmission electron microscope (STEM), we can directly visualize and quantify molecular distributions on gold nanorods (AuNRs). By contrasting the average distributions of two organic ligands across dozens of nanoparticles, we find that (16-mercaptohexadecyl)trimethylammonium bromide (MTAB) forms a uniform coating, while the distribution of cetyltrimethylammonium bromide (CTAB) his highly anisotropic. On average, CTAB binding density is reduced on the ends of gold nanorods, consistent with the higher reactivity of the nanorod ends reported in the literature [2]. Our results demonstrate the potential of our methods to directly probe local molecular distributions at soft-hard interfaces in order to understand nanoscale variations in the growth and reactivity of colloidal nanocrystals.