Editorial: The molecular underpinnings of nanoscale semiconductor synthesis

Abstract

Colloidal semiconductor nanocrystals have attracted considerable attention over the past several decades due to their size-dependent optoelectronic properties, which have driven their integration into cutting-edge applications ranging from LEDs and displays to quantum computing and biosensing. The utility of these materials stems from their solution processability, broad absorption profiles, narrow photoluminescence emission, and surfaces that can be easily modulated. Wet chemical synthesis of these materials provides a versatile space for development of new compositions, morphologies, heterostructures, and coordination environments simply by changing precursors, ligands, concentrations, and temperatures. Mechanistic studies into molecular and cluster intermediates during formation can direct researchers towards better control over synthetic outcomes. Furthermore, the high surface to volume ratios inherent to nanocrystals makes the study of their surfaces and their stabilizing ligands particularly important, with surface accessibility controlling reaction and charge transfer rates in catalytic applications and photovoltaics. We organized this Research Topic to highlight some of the recent advances in the field of nanocrystal synthesis. We are particularly interested in understanding the reactions that make and modify nanocrystals at the atomic level, including precursor conversion, ligand exchange, and cluster formation and dissolution. By understanding the molecular underpinnings of nanoscale semiconductor synthesis, it becomes possible to control end products and their properties. Precursor reactivity gates the nucleation and growth of nanocrystals in colloidal syntheses. In the synthesis of WSe2, tungsten hexacarbonyl is often used as the metal precursor, which typically requires high reaction temperatures to force the cleavage of the strongW–CO bond. Schimpf and colleagues demonstrate thatW–CO bond labilization, and hence the availability of tungsten metal for subsequent monomer formation, can be tuned through the inclusion of common ligands such as trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) (Geisenhoff et al.). Using IR spectroscopy for reaction monitoring in the presence of TOPO, the authors noted W(CO)6 rapidly decomposes into W(CO)6-x(TOPO)x, which promoted rapid nucleation of WSe2 nanocrystals and lower reaction temperatures. The structural assignment of this intermediate was corroborated through the growth of a diffraction-quality single crystal of the triarylphosphine analogue W(CO)5(TPPO) (TPPO = triphenylphosphine oxide). On the other hand, the use of strongly coordinating triphenylphosphine (TPP) was found to sequester tungsten as W(CO)5(TPP), OPEN ACCESS