Inorganic Caps Give Nanocrystals A Boost

Capping semiconductor nanocrystals with inorganic complexes instead of the usual organic ones can improve the particles’ electron-transport abilities without adversely affecting their optical and other properties, according to researchers at the University of Chicago (Nat. Nanotechnol., DOI: 10.1038/nnano.2011.46). Organic molecules with long hydrocarbon chains often play a subtle but critical role in controlling nanoparticle size, morphology, and stability. Yet these ligands, which cap the particle surfaces, act as insulating layers that limit electron transport between particles and reduce the particles’ effectiveness in electronic devices. To sidestep these problems, Jong-Soo Lee, Dae Sung Chung, Dmitri V. Talapin, and coworkers used standard methods to prepare CdSe and CdSe/CdS core-shell nanoparticles that were capped with octadecylphosphonate and oleate groups, respectively. Then they used a hydrazine solution of In₂Se₃ and selenium to replace the organic ligands with In₂Se₄ ^2–. The team reports that replacing the capping ligands causes little or no change to the nanoparticles’ sizes and shapes or their optical and spectroscopic properties. Yet transistors and photodetectors made from the new products exhibit improved electron mobility and sensitivity, they note.