A facile method is reported for the direct (polymer-free) transfer of layer-area graphene from metal growth substrates to selected target substrates. The direct route, by avoiding several wet chemical steps and accompanying mechanical stresses and contamination common to all presently reported layer-area graphene transfer methods, enables fabrication of layer-area graphene devices with unprecedented quality. To demonstrate, we directly transfer layer-area graphene from Cu growth substrates to holey amorphous carbon transmission electron microscopy (TEM) grids, resulting in robust, clean, full-coverage graphene grids ideal for high resolution TEM.

Superefficient light emission: A challenge to improving synthesis methods for superefficient light-emitting semiconductor nanoparticles is that current analytical methods cannot measure efficiencies above 99%. Hanifi et al. used photothermal deflection spectroscopy to measure very small nonradiative decay components in quantum dot photoluminescence. The method allowed them to tune the synthesis of CdSe/CdS quantum dots so that the external luminescent efficiencies exceeded 99.5%. This is important for applications that require an absolute minimum amount of photon energy to be lost as heat, such as photovoltaic luminescent concentrators. Science , this issue p. 1199

Synthesis approaches to colloidal Cu₃P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu_3-xP NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu₃P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu_3-xP NCs. It is likely that both the LSPR and the p-type character of our Cu_3-xP NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu_3-xP NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu_3-xP NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu_3-xP is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu_3-xP/InP heterostructures, as a consequence of the fact that the exchange between Cu⁺ and In³⁺ ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu_3-xP NCs an interesting material platform from which to access other metal phosphides by cation exchange.