Nanocrystal quantum dots are generally coated with an organic ligand layer. These layers are a necessary consequence of their chemical synthesis, and in addition they play a key role in controlling the optical and electronic properties of the system. Here we describe a method for quantitative measurement of the ligand layer in 3 nm diameter lead sulfide–oleic acid quantum dots. Complementary small-angle X-ray and neutron scattering (SAXS and SANS) studies give a complete and quantitative picture of the nanoparticle structure. We find greater-than-monolayer coverage of oleic acid and a significant proportion of ligand remaining in solution, and we demonstrate reversible thermal cycling of the oleic acid coverage. We outline the effectiveness of simple purification procedures with applications in preparing dots for efficient ligand exchange. Our method is transferrable to a wide range of colloidal nanocrystals and ligand chemistries, providing the quantitative means to enable the rational design of ligand-exchange procedures.

Controlling the dispersibility of crystalline inorganic quantum dots (QD) within organic-QD nanocomposite films is critical for a wide range of optoelectronic devices. A promising way to control nanoscale structure in these nanocomposites is via the use of appropriate organic ligands on the QD, which help to compatibilize them with the organic host, both electronically and structurally. Here, using combined small-angle X-ray and neutron scattering, the authors demonstrate and quantify the incorporation of such a compatibilizing, electronically active, organic semiconductor ligand species into the native oleic acid ligand envelope of lead sulphide, QDs, and how this ligand loading may be easily controlled. Further more, in situ grazing incidence wide/small angle X-ray scattering demonstrate how QD ligand surface chemistry has a pronounced effect on the self-assembly of the nanocomposite film in terms of both small-molecule crystallization and QD dispersion versus ordering/aggregation. The approach demonstrated here shows the important role which the degree of incorporation of an active ligand, closely related in chemical structure to the host small-molecule organic matrix, plays in both the self-assembly of the QD and small-molecule components and in determining the final optoelectronic properties of the system.

Localized electroluminescent ͑EL͒ light emissions have been imaged in ZnS/Cu ac EL ͑ACEL͒ powder phosphor particles embedded under high-refractive index glass. Undistorted well-resolved images recorded at a series of depths from base to apex of individual particles show that in sharp focus the EL emissions are always small ͑1-2 m͒ bright dots, often arranged along short straight lines. Comparison with backlit images shows that EL emission sites are near the phosphor surface. Image series recorded over a range of excitation voltages show that this surface luminous structure is unaltered under increased field strength, but more sites become active. There is no evidence for luminous comets within the particles. The data, clearly showing alternation of EL emission from side to side of the particles on opposite-polarity ac half-cycles, continue to support a mechanistic model in which electrons and holes are separated during one polarity and then undergo radiative recombination when that polarity is reversed on the succeeding half cycle. The small, surface-positioned emissive spots indicate that this charge-carrier separation does not occur at long acicular internal structures but rather at short Cu 2 S structures active only at the ZnS surface.

The residual stresses in spin‐coated films can be exploited to produce highly controlled nanoscale patterns via pressure‐induced local rupturing and dewetting of thin films. Residue‐free holes as small as 28 nm in diameter formed over large areas by pressing sharp stamps into polymer films at temperatures well below the glass transition temperature.

Hybrid small-molecule/quantum dot films have the potential to reduce thermalization losses in single-junction photovoltaics as photon multiplication devices. Here grazing incidence X-ray scattering, optical microscopy and IR fluorescence microscopy (probing...