Nanostructured Bi1–x Sb x alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we ...developed the colloidal synthesis of monodisperse sub-10 nm Bi1–x Sb x alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry of Bi1–x Sb x NCs was tailored with inorganic ligands to improve the interparticle charge transport as well as to control the carrier concentration. Temperature-dependent (10–300 K) electrical measurements were performed on the Bi1–x Sb x NC based pellets to investigate the effect of surface chemistry and grain size (∼10–40 nm) on their charge transport properties. The Hall effect measurements revealed that the temperature dependence of carrier mobility and concentration strongly depended on the grain size and the surface chemistry, which was different from the reported bulk behavior. At low temperatures, electron mobility in nanostructured Bi1–x Sb x was directly proportional to the average grain size, while the concentration of free carriers was inversely proportional to the grain size. We propose a model explaining such behavior. Preliminary measurements of thermoelectric properties showed a ZT value comparable to those of bulk Bi1–x Sb x alloys at 300 K, suggesting a potential of Bi1–x Sb x NCs for low-temperature thermoelectric applications.
CdSe/CdS nanocrystal tetrapods are interesting building blocks for excitonic circuits, where the flow of excitation energy is gated by an external stimulus. The physical morphology of the ...nanoparticle, along with the electronic structure, which favors electron delocalization between the two semiconductors, suggests that all orientations of a particle relative to an external electric field will allow for excitons to be dissociated, stored, and released at a later time. While this approach, in principle, works, and fluorescence quenching of over 95% can be achieved electrically, we find that discrete trap states within the CdS are required to dissociate and store the exciton. These states are rapidly filled up with increasing excitation density, leading to a dramatic reduction in quenching efficiency. Charge separation is not instantaneous on the CdS excitonic antennae in which light absorption occurs, but arises from the relaxed exciton following hole localization in the core. Consequently, whereas strong electromodulation of the core exciton is observed, the core multiexciton and the CdS arm exciton are not affected by an external electric field.
We extends pair distribution function (PDF) analysis into the small-angle scattering (SAS) regime and describe the data collection protocol for optimum data quality. We also present the PDFgetS3 ...software package that can be readily used to extract the PDF from small-angle scattering data. We then apply the sasPDF method to investigate structures of some representative nanoparticle assemblies (NPA) samples with different levels of structural order.
All-inorganic colloidal nanocrystals were synthesized by replacing organic capping ligands on chemically synthesized nanocrystals with metal-free inorganic ions such as S2-, HS–, Se2-, HSe–, Te2-, ...HTe–, TeS3 2-, OH– and NH2 –. These simple ligands adhered to the NC surface and provided colloidal stability in polar solvents. The versatility of such ligand exchange has been demonstrated for various semiconductor and metal nanocrystals of different size and shape. We showed that the key aspects of Pearson’s hard and soft acids and bases (HSAB) principle, originally developed for metal coordination compounds, can be applied to the bonding of molecular species to the nanocrystal surface. The use of small inorganic ligands instead of traditional ligands with long hydrocarbon tails facilitated the charge transport between individual nanocrystals and opened up interesting opportunities for device integration of colloidal nanostructures.
Keime verändern alles: Durch einen ungewöhnlich schnellen Kationenaustausch auf Nanometerebene gelingt es, die Keimbildung von Nanokristallen genau zu steuern. Als Modellsystem dienten 3.2–14 nm ...große PbSe‐Nanokristalle, die über eine Keimbildungsreaktion von Pb2+ mit unbeständigen SnSe‐Kernen gebildet werden (siehe Bild). Dabei lässt sich die Oberfläche der PbSe‐Nanokristalle mit verschiedenen Liganden modifizieren.
Nonradiative processes limit optoelectronic functionality of nanocrystals and curb their device performance. Nevertheless, the dynamic structural origins of nonradiative relaxations in nanocrystals ...are not understood. Here, femtosecond electron diffraction measurements corroborated by atomistic simulations uncover transient lattice deformations accompanying radiationless electronic processes in semiconductor nanocrystals. Investigation of the excitation energy dependence shows that hot carriers created by a photon energy considerably larger than the bandgap induce structural distortions at nanocrystal surfaces on few picosecond timescales associated with the localization of trapped holes. On the other hand, carriers created by a photon energy close to the bandgap result in transient lattice heating that occurs on a much longer 200 ps timescale, governed by an Auger heating mechanism. Elucidation of the structural deformations associated with the surface trapping of hot holes provides atomic-scale insights into the mechanisms deteriorating optoelectronic performance and a pathway towards minimizing these losses in nanocrystal devices.
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