Highly porous self-supported three-dimensional aerogel monoliths are synthesized from strongly quantum confined quantum wells, namely, 5 monolayer thick CdSe and CdSe/CdS core/crown nanoplatelets. The aerogels are synthesized by hydrogelation of the aqueous quantum well solutions and subsequent supercritical drying. The aerogels are optically characterized by UV−vis absorption spectroscopy, emission spectroscopy, and photoluminescence (PL) decay analysis. Morphological and structural characterizations are achieved by transmission electron microscopy, scanning electron microscopy, and X-ray diffractometry. The macroscopic aerogels exhibit extremely low densities of 0.038 ± 0.007 g•cm −3 and a significantly high specific surface area of 219 m 2 •g −1 with nearly entirely (111) as the exposed crystal facet. Moreover, the aerogels feature properties related to quantum confinement comparable to those of their original building blocks with photoluminescence quantum yields up to 10.3%.

No abstract

The charge transport through ferrocene 1,1′‐diamine (FDA) molecules between gold electrodes is investigated using the mechanically controllable break junction technique combined with a theoretical framework of density functional theory simulations to understand the physics of these molecular junctions. The characteristic conductances of the molecule are measured at low bias as well as current–voltage (IV) characteristics. By fitting the IV characteristics to the single‐level model, the values for the position of the molecular level, mainly responsible for the transport, and its coupling to the leads, are obtained. The influence of the binding sites, molecular conformation, and electrode distance are systematically studied from a theoretical perspective. While a strong dependence of conductance on the adsorption geometry is found, the decrease of conductance as a function of electrode distance arises mainly from a decrease of coupling strength of the molecular electronic orbitals through a reduced overlap and, to a lesser extent, from a shift of their alignment with respect to the Fermi energy.

SummaryThe contacts and the chemical bonds formed between metallic electrodes and molecules determine to a large extent the conductive properties of single molecular junctions, which represent the smallest possible active elements in an electronic circuit. We therefore investigated in a comparative study, using the break junction technique (MCBJ), the conductive properties of [1,1’-biphenyl]-4,4’-dithiol (M1) and of 4’-mercapto-[1,1’-biphenyl]-4-carbonitrile (M2) between gold electrodes. As a function of electrode separation, characterized by the conductance close to 0 V, we found several plateaus of relative stability, with those close to 0.01G0 being the most pronounced. The overall conductance of symmetric and asymmetric molecules were surprisingly similar, only the range of stability was smaller for M2. While M1 yielded symmetric I–V-curves, only small asymmetries were detected for M2. These are also reflected in the comparable values for coupling parameters using the single level resonance model. The high conductance for the asymmetric molecule is interpreted as a result of coherent coupling of electronic states through the whole molecule, so that the outcome cannot be predicted just by adding conductive properties of individual molecular groups.

This article is part of the Thematic Series "Functional nanostructureselectronic structure, charge and heat transport".