The discovery of lead-based organicinorganic perovskite materials for optoelectronic applications has triggered a revolution in photovoltaic material research. Despite their exceptional material properties such as strong light absorption, long charge carrier lifetimes in combination with high carrier mobility, and low production costs, their long-term instability, and the toxicity of lead currently hamper their deployment at an industrial scale. [1] To overcome this drawback, double perovskites with the general formula A 2 1+ M 1+ M′ 3+ X 6 have been proposed as candidate materials providing leadfree alternatives in the vastly expanding research field of perovskites. One of the first materials investigated in this branch of the perovskite catalog is Cs 2 AgBiBr 6 , demonstrating high stability in devices [2,3] and low effective carrier masses [4] with the long carrier recombination lifetimes Lead-free double perovskites have great potential as stable and nontoxic optoelectronic materials. Recently, Cs 2 AgBiBr 6 has emerged as a promising material, with suboptimal photon-to-charge carrier conversion efficiency, yet well suited for high-energy photon-detection applications. Here, the optoelectronic and structural properties of pure Cs 2 AgBiBr 6 and alkalimetal-substituted (Cs 1−x Y x) 2 AgBiBr 6 (Y: Rb + , K + , Na + ; x = 0.02) single crystals are investigated. Strikingly, alkali-substitution entails a tunability to the material system in its response to X-rays and structural properties that is most strongly revealed in Rb-substituted compounds whose X-ray sensitivity outperforms other double-perovskite-based devices reported. While the fundamental nature and magnitude of the bandgap remains unchanged, the alkali-substituted materials exhibit a threefold boost in their fundamental carrier recombination lifetime at room temperature. Moreover, an enhanced electron-acoustic phonon scattering is found compared to Cs 2 AgBiBr 6. The study thus paves the way for employing cation substitution to tune the properties of double perovskites toward a new material platform for optoelectronics.
COMMUNICATION (1 of 8)properties in graphene, such as (tunable) bandgaps [12] or p-n junctions. [13] Metal atoms and nanoparticles are interesting candidates to tailor graphene. [14] The charge transfer between adparticles and graphene results in tunable (surface) electronic states, which can act as active sites for heterogeneous catalysis, [4,[15][16][17] or enhance the sensitivity and selectivity of graphene gas sensors (see ref.[18] and references therein). Furthermore, metal adparticles are prime candidates to induce a (tunable) spin-orbit coupling in graphene, enhancing for instance the spin Hall effect, [19] which further augments graphene's spintronic potential. [20] Due to the extreme sensitivity of graphene devices, one desires a high level of control in adsorbing metal adparticles. Such control is offered by state-of-the-art cluster fabrication and deposition techniques, which allows to select the size and composition of clusters with atomic resolution, and tune the deposition energy and adparticle density. [21] Using these techniques, ultrasmall few-atom clusters in gas-phase showcased a distinct atom-by-atom size-dependence in the electronic and structural properties, leading to different and unique physicochemical properties. [22] The size-dependent characteristics can be preserved in the interaction of a cluster with a support. For specific gold, cobalt and germanium clusters, dedicated atomic resolution surface probe studies, using scanning tunneling microscopy [23,24] and scanning transmission electron microscopy, [25][26][27][28] have, in combination with density functional theory (DFT) simulations, allowed for a detailed morphological characterization of clusters on supports. The overall properties of a cluster-support system retain a dependence on the exact cluster size. [15] As such, cluster-support systems, engineered with atomic precision, are, among others, of interest as catalysts [29][30][31][32] and lowreactive building blocks for nanosystems. [33] In the size-regime in between single atoms and larger nanometer-sized particles, clusters offer diverse possibilities in functionalizing graphene.To the best of our knowledge, there has been no realization yet of an electronic device, in which the rich size-dependence of few-atom metal clusters is transpired in the properties of the device, although this has been proposed in several computational studies for few-atom metal clusters on graphene. [34][35][36] To that avail, we combine in this work single layer graphene (G) with few-atom gold clusters. In particular, these clusters Graphene's sensitivity to adsorbed particles has attracted widespread attention because of its potential sensor applications. Size-selected few-atom clusters are promising candidates as adparticles to graphene. Due to their small size, physicochemical properties are dominated by quantum size effects. In particular, few-atom gold clusters demonstrate a significant catalytic activity in various oxidation reactions. In this joint experimental and computational work, size-...
Giant fractional Shapiro steps have been observed in Josephson junction arrays as resulting from magnetic flux quantization in the two-dimensional array. We demonstrate experimentally the appearance of giant fractional Shapiro steps in anisotropic Josephson junction arrays as unambiguous evidence of a skewed current phase relationship. Introducing anisotropy in the array results in a giant collective high frequency response that reflects the properties of a single junction, as evidenced by the observation of a Fraunhofer like magnetic field dependence of the total critical current of the system. The observed phase dynamics can be perfectly captured within an extended resistively shunted Josephson junction model. These results directly indicate the potential of Josephson junction arrays to explore the current phase relation in a very broad frequency range (down to 50 MHz) and in a wide variety of novel link materials exhibiting non-conventional current phase relationships.
We developed a novel two-point contacting approach to atomically controlled single nano-objects under pristine conditions. This technique is used to realize SET devices.
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