Electrical transport through self-assembled colloidal nanomaterials and their perspectives

Colloidal nanoparticles developed as interesting objects to establish two- or three-dimensional super-structures with properties not known from conventional bulk materials. Beyond, the properties can be tuned and quantum effects can be exploited. This allows understanding electronic and optoelectronic transport phenomena and developing corresponding devices. The state-of-the-art in this field will be reviewed and possible challenges and prospects will be identified.Comment: 8 pages. arXiv admin note: text overlap with arXiv:1501.0236

Tuning the Elasticity of Cross-Linked Gold Nanoparticle Assemblies

Composite materials of organically stabilized or cross-linked metal nanoparticles represent a versatile material class with manifold potential applications. Numerous studies explored their tunable optical and charge transport properties. However, due to challenging experimental requirements, only a few studies addressed their mechanical properties. Here, we report the first investigation on the tunability of the elastic properties of cross-linked gold nanoparticle (GNP) composites. Thin films consisting of GNPs (diameter 3–4 nm) cross-linked with α,ω-alkanedithiols of different chain length, as well as 1,4-benzenedithiol, were fabricated by spin-coating and transferred onto circular apertures with diameters of ∼100 μm. The mechanical properties of thus-prepared freestanding membranes with thicknesses between 21 and 51 nm were probed using bulge tests with atomic force microscopy (AFM) based deflection readout. We demonstrate that, along with their optical and charge transport characteristics, the elastic modulus of these GNP composites can be adjusted in a range from ∼3.6 to ∼10 GPa by shortening the α,ω-alkanedithiol chain length from 10 to 3 methylene units. These variations in elasticity are attributed to the varying fraction of soft organic matter and to structural differences within the composites. Our results provide a basis for further experimental and theoretical studies, as well as for applications of cross-linked nanoparticle composites in future micro- and nanoelectromechanical (MEMS/NEMS) devices, their design, and modeling

Induced deactivation of genes encoding chlorophyll biosynthesis enzymes disentangles tetrapyrrole-mediated retrograde signalling.

In photosynthetic organisms, tetrapyrrole-mediated retrograde signals are proposed to contribute to a balanced nuclear gene expression (NGE) in response to metabolic activity in chloroplasts. We followed an experimental short-term approach that allowed the assessment of modified NGE during the first hours of specifically modified enzymatic steps of the Mg branch of tetrapyrrole biosynthesis, when pleiotropic effects of other signals can be avoided. In response to 24 h-induced silencing of CHLH, CHLM and CHL27 encoding the CHLH subunit of Mg chelatase, the Mg protoporphyrin methyltransferase and Mg protoporphyrin monomethylester cyclase, respectively, deactivated gene expression rapidly led to reduced activity of the corresponding enzymes and altered Mg porphyrin levels. But NGE was not substantially altered. When these three genes were continuously inactivated for up to 4 days, changes of transcript levels of nuclear genes were determined. CHL27 silencing for more than 24 h results in necrotic leaf lesions and modulated transcript levels of oxidative stress-responsive and photosynthesis-associated nuclear genes (PhANGs). The prolonged deactivation of CHLH and CHLM results in slightly elevated transcript levels of PhANGs and tetrapyrrole-associated genes. These time-resolved studies indicate a complex scenario for the contribution of tetrapyrrole biosynthesis on NGE mediated by (1)O2-induced signalling and feedback-regulated ALA synthesis

Elastic and Viscoelastic Properties of Cross-Linked Gold Nanoparticles Probed by AFM Bulge Tests

To enable applications of nanoparticle films in flexible electronics, actuators, and sensors, their mechanical properties are of critical concern. Here, we demonstrate that the elastic and viscoelastic properties of covalently cross-linked gold nanoparticles (GNPs) can be probed using AFM bulge tests. For this purpose 30–60 nm thick films consisting of 1,9-nonanedithiol (NDT) cross-linked GNPs (3.8 nm core diameter) were transferred onto substrates with ∼100 μm circular apertures. The resulting freestanding membranes were bulged by applying pressure differences of up to 10 kPa, and the deflection was measured by intermittent contact atomic force microscopy (AFM). Analyzing the pressure-deflection data using the spherical cap model, either by taking into account the peak deflection values or the measured arc profiles of the bulge, yielded 2.3 ± 0.3 and 2.7 ± 0.4 GPa for Young’s modulus, respectively. When cycling the stress–strain measurements at overpressures up to 2.4 kPa, hysteresis was observed and assigned to viscoelastic effects. Creep tests performed at a pressure of 2 kPa revealed both viscoelastic retardation (time constant: 3.3 × 10^–3 s^–1) and nonrecoverable relaxation (creep rate: 9.0 × 10^–8 s^–1). Several membranes resisted pressures up to 10 kPa without fracturing, indicating that the ultimate biaxial tensile strength of the films was above ∼30 MPa

Alu-Mediated Recombination Defect in IGF1R: Haploinsufficiency in a Patient with Short Stature

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