Electrogravimetry and Structural Properties of Thin Silicon Layers Deposited in Sulfolane and Ionic Liquid Electrolytes.

Potentiostatic deposition of silicon is performed in sulfolane (SL) and ionic liquid (IL) electrolytes. Electrochemical quartz crystal microbalance with damping monitoring (EQCM-D) is used as main analytical tool for the characterization of the reduction process. The apparent molar mass (Mapp) is applied for in situ estimation of the layer contamination. By means of this approach, appropriate electrolyte composition and substrate type are selected to optimize the structural properties of the layers. The application of SL electrolyte results in silicon deposition with higher efficiency compared to the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][TFSI]. This has been associated with the instability of the IL in the presence of silicon tetrachloride and the enhanced incorporation of IL decomposition products into the growing silicon deposit. X-ray photoelectron spectroscopy (XPS) analysis supports the results about the layer composition, as suggested from the microgravimetric experiments. Attention has been given to the impact of practically relevant substrates (i.e., Cu, Ni, and vitreous carbon) on the reduction process. An effective deposition can be carried out on the metal electrodes in both electrolytes due to accelerated reaction kinetics for these types of substrates. However, on vitreous carbon (VC), a successful reduction of SiCl4 can only be accomplished in the IL, while the electroreduction process in SL is dominated by the decomposition of the electrolyte. For short deposition times, the scanning electron microscopy (SEM) images display rough morphologies in the nanometer range, which evolve further to structures with increased length scale of the surface roughness. The development of a rough interface during deposition, resulting in QCM damping at advanced stages of the process, is interpreted by a model accounting for the resistive force caused by the interaction of the liquid with a nonuniform layer interface. By using this approach, the individual contributions of the surface roughness and viscoelastic effects to the measured damping values are estimated.

A Unidirectional Transducer Design for Scaling GHz AlN-Based RF Microsystems.

In this work, we present a novel unidirectional transducer design for frequency scaling aluminum nitride (AlN)-based radio frequency (RF) microsystems. The proposed thickness-field-excited single-phase unidirectional transducers (TFE-SPUDT) adopt 5/16 wavelength electrodes and, thus, enable efficient piezoelectric transduction with better frequency scalability. The design space of the TFE-SPUDT is theoretically explored and validated using the acoustic delay line (ADL) testbeds. The ADL testbeds with a large feature size of [Formula: see text] show a center frequency of 1 GHz, a minimum insertion loss (IL) of 4.9 dB, and a fractional bandwidth (FBW) of 5.3%, significantly surpassing the IL and frequency scalability of the previously reported AlN transducers. The design approach can potentially contribute to various AlN-based RF microsystems for signal processing, physical sensing, optomechanical interaction, and quantum acoustic applications, and are readily extendable to other piezoelectric platforms.

Alternative splicing affects the subcellular localization of Drosha.

The RNase III enzyme Drosha is a key factor in microRNA (miRNA) biogenesis and as such indispensable for cellular homeostasis and developmental processes. Together with its co-factor DGCR8, it converts the primary transcript (pri-miRNA) into the precursor hairpin (pre-miRNA) in the nucleus. While the middle and the C-terminal domain are crucial for pri-miRNA processing and DGCR8 binding, the function of the N-terminus remains cryptic. Different studies have linked this region to the subcellular localization of Drosha, stabilization and response to stress. In this study, we identify alternatively spliced Drosha transcripts that are devoid of a part of the arginine/serine-rich (RS-rich) domain and expressed in a large set of human cells. In contrast to their expected habitation, we find two isoforms also present in the cytoplasm, while the other two isoforms reside exclusively in the nucleus. Their processing activity for pri-miRNAs and the binding to co-factors remains unaltered. In multiple cell lines, the endogenous mRNA expression of the Drosha isoforms correlates with the localization of endogenous Drosha proteins. The pri-miRNA processing efficiency is not significantly different between groups of cells with or without cytoplasmic Drosha expression. In summary, we discovered novel isoforms of Drosha with differential subcellular localization pointing toward additional layers of complexity in the regulation of its activity.

Electropolymerized three-dimensional randomly branched EDOT-containing copolymers.

The potential of 2,2';3,2″-terthiophene (3T) as branching units in 3D copolymers is presented with EDOT as an example comonomer. Branched EDOT/3T polythiophenes were prepared by electropolymerization, and their electrochemical and optical properties are discussed. Two different approaches were employed: (i) the direct electropolymerization of a novel branched thiophene monomer (3TE3) consisting of a 3T core that contains three outer EDOT end groups and (ii) the electrochemical copolymerization of a EDOT/3T mixture in different ratios from [1:1] to [1:10]. Cyclic voltammetric and vis spectrometric experiments show that the EDOT content within the polymer has a strong influence on the electronic properties of the material: with increasing EDOT content, the HOMO-LUMO gap is decreased. To prove copolymer formation of EDOT and 3T, chemically synthesized reference copolymers of EDOT and 3T were prepared by oxidative coupling using FeCl3, and their optical and electronic properties were compared to those of the electrodeposited films. In addition, the copolymer formation is indicated by the comparison of the electrochemical and spectroscopic results with those of the homopolymers P3T and PEDOT.

Loop-miRs: active microRNAs generated from single-stranded loop regions.

MicroRNAs (miRNAs) are key mediators of post-transcriptional gene regulation. The miRNA precursors are processed by the endonucleases Drosha and Dicer into a duplex, bound to an Argonaute protein and unwound into two single-stranded miRNAs. Although alternative ways to generate miRNAs have been discovered, e.g. pre-miRNA cleavage by Ago2 or cleavage products of snoRNAs or tRNAs, all known pathways converge on a double-stranded RNA duplex. Exogenous single-stranded siRNAs (ss-siRNAs) can elicit an effective RNA interference reaction; recent studies have identified chemical modifications increasing their stability and activity. Here, we provide first evidence that endogenous, unmodified, single-stranded RNA sequences are generated from single-stranded loop regions of human pre-miRNA hairpins, the so called loop-miRs. Luciferase assays and immunoprecipitation validate loop-miR activity and incorporation into RNA-induced silencing complexes. This study identifies endogenous miRNAs that are generated from single-stranded regions; hence, it provides evidence that precursor-miRNAs can give rise to three distinct endogenous miRNAs: the guide strand, the passenger strand and the loop-miR.

Optoelectronic properties of hyperbranched polythiophenes.

Branched conjugated architectures should possess the advantage of isotropic charge transport compared to conventional linear conjugated polymers, as for example poly(3-hexylthiophene) (P3HT) which is commonly used in organic solar cells. This contribution investigates the optoelectronic properties of branched poly(thiophene)s p3T and p4T synthesized in a straightforward one-pot procedure by oxidative coupling of branched trithiophene and tetrathiophene monomers with FeCl(3). These polymers can be regarded as model systems for ideal amorphous conjugated materials. Optical characterization in solution and in thin films together with cyclic voltammetry data suggests the applicability of these materials for the use in organic solar cell devices. In particular, the HOMO and LUMO levels of the branched polythiophenes are shifted to lower energy values as compared to linear P3HT. Field effect mobilities are in the order of 10(-4) cm(2)/(V s). A first optimization of solar cell devices based on the branched polythiophene materials in combination with PCBM as acceptor resulted in efficiencies of 0.6% with open-circuit voltages being about 30% higher (up to 714 mV) than normally found with P3HT.

Electrochemical behavior of electropolymerized and chemically synthesized hyperbranched polythiophenes.

Hyperbranched polythiophenes were synthesized by potentiodynamic electropolymerization of 2,2';3',2''-terthiophene and 5'-(2-thienyl)-2,2';3',2''-terthiophene. The molecular architecture, i.e., the extent of branching of the resulting polymers, could be adjusted by varying the switching potentials. We compare these systems to hyperbranched polythiophenes which we obtained via a simple one-pot synthesis route based on FeCl(3) oxidative polymerization of the monomers. Interestingly, we find that the properties of the electropolymerized materials obtained with high switching potentials are comparable to those of the chemically synthesized polythiophenes. A detailed optical and electrochemical characterization of these systems is performed showing the high potential of this material class for optoelectronic applications. Cyclic voltammetry coupled with in situ conductance measurements further reveal reversible doping upon oxidation (p-doping) and reduction (n-doping) and comparable values for the conductance for the chemically and electrochemically synthesized materials.

Design of soluble hyperbranched polythiophenes with tailor-made optoelectronic properties.

Hyperbranched polythiophenes were prepared via a simple one-pot synthesis approach based on oxidative coupling of branched conjugated monomers. Only small variations in the building unit and architecture lead to large differences of absorption and photoluminescence properties. Interestingly, soluble hyperbranched polythiophenes with relatively small molecular weights show enhanced absorption at low and high wavelengths compared to linear analogues, such as poly(3-hexyl thiophenes) with high molecular weights. With this versatile approach we present a method to design tailor made, functional materials with potential applications in optoelectronics.