Maren Müller

Organic Field-Effect Transistors based on Highly Ordered Single Polymer Fibers

Ultrahigh-mobility organic field-effect transistors (OFETs) based on a CDT-BTZ donor-acceptor copolymer are realized by reaching high molecular order and pronounced alignment in single fibers within a short OFET channel via solution processing. The macromolecules directionally self-assemble in a quasi crystal-like order in the fibers providing in this way an unhindered charge carrier pathway with mobilities as high as 5.5 cm(2) V(-1) s(-1).

From three-dimensional polyphenylene dendrimers to large graphite subunits

Abstract Here we present a new approach to extremely large polycyclic aromatic hydrocarbons (PAHS) based on a cyclodehydrogenation method for polyphenylene dendrimers. These polyphenylene dendrimers are synthesized by repeated Diels-Alder reactions of ethynyl-substituted tetraphenylcyclopentadienones (1b) to the tetraethynylbiphenyl (2) core. Molecular mechanics and molecular dynamics calculations revealed that the dendrimers are shape-persistent due to the steric “overcrowding” of the benzene rings. The chemical and physical properties of the dendrimers can be controlled by varying the cyclopentadienones used in the last growth step.

Nanomechanical cantilever active probes for ultrasmall mass detection

The objective of this study is to employ piezoelectrically driven nanomechanical cantilevers (so-called “active probes”) for ultrasmall mass detection. The idea originates from utilizing the unique configuration and the embedded piezoelectricity of active probes for high amplitude vibration, the attribute that is essential for precise measurement of ultrasmall mass by cantilever-based vibratory sensors. In this work, using focused ion beam technique, a small mass in the order of picograms is added at the tip of active probes. To detect the added mass, a precise model for modal characterization of the probe with geometrical discontinuities is utilized along with a parameter estimation technique for system identification. Using the shifts in the resonant frequencies of the identified system, the amount of added tip mass is estimated at the most sensitive mode of operation. Through a sensitivity analysis, it is shown that the second mode of the present configuration of the active probe is the most reliable mode for mass detection. Moreover, the effect of parameters’ uncertainties on the sensitivity of measurements is studied in more detail. Results indicate that system identification procedure proposed in this work is an inevitable step toward achieving precise measurement of ultrasmall masses through active probes with great potential in bio- and chemomass detection applications.

Hyperthermic Effect in Suspension of Magnetosomes Prepared by Various Methods

The magnetic properties and hyperthermia effect were studied in solution of magnetosomes obtained by changing conditions during biomineralization of magnetotactic bacteria Magnetospirillum sp.AMB-1. It was shown that adding a higher amount of Wolfes vitamin solution (WVS) or ferric quinate (FQ) cause increase of the mean diameter from 47 nm (normal condition) up to 52 nm and 58 nm respectively. As a consequence of this change the preparation conditions coercivity and Specific Absorption Rate (SAR) increased up to 20 Oe and 949 W/gFe for sample FQ, respectively. On the other hand the process of cultivation at the changed conditions markedly reduced the cultivation time. Also the isolated chains of magnetosome were shorter containing less amount of magnetosomes too.

The benzene ring as modulus: synthesis and supramolecular ordering of novel conjugated polymers

Conjugated polymers possess attractive electronic and optical properties which also qualify them as active components of devices. Many conjugated polymers are made up of benzenoid building blocks. The functionalization of benzene rings is therefore a key step in polymer synthesis. Particularly important are functionalizations leading to direct aryl–aryl coupling and to the incorporation of vinylene and ethynylene units. On the other hand the benzene ring serves as a modular building block for controlling the supramolecular structures of macromolecules. The formation of aggregates or of liquid crystalline phases are typical examples (Dietrich et al. 1993). Herein, we present modular approaches towards the synthesis and supramolecular ordering of: (1) ladder–type poly(para–phenylene) (LPP); (2) donor–acceptor–substituted poly(para–phenylene–vinylene) (D/A-PPV); (3) poly(para–phenylenesulphide–para–phenyleneamine) (PPSA); (4) graphite sheets.

Growth‐induced lowering of magnetoelastic symmetry

Growth‐induced nonrandom ordering of ions on crystallographically equivalent sites of cubic magnetic garnets may reduce the symmetry of both the anisotropy and magnetoelastic tensors. The crystal tensors can be evaluated as weighted sums over all sites of the local ionic tensors. Such sums reflect both the site symmetries and the site occupation preferences. Unlike the anisotropy (whose growth‐induced axial terms are of lower order in the spin components than the cubic terms) the growth‐induced magnetoelastic tensor is of the same rank as the cubic component; it may, however, lack the symmetry between strain and spin components imposed by the cubic point group. We determine the symmetry and estimate the magnitude of the non‐cubic magnetostriction associated with nonrandom rare earth site occupation, an effect that should be observable. We argue on plausible grounds that the non‐cubicity associated with iron ions should be much smaller.

Stiffness and mass detection of nano layers using piezoresponse force microscopy

Piezoresponse force microscopy (PFM) is proposed in this article as a new technique for identification of elastically distributed thin layers on top of microcantilever sensors. Using the conventional actuation methods such as base excitation, the ratio of stiffness over the layer mass per unit length affects the resonant frequencies of the system as a single parameter. However, due to tip/sample elastic contact in PFM, these two parameters can be separately identified using the frequency shifts before and after attaching the layer. The concept is theoretically proven here using the modal analysis of the system. For practical verification, three gold-coated AFM microcantilevers were primarily tested for their initial resonant frequencies. The Focused Ion Beam (FIB) technique was then employed to deposit thin layers of Pt-based material in different configurations on the cantilevers’ surfaces. The microcantilevers were then reexamined for their new resonances, and the properties of the deposits were identified using a robust system identification procedure. Results indicate acceptable estimation of the cantilevers’ added mass and stiffness, making the technique suitable for detection of elastically distributed biological species.Copyright