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- ItemSurface modification of silicon nanowire based field effect transistors with stimuli responsive polymer brushes for biosensing applications(Basel : MDPI, 2020) Klinghammer, Stephanie; Rauch, Sebastian; Pregl, Sebastian; Uhlmann, Petra; Baraban, Larysa; Cuniberti, GianaurelioWe demonstrate the functionalization of silicon nanowire based field effect transistors (SiNW FETs) FETs with stimuli-responsive polymer brushes of poly(N-isopropylacrylamide) (PNIPAAM) and poly(acrylic acid) (PAA). Surface functionalization was confirmed by atomic force microscopy, contact angle measurements, and verified electrically using a silicon nanowire based field effect transistor sensor device. For thermo-responsive PNIPAAM, the physicochemical properties (i.e., a reversible phase transition, wettability) were induced by crossing the lower critical solution temperature (LCST) of about 32 C. Taking advantage of this property, osteosarcomic SaoS-2 cells were cultured on PNIPAAM-modified sensors at temperatures above the LCST, and completely detached by simply cooling. Next, the weak polyelectrolyte PAA, that is sensitive towards alteration of pH and ionic strength, was used to cover the silicon nanowire based device. Here, the increase of pH will cause deprotonation of the present carboxylic (COOH) groups along the chains into negatively charged COO- moieties that repel each other and cause swelling of the polymer. Our experimental results suggest that this functionalization enhances the pH sensitivity of the SiNW FETs. Specific receptor (bio-)molecules can be added to the polymer brushes by simple click chemistry so that functionality of the brush layer can be tuned optionally. We demonstrate at the proof-of concept-level that osteosarcomic Saos-2 cells can adhere to PNIPAAM-modified FETs, and cell signals could be recorded electrically. This study presents an applicable route for the modification of highly sensitive, versatile FETs that can be applied for detection of a variety of biological analytes. © 2020 by the authors.
- ItemDetermination of the Entire Stent Surface Area by a New Analytical Method(Basel : MDPI, 2020) Saqib, Muhammad; Bernhardt, Ricardo; Kästner, Markus; Beshchasna, Natalia; Cuniberti, Gianaurelio; Opitz, JörgStenting is a widely used treatment procedure for coronary artery disease around the world. Stents have a complex geometry, which makes the characterization of their corrosion difficult due to the absence of a mathematical model to calculate the entire stent surface area (ESSA). Therefore, corrosion experiments with stents are mostly based on qualitative analysis. Additionally, the quantitative analysis of corrosion is conducted with simpler samples made of stent material instead of stents, in most cases. At present, several methods are available to calculate the stent outer surface area (SOSA), whereas no model exists for the calculation of the ESSA. This paper presents a novel mathematical model for the calculation of the ESSA using the SOSA as one of the main parameters. The ESSA of seven magnesium alloy stents (MeKo Laser Material Processing GmbH, Sarstedt, Germany) were calculated using the developed model. The calculated SOSA and ESSA for all stents are 33.34%(±0.26%) and 111.86 mm (±0.85 mm), respectively. The model is validated by micro-computed tomography (micro-CT), with a difference of 12.34% (±0.46%). The value of corrosion rates calculated using the ESSA computed with the developed model will be 12.34% (±0.46%) less than that of using ESSA obtained by micro-CT.
- ItemBoron doping of SWCNTs as a way to enhance the thermoelectric properties of melt‐mixed polypropylene/SWCNT composites(Basel : MDPI, 2020) Krause, Beate; Bezugly, Viktor; Khavrus, Vyacheslav; Ye, Liu; Cuniberti, Gianaurelio; Pötschke, PetraComposites based on the matrix polymer polypropylene (PP) filled with single‐walled carbon nanotubes (SWCNTs) and boron‐doped SWCNTs (B‐SWCNTs) were prepared by melt‐mixing to analyze the influence of boron doping of SWCNTs on the thermoelectric properties of these nanocomposites. It was found that besides a significantly higher Seebeck coefficient of B‐SWCNT films and powder packages, the values for B‐SWCNT incorporated in PP were higher than those for SWCNTs. Due to the higher electrical conductivity and the higher Seebeck coefficients of B‐SWCNTs, the power factor (PF) and the figure of merit (ZT) were also higher for the PP/B‐SWCNT composites. The highest value achieved in this study was a Seebeck coefficient of 59.7 μV/K for PP with 0.5 wt% B‐SWCNT compared to 47.9 μV/K for SWCNTs at the same filling level. The highest PF was 0.78 μW/(m∙K2) for PP with 7.5 wt% B‐SWCNT. SWCNT macro‐ and microdispersions were found to be similar in both composite types, as was the very low electrical percolation threshold between 0.075 and 0.1 wt% SWCNT. At loadings between 0.5 and 2.0 wt%, B‐SWCNT‐based composites have one order of magnitude higher electrical conductivity than those based on SWCNT. The crystallization behavior of PP is more strongly influenced by B‐SWCNTs since their composites have higher crystallization temperatures than composites with SWCNTs at a comparable degree of crystallinity. Boron doping of SWCNTs is therefore a suitable way to improve the electrical and thermoelectric properties of composites. © 2020 by the authors.
- ItemSTM induced manipulation of azulene-based molecules and nanostructures: the role of the dipole moment(Cambridge : RSC Publ., 2020) Kühne, Tim; Au-Yeung, Kwan Ho; Eisenhut, Frank; Aiboudi, Oumaima; Ryndyk, Dmitry A.; Cuniberti, Gianaurelio; Lissel, Franziska; Moresco, FrancescaAmong the different mechanisms that can be used to drive a molecule on a surface by the tip of a scanning tunneling microscope at low temperature, we used voltage pulses to move azulene-based single molecules and nanostructures on Au(111). Upon evaporation, the molecules partially cleave and form metallo-organic dimers while single molecules are very scarce, as confirmed by simulations. By applying voltage pulses to the different structures under similar conditions, we observe that only one type of dimer can be controllably driven on the surface, which has the lowest dipole moment of all investigated structures. Experiments under different bias and tip height conditions reveal that the electric field is the main driving force of the directed motion. We discuss the different observed structures and their movement properties with respect to their dipole moment and charge distribution on the surface.
- ItemTwo-Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device(Weinheim : Wiley-VCH, 2020) Park, SangWook; Liao, Zhongquan; Ibarlucea, Bergoi; Qi, Haoyuan; Lin, Hung-Hsuan; Becker, Daniel; Melidonie, Jason; Zhang, Tao; Sahabudeen, Hafeesudeen; Baraban, Larysa; Baek, Chang-Ki; Zheng, Zhikun; Zschech, Ehrenfried; Fery, Andreas; Heine, Thomas; Kaiser, Ute; Cuniberti, Gianaurelio; Dong, Renhao; Feng, XinliangDespite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin-film through solvothermal method and on-solid-surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin-film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin-film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two-dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF-PP or 2D BECOF-PN) by employing a surfactant-monolayer-assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF-PP is featured as free-standing thin film with large single-crystalline domains up to ≈60 μm2 and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF-PP film on silicon nanowire-based field-effect transistor is demonstrated as a bio-inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.