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- ItemFabrication and investigation of three-dimensional ferroelectric capacitors for the application of FeRAM(New York : American Institute of Physics, 2016) Yeh, Chia-Pin; Lisker, Marco; Kalkofen, Bodo; Burte, Edmund P.Ferroelectric capacitors made by lead zirconate titanate (PZT) thin films and iridium electrodes are fabricated on three-dimensional structures and their properties are investigated. The iridium films are grown by Plasma Enhanced MOCVD at 300°C, while the PZT films are deposited by thermal MOCVD at different process temperatures between 450°C and 550°C. The step coverage and composition uniformity of the PZT films on trench holes and lines are investigated. Phase separation of PZT films has been observed on both 3D and planar structures. No clear dependences of the crystallization and composition of PZT on 3D structure topography have been found. STEM EDX line scans show a uniform Zr/(Zr+Ti) concentration ratio along the 3D profile but the variation of the Pb/(Zr+Ti) concentration ratio is large because of the phase separation. 3D ferroelectric capacitors show good ferroelectric properties but have much higher leakage currents than 2D ferroelectric capacitors. Nevertheless, during cycling tests the degradation of the remnant polarization between 2D and 3D capacitors is similar after 109 switching cycles. In addition, the sidewalls and bottoms of the 3D structures seem to have comparable remnant polarizations with the horizontal top surfaces.
- ItemUltracompact three-dimensional tubular conductivity microsensors for ionic and biosensing applications(Washington, DC : American Chemical Society, 2014) Martinez-Cisneros, C.S.; Sanchez, S.; Xi, W.; Schmidt, O.G.We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection = 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.
- ItemNiobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes(London [u.a.] : RSC, 2016) Tolosa, Aura; Krüner, Benjamin; Fleischmann, Simon; Jäckel, Nicolas; Zeiger, Marco; Aslan, Mesut; Grobelsek, Ingrid; Presser, VolkerThis study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m2 g−1. These nanofibers show a maximum specific energy of 19.5 W h kg−1 at low power and 7.6 W h kg−1 at a high specific power of 30 kW kg−1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g−1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g−1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg−1 was obtained. The high specific power for both systems, NbC–CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure.
- ItemReal-time image processing for label-free enrichment of Actinobacteria cultivated in picolitre droplets(London [u.a.] : Royal Society of Chemistry, 2013) Zang, E.; Brandes, S.; Tovar, M.; Martin, K.; Mech, F.; Horbert, P.; Henkel, T.; Figge, M.T.; Roth, M.The majority of today's antimicrobial therapeutics is derived from secondary metabolites produced by Actinobacteria. While it is generally assumed that less than 1% of Actinobacteria species from soil habitats have been cultivated so far, classic screening approaches fail to supply new substances, often due to limited throughput and frequent rediscovery of already known strains. To overcome these restrictions, we implement high-throughput cultivation of soil-derived Actinobacteria in microfluidic pL-droplets by generating more than 600000 pure cultures per hour from a spore suspension that can subsequently be incubated for days to weeks. Moreover, we introduce triggered imaging with real-time image-based droplet classification as a novel universal method for pL-droplet sorting. Growth-dependent droplet sorting at frequencies above 100 Hz is performed for label-free enrichment and extraction of microcultures. The combination of both cultivation of Actinobacteria in pL-droplets and real-time detection of growing Actinobacteria has great potential in screening for yet unknown species as well as their undiscovered natural products.
- ItemOperation mechanism of high performance organic permeable base transistors with an insulated and perforated base electrode(Melville, NY : American Inst. of Physics, 2016) Kaschura, Felix; Fischer, Axel; Klinger, Markus P.; Doan, Duy Hai; Koprucki, Thomas; Glitzky, Annegret; Kasemann, Daniel; Widmer, Johannes; Leo, KarlThe organic permeable base transistor is a vertical transistor architecture that enables high performance while maintaining a simple low-resolution fabrication. It has been argued that the charge transport through the nano-sized openings of the central base electrode limits the performance. Here, we demonstrate by using 3D drift-diffusion simulations that this is not the case in the relevant operation range. At low current densities, the applied base potential controls the number of charges that can pass through an opening and the opening is the current limiting factor. However, at higher current densities, charges accumulate within the openings and in front of the base insulation, allowing for an efficient lateral transport of charges towards the next opening. The on-state in the current-voltage characteristics reaches the maximum possible current given by space charge limited current transport through the intrinsic semiconductor layers. Thus, even a small effective area of the openings can drive huge current densities, and further device optimization has to focus on reducing the intrinsic layer thickness to a minimum.
- ItemHigh-defect hydrophilic carbon cuboids anchored with Co/CoO nanoparticles as highly efficient and ultra-stable lithium-ion battery anodes(Cambridge : Royal Society of Chemistry, 2016) Sun, Xiaolei; Hao, Guang-Ping; Lu, Xueyi; Xi, Lixia; Liu, Bo; Si, Wenping; Ma, Chuansheng; Liu, Qiming; Zhang, Qiang; Kaskel, Stefan; Schmidt, Oliver G.We propose an effective strategy to engineer a unique kind of porous carbon cuboid with tightly anchored cobalt/cobalt oxide nanoparticles (PCC–CoOx) that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The host carbon cuboid features an ultra-polar surface reflected by its high hydrophilicity and rich surface defects due to high heteroatom doping (N-/O-doping both higher than 10 atom%) as well as hierarchical pore systems. We loaded the porous carbon cuboid with cobalt/cobalt oxide nanoparticles through an impregnation process followed by calcination treatment. The resulting PCC–CoOx anode exhibits superior rate capability (195 mA h g−1 at 20 A g−1) and excellent cycling stability (580 mA h g−1 after 2000 cycles at 1 A g−1 with only 0.0067% capacity loss per cycle). Impressively, even after an ultra-long cycle life exceeding 10 000 cycles at 5 A g−1, the battery can recover to 1050 mA h g−1 at 0.1 A g−1, perhaps the best performance demonstrated so far for lithium storage in cobalt oxide-based electrodes. This study provides a new perspective to engineer long-life, high-power metal oxide-based electrodes for lithium-ion batteries through controlling the surface chemistry of carbon host materials.
- ItemEffect of cation size of binary cation ionic liquid mixtures on capacitive energy storage(New York, NY [u.a.] : Elsevier, 2023) Seltmann, Anna; Verkholyak, Taras; Gołowicz, Dariusz; Pameté, Emmanuel; Kuzmak, Andrij; Presser, Volker; Kondrat, SvyatoslavIonic liquid mixtures show promise as electrolytes for supercapacitors with nanoporous electrodes. Herein, we investigate theoretically and with experiments how binary electrolytes comprising a common anion and two types of differently-sized cations affect capacitive energy storage. We find that such electrolytes can enhance the capacitance of single nanopores and nanoporous electrodes under potential differences negative relative to the potential of zero charge. For a two-electrode cell, however, they are beneficial only at low and intermediate cell voltages, while a neat ionic liquid performs better at higher voltages. We reveal subtle effects of how the distribution of pores accessible to different types of ions correlates with charge storage and suggest approaches to increase capacitance and stored energy density with ionic liquid mixtures.
- ItemNaphtalenediimide-based donor-acceptor copolymer prepared by chain-growth catalyst-transfer polycondensation: Evaluation of electron-transporting properties and application in printed polymer transistors(London [u.a.] : Royal Society of Chemistry, 2014) Schmidt, G.C.; Höft, D.; Haase, K.; Hübler, A.C.; Karpov, E.; Tkachov, R.; Stamm, M.; Kiriy, A.; Haidu, F.; Zahn, D.R.T.; Yan, H.; Facchetti, A.The semiconducting properties of a bithiophene-naphthalene diimide copolymer (PNDIT2) prepared by Ni-catalyzed chain-growth polycondensation (P1) and commercially available N2200 synthesized by Pd-catalyzed step-growth polycondensation were compared. Both polymers show similar electron mobility of ∼0.2 cm2 V-1 s-1, as measured in top-gate OFETs with Au source/drain electrodes. It is noteworthy that the new synthesis has several technological advantages compared to traditional Stille polycondensation, as it proceeds rapidly at room temperature and does not involve toxic tin-based monomers. Furthermore, a step forward to fully printed polymeric devices was achieved. To this end, transistors with PEDOT:PSS source/drain electrodes were fabricated on plastic foils by means of mass printing technologies in a roll-to-roll printing press. Surface treatment of the printed electrodes with PEIE, which reduces the work function of PEDOT:PSS, was essential to lower the threshold voltage and achieve high electron mobility. Fully polymeric P1 and N2200-based OFETs achieved average linear and saturation FET mobilities of >0.08 cm2 V-1 s-1. Hence, the performance of n-type, plastic OFET devices prepared in ambient laboratory conditions approaches those achieved by more sophisticated and expensive technologies, utilizing gold electrodes and time/energy consuming thermal annealing and lithographic steps.
- ItemAnodically fabricated TiO2–SnO2 nanotubes and their application in lithium ion batteries(Cambridge : Royal Society of Chemistry, 2016) Madian, M.; Klose, M.; Jaumann, T.; Gebert, A.; Oswald, S.; Ismail, N.; Eychmüller, A.; Eckerta, J.; Giebeler, L.Developing novel electrode materials is a substantial issue to improve the performance of lithium ion batteries. In the present study, single phase Ti–Sn alloys with different Sn contents of 1 to 10 at% were used to fabricate Ti–Sn–O nanotubes via a straight-forward anodic oxidation step in an ethylene glycolbased solution containing NH4F. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. Our results reveal the successful formation of mixed TiO2/SnO2 nanotubes in the applied voltage range of 10–40 V. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage which turns Ti–Sn–O nanotubes into highly attractive materials for various applications. As an example, the Ti–Sn–O nanotubes offer promising properties as anode materials in lithium ion batteries. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at a current density of 504 mA cm2. The results demonstrate that TiO2/SnO2 nanotubes prepared at 40 V on a TiSn1 alloy substrate display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. This electrode was tested at current densities of 50, 100, 252, 504 and 1008 mA cm2 exhibiting average capacities of 780, 660, 490, and 405 mA cm2 (i.e. 410, 345, 305 and 212 mA h g1), respectively. The remarkably improved electrochemical performance is attributed to enhanced lithium ion diffusion which originates from the presence of SnO2 nanotubes and the high surface area of the mixed oxide tubes. The TiO2/SnO2 electrodes retain their original tubular structure after electrochemical cycling with only slight changes in their morphology.
- ItemComputational design and optimization of electro-physiological sensors([London] : Nature Publishing Group UK, 2021) Nittala, Aditya Shekhar; Karrenbauer, Andreas; Khan, Arshad; Kraus, Tobias; Steimle, JürgenElectro-physiological sensing devices are becoming increasingly common in diverse applications. However, designing such sensors in compact form factors and for high-quality signal acquisition is a challenging task even for experts, is typically done using heuristics, and requires extensive training. Our work proposes a computational approach for designing multi-modal electro-physiological sensors. By employing an optimization-based approach alongside an integrated predictive model for multiple modalities, compact sensors can be created which offer an optimal trade-off between high signal quality and small device size. The task is assisted by a graphical tool that allows to easily specify design preferences and to visually analyze the generated designs in real-time, enabling designer-in-the-loop optimization. Experimental results show high quantitative agreement between the prediction of the optimizer and experimentally collected physiological data. They demonstrate that generated designs can achieve an optimal balance between the size of the sensor and its signal acquisition capability, outperforming expert generated solutions.