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A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in a H2O steam and conventional thermal annealing (CTA) in a furnace at 150 °C in ambient were used as post-growth treatments to improve the material properties. Herein, the morphological, optical, chemical, structural, vibrational, and gas sensing performances of the as-electrodeposited and treated specimens are investigated and presented in detail. By varying the growth temperature and type of post-growth treatment, the morphology is maintained, whereas the optical and structural properties show increased sample crystallization. It is shown that HT in H2O vapors affects the optical and vibrational properties of the material. After investigation of nanodevices based on single ZnO NR/NWs, it was observed that higher temperature during the synthesis results in a higher gas response to H2 gas within the investigated operating temperature range from 25 to 150 °C. CTA and HT or autoclave treatment showed the capability of a further increase in gas response of the prepared sensors by a factor of ∼8. Density functional theory calculations reveal structural and electronic band changes in ZnO surfaces as a result of strong interaction with H2 gas molecules. Our results demonstrate that high-performance devices can be obtained with high-crystallinity NWs/NRs after HT. The obtained devices could be the key element for flexible nanoelectronics and wearable electronics and have attracted great interest due to their unique specifications.

Hierarchical, conductive, porous, three-dimensional (3D) carbon networks based on carbon nanotubes are used as a scaffold material for the incorporation of sulfur in the vapor phase to produce carbon nanotube tube/sulfur (CNTT/S) composites for application in lithium ion batteries (LIBs) as a cathode material. The high conductivity of the carbon nanotube-based scaffold material, in combination with vapor infiltration of sulfur, allows for improved utilization of insulating sulfur as the active material in the cathode. When sulfur is evenly distributed throughout the network via vapor infiltration, the carbon scaffold material confines the sulfur, allowing the sulfur to become electrochemically active in the context of an LIB. The electrochemical performance of the sulfur cathode was further investigated as a function of the temperature used for the vapor infiltration of sulfur into the carbon scaffolds (155, 175, and 200 °C) in order to determine the ideal infiltration temperature to maximize sulfur loading and minimize the polysulfide shuttle effect. In addition, the nature of the incorporation of sulfur at the interfaces within the 3D carbon network at the different vapor infiltration temperatures will be investigated via Raman, scanning electron microscopy/energy dispersive X-ray, and X-ray photoelectron spectroscopy. The resulting CNTT/S composites, infiltrated at each temperature, were incorporated into a half-cell using Li metal as a counter electrode and a 0.7 M LiTFSI electrolyte in ether solvents and characterized electrochemically using cyclic voltammetry measurements. The results indicate that the CNTT matrix infiltrated with sulfur at the highest temperature (200 °C) had improved incorporation of sulfur into the carbon network, the best electrochemical performance, and the highest sulfur loading, 8.4 mg/cm2, compared to the CNTT matrices infiltrated at 155 and 175 °C, with sulfur loadings of 4.8 and 6.3 mg/cm2, respectively.

In this study, a strategy to prepare CuO/Cu2O/Cu microwires that are fully covered by a nanowire (NW) network using a simple thermal-oxidation process is developed. The CuO/Cu2O/Cu microwires are fixed on Au/Cr pads with Cu microparticles. After thermal annealing at 425 °C, these CuO/Cu2O/Cu microwires are used as room-temperature 2-propanol sensors. These sensors show different dominating gas responses with operating temperatures, e.g., higher sensitivity to ethanol at 175 °C, higher sensitivity to 2-propanol at room temperature and 225 °C, and higher sensitivity to hydrogen gas at ∼300 °C. In this context, we propose the sensing mechanism of this three-in-one sensor based on CuO/Cu2O/Cu. X-ray diffraction (XRD) studies reveal that the annealing time during oxidation affects the chemical appearance of the sensor, while the intensity of reflections proves that for samples oxidized at 425 °C for 1 h the dominating phase is Cu2O, whereas upon further increasing the annealing duration up to 5 h, the CuO phase becomes dominant. The crystal structures of the Cu2O-shell/Cu-core and the CuO NW networks on the surface were confirmed with a transmission electron microscope (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED), where (HR)TEM micrographs reveal the monoclinic CuO phase. Density functional theory (DFT) calculations bring valuable inputs to the interactions of the different gas molecules with the most stable top surface of CuO, revealing strong binding, electronic band-gap changes, and charge transfer due to the gas molecule interactions with the top surface. This research shows the importance of the nonplanar CuO/Cu2O layered heterostructure as a bright nanomaterial for the detection of various gases, controlled by the working temperature, and the insight presented here will be of significant value in the fabrication of new p-type sensing devices through simple nanotechnology.

Monitoring volatile organic compounds (VOCs) in harsh environments, especially for safety applications, is a growing field that requires specialized sensor structures. In this work, we demonstrate the sensing properties toward the most common VOCs of columnar Al

The gas sensing properties of heterojunctions based on binary and ternary metal oxides (CuAl 2 O 4 /Al 2 O 3 /CuO/Cu 2 O, ZnAl 2 O 4 /ZnO and Zn 2 SnO 4 ) were investigated in detail and demonstrated excellent sensitivity and selectivity to a series of gases and volatile organic compounds (VOCs), such as H 2 , CO and ethanol. The dynamic measurements showed excellent response stability at low and high relative humidity, which is very important for applications like diseases detection by breath analysis.

Nanosensors and microsensors are important for environmental and biomedical monitoring due to their extraordinary properties. In this work sensor devices are fabricated for the detection of H 2 gas and ethanol vapors. These devices are based on ZnO single nanowires, heterostructures composed of TiO 2 /ZnO columns doped with Cd, as well as TiO 2 /CuO:Ni, Ag and on a functionalization with Pd and other noble nanodots.

In this study, double hierarchical and highly porous 3D carbon nanotube/sulfur (CNTT/S) composites were synthesized. By coating a ceramic template material with a simple and versatile infiltration process of an aqueous carbon nanotube (CNT) dispersion a self-organized CNT layer is formed. After removing the template material, a freestanding double hierarchical network is created that show excellent electrical conductivity of 6.02 S m -1 and a high specific BET surface area of 630 m 2 g -1 with the presence of micro-, mesopores (up to 4 nm) and macropores (>>50 nm) simultaneously. A combined analysis of gas sorption measurements and elemental mapping using EFTEM after sulfur vapor deposition revealed that only the micro- and mesopores were accessible and that the sulfur is encapsulated within the double hierarchy. Hence, the electric percolation remains high without losing the necessary outer conductivity. Thereafter, these composites were employed in a proof-of-concept study as a sulfur cathode, demonstrating the importance of predesigning an electrode structure, shown in electrochemical performance data. With the aid of this hierarchical 3D composite structure, it is possible to achieve a stability over 100 cycles with ≈ 5.8 mAh cm -1 as a sulfur cathode in lithium half-cell tests.

A comparative investigation of the post-electroplating treatment influence on the gas detecting performances of single ZnO nanorod/nanowire (NR/NW), as grown by electrochemical deposition (ECD) and integrated into nanosensor devices, is presented. In this work, hydrothermal treatment (HT) in a H

In this study, a strategy to prepare CuO/Cu

Gas sensors are demanded in many different application fields. Especially the ever-growing field of batteries creates a great need for early hazard detection by gas sensors. Metal oxides are well known for gas sensing; however, moisture continues to be a major problem for the sensors, especially for the application in battery systems. This study reports on a new type of moisture protected gas sensor, which is capable to solve this problem. Sensitive nano-materials of CuO/Cu2O/ZnO:Fe heterostructures are grown and subsequently coated with an ultrathin hydrophobic cyclosiloxane-polymer film via initiated chemical vapor deposition to protect the sensor from moisture. The monomer 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane is combined with the initiator perfluorobutanesulfonyl fluoride to obtain hydrophobic properties. Surface chemistry, film formation and preservation of functional groups are confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. It turns out that the hydrophobicity is retained even after annealing at 400 °C, which is ideal for gas sensing. Molecular distances in the polymer nanolayer are estimated by geometry optimization via MMFF94 followed by density functional theory. Compared with unprotected CuO/Cu2O/ZnO:Fe, the coated CuO/Cu2O/ZnO:Fe exhibit a much better sensing performance at a higher relative humidity, as well as tunability of the gas selectivity. This is highly beneficial for hazard detection in case of thermal runaway in batteries because the sensors can be used under high concentrations of relative humidity, which is ideal for Li–S battery applications.

We prove that the exponential decay rate in expectation is well defined and is equal to the Lyapunov exponent, for supercritical almost Mathieu operators with Diophantine frequencies.

We construct a limit-periodic Schrodinger operator for which the Lyapunov exponent has a positive measure set of discontinuities. We also show that the limit-periodic potentials for which the Lyapunov exponent is discontinuous are dense in the space of limit-periodic potentials.

Crystalline silicon is an ideal anode candidate for lithium ion batteries as it offers a high Li+ ion storage capacity, direct current pathway and is a stable and earth abundant element. In order to match the high theoretical energy density of silicon in lithium ion batteries a suitable cathode material is required. Sulfur based cathodes have a high theoretical storage capacity for application in lithium ion batteries, based on the conversion reaction of the cyclic S8 molecule with lithium to form smaller lithium polysulfides up to Li2S, and are also cheap and earth abundant. One of the major drawbacks of lithium sulfur cathode materials is the tendency of lithium polysulfides to be dissolved by the electrolyte, which causes the polysulfides to migrate away from the cathode, leading to an overall capacity loss. For application of porous silicon in a full cell lithium ion battery with sulfur it is important to understand the impact the presence of lithium polysulfides can have on the functionality of porous silicon as an anode. In this study porous silicon anodes with thicknesses of 6 µm and 12 µm were cycled in a half cell in the presence of varying concentrations of Li2S6 (0 M, 0.017 M and 0.083 M). For the electrolyte with 0.017 M Li2S6 the cycling behavior was comparable, or better, than the electrolyte with no polysulfides. The SEI layer formed on the surface of the porous silicon anodes was investigated ex situ with X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy after one, five and ten cycles. It was seen that in the first cycle lithium polysulfides are contained in the SEI and undergo an oxidation reaction to form sulfates over the following cycles. This leads to a more inorganic SEI layer in the presence of polysulfides, especially in the case of the 12 µm porous silicon, and long term cycling stability. The 12 µm porous silicon anode cycled in the presence of 0.083 M Li2S6 showed stable cycling behavior over one hundred cycles, with limited capacity loss and coulombic efficiencies of 96.2 % after one hundred cycles.

Three-dimensional (3D) assemblies based on carbon nanomaterials still lag behind their individual one-dimensional building blocks in terms of mechanical and electrical properties. Here we demonstrate a simple strategy for the fabrication of an open porous 3D self-organized double-hierarchical carbon nanotube tube structure with properties advantageous to those existing so far. Even though no additional crosslinking exists between the individual nanotubes, a high reinforcement effect in compression and tensile characteristics is achieved by the formation of self-entangled carbon nanotube (CNT) networks in all three dimensions, employing the CNTs in their high tensile properties. Additionally, the tubular structure causes a self-enhancing effect in conductivity when employed in a 3D stretchable conductor, together with a high conductivity at low CNT concentrations. This strategy allows for an easy combination of different kinds of low-dimensional nanomaterials in a tube-shaped 3D structure, enabling the fabrication of multifunctional inorganic-carbon-polymer hybrid 3D materials., Low-dimensional nanomaterials are crucial conducting components of stretchable electronics, but their mechanical reinforcement remains challenging. Here, the authors infiltrate carbon nanotubes into a porous ceramic network to produce a 3D nanofelted self-entangled assembly with high conductivity and mechanical stability.

Lithium-sulfur batteries are one of the most promising Li-Ion batteries. Sulfur, with the highest gravimetric capacity of all cathode materials, allows a theoretical energy density that is five times higher than state of the art rechargeable batteries. Furthermore, sulfur is a cheap and earth abundant material, which makes it possible to be used in large-scale applications. Hereby, progress in the field of mobile energy storage can be achieved.[1] However, rechargeable lithium-sulfur batteries still suffer from the intrinsic problems of sulfur in the battery environment. The insulating character, the expansion of sulfur during cycling as well as the well-known polysulfide shuttle effect are still a challenge and are studied with great effort. The phenomena described lead to lowered sulfur utilization and loss of active material during cycling, resulting in an overall reduced energy density and a continuous fading of the battery capacity, unsuitable for practical applications. The shuttle effect, characterized by the dissolution of sulfur into the electrolyte during cycling, is still a major concern, but can be reduced by using for example nanomaterials.[2][3] Much of the research is done on the electrolyte or electrode composition, but the structural design of the cathode plays major role. The use of nanomaterials based on carbon, such as graphene, graphene oxide or carbon nanotubes, have shown already huge potential in the use as a cathode scaffold material.³ However, these materials need to be arranged into a macroscopic 3D structure to make use of their extraordinary electrical and mechanical properties. The approach presented here is based on the fabrication process established in a previous work[4], for the preparation of an open porous 3D self-organized hierarchical carbon nanotube tube network, used to minimize the shuttle effect. A highly porous 3D network based on tetrapodal zinc oxide[5] is coated with carbon nanotubes using wet chemical techniques. The tetrapodal zinc oxide is used as a removable scaffold material, giving the cathode a defined 3D structure. After zinc oxide removal, a conductive, mechanically stable, 3D scaffold of carbon nanotubes remains possessing a hierarchical porous structure. The structure has a large pore to volume ratio and therefore a large reachable surface inside the cathode material. By employing these open porous network structures in combination with sulfur vapour deposition methods, the sulfur is homogenously distributed throughout the structure, improving the sulphur utilization and improving the overall contact to the highly conductive carbon host scaffold. In addition the structure of the network acts as a trap for polysulfide due to tailorable micro and macro pores, reducing capacity fading of the battery from the shuttle effect. The performance of these sulphur cathodes was shown to be almost constant from the 5th to the 50th cycle with a capacity of 950mAh/g and sulfur loadings up to 50wt.%. This novel electrode design is able to counteract the polysulfide-shuttle effect, withstand the expansion of sulfur during cycling, and offers promising results in the battery performance. [1] Manthiram, Arumugam; Fu, Yongzhu; Chung, Sheng-Heng; Zu, Chenxi; Su, Yu-Sheng (2014): Rechargeable lithium-sulfur batteries. In: Chemical reviews 114 (23), S. 11751–11787. DOI: 10.1021/cr500062v. [2] Liquid electrolyte lithium/sulfur battery. Fundamental chemistry, problems, and solutions (2013). In: Journal of Power Sources 231, S. 153–162. [3] Wang, Hailiang; Yang, Yuan; Liang, Yongye; Robinson, Joshua Tucker; Li, Yanguang; Jackson, Ariel et al. (2011): Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium–Sulfur Battery Cathode Material with High Capacity and Cycling Stability. American Chemical Society [4]Schütt, Fabian; Signetti, Stefano; Krüger, Helge; Röder, Sarah; Smazna, Daria; Kaps, Sören et al. (2017): Hierarchical self-entangled carbon nanotube tube networks. In: Nature Communications 8 (1), S. 1215. DOI: 10.1038/s41467-017-01324-7. [5] Mishra, Yogendra Kumar; Adelung, Rainer (2018): ZnO tetrapod materials for functional applications. In: Materials Today 21 (6), S. 631–651. DOI: 10.1016/j.mattod.2017.11.003.

We prove that the exponential moments of the position operator stay bounded for the supercritical almost Mathieu operator with Diophantine frequency.

Three-dimensional (3D) assemblies based on carbon nanomaterials still lag behind their individual one-dimensional building blocks in terms of mechanical and electrical properties. Here we demonstrate a simple strategy for the fabrication of an open porous 3D self-organized double-hierarchical carbon nanotube tube structure with properties advantageous to those existing so far. Even though no additional crosslinking exists between the individual nanotubes, a high reinforcement effect in compression and tensile characteristics is achieved by the formation of self-entangled carbon nanotube (CNT) networks in all three dimensions, employing the CNTs in their high tensile properties. Additionally, the tubular structure causes a self-enhancing effect in conductivity when employed in a 3D stretchable conductor, together with a high conductivity at low CNT concentrations. This strategy allows for an easy combination of different kinds of low-dimensional nanomaterials in a tube-shaped 3D structure, enabling the fabrication of multifunctional inorganic-carbon-polymer hybrid 3D materials.

I analyze the microscopic behavior of the eigenvalues of skew-shift Schrodinger operators, and show that their statistics must resemble the one of the Anderson model rather than the one of quasi-periodic Schrodinger operators.

I consider random Schrodinger operators with exponentially decaying single site potential, which is allowed to change sign. For this model, I prove Anderson localization both in the sense of exponentially decaying eigenfunctions and dynamical localization. Furthermore, the results imply a Wegner-type estimate strong enough to use in classical forms of multi-scale analysis.

We construct examples that log Holder continuity of the integrated density of states cannot be improved. Our examples are limit-periodic. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A variant of multiscale analysis for ergodic Schrodinger operators is developed. This enables us to prove positivity of Lyapunov exponents, given initial scale estimates and an initial Wegner estimate. This postivivity is then applied to high-dimensional skew-shifts at small coupling, where initial conditions are checked using the Pastur–Figotin formalism.

Using relative oscillation theory and the reducibility result of Eliasson, we study perturbations of quasiperiodic Schrodinger operators. In particular, we derive relative oscillation criteria and eigenvalue asymptotics for critical potentials.

By approximation, I show that the spectrum of the Schr\"odinger operator with potential $V(n) = f(n\rho \pmod 1)$ for f continuous and $\rho > 0$, $\rho \notin \N$ is an interval., Comment: Comm. Math. Phys. (to appear)

We explore the spectral theory of the orthogonal polynomials associated to the classical Cantor measure and similar singular continuous measures. We prove regularity in the sense of Stahl-Totik with polynomial bounds on the transfer matrix. We present numerical evidence that the Jacobi parameters for this problem are asymptotically almost periodic and discuss the possible meaning of the isospectral torus and the Szeg? class in this context.

I give an example of a family of orthogonal polynomials on the unit circle with Verblunsky coefficients given by the skew-shift for which the associated measures are supported on the entire unit circle and almost every Aleksandrov measure is pure point. Furthermore, I show in the case of the two-dimensional skew-shift that the zeros of para-orthogonal polynomials obey the same statistics as an appropriate irrational rotation. The proof is based on an analysis of the associated CMV matrices.

We establish unique continuation for various discrete nonlinear wave equations. For example, we show that if two solutions of the Toda lattice coincide for one lattice point in some arbitrarily small time interval, then they coincide everywhere. Moreover, we establish analogous results for the Toda, Kac-van Moerbeke, and Ablowitz-Ladik hierarchies. Although all these equations are integrable, the proof does not use integrability and can be adapted to other equations as well., Comment: 10 pages

We review recent results on localization for discrete alloy-type models based on the multiscale analysis and the fractional moment method, respectively. Th e discrete alloy-type model is a family of Schrodinger operators \( H_\omega = - \Delta + V_\omega\) on \( l^{^2 } (\mathbb{Z}^d )\) where Δ is the discrete Laplacian and \(V_\omega\) the multiplication by the function \(V_\omega (x) = \sum _{k \in\mathbb{Z}^d } \omega _k u(x - k) \cdot\)Here \(\omega _k,k \in \mathbb{Z}^d \) are i.i.d. random variables and \( u \in l^1 (\mathbb{Z}^d ;\mathbb{R}) \) is a so-called single-site potential. Since u may change sign, certain properties of \(H\omega\) depend in a non-monotone way on the random parameters \( \omega _k\). This requires new methods at certain stages of the localization proof.

We discuss discrete one-dimensional Schr\"odinger operators whose potentials are generated by an invertible ergodic transformation of a compact metric space and a continuous real-valued sampling function. We pay particular attention to the case where the transformation is a minimal interval exchange transformation. Results about the spectrum and the spectral type of these operators are established. In particular, we provide the first examples of transformations for which the associated Schr\"odinger operators have purely singular spectrum for every non-constant continuous sampling function.

We apply the method of nonlinear steepest descent to compute the long-time asymptotics of the periodic (and slightly more generally of the quasi-periodic finite-gap) Toda lattice for decaying initial data in the soliton region. In addition, we show how to reduce the problem in the remaining region to the known case without solitons., 28 pages

The purpose of this article is to give a streamlined and self-contained treatment of the long-time asymptotics of the Toda lattice for decaying initial data in the soliton and in the similarity region via the method of nonlinear steepest descent., Comment: 41 pages

We apply the method of nonlinear steepest descent to compute the long-time asymptotics of the Toda lattice for decaying initial data in the soliton region. In addition, we point out how to reduce the problem in the remaining region to the known case without solitons., Comment: 18 pages

1. Zuchtmethodische Arbeiten ergaben, das sowohl uber fortgesetzte Individualauslese als auch uber innersortliche Linienkreuzung eine Erhohung des Fettgehaltes von Rapspopulationen bei gleichzeitige Steigerung der Samenertrage moglich ist.

I prove that the spectrum of a skew-shift Schrodinger operator contains large intervals in the semi-classical regime. In the semi-classical limit, these intervals approach the range of the potential.

I relate the existence of eigenfunctions of decaying perturbations of the free Laplacian to the semi-classical behavior of the spectrum of quasi-periodic Schrödinger operators. In particular, I construct embedded eigenvalues in the spectrum of the discrete Laplacian perturbed by a potential of generalized bounded variation.

We present a streamlined approach to relative oscillation criteria based on effective Pruefer angles adapted to the use at the edges of the essential spectrum. Based on this we provided a new scale of oscillation criteria for general Sturm-Liouville operators which answer the question whether a perturbation inserts a finite or an infinite number of eigenvalues into an essential spectral gap. As a special case we recover the Gesztesy-Uenal criterion (which works below the spectrum and contains classical criteria by Kneser, Hartman, Hille, and Weber) and the well-known results by Rofe-Beketov including the extensions by Schmidt., 22 pages