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- ItemMicrostructural defects in hot deformed and as-transformed τ-MnAl-C(Lausanne : Elsevier, 2021) Zhao, P.; Feng, L.; Nielsch, K.; Woodcock, T.G.In this study, detailed microstructural characterisation has been conducted in both as-transformed and hot deformed samples of τ-MnAl-C using transmission electron microscopy. After hot deformation, true twins, dislocations, intrinsic stacking faults and precipitates of Mn3AlC are the main defects in the recrystallised grains. True twins and order twins were distinguished based on differences in their diffraction patterns. A significant fraction of non-recrystallised grains existed, which had microstructures based on combinations of high densities of true twins, dislocations, and deformation bands. The formation of the Mn3AlC precipitates was confirmed and related to the reduction of saturation magnetization and the increase in the Curie temperature of τ-MnAl-C after hot deformation. Antiphase boundaries, which are believed to act as nucleation sites for reverse domains, were not observed in the hot deformed sample.
- ItemDielectric Properties and Spectral Characteristics of Photocatalytic Constant of TiO2 Nanoparticles Doped with Cobalt(Basel : MDPI, 2021) Bessergenev, V.G.; Mariano, J.F.; Mateus, M.C.; Lourenço, J.P.; Ahmed, A.; Hantusch, M.; Burkel, E.; Botelho do Rego, A.M.Dielectric properties and spectral dependence of the photocatalytic constant of Co doped P25 Degussa powder were studied. Doping of TiO2 matrix with cobalt was achieved by precipitation method using of Tris(diethylditiocarbamate)Co(III) precursor (CoDtc–Co[(C2H5)2NCS2]3). Five different Co contents with nominal Co/Ti atomic ratios of 0.005, 0.01, 0.02, 0.05 and 0.10 were chosen. Along with TiO2:Co samples, a few samples of nanopowders prepared by Sol-Gel method were also studied. As it follows from XPS and NMR studies, there is a concentration limit (TiO2:0.1Co) where cobalt atoms can be uniformly distributed across the TiO2 matrix before metallic clusters start to form. It was also shown that CoTiO3 phases are formed during annealing at high temperatures. From the temperature dependence of the dielectric constant it can be concluded that the relaxation processes still take place even at temperatures below 400 °C and that oxygen defect Ti–O octahedron reorientation take place at higher temperatures. The spectral dependency of the photocatalytic constant reveals the presence of some electronic states inside the energy gap of TiO2 for all nanopowdered samples.
- ItemVanadium Pentoxide Nanofibers/Carbon Nanotubes Hybrid Film for High-Performance Aqueous Zinc-Ion Batteries(Basel : MDPI, 2021) Liu, Xianyu; Ma, Liwen; Du, Yehong; Lu, Qiongqiong; Yang, Alkai; Wang, YinyuAqueous zinc-ion batteries (ZIBs) with the characteristics of low production costs and good safety have been regarded as ideal candidates for large-scale energy storage applications. However, the nonconductive and non-redox active polymer used as the binder in the traditional preparation of electrodes hinders the exposure of active sites and limits the diffusion of ions, compromising the energy density of the electrode in ZIBs. Herein, we fabricated vanadium pentoxide nanofibers/carbon nanotubes (V2O5/CNTs) hybrid films as binder-free cathodes for ZIBs. High ionic conductivity and electronic conductivity were enabled in the V2O5/CNTs film due to the porous structure of the film and the introduction of carbon nanotubes with high electronic conductivity. As a result, the batteries based on the V2O5/CNTs film exhibited a higher capacity of 390 mAh g−1 at 1 A g−1, as compared to batteries based on V2O5 (263 mAh g−1). Even at 5 A g−1, the battery based on the V2O5/CNTs film maintained a capacity of 250 mAh g−1 after 2000 cycles with a capacity retention of 94%. In addition, the V2O5/CNTs film electrode also showed a high energy/power density (e.g., 67 kW kg−1/267 Wh kg−1). The capacitance response and rapid diffusion coefficient of Zn2+ (~10−8 cm−2 s−1) can explain the excellent rate capability of V2O5/CNTs. The vanadium pentoxide nanofibers/carbon nanotubes hybrid film as binder-free cathodes showed a high capability and a stable cyclability, demonstrating that it is highly promising for large-scale energy storage applications.
- ItemCarbon Nanohorns as Effective Nanotherapeutics in Cancer Therapy(Basel : MDPI, 2021) Curcio, M.; Cirillo, G.; Saletta, F.; Michniewicz, F.; Nicoletta, F.; Vittorio, O.; Hampel, S.; Iemma, F.Different carbon nanostructures have been explored as functional materials for the development of effective nanomaterials in cancer treatment applications. This review mainly aims to discuss the features, either strength or weakness, of carbon nanohorn (CNH), carbon conical horn-shaped nanostructures of sp2 carbon atoms. The interest for these materials arises from their ability to couple the clinically relevant properties of carbon nanomaterials as drug carriers with the negligible toxicity described in vivo. Here, we offer a comprehensive overview of the recent advances in the use of CNH in cancer treatments, underlining the benefits of each functionalization route and approach, as well as the biological performances of either loaded and unloaded materials, while discussing the importance of delivery devices.
- ItemHigh-Pressure-Sintering-Induced Microstructural Engineering for an Ultimate Phonon Scattering of Thermoelectric Half-Heusler Compounds(Weinheim : Wiley-VCH, 2021) He, Ran; Zhu, Taishan; Ying, Pingjun; Chen, Jie; Giebeler, Lars; Kühn, Uta; Grossman, Jeffrey C.; Wang, Yumei; Nielsch, KorneliusThermal management is of vital importance in various modern technologies such as portable electronics, photovoltaics, and thermoelectric devices. Impeding phonon transport remains one of the most challenging tasks for improving the thermoelectric performance of certain materials such as half-Heusler compounds. Herein, a significant reduction of lattice thermal conductivity (κL) is achieved by applying a pressure of ≈1 GPa to sinter a broad range of half-Heusler compounds. Contrasting with the common sintering pressure of less than 100 MPa, the gigapascal-level pressure enables densification at a lower temperature, thus greatly modifying the structural characteristics for an intensified phonon scattering. A maximum κL reduction of ≈83% is realized for HfCoSb from 14 to 2.5 W m−1 K−1 at 300 K with more than 95% relative density. The realized low κL originates from a remarkable grain-size refinement to below 100 nm together with the abundant in-grain defects, as determined by microscopy investigations. This work uncovers the phonon transport properties of half-Heusler compounds under unconventional microstructures, thus showing the potential of high-pressure compaction in advancing the performance of thermoelectric materials.
- ItemInterface-Dominated Topological Transport in Nanograined Bulk Bi2 Te3(Weinheim : Wiley-VCH, 2021) Izadi, Sepideh; Han, Jeong Woo; Salloum, Sarah; Wolff, Ulrike; Schnatmann, Lauritz; Asaithambi, Aswin; Matschy, Sebastian; Schlörb, Heike; Reith, Heiko; Perez, Nicolas; Nielsch, Kornelius; Schulz, Stephan; Mittendorff, Martin; Schierning, Gabi3D topological insulators (TI) host surface carriers with extremely high mobility. However, their transport properties are typically dominated by bulk carriers that outnumber the surface carriers by orders of magnitude. A strategy is herein presented to overcome the problem of bulk carrier domination by using 3D TI nanoparticles, which are compacted by hot pressing to macroscopic nanograined bulk samples. Bi2Te3 nanoparticles well known for their excellent thermoelectric and 3D TI properties serve as the model system. As key enabler for this approach, a specific synthesis is applied that creates nanoparticles with a low level of impurities and surface contamination. The compacted nanograined bulk contains a high number of interfaces and grain boundaries. Here it is shown that these samples exhibit metallic-like electrical transport properties and a distinct weak antilocalization. A downward trend in the electrical resistivity at temperatures below 5 K is attributed to an increase in the coherence length by applying the Hikami–Larkin–Nagaoka model. THz time-domain spectroscopy reveals a dominance of the surface transport at low frequencies with a mobility of above 103 cm2 V−1 s−1 even at room temperature. These findings clearly demonstrate that nanograined bulk Bi2Te3 features surface carrier properties that are of importance for technical applications.
- ItemImperceptible Supercapacitors with High Area-Specific Capacitance(Weinheim : Wiley-VCH, 2021) Ge, Jin; Zhu, Minshen; Eisner, Eric; Yin, Yin; Dong, Haiyun; Karnaushenko, Dmitriy D.; Karnaushenko, Daniil; Zhu, Feng; Ma, Libo; Schmidt, Oliver G.Imperceptible electronics will make next-generation healthcare and biomedical systems thinner, lighter, and more flexible. While other components are thoroughly investigated, imperceptible energy storage devices lag behind because the decrease of thickness impairs the area-specific energy density. Imperceptible supercapacitors with high area-specific capacitance based on reduced graphene oxide/polyaniline (RGO/PANI) composite electrodes and polyvinyl alcohol (PVA)/H2SO4 gel electrolyte are reported. Two strategies to realize a supercapacitor with a total device thickness of 5 µm—including substrate, electrode, and electrolyte—and an area-specific capacitance of 36 mF cm−2 simultaneously are implemented. First, the void volume of the RGO/PANI electrodes through mechanical compression is reduced, which decreases the thickness by 83% while retaining 89% of the capacitance. Second, the PVA-to-H2SO4 mass ratio is decreased to 1:4.5, which improves the ion conductivity by 5000% compared to the commonly used PVA/H2SO4 gel. Both advantages enable a 2 µm-thick gel electrolyte for planar interdigital supercapacitors. The impressive electromechanical stability of the imperceptible supercapacitors by wrinkling the substrate to produce folds with radii of 6 µm or less is demonstrated. The supercapacitors will be meaningful energy storage modules for future self-powered imperceptible electronics.
- ItemImpedimetric Microfluidic Sensor-in-a-Tube for Label-Free Immune Cell Analysis(Weinheim : Wiley-VCH, 2021) Egunov, Aleksandr I.; Dou, Zehua; Karnaushenko, Dmitriy D.; Hebenstreit, Franziska; Kretschmann, Nicole; Akgün, Katja; Ziemssen, Tjalf; Karnaushenko, Daniil; Medina-Sánchez, Mariana; Schmidt, Oliver G.Analytical platforms based on impedance spectroscopy are promising for non-invasive and label-free analysis of single cells as well as of their extracellular matrix, being essential to understand cell function in the presence of certain diseases. Here, an innovative rolled-up impedimetric microfulidic sensor, called sensor-in-a-tube, is introduced for the simultaneous analysis of single human monocytes CD14+ and their extracellular medium upon liposaccharides (LPS)-mediated activation. In particular, rolled-up platinum microelectrodes are integrated within for the static and dynamic (in-flow) detection of cells and their surrounding medium (containing expressed cytokines) over an excitation frequency range from 102 to 5 × 106 Hz. The correspondence between cell activation stages and the electrical properties of the cell surrounding medium have been detected by electrical impedance spectroscopy in dynamic mode without employing electrode surface functionalization or labeling. The designed sensor-in-a-tube platform is shown as a sensitive and reliable tool for precise single cell analysis toward immune-deficient diseases diagnosis.
- ItemSwitching Propulsion Mechanisms of Tubular Catalytic Micromotors(Weinheim : Wiley-VCH, 2021) Wrede, Paul; Medina-Sánchez, Mariana; Fomin, Vladimir M.; Schmidt, Oliver G.Different propulsion mechanisms have been suggested for describing the motion of a variety of chemical micromotors, which have attracted great attention in the last decades due to their high efficiency and thrust force, enabling several applications in the fields of environmental remediation and biomedicine. Bubble-recoil based motion, in particular, has been modeled by three different phenomena: capillary forces, bubble growth, and bubble expulsion. However, these models have been suggested independently based on a single influencing factor (i.e., viscosity), limiting the understanding of the overall micromotor performance. Therefore, the combined effect of medium viscosity, surface tension, and fuel concentration is analyzed on the micromotor swimming ability, and the dominant propulsion mechanisms that describe its motion more accurately are identified. Using statistically relevant experimental data, a holistic theoretical model is proposed for bubble-propelled tubular catalytic micromotors that includes all three above-mentioned phenomena and provides deeper insights into their propulsion physics toward optimized geometries and experimental conditions.