11 research outputs found
Formkontrollierte Herstellung von mikro-/nanostrukturierten Kupfer- und Eisenverbindungen sowie Anwendungsbeispiele
No full textDas Verständnis von Nanostrukturen verschiedener Formen und Materialzusammensetzungen spielt in der heutigen Zeit insbesondere hinsichtlich der vielfältigen technologischen Applikationsmöglichkeiten eine wichtige Rolle [1]. Hierbei ist nicht nur deren Oberflächen-Volumen-Verhältnis entscheidend, sondern auch die Material- sowie Formbeständigkeit während der jeweiligen Anwendung [2].
In der vorliegenden Arbeit werden Möglichkeiten zur Herstellung von Mikro /Nanostrukturen verschiedener Größen und Formen vorgestellt. Der Fokus liegt im ersten Teil auf der Synthese von Draht- und Röhrenstrukturen durch chemische Abscheideverfahren in ionenspurgeätzten Polymer-Membranen als Templat mit hohen Längen-zu-Durchmesser-Aspektverhältnissen bis zu 469:1. Sie finden Verwendung als formgebende Schablonen zum Erhalt von eindimensionalen Nanostrukturen mit verschiedenen Längen und Durchmessern.
Die Synthese solcher Strukturen wird durch vier verschiedene Abscheideverfahren, wie im ersten Abschnitt der vorliegenden Arbeit beschrieben, gewährleistet. Es wird ein Vergleich bezüglich der Reproduzierbarkeit und der Bandbreite an Möglichkeiten im Falle der hohlzylindrischen Formen durchgeführt.
Die Synthese wird durch die elektrochemische und stromlose Abscheidung von Kupfer-Nanoröhren möglich. Die Herstellung von Kuprit-Röhren gelingt durch eine substratkatalysierte stromlose Abscheidung, wobei in dieser Arbeit unter Betrachtung von relevanten Reaktionsparametern der Herstellungsweg zum Erhalt von homogenen Wandstärken genau evaluiert wird. Eine weitere vorgestellte Synthesemethode ist die Herstellung von Lepidocrocit (ɣ-FeOOH)-Nanoröhren durch Partikelaggregation. Hier werden in einem Zwischenschritt Nano-Partikel in wässriger Lösung durch eine Fällungsreaktion hergestellt und anschließend durch das Deponieren auf der Porenoberfläche der ionenspurgeätzten Membran in eine eindimensionale Form gebracht.
Im zweiten Teil der vorliegenden Arbeit sind Herstellungsverfahren zum Erhalt von kupferoxidischen Verbindungen durch Fällungsreaktionen in wässriger Lösung beschrieben. Dabei wird zunächst die aus der Literatur bekannte Fehling-Probe für die Herstellung von Kuprit-Partikeln angewandt. Durch das Verändern der Konzentrationsverhältnisse der Ausgangsmaterialien entstehen in Abhängigkeit der Reaktionszeit verschiedene Partikel-Formen. Es wird die reproduzierbare Synthese von Polyeder-Gebilden und Skelett-Strukturen diskutiert.
Beide Kuprit-Formen werden auf ihre elektrochemische Aktivität gegenüber der Glucose-Oxidation getestet. Der Fokus liegt auf der Bestimmung der Sensitivität und der Selektivität durch Vergleich des elektrochemischen Ansprechvermögens gegenüber Harnsäure, Fruktose und Ascorbinsäure.
Ein weiteres Herstellungsverfahren von kupferoxidischen Verbindungen in der Oxidationsstufe +1 und +2 wird im letzten Kapitel der vorliegenden Arbeit durch ein Zwei-Stufen-Verfahren beschrieben, welches sowohl die Synthese von Kuprit-Mikrostrukturen mit nanoporöser Oberfläche als auch Kupfermonoxid-Gebilde in Form von gebündelten Nadeln ermöglicht.
Die gebündelten Kupfermonoxid-Nanonadeln werden anschließend auf ihre Eignung als Elektrodenmaterial in Lithium-Ionen-Batterien bei Anwendung zweier verschiedener Bindemittel getestet. Die hierbei angewandten Methoden schließen Zyklentests und Zyklovoltammetrie-Messungen ein
Uniaxial magnetization reversal process in electrodeposited high-density iron nanowire arrays with ultra-large aspect ratio
No full textIn this study, magnetization reversal modes of iron nanowire arrays with large aspect ratios were investigated by Shtrikman's micromagnetic theory. The iron nanowire arrays were potentiostatically electrodeposited into anodized aluminum oxide nanochannels with average diameters, Dp, of ca. 33 nm, 52 nm, 67 nm, and 85 nm. The growth rate of the iron nanowires was ca. 105 nm s−1 at the cathode potential of −1.2 V (vs. an Ag/AgCl reference), and the axial length, Lw, reached up to ca. 60 µm. Maximum aspect ratio, Lw/Dw of the iron nanowires was found to be ca. 1800, and the axial direction coincided with 〈1 1 0〉 direction of the bcc-Fe crystal structure. The effect of the average diameter size on the coercivity of iron nanowire arrays corresponded well to the theoretical estimate, which was calculated by the magnetization curling mode in Shtrikman's micromagnetic theory. As the average diameter of the iron nanowires was decreased, coercivity and squareness of the nanowire arrays increased up to 1.63 kOe and 0.87, respectively
Preparation of multilayered nanowires with well-defined segments of constant lengths in ion track etched polymer templates
No full textCopper Nanowires, Nanotubes, and Hierarchical Nanopatterns: One-Dimensional Architectures using Ion Track Etched Templates
No full text4-(Dimethylamino)pyridine as a Powerful Auxiliary Reagent in the Electroless Synthesis of Gold Nanotubes
No full textGold nanotubes of small particle sizes down to 5 nm and high aspect ratios were synthesized in ion track etched polycarbonate following a rational reaction design. 4-(Dimethylamino)pyridine (DMAP) was employed to adjust the electroless deposition by interfering with the autocatalytically active gold surface. Modification of the pH value and DMAP concentration led to a wide range of products which were characterized by SEM, TEM, and EDS. Filigree nanotubes of 10-15 nm wall thickness and 5.0 ± 2.1 nm grain size were obtained as well as robust and free-standing structures proving homogeneous deposition along the whole template length of 30 μm. Template-supported gold nanotubes were applied in the UV-vis monitored reduction of 4-nitrophenol by sodium borohydride under pseudo-first-order conditions. They proved to be a reliable microfluidic system of excellent catalytic activity coming up with an apparent rate constant of 1.3 x 10E-2 s-1. Despite a high flow rate, the reaction showed 99% conversion after a distance of just 60 µm
Impact of Specifically Adsorbing Anions on the Electroless Growth of Gold Nanotubes
No full textElectroless metal deposition on nanochannel-containing templates is a versatile route towards metal nanotubes and nanowires if the plating reaction can be sufficiently controlled. In this study, disulfitoaurate-formaldehyde-based gold plating baths were modified by the addition of halides, pseudohalides, and EDTA. The introduction of specifically adsorbing anions strongly affected the heterogeneously autocatalyzed plating reaction and allowed the regulation of the reaction rate and the product morphology. The new plating baths showed enhanced stability and allowed the synthesis of homogeneous nanotubes of high aspect ratios (>150) in 30 μm thick ion track-etched polymer templates. Depending on the reaction conditions, solid and porous structures consisting of gold nanoparticles of differing size and shape were accessible. The presented strategy offers adapted gold thin films, nanotubes, and nanowires for applications in catalysis or sensing
Impact of Specifically Adsorbing Anions on the Electroless Growth of Gold Nanotubes
No full textElectroless metal deposition on nanochannel-containing templates is a versatile route towards metal nanotubes and nanowires if the plating reaction can be sufficiently controlled. In this study, disulfitoaurate-formaldehyde-based gold plating baths were modified by the addition of halides, pseudohalides, and EDTA. The introduction of specifically adsorbing anions strongly affected the heterogeneously autocatalyzed plating reaction and allowed the regulation of the reaction rate and the product morphology. The new plating baths showed enhanced stability and allowed the synthesis of homogeneous nanotubes of high aspect ratios (>150) in 30 μm thick ion track-etched polymer templates. Depending on the reaction conditions, solid and porous structures consisting of gold nanoparticles of differing size and shape were accessible. The presented strategy offers adapted gold thin films, nanotubes, and nanowires for applications in catalysis or sensing
Superconducting Proximity Effect in Crystalline Co and Cu Nanowires
No full textSuperconducting proximity effect is investigated by electrical resistance measurements in individual single-crystal Cu and polycrystalline Co nanowires in contact with a W-based floating inducer electrode (Tc= 5.2 K). Our analysis of the resistance drops shows that in both nanowires,(i)the superconducting proximity length
ξ is of the order of 1μm at 2.4 K and (ii) its temperature dependencies can be fitted well to an expression of the form ξ(T)∝√
1/Tin a wide temperature range, in good agreement with the theoretical predictions for ξ(T )in the diffusive limit. For the Co
nanowire, dependencies of the spin-triplet ξ upon current
and magnetic field are also reporte
Proximity-induced superconductivity in crystalline Cu and Co nanowires and nanogranular Co structures
No full textWe report an experimental study of proximity effect-induced superconductivity in crystalline Cu and Co nanowires and a nanogranular Co nanowire structure in contact with a superconducting W-based floating electrode (inducer). For electrical resistance measurements up to three pairs of Pt-based voltage leads were attached at different distances beside the inner inducer electrode, thus allowing us to probe the proximity effect over a length of 2-12 µm. Up to 30% resistance drops with respect to the normal-state value have been observed for the crystalline Co and Cu nanowires when sweeping the temperature below Tc of the inducer (5.2 K). By contrast, relative R(T) drops were found to be an order of magnitude smaller for the nanogranular Co nanowire structure. Our analysis of the resistance data shows that the superconducting proximity length in crystalline Cu and Co is about 1 µm at 2.4 K, attesting to a long-range proximity effect in the Co nanowire. Moreover, this long-range proximity effect is insusceptible to magnetic fields up to 11 T, which is indicative of spin-triplet pairing. At the same time, proximity-induced superconductivity in the nanogranular Co nanowire is strongly suppressed due to the dominating Cooper pair scattering caused by its intrinsic microstructure
Facile wet-chemical synthesis of differently shaped cuprous oxide particles and a thin film: Effect of catalyst morphology on the glucose sensing performance
No full textAbstract In this work, different facile synthesis routes were developed to create cuprite-based catalyst systems for the amperometric detection of glucose, allowing us to evaluate the impact of important electrode fabrication parameters on the glucose sensing performance. Using homogenous precipitation routes based on a redox system, two differently shaped cuprite particles - skeletons and polyhedrons - could be obtained. Furthermore, a novel electroless deposition technique was introduced that does not require sensitization and activation pretreatments, allowing for the direct modification of the glassy carbon. This technique produced electrodes with dense thin film consisting of merged, octahedral cuprite crystals. Afterward, these materials were tested as potential catalysts for the electrochemical detection of glucose. While the catalyst powders obtained by precipitation required Nafion® to be attached to the electrode, the thin film synthesized using electroless plating could be realized with and without additive. Summarizing the results, it was found that Nafion® was not required to achieve glucose selectivities typically observed for cuprite catalysts. Also, the type of catalyst application (direct plating vs. ink drop coating) and the particle shape had a pronounced effect on the sensing performance. Compared to the thin film, the powder-type materials showed significantly increased electrochemical responses. The best overall performance was achieved with the polyhedral cuprite particles, resulting in a high sensitivity of 301 μA mmol-1 cm-2, a linear range up to 298 μmol L-1 and a limit of detection of 0.144 μmol L-1
