Rainer Adelung

Rapid Fabrication Technique for Interpenetrated ZnO Nanotetrapod Networks for Fast UV Sensors

Two flame-based synthesis methods are presented for fabricating ZnO-nanostructure-based UV photodetectors: burner flame transport synthesis (B-FTS)and crucible flame transport synthesis (C-FTS). B-FTS allows rapid growth of ZnO nanotetrapods and in situ bridging of them into electrical contacts. The photo detector made from interconnected ZnO nanotetrapod networks exhibits fast response/recovery times and a high current ratio under UV illumination.

Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with Outstanding Mechanical Performance

An ultra lightweight carbon microtube material called Aerographite is synthesized by a novel single-step chemical vapor deposition synthesis based on ZnO networks, which is presently the lightest known material with a density smaller than μg/cm(3). Despite its low density, the hierarchical design leads to remarkable mechanical, electrical, and optical properties. The first experiments with Aerographite electrodes confirm its applicability.

Sharper images by focusing soft X-rays with photon sieves.

Fresnel zone plates consisting of alternating transmissive and opaque circular rings can be used to focus X-rays. The spatial resolution that can be achieved with these devices is of the order of the width of the outermost zone and is therefore limited by the smallest structure (20–40 nm) that can be fabricated by lithography today. Here we show that a large number of pinholes distributed appropriately over the Fresnel zones make it possible to focus soft X-rays to spot sizes smaller than the diameter of the smallest pinhole. In addition, higher orders of diffraction and secondary maxima can be suppressed by several orders of magnitude. In combination with the next generation of synchrotron light sources (free-electron lasers) these ‘photon sieves’ offer new opportunities for high-resolution X-ray microscopy and spectroscopy in physical and life sciences.

Direct Growth of Freestanding ZnO Tetrapod Networks for Multifunctional Applications in Photocatalysis, UV Photodetection, and Gas Sensing

Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide tetrapods (ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO tetrapod structure are presented. The involved growth mechanism for ZnO tetrapods with various arm morphologies is discussed with respect to variations in experimental conditions. These ZnO-T have been utilized for photocatalytic degradation and nanosensing applications. The photocatalytic activities of these ZnO-T with different arm morphologies forming networks have been investigated through the photocatalytic decolorization of a methylene blue (MB) solution under UV light illumination at ambient temperature. The results show that these ZnO-T exhibit strong photocatalytic activities against MB and its complete degradation can be achieved in very short time. In another application, a prototype of nanoelectronic sensing device has been built from these ZnO-T interconnected networks and accordingly utilized for UV detection and H2 gas sensing. The fabricated device structures showed excellent sensing behaviors for promising practical applications. The involved sensing mechanisms with respect to UV photons and H2 gas are discussed in detail. We consider that such multifunctional nanodevices based on ZnO tetrapod interconnected networks will be of interest for various advanced applications.

A Novel Concept for Self‐Reporting Materials: Stress Sensitive Photoluminescence in ZnO Tetrapod Filled Elastomers

Early detection of failure development in materials is an important requirement for the prevention of catastrophic losses. A new class of materials in which the internal damages can be detected by non-destructive methods, is called ‘‘self-reporting” materials. [ 1 ] Materials exhibiting both self-reporting and loadbearing properties would be benefi cial for several important applications, e.g., in wind mills, automobile and aerospace industries. [ 2 ] Polymer composites with multi-functional characteristics are often the material of choice. [ 3 ] On demand, they can be designed to achieve light-weight, mechanically robust, abrasive-resistant and still the least expensive materials. [ 4 ] Such materials have been widely used in diverse fi elds from dental implants to spacecrafts. [ 5 ] These special functionalities of polymer composites are generally determined by the size and the type of fi ller materials used. ZnO has gained much interest due to its functional properties such as the wide band gap, piezoelectric property, radiation resistance, biocompatibility, the variety of morphology in microand nanostructures and thus many promising applications. [ 6 ]

Single step integration of ZnO nano- and microneedles in Si trenches by novel flame transport approach: whispering gallery modes and photocatalytic properties.

Direct growth of quasi-one-dimensional nano- and microstructures in desired places of complex shaped substrates using simple growth methods is highly demanded aspect for various applications. In this work, we have demonstrated direct integration of ZnO nano- and microneedles into Si trenches by a novel flame transport synthesis approach in a single fabrication step. Growth of partially and fully covered or filled trenches in Si substrate with ZnO nano- and microneedles has been investigated and is discussed here. Detailed microstructural studies revealed the evolution of the ZnO nano- and microneedles as well as their firm adhesion to the wall in the Si trenches. Micro-photoluminescence measurements at different locations along the length of needles confirmed the good crystalline quality and also the presence of whispering gallery mode resonances on the top of needles due to their hexagonal shape. Faceted ZnO nano- and microstructures are also very important candidates with regard to photocatalytic activity. First, photocatalytic measurements from the grown ZnO nano- and microneedles have shown strong degradation of methylene blue, which demonstrate that these structures can be of significant interest for photocatalysis and self-cleaning chromatography columns.

Virostatic potential of micro–nano filopodia-like ZnO structures against herpes simplex virus-1

Herpes simplex virus type-1 (HSV-1) entry into target cell is initiated by the ionic interactions between positively charged viral envelop glycoproteins and a negatively charged cell surface heparan sulfate (HS). This first step involves the induction of HS-rich filopodia-like structures on the cell surface that facilitate viral transport during cell entry. Targeting this initial first step in HSV-1 pathogenesis, we generated different zinc oxide (ZnO) micro-nano structures (MNSs) that were capped with multiple nanoscopic spikes mimicking cell induced filopodia. These MNSs were predicted to target the virus to compete for its binding to cellular HS through their partially negatively charged oxygen vacancies on their nanoscopic spikes, to affect viral entry and subsequent spread. Our results demonstrate that the partially negatively charged ZnO-MNSs efficiently trap the virions via a novel virostatic mechanism rendering them unable to enter into human corneal fibroblasts - a natural target cell for HSV-1 infection. The anti-HSV-1 activity of ZnO MNSs was drastically enhanced after creating additional oxygen vacancies under UV-light illumination. Our results provide a novel insight into the significance of ZnO MNSs as the potent HSV-1 inhibitor and rationalize their development as a novel topical agent for the prevention of HSV-1 infection.

Crystal growth behaviour in Au-ZnO nanocomposite under different annealing environments and photoswitchability

The growth of gold nanoparticles and ZnO nanorods in atom beam co-sputtered Au-ZnO nanocomposite (NC) system by annealing at two different ambient conditions is demonstrated in this work. Annealing in a furnace at 600 °C (air environment) confirmed the formation of ZnO nanorods surrounded with Au nanoparticles. In-situ annealing inside a transmission electron microscope (TEM) led to the formation of gold nanocrystals with different polygonal shapes. TEM micrographs were obtained in real time at intermediate temperatures of 300 °C, 420 °C, and 600 °C under vacuum. The growth mechanisms of Au nanocrystals and ZnO nanorods are discussed in the framework of Au-Zn eutectic and Zn-melting temperatures in vacuum and air, respectively. Current-voltage responses of Au-ZnO NC nanorods in dark as well as under light illumination have been investigated and photoswitching in Au-ZnO NC system is reported. The photoswitching has been discussed in terms of Au-ZnO band-diagram.

Prophylactic, therapeutic and neutralizing effects of zinc oxide tetrapod structures against herpes simplex virus type-2 infection

The attachment of Herpes simplex virus type-2 (HSV-2) to a target cell requires ionic interactions between negatively charged cell surface co-receptor heparan sulfate (HS) and positively charged residues on viral envelop glycoproteins, gB and gC. Effective blocking of this first step of HSV-2 pathogenesis demonstrates significant prophylactic effects against the viral disease; any in vitro therapeutic effects of blocking this interaction, however, are not clear. Here, we provide new evidence that zinc oxide tetrapod micro-nanostructures synthesized by flame transport approach significantly block HSV-2 entry into target cells and, in addition, demonstrate the potential to stop the spread of the virus among already infected cells. The zinc oxide tetrapods (ZnOTs) also exhibit the ability to neutralize HSV-2 virions. Natural target cells such as human vaginal epithelial and HeLa cells showed highly reduced infectivity when infected with HSV-2 virions that were pre-incubated with the ZnOTs. The mechanism behind the ability of ZnOTs to prevent, neutralize or reduce HSV-2 infection relies on their ability to bind the HSV-2 virions. We used fluorescently labeled ZnOTs and GFP-expressing HSV-2 virions to demonstrate the binding of the ZnOTs with HSV-2. We also show that the binding and hence, the antiviral effects of ZnOTs can be enhanced by illuminating the ZnOTs with UV light. Our results provide new insights into the anti-HSV-2 effects of ZnOT and rationalize their development as a HSV-2 trapping agent for the prevention and/or treatment of infection. The observed results also demonstrate that blocking HSV-2 attachment can have prophylactic as well as therapeutic applications.

Joining the Un‐Joinable: Adhesion Between Low Surface Energy Polymers Using Tetrapodal ZnO Linkers

Tetrapodal ZnO crystals are used for mechanical interlocking of PTFE and cross-linked PDMS, classically non-adhesive polymers. This novel approach is straightforward and easily applicable and leads to a peel strength that is higher than 200 N m(-1) without chemical modification of the surfaces. The shape of these fillers emerged as a crucial aspect of the interlocking mechanism.