Characterization of Nanomaterials: Selected Papers from 6th Dresden Nanoanalysis Symposiumc

This Special Issue “Characterization of Nanomaterials” collects nine selected papers presented at the 6th Dresden Nanoanalysis Symposium, held at Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, on 31 August 2018. Following the specific motto of this annual symposium “Materials challenges—Micro- and nanoscale characterization”, it covered various topics of nanoscale materials characterization along the whole value and innovation chain, from fundamental research up to industrial applications. The scope of this Special Issue is to provide an overview of the current status, recent developments and research activities in the field of nanoscale materials characterization, with a particular emphasis on future scenarios. Primarily, analytical techniques for the characterization of thin films and nanostructures are discussed, including modeling and simulation. We anticipate that this Special Issue will be accessible to a wide audience, as it explores not only methodical aspects of nanoscale materials characterization, but also materials synthesis, fabrication of devices and applications

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Applications of Reflectometry Towards the Development of MEMS Gas Sensors

Reflectometry or reflectance spectroscopy is a relatively simple characterization technique based on the analysis of reflected light from a surface. Herein, reflectometry is used to attain significant insights towards the development of micro-electro-mechanical systems (MEMS) based gas sensors. Two main reflectometry applications are demonstrated which led to formation of unique MEMS gas sensor devices. The first application was the use of in-situ reflectance spectroscopy to characterize the growth behavior of metal oxide films grown by atmospheric pressure-spatial atomic layer deposition. The technique revealed an initial film nucleation period, where the length of the nucleation time was sensitive to the deposition process parameters. The in-situ reflectometry technique was then used to study and monitor the growth behavior of metal oxide films on various non-conventional surfaces. Doing so allowed for the accurate deposition of zinc oxide films on a variety of surfaces with desired thickness. This was instrumental, as it enabled the integration of the zinc oxide films into a novel MEMS resonant cantilever architecture for gas sensing. In this device, the zinc oxide layer serves as both the cantilever structural layer as well as the gas sensitive receptor layer. A key advantage of the approach was the reduction in overall mass of the cantilever which can lead to an enhancement in sensitivity to low quantities of analyte gases. The sensor had an outstanding sensitivity to low levels of relatively humidity(RH) when compared to other frequency shift-based humidity sensors. The zinc oxide cantilever demonstrated a sensitivity of 23649 ppm⁄%RH at 5.9 % RH and an average sensitivity of 1556 ppm⁄%RH in the range of 30-60% RH. The second application of reflectometry was its use as a screening technique to find suitable gas sensitive receptor materials for static deflection type MEMS gas sensors. The reflectance intensity of various materials exposed to gases, was monitored, where changes in the intensity indicated that the material was physically changing in the presence of the gas. This expansion behavior is ideal for static deflection type MEMS gas sensors such as the nanomechanical membrane type surface stress sensor (MSS) architecture. The reflectance screening technique identified that laser treated two dimension materials such as graphene oxide, molybdenum disulfide and tungsten disulfide were suitable candidates to be integrated as the receptor layer in the MSS platform. The sensing response of the coated devices was obtained for a select group of volatile organic compounds. The results showed that the laser treatment technique was advantageous to enhancing the sensor response and sensitivity, as it introduces defects, dopants and functional groups to the receptor materials for improved gas adsorption

A Tracking Review on Non Arc Melting Processes for Improved Surface Properties in Metallic Materials

Most metallic materials lack the adequate surface characteristics to satisfactorily perform intended service functions. In such instance, the surface properties are modified by altering the chemistry, structure and/topology of the top surface of the surface via modification techniques. There exists wide options of techniques for modifying the surface properties and these are well documented in the literature. However, these techniques have different scientific underpinnings controlling them such that it is difficult to use a single mechanism to characterize the techniques. Arising from this, it is imperative that a holistic understanding of the various processes is provided. Therefore, in this paper, research status on the wide range of non-melting technique for surface modification is presented. The presentation discusses the investigation conducted on the various non-surface melting techniques and provides a comparison across the techniques. Recent developments in these techniques are equally presented. Existing challenges and emerging trends in the field are also highlighted.  . Keywords: coating composition, coating techniques, metallic materials, substrate, surface properties DOI: 10.7176/CMR/13-2-01 Publication date:May 31st 202

Photoconductivity and gas sensing properties of ZnO nanowire devices

ZnO nanowires are excellent candidates as building components for a novel generation of miniaturized electronic circuits, which can be exploited in particular as UV photodetectors and gas sensors. However, the large-scale applicability of ZnO nanowire devices is currently hindered by the limited control over their electrical properties. This thesis addresses in particular three main issues, which are discussed in distinct chapters: 1) the determination of the defect states in such devices and their impact on the below band gap photoconductivity, 2) the origin of the persistent photoconductivity after UV excitation, 3) the impact of doping by ion beam implantation as well as thermal annealing and plasma treatments on the photoconductivity and the detection of hydrogen molecules. 1) The analysis reveals the contribution of interfacial levels located between the nanowire and the gate oxide to the below band gap photoconductivity. Furthermore, in ZnO nanowire based field effect transistors the gate voltage can control the occupation of such defect levels. 2) A quantitative model is proposed, in order to investigate the recombination dynamics of the photogenerated charge carriers. The model is based on the so-called Elovich equation, which describes the adsorption of oxygen molecules on the nanowire surface and the simultaneous trapping of photogenerated electrons. 3) Doping by implantation of aluminum ions induces a drastic enhancement of the persistent photoconductivity, which is caused by the generation of defect levels during the implantation process. Plasma treatments in argon and oxygen atmospheres lead to vanishing hydrogen sensitivity, while thermal annealing in oxygen has a beneficial effect. The optimization of the thermal annealing conditions is also discussed

Assessing the Effect of Twisting and Twisting Fatigue on ZnO:Al Thin Film Performance on PEN and PET Substrates

This study examines the electromechanical characteristics of aluminium-doped zinc oxide (AZO) films. The films were produced using the RF magnetron sputtering process with a consistent thickness of 150 nm on various polymer substrates. The study focuses on assessing the electro-mechanical failure processes of coated segments using flexible substrates, namely polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), with a specific emphasis on typical cracking and delamination occurrences. This examination involves conducting twisting deformation together with using standardised electrical resistance measurements and optical microscope monitoring instruments. It was found that the crack initiation angle is mostly dependent on the mechanical mismatch between the coating and substrate. Higher critical twisting angle values are observed for the AZO/PEN film during twisting testing. Relative to the perpendicular plane of the untwisted sample, it was found that cracks initiated at a twist angle equal to 42° ± 2.1° and 38° ± 1.7° for AZO/PEN and AZO/PET, respectively, and propagated along the sample length. SEM images indicate that the twisting motion results in deformation in the thin film material, leading to the presence of both types of stress in the film structure. These discoveries emphasise the significance of studying the mechanical properties of thin films under different stress conditions, as it can impact their performance and reliability in real-world applications. The electromechanical stability of AZO was found to be similar on both substrates during fatigue testing. Studying the electromechanical properties of various material combinations is important for selecting polymer substrates and predicting the durability of flexible electronic devices made from polyester

Influence of Annealing Temperature on the Mechanical Properties of Sol-Gel ZnO Films

Transparent conducting oxides (TCO\u27s) are widely adopted coatings applied to a wide range of applications including; optoelectronics, touch-screens, smart systems, organic light emitting diodes (OLED\u27s), and solar panel technologies. During both fabrication and service, the mechanical reliability of these coatings, such as wear and scratch resistance, is of great importance. Zinc Oxide (ZnO) coatings have emerged as a highly desirable, and low cost alternative to the commonly adopted Indium Tin Oxide (ITO) since they offer; wide band gap energy (3.34eV), high optical transmission, and are both chemically and thermally stable.;In this work, the mechanical properties of sol-gel ZnO films deposited on soda lime glass substrates via the dip coating method was investigated. The objective of this work is to study the influence of differing annealing temperatures may have on the structural, optical, and mechanical properties of sol-gel ZnO films. For this purpose; x-ray diffraction, nanoindentation, scratch testing, and tribological techniques were utilized in order to gain an understanding of how the sol-gel ZnO films properties are affected as annealing temperature is increased. Structural analysis indicated that all films were polycrystalline with a wurtzite structure and displayed an increase in crystallinity as the annealing temperature was increased. Using nanoindentation it was observed that the Hardness and Young\u27s Modulus increased from 1.79+/-0.57 to 2.68+/-0.87 GPa and 70.19+/-17.89 to 73.72+/-11.84 GPa respectively as a result of increasing annealing temperature. Tribological and scratch testing techniques indicated that the adhesion properties of ZnO films were also improved as a result of increased annealing temperature. On the other hand, optical transmission had been significantly reduced as a result of increasing grain size and coating thickness at higher annealing temperatures

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

Al-doped ZnO ceramic sputtering targets based on nanocrystalline powders produced by emulsion detonation synthesis – deposition and application as a transparent conductive oxide material

Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics. The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices. The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 × 10-4 Ωcm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties. In parallel, the influence of several deposition parameters in the film´s properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO – indium tin oxide (ITO), namely low electrical resistivity of 5.45 × 10-4 Ωcm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 × 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices