Method to reduce the formation of crystallites in ZnO nanorod thin-films grown via ultra-fast microwave heating

© 2018 This paper discusses the nucleation and growth mechanisms of ZnO nanorod thin-films and larger sized crystallites that form within the solution and on surfaces during an ultra-fast microwave heating growth process. In particular, the work focusses on the elimination of crystallites as this is necessary to improve thin-film uniformity and to prevent electrical short circuits between electrodes in device applications. High microwave power during the early stages of ZnO deposition was found to be a key factor in the formation of unwanted crystallites on substrate surfaces. Once formed, the crystallites, grow at a much faster rate than the nanorods and quickly dominate the thin-film structure. A new two-step microwave heating method was developed that eliminates the onset of crystallite formation, allowing the deposition of large-area nanorod thin-films that are free from crystallites. A dissolution-recrystallization mechanism is proposed to explain why this procedure is successful and we demonstrate the importance of the work in the fabrication of low-cost memristor devices

Where Do New Materials Come From? Neither the Stork nor the Birds and the Bees! In Search of the Next “First Material”

Materials discovery and optimization has driven the rapid technological advancements that have been observed in our lifetimes. For this advancement to continue, solid-state chemists must continue to develop new materials. Where do these new materials come from? In this review, we discuss the approaches used by the zur Loye group to discover the next “First Material”, a new material exhibiting a desired or not previously observed property that can be optimized for use in the technologies of tomorrow. Specifically, we discuss several crystal growth techniques that we have used with great success to synthesize new materials: the flux growth method, the hydroflux method, and the mild-hydrothermal method

Improved Interyarn Friction, Impact Response, and Stab Resistance of Surface Fibrilized Aramid Fabric

Improvement of the ballistic performance of aramid fabric is an important topic in the study of soft body armors, especially with their increasing use in such applications over the past decades. To enhance and tailor the performance of fabrics, having control over one of its primary energy absorption mechanisms, interyarn friction, is required. Here, a recently reported surface fibrilization method is exploited and optimized to improve interyarn friction in aramid fabrics. Through tow pullout testing of fibrilized fabrics, the fibrilization treatment is shown to provide up to seven times higher pullout energy and six times higher peak load. To correlate the effects of the treatment on the ballistic response, impact tests are conducted on treated fabric targets using a gas gun setup. The fibrilized fabrics displayed a 10 m s‐1 increase in V50 velocity, compared to that of untreated fabrics, while retaining its original flexibility and mechanical strength. Similarly, the fibrilization treatment also resulted in 230% improvement in depth of penetration when dynamically stabbed using a spike impactor. The results demonstrate the potential of the proposed surface fibrilization treatment as a fast and cost‐effective technique to improve the ballistic and stab performance of aramid‐based soft body armors.This work shows improved interyarn, ballistic, and stab resistance properties in aramid fabric through a basic fibrilization treatment. The treated aramid fabrics display a maximum improvement of 665% in yarn pullout energy, a 10 m s−1 increase in V50 velocity, and 230% higher stab impact resistance, while maintaining its original tensile properties.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151907/1/admi201900881.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151907/2/admi201900881_am.pd

Nanowires on a Film for Photoelectrochemical Water Splitting

International audienc

Laser-assisted synthesis and optical properties of bismuth nanorods

Bismuth in the bulk form is a semimetal with a rhombohedral structure. It has a small band overlap between the conduction and valence bands and a highly anisotropic electron effective-mass tensor. Thermoelectric materials, in which one of the three dimensions is in the nanometer regime, exhibit unique quantum confinement properties and have generated much interest in recent years. Theoretical investigations have suggested that nanowires with diameters \u3c10 nm will possess a figure-of-merit ZT\u3e2. Prior to this research, it has been shown by the Dresselhaus group at MIT that Bi nanowires with small enough diameters (~50 nm), prepared via the template-method, undergo a transition from a semimetal with a small band overlap to a semiconductor with a small indirect band gap. Infrared absorption, temperature-dependent electrical resistance and magneto-resistance measurements were used to confirm this semimetal-to-semiconductor phase transition. In this thesis, we report the synthesis of ~10 nm diameter Bi nanorods using a pulsed laser vaporization method that was previously developed for preparing single-wall carbon nanotubes. The high resolution transmission electron microscopy images of our Bi nanorods show a crystalline Bi core oriented along \u3c012\u3e direction, and coated with a thin amorphous bismuth oxide layer. The infrared absorption and the surface plasmon peaks in our Bi nanorods are blue-shifted in energy when compared to the corresponding spectra in bulk Bi, and relative to those reported by the Dresselhaus group in 45 - 200 nm diameter Bi nanowires

Mechanical and Electrical Characterization of Carbon Fiber/Bucky Paper/Zinc Oxide Hybrid Composites

The quest for multifunctional carbon fiber reinforced composites (CFRPs) expedited the use of several nano reinforcements such as zinc oxide nanorods (ZnO) and carbon nanotubes (CNTs). Zinc oxide is a semi-conductor with good piezoelectric and pyroelectric properties. These properties could be transmitted to CFRPs when a nanophase of ZnO is embedded within CFRPs. In lieu of ZnO nanorods, Bucky paper comprising mat of CNTs could be sandwiched in-between composite laminae to construct a functionally graded composite with enhanced electrical conductivities. In this study, different configurations of hybrid composites based on carbon fibers with different combinations of ZnO nanorods and Bucky paper were fabricated. The composites were tested mechanically via tensile and dynamic mechanical analysis (DMA) tests to examine the effect of the different nanoadditives on the stiffness, strength and the damping performance of the hybrid composites. Electrical resistivities of the hybrid composites were probed to examine the contributions of the different nanoadditives. The results suggest that there are certain hybrid composite combinations that could lead to the development of highly multifunctional composites with better strength, stiffness, damping and electrical conductivity

Review: Biosensors for the detection of Escherichia coli

The supply of safe potable water, free from pathogens and chemicals, requires routine  analyses and the application of several diagnostic techniques. Apart from being  expensive, many of the detection methods require trained personnel and are often time-consuming. With drastic climate changes, severe droughts, increases in  population and pollution of natural water systems, the need to develop ultrasensitive, low-cost and hand-held, point-of-use detection kits to monitor water quality is critical. Although Escherichia coli is still considered the best indicator of water quality, cell numbers may be below detection limits, or the cells may be non-culturable and thus only detected by DNA amplification. A number of different biosensors have been developed to detect viable, dead or non-culturable microbial cells and chemicals in water. This review discusses the differences in these biosensors and evaluates the application of microfluidics in the design of ultra-sensitive nano-biosensors.Keywords: Biosensors, microfluidics, nano-biosensors, E. coli detectio

Facile synthesis and electrical characteristics of n-SnO2/p-NiO nanowire heterojunctions

In the current work, we report a facile synthesis of n-SnO2/p-NiO nanowire heterojunctions by a drop-coating approach. The pure SnO2 and NiO nanowires (NWs) were grown by chemical vapor deposition (CVD) and hydrothermal methods, respectively. Morphology, composition and crystal structures of the NWs and heterojunctions were investigated by means of field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The data showed that SnO2 NWs were grown with their average diameter of 200 nm and length of about 10 mm. The NiO NWs were also synthesized with a shorter average length and smaller average diameter compared to those of the SnO2 NWs. The EDS results indicated no impurity present in both SnO2 and NiO NWs. The XRD patterns pointed out the tetragonal rutile and cubic structures of SnO2 and NiO, respectively. Interestingly, electrical properties of the NWs and heterojunctions were studied through the Keithley 2602A sourcemeter-based I-V characterizations. The results confirm the nature of the metal semiconducting oxides. The formation of the n-SnO2/p-NiO heterojunctions was certified through the rectifying behavior of the I-V curves with the rectification ratio of about 5 at ± 3V and 350 oC. The potential energy barrier between the NWs was also estimated to be about 1.16 eV. The band energy structure was also proposed to get insight into characteristics of the n-SnO2/p-NiO heterojunction