ABSTRACT
Crackling noise is a scale-invariant phenomenon found in various driven nonlinear dynamical material systems as a response to external stimuli such as force or external fields. Jerky material movements in the form of avalanches can span many orders of magnitude in size and follow universal scaling rules described by power laws. The concept was originally studied as Barkhausen noise in magnetic materials and now is used in diverse fields from earthquake research and building materials monitoring to fundamental research involving phase transitions and neural networks. Here, we demonstrate a method for nanoscale crackling noise measurements based on AFM nanoindentation, where the AFM probe can be used to study the crackling of individual nanoscale features, a technique we call crackling noise microscopy. The method is successfully applied to investigate the crackling of individual topological defects, i.e. ferroelectric domain walls. We show that critical exponents for avalanches are altered at these nanoscale features, leading to a suppression of mixed-criticality, which is otherwise present in domains. The presented concept opens the possibility of investigating the crackling of individual nanoscale features in a wide range of material systems.
ABSTRACT
Over millions of years, nature has created complex hierarchical structures with exceptional mechanical properties. The nacre of various seashells is an example of such structures, which is formed out of a mainly inorganic mineral with organic material inclusions in a layered arrangement. Due to its high impact-resisting mechanical properties, these structures have been widely investigated and mimicked in artificial nacre-type composite materials. The artificial creation of nacre analogues for future applications requires an accurate understanding of their mechanical properties on the length scale of the nanoscale composite components. Here, we present an in-depth AFM study of the mechanical properties of Paua nacre (Haliotis iris, 'rainbow abalone') and quantify the elastic modulus as well as related energy scales of both its main nanoscale constituents. We use AFM-based nano-indentation compared to standard micro/nano-indentation, which enables the direct determination of the mechanical properties of the biopolymer layer in nacre, including plastic and elastic energies during indentation. By combining three different AFM-based mechanical characterization methods we affirm the quantitativeness of our mechanical measurements and show that the organic layers have about half the elastic modulus of the inorganic aragonite regions. The obtained results reveal the detailed mechanical properties of the hierarchical structure of nacre and provide a strategy for accurately testing nanoscale mechanical properties of advanced composite materials.
ABSTRACT
We showed well-aligned zinc oxide (ZnO) nanorod arrays synthesized using hydrothermal method at atmospheric pressure. The influence of fabrication conditions such as Zn2+/hexamethylentriamin concentration ratio, and growth temperature on the formation of ZnO nanorods was investigated. Scanning Electron Microscope (SEM) images and X-ray Diffraction (XRD) analysis were used to confirm the single crystal of ZnO nanorods, which showed wurtzite structure with growth direction of [0001] (the c-axis). Photoluminescence (PL) measurements of ZnO nanorods revealed an intense ultraviolet peak at 388.5 nm (3.19 eV) at room temperature. The results showed that the ZnO seed layers had strong influence on the growth of vertically aligned ZnO nanorods. The gas sensor based on ZnO nanorod arrays had the most selectivity with n-butanol gas (within 2 surveyed gas: ethanol and n-butanol) and showed a higher sensitivity of 222, fast response time of 15 seconds, recovery time of 110 seconds and lower operating temperature of 200-250 °C than the sensor based on the ZnO film in the same detecting conditions.
