C. Lu

Microstructure of epitaxial La0.7Ca0.3MnO3 thin films grown on LaAlO3 and SrTiO3

Epitaxial La0.7Ca0.3MnO3 (LCMO) thin films of a thickness ∼170 nm were grown on (001) LaAlO3 (LAO) and (001) SrTiO3 (STO) substrates by pulsed laser deposition. Transmission electron microscopy and associated techniques have been applied to investigate the microstructures introduced by lattice mismatch that are responsible for the observed differences in properties between these two films. Numerous secondary phase rods were observed in both films. For the LCMO/LAO film, Ca-deficient secondary-phase rods originated in the film after a thickness of about 25 nm and were found to be responsible for relieving in-plane compressive stress during the island growth. In the case of STO substrate, however, almost all of secondary-phase rods initiated at the film–substrate interface. The lattice mismatch between LCMO and STO is relaxed into regions of good coherent fit separated by such secondary phases, possibly resulting from interfacial reaction. The two types of substrates lead to the formation of two different c...

Tribotronic Transistor Array as an Active Tactile Sensing System

Large-scale tactile sensor arrays are of great importance in flexible electronics, human-robot interaction, and medical monitoring. In this paper, a flexible 10 × 10 tribotronic transistor array (TTA) is developed as an active tactile sensing system by incorporating field-effect transistor units and triboelectric nanogenerators into a polyimide substrate. The drain-source current of each tribotronic transistor can be individually modulated by the corresponding external contact, which has induced a local electrostatic potential to act as the conventional gate voltage. By scaling down the pixel size from 5 × 5 to 0.5 × 0.5 mm2, the sensitivities of single pixels are systematically investigated. The pixels of the TTA show excellent durability, independence, and synchronicity, which are suitable for applications in real-time tactile sensing, motion monitoring, and spatial mapping. The integrated tribotronics provides an unconventional route to realize an active tactile sensing system, with prospective applications in wearable electronics, human-machine interfaces, fingerprint identification, and so on.

180° domain structure and its evolution in Ca0.28Ba0.72Nb2O6 ferroelectric single crystals of tungsten bronzes structure

Ferroelectric domain structure and its evolution in uniaxial relaxor Ca0.28Ba0.72Nb2O6 single crystals were investigated using transmission electron microscopy. It was found that there exists a high density of 180° domain walls in the crystals. The domains appear predominantly spike shaped along the polar axis and have a typical diameter of 50–500nm. Domain wall motion was occasionally induced by electron beam irradiation. Macrodomains-to-microdomains switching has been observed corresponding to the normal-to-relaxor ferroelectrics transition during an in situ heating experiments. At temperature just below ferroelectric phase transition temperature TC, zero-field-cooled needlelike nanodomains were also observed.

Effect of grain boundary on local surface conductivity of diamond film

In this article, the direct experimental evidences to determine the effect of grain boundary on local surface conductivity (SC) of diamond films were provided by the measurement using double probe scanning electron microscopy (SEM) technology. Undoped diamond films with (001) orientation were first grown by microwave plasma enhanced chemical vapor deposition and were then hydrogenated at different conditions for SC measurement. In the SEM system, double probes with tiny tip radius severed as two leads were moved along and contacted with the diamond film surface to directly test the local SC of diamond film. The surface electrical property results indicate that for the same distance between the two probes, the local SC of the area across grain boundary is much higher than that of area without grain boundary for the same duration of hydrogenation degrees. In addition, local SC of the area between the two probes increases with the number of grain boundaries in this area, which demonstrates that the grain bou...

Layered microdomains and columnar grains in epitaxial La0.7Ca0.3MnO3 films and Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3 multilayers

Epitaxial La0.7Ca0.3MnO3 thin film and [Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3](10) multilayers of about 140 nm in thickness were grown by pulsed laser deposition on (001)LaAlO3. Their microstructures were investigated by transmission electron microscopy and associated techniques. It was found that both the film and the multilayers contain an almost defect-free layer near the substrate, followed by columnar grain grown. The columns were separated by strained regions in the top layer. No interfacial dislocations were observed at either of the La0.7Ca0.3MnO3/LaAlO3 or the Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3 interfaces. Interestingly, both the epitaxial film and the multilayers exhibited layered crystallographic domains. The formation mechanisms of the layered domain structures observed are discussed.

Characteristics of triboelectrification on dielectric surfaces contacted with a liquid metal in different gases

Triboelectric nanogenerators attract more and more research attention, for their high efficiency, low fabrication cost, and high flexibility. However, the mechanism about triboelectrification remains highly debated. In this work, we constructed a liquid-metal based triboelectric nanogenerator (LM-TENG) and investigated the influence of the gas atmosphere on the triboelectrification between the liquid metal and the dielectric materials, such as PTFE, Kapton, and Nylon. It was found that the dielectric materials were negatively charged on contact with the liquid metal in ambient air. But in the nitrogen conditions, the polarity of the charges was reversed. Oxygen was excluded, which is responsible for the polarity reversal in contact electrification. Based on X-ray photoelectron spectroscopy, energy-dispersive X-ray, and SKFM data, a possible mechanism was proposed.