Search

A self-powered field emission device (FED) driven by a single-electrode tribo-electric nanogenerator (TENG) is demonstrated. The mechanical motion works as both a power supply to drive the FED and a control unit to regulate the amount of emitted electrons. By using the Fowler-Nordheim equation and Kirchhoff laws, a theoretical model of this self-powered FED is proposed, and accordingly the real-time output characteristics of the device are systematically investigated. It is found that the motion distance of the TENG controls switch-on of the FED and determines the charge amount for emission, while the motion velocity regulates the amplitude of emission current. The minimum contact area for the TENG to generate field emission is about 9 cm², which can be improved by optimizing FED structure and the tribo-materials of TENG. The demonstrated concept of this self-powered FED as well as the proposed physical analysis can serve as guidance for further applications of FED in such fields of self-powered electronics and soft electronics. [ABSTRACT FROM AUTHOR]

Field emission devices using a wet-processed composite cathode of carbon nanotube films coated with titanium dioxide exhibit outstanding field emission characteristics, including ultralow turn on field of 0.383 V μm-1 and threshold field of 0.657 V μm-1 corresponding with a very high field enhancement factor of 20000, exceptional current stability, and excellent emission uniformity. The improved field emission properties are attributed to the enhanced edge effect simultaneously with the reduced screening effect, and the lowered work function of the composite cathode. In addition, the highly stable electron emission is found due to the presence of titanium dioxide nanoparticles on the carbon nanotubes, which prohibits the cathode from the influence of ions and free radical created in the emission process as well as residual oxygen gas in the device. The high-performance solution-processed composite cathode demonstrates great potential application in vacuum electronic devices. [ABSTRACT FROM AUTHOR]

In addition to Ni, Co, and Fe, the authors show that a copper (Cu) chromium (Cr) alloy can be a good catalyst for controlled growth of carbon nanotubes (CNTs). A thermal chemical vapor deposition was used at 600 °C to deposit the CNTs, and a dual-target magnetron sputtering system was used to control the ratio of the Cu/Cr alloy. The material properties of the CNTs, such as concentration, diameter, and density, are directly affected by the ratio of Cu/Cr alloy, which subsequently affect the field-emission properties. Their results showed that Cr can be used to effectively control the catalytic effects of the Cu catalysts, where the quality of the CNTs could vary while the density could be controlled from 4×107 to 5×1010 tubes/cm2. The field-emission current density of the CNT film increases with Cu/Cr ratio from 1/6.4 to 4.6/1 and decreases when the Cu/Cr ratio is more than 4.8/1 in the alloy film. When the Cu/Cr ratio is at 4.6/1, the average current density peaks at 5129 μA/cm2 at the applied field of 3.53 V/μm, showing an optimized field-emission property. [ABSTRACT FROM AUTHOR]

Freestanding two-dimensional (2D) few-layer graphene was formed through laser exfoliation of highly ordered pyrolytic graphite, using a pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Graphene sheets of several nanometers in thickness and micrometers in size were obtained. The laser exfoliation process was investigated at different laser fluences and distances between target and substrate. Three different phases, amorphous carbon, few-layer graphene sheets, and thin graphite films, were obtained as the laser fluence increased. This study reveals an existing route of forming freestanding 2D nanostructures through laser exfoliation. [ABSTRACT FROM AUTHOR]

Although the size- and shape-induced blueshift in the photoluminescence and photoabsorption of nanostructured ZnO has been extensively investigated, the underlying mechanism remains yet unclear. Here we show that theoretical reproduction of the observed trends clarifies that the blueshift originates from the Hamiltonian perturbation due to the broken-bond-induced local strain and quantum trapping and electron-phonon coupling in the surface skin up to two atomic layers in depth while bonds in the core interior retain their bulk nature. The extent of the blue shift depends on the tunable fraction of undercoordinated atoms in the surface skin. Therefore, the quantum confinement effect is indeed more “superficial” than first thought [H. Winn, OE Mag. 8, 10 (2005)]. [ABSTRACT FROM AUTHOR]