Well-aligned Ga-doped ZnO nanorod arrays with high optical and electrical property were fabricated by catalyst-free thermal evaporation on p-silicon substrate. As the Ga/Zn atom ratio in the source material was tuned from 0 to 0.2, wurtzite structure ZnO nanorod arrays were realized with length of -6 microm and growth direction along c-axis. With the addition of Ga, the intensity of the near-band-edge emission was enhanced and the deep-level emissions maintained neglectable. As the Ga/Zn atom ratio increased from 0 to 0.1, the red shift of the near-band-edge emission occurred due to Ga-doping induced band gap renormalization effect related with the enhancement of the carrier density, while the blue shifts of the emission were found once the Ga/Zn ratio is higher than 0.1 resulting from Burstein-Moss effect. The configuration of the vertical-aligned Ga-doped ZnO nanorod arrays on p-Si substrate makes it straightforward for the fabrication of p-n nanodiode, which shows an excellent rectifying characteristic with threshold voltage as low as -4.7 V with the Ga/Zn atomic ratio of 0.2.
The research and development of low-powerconsumption and room-temperature hydrogen sensors are of great significance for the safe application of hydrogen energy. Herein, orthorhombic Nb 2 O 5−x nanobelts are prepared through a combined procedure of hydrothermal, ion exchange, and annealing treatment in Ar. The topological transformation process results in the formation of abundant surface defects including chemical defects such as Nb 4+ , oxygen vacancies, and disordered microregions, which lead to the abnormal p-type conducting and hydrogen sensing behavior. Moreover, the orthorhombic Nb 2 O 5−x nanobelts exhibit fast and sensitive room-temperature hydrogen sensing performance, which shows greater advancement than the monoclinic, tetragonal, and hexagonal Nb 2 O 5 one-dimensional (1D) nanostructures. The response time and lowest limit of detection of the as-fabricated room-temperature sensor decrease to 28 s and 3.5 ppm, respectively. The sensor also exhibits a highly selective hydrogen response against CO, CH 4 , ethanol, H 2 S, and NH 3 . The hydrogen response of the Nb 2 O 5−x nanobelts can be attributed to the redox reaction between hydrogen and preadsorbed oxygens. The defective surface structure and the prolonged dimension of the nanobelts give rise to the highly reactive surface and the suppression of the negative nanojunction effect, which greatly improves the sensing performance. The orthorhombic lattice structure can also promote gas adsorption and diffusion behavior due to its specific catalytic and pathway effect. The results of this work can be helpful for the rational design and defect engineering of the Nb 2 O 5 -based 1D nanostructures for room-temperature hydrogen sensing applications.
Micro/nano-scaled pressure sensors that can detect the pressure from an external environment to analyze the location, quantity, and configuration of the applied force, are in high demand for electronic screen, electronic skin, motion monitoring, artificial tactile system and several other fields. In this study, a pressure sensor matrix that can realize the two-dimensional pressure mapping is successfully developed by utilizing the patterned piezoelectric (K,Na)NbO 3 (KNN) nanorod arrays. The as-synthesized orthorhombic KNN nanorods exhibit outstanding mechanical flexibility and elasticity, together with high piezoelectric performance, which render outstanding piezoelectric response towards mechanical stimulation by external forces. A high sensitivity of single unit up to 0.20 V N −1 is achieved, with a detection limit down to 20 g and excellent stability, thanks to the highly flexible and elastic properties of the sensitive KNN nanorods. The micro sensor matrix with each unit separated spatially facilitates the detection of the pressure distribution in the effective areas with no cross-interference, which can accurately realize a selfpowered pressure mapping and precisely analyze the mechanical stimulations.
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