Needle‐like ZnO nanowires with high density are grown uniformly and vertically over an entire Ga‐doped conductive ZnO film at 550 °C. The nanowires are grown preferentially in the c‐axis direction. The X‐ray diffraction (XRD) θ‐scan curve shows a full width at half maximum (FWHM) value of 2°. This indicates that the c‐axes of the nanorods are along the normal direction of the substrate surface. The investigation using high‐resolution transmission electron microscopy (HRTEM) confirmed that each nanowire is a single crystal. A room‐temperature photoluminescence (PL) spectrum of the wires consists of a strong and sharp UV emission band at 380 nm and a weak and broad green–yellow band. It reveals a low concentration of oxygen vacancies in the ZnO nanowires and their high optical quality. Field electron emission from the wires was also investigated. The turn‐on field for the ZnO nanowires was found to be about 18 V μm–1 at a current density of 0.01 μA cm–2. The emission current density from the ZnO nanowires reached 0.1 mA cm–2 at a bias field of 24 V μm–1.
This study presents a new pneumatic micropump featuring three membrane-enclosed air chambers with different volumes, such that serially connected actuation of these membranes can generate fluid movement. When compressed air fills the chambers, the membranes are pushed downward sequentially, resulting in the liquid in the underlying fluid channels being pumped forward peristaltically. Since the chambers are filled up sequentially with compressed air, from the smallest to largest chamber, this time delay generates a peristaltic motion in the membranes and forces the liquids to flow only along one direction. The pneumatic micropump is made of polydimethylsiloxane (PDMS) using soft lithography techniques. When compared with other pneumatic micropumps that usually require at least three electromagnetic valves (EMV), this new micropump can be operated by using a single EMV. Experimental results show that the micropump provides good performance even at low flow rates. The back pressure of the pneumatic micropump is measured at a fixed peak frequency to demonstrate the functionality of the micropump. The optimum operating conditions and geometric parameters of the micropump are systematically explored. A maximum flow of 108 µl min−1 is obtained at a driving frequency of 10 Hz and an air pressure of 25 psi (172.4 kPa) when a membrane with a thickness of 80 µm and a microchannel with a width of 500 µm are tested. The development of these micropumps could be crucial for automatic miniature biomedical and chemical analysis systems.
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