Outstanding wide‐bandgap semiconductor material such as gallium nitride (GaN) has been extensively utilized in power electronics, radiofrequency amplifiers, and harsh environment devices. Due to its quantum confinement effect in enabling desired deep‐ultraviolet emission, excitonic impact, and electronic transport features, 2D or ultrathin quasi‐2D GaN semiconductors have been one of the most remarkable candidates for future growth of microelectronic devices. Here, for the first time, the authors report a large area, wide bandgap, and room‐temperature quasi‐2D GaN synthesis and printing strategy through introducing the plasma medicated liquid metal gallium surface‐confined nitridation reaction mechanism. The developed direct fabrication and compositional process is consistent with various electronics manufacturing approaches and thus opens an easy going way for cost‐effective growth of the third‐generation semiconductor. In particular, the fully printed field‐effect transistors relying on the GaN thus made show p‐type switching with an on/off ratio greater than 105, maximum field‐effect hole mobility of 53 cm2 V−1 s−1, and a small sub‐threshold swing. As demonstrated, the present method allows to produce at room temperature the GaN with thickness spanning from 1 nanometer to nanometers. This basic method can be further extended, generalized, and utilized for making various electronic and photoelectronic devices in the coming time.
In order to optimize laser ablation performance of a micro-thruster with 1U dimensions, which employs a micro semiconductor laser, the impacts of pulse width and glycidyl azide polymer (GAP) thickness on thrust performance was researched. The results showed that with a GAP thickness of 200 μm, the single-pulse impulse (I) increased gradually with the increase in the laser pulse width from 50 to 800 μs, while the specific impulse (Isp), impulse coupling coefficient (Cm), and ablation efficiency (η) all reached optimal values with a 200 μs pulse width. It’s worth noting that the optimal pulse width is exactly the ignition delay time. Both Cm and η peaked with the pulse width of 200 μs, reaching 242.22 μN/W and 35.4%, respectively. With the increase in the GAP thickness, the I and the Cm increased gradually. The GAP of different thickness corresponded to different optimal laser pulse width. Under a certain laser pulse width, the optimal GAP thickness should be the most vertical thickness of the ablation pit, and the various propulsion performance parameters at this time were also optimal. With the current laser parameters, the optimal GAP thickness was approximately 150 μm, the Isp was approximately 322.22 s, and the η was approximately 34.94%.
In the field of laser ablation micro-propulsion, the property of double-layer tape has significant impact on the propulsion performance. In this paper, low temperature plasma was used to treat the surface of polyethylene terephthalate (PET) to improve its adhesion with energetic polymer. The PET surface pre- and post-plasma treatment was characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), and the enhancement mechanism of the interface adhesion was discussed. In addition, the ablation performance of the double-layer tape after the plasma treatment was studied. The results showed that the plasma etching effect increased the root mean square roughness of the PET surface from 1.74 nm to 19.10 nm. In addition, after the plasma treatment, the number of C–OH/COOH bonds and O=C–O bonds increased, which also greatly improved the adhesion between the PET and energetic polymers. In the optimization of the ablation performance, the optimal laser pulse width was about 200 μs. The optimal values of the specific impulse (Isp), impulse coupling coefficient (Cm), and ablation efficiency (η) were 390.65 s, 250.82 μN/W, and 48.01%, respectively. The optimization of the adhesion of the double-layer tape and the ablation performance lay the foundation for the engineering application of laser ablation micro-thrusters.
Outstanding wide-bandgap semiconductor materials like gallium nitride (GaN) have been extensively utilized in power electronics, radiofrequency power amplifiers, and harsh environment adaptability. Due to its quantum confinement impact in enabling desired deep-ultraviolet emission, excitonic impact, and electronic transport features, two-dimensional (2D) GaN has been one of the most remarkable areas for the future growth of microelectronic devices. Here, for the first time, we report a large area, wide bandgap, and room-temperature 2D GaN synthesis and printing strategy via liquid metal gallium surface-confined nitridation reaction. The developed low-temperature synthesis and printing process is consistent with various electronic device manufacturing methods and thus opens a way for the cost-effective growth of the third-generation semiconductor. In particular, the fully printed field-effect transistors relying on the GaN show p-type switching with an on/off ratio greater than 105, maximum field-effect hole mobility of 53 cm2 V−1 s−1, and a small sub-threshold swing at room temperature. The current study establishes a room temperature way to produce the GaN, which can be further verified, generalized, and realized for various upcoming electronic and photoelectronic applications.
Laser ablation micropropulsion technology has the characteristics of high specific impulse, high thrust ratio and precise thrust control, which is a good choice for many micro/nano satellite power systems such as meteorology, remote sensing and reconnaissance. In order to provide optimal power support for micro-nano satellites and improve the propulsion performance of laser ablation microthrust, in this paper, the ablative material is GAP+3% nano carbon powder, doped with 5%, 8%, 10%, 15% LiAlH4 or 5%, 10%, 20%, 30% AP, respectively. A semiconductor laser with a wavelength of 975nm was used to ablate different doping substances and materials with different doping ratios, and the ablative properties were compared. The mechanism of the difference in ablative properties of different materials was analyzed by electron microscopy. The results show that LiAlH4 and AP can improve the laser ablation performance when they are mixed into GAP as oxidants because of their strong oxidability. When 10% LiAlH4 was added into the material, the average values of specific impulse and single impulse were 235s and 13.36μN•s, respectively. The propulsive performance parameters of 10% doped AP are slightly lower, but the error is smaller and the propulsive performance is more stable.
Surface‐Confined Nitridation Reaction
In article number 2200733, Jing Liu and co‐workers report a fundamental strategy for directly printing GaN semiconductor film with finest thickness of 1nm on the surface of liquid gallium at room temperature. The new chemical reaction was defined and experimentally demonstrated as N2+2Ga→plasma2GaN${{\rm{N}}_2} + 2{\rm{Ga}}\xrightarrow{{{\rm{plasma}}}}2{\rm{GaN}}$. Such 2D GaN film with large area, uniformity and controllable thickness can be deposited on various substrates. This opens the way for facilely printing GaN based electronic devices in the coming time.
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