It has long been an aspirational goal to create artificial evaporators that allow omnidirectional energy absorptance, adequate water supply, and fast vapor transportation, replicating the feat of plant transpiration, to solve the global water crisis. This work reveals that magnolia fruits, as a kind of tree‐like living organism, can be outstanding 3D tree‐like evaporators through a simple carbonization process. The arterial pumping, branched diffusion, and confined evaporation are achieved by the “trunk,” “branches,” and “leaves,” respectively, of the mini tree. The mini tree possesses omnidirectional high light absorptance with minimized heat loss and gains energy from the environment. Water confined in the fruit possesses reduced vaporization enthalpy and transports quickly following the Murray's law. A record‐high vapor generation rate of 1.22 kg m−2 h−1 in dark and 3.15 kg m−2 h−1 under 1 sun illumination is achieved under the assistance of the gully‐like furry surface. The “absorption of nutrients” enables the fruit to recover valuable heavy metals as well as to produce clean water from wastewater efficiently. These findings not only reveal the hidden talent of magnolia fruits as cheap materials for vapor generation but also inspire future development of high‐performance, full‐time, and all‐weather vapor generation and water treatment devices.
Integration of intriguing ferroelectric κ-Ga2O3 on other oxide semiconductors opens an exciting avenue to invoke emergent transport phenomena and enable rational design of advanced device architectures, whereas the fundamental growth dynamics and physical properties of metastable κ-Ga2O3 are still far unexplored. In this work, we report on the heterostructure construction of single crystalline metastable orthorhombic κ-Ga2O3 epilayers and cubic In2O3(111) by means of laser molecular beam epitaxy. Elements of Sn and In are found to segregate to the growth surface and serve as surfactants to reduce the total surface energy and diffusion barrier of oxygen adatoms, hence producing Ga-rich conditions on the growth front, which in turn facilitates the stabilization of κ-phase Ga2O3. Depth-profiled X-ray photoemission spectral (XPS) analysis identified a type-I band alignment with a conduction band offset (CBO) of 0.45 eV and a valence band offset (VBO) of −1.15 eV for a κ-Ga2O3/In2O3 heterostructure. Determined by the analysis of Hall results with a double-layer model, a two-dimensional electron gas (2DEG) with a sheet carrier concentration of 1.2 × 1014 cm–2 and an enhanced mobility of 192 cm2/(V s) is confined at the heterostructure interface. The self-consistent Poisson–Schrödinger calculations indicate that the enhanced interfacial conductivity is a result of the combination of polarization manipulation and band discontinuity, well-supported by the characteristics of piezoelectric force microscopy and depth-profiled XPS. Integrating κ-Ga2O3 on other hexagonal polar semiconductors may open a possibility to manipulate the interfacial conductivity through polarization engineering and deliver advanced devices with multiple functionalities.
The emergent ferroelectric property of κ-Ga2O3 is expected to deliver advanced functional memory and ultralow-loss transistors, while the commonly observed rotational domains in κ-Ga2O3 make the origin of ferroelectricity mysterious. In this work, the single-domain heteroepitaxy of orthorhombic κ-Ga2O3 epilayers on sapphire has been demonstrated by the halide vapor-phase epitaxy (HVPE) technique. The optimal temperature of 550 °C is energetically favorable for the stabilization of κ-Ga2O3 on sapphire without impurity phases, and the growth dynamics is dominated by the surface-reaction-limited mechanism. The evolution of microstructures and optical characteristics indicate that the κ–β phase transition occurs at an elevated temperature of over 575 °C together with a remarkable reduction of growth rate. With proper phase engineering, the single-domain κ-Ga2O3 epilayers have been ultimately achieved, exhibiting multisteps resembling a terrace morphology, a relatively low screw dislocation density of 5.2 × 107 cm–2, and reduced band tail subgap states. The single-domain structure of orthorhombic κ-Ga2O3 was identified by the XRD ϕ-scans and transmission electron microscopic analysis. The realization of single-domain epitaxy allows one to uncover the driving force for the intriguing ferroelectric behavior of κ-Ga2O3 and to design power devices with improved performance.
The generation of p-type GaN through ion implantation is an attractive proposition in the massive production of GaN-based bipolar devices, whereas the removal of implantation induced lattice disturbances and defects is a difficult exercise and hampers the conversion of conductivity in GaN. Pulsed laser annealing is an effective annealing technique to recover lattice crystallinity and activate dopants with the preserved implanted profile. In this work, the effect of pulsed laser annealing on structural and optical recovery in high-dose magnesium (Mg) ion-implanted GaN has been investigated. The structural evolution and vibrational dynamics indicate an obvious structural recovery and partial strain release of Mg-implanted GaN during the pulsed laser annealing process, with a threshold laser fluence of 400 mJ/cm2, while rough surface structures are a result of the regrowth mechanism similar to liquid phase epitaxy. The enhanced donor–acceptor transition at 3.35 eV after pulsed laser irradiation is a sign of the effective activation of Mg from interstitial sites into the substitution of Ga ions. These results suggest that further optimization of the laser annealing technique has promising potential to manipulate the p-type conductivity of Mg-implanted GaN and to be implemented in GaN bipolar devices for practical applications.
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