Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research in... more Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research interest owing to their exotic physical and mechanical properties, which have enabled their applications in electronics, optoelectronics, electrochemical and biomedical devices. Current synthesis strategies rely largely on top-down approaches such as etching and exfoliation. Among bottom-up approaches in literature, there lacks a systematic understanding of the mechanisms of 2D crystal growth, unlike one-dimensional nanomaterials whose growth mechanisms have been well documented. To date, the growth design of free-standing 2D nanomaterials has remained a case-by-case practice. This review focuses on the bottom-up solution synthesis of free-standing 2D nanomaterials and summarizes the general mechanisms and empirical methodologies that can lead to 2D crystal growth. A brief outlook on the development of synthesis and application of solution-grown 2D nanomaterials is also presented.
An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into... more An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into a ZnO nanowire (NW) lattice. Through this approach, antimony-doped ZnO NWs were successfully synthesized in an aqueous solution containing zinc nitrate and hexamethylenetetramine with antimony acetate as the dopant source. By introducing glycolate ions into the solution, a soluble antimony precursor (antimony glycolate) was formed and a good NW morphology with a controlled antimony doping concentration was successfully achieved. A doping concentration study suggested an antimony glycolate absorption doping mechanism. By fabricating and characterizing NW-based field effect transistors (FETs), stable p-type conductivity was observed. A field effect mobility of 1.2?cm2?V ? 1?s ? 1 and a carrier concentration of 6 × 1017?cm ? 3 were achieved. Electrostatic force microscopy (EFM) characterization on doped and undoped ZnO NWs further illustrated the shift of the metal?semiconductor barrier due to Sb doping. This work provided an effective large-scale synthesis strategy for doping ZnO NWs in aqueous solution.
Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a cr... more Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a critical strategy for tailoring the performance of nanodevices. ZnO NWs grown by hydrothermal method are pervasively used in optoelectronic, photovoltaic, and piezoelectric energy-harvesting devices. We synthesized in situ Cl-doped ZnO NWs with metallic conductivity that would fit seamlessly with these devices and improve their performance. Possible Cl doping mechanisms were discussed. UV–visible absorption spectroscopy confirmed the visible light transparency of Cl-doped ZnO NWs. Cl-doped ZnO NW/TiO2 core/shell-structured photoelectrochemical (PEC) anode was fabricated to demonstrate the application potential of highly conductive ZnO NWs. Higher photocurrent density and overall PEC efficiency compared with the undoped ZnO NW-based device were achieved. The successful doping and low resistivity of ZnO could unlock the potential of ZnO NWs for applications in low-cost flexible transparent electrodes.
Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research in... more Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research interest owing to their exotic physical and mechanical properties, which have enabled their applications in electronics, optoelectronics, electrochemical and biomedical devices. Current synthesis strategies rely largely on top-down approaches such as etching and exfoliation. Among bottom-up approaches in literature, there lacks a systematic understanding of the mechanisms of 2D crystal growth, unlike one-dimensional nanomaterials whose growth mechanisms have been well documented. To date, the growth design of free-standing 2D nanomaterials has remained a case-by-case practice. This review focuses on the bottom-up solution synthesis of free-standing 2D nanomaterials and summarizes the general mechanisms and empirical methodologies that can lead to 2D crystal growth. A brief outlook on the development of synthesis and application of solution-grown 2D nanomaterials is also presented.
An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into... more An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into a ZnO nanowire (NW) lattice. Through this approach, antimony-doped ZnO NWs were successfully synthesized in an aqueous solution containing zinc nitrate and hexamethylenetetramine with antimony acetate as the dopant source. By introducing glycolate ions into the solution, a soluble antimony precursor (antimony glycolate) was formed and a good NW morphology with a controlled antimony doping concentration was successfully achieved. A doping concentration study suggested an antimony glycolate absorption doping mechanism. By fabricating and characterizing NW-based field effect transistors (FETs), stable p-type conductivity was observed. A field effect mobility of 1.2?cm2?V ? 1?s ? 1 and a carrier concentration of 6 × 1017?cm ? 3 were achieved. Electrostatic force microscopy (EFM) characterization on doped and undoped ZnO NWs further illustrated the shift of the metal?semiconductor barrier due to Sb doping. This work provided an effective large-scale synthesis strategy for doping ZnO NWs in aqueous solution.
Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a cr... more Doping semiconductor nanowires (NWs) for altering their electrical and optical properties is a critical strategy for tailoring the performance of nanodevices. ZnO NWs grown by hydrothermal method are pervasively used in optoelectronic, photovoltaic, and piezoelectric energy-harvesting devices. We synthesized in situ Cl-doped ZnO NWs with metallic conductivity that would fit seamlessly with these devices and improve their performance. Possible Cl doping mechanisms were discussed. UV–visible absorption spectroscopy confirmed the visible light transparency of Cl-doped ZnO NWs. Cl-doped ZnO NW/TiO2 core/shell-structured photoelectrochemical (PEC) anode was fabricated to demonstrate the application potential of highly conductive ZnO NWs. Higher photocurrent density and overall PEC efficiency compared with the undoped ZnO NW-based device were achieved. The successful doping and low resistivity of ZnO could unlock the potential of ZnO NWs for applications in low-cost flexible transparent electrodes.
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Papers by Fei Wang