Oriented attachment of nanoparticles to form micrometer-sized nanosheets/nanobelts by topotactic reaction on rigid/flexible substrates with improved electronic properties

Abstract

We report a topotactic reaction strategy to achieve the oriented attachment (OA) of colloidal metal chalcogenide quantum dots into micrometer-sized nanosheets and nanobelts (up to 6–7 μm) on both mechanically rigid and flexible substrates. The non-stoichiometric composition, crystallization and Ag doping were controlled. The strong surface adsorption of cations and thiol ligands facilitated micrometer-scale three-dimensional OA. The cations induced the formation of electrostatic forces, cation passivation on the nanosheet surface and overlap packing of the nanosheets, enabling good contact with the substrates and improved electron transport without severe obstruction of organic insulating barriers. The observation of weak anti-localization phenomena and Hall effect sensitivity (up to 188%) of non-stoichiometric Ag2-δTe nanosheet films as well as the improved I-V and photoresponse properties of Ag-doped CdX nanosheet films confirm efficient electron transport. The stable I-V properties of these nanosheet films on flexible substrates, even under bending forces, testify to their potential in flexible device applications. Chinese scientists have developed an improved strategy for incorporating ultrabright quantum dots into flexible displays and solar cells. Quantum dots are usually difficult to process into films because they are protected with insulating layers of organic films. To overcome this problem, Jia-tao Zhang from the Beijing Institute of Technology and colleagues turned to ‘oriented attachment’ chemical reactions that cause tiny colloids to undergo crystal growth in specific crystallographic orientations. The team fixed two-dimensional nanosheets of silver particles to either rigid or flexible substrates by reacting them with organic sulfur precursors. They then used cation exchange reactions to insert cadmium ions into the nanosheets, generating quantum dot arrays with excellent device conductivity. The strong surface absorption of this technique is suitable for producing mechanically stable micrometer-scale patterns as well as enhancing the photoresponse properties. A topotactic reaction strategy has been reported to achieve the oriented attachment of colloidal metal chalcogenide quantum dots into micrometer-sized nanosheets and nanobelts (up to 6-7 μm) on both mechanically rigid and flexible substrates. The non-stoichiometric compositions, crystallization, Ag doping and good contact with substrate were controlled well. The observation of weak anti-localization phenomena and Hall effect sensitivity, the improved I-V and photoresponse property and the stable I-V property of these nanosheet films on flexible substrates under bending force testify their potential electronic device application.