Credit: National University of SingaporeResearchers from the National University of Singapore have made a significant breakthrough in the field of monostructure fabrication. Through the use of an innovative precursor and doping with selenium they have for the first time precisely manipulated nanomaterials conformational discipline, opening the door to nanostructures that are highly custom-designed and well-functioning.
Utilizing Plastic Precursors
Classically, on-surface synthesis based on conformationally rigid precursors dominated due to broader technical limitations. In contrast, the NUS research team saw unprecedented opportunity in working with flexible precursors — a vast potential yet to be unfolded across a variety of complex and controllable nanomaterials achievable.
Their efforts were focused on a versatile precursor called mTBPT, which contains a triazine ring with three meta-bromophenyl units. The precursor can then occupy distinct conformational states, or conformers, which differ in their spatial arrangements because of the rotation about single bonds. With a series of controlled experiments the researchers constructed the conditions that allow conformer A or B to form selectively, which is a vital step in enabling nanostructure functionality.
The Selenium Doping Advantage
That study now reports that the success of those researchers depended in part on how they doped the graphene with selenium (Se). With just a touch of selenium (0.01 monolayers) on the copper (Cu(111)) substrate, the researchers turned up selectivity for the C3h conformer of the mTBPT precursor. This conformer, which displayed precise symmetry, self-assembled to an ordered 2D MOF on the surface, leading to much improved structural homogeneity of the nano-crystals.
To probe the emergence and transition of the mTBPT conformers on copper substrate, the scientists employed a myriad of state-of-the-art characterization methods such as high-resolution scanning tunneling microscopy (STM) imaging, spectroscopy and non-contact atomic force microscopy. They also exploited density functional theory calculations to simulate the selenium doping for stability and preference of C3h over Cs conformer.
Conclusion
What the NUS research team has accomplished for the first time in their groundbreaking work, is to show that selenium doping allows one to exert an immense control over the conformational arrangements of these nanostructures. They have demonstrated that by harnessing the versatility of flexible precursors and also the selective properties of selenium, custome designed routes to highly engineered nanomaterials with improved structural characteristics and homogeneity are wide open. This ground-breaking method opens up a new paradigm for the synthesis of advanced functional nanomaterials that can find applications from electronic to energy storage and beyond in the future.
