研究目的
Investigating the interaction between C60 and C70 molecules to understand how the shape of building blocks affects self-assembly and strain minimization at interfaces in van der Waals molecular heterostructures.
研究成果
The ellipsoidal shape of C70 enables strain-free heterostructures with C60 through orientational epitaxy, where C70 molecules adopt upright orientations to lattice-match with C60 layers. This reduces interfacial energy and entropy, facilitating the fabrication of multilayer van der Waals structures. The phenomenon is scalable to other nonspherical systems and has potential applications in nanomaterials fabrication.
研究不足
The study is limited to HOPG substrates; other substrates with stronger directional bonds may not allow orientational changes. Layer-by-layer growth is challenging due to premature second layer formation. Experimental conditions like deposition flux and temperature may need optimization for pure epitaxy.
1：Experimental Design and Method Selection:
The study uses scanning tunnelling microscopy (STM) to investigate the structure of C60/C70 interfaces on HOPG substrates. Sequential deposition of C60 and C70 molecules at room temperature and annealing are employed to study orientational epitaxy and strain relief mechanisms.
2：Sample Selection and Data Sources:
Highly oriented pyrolytic graphite (HOPG) is used as the substrate. C60 and C70 molecules are deposited from effusion cells. STM images are collected to analyze molecular layers and interfaces.
3：List of Experimental Equipment and Materials:
HOPG substrate (Goodfellow, 99.99% purity), C60 and C70 molecules (MER, 99.5% purity), home-built effusion cells for sublimation, Omicron UHV variable temperature STM with tungsten tips.
4：99% purity), C60 and C70 molecules (MER, 5% purity), home-built effusion cells for sublimation, Omicron UHV variable temperature STM with tungsten tips.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Clean HOPG by annealing in UHV at 475 K. Deposit C60 and C70 sequentially with specified rates. Anneal samples at 425 K for mixing. Perform STM imaging in constant current mode with tunnelling current of 0.1 nA and bias voltage between +2.00 and +2.58 V.
5：1 nA and bias voltage between +00 and +58 V.
Data Analysis Methods:
5. Data Analysis Methods: Analyze STM images to measure heights, lattice parameters, and molecular orientations. Compare with bulk fullerite structures using X-ray diffraction data for validation.
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