Tuning Structural and Mechanical Properties of Two-Dimensional Molecular Crystals: The Roles of Carbon Side Chains

• Published in: Nano letters Vol. 12; no. 3; pp. 1229 - 1234
• Main Authors: Cun, Huanyao, Wang, Yeliang, Du, Shixuan, Zhang, Lei, Zhang, Lizhi, Yang, Bing, He, Xiaobo, Wang, Yue, Zhu, Xueyan, Yuan, Quanzi, Zhao, Ya-Pu, Ouyang, Min, Hofer, Werner A, Pennycook, Stephen J, Gao, Hong-jun
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.03.2012
• Subjects: Applied sciences; CARBON; Carbon - chemistry; CHAINS; CHEMICAL PROPERTIES; Computer Simulation; Condensed matter: structure, mechanical and thermal properties; Crystal structure; Crystallization - methods; DEFORMATION; Elastic Modulus; ELASTICITY; Electronics; Exact sciences and technology; Heterocyclic Compounds, 4 or More Rings - chemistry; Macromolecular Substances - chemistry; MATERIALS SCIENCE; Mathematical models; Mechanical and acoustical properties of condensed matter; MECHANICAL PROPERTIES; Mechanical properties of nanoscale materials; Models, Chemical; Models, Molecular; Modulus of elasticity; Molecular Conformation; MOLECULAR CRYSTALS; Molecular electronics, nanoelectronics; Nanostructures - chemistry; Nanostructures - ultrastructure; Origins; Particle Size; Physics; Resilience; SCANNING TUNNELING MICROSCOPY; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface Properties; Tensile Strength; TUNING; self-assembly; molecular side chain; Two-dimensional molecular crystal; scanning tunneling microscopy; elastic properties; Chain length; Molecular crystals; Mechanical properties; Carbon; Physical properties; Thin films; Young modulus; Scanning tunneling microscopy; Molecular electronics; Strains; Molecular models; Chemical properties; Elastic properties
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl203591t

A key requirement for the future applicability of molecular electronics devices is a resilience of their properties to mechanical deformation. At present, however, there is no fundamental understanding of the origins of mechanical properties of molecular films. Here we use quinacridone, which possesses flexible carbon side chains, as a model molecular system to address this issue. Eight molecular configurations with different molecular coverage are identified by scanning tunneling microscopy. Theoretical calculations reveal quantitatively the roles of different molecule–molecule and molecule–substrate interactions and predict the observed sequence of configurations. Remarkably, we find that a single Young’s modulus applies for all configurations, the magnitude of which is controlled by side chain length, suggesting a versatile avenue for tuning not only the physical and chemical properties of molecular films but also their elastic properties.