Molecular Modelling Of The Early Stages Of Metal Organic Framework Self Assembly

Author : Shaoze Wang
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)

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Download or read book Exotic Properties of Multi-dimensional Molecular Systems on Metal Surfaces written by Shaoze Wang and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanoscience research is important to our life. Exotic properties of molecules are of interest to physics, chemistry, biology, materials science and even industries for their applications ranging from the nature of molecular synthesis to optical, electronic, and biological use as well as quantum information processing. Using a scanning tunneling microscope tip as a characterization and manipulation tool, individual molecules as well as some self-assembled networks of four molecular systems on metal surfaces are investigated in this dissertation. Depending on the uniqueness of the system of study, the investigations include electronic, vibronic, structural, and mechanical properties of individual molecules or self-assembled molecular networks at the atomically clean environment. As one type of blue organic light emission diode (OLED), sexiphenyl molecule offers great applications in light emission with its unique electronic structure. Molecular vibrations are important for understanding its energetic dissipation. In order to understand the molecular vibrations, first, physical properties of 1D sexiphenyl molecules are characterized. Then vibrational modes of sexiphenyl molecules adsorbed on Ag(111) are studied. Two molecular vibrational modes are found at one monolayer of sexiphenyl film. In addition, the surface phonon excitation of the Ag(111) substrate is verified to be coupled with the molecular vibrations. Metal-organic frameworks are useful in their gas separation, fuel storage and catalysis. Moreover, similar to their semiconductor counterpart, the heterostructure of MOFs also plays a key platform for band gap tuning, band alignment and charge confinement. Here, physical structures of self-assembled molecular networks of 1D terphenyl and sexiphenyl molecules are studied. The exotic patterns of zigzag and honeycomb networks are formed in specific deposition conditions and metal organic framework (MOF) models are proposed to explain the periodical unit formations. A structural transition between two different MOFs is observed in the molecular heterostructure. Lateral manipulations of individual molecules demonstrate the flexibility of the bent structures while the electronic properties of sexiphenyl molecules provide the energy gaps. Then the electronic structures at the interface between two different networks are investigated. Rare earth molecules are of interest to the research due to their strong magnetic behaviors. Protected by the outer shell electron clouds, the inner 4f shell electrons own dominating spin-orbit couplings and lead to their applications in quantum regime as well as photon upconversion. In addition, chirality in the molecular networks have potential usage in chiral induced spin selectivity and may be regarded as a spin filter. In order to explore the physics behind a rare earth based self-assembled molecular networks, a molecular system, Eu(Pcam-Br)3, adsorbed on Au(111)surface is investigated. Self-assembled hexagonal networks of Eu(Pcam-Br)3 molecules are formed by the same dog-bone shape basic molecular units, which are composed of two individual molecules covalently linked via Ullmann coupling mechanism. Hexagonal symmetry of self-assembly is achieved by six basic units forming a gear shape structure. Furthermore, these gear shape structures exhibit left and right handedness and thus the entire hexagonal network become chiral. The origin of chirality is traced to the unique asymmetric structure of each basic molecular unit. Molecular propeller is one type of molecular machine, and can be utilized to fulfill the gear chain rotations at nanoscale. For the sake of investigating functional rotational applications, a 3D molecular propeller is studied with a focus on its mechanical and inelastic electron tunneling (IET) induced rotations. Unidirectional rotations based on chirality are performed either in clockwise or counterclockwise directions by laterally manipulating with a scanning tunneling microscope tip. Statistical analysis on the switching events unveils the mechanical and electronic processes of the detailed molecular rotations. Using the scanning tunneling microscope tip and metal substrate as the electrode, four different molecular systems are investigated in various aspects. The exotic properties in single molecules and self-assembled molecular networks exhibit the huge importance to scientific discoveries as well as industrial applications. Here, the studies in this dissertation provide the basic physical understandings of the molecular systems at the atomic scale