Prof. M. Sahabul Alam研究セミナーのご案内
講演者氏名: Prof. M. Sahabul Alam
(University of Dhaka, Bangladesh、Visiting Researcher of Nihon University)
講演題目:Structural and Electrical properties of a single metal organic framework (MOF)
- A potential candidate for future molecular electronics
開催日時 2012年7月11日(水), 16:00ー
場所: 中央大3号館3階3300号室
講演内容:
The deposition of functional molecules/supramolecules and their structure formation processes on surfaces has recently been the subject of intense investigation in the field of nanotechnology. Nanotechnology refers to the ability to control individual atoms and molecules or to build machines or electronic devices on the nanometer scale. The down-scaling of lithographic processes in the ‘‘top-down’’ approach for silicon chip manufacturing will soon lead to fundamental physical limits. A new and promising approach to miniaturize the structures is the so-called bottom-up technique. The bottom-up approach is based on the formation of devices by specially designed molecular building blocks. Supramolecules are considered good candidates as basic building blocks for future molecular based electronics
With the scanning probe microscopy (SPM) techniques, scientists are capable of imaging a single molecule. This allows one to investigate molecular electronics, which could eventually replace the classic semiconductor electronics. In this context, scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) were carried out on various types of supramolecular metal ion nanoarchitectures to achieve topographic as well as spatially resolved electronic structural information at the single molecule level. Different types of square and star-like metal ion arrays, a supramolecular copper-oxygen assembly embedded into a polyoxotung?state wheel, a coordination polymer based on amino acids as well as iron (II) spin cross-over (SCO) complexes were investigated.
In the CITS images of single molecules a strong tunneling current contrast at the positions of the metal ions was observed. These data can be interpreted by the fact that the bonds coordinating the metal ions are weaker than the ones of the surrounding ligands; therefore the energy levels next to the Fermi energy of the molecule should be dominated by metal ion orbitals. This interpretation is consistent with density-functional theory calculations (DFT) that predict a nearly exclusive contribution of metal 3d orbitals near the Fermi energy, i.e. in all cases the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) are dominated by transition metal 3d orbitals.
Using a home-built low-drift microscope, even at ambient conditions CITS investigations allowed the localiza?tion of the positions of transition metal centers due to a selective mapping of the coordina?tive metal-ligand bonds. In this sense, CITS at ambient conditions is a practicable and straight?forward procedure to address metal centers within rather complex supramolecular metal-ion assemblies by spectroscopic tunneling techniques, even if these ions are buried by the constitut?ing organic ligand material.
世話人:芳賀正明