University of Cambridge > > Semiconductor Physics Group Seminars > Electron Tunnelling through Rigid Molecular Wire Anchored between Nanogap Electrodes and on Metal Surface (SP Workshop)

Electron Tunnelling through Rigid Molecular Wire Anchored between Nanogap Electrodes and on Metal Surface (SP Workshop)

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The ultimate aim of molecular electronics is to develop and master single molecule device. Prior to this, it is important to understand the electron transport behavior through -conjugation system [1-3]. Molecular wires are one of candidates and commonly used for single electron transistor [4,5]. Here, we have synthesized a novel rigid molecular wire, named carbon-bridged oligo(phenylenevinylene)s (COPVn), which has flat and rigid -conjugated structure and were demonstrated high electron transfer (ET) rate [6,7]. HS-COPV2-SH and HS-COPV6-SH wires with different length are chosen and introduced into electroless Au plated nanogap electrodes studied by low-temperature probe and onto metal surface measured by UHV -STM. We have established the fabrication process of stable nanogap electrodes by combining top-down process of electron-beam lithography and bottom-up process of electroless-Au plating (ELGP), in which the gap separation can be controlled at nearly 3.0 nm in this experiments with the yield of 90% due to a self-terminating mechanism of ELGP [8-10]. These ELGP nanogap electrodes are stable up to 170 C annealing, and are useful for the platform of nanogap devices such as single-electron transistors with ideal Coulomb diamonds and availability of logic operations [11-13]. The target molecular wires were introduced between Au electrodes and measured by low-temperature probe system. The temperature of the system is 9 K and pressure is controlled near 10-5 Pa. The projects concerning UHV -STM measurement were conducted by UNISOKU in Tokyo Tech and OMICRON in RIKEN , separately. We introduced HS-COPV2-SH molecular wires and C8S mix SAM onto Au(111) surface, and scanned the surface in 3.010-8 Pa condition with temperature of nearly 70 K. In order to obtain higher resolution images and scanning tunneling luminescence spectra, the HS-COPV6-SH molecular wires were chosen and introduced onto Ag(111) surface, and were measured in 3.010-9 Pa with temperature of nearly 4.7 K. For HS-COPV6-SH molecular wires, we have observed Coulomb blockade and resonant tunneling phenomena both in nanogap electrodes and STM system. Single electron tunneling and coherent resonant tunneling through molecular orbitals are expected. The similar results can be also found in HS-COPV2-SH molecular wires. Furthermore, we found current abrupt change in COPV2 nanogap device, whose reason remains unexplored. This work was carried out in collaboration with Mr. K. Hashimoto, Mr. M. Koshimura, Mr. K. Kimura, Mr. Y. Ito, and Dr. N. Umezawa, Dr. H. Imada, Dr. H. Walen. This study was partially supported by MEXT Elements Strategy Initiative to Form Core Research Center from the Ministry of Education, Culture, Sports, Science, and Technology, Japan; the Collaborative Research Project of Laboratory for Materials and Structures, Tokyo Institute of technology; the Collaborative Research Project of the Institute of Chemical Research, Kyoto University (Grant 2016-74); the BK Plus program, Basic Science Research program (NRF-2014R1A6A1030419).

References [1] Nature Nanotech. 4, 551-556 (2009) [2] Nature Nanotech. 3, 569-574 (2008) [3] Nature Nanotech. 1, 173-181 (2006) [4] Nature 417, 722-725 (2002) [5] Nature 407, 57-60 (2000) [6] J. Am. Chem. Soc. 134, 19254-19259 (2012) [7] Nature Chem. 6, 899-905 (2014) [8] Appl. Phys. Lett. 91, 203107(3) (2007) [9] Nanoscale 4, 7161-7167 (2012) [10] RSC Advances 5, 22160-22167 (2015) [11] ACS Nano 6 2798-2803 (2012) [12] Jpn. J. Appl. Phys. 49 090206(3) (2010) [13] Nanoscale 8 4720-4726 (2016)

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