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PGI-1 Seminar: Prof. Jun-Hyung Cho

1D atom and molecule wires on the Si(001) surface

14:00 PGI-Hörsaal

Hanyang University, Seoul


The development of modern nanoelectronics relies crucially on the identification of various novel types of quantized structures. In particular, the artificially synthesized quantum 1D structures show a variety of intriguing physical phenomena distinct from their bulk counterparts due to the confinement of electrons in only one direction. In most of the 1D structures, the significantly enhanced couplings between charge, lattice, and spin degrees of freedom could lead to exotic phenomena such as Peierls instability, spin orderings, and the formation of Luttinger-liquid ground state. I will introduce a long-standing goal to create magnetism in a non-magnetic material by manipulating its structure at the nanoscale. Many structural defects have unpaired spins; an ordered arrangement of these can create a magnetically ordered state. I demonstrate theoretically that the dangling-bond wires fabricated on silicon surfaces [1] and graphene [2] achieve this state with polarized electron spins. Besides the presence of exotic ground states, potentially even more intriguing are their elementary excitations. I will present a combined STM and first-principles study for the structural and electronic properties of quasi-1D indium chains on Si(111) surface, including the structure, energetics, and dynamics of topological solitary excitations or solitons at the atomic scale [3].

Based on first-principles density-functional calculations, we propose novel growth mechanisms of the one-dimensional (1D) molecular lines on the H-terminated Si(001) surface. We present a facile method for the self-directed growth of 1D molecular lines along the Si dimer rows [4]. Instead of a previously employed single dangling bond, we here employ a single H-free Si dimer as a reaction site, resulting in an enhanced stability of the radical intermediate for the Ophthalaldehyde (OP) molecule containing two carbonyl groups. This radical intermediate easily abstracts two H atoms from a neighboring Si dimer, thereby allowing the chain reaction for a 1D molecular line. Such a fabricated OP line will be stable at higher temperatures compared to previously reported alkene lines because of its enhanced stability. In addition, we propose a growth mechanism of the recently observed allyl mercaptan (ALM) line, where the line is directed across the Si dimer rows [5]. The proposed structural model shows that the molecules adsorb across two Si dimers in the adjacent dimer rows with the Si-C and Si-S bonds, thereby yielding a higher thermodynamic stability compared to other alkene lines (containing a single Si-C bond per molecule) grown along the dimer rows. This accounts for a successful growth of ALM lines which were observed to be stable even at a high temperature of 650 K.