15:30-16:00

The Coexistence of Low Work Function and High Inertness in an Electric Dipole Surface

It is commonly believed that a low work function and a high inertness are two incompatible properties for a metal surface. A low work function for a metal surface suggests loosely bound valance electrons which easily participate in bond-forming with reactants. This high chemical reactivity is the origin of surface instability for a low work function metal being exposed to contaminants. In theory, if a metal surface is composed of an electric dipole layer with a particular orientation, a low surface work function and high surface inertness could coexist. Such a surface will show a great advantage in applications of vacuum electron emission devices, where a low work function is required for easy electron escape and high surface inertness is desired for contamination-proof. We demonstrated experimentally, for the first time, that such a surface can indeed be formed on the tip apex of a single nanowire out of the compound LaB6. The exotic phenomenon is evidenced by direct atom-resolved imaging through field-ion microscopy and field emission microscopy. Surface stability is evaluated by comparing room temperature field emission current decay from the LaB6 emitter with that from the W emitter. Though LaB6 has a much lower work function than W, the field emission current from the LaB6 dipole surface shows no decay for 3 hours while that from the W metal surface decays as much as 80% in less than 20 minutes under a similar experimental condition.

Speaker

Dr. Han Zhang, ICYS-Sengen Reseacrher, NIMS

Chair

Dr. Yasushi Yamauchi, Nano Characterization Unit, NIMS

16:00-16:45

Structural and electronic properties of silicene growth on Ag(110) and Ag(111)

Silicene, one Si atom tick arranged in honeycomb structure, have been synthesized upon the shapes of either isolated one-dimensional (1D) Si nanoribbons (SiNRs) or dense array of SiNRs on Ag(110) and 2D Si layer on Ag(111).

Angle-resolved photoemission of Si bands identified states corresponding to the one-dimensional projection of π and π* Dirac cones in silicene grown on Ag(110) and π Dirac cone in 2D silicene on Ag(111).

Structural and electronic properties of clean and oxidized silicene nnanoribbons will be presented by photoemission and STM measurements. The strong resistance towards oxidation of the SiNRs grating due to the sp² hybridization of the silicon valence orbitals, measured by reflection electron energy loss spectroscopy, confirmed the honeycomb graphene-like structure found by STM.

Speaker

Dr. Irene Paola De Padova, The Institute of Structure of Matter, The Italian National Research Council, Italy

Chair

Dr. Tomonobu Nakayama, MANA Principal Investigator, NIMS