Han Woong Yeom

Stress relief as the driving force for self-assembled bi nanolines.

Bi nanolines self-assemble on Si(001) and are remarkable for their straightness and length-they are often more than 400 nm long, and a kink in a nanoline has never been observed. Through electronic structure calculations, we have found an energetically favorable structure for these nanolines that agrees with our scanning tunneling microscopy and photoemission experiments; the structure has an extremely unusual subsurface structure, comprising a double core of seven-membered rings of silicon. Our proposed structure explains all the observed features of the nanolines, and shows that surface stress resulting from the mismatch between the Bi and the Si substrates is responsible for their self-assembly. This has wider implications for the controlled growth of nanostructures on semiconductor surfaces.

Characterization of films and interfaces in n-ZnO/p-Si photodiodes

We report on the fabrication of n-ZnO/p-Si heterojunction photodiodes. RF sputtering was performed to deposit ZnO films on p-Si substrates at various substrate temperatures of 300, 480 and 550 °C using Ar:O2 ratios of 6:1. Typical rectifying behaviors were observed from most of the diodes as characterized by the current–voltage (I–V) measurement. Some of the diodes exhibit photoelectric effects under illumination using monochromatic red light with a wavelength of 670 nm. Maximum quantum efficiency of 53% was obtained under a reverse bias condition from a diode with ZnO film deposited at 480 °C. Measuring photoluminescence, transmittance, sheet resistance from the ZnO films, and characterizing the n-ZnO/p-Si interface with X-ray photoelectron spectroscopy, it is concluded that the diodes with n-ZnO deposited at 480 °C conserve relatively a high film quality and good interface junction to exhibit the best photoelectric property.

Self-Assembled Nanowires with Giant Rashba Split Bands

We investigated Pt-induced nanowires on the Si(110) surface using scanning tunneling microscopy (STM) and angle-resolved photoemission. High resolution STM images show a well-ordered nanowire array of 1.6 nm width and 2.7 nm separation. Angle-resolved photoemission reveals fully occupied one-dimensional (1D) bands with a Rashba-type split dispersion. Local dI/dV spectra further indicate well-confined 1D electron channels on the nanowires, whose density of states characteristics are consistent with the Rashba-type band splitting. The observed energy and momentum splitting of the bands are among the largest ever reported for Rashba systems, suggesting the Pt-Si nanowire as a unique 1D giant Rashba system. This self-assembled nanowire can be exploited for silicon-based spintronics devices as well as the quest for Majorana fermions.

Edge and interfacial states in a two-dimensional topological insulator: Bi(111) bilayer onBi2Te2Se

The electronic states of a single Bi(111) bilayer and its edges, suggested as a two dimensional topological insulator, are investigated by scanning tunneling spectroscopy (STS) and first-principles calculations. Well-ordered bilayer films and islands with zigzag edges are grown epitaxially on a cleaved Bi

Valley spin polarization by using the extraordinary Rashba effect on silicon

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Amorphous-to-crystalline phase transformation of thin film rubrene.

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Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2

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Nearly massless electrons in the silicon interface with a metal film

Se crystal. The calculation shows that the band gap of the Bi bilayer closes with a formation of a new but small hybridization gap due to the strong interaction between Bi and Bi

Chiral solitons in a coupled double Peierls chain.

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Optimum Thickness of SiO2 Layer Formed at the Interface of N-ZnO/P-Si Photodiodes

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