Browsing by Author "Ou, Keng-Liang"

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Magnetic Interaction between Surface-Engineered Rare-Earth Atomic Spins
(2012-06-22)
Lin, Chiung-Yuan
;
Li, Jheng-Lian
;
Hsieh, Yao-Hsien
;
Ou, Keng-Liang
;
Jones, B. A.
We report the ab-initio study of rare-earth adatoms (Gd) on an insulating surface. This surface is of interest because of previous studies by scanning tunneling microscopy showing spin excitations of transition-metal adatoms. The present work is the first study of rare-earth spin-coupled adatoms, as well as the geometry effect of spin coupling and the underlying mechanism of ferromagnetic coupling. The exchange coupling between Gd atoms on the surface is calculated to be antiferromagnetic in a linear geometry and ferromagnetic in a diagonal geometry. We also find that the Gd dimers in these two geometries are similar to the nearest-neighbor and the next-nearest-neighbor Gd atoms in GdN bulk. We analyze how much direct exchange, superexchange, and Ruderman-Kittel-Kasuya-Yosida interactions contribute to the exchange coupling for both geometries by additional first-principles calculations of related model systems.
Surface Cleaning of the Nanowire Field-Effect Transistor for Gene Detection
(2011-12-01)
Wu, Chi-Chang
;
Liu, Fu-Ken
;
Lin, Ling-Hung
;
Pang, See-Tong
;
Chuang, Cheng-Keng
The efficiency of DNA immobilization by using various surface cleaning methods is studied in this work. The degree of surface cleaning is evaluated by the surface tension measurement to reveal the contribution from the polar and apolar terms. The observation from the fluorescent microscope images indicates the effectiveness of surface clean by the acetone and ethanol mixtures, as well as the sulphuric acid and hydrogen peroxide mixtures. We also fabricate a series of back-gated, 60-nm nanowired (NW) field-effect transistor (FET) sensors for mutation gene detection by following the developed acetone and ethanol mixtures. Electrical properties of the NWFET sensor demonstrate the n-channel depletion characteristics. The current of the sensor is reduced once the attachment of negative charge molecules. The single-stranded capture DNA is chemically immobilized onto the surface of silicon NWFET by three-step reactions. The sensor surface demonstrates the great performance of current shift after the suitable cleaning. The NWFET sensor is successfully applied to detect the BRAF(V599E) mutation genes from the hybridized processes. The sensing behaviour estimated from the electrical signal reaches the femtomolar level.