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Nano Bio Technologies




“Electric property evolution of structurally defected multilayer graphene”

Nano Letters 8(10), 2008, 3092

We report on the influence of structural disorder on the electrical properties of multilayer graphene (MLG). Exponential decreases in the conductance and transconductance with increase of defects in the MLG were observed, which could be explained by the percolation and the variable range hopping conduction. An enhancement of p-type nature with increasing disorders was considered to be the result of oxygen doping in the graphene sheets introduced by oxygen plasma. The rapid increase of low-frequency noise was attributed to the formation of conductive network through the continuum percolation, as the low-frequency noise could be increased by the enhanced carrier scattering at the defect sites. We hope that our result should suggest a simple method of tuning the electrical properties of graphene.

“Size-controlled synthesis of machinable single crystalline gold nanoplates”

Chem. Mater., 2005 17, 5558.

Monodispersive size-controlled gold nanoplates were synthesized with high purity from the reduction of hydrogen tetrachloroaurate by reduced amount of sodium citrate, which kinetically controls the reaction pathway, in the presence of poly(vinyl pyrrolidone) (PVP). With the insufficient addition of the reductant, the molar ratio of sodium citrate and PVP relative to hydrogen tetrachloroaurate played an important role in determining the geometric shape and size of the product. These nanoplates were single crystals with planar width of 80−500 nm and thickness of 10−40 nm, exhibiting strong surface plasmon absorption in the near-infrared (NIR) region of 700−2000 nm. The gold nanoplates were used as the synthetically provided nanoblocks to fabricate single-crystalline nanocomponents, such as a nanoscaled gear or a nanoscaled letter.

“Origin of gate hysteresis in carbon nanotube field-effect transistors”

J. Phys. Chem. C, 2007 111(34), 12504

We have studied gate hysteresis of carbon nanotube field-effect transistors (CNFETs) on silicon oxide substrates in an ultrahigh vacuum (UHV) at low temperatures. It is found that the hysteresis is neither reduced by thermal annealing at temperatures over 300 °C under UHV nor significantly affected by independent adsorption of ammonia or water at T = 56 K. However, the hysteresis decreases greatly upon coadsorption of water and ammonia below condensation temperatures and restores completely with desorption of the adsorbed water layer. On the basis of these results, it is concluded that the main cause of gate hysteresis in CNFETs on silicon oxide substrate is charge transfer between the carbon nanotube and charge traps at the silicon oxide/ambient interface. We propose a mechanism for gate hysteresis that involves surface silanol groups as the major sources of screening charges. This surface silanol model is supported by results from scanning surface potential microscopy (SSPM).

"Ferroelectric properties of individual barium titanate nanowires investigated by scanned probe microscopy" Nano Letters, 2002, 2, 447.

We report scanned probe investigations on the ferroelectric properties of individual single-crystalline barium titanate nanowires. We show that nonvolatile electric polarization can be reproducibly induced and manipulated on these nanowires, thereby demonstrating that nanowires as small as 10 nm in diameter retain ferroelectricity. The coercive field for polarization reversal is determined to be ∼7 kV/cm, and the retention time for the induced polarization exceeds 5 days. These nanowires should provide promising materials for fundamental investigations on nanoscale ferroelectricity, and they may also be useful in nanoscale nonvolatile memory applications.



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