The effect of trapped charge on silicon nanowire pseudo-MOSFETs.

The effects of organic molecules grafted on top of silicon nanowires are modeled as the oxide trap charges (Qot) and interface trap charges (Qit). The device investigated here is a pseudo-MOSFET with a thick bottom oxide (200 nm) and only a thin native oxide (5 nm) on top. With Qot = -5.0 x 10(11) cm(-2) and the U-shaped distribution of interface trap density (Dit) as a function of trap energy (Et), the structures are reproduced through the conventional technology computer aided design (TCAD) simulation tool, and the channel is imaginarily divided into several sections (5 x 5 regions) to apply the localized traps. The electrical parameters are extracted from the each part to quantitatively compare their effectiveness. The local position of the grafted molecules, modeled by these charges, is shown to result in strong variations in the relative change in the threshold voltage and subthreshold swing. These variations are explained by the surface depletion and scattering near the edges of the etched device and the series resistance effect.

Controlled growth of single-walled carbon nanotubes for unique nanodevices.

The controlled growth of bent and horizontally aligned single-walled carbon nanotubes (SWNTs) is demonstrated in this study. The bent SWNTs growth is attributed to the interaction between van der Waals force with substrate and aerodynamic force from gas flow. The curvature of bent SWNTs can be tailored by adjusting the angle between gas flow and step-edge direction. Electrical characterization shows that the one-dimensional resistivity of bent SWNTs is correlated with the curvature, which is due to strain induced energy bandgap variation. Additionally, a downshift of 10 cm(-1) in G-band is found at curved part by Raman analysis, which may be resulted from the bending induced carbon-carbon bond variation. In addition, horizontally aligned SWNTs and crossbar SWNTs were demonstrated. To prove the possibility of integrating the SWNTs having controllable morphology in carbon nanotube based electronics, an inverter with a gain of 2 was built on an individual horizontally aligned carbon nanotube.

Thermal conversion of electronic and electrical properties of AuCl3-doped single-walled carbon nanotubes.

By using carbon-free inorganic atomic layer involving heat treatment from 150 to 300 °C, environmentally stable and permanent modulation of the electronic and electrical properties of single-walled carbon nanotubes (SWCNTs) from p-type to ambi-polar and possibly to n-type has been demonstrated. At low heat treatment temperature, a strong p-doping effect from Au(3+) ions to CNTs due to a large difference in reduction potential between them is dominant. However at higher temperature, the gold species are thermally reduced, and thermally induced CNT-Cl finally occurs by the decomposition reaction of AuCl(3). Thus, in the AuCl(3)-doped SWCNTs treated at higher temperature, the p-type doping effect is suppressed and an n-type property from CNT-Cl is thermally induced. Thermal conversion of the majority carrier type of AuCl(3)-doped SWNTs is systematically investigated by combining various optical and electrical tools.

Adaptive logic circuits with doping-free ambipolar carbon nanotube transistors.

A CMOS-like inverter was integrated by using ambipolar carbon nanotube (CNT) transistors without doping. The ambipolar CNT transistors automatically configure themselves to play a role as an n-type or p-type transistor in a logic circuit depending on the supply voltage (V(DD)) and ground. A NOR (NAND) gate is adaptively converted to a NAND (NOR) gate. This adaptiveness of logic gates exhibiting two logic gate functions in a single logic circuit offers a new opportunity for designing logic circuits with high integration density for next generation applications.

Reduction-controlled viologen in bisolvent as an environmentally stable n-type dopant for carbon nanotubes.

Various viologens have been used to control the doping of single-walled carbon nanotubes (SWCNTs) via direct redox reactions. A new method of extracting neutral viologen (V(0)) was introduced using a biphase of toluene and viologen-dissolved water. A reductant of sodium borohydride transferred positively charged viologen (V(2+)) into V(0), where the reduced V(0) was separated into toluene with high separation yield. This separated V(0) solution was dropped on carbon nanotube transistors to investigate the doping effect of CNTs. With a viologen concentration of 3 mM, all the p-type CNT transistors were converted to n-type with improved on/off ratios. This was achieved by donating electrons spontaneously to CNTs from neutral V(0), leaving energetically stable V(2+) on the nanotube surface again. The doped CNTs were stable in water due to the presence of hydrophobic V(0) at the outermost CNT transistors, which may act as a protecting layer to prevent further oxidation from water.