Cheng-Tzu Kuo

Preparation and phase transformation of highly ordered TiO2 nanodot arrays on sapphire substrates

Ordered nanodot arrays of titanium oxide (TiO2) were prepared from an epitaxial Al/TiN bilayered film on a sapphire substrate by electrochemical anodization of the TiN layer using a nanoporous anodic aluminum oxide (AAO) film as the template. The nanodots with an average diameter of about 60 nm can faithfully duplicate the size, shape, and hexagonal pore pattern of the AAO nanopores. The phase development of the isolated TiO2 nanodots is very much different from TiO2 thin films and powders. After high temperature annealing, the nanodots are polycrystalline and consist of a mixed phase of anatase and rutile instead of single rutile phase. We expect that TiO2 nanodots with a single phase of anatase can be realized as long as the size of the nanodots is smaller than the critical nuclei size for rutile formation.

Field emission of carbon nanotubes on anodic aluminum oxide template with controlled tube density

The tube number density of aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH4∕H2 feed ratio during the CNT growth. We ascribe the variation of the tube density as a function of the CH4∕H2 feed ratio to the kinetic competition between outgrowth of cobalt-catalyzed CNTs from the AAO pore bottom and deposition of the amorphous carbon (a-C) overlayer on the AAO template. A pore-filling ratio of 18% to 82% for the nanotubes overgrown out of nanopores on the AAO template can be easily achieved by adjusting the CH4∕H2 feed ratio. Enhanced field emission properties of CNTs were obtained by lowering the tube density on AAO. However, at a high CH4 concentration, a-C by-product deposit on the CNT surface can degrade the field emission property due to a high energy barrier and significant potential drop at the emission site.

Effect of graded-temperature arsenic prelayer on quality of GaAs on Ge/Si substrates by metalorganic vapor phase epitaxy

The growth of GaAs epitaxy on Ge/Si substrates with an arsenic prelayer grown with graded temperature ramped from 300 to 420u2009°C is investigated. It is demonstrated that the graded-temperature arsenic prelayer grown on a Ge/Si substrate annealed at 650u2009°C not only improves the surface morphology (roughness: 1.1u2009nm) but also reduces the anti-phase domains’ (APDs) density in GaAs epitaxy (dislocation density: ∼2u2009×u2009107u2009cm−2). Moreover, the unwanted interdiffusion between Ge and GaAs epitaxy is suppressed by using the graded-temperature arsenic prelayer due to the low energy of the Ge-As bond and the use of a low V/III ratio of 20.

Effect of substrate misorientation on the material properties of GaAs/Al0.3Ga0.7As tunnel diodes

The effect of substrate misorientation on the material quality of the N++–GaAs/P++–AlGaAs tunnel diodes (TDs) grown on these substrates is investigated. It is found that the misorientation influences both surface roughness and interface properties of the N++–GaAs/P++–AlGaAs TDs. Smooth surface (rms roughness: 1.54 A) and sharp interface for the GaAs/Al0.3Ga0.7As TDs were obtained when the (100) tilted 10° off toward [111] GaAs substrate was used. Besides, the oxygen content in N++–GaAs and P++–AlGaAs layers grown on the 10° off GaAs substrates was reduced due to the reduction of sticking coefficient and number of anisotropic sites.The effect of substrate misorientation on the material quality of the N++–GaAs/P++–AlGaAs tunnel diodes (TDs) grown on these substrates is investigated. It is found that the misorientation influences both surface roughness and interface properties of the N++–GaAs/P++–AlGaAs TDs. Smooth surface (rms roughness: 1.54 A) and sharp interface for the GaAs/Al0.3Ga0.7As TDs were obtained when the (100) tilted 10° off toward [111] GaAs substrate was used. Besides, the oxygen content in N++–GaAs and P++–AlGaAs layers grown on the 10° off GaAs substrates was reduced due to the reduction of sticking coefficient and number of anisotropic sites.

P‐103: Anodic‐Aluminum‐Oxide Templated Carbon Nanotubes in the Field Emission Triode

To fabricate the field-emission triode structure, carbon nanotubes (CNT) were used as field emitters and grown in the anodic aluminum oxide (AAO). AAO thin layer with vertical pore channels was first prepared on the Si (100) substrate and was used to template the following growth of CNTs in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. The tetraethoxysilane (TEOS) oxide and Al layer were deposited on the CNTs and acted as the dielectric layer and gate electrode layers for the triode structure, respectively. Reactive ion and wet etches were then used to open the field-emission area in the triode. Field-emission characteristics of the CNT emitters have been studied and an anode turn-on field of ∼ 8.05 V/μm was measured.