An investigation of electrical and optical properties of reactively sputtered silicon nitride and amorphous hydrogenated silicon thin films

Thin films of silicon nitride and amorphous hydrogenated silicon were prepared by radio frequency reactive sputter deposition and their properties optimized for their use as low temperature passivation coatings for optoelectronic devices. The effect of various sputter deposition parameters on the conduction and optical properties were studied. Infrared spectrophotometry and ellipsometry were used to determined the optical properties of the films whereas the electrical properties were determined from current-voltage measurements of MIS capacitors. Typical parameters of a sputter deposition run for the best Si3N4 films were: base pressure, 1-2x10-6 torr; sputtering pressure, 5 mtorr; nitrogen partial pressure, 16.5%; cathode anode gap, 10 cm; target power density, 1.97watts/cm2; and cathode voltage, 1.0 kvolts. Films of thickness 50-120nm, refractive index 1.94-2.2, and low conductivity (resistivity of 1011 Ω-cm) were obtained. The deposition rate was in the ranged of 5-8 nm/min depending on the sputtering pressure, the appied target power, and the nitrogen partial pressure. It was concluded that the quality of the silicon nitride films is strongly dependent on the total deposition pressure, nitrogen partial pressure, applied target power voltage, and possibly cathode voltage. It was also concluded that the water vapor background was the major factor in increasing the conductivity of the best films to values about three orders of magnitude above those for the best bulk silicon nitride material. Typical sputtering parameters for depositing a-Si:H films were: base pressure, 1-2x10-6 torr; sputtering pressure, 7 mtorr; hydrogen partial pressure, 5-20%; cathode anode gap, 7.6 cm; r.f. target power density, 1.58-1.82 watts/cm2; cathode voltage, 1.8-1.9 kvolts. Films of thicknesses 78-150 nm, refractive index 3.25 - 4.0, and strong absorption at 2000 cm-1 of infrared spectra were obtained. It was concluded that stoichiometric a -Si:H films can be prepared by reactive sputtering of a silicon target in the environment of argon and hydrogen

"Choice of Air Cargo Transshipment Airport: An Application to Air Cargo Traffic to/from Northeast Asia"

Based on a unique data set of 760 air cargo transshipment routings to/from the Northeast Asian region in 2000, this paper applies an aggregate form of multinomial logit model to identify the critical factors influencing air cargo transshipment route choice decisions. The analysis focuses on the trade-off between monetary cost and time cost while considering other variables relevant for choice of transshipment airport. The estimation method considers the presence of unobserved attributes, and corrects for resulting endogeneity via a two-stage least squares estimation using instrumental variables. Our empirical results show that choice of air cargo transshipment hub is more sensitive to time cost than the monetary costs such as landing fees and line-haul price. For example, our simulation results suggest that a one-hour reduction in total transport and processing time for a particular O-D air cargo traffic would be more effective than a US$1,000 reduction in airport charges. This suggests that it is important to reduce air cargo connecting time at an airport via adequate investment in capacity and automation even by increasing landing and other airport charges.

Numerical analysis of high-index nanocomposite encapsulant for light-emitting diodes

We used two-dimensional Finte-Difference-Time-Domain (FDTD) software to study the transition behavior of nano-particles from scatterers to an optically uniform medium. We measured the transmission efficiency of the dipole source, which is located in the high refractive index medium(index=2.00) and encapsulated by low index resin(index=1.41). In an effort to compose index-matched resin and to reduce internal reflection, high-index nano-particles are added to low-index resin in simulations of various sizes and densities. As the size of the nano-particles and the average spacing between particles are reduced to 0.02 lambda and 0.07 lambda respectively, the transmission efficiency improves two-fold compared to that without nanoparticles. The numerical results can be used to understand the optical behavior of nano-particles and to improve the extraction efficiency of high brightness light-emitting-diodes(LEDs), through the use of nano-composite encapsulant.Comment: 9 pages, 5 jpg figure

Cross-Layer Resilience Based On Critical Points in MANETs

A fundamental problem in mobile ad hoc and unstructured sensor networks is maintaining connectivity. A network is connected if all nodes have a communication route (typically multi-hop) to each other. Maintaining connectivity is a challenge due to the unstructured nature of the network topology and the frequent occurrence of link and node failures due to interference, mobility, radio channel effects and battery limitations. In order to effectively deploy techniques to improve the resilience of sensor and mobile ad hoc networks against failures or attacks one must be able to identify all the weak points of a network topology. Here we define the weak or critical points of the topology as those links and nodes whose failure results in partitioning of the network. In this dissertation, we propose a set of algorithms to identify the critical points of a network topology. Utilizing these algorithms we study the behavior of critical points and the effect of using only local information in identifying global critical points. Then, we propose both local and global based resilient techniques that can improve the wireless network connectivity around critical points to lessen their importance and improve the network resilience. Next we extend the work to examine the network connectivity for heterogeneous wireless networks that can be result due to factors such as variations in transmission power and signal propagation environments and propose an algorithm to identify the connectivity of the network. We also propose two schemes for constructing additional links to enhance the connectivity of the network and evaluate the network performance of when a random interference factor occurs. Lastly, we implement our resilience techniques to improve the performance