Correlation between the performance and microstructure of Ti/Al/Ti/Au Ohmic contacts to p-type silicon nanowires

Understanding the electrical and microstructural aspects of contact formation at nanoscale is essential for the realization of low-resistance metallization suitable for the next generation of nanowire based devices. In this study, we present detailed electrical and microstructural characteristics of Ti/Al/Ti/Au metal contacts to p-type Si nanowires (SiNWs) annealed at various temperatures. Focused ion beam cross-sectioning techniques and scanning transmission electron microscopy (STEM) were used to determine the microstructure of the source/drain metal contacts of working SiNW field-effect transistors (FETs) annealed for 30 s in the 450-850?°C temperature range in inert atmosphere. Formation of titanium silicides is observed at the metal/semiconductor interface after the 750?°C anneal. Extensive Si out-diffusion from the nanowire after the 750?°C anneal led to Kirkendall void formation. Annealing at 850?°C led to almost complete out-diffusion of Si from the nanowire core. Devices with 550?°C annealed contacts had linear electrical characteristics; whereas the devices annealed at 750?°C had the best characteristics in terms of linearity, symmetric behavior, and yield. Devices annealed at 850?°C had poor yield, which can be directly attributed to the microstructure of the contact region observed in STEM.     

Guided search for hybrid systems based on coarse-grained space abstractions

Hybrid systems represent an important and powerful formalism for modeling real-world applications such as embedded systems. A verification tool like SpaceEx is based on the exploration of a symbolic search space (the region space). As a verification tool, it is typically optimized towards proving the absence of errors. In some settings, e.g., when the verification tool is employed in a feedback-directed design cycle, one would like to have the option to call a version that is optimized towards finding an error trajectory in the region space. A recent approach in this direction is based on guided search. Guided search relies on a cost function that indicates which states are promising to be explored, and preferably explores more promising states first. In this paper, we propose an abstraction-based cost function based on coarse-grained space abstractions for guiding the reachability analysis. For this purpose, a suitable abstraction technique that exploits the flexible granularity of modern reachability analysis algorithms is introduced. The new cost function is an effective extension of pattern database approaches that have been successfully applied in other areas. The approach has been implemented in the SpaceEx model checker. The evaluation shows its practical potential.     

From real cities to virtual worlds using an open modular architecture

The technologies for the Web and virtual worlds are currently converging, but although there are some efforts made to integrate them with each other, they typically rely on technologies foreign to most Web developers. In this paper, we present a new open architecture that combines several emerging and established technologies to provide convenient tools for developing virtual worlds directly in the Web. These technologies are easy to learn and understand by the Web community and allow for quick prototyping. Overall the modular architecture allows virtual worlds to be developed more quickly and more widely deployed. Additionally, we demonstrate that creating an adequate virtual environment can be an easy task when applying the principles of crowd-sourcing. We present an application that uses one of the largest available open data sources of geospatial information to bring 3D cities from the real world into the virtual environment.     

D’Alembert sums for a vibrating bar with viscous ends

We describe a new method for finding analytic solutions to some initial-boundary problems for partial differential equations with constant coefficients. The method is based on expanding the denominator of the Laplace-transformed Green’s function of the problem into a convergent geometric series. If the denominator is a linear combination of exponents with real powers, then one obtains a closed-form solution as a sum with a finite but time-dependent number of terms. We call it a d’Alembert sum. This representation is computationally most effective for small evolution times, but it remains valid even when the system of eigenmodes is incomplete and the eigenmode expansion is unavailable. Moreover, it simplifies in such cases. In vibration problems d’Alembert sums represent superpositions of original and partially reflected traveling waves. They generalize the d’Alembert type formulas for the wave equation and reduce to them when original waves can undergo only finitely many reflections in the entire course of evolution. The method is applied to vibrations of a bar with viscous ends and an internal damper. The results are illustrated by computer simulations and comparisons to modal and finite-element method (FEM) solutions.