Electronics

We present Suspended Carbon Nanofibers featuring a central nanometric gap fabricated by integration of Electro-Mechanical Spinning, pyrolysis of ultraviolet-cured microstructures and a Joule heating process. Photopatterned walls were used to suspend polymeric electrospun fibers based on a solution of SU-8. After pyrolysis, the complete structure was converted into a monolithic carbon microstructure featuring stable ohmic contact between the suspended fibers and the supporting walls without the need of further processing. By applying an electrical bias through the electrodes, the wire can be gradually thinned by excessive Joule heating, eventually forming a nanogap. The maximum supported current density in the fibers was found to be of the order of 10 5 A/cm 2. Furthermore, the electrical characteristics of carbon nanofibers and the dimensions of the nanogaps were demonstrated to be dependent on the length of the fiber and atmosphere conditions, i.e. air or vacuum. A finite element simulation was used to gain insight into the influence of length on nanogap size. The shorter fibers modeled portrayed a significantly steeper temperature gradient, which agrees with the experimental observation of smaller gaps. The presented method facilitates an inexpensive manufacturing technique of nanogaps as small as 12 nm, holding potential for the preparation molecular electronics devices.

The introduction of two-photon polymerization (TPP) into the area of Carbon Micro Electromechanical Systems (C-MEMS) has enabled the fabrication of three-dimensional glassy carbon nanostructures with geometries previously unattainable through conventional UV lithography. Pyrolysis of TPP structures conveys a characteristic reduction of feature size-one that should be properly estimated in order to produce carbon microdevices with accuracy. In this work, we studied the volumetric shrinkage of TPP-derived microwires upon pyrolysis at 900°C. Through this process, photoresist microwires thermally decompose and shrink by as much as 75%, resulting in glassy carbon nanowires with linewidths between 300 and 550 nm. Even after the thermal decomposition induced by the pyrolysis step, the linewidth of the carbon nanowires was found to be dependent on the TPP exposure parameters. We have also found that the thermal stress induced during the pyrolysis step not only results in axial elongation of the nanowires, but also in buckling in the case of slender carbon nanowires (for aspect ratios greater than 30). Furthermore, we show that the calculated residual mass fraction that remains after pyrolysis depends on the characteristic dimensions of the photoresist microwires, a trend that is consistent with several works found in the literature. This phenomenon is explained through a semi-empirical model that estimates the feature size of the carbon structures, serving as a simple guideline for shrinkage evaluation in other designs.

The task allocation problem is a key element in the solution of several applications from different engineering fields. With the explosion of the amount of information produced by the today Internet-connected solutions, scheduling techniques for the allocation of tasks relying on grids, clusters of computers, or in the cloud computing, is at the core of efficient solutions. The task allocation is an important problem within some branch of the computer sciences and operations research, where it is usually modeled as an optimization of a combinatorial problem with the inconvenience of a state explosion problem. This chapter proposes the modeling of the task allocation problem by the use of Colored Petri nets. The proposed methodology allows the construction of compact models for task scheduling problems. Moreover, a simulation process is possible within the constructed model, which allows the study of some performance aspects of the task allocation problem before any implementation stage.