Network Overload due to Massive Attacks

We study the cascading failure of networks due to overload, using the betweenness centrality of a node as the measure of its load following the Motter and Lai model. We study the fraction of survived nodes at the end of the cascade $p_f$ as function of the strength of the initial attack, measured by the fraction of nodes $p$, which survive the initial attack for different values of tolerance $\alpha$ in random regular and Erd\"os-Renyi graphs. We find the existence of first order phase transition line $p_t(\alpha)$ on a $p-\alpha$ plane, such that if $p <p_t$ the cascade of failures lead to a very small fraction of survived nodes $p_f$ and the giant component of the network disappears, while for $p>p_t$, $p_f$ is large and the giant component of the network is still present. Exactly at $p_t$ the function $p_f(p)$ undergoes a first order discontinuity. We find that the line $p_t(\alpha)$ ends at critical point $(p_c,\alpha_c)$ ,in which the cascading failures are replaced by a second order percolation transition. We analytically find the average betweenness of nodes with different degrees before and after the initial attack, investigate their roles in the cascading failures, and find a lower bound for $p_t(\alpha)$. We also study the difference between a localized and random attacks

Microplasma-Enabled Sputtering of Nanostructured Materials for the Agile Manufacture of Electronic Components

Additive manufacturing has revolutionized the low-volume manufacturing space; for example, polymers can be extruded and joined together to produce arbitrary shapes at the push of a button. However, this revolution is primarily confined to thermoplastics, and more broadly, to structural materials. The ability to add electronic capabilities to these printed shapes would greatly enhance their utility. Unfortunately, most additive manufacturing methods for conductive features do not produce high-quality films, or require processing that can damage printed surfaces. Cleanroom technology is unmatched in its ability to produce high-resolution, high-quality interconnects and electronic features, but it has rigid requirements. The best results require precision equipment, tightly controlled environments, and are limited to patterning planar wafers and removing unwanted material to produce the desired patterns. This thesis develops and demonstrates the capabilities of a microplasma-based atmospheric-pressure sputterer, which combines the strengths of both. This microsputterer was developed in order to achieve a direct-write method to deposit arbitrary patterns of electronics-quality thin films for additive manufacturing at room temperature. It uses a sputtering plasma, scaled down to millimeter scale and operated at atmospheric pressure, without the benefit of pre- or post-processing, and with a minimally controlled environment. Process parameters’ impact on the material and manufacturing properties (i.e., adhesion, conductivity, resolution, speed) of the deposits are discussed. The results of this thesis include near-bulk electrical conductivity for gold films with sub-millimeter resolution and significantly better adhesion than traditionally sputtered films, and alumina films with a breakdown strength that surpasses the state of the art. The printer’s multimaterial capabilities and control over the sheath gas will allow for the creation of objects made of different materials with different electrical properties. This capability allows for the demonstration of practical applications that showcase the printer’s capabilities, including an ultrathin capacitor, produced entirely through microplasma sputtering.Ph.D

Focused atmospheric-pressure microsputterer for additive manufacturing of microelectronics interconnects

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 45-49).The past decade has seen a new manufacturing revolution, in the form of additive manufacturing. While recent additive manufacturing processes can produce structural materials in intricate shapes not previously possible, additive manufacturing of functional materials remains a challenge. In particular, functional electronics must still be made via traditional lithographic and etching processes. This thesis introduces a microsputtering method to directly write metals with high resolution. A wire feed enables continuous, extended use of the system. We motivate, simulate, and test a novel electrostatic focusing system to improve the resolution of the imprints; this focusing scheme combines electrostatic and fluid effects to direct the sputtered material into a strip as narrow as 9 pm. The microstructure of the deposits, which affects their conductivity, is also explored and modified. Using gold as printable feedstock, this technology allows for smooth (55 nm roughness) deposits with ~65X the electrical conductivity of bulk metal.by Yosef S. Kornbluth.S.M