Variability Effects in Graphene: Challenges and Opportunities for Device Engineering and Applications

Variability effects in graphene can result from the surrounding environment and the graphene material itself, which form a critical issue in examining the feasibility of graphene devices for large-scale production. From the reliability and yield perspective, these variabilities cause fluctuations in the device performance, which should be minimized via device engineering. From the metrology perspective, however, the variability effects can function as novel probing mechanisms, in which the 'signal fluctuations' can be useful for potential sensing applications. This paper presents an overview of the variability effects in graphene, with emphasis on their challenges and opportunities for device engineering and applications. The discussion can extend to other thin-film, nanowire and nanotube devices with similar variability issues, forming general interest in evaluating the promise of emerging technologies.Comment: Accepted by Proceedings of the IEE

Reverse Flooding: exploiting radio interference for efficient propagation delay compensation in WSN clock synchronization

Clock synchronization is a necessary component in modern distributed systems, especially Wirless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-stamping precision was a more limiting factor for the accuracy achievable with a synchronization scheme. However, the recent introduction of efficient flooding schemes based on constructive interference has greatly improved the achievable accuracy, to the point where propagation delays can effectively become the main source of error. In this paper, we propose a method to estimate and compensate for the network propagation delays. Our proposal does not require to maintain a spanning tree of the network, and exploits constructive interference even to transmit packets whose content are slightly different. To show the validity of the approach, we implemented the propagation delay estimator on top of the FLOPSYNC-2 synchronization scheme. Experimental results prove the feasibility of measuring propagation delays using off-the-shelf microcontrollers and radio transceivers, and show how the proposed solution allows to achieve sub-microsecond clock synchronization even for networks where propagation delays are significant