Enabling Design and Simulation of Massive Parallel Nanoarchitectures

A common element in emerging nanotechnologies is the increasing complex- ity of the problems to face when attempting the design phase, because issues related to technology, specific application and architecture must be evalu- ated simultaneously. In several cases faced problems are known, but require a fresh re-think on the basis of different constraints not enforced by standard design tools. Among the emerging nanotechnologies, the two-dimensional structures based on nanowire arrays is promising in particular for massively parallel architec- tures. Several studies have been proposed on the exploration of the space of architectural solutions, but only a few derived high-level information from the results of an extended and reliable characterization of low-level structures. The tool we present is of aid in the design of circuits based on nanotech- nologies, here discussed in the specific case of nanowire arrays, as best candi- date for massively parallel architectures. It enables the designer to start from a standard High-level Description Languages (HDL), inherits constraints at physical level and applies them when organizing the physical implementation of the circuit elements and of their connections. It provides a complete simu- lation environment with two levels of refinement. One for DC analysis using a fast engine based on a simple switch level model. The other for obtaining transient performance based on automatic extraction of circuit parasitics, on detailed device (nanowire-FET) information derived by experiments or by existing accurate models, and on spice-level modeling of the nanoarray. Re- sults about the method used for the design and simulation of circuits based on nanowire-FET and nanoarray will be presente

Modeling, Design, and Analysis of MagnetoElastic NML Circuits

With the predicted end of CMOS scaling process, researchers started to study several alternative technologies. Among them NanoMagnet Logic (NML) offers advantages complementary to MOS transistors especially for its magnetic nature. Its intrinsic memory capability makes it suitable for zero stand-by power and logic-in-memory applications. NML requires a clock system that, if based on a magnetic field, highly increases the circuit dynamic power consumption. We have recently proposed a solution based on the magnetoelastic effect (ME-NML) [1] and on currently available fabrication processes, which drastically reduces dynamic power consumption. However, many questions still remain unanswered. Which kind of applications are best suited for this technology? How can we effectively design, analyze, and compare ME-NML circuits? Does it really offer advantages over state-of-the-art CMOS transistors? In this paper, we provide answers to all these questions and the results prove that this technology offers indeed extremely good performance. We have designed a Galois field multiplier with a systolic array structure to reduce interconnection overhead. We developed a new RTL model that allows us to easily describe and simulate circuits of any complexity, evaluating at the same time the performance and keeping into account technology constraints. We approach for the first time in the NML scenario the design of ME-NML circuits adopting the standard-cell method used in standard technologies and fulfill the design down to the physical level. The same circuit is designed also with NML technology based on magnetic fields and with a 28 nm low power CMOS bulk technology for comparison. The CMOS circuit is obtained through physical place&route with a commercial tool, providing, therefore, the most accurate comparison ever presented in literature. Power analysis shows that ME-NML circuits have a considerable advantage over both NML and state-of-the-art CMOS bulk technology. As a further by-product results clearly highlight which kind of architectures can better exploit the true potential of NML technology

Plasmonic antennas and zero mode waveguides to enhance single molecule fluorescence detection and fluorescence correlation spectroscopy towards physiological concentrations

Single-molecule approaches to biology offer a powerful new vision to elucidate the mechanisms that underpin the functioning of living cells. However, conventional optical single molecule spectroscopy techniques such as F\"orster fluorescence resonance energy transfer (FRET) or fluorescence correlation spectroscopy (FCS) are limited by diffraction to the nanomolar concentration range, far below the physiological micromolar concentration range where most biological reaction occur. To breach the diffraction limit, zero mode waveguides and plasmonic antennas exploit the surface plasmon resonances to confine and enhance light down to the nanometre scale. The ability of plasmonics to achieve extreme light concentration unlocks an enormous potential to enhance fluorescence detection, FRET and FCS. Single molecule spectroscopy techniques greatly benefit from zero mode waveguides and plasmonic antennas to enter a new dimension of molecular concentration reaching physiological conditions. The application of nano-optics to biological problems with FRET and FCS is an emerging and exciting field, and is promising to reveal new insights on biological functions and dynamics.Comment: WIREs Nanomed Nanobiotechnol 201

Development of Zeolitic Imidazolate Framework-Derived Carbon Hosts for Advanced Lithium Metal Anodes

Lithium (Li) metal batteries have recently gained tremendous attention owing to their high energy capacity compared to other rechargeable batteries. Nevertheless, Li dendritic growth causes low Coulombic efficiency, thermal runaway, and safety issues, all of which hinder the practical application of Li metal as a promising anodic material. From the material development aspect, new and creative solutions are required to resolve the current technical issues on advanced Li batteries and improve their safety during operation. The research encompassed in this work spans a broad investigation of utilizing Zeolitic imidazolate framework derived carbon (ZIF-C) as a 3D host material in Li metal batteries. The reason behind choosing ZIF-C in this thesis not only relies on its flexibility with which constituents’ geometry, size, and functionality can be modified to match application needs, but also because it exhibits several outstanding properties, such as robust mechanical strength, large surface area and pore volume, and adequate electrical conductivity, making it a potential candidate for cost-effective practical usage. These host materials, however, could suffer from poor Li wettability, which results in significant nucleation barriers and upper surface electrodeposition of Li metal, leading to dendritic growth and safety concerns. This thesis covers multiple aspects related to ZIF-C material. Firstly, the physical properties of porous ZIF-C, which can be controlled by the inorganic components, were thoroughly studied. This provided the basis of enhancing the properties of ZIF-C by varying the ratios of zinc/cobalt ion metallic precursors. A key finding from this study is that the initiation of carbon nanotubes growth and the pore size on the surface of ZIF-C is highly dependent on the Co/Zn ratio. Secondly, we theoretically demonstrated and experimentally correlated the growth mechanism of Li clusters on the surface of Co/Zn ZIF-C by employing different heteroatoms (pyridinic N, pyrrolic N, quaternary N, and Co-N4). As a key feature, the Co-N4 affects the Li deposition behavior with axial Li growth on the surfaces of the carbon frameworks, while the other heteroatoms (i.e., nitrogen defects) induce unfavorable vertical Li growth. Thirdly, we functionalized the Co/Zn ZIF-C with oxidized nitrogen groups by utilizing nitric acid. We found that the functionalized porous carbon demonstrated an enhanced wettability compared to its non-functionalized counterpart. Moreover, by functionalizing the carbon surface with oxidized nitrogen during Li plating and stripping, catalyzed Li nitride (Li3N) formed in the solid electrolyte interphase which effectively enhanced the surface morphology of Li deposition. The electrochemical measurements showed a massive improvement in the capacitive behavior of the functionalized porous carbon and an enhanced electrochemistry performance in terms of cyclability and reversibility. Some additional theoretical and experimental work, involving advanced computational simulations and in situ characterization techniques, opens the door to further work in developing high-performance battery materials for the advance of a new generation of Li-based batteries

Feedbacks in QCA: a Quantitative Approach

In the post-CMOS scenario a primary role is played by the quantum-dot cellular automata (QCA) technology. Irrespective of the specific implementation principle (e.g., either molecular, or magnetic or semiconductive in the current scenario) the intrinsic deep-level pipelined behavior is the dominant issue. It has important consequences on circuit design and performance, especially in the presence of feedbacks in sequential circuits. Though partially already addressed in literature, these consequences still must be fully understood and solutions thoroughly approached to allow this technology any further advancement. This paper conducts an exhaustive analysis of the effects and the consequences derived by the presence of loops in QCA circuits. For each problem arisen, a solution is presented. The analysis is performed using as a test architecture, a complex systolic array circuit for biosequences analysis (Smith–Waterman algorithm), which represents one of the most promising application for QCA technology. The circuit is based on nanomagnetic logic as QCA implementation, is designed down to the layout level considering technological constraints and experimentally validated structures, counts up to approximately 2.3 milion nanomagnets, and is described and simulated with HDL language using as a testbench realistic protein alignment sequences. The results here presented constitute a fundamental advancement in the emerging technologies field since: 1) they are based on a quantitative approach relying on a realistic and complex circuit involving a large variety of QCA blocks; 2) they strictly are reckoned starting from current technological limits without relying on unrealistic assumptions; 3) they provide general rules to design complex sequential circuits with intrinsically pipelined technologies, like QCA; and 4) they prove with a real application benchmark how to maximize the circuits performance

Micromagnetic Simulation of Three-dimensional Nanoarchitectures

The thesis discusses micromagnetic simulation studies on high-frequency magnetic dynamics in three-dimensional ferromagnetic nanoarchitectures made of interconnected magnetic nanowire networks. Such artificial magnetic materials with nanoscale features have recently emerged as a vivid topic of research, as their geometry has a decisive impact on their magnetic properties. By studying their static magnetization structure, we find that these systems display a behavior analogous to that of 3D artificial spin ice lattices, with frustrated interactions and the emergence of monopole-like defect structures at the wires' intersection points. Our simulations reveal a high activity of these defect sites in the magnonic high-frequency spectrum. We study various 3D nanoarchitectures and show that their geometry and magnetization state results in characteristic high-frequency signatures. Controlling these features could open new pathways for magnonics research and reprogrammable magnetic metamaterials

Dirac half-semimetallicity and antiferromagnetism in graphene nanoribbon/hexagonal boron nitride heterojunctions

Half-metals have been envisioned as active components in spintronic devices by virtue of their completely spin-polarized electrical currents. Actual materials hosting half-metallic phases, however, remain scarce. Here, we predict that recently fabricated heterojunctions of zigzag nanoribbons embedded in two-dimensional hexagonal boron nitride are half-semimetallic, featuring fully spin-polarized Dirac points at the Fermi level. The half-semimetallicity originates from the transfer of charges from hexagonal boron nitride to the embedded graphene nanoribbon. These charges give rise to opposite energy shifts of the states residing at the two edges while preserving their intrinsic antiferromagnetic exchange coupling. Upon doping, an antiferromagnetic-to-ferrimagnetic phase transition occurs in these heterojunctions, with the sign of the excess charge controlling the spatial localization of the net magnetic moments. Our findings demonstrate that such heterojunctions realize tunable one-dimensional conducting channels of spin-polarized Dirac fermions that are seamlessly integrated into a two-dimensional insulator, thus holding promise for the development of carbon-based spintronics

EE-BESD: Molecular FET Modeling for Efficient and Effective Nanocomputing Design

Molecular transistor is a good candidate as substitute of CMOS device due to small size, expected good performance and suitability to be included in high density-circuits. To date a lot of effort has been carried out to under- stand the conduction properties in molecular devices. However, minor effort has been devoted to reduce their computational complexity to obtain a compact molec- ular model. First-principle based methods frequently used are highly computational demanding for a single device, thus they are not suitable for complex circuit design. In this paper we present an accurate and at the same time computationally efficient method (named Efficient and Effective model based on Broadening level, Evalua- tion of peaks, Scf and Discrete levels, ee-besd) to calcu- late the electron transport characteristics of molecular transistors in presence of applied bias and gate voltages. The results obtained show a remarkable improve- ment in terms of computational time with respect to existing approaches, while maintaining a very good ac- curacy. Finally, the ee-besd model has been embedded in a circuit level simulator in order to show its function- alities and, particularly, its computational cost. This is shown to be affordable even for circuits based on a high number of devices