Department of Electrical and Computer Engineering
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Browsing Department of Electrical and Computer Engineering by Author "Blair, Enrique Pacis."
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Item A model of clocked electric field inputs for molecular quantum-dot cellular automata.(2019-11-08) Henry, Jackson Alan, 1994-; Blair, Enrique Pacis.Quantum-dot cellular automata (QCA) is a low-power, high-speed, beyond- CMOS approach to general-purpose computing [1]. Elementary devices called “cells” are implemented using mixed-valence molecules with redox centers having a few quan- tum dots. These support three distinct localized electronic states labeled “0”, “1”, and “Null”. Cells can be clocked to either the “Null” state or an active (“0” or “1”) state using the vertical component of an applied electric field. Clocking provides power gain for restoring weakened signals and allows synchronous control of QCA circuits. In this paper, clocked molecular QCA circuits are simulated in the presence of an applied input field, using the intercellular Hartree-Fock approximation [2]. In- put circuits and down-stream circuits function in the presence of the input field and unwanted field fringing from electrodes. This emphasizes that widely-available fabri- cation techniques may be used to form electrodes for writing bits to molecular QCA circuits.Item Ab-initio models of quantum dot cellular automata molecules.(December 2022) Liza, Nishat Tasnim, 1993-; Blair, Enrique Pacis.Molecular quantum-dot cellular automata (QCA) is a charge based, low-power, energy-efficient alternative to transistor-based, general-purpose computation. In molecular QCA, redox centers of a mixed-valence (MV) molecule function as coupled quantum dots, and localized charge states of the molecule encode binary information useful for classical computing. Molecular QCA promises ultra-high device densities, THz-scale switching speeds and room temperature readout. While the fundamental principle of molecular QCA have been tested and established, major challenges must be overcome to successfully implement molecular QCA. This work applies ab-initio techniques in the design and modeling of candidate MV molecules for QCA. Here, we study and characterize ∼ 1-nm-scale MV QCA molecules using first principle calculations. The structural and electronic properties of QCA molecules are calculated utilizing Hartree-Fock, Post-Hartree-Fock and Density functional theory (DFT) methods. Asymmetric, cationic, MV molecules are designed for spectroscopic state readout of QCA devices at room temperature. Tip-enhanced Raman spectroscopy is proposed to detect the state of QCA devices in a circuit if the QCA molecules have slightly dissimilar quantum dots. Clocked zwitterionic three-dot QCA molecules with built-in counterions at the center of the molecules are modeled. The choice and design of the central linkers of these molecules determines number of mobile charges in the molecules for encoding the device states on the three quantum dots. These molecules show different device responses to applied clocking electric field based on different central linkers designed and used, similar to the complementary responses of PMOS and NMOS transistors to gated voltage control. Counterion effects on QCA candidate molecules are also explored in terms of electron transfer parameters. The complete active space self consistent field (CASSCF) method is used to calculate electron transfer (ET) matrix element and inner-sphere reorganization energy of the molecules in the presence of nearby counterions. Results demonstrate that randomly placed externel counterions may degrade device states by causing mobile charge to localize in undesirable ways on the QCA molecule. New zwitterionic molecules with a built-in counterion are proposed to eliminate unpredictable effects of external counterions in QCA circuits. Novel organometallic zwitterionic QCA molecules with ferrocene dots are designed and proposed for synthesis. The chemical stability of these ferrocene based molecules are evaluated by theoretical calculations. The synthesis of these stable zwitterionic molecules by collaborating experimental chemists is in progress and may open a new path to realize molecular QCA computing. A new machine-learning-based DFT functional, DM21 is investigated and benchmarked against traditional methods by comparing the calculated ET matrix elements of several QCA molecules. Preliminary results calculated from DM21 functional did not show significant improvements in accuracy and computational cost. Modification and improvement of the neural network used in the development of the functional, as well as the underlying code is proposed which might open new path to computationally inexpensive QCA calculations.Item An explicit electron-vibron model for olfactory inelastic electron transfer spectroscopy.(2019-04-01) Liza, Nishattasnim, 1993-; Blair, Enrique Pacis.The vibrational theory of olfaction was posited to explain subtle effects in the sense of smell inexplicable by models in which molecular structure alone determines an odorant’s smell. Amazingly, behavioral and neurophysiological evidence suggests that humans and some insects can be trained to distinguish isotopologue molecules related by isotope substitution. How is it possible to smell a neutron? Inelastic electron transfer spectroscopy (IETS) is a proposed mechanism to explain such subtle olfactory effects: the vibrational spectrum of an appropriately-quantized odorant molecule may enhance a transfer rate in a discriminating electron transfer (ET) process. In contrast to existing models of olfactory IETS, the model presented here explicitly treats the dynamics of the dominant odorant vibrational mode. Power is dissipated directly from electron to environment and indirectly via damped odorant vibrations. The spectroscopic behavior in ET rate is unmasked if the direct-path dissipation is negligible. This may support olfactory isotopomer discrimination.Item Models and designs of clocked molecular quantum-dot cellular automata circuits.(2022-03-30) Cong, Peizhong, 1991-; Blair, Enrique Pacis.Quantum-dot cellular automata (QCA) is a general-purpose, low-energy, high-efficiency, general purpose computing paradigm. QCA computation may overcome challenges such as heat dissipation and the clock speed bottleneck facing the extreme scaling of CMOS. A molecular implementation of QCA promises nanometer-scale device sizes, ultra high device densities, and ∼THz clock speed all at room temperature. We model and design molecular QCA circuits immersed in applied electric fields to address various technical challenges in the path to realizing molecular QCA. We explore the use of molecular QCA circuits and field-generating electrodes for both the write-in and read-out of classical bits, two problems central to interfacing conventional semiconductor logic with molecular QCA logic. We design and model novel circuits which may support the input and output of classical bits with the help of an applied electric field. While electric fields are useful for input and output circuits, they may disrupt information-processing circuits. Therefore, we also explore the extent to which molecular circuits (logic and interconnects) tolerate applied electric fields. We demonstrate that molecular QCA circuits can tolerate significant unwanted electric fields, well beyond those fields required for bit input or output.