The growing interest in tuning the conduction properties of single-molecule junctions has drawn attention to studying their interaction with incident electromagnetic fields. The theoretical complexity of this problem necessitates the use of nonequilibrium statistical mechanics combined with quantum electrodynamics, leading to extremely time-consuming simulations. In this work, we propose a computationally efficient algorithm, which combines EE-BESD—an efficient and effective simulator of current–voltage characteristics in dark conditions—with approximated models for light interaction, specifically the Tien-Gordon and Floquet models. We validate EE-BESD-PAT through comparison with ab initio calculations and experimental data from the literature. Our computational model demonstrates good agreement with both experimental and density functional theory calculations, demonstrating that the proposed method is a promising computationally efficient tool without sacrificing accuracy.

Junctionless Nanosheet gate-all-around Field Effect Transistor (JL-NSGAAFET) is a promising technology characterized by the absence of any junctions between source-channel-drain. This absence allows to further scale down transistors while limiting short-channel effects. In this article, JL-NSGAAFET is explored as a potential candidate for the next 3 nm technology node through 3D TCAD simulations. First, we propose and simulate, through fabrication process simulations, a fabrication strategy for the JL-NSGAAFET compatible with the current manufacturing technology and based on the inversion mode NSGAAFET fabrication process. The high-k gate dielectric (HfO2) and metal-gate technology (TiN) are also adopted in the fabrication process to enhance the electrostatic gate control over the channel for the n-type and p-type transistors. Then, we perform electrical simulations of the device by also including drift-diffusion model and quantum density gradient correction. We characterize the device in terms of electrical performance and compare with the conventional NSGAAFET. Furthermore, to investigate the impact of the device scaling on the unwanted short channel effects, we simulate and analyze the devices while varying the gate length (LG) from 20 nm to 12 nm. Our reported simulation results prove that JL-NSGAAFET exhibits near-ideal subthreshold slope, low drain-induced barrier lowering (DIBL) and high on-to-off current ratio (ION/IOFF) with superior advantages of greater drive currents and a simpler fabrication process because of the absence of junctions.

Molecular field-coupled nanocomputing (molFCN) encodes information in the molecule charge distribution and elaborates it through electrostatic coupling. Despite the advantageous sub-nanometric size and low-power dissipation, only a few attempts have been made to validate the technology experimentally. One of the obstacles is the difficulty in measuring molecule charges to validate information encoding or integrate molFCN with complementary-metal-oxide-semiconductor (CMOS). In this work, we propose a paradigm preserving the advantages of molFCN, which exploits the position of waiving molecules to augment the information encoding. We validate the paradigm, named bend-boosted molFCN, with density functional theory using 6-(ferrocenyl)hexanethiol cations. We demonstrate that the encoded information can be electrically read by constituting a molecular junction. The paradigm is compatible with the charge-based molFCN, thus acting as a readout system. The obtained results favor the experimental assessment of the molFCN principle through scanning probe microscopy techniques and the design of molFCN-CMOS heterogeneous circuits.

The aflatoxin B1 (AFB1) is a cancerogenic compound affecting the agri-food chain, endangering food safety and public health. Worldwide regulatory agencies establish strict limitations for the presence of AFB1 in crops. Current detection methods require bulky equipment, long measurement time, and skilled laboratory researchers, which make it challenging to measure the AFB1 in the whole food chain pervasively. In this field, molecular junctions represent an exciting alternative in the sensing application, providing a highly integrable device for the fast measurement of chemical compounds. Through ab initio simulation, this work investigates graphene junctions for detecting AFB1. The results show that applying a bias voltage of 1.2V to a graphene layer permits varying the electrical current of the junction by more than 3 mu A when the AFB1 is present. The obtained results motivate research on the integrability of the device in more complex sensing systems such as intelligent sensors and electronic noses.

The metal-electrode interface is key to unlocking emergent behaviour in all organic electrified systems, from battery technology to molecular electronics. In the latter, interfacial engineering has enabled efficient transport, higher device stability, and novel functionality. Mechanoresistivity – the change in electrical behaviour in response to a mechanical stimulus and a pathway to extremely sensitive force sensors – is amongst the most studied phenomena in molecular electronics, and the molecule-electrode interface plays a pivotal role in its emergence, reproducibility, and magnitude. In this contribution, we show that organometallic molecular wires incorporating a Pt(II) cation show mechanoresistive behaviour of exceptional magnitude, with conductance modulations of more than three orders of magnitude upon compression by as little as 1 nm. We synthesised series of cyclometalated Pt(II) molecular wires, and used scanning tunnelling microscopy – break junction techniques to characterise their electromechanical behaviour. Mechanoresistivity arises from an interaction between the Pt(II) cation and the Au electrode triggered by mechanical compression of the single-molecule device, and theoretical modelling confirms this hypothesis. Our study provides a new tool for the design of functional molecular wires by exploiting previously unreported ion-metal interactions in single-molecule devices, and develops a new framework for the development of mechanoresistive molecular junctions.

Mechanosensitive molecular junctions, where conductance is sensitive to an applied stress such as force or displacement, are a class of nanoelectromechanical systems unique for their ability to exploit quantum mechanical phenomena. Most studies so far relied on reconfiguration of the molecule-electrode interface to impart mechanosensitivity, but this approach is limited and, generally, poorly reproducible. Alternatively, devices that exploit conformational flexibility of molecular wires have been recently proposed. The mechanosensitive properties of molecular wires containing the 1,1'-dinaphthyl moiety are presented here. Rotation along the chemical bond between the two naphthyl units is possible, giving rise to two conformers (transoid and cisoid) that have distinctive transport properties. When assembled as single-molecule junctions, it is possible to mechanically trigger the transoid to cisoid transition, resulting in an exquisitely sensitive mechanical switch with high switching ratio (> 102). Theoretical modeling shows that charge reconfiguration upon transoid to cisoid transition is responsible for the observed behavior, with generation and subsequent lifting of quantum interference features. These findings expand the experimental toolbox of molecular electronics with a novel chemical structure with outstanding electromechanical properties, further demonstrating the importance of subtle changes in charge delocalization on the transport properties of single-molecule devices.

We investigate through ab-initio simulations the gold-8PyrroleDiThiol-gold (Au-8PyDT) molecular quantum dot as an amperometric single-molecule sensor for the aflatoxin B1 (AFB1) detection. We study the chemical-physical interaction of AFB1 with the Au-8PyDT, and we analyze the transport characteristics of the four most probable adsorption configurations. We also investigate the link between transport modulation and adsorption mechanism. Interestingly, the investigated sensor exhibits conduction features similar to other types of quantum dot-based sensors. A significant current suppression occurs in all cases, with almost two orders of magnitude of current decrease in presence of AFB1 at 0.6 V. Considering the sensor robustness w.r.t. the specific adsorption configurations, our study motivates future research in this field.

We investigate the use of endohedral fullerenes and 6-(Ferrocenyl)hexanethiol cation as molecular non-volatile memory devices. We demonstrate stable encoding of the information in the geometry and dipole moment of these molecules. The write operation can be performed with external programming electric fields that drive the switching of the molecule conformation. The read operation can be performed by reading the dipole moment through the generated electric fields. Moreover, the dipole moment encoding enables the integration of proposed memories with molecular Field-Coupled Nanocomputing logic. The capability to realize compatible and purely molecular memory and logic devices paves the way for molecular MemComputing, with new possibilities for nanoscale computing paradigms.

Food contamination by aflatoxins is an urgent global issue due to its high level of toxicity and the difficulties in limiting the diffusion. Unfortunately, current detection techniques, which mainly use biosensing, prevent the pervasive monitoring of aflatoxins throughout the agri-food chain. In this work, we investigate, through ab initio atomistic calculations, a pyrrole-based Molecular Field Effect Transistor (MolFET) as a single-molecule sensor for the amperometric detection of aflatoxins. In particular, we theoretically explain the gate-tuned current modulation from a chemical–physical perspective, and we support our insights through simulations. In addition, this work demonstrates that, for the case under consideration, the use of a suitable gate voltage permits a considerable enhancement in the sensor performance. The gating effect raises the current modulation due to aflatoxin from 100% to more than 103÷104%. In particular, the current is diminished by two orders of magnitude from the μA range to the nA range due to the presence of aflatoxin B1. Our work motivates future research efforts in miniaturized FET electrical detection for future pervasive electrical measurement of aflatoxins.

NanoSheet-Gate-All-Around-FETs (NS-GAAFETs) are commonly recognized as the future technology to push the digital node scaling into the sub-3 nm range. NS-GAAFETs are expected to replace FinFETs in a few years, as they provide highly electrostatic gate control thanks to the GAA structure, with four sides of the NS channel entirely enveloped by the gate. At the same time, the NS rectangular cross-section is demonstrated to be effective in its driving strength thanks to its high saturation current, tunable through the NS width used as a design parameter. In this work, we develop a NS-GAAFET compact model and we use it to link peculiar single-device parameters to digital circuit performance. In particular, we use the well-known BSIM-CMG core solver for multigate transistors as a starting point and develop an ad hoc resistive and capacitive network to model the NS-GAAFET geometrical and physical structure. Then, we employ the developed model to design and optimize a digital inverter and a five-stage ring oscillator, which we use as a performance benchmark for the NS-GAAFET technology. Through Cadence Virtuoso SPICE simulations, we investigate the digital NS-GAAFET performance for both high-performance and low-power nodes, according to the average future node present in the International Roadmap for Devices and Systems. We focus our analysis on the main different technological parameters with regard to FinFET, i.e., the inner and outer spacers. Our results highlight that in future technological nodes, the choice of alternative low-K dielectric materials for the NS spacers will assume increasing importance, being as relevant, or even more relevant, than photolithographic alignment and resolution at the sub-nm scale.

We investigate through ab-initio simulations the gold-8PyrroleDiThiol-gold (Au-8PyDT) molecular quantum dot as an amperometric single-molecule sensor for the aflatoxin B1 (AFB1) detection. We study the adsorption of AFB1 onto the Au-8PyDT and we analyze the transport characteristics for the most probable adsorption configuration. We find that a significant current modulation occurs, with around 80% of current decrease in presence of AFB1. Interestingly, the investigated sensor exhibits a voltage-dependent response, that we motivate through a transmission properties analysis. Our results, considering the synthesis simplicity of PolyPyrroles and their non-toxicity, motivate future research efforts in this direction.

We investigate through ab initio calculation the endohedral monometallofullerene Cr@C28 as a candidate for data storage applications.First, we study the encapsulation energy and the electronic properties of two stable states of the Cr@C28 -namely I-Cr@C28 and II-Cr@C28.Then, we address the adsorption of C28, I-Cr@C28, and II-Cr@C28 onto a gold substrate.Finally, by emulating a Scanning Tunneling Microscope (STM) break-junction experimental setup, we analyze the STM-mediated transport characteristics for the most probable adsorption configurations.We find and discuss a significant and measurable current difference between the two stable states.This outcome enables the binary encoding of the information, making the proposed device promising as a single-molecule data storage element for future high-density integrated circuits.

Tunnel Field-Effect Transistors (TFETs) have been considered one of the most promising technologies to complement or replace CMOS for ultra-low-power applications, thanks to their subthreshold slope below the well-known limit of 60 mV/dec at room temperature holding for the MOSFET technologies. Nevertheless, TFET technology still suffers of ambipolar conduction, limiting its applicability in digital systems. In this work, we analyze through SPICE simulations, the impact of the symmetric and asymmetric ambipolarity in failure and power consumption for TFET-based complementary logic circuits. Our results clarify the circuit-level effects induced by the ambipolarity feature, demonstrating that it affects the correct functioning of logic gates and strongly impacts power consumption. We believe that our outcomes motivate further research towards technological solutions for ambipolarity suppression in TFET technology for near-future ultra-low-power applications.

We investigate through atomistic calculation the electronic structure and transport properties of 3-phenylethynylene (OPE3), 7-phenylvynylene (OPV7), and [3, 3]paraCyclophane (pCp)-based molecules. We reveal and analyze the Destructive Quantum Interference (DQI) phenomenon for the pCp single-molecule junction. The provided explanation of DQI via the dominant concurrence of inter-orbital and intra-orbital interference may support DQI engineering through the chemical synthesis of ad hoc molecular channel. Furthermore, we propose a Back gate Biasing-based method for the ON/OFF CUrrent Ratio Enhancement of the single-molecule Field-Effect transistor via the control of DQI (BBB-CURE-DQI). As an important outcome of the proposed method, an ON/OFF current ratio of 103 is achieved for pCp single-molecule FET. This value is orders of magnitude larger than typical values presented in the literature. The benefit of the DQI and the effectiveness of the BBB-CURE-DQI method are finally demonstrated at the circuital level by SPICE simulations of digital inverters implemented with the investigated molecules. Our analysis and results motivate the importance of future research investment for DQI manipulation via chemical synthesis and successive control to enable single-molecule FET-based nanocomputing applications.

The recent growth of Artificial Neural Networks fueled the design of numerous Artificial Intelligence (AI) dedicated hardware implementations. High power dissipation, computational complexity, and large area footprints currently limit CMOS based real-time embedded AI applications. In this work, we design and simulate through SPICE, for the first time, an artificial analog neuron based on the molecular Field-Effect Transistor (molFET) technology. MolFETs are described by a circuital model whose physical characteristics are extracted from atomistic simulations. The designed neuron is a single column of a crossbar-like circuit representing a layer of seven parallel neurons. The drain currents sum up in a soma-like circuit - modelled through a comparator - and trigger the output pulses. We demonstrate the advantages of the molFET in terms of area, power, and speed by comparing it with a conventional MOSFET implementation. The results confirm the molecular technology is a promising candidate for accomplishing high neuron throughput capability and massive redundancy, still providing high energy efficiency. The obtained results foster further investigation of molFET technology both at the device and circuit level.

In the last 50 years, Moore's law has fueled the development of the computing field. Nowadays, skyrocketing fabrication costs and increasing demand for miniaturization, high performance and low power consumption are becoming incredibly challenging, pushing the research effort towards Beyond-CMOS technologies and innovative architectural solutions. In this scenario, molecular electronics paves the way for smart and cheap technological processes based on self-assembly. The possibility to produce artificial molecules with nano-scaled dimensions and engineered properties, is really attractive, since enables extremely high integration with fewer power issues accomplishing a variety of electronic tasks, including conducting wire, rectification, memory, sensor and switching only by simply changing the type of molecule. This thesis work investigates molecular nanocomputing solutions based on electronic transport, spacing from physical level to the application abstraction level, with constant attention devoted to providing a physical insight from an Electronics Engineer standpoint. The first part of this work deepens at the very physical level of abstraction in quantum transport models and the theory of conduction at nanoscale. With the aim to provide a practical understanding, theory's outcomes are aided in parallel by atomistic simulations. The second part is devoted to the device level of abstraction: different molecules from the state-of-art literature synthesized ad-hoc for computing applications are engineered in a device configuration and characterized by means of ab-initio simulations. Proper figures of merit are extracted. Finally, the aim of the last part is to investigate at architectural level how to overcome the limitations of present computational systems by exploiting the possibilities offered by molecular technology and unconventional architectures. Firstly a molecular implementation of logic (logic gates, Half- Adder, Full-Adder) and memory (SRAM) elements is performed, and then a target Logic-in-Memory application is discussed and implemented. Design, functional verifications, performance analysis are performed in Cadence Virtuoso both for molecular ambipolar transistors and FD-SOI MOSFET (28 nm) technologies in order to be compared and demonstrate the benefits and problems, for this specific application, in migrating from conventional to a molecular technology. At last, the stated goal of the thesis is achieved. It reaches an adequate awareness of how the nature of molecular technology is often very different from CMOS established one. As a consequence conventional architectural paradigms cannot really do justice of its overwhelming potentialities. Therefore possible alternative solutions are proposed and briefly analyzed in view of seeking out a deeper understanding of the physics of transport and storage inside molecules and boldly go where no silicon-based computing system has gone before!