Molecular Electronic Circuits Research Articles

Missing-cell defects in QCA wires: The ground and excited electronic states perspectives

Quantum Cellular Automata (QCA) technology offers promising prospects for designing molecular electronic circuits that operate at high frequencies and with ultra-low power consumption. QCA wires serve as crucial conduits for digital data transmission between logic gates. A series of QCA cells arranged sequentially forms these wires, with data written or read using paired nanogap electrodes. In this study, employing a simplified full-basis quantum mechanical model, we investigate the impact of single and double missing cells on the response function and output voltage of wires implemented within the two-dot QCA architecture. The electronic coupling between the quantum dots within each QCA cell stands out as a critical structural parameter influencing both the nonlinearity of the response function and the level of output voltage. Ground state analyses of wires affected by missing-cell defects suggest that employing QCA cells with weak electronic coupling could potentially enhance fault tolerance. However, examination of excited states reveals that reducing electronic coupling may compromise the thermal robustness of such defective QCA wires.

Connections to the Electrodes Control the Transport Mechanism in Single-Molecule Transistors.

When designing a molecular electronic device for a specific function, it is necessary to control whether the charge-transport mechanism is phase-coherent transmission or particle-like hopping. Here we report a systematic study of charge transport through single zinc-porphyrin molecules embedded in graphene nanogaps to form transistors, and show that the transport mechanism depends on the chemistry of the molecule-electrode interfaces. We show that van der Waals interactions between molecular anchoring groups and graphene yield transport characteristic of Coulomb blockade with incoherent sequential hopping, whereas covalent molecule-electrode amide bonds give intermediately or strongly coupled single-molecule devices that display coherent transmission. These findings demonstrate the importance of interfacial engineering in molecular electronic circuits.

Single‐Molecule Doping: Conductance Changed By Transition Metal Centers in Salen Molecules

AbstractThe creation of molecular components for use as electronic devices has made enormous progress. In order to advance the field further toward realistic electronic concepts, methods for the controlled modification of the conducting properties of the molecules contacted by metallic electrodes need to be further developed. Here a comprehensive study of charge transport in a class of molecules that allows modifications by introducing metal centers into organic structures is presented. Single molecules are electrically contacted and characterized in order to understand the role of the metal centers in the conductance mechanism through the molecular junctions. It is shown that the presence of single metal ions modifies the energy levels and the coupling of the molecules to the electrical contacts, and that these modifications lead to systematic variations in the statistical behavior of transport properties of the molecular junctions. A rigorous statistical analysis of thousands of junctions is performed to reveal this correlation. The understanding of the role of the metal ion in the resulting conductance properties is an essential step toward the development of molecular electronic circuits.

A quinone based single-molecule switch as building block for molecular electronics

Using a model molecule, we show that it is possible to create molecules that show the required properties for use as elements in a molecular circuit or computer: two conformations with similar energy but different electric conductivity, and the possibility to switch between those by applying an external electric field.

Attenuation of Redox Switching and Rectification in Azulenequinones/Hydroquinones after B and N Doping: A First‐Principles Investigation

AbstractThe redox switching of doped 1,5‐azulenequinones/hydroquinones wired between gold electrodes is investigated using density functional theory and the nonequilibrium Green's function. Their electronic transport properties when separately doped with nitrogen and boron as well as co‐doping of these atoms are examined. The results illustrate a significant enhancement of the current at low bias voltage in some of the 12 doped studied systems, leading to “switching on” the transmission, where the greatest switching ratio is 18. These systems also exhibit a modest rectification in which the greatest rectification ratio is 4. The significance of the position of the doped atom and the functional group on the switching behavior is analyzed through the transmission spectra and molecular orbitals. The present study broadens knowledge of organic redox switching bringing in potential diverse options for future molecular electronic circuit components.

Mathametical Modelling of Full Adder using Carbon Nanorods

Nanomechanical computational systems proposed by K.Drexler is one of the approaches to molecular scale electronic circuits for memory and logic applications. The nanomechanical rod logic proposed is distinguished by its small size and very low energy dissipation, compared to transistors. it has been found from the sources available to us, that presently the idea was highly unexplored and still remains in its nascent stages This paper presents the use of nanorods as variant to the existing silicon technology for the design of a full adder circuit along with the speed, power and energy dissipation characteristics. The full adder circuit is then extended to an n-bit adder (which forms the basis of an ALU circuit). The paper also addresses the use of parallel architectures to overcome the limitations of switching speeds.

Construction and Analysis of Double Helix for Triangular Bipyramid and Pentangular Bipyramid.

DNA cages can be joined together to make larger 3D nanostructures on which molecular electronic circuits and tiny containers are built for drug delivery. The mathematical models for these promising nanomaterials play important roles in clarifying their assembly mechanism and understanding their structures. In this study, we propose a mathematical and computer method to construct permissible topological structures with double-helical edges for a triangular bipyramid and pentangular bipyramid. Furthermore, we remove the same topological links, without eliminating the nonrepeated ones for a triangular bipyramid and pentangular bipyramid. By analyzing characteristics of these unique links, some self-assembly and statistic rules are discussed. This study may obtain some new insights into the DNA assembly from the viewpoint of mathematics, promoting the comprehending and design efficiency of DNA polyhedra with required topological structures.

Nanoparticle Linker‐Controlled Molecular Wire Devices Based on Double Molecular Monolayers

Highly conductive molecular wires are an important component for realizing molecular electronic devices and have to be explored in terms of interactions between molecules and electrodes in their molecular junctions. Here, new molecular wire junctions are reported to enhance charge transport through gold nanoparticle (AuNP)-linked double self-assembled monolayers (SAMs) of cobalt (II) bis-terpyridine molecules (e.g., Co(II)(tpyphS)2 ). Electrical characteristics of the double-SAM devices are explored in terms of the existence of AuNP. The AuNP linker in the Co(II)(tpyphS)2 -AuNP-Co(II)(tpyphS)2 junction acts as an electronic contact that is transparent to electrons. The weak temperature dependency of the AuNP-linked molecular junctions strongly indicates sequential tunneling conduction through the highest occupied molecular orbitals (HOMOs) of Co(II)(tpyphS)2 molecules. The electrochemical characteristics of the AuNP-Co(II)(tpyphS)2 SAMs reveal fast electron transfer through molecules linked by AuNP. Density functional theory calculations reveal that the molecular HOMO levels are dominantly affected by the formation of junctions. The intermolecular charge transport, controlled by the AuNP linker, can provide a rational design for molecular connection that achieves a reliable electrical connectivity of molecular electronic components for construction of molecular electronic circuits.

Chemical Self-Assembly Strategies for Designing Molecular Electronic Circuits: Demonstration of Concept

The design of molecular electronic circuits will require the development of strategies for making controlled interconnections between nanoelectrodes. The simplest example of a molecular electronic component consists of aryl rings with para-anchoring functionalities, commonly isocyanide or thiol groups. In particular, 1,4-phenylene diisocyanobenzene (1,4-PDI) has been shown to form conductive one-dimensional, oligomeric chains that are composed of alternating gold and 1,4-PDI units in which a gold adatom is linked to two trans isocyanide groups. Density functional theory (DFT) calculations of the oligomerization pathway reveal that growth occurs via a vertical, mobile Au–PDI adatom complex that forms by binding to the gold substrate and oligomerizes by the gold adatom attaching to the isocyanide terminus of a growing chain. In this case, the gold atoms in the oligomer derive from the gold substrate. In principle, bridging between adjacent electrodes could be tuned by controlling the 1,4-PDI dose. However, ...

Control of quantum dynamics of electron transfer in molecular loop structures: Spontaneous breaking of chiral symmetry under strong decoherence

Manipulation of quantum systems is the basis for many promising quantum technologies. However, how quantum mechanical principles can be used to manipulate the dynamics of quantum dissipative systems remains unanswered because of strong decoherence effects arising from interaction with the surrounding environment. In this work, we demonstrate that electron transfer dynamics in molecular loop structures can be manipulated with the use of Floquet engineering by applying a laser field. Despite strong dephasing, the system's dynamics spontaneously breaks the chiral symmetry of the loop in a controllable fashion, followed by the generation of a robust steady-state electronic current without an external voltage. An exponential scaling law that relates the magnitude of the current to the system-environment coupling strength is revealed numerically. The breaking of chiral symmetry and the consequent controllable unidirectional flow of electrons could be employed to construct functional molecular electronic circuits.

Chemical self-assembly strategies for designing molecular electronic circuits.

Design principles are demonstrated for fabricating molecular electronic circuits using the inherently self-limiting growth of molecular wires between gold nanoparticles from the oligomerization of 1,4-phenylene diisocyanide.

Rotational switches in the two-dimensional fullerene quasicrystal.

One of the essential components of molecular electronic circuits are switching elements that are stable in two different states and can ideally be switched on and off many times. Here, distinct buckminsterfullerenes within a self-assembled monolayer, forming a two-dimensional dodecagonal quasicrystal on a Pt-terminated Pt3Ti(111) surface, are identified to form well separated molecular rotational switching elements. Employing scanning tunneling microscopy, the molecular-orbital appearance of the fullerenes in the quasicrystalline monolayer is resolved. Thus, fullerenes adsorbed on the 36 vertex configuration are identified to exhibit a distinctly increased mobility. In addition, this finding is verified by differential conductance measurements. The rotation of these mobile fullerenes can be triggered frequently by applied voltage pulses, while keeping the neighboring molecules immobile. An extensive analysis reveals that crystallographic and energetic constraints at the molecule/metal interface induce an inequality of the local potentials for the 36 and 32.4.3.4 vertex sites and this accounts for the switching ability of fullerenes on the 36 vertex sites. Consequently, a local area of the 8/3 approximant in the two-dimensional fullerene quasicrystal consists of single rotational switching fullerenes embedded in a matrix of inert molecules. Furthermore, it is deduced that optimization of the intermolecular interactions between neighboring fullerenes hinders the realization of translational periodicity in the fullerene monolayer on the Pt-terminated Pt3Ti(111) surface.

Electrostatic Gate Control in Molecular Transistors.

Molecular transistors, in which single molecules serve as active channel components in a three-terminal device geometry, constitute the building blocks of molecular scale electronic circuits. To demonstrate such devices, a gate electrode has been incorporated in several test beds of molecular electronics. The frontier orbitals' alignments of a molecular transistor can be delicately tuned by modifying the molecular orbital energy with the gate electrode. In this review, we described electrostatic gate control of solid-state molecular transistors. In particular, we focus on recent experimental accomplishments in fabrication and characterization of molecular transistors.

Self‐assembled gold nanoparticle–molecular electronic networks

Electronic transport through self‐assembled networks consisting of colloidal gold particles interconnected with thiolated alkane molecules is studied using a combination of broad area and scanning probe microscope‐based measurements. The molecule–gold nanoparticle ratio and/or type of molecules is used to alter electronic transport paths through the network and allow the resistance to be controllably tuned by several orders of magnitude (∼105–1011 ohms for the structures studied). Local probing and imaging of the colloidal gold networks via atomic force microscopy is able to detect the presence of molecular connections and also indicates that the number of molecules is important for achieving good network packing with a minimum ratio of molecules to particles between 1:1 and 5:1 found to be needed in order to form well‐connected molecular electronic circuits. Circuit simulations used to model the electrical behavior of the self‐assembled nanoscale networks based on different morphologies and dimensions show good agreement with experiment and provide a guide for engineering network properties using superstructures of different molecules. These results demonstrate directed self‐assembly as a potential avenue for the creation of molecular integrated circuits.

DNA-Metalization: Synthesis and Properties of Novel Silver-Containing DNA Molecules (Adv. Mater. 24/2016).

D. Porath, A. Kotlyar, and co-workers transform DNA to a conducting material by metalization through coating or chemical modifications, as described on page 4839. Specific and reversible metalization of poly(dG)-poly(dC) DNA by migration of atoms from silver nanoparticles to the DNA is demonstrated. As the transformation occurs gradually, novel, truly hybrid molecular structures are obtained, paving the way to their usage as nanowires in programmable molecular electronic devices and circuits.

A Bioinspired Light‐Controlled Ionic Switch Based on Nanopipettes

AbstractDevelopment of new principles for fabrication of novel ionic devices has attracted much attention due to the potential applications of ionic devices in molecular computer, biosensing and electronic circuit. Inspired by optogenetics altering membrane voltage via light‐controlled proteins, a new kind of light‐controlled ionic switch was demonstrated here based on nanopipettes. Upon exposure to visible light, spiropyran (SP) does not coordinate with Zn2+, resulting in a relatively large ionic current. While, upon UV light irradiation, SP was transformed into merocyanine (MC) that coordinates with Zn2+ and thereby results in the decrease in the ionic current. The ionic current could be reversibly modulated by UV/Vis light irradiation. The finite‐element simulation was performed to understand the possible mechanism underlying the light‐controlled ionic switch based on nanopipettes.

English

Although molecular electronics is in its infancy, there are many significant advances in understanding and implementing computational functions based on molecular electronic devices. In order to evaluate a molecular electronic circuit, a model is needed. In existing literature, only a few models have been introduced for molecular electronics, all of which do not support the hysteresis phenomenon. To the best of the authors’ knowledge, for the first time, this paper introduces a behavioral model in SPICE which is able to imitate hysteresis behavior in a desired molecular circuit. The proposed model is then modified in order to guarantee continuous behavior in its I/V curves. Some molecular electronic I/V curves from the literature are selected and by utilizing the proposed model, its correct operation are investigated.   Key words: Molecular electronics, behavioral model, hysteresis phenomenon, SPICE.

Electrical switching in a Fe-thiacrown molecular device

First-principles calculations are performed to inspect the electronic and transport properties of a Fe-thiacrown molecular device, namely, a Au-Fe(9S3)2-Au junction. It is found that the junction has a low-spin (LS) ground state and a high-spin (HS) metastable state. Further study shows that the HS state is a conducting state while the LS state is a nearly insulating one, which means that a switch between these two spin configurations results in a good electrical switching behavior and can serve as an ON/OFF state for a logic unit. Thus, it may find applications as switches or memories in molecular electronic circuits.

Current Transportation in Semiconductor Devices and Molecular Material Devices and Perspectives

The capacity and minimization of storage information and operation are rapidly reaches to a limit. Available materials in the nature used for electronic circuits, Communication, optoelectronic devices and display devices is identified. Molecular electronics and molecular computing is good solution to overcome the present limitation of computing devices and storage information, speed of operation. Molecular electronics as technology using single molecule, small group of molecules, carbon nanotubes or semiconductor to perform electronic function. Such designs related to conductive mono molecular circuit configuration that can be million times smaller than the conventional solid state electronic circuits and computers. Designed molecular circuits appear that Nanometer scale molecular electronic circuits fabricated and tested in the foreseeable future. Finally molecular logic circuits and computational devices are final limits of the electronic computer circuit miniaturization. This research paper overview the evaluation of current flow in solid state devices, to present available molecular material polyphenylene base molecule material and its derivatives.

Nanoscale Origin of Defects at Metal/Molecule Engineered Interfaces

The control and repair of defects at metal/molecule interfaces is central to the realization of molecular electronic circuits with reproducible performance. The fundamental mechanism governing defect (pore) evolution on mica-supported metal surfaces, its propagation in self-assembled molecular layers, and its implications for molecular junction devices are discussed. Pore eradication by replacing mica with halide platforms coupled with elevated substrate temperature during metal deposition yields exceptionally ultraflat metal landscapes. In situ scanning tunneling microscopy further substantiates molecular locking at defect sites and upon defect healing; the emergence of a closely packed 2-D molecular architecture is demonstrated with nanometer-scale spatial resolution in liquids.