Molecular Field-effect Transistors Research Articles

Enhancing Gating Performance in Organic Molecular Field-Effect Transistors by Introducing Polar Azulene Components.

Organic molecular field-effect transistors (FETs) are promising building components for future electronic circuits. Efficient control of charge transport properties is one key issue in the design of organic molecular FETs. In this study, we propose a redesign of a naphthalene-based FET by introducing two azulene components in opposite dipole moment directions. Using density functional theory combined with non-equilibrium Green's function, the simulated electronic transport characteristics reveal that the introduction of polar azulene components effectively narrows the frontier molecular orbitals gap, leading to an increase in the ON-state current. Meanwhile, the OFF-state current is significantly suppressed by highly localizing the dominant electronic transport channel. As a result, improved gate controllability is achieved with a higher ON-OFF current ratio, which is nearly seven times higher than that of the naphthalene-based FET device. These findings provide theoretical directions for future design of organic molecular FET devices with enhanced gating regulation efficiency.

Hybrid molecular graphene transistor as an operando and optoelectronic platform

Lack of reproducibility hampers molecular devices integration into large-scale circuits. Thus, incorporating operando characterization can facilitate the understanding of multiple features producing disparities in different devices. In this work, we report the realization of hybrid molecular graphene field effect transistors (m-GFETs) based on 11-(Ferrocenyl)undecanethiol (FcC11SH) micro self-assembled monolayers (μSAMs) and high-quality graphene (Gr) in a back-gated configuration. On the one hand, Gr enables redox electron transfer, avoids molecular degradation and permits operando spectroscopy. On the other hand, molecular electrode decoration shifts the Gr Dirac point (VDP) to neutrality and generates a photocurrent in the Gr electron conduction regime. Benefitting from this heterogeneous response, the m-GFETs can implement optoelectronic AND/OR logic functions. Our approach represents a step forward in the field of molecular scale electronics with implications in sensing and computing based on sustainable chemicals.

Design of Pyrrole-Based Gate-Controlled Molecular Junctions Optimized for Single-Molecule Aflatoxin B1 Detection.

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.

Impact of surface roughness on conduction in molecular semiconductors

The interface roughness between gate insulator and semiconductor is expected to reduce the conductance of molecular field-effect transistors. This study merges atomic force microscopy data of layer topographies with self-consistent calculations of charge carrier densities and conductances within the channel region. It is found that a roughness equivalent to one monolayer reduces the conductance by nearly 50%. Currents flow mainly within the first monolayer of the semiconductor and along percolation pathways, where charges rarely undergo transfers between adjacent monolayers.

Switching characteristics of anthraquinone molecular devices based on graphene electrodes

With the development of microelectronics and the miniaturization of electronic devices, the use of molecular materials to construct various components in electronic circuits has become a most likely development trend. Compared with silicon-based semiconductor components, molecular electronic device has the advantages of small size, high integration, low energy consumption and fast response. In recent years, more and more molecules have been used to design molecular devices such as molecular diodes, molecular switches, molecular field effect transistors and molecular memories. In this paper, sandwich structure devices based on graphene nanoribbon electrodes are constructed. The first-principles calculation method combining density functional theory and non-equilibrium Green’s function is adopted to design the molecular devices with functional characteristics. The effects of redox reactions on the electrical transport properties of molecular devices are systematically discussed. The main research contents of this paper are as follows. The switching characteristics of an anthraquinone molecular device based on graphene electrode are studied. The zigzag-edge nanoribbons and armchair-edge graphene nanoribbons are selected as electrodes. Considering the two isomers of anthraquinone (HQ) and anthraquinone (AQ) molecules in the redox reaction, the double electrode molecular junction is constructed. The effects of redox reaction and electrode structure on the switching characteristics of anthraquinone molecular devices are discussed. It is found that the current in the HQ configuration is significantly greater than that in the AQ configuration, regardless of the zigzag-edge graphene electrode or the armchair-edge graphene electrode. That is, under the redox reaction, the anthraquinone molecules show significant switching characteristics. The switching ratio of zigzag-edge graphene electrode is selected to reach a maximum of 3125, and that of armchair-edge graphene electrode is selected to maximum of 1538. In addition, when the armchair-edge graphene is used as an electrode in the HQ configuration, the negative differential resistance is obviously between 0.7 and 0.9 V.

Kees Hummelen: a creative, inspirational and unorthodox scientist from Groningen

To mark the occasion of the official retirement of Prof. J. C. (Kees) Hummelen, the Journal of Materials Chemistry C has dedicated a special issue to honour his achievements in the field of materials chemistry. This personal essay, written by his study mate, close colleague and long-standing friend, highlights the pioneering contributions that Kees Hummelen has made in various fields of organic and materials chemistry during his 45 year long career. His research in chemistry began with asymmetric synthesis and chemiluminescence and culminated in his most notable results in the field of fullerene chemistry and the development of organic photovoltaic technology. More recently, he has also been active in the field of materials for molecular field-effect transistors, biosensors and the development of single molecule electronics based on internal π logic. He was also a dedicated teacher and was deeply involved in societal challenges. Because of my personal relationship with Kees during all of those 45 years, I have written this essay in a somewhat unorthodox way; a way that is so characteristic of Kees.

Molecule-Based Transistors: From Macroscale to Single Molecule.

Molecule-based field-effect transistors (FETs) are of great significance as they have a wide range of application prospects, such as logic operations, information storage and sensor monitoring. This account mainly introduces and reviews our recent work in molecular FETs. Specifically, through molecular and device design, we have systematically investigated the construction and performance of FETs from macroscale to nanoscale and even single molecule. In particular, we have proposed the broad concept of molecular FETs, whose functions can be achieved through various external controls, such as light stimulation, and other physical, chemical or biological interactions. In the end, we tend to focus the discussion on the development challenges of single-molecule FETs, and propose prospects for further breakthroughs in this field.

Ternary inverter gate designs using OPV5-based single-molecule field-effect transistors

Over recent decades, much effort has been invested in the implementation of digital circuits using multivalued and fuzzy logic, as they are more similar to real-world arithmetic and logic. Ternary logic can be implemented in molecular electronics using transistors based on benzene rings because of their special characteristics. A dual-gate molecular field-effect transistor based on the oligo (phenylene vinylene) molecule, which consists of aromatic rings, is proposed herein. Moreover, models for the implementation of all the different types of ternary inverter, viz. a negative ternary inverter, standard ternary inverter, and positive ternary inverter, as well as a binary full adder (FA) cell are proposed. Of note, each of the ternary inverters is implemented using just one transistor, while the FA cell is implemented using two transistors. The transistor, the inverters, and the FA cell are simulated using standard tools to verify their functionality.

Single Molecule-Based Electronic Devices: A Review

In the face of the fact that the development of traditional silicon-based electronic devices is increasingly limited, single molecule electronic device, which has been attracting more and more attention, is considered as one of the most hopeful candidates to realize the miniaturization of conventional electronic devices. In this paper, an overview of single molecule electronic devices is provided, including molecular electronic devices and electrode types. First, several molecular electronic devices are presented, including molecular diodes, molecular memories, molecular wires, molecular field effect transistors (FET) and molecular switches. Then the influence of different electrode types of the transport characteristics is introduced, showing that graphene is a promising electrode material for single molecule electronic devices. Moreover, other excellent characteristics of molecular devices are briefly introduced, such as potential thermoelectric effects, new thermally induced spin transport phenomena and negative differential resistance (NDR) behavior. Finally, the future challenges to the development of electronic devices based on single molecules are described.

Lateral scaling and positioning effects of top-gate electrodes on single-molecule field-effect transistors

Molecular electronics aims at integrating controllable molecular devices into circuits or machines to realize certain functions. According to device configuration, molecular field-effect transistors with top-gate electrodes have great advantages for integration. Nevertheless, from technical aspects, it is difficult to control lateral scale and position of a top-gate electrode precisely. Therefore, one problem arises in how lateral scaling and positioning effects of a top-gate electrode affect device performance. To solve this problem, the electronic transport properties of single-molecule field-effect transistor configurations modulated by a series of partial-scale top-gate electrodes with different lateral scales and positions are studied by using non-equilibrium Green’s function in combination with density functional theory, and compared with those of the full gate electrode (can be considered as a bottom gate electrode). The results show that lateral scaling and positioning effects indeed have a great impact on electronic transport properties of single-molecule field-effect transistor configurations. For -saturated 1,12-dodecanedithiol devices, larger lateral scale of a partial-scale top-gate electrode obtains larger amplification coefficient (ratio of device conductances with/without a gate electrode), and even larger than that of the full gate electrode. While lateral positioning effect has little influence on this device. For -conjugated 1,3,5,7,9,11-dodehexaene-1,12-dithiol devices, performance of a partial-scale top-gate electrode mainly depends on locations of its two edges, i.e. the number of bonds that it breaks. These results will provide theoretical directions in device designing and manufacturing in the future.

Probing the Electronic Properties of Monolayer MoS2 via Interaction with Molecular Hydrogen

AbstractThis work presents a detailed experimental investigation of the interaction between molecular hydrogen (H2) and monolayer MoS2 field effect transistors (MoS2 FET), aiming for sensing application. The MoS2 FET exhibits a response to H2 that covers a broad range of concentration (0.1–90%) at a relatively low operating temperature range (300–473 K). Most important, H2 sensors based on MoS2 FETs show desirable properties such as full reversibility and absence of catalytic metal dopants (Pt or Pd). The experimental results indicate that the conductivity of MoS2 monotonically increases as a function of the H2 concentration due to a reversible charge transferring process. It is proposed that such process involves dissociative H2 adsorption driven by interaction with sulfur vacancies in the MoS2 surface (VS). This description is in agreement with related density functional theory studies about H2 adsorption on MoS2. Finally, measurements on partially defect‐passivated MoS2 FETs using atomic layer deposited aluminum oxide consist of an experimental indication that the VS plays an important role in the H2 interaction with the MoS2. These findings provide insights for future applications in catalytic process between monolayer MoS2 and H2 and also introduce MoS2 FETs as promising H2 sensors.

(Invited) Fabrication and Characterization of Carbon-Based Nanoscale Devices: Insights and Applications

Nanoscale devices made from carbon-based materials are investigated for a variety of unique properties and features, including their promise to improve performance, decrease production costs, or provide totally new functionality relative to extant electronic devices. Because these devices have active areas composed of materials that are much thinner than those used in conventional devices, the details of the interfaces can often act to control the physics that lead to the operational device characteristics in unexpected ways. This is particularly true in molecular electronics, where design rules based on chemical intuition often fail to account for key physical aspects that dominate device behaviour. Thus, the ability to modify interfaces in a way that leads to control of device properties is a key to enabling next-generation devices based on nanoscale phenomenon. In addition, it is important to achieve an understanding of the processes that occur during carrier transport in nanoscale devices in order to obtain desirable functionality. This presentation will describe several aspects of carbon-based nanoscale devices, including fabrication and operation of molecular electronics and graphene field effect transistors (GFETs). After a discussion of some general physical principles that operate within the interfacial energy level alignment regime in molecular electoronics, a discussion of how light emission from nanoscale devices can be used to characterize them will be provided. In particular, we have used light emission from both large area molecular junctions and GFETs to understand important distance scales (elastic limits) and processes (transport and emission mechanisms). The data indicate that processes that involve hot carrier interactions with plasmonic structures in the devices lead to light emission, and that this phenomenon can be used to measure energy losses of carriers as they traverse a molecular layer. Results indicate that carriers can travel approximately 7 nm through a molecular junction before energy losses become significant, indicating that elastic transport is achieved for thin layers, but a transition in mechanism occurs for thicker films. The characteristics of the energy losses are reported for several different structures, providing insights into the nature of the transport in molecular electronics. Light emission from GFETs, on the other hand, appears to follow a novel mechanism that involves the excitation of plasmons in the graphene by hot carriers followed by decay through photon emission. By controlling the location of defects in the graphene lattice and the nanostructures around these scattering sites, emission could be localized to regions where this coupling is more optimized. In this second case, the devices may be able to be engineered through nanostructuring in order to gain control over the character of light emission. Finally, a few novel and emerging applications of nanoscale devices will be discussed, including using molecular devices in audio circuits, as well as for high frequency harmonic generation.

Effect of anchoring atom and electrostatic gating on the electronic transport properties in single molecular electronic devices

The effect of anchoring atom and electrostatic gate on the electron transport through gated thiophene single molecular device is studied by utilizing non-equilibrium Green’s function coupled with self-consistent extended Huckel theory. Gated gold–molecule–gold junctions are built using thiophene (Tp) molecule as functional component and sulphur (S) and selenium (Se) as anchoring atoms in field effect transistor (FET) configuration. The electron transport analysis of the gated thiophene single molecular device is investigated through the current–voltage and the electron transmission spectra. The results show that the anchoring atoms modulate the transport nature of these devices in a controlled manner. We find that the S–Tp–S device produces larger current than Se–Tp–Se device. Also we studied the effect of electrostatic gating on S–Tp–S and Se–Tp–Se device. We find that, positive bias or negative bias for Vg, will correspondingly, raise or lower the transmission coefficients T(E) in relation to the Fermi level (EF) for both the devices. Our results show that magnitude of Isd current varies more than one order for same Vsd over different Vg bias for S–Tp–S device, whereas for Se–Tp–Se device Isd current varies more than five times for same Vsd over different Vg bias. Se–Tp–Se device shows gate controlled NDR behavior. Finally, we demonstrated the application of using thiophene based single molecular FET to realize five basic logic gates very low Vsd bias. The key feature of the suggested design is the opportunity of demonstrating various logic gates with just one molecular unit transistor and demonstrated at very low Vsd bias.

ChemInform Abstract: Recent Progress in the Synthesis and Application of Saddle‐Shaped Cyclooctatetrathiophenes and Their Derivatives

AbstractReview: 25 refs.

Unveiling the structural origin of the high carrier mobility of a molecular monolayer on boron nitride

Very recently, it was demonstrated that the carrier mobility of a molecular monolayer dioctylbenzothienobenzothiophene (C8-BTBT) on boron nitride can reach 10 cm2/Vs, the highest among the previously reported monolayer molecular field-effect transistors. Here we show that the high-quality single crystal of the C8-BTBT monolayer may be the key origin of the record-high carrier mobility. We discover that the C8-BTBT molecules prefer layer-by-layer growth on both hexagonal boron nitride and graphene. The flatness of these substrates substantially decreases the C8-BTBT nucleation density and enables repeatable growth of large-area single crystal of the C8-BTBT monolayer. Our experimental result indicates that only out-of-plane roughness greater than 0.6 nm of the substrates could induce disturbance in the crystal growth and consequently affect the charge transport. This information would be important in guiding the growth of high-quality epitaxy molecular film.

Recent Progress in the Synthesis and Application of Saddle‐shaped Cyclooctatetrathiophenes and Their Derivatives

AbstractCyclooctatetrathiophene (COTh) shows a novel saddle‐shaped molecular structure, which has been applied in organic synthesis and material science. In this paper, the design and synthesis of COThs and their derivatives were described. The derivatives of COThs include mainly four types. One is isomer with different sequences of the four thiophene rings; the second is oligomer such as dimmer and dendrimer; the third is derivative functionalized by substituent groups at the four α positions; the last is the one planarized by sulfur, silicon or sulfone bridges. The applications of COThs and their derivatives in molecular muscles and field effect transistors were also discussed.

Trichlorosilanes as Anchoring Groups for Phenylene‐Thiophene Molecular Monolayer Field Effect Transistors

Self assembled monolayer field effect transistors (SAMFETs) are reported using a phenylene‐thiophene containing semiconducting mesogen attached through a trichlorosilane anchoring group. Monolayer films, covalently attached to silicon dioxide substrates, form in less than 10 h from solution, thanks to the accelerated reaction of the trichlorosilane anchor. Devices exhibit mobilities as high as 1.7 × 10−2 cm2 V−1 s−1, currents of up to 15 μA (on/off current ratio of 106) with device yields close to unity over large areas for channel lengths up to 100 μm.

Sulphur bridged [22]annulene[2.1.2.1] based organic field-effect transistors: interplay of the steric bulk and charge transport

New, neutral, slightly puckered aromatic meso-substituted tetrathia[22]porphyrin(2.1.2.1) macrocyclic architectures display efficacious p-type semiconductor behaviour with improved on/off ratios.

Superconductivity in two-dimensional NbSe2 field effect transistors

We describe investigations of superconductivity in few molecular layer NbSe2 field effect transistors. While devices fabricated from NbSe2 flakes less than eight molecular layers thick did not conduct, thicker flakes were superconducting with an onset Tc that was only slightly depressed from the bulk value for 2H-NbSe2 (7.2 K). The resistance typically showed a small, sharp high temperature transition followed by one or more broader transitions which usually ended in a wide tail to zero resistance at low temperatures. We speculate that these multiple resistive transitions are related to disorder in the layer stacking. The behavior of several flakes has been characterized as a function of temperature, applied field and back-gate voltage. We find that the conductance in the normal state and transition temperature depend weakly on the gate voltage, with both conductivity and Tc decreasing as the electron concentration is increased. The application of a perpendicular magnetic field allows the evolution of different resistive transitions to be tracked and values of the zero temperature upper critical field, Hc2(0), and coherence length, ξ(0), to be independently estimated. Our results are analyzed in terms of available theories for these phenomena.

Effect of the orientation of nitro group on the electronic transport properties in single molecular field-effect transistors

Molecular devices with nitro groups display unique electronic transport properties in experiments. By applying the non-equilibrium Green's function combined with density functional theory, we find that the orientation of the nitro group with respect to the backbone of the molecule has a crucial effect on the device performance and can show unusual experimental phenomena. Furthermore, molecular devices with a nitro group are sensitive to gate voltage and suitable for making effective single molecular field-effect transistors. These results provide an important theoretical support to experiments and the design of future molecular devices by using nitro groups.