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Efficient electronic transport at room temperature by T-shaped molecules in graphene based chemically modified three-terminal nanodevices

Periodic Reporting for period 2 - Tmol4TRANS (Efficient electronic transport at room temperature by T-shaped molecules in graphene based chemically modified three-terminal nanodevices )

Reporting period: 2018-09-01 to 2020-02-29

Tmol4TRANS emerged as a sensible strategy to unblock the development of single-molecule graphene-based three-terminal nanodevices.
Graphene is an appealing material for the creation of robust electrodes displaying fascinating properties (thermal conductivity, mechanical stiffness, high electron mobility, electrical conductivity, etc.). In addition, the idea of transistors based on graphene fulfils the basics toward a realistic application, where nanodevices will perform at room temperature. Related to this matter, molecules with high content of polycyclic aromatic hydrocarbon groups present strong affinity for such 2D material and are great candidates to function as nano-wires that can communicate graphene-based electrodes. For that, at the nanoscale, two graphene electrodes (source/emitter and drain/collector) must be separated by a nanogap. Final transistors include in their support the third electrode (in gate/base) that separates from the graphene electrodes by an insulator (e.g.: Si/SiO2).
Nowadays prototypes can be made with these basic tools and single-molecule transport measured. However, the implementation of such nanodevises is hampered by unresolved issues, as the absence in the control of deposition of the molecules (having a low percentage of responsive nanodevices) and deficiencies in the conductance values and therefore efficiency.
Tmol4TRANS delivers a straightforward methodology to improve those limitations by combining the chemical modification of the nanodevices (based on Si/SiO2-grahene) with T-shaped molecules. These molecules are capable of recognizing targets in the setups and accommodate within the nanogap created among the three electrodes that compose the transistors. The design of the T-shaped molecules is crucial, as they will be functioning as active components in the graphene-based nanodevice. In Tmol4TRANS, the required steps to achieve efficient transistor are straightforward, beyond present technology and avoids drastic economical investments.
The objectives of Tmol4TRANS is the creation of a hybrid molecular-based graphene transistor with reliable conductance values and further possibilities, related the latest to the reactivity and properties of the molecular materials inserted in the nanodevices.
Tmol4TRANS focuses on the creation of reliable wires and transistors at the nanoscale, having a large impact in a number of technological areas and, therefore, in advanced applications (chips, communications, computers affecting therefore drug discovery, bioinformatics, medical imaging and diagnostics, among others). Furthermore, functionalized molecules, possessing right optical, magnetic, thermoelectric and/or electrochemical properties, are suitable for harder tasks as sensors or logic operations facts that are not possible using conventional materials or approaches. The study of single-molecule transport will bring light to chemical, electrochemical and biological processes based on electron transfer, being crucial for fundamental research. Additional benefits as less power consumption, information operation speed and low production cost to compete with current silicon-based technology are expected as well. Molecular electronics has the potential to dramatically extend the miniaturization that has driven the density and speed advantages of the integrated circuits.
The work, performed up to now, relates to the creation of optimal T-shaped molecules and their attachment to SiO2/Si electrodes (gate/base).
The synthetic studied started with two families of molecules, porphyrinoids (PDDs) and curcuminoids (CCMoids) and has been extended with the latest toward the achievement of systems that present: (i) a conjugated skeleton that allows coordination (body); (ii) two moieties at the sides of the molecules with polycyclic aromatic hydrocarbon groups (arms) and (iii) an extra functional group with an active ending that can bind (leg).
The arms and leg units endorse the ability of the molecules to attach to graphene electrodes (using the arms, by strong pi-pi interactions, where the graphene electrodes function as source/emitter and drain/collector) and SiO2/Si electrode (that function as a gate/base, by covalent/supramolecular attachments with the leg). The extra functionality of the molecular body allows recognition of metal/metalloid ions from the molecule and therefore the capability of varying the electronic properties and/or acting as sensors.
The immobilization studies in solution at room temperature show that effective attachments of molecules can be performed with the SiO2/Si by activating or functionalizing the substrate. The tuning of the synthetic parameters in mild conditions (solubility, concentration of samples, humidity, etc.) allows efficient bonding. The study of different legs is crucial for a better understanding of the connection of the molecule with the SiO2/Si electrode and the evaluation of the impact that this can have in the electron transport of final nanodevices.
Here, toward the optimal performance at the nanoscale special attention is made on the purification processes of the materials.
The progress of single-molecule graphene-based three-terminal nanodevices presents several hindrances faced in Tmol4TRANS. The design of T-shaped molecules brings the possibility of controlling factors that so far, in the field of Molecular Electronics, have been accomplished by serendipity. T-shaped molecules are formed by: (i) a conjugated skeleton, (ii) polycyclic aromatic hydrocarbon groups on two sites of the molecule and (iii) an extra ending groups capable of bonding. The designed anchoring groups (polycyclic aromatic groups and additional ending groups) will provide an effective coupling between the molecule and the electrodes that form part of the transistor improving reproducibility and overall performance. The molecules will be fixed, organized and therefore controlled on precise positions within the nanodevices. These ideas are beyond present research in the field of Molecular Electroncis and will clear the path in the creation and implementation of single-molecule graphene-based transistors.
At the moment, creation of advanced T-shaped molecules is in progress, with molecular systems in their final development phases. In the second part of the project is expected to provide a selected number of these molecules in high amounts and purity. They will be inserted in two types of graphene-based three-terminal devices: nano-Field Effect Transistors (nano-FETs) and nano-Bipolar Junction Transistors (nano-BJTs). Both types of nanodevices will contain the same number and nature of electrodes: two graphene electrodes (source/emitter and drain/collector) and a Si electrode (gate/base). They will be separate by different thickness of SiO2 (insulator).
The creation of the nanogap between the graphene electrodes will be carried out by means of the feedback-controlled burning technique. The use of single-layer graphene for such purpose will provide fixed distances between the molecules and the SiO2/Si electrode. Studies varying the thickness of the insulator (SiO2) will provide information on the efficiency of the nanodevices too. The testing of both types of transistors, nano-FETs and –BJTs, with T-shaped molecules will provide, as a result, operational and reproducible nanodevices made under mild conditions, stable at room temperature and with high conductance.
Overview of single-molecule graphene-based transistors