Periodic Reporting for period 5 - Tmol4TRANS (Efficient electronic transport at room temperature by T-shaped molecules in graphene based chemically modified three-terminal nanodevices )
Periodo di rendicontazione: 2023-03-01 al 2023-08-31
Tmol4TRANS emerged as a sensible strategy to unlock the development of molecular nanowires on three-terminal graphene hybrid nanodevices.
Graphene-based transistors meet the basic requirements for a realistic application, where nanodevices can operate at room temperature. Related to this issue, molecules with a high content of polycyclic aromatic hydrocarbons (PAHs) have a strong affinity for such 2D material and are strong candidates to function as nanowires that can communicate graphene-based electrodes. Today, prototypes can be fabricated with basic tools and single-molecule transport can be measured. However, the application of these nanodevices is hampered by unresolved issues such as stability of the nanodevices and low conductance values.
Tmol4TRANS offers a simple methodology to improve these limitations by combining the chemical modification of the nanodevices (based on Si/SiO2-graphene) with T-shaped molecules. These molecules are able to fit inside the nanogap, created between the three electrodes that make up the transistor. The design of the T-shaped molecules is crucial, as they will function as active components in the graphene-based nanodevice. Tmol4TRANS shows the steps needed to achieve an efficient transistor in a simple way, going beyond current technology and avoiding drastic economic investments. The study of unimolecular transport will shed light on chemical, electrochemical and biological processes based on electron transfer and is crucial for fundamental research and, subsequently, for technological advances and societal improvements. Additional advantages such as lower power consumption, speed of information operation and low production cost are also expected to compete with current silicon-based technology. Molecular electronics has the potential to dramatically extend the miniaturisation that has driven the density and speed advantages of integrated circuits.
Graphene-based transistors meet the basic requirements for a realistic application, where nanodevices can operate at room temperature. Related to this issue, molecules with a high content of polycyclic aromatic hydrocarbons (PAHs) have a strong affinity for such 2D material and are strong candidates to function as nanowires that can communicate graphene-based electrodes. Today, prototypes can be fabricated with basic tools and single-molecule transport can be measured. However, the application of these nanodevices is hampered by unresolved issues such as stability of the nanodevices and low conductance values.
Tmol4TRANS offers a simple methodology to improve these limitations by combining the chemical modification of the nanodevices (based on Si/SiO2-graphene) with T-shaped molecules. These molecules are able to fit inside the nanogap, created between the three electrodes that make up the transistor. The design of the T-shaped molecules is crucial, as they will function as active components in the graphene-based nanodevice. Tmol4TRANS shows the steps needed to achieve an efficient transistor in a simple way, going beyond current technology and avoiding drastic economic investments. The study of unimolecular transport will shed light on chemical, electrochemical and biological processes based on electron transfer and is crucial for fundamental research and, subsequently, for technological advances and societal improvements. Additional advantages such as lower power consumption, speed of information operation and low production cost are also expected to compete with current silicon-based technology. Molecular electronics has the potential to dramatically extend the miniaturisation that has driven the density and speed advantages of integrated circuits.
Tmol4TRANS is related to the creation of optimal T-shaped molecules and their efficient binding to graphene-based three-terminal hybrid devices.
Synthetic studies started from two families of molecules, the porphyrinoids (PDDs) and curcuminoids (CCMoids) towards the achievement of systems featuring: (i) a conjugated skeleton allowing coordination (parts referred to here as body, for PDDs and CCMoids); (ii) two side units with polycyclic aromatic hydrocarbons (PAHs) and (iii) an extra functional group with an active termination that can bind/fix the molecule.
The best molecular candidates have been accompanied by the search for optimal synthetic methodologies. In this sense, CCMoids were chosen over PDDs, as the best candidates to create T-shaped molecules, finding for the former suitable strategies to be achieved in a simple way, with a short number of steps, reasonable yields, and easy purifications (presenting PDDs limitations in most of these points). We have arrived at PAH-CCMoids with extensions greater than 3 nm (from simulation calculations). In addition, an optimised route has been created to deposit T-shaped CCMoid moleculeson functionalised SiO2. Our studies have shown that these substrates are sensors for BF3, a well-known (and widely used) toxic gas in electronic processes. In short, these results show that we have created a sensitive substrate that can also act as sensors.
The control of the interface, molecule-electrode interactions, is the one of the key points to obtaining reliable devices. Apart from the functionalisation of SiO2, we have explored molecular deposition by sublimation processes. The idea was to evaluate the avoidance of solvent on the device, which can lead to additional problems such as the inclusion of impurities. To sublimate molecules directly onto devices, we have designed a prototype which is patented at Spanish level, being currently in the process of extension to European patent. This result is highly beneficial, for us and for others working in the field of molecular electronics, as it allows the easy deposition of molecules and extends its uses to any type of substrate (device). The prototype is so versatile that will be further analysed in an ERC PoC project for full validation.
In terms of device creation (e.g. nanoFETs), the use of single-layer graphene eased the creation of GFETs, as the distance from the molecule to SiO2 was fixed. The steps for micropatterning and electrode connections have been standardised achieving GFETs (graphene field effect transistors) in good yields. Different SiO2 thicknesses have been studied, 300 and 90 nm, which have a dramatic impact on the creation of the final devices. For this reason, and in order to find a reproducible methodology, the thicker one was chosen, since the latter was complicated to process and the GFETs presented poor reproducibility.
The most dramatic and limiting steps encountered in the project are those related to the micro-/nanopatterning for the creation of the nanogaps. Our findings show that any particular irregularity in the graphene can greatly affect the opening of the holes, including irreparable damage to the three-terminal devices, which are also very sensitive to communication with electronic equipment, making it difficult to obtain devices in good yields. In order to achieve reliable measurements, we have been working closely with our partners on the subject and also performed the measurements on their facilities (Delft University). We have measured a PAH-CCMoid and fully characterised it at room and low temperature; our results show that the molecular design facilitates contact with graphene electrodes providing higher conductance values.
Synthetic studies started from two families of molecules, the porphyrinoids (PDDs) and curcuminoids (CCMoids) towards the achievement of systems featuring: (i) a conjugated skeleton allowing coordination (parts referred to here as body, for PDDs and CCMoids); (ii) two side units with polycyclic aromatic hydrocarbons (PAHs) and (iii) an extra functional group with an active termination that can bind/fix the molecule.
The best molecular candidates have been accompanied by the search for optimal synthetic methodologies. In this sense, CCMoids were chosen over PDDs, as the best candidates to create T-shaped molecules, finding for the former suitable strategies to be achieved in a simple way, with a short number of steps, reasonable yields, and easy purifications (presenting PDDs limitations in most of these points). We have arrived at PAH-CCMoids with extensions greater than 3 nm (from simulation calculations). In addition, an optimised route has been created to deposit T-shaped CCMoid moleculeson functionalised SiO2. Our studies have shown that these substrates are sensors for BF3, a well-known (and widely used) toxic gas in electronic processes. In short, these results show that we have created a sensitive substrate that can also act as sensors.
The control of the interface, molecule-electrode interactions, is the one of the key points to obtaining reliable devices. Apart from the functionalisation of SiO2, we have explored molecular deposition by sublimation processes. The idea was to evaluate the avoidance of solvent on the device, which can lead to additional problems such as the inclusion of impurities. To sublimate molecules directly onto devices, we have designed a prototype which is patented at Spanish level, being currently in the process of extension to European patent. This result is highly beneficial, for us and for others working in the field of molecular electronics, as it allows the easy deposition of molecules and extends its uses to any type of substrate (device). The prototype is so versatile that will be further analysed in an ERC PoC project for full validation.
In terms of device creation (e.g. nanoFETs), the use of single-layer graphene eased the creation of GFETs, as the distance from the molecule to SiO2 was fixed. The steps for micropatterning and electrode connections have been standardised achieving GFETs (graphene field effect transistors) in good yields. Different SiO2 thicknesses have been studied, 300 and 90 nm, which have a dramatic impact on the creation of the final devices. For this reason, and in order to find a reproducible methodology, the thicker one was chosen, since the latter was complicated to process and the GFETs presented poor reproducibility.
The most dramatic and limiting steps encountered in the project are those related to the micro-/nanopatterning for the creation of the nanogaps. Our findings show that any particular irregularity in the graphene can greatly affect the opening of the holes, including irreparable damage to the three-terminal devices, which are also very sensitive to communication with electronic equipment, making it difficult to obtain devices in good yields. In order to achieve reliable measurements, we have been working closely with our partners on the subject and also performed the measurements on their facilities (Delft University). We have measured a PAH-CCMoid and fully characterised it at room and low temperature; our results show that the molecular design facilitates contact with graphene electrodes providing higher conductance values.
The creation of simple methodologies to achieve functional T-shaped molecules. For that CCMoids have been chosen, designing strategies for the creation of T-shaped molecules with synthetic paths with a limited the number of steps, reasonable yields, and straightforward purifications.
Studies related to the deposition of a type of T-shaped CCMoids have led to the creation of functionalised SiO2 substrates that are sensitive to environment. The study has proven the efficiency of the covalent bonds of the molecules to the surfaces and the robustness of the configuration; in particular, such hybrid supports have been shown to be sensors of BF3 molecules.
Deposition studies have led to the creation of a prototype sublimation device that allows the direct sublimation/deposition of molecules on any kind of substrates under mild temperature and vacuum conditions. A Spanish patent exists for the device, which is in the process of being extended to a European patent. Its potential will also be examined in a new ERC PoC project (101138186).
In the last part of Tmol4TRANS, the creation of devices containing graphene nanogaps of the nanoFET type has been inspected and, together with expert collaborators in the field, a PAH-CCMoid system has been evaluated resulting in an extensive amount of data at room and low temperature, where the enhanced conductance values due to the improved molecular design have been corroborated.
Studies related to the deposition of a type of T-shaped CCMoids have led to the creation of functionalised SiO2 substrates that are sensitive to environment. The study has proven the efficiency of the covalent bonds of the molecules to the surfaces and the robustness of the configuration; in particular, such hybrid supports have been shown to be sensors of BF3 molecules.
Deposition studies have led to the creation of a prototype sublimation device that allows the direct sublimation/deposition of molecules on any kind of substrates under mild temperature and vacuum conditions. A Spanish patent exists for the device, which is in the process of being extended to a European patent. Its potential will also be examined in a new ERC PoC project (101138186).
In the last part of Tmol4TRANS, the creation of devices containing graphene nanogaps of the nanoFET type has been inspected and, together with expert collaborators in the field, a PAH-CCMoid system has been evaluated resulting in an extensive amount of data at room and low temperature, where the enhanced conductance values due to the improved molecular design have been corroborated.