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.
