MXene and Graphene: DFT and NEGF Studies*

Recently, 2D MXenes have emerged as promising alternative materials for DNA nucleobase detection. A recent molecular dynamics simulation study using Ti₃C₂ MXene nanopores showed its potential for detecting nucleobases based on physical features such as ionic current and dwell time. However, molecular dynamics simulation can’t capture the electronic interactions between nucleobases and Ti₃C₂ which are very crucial for nucleobase detection. We investigated the electronic interaction of DNA nucleobases [adenine (A), guanine (G), thymine (T), and cytosine (C)] with single-layer Ti₃C₂ MXene using vdW-corrected DFT and NEGF methods. All calculations were benchmarked against graphene. We showed that depending on the initial vertical height of a nucleobase above the Ti₃C₂ surface, two interaction mechanisms are possible, namely: physisorption and chemisorption.  For graphene, DNA nucleobases always physisorped onto the graphene surface irrespective of the initial vertical height of nucleobase above graphene sheet. The PBE+vdW binding energies for graphene are high (0.55 – 0.74 eV) and follow the order G > A > T > C, with adsorption heights in the range 3.16 – 3.22 Å, indicating strong physisorption. For Ti₃C₂, the PBE+vdW binding energies are relatively weaker (0.16 – 0.20 eV) and follow the order A > G = T > C, with adsorption heights in the range 5.51 – 5.60 Å indicating weak physisorption. The binding energies for chemisorption follow the order G > A >T > C, which is the same order for physisorption. The binding energy values (5.3 – 7.5 eV) indicate very strong chemisorption (~40 times larger than the physisorption binding energies). Furthermore, our band structure and electronic transport analysis showed that for physisorption, there are neither significant variation in band structure nor modulations in the transmission function and device density of states (DDOS). The relatively weak physisorption and strong chemisorption shows that Ti₃C₂ might not be capable of identifying DNA nucleobases using the physisorption method.