MXenes-Based Optoelectronic Devices by Film Transfer

MXenes remarkable rise amongst a new generation of low dimension materials is a result of its broad range of applications ranging from medicine, water purification, electrochemistry, energy and electronic devices. It is moreover a class of materials compatible with low temperature, ambient pressure fabrication processes such as spin-coating, spray-coating or dip coating. One of the main features of MXene is its tunability through its synthesis and deposition steps, combined with charge transport properties close to a metal.<br/><br/>In this study, we manufacture optoelectronic devices inspired by field effect transistors on i-Si substrate using Ti3C2Tx as a conductive channel, Au pads as drain/source terminals, and a MOS TiO₂/Metal gate terminal. The complete device fabrication involves a three steps photolithography process for the drain/source, channel, and gate terminal respectively. MXenes sheets are synthetized by selectively etching a Ti3AlC2 (MAX) phase using the minimum intensive layer delamination (MILD) method, forming in-situ HF allowing the selective removal of aluminum from the bulk MAX phase. Ti3C2TX solution is synthetized and purified, the solution is vacuum-filtered on a Nitrate Cellulose (NC) filter membrane. After the filtration, Ti3C2Tx films are transferred on soda lime glass (SLG) and Si substrates via a heating process at 100 ^oC. This process allows the uniform and reproducible transfer of Ti3C2Tx films on substrates up to 20 cm² with a range of film thickness varying from the nano- to micro scale. This approach is the main originality of this contribution, as it is to our knowledge is the first time that film transfer deposition of MXene is assessed for electronic applications. As a comparison, MXenes will also be deposited by spray coating to highlight the difference in the layer’s properties between the two deposition techniques. Subsequently to the deposition of the channel, and before the realization of the gate terminal, a thermal annealing at 400 ^oC in Ar atmosphere is performed to remove solvent intercalants (i.e. H₂O molecule) and a possible functionalization of the surface will be investigated. While the gate terminal is typically deposited by Atomic Layer Deposition (ALD) to obtain an ultrathin layer of TiO2, the realization of an ultrathin TiO2 layer can also be obtained by treating the surface of the as-annealed MXenes layer with an ozone treatment. The device characterization will focus on J-V analysis of the channel for various gate voltages, highlighting the interplay between the functionalized MXene and an external electric field.<br/><br/>Additional advanced characterization will be performed on the MXenes layer including UV-Vis spectroscopy, confocal profilometry, EQE, Raman spectroscopy, SEM, XPS and XRD to provide insights regarding optical properties and physico-chemical composition of the films, as well as the impact of possible intercalation agents. The complete set of results will be presented.