AVS 71 Session 2D-TuA: 2D Materials: Theory and Applications

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have sparked significant research interest in gas sensing technologies owing to their large specific surface area, excellent sensitivity, high power efficiency, and ability to function at room temperature (RT). The present investigation outlines a highly selective and fully recoverable RT nitrogen dioxide (NO₂) gas sensor based on molybdenum diselenide (MoSe₂) and tungsten disulfide (WS₂) nanocomposite co-sputtered directly over electrochemically anodized porous silicon substrate (PSi) employing the DC magnetron sputtering technique. Here, the PSi substrate substantially boosts the sensor’s characteristics by providing a large surface area for the growth of nanostructured sensing film, facilitating numerous active sites for the target gas interaction. In addition, the PSi structure makes the sensor’s surface highly hydrophobic, making it an ideal candidate for sensing applications in harsh and humid atmospheres. Compared to their pristine counterparts (MoSe₂/PSi and WS₂/PSi), the hybrid WS₂-MoSe₂/PSi nanostructured sensor demonstrates a superior sensor response of ~34.14% with a fast response/recovery time (~17.67 s / ~41.05 s) towards 50 ppb NO₂ gasat RT, highlighting the enhanced synergistic effects within the nanocomposite sensor. The proposed WS₂-MoSe₂/PSi gas sensor delivers exceptional selectivity and commendable stability for over 100 days with retention of ~90.9% towards 50 ppb NO₂ gas, even at RT (27˚C). Moreover, the sensor retains ~92.44% of its original response towards 50 ppb NO₂ under high relative humidity (~80% RH). Therefore, the remarkable sensing properties exhibited by the developed WS₂-MoSe₂/PSi sensor render enticing possibilities for developing next-generation room temperature NO₂ gas sensors.

Research development of integrated silicon photonics in the mid-infrared (MIR) range has gained considerable momentum over the past decades, driven by its vital applications in biochemical sensing, medicine, and even astronomy communications. However, progress has been hampered by the limitation by the energy bandgap and optical transparency in conventional material. Very recently, it has been reported that 2D bilayer silicon (BLSi) demonstrates unique optical properties across the MIR spectrum. By adjusting the strain, the optical absorptions can be tuned in a wide range of wavelength from 1.5 -11.5 mm. However, experimentally the maximum in-plane strain achieved is ∼7% in a lattice-matching expitaxial silicon. Remote- and Van der Waals expitaxy methods can break the lattice-mismatch constraint to obtain single crystal 2D materials, but with an insufficient in-plane strain preserved in the 2D films.

Molecular design is a powerful tool for growing graphene nanostructures with atomic precision, enabling control over their electronic and physical properties. Precisely tuning these properties is essential for advancing the next generation of graphene-based 2D electronic devices. In this presentation, I will discuss the on-surface synthesis of novel nanoporous graphene (NPG) materials, whose electronic bandgaps can be tuned from semiconducting to nearly metallic through rational molecular design. These NPGs were synthesized using custom-designed polyaromatic precursors deposited on Au(111) and thermally activated under ultra-high vacuum via surface-assisted chemical reactions. Scanning tunneling microscopy (STM) reveals the structural integrity and periodicity of nanoporous networks. Scanning tunneling spectroscopy (STS), in combination with density functional theory (DFT), shows that strategic modifications in the pore size, topology, and connectivity can reduce the bandgap to as low as 0.05 eV, approaching metallic behavior. This work not only demonstrates the feasibility of tailoring graphene’s electronic structure with sub-nanometer precision but also establishes a versatile platform for engineering low-bandgap 2D materials.