Surface Plasmon Resonance-Enhanced Near-Infrared Absorption in Single-Layer MoS₂ with Vertically Aligned Nanoflakes

The development of MoS₂ with two- or three-dimensional heterostructures can provide a significant breakthrough for the enhancement of photodetection abilities such as increase in light absorption and expanding the detection ranges. Till date, although the synthesis of a MoS₂ layer with three-dimensional nanostructures using a chemical vapor deposition (CVD) process has been successfully demonstrated, most studies have concentrated on electrochemical applications that utilize structural strengths, for example, a large specific surface area and electrochemically active sites. Here, for the first time, we report spectral light absorption induced by plasmon resonances in single-layer MoS₂ (SL-MoS₂) with vertically aligned nanoflakes grown by a CVD process. Treatment with oxygen plasma results in the formation of a substoichiometric phase of MoO in the vertical nanoflakes, which exhibit a high electron density of 4.5 × 10¹³ cm^-2. The substoichiometric MoO with a high electron-doping level that is locally present on the SL-MoS₂ surface induces an absorption band in the near-infrared (NIR) wavelength range of 1000-1750 nm because of the plasmon resonances. Finally, we demonstrate the enhancement of photodetection ability by broadening the detection range from the visible region to the NIR region in oxygen-treated SL-MoS₂ with vertically aligned nanoflakes.