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_x in the vertical nanoflakes, which exhibit a high electron density of 4.5 × 10¹³ cm^–2. The substoichiometric MoO_x 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.