Nano-patterning on multilayer MoS2 via block copolymer lithography for highly sensitive and responsive phototransistors

Abstract

Indirect bandgap of multilayer molybdenum disulfide has been recognized as a major hindrance to high responsivity of MoS2 phototransistors. Here, to overcome this fundamental limitation, we propose a structural engineering of MoS2 via nano-patterning using block copolymer lithography. The fabricated nanoporous MoS2, consisting of periodic hexagonal arrays of hexagon nanoholes, includes abundant edges having a zigzag configuration of atomic columns with molybdenum and sulfur atoms. These exposed zigzag edges are responsible for multiple trap states in the bandgap region, as confirmed by photo-excited charge-collection spectroscopy measurements on multilayer nanoporous MoS2 phototransistors, showing that in-gap states only near the valence band can result in a photogating effect. The effect of nano-patterning is therefore to significantly enhance the responsivity of multilayer nanoporous MoS2 phototransistors, exhibiting an ultra-high photoresponsivity of 622.2 A W−1. Our nano-patterning of MoS2 for photosensing application paves a route to structural engineering of two-dimensional materials for highly sensitive and responsive optoelectronic devices.

Probing the Efficacy of Large-Scale Nonporous IGZO for Visible-to-NIR Detection Capability: An Approach toward High-Performance Image Sensor Circuitry

“…The block copolymer constituting polystyrene (PS) and poly(methyl methacrylate) (PMMA) undergoes self-assemblage due to the supplied thermal energy (equivalent to 200 °C for 2 h) and further selective removal of PMMA locally masks the SiO 2 and IGZO beneath, which creates a systematic nonporous morphology. 28 The selective etching of SiO 2 (a transient layer on top of IGZO) via a BCP selfassembled mask is performed by sulfur hexafluoride (SF 6 ) plasma. A gradual increase in SF 6 expose time increased the pore size of the BCP mask, as shown in Figure S2a−d.…”

Large-Area MoS2 Nanosheets with Triangular Nanopore Arrays as Active and Robust Electrocatalysts for Hydrogen Evolution

“…The fabrication process of nanoporous MoS 2– x with triangular nanoholes is presented in Figure c. BCP lithography was used to obtain a uniform nanohole array throughout the MoS 2 nanosheets. , In detail, the spin-coated BCP layer on the MoS 2 surface was subject to phase separation in a vacuum annealing process, resulting in a self-assembled nanoporous structure (Figure S1). Using the BCP layer as a pattern mask, the MoS 2 was perforated through two consecutive etching steps: (i) dry etching using O 2 plasma reactive ion etching (RIE) and (ii) wet etching using potassium ferricyanide solution.…”

Ultrasensitive and Selective Field-Effect Transistor-Based Biosensor Created by Rings of MoS2 Nanopores

“…We studied the generation of trap states in the nanoporous MoS 2 structure in a previous work. 48 When negatively charged cortisols are adsorbed at the nanoring edge area, the negative potential is accumulated on the MoS 2 edge area and induces depletion of the electron carriers by inhibiting the electron migration in the channel, further raising the energy band at the edge area. 49−51 Eventually, it seems to result in a higher energy barrier (purple hole and the corresponding energy diagram in Figure 4A).…”

“…Cortisol takes a negative charge under the measurement condition (pH 7.4) since the isoelectric point of cortisol is around 5.2. , The nanopore on the MoS 2 lattice provides energy barriers due to the conductivity difference between the MoS 2 basal plane and edge area (green hole and the corresponding energy diagram in Figure A). , The low conductivity of the edge regions is derived from scattering and trapping of mobile carriers at the newly generated trap states. We studied the generation of trap states in the nanoporous MoS 2 structure in a previous work . When negatively charged cortisols are adsorbed at the nanoring edge area, the negative potential is accumulated on the MoS 2 edge area and induces depletion of the electron carriers by inhibiting the electron migration in the channel, further raising the energy band at the edge area. − Eventually, it seems to result in a higher energy barrier (purple hole and the corresponding energy diagram in Figure A).…”