title: Tip-Enhanced Raman Scattering Imaging of Two-Dimensional Tungsten Disulfide with Optimized Tip Fabrication Process.
abstract: We successfully achieve the tip-enhanced nano Raman scattering images of a tungsten disulfide monolayer with optimizing a fabrication method of gold nanotip by controlling the concentration of etchant in an electrochemical etching process. By applying a square-wave voltage supplied from an arbitrary waveform generator to a gold wire, which is immersed in a hydrochloric acid solution diluted with ethanol at various ratios, we find that both the conical angle and radius of curvature of the tip apex can be varied by changing the ratio of hydrochloric acid and ethanol. We also suggest a model to explain the origin of these variations in the tip shape. From the systematic study, we find an optimal condition for achieving the yield of ~60% with the radius of ~34 nm and the cone angle of ~35°. Using representative tips fabricated under the optimal etching condition, we demonstrate the tip-enhanced Raman scattering experiment of tungsten disulfide monolayer grown by a chemical vapor deposition method with a spatial resolution of ~40 nm and a Raman enhancement factor of ~4,760.
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.
authors.forename: Chanwoo
authors.initials: C
authors.lastname: Lee
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.|Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea.
authors.forename: Sung Tae
authors.initials: ST
authors.lastname: Kim
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.
authors.forename: Byeong Geun
authors.initials: BG
authors.lastname: Jeong
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.|Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea.
authors.forename: Seok Joon
authors.initials: SJ
authors.lastname: Yun
authors.affiliation: SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, Republic of Korea.|Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea.
authors.forename: Young Jae
authors.initials: YJ
authors.lastname: Song
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.|Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea.|Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea.
authors.forename: Young Hee
authors.initials: YH
authors.lastname: Lee
authors.affiliation: Department of Physics, Hallym University, Hallymdaehakgil 1, Chuncheon 24252, Republic of Korea.
authors.forename: Doo Jae
authors.initials: DJ
authors.lastname: Park
authors.affiliation: Department of Energy Science, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.|Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon 16419, Republic of Korea.
authors.forename: Mun Seok
authors.initials: MS
authors.lastname: Jeong