title: Angle resolved vibrational properties of anisotropic transition metal trichalcogenide nanosheets.
abstract: Layered transition metal trichalcogenides (TMTCs) are a new class of anisotropic two-dimensional materials that exhibit quasi-1D behavior. This property stems from their unique highly anisotropic crystal structure where vastly different material properties can be attained from different crystal directions. Here, we employ density functional theory predictions, atomic force microscopy, and angle-resolved Raman spectroscopy to investigate their fundamental vibrational properties which differ significantly from other 2D systems and to establish a method in identifying anisotropy direction of different types of TMTCs. We find that the intensity of certain Raman peaks of TiS3, ZrS3, and HfS3have strong polarization dependence in such a way that intensity is at its maximum when the polarization direction is parallel to the anisotropic b-axis. This allows us to readily identify the Raman peaks that are representative of the vibrations along the b-axis direction. Interestingly, similar angle resolved studies on the novel TiNbS3TMTC alloy reveal that determination of anisotropy/crystalline direction is rather difficult possibly due to loss of anisotropy by randomization distribution of quasi-1D MX6chains by the presence of defects which are commonly found in 2D alloys and also due to the complex Raman tensor of TMTC alloys. Overall, the experimental and theoretical results establish non-destructive methods used to identify the direction of anisotropy in TMTCs and reveal their vibrational characteristics which are necessary to gain insight into potential applications that utilize direction dependent thermal response, optical polarization, and linear dichroism.
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Wilson
authors.initials: W
authors.lastname: Kong
authors.affiliation: Department of Physics, Izmir Institute of Technology, 35430 Izmir, Turkey.
authors.forename: Cihan
authors.initials: C
authors.lastname: Bacaksiz
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Kedi
authors.initials: K
authors.lastname: Wu
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Mark
authors.initials: M
authors.lastname: Blei
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Xi
authors.initials: X
authors.lastname: Fan
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Yuxia
authors.initials: Y
authors.lastname: Shen
authors.affiliation: Department of Photonics, Izmir Institute of Technology, 35430 Izmir, Turkey.
authors.forename: Hasan
authors.initials: H
authors.lastname: Sahin
authors.affiliation: LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: David
authors.initials: D
authors.lastname: Wright
authors.affiliation: Department of Physics, Alliance College of Engineering and Design (ACED), Alliance University, Chandapura, Anekal, Bangalore, 562106 Karnataka, India.
authors.forename: Deepa S
authors.initials: DS
authors.lastname: Narang
authors.affiliation: School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA. sefaattin.tongay@asu.edu.
authors.forename: Sefaattin
authors.identifier: http://orcid.org/0000-0001-8294-984X
authors.initials: S
authors.lastname: Tongay