Direct observation of interlayer coherent acoustic phonon dynamics in bilayer and few-layer PtSe<sub>2</sub>

Xin Chen; Saifeng Zhang; Lei Wang; Yi-Fan Huang; Huiyan Liu; Jiawei Huang; Ningning Dong; Weimin Liu; Ivan M. Kislyakov; Jean Michel Nunzi; Long Zhang; Jun Wang

doi:10.1364/PRJ.7.001416

Photonics Research, Volume. 7, Issue 12, 1416(2019)

Direct observation of interlayer coherent acoustic phonon dynamics in bilayer and few-layer PtSe₂

Xin Chen^1,2,3, Saifeng Zhang^1,2,3,8, Lei Wang^1,2,3, Yi-Fan Huang^4,5, Huiyan Liu^4,5, Jiawei Huang^1,2,3, Ningning Dong^1,2,3, Weimin Liu^4,5, Ivan M. Kislyakov¹, Jean Michel Nunzi^1,6, Long Zhang^1,2,3,7, and Jun Wang^1,2,3,7、*

Author Affiliations

¹Laboratory of Micro-Nano Optoelectronic Materials and Devices, Key Laboratory of Materials for High-Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

²Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

³State Key Laboratory of High Field Laser Physics, CAS Center for Excellence in Ultra-intense Laser Science, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

⁴School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

⁵STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China

⁶Department of Physics, Engineering Physics & Astronomy and Department of Chemistry, Queen’s University, Kingston, K7L-3N6 Ontario, Canada

⁷State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

⁸e-mail: sfzhang@siom.ac.cn

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Figures & Tables(9)

Fig. 1. AFM images of (a) 2 L-, (b) 5 L-, (c) 8 L-PtSe2; the insets show the height profile. (d) The layer-dependent Raman spectra of PtSe2. (e) The peak positions of Eg, A1g, and LO modes and (f) the intensity ratio of A1g/Eg with the increasing number of layers. (g) The layer-dependent Tauc plots of PtSe2.

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Fig. 2. (a) Transmission signal of 15 L-PtSe2 (gray dots) and the fitting curves with/without oscillations (black/red line). The inset is the fast Fourier transform (FFT) of the oscillation signal. (b) The diagram of the oscillations decomposed into two different sinusoidal decaying components. Mode 1 corresponds to the higher frequency (0.15 THz) and Mode 2 corresponds to the lower one (0.05 THz). (c) The oscillation experimental data and the fitting results of PtSe2 with different layers. (d) The FFT of all oscillation signals.

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Fig. 3. (a) Low-frequency Raman spectra of 2 L-, 5 L-, 8 L-PtSe2. The green region is the laser line. (b) The comparison of LBMs obtained from low-frequency Raman spectroscopy, coherent phonon method, and theoretical calculation. The polarization behavior of Raman amplitude of (c) Mode 1, (d) Eg and A1g modes of 2 L-PtSe2.

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Fig. 4. Diagram of vibrational displacements of the layer-breathing mode and the standing wave mode in PtSe2.

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Fig. 5. Layer-dependent oscillations of (a) Mode 1 (LBM) and (b) Mode 2 (SWM) with the fitting curves. The blue hollow circles in (a) are low-frequency Raman peak positions. The insets: the black and sky-blue balls represent Pt and Se atoms, respectively. Each arrow points to the direction of the movement of that layer.

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Fig. 6. AFM images of PtSe2 with (a) 10 L, (b) 15 L, (c) 17 L, and (d) 23 L.

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Fig. 7. Reflection (R), transmission (T), and absorption (A) spectra from 400 nm to 1100 nm of PtSe2 films with (a) 2 L, (b) 5 L, (c) 8 L, (d) 10 L, (e) 15 L, (f) 17 L, and (g) 23 L. The absorption spectra are calculated by A=1−R−T. (h) The Tauc plots of layer-dependent PtSe2. (i) The bandgap of each film obtained from Tauc plots. The bandgaps are approximately 1.32 eV (2 L), 0.76 eV (5 L), 0.44 eV (8 L), 0.18 eV (10 L), and 0 eV (15 L, 17 L, and 23 L), respectively.

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Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and ${cm}^{- 1}$ and the Decay Times of These Two Modes in 2–23 L ${PtSe}_{2}$

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Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and ${cm}^{- 1}$ and the Decay Times of These Two Modes in 2–23 L ${PtSe}_{2}$

	LBM (Mode 1)				SWM (Mode 2)
Number of Layers (L)	Frequency (THz)	Wave-number ( ${cm}^{- 1}$ )	Low-frequency Raman Shift ( ${cm}^{- 1}$ )	Decay Time (ps)	Frequency (THz)	Period (ps)	Decay Time (ps)
2	$0.73 \pm 0.06$	$24.17 \pm 2.12$	25.3	$1.63 \pm 0.51$	$0.27 \pm 0.060$	$3.68 \pm 1.05$	$0.85 \pm 0.10$
5	$0.33 \pm 0.15$	$10.83 \pm 5.02$	14.3	$1.12 \pm 0.22$	$0.13 \pm 0.008$	$7.69 \pm 0.54$	$7.06 \pm 1.63$
8	$0.24 \pm 0.10$	$8.00 \pm 3.45$	10.2	$1.30 \pm 0.06$	$0.08 \pm 0.005$	$12.12 \pm 0.88$	$10.81 \pm 1.53$
10	$0.17 \pm 0.02$	$5.80 \pm 0.44$	N.A.	$6.67 \pm 2.06$	$0.07 \pm 0.009$	$14.00 \pm 1.96$	$16.02 \pm 1.84$
15	$0.15 \pm 0.03$	$5.00 \pm 1.00$	N.A.	$6.84 \pm 0.52$	$0.05 \pm 0.005$	$20.41 \pm 1.76$	$21.05 \pm 1.47$
17	$0.11 \pm 0.04$	$3.67 \pm 1.40$	N.A.	$7.64 \pm 0.70$	$0.04 \pm 0.002$	$23.26 \pm 1.03$	$20.61 \pm 1.91$
23	$0.10 \pm 0.02$	$3.43 \pm 0.57$	N.A.	$11.97 \pm 0.76$	$0.03 \pm 0.008$	$31.25 \pm 0.80$	$130.07 \pm 18.10$

Table 2. Thickness, Linear Absorption Coefficient $α$ , and Penetration Depth $ξ = α^{- 1}$ of 2–23 L ${PtSe}_{2}$

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Table 2. Thickness, Linear Absorption Coefficient $α$ , and Penetration Depth $ξ = α^{- 1}$ of 2–23 L ${PtSe}_{2}$

Number of Layers (L)	Thickness Measured by AFM (nm)	Linear Absorption Coefficient $α$ ( ${cm}^{- 1}$ )	Penetration Depth $ξ$ (nm)
2	∼1.19	$0.36 \times 10^{5}$	274.73
5	∼2.66	$2.10 \times 10^{5}$	47.71
8	∼4.61	$2.60 \times 10^{5}$	38.52
10	∼5.92	$4.11 \times 10^{5}$	24.35
15	∼8.98	$4.53 \times 10^{5}$	22.09
17	∼9.87	$4.14 \times 10^{5}$	24.17
23	∼13.58	$3.93 \times 10^{5}$	25.48

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Xin Chen, Saifeng Zhang, Lei Wang, Yi-Fan Huang, Huiyan Liu, Jiawei Huang, Ningning Dong, Weimin Liu, Ivan M. Kislyakov, Jean Michel Nunzi, Long Zhang, Jun Wang, "Direct observation of interlayer coherent acoustic phonon dynamics in bilayer and few-layer PtSe₂," Photonics Res. 7, 1416 (2019)

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Paper Information

Category: Optical and Photonic Materials

Received: Sep. 19, 2019

Accepted: Sep. 20, 2019

Published Online: Nov. 14, 2019

The Author Email: Jun Wang (jwang@siom.ac.cn)

DOI:10.1364/PRJ.7.001416

Topics

laser devices and laser physics

Lasers and Laser Optics

Laser physics

laser manufacturing

Instrumentation, Measurement and Metrology

Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and cm−1 and the Decay Times of These Two Modes in 2–23 L PtSe2

Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and cm−1 and the Decay Times of These Two Modes in 2–23 L PtSe2

Table 2. Thickness, Linear Absorption Coefficient α, and Penetration Depth ξ=α−1 of 2–23 L PtSe2

Table 2. Thickness, Linear Absorption Coefficient α, and Penetration Depth ξ=α−1 of 2–23 L PtSe2

Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and ${cm}^{- 1}$ and the Decay Times of These Two Modes in 2–23 L ${PtSe}_{2}$

Table 1. Vibrational Frequencies in the Unit of Terahertz (THz), Picosecond (ps), and ${cm}^{- 1}$ and the Decay Times of These Two Modes in 2–23 L ${PtSe}_{2}$

Table 2. Thickness, Linear Absorption Coefficient $α$ , and Penetration Depth $ξ = α^{- 1}$ of 2–23 L ${PtSe}_{2}$

Table 2. Thickness, Linear Absorption Coefficient $α$ , and Penetration Depth $ξ = α^{- 1}$ of 2–23 L ${PtSe}_{2}$