# Anisotropic Optical and Vibrational Properties of GeS

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Samples

#### 2.2. Experimental Techniques

#### 2.3. Theoretical Calculations

## 3. Results

#### 3.1. Crystallographic Structure

#### 3.2. Optical Properties

#### 3.3. Vibrational Properties

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A. The Temperature Dependence of the Raman Scattering Spectra

**Figure A1.**Raman scattering spectra measured on GeS as a function of temperature in range from 5 K to 300 K under 1.96 eV excitation.

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**Figure 1.**(

**a**) Top and side views of the GeS crystal structure for a single layer. The armchair and zigzag directions are shown in relation to the crystal orientation and lattice parameters. (

**b**) Geometrical structure of multilayer GeS.

**Figure 2.**(

**a**) The low-temperature (T = 5 K) PL (blue curve) and RC (red curve) spectra measured on the GeS flake. Polar plots of the integrated intensities of the X transitions from the (

**b**) PL and (

**c**) RC spectra.

**Figure 3.**(

**a**) False-color map of low-temperature PL spectra of GeS as a function of the detection angle of linear polarization under 1.88 eV laser light excitation. (

**b**) Temperature evolution of the PL spectra measured on GeS. The spectra are vertically shifted for clarity and some of them are multiplied by scaling factors for more clarity.

**Figure 4.**(

**a**) Atom displacements (green arrows) for the Raman-active modes. Axes indicate two view perspectives: armchair and zigzag directions. (

**b**) The calculated phonon dispersion of GeS. (

**c**) RS spectra measured on GeS at low (T = 5 K) and room (T = 300 K) temperatures. The spectra are vertically shifted for clarity.

**Figure 5.**Polar plots of the integrated intensities of the phonon modes: (

**a**) A${}_{\mathrm{g}}^{1}$, (

**b**) A${}_{\mathrm{g}}^{2}$, (

**c**) A${}_{\mathrm{g}}^{3}$, (

**d**) A${}_{\mathrm{g}}^{4}$, (

**e**) B${}_{\mathrm{g}}^{1}$, and (

**f**) B${}_{\mathrm{g}}^{2}$, measured on GeS at T = 300 K under 1.96 eV excitation. The green lines on polar plots are along polarization axes of modes.

**Figure 6.**Polar plots of the integrated intensities of the phonon modes B${}_{\mathbf{1}\mathbf{g}}^{2}$, A${}_{\mathbf{g}}^{3}$, and A${}_{\mathbf{g}}^{4}$ measured on GeS at T = 300 K under 2.54 eV, 2.41 eV, and 2.21 eV excitation. The green lines on polar plots are along polarization axes of modes.

**Figure 7.**The effect of the excitation energy on the polarization axes of three phonon modes: B${}_{1\mathrm{g}}^{2}$, A${}_{\mathrm{g}}^{3}$, and A${}_{\mathrm{g}}^{4}$.

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**MDPI and ACS Style**

Zawadzka, N.; Kipczak, Ł.; Woźniak, T.; Olkowska-Pucko, K.; Grzeszczyk, M.; Babiński, A.; Molas, M.R.
Anisotropic Optical and Vibrational Properties of GeS. *Nanomaterials* **2021**, *11*, 3109.
https://doi.org/10.3390/nano11113109

**AMA Style**

Zawadzka N, Kipczak Ł, Woźniak T, Olkowska-Pucko K, Grzeszczyk M, Babiński A, Molas MR.
Anisotropic Optical and Vibrational Properties of GeS. *Nanomaterials*. 2021; 11(11):3109.
https://doi.org/10.3390/nano11113109

**Chicago/Turabian Style**

Zawadzka, Natalia, Łucja Kipczak, Tomasz Woźniak, Katarzyna Olkowska-Pucko, Magdalena Grzeszczyk, Adam Babiński, and Maciej R. Molas.
2021. "Anisotropic Optical and Vibrational Properties of GeS" *Nanomaterials* 11, no. 11: 3109.
https://doi.org/10.3390/nano11113109