# Effect of the Surface Roughness of Tungsten on the Sputtering Yield under Helium Irradiation: A Molecular Dynamics Study

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## Abstract

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## 1. Introduction

## 2. Simulation Method

- The system has a width of 9.4956 nm × 9.4956 nm and the height varies throughout the COD;
- x-y directions of the system adopt periodic boundary conditions;
- A He ion was irradiated every $0.5$ ps until 500 ps. The total number of the He ions is the same in our simulations;
- He ions are irradiated to a random position by a random function. However, each geometry has the same coordinate where ions are irradiated;
- When CN (coordination number) = 0, the tungsten atoms are assumed to be sputtered. CN is defined as the number of tungsten particles adjacent to the tungsten particle. Thus, CN = 0 means that there are no other tungsten particles near the tungsten particle. It indicates that the tungsten particles with CN = 0 are sputtered particles.

Incident Direction | Vector |

Direction 1 | <$-1$, $-1$, $-1$> |

Direction 2 | <$-1$, 0, $-1$> |

Direction 3 | <$-1$, $-1$, 0> |

Direction 4 | <$-1$, 0, 0> |

Direction 5 | <0, 0, $-1$> |

## 3. Results and Discussion

## 4. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**The geometry of the simulation system: each geometry has the same width (9.4956 nm × 9.4956 nm), but the height varies through the curvature of the dome part.

**Figure 5.**The directions of the progress of incident particles according to the z component. Black arrows have a negative value on the z component of the vector. Orange arrows have a zero value on the z component of the vector. This is because when the z component of the vector has a value of zero, the direction of the orange arrow is parallel in the $xy$ plane.

**Figure 6.**Changes in the number of bonding of W atoms increased with COD. If the COD increased, then the number of bonding atoms would be decreased.

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**MDPI and ACS Style**

Kim, H.; Kwon, J.; Chang, K.
Effect of the Surface Roughness of Tungsten on the Sputtering Yield under Helium Irradiation: A Molecular Dynamics Study. *Metals* **2021**, *11*, 1532.
https://doi.org/10.3390/met11101532

**AMA Style**

Kim H, Kwon J, Chang K.
Effect of the Surface Roughness of Tungsten on the Sputtering Yield under Helium Irradiation: A Molecular Dynamics Study. *Metals*. 2021; 11(10):1532.
https://doi.org/10.3390/met11101532

**Chicago/Turabian Style**

Kim, Hyeonho, Joongseok Kwon, and Kunok Chang.
2021. "Effect of the Surface Roughness of Tungsten on the Sputtering Yield under Helium Irradiation: A Molecular Dynamics Study" *Metals* 11, no. 10: 1532.
https://doi.org/10.3390/met11101532