Helium Ion implementation Diamond

Simulation Software Used

I simulated the mechanical deformation of a thin diamond film subjected to localized bombardment by helium ions. The deformation was modeled based on the formation of vacancies resulting from the ion implantation process. This is replicated from the work done by F. Bosia, P. Olivero, and E. Vittone presented at COLSOL Conference 2009 in Milan.

The ion bombardment was simulated using SRIM (Stopping and Range of Ions in Matter), a Monte Carlo-based software tool that provides detailed information on ion trajectories, energy dissipation, vacancy production, and ion distribution within the target material.

In SRIM helium was chosen as the ion. The energy of the helium was set to 1800 keV (1.8 MeV). There is only one layer simulated here, and its density is set to 3.5 g/cm3, the typical density of a diamond film. The film was made 10 m thick. The Damage (eV) parameters were all pulled from diamond properties information. Finally, the simulation was set to 50,000 ions to generate a reasonable set of statistics to work with.

A screenshot of the parameters I used is below.

The simulation generated a data file containing the number of carbon vacancies/(Å-Ion). To get the vacancy density, you take the data from the file, multiply it by the fluence (which is the # ions/cm2).

For helium ions with energy 1.8 MeV striking a diamond surface, the plot of the vacancy density (from the file) is:

The creation of vacancies within the diamond film alters the properties of the diamond film, in particular the density, Poisson’s Ratio, and Young’s Modulus. The vacancies also create internal stress inside the diamond.

We model the changes in the parameters with the following general equation:

Equation 1

Where A [A(z), A_d, and A_pd ]are the physical properties of interest, such as density. A_d is the unaffected material property, A_pd is the saturated property (when the area becomes saturated with vacancies, or when the exponent reaches infinity). F is the fluence of the beam, 𝜆(z) is the simulated data acquired from the SRM calculations, and 𝛼 is a scaling constant (usually around 10^-28). A plot the density is below.

The beam has the following profile.

The COMSOL simulation was composed of a disk of radius 300 μm and thickness of 10 μm, and given the material properties of C (diamond) [type I]. The beam has a profile provided by the x and y profiles shown in Plot 5 and Plot 6. The depth profiles for the variables were modified by the beam profiles. So if the functions for the beam profiles are g(x) and h(y) for the x and y profiles and A(z) for the properties as a function of z, each parameter was determined by the function: g(x)h(y)A(z).

The resulting displacement of the diamond on the surface is shown below: