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NANOTECHNOLOGY UNDERGRADUATE EDUCATION - 2007

In Situ Real-time Atomic Scale Nanostructural Synthesis, Characterization and Modeling

Focused Ion Beam Sputtering Yield Calculator:

Yamamura et al[1,2] have proposed a empirical formula to calculate the sputtering yield (number of target atoms removed by a single projectile ion) for various projectile ion-target combinations over a wide incident ion energy range and a range of incidence angles. The projectile ion loses energy by two distinct mechanisms:

1. Collisions with the target nuclei (Nuclear losses)

2. Collisions with electrons in the target (Electronic losses)

The contributions of each of these energy loss mechanisms to the net energy loss is infuenced by the incident ion energy and the target to projectile mass ratio.

Projectile Ion Energy: keV (Enter a value between 1 - 30 keV)

Select the Projectile Ion:

Select the Target Material:

The Sputtering Yield also has a dependence on the angle at which the projectile ion hits the target surface. Incidence angles are calculated from the surface normal. Zero degrees corresponds to normal incidence. As the incidence angle increases the Sputtering Yield is seen to increase: the sputtering process becomes more effective. However at large angles (when the projectile ion travels almost parallel to the surface) "surface channeling" effects reduce the Sputtering Yield.

Projectile Ion Incidence Angle: deg. (Enter a value between 0-90)

Beam Current: nA (Enter a value between 0.1 - 10 nA)

Total sputtering yield calculates the number of target atoms ejected on incidence of a single projectile ion. A more experimentally intuitive quantity is the Total Sputtering Rate which indicates the volume of target materials sputtered per second. As shown in the figure (NiTi sample), the sample volume sputtered on both side of the wedge can be approximated.

Volume of Target Sputtered Away: cubicmicrons

Total Sputtering Yield: target atoms/projectile ion

Total Sputtering Rate: cubicmicrons/second

Total Milling Time: minutes

In the above calculations is is assumed that the target material structure is isotropic - amorphous. In real crystalline solids, preferential channeling of the ions might occur if the incident ions are directed normal to low-index planes of the target material, reducing sputter yield. The total sputtering rate calculated in these simple cases also neglects redeposition of a portion of ejected atoms after bumping into an already sputtered surface.

References:

1. Y. Yamamura et al., Atomic Data and Nuclear Data Tables, Vol. 62, p.149, 1996

2. Y. Yamamura et al., IIPJ-AM-26, Institute of Plasma Physics, Nagoya University, 1983