Sputtering of Au Induced by Single Xe Ion Impacts
- PDF / 1,545,982 Bytes
- 5 Pages / 417.6 x 639 pts Page_size
- 3 Downloads / 164 Views
117 Mat. Res. Soc. Symp. Proc. Vol. 585 ©2000 Materials Research Society
computer code TRIM [9], and has been accounted for in presentation of our results. TRIM calculations indicate that in both experimental geometries all sputtered Au was stopped in the near surface region of the carbon foil, and the maximum amount of carbon injected into the Au specimen was less than 0.3 at. %. At the low Au coverages achieved on the collector foils, resputtering of collected Au is not a concern. The total amount of Au deposited on a collector foil, either on the surface or incorporated within the carbon collector foil, was determined after irradiation by x-ray energy dispersive spectroscopy (EDS) in a JEOL 100-CX electron microscope using the intensity of the Au Loc peak. A 27 nm thick Au foil (as measured by Rutherford back scattering) was used for calibration. In both experimental geometries the carbon collector foil and the gold film were approximately 40 pm apart. By adjusting the specimen height in the TEM it was possible to view either the carbon foil or the gold film with the other contributing an out-of-focus background to the image. In this way, the gold accumulated on the collector foils could be observed with a resolution of approximately 1 nm. TEM images were recorded both, during irradiation, with a Gatan 622 video camera and image-intensification system and, during interruption of the irradiation, on photographic film. The video images were recorded with a time resolution of 1/30th second (a single video frame). RESULTS and DISCUSSION The transmission and reflection sputtering yields as functions of Xe ion energy are shown in Figure 1 for the 62 nm Au film. EDS measurement after completion of a Xe irradiation yielded the amount of Au collected on the carbon foils. Similar observations and measurements were made at all ion energies used. Measurements from in situ recordings, based on the fraction of the image of the collector foil covered by Au, indicate that the Au accumulation increases approximately linearly with ion dose at the low ion doses used. The ion energies plotted in figure 1 for reflection sputtering have been corrected for ion energy loss in the carbon collector foil located in front of the specimen. Also shown for comparison in Figure 1 are experimental results for Au self ion sputtering [ 10,11 ] and calculations of the reflection sputtering yield for Xe, made using the theory developed by Sigmund [12]. The yield for reflection sputtering of Au by Xe exhibits a maximum at ion energies between 200 and 400 keV. The yield for self-ion sputtering also has a broad maximum above 200 keV. The maximum in the reflection sputtering yield with increasing ion energy is due to increasing ion penetration and reduced energy deposition at the surface. Although theoretical estimates were a factor of two too low, the maximum for self ions was attributed to nonlinear effects arising from cascade spikes [1]. Transmission sputtering increases with increasing Xe energy over the range studied due to increasing energy de
Data Loading...
