3 Results and Discussion dies 
3.1 Sputter cleaning we 
In the initial state, samples include precipitations in the scale of a few um containing the elements ae wr 
aluminium, silicon, iron and additionally manganese and copper in case of alloy 2024. Because of os 
differences in hardness the precipitations protrude from of the polished surface (fig. 1a). um) A 
have“ 
At the beginning of the sputtering treatment the surface changes significantly. Unexpectedly, at first ous 17 
a relatively thick oxide coverage is formed. Only the mentioned precipitations look out (fig. 1b). A wl 
minimum coatings thickness of 0.1 pm was estimated on the basis of EDXS measurements. The lr 7% 
coverage contains up to approximately 65 at.-% oxygen. In the case of alloy 2024 magnesium is en- gor 
riched significantly. Comparing the number of atoms for the elements Mg and Al the ratio of 1:6 is Du 
tenfold higher as in the alloy. Using secondary electron imaging the underlying metallic body can % 
not be seen clearly (fig. 1b). But in backscattered electron images changes of microstructure are ur 
evident (fig. 1c). Additional precipitations seen as bright features consist of aluminium and copper. 
It is assumed that plate like ALCu precipitations have formed during sputtering. Partially, a pre- The oo 
ferred orientation of the precipitations is seen indicating their coherency. The dark regions are pores formar: 
showing likewise preferred orientation. For evaluation a comparative study was performed at an of oxide 1 
2024 sample after polishing and annealing at 400°C. The formation of precipitations is the same, in the casi 
thus this phenomenon may be attributed to a thermal effect. But the formation of pores has been type, inter 
only observed after plasma treatment. Additionally, the enrichment of Mg inside the oxide coverage tion is pr 
is combined with a drastically reduce of the Mg content in the region underneath the coverage. as the fon 
ing will di 
The period of the formation of the oxide coverage is followed by the period of its removal. The ’ 
chronology of this process is demonstrated in fig. 2. The removing process is not uniformly. Bit by The eas 
bit. small areas in a scale of a few micrometers will be uncovered. Obviously, the force of the glow is not yet 
350°C bei 
taminatiot 
32 itr 
After surl 
start. The 
and alum 
fig. ab 
ho due to th 
Fig. 1: SEM micrographs of alloy 2024 after grinding and polishing (a) and after 10-20 min sputtering (b,c). cally. Di 
a,b: SE imaging (45° tilt), c: BE imaging (without tilting) ferent ch 
from the 
founding 
In this w; 
The degr 
phere dir 
Sputtering 
faver fg 
sin pli 
> . reas ; 
Fig. 2: SEM micrographs (45° tilt), surface of Al99.5 after different sputtering times in Ar atmosphere: 30 min fo 
(a), 45 min (b) and 60 min (¢) TU 
164