a 
je "Lateral drift was generally found to be in the Y-direction, i.e. the image would drift upwards on the 
screen when an animation of the raw data was viewed. This happened to of all the samples, altough 
the movement seemed to halt at the end of some of the four-hour experiments. The explanation was 
that the temperature in the laboratory generally increased during the day when the measurements 
cally 10 yi were made, typically from 24 to 28 °C. Fig. 3 shows the strong correlation between temperature and 
dled pg drift in the Y-direction for the eight experimental series from Fi g. 2. Dispite the statistical noise and 
8 therefore no the fact that some series have quite short temperature spans, it is clear that the temperature effect 
Ue nrg causes a linear drift in all experiments with the same shift per degree temperature increase. Due to 
010 if elgg the construction of the interferometer (Fig. 1), the lens on the microscope unit is located 35 cm 
icing horizontally from the supporting vertical beam. The thermal expansion for a 35 cm long rod of steel 
lest ig is plotted in Fig. 3 as a dotted line. The match with the data is quite good, and would be perfect for 
Grecton ofen as a 40 cm steel rod. The interferometer and XY stage are mounted on a plate made mostly of quarts, 
its coefficient of thermal expansion being neglectable in comparison to steel. When the temperature 
rises and the steel casing of the interferometer expands, the lens moves outwards, towards the 
eed rasa operator, thus making it seem like the sample moves in the opposite direction. 
I It is therefore established that for long term experiments with a NT-2000 interferometer, itis 
ees of he preferable to keep the room temperature constant to avoid unwanted specimen drift. However, if the 
J se temperature is monitored, thermal drift can be corrected for by the analysis software since the effect 
oo is linear and predictable. 
ne focus gives a 
ata in Fig, 2 have 
Al expansion of 35 ~ 
ard fine focus 
vertical drift can 30 e DD 
= 25 : © DD2 Boe 
3 A DU oe 
m 20 | A DU2 op" . 
451 = UD g 3 or 
v Oo UD2 3 a oS 
* 10 - ® UU a ° © ie 
o® > © a cL } 
Oo uu2 Oo ¢ © qv 
5 od > 4 
----- 35cm steel a © 
0 L a 3 °e 
20 oF 24 26 28 3 22 
Temperature [°C] 
Fig. 3: Plot of lateral drift in the Y-direction vs. the temperature measured on the XY sample 
stage. The experiments lasted over four hours each and were made at different times of the 
day, thus beginning and ending at different temperatures. 
a The first test results from etching of a mill finish rolled aluminum surface are presented in Fig 4 and 
. 5. An experiment of corrosion on different particles in an aluminum alloy has also been performed. 
Further testing will include evaporation of metal on polymer, electropolishing of bright rolled 
aluminum surfaces and lithographic etching of silicon. 
22 30 Ai 
127