Si(111) preparation in UHV
Previous sample handle:
manipulation of sample –NO metal tweezers
holder sample –molybdenum or tantalum
Sample cleaning:
triclor ethylene
acetone
ethanol
(5 minutes each)
dry with nitrogen flow
UHV preparation:
The preparation of Si(111) consist on heating the sample (by electron
bombardment or by direct current –doped Si needed-) in different phases.
The sample must be degassed several hours at 600ºC, before first preparation.
First step is to heat the sample from 600ºC to 850ºC, increasing the
temperature slowly 10ºC/ minute.
With the sample at 850ºC, the temperature is increased instantly at 1200ºC
(flash) for 20-60 sec, in order to clean the surface of contaminants (particularly
carbon). Generally, the time of the applied flash depends on the pressure value. It
is advisable that the pressure does not increase more than 510-10Torr. Use
Nitrogen traps for improve the pressure. When preparing for the first time, it is
difficult to achieve the pressure limit, and the flash takes few seconds. With time,
the flash can be longer. It can take a couple of days before this. It depends on how
good is your base-pressure and how good is out-gassed the heater, the
manipulator and the sample holder.
After the application of 3-4 flashes, the temperature is decreased at a
constant rhythm from 850ºC to 600ºC , for 30-40 minutes. We use a computer
controlled power supply.
(From Nicoleta Nicoara)