Hi all,

we have recently started to work with Al single crystals for surface science experiments. Unfortunately, after a few cleaning cycles the crystal surface gets cloudy or "milky". Our typical cleaning cycle involves 1 kV Ar sputtering (ion current around 3-5 uA) x 30-60 min followed by annealing to 600-700 K (time varies, but typically not less than 15 min with somewhat fast ramping up and down, but no quenching). A high resolution XPS does not show any considerable amount of adsorbates or anything unusual whatsoever (some traces of oxygen which were there even for the mirror-like surface, some traces of carbon). Therefore, I suspect the crystal experienced some faceting/graining of the surface which resulted in that the surface has become mesoscopically rough. LEED spots have possibly become somewhat broader but this is really hard to estimate. Unfortunately, we had no time to perform AFM measurements on this surface. But it looks indeed as an annealing protocol is vitally important to keep the surface nice and well-defined. Therefore, I wonder if anyone else has experienced the same problem with Al (or maybe other crystals, too?) and/or knows how to overcome this issue? Maybe someone could share an annealing protocol or give a link to such a protocol if published? Tips and tricks? All meaningful opinions are welcome!