Sputter annealing

We use commercial Ti02 crystals (Pi-Kent) cut and polished to within 0.3° of the (110) face and we prepare them further with cycles of Ar + bombardment and U H V annealing to approximately 950-1100 K, typically 5-10 min for each cycle. The samples are mounted onto tantalum back-plates via strips of tantalum spot-welded to the back-plate. Annealing is performed by high-energy electron bombardment of the back-plate from a hot filament. Temperatures are measured from optical pyrometers (Minolta) focused on the back-plate. The temperatures are not measured directly from the samples because they are translucent and get darker with each sputter/anneal cycle. 

To reduce the exposure to residual gas from the vacuum, our samples are sputtered/annealed in separate preparation chambers attached via valves to the SPM chambers. After the final anneal cycle of the cleaning procedure, the sample is transferred to the SPM chamber within a minute or so where the pressure is lower. 

Figure 8.6 summarizes our current knowledge of the appearance of point defects in STM images. The most prevalent point defects on sputtered/annealed Ti02(l 1 0) lxl surfaces have been identified as Ob-vacs, OHb, and OHb pairs and these are shown in a ball model together with an STM image decorated with a number of all three types of defects. 

Figure 8.4 Sequential (285Ax250A) STM images of Ti02(l 1 0). (a) Sputtered/annealed Ti02(l 1 0) with approximately 3.5 and 5.5% M L Ab and Ad defects, respectively. The blue crosses denote Ad defects that are also present in (b), the red circles denote Ab defects, and the yellow circles denote Ab defects that are removed to form the image in (b). (b) Following a +3V scan. The yellow lines indicate the approximate boundaries beneath which the + 3V scan was applied. Blue crosses and red circles denote Ad...

Sample treatment Distance calibration Field desorption, annealing, sputtering Annealing, sputtering, cleaving a single crystal... 

Instead of the usual sputter/annealing preparation of new crystals, oxygen plasma treatment appears to be a quite efficient treatment for producing clean, (1x1) terminated terraces [83]. Plasma treatment removed Ca (that often segregates to the surface initially) quickly. At relatively low temperature it produced larger terraces (1500 A in width) and straight step edges than typically found on sputtered/annealed surfaces. 

Sample was grown as Pt25Cu75, bulk composition given reflects estimated Pt enrichment due to many sputtering/annealing cycles and possible Cu evaporation at high temperatures. 

Figure 14.3b presents a LEED picture of the sapphire (1120) surface after the UFIV sputter/annealing treatment. Note that charging does complicate the... 

It turned out that early attempts to prepare or clean this surface in UHV using sputter/annealing cycles experienced difficulties arising from a sensitive dependence on... 

Figure 1. Comparison of lead UPD on Cu(lll) (a) AES (3 keV incident beam) and LEED (60 eV) of a crystal prepared in UHV by sputter/anneal cycles, (b) crystal prepared by the electropolishing procedure. 0.1 M HF, 10 mV/s. The dotted line marks the peak potentials in the cyclic voltammograms. (Reproduced with permission from references. Copyright 1995, ACS)...

Because of the chemical and structural damage inherent in sputter annealing, alternative approaches have been investigated. One is to transfer a sample from air to UHV, then heat it to sublime the surface oxide. Little work has been done to characterize surfaces produced by this method, except that STM images reveal faceted voids that may reflect metal evaporation [74]. Another approach is to fracture the sample [64-67,75-78]. This approach clearly causes the least chemical damage, but it may produce a nonequihbrium structure. An even larger problem is that fracture consumes samples irreversibly. 

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