Annealing cycle

MOCVD reactions are used increasingly, such as the pyrolysis of tantalum ethylate, Ta(OC2H5)5, in oxygen and nitrogen at 340-450°C and at a pressure of <1 Torr. This is followed by an annealing cycle at 600-900°C.P l Tantala is also deposited by the pyrolysis of the tantalum dichlorodiethoxy acetylacetonate at 300-500°C.P ]... 

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. 

The (8X2)-TiOr film can also be synthesized by the stepwise direct deposition of Ti onto an oxygen-covered Mo(112) surface followed by subsequent oxidation-annealing cycles. However, the quality and reproducibility are not comparable with growth on the SiOz film. In either case, analysis of the HREELS and XPS results indicate that the oxidation state of the Ti is probably +3. This reduced Ti state is apparently responsible for the ability of Au and other metals to wet the surface. 

The rate of recovery is normally highest at the start of an isothermal annealing cycle because the driving force is largest at that time. As recovery continues, the driving force diminishes as the available strain energy is used up and the rate of recovery falls continuously toward zero. A plot of the rate of recovery as a function of time yields a curve that is somewhat similar in appearance to an exponential decay curve. The rate of recovery is also temperature dependent and may be expressed, in a number of cases, by a simple empirical equation of the form... 

Figure 23.2 (a) XPS C(Is) spectrum of the untreated Mo2C sample, (b) spectrum obtained following several annealing cycles to 1400 K in UHV. 

The ability to produce polyurethane parts with a large cross-section (>30 mm) easily is a major advantage over other polymers. A conventional polymer such as polyethylene requires heat under pressure to form a thick cross-section with a long, slow cooling/annealing cycle to prevent stress and voids in the part. The production of other than simple-shaped articles is very difficult. After this molding process, postmachining also needs to be carried out. 

Samples are normally heated to just above softening point and then allowed to cool down before a test is carried out. With castable polyurethanes, decomposition takes place when the sample is softened, so either the annealing cycle must not be used or the temperatures must not be taken up as high. 

Clean substrate surfaces for nonoptical experiments were prepared by a series of Ar+-sputtering/thermal annealing cycles to remove surface impurities and restore atomic smoothness, respectively, using AES and/or XPS to determine cleanliness and LEED to assess surface ordering for single crystal specimens. Most of the work so far reported has involved nominally unreactive substrates, namely Ag and Au. 

For these experiments, a polycrystalline silver foil (Alfa Products, m3N, 0.127 mm thick) cleaned by multiple Ar+ sputtering/thermal annealing cycles [54] was used as a substrate. 

Measurements were conducted in UHV chamber B using an A1 foil (Alfa, 0.13 mm thick, m5N in purity), cleaned by a series of Ar+ (600 eV) sputtering and annealing cycles to 600°C. 

The RAIRS study of this system [87] has probed the orientation of formate on Ti02(l 10)1x1, the substrate being prepared via sputter/UHV anneal cycles with a final anneal in 1x10" mbar of oxygen to minimise surface oxygen vacancies, p-polarised RAIRS measurements were recorded as a function of azimuthal incidence angle. Two bands were observed, one absorption the second transmission, which were assigned to the antisymmetric and symmetric vibrational modes of formate, respectively. These data evidence the presence of not one but two surface formate species (A and B). A, which is the majority species, is oriented such that its molecular plane is in the [001] azimuth, which... 

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. 

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