Film sintering

Consequently, the pressed ZnO sample possesses intercrystalline barriers characterized by a wide spread with respect to the height which can be considered as a specific type of intercrystalline contacts. At the same time a rigorous compliance with the Ohm law over the whole interval of applied fields is observed for a ZnO film sintered under vacuum conditions. This result and the fact that the estimation of the average value of the voltage drop per contact is about 0.2 eV kT 0.025 eV... 

Numerous studies of broadband oxide semiconductors made in tiie form of a relatively thin monocrystal or a thin film sintered on a dielectric substrate revealed that if oxides ZnO, Ti02, SnC>2, CdO, or similar ones are used, it is possible to determine with sufficient accuracy trace concentrations of such active molecules, atoms and radicals as O2, CI2, Br2, J2, H2, H, N, O, OH, Cl, OH, Cl, CH3, CjHj, C3H7, NHj, NH as well as atoms of many metals (Na, Ag, Zn, Cd, Pb, Fe, Pd, Pt, etc.) without the need of prior activating adsorbates. 

Further progress in the study of the Cu-Ni system awaited the preparation and careful characterization of alloy films of known bulk and surface composition. The essential step was taken by Sachtler and his co-workers 28, 88, 114) who prepared Cu-Ni alloy films by successive evaporation of the component metals in UHV. After evaporation the films were homogenized by heating in vacuum at 200°C. The bulk composition of the alloys was derived from X-ray diffraction, and the photoelectric work function of the films was also measured. A thermodynamic analysis, summarized by Fig. 13, indicated that alloy films sintered at 200°C should consist, at equilibrium, of two phases, viz., phase I containing 80% Cu and phase II containing 2% Cu. Evidence was presented that alloys within the... 

It is shown in this section with the help of hydrogen sorption isobars on evaporated metal films sintered at various temperatures that the sorption process consists of absorption into the interior of the structure as well as of... 

It is obvious that the isobars shown in Fig. 4 cannot be explained by adsorption. In the first place, the difference between the adsorption at —196° as obtained initially and the total sorption found at —196°, after obtaining the isobars, decreases little with increased temperature of sintering. Films sintered at 23° have about ten times the initial adsorption at — 196°C. of films sintered at 200° and about 175 times the... 

Fig. 5. Correlation of catalytic activity with adsorption and the surface area. (The ordinate represents fraction of respective values obtained for films sintered at 23°C.)...

Figure 5 shows data for catalytic activity, CO adsorption at 23°, surface area by the B.E.T. method using krypton at —196°, and the fast hydrogen adsorption at —196° plotted against the temperature at which the various films were sintered. All quantities were taken as unity for films sintered at 23°C. These experiments clearly indicate that the previously observed slow adsorption of hydrogen on nickel catalysts is not adsorption but is sorption consisting of adsorption and... 

Fig. 6. Sorption isobars at 0.1 mm. pressure of hydrogen on an evaporated nickel film sintered at 23°C. (To obtain the ordinate in molecules X 10 18/100 mg., divide by 9.07.)...

A few measurements have been carried out on iron, and Fig. 10 shows an ascending and descending isobar at 0.1 mm. pressure (analogous to that shown for nickel in Fig. 4) for an iron film sintered at 200°. The behavior is clearly very similar to that of nickel. 

Fig. 11. Activity pattern for benzene hydrogenation at 150°C. pHl = 322 Torr pbcnl = 5.8 Torr. O, Nickel deposited on top of copper, films sintered at 200°C for 18 to 20 hours A, copper deposited on top of nickel, films sintered at 200"C for 18 to 20 hours V, copper deposited on top of nickel, films sintered at 300°C for 14 hours. From van der Plank and Sachtler (101).

Fiq. 7. Reaction of cyclohexene with deuterium over iron films (52). (a) Final product distribution over unsintered films A, —35° B, 0° C, 26° D, 89°. (b) Final product distribution at 0° over A, unsintered film B, film sintered at 196°. 

Few studies have been made of the hydrogenation characteristics of these classes of molecule. The deuteration of cyclopentadiene 52) occurred very rapidly at — 34° at the surface of an iron film cyclopen-tene was probably produced as an intermediate but full deuteration to cyclopentane was the only measurable process. A film sintered for 16 min at 200° was active for diene exchange at 90° and yielded product containing one deuterium atom, but it was not active for the addition reaction. 

Figure 1. Broken surface of the Feo9sSi2,o Mn os thick films sintered in various temperatures.

The hot stage has not only been applied to optical and atomic force microscopes, but also to scanning electron microscopes. Hot-stage accessories are available on environmental SEMs that can collect ESEM images at elevated temperatures. Applications to the electronics industry include fluxless soldering, intermetallic growth studies, and copper thick-film sintering studies (92-94). 

Static measurements of the decomposition of formic acid vapor at 10-50-mm. pressure on randomly oriented evaporated nickel films sintered at 190° show the decomposition to be a simultaneous dehydrogenation and dehydration in the ratio 3 1 and to be zero order in initial rate. 

Figure 3-8. The images of Sm-doped ceria film on Pt the cross section of the film sintered at 800°C (a) and AFM images of the film surface sintered at 800°C (b) and 1,000°C (c)...

In the case of thin film sintering the lateral constraint imposed by a rigid substrate allows a shrinkage only in the direction (z-direction) perpendicular to the film. The imposed constraint induces an in-plane tensile stress and the stress accelerates the shrinkage in the z-direction. From the lateral constraint Ex = Sy = 0, cr = 0, and cTx = cry = cr, and the expressions of the uniaxial strain rates in Eq. (5.33), the densification rate in the z-direction is expressed as... 

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