Columnar Microstructure

Fig. 21. Deuterium concentration profiles, obtained by SIMS, for n-type doped a-Si H (10 4[PH3]/[SiH4]) with columnar microstructure. The bottom curve is the profile for the as grown sample, while the middle and top profiles (vertical scale offset) are obtained after annealing at 240°C for 35 min. and 24 hours, respectively (Street and Tsai. 1988).

Researchers who have focused more on understanding cause-effect relationships in solution processing have given attention to film drying and pyrolysis behavior, densification processes, and nucleation and growth into the desired crystalline state. Both thermodynamic and kinetic factors associated with the phase transformation from the amorphous state to the crystalline state have been considered.11 119 Control of these factors can lead to improvements in the ability to influence the microstructure. It is noted that in the previous sentence, influence has been carefully chosen, since the ability to manipulate the factors that govern the nature of the phase transformation to the extent that full control of the microstructure is possible remains to be demonstrated. However, trends in characteristics such as film orientation and columnar versus uniaxial grains have certainly already been achieved.120... 

Figure 2.16. (a-c) Simulations of film structural evolution for PZT thin films at various times during heat treatment.15 (d) A representative SEM photomicrograph illustrating the columnar microstructure of PZT.48 The lower layer is the lower Pt electrode, the middle layer is the PZT, and the upper layer is the top Pt electrode, [(a)-(c) Reprinted with permission from Ref. 15. (d) Reprinted with permission from Ref. 9. Copyright 1997 American Chemical Society.] (See color insert.)... 

Hoffmann, S. Haxenkox, U. Waser, R. Jia, J. L. Urban, K. 1997. Chemical solution deposition of BaTi03 and SrTi03 with columnar microstructures. In Science and Technology of Semiconductor Surface Preparation, edited by Hagashi, G. S. Hirose, M. Ragahavan, S. Verhaverbeke, S. Mat. Res. Soc. Symp. Proc. 477 9-14. 

Ni-YSZ cermets deposited by RF sputtering (230 nm) were found to have micro-structural features consisting of columnar grains 13 to 75 nm long and 9 to 22 nm wide, and showed good adhesion to the YSZ layer on which they were deposited [128], In a three-layer Ni-YSZ-Ni film deposited on NiO by RF sputtering in another study, the YSZ layer exhibited a columnar structure with some pinholes [129], Microstructural and electrochemical features of Pt electrodes patterned by lithography on YSZ have also been studied [130,131]. 

In Chapter 7 various growth models were described layer growth (Section 7.9), nucleation-coalescence growth (Section 7.10), development of texture (Section 7.11), columnar microstructure (Section 7.12), and other structural forms (Section 7.13). In this section we discuss the effects of additives on these growth mechanisms. 

Figure 7.17. Theoretical model of the microstructure of the columnar film, parallel to the substrate, at different depths, td> tc> tb> ta (/, time of deposition). (From Section 7.15 Ref. 35, with permission from American Institute of Physics.)...

Studies were also performed with an artificial fixed bed composed of an array of microstructured columns made by a plasma etch process. These columns were made porous to increase the surface area to 100 m2, which is not far from the porosity of catalyst particles in fixed beds, and then coated with a catalyst [278]. The performance of such catalytic microcolumns was compared with that of a catalytic fixed bed reactor. When normalized to the metal content, the reaction rates of the columnar and the particle-containing reactor are similar with 6.5 x 10 5 and 4.5 x 10-5 mol/(minm2), respectively. 

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