| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF1-ThM |
| Session: | Control and Modeling of Thin Film Growth and Film Characterization |
| Presenter: | Jerrold Floro, University of Virginia |
| Authors: | J.A. Floro, University of Virginia J. Amatya, University of Virginia C. Duska, University of Virginia C.W. Petz, University of Virginia D. Yang, University of Pittsburgh J. Levy, University of Pittsburgh |
| Correspondent: | Click to Email |
This talk will examine the perils, pitfalls, and possibilities for creating order across different lengthscales and dimensionalities in heteroepitaxial Group IV thin films and nanostructures. I will review our results in three projects: (i) Direct writing of ordered arrays of 3C-SiC quantum dots on Si (001); (ii) Directed self-assembly of 2D and 3D ordered arrays of Ge quantum dots on Si (001); and (iii) chemical ordering in Si1-xGex alloys on Si (001). Herein, all the materials are grown by molecular beam epitaxy. Even though Group IV materials are amongst the most heavily studied epitaxial growth systems, in all three cases discussed here there were significant surprises, some “good” and some “bad”. First I will briefly review our goal of using carbonaceous bumps, written on Si (001) by fine-spot electron-beam cracking of hydrocarbons, to direct the self-assembly of Ge quantum dots. We did not observe the latter to occur, but the formation of epitaxial 3C-SiC was itself interesting, and the carbide dots were successfully encapsulated in a Si matrix under optimized overgrowth conditions. We then used Ga focused ion beams (FIB) to create surface morphology that directs the self-assembly of Ge quantum dots. Atomic force microscopy (AFM) showed beautiful long-range order, both in single layers of dots, and in multiple layers of dots. However, cross-section transmission electron microscopy told a rather different story to the AFM, and this ultimately led us to abandon FIB as our patterning method of choice, in favor of electron beam lithography (ongoing). Finally, we recently revisited chemical ordering in Si1-xGex alloys, which was intensively studied in the 1990’s. Our work was driven by predictions that chemical ordering, with large order parameters, could produce observable effects on thermal transport, and likely on electrical transport as well. This could improve the thermoelectric figure of merit. However, despite an extensive survey of growth-parameter space, we never observed order parameters to exceed 0.24. We found it necessary to be very careful in our quantification of the order parameter. More interestingly, our results seem to suggest three mutually inconsistent results with regard to how ordering is affected by step density. Hence there is much more to be understood about the interactions of strain, steps, faceting, and dislocations on chemical ordering. We gratefully acknowledge the support of the Department of Energy Office of Basic Energy Sciences, the II-VI Foundation, and the National Science Foundation Division of Materials Research. Research was performed in part at the NIST Center for Nanoscale Science and Technology.