Field decrystallization and structural modifications of highly doped silicon in a 2.45-GHz microwave single-mode cavity
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Field decrystallization and structural modifications of highly doped silicon in a 2.45-GHz microwave single-mode cavity Ramesh Peelamedu,a) Rustum Roy, Dinesh Agrawal, and William Drawl Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 20 January 2004; accepted 3 March 2004)
Highly doped n-type silicon powder responds aggressively to a 2.45-GHz microwave E-field, whereas it remains unperturbed in the H-field. In the E-field, after about 30 s of treatment, the silicon powder attained submelting temperatures and thus coagulated to a bulk solid piece. X-ray diffraction analysis of the surface and the cross section of this solid material failed to show any detectable peaks, ascertaining the fact that the material had decrystallized. The Raman spectra of the material had broad and shallow peaks quite different from the thin, sharp lines exhibited by Si wafer. It appears that the E-field treatment has considerably distorted the lattice structure creating lattice strains throughout the sample. These lattice strains were relieved by grinding (recrystallized). Previous publications from this1–3 and other laboratories4–7 reported that a number of materials are highly responsive in a microwave cavity. The construction of the single-mode TE103 cavity at the Pennsylvania State University has resulted in the ability to work in either Eor H-fields separately for materials processing.8 The fact that certain materials can be heated very effectively in H-field is in contrast with the conventional belief (as observed from the power equation, P ⳱ 2ƒ⑀ o ⑀ r⬘ tan␦|E|2) that the E-field alone is contributing to microwave heating. For any material processed in a multimode microwave field, the magnetic field contribution should not be ignored in the power equation for heating. In a single mode (either in E- or H-field or in a mixed mode), the material heating occurs rather quickly compared to a multimode microwave due to the high field concentration around the sample. Recently, we studied the field distributions in a single-mode cavity by monitoring loop currents around the sample during heating.9 In the case of E-field, it is known that material parameters such as tan␦ and ⑀r⬘ play a crucial role in determination of heating, whereas, in the case of H-field, the equivalent terms such as tan⭸ and r⬘ are important. However, the factors such as electric field current (eddy current) and magnetic field perturbation (induction current) currents are equally important and cannot be ignored. In addition to the E and H
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0223 J. Mater. Res., Vol. 19, No. 6, Jun 2004
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effects, the heating is also microwave frequency dependent. In our previous papers, we have discussed the heating differences in magnetite (Fe3O4) and Hematite (Fe2O3). Takizawa et al.10 have reported synthesis of various compounds by using Fe2O3 in a 28-GHz microwave facility
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