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- ItemOn the interaction of glasses with high-energy radiation - Combined ESR and optical studies(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Nofz, Marianne; Reich, Christian; Stösser, Reinhard; Bartoll, Jens; Janata, EberhardThis paper will discuss some aspects of the induced physical processes and chemical reactions which are observed when Silicate and aluminosilicate glasses are exposed to UV radiation (248 nm; excimer laser), γ radiation (⁶⁰Co) and pulses of fast electrons (3.8 MeV). The stimulated emission and absorption of short-lived defects and Čerenkov radiation are detected in the optical ränge between 200 and 800 nm and on the microsecond time scale. Stahle hole centres (Si-0⁻/h⁺, Si-O-Al/h⁺) and electron centres (among others Zn⁺, Cd⁺, (Fe³⁺)⁻) are detected by ESR spectroscopy at room temperature. They show surprising differences in regard to their thermal stability, i.e., the distribution and mean value of their trap depths. Induced absorption in the UV/VIS range exhibits broad and overlapping bands, some of which can be partially assigned to centres detected by ESR spectroscopy. Therefore, UV/VIS spectroscopy provides complementary information, an induced absorption at 300 nm for example, which has no analogy in ESR measurements.
- ItemThermal expansion behaviour of unidirectionally SiC fibre-reinforced MAS and BMAS glass-ceramics(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Reich, Christian; Brückner, RolfThe thermal expansion behaviour of SiC fibre-reinforced Magnesium-Aluminium-Silicate (MAS) and Barium-Magnesium- Aluminium-Silicate (BMAS) glass-ceramics was studied in air as well as in argon furnace atmosphere. The results show that the coefficients of thermal expansion up to a temperature of 800 C are influenced to a minor degree by the furnace atmosphere and to a major degree by the phase composition of the matrices and the fibre concentration. The largest values in air and argon atmosphere are obtained from BMAS(14)/SiC fibre composites with α₁₅₀/₈₀₀ = 3.92 * 10⁻⁶ K⁻¹ and 3.87 * 10⁻⁶ K⁻¹ respectively, at a fibre content of 52 vol.%, while the lowest values are found for BMAS(9)/SiC fibre composites in air with α₁₅₀/₈₀₀ = 3.24 * 10⁻⁶ K⁻¹ and in argon with α₁₅₀/₈₀₀ = 3.11 * 10⁻⁶ K⁻¹ at a fibre content of about 25 vol.%. Increasing fibre concentration leads to increasing thermal expansion. The experimentally determined values were compared with calculated ones by the mixing rule and a good agreement was found, particularly for the BMAS(14) composites.
- ItemSelective lateral germanium growth for local GeOI fabrication(Pennington, NJ : ECS, 2014) Yamamoto, Yuji; Schubert, Markus Andreas; Reich, Christian; Bernd Tillack, Bernd TillackHigh quality local Germanium-on-oxide (GeOI) wafers are fabricated using selective lateral germanium (Ge) growth technique by a single wafer reduced pressure chemical vapor deposition system. Mesa structures of 300 nm thick epitaxial silicon (Si) interposed by SiO2 cap and buried oxide are prepared. HCl vapor phase etching of Si is performed prior to selective Ge growth to remove a part of the epitaxial Si to form cavity under the mesa. By following selective Ge growth, the cavity was filled. Cross section TEM shows dislocations of Ge which are located near Si / Ge interface only. By plan view TEM, it is shown that the dislocations in Ge which direct to SiO2 cap or to buried-oxide (BOX) are located near the interface of Si and Ge. The dislocations which run parallel to BOX are observed only in [110] and [1–10] direction resulting Ge grown toward [010] direction contains no dislocations. This mechanism is similar to aspect-ratio-trapping but here we are using a horizontal approach, which offers the option to remove the defective areas by standard structuring techniques. A root mean square of roughness of ∼0.2 nm is obtained after the SiO2 cap removal. Tensile strain in the Ge layer is observed due to higher thermal expansion coefficient of Ge compared to Si and SiO2.