PhD Thesis Arne Lüker final version V4 - Cranfield University

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PST directly on SiO2 second rearrangement leads to the “buckled row” reconstruction, Fig. 7.5(b), in which one atom of each dimer lifts up and the other shifts down, resulting in a buckled dimer. This buckling causes both electrons to localise in the upper silicon atom of a dimer, whereas the other silicon atom with the empty dangling bond prefers a more planar arrangement [2]. (a) (b) (c) RMS: 0.686 nm RMS: 0.777 nm RMS: 7.095 nm Fig. 1307.4: AFM- and SEM imagines of PST on SiO2/Si annealed at (a) 550°C, (b) 600°C, and (c) 650°C
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications Even at room temperature, the buckling pattern is dynamic, with the dimers executing a kind of "rocking" motion or oscillation around the idealized structure of Figure 7.5(a). As a result the surface dimers are chemically very reactive and can serve as receptors for certain types of atoms or even molecules. The most common atom in nature which docks onto this structure is O, forming the native SiO2 layer, Fig.7.6. But Sr ad-atoms will saturate the dangling bonds of one silicon dimer with its two valence electrons as well. A saturated dimer looses its buckling, since all dangling bonds are filled and both Si atoms prefer the tetragonal sp 3 configuration. The Sr atom first occupies the trough between the dimer rows, in the center of four dimers. C.J. Först et al. [3, 4] have simulated this adsorption process of Sr ad-atoms onto Si in more detail. The result is shown in Fig. 7.7. One of the Sr neighboring Si dimers is unbuckled due to the electron donation from the ad- atom. The others three dimers are orientated such that the upper, and thus negatively charged Si (a) (b) Fig. 7.5: The top surface of silicon; (a), the “dimer row” reconstruction, and (b), the “buckled row” reconstruction [2]. Fig. 7.6: The Si-SiO2 interface. Black atoms are Oxygen atom points towards the Sr 2+ ion. The energy penalty for placing a lower and thus positively charged silicon atom next to a Sr ad-atom is roughly 0.4 eV. Therefore the ad- atoms pin the dimer buckling as observed experimentally [5]. The filled dimer offers a 131
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Sol-Gel derived Ferroelectric Thin
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Abstract Ferroelectric perovskite t
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Table of Content Introduction and M
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Page 81 and 82: Sol-Gel derived Ferroelectric Thin
Page 99 and 100: Intensity [arb. Units] (g) (f) (e)
Page 103 and 104: Relative diel. diel. constant Const
Page 113 and 114: Intensity [arb. Units] Intensity [a
Page 121 and 122: Tunability [%] 100 90 80 70 60 50 4
Page 131: (g) (f) (e) (d) (c) (b) (a) Sol-Gel
Page 149 and 150: Intensity [arb. Units] Sol-Gel deri
Page 175 and 176: Internships: Sol-Gel derived Ferroe
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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