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Register a new userElectronic states in ideal free standing films
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Shang Yuan Ren
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Exact and general results on the electronic states in ideal free standing films are presented. In many interesting cases, such as in FCC (001) films and in FCC (110) films, the energies of most electronic states in the film can be analytically obained from the corresponding energy band structure of the bulk. This approach can be further extended to obtain exact and general results on the electronic states in quantum wires and quantum dots.
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The origin of the unusual 90^o ferroelectric / ferroelastic domains, consistently observed in recent studies on meso and nanoscale free-standing single crystals of BaTiO3 [Schilling et al., Physical Review B, 74, 024115 (2006); Schilling et al., Nano Letters, 7, 3787 (2007)], has been considered. A model has been developed which postulates that the domains form as a response to elastic stress induced by a surface layer which does not undergo the paraelectric-ferroelectric, cubic-tetragonal phase transition. This model was found to accurately account for the changes in domain periodicity as a function of size that had been observed experimentally. The physical origin of the surface layer might readily be associated with patterning damage, seen in experiment; however, when all evidence of physical damage is removed from the BaTiO3 surfaces by thermal annealing, the domain configuration remains practically unchanged. This suggests a more intrinsic origin, such as the increased importance of surface tension at small dimensions. The effect of surface tension is also shown to be proportional to the difference in hardness between the surface and the interior of the ferroelectric. The present model for surface tension induced twinning should also be relevant for finely grained or core-shell structured ceramics.
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Si dangling bonds without H termination at the interface of quasi-free standing monolayer graphene (QFMLG) are known scattering centers that can severely affect carrier mobility. In this report, we study the atomic and electronic structure of Si dangling bonds in QFMLG using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS), atomic force microscopy (AFM), and density functional theory (DFT) calculations. Two types of defects with different contrast were observed on a flat terrace by STM and AFM. Their STM contrast varies with bias voltage. In STS, they showed characteristic peaks at different energies, 1.1 and 1.4 eV. Comparison with DFT calculations indicates that they correspond to clusters of 3 and 4 Si dangling bonds, respectively. The relevance of these results for the optimization of graphene synthesis is discussed.
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