Using quasi-in-situ scanning force microscopy we study the details of nanopattern alignment in ABC terblock copolymer thin films in the presence of an in-plane electric field. Because of the surface interactions and electric field the lamellae are oriented both perpendicular to the plane of the film and parallel to the electric field. We identified two distinct defect types which govern the orientation mechanism. Ring-like (tori) and open-end defects dominate at the early stage of the orientation process, while mainly classic topological defects (disclinations and dislocations) are involved in long-range ordering at the late stages. Comparison of the time evolution of the defect density with the evolution of the orientational order parameter suggests that tori-defects are essential for the effective reorientation. Further, the quasi-in-situ SFM imaging allowed us to elucidate the influence of the electric field strength on the propagation velocity of the topological defects.

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The photoluminescence properties of silicon quantum dots may be tailored by surface states via efficient coupling to resonant bulk states. Therefore various wet-chemistry procedures were developed to fabricate silicon quantum dots with adjustable sizes and surface properties. While the energy gap of the Si core is tuned by the size, resonant electronic surface states may be attained by varying the structure and chemical composition of the grafting. The strength of electronic couplings between surface and bulk states determines the timescale of both photo-induced electron transfer from excited surface states to conduction band states and capture of conduction band electrons by surface states. Whereas the origin of photoluminescence and therewith the quantum dot size distribution may be elucidated by stationary luminescence spectroscopy, ultrafast optical spectroscopy techniques, for instance the femtosecond transient absorption spectroscopy, allow to monitor photo-induced electron transfer between surface and bulk states and carrier trapping on the subpicosecond timescale.Temporal evolution of transient absorption spectra of 3-ethenylthiophene terminated Si qdot colloids excited at 390 nm with 150 fs pulses. Surface states as tool to control photoluminescence of Si qdotsOne major objective of Si-based nanophotonics and optoelectronics [1,2] is the development of silicon quantum dots (Si qdots) with optically or electrically controllable luminescence properties. The luminescence of silicon quantum dots smaller than free-exciton Bohr's radius (4.3 nm) is attributed to the radiative recombination of carriers confined in the core [3,4]. Quantum confinement allows for tuning the luminescence wavelength in the visible range due to suitably adjusting the Si qdot size [5-10]. On the other hand, quantum confinement is associated with large carrier wavefunction amplitudes at the quantum dot surfaces that are natively passivated by oxidation. The native passivation shell as an amorphous SiO x layer offers a broad variety of defect structures which are in main optically inactive. Defect structures may efficiently capture the carriers and thereupon reduce the luminescence quantum yield by providing nonradiative recombination centers for the electron-hole pairs [11][12][13]. Therefore Si qdot surfaces are needed to be modified, at least by saturating all dangling bonds and removing defect structures.