Stefan Ostendorp

Controllable Growth and Field-Effect Property of Monolayer to Multilayer Microstripes of an Organic Semiconductor

The controllable growth of partially aligned monolayer to multilayer micrometer stripes was demonstrated by adjusting the pulling speed in a dip-coating process. The number of molecular layers decreases with the increasing pulling speed. A lower pulling speed yields mixed multilayers (3-9 monolayers). It is noteworthy that pure monolayer and bilayer microstripes over large areas can be obtained at high pulling speeds. The stripe morphology strongly depends on the pulling speed or the number of molecular layers. XRD and confocal fluorescence measurements manifest that monolayer stripes are amorphous, while multilayer stripes (> or = 2) consist of crystalline states. FET devices were fabricated on these stripes. Monolayer stripes failed to reveal a field effect due to their amorphous state. In contrast, multilayer stripes exhibit good field-effect behavior. This study provides useful information for future molecular design in controlling molecular architectures. The controllable growth from monolayer to multilayer offers a powerful experimental system for fundamental research into the real charge accumulation and transporting layers for OFETs.

Ultrathin alumina membranes for surface nanopatterning in fabricating quantum-sized nanodots.

Using ultrathin alumina membranes (UTAMs) as evaporation or etching masks large-scale ordered arrays of surface nanostructures can be synthesized on substrates. However, it is a challenge for this technique to synthesize quantum-sized surface structures. Here an innovative approach to prepare UTAMs with regularly arrayed pores in the quantum size range is reported. This new approach is based on a well-controlled pore-opening process and a modulated anodization process. Using UTAMs with quantum-sized pores for the surface patterning process, ordered arrays of quantum dots are synthesized on silicon substrates. This is the first time in realizing large-scale regularly arrayed surface structures in the quantum size range using the UTAM technique, which is an important breakthrough in the field of surface nanopatterning.

Sub-micron strain analysis of local stick-slip motion of individual shear bands in a bulk metallic glass

Nanodot deposition on a side surface of a rectangular sample and digital image correlation are used to quantify the in-plane strain fields associated with the propagation of a shear band in a PdNiP bulk metallic glass, induced by rolling. Within the resolution of the method related to an average inter-dot distance of 100 nm, deformation is found to be highly localized at the shear bands, while alternating areas with a size of 100–400 nm with opposite local shear strains are found. This phenomenon substantiates a local stick-slip nature of shear band propagation during the metallic glass deformation, even during rolling.