@article{PietschGrenzerGrigorianetal.2004,
  author    = {Pietsch, Ullrich and Grenzer, J{\"o}rg and Grigorian, Souren A. and Weyers, Markus and Zeimer, Ute and Feranchuk, S. and Fricke, J. and Kissel, H. and Knauer, A. and Tr{\"a}nkle, G.},
  title     = {Nanoengineering of lateral strain-modulation in quantum well heterostructures},
  year      = {2004},
  abstract  = {We have developed a method to design a lateral band-gap modulation in a quantum well heterostructure. The lateral strain variation is induced by patterning of a stressor layer grown on top of a single quantum well which itself is not patterned. The three-dimensional (3D) strain distribution within the lateral nanostructure is calculated using linear elasticity theory applying a finite element technique. Based on the deformation potential approach the calculated strain distribution is translated into a local variation of the band-gap energy. Using a given vertical layer structure we are able to optimize the geometrical parameters to provide a nanostructure with maximum lateral band-gap variation. Experimentally such a structure was realized by etching a surface grating into a tensile-strained InGaP stressor layer grown on top of a compressively strained InGaAs-single quantum well. The achieved 3D strain distribution and the induced band-gap variation are successfully probed by x-ray grazing incidence diffraction and low-temperature photoluminescence measurements, respectively},
  language  = {en}
}
@article{PietschGrigorianGrenzeretal.2003,
  author    = {Pietsch, Ullrich and Grigorian, Souren A. and Grenzer, J{\"o}rg and Vartanyants, Ivan A.},
  title     = {Thermal diffuse scattering in grazing incidence diffraction},
  year      = {2003},
  language  = {en}
}
@article{PietschGrigorianGrenzeretal.2003,
  author    = {Pietsch, Ullrich and Grigorian, Souren A. and Grenzer, J{\"o}rg and Feranchuk, S. and Zeimer, Ute},
  title     = {Grazing-incidence diffraction study of strain-modulated single quantum well nanostructures},
  year      = {2003},
  language  = {en}
}
@article{PietschZeimerGrenzeretal.2003,
  author    = {Pietsch, Ullrich and Zeimer, Ute and Grenzer, J{\"o}rg and Grigorian, Souren A. and Fricke, J. and Gramlich, S. and Bugge, F. and Weyers, Markus and Trankle, G.},
  title     = {Influence of lateral patterning geometry on lateral carrier confinement in strain-modulated InGaAs- nanostructures},
  year      = {2003},
  language  = {en}
}
@article{ZenSaphiannikovaNeheretal.2006,
  author    = {Zen, Achmad and Saphiannikova, Marina and Neher, Dieter and Grenzer, J{\"o}rg and Grigorian, Souren A. and Pietsch, Ullrich and Asawapirom, Udom and Janietz, Silvia and Scherf, Ullrich and Lieberwirth, Ingo and Wegner, Gerhard},
  title     = {Effect of molecular weight on the structure and crystallinity of poly(3-hexylthiophene)},
  doi       = {10.1021/Ma0521349},
  year      = {2006},
  abstract  = {Recently, two different groups have reported independently that the mobility of field-effect transistors made from regioregular poly(3-hexylthiophene) (P3HT) increases strongly with molecular weight. Two different models were presented: one proposing carrier trapping at grain boundaries and the second putting emphasis on the conformation and packing of the polymer chains in the thin layers for different molecular weights. Here, we present the results of detailed investigations of powders and thin films of deuterated P3HT fractions with different molecular weight. For powder samples, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were used to investigate the structure and crystallization behavior of the polymers. The GPC investigations show that all weight fractions possess a rather broad molecular weight distribution. DSC measurements reveal a strong decrease of the crystallization temperature and, most important, a significant decrease of the degree of crystallinity with decreasing molecular weight. To study the structure of thin layers in lateral and vertical directions, both transmission electron microscopy (TEM) and X-ray grazing incidence diffraction (GID) were utilized. These methods show that thin layers of the low molecular weight fraction consist of well-defined crystalline domains embedded in a disordered matrix. We propose that the transport properties of layers prepared from fractions of poly(3-hexylthiophene) with different molecular weight are largely determined by the crystallinity of the samples and not by the perfection of the packing of the chains in the individual crystallites},
  language  = {en}
}
@article{JoshiPingelGrigorianetal.2009,
  author    = {Joshi, Siddharth and Pingel, Patrick and Grigorian, Souren and Panzner, Tobias and Pietsch, Ullrich and Neher, Dieter and Forster, Michael and Scherf, Ullrich},
  title     = {Bimodal temperature behavior of structure and mobility in high molecular weight p3ht thin films},
  issn      = {0024-9297},
  doi       = {10.1021/Ma900021w},
  year      = {2009},
  abstract  = {We report a temperature dependent crystalline structure of spin-coated thin films of high molecular weight regioregular poly(3-hexylthiophene) (P3HT) (M-n similar to 30000 g/mol) and its correlation with charge carrier mobility. These investigations show a reversible change of the crystalline structure, where the interlayer lattice spacing (100)along the alkyl side chains continuously increases up to a temperature of about 220 degrees C; in contrast, the in-plane pi-pi distance reduces with increasing temperature. These changes in structure are reversible and can be repeated several times. The temperature-induced structural properties differ for thick and thin films, pointing to a surface/interface role in stabilization of the layer morphology. In contrast to the structural changes, the carrier mobility is rather constant in the temperature range from room temperature up to 100-120 degrees C, followed by a continuous decrease. For thick layers this drop is significant and the transistor performance almost vanishes at high temperature, however, it completely recovers upon cooling back to roorn temperature. The drop of the charge carrier mobility at higher temperatures is in contrast with expectations front the structural studies, considering the increase of crystalline fraction of the polycrystalline layer. our electrical measurements Underscore that the reduction of the macroscopic mobility is mostly caused by it pronounced decrease of the intergrain transport. The thermally induced crystallization along(100) direction and the creation of numerous small crystallites at the film-substrate interface reduce the number of long polymer chain, bridging crystalline domains, which ultimately limits the macroscopic charge transport.},
  language  = {en}
}