Nucleation and growth of thin films of rod--like conjugated molecules

Thin films formed from small molecules rapidly gain importance in different technological fields. To explain their growth, methods developed for zero--dimensional atoms as the film forming particles are applied. However, in organic thin film growth the dimensionality of the building blocks comes into play. Using the special case of the model molecule para--Sexiphenyl, we will emphasize the challenges that arise from the anisotropic and one--dimensional nature of building blocks. Differences or common features with other rodlike molecules will be discussed. The typical morphologies encountered for this group of molecules and the relevant growth modes will be investigated. Special attention is given to the transition between flat lying and upright orientation of the building blocks during nucleation. We will further discuss methods to control the molecular orientation and describe the involved diffusion processes qualitatively and quantitatively.Comment: as submitted to JPCM (revised version) fixed figures and a few lines of tex

Improved recursive Green's function formalism for quasi one-dimensional systems with realistic defects

We derive an improved version of the recursive Green's function formalism (RGF), which is a standard tool in the quantum transport theory. We consider the case of disordered quasi one-dimensional materials where the disorder is applied in form of randomly distributed realistic defects, leading to partly periodic Hamiltonian matrices. The algorithm accelerates the common RGF in the recursive decimation scheme, using the iteration steps of the renormalization decimation algorithm. This leads to a smaller effective system, which is treated using the common forward iteration scheme. The computational complexity scales linearly with the number of defects, instead of linearly with the total system length for the conventional approach. We show that the scaling of the calculation time of the Green's function depends on the defect density of a random test system. Furthermore, we discuss the calculation time and the memory requirement of the whole transport formalism applied to defective carbon nanotubes

Electronic transport in metallic carbon nanotubes with mixed defects within the strong localization regime

We study the electron transport in metallic carbon nanotubes (CNTs) with realistic defects of different types. We focus on large CNTs with many defects in the mesoscopic range. In a recent paper we demonstrated that the electronic transport in those defective CNTs is in the regime of strong localization. We verify by quantum transport simulations that the localization length of CNTs with defects of mixed types can be related to the localization lengths of CNTs with identical defects by taking the weighted harmonic average. Secondly, we show how to use this result to estimate the conductance of arbitrary defective CNTs, avoiding time consuming transport calculations

Influence of defect-induced deformations on electron transport in carbon nanotubes

We theoretically investigate the influence of defect-induced long-range deformations in carbon nanotubes on their electronic transport properties. To this end we perform numerical ab-initio calculations using a density-functional-based tight-binding (DFTB) model for various tubes with vacancies. The geometry optimization leads to a change of the atomic positions. There is a strong reconstruction of the atoms near the defect (called "distortion") and there is an additional long-range deformation. The impact of both structural features on the conductance is systematically investigated. We compare short and long CNTs of different kinds with and without long-range deformation. We find for the very thin (9,0)-CNT that the long-range deformation additionally affects the transmission spectrum and the conductance compared to the short-range lattice distortion. The conductance of the larger (11,0)- or the (14,0)-CNT is overall less affected implying that the influence of the long-range deformation decreases with increasing tube diameter. Furthermore, the effect can be either positive or negative depending on the CNT type and the defect type. Our results indicate that the long-range deformation must be included in order to reliably describe the electronic structure of defective, small-diameter zigzag tubes.Comment: Materials for Advanced Metallization 201

Impact of local knowledge endowment on employment growth in nanotechnology

This paper investigates the contribution of local knowledge endowment to employment growth in nanotechnology firms. We exploit a unique data set focusing on firms operating in fields that apply nanotechnology. Our findings suggest that regions that offer knowledge can stimulate employment growth in smaller and younger firms. By contrast, being embedded into specialised regions might be counterproductive, especially for firms belonging to a particularly knowledge intensive sector and older firms. --employment growth,local knowledge endowment,general purpose technology,specialisation,nanotechnology,spillover

Zwei Begriffe personaler Identität

Die Divergenz zweier Identitätskonzeptionen wird deutlich, wenn man bedenkt, dass in Praktischer Philosophie, Psychologie, Sozialwissenschaften und im Alltag davon gesprochen wird, eine Person bilde ihre Identität aus, verändere ihre Identität, verlöre ihre Identität oder sie habe gar mehrere Identitäten. Der theoretische Identitätsbegriff scheint mit solchen Redeweise nicht vereinbar zu sein, denn ein verbreiteter Konsens besagt ‚No entity without identity" und das impliziert die Überzeugung, dass eine Entität jeweils eine Identität hat, nicht mehr und nicht weniger. Die Selbigkeit einer Entität beinhaltet die Veränderungen, die ihr widerfahren; Veränderungen führen nicht zu einer Vielzahl von Identitäten. Ebenso wird ausgeschlossen, dass etwas noch keine Identität besitzt, sondern diese erst im Lauf einer Entwicklung erwirbt