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SAXS-Gerät

Fachliche Zuordnung Physik der kondensierten Materie
Förderung Förderung in 2014
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 268482124
 
Erstellungsjahr 2019

Zusammenfassung der Projektergebnisse

1. Structure, transport and photoconductance of PbS quantum dot monolayers functionalized with a copper phthalocyanine derivative. Chem. Commun., 2017,53, 1700-1703. We simultaneously surface-functionalize PbS nanocrystals with Cu 4,4′,4′′,4′′′-tetraaminophthalocyanine and assemble this hybrid material into macroscopic monolayers. Electron microscopy and X-ray scattering reveal a granular mesocrystalline structure with strong coherence between the atomic lattice and the superlattice of nanocrystals within each domain. Terahertz spectroscopy and field-effect transistor measurements indicate efficient coupling of holes throughout the hybrid thin film, in conjunction with a pronounced photoresponse. We demonstrate the potential of this material for optoelectronic applications by fabricating a light-effect transistor. GISAXS/GIWAXS measurements. 2. Surface functionalization with copper tetraaminophthalocyanine enables efficient charge transport in indium tin oxide nanocrystal thin films. ACS Appl. Mater. Interfaces, 2017, 9 (16), 14197–14206. Macroscopic superlattices of tin-doped indium oxide (ITO) nanocrystals (NCs) are prepared by self-assembly at the air/liquid interface followed by simultaneous ligand exchange with the organic semiconductor copper 4,4′,4″,4‴-tetraaminophthalocyanine (Cu4APc). By using X- ray photoelectron spectroscopy (XPS), grazing-incidence small-angle X-ray scattering (GISAXS), and ultraviolet–visible–near-infrared (UV–vis–NIR) spectroscopy, we demonstrate that the semiconductor molecules largely replace the native surfactant from the ITO NC surface and act as cross-linkers between neighboring particles. Transport measurements reveal an increase in electrical conductance by 9 orders of magnitude, suggesting that Cu4APc provides efficient electronic coupling for neighboring ITO NCs. This material provides the opportunityto study charge and spin transport through phthalocyanine monolayers. 3. Monitoring self-assembly and ligand exchange of PbS nanocrystal superlattices at the liquid/air interface in real time. J. Phys. Chem. Lett., 2018, 9 (4), 739–744. We investigate in situ the structural changes during self-assembly of PbS nanocrystals from colloidal solution into superlattices, solvent evaporation, and ligand exchange at the acetonitrile/air interface by grazing incidence small-angle X-ray scattering (GISAXS). We simulate and fit the diffraction peaks under the distorted wave Born approximation (DWBA) to determine the lattice parameters. We observe a continuous isotropic contraction of the superlattice in two different assembly steps, preserving the body-centered cubic lattice with an overall decrease in the lattice constants of 11%. We argue that the first contraction period is due to a combination of solvent evaporation/annealing and capillary forces acting on the superlattice, whereas the second period is dominated by the effect of replacing oleic acid on the nanocrystal surface with the short and rigid cross-linker tetrathiafulvalene dicarboxylate. This work provides guidelines for optimized ligand exchange conditions and highlights the structural particularities arising from assembling NCs on liquid surfaces. 4. Electron-conducting PbS nanocrystal superlattices with long-range order enabled by terthiophene molecular linkers. ACS Appl. Mater. Interfaces, 2018, 10 (29), 24708–24714. PbS nanocrystals are surface-functionalized with the organic semiconductor 5,5″-dithiol-[2,2′:5,2″-terthiophene] and assembled to afford hybrid nanostructured thin films with a large structural coherence and an electron mobility of 0.2 cm2/(V s). Electrochemistry, optical spectroscopy, and quantum mechanical calculations are applied to elucidate the electronic structure at the inorganic / organic interface, and it is established that electron injection into the molecule alters its (electronic) structure, which greatly facilitates coupling of the neighboring PbS 1Se states. This is verified by field-effect and electrochemically gated transport measurements, and evidence is provided that carrier transport occurs predominantly via the 1Se states. The presented material allows studying structure–transport correlations and exploring transport anisotropies in semiconductor nanocrystal superlattices. 5. Understanding the formation of conductive mesocrystalline superlattices with cubic PbS nanocrystals at the liquid/air interface. J. Phys. Chem. C, 2019, 123 (2), 1519– 1526. We report the formation of conductive mesocrystalline superstructures of cubic PbS nanocrystals (NCs) through directional cross-linking with organic semiconductors at the liquid/air interface monitored simultaneously by in situ grazing incidence small angle X-ray scattering and grazing incidence X-ray diffraction. We determine the superlattice type, its symmetry and parameters, and the atomic orientation of NCs from the time-resolved scattering patterns. The superlattice contraction follows an exponential decay during ligand exchange, preserving always the two-dimensional square geometry. We attribute the contraction to the continuous replacement of oleic acid with smaller cobalt/copper 4,4′,4″,4‴-tetraaminophthalocyanine molecules. In these superlattices, the NCs are directed with a [100]AL axis perpendicular to the liquid surface for the whole assembly period. The kinetics and structural results provide a direct correlation between the superstructure and their atomic orientation on the liquid surface during self-assembly followed by ligand exchange. 6. Electronically coupled, two-dimensional assembly of Cu1.1S nanodiscs for selective vapour sensing applications. J. Phys. Chem. C, 2018, 122 (41), 23720–23727. We study temperature-dependent charge transport in two-dimensional assemblies of copper sulfide nanodiscs in the covellite crystal phase (Cu1.1S). To enhance interparticle coupling, we cross-link the nanocrystals with the organic π-system Cu-4,4′,4″,4‴-tetra-aminophthalocyanine and observe an increase in the conductivity by 6 orders of magnitude. The electrical properties of monolayers of this hybrid ensemble are consistent with a two-dimensional semiconductor and exhibit two abrupt changes at discrete temperatures (120 and 210 K), which may be interpreted as phase changes. X-ray scattering experiments serve to study the importance of electronic conjugation in the organic π-system vs interparticle spacing for efficient charge transport. Applying the hybrid ensemble as a chemiresistor in organic vapor sensing experiments reveals a strong selectivity between polar and nonpolar analytes, which we discuss in light of the role of the organic π-system and its metal center. 7. Crowding-controlled cluster size in concentrated aqueous protein solutions: structure, selfand collective diffusion. J. Phys. Chem. Lett., 2017, 8 (12), 2590–2596. We have performed a systematic study on clustering in solutions of bovine beta-lactoglobulin (BLG)(Braun et al. 2017a). Here, clustering is induced solely by a high protein volume fraction, i.e. by crowding, without the necessity for the presence of salt or a non-neutral pH. We combine structural investigations using SAXS with dynamic investigations using both neutron spin-echo (NSE) and neutron backscattering spectroscopy (NBS) to arrive at a consistent picture on cluster formation and structure. By combining the results from these static and dynamic methods, we obtain a conclusive picture of the presence of clusters in BLG solutions that are static on the accessible observation time scale of several nanoseconds. The SAXS data are consistent with a disordered assembly of BLG dimers that form compact clusters. The experimental SAXS structure factor agrees with a model of short-ranged attractions and long-ranged repulsions consistent with the presence of clusters. The spectroscopic data from both the NBS and NSE experiments, respectively, yield equal diffusion coefficients at the overlapping q within the errors. These diffusion coefficients are in agreement with static BLG clusters on the experimental observation time scale (coherence time) of up to 50 ns in the case of NSE. Moreover, the NSE data are consistent with the SAXS data. The combination of the SAXS and NSE results points to the general possibility to refine the analysis of static SAXS data by employing complementary NSE experiments. Our analysis shows that the combination of the SAXS, NSE and NBS results provides a robust quantitative picture of the cluster size and compactness depending on the protein concentration in the solution, a criterion for the choice of the SAXS model, and information on the cluster lifetime. Part of the SAXS measurements were performed on Xeuss 2.0.

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