There must be order: Structure-transport correlations in self-assembled nanocrystal superlattices

In recent years, nanocrystal building blocks and their controlled self-assembly into highly ordered superlattices have created new opportunities for scientists and engineers to build novel materials with structure-related optoelectronic properties by design. However, sufficient experimental evidence for such theoretically predicted structure-property relationships is still lacking until now. This cumulative dissertation is based on three publications and addresses the question whether structural order has a significant effect on the electronic properties of nanocrystal ensembles, focussing on -system functionalized lead sulfide (PbS) nanocrystals and atom-precise gold (Au32) nanoclusters as model systems. First, a soft-lithography technique is developed to fabricate micrometer-sized channels of long-range ordered PbS nanocrystal superlattices with dimensions approaching the size of typical single-crystalline domains of only a few μm2. By means of microcontact printing, hundreds of superlattice microchannels can be realized, enabling a statistically meaningful investigation of charge transport in single-crystalline superlattice domains. Indicated by conductivity and field-effect transistor measurements, charge transport within those superlattice microchannels is found to be orders of magnitude more efficient compared to state-of-the art channels where transport is averaged over large scales. This clearly emphasizes the advantage of the near single-crystalline superlattice microchannels for the characterization of intrinsic charge transport properties. Then, the developed microcontact printing process is applied to fabricate superlattice microchannels on X-ray transparent devices, enabling a correlative investigation of the structural and the electronic properties of the same PbS superlattice domains. A full structural characterization of the superlattice symmetry and nanocrystal orientation within is achieved by synchrotron-based X-ray nano-diffraction in combination with angular X-ray cross-correlation analysis. The direct correlation of structural properties, such as superlattice type and particle spacing, with the conductivity of hundreds of superlattice channels provides meaningful evidence for structure-transport relationships. It is shown that the conductivity decreases with the interparticle spacing and that the crystallinity of the superlattices has a beneficial effect on charge transport. Further, an anisotropy of charge transport in long-range ordered monocrystalline superlattices is revealed, based on the dominant effect of shortest interparticle hopping distances. Thus, anisotropic charge transport could be considered an inherent feature of weakly coupled superlattices. Finally, atom-precise Au32 nanoclusters are self-assembled into well-defined microcrystals, which are investigated by grazing-incident small-angle X-ray scattering, absorption spectroscopy as well as conductivity and field-effect transistor measurements. It is demonstrated that the conductivity and charge carrier mobility of these long-range ordered crystalline domains exceed that of glassy assemblies of the same nanoclusters by two orders of magnitude. Along with additionally emerging optical transitions, this effect indicates an enhanced electronic coupling in highly ordered superstructures, attributed to a vanishing degree of structural and energetic disorder and a significantly reduced activation energy to charge transport. This thesis provides experimental evidence for structure-related electronic properties of self-assembled nanocrystal superlattices and illustrates the advantageous effect of long-range structural order on charge transport.In den letzten Jahren hat die Verwendung von Nanokristallen als Bausteine neue Möglichkeiten für Wissenschaft und Technik eröffnet. Durch ihre kontrollierte Selbstassemblierung zu hochgeordneten Übergittern lassen sich neuartige und maßgeschneiderte Materialien herstellen, deren optoelektronischen Eigenschaften als strukturabhängig gelten. Experimentelle Nachweise entsprechender theoretisch vorhergesagten Struktur- Eigenschafts-Beziehungen sind jedoch bisher nur spärlich vorhanden. Die vorliegende kumulative Dissertation basiert auf drei Publikationen und geht der Frage nach, ob strukturelle Ordnung einen signifikanten Einfluss auf die elektronischen Eigenschaften von Nanokristall-Ensembles hat. Hierfür werden -funktionalisierte Bleisulfid (PbS) Nanokristalle und atompräzise Gold (Au32) Nanocluster als Modellsysteme verwendet. Zunächst wird eine Stempel-Lithographie-Technik entwickelt, um mikrometergroße Kanäle aus langreichweitig geordneten PbS Nanokristallübergittern herzustellen, deren Abmessungen der Größe typischer einkristalliner Domänen von nur wenigen μm2 entsprechen. Mittels Mikrokontaktdruck können so hunderte Übergitter-Mikrokanäle hergestellt werden, was eine statistisch aussagekräftige Untersuchung des Ladungstransports in einkristallinen Übergitterdomänen ermöglicht. Anhand von Leitfähigkeits- und Feldeffekttransistormessungen kann gezeigt werden, dass der Ladungstransport in diesen Übergitter-Mikrokanälen um Größenordnungen effizienter ist als in konventionellen Kanälen, bei denen der Ladungstransport über weitaus größere Bereiche gemittelt wird. Dies ist ein deutlicher Hinweis auf den Vorteil einkristalliner Übergitter-Mikrokanäle für die Charakterisierung von intrinsischen Transporteigenschaften. Anschließend wird der im Rahmen dieser Arbeit entwickelte Mikrokontaktdruck- Prozess angewandt, um Übergitter-Mikrokanäle auf röntgentransparenten Substraten herzustellen. Dies ermöglicht eine korrelative Untersuchung der strukturellen und der elektronischen Eigenschaften derselben PbS-Übergitterdomänen. Eine vollständige strukturelle Charakterisierung der Übergitter-Symmetrie und der Nanokristall-Orientierung wird durch synchrotronbasierte Röntgenstreuung mit einem nanofokussiertem Strahl in Kombination mit winkelabhängiger Röntgendiffraktions-Kreuzkorrelationsanalyse erreicht. Die direkte Korrelation der strukturellen Eigenschaften, wie z.B. Übergitter-Typ und Partikelabstand, mit der Leitfähigkeit von Hunderten von Übergitter-Kanälen liefert aussagekräftige Hinweise auf die Existenz von Struktur-Transport-Beziehungen. Es wird gezeigt, dass mit zunehmendem interpartikulärem Abstand die Leitfähigkeit sinkt und dass die Kristallinität der Übergitter einen positiven Effekt auf den Ladungstransport hat. Außerdem wird eine Anisotropie des Ladungstransports in langreichweitig geordneten monokristallinen Übergittern aufgezeigt, die auf den dominierenden Effekt der kürzesten interpartikulären Sprungdistanzen zurückzuführen ist. Somit kann angenommen werden, dass anisotroper Ladungstransport generell eine intrinsische Eigenschaft von schwach gekoppelten Übergittern ist. Schließlich werden atompräsize Au32 Nanocluster zu definierten Mikrokristallen selbstassembliert, die mittels Kleinwinkel-Röntgenstreuung im streifenden Einfall, Absorptionsspektroskopie sowie Leitfähigkeits- und Feldeffekttransistormessungen untersucht werden. Für dieses neuartige halbleitende Material wird gezeigt, dass die Leitfähigkeit und Ladungsträgerbeweglichkeit von langreichweitig geordneten kristallinen Domänen die von polykristallinen/glasartigen Anordnungen der gleichen Nanocluster um zwei Größenordnungen übersteigt. Zusammen mit zusätzlich auftretenden optischen Übergängen deutet dieser Effekt auf eine verstärkte elektronische Kopplung in hochgeordneten Überstrukturen hin. Diese lässt sich auf einen verschwindend geringen Grad an struktureller und energetischer Unordnung und somit auf eine drastisch reduzierte Aktivierungsenergie für den Ladungstransport zurückführen. Diese Arbeit liefert somit experimentelle Hinweise auf strukturabhängige elektronische Eigenschaften von selbstorganisierten Nanokristall-Übergittern und veranschaulicht die Auswirkungen von langreichweitiger struktureller Ordnung auf den Ladungstransport

The Certification of the Mass fractions of PAH Metabolites (1-hydroxyphenanthrene, 1-hydroxypyrene, and 3-hydroxybenzo(a)pyrene) in Two Fish Bile Materials, BCR-720 (sedement-exposed flounder bile), BCR-721 (oil-exposed plaice bile).

Abstract not availableJRC.D-Institute for Reference Materials and Measurements (Geel

Electrical detection of 31P spin quantum states

In recent years, a variety of solid-state qubits has been realized, including quantum dots, superconducting tunnel junctions and point defects. Due to its potential compatibility with existing microelectronics, the proposal by Kane based on phosphorus donors in Si has also been pursued intensively. A key issue of this concept is the readout of the P quantum state. While electrical measurements of magnetic resonance have been performed on single spins, the statistical nature of these experiments based on random telegraph noise measurements has impeded the readout of single spin states. In this letter, we demonstrate the measurement of the spin state of P donor electrons in silicon and the observation of Rabi flops by purely electric means, accomplished by coherent manipulation of spin-dependent charge carrier recombination between the P donor and paramagnetic localized states at the Si/SiO2 interface via pulsed electrically detected magnetic resonance. The electron spin information is shown to be coupled through the hyperfine interaction with the P nucleus, which demonstrates the feasibility of a recombination-based readout of nuclear spins

Structure-transport correlation reveals anisotropic charge transport in coupled PbS nanocrystal superlattices

Semiconductive nanocrystals (NCs) can be self-assembled into ordered superlattices (SLs) to create artificial solids with emerging collective properties. Computational studies have predicted that properties such as electronic coupling or charge transport are determined not only by the individual NCs but also by the degree of their organization and structure. However, experimental proof for a correlation between structure and charge transport in NC SLs is still pending. Here, we perform X-ray nano-diffraction and apply Angular X-ray Cross-Correlation Analysis (AXCCA) to characterize the structures of coupled PbS NC SLs, which are directly correlated with the electronic properties of the same SL microdomains. We find strong evidence for the effect of SL crystallinity on charge transport and reveal anisotropic charge transport in highly ordered monocrystalline hexagonal close-packed PbS NC SLs, caused by the dominant effect of shortest interparticle distance. This implies that transport anisotropy should be a general feature of weakly coupled NC SLs.Comment: 49 pages, 20 Figure

ART^2 : Coupling Lyman-alpha Line and Multi-wavelength Continuum Radiative Transfer

Narrow-band Lya line and broad-band continuum have played important roles in the discovery of high-redshift galaxies in recent years. Hence, it is crucial to study the radiative transfer of both Lya and continuum photons in the context of galaxy formation and evolution in order to understand the nature of distant galaxies. Here, we present a three-dimensional Monte Carlo radiative transfer code, All-wavelength Radiative Transfer with Adaptive Refinement Tree (ART^2), which couples Lya line and multi-wavelength continuum, for the study of panchromatic properties of galaxies and interstellar medium. This code is based on the original version of Li et al., and features three essential modules: continuum emission from X-ray to radio, Lya emission from both recombination and collisional excitation, and ionization of neutral hydrogen. The coupling of these three modules, together with an adaptive refinement grid, enables a self-consistent and accurate calculation of the Lya properties. As an example, we apply ART^2 to a cosmological simulation that includes both star formation and black hole growth, and study in detail a sample of massive galaxies at redshifts z=3.1 - 10.2. We find that these galaxies are Lya emitters (LAEs), whose Lya emission traces the dense gas region, and that their Lya lines show a shape characteristic of gas inflow. Furthermore, the Lya properties, including photon escape fraction, emergent luminosity, and equivalent width, change with time and environment. Our results suggest that LAEs evolve with redshift, and that early LAEs such as the most distant one detected at z ~ 8.6 may be dwarf galaxies with a high star formation rate fueled by infall of cold gas, and a low Lya escape fraction.Comment: 20 pages, 16 figures, accepted for publication in MNRA

Frequency and gender differences in the use of professional home care in late life: Findings from three German old-age cohorts

Aim: The aim of this study was to investigate the frequency of and the gender differences in the use of professional home care in Germany. Methods: We used harmonized data from three large cohort studies from Germany (“Healthy Aging: Gender-specific trajectories into the latest life”; AgeDifferent.de Platform). Data were available for 5,393 older individuals (75 years and older). Mean age was 80.2 years (SD: 4.1 years), 66.6% were female. Professional homecare outcome variables were use of outpatient nursing care, paid household assistance, and meals on wheels’ services. Logistic regression models were used, adjusting for important sociodemographic variables. Results: Altogether 5.2% of older individuals used outpatient nursing care (6.2% women and 3.2% men; p < 0.001), 24.2% used paid household assistance (26.1% women and 20.5% men; p < 0.001) and 4.4% used meals on wheels’ services (4.5% women and 4.0% men; p = 0.49). Regression analysis revealed that women had higher odds of using paid household assistance than men (OR = 1.48, 95% CI: [1.24–1.76]; p < 0.001), whereas they had lower odds of using meals on wheels’ services (OR = 0.64, 95% CI: [0.42–0.97]; p < 0.05). No statistically significant differences in using outpatient nursing care between women and men were found (OR = 1.26, 95% CI: [0.87–1.81]; p = 0.225). Further, the use of home care was mainly associated with health-related variables (e.g., stroke, Parkinson’s disease) and walking impairments. Conclusions: Our study showed that gender differences exist in using paid household assistance and in culinary dependency. For example, meals on wheels’ services are of great importance (e.g., for individuals living alone or for individuals with low social support). Gender differences were not identified regarding outpatient nursing care. Use of professional home care servicesmay contribute to maintaining autonomy and independence in old age

Measurement of the Ratio Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu) and Extraction of the CP Violation Parameter |eta+-|

We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.Comment: 20 pages, 7 figures, accepted by Phys. Lett.