Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 03/05

The process of miniaturization brings benefits in many areas of every day life. It describes the

process of down-scaling mechanical, optical and electronic devices while maintaining their function.

This continuous process has brought up the field of nanotechnology. It allows computers to run

faster and faster while reducing their size and energy consumption. Many bio-analytical applications

profit from smaller sizes to be more sensitive with lower sample volumes. Finally, each and every

living cell contains the most complex nanoscopic machinery.

In order to mimic nature’s highly efficient concepts, they first of all need to be understood. Their

nanoscopic dimensions, however, make this task a very challenging one. Direct observation of subcellular

processes by conventional light microscopy is difficult as almost all cellular components are

colorless. Fluorescence microscopy introduces sufficient contrast and can be specifically applied to

many different target molecules but remains limited in its spatial resolution.

In this work, a new approach to increase the resolution of fluorescence microscopy is presented

that is termed “blink microscopy”. It is based on the subsequent localization of single molecules as

it is realized in recent techniques known as STORM or PALM, but does not require special photoswitchable

fluorophores or multiple lasers. Instead of photoswitching, reversible electron transfer

reactions are used to generate the required dark states.

Motivated by the task to assess the resolution of blink microscopy, DNA nanotechnology is used

for nano-construction of a calibration structure. The DNA origami technique, developed by Paul

Rothemund in 2006, allows for arranging of individual fluorophores at distances of 1–100 nm on

a DNA nanostructure. While it is impossible to resolve two spots at a distance below 200 nm

with conventional fluorescence microscopy, it was possible to confidently resolve 50 nm with blink

microscopy. These experiments prove both, blink microscopy to be able to reliably resolve small

distances and DNA origami structures to be well suited as a rigid breadboard for fluorescence

experiments.

This research pioneering the combination of the two powerful tools of nano-imaging and nanoconstruction

set the ground for further experiments. After the rigidity of DNA origami structures

was used to characterize a fluorescence technique, single-molecule fluorescence could also help to

characterize properties of the DNA origami. Namely, dynamic processes on a DNA nanostructure

were exemplarily studied by reversible binding of a fluorescently labeled DNA strand while observing

this process in real-time on a fluorescence microscope. With the knowledge about binding and

unbinding kinetics of DNA and imaging of single molecules, another super-resolution approach was

developed that is simply and flexibly implemented in DNA structures, not limited by photobleaching,

easy to extend to multiple colors and that shows potential for cellular imaging.

One of the physics goals of the COMPASS experiment at CERN was

to measure the contribution of gluons to the nucleon spin. To achieve

this, it was proposed to scatter polarized \Value{160}{GeV/c} muons on a

polarized deuteron target and to detect $D$ mesons in the final state.

The underlying process in this $D$ meson production

is supposed to be the \Gls{PGF}, where

a virtual photon emitted by the muon interacts

with a gluon from the target nucleon, producing a charm-anticharm quark pair.

Fragmentation of a charm (anticharm) quark leads with high probability to the creation of

a $\DZ$ or $D^*$ meson, which COMPASS detects via

the $D^0 \to K\pi$ and $D^{*} \to D^0 \pi \to K\pi\pi$ decay modes.

From the longitudinal cross section spin asymmetries of the $D$ meson production and theoretical

predictions for the \Gls{PGF} cross section, the gluon contribution to the nucleon spin

has been measured by the COMPASS experiment.

The results presented in the thesis are the following.

Based on data from the year 2004 a total visible cross section of \TotalCrossSection,

for the $D^*$ meson production, has been measured, with

the error being dominated by systematic effects.

It is validated that the $D$ mesons are indeed produced through

the \Gls{PGF} process, by comparison of measured $D$ meson kinematic distributions

to the ones predicted by a theory (AROMA generator).

A good agreement was found for the distribution shapes,

which confirms that \Gls{PGF} plays a major role.

However, a $20\%$ difference was found in the number of

produced $\DZ$ and $\aDZ$ mesons (and for the $D^{*+}$ and $D^{*-}$ mesons as well)

which is significantly larger than predicted by AROMA.

Kinematic distributions of $D^0$ and $D^*$ mesons

were compared with the background

and also with the nearby $\KTS$ resonance,

using all longitudinal data taken in 2002-2006.

The particle-antiparticle

asymmetry has been studied as a function of several kinematic variables. The $20\%$ excess

of mesons decaying into $K^+\pi^-$ over

mesons decaying into $K^-\pi^+$ was observed for all three mesons.

The behavior of the $\DZ/\aDZ$ (and $D^{*+}/D^{*-}$) asymmetries

as a function

of virtual photon energy suggests that associated production of $D^{*-}\Lambda_c^+$ or $\overline{D^0}\Lambda_c^+$

may be responsible for the observed effect.

The longitudinal double spin asymmetries have been studied for the $D^0$, $D^*$ and $\KTS$ mesons

separately for particle, antiparticle and for the sum of particle and antiparticle.

It was found that the asymmetries extracted for $D^0$ and $D^*$ mesons

are compatible with zero. A 3-sigma deviation

from zero asymmetry was observed for the $\KTS$ meson. An investigation of the $\KTS$ double spin asymmetry

reveals a dependence as function of the Bjorken $x_{Bj}$ variable.

The SI-unit kilogram is scheduled to be re-defined within the next years. In the attempt to link it to a fundamental constant of nature – namely the Planck constant or the Avogadro constant – some discrepancies appeared. A direct determination of the molar Planck constant helps to trace this discrepancy. Such a determination can be done with the gamma-spectrometer Gams, that exists at the ILL. However, the instrument is not stable enough to provide the required accuracy of 2×10^(−8) (relative). To improve stability and accuracy, a complete new instrument was designed and built. For this purpose, the instrument core, an angle interferometer, had to be set up in vacuum. Drift-free fixation-methods and new designs for the optical elements, like corner-cube retro-reflectors, were developed. A new data acquisition system was elaborated, and also the mathematical theory to evaluate the acquired data. The new concepts for the instrument were completed, manufactured and assembled. First performance tests showed a quite convincing result in terms of stability.

During the development of the new instrument, the old instrument Gams4 was optimized. The neutron binding energy of chlorine-36 was determined to be (8579797.4±1.8)eV. The relative uncertainty is 2.7 times smaller than the previous value. It is two times smaller than the uncertainty of any other comparable binding energy.

This Thesis is dedicated to a

comparison of the two means of studying the electromagnetic

properties of the QCD vacuum -- holography and resummed field

theory. In the UV range the non-pertubative QCD effects play an

insignificant role and the dynamics of the theory is exactly

predicted by the perturbation theory. On the contrary, the IR

physics (e.g. light meson spectra and decays) is very sensitive to

the non-perturbative features of the theory. Archetypal examples

of a non-perturbative parameter in QCD are gluon condensate and

quark condensate. Condensates enter into many low-energy

observables and thus are directly experiment-related. On the other

hand, the power of modern experimental laser-physics facilities

being planned (e.g. the ELI project) is already almost reaching

the boundary of quark scales (though not hadron scales yet).

Thus the dynamics of the condensates is of special importance. Yet

little is known about the generation mechanism of either of the

condensates and various hypotheses are on the market. Therefore, a

model-building approach might be useful here. In this Thesis I

compare two classes of distinct models for the dynamics of the

condensates. The first class consists of the so-called holographic

models of QCD. Based upon the Maldacena conjecture, it tries to

establish the properties of QCD correlation functions from the

behavior of classical solutions of field equations in a

higher-dimensional theory. The advantage of the holographic models

is that they render a strongly-coupled four-dimensional gauge

theory as a dual of some weakly-coupled string/supergravity. This

is actually the reason of the immense popularity of holographic

models nowadays. The problem of these models is their relevance to

actual QCD. None of the models currently on the market is supposed

to be ``exactly'' dual to real-life QCD. The possible shortcomings

of duality are the presence of extra particles in the spectrum,

remaining supersymmetries, wrong reproduction of the meson and

baryon spectra etc. Yet in many aspects the holographic approach

has been found to be in an excellent agreement with data. These

successes are the prediction of the very small

viscosity-to-entropy ratio and the predictions of meson spectra up

to 5\% accuracy in several models.

On the other hand, the resummation methods in field theory have

not been discarded so far. There exists a whole industry of

resummation for the correlators in QCD, by means of integral

equations, Dyson--Schwinger equations first of all. Non-local

observables, such as Wilson loops, are also subjects to

resummations, as proposed by Erickson and Zarembo. The success of

resummation methods was marked by the agreement of lattice

calculations of Green functions with Dyson--Schwinger results.

Both classes of methods have access to condensates. Thus a

comprehensive study of condensates becomes possible, in which I

compare my calculations in holography and resummed field theory

with each other, as well as with lattice results, field theory and

experiment. I prove that the low-energy theorems of QCD keep their

validity in holographic models with a gluon condensate in a

non-trivial way. I also show that the so-called decoupling

relation holds in holography models with chiral and gluon

condensates, whereas this relation fails in the Dyson--Schwinger

approach. On the contrary, my results on the chiral magnetic

effect in holography disagree with the weak-field prediction; the

chiral magnetic effect (that is, the electric current generation

in a magnetic field) is three times less than the current in the

weakly-coupled QCD. The chiral condensate behavior is found to be

quadratic in external field both in the Dyson--Schwinger approach

and in holography, yet we know that in the exact limit the

condensate must be linear, thus both classes of models are

concluded to be deficient for establishing the correct condensate

behaviour in the chiral limit. The magnetization of the QCD vacuum

does not agree

Since the original prediction and demonstration of attosecond pulses, attosecond physics has entrenched itself in the ultrafast sciences, and promises to advance a wide range of scientific disciplines. It has the potential to provide key developments and insights in several research areas, such as atomic physics, quantum chemistry, biology and medicine.

At present, engaging in this novel field of research is rather prohibitive, due to the high costs of cutting-edge technology and a steep learning curve. After all, playing with attosecond pulses is tantamount to playing with the shortest events ever made by man! Nonetheless, these are just typical growing pains of a new and exciting research area, and will eventually subside to make attosecond science accessible to a broad research community. In the meanwhile, as this promising field is taking its baby steps, it is the responsibility of those working at the cutting edge to propose novel experiments, and develop the tools and models that will be used in the future, as the field matures.

Attosecond science comprises two frontiers: (i) the generation and characterization of increasingly intense, energetic, short and isolated attosecond pulses; and (ii) the design of experiments to probe physical systems on the attosecond time scale, the holy grail being the attosecond pump-attosecond probe time-resolved spectroscopic measurement. The second frontier offers a deeper understanding of the temporal behavior of the microcosm, but relies on advancements made in the first one. At present, both of these frontiers heavily rely on the attosecond streaking technique, which consists in energy-resolving photoelectrons ejected by an attosecond extreme ultraviolet pulse, in the presence of a phase-stabilized and temporally synchronized near-infrared field. Although it was originally devised as a means to characterize attosecond pulses, this measurement technique has even produced new discoveries in atomic and solid-state physics, due to pioneering experiments by M. Drescher, A. Cavalieri, G. Sansone, M. Schultze, and others, and has inspired novel theories of laser-dressed photoionization by V. S. Yakovlev, A. Scrinzi, O. Smirnova, M. Y. Ivanov and others.

In the first part of this thesis, I focus on new methods I developed for the analysis of attosecond streaking measurements. One of these methods, based on a formalism I devised based on electron trajectories in a laser field, can directly recover the chirp of an attosecond pulse from a set of streaked photoelectron spectra. Next, I describe a robust optimization algorithm, based on a formalism due to M. Kitzler et al., that can completely recover the temporal profile of an attosecond pulse with an arbitrary shape. This optimization algorithm was used to characterize the field of 80 as pulses, the shortest on record, and to uncover a delay of 20 as between the photoemissions from the 2s and 2p sub-shells of neon; both experiments were performed here at the Max Planck Institut fuer Quantenoptik in 2008 and 2010, respectively.

Moreover, during the course of this work, it was established by V. S. Yakovlev et al. that the attosecond streaking technique generally measures a quantity that is related to the photoelectron wave packet, not the attosecond light pulse. Only when the energy-resolved dipole response, given by the bound-free transition matrix elements, is nearly constant can we take the electron wave packet as a replica of the attosecond pulse. In light of this finding, I show that the attosecond streaking technique provides a means to measure and even time-resolve the energy-dependent phase of transition dipole matrix elements.

Finally, I consider the laser-dressed scattering of an attosecond photoelectron wave packet. I show that the scattering of a photoelectron, emitted by an attosecond pulse from a localized state in a spatially extended system, can be influenced by a near-infrared laser field. Measuring the photoelectron spectrum

Die biologische und medizinische Forschung stellt immer mehr Informationen über die Funktion des Lebens bereit. Dem voraus geht eine hochpräzise und spezifische Diagnostik. Allerdings gibt es noch keine überzeugenden Lösungen für die Lebend-Überwachung von Substanzen, die möglicherweise an Demenzkrankheiten oder Alterserscheinungen beteiligt sind. Die vorliegende Arbeit beschäftigt sich mit Grundlagenforschung zur Entwicklung eines Sensors, der in der Lage ist Änderungen des elektrischen Potentials, z.B. neuronale Aktivität, in biologisch relevanter Umgebung zu detektieren.

In dem hier behandelten Ansatz wird eine Sensorfläche eingesetzt, welche vollständig aus organischen Materialien aufgebaut ist. Die effektive Schnittstelle zwischen dem Sensor und den Zellen ist eine künstliche Zellmembran, die mit einer Bindungseinheit ausgestattet ist, deren Aufbau dem Vorbild der Natur nachempfunden ist. Der Sensor selbst ist ein organischer Dünnschichttransistor, der seine Sensitivität aus den elektronischen Eigenschaften des organischen Halbleiters erhält. Zudem hat die aktive Schicht eine Dicke von nur 50nm.

Entscheidend im Umgang mit organischen Molekülen ist die enge Beziehung zwischen Struktur und Funktion. Die starke Anisotropie der Struktur spiegelt sich in den elektronischen Eigenschaften wider. Die molekulare Anordnung wiederum hängt sensibel von den verwendeten Prozessparametern bei der Herstellung der Schichten ab. Wichtig sind z.B. die Rate, die Temperatur oder die physikalischen Eigenschaften der Oberfläche (polar, nicht-polar, rau etc.). Die so gewonnenen organischen Multischichtsysteme wurden mit Hilfe von Röntgen- und Neutronenstreuung an Großgeräten (Synchrotron, Reaktor) charakterisiert.

Ein Schwerpunkt der vorliegenden Arbeit ist das Auffinden und Beeinflussen der Struktur der verwendeten Materialien auf molekularer Ebene. Zunächst werden Konzepte und Aggregationsmechanismen von Molekülen auf Oberflächen vorgestellt. Der experimentelle Teil widmet sich der Herstellung der organischen Halbleiterschicht aus Pentacen (C22H14) auf unterschiedlichen Oberflächen. Durch chemische Modifikation von Diamantoberflächen konnten Pentacen-Filme kontrolliert in stehender oder liegender Phase gewachsen werden. Ferner wurde die Verkapselung organischer Filme mit verschiedensten Techniken und Materialien untersucht. Die Verwendung der Vakuumsublimations-Technik ermöglichte die Konservierung der "Dünnfilmphase" von Pentacen durch Verkapseln mit dem Alkan Tetratetracontan (TTC, C44H90). Somit konnte der stabile Betrieb eines organischen Transistors in ionischer wässeriger Umgebung ermöglicht werden, was den entscheidenden Schritt in Richtung Sensorik darstellt.

Des Weiteren gelang der Aufbau einer vielseitig funktionalen Beschichtung, welche von Zellen als ihre natürliche Umgebung akzeptiert wird. Basierend auf substratgestützten Lipid-Doppelschichten wurde mit Hilfe der Biotinbindung ein synthetischer Peptid-Komplex über eine Protein-Zwischenschicht an die Oberfläche gebunden. Dieser Komplex enthält mehrfach die RGD Sequenz, eine Aminosäure-Sequenz, die für die Bindung von Proteinen an ihre Zellrezeptoren verantwortlich ist. Die Struktur der Beschichtung wurde mit Röntgen- und Neutronenbeugung mit einer Auflösung von 5Å bestimmt. Es zeigt sich eine mehrlagige Schichtung beginnend mit einer 36Å Lipidmembran, darüber eine stark hydrierte Zwischenschicht (26Å), gefolgt von einer 38Å dicken Streptavidinschicht und abschließend eine 30Å Schicht aus dicht gepackten, seitlich liegenden Bindungskomplexen. Neuronale Stammzellen wurden auf dieser Beschichtung kultiviert und zeigten rasche Anlagerung sowie eine Ausbreitung auf der angebotenen Oberfläche.

Die Kompatibilität der Beschichtung mit dem verkapselten Transistor wurde durch das Ausbilden einer Lipidschicht auf der Sensoroberfläche bestätigt. In Zukunft sollen die Möglichkeiten erforscht werden, mit dieser Anordnung Änderungen des elektrischen Potentials zu messen. Dazu detektiert man zunä

The structure of the proton and the origin of the proton spin has been a puzzle for many years. The EMC collaboration at CERN provided the first experimental data on the spin structure of the proton. The result was almost zero net contribution from quarks. Over the past 20 years new measurements of polarized parton distributions became available.

The present value of the quark contribution to the proton spin is one third.

The remaining 60 percent of the proton spin come from the gluons and orbital angular momentum of quarks and gluons.

We investigate how the spin of the proton originates from the spin of its constituents. We study the proton using the phenomenologically accessible parameters such as distribution functions for quarks and gluons.

The basic understanding of the proton structure (and in particular its spin structure) is important for interpreting the results of the LHC, which in turn can be used to refine the present knowledge.

The proton spin structure gives a detailed information about the dynamical structure of the proton. Based on the present experimental data we suggest that the gluons and quarks play equally important role in the structure of the proton.