Archiv 2019

Raum: Seminar Room V, O1.109

Near-Field Physics and Chemistry in Plasmonic STM junctions

MPSD Seminar
Plasmonic cavities exhibit many intriguing properties and phenomena resulting from strong field enhancement and confinement. Recently, both experimental and theoretical studies have revealed crucial roles of atomistic structures and quantum mechanical effects in plasmonic nanostructures [1-3]. [mehr]

Presentation Skills (IMPRS-UFAST Skills Course)

IMPRS-UFAST skills course
“Poets are born – speakers are made” Public speaking is a necessity in scientific life. Take part in this two-days course, find out what your strengths are and develop your individual presentation profile. Take steps to learn how to lead the audience from your first appearance on stage until the last question in the discussion. Be authentic, enthusiastic and convincing! [mehr]

Growth Dynamics of Graphene on molten copper

MPSD Seminar
Since it’s discovery in 2006, Graphene has known no rivals in terms of number of applications that scientists from all over the globe have thought for him, ranging from spintronics to energy storage, from transistors to bio-compatible devices. However, what’s still hindering his big step from laboratories to industry is a cost-effective method to synthesize large-scale good-quality crystals. Over the past decade, great improvements have been made in this direction, and CVD consolidated as an excellent candidate for this arduous task. Among other methods, a novel technique consisting in the synthesis of crystals on transition metals in the liquid phase has proven to overcome many difficulties related to defect-inducing dislocations and low-diffusivity of solid substrates. Nevertheless, a clear physical insight over the processes involved during graphene nucleation and growth is still lacking, and many of its parameters are derived by post-process analyses, neglecting those crucial intermediate steps that may conceal key-factors involved in the process. The reason for this trend is that it’s technically difficult to combine different experimental set-ups, and an ad-hoc design is more than ever needed to conduct a complete and satisfying investigation. This is the reason behind the LMCat project, that developed a reactor suitable both for CVD growth at high temperature by hydrocarbon decomposition and for in-situ Raman and optical studies, in order to follow in real time the growth of graphene flakes and, at the same time, determine its physical properties. Additionally, it aims to prove X-ray techniques, such as GID and XRR, as an efficient tool for high temperature characterization, a feat never achieved before. This is the framework of this thesis work, which can of course cover it only partially and at a rather early stage. The focus has been put on the surprising high contrast showed by radiative optical microscopy at high temperatures (∼ 1100 C°) and on the first, surprising results coming from X-ray analysis. The former has been proven as an effective tool for following the growth and derive kinematical parameters, the latter as a potential tool for quantitatively estimate its crystal structure at conditions prohibitive for standard probes. [mehr]

Electronic and Vibrational Properties of Colloidal Nanocrystals

MPSD Seminar
Colloidal nanocrystals (CNCs) are nanometer sized crystals grown in solution. Due to their size-tunable optical properties, CNCs have emerged as a novel material platform for numerous applications such as displays, photovoltaics, and biological tagging. However, the colloidal growth process results in an unavoidable distribution of CNC size that inhomogeneously broadens optical absorption/luminescence lineshapes. 2-D spectroscopy is a technique capable of circumventing inhomogeneous broadening by correlating absorption and emission dynamics. In this talk I will present our results from applying 2-D spectroscopy to CNCs at cryogenic temperatures. I will first discuss our experiments on conventional CdSe CNCs, in which we have simultaneously observed both bulk-like acoustic phonons and acoustic vibrations discretized by the nanocrystal geometry for the first time. Next, I discuss our experiments on perovskite CNCs, which are a new class of materials first synthesized in 2015. We demonstrate that coherences due to vibrational coupling exhibit anomalous dephasing dynamics, which we attribute to a cascaded coherence transfer process. Finally, I discuss our observations of coherences between so-called bright-triplet exciton states, which are robust at high temperatures and polarization-selective. [mehr]

Solid State Physics

IMPRS-UFAST core course
From a microscopic point of view, a solid is just a regular arrangement of atoms, embedded in a soup of electrons. Yet, a remarkably rich manifold of phenomena emerges from this simple starting point, ranging from simple metals and semiconductors to multiple kinds of magnetic order or superconductivity. In this course we will discuss basic properties of solids and their microscopic understanding.Topics include:- band theory- screening- phonons - ordered phases [mehr]

Ab-initio description for propagation of extreme light pulse in solids: recent progresses

MPSD Seminar
When we theoretically investigate interaction of an intense and ultrashort laser pulse with solids, there are two aspects that should be considered: the strong electric field of the light pulse induces nonlinear electron dynamics in solids, and the nonlinear polarization that arises from the electron dynamics affects the propagation of the light pulse. [mehr]
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