Handan

Halide Edip'in Tanin'de tefrika edilen Handan adlı romanıTelif hakları nedeniyle romanın tam metni verilememiştir

Coherent and incoherent excitation pathways in time-resolved photoemission orbital tomography of CuPc/Cu(001)-2O

Time-resolved photoemission orbital tomography (tr-POT) offers unique possibilities for tracing molecular electron dynamics. The recorded pump-induced changes of the angle-resolved photoemission intensities allow to characterize unoccupied molecular states in momentum space and to deduce the incoherent temporal evolution of their population. Here, we show for the example of CuPc/Cu(001)-2O that the method also gives access to the coherent regime and that different excitation pathways can be disentangled by a careful analysis of the time-dependent change of the photoemission momentum pattern. In particular, we demonstrate by varying photon energy and polarization of the pump light, how the incoherent temporal evolution of the LUMO distribution can be distinguished from coherent contributions of the projected HOMO. Moreover, we report the selective excitation of molecules with a specific orientation at normal incidence by aligning the electric field of the pump light along the molecular axis

Nanoscale engineering with molecules at surfaces

The study of molecular adsorption at surfaces has long been a focus of surface science. With increasing complexity of the molecules, new properties and phenomena emerge, and the design of functional single molecule devices becomes possible. In my talk I will present recent examples from our research that illustrate the intriguing physics and functionalities of complex molecules at surfaces

Nanoscale engineering at surfaces

The increasing interest in quantum technologies puts tailor-made materials into the focus. In this context the term material is more and more understood in a wider sense to also include designer structures beyond a single crystalline phase. For example, such designer structures can be customized stacks of 2D materials as well as surface-supported nanostructures made by assembling individual atoms or molecules. A further challenge, apart from crafting the structures, is studying their properties. Often, this requires the refinement of existing experimental methodologies. In my talk, I will report on our recent work regarding tailor-made materials based on graphene and designer structures based on individual atoms and molecules. With increasing complexity, new properties and phenomena emerge, and the design of functional (quantum) devices becomes possible. As it turns out, even relatively simple designer structures show intriguing functionalities, including quantum dot behaviour, electrostatic potential sensing, and coherent single-electron field emission. On the analytic side, I will illustrate the power of several advanced experimental methodologies

The role of surface corrugation and tip oscillation in single-molecule manipulation with a non-contact atomic force microscope

Scanning probe microscopy (SPM) plays an important role in the investigation of molecular adsorption. The possibility to probe the molecule–surface interaction while tuning its strength through SPM tip-induced single-molecule manipulation has particularly promising potential to yield new insights. We recently reported experiments, in which 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules were lifted with a qPlus-sensor and analyzed these experiments by using force-field simulations. Irrespective of the good agreement between the experiment and those simulations, systematic inconsistencies remained that we attribute to effects omitted from the initial model. Here we develop a more realistic simulation of single-molecule manipulation by non-contact AFM that includes the atomic surface corrugation, the tip elasticity, and the tip oscillation amplitude. In short, we simulate a full tip oscillation cycle at each step of the manipulation process and calculate the frequency shift by solving the equation of motion of the tip. The new model correctly reproduces previously unexplained key features of the experiment, and facilitates a better understanding of the mechanics of single-molecular junctions. Our simulations reveal that the surface corrugation adds a positive frequency shift to the measurement that generates an apparent repulsive force. Furthermore, we demonstrate that the scatter observed in the experimental data points is related to the sliding of the molecule across the surface

Tailoring metal–organic hybrid interfaces: heteromolecular structures with varying stoichiometry on Ag(111)

The physical properties of interfaces between organic semiconductors and metal surfaces crucially influence the performance of organic electronic devices. In order to enable the tailoring of such metal–organic hybrid interfaces we study the adsorption of heteromolecular thin films containing the prototypical molecules copper-II-phthalocyanine (CuPc) and 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) on the Ag(111) surface. Here, we demonstrate how the lateral order can be tuned by changing the relative coverage of both adsorbates on the surface. The layer growth has been studied in real time with low energy electron microscopy, and—for different stoichiometries—the geometric properties of three heteromolecular submonolayer phases have been investigated using high resolution low energy electron diffraction and low temperature scanning tunneling microscopy. Furthermore, we have used a theoretical approach based on van der Waals and electrostatic potentials in order to reveal the influence of the intermolecular and the molecule–substrate interactions on the lateral order of heteromolecular films