Poster presentations

Nowadays, field effect transistors are actively used in basic research to study the electronic properties and the transport characteristics of different 
type of semiconductors. Besides the different way to induce and stabilize the charge carriers in the sample under investigation, the electrolyte gated transistors works 
in a similar way as the field effect transistor. The potential of the gate electrode determines the carrier density and thus the energy of the Fermi level. The electronic 
(transport) properties can thus be measured for the different Fermi level positions. By the differential capacitance measurements the density of the electronic states 
(DOS($ mathrm{E_{F}} $) will be measured for a slight change of the Fermi level. The actual position of the Fermi level can be obtained by measuring the inter-band 
light absorption quenching which monitors the occupation of the bands, not the defect levels. Therefore, the genuine band structure and the density of the defect levels 
at the Fermi energy can be determined by the combination of differential capacitance measurements and optical spectroscopy. Such experiments have been successfully 
performed on conventional CdSe QD solids. In our research, we compare the transport properties between QDs mono-layer and 2-D dimensional semiconductors with a square 
and honeycomb structures.

H.M. Baghramyan1, M.G. Barseghyan2,3, D. Laroze1,4, J. Bragard5, A.A. Kirakosyan2

1. Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
2. Department of Solid State Physics, Yerevan State University, Alex Manoogian 1, 0025 Yerevan, Armenia
3. National University of Architecture and Construction of Armenia, Teryan 105, 0009 Yerevan, Armenia
4. SUPA School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
5. Departamento de Física y Matemática Aplicada, Universidad de Navarra 31080, Pamplona, Spain

The effects of a lateral electric field on intraband absorption in GaAs/GaAlAs two-dimensional coupled quantum dot-ring structure Somaschini with an on-centre hydrogenic donor 
impurity is investigated. The confining potential of the system consists of two parabolas with various confinement energies Peeters. The calculations are made using the 
exact diagonalization technique. A selection rule for intraband transitions was found for x-polarized incident light. The absorption spectrum mainly exhibits a redshift with the 
increment of electric field strength. On the other hand, the absorption spectrum can exhibit either a blue- or redshift depending on the values of confinement energies of dot and 
ring. Additionally, electric field changes the energetic shift direction influenced by the variation of barrier thickness of the structure.
We hope, that the obtained in the work dependence of intraband absorption phenomena on simultaneous influence of electric field and confinement potential's characteristics can 
help with the understandance of optical properties of coupled nanostructures with the geometry similar to dot-ring structure.

Somaschini: C. Somaschini, S. Bietti, N. Koguchi, Coupled quantum dot–ring structures by droplet epitaxy, Nanotechnology 22 (2011) 185602.
Peeters: B. Szafran, F.M. Peeters, S. Bednarek, Electron spin and charge switching in a coupled quantum-dot-quantum ring system, Phys. Rev. B 70 (2004) 125310.

Albrecht Benad, Dr. Christoph Ziegler, Prof. Alexander Eychmüller

Aerogels are materials with a very low density and a large specific surface area. Nowadays aerogels can be produced from many different substances like noble metals, 
semiconductors and metal oxides. Especially in heterogeneous catalysis combinations of metals and metal oxides turned out to be very efficient. Here we present a facile method 
to produce mixed metal/zinc oxide aerogels in a one-pot reaction. So far we were able to immobilize Ni, Pd, Pt, Ru and Rh on the ZnO scaffold. For some of the metals, a subsequent 
reductive treatment leads to the formation of the respective intermetallic compound.
It is very likely that the method presented can be applied to many different metal oxide/transition metal systems and hence opens a door to many new materials.

Quantum dot superlattices exhibit electronic properties that are defined by the overlap of wave functions between adjacent particles, as well as the electronic 
structure of individual themselves. In this work we demonstrate how the spatial overlap of electrons and holes inside semiconductor nanocrystals can be controlled by a 
separating layer. This in turn will significantly influence the interaction of such particles in a superlattice.
We employ cation exchange and seeded growth reactions to fabricate complex core/barrier/shell particles with type-II band alignment. The effects of barrier thickness and 
shelling temperature are studied in detail. Steady-state and transient absorption spectroscopy data is used to construct a model of the charge carrier relaxation dynamics 
and lifetimes. Charge carrier extraction or delocalisation in a superstructure will compete with radiative or non-radiative recombination of confined charge carriers. Their 
relative rates will strongly affect uses in lasing, electronic devices, or photovoltaics. 

Assembly of nanoparticles into aerogel structures has been attracted increasing interests due to their extremely low densities, high porosity, and large surface 
area. Noble metal nanocrystals have been extensively demonstrated as promising materials for heterogeneous catalysis and energy-based electrochemical catalysis. Metallic 
aerogels, especially catalytically active noble metals, retain the inherent characteristics (e.g. high electrical conductivity and intrinsic catalytic activity) of the 
metal materials, which enabled them tremendous potential in electrocatalysis.[1] Consequently, it is of great interest to design efficient electrocatalysts based on noble 
metal involved metallic aerogels.
Recently, our efforts have been focused on the self-assembly of noble metal nanoparticles (e.g. Pt, Pd, Au) into aerogel structures and the investigation of their electrocatalytic 
properties. Pure Pd and PdxPty aerogels have been achieved by a spontaneous gelation method and they showed highly improved electrocatalytic activities for ethanol oxidation and 
oxygen reduction reactions.[2] In addition, we realized the controlled growth of Pd aerogels with different porosities and surface areas via a cation-induced destabilization 
route. They provided a three-dimensional matrix with high electrical conductivity and high porosity for enzyme loading, showing a promoted bioelectrocatalysis and biofuel 
cell application.[3] Currently, we are trying to design metallic aerogels derived from morphology-controlled noble metal nanocrystals and investigate their electrocatalysis 
applications.

References
[1]	W. Liu, A. K. Herrmann, N. C. Bigall, P. Rodriguez, D. Wen, M. Oezaslan, T. J. Schmidt, N. Gaponik, A. Eychmuller, Acc. Chem. Res. 2015, 48, 154-162.
[2]	a) W. Liu, A. K. Herrmann, D. Geiger, L. Borchardt, F. Simon, S. Kaskel, N. Gaponik, A. Eychmuller, Angew. Chem. Int. Ed. 2012, 51, 5743-5747; b) W. Liu, P. Rodriguez, 
L. Borchardt, A. Foelske, J. Yuan, A. K. Herrmann, D. Geiger, Z. Zheng, S. Kaskel, N. Gaponik, R. Kotz, T. J. Schmidt, A. Eychmuller, Angew. Chem. Int. Ed. 2013, 52, 9849-9852.
[3]	a) D. Wen, A. K. Herrmann, L. Borchardt, F. Simon, W. Liu, S. Kaskel, A. Eychmuller, J. Am. Chem. Soc. 2014, 136, 2727-2730; b) D. Wen, W. Liu, A. K. Herrmann, 
A. Eychmuller, Chem. Eur. J. 2014, 20, 4380-4385.

We propose a new design of terahertz oscillator based on hybrid graphene superlattices. By depositing a set of ferromagnetic insulator strips on top of a graphen 
nanoribbon, a spin-dependent potential is created in the system which  induces a proximity exchange splitting of the electronic states in the graphene monolayer [1,2]. If the 
system is additionaly affected by a potential drop between source and drain, the electrons excited to the lowest conduction band perform Bloch oscillations in the terahertz 
range. Our numerical simulations of the Dirac equation in the lowest conduction band of the spin-dependent superlattice conclude that the frequency of the coherent oscillation 
is independent of the electron spin. On the contrary, the Bloch amplitude may differ significantly due to the different band-widths for both spins. The different spatial extent 
of the electron motion in real space yields a spin-polarized ac electric current in the terahertz domain. The resulting ultrafast magnetization  could  be  detected  with  
terahertz  emission spectroscopy.

[1] J. Munarriz, C. Gaul, A. V. Malyshev, P. A. Orellana, C. A. Mueller, and F.
Domínguez-Adame, Phys. Rev. B 88, 155423 (2013).
[2] H. Haugen, D. Huertas-Hernando, and A. Brataas, Phys. Rev. B 77,115406 (2008).
[3] E. Beaurepaire, G. M. Turner, S. M. Harrel, M. C. Beard, J.-Y. Bigot, and
C. A. Schmuttenmaer, Appl. Phys. Lett. 84, 3465 (2004)

We report on a generic approach for immobilizing quantum dots (CdTe nanoparticles) on thin stimuli-responsive polymer network (about 50 µm) consisting of 
poly(acrylic acid) (PAA) polymer gel attached by one end to an underlying substrate. The protocol involves covalent bonding (amide linkage) between amino groups present 
on the surface of CdTe nanoparticles and carboxylic groups of PAA polymer gel. Use of such a polymer gel prevents nanoparticle aggregation and facilitates complete surface 
coverage. The change in the optical properties of the quantum dots after immobilization was studied by photoluminescence spectroscopy and fluorescence microscopy in different 
buffer solutions. The results suggest a simple, effective and highly versatile microfluidic set-up as pH-sensitive sensor.

A versatile method to fabricate extremely low density self-supported macroscopic monoliths will be presented. The nano- and microscopic morphology of the resulting 
superstructures can be described as thin platelets of assembled nanocrystals, which form a voluminous network responsible for the extremely low macroscopic density of the resulting 
aerogel. The approach was successfully tested for noble metals, metal oxides such as iron oxide, and semiconductor materials such as CdSe/CdS quantum rods, and in principle can be 
expanded to many other colloidal nanoparticle materials. In addition this method allows the shaping of the resulting aerogel not only as monolith but also as i.e. thin films or 
other desired geometries. The aerogels are characterized by scanning and transmission electron microscopy, optical spectroscopy, electrochemically (surface area), and possible 
applications in catalysis are discussed.

A simple single-step chemical vapor deposition (CVD) method has been used to grow the faceted Au-ZnO hetero-nanostructures (HNs) either with nanowires (NWs) or 
with triangular nanoflakes (TNFs) on crystalline silicon wafers with varying oxygen defect density in ZnO nanostructures. XPS analysis confirms that TNFs sample has much more 
oxygen related defects in comparison with NWs sample. Using Scanning Kelvin Probe Microscopy (SKPM) technique we have determined average work function (phi) of the two samples, 
which appears to be approx 0.45 eV less for TNFs sample. Here, we explore the enhanced Field emission (FE) properties of Au-ZnO TNFs sample compared to Au-ZnO NWs sample, 
following its approx 2 times lower turn-on voltage with very high field enhancement factor Beta approx 10^6. We have discussed this enhanced FE performances of TNFs sample in 
the light of SKPM along with XPS results and validated by 1st principle density functional calculations. The superiority in the FE performances of the TNFs sample are proposed 
to be depending on two factors: sharp tip tapered geometry and oxygen vacancy promoted excess unshared d-electrons of Zn atoms (nearest to O vacancy site) present in the TNFs, lead 
to increase in electron donating/tunneling capability via pinning of effective work function (phi).

Recently, we have demonstrated a new kind of photoluminescent nanocrystal which is known as carbon-dots. Here we present, the theoretical and experimental insight of the 
electron-photon interaction of the carbon-dots. We apply this carbon-dots to achieve a nanoscale one dimensional flow systems. The one-dimensional flow was observed by confining two 
spatial domain (x and y) into few tens of nanometer keeping the other spatial axis free. Such nanochannel configuration along with single molecule like concentration of carbon-dots 
retard the Brownian motion and assist them to flow in one dimension. Using a dual-foci-fluorescence correlation spectroscopy technique we measure the flow speed and burst size 
distributions of single carbon-dots. The experimental setup allows us to foresee an efficient single molecule level trapping system. 

1. Ghosh, S. and Niehaus, T , Time dependent density functional response theory unfolds the Anti-Kasha photoluminescence behaviour of carbon-nanodots. (Under preparation)
2. Ghosh, S. et al., Photoluminescence of Carbon Nanodots: Dipole Emission Centers and Electron–Phonon Coupling. Nano Lett., 2014, 14 (10), pp 5656-5661
3. Ghosh, S. et al. "Single-molecule fluorescence inside solid-state nanochannels." SPIE BiOS. International Society for Optics and Photonics, 2014.

Synthesis and Applications of Tetrazole-stabilized Metal Nanoparticles (NPs) and Quantum Dots (QDs)

C. Guhrenz, A. Wolf, S. V. Voitekhovich, N. Gaponik, A. Eychmüller

Tetrazoles are five-membered heterocycles consisting of one carbon and four nitrogen atoms with different substitutions. Because of their complexing properties, the high nitrogen 
content (80 wt%) and their bioisosteric behavior to the carboxyl group they found applications in pyrotechnics, rocket fuels and pharmacy.[1,2] In addition, MURRAY et al.[3] 
described firstly the use of aminotetrazoles as stabilizing agents in colloidal synthesis of CdS NPs. 
In recent years different aqueous and organic approaches for the preparation of tetrazole-stabilized metal NPs (Au, Ag, Pt, Pd) and QDs (CdSe, CdTe, CdSe/CdS) have been published.[3-6]
Additionally, disubstituted tetrazoles produce easily metal-tetrazole-complexes (M = Cd2+, Zn2+, Pb2+) which can be used as single precursors in QDs synthesis.[7]
Herein, we report on the synthesis and applications of tetrazole-stabilized Au NPs. The monosubstituted 5 mercaptoethyltetrazole is used in the synthesis of metal NPs which are 
attractive for catalytic applications. Therefore, a thermal treatment induces the decomposition of the tetrazole under the formation of a high proportion of gaseous products which 
results in ligand free, catalytically active particles. The activity of the Au NPs on TiO2 is demonstrated in CO oxidation.

[1]	H. R. Meier, H. Heimgartner, Methoden der Organischen Chemie (Houben-Weyl), Thieme, Stuttgart, 1994.
[2]	P. N. Gaponik, S. V. Voitekhovich, O. A. Ivashkevich, Russ. Chem. Rev. 2006, 75, 507-539.
[3]	C. Murray, E. Shevchenko, D. Talapin, Nanomaterials with Tetrazole-Based Removable Stabilizing Agents, 2007, US 20070057255.
[4]	V. Lesnyak, S. V. Voitekhovich, P. N. Gaponik, N. Gaponik, A. Eychmüller, ACS Nano 2010, 4, 4090-4096.
[5]	V. Lesnyak, A. Wolf, A. Dubavik, L. Borchardt, S. V. Voitekhovich, N. Gaponik, S. Kaskel, A. Eychmüller, J. Am. Chem. Soc. 2011, 133, 13413-13420.
[6]	M. N. Nichick, S. V. Voitekhovich, A. Shavel, A. I. Lesnikovich, O. A. Ivashkevich, Polyhedron 2009, 28, 3138-3142.
[7]	S. V. Voitekhovich, D. V. Talapin, C. Klinke, A. Kornowski, H. Weller, Chem. Mater. 2008, 20, 4545-4547. 

Laura Kühn (1), Sebastian Henning (2), Juan Herranz (2), Wei Liu (1), Anne-Kristin Herrmann (1), Nikolai Gaponik (1), Alexander Eychmüller (1), Thomas J. Schmidt (2,3)

(1) Physical Chemistry, TU Dresden, Bergstraße 66b, D-01069 Dresden, Germany
(2) Electrochemistry Laboratory, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
(3) Laboratory of Physical Chemistry, ETH Zürich, CH-8093 Zürich, Switzerland

Polymer electrolyte membrane fuel cells (PEMFCs) constitute a promising emission-free technology for power generation. Due to the sluggish reaction kinetics of the oxygen reduction 
reaction (ORR) at the cathode, efficient catalysts are required. Despite large efforts in research to develop such materials, high cost, low stability and insufficient catalytic activity 
still remain critical issues. Aerogels, a unique class of inorganic materials with a highly porous network structure, are excellent candidates to meet these demands as they are purely 
metallic without the use of any catalyst support. Recently, we have shown that bimetallic Pt-Pd aerogels are highly efficient ORR catalysts with excellent long-term stability.textsuperscript{[1]}

In order to reduce costs and enhance the catalytic properties, we aim to design bimetallic aerogels of Pt and non-precious metals. This poster presents our most recent results including 
first electrochemical tests. We successfully synthesized Pt-Ni aerogels via a facile one-step procedure. The obtained materials possess a highly porous structure with large specific 
surface areas. Both metals form an alloy as proven by powder X-ray diffraction (XRD). Pttextsubscript{3}Ni aerogels were up to 10 times more active towards ORR than both pure Pt aerogels 
and commercial Pt/C.
In conclusion, we developed a facile one-step synthesis route for alloyed Pt-Ni aerogels. The obtained material is an excellent ORR catalyst.

[1] W. Liu et al., Angew. Chem. Int. Ed. 2013, 52, 9849–52. 

DNA nanotechnology offers great potential for the precise assembly of nanoparticles into highly functional arrays. These are especially attractive for nanoscale 
optoelectronics and plasmonics. Their versatility together with the high structural precision make DNA origami particularly attractive as template structures. The present work will 
show recent achievements on the targeted functionalization of well-defined metal and semiconductor nanoparticles as well as the deposition of NPs onto pre-functionalized contact 
areas on the DNA origami. Thereby the work contributes to the preparation of precisely controllable hybrid structures.

The fluorescence resonance energy transfer (FRET) in double and triple ensembles of densely-packed PbS nanocrystals (NC) of different sizes was studied using transient 
and steady-state photoluminescence (PL) spectroscopy. It was found that FERT between nanocrystlas leads to drastic increase of NC-acceptor PL lifetimes. The observed slowdown in the 
PL decay is attributed to FRET from the long-lived in-gap state of NC-donor. Simultaneous reduction of PL lifetimes of NC-donors and increase of PL lifetimes of NC-acceptors leads to 
merging of PL decays recorded for QDs of different sizes.

M.E. Madjet$^{1}$, A. Akimov$^{2}$, F. El-Mellouhi$^{1}$, G. Berdiyorov$^{1}$, S. Ashhab$^{1}$ and S. Kais$^{1}$
$^{1}$ Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation, PO Box 5825, Doha, Qatar
 $^{2}$ Department of Chemistry, University of Southern California, Los Angeles, CA 90089

Hybrid organic-inorganic lead halide perovskites have recently emerged as a very promising family of materials for photovoltaic applications. They possess high absorption coefficients, 
good electron and hole mobilities, long recombination times, and they can be synthesized using low-cost processing techniques. The highest power conversion efficiencies, now exceeding 
20%, have been obtained with the pure iodide material CH3NH3PbI$_{3}$ (MAPbI$_{3}$). This high efficiency is mainly due to low sensitivity to defects, the long diffusion lengths and high 
mobility of charge carriers. However, many fundamental processes related to the photo-physics of these materials remain not fully understood. The excitation of electrons from the valence 
band to conduction band results in the formation of excited electrons and holes, both of which lose most of their energy by cooling down to the band edges. In this contribution, we address 
the non-radiative relaxation dynamics of electrons and holes in organic-ionorganic perovskite materials when electrons are promoted from the valence band to the conduction band.
We perform nonadiabatic molecular dynamics (NA-MD) simulations using a combination of the PYthon eXtension for Ab Initio Dynamics (PYXAID) [1] package for quantum dynamics.
Results on perovskite materials MAPbI$_{3}$, MAPbBr$_{3}$, MAPbCl$_{3}, MAPbI$_{3-x}$Br$_{x}$, MAPbI$_{3-x}$Cl$_{x}$ will be presented and discussed.
Our computed values for the electron relaxation time obtained for MAPbI$_{3}$ are in good agreement with the experimental data reported in Ref. [2]. We also found that halogen-mixing 
MAPbI$_{3-x}$Cl$_{x}$ results in slowing down the electron and hole relaxation process, suggesting a longer life time in low Cl-doped systems.

[1] A.V. Akimov and O.V. Prezhdo, J. Chem. Theory Comput. 9, 4959 (2013).
[2] Hung-Yu Hsu et al, Angew.Chem. Int. Ed. 53, 1 (2014).

Recently it has been developed a new method for the packing of nanosized particles into so-called supraballs [1] by dispersing the particles into a fluid phase, and preparing 
an emulsion of this phase into another fluid with which the first fluid is no miscible. By allowing the droplets of the first fluid to evaporate, the particles are spherically confined more 
and more, causing them to finally compact into geometries that are not accessible in other ways. When performing this method with luminescent nanocrystals (quantum dots, QDs) it was found 
that not only the emissive properties were preserved in the new geometry, but also new optical features, like whispering gallery modes, were present [2]. 
In this talk I will present supraparticles both on a chemical and on a physical point of view: I will show supraparticle made of different kind of luminescent nanocrystals (e.g. quantum 
dots, nanoplatelets) along with the synthesis procedure we used, then I will focus on the physical properties of this new intriguing superstructures presenting the last results of the 
optical characterization.

[1] B. de Nijs, S. Dussi, F. Smallenburg, J.D. Meeldijk, D.J. Groenendijk, L. Filion, A. Imhof, A. van Blaaderen, and M. Dijkstra, "Entropy-driven formation of large icosahedral 
coloidal clusters by spherical confinement", Nature Materials  (2014).
[2] D. Vanmaekelbergh, L.K. Van Vugt, H.E. Bakker, F.T. Rabouw, B. de Nijs, R.J.A. van Dijk-Moes, M.A. van Huis, P.J. Baesjou, A. van Blaaderen, "Shape-Dependent Multiexciton 
Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum Dots", ACS Nano (2015).

Authors: S. Oh$^{1}$, Y. Zhang$^{2}$, F.H. Alharbi$^{1}$, G. Engel$^{3}$, and S. Kais$^{1,2}$

(1) Qatar Environment and Energy Research Institute, Doha, Qatar
(2) Department of Chemistry, Physics and Birck Nanotechnology Center, Purdue University, West Lafayette, USA
(3) Department of Chemistry, University of Chicago, Chicago, USA

Abstract

Long quantum coherence in photosynthetic complexes is believed to play a key role in the highly efficient transport of excited electrons [1,2]. This discovery has inspired researchers 
to explore new routes to utilize the quantum effects for high efficient photovoltaic devices and artificial light-harvesting systems [3]. Scully's group [4,5] showed that the noise-induced
coherence suppresses the spontaneous emission of excited electrons and thus enhances the efficiency of photocells. Creatore et al. [6] explored that the quantum interference of the 
de-localized state of the two coupled-dipole donor could enhance the efficiency of the photocell. Recently, we proposed a photocell with the three coupled dipole donor [7], and showed 
the quantum interference of the de-localized state gives rise to even higher efficiency in compared with uncoupled dipoles. We obtain the current-voltage curve by solving the master 
equation with the pumping term of the light. We study the scaling of the donor size for linear chains or rings. Also we discuss the effect of inhomogeneity of donor-acceptor systems 
on the efficiency of the solar cell.

References

[1] G. Engel, T. Calhoun, E. Read, T. Ahn, T. Mancal, Y. Cheng, R.Blankenship, G. Fleming, Nature (London) 446, 782 (2007).
[2] E. Romero R. Augulis, V. Novoderezhkin, M. Ferretti, J. Thieme, D. Zigmantas, R. van Grondelle, Nature Phys. 10, 676 (2014).
[3] C. Creatore, A. Chin, M. Parker, S. Emmott, Frontiers in Materials 2, 6 (2015). 
[4] K. Dorfman, D. Voronine, S. Mukamel, M. Scully, Proc. Natl. Acad. Sci. 110 (2013) 2746
[5] M. Scully, K. Chapin, K. Dorfman, M. Kim, A. Svidzinsky, Proc. Natl. Acad. Sci. 108, 15097 (2011)
[6] C. Creatore, M. Parker, S. Emmott, A. Chin, Phys. Rev. Lett. 111, 253601  (2013).
[7] Y. Zhang, S. Oh, F. Alharbi, G. Engel, S. Kais, Phys. Chem. Chem. Phys. 17, 5743 (2015).

Transfer processes across hybrid inorganic/organic interfaces have become one of the key research topics. While very much data has been gathered by measurements, so far 
their detailed understanding still lacks in theoretical models. The poster on show presents a theoretical study which gives insight into the nature of excitation energy transfer processes 
in a very realistic hybrid semiconductor/molecular system. Inspired by experiments, it consists of a spherical CdSe nanocrystal (4.5 nm diameter) placed nearby a gigantic tubular cyanin 
dye aggregate (63 nm length and 15 nm diameter). Transitions are described across the interface from Frenkel excitons in the tube to Wannier-Mott excitions in the nanocrystal. Despite 
the huge size of the system the whole study is implemented in a full atomistic picture [1].
The nuclear structure of the tube is obtained by molecular dynamics simulations and the Frenkel excitons follow from the single molecular excited states [1,2]. First of all, both are 
based on diverse ab-initio DFT studies. The Wannier-Mott excitons, on the other hand, are described in terms of Coulomb correlated electron-hole pair states. The latter approach uses 
effective single particle states of electrons and holes which themselves result from a tight-binding model of the nanocrystal.
Finally, excitonic couplings among both bodies and FRET-type rates are presented for various spatial set-ups. Even placed in direct contact, the transfer stays incoherent as indicated 
by rates somewhat larger than $10^9/s$. In rather coincidence with preliminary experiments [3], it demonstrates the power of the approach and calls for further practice.

mbox{[1]} T. Plehn, D. Ziemann, J. Megow and V. May, J. Phys. Chem. B, Article ASAP, DOI: 10.1021/jp5111696
\ mbox{[2]} J. Megow, M. Röhr, M. Schmidt am Busch, Th. Renger, R. Mitric, S. Kirstein, J. Rabe, and V. May, Phys. Chem. Chem. Phys. 17, 6741 (2015)
\ mbox{[3]} Y. Qiao, F. Polzer, H. Kirmse, E. Steeg, S. Kühn, S. Friede, S. Kirstein and J. Rabe, ACS Nano 9, 1552 (2015)

We study intraband optical transitions in a degenerate valence band of spherical nanocrystals made of semiconductors of $T_d$ and $O_h$ symmetries. The energy spectrum of 
holes is calculated using $kp$ perturbation theory. We derive analytical expressions for the matrix elements of the interaction between holes and photons. It is shown that the size 
dependency of these matrix elements is determined by the quantum states involved in the transitions. The selection rules obtained allow transitions between many states of different 
symmetries, which are forbidden in the conduction band. We calculate the radiation lifetimes of the valance band states as functions of the nanocrystal radius, and show that they can 
vary in a broad range from 10-3 to 10-12 s.

 We investigate the effect of inter-mode coupling on the vibrational relaxation dynamics of molecules in weak dissipative environments. The simulations are performed within 
the reduced density matrix formalism in the Markovian regime, assuming a Lindblad form for the system-bath interaction. We focus on the response of small ensembles of adsorbed CO 
molecules upon vibrational excitation, in order to study how reaction pathways are influenced by molecular packing. Since dissipative dynamics is non-unitary, the choice of representation 
will affect the evolution of the reduced density matrix. Two alternative representations for computing the relaxation rates and the associated operators are thus compared: the fully 
coupled spectral basis, and a factorizable ansatz. The former is well-established and serves as a benchmark for the solution of Liouville-von Neumann equation. In the latter, a contracted 
grid basis of potential-optimized discrete variable representation is tailored to incorporate most of the inter-mode coupling, while the Lindblad operators are represented as tensor 
products of one-dimensional operators, for consistency. This procedure results in a marked reduction of the grid size and in a much more advantageous scaling of the computational cost 
with respect to the increase of the dimensionality of the system. The new methodology is applied first to a prototypical two-dimensional model system representing two CO molecules 
approaching a Cu(100) surface. The molecule-surface interaction is adapted from an ab initio potential, while the diatom-diatom vibrational coupling strength is systematically varied. 
The factorizable method is found to provide an accurate description of the dissipative quantum dynamics of the model system, specifically of the time evolution of the state populations 
and of the probability density distribution of the molecular wave packet. The influence of intra-molecular vibrational energy redistribution is properly taken into account by the new 
model on the whole range of coupling strengths. Finally, simulations of the vibrational relaxation dynamics are carried out for varying molecular packings.

The morphology and optical properties of nanocrystal (NC) superlattices (SLs) formed by the self-assembly of lead sulfide NCs covered with oleic acid (OA) on glass substrates 
is studied by the X-ray diffraction analysis, together with steady-state and transient optical spectroscopy. The period of self-assembled lattices is proportional to the NC diameter, 
increasing slightly with its size due to the increase in thickness of OA layer on the NC surface.  Chemical removal of the OA from the NC surface affects on the SLs morphology. For large 
NCs the SL structure homogeneity is improved, with an inter-particle distance down to 0.4 nm. This SL morphology allows a rapid charge carrier transport through the SLs. The steady-state 
optical properties of such structures does not have significant changesin respect of optical properties of initial colloidal solutions of NCs, nevertheless, the luminescence decay time 
is reduced dramatically, due to the appearance of additionnal nonradiative relaxation channels.

A recently developed quantum kinetic theory of the dynamic response of typical noble metals is presented.
The proposed approach is based on the density functional theory (DFT) and incorporates new important elements as compared to the conventional time-dependent DFT formalism. The kinetic DFT 
is derived from the master equation of motion for the density matrix, which involves both momentum and energy relaxation processes. Therefore, the quantum system is described by two 
relaxation parameters, unlike the conventional time-dependent DFT which incorporates only one relaxation parameter.
This allows us to describe both the absorption of light and the generation of hot plasmonic electrons. Using this kinetic DFT theory we also observe the transition from the multiple peaks 
in small size-quantized systems to the intensive plasmonic resonance in large classical systems. Unlike the standard picture of collisional broadening of the plasmon peak in small systems, 
we observe a very different scenario: the formation of multiple plasmonic-like peaks in small quantized systems. These peaks are the result of a hybridization of the collective plasmon mode 
and the single-particle transitions in a quantized electron gas. Our approach also incorporates the interband transitions, which are important for a qualitative description of gold and 
silver. The kinetic DFT formalism developed here can be employed to model and predict a variety of metal and hybrid nanostructures for applications in photocatalysis, sensors, photodetectors, 
metamaterials, etc. In support of this, we show recent results for composite systems of gold nanodisks separated from a continuous gold layer by a dielectric spacer, where the insights 
provided by this formalism are used to interpret the origin of anomalous ultrafast plasmonic electrons generated in the hot spots of such a system.

Hana Vrbovská and Melánia Babincová

Comenius University, Faculty of Mathematics, Physics and Informatics, Department of Nuclear Physics and Biophysics, 842 48 Bratislava, Slovakia.

Dopamine is a significant molecule in case of one of the neurodegenerative diseases - Parkinson's disease. This neurotransmitter is usually synthesized and secreted in dopaminergic 
neurons in substantia nigra of brain. However, in case of Parkinson's disease the dopaminergic neurons are being destroyed which leads to dopamine deficiency in the synapses of 
striatum and development of the characteristic symptoms: muscle rigidity, bent posture, slow movements and tremors that are more obvious when the patient is at rest [1].
Treatment of this condition is a rather difficult, because dopamine does not cross the blood-brain barrier, so it cannot be replenished by simple IV injection.  Therefore we propose 
treatment of Parkinson's disease based on dopamine delivered to the brain by nanoparticles that can be modified to cross this barrier. To make this happen, there is a lot of steps that 
need to be taken before such treatment can even enter clinical trial. 
We decided to start from the very beginning - by studying spectral characteristic of dopamine and its antioxidant properties which may be important in liposomal preparations with dopamine 
but also when delivering it to the brain, because etiology of Parkinson's disease is largely associated with oxidative stress. The antioxidant properties were studied on a liposomal model 
with oxidation induced by Fenton's reagent and we concluded that dopamine has some antioxidant properties, but it is not as strong as other antioxidants such as α-tocopherol or lipoic acid [2].
Then we prepared multilamellar and unilamellar liposomes with dopamine encapsulated in the aqueous medium inside the vesicle and studied percent of encapsulation when the soybean lecithin 
liposomes were prepared by simple hydration method. The reason behind the choice of liposomes as our carrier systems is that liposomes are versatile nanoparticles that can be easily modified 
by ligands that are recognized by stereospecific transporters on the blood-brain barrier and therefore could cross into the brain. Further the percentage of encapsulation was determined 
for both multilamellar as well as unilamellar liposomes.
In the last phase we prepared DPPC magnetoliposomes that contained dextran-magnetite 10 nm particles in the lipid bilayer and dopamine inside the vesicles. The advantage of magnetoliposomes 
is that they move alongside the gradient of the magnetic field and the release of the drug can be triggered by alternating magnetic field. The magnetic nanoparticles align themselves along 
the magnetic field and then relax by Brown or Neél relaxation. The dissipation of energy during this process leads to heating of the magnetic nanoparticles and their surroundings 
which causes mechanical ruptures in the lipid membrane and its phase transition to liquid-crystalline phase where the membrane is more permeable. We studied the release of dopamine after 
exposure to 3,5 MHz alternating magnetic field for different times. After one hour most of the dopamine encapsulated in the magnetoliposomes was released to the outside.

1. Lotharius, J., Brundin, P. Pathogenesis of Parkinson's Disease: Dopamine, Vesicles and α-Synuclein. In: Nature Reviews Neuroscience. 2002, 3(12), p.932-942.
2. Durdík, S., Vrbovská, H., Olas, A., Babincová, M. Influence of naturally occurring antioxidants on magnetic nanoparticles: Risks, benefits, and possible therapeutic 
applications. In: Gen Physiol. Biophys. 2013, 32(2), p.173-177.

Gels assembled from semiconductor quantum dots (QDs) have great prospects for application in such areas as catalysis, sensing and photonics.(1) However, assembly of nanoparticles 
into multifunctional macroscopic solids is often demanded for these applications but still challenging. Aiming high quantum yields for the porous three dimensional macroscopic network, 
new strategies like transferring of highly luminescent QDs from organic to water media by ligand exchange or silica shelling are looking promising.(2)
In this work we present the next step forward by preparing highly luminescent water based QDs concomitant with a controllable gelation mechanism. By adroit modification of the Tetrazole 
ligand, the photoluminescence quantum yield is significantly enhanced up to 77% in comparison to previous studies while the excellent reversible gelation properties via 
Tetrazole-metal-complexes are kept.(3)

(1) 	Arachchige I. U. and Brock S. L. Acc. Chem. Res., 2007, 40, 9, 801-809 
Gaponik, N. et al. J. Phys. Chem. Lett. 2012, 3, 8-17.
(2) 	Rengers, C. et al. submitted.
(3) 	Lesnyak, V. et al. ACS Nano 2010, 4, 4090-4096. 

The potential of metal semiconductor core-shell systems for applications in photovoltaics and plasmonics has led to an increasing number of experimental studies in this 
field. Of particular interest is the interaction of metal nanoparticle plasmons with semiconductor excitons in such a system. This poster focuses on the excitons in the semiconductor 
shell. These excitons are on the one side modified by the polarisation of the metal and on the other side quenched due to excitation energy transfer from the semiconductor shell to the 
metal core. 
The metal nanoparticle is described by an effective Hamiltonian, which also accounts for higher plasmon modes, while the semiconductor shell is modeled on an atomistic level where the 
exciton states are described by a configuration interaction scheme. The resulting lifetimes of plasmons as well as semiconductor excitons are in line with recent experiments [1].

[1] S. Lambright et al. ACS Nano (2014), 8, 352-361.