Single Nanostructures, Nanomaterials, Aerogels and their Interactions: Combining Quantum Physics and Chemistry

For each poster contribution there will be one poster wall (width: 97 cm, height: 250 cm) available. Please do not feel obliged to fill the whole space. Posters can be put up for the full duration of the event.

Quantum Dots synthesis through Direct Laser Patterning

Antolini, Francesco

The synthesis of colloidal photo-luminescent semiconductor quantum dots (QDs), belonging to II-VI groups, even from single source precursors is presented. Since three decades their synthesis has been pursued implementing new and easier synthetic conditions that standardize their production. In this work is reported the production of luminescent of CdS QDs in a polymeric film induced by laser processing. A film of PMMA doped with two types of precursors (cadmium xanthates) is irradiated with an UV laser source with different energy doses. The structured film will then be observed with confocal fluorescent microscope The interesting results shows that the two different xanthates display a different behaviour under the laser source even if their absorption spectrum is similar. The second interesting result is that the effect of the laser is the production luminescent pattern only for certain fluences and that the same film treated with the temperature did not show any luminescent. These results points out the role of the laser light in the process of luminescent QDs growth that the temperature can’t activate.

Electrochemical doping of HfNCl: spin-orbit coupling, spin texture, and Ising superconductivity

Brumme, Thomas

In recent years it became possible to dope few-layer materials in the order of $10^{14}$ charge carriers $\mathrm{cm}^{-2}$ using ionic-liquid based field-effect transistors. This allows for the exploration of the semiconducting, metallic, superconducting, and charge-density-wave regimes in reduced dimensionality. Especially, the transition-metal dichalcogenides (TMDs) have received a lot of attention as possible candidates to build valleytronic devices in which the valley degree of freedom is used to store and process information. Furthermore, as the spin is polarized perpendicularly to the layer for charge carriers in the spin-orbit split band extrema, TMDs show so-called Ising superconductivity:[1-3] electrons with opposite out-of-plane spins in opposite K and K′ valleys form singlet Cooper pairs, thus increasing the upper critical field that is needed to destroy the superconducting state. The related transition-metal chloronitride HfNCl is usually not considered in this context, as the bands are not spin-orbit split due to the presence of inversion symmetry. Yet, in a field-effect setup the asymmetric external electric field leads to a breaking of the inversion symmetry. We calculate within density-functional theory[4,5] the band structure and spin-orbit splitting for field-effect doped HfNCl. We show how the external electric field leads to changes in the spin texture in the conduction band minimum and estimate the in-plane, upper critical field $H_{c2}^{||}$. [1] J. M. Lu, O. Zheliuk, I. Leermakers, N. F. Q. Yuan, U. Zeitler, K. T. Law & J. T. Ye, Science 350, 1353 (2015) [2] X. Xi, Z. Wang, W. Zhao, J.-H. Park, K. T. Law, H. Berger, L. Forró, J. Shan & K. F. Mak, Nat. Phys. 12, 139 (2016) [3] S. C. de la Barrera, M. R. Sinko, D. P. Gopalan, N. Sivadas, K. L. Seyler, K. Watanabe, T. Taniguchi, A. W. Tsen, X. Xu, D. Xiao & B. M. Hunt, Natu. Commun. 9, 1427 (2018) [4] T. Brumme, M. Calandra & F. Mauri, Phys. Rev. B 89, 245406 (2014) [5] T. Brumme, M. Calandra & F. Mauri, Phys. Rev. B 91, 155436 (2015)

Upconversion-Gold hybrid nanosystems for oligonucleotide detection based on Foerster energy resonant transference

Cabrera Granado, Eduardo

The development of UCNP-based FRET systems for biosensing requires the optimization of the energy transfer between the donor-acceptor pair. We have optimized the FRET efficiency of UCNPs in the presence of AuNPs. The effect of the AuNP size on the fluorescence quenching shows an optimum particle size for FRET biosensing. Upconversion nanoparticles (UCNPs) have been proven to be promising candidates for detection of small oligonucleotides used as biomarkers in different diseases [1]. Our aim is to develop a Förster resonance energy transfer (FRET)-based nanosensor for detection of oligonucleotides. We use UCNPs as donors, and gold nanoparticles (AuNPs) as acceptors. We synthesized 18 nm NaYF4:Yb,Er nanoparticles coated with a 4 nm silica shell and functionalized with amino groups. We also synthesized AuNPs with different diameters from 5 nm to 70 nm functionalized with citrate groups. AuNPs were electrostatically absorbed onto the UCNPs silica shell giving rise to disordered nanoassembly. We employed steady-state and time-resolved fluorescence spectroscopic techniques to analyze the fluorescence quenching of the UCNPs in the presence of AuNPs [2]. We study the effect of the AuNP size and concentration on the upconversion fluorescence quenching. The experimental measurements are supported by numerical analysis based on Finite-Difference-Time-Domain (FDTD) simulations. We find a dependency of the maximum FRET efficiency with the AuNP radius and with bare UCNP quantum efficiency. All these findings allow us to narrow the optimum experimental conditions to maximize the FRET efficiency for biosensing applications. [1] D. Mendez-Gonzalez, M. Laurenti, A. Latorre, A. Somoza, A. Vazquez, A.I. Negredo, E. Lopez-Cabarcos, O.G. Calderon, S. Melle, J. Rubio-Retama, Oligonucleotide sensor based on selective capture of upconversion nanoparticles triggered by target-induced DNA interstrand ligand reaction ACS Appl. Mater. Interfaces. 9, 12272 (2017). [2] L. Zhengquan, L. Wang, Z. Wang, X. Liu, Y. Xiong, Modification of NaYF4:Yb,Er@SiO2 Nanoparticles with Gold Nanocrystals for Tunable Green-to-Red Upconversion Emissions J. Phys. Chem. C 115, 3291 (2011).

Study of shear and flow of soft amorphous materials

Chand, Ram

We study the shear and flow of amorphous solids. We do this using video and confocal microscopy of emulsion samples as they are sheared. An emulsion is a mixture of two different liquids that don’t blend. That usually forms a two phase system. One of the two liquids is dispersed in the mixture, forming the dispersed phase. The other liquid is known as the continuous phase. Dispersed phase consists of the same size of particles (droplets) or different sizes (polydisperse) of particles. Our interest is in highly polydisperse emulsions, where the largest droplets are ten times the radius of the smallest droplets (or more). We follow the motion of droplets in our samples in 2D and 3D as they undergo shear, and quantify their behavior. When a large shear is applied, droplets will be forced to rearrange irreversibly. Our goal is to understand what these rearrangements look like, how they relate to the size of the droplets, and most especially how this depends on the droplet size distribution.

Alternative Plasmonic Materials – Colloid Chemical Synthesis, Characterization and Properties

Dorfs, Dirk

The most famous classes of colloidal plasmonic nanoparticles are still Ag and Au nanostructures. Nevertheless, there are plenty of alternative materials other than elemental metals, which also show plasmonic properties. In this talk, several recently investigated alternative plasmonic materials ranging from degenerately doped semiconductors (e.g. Cu$_{2-x}$Se[1-5] to metallic compounds (e.g. Cu$_{1.1}$S[2] and various nickel sulfides[6-7]) in form of colloidal nanocrystals will be discussed concerning their colloid chemical synthesis and optical properties. It will be shown that the localized surface plasmon resonances (LSPRs) of these particles are capable of covering a wide spectral range (NIR and visible spectral range). Also, multicomponent nanocrystals composed of a combination of these alternative plasmonic materials and traditional metal domains will be presented and discussed.[6-8] 1. Wolf, A.; Hartling, T.; Hinrichs, D.; Dorfs, D., ChemPhysChem 2016, 17 (5), 717-723. 2. Wolf, A.; Kodanek, T.; Dorfs, D., Nanoscale 2015, 7 (46), 19519-19527. 3. Dilena, E.; Dorfs, D.; George, C.; Miszta, K.; Povia, M.; Genovese, A.; Casu, A.; Prato, M.; Manna, L., J. Mater. Chem. 2012, 22 (26), 13023-13031. 4. Scotognella, F.; Della Valle, G.; Kandada, A. R. S.; Dorfs, D.; Zavelani-Rossi, M.; Conforti, M.; Miszta, K.; Comin, A.; Korobcheyskaya, K.; Lanzani, G.; Manna, L.; Tassone, F., Nano Lett. 2011, 11 (11), 4711-4717. 5. Dorfs, D.; Hartling, T.; Miszta, K.; Bigall, N. C.; Kim, M. R.; Genovese, A.; Falqui, A.; Povia, M.; Manna, L., J. Am. Chem. Soc. 2011, 133 (29), 11175-11180. 6. Himstedt, R.; Hinrichs, D.; Dorfs, D., Z. Phys. Chem., 2018, published online, DOI: 10.1515/zpch-2018-1165 7. Himstedt, R.; Rusch, P.; Hinrichs, D.; Kodanek, T.; Lauth, J.; Kinge, S.; Siebbeles, L. D. A.; Dorfs, D., Chem. Mater. 2017, 29 (17), 7371-7377. 8. Wolf, A.; Hinrichs, D.; Sann, J.; Miethe, J. F.; Bigall, N. C.; Dorfs, D., J. Phys. Chem. C 2016, 120 (38), 21925-21931.

Polymer Encapsulation of Perovskites to Obtain Air-Stable Nanocomposites

Dubavik, Aliaksei

The aim of the research is the encapsulation of the perovskite nanocrystals into the polymer and investigation of robust and cost-effective sealing procedures to stabilize the devices for solar cell applications since the degradation mechanisms are mainly related to environmental stability, thermal stability and photo-stability.

Metallic Gel for large-scale application

Georgi, Maximilian

Because of their large specific surface areas and properties that are inferred by the nanomaterials they consist of, metallic aerogels are promising for the use as electrocatalysts, sensors, adsorbers, etc. Noble metal aerogels show excellent catalytic activities in a wide range of reactions. But their availability is limited and their costs are high. That is why the field of interest moves to bimetallic aerogels with only a partial or even no noble metal content. In the most cases the bimetallic compounds show better catalytic activities in comparison to the monometallic ones. One of the big barriers to achieve commercial use of metallic aerogels is their complex handling and the low production quantity. In this work, we present ways to upscale the synthesis of metallic hydrogels to form solvogel-inks for printing. Using techniques like ink-jet or relief printing would reduce the costs and the required energy for the application drastically. In addition, our methods allow the efficient use of the noble metals and the resulting catalysts require no supporting material. The properties of the gel inks made from the solvogels themselves or from dispersed and crushed aerogels are compared. The options to eliminate the supercritical drying step during the processing of the inks are discussed. Moreover, the gels obtained from different synthesis routes in water and organic solvents are compared regarding their structure (specific surface, porosity and metal distribution) and electrocatalytic activity.

Theory of single- and many-particle states in graded CdZnSe nanocrystals

Golovatenko, Aleksandr

We present comparative study of two lowest single-particle states in conventional abrupt "infinite-box" potential usually applied for bare-core CdSe nanocrystals and in smooth parabolic and Gaussian-like potentials reflecting concentration gradient in newly developed CdZnSe nanocrystals with graded structure. In our calculations we take into account complex strucure of the valence subband $\Gamma_8$ and axial assymetry of nanocrystal shape. It is established that in smooth potentials energy spacing between two lowest hole states, as well as the sign of anisotropic splitting of these states is drastically different for abrupt and smooth potentials. For smooth potentials results obtained by variational approach are in a good agreement with direct numerical calculations, so that chosen trial wavefunctions can be applied by other researchers. Using solutions of single-particle problem we calculate energies of excitons and biexcitons taking into account inter-perticle correlations in the frame of varitional approach. We consider biexciton states with different configuration of hole energy states, as well as with different total angular momentum of two holes. Calculated values of the biexction binding energy are in a good agreement with results obtained by other approaches (tight-binding and pseudopotential methods). Drop of the biexction binding energy with increase of nanocrystal diameter is more pronounced for the abrupt potential.

Investigation of semiconductor nanocrystals be MCD spectroscopy

Gromova, Yulia

Optical properties of colloidal nanocrystals were investigated by magnetic circular dichroism spectroscopy (MCD). The main attention was paid to the investigation of size dependencies of MCD signal in CdSe/ZnS. The physical model for observed phenomena is proposed. The MCD in the colloidal CdS nanoplatelets also was investigated.

Influencing noble metal aerogel structures

Hiekel, Karl

Noble metal aerogels combine high selectivity, conductivity and corrosion resistance with large inner surface area in a porous network. Respectively, these materials show a great potential in different applications, e.g. electrocatalysis, fuel cells.[1,2] Up until now, there is no general model about the influencing factors of the gel morphology. In this account, we investigate possibilities how to affect the structure of pure gold and silver aerogels and to fine-tune them for their respective applications. The gel morphology depends obviously on the initial particle size and on the number of branching events per volume. The particle size can be influenced by the ratio of reducing agent to metal salt precursor and other factors. The branching depends on the electrostatic stability of the particles accompanied by the surface charge. This can be affected by the addition of ancillary ions or by replacing the solvent.[3] Newest results from our Dresden team will be incorporated to show further ways in influencing the gel morphology. In this work, we focus on how to influence the gel structure, especially the web thickness and homogeneity by changing the reaction conditions. The focus will lie on altering the solvent, the ratio and concentration of the used compounds, and other terms. In this manner, we gain insights into the morphology control and branching for producing custom-made pure gold and silver aerogels. The authors acknowledge financial support from the AEROCAT ERC-grant no. 340419. [1] F. Rechberger, M. Niederberger, Nanoscale Horiz. 2017, 2, 1–66. [2] W. Liu, D. Haubold, B. Rutkowski, M. Oschatz, R. Hübner, M. Werheid, C. Ziegler, L. Sonntag, S. Liu, Z. Zheng, et al., Chem. Mater. 2016, 28, 6477–6483. [3] H. Zhang, D. Wang, Angew. Chemie - Int. Ed. 2008, 47, 3984–3987.

Gold Nanorods - Metal Oxide Gel Composites as SERS-Substrates

Klemmed, Benjamin

B. Klemmed, A. Benad, C. Ziegler, A. Eychmüller Physical Chemistry, Technische Universität Dresden, Bergstraße 66b, 01062 Dresden, Germany To answer new and upcoming analytical questions, the development of sensitive and precise analytical methods is highly demanded. Raman spectroscopy is a selective and non-invasive method to characterize a wide range of materials. An enhancement of the detection limit over several orders of magnitude can be reached by applying the SERS technique. Typically, plasmonic nanoparticles based on gold or silver act as amplifiers and are deposited on glass or other substrates. However, a reproducibility of signals seems to be difficult due to non-homogenous substrate surfaces. To overcome this deficit, we focused on new composites based on plasmonic particles, here gold nanorods (AuNR), and metal oxide gels (zinc oxide and aluminum oxide). Our facile one-pot synthesis leads to well-distributed gold particles within the oxide matrices. Moreover these materials are easy to handle and can be coated on various surfaces. The resulting gel composite ties advantages of both, SERS active AuNRs and a macroscopic body. Static tests with Rhodamine 6G (Rh6G) solutions were carried out to evaluate the quality of the substrates regarding the signal enhancement and reproducibility of the signals, respectively. The obtained results exhibit a significant signal enhancement of several orders of magnitude, which enables measurements down to ppm concentrations. Furthermore, we obtained a remarkably low signal intensity variation of less than 10 $\%$ for all measured positions on the aerogel, which is in accordance with the well-distributed AuNR throughout the matrix. Moreover, we studied transport processes in these new porous composite materials by following the SERS signal of an analyte (Rh6G) in a flow cell setup. Therefore, we tracked the analyte transport into and out of the meso- /macroporous gel structures using the prominent Raman signal of Rh6G at 1510 $cm^{-1}$. Afterwards kinetic data were sub-divided in adsorption, desorption as well as diffusion processes and evaluated by the model of Karlsson et al.[1] In this regard, the kinetics seems to be strongly connected to the type of gel matrix. For instance, the highly porous structure of alumina aerogels leads to a slower adsorption in comparison to ribbon-like and more open-pore zinc oxide. Hence, this approach allows us to characterize the behaviour between gels and adsorbates in further applications like catalysis and photo catalysis. Literature: [1] J. Karlsson, International Journal of Nanomedicine 2015, 10, 4425–4436.

Effects of Coulomb interaction on wave packet dynamics in semiconductor heterostructures

Lengers, Frank

The progress in spatially focused ultrafast measurements, e.g. by near field tips or plasmonic nanostructures, opens up ways to study carrier dynamics on extremely small scales in space and time. The spatio-temporal dynamics of the excited localized wave packets can be crucial for fundamental physical processes like e.g. carrier capture [1]. While often the low-density case is considered, we here focus on the excitation of a strongly localized few-carrier system. At this excitation condition the Coulomb interaction plays a crucial role in the wave packet dynamics. To study this, we here simulate carrier dynamics in a GaAs quantum wire resulting from a strong spatially focused ($\approx$ 10 nm) optical pulse. Restricting ourselves to a system with maximally two excited electron-hole pairs due to the strong spatial localization, we can formulate a wave function approach treating the carrier-carrier correlations exactly for this system. We compare our results with a Hartree-Fock description of the same system within a density matrix approach and can thereby directly point out the correlation contribution to the spatio-temporal dynamics. We find that depending on the excitation power the optical excitation results in the creation of a mixture of excitonic wave packets and independent electron wave packets travelling along the wire. [1] R. Rosati, D. E. Reiter, and T. Kuhn, Phys. Rev. B 95, 165302 (2017)

Stabilization of Highly Expansive Black Cotton Soils by Means of Geopolymerization

Miao, Shiding

This presentation provides a method of geo-polymerizing a type highly expansive soil, black cotton soil (BCS), to ascertain its performance in the subgrade application. The raw BCS is unsuitable for pavement due to its swelling characteristics and strength weakness. Herein, alkalis of Ca(OH)2 and KOH were used to stabilize BCS, and geopolymers were produced. Parameters including Atterberg limits, maximum dry density (MDD), optimum moisture content (OMC), unconfined compressive strength (UCS) and swelling percentages were tested. The combination use of volcanic ashes and alkalis was found to reduce the plasticity index from 28% to ~16.8%. KOH were found to be more efficient in solidifying the BCS than Ca(OH)2. The swelling percentage of raw BCS decreases from 15.7% to 2.3~4.2% after this treatment. The mechanical strength was observed to have an increasing trend during the curing periods, and the UCS reaches 16.55 MPa after 90 days. Characterizations including XRD, TEM and IR analyses were used to reveal the mineralogical transitions during the geopolymerization, and a two-stage reaction mechanism was proposed.

New Generation Electrode Materials from Porous Carbon of Bacterial Cellulose/Polyacrylonitrile Composite

Nandi, Mahasweta

Activated carbon monolith with a network of co-continuous porous structure has been fabricated by carbonization of bacterial cellulose-polyacrylonitrile (PAN) composite monolith by physical activation in presence of CO2.1 Bacterial cellulose gel (BC) is synthesized by static culture process at the interface between air and medium by cellulose-producing bacteria, Gluconacetobacter xylinus. The solvent-exchanged BC gel is incorporated into PAN solution by a simple and versatile method involving a combination of thermally induced phase separation2 and solvent substitution to obtain the composite monolith. Unique morphologies are observed for the BC gel, the top view showed a uniform network of fibrous structure whereas the side view displayed a layered structure. Such interesting morphological feature is propagated to the composite monolith and is restored even in the activated carbon which is obtained by high temperature synthetic route. The BC nanofibers are found to remain entwined throughout the porous skeleton of the entire PAN backbone and such cross-linking helps in retaining the continuity of the matrix even after carbonization. Thus, the grain boundary impedance for electrical conduction of the composite is very small due to orientation of the tabular grains even without the addition of any external binding agent. Cyclic voltammetry shows that these activated carbons with large specific surface area and high microporosity are excellent electrode materials in electric double layer capacitors3 (EDLC) with capability of high-speed charging and discharging. Thus, these activated monoliths can be used as high performance electrode material for capacitors which can function even without the addition of a conductive auxiliary agent.

Multicompound Gel Networks of Nanoparticles for Photoelectrochemical Applications

Rosebrock, Marina

Nanoparticles are well researched compounds with controllable size[1] and shape[2]. A large number of materials is suitable for nanoparticle synthesis with bottom up methods. The difference of properties between nanoparticles and their bulk material leads to interesting phenomena like sizedepending band gaps[3]. Accordingly, nanoparticles are part of a large research area. As a strategy for use of nanoparticles to form self-supporting superstructures, a gelation process is appropriate. A big improvement of material properties is the combination of different materials on the nanoscale. For this objective, a multicompound superstructure system of semiconductor and metal nanoparticles provides application-oriented properties. The main fields of application are photoconducting systems and photocatalysis. By illumination of the semiconductor compound an exciton is generated. The contact to a metal compound will force the electron to go to the metal domain while the hole is fixed to the semiconductor. A charge carrier separation occurs and can be used for oxidation (hole) and reduction (electron). The above-mentioned system is composed of CdSe/CdS nanorods and noble metal nanoparticles as two different compounds in a gel network. [1] Jana, N. R., Gearheart, L., & Murphy, C. J. (2001). Seeding growth for size control of 5-40 nm diameter gold nanoparticles. Langmuir, 17(22), 6782–6786 [2] Peng, X., Manna, L., Yang, W., Wickham, J., Scher, E., Kadavanich, A., & Alivisatos, A. P. (2000). Shape control of CdSe nanocrystals. Nature, 404(6773), 59–61 [3] Brus, L. E. (1984). Electron-electron and electron-hole interactions in small semiconductor crystallites: The size dependence of the lowest excited electronic state. The Journal of Chemical Physics, 80(9), 4403–4409

Silica shell growth around CdSe/CdS nanorod aerogels

Rusch, Pascal

A gelation as the assembly of nanoparticles into network structures gels is a promissing approach to immobilization of said particles. For a potential applications in electrochemisty, catalysis and sensing this immobilization is often needed. An important advantage of gel formation is the preservation of the nanoscopic properties of the particle building blocks such as fluorescence and their high surface to volume ratio. Additionally new properties exclusive to the gel can be introduced as our group was able to show. One problem of nanoparticle gels is their mechanical stability. An additional modification step after the gel preparation can be a way to address this problem and furthermore introduce new functionalities into the material. Contrary to other methods the particles are not embedded in a silica matrix but the initial nanoparticle network is encased in a silica shell. This new material is evaluated regarding optical and structural properties and its mechanical strength.

Plasmonics-Metallic Nanoparticles For Solar Cell Structure Models

Shabat, Mohammed

Solar cells convert visible light to electricity. It is one of the clean sources of energy. Plasmonics-Metallic nanoparticles have fascinated scientist for over a century and are now heavily utilized in solar cell devices. They are a focus of interest because of their huge potential in nanotechnology. The presence of nanoparticles in solar cells is to improving the efficiency of solar cells. In this paper, we investigated the transmission, reflection and absorption coefficients of different incident angles of light in visible light (300nm – 1100nm). A design structure for solar cell is containing four layers. The layers are placed respectively Air, SiN, Metallic two nanoparticles; Ag and Au; and substrate SiO2. The numerical results have been obtained by MAPLE program.

The effect of gold nanorods on luminescence of quantum dots in electrostatic complexes

Trotsiuk, Liudmila

Quantum dots (QDs) find wide application in different areas particularly in the producing of LEDs, solar cells, TV displays, as well as in biomedical diagnostics. Therefore, the study of improving their properties is in focus of many scientific groups. Plasmon-enhanced luminescence allows increasing the sensitivity of diagnostic methods and improving the luminescent characteristics of different optical devices. It is known, that the incident light induces in metal nanoparticles the collective oscillations of conductive band electrons called plasmons, which create their own localized strong electromagnetic field around a nanoparticle. This field enhances by several orders of magnitude such effects as the Raman scattering and photoluminescence of analytes near nanoparticle surface. In this regard, gold nanorods (NRs) are of great interest because of the presence of two (transversal and longitudinal) plasmon resonances. AuNRs have the advantage over spherical nanoparticles due to the tunable longitudinal plasmon band. In this work, we studied the effect of AuNRs and the thickness of their dielectric shell as well as the QD concentration on the luminescence intensity of QDs. Aqueous solutions of AuNR-QD electrostatic complexes were prepared using layer-by-layer technique with 0, 2 and 4 polyelectrolyte layers as dielectric spacer. Luminescence enhancement was observed only in complexes with low amount of QDs and in the presence of PE shell on the gold surface. The absence of spacer led to the strong quenching of QD luminescence, probably, because of the nonradiative energy transfer.