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Journal of synchrotron radiation 28(3), 812-823 (2021). doi:10.1107/S1600577521003404, Small-angle X-ray scattering (SAXS) is an established method for studyingnanostructured systems and in particular biological macromolecules in solution.To obtain element-specific information about the sample, anomalous SAXS(ASAXS) exploits changes of the scattering properties of selected atoms whenthe energy of the incident X-rays is close to the binding energy of their electrons.While ASAXS is widely applied to condensed matter and inorganic systems, itsuse for biological macromolecules is challenging because of the weak anomalouseffect. Biological objects are often only available in small quantities and areprone to radiation damage, which makes biological ASAXS measurements verychallenging. The BioSAXS beamline P12 operated by the European MolecularBiology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg)is dedicated to studies of weakly scattering objects. Here, recent developmentsat P12 allowing for ASAXS measurements are presented. The beamline control,data acquisition and data reduction pipeline of the beamline were adaptedto conduct ASAXS experiments. Modelling tools were developed to computeASAXS patterns from atomic models, which can be used to analyze the data andto help designing appropriate data collection strategies. These developments areillustrated with ASAXS experiments on different model systems performed atthe P12 beamline., Published by Wiley-Blackwell, [S.l.]

Hot electrons in metal nanoparticles thermalize with the lattice via electron–phonon coupling. Size dependency is controversially discussed in literature. Here we investigate poly- and monocrystall...

Photocatalysis based on plasmonic nanoparticles has emerged as a promising approach to facilitate light-driven reactions under far milder conditions than thermal catalysis. Several effects, such as strong local electromagnetic fields, increased electron and lattice temperatures, or the transfer of nonthermal charge carriers, could contribute to the reaction rate enhancement. In order to understand plasmon-enhanced catalysis and to enable plasmonic platforms, a distinction between the different underlying effects is required. We investigate the electrochemical model reactions oxidative hydroxide adsorption and glucose oxidation and deconvolve the enhancement processes via their dependence on the excitation wavelength. We observe that nonthermal effects contribute significantly to the plasmonic enhancement.

Journal of applied crystallography 52(4), 777 - 782 (2019). doi:10.1107/S1600576719007568, An X-ray cross-correlation study of the local orientational order in self-assembled films made from PEGylated gold nanoparticles is presented. The local structure of this model system is dominated by four- and sixfold order. Coadsorption of shorter ligands in the particle's ligand layer and variation of salt concentration in the suspension prior to self-assembly result in a change of local orientational order. The degree of sixfold order is reduced after salt addition. This decrease of order is less pronounced for the fourfold symmetry. The results presented here suggest complex symmetry-selective order formation upon ligand exchange and salt addition and demonstrate the versatility of X-ray cross-correlation methods for nanoparticle superlattices., Published by IUCr, Chester

The new European Emission Standard Euro 6d will limit the particulate number emissions under real driving conditions for gasoline engines, and meeting these new requirements will be quite challenging for modern direct-injection spark ignition (DISI) engines. In these engines, the source of soot particles are fuel rich zones above fuel films resulting from spray impingement onto the piston and the cylinder wall. To reduce these exhaust emissions, the deposition of fuel wall films must be minimized, or ideally avoided. In order to do this, the formation behaviour of fuel films has to be studied and understood. The present paper aims at providing a broad overview over factors influencing the fuel wall film formation, this paper merges the results of four fuel wall film measurement campaigns. This way it is possible to present the influence of different important parameters on film formation, including ambient pressure and temperature, rail pressure, fuel temperature, nozzle/wall distance and spray impingement angle. To measure the wall film patterns, masses and areas the method of laser-induced fluorescence was applied. The measurements were performed using iso-octane, with 3-pentanone dissolved as fluorescence tracer. For the spray generating a high-pressure, six-hole nozzle was used. The acquired results show that with increasing initial fuel temperature, surrounding temperature, rail pressure and nozzle/wall distance, the wall film mass decreases. Increasing ambient pressure – up to values representative for turbo- or super charging – was found to increase the film mass. Additionally, flatter impingement angles increase the wall film area but decreases the total fuel film mass. With the results provided in this paper, the effects of several major engine operating parameters on fuel wall film formation are quantified.

In this study, a highly responsive humidity sensor is developed by printing gold nanoparticles (GNPs) grafted with a hygroscopic polymer. These GNPs are inkjet-printed to form a uniform thin film over an interdigitated electrode with a controllable thickness by adjusting the printing parameters. The resistance of the printed GNP thin film decreases significantly upon exposure to water vapor and exhibits a semi-log relationship with relative humidity (RH). The sensor can detect RH variations from 1.8 to 95% with large resistance changes up to 4 orders of magnitude with no hysteresis and small temperature dependence. In addition, with a small thickness, the sensor can reach absorption equilibrium quickly with response and recovery times of ≤1.2 and ≤3 s, respectively. The fast response to humidity changes also allows the GNP thin-film sensor to distinguish signals from intermittent humidification/dehumidification cycles with a frequency up to 2.5 Hz. The printed sensors on flexible substrates show little sensitivity to bending deformation and can be embedded in a mask for human respiratory detection. In summary, this study demonstrates the feasibility of applying printing technology for the fabrication of thin-film humidity sensors, and the methodology developed can be further applied to fabricate many other types of nanoparticle-based sensor devices.

Spray tools with multi-nozzle-arrays are used in a wide variety of applications. Monitoring the functionality of complex spraying tools with a large number of individual nozzles is a great challenge. For this purpose, we have developed a measurement technique based on the wetting pattern, which forms on a surface during spray impingement. To investigate the performance of this measurement technique we applied a spraying tool with nine external mixing air-water nozzles, the geometric alignment of which can be freely adjusted. In the first test series, the precision of the evaluation of the nozzle alignment is determined. The second test series focuses on the individual sizes of the wetted areas. Here the reproducibility, the influences of the operating modes and the nozzle type were evaluated. Subsequently, the functionality is tested in an exemplary test case in which two of nine nozzles were readjusted in a defined manner. Finally, the wetting pattern resulting from injecting a full spray is discussed and the necessary image processing steps are provided. In summary, this measuring system allows efficient, fast and cost-effective control and documentation of the alignment and functionality of spraying tools, thereby avoiding production downtime and related costs.

Surface-enhanced vibrational spectroscopy strongly increases the cross section of Raman scattering and infrared absorption, overcoming the limited sensitivity and resolution of these two powerful analytic tools. While surface-enhanced setups with maximum enhancement have been studied widely in recent years, substrates with reproducible, uniform enhancement have received less attention although they are required in many applications. Here, we show that plasmonic supercrystals are an excellent platform for enhanced spectroscopy because they possess a high density of hotspots in the electric field. We describe the near field inside the supercrystal within the framework of plasmon polaritons that form due to strong light-matter interaction. From the polariton resonances we predict resonances in the far-field enhancement for Raman scattering and infrared absorption. We verify our predictions by measuring the vibrations of polystyrene molecules embedded in supercrystals of gold nanoparticles. The intensity of surface-enhanced Raman scattering is uniform within 10% across the crystal with a peak integrated enhancement of up to 300 and a peak hotspot enhancement of 105. The supercrystal polaritons induce pairs of incoming and outgoing resonances in the enhanced cross section as we demonstrate experimentally by measuring surface-enhanced Raman scattering with multiple laser wavelengths across the polariton resonance. The infrared absorption of polystyrene is likewise enhanced inside the supercrystals with a maximum enhancement of 400%. We show with a coupled oscillator model that the increase originates from the combined effects of hotspot formation and the excitation of standing polariton waves. Our work clearly relates the structural and optical properties of plasmonic supercrystals and shows that such crystals are excellent hosts and substrates for the uniform and predictable enhancement of vibrational spectra.

Optica 8(1), 15 - 23 (2021). doi:10.1364/OPTICA.410851, Single particle imaging at x-ray free electron lasers (XFELs) has the potential to determine the structure and dynamics of single biomolecules at room temperature. Two major hurdles have prevented this potential from being reached, namely, the collection of sufficient high-quality diffraction patterns and robust computational purification to overcome structural heterogeneity. We report the breaking of both of these barriers using gold nanoparticle test samples, recording around 10 million diffraction patterns at the European XFEL and structurally and orientationally sorting the patterns to obtain better than 3-nm-resolution 3D reconstructions for each of four samples. With these new developments, integrating advancements in x-ray sources, fast-framing detectors, efficient sample delivery, and data analysis algorithms, we illuminate the path towards sub-nanometer biomolecular imaging. The methods developed here can also be extended to characterize ensembles that are inherently diverse to obtain their full structural landscape., Published by OSA, Washington, DC

Particle & particle systems characterization 38(9), 2100087 (2021). doi:10.1002/ppsc.202100087, Self-assembly of nanoparticles (NPs) has evolved into a powerful tool for the synthesis of superstructures with tailored properties. The quality, diversity, and complexity of synthesized structures are continuously improving and fascinating new collective properties are demonstrated. At the same time, the rapid development of electron microscopy and synchrotron sources for X-rays has enabled new exciting experimental approaches to study structure and structure formation in the context of NP self-assembly. In this review, some recent studies and what can be learned from them are highlighted and discussed. It is started with a general introduction covering important concepts, experimental approaches, commonly obtained structures, the ideas of artificial atoms, and emerging properties are discussed. Recent experimental in situ and ex situ approaches with state-of-the-art electron microscopy and X-ray diffraction and scattering that helped to obtain a detailed picture of NP self-assembly processes and resulting structures are then presented., Published by Wiley-VCH, Weinheim

Soft matter 16(11), 2864-2872 (2020). doi:10.1039/C9SM02230A, We investigate the out-of-equilibrium dynamics of a colloidal gel obtained by quenching a suspension of soft polymer-coated gold nanoparticles close to and below its gelation point using X-ray Photon Correlation Spectroscopy (XPCS). A faster relaxation process emergent from the localized motions of the nanoparticles reveals a dynamically-arrested network at the nanoscale as a key signature of the gelation process. We find that the slower network dynamics is hyperdiffusive with a compressed exponential form, consistent with stress-driven relaxation processes. Specifically, we use direction-dependent correlation functions to characterize the anisotropy in dynamics. We show that the anisotropy is greater for the gel close to its gelation point than at lower temperatures, and the anisotropy decreases as the gel ages. We quantify the anisotropic dynamical heterogeneities emergent in such a stress-driven dynamical system using higher order intensity correlations, and demonstrate that the aging phenomenon contributes significantly to the properties evaluated by the fluctuations in the intensity correlations. Our results provide important insights into the structural origin of the emergent anisotropic and cooperative heterogeneous dynamics, and we discuss analogies with previous work on other soft disordered systems., Published by Royal Soc. of Chemistry, London

Nature Communications 11, 3821 (2020). doi:10.1038/s41467-020-17632-4, The assembly of plasmonic nanoparticles into ordered 2D- and 3D-superlattices could pave the way towards new tailored materials for plasmonic sensing, photocatalysis and manipulation of light on the nanoscale. The properties of such materials strongly depend on their geometry, and accordingly straightforward protocols to obtain precise plasmonic superlattices are highly desirable. Here, we synthesize large areas of crystalline mono-, bi- and multilayers of gold nanoparticles >20 nm with a small number of defects. The superlattices can be described as hexagonal crystals with standard deviations of the lattice parameter below 1%. The periodic arrangement within the superlattices leads to new well-defined collective plasmon-polariton modes. The general level of achieved superlattice quality will be of benefit for a broad range of applications, ranging from fundamental studies of light–matter interaction to optical metamaterials and substrates for surface-enhanced spectroscopies., Published by Nature Publishing Group UK, [London]

CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior FINEP - Financiadora de Estudos e Projetos, Financiadora de Estudos e Projetos Tip-enhanced Raman spectroscopy (TERS) has reached nanometer spatial resolution for measurements performed at ambient conditions and subnanometer resolution at ultrahigh vacuum. Super-resolution (beyond the tip apex diameter) TERS has been obtained mostly in the gap mode configuration, where a conductive substrate localizes the electric fields. Here we present experimental and theoretical TERS to explore the field distribution responsible for spectral enhancement. We use gold tips of 40 ± 10 nm apex diameter to measure TERS on graphene, a spatially delocalized two-dimensional sample, sitting on different substrates: (i) glass, (ii) a thin layer of gold and (iii) a surface covered with 12 nm diameter gold spheres, for which 6 nm resolution is achieved at ambient conditions. The super-resolution is due to the field configuration resulting from the coupled tip-sample-substrate system, exhibiting a nontrivial spatial surface distribution. The field distribution and the symmetry selection rules are different for nongap versus gap mode configurations. This influences the overall enhancement which depends on the Raman mode symmetry and substrate structure.

One important parameter influencing mixture formation and spray/wall interaction within engines is the geometry of the nozzle. In contrast to Diesel nozzles, the influence of the orifice geometry on spray formation has hardly be investigated for gasoline nozzles. In order to demonstrate the potential of adjusting the nozzle geometry of a modern GDI nozzle, we compare two six-hole, high-pressure nozzles with an identical structure, but different rounding radius of the orifice hole-inlet and different orifice hole-geometries: nozzle A with a rounded inlet and an orifice length to diameter ratio of 3/2 and nozzle B with a sharp inlet and an orifice length to diameter ratio of 1. In a first measurement campaign the spray formation is visualized using high-speed shadowgraphy imaging. The results show differences in spray angle and penetration depth. In a second measurement campaign we examine the spray/wall interaction and wall film formation by means of infrared thermography. The thermography measurements indicate that the geometry of nozzle B produces sprays with beneficial characteristics. This is very important for a clean combustion process and a decrease of soot emissions.

The variety of fuels used in GDI engines is constantly increasing. This affects the combustion process because the spray formation and the mixture preparation is greatly influenced by the fuel properties. In particular, the reduction of the saturation temperature is promoting the so-called flash-boiling effect, when the bulk liquid or a component of the fuel mixture becomes superheated during the injection into the low-pressure combustion chamber. This study reveals the enormous influence of flash-boiling on the spray/wall interaction and the consequent deposition of fuel wall films. This is of major importance because the formation of wall films must be avoided, since they are the main route to soot particle emissions. In order to increase the understanding of the wall film formation the spray/wall interaction is investigated under conditions representative of a homogeneously charged gasoline engine. Gasoline and iso-octane are injected using a modern six-hole nozzle. Emphasis is placed on the influence of the initial fuel temperature. Using high-speed imaging and infrared thermography, the spray propagation, the spray-targeting and the evaporation duration of the wall films are analysed. It is found that increasing the fuel temperature does not lead to a constant reduction of the wall film problem. Rather, the flash-boiling-induced ‘contraction’ of the spray leads to an accumulation of the wall film mass in a small area. This delays the evaporation process to a great extent and can lead to increased soot particle emissions. From the results, a critical value of the degree of superheat is identified and the findings transferred to various single component fuels, in order to avoid undesired fuel film accumulation.

The decay of a plasmon leads to a hot electron distribution in metallic nanoparticles. Depending on the processes involved in the excitation, different distributions are obtained, which thermalize differently. We experimentally investigate excitation-wavelength and size-dependences on the generation and thermalization of the hot-electrons. We can confirm the absence of size-dependences, and we clearly observe two regimes with significantly different relaxation dynamics depending on the photon energy. The hot electron generation is more efficient when exciting with light that enables interband transitions.

An ideal plasmonic system for hot-electron generation allows the optical excitation of plasmons, limits radiation losses, exhibits strong non-radiative electron damping, and is made from scalable and cost-effective materials. Here we demonstrate the optical excitation of dark interlayer plasmons in bilayers of colloidal gold nanoparticles. This excitation is created by an antiparallel orientation of the dipole moments in the nanoparticle layers; it is expected to exhibit strongly reduced radiative damping. Despite the vanishing dipole moment, an incoming electromagnetic wave that is propagating normal to the surface will excite the dark mode due to field retardation. We observe a strong peak in the absorption spectrum of a colloidal gold bilayer (nanoparticle diameter = 46 nm); this peak is absent for a nanoparticle monolayer. The full width at half maximum of the dark mode is 230 meV for an ideal nanoparticle crystal and 320 meV for the structure produced by self-assembly out of solution. The position and width of the dark plasmon are efficiently tailored by the interparticle distance within the layer, nanoparticle size and layer number. We present time-resolved pump and probe experiments of hot-electron generation by bright and dark bilayer nanoparticle modes.

The journal of physical chemistry / C C, Nanomaterials and interfaces 123, 29994-30000 (2019). doi:10.1021/acs.jpcc.9b08173, We demonstrate the pressure-induced formation of supercrystalsmade from PEGylated gold nanorods (NRs) in aqueous suspension.Utilizing the combined effect of hydrostatic pressure and salt on the solubilityof the organic poly(ethylene glycol) (PEG) shell that passivates the NRs, thereversible formation of two-dimensional hexagonal supercrystals has beenobserved by means of small-angle X-ray scattering. The pressure dependenceof the crystal lattice’s structural parameters is determined. By time-resolvedmeasurements performed after a pressure jump, the growth process of thecrystals is found to be completed already after a few seconds. The presented results demonstrate that by PEGylatingnanoparticles, pressure-induced homogeneous supercrystals can be formed for different particle shapes, in particular, anisotropicNRs, which determine the resulting lattice type., Published by Soc., Washington, DC

Physical chemistry, chemical physics 21(38), 21349 - 21354 (2019). doi:10.1039/C9CP04658E, Colloidal nanocrystals (NC) are known to self-organize into superlattices that promise many applications ranging from medicine to optoelectronics. Recently, the formation of high-quality PEGylated gold NC was reported at high hydrostatic pressure and high salt concentrations. Here, we study the formation kinetics of these superlattices after pressure jumps beyond their crystallisation pressure by means of small-angle X-ray scattering with few ms experimental resolution. The timescale of NC formation was found to be reduced the larger the width of the pressure jump. This is connected to an increase of crystal quality, i.e., the faster the NC superlattice forms, the better the crystal quality. In contrast to the formation kinetics, the melting of the NC superlattice is approximately one order of magnitude slower and shows linear kinetics., Published by RSC Publ., Cambridge

We studied the aggregation of AuNP induced by small aromatic molecules under different conditions. In water, the aggregation was found to be difficult to control. Phase transfer of the particles into toluene by using oleylamine as a ligand allows for a more controlled and reliable synthesis. Using nonane-1,9-dithiol as a control, our experiments demonstrate that the molecular structure of the linker has a decisive influence on the aggregation. Aromatic dithiols yielded spherical aggregates in the range of 100 nm, whereas the aliphatic linker produced large aggregates in the µm range. The length of the aromatic linker (2 vs. 3 phenylene units) strongly affected aggregation kinetics and the structure of the produced aggregates. With UV/Vis and DLS based experiments it was possible to distinguish the process of ligand layer formation and aggregation. Our results will help to develop syntheses of defined spherical aggregates and possibly more complex structures.

The combustion of gasoline in modern homogeneously operated DISI engines can result in soot particles and unburned hydrocarbons. One major source for these pollutants is the delayed evaporation of fuel wall films resulting from the impingement of the fuel spray onto cylinder walls or the piston, especially during warm-up when the walls have not yet reached operating temperatures and for early injection timings when the piston is still close to the injector. To reduce exhaust emissions and fuel consumption the behaviour of fuel films must be understood. This paper provides new findings of the influence of different boundary conditions on the wall film mass. In order to provide constant and defined boundary conditions, measurements were performed inside a pressure vessel. To reflect the wide range of operating conditions during the injection within an homogeneously charged engine, the vessel pressure, vessel temperature, rail pressure and distance between nozzle and wall were varied. The wall film patterns and masses were measured using the non-invasive method of laser-induced fluorescence. The spray was generated by a standard high-pressure, six-hole nozzle. Iso-octane was used as non-fluorescing surrogate fuel with 3-pentanone added as a well-characterised fluorescence tracer. It was found that with increasing surrounding temperature and increasing distance between nozzle and wall, the wall film mass decreases. Contrary to general assumptions, higher cylinder pressure, e.g. due to turbocharging, was found to increase fuel deposits. Higher rail pressures do not have a positive effect at low cylinder pressures but under turbocharged conditions the wall film mass can be reduced by increasing the rail pressure.

Advanced materials interfaces 7(19), 1-9 (2020). doi:10.1002/admi.202000919, Supercrystals composed of plasmonic nanoparticles constitute a promising material platform for tailored light‐matter interactions. The optimization of their optical properties requires precise syntheses and a detailed structural characterization that addresses not only the basic geometrical parameters but also the degree of order. Herein, plasmonic supercrystals with a well‐defined layered structure are studied by a combined transmission electron microscopy, small‐angle X‐ray scattering and X‐ray cross‐correlation analysis (TEM‐SAXS‐XCCA) approach. It is demonstrated that scanning small‐angle x‐ray scattering (SAXS) data can unambiguously be assigned to the number of crystalline layers by comparison with complementary transmission electron microscopy (TEM) experiments on the same regions of interest. A small but significant increase of the lattice constant with increasing number of layers and a high degree of orientational order irrespective of the number of layers is found. This points to specifics of the supercrystal formation mechanism that could be utilized to improve the control of self‐assembly for supercrystal geometries with subnanometer precision., Published by Wiley-VCH, Weinheim

Scientific reports 8(1), 16561 (2018). doi:10.1038/s41598-018-34925-3, Accurate in vivo localisation of minimal amounts of functionalised gold-nanoparticles, enabling e.g. early-tumour diagnostics and pharmacokinetic tracking studies, requires a precision imaging system offering very high sensitivity, temporal and spatial resolution, large depth penetration, and arbitrarily long serial measurements. X-ray fluorescence imaging could offer such capabilities; however, its utilisation for human-sized scales is hampered by a high intrinsic background level. Here we measure and model this anisotropic background and present a spatial filtering scheme for background reduction enabling the localisation of nanoparticle-amounts as reported from small-animal tumour models. As a basic application study towards precision pharmacokinetics, we demonstrate specific localisation to sites of disease by adapting gold-nanoparticles with small targeting ligands in murine spinal cord injury models, at record sensitivity levels using sub-mm resolution. Both studies contribute to the future use of molecularly-targeted gold-nanoparticles as next-generation clinical diagnostic and pharmacokinetic tools., Published by Springer Nature, [London]

We demonstrate the excitation of dark plasmon modes with linearly polarized light at normal incidence in self-assembled layers of gold nanoparticles. Because of field retardation, the incident light field induces plasmonic dipoles that are parallel within each layer but antiparallel between the layers, resulting in a vanishing net dipole moment. Using microabsorbance spectroscopy we measured a pronounced absorbance peak and reflectance dip at 1.5 eV for bi- and trilayers of gold nanoparticles with a diameter of 46 nm and 2 nm interparticle gap size. The excitations were identified as dark interlayer plasmons by finite-difference time-domain simulations. The dark plasmon modes are predicted to evolve into standing waves when further increasing the layer number, which leads to 90% transmittance of the incident light through the nanoparticle film. Our approach is easy to implement and paves the way for large-area coatings with tunable plasmon resonance.

The journal of physical chemistry letters 2018(9), 4720 − 4724 (2018). doi:10.1021/acs.jpclett.8b02145, Nanoparticles can self-organize into “supercrystals” with many potential applications. Different paths can lead to nanoparticle self-organization into such periodic arrangements. An essential step is the transition from an amorphous state to the crystalline one. We investigate how pressure can induce a phase transition of a nanoparticle model system in water from the disordered liquid state to highly ordered supercrystals. We observe reversible pressure-induced supercrystal formation in concentrated solutions of gold nanoparticles by means of small-angle X-ray scattering. The supercrystal formation occurs only at high salt concentrations in the aqueous solution. The pressure dependence of the structural parameters of the resulting crystal lattices is determined. The observed transition can be reasoned with the combined effect of salt and pressure on the solubility of the organic PEG shell that passivates the nanoparticles., Published by ACS, Washington, DC

Particle & particle systems characterization 35(2), 1700319 (2018). doi:10.1002/ppsc.201700319, Ligand-layer structure and stability of gold nanoparticles (AuNP) coated with α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) layers and mixed layers of PEGMUA and 11-mercaptoundecanoic acid (MUA) at high AuNP concentrations are studied in situ by small-angle X-ray scattering (SAXS). The thickness of the ligand layer is modified by the molecular weight of the PEG-ligands (2 and 5 kDa), and the PEG-grafting density is decreased by coadsorption of MUA. The response of the conjugates to a pressure of up to 4 kbar is probed. The results indicate strongly hydrated PEG layers at high grafting densities. The stability of the mixed ligand-layer conjugates is lower. This is most probably due to enhanced interparticle PEG–PEG interactions at lower grafting densities. The presented study demonstrates that a detailed structural characterization of polymer ligand layers in situ and in response to external stimuli is possible with SAXS., Published by Wiley-VCH, Weinheim

We present a route for the functionalization of gold nanoparticles (AuNP) based on phase transfer functionalization in order to optimize the stability and the potential for self-assembly. Depending on the desired size, different ligand exchanges have to be employed: The maximum AuNP size that can be stabilized without concentration loss is 46 nm for polystyrene-based ligands with 5 and 10 kDa. Small particles

The use of mixed ligand layers including poly(ethylene glycol)-based ligands for the functionalization of nanoparticles is a very popular strategy in the context of nanomedicine. However, it is challenging to control the composition of the ligand layer and maintain high colloidal and chemical stability of the conjugates. A high level of control and stability are crucial for reproducibility, upscaling, and safe application. In this study, gold nanoparticles with well-defined mixed ligand layers of α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy and gel electrophoresis. The colloidal and chemical stability of the conjugates was tested by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and UV/vis spectroscopy based experiments, and their interactions with cells were analyzed by elemental analysis. We demonstrate that the alkylene spacer in PEGMUA is the key feature for the controlled synthesis of mixed layer conjugates with very high colloidal and chemical stability and that a controlled synthesis is not possible using regular PEG ligands without the alkylene spacer. With the results of our stability tests, the molecular structure of the ligands can be clearly linked to the colloidal and chemical stabilization. We expect that the underlying design principle can be generalized to improve the level of control in nanoparticle surface chemistry.

In this contribution a facile, one-step synthesis of tridentate thiol-functionalized PEO ligands and their ability to stabilize CdSe/CdS/ZnS core-shell-shell nanoparticles In aqueous media are described. The PEO-coated quantum dots show colloidal stability as well as preserved fluorescence even at very low concentrations of a few nM. For improved ligand attachment and enhanced fluorescence properties a method for ligand exchange was developed, which includes formation of a ligand zinc complex before the actual exchange reaction. The stability and fluorescence properties in various aqueous buffers and cell media and at pH values down to pH 3 were investigated. The firm binding of the tridentate ligands to the particle surface makes this ligand particle system a promising tool for biological applications. In addition, activation of the ligands' terminal hydroxyl group for covalent biofunctionalization by esterification with succinic acid is reported.

This paper focusses on fundamental investigations of fuel wall films, which are formed when the spray impinges on the piston or cylinder walls. To reproduce the wide range of operating conditions within homogeneously charged gasoline direct-injection engines, it is necessary to use a film thickness measurement method, which can be applied inside a high-pressure, high-temperature vessel. Hence, we developed a method based on laser-induced fluorescence that reaches: a precision better than 1 µm, a geometric resolution of 31 µm and a practical applicability for wall film thicknesses smaller 80 µm. To obtain accurate film thickness results, we provide a detailed description of the selection of the surrogate fuel isooctane with 3-pentanone as fluorescence tracer and the resulting assembly of the excitation source, beam expander, filters, camera and the essential image processing. Furthermore, advantages and disadvantages of other possible solutions are discussed. Earlier publications provide only little information about the accuracy of their calibration and measurement procedures. Therefore, we tested and compared three basic calibration methods to each other and provide an analysis of possible errors, such as the influence of the preferential evaporation of 3-pentanone. Finally, images of resulting wall films are presented, and practical considerations for the execution of the measurements like recording timings are discussed.

We study the application of tunable ultrafast laser pulses in micropatterning self- assembled organic monolayer (SAMs) employing non collinear optical parametric amplification (NOPA). SAMs are ultrathin organic monolayers, which can be used in a variety of ways to assemble functionalized surface structures. In our study, we investigate the characteristics of SAMs as monomolecular resists during etching of gold. NOPA is a versatile method which provides the generation of ultrafast laser pulses, with a tunable wavelength in the visible and near infrared range. Due to the noncollinear geometry, a broadened spectral range can be amplified. The NOPA delivers wavelengths in the range of 480 nm to 950 nm at laser pulse lengths in the sub- 30 femtosecond range using a prism compressor after the nonlinear conversion. The ultrashort laser technology together with the advantages of the NOPA system guarantee high precision and allows us to determine the optimum conditions of sub-wavelength patterning by studying the effects of the fluence and the wavelength. At the same time, single-pulse processing allows us to selectively remove the ultrathin organic coating, while it ensures short processing time. In our study we used thiol-based SAMs as ultrathin layers on gold-coated glass substrates with a film thickness of 1-2 nm and 40 nm respectively.

An electrospray unit was built in order to deposit preformed metal nanoparticles on various substrates. Furthermore, due to treatment of the deposited particles with an oxygen plasma, the particles were stripped of their ligands and strongly fixed to the surface. These treated surfaces can be expected to exhibit properties that differ characteristically from bare surfaces. Depending on the substrate itself, but even more on the size and the density of the deposited nanoparticles, the contact angles and thereby the wettability could be varied drastically. Gold nanoparticles of 17 nm diameter on titanium decreased the contact angle from 82° to 34°, whereas 6–8 nm palladium particles increased the wettabilty to such a degree that a contact angle could not be determined. In contrast to the electrospray technique, a pneumatically operated device was constructed, allowing simultaneous spraying and plasma pyrolysis.

Self-assembled monolayers (SAMs) are ultra-thin organic monolayers, which can be used in different ways to assemble functionalized surface structures. This potential is caused by the ability of the SAMs to tie further molecules and components through the terminal groups of the organic layers. Additional applications for microfluidics and micromechanics require micro and nano structuring of the SAMs. In combination with multi-photon lithography (MPL) SAMs are offering advantageous properties as ultra thin layers. Thus, the processing with single pulses is feasible and results in very short processing times without the appearance of bubbles and formation of particles compared to photo resists. For our experiments, we used a non-collinear optical parametric amplifier (NOPA) which has the ability to generate short pulses of sub-30fs in the visible and near-infrared (NIR) range of light. The NOPA can be tuned in the range of 480 nm to 950 nm without spectral gaps.We used thiol based SAMs as ultra thin layers on gold substrates. The selected laser power offers the possibility of ablation of the SAMs without damaging the gold layer. Thereby we investigate the characteristics of thiol-based SAMs as monomolecular resists during etching of gold. We also investigate the wavelength dependencies of the substrate to get an optimal process window for the ablation process. Minimum structure sizes at a 1/e laser spot diameter of about 1.6 µm are close to 1/5 of the spot diameter.Self-assembled monolayers (SAMs) are ultra-thin organic monolayers, which can be used in different ways to assemble functionalized surface structures. This potential is caused by the ability of the SAMs to tie further molecules and components through the terminal groups of the organic layers. Additional applications for microfluidics and micromechanics require micro and nano structuring of the SAMs. In combination with multi-photon lithography (MPL) SAMs are offering advantageous properties as ultra thin layers. Thus, the processing with single pulses is feasible and results in very short processing times without the appearance of bubbles and formation of particles compared to photo resists. For our experiments, we used a non-collinear optical parametric amplifier (NOPA) which has the ability to generate short pulses of sub-30fs in the visible and near-infrared (NIR) range of light. The NOPA can be tuned in the range of 480 nm to 950 nm without spectral gaps.We used thiol based SAMs as ultra thin layers o...