33 results
Search Results
Now showing 1 - 10 of 33
- ItemComparative study of sculptured metallic thin films deposited by oblique angle deposition at different temperatures(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2018) Liedtke, Susann; Grüner, Christoph; Gerlach, Jürgen W.; Rauschenbach, BerndMetals with a wide range of melting points are deposited by electron beam evaporation under oblique deposition geometry on thermally oxidized Si substrates. During deposition the sample holder is cooled down to 77 K. It is observed that all obliquely deposited metals grow as tilted, high aspect ratio columns and hence with a similar morphology. A comparison of such columns with those deposited at room temperature (300 K) reveals that shadowing dominates the growth process for columns deposited at 77 K, while the impact of surface diffusion is significantly increased at elevated substrate temperatures. Furthermore, it is discussed how the incidence angle of the incoming particle flux and the substrate temperature affect the columnar tilt angles and the porosity of the sculptured thin films. Exemplarily for tilted Al columns deposited at 77 K and at 300 K, in-plane pole figure measurements are carried out. A tendency to form a biaxial texture as well as a change in the crystalline structure depending on the substrate temperature is found for those films.
- ItemCoordination chemistry and photoswitching of dinuclear macrocyclic cadmium-, nickel-, and zinc complexes containing azobenzene carboxylato co-ligands(Frankfurt, Main : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2019) Klose, Jennifer; Severin, Tobias; Hahn, Peter; Jeremies, Alexander; Bergmann, Jens; Fuhrmann, Daniel; Griebel, Jan; Abel, Bernd; Kersting, BertholdThe synthesis of mixed-ligand complexes of the type [M2L(μ-L')]+, where L represents a 24-membered macrocyclic hexaaza-dithiophenolate ligand, L' is an azobenzene carboxylate co-ligand, and M = Cd(II), Ni(II) or Zn(II), is reported. A series of new complexes were synthesized, namely [M2L(μ-L')]+ (L' = azo-H, M = Cd (1), Ni (2); L' = azo-OH, M = Zn (3), Ni (4); L' = azo-NMe2, M = Zn (5), Cd (6), Ni (7); L' = azo-CO2Me, M = Cd (8), Ni (9)), and characterized by elemental analysis, electro-spray ionization mass spectrometry (ESIMS), IR, UV–vis and NMR spectroscopy (for diamagnetic Zn and Cd complexes) and X-ray single crystal structure analysis. The crystal structures of 3' and 5–8 display an isostructural series of compounds with bridging azobenzene carboxylates in the trans form. The paramagnetic Ni complexes 2, 4 and 7 reveal a weak ferromagnetic exchange interaction with magnetic exchange coupling constant values between 21 and 23 cm−1 (H = −2JS1S2). Irradiation of 1 with λ = 365 nm reveals a photoisomerization of the co-ligand from the trans to the cis form. © 2019 Klose et al.
- ItemDeposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017) Börner, Martin; Blömer, Laura; Kischel, Marcus; Richter, Peter; Salvan, Georgeta; Zahn, Dietrich R. T.; Siles, Pablo F.; Fuentes, Maria E. N.; Bufon, Carlos C. B.; Grimm, Daniel; Schmidt, Oliver G.; Breite, Daniel; Abel, Bernd; Kersting, BertholdThe chemisorption of magnetically bistable transition metal complexes on planar surfaces has recently attracted increased scientific interest due to its potential application in various fields, including molecular spintronics. In this work, the synthesis of mixed-ligand complexes of the type [NiII2L(L’)](ClO4), where L represents a 24-membered macrocyclic hexaazadithiophenolate ligand and L’ is a ω-mercapto-carboxylato ligand (L’ = HS(CH2)5CO2− (6), HS(CH2)10CO2− (7), or HS(C6H4)2CO2− (8)), and their ability to adsorb on gold surfaces is reported. Besides elemental analysis, IR spectroscopy, electrospray ionization mass spectrometry (ESIMS), UV–vis spectroscopy, and X-ray crystallography (for 6 and 7), the compounds were also studied by temperature-dependent magnetic susceptibility measurements (for 7 and 8) and (broken symmetry) density functional theory (DFT) calculations. An S = 2 ground state is demonstrated by temperature-dependent susceptibility and magnetization measurements, achieved by ferromagnetic coupling between the spins of the Ni(II) ions in 7 (J = +22.3 cm−1) and 8 (J = +20.8 cm−1; H = −2JS1S2). The reactivity of complexes 6–8 is reminiscent of that of pure thiolato ligands, which readily chemisorb on Au surfaces as verified by contact angle, atomic force microscopy (AFM) and spectroscopic ellipsometry measurements. The large [Ni2L] tail groups, however, prevent the packing and self-assembly of the hydrocarbon chains. The smaller film thickness of 7 is attributed to the specific coordination mode of the coligand. Results of preliminary transport measurements utilizing rolled-up devices are also reported.
- ItemSynthesis of High Crystalline TiO2 Nanoparticles on a Polymer Membrane to Degrade Pollutants from Water(Basel : MDPI, 2018-9-5) Fischer, Kristina; Schulz, Paulina; Atanasov, Igor; Abdul Latif, Amira; Thomas, Isabell; Kühnert, Mathias; Prager, Andrea; Griebel, Jan; Schulze, AgnesTitanium dioxide (TiO2) is described as an established material to remove pollutants from water. However, TiO2 is still not applied on a large scale due to issues concerning, for example, the form of use or low photocatalytic activity. We present an easily upscalable method to synthesize high active TiO2 nanoparticles on a polyethersulfone microfiltration membrane to remove pollutants in a continuous way. For this purpose, titanium(IV) isopropoxide was mixed with water and hydrochloric acid and treated up to 210 °C. After cooling, the membrane was simply dip-coated into the TiO2 nanoparticle dispersion. Standard characterization was undertaken (i.e., X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, water permeance, contact angle). Degradation of carbamazepine and methylene blue was executed. By increasing synthesis temperature crystallinity and photocatalytic activity elevates. Both ultrasound modification of nanoparticles and membrane pre-modification with carboxyl groups led to fine distribution of nanoparticles. The ultrasound-treated nanoparticles gave the highest photocatalytic activity in degrading carbamazepine and showed no decrease in degradation after nine times of repetition. The TiO2 nanoparticles were strongly bound to the membrane. Photocatalytic TiO2 nanoparticles with high activity were synthesized. The innovative method enables a fast and easy nanoparticle production, which could enable the use in large-scale water cleaning.
- ItemDinuclear lanthanide complexes supported by a hybrid salicylaldiminato/calix[4]arene-ligand: Synthesis, structure, and magnetic and luminescence properties of (HNEt3)[Ln2(HL)(L)] (Ln = SmIII, EuIII, GdIII, TbIII)(London : Soc., 2019) Ullmann, Steve; Hahn, Peter; Blömer, Laura; Mehnert, Anne; Laube, Christian; Abel, Bernd; Kersting, BertholdThe synthesis, structures, and properties of a new calix[4]arene ligand with an appended salicylaldimine unit (H4L = 25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and four lanthanide complexes (HNEt3)[Ln2(HL)(L)] (Ln = SmIII (4), EuIII (5), GdIII (6), and TbIII (7)) are reported. X-ray crystallographic analysis (for 4 and 6) reveals an isostructural series of dimeric complexes with a triply-bridged NO3Ln(μ-O)2(OH⋯O)LnO3N core and two seven coordinated lanthanide ions. According to UV-vis spectrometric titrations in MeCN and ESI-MS the dimeric nature is maintained in solution. The apparent stability constants range between logK = 5.8 and 6.3. The appended salicylaldimines sensitize EuIII and TbIII emission (λexc 311 nm) in the solid state or immersed in a polycarbonate glass at 77 K (for 5, 7) and at 295 K (for 7). © The Royal Society of Chemistry 2019.
- ItemPolyoxometalates as components of supramolecular assemblies(Cambridge : RSC, 2019) Stuckart, Maria; Monakhov, Kirill Yu.The non-covalent interaction of polyoxometalates (POMs) with inorganic- or organic-based moieties affords hybrid assemblies with specific physicochemical properties that are of high interest for both fundamental and applied studies, including the discovery of conceptually new compounds and unveiling the impact of their intra-supramolecular relationships on the fields of catalysis, molecular electronics, energy storage and medicine. This minireview summarises the recent advances in the synthetic strategies towards the formation of such non-covalent POM-loaded assemblies, shedding light on their key properties and the currently investigated applications. Four main emerging categories according to the nature of the conjugate are described: (i) POMs in metal-organic frameworks, (ii) POMs merged with cationic metal complexes, (iii) architectures generated with solely POM units and (iv) POMs assembled with organic molecular networks. © 2019 The Royal Society of Chemistry.
- ItemDavydov splitting and singlet fission in excitonically coupled pentacene dimers(Cambridge : RSC, 2019) Basel, Bettina Sabine; Hetzer, Constantin; Zirzlmeier, Johannes; Thiel, Dominik; Guldi, Rebecca; Hampel, Frank; Kahnt, Axel; Clark, Timothy; Guldi, Dirk Michael; Tykwinski, Rik R.Singlet fission (SF) allows two charges to be generated from the absorption of a single photon and is, therefore, potentially transformative toward improving solar energy conversion. Key to the present study of SF is the design of pentacene dimers featuring a xanthene linker that strictly places two pentacene chromophores in a rigid arrangement and, in turn, enforces efficient, intramolecular π-overlap that mimics interactions typically found in condensed state (e.g., solids, films, etc.). Inter-chromophore communication ensures Davydov splitting, which plays an unprecedented role toward achieving SF in pentacene dimers. Transient absorption measurements document that intramolecular SF evolves upon excitation into the lower Davydov bands to form a correlated triplet pair at cryogenic temperature. At room temperature, the two spin-correlated triplets, one per pentacene moiety within the dimers, are electronically coupled to an excimer state. The presented results are transferable to a broad range of acene morphologies including aggregates, crystals, and films. © 2019 The Royal Society of Chemistry.
- ItemGratings for synchrotron and FEL beamlines: a project for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin(Chester : IUCr, 2018) Siewert, F.; Löchel, B.; Buchheim, J.; Eggenstein, F.; Firsov, A.; Gwalt, G.; Kutz, O.; Lemke, St.; Nelles, B.; Rudolph, I.; Schäfers, F.; Seliger, T.; Senf, F.; Sokolov, A.; Waberski, Ch.; Wolf, J.; Zeschke, T.; Zizak, I.; Follath, R.; Arnold, T.; Frost, F.; Pietag, F.; Erko, A.Blazed gratings are of dedicated interest for the monochromatization of synchrotron radiation when a high photon flux is required, such as, for example, in resonant inelastic X-ray scattering experiments or when the use of laminar gratings is excluded due to too high flux densities and expected damage, for example at free-electron laser beamlines. Their availability became a bottleneck since the decommissioning of the grating manufacture facility at Carl Zeiss in Oberkochen. To resolve this situation a new technological laboratory was established at the Helmholtz Zentrum Berlin, including instrumentation from Carl Zeiss. Besides the upgraded ZEISS equipment, an advanced grating production line has been developed, including a new ultra-precise ruling machine, ion etching technology as well as laser interference lithography. While the old ZEISS ruling machine GTM-6 allows ruling for a grating length up to 170 mm, the new GTM-24 will have the capacity for 600 mm (24 inch) gratings with groove densities between 50 lines mm−1 and 1200 lines mm−1. A new ion etching machine with a scanning radiofrequency excited ion beam (HF) source allows gratings to be etched into substrates of up to 500 mm length. For a final at-wavelength characterization, a new reflectometer at a new Optics beamline at the BESSY-II storage ring is under operation. This paper reports on the status of the grating fabrication, the measured quality of fabricated items by ex situ and in situ metrology, and future development goals.
- ItemMagnetically responsive composites: electron beam assisted magnetic nanoparticle arrest in gelatin hydrogels for bioactuation(Cambridge : RSC Publ., 2019) Deuflhard, Marie; Eberbeck, Dietmar; Hietschold, Philine; Wilharm, Nils; Mühlberger, Marina; Friedrich, Ralf P.; Alexiou, Christoph; Mayr, Stefan G.As emerging responsive materials, ferrogels have become highly attractive for biomedical and technical applications in terms of soft actuation, tissue engineering or controlled drug release. In the present study, bioderived ferrogels were fabricated and successfully deformed within moderate, heterogeneous magnetic fields. Synthesis was realized by arresting iron oxide nanoparticles in porcine gelatin by introduction of covalent crosslinks via treatment with energetic electrons for mesh refinement. This approach also allows for tuning thermal and mechanical stability of the gelatin matrix. Operating the bioferrogel in compression, magnetic forces on the nanoparticles are counterbalanced by the stiffness of the hydrogel matrix that is governed by a shift in thermodynamic equilibrium of swelling, as derived in the framework of osmosis. As gelatin and iron oxide nanoparticles are established as biocompatible constituents, these findings promise potential for in vivo use as contactless mechanical transducers.
- ItemPeptides@mica: From affinity to adhesion mechanism(Cambridge : RSC Publ., 2016) Gladytz, A.; John, T.; Gladytz, T.; Hassert, R.; Pagel, M.; Risselada, H.J.; Naumov, S.; Beck-Sickinger, A.G.; Abel, B.Investigating the adsorption of peptides on inorganic surfaces, on the molecular level, is fundamental for medicinal and analytical applications. Peptides can be potent as linkers between surfaces and living cells in biochips or in implantation medicine. Here, we studied the adsorption process of the positively charged pentapeptide RTHRK, a recently identified binding sequence for surface oxidized silicon, and novel analogues thereof to negatively charged mica surfaces. Homogeneous formation of monolayers in the nano- and low micromolar peptide concentration range was observed. We propose an alternative and efficient method to both quantify binding affinity and follow adhesion behavior. This method makes use of the thermodynamic relationship between surface coverage, measured by atomic force microscopy (AFM), and the concomitant free energy of adhesion. A knowledge-based fit to the autocorrelation of the AFM images was used to correct for a biased surface coverage introduced by the finite lateral resolution of the AFM. Binding affinities and mechanisms were further explored by large scale molecular dynamics (MD) simulations. The combination of well validated MD simulations with topological data from AFM revealed a better understanding of peptide adsorption processes on the atomistic scale. We demonstrate that binding affinity is strongly determined by a peptide's ability to form salt bridges and hydrogen bonds with the surface lattice. Consequently, differences in hydrogen bond formation lead to substantial differences in binding affinity despite conservation of the peptide's overall charge. Further, MD simulations give access to relative changes in binding energy of peptide variations in comparison to a lead compound.