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- ItemResearch Update: Van-der-Waals epitaxy of layered chalcogenide Sb2Te3 thin films grown by pulsed laser deposition(Melville, NY : AIP Publ., 2017) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, BerndAn attempt to deposit a high quality epitaxial thin film of a two-dimensionally bonded (layered) chalcogenide material with van-der-Waals (vdW) epitaxy is of strong interest for non-volatile memory application. In this paper, the epitaxial growth of an exemplary layered chalcogenide material, i.e., stoichiometric Sb2Te3 thin films, is reported. The films were produced on unreconstructed highly lattice-mismatched Si(111) substrates by pulsed laser deposition (PLD). The films were grown by vdW epitaxy in a two-dimensional mode. X-ray diffraction measurements and transmission electron microscopy revealed that the films possess a trigonal Sb2Te3 structure. The single atomic Sb/Te termination layer on the Si surface was formed initializing the thin film growth. This work demonstrates a straightforward method to deposit vdW-epitaxial layered chalcogenides and, at the same time, opens up the feasibility to fabricate chalcogenide vdW heterostructures by PLD.
- ItemSchlussbericht zum BMBF-Vorhaben: Compact optohybrids (CoOp), Teilvorhaben: Ionenätzverfahren für die Strukturierung(Hannover : Technische Informationsbibliothek (TIB), 2006) Schindler, Axel[no abstract available]
- ItemMembrane Functionalization in Pilot Scale: Roll‐to‐Roll Electron Beam System with Inline Contact Angle Determination(Weinheim : Wiley-VCH, 2021) Schulze, Agnes; Drößler, Lutz; Weiß, Steffen; Went, Marco; Abdul Latif, Amira; Breite, Daniel; Fischer, KristinaTo increase the permeation performance and antifouling properties of polymer membranes, a one-step reaction using electron irradiation was developed. This process combines the surface activation of the membrane polymer and the simultaneous permanent immobilization of hydrophilic molecules. This technology can be applied to various polymers, flat sheet/hollow fiber membranes and all pore ranges. The roll-to-roll system developed for this enables all process steps including inline analysis for quality control of the membrane surface in a continuously operated system. © 2021 The Authors. Chemie Ingenieur Technik published by Wiley-VCH GmbH
- ItemPolymeric monolithic materials: Syntheses, properties, functionalization and applications(Amsterdam : Elsevier, 2007) Buchmeiser, M.R.The synthetic particularities for the synthesis of polymer-based monolithic materials are summarized. In this context, monoliths prepared via thermal-, UV- or electron-beam triggered free radical polymerization, controlled TEMPO-mediated radical polymerization, polyaddition, polycondensation as well as living ring-opening metathesis polymerization (ROMP) will be covered. Particular attention is devoted to the aspects of controlling pore sizes, pore volumes and pore size distributions as well as functionalization of these supports. Finally, selected, recent applications in separation science, (bio-) catalysis and chip technology will be summarized. © 2007 Elsevier Ltd. All rights reserved.
- ItemAsh transformation mechanism during combustion of rice husk and rice straw(New York, NY [u.a.] : Elsevier, 2022) Beidaghy Dizaji, Hossein; Zeng, Thomas; Hölzig, Hieronymus; Bauer, Jens; Klöß, Gert; Enke, DirkBiomass is an alternative energy resource to fossil fuels because of its potential to reduce greenhouse gas emissions. However, ash-related problems are serious obstacles for this development, especially for the use in combustion plants. Thus, design and operation of biomass boilers require detailed understanding of ash transformation reactions during thermochemical conversion. To evaluate ash transformation in silica-rich biomass fuels, rice husk and rice straw were selected because of their abundance, limited utilization conflicts with the food sector, as well as their potential in both energy and material applications. This paper reveals ash transformation mechanisms relevant for the ash melting behaviour of silica-rich biomass fuels considering chemical and phase composition of the ashes. In this regard, several advanced spectroscopic methods and diffractometry were employed to characterize the materials. The ash transformation reactions and the viscosity were simulated using thermodynamic equilibrium calculations and a slag viscosity modeling toolbox. The results illustrate the impact of impurities on the atomic structure of the silica resulting in an altered ash melting behaviour and viscosity of the silica-rich ashes. Chemical water washing, acid leaching, and blending of rice straw with rice husk strongly influenced the chemical composition of the ashes and improved ash melting behaviour. The analysis also revealed the correlation between the crystalline fraction and the porosity in silica-rich biomass ashes, as well as a crystallinity threshold. These findings are highly relevant for future investigations in boiler designs and production of biogenic silica for material applications.
- ItemSchlussbericht zum Verbundprojekt: Wachstumskern INNOCIS, Teilvorhaben: Organische Schutzschichten für flexible Solarzellen-Materialien(Hannover : Technische Informationsbibliothek (TIB), 2004) von Sonntag, Justus[no abstract available]
- ItemTopography evolution of germanium thin films synthesized by pulsed laser deposition(New York, NY : American Inst. of Physics, 2017) Schumacher, P.; Mayr, S.G.; Rauschenbach, B.Germanium thin films were deposited by Pulsed Laser Deposition (PLD) onto single crystal Ge (100) and Si (100) substrates with a native oxide film on the surface. The topography of the surface was investigated by Atomic Force Microscopy (AFM) to evaluate the scaling behavior of the surface roughness of amorphous and polycrystalline Ge films grown on substrates with different roughnesses. Roughness evolution was interpreted within the framework of stochastic rate equations for thin film growth. Here the Kardar-Parisi-Zhang equation was used to describe the smoothening process. Additionally, a roughening regime was observed in which 3-dimensional growth occurred. Diffusion of the deposited Ge adatoms controlled the growth of the amorphous Ge thin films. The growth of polycrystalline thin Ge films was dominated by diffusion processes only in the initial stage of the growth.
- ItemSurface cleaning and sample carrier for complementary high-resolution imaging techniques(Melville, NY : AIP, 2020) Benettoni, Pietro; Ye, Jia-Yu; Holbrook, Timothy R.; Calabrese, Federica; Wagner, Stephan; Zarejousheghani, Mashaalah; Griebe, Jan; Ullrich, Maria K.; Musat, Niculina; Schmidt, Matthias; Flyunt, Roman; Reemtsma, Thorsten; Richnow, Hans-Hermann; Stryhanyuk, HryhoriyNowadays, high-resolution imaging techniques are extensively applied in a complementary way to gain insights into complex phenomena. For a truly complementary analytical approach, a common sample carrier is required that is suitable for the different preparation methods necessary for each analytical technique. This sample carrier should be capable of accommodating diverse analytes and maintaining their pristine composition and arrangement during deposition and preparation. In this work, a new type of sample carrier consisting of a silicon wafer with a hydrophilic polymer coating was developed. The robustness of the polymer coating toward solvents was strengthened by cross-linking and stoving. Furthermore, a new method of UV-ozone cleaning was developed that enhances the adhesion of the polymer coating to the wafer and ensures reproducible surface-properties of the resulting sample carrier. The hydrophilicity of the sample carrier was recovered applying the new method of UV-ozone cleaning, while avoiding UV-induced damages to the polymer. Noncontact 3D optical profilometry and contact angle measurements were used to monitor the hydrophilicity of the coating. The hydrophilicity of the polymer coating ensures its spongelike behavior so that upon the deposition of an analyte suspension, the solvent and solutes are separated from the analyte by absorption into the polymer. This feature is essential to limit the coffee-ring effect and preserve the native identity of an analyte upon deposition. The suitability of the sample carrier for various sample types was tested using nanoparticles from suspension, bacterial cells, and tissue sections. To assess the homogeneity of the analyte distribution and preservation of sample integrity, optical and scanning electron microscopy, helium ion microscopy, laser ablation inductively coupled plasma mass spectrometry, and time-of-flight secondary ion mass spectrometry were used. This demonstrates the broad applicability of the newly developed sample carrier and its value for complementary imaging. © 2020 Author(s).
- ItemLow-energy constraints on photoelectron spectra measured from liquid water and aqueous solutions(Cambridge : RSC Publ., 2021) Malerz, Sebastian; Trinter, Florian; Hergenhahn, Uwe; Ghrist, Aaron; Ali, Hebatallah; Nicolas, Christophe; Saak, Clara-Magdalena; Richter, Clemens; Hartweg, Sebastian; Nahon, Laurent; Lee, Chin; Goy, Claudia; Neumark, Daniel M; Meijer, Gerard; Wilkinson, Iain; Winter, Bernd; Thürmer, StephanWe report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV, on the photoemission spectra of liquid water. We show that the nascent photoelectron spectrum and, hence, the inferred electron binding energy can only be accurately determined if electron energies are large enough that cross sections for quasi-elastic scattering processes, such as vibrational excitation, are negligible. Otherwise, quasi-elastic scattering leads to strong, down-to-few-meV kinetic energy scattering losses from the direct photoelectron features, which manifest in severely distorted intrinsic photoelectron peak shapes. The associated cross-over point from predominant (known) electronically inelastic to quasi-elastic scattering seems to arise at surprisingly large electron kinetic energies, of approximately 10–14 eV. Concomitantly, we present evidence for the onset of indirect, autoionization phenomena (occurring via superexcited states) within a few eV of the primary and secondary ionization thresholds. These processes are inferred to compete with the direct ionization channels and primarily produce low-energy photoelectrons at photon and electron impact excitation energies below ∼15 eV. Our results highlight that vibrational inelastic electron scattering processes and neutral photoexcitation and autoionization channels become increasingly important when photon and electron kinetic energies are decreased towards the ionization threshold. Correspondingly, we show that for neat water and aqueous solutions, great care must be taken when quantitatively analyzing photoelectron spectra measured too close to the ionization threshold. Such care is essential for the accurate determination of solvent and solute ionization energies as well as photoelectron branching ratios and peak magnitudes.
- ItemInfluence of substrate dimensionality on the growth mode of epitaxial 3D-bonded GeTe thin films: From 3D to 2D growth(Amsterdam [u.a.] : Elsevier Science, 2019) Hilmi, Isom; Lotnyk, Andriy; Gerlach, Jürgen W.; Schumacher, Philipp; Rauschenbach, BerndThe pseudo-binary line of Sb2Te3-GeTe contains alloys featuring different crystalline characteristics from two-dimensionally (2D-) bonded Sb2Te3 to three-dimensionally (3D-) bonded GeTe. Here, the growth scenario of 3D-bonded GeTe is investigated by depositing epitaxial GeTe thin films on Si(111) and Sb2Te3-buffered Si(111) substrates using pulsed laser deposition (PLD). GeTe thin films were grown in trigonal structure within a temperature window for epitaxial growth of 210–270 °C on unbuffered Si(111) substrates. An unconventional growth onset was characterized by the formation of a thin amorphous GeTe layer. Nonetheless, the as-grown film is found to be crystalline. Furthermore, by employing a 2D-bonded Sb2Te3 thin film as a seeding layer on Si(111), a 2D growth of GeTe is harnessed. The epitaxial window can substantially be extended especially towards lower temperatures down to 145 °C. Additionally, the surface quality is significantly improved. The inspection of the local structure of the epitaxial films reveals the presence of a superposition of twinned domains, which is assumed to be an intrinsic feature of such thin films. This work might open a way for an improvement of an epitaxy of a 3D-bonded material on a highly-mismatched substrate (e.g. Si (111)) by employing a 2D-bonded seeding layer (e.g. Sb2Te3).