Dr. Julia Susanne Gebauer

Nanoparticle Process Technology
University of Duisburg-Essen


  • High performance printed oxide field-effect transistors processed using photonic curing
    Garlapati, S.K. and Marques, G.C. and Gebauer, J.S. and Dehm, S. and Bruns, M. and Winterer, M. and Tahoori, M.B. and Aghassi-Hagmann, J. and Hahn, H. and Dasgupta, S.
    Nanotechnology 29 (2018)
    Oxide semiconductors are highly promising candidates for the most awaited, next-generation electronics, namely, printed electronics. As a fabrication route for the solution-processed/printed oxide semiconductors, photonic curing is becoming increasingly popular, as compared to the conventional thermal curing method; the former offers numerous advantages over the latter, such as low process temperatures and short exposure time and thereby, high throughput compatibility. Here, using dissimilar photonic curing concepts (UV-visible light and UV-laser), we demonstrate facile fabrication of high performance In2O3 field-effect transistors (FETs). Beside the processing related issues (temperature, time etc.), the other known limitation of oxide electronics is the lack of high performance p-type semiconductors, which can be bypassed using unipolar logics from high mobility n-type semiconductors alone. Interestingly, here we have found that our chosen distinct photonic curing methods can offer a large variation in threshold voltage, when they are fabricated from the same precursor ink. Consequently, both depletion and enhancement-mode devices have been achieved which can be used as the pull-up and pull-down transistors in unipolar inverters. The present device fabrication recipe demonstrates fast processing of low operation voltage, high performance FETs with large threshold voltage tunability. © 2018 IOP Publishing Ltd.
    view abstract10.1088/1361-6528/aab7a2
  • Tailoring metal oxide nanoparticle dispersions for inkjet printing
    Gebauer, J.S. and Mackert, V. and Ognjanović, S. and Winterer, M.
    Journal of Colloid and Interface Science 526 (2018)
    There is a growing interest in science and industry for printed electronics. Printed electronics enable the production of large quantities of electronic components at low cost. Even though organic semiconductors are already widely used for printed components, inorganic materials may be advantageous due to their higher durability and superior device performance. Nevertheless, inorganic materials still remain difficult to print making the development of printable and functional inks a necessity. In this work we present the formulation, inkjet printing and processing of newly developed inks based on ethylene glycol as dispersion medium. Different metal oxide nanoparticles (ZnO, TiO2, CuO, SnO2 and In2O3) with high crystallinity and narrow size distribution were produced by chemical vapor synthesis. The particles were stabilized and the colloidal stability was evaluated by a combination of DLVO simulations and dynamic light scattering measurements. Measurements of rheological and interfacial properties, like viscosity and surface tension, are used to determine the printability on the basis of the inverse Ohnesorge number. Inks, developed in this work, have adjustable rheological properties as well as long-term stabilities without particle sedimentation over a period of several months. They are suitable for printing on different substrate materials like silicon and flexible polymeric substrates. © 2018 Elsevier Inc.
    view abstract10.1016/j.jcis.2018.05.006
  • Zinc stannate by reactive laser sintering
    Mackert, V. and Gebauer, J.S. and Notthoff, C. and Winterer, M.
    Applied Surface Science 457 (2018)
    A novel procedure for producing polycrystalline zinc stannate (Zn 2 SnO 4 , ZTO) films is presented in this paper. Nanocrystals of zinc oxide (ZnO) and tin dioxide (SnO 2 ) are prepared by chemical vapor synthesis (CVS) and processed into stable aqueous dispersions including mixed colloids. These colloids are transformed into nanostructured films via electrophoretic deposition where the mixed colloid forms a homogeneous, nanoscaled composite. Ultraviolet (UV) laser sintering of these codeposited ZnO-SnO 2 nanocrystals generates the inverse cubic spinel Zn 2 SnO 4 phase by chemical reaction on the area of interest. The effects of UV laser sintering at a wavelength of 325 nm on the nanoscaled microstructure of pure deposited films are investigated by variation of laser power and scanning speed. The microstructure of composite films is compared to a film obtained by classical reactive sintering in a furnace. High-resolution scanning electron microscopy and energy dispersive X-ray spectroscopy are used to investigate film morphology and chemical composition. Structural characterization is performed by X-ray diffraction. © 2018 Elsevier B.V.
    view abstract10.1016/j.apsusc.2018.06.304
  • Room-Temperature Processing of Printed Oxide FETs Using Ultraviolet Photonic Curing
    Garlapati, S.K. and Gebauer, J.S. and Dehm, S. and Bruns, M. and Winterer, M. and Hahn, H. and Dasgupta, S.
    Advanced Electronic Materials (2017)
    Oxide semiconductors are highly suitable materials for solution-processed/printed electronics (PE); the growing interest in them can be related to their excellent intrinsic properties, such as high mobility, optical transparency, thermal and environmental stability, and so on. However, high process temperatures remain as the foremost challenge that may limit the compatibility of printed oxide electronics to inexpensive flexible substrates. Here, the possibility of using photonic curing methods to lower the process temperature is investigated, even down to room temperature (RT). Two distinct ultraviolet (UV) curing techniques, involving UV-visible light pulses and continuous-wave UV lasers are exercised and compared. Combining UV curing with oxide nanoparticulate channel layer and electrolytic gate insulators, it is demonstrated that high performance field-effect transistors (FETs) with device mobility as high as 12 cm2 V-1 s-1 can be processed entirely at room temperature and realized on plastic substrates. The fabrication steps include printing of a heavily stabilized semiconducting nanoparticulate channel layer, followed by decomposition and removal of the semi-insulating polymer ligands using UV-photon energies. The curing process is found to be fast and high-throughput manufacturing technique compatible. At the same time, the energy requirement to remove the polymer stabilizers is insignificant, thereby ensuring no temperature rise of the parent substrates. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/aelm.201600476
  • Validation of weak biological effects by round robin experiments: Cytotoxicity/biocompatibility of SiO2 and polymer nanoparticles in HepG2 cells
    Landgraf, L. and Nordmeyer, D. and Schmiel, P. and Gao, Q. and Ritz, S. and Gebauer, J.S. and Graß, S. and Diabaté, S. and Treuel, L. and Graf, C. and Rühl, E. and Landfester, K. and Mailänder, V. and Weiss, C. and Zellner, R. and Hilger, I.
    Scientific Reports 7 (2017)
    All over the world, different types of nanomaterials with a diversified spectrum of applications are designed and developed, especially in the field of nanomedicine. The great variety of nanoparticles (NPs), in vitro test systems and cell lines led to a vast amount of publications with conflicting data. To identify the decisive principles of these variabilities, we conducted an intercomparison study of collaborating laboratories within the German DFG Priority Program SPP1313, using well-defined experimental parameters and well-characterized NPs. The participants analyzed the in vitro biocompatibility of silica and polymer NPs on human hepatoma HepG2 cells. Nanoparticle mediated effects on cell metabolism, internalization, and inflammation were measured. All laboratories showed that both nanoparticle formulations were internalized and had a low cytotoxicity profile. Interestingly, small variations in nanoparticle preparation, cell handling and the type of culture slide influenced the nanoparticle stability and the outcomes of cell assays. The round robin test demonstrated the importance of the use of clearly defined and characterized NPs and parameters for reproducible results across laboratories. Comparative analyses of in vitro screening methods performed in multiple laboratories are absolutely essential to establish robust standard operation procedure as a prerequisite for sound hazard assessment of nanomaterials. © The Author(s) 2017.
    view abstract10.1038/s41598-017-02958-9
  • Quantitative replacement of citrate by phosphane on silver nanoparticle surfaces monitored by Surface-Enhanced Raman Spectroscopy (SERS)
    Grass, S. and Diendorf, J. and Gebauer, J.S. and Epple, M. and Treuel, L.
    Journal of Nanoscience and Nanotechnology 15 (2015)
    Chemical approaches to metal NP synthesis commonly use capping agents to achieve a desired NP size and shape. Frequently, such NPs require chemically different surface ligands after synthesis to generate desired NP properties (e.g., charge or hydrophilicity) and to increase their long term colloidal stability. Here, we prepared SERS active citrate-stabilized silver NPs (d = 38 ± 4 nm), purified them from remaining reactants by ultracentrifugation and redispersion, and immersed them into solutions containing different concentrations of Tris(sodium-m-sulfonatophenyl)phosphine (TPPTS), which is often used in such ligand replacement approaches to increase colloidal stability. After equilibration, SERS spectra were acquired, elucidating the concentration dependence of the ligand replacement reaction. SERS data were complemented by concentration dependent size measurements and relations between ligand exchange and colloidal stability are discussed. Copyright © 2015 American Scientific Publishers
    view abstract10.1166/jnn.2015.9143
  • Impact of the nanoparticle-protein corona on colloidal stability and protein structure
    Gebauer, J.S. and Malissek, M. and Simon, S. and Knauer, S.K. and Maskos, M. and Stauber, R.H. and Peukert, W. and Treuel, L.
    Langmuir 28 (2012)
    In biological fluids, proteins may associate with nanoparticles (NPs), leading to the formation of a so-called "protein corona" largely defining the biological identity of the particle. Here, we present a novel approach to assess apparent binding affinities for the adsorption/desorption of proteins to silver NPs based on the impact of the corona formation on the agglomeration kinetics of the colloid. Affinities derived from circular dichroism measurements complement these results, simultaneously elucidating structural changes in the adsorbed protein. Employing human serum albumin as a model, apparent affinities in the nanomolar regime resulted from both approaches. Collectively, our findings now allow discrimination between the formation of protein mono- and multilayers on NP surfaces. © 2012 American Chemical Society.
    view abstract10.1021/la301104a
  • Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles
    Gebauer, J.S. and Treuel, L.
    Journal of Colloid and Interface Science 354 (2011)
    The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs. © 2010 Elsevier Inc.
    view abstract10.1016/j.jcis.2010.11.016
  • The influence of proteins on the dispersability and cell-biological activity of silver nanoparticles
    Kittler, S. and Greulich, C. and Gebauer, J.S. and Diendorf, J. and Treuel, L. and Ruiz, L. and Gonzalez-Calbet, J.M. and Vallet-Regi, M. and Zellner, R. and Köller, M. and Epple, M.
    Journal of Materials Chemistry 20 (2010)
    Spherical silver nanoparticles with a diameter of 50 ± 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI-BSA mixture within a few hours, the particles remained well dispersed in RPMI-FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI-BSA and RPMI-FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins. © The Royal Society of Chemistry 2010.
    view abstract10.1039/b914875b
  • The influence of surface composition of nanoparticles on their interactions with serum albumin
    Treuel, L. and Malissek, M. and Gebauer, J.S. and Zellner, R.
    ChemPhysChem 11 (2010)
    Interactions between differently functionalised silver and gold nanoparticles (NPs) as well as polystyrene nanoparticles with bovine serum albumin (BSA) are studied using circular dichroism (CD) spectroscopy. It is found that the addition of NPs to the protein solution destroys part of the helical secondary structure of the protein as a result of surface adsorption. From the loss of free protein and hence the extent of their structural change adsorption equilibrium constants are derived. The results reveal that citrate-coated gold and silver NPs exhibit much stronger interactions with BSA than polymeric or polymer-coated metallic NPs. It is therefore concluded that for the particles considered, the influence of surface composition on the interaction behaviour dominates that of the core. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cphc.201000174
  • nanoparticles

  • optical spectroscopy

  • printable electronics

  • semiconductors

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