Co-reporter:Christian E. Halbig, Thomas J. Nacken, Johannes Walter, Cornelia Damm, Siegfried Eigler, Wolfgang Peukert
Carbon 2016 Volume 96() pp:897-903
Publication Date(Web):January 2016
DOI:10.1016/j.carbon.2015.10.021
In the view of technical and medical applications we examined the effect of ultrasonication and ball milling of oxo-functionalized graphene bearing an almost intact carbon lattice (oxo-G) with respect to the lateral flake size reduction and defect formation in the carbon lattice for the first time. The energy input was screened for both methods and quantitative changes in lateral flake size distribution were characterized in solution by analytical ultracentrifugation (AUC) supported by atomic force microscopy (AFM). For the first time, we applied statistical Raman spectroscopy to reliably evaluate the formation of lattice defects with processing time. Surprisingly, the density of lattice defects remains unaffected with energy inputs below a limiting threshold. Furthermore, for both processing techniques, the size reduction scales with the energy input according to a power law function, which is well known for emulsification and mechanical comminution processes. With the results of this study it is possible to precisely predetermine the lateral size of flakes of oxo-G upon sonication or milling processing, preserving the carbon lattice. Understanding this controlled formation of oxo-G flakes enables target oriented technical, medical and electronic applications with tailored properties.
Co-reporter:Zhenxing Wang, Siegfried Eigler, Yoshitaka Ishii, Yichen Hu, Christian Papp, Ole Lytken, Hans-Peter Steinrück and Marcus Halik
Journal of Materials Chemistry A 2015 vol. 3(Issue 33) pp:8595-8604
Publication Date(Web):16 Jul 2015
DOI:10.1039/C5TC01861G
Memory devices are a key technology of our era and one of the constant challenges is the reduction of their power consumption. Herein, we demonstrate that graphene oxide with very few defects, that is, about 1 nm thin oxo-functionalized graphene derivative, can be used in memory devices operating at 3 V. A memory device stores charges in the material of the active channel. Thereby, writing and erasing information can be performed at low voltage, facilitating low power consumption. To enable operation at low voltage, a novel synthetic approach is necessary. We find that the selective non-covalent electrostatic functionalization of mainly organosulfate ions is possible with dodecylammonium. This functionalization allows the non-covalent coating of flakes with a polystyrene-derivative as nm-thin dielectric medium. The resulting polymer-wrapped composite has a height of about 5 nm. We find that the thin coating of a few nm is mandatory to make the memory device work at low voltage. Furthermore, a self-assembled monolayer of an imidazolium derivative further enhances the function of the memory device. The prepared composite materials are characterized by state-of-the-art analysis including solid state nuclear magnetic resonance spectroscopy and thermogravimetric analysis coupled with gas chromatography, mass spectroscopy or infrared spectroscopy. Reference experiments prove the importance of the controlled synthesis to enable the function of the memory device.
Co-reporter:Cordula D. Wessendorf, Regina Eigler, Siegfried Eigler, Jonas Hanisch, Andreas Hirsch, Erik Ahlswede
Solar Energy Materials and Solar Cells 2015 Volume 132() pp:450-454
Publication Date(Web):January 2015
DOI:10.1016/j.solmat.2014.09.038
•We investigated four pentaarylazafullerenes as acceptors for BHJ solar cells.•The pentaarylazafullerene derivatives have raised LUMO levels compared to PC61BM.•High VOCs up to 837 mV and moderate PCEs up to 0.9% are obtained.•With 1-methylnaphtalene as additive the morphology and performance can be improved.In a comparative study a novel class of pentaarylazafullerene derivatives is investigated as acceptor material in solution-processed organic solar cells. Due to their raised lowest unoccupied molecular orbital (LUMO) compared to phenyl-C61-butyric acid methyl ester (PC61BM) the orbital matching to P3HT is optimized so that an increased open-circuit voltage (VOC) compared to the standard PC61BM acceptor is gained. However, the performance of pentaarylazafullerene solar cells is limited by rather low short circuit currents (JSC) and fill factors (FF) which can be partially improved by using 1-methylnaphtalene as additive. Within this series the azafullerenes with phenoxyphenyl and phenoxymethyl addends 1 and 3 show the best results with encouraging VOCs of >800 mV and power conversion efficiencies (PCEs) of 0.9%.
Co-reporter:Dr. Siegfried Eigler;Dr. Andreas Hirsch
Angewandte Chemie 2014 Volume 126( Issue 30) pp:7852-7872
Publication Date(Web):
DOI:10.1002/ange.201402780
Abstract
Die chemische Herstellung von Graphen sowie seine kontrollierte nasschemische Modifikation sind anspruchsvolle Ziele für Synthesechemiker. Ebenso bedarf es ausgeklügelter analytischer Methoden, um Reaktionsprodukte zu charakterisieren. In diesem Aufsatz beschreiben wir zunächst die Struktur von Graphen und Graphenoxid. Anschließend stellen wir die gängigsten Methoden für die Synthese dieser auf Kohlenstoff basierenden Nanomaterialien vor. Wir fassen den wissenschaftlichen Erkenntnisstand zur nichtkovalenten und kovalenten chemischen Funktionalisierung zusammen und legen besonderen Wert auf die Unterscheidung der Begriffe Graphit und Graphen sowie Graphitoxid und Graphenoxid. Für die Entwicklung alltagstauglicher Anwendungen ist ein verbessertes grundlegendes Verständnis der Struktur und chemischen Eigenschaften von Graphen und Graphenoxid unerlässlich.
Co-reporter:Dr. Siegfried Eigler;Dr. Andreas Hirsch
Angewandte Chemie International Edition 2014 Volume 53( Issue 30) pp:7720-7738
Publication Date(Web):
DOI:10.1002/anie.201402780
Abstract
The chemical production of graphene as well as its controlled wet chemical modification is a challenge for synthetic chemists. Furthermore, the characterization of reaction products requires sophisticated analytical methods. In this Review we first describe the structure of graphene and graphene oxide and then outline the most important synthetic methods that are used for the production of these carbon-based nanomaterials. We summarize the state-of-the-art for their chemical functionalization by noncovalent and covalent approaches. We put special emphasis on the differentiation of the terms graphite, graphene, graphite oxide, and graphene oxide. An improved fundamental knowledge of the structure and the chemical properties of graphene and graphene oxide is an important prerequisite for the development of practical applications.
Co-reporter:Dr. Siegfried Eigler;Stefan Grimm ;Dr. Andreas Hirsch
Chemistry - A European Journal 2014 Volume 20( Issue 4) pp:984-989
Publication Date(Web):
DOI:10.1002/chem.201304048
Abstract
In this study, we use our recently prepared graphene oxide (GO) with an almost intact σ-framework of carbon atoms (ai-GO) to probe the thermal stability of the carbon framework for the first time. Ai-GO exhibits few defects because CO2 formation is prevented during synthesis. Ai-GO was thermally treated before chemical reduction and the resulting defect density in graphene was subsequently determined by statistical Raman microscopy. Surprisingly, the carbon framework of ai-GO is stable in thin films up to 100 °C. Furthermore, we find evidence for an increase in the quality of ai-GO upon annealing at 50 °C before reduction. The carbon framework of GO prepared according to the popular Hummers’ method (GO-c) appears to be less stable and decomposition starts at 50 °C, which is qualitatively indicated by CO2-trapping experiments in μm-thin films. Information about the stability of GO is important for storing, processing, and using GO in many applications.
Co-reporter:Siegfried Eigler, Yichen Hu, Yoshitaka Ishii and Andreas Hirsch
Nanoscale 2013 vol. 5(Issue 24) pp:12136-12139
Publication Date(Web):14 Oct 2013
DOI:10.1039/C3NR04332K
We present the first example of azide functionalization on the surface of graphene oxide (GO), which preserves thermally unstable groups in GO through the mild reaction with sodium azide in solids. Experimental evidence, by 15N solid-state NMR and other spectroscopic methods, indicates the substitution of organosulfate with azide anions as the reaction mechanism.
Co-reporter:Siegfried Eigler, Stefan Grimm, Ferdinand Hof and Andreas Hirsch
Journal of Materials Chemistry A 2013 vol. 1(Issue 38) pp:11559-11562
Publication Date(Web):15 Aug 2013
DOI:10.1039/C3TA12975F
The effect of NaOH and HCl on the stability of the carbon framework in graphene oxide (GO) after substitution or etherification reaction in GO is demonstrated at 10 °C and 40 °C, respectively. Our results allow the preparation of functionalized GO based architectures with an intact σ-framework of carbon atoms.
Co-reporter:Siegfried Eigler, Stefan Grimm, Ferdinand Hof and Andreas Hirsch
Journal of Materials Chemistry A 2013 - vol. 1(Issue 38) pp:NaN11562-11562
Publication Date(Web):2013/08/15
DOI:10.1039/C3TA12975F
The effect of NaOH and HCl on the stability of the carbon framework in graphene oxide (GO) after substitution or etherification reaction in GO is demonstrated at 10 °C and 40 °C, respectively. Our results allow the preparation of functionalized GO based architectures with an intact σ-framework of carbon atoms.
Co-reporter:Zhenxing Wang, Siegfried Eigler, Yoshitaka Ishii, Yichen Hu, Christian Papp, Ole Lytken, Hans-Peter Steinrück and Marcus Halik
Journal of Materials Chemistry A 2015 - vol. 3(Issue 33) pp:NaN8604-8604
Publication Date(Web):2015/07/16
DOI:10.1039/C5TC01861G
Memory devices are a key technology of our era and one of the constant challenges is the reduction of their power consumption. Herein, we demonstrate that graphene oxide with very few defects, that is, about 1 nm thin oxo-functionalized graphene derivative, can be used in memory devices operating at 3 V. A memory device stores charges in the material of the active channel. Thereby, writing and erasing information can be performed at low voltage, facilitating low power consumption. To enable operation at low voltage, a novel synthetic approach is necessary. We find that the selective non-covalent electrostatic functionalization of mainly organosulfate ions is possible with dodecylammonium. This functionalization allows the non-covalent coating of flakes with a polystyrene-derivative as nm-thin dielectric medium. The resulting polymer-wrapped composite has a height of about 5 nm. We find that the thin coating of a few nm is mandatory to make the memory device work at low voltage. Furthermore, a self-assembled monolayer of an imidazolium derivative further enhances the function of the memory device. The prepared composite materials are characterized by state-of-the-art analysis including solid state nuclear magnetic resonance spectroscopy and thermogravimetric analysis coupled with gas chromatography, mass spectroscopy or infrared spectroscopy. Reference experiments prove the importance of the controlled synthesis to enable the function of the memory device.
Co-reporter:Siegfried Eigler ; Ferdinand Hof ; Michael Enzelberger-Heim ; Stefan Grimm ; Paul Müller ;Andreas Hirsch
The Journal of Physical Chemistry C () pp:
Publication Date(Web):March 18, 2014
DOI:10.1021/jp500580g
Graphene oxide can be used as a precursor to graphene, but the quality of graphene flakes is highly heterogeneous. Scanning Raman microscopy (SRM) is used to characterize films of graphene derived from flakes of graphene oxide with an almost intact carbon framework (ai-GO). The defect density of these flakes is visualized in detail by analyzing the intensity and full width at half-maximum of the most pronounced Raman peaks. In addition, we superimpose the SRM results with AFM images and correlate the spectroscopic results with the morphology. Furthermore, we use the SRM technique to display the amount of defects in a film of graphene. Thus, an area of 250 × 250 μm2 of graphene is probed with a step-size increment of 1 μm. We are able to visualize the position of graphene flakes, edges and the substrate. Finally, we alter parameters of measurement to analyze the quality of graphene in a fast and reliable way. The described method can be used to probe and visualize the quality of graphene films.
