2021, Carnis, Jerome, Kirner, Felizitas, Lapkin, Dmitry, Sturm, Sebastian, Kim, Young Yong, Baburin, Igor A., Khubbutdinov, Ruslan, Ignatenko, Alexandr, Iashina, Ekaterina, Mistonov, Alexander, Steegemans, Tristan, Wieck, Thomas, Gemming, Thomas, Lubk, Axel, Lazarev, Sergey, Sprung, Michael, Vartanyants, Ivan A., Sturm, Elena V.

Correction for ‘Exploring the 3D structure and defects of a self-assembled gold mesocrystal by coherent X-ray diffraction imaging’ by Jerome Carnis et al., Nanoscale, 2021, DOI: 10.1039/D1NR01806J.

2021, Mendes, Rafael G., Ta, Huy Q., Yang, Xiaoqin, Bachmatiuk, Alicja, Praus, Petr, Mamakhel, Aref, Iversen, Bo B., Su, Ren, Gemming, Thomas, Rümmeli, Mark H.

Two-dimensional polymeric graphitic carbon nitride (g-C3N4) is a low-cost material with versatile properties that can be enhanced by the introduction of dopant atoms and by changing the degree of polymerization/stoichiometry, which offers significant benefits for numerous applications. Herein, we investigate the stability of g-C3N4 under electron beam irradiation inside a transmission electron microscope operating at different electron acceleration voltages. Our findings indicate that the degradation of g-C3N4 occurs with N species preferentially removed over C species. However, the precise nitrogen group from which N is removed from g-C3N4 (C–N–C, [double bond, length as m-dash]NH or –NH2) is unclear. Moreover, the rate of degradation increases with decreasing electron acceleration voltage, suggesting that inelastic scattering events (radiolysis) dominate over elastic events (knock-on damage). The rate of degradation by removing N atoms is also sensitive to the current density. Hence, we demonstrate that both the electron acceleration voltage and the current density are parameters with which one can use to control the stoichiometry. Moreover, as N species were preferentially removed, the d-spacing of the carbon nitride structure increased. These findings provide a deeper understanding of g-C3N4.

2019, Gonzalez-Martinez, Ignacio G., Bachmatiuk, Alicja, Gemming, Thomas, Trzebicka, Barbara, Liu, Zhongfan, Rummeli, Mark H.

Multiple methods with distinctive strengths and drawbacks have been devised so far to produce graphene. However, they all need post-synthesis transfer steps to characterize the product. Here we report the synthesis of pristine graphene inside the transmission electron microscope using gold as catalyst and self-removing substrate without employing a specialized specimen holder. The process occurs at room temperature and takes place within milliseconds. The method offers the possibility of precise spatial control for graphene production and immediate characterization. Briefly, the irradiating electrons generate secondary electrons leading to surface charging if the gold particles reside on a poorly conducting support. At a critical charge density, the particle ejects ions mixed with secondary electrons (plasma) causing the particle to shrink. Simultaneously, hydrocarbon contamination within the electron microscope is cracked, thus providing carbon for the growth of graphene on the particle’s surface. The Technique is potentially attractive for the manufacture of in situ graphene-based devices. © 2019, The Author(s).

2015, Mendes, Rafael Gregorio, Koch, Britta, Bachmatiuk, Alicja, Ma, Xing, Sanchez, Samuel, Damm, Christine, Schmidt, Oliver G., Gemming, Thomas, Eckert, Jürgen, Rümmeli, Mark H.

Graphene oxide (GO) has attracted great interest due to its extraordinary potential for biomedical application. Although it is clear that the naturally occurring morphology of biological structures is crucial to their precise interactions and correct functioning, the geometrical aspects of nanoparticles are often ignored in the design of nanoparticles for biological applications. A few in vitro and in vivo studies have evaluated the cytotoxicity and biodistribution of GO, however very little is known about the influence of flake size and cytotoxicity. Herein, we aim at presenting an initial cytotoxicity evaluation of different nano-sized GO flakes for two different cell lines (HeLa (Kyoto) and macrophage (J7742)) when they are exposed to samples containing different sized nanographene oxide (NGO) flakes (mean diameter of 89 and 277 nm). The obtained data suggests that the larger NGO flakes reduce cell viability as compared to smaller flakes. In addition, the viability reduction correlates with the time and the concentration of the NGO nanoparticles to which the cells are exposed. Uptake studies were also conducted and the data suggests that both cell lines internalize the GO nanoparticles during the incubation periods studied.

2023, Hasan, Maria, Ta, Huy Q., Ullah, Sami, Yang, Xiaoqin, Luo, Jingping, Bachmatiuk, Alicja, Gemming, Thomas, Trzebicka, Barbara, Mahmood, Azhar, Zeng, Mengqi, Fu, Lei, Liu, Lijun, Rümmeli, Mark H.

The field of two dimensional (2D) materials experienced a surge of discoveries after the isolation of graphene. Among these, the transition metal compounds of Molybdenum and tungsten have been the most extensively studied materials after graphene. More recently, their group member chromium has only recently come to the limelight after the discovery of its exciting magnetic properties. As such the body of work surrounding 2D chromium-based materials is growing. Here, we present an up-to-date summary of the chromium 2D materials showing the latest advances in their experimental synthesis, characterization and the applications of 2D Chromium-based compounds. Finally, we conclude with a perspective on the future of 2D chromium-based materials. We believe that this study will be helpful to understand the field of chromium-based 2D compounds.

2020, Ta, Huy Quang, Bachmatiuk, Alicja, Mendes, Rafael Gregorio, Perello, David J., Zhao, Liang, Trzebicka, Barbara, Gemming, Thomas, Rotkin, Slava V., Rümmeli, Mark H.

In 1665 Christiaan Huygens first noticed how two pendulums, regardless of their initial state, would synchronize. It is now known that the universe is full of complex self-organizing systems, from neural networks to correlated materials. Here, graphene flakes, nucleated over a polycrystalline graphene film, synchronize during growth so as to ultimately yield a common crystal orientation at the macroscale. Strain and diffusion gradients are argued as the probable causes for the long-range cross-talk between flakes and the formation of a single-grain graphene layer. The work demonstrates that graphene synthesis can be advanced to control the nucleated crystal shape, registry, and relative alignment between graphene crystals for large area, that is, a single-crystal bilayer, and (AB-stacked) few-layer graphene can been grown at the wafer scale. © 2020 The Authors. Published by Wiley-VCH GmbH

2019, Richard, Cynthia, Fakhfouri, Armaghan, Colditz, Melanie, Striggow, Friedrich, Kronstein-Wiedemann, Romy, Tonn, Torsten, Medina-Sánchez, Mariana, Schmidt, Oliver G., Gemming, Thomas, Winkler, Andreas

The ability to separate specific biological components from cell suspensions is indispensable for liquid biopsies, and for personalized diagnostics and therapy. This paper describes an advanced surface acoustic wave (SAW) based device designed for the enrichment of platelets (PLTs) from a dispersion of PLTs and red blood cells (RBCs) at whole blood concentrations, opening new possibilities for diverse applications involving cell manipulation with high throughput. The device is made of patterned SU-8 photoresist that is lithographically defined on the wafer scale with a new proposed methodology. The blood cells are initially focused and subsequently separated by an acoustic radiation force (ARF) applied through standing SAWs (SSAWs). By means of flow cytometric analysis, the PLT concentration factor was found to be 7.7, and it was proven that the PLTs maintain their initial state. A substantially higher cell throughput and considerably lower applied powers than comparable devices from literature were achieved. In addition, fully coupled 3D numerical simulations based on SAW wave field measurements were carried out to anticipate the coupling of the wave field into the fluid, and to obtain the resulting pressure field. A comparison to the acoustically simpler case of PDMS channel walls is given. The simulated results show an ideal match to the experimental observations and offer the first insights into the acoustic behavior of SU-8 as channel wall material. The proposed device is compatible with current (Lab-on-a-Chip) microfabrication techniques allowing for mass-scale, reproducible chip manufacturing which is crucial to push the technology from lab-based to real-world applications. © The Royal Society of Chemistry.

2021, Nsamela, Audrey, Sharan, Priyanka, Garcia‐Zintzun, Aidee, Heckel, Sandra, Chattopadhyay, Purnesh, Wang, Linlin, Wittmann, Martin, Gemming, Thomas, Saenz, James, Simmchen, Juliane

Although many biological fluids like blood and mucus exhibit high viscosities, there are still many open questions concerning the swimming behavior of microswimmers in highly viscous media, limiting research to idealized laboratory conditions instead of application-oriented scenarios. Here, we analyze the effect of viscosity on the swimming speed and motion pattern of four kinds of microswimmers of different sizes which move by contrasting propulsion mechanisms: two biological swimmers (bovine sperm cells and Bacillus subtilis bacteria) which move by different bending patterns of their flagella and two artificial swimmers with catalytic propulsion mechanisms (alginate microtubes and Janus Pt@SiO2 spherical microparticles). Experiments consider two different media (glycerol and methylcellulose) with increasing viscosity, but also the impact of surface tension, catalyst activity and diffusion coefficients are discussed and evaluated.