Fabrication of carbon nanomembranes by helium ion beam lithography

Zhang X, Vieker H, Beyer A, Gölzhäuser A. Fabrication of carbon nanomembranes by helium ion beam lithography. Beilstein Journal of Nanotechnology. 2014;5:188-194.The irradiation-induced cross-linking of aromatic self-assembled monolayers (SAMs) is a universal method for the fabrication of ultrathin carbon nanomembranes (CNMs). Here we demonstrate the cross-linking of aromatic SAMs due to exposure to helium ions. The distinction of cross-linked from non-cross-linked regions in the SAM was facilitated by transferring the irradiated SAM to a new substrate, which allowed for an ex situ observation of the cross-linking process by helium ion microscopy (HIM). In this way, three growth regimes of cross-linked areas were identified: formation of nuclei, one-dimensional (1D) and two-dimensional (2D) growth. The evaluation of the corresponding HIM images revealed the dose-dependent coverage, i.e., the relative monolayer area, whose density of cross-links surpassed a certain threshold value, as a function of the exposure dose. A complete cross-linking of aromatic SAMs by He+ ion irradiation requires an exposure dose of about 850 mu C/cm(2), which is roughly 60 times smaller than the corresponding electron irradiation dose. Most likely, this is due to the energy distribution of secondary electrons shifted to lower energies, which results in a more efficient dissociative electron attachment (DEA) process

Energy-filtered transmission electron microscopy of biological samples on highly transparent carbon nanomembranes

Ultrathin carbon nanomembranes (CNM) comprising crosslinked biphenyl precursors have been tested as support films for energy-filtered transmission electron microscopy (EFTEM) of biological specimens. Due to their high transparency CNM are ideal substrates for electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) of stained and unstained biological samples. Virtually background-free elemental maps of tobacco mosaic virus (TMV) and ferritin have been obtained from samples supported by ~ 1 nm thin CNM. Furthermore, we have tested conductive carbon nanomembranes (cCNM) comprising nanocrystalline graphene, obtained by thermal treatment of CNM, as supports for cryoEM of ice-embedded biological samples. We imaged ice-embedded TMV on cCNM and compared the results with images of ice-embedded TMV on conventional carbon film (CC), thus analyzing the gain in contrast for TMV on cCNM in a quantitative manner. In addition we have developed a method for the preparation of vitrified specimens, suspended over the holes of a conventional holey carbon film, while backed by ultrathin cCNM

Single-walled carbon nanotubes and nanocrystalline graphene reduce beam-induced movements in high-resolution electron cryo-microscopy of ice-embedded biological samples

For single particle electron cryo-microscopy (cryoEM), contrast loss due to beam-induced charging and specimen movement is a serious problem, as the thin films of vitreous ice spanning the holes of a holey carbon film are particularly susceptible to beam-induced movement. We demonstrate that the problem is at least partially solved by carbon nanotechnology. Doping ice-embedded samples with single-walled carbon nanotubes (SWNT) in aqueous suspension or adding nanocrystalline graphene supports, obtained by thermal conversion of cross-linked self-assembled biphenyl precursors, significantly reduces contrast loss in high-resolution cryoEM due to the excellent electrical and mechanical properties of SWNTs and graphene

TLC-SERS Plates with a Built-In SERS Layer Consisting of Cap-Shaped Noble Metal Nanoparticles Intended for Environmental Monitoring and Food Safety Assurance

Takei H, Saito J, Kato K, Vieker H, Beyer A, Gölzhäuser A. TLC-SERS Plates with a Built-In SERS Layer Consisting of Cap-Shaped Noble Metal Nanoparticles Intended for Environmental Monitoring and Food Safety Assurance. Journal of Nanomaterials. 2015;2015: 316189 .We report on a thin layer chromatograph (TLC) with a built-in surface enhanced Raman scattering (SERS) layer for in-situ identification of chemical species separated by TLC. Our goal is to monitor mixture samples or diluted target molecules suspended in a host material, as happens often in environmental monitoring or detection of food additives. We demonstrate that the TLC-SERS can separate mixture samples and provide in-situ SERS spectra. One sample investigated was a mixture consisting of equal portions of Raman-active chemical species, rhodamine 6 G (R6G), crystal violet (CV), and 1,2-di(4-pyridyl)ethylene (BPE). The three components could be separated and their SERS spectra were obtained from different locations. Another sample was skim milk with a trace amount of melamine. Without development, no characteristic peaks were observed, but after development, a peak was observed at 694 cm(-1). Unlike previous TLC-SERS whereby noble metal nanoparticles are added after development of a sample, having a built-in SERS layer greatly facilitates analysis as well as maintaining high uniformity of noble metal nanoparticles

Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers

Rueckriem K, Grotheer S, Vieker H, et al. Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers. BEILSTEIN JOURNAL OF NANOTECHNOLOGY. 2016;7:852-861.Copper(II) oxalate grown on carboxy-terminated self-assembled monolayers (SAM) using a step-by-step approach was used as precursor for the electron-induced synthesis of surface-supported copper nanoparticles. The precursor material was deposited by dipping the surfaces alternately in ethanolic solutions of copper(II) acetate and oxalic acid with intermediate thorough rinsing steps. The deposition of copper(II) oxalate and the efficient electron-induced removal of the oxalate ions was monitored by reflection absorption infrared spectroscopy (RAIRS). Helium ion microscopy (HIM) reveals the formation of spherical nanoparticles with well-defined size and X-ray photoelectron spectroscopy (XPS) confirms their metallic nature. Continued irradiation after depletion of oxalate does not lead to further particle growth giving evidence that nanoparticle formation is primarily controlled by the available amount of precursor

Imaging of carbon nanomembranes with helium ion microscopy

Beyer A, Vieker H, Klett R, Meyer Zu Theenhausen H, Angelova P, Gölzhäuser A. Imaging of carbon nanomembranes with helium ion microscopy. Beilstein Journal of Nanotechnology. 2015;6:1712-1720.Carbon nanomembranes (CNMs) prepared from aromatic self-assembled monolayers constitute a recently developed class of 2D materials. They are made by a combination of self-assembly, radiation-induced cross-linking and the detachment of the cross-linked SAM from its substrate. CNMs can be deposited on arbitrary substrates, including holey and perforated ones, as well as on metallic (transmission electron microscopy) grids. Therewith, freestanding membranes with a thickness of 1 nm and macroscopic lateral dimensions can be prepared. Although free-standing CNMs cannot be imaged by light microscopy, charged particle techniques can visualize them. However, CNMs are electrically insulating, which makes them sensitive to charging. We demonstrate that the helium ion microscope (HIM) is a good candidate for imaging freestanding CNMs due to its efficient charge compensation tool. Scanning with a beam of helium ions while recording the emitted secondary electrons generates the HIM images. The advantages of HIM are high resolution, high surface sensitivity and large depth of field. The effects of sample charging, imaging of multilayer CNMs as well as imaging artefacts are discussed

39K and 77Se NMR study of the paraelectric-to-incommensurate phase transition of K2SeO4

Topic B, von Kienlin A, Gölzhäuser A, Haeberlin U, Blinc R. 39K and 77Se NMR study of the paraelectric-to-incommensurate phase transition of K2SeO4. Physical Review, B. 1988;38(13):8625-8632.The 39K quadrupole-coupling and chemical-shift tensors have been determined from the angular dependences of the 39K line shifts of the 39K±(1/2 ± 1) / 2 central NMR transitions in the paraelectric (P) and incommensurate (I) phases of K2SeO4. The main effect of the P-I phase transition on these tensors is the appearance of nonzero off-diagonal elements Vab and Vbc which reflects the destruction of mirror planes by frozen-in soft-mode displacements along the b axis. From the angular dependences of the 77Se line shifts the 77Se chemical-shift tensor has been determined in the paraelectric phase of K2SeO4. In contrast to the 39K quadrupole-coupling and chemical-shift tensors it remains unaffected on going through TI and changes only slightly at TC

New Polymers for Needleless Electrospinning from Low-Toxic Solvents.

Wortmann M, Frese N, Sabantina L, et al. New Polymers for Needleless Electrospinning from Low-Toxic Solvents. Nanomaterials (Basel, Switzerland). 2019;9(1): 52

Ultrahigh Ionic Exclusion through Carbon Nanomembranes.

Yang Y, Hillmann R, Qi Y, et al. Ultrahigh Ionic Exclusion through Carbon Nanomembranes. Advanced materials . 2020;32(8): e1907850.The collective "single-file" motion of water molecules through natural and artificial nanoconduits inspires the development of high-performance membranes for water separation. However, a material that contains a large number of pores combining rapid water flow with superior ion rejection is still highly desirable. Here, a 1.2 nm thick carbon nanomembrane (CNM) made from cross-linking of terphenylthiol (TPT) self-assembled monolayers is reported to possess these properties. Utilizing their extremely high pore density of 1 sub-nm channel nm-2 , TPT CNMs let water molecules rapidly pass, while the translocation of ions, including protons, is efficiently hindered. Their membrane resistance reaches 104 Omega cm2 in 1 m Cl- solutions, comparable to lipid bilayers of a cell membrane. Consequently, a single CNM channel yields an 108 higher resistance than pores in lipid membrane channels and carbon nanotubes. The ultrahigh ionic exclusion by CNMs is likely dominated by a steric hindrance mechanism, coupled with electrostatic repulsion and entrance effects. The operation of TPT CNM membrane composites in forward osmosis is also demonstrated. These observations highlight the potential of utilizing CNMs for water purification and opens up a simple avenue to creating 2D membranes through molecular self-assembly for highly selective and fast separations. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Technical feasibility study for production of tailored multielectrode arrays and patterning of arranged neuronal networks

Schürmann M, Shepheard N, Frese N, et al. Technical feasibility study for production of tailored multielectrode arrays and patterning of arranged neuronal networks. PLOS ONE. 2018;13(2): e0192647.In this manuscript, we first reveal a simple ultra violet laser lithographic method to design and produce plain tailored multielectrode arrays. Secondly, we use the same lithographic setup for surface patterning to enable controlled attachment of primary neuronal cells and help neurite guidance. For multielectrode array production, we used flat borosilicate glass directly structured with the laser lithography system. The multi layered electrode system consists of a layer of titanium coated with a layer of di-titanium nitride. Finally, these electrodes are covered with silicon nitride for insulation. The quality of the custom made multielectrode arrays was investigated by light microscopy, electron microscopy and X-ray diffraction. The performance was verified by the detection of action potentials of primary neurons. The electrical noise of the custom-made MEA was equal to commercially available multielectrode arrays. Additionally, we demonstrated that structured coating with poly lysine, obtained with the aid of the same lithographic system, could be used to attach and guide neurons to designed structures. The process of neuron attachment and neurite guidance was investigated by light microscopy and charged particle microscopy. Importantly, the utilization of the same lithographic system for MEA fabrication and poly lysine structuring will make it easy to align the architecture of the neuronal network to the arrangement of the MEA electrode.. In future studies, this will lead to multielectrode arrays, which are able to specifically attach neuronal cell bodies to their chemically defined electrodes and guide their neurites, gaining a controlled connectivity in the neuronal network. This type of multielectrode array would be able to precisely assign a signal to a certain neuron resulting in an efficient way for analyzing the maturation of the neuronal connectivity in small neuronal networks