Chemists of all fields currently publish about 50 000 crystal structures per year, the vast majority of which are X‐ray structures. We determined two molecular structures by employing electron rather ...than X‐ray diffraction. For this purpose, an EIGER hybrid pixel detector was fitted to a transmission electron microscope, yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Å resolution from a crystal smaller than 1×2 μm2. Several thousand active pharmaceutical ingredients (APIs) are only available as submicrocrystalline powders. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X‐ray crystallography and is the technique of choice for all unsolved cases in which submicrometer‐sized crystals were the limiting factor.
Electrons instead of X‐rays: An electron diffractometer was tailored and employed for de novo structure determination from submicrometer‐sized crystals. A new methylene blue derivative was analysed together with a microcrystalline extract of an active pharmaceutical ingredient from a pill. The results obtained on submicrometer‐sized samples complement X‐ray crystallography.
Conventional memory elements code information in the Boolean “0” and “1” form. Devices that exceed bistability in their resistance are useful as memory for future data storage due to their enhanced ...memory capacity, and are also a necessity for contemporary applications such as neuromorphic computing. Here, with the aid of an experimentally validated device model, design rules are outlined and more than two stable resistance states in a graphene ferroelectric field‐effect transistor are experimentally demonstrated. The design methodology can be extrapolated for on‐demand introduction of multiple resistance states in ferroelectric transistors for applications both in data storage and neuromorphic computing.
The design rules for a graphene ferroelectric transistor with multi‐level resistance states through patterning the ferroelectric gate are outlined and validated. The multiplicity is demonstrated in transistors with polymeric ferroelectric gate insulator. The methodology to create deterministic multiple resistance states in transistors is generic and applicable to other material systems that are envisioned for nonvolatile memory and neuromorphic applications.
•Ferroelectric field-effect transistor memories based on solution-processed graphene have been demonstrated.•The on/off ratio in the graphene FeFET can be tuned by a second non-ferroelectric ...gate.•Graphene FeFETs showed long retention time.
Memories based on graphene that could be mass produced using low-cost methods have not yet received much attention. Here we demonstrate graphene ferroelectric (dual-gate) field effect transistors. The graphene has been obtained using electrochemical exfoliation of graphite. Field-effect transistors are realized using a monolayer of graphene flakes deposited by the Langmuir-Blodgett protocol. Ferroelectric field effect transistor memories are realized using a random ferroelectric copolymer poly(vinylidenefluoride-co-trifluoroethylene) in a top gated geometry. The memory transistors reveal ambipolar behaviour with both electron and hole accumulation channels. We show that the non-ferroelectric bottom gate can be advantageously used to tune the on/off ratio.
Doping-free transfer of graphene produced by catalytic chemical vapor deposition (CVD) on copper foil, is still a technical challenge since unintentional doping of the transferred graphene layer ...yields an uncontrolled shift of Dirac point in graphene-based field-effect transistors (FETs). Typically, CVD graphene is released from the growth template by etching of the template,
i.e.
copper. During the etching process, ions adhere to the graphene layer resulting in unintentional doping. We demonstrate that washing a CVD graphene layer in an aqueous ammonia flow bath after etching copper, removes the majority of the unintentional dopants. FETs fabricated from graphene after washing in DI-water display a large scattering in Dirac bias with lowered mobility. In contrast, FETs from graphene that is washed in ammonia furnish better performance with high geometrically normalized mobility exceeding 2.4 × 10
4
cm
2
V
−1
s
−1
, balanced transport and a Dirac voltage near zero. We attribute the improved FET behavior to effective removal of the ions with a typical density of 4 × 10
12
cm
−2
from the graphene layer.
The paper addresses the technical challenge of producing doping-free transferred graphene layers produced by catalytic chemical vapor deposition (CVD), thereby preventing uncontrolled shift of the Dirac point in comprising field-effect transistors.
Despite the great progress of ferroelectric gated field-effect transistors (Fe-FETs) based on graphene and other 2D materials, a device model that accurately describes the hysteretic transfer ...characteristics and provides guidelines on performance enhancement of the Fe-FET is still lacking. Here, we present an experimentally validated analytical model that couples charge displacement of the ferroelectric layer with the charge transport in the graphene layer. The model describes hysteretic transfer characteristics of the Fe-FETs with good accuracy and predicts that the on/off ratio of the graphene Fe-FET is determined by Dirac bias and the charge carrier mobility. The model predicts the unsuitability of an ideal graphene layer for memory application and outlines the conditions to achieve the best memory performance in graphene Fe-FETs. The model is generic and can be as well used for Fe-FETs based on other 2D materials.
3D electron diffraction has reached a stage where the structures of chemical compounds can be solved productively. Instrumentation is lagging behind this development, and to date dedicated electron ...diffractometers for data collection based on the rotation method do not exist. Current studies use transmission electron microscopes as a workaround. These are optimized for imaging, which is not optimal for diffraction studies. The beam intensity is very high, it is difficult to create parallel beam illumination and the detectors used for imaging are of only limited use for diffraction studies. In this work, the combination of an EIGER hybrid pixel detector with a transmission electron microscope to construct a productive electron diffractometer is described. The construction not only refers to the combination of hardware but also to the calibration of the system, so that it provides rapid access to the experimental parameters that are necessary for processing diffraction data. Until fully integrated electron diffractometers become available, this describes a setup for productive and efficient operation in chemical crystallography.
Installation of the EIGER X 1M detector onto an electron microscope and system calibration for data collection turns a transmission electron microscope into an electron diffraction instrument. Data can be collected and processed with a throughput that meets the requirements of a modern X‐ray facility. The setup described here offers access to single‐crystal structure determination from microcrystalline powder when large single crystals cannot be produced.
Re-establishment of electrical conductivity in graphene oxide (GO), the insulating form of graphene, is (partially) accomplished by reduction through high temperature treatments in a reducing ...atmosphere, or using strongly reducing chemicals or electrolytic processes. The reduction methods are suited for bulk graphene oxide. Spatially resolved reduction of thin films of graphene oxide is important for a wide range of applications such as in microelectronics, where an electrolyte-free, room temperature reduction process is needed. Here, we present spatially resolved solid-state reduction of graphene oxide thin films. We demonstrate that the reduction mechanism is based on electrolysis of water that is adsorbed on the graphene oxide thin film. The reduced graphene oxide thin-films show sheet resistance of only several kOhm, with weak temperature dependence. Graphene oxide can be produced on a large scale and processed using low-cost solution casting techniques. Spatially resolved re-establishment of conductivity in GO can be used in electrically controlled water permeation or in micro- and nanoelectronic applications for instance as an anti-fuse.
Re-establishment of electrical conductivity in graphene oxide (GO), the insulating form of graphene, is (partially) accomplished by reduction through high temperature treatments in a reducing ...atmosphere, or using strongly reducing chemicals or electrolytic processes. The reduction methods are suited for bulk graphene oxide. Spatially resolved reduction of thin films of graphene oxide is important for a wide range of applications such as in microelectronics, where an electrolyte-free, room temperature reduction process is needed. Here, we present spatially resolved solid-state reduction of graphene oxide thin films. We demonstrate that the reduction mechanism is based on electrolysis of water that is adsorbed on the graphene oxide thin film. The reduced graphene oxide thin-films show sheet resistance of only several kOhm, with weak temperature dependence. Graphene oxide can be produced on a large scale and processed using low-cost solution casting techniques. Spatially resolved re-establishment of conductivity in GO can be used in electrically controlled water permeation or in micro- and nanoelectronic applications for instance as an anti-fuse.
Controlled reduction of GO thin-films at room temperature with spatial resolution simply by application of a voltage, without the intentional use of electrolytes, has been demonstrated.
Derzeit publizieren Chemiker aller Fachrichtungen ca. 50 000 Kristallstrukturen pro Jahr, von denen es sich bei der überwältigenden Mehrheit um Röntgenstrukturen handelt. Wir setzen Elektronen‐ statt ...Röntgenbeugung ein, um die Struktur zweier molekularer Verbindungen zu bestimmen. Zu diesem Zweck wurde ein EIGER‐Hybridpixeldetektor an ein Transmissionselektronenmikroskop angebaut und so ein Elektronendiffraktometer konstruiert. Die Struktur eines neuen Methylenblauderivates wurde aus einem Kristall kleiner als 1×2 μm2 mit einer Auflösung von 0.9 Å bestimmt. Mehrere tausend Wirkstoffe sind nur als submikrokristallines Pulver verfügbar. Um das Potenzial für die pharmazeutische Industrie zu verdeutlichen, haben wir die Struktur eines Wirkstoffs direkt aus einer Tablette bestimmt. Wir demonstrieren, dass Elektronenkristallographie die Röntgenkristallographie ergänzt und die Methode der Wahl ist für alle ungelösten Strukturen von submikrometergroßen Kristallen. Die Größe der Kristalle ist uns hier wichtig als Kriterium für die Elektronenbeugung.
Elektronen ersetzen Röntgen‐Strahlen bei der De‐novo‐Strukturbestimmung an submikrometergroßen Kristallen mit einem Elektronendiffraktometer. Auf diese Weise wurden ein Methylenblauderivat und ein mikrokristallines Wirkstoffextrakt aus einer Pille untersucht und Details der dreidimensionalen Molekülstruktur ermittelt. Die mithilfe von submikrometergroßen Proben erhaltenen Ergebnisse ergänzen die Röntgen‐Kristallographie.
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