Search

Your search keyword '"Fink, H-W"' showing total 46 results
Start Over Author "Fink, H-W"
46 results on '"Fink, H-W"'

4. Individual filamentous phage imaged by electron holography

Author

Stevens, G B, Krüger, M, Latychevskaia, T, Lindner, P, Plückthun, A, Fink, H-W, University of Zurich, and Stevens, G B

Subjects
530 Physics, 10019 Department of Biochemistry, 570 Life sciences, biology, 10192 Physics Institute, 1304 Biophysics
Abstract

An in-line electron hologram of an individual f1.K phage was recorded with a purpose-built low energy electron point source (LEEPS) microscope. Cryo-microscopic methods were employed to prepare the specimen so that a single phage could be presented to the coherent low energy electrons: An aqueous phage suspension was applied to a thin carbon membrane with micro-machined slits. The membrane was rapidly cooled to freeze the remaining water as an amorphous ice sheet, which was then sublimated at low temperatures and pressures to leave individual free-standing phages suspended across slits. An image of a phage particle, depicted as the amplitude of the object wave, was reconstructed numerically from a digitized record of the hologram, obtained using 88eV coherent electrons. The reconstructed image shows a single phage suspended across a slit in a supporting carbon membrane, magnified by a factor of 100,000. The width and shape in the reconstructed image compared well with a TEM image of the same filament. It is thus possible to record and reconstruct electron holograms of an individual phage. The challenge now is to improve the resolution of reconstructed images obtained by this method and to extend these structural studies to other biological molecules

Published
2018

7. Resolution enhancement by extrapolation of coherent diffraction images: A quantitative study on the limits and a numerical study of non-binary and phase objects

Author

Latychevskaia, Tatiana, Chushkin, Yuriy, Fink, H-W, University of Zurich, and Latychevskaia, Tatiana

Subjects
2734 Pathology and Forensic Medicine, 530 Physics, Physics - Data Analysis, Statistics and Probability, Physics::Optics, FOS: Physical sciences, 10192 Physics Institute, Astrophysics - Instrumentation and Methods for Astrophysics, 2722 Histology, Instrumentation and Methods for Astrophysics (astro-ph.IM), Data Analysis, Statistics and Probability (physics.data-an), Physics - Optics, Optics (physics.optics)
Abstract

In coherent diffractive imaging (CDI) the resolution of the reconstructed object is limited by the numerical aperture of the experimental setup. We present here a theoretical and numerical study for achieving super-resolution by post-extrapolation of coherent diffraction images, such as diffraction patterns or holograms. We demonstrate that a diffraction pattern can unambiguously be extrapolated from only a fraction of the entire pattern and that the ratio of the extrapolated signal to the originally available signal is linearly proportional to the oversampling ratio. While there could be in principle other methods to achieve extrapolation, we devote our discussion to employing iterative phase retrieval methods and demonstrate their limits. We present two numerical studies; namely the extrapolation of diffraction patterns of non-binary and that of phase objects together with a discussion of the optimal extrapolation procedure.

Published
2015
Full Text
View/download PDF

9. Non-destructive imaging of an individual protein

Author

Longchamp, J-N, Latychevskaia, T, Escher, C, Fink, H-W, and University of Zurich

Subjects
530 Physics, 10192 Physics Institute, 3101 Physics and Astronomy (miscellaneous)
Published
2012

15. Electron beam collimation with a 40 000 tip metallic double-gate field emitter array and in-situ control of nanotip sharpness distribution

Author

Helfenstein, P, Guzenko, V A, Fink, H W, Tsujino, S, Helfenstein, P, Guzenko, V A, Fink, H W, and Tsujino, S

Abstract

The generation of highly collimated electron beams from a double-gate field emitter array with 40000 metallic tips and large collimation gate apertures is reported. Field emission beam measurements demonstrated the reduction of the beam envelope down to the array size by applying a negative potential to the on-chip gate electrode for the collimation of individual field emission beamlets. Owing to the optimized gate structure, the concomitant decrease of the emission current was minimal, leading to a net enhancement of the current density. Furthermore, a noble gas conditioning process was successfully applied to the double-gate device to improve the beam uniformity in-situ with orders of magnitude increase of the active emission area. The results show that the proposed double-gate field emission cathodes are promising for high current and high brightness electron beam applications such as free-electron lasers and THz power devices.

Published
2013

17. Fabrication of metallic double-gate field emitter arrays and their electron beam collimation characteristics

Author

Helfenstein, P, Jefimovs, K, Kirk, E, Escher, C, Fink, H-W, Tsujino, S, Helfenstein, P, Jefimovs, K, Kirk, E, Escher, C, Fink, H-W, and Tsujino, S

Abstract

The fabrication of double-gate metallic field emitter arrays with large collimation gate apertures and their field emission beam characteristics are reported. The device fabrication steps, including the molding technique for array fabrication, the electron extraction gate fabrication by the self-aligned resist etch-back method, and the fabrication of the collimation gate electrode using a focused ion beam assisted method are described in detail. The experimental results of 2 × 2 tip arrays with the proposed double-gate structure demonstrate an order of magnitude enhancement in beam brightness with minimal current loss. A similarly high beam brightness enhancement was achieved with a 20 × 20 tip array device, showing the scalability of the proposed structure. The observation of improved current-voltage characteristics with the 20 × 20 tip array is ascribed to the difference in gate aperture shape. The possibility of further improving the beam characteristics of double-gate field emitter arrays and the reduction of the transverse electron velocity spread are discussed.

Published
2012

18. Highly collimated electron beams from double-gate field emitter arrays with large collimation gate apertures

Author

Helfenstein, P, Kirk, E, Jefimovs, K, Vogel, T, Escher, C, Fink, H W, Tsujino, S, Helfenstein, P, Kirk, E, Jefimovs, K, Vogel, T, Escher, C, Fink, H W, and Tsujino, S

Abstract

Electron collimation in field emitter arrays with electron extraction gate and collimation gate electrodes is studied with the goal to develop a high-brightness high current cathode. Using metallic field emitter arrays prepared by the molding method, we fabricated a stacked double-gate device with the two gates differing in diameter by a process utilizing focused-ion beam milling. We measured the field-emission beam characteristics and demonstrated a reduction of the emission angle by a factor of 7.1±0.8 with minimal emission current decrease under collimating conditions, resulting in a current density increase by a factor of 13.9±1.0.

Published
2011

19. Depth-resolved holographic reconstructions by three-dimensional deconvolution

Author

Latychevskaia, T, Gehri, F, Fink, H W, Latychevskaia, T, Gehri, F, and Fink, H W

Abstract

Methods of three-dimensional deconvolution with a point-spread function as frequently employed in optical microscopy to reconstruct true three-dimensional distribution of objects are extended to holographic reconstructions. Two such schemes have been developed and are discussed: an instant deconvolution using the Wiener filter as well as an iterative deconvolution routine. The instant 3d-deconvolution can be applied to restore the positions of volume-spread objects such as small particles. The iterative deconvolution can be applied to restore the distribution of complex and extended objects. Simulated and experimental examples are presented and demonstrate artifact and noise free three-dimensional reconstructions from a single two-dimensional holographic record.

Published
2010

20. Field-emission characteristics of molded molybdenum nanotip arrays with stacked collimation gate electrodes

Author

Tsujino, S, Helfenstein, P, Kirk, E, Vogel, T, Escher, C, Fink, H-W, Tsujino, S, Helfenstein, P, Kirk, E, Vogel, T, Escher, C, and Fink, H-W

Abstract

Double-gate field-emission characteristics of metallic field-emitter-array (FEA) cathodes fabricated by molding with stacked collimation gate electrodes with planar end plane are reported. The collimation of field-emission electron beam with minimal reduction of emission current is demonstrated when a negative bias is applied to the collimation gate, whereas when the two electrodes are at the same potential, the emission characteristic of the double-gate device is the same as that of the single-gate device that shows an emission current of ~1 mA from 40 × 40 tip arrays. Results indicate that the device structure of the fabricated double-gate FEAs is promising for high-brilliance cathode applications

Published
2010

26. Electrical conduction through DNA molecules.

Author

Fink, H.-W.

Subjects
*DNA, *MOLECULES, *CHARGE transfer in biology
Abstract

The first direct experimental evidence for effective charge transport though individual DNA molecules will be discussed. Visualization of the DNA molecules as well as mechanical and electrical manipulations is carried out in the Low Energy Electron Point Source Microscope whose principle of operation will be illustrated. [ABSTRACT FROM AUTHOR]

Published
2000

41. Electrical conduction through DNA molecules.

Author

Fink HW and Schönenberger C

Subjects
DNA ultrastructure, Electric Conductivity, Electrochemistry, Electrons, Microscopy, Electron methods, Microscopy, Electron, Scanning, DNA chemistry
Abstract

The question of whether DNA is able to transport electrons has attracted much interest, particularly as this ability may play a role as a repair mechanism after radiation damage to the DNA helix. Experiments addressing DNA conductivity have involved a large number of DNA strands doped with intercalated donor and acceptor molecules, and the conductivity has been assessed from electron transfer rates as a function of the distance between the donor and acceptor sites. But the experimental results remain contradictory, as do theoretical predictions. Here we report direct measurements of electrical current as a function of the potential applied across a few DNA molecules associated into single ropes at least 600 nm long, which indicate efficient conduction through the ropes. We find that the resistivity values derived from these measurements are comparable to those of conducting polymers, and indicate that DNA transports electrical current as efficiently as a good semiconductor. This property, and the fact that DNA molecules of specific composition ranging in length from just a few nucleotides to chains several tens of micrometres long can be routinely prepared, makes DNA ideally suited for the construction of mesoscopic electronic devices.

Published
1999
Full Text
View/download PDF

44. Letter: High fever.

Author

Fink HW

Subjects
Child, Humans, Pneumonia diagnosis, Fever
Published
1975

Catalog

Books, media, physical & digital resources
See catalog results