OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 12 — Jun. 6, 2011
  • pp: 11059–11070
« Show journal navigation

X-ray holographic microscopy with zone plates applied to biological samples in the water window using 3rd harmonic radiation from the free-electron laser FLASH

T. Gorniak, R. Heine, A. P. Mancuso, F. Staier, C. Christophis, M. E. Pettitt, A. Sakdinawat, R. Treusch, N. Guerassimova, J. Feldhaus, C. Gutt, G. Grübel, S. Eisebitt, A. Beyer, A. Gölzhäuser, E. Weckert, M. Grunze, I. A. Vartanyants, and A. Rosenhahn  »View Author Affiliations


Optics Express, Vol. 19, Issue 12, pp. 11059-11070 (2011)
http://dx.doi.org/10.1364/OE.19.011059


View Full Text Article

Acrobat PDF (1236 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

The imaging of hydrated biological samples – especially in the energy window of 284-540 eV, where water does not obscure the signal of soft organic matter and biologically relevant elements – is of tremendous interest for life sciences. Free-electron lasers can provide highly intense and coherent pulses, which allow single pulse imaging to overcome resolution limits set by radiation damage. One current challenge is to match both the desired energy and the intensity of the light source. We present the first images of dehydrated biological material acquired with 3rd harmonic radiation from FLASH by digital in-line zone plate holography as one step towards the vision of imaging hydrated biological material with photons in the water window. We also demonstrate the first application of ultrathin molecular sheets as suitable substrates for future free-electron laser experiments with biological samples in the form of a rat fibroblast cell and marine biofouling bacteria Cobetia marina.

© 2011 OSA

1. Introduction

The most recent step in the development of highly brilliant and coherent X-ray light sources is the evolution from 3rd generation synchrotrons to free-electron lasers (FELs) [1

1. C. A. Brau, “Free-electron lasers,” Science 239(4844), 1115–1121 (1988). [CrossRef] [PubMed]

,2

2. J. Feldhaus, J. Arthur, and J. Hastings, “X-ray free-electron lasers,” J. Phys. B: At. Mol. Opt. Phys. 38(9), S799–S819 (2005). [CrossRef]

]. The free-electron laser in Hamburg (FLASH) [3

3. W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, J. T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, H. T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, C. Gerth, M. Görler, N. Golubeva, H. J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, J. R. Schneider, E. A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, A. V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, M. V. Yurkov, I. Zagorodnov, and K. Zapfe, “Operation of a free-electron laser from the extreme ultraviolet to the water window,” Nat. Photonics 1(6), 336–342 (2007). [CrossRef]

,4

4. K. Tiedtke, A. Azima, N. von Bargen, L. Bittner, S. Bonfigt, S. Düsterer, B. Faatz, U. Frühling, M. Gensch, C. Gerth, N. Guerassimova, U. Hahn, T. Hans, M. Hesse, K. Honkavaar, U. Jastrow, P. Juranic, S. Kapitzki, B. Keitel, T. Kracht, M. Kuhlmann, W. B. Li, M. Martins, T. Núñez, E. Plönjes, H. Redlin, E. L. Saldin, E. A. Schneidmiller, J. R. Schneider, S. Schreiber, N. Stojanovic, F. Tavella, S. Toleikis, R. Treusch, H. Weigelt, M. Wellhöfer, H. Wabnitz, M. V. Yurkov, and J. Feldhaus, “The soft x-ray free-electron laser FLASH at DESY: beamlines, diagnostics and end-stations,” N. J. Phys. 11(2), 023029 (2009). [CrossRef]

] operates in the extreme ultraviolet regime (XUV) down to 4.15 nm with lasing demonstrated to occur even in the 5th harmonic [5

5. C. Gutt, L. M. Stadler, S. Streit-Nierobisch, A. P. Mancuso, A. Schropp, B. Pfau, C. M. Günther, R. Könnecke, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, I. A. Vartanyants, O. Hellwig, F. Staier, R. Barth, M. Grunze, A. Rosenhahn, D. Stickler, H. Stillrich, R. Frömter, H. P. Oepen, M. Martins, T. Nisius, T. Wilhein, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. Schneidmiller, M. Yurkov, S. Eisebitt, and G. Grübel, “Resonant magnetic scattering with soft x-ray pulses from a free-electron laser operating at 1.59 nm,” Phys. Rev. B 79(21), 212406 (2009). [CrossRef]

]. Its successors at shorter wavelengths such as the LCLS in the US [6

6. P. Emma, R. Akre, J. Arthur, R. Bionta, C. Bostedt, J. Bozek, A. Brachmann, P. Bucksbaum, R. Coffee, F. J. Decker, Y. Ding, D. Dowell, S. Edstrom, A. Fisher, J. Frisch, S. Gilevich, J. Hastings, G. Hays, P. Hering, Z. Huang, R. Iverson, H. Loos, M. Messerschmidt, A. Miahnahri, S. Moeller, H. D. Nuhn, G. Pile, D. Ratner, J. Rzepiela, D. Schultz, T. Smith, P. Stefan, H. Tompkins, J. Turner, J. Welch, W. White, J. Wu, G. Yocky, and J. Galayda, “First lasing and operation of an ångstrom-wavelength free-electron laser,” Nat. Photonics 4(9), 641–647 (2010). [CrossRef]

] and the European XFEL [7

7. M. Altarelli, R. Brinkmann, M. Chergui, W. Decking, B. Dobson, S. Düsterer, G. Grübel, W. Graeff, H. Graafsma, J. Hajdu, J. Marangos, J. Pflüger, H. Redlin, D. Riley, I. Robinson, J. Rossbach, A. Schwarz, K. Tiedtke, T. Tschentscher, I. Vartanyants, H. Wabnitz, H. Weise, R. Wichmann, K. Witte, A. Wolf, M. Wulff, and M. Yurkov, “The European X-Ray Free-Electron Laser. Technical Design Report” (2006), retrieved http://xfel.desy.de/tdr/tdr/.

] – which are expected to reach much higher (keV) photon energies at strongly increased peak brilliance – offer stunning opportunities to scientists who are working in the fields of physics, chemistry, medicine and biology [8

8. H. N. Chapman, “X-ray imaging beyond the limits,” Nat. Mater. 8(4), 299–301 (2009). [CrossRef] [PubMed]

,9

9. N. Patel, “Shorter, brighter, better,” Nature 415(6868), 110–111 (2002). [CrossRef] [PubMed]

]. The above FELs which are based on the self-amplified spontaneous emission (SASE) principle [10

10. E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov, The Physics of Free Electron Lasers (Springer, 1999).

] have one key property: they provide ultrashort coherent light pulses, with pulse lengths down to a few femtoseconds. These ultrashort X-ray pulses open the door to high resolution imaging with intense radiation at short wavelengths with a single pulse. The ultrashort pulses allow the evasion of conventional resolution limitations set by radiation damage [11

11. R. Neutze, R. Wouts, D. van der Spoel, E. Weckert, and J. Hajdu, “Potential for biomolecular imaging with femtosecond X-ray pulses,” Nature 406(6797), 752–757 (2000). [CrossRef] [PubMed]

]. The availability of these sources stimulates the development of coherent imaging techniques that are capable of tapping the full potential of these 4th generation light sources. Coherent X-ray diffraction imaging (CXDI) [12

12. J. Miao, P. Charalambous, J. Kirz, and D. Sayre, “Extending the methodology of X-ray crystallography to allow imaging of micrometre-sized non-crystalline specimens,” Nature 400(6742), 342–344 (1999). [CrossRef]

] is one prominent and successful approach. The theoretical potential [13

13. J. Miao, K. O. Hodgson, and D. Sayre, “An approach to three-dimensional structures of biomolecules by using single-molecule diffraction images,” Proc. Natl. Acad. Sci. U.S.A. 98(12), 6641–6645 (2001). [CrossRef] [PubMed]

,14

14. I. A. Vartanyants, I. K. Robinson, I. McNulty, C. David, P. Wochner, and T. Tschentscher, “Coherent X-ray scattering and lensless imaging at the European XFEL Facility,” J. Synchrotron Radiat. 14(6), 453–470 (2007). [CrossRef] [PubMed]

] as well as the practical feasibility [15

15. H. N. Chapman, A. Barty, M. J. Bogan, S. Boutet, M. Frank, S. P. Hau-Riege, S. Marchesini, B. W. Woods, S. Bajt, W. H. Benner, R. A. London, E. Plönjes, M. Kuhlmann, R. Treusch, S. Düsterer, T. Tschentscher, J. R. Schneider, E. Spiller, T. Möller, C. Bostedt, M. Hoener, D. A. Shapiro, K. O. Hodgson, D. Van der Spoel, F. Burmeister, M. Bergh, C. Caleman, G. Huldt, M. M. Seibert, F. R. N. C. Maia, R. W. Lee, A. Szöke, N. Timneanu, and J. Hajdu, “Femtosecond diffractive imaging with a soft-X-ray free-electron laser,” Nat. Phys. 2(12), 839–843 (2006). [CrossRef]

] of CXDI as a single-pulse experiment have both been demonstrated. However, CXDI is inseparably linked to the so-called phase problem [16

16. J. Miao, J. Kirz, and D. Sayre, “The oversampling phasing method,” Acta Crystallogr. D Biol. Crystallogr. 56(10), 1312–1315 (2000). [CrossRef] [PubMed]

]. Its solution relies on sophisticated iterative algorithms that may not always converge to the correct solution. Even though progress in solving the phase problem has been made in the last years [17

17. V. Elser, “Phase retrieval by iterated projections,” J. Opt. Soc. Am. A 20(1), 40–55 (2003). [CrossRef]

19

19. S. Marchesini, “A unified evaluation of iterative projection algorithms for phase retrieval,” Rev. Sci. Instrum. 78(1), 011301–011310 (2007). [CrossRef] [PubMed]

], it remains challenging. At FLASH, recent CXDI data in the 3rd harmonic at a photon energy of 462 eV was recorded, but the phase retrieval was hampered due to the limited coherence length in this case [20

20. A. P. Mancuso, T. Gorniak, F. Staier, O. M. Yefanov, R. Barth, C. Christophis, B. Reime, J. Gulden, A. Singer, M. E. Pettit, T. Nisius, T. Wilhein, C. Gutt, G. Grübel, N. Guerassimova, R. Treusch, J. Feldhaus, S. Eisebitt, E. Weckert, M. Grunze, A. Rosenhahn, and I. Vartanyants, “Coherent imaging of biological samples with femtosecond pulses at the free-electron laser FLASH,” N. J. Phys. 12(3), 035003 (2010). [CrossRef]

,21

21. I. A. Vartanyants, A. P. Mancuso, A. Singer, O. M. Yefanov, and J. Gulden, “Coherence measurements and coherent diffractive imaging at FLASH,” J. Phys. At. Mol. Opt. Phys. 43(19), 194016 (2010). [CrossRef]

]. Contrary to CXDI, holography [22

22. D. Gabor, “A new microscopic principle,” Nature 161(4098), 777–778 (1948). [CrossRef] [PubMed]

] is a coherent projection microscopy technique. Regardless of the specific approach – in-line, off-axis or Fourier transform holography (FTH) [23

23. A. Rosenhahn, F. Staier, T. Nisius, D. Schäfer, R. Barth, C. Christophis, L.-M. Stadler, S. Streit-Nierobisch, C. Gutt, A. Mancuso, A. Schropp, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, M. Martins, B. Faatz, N. Guerassimova, K. Honkavaara, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, I. Vartanyants, G. Grübel, M. Grunze, and T. Wilhein, “Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH,” Opt. Express 17(10), 8220–8228 (2009). [CrossRef] [PubMed]

28

28. C. M. Günther, B. Pfau, R. Mitzner, B. Siemer, S. Roling, H. Zacharias, O. Kutz, I. Rudolph, D. Schondelmaier, R. Treusch, and S. Eisebitt, “Sequential femtosecond X-ray imaging,” Nat. Photonics 5(2), 99–102 (2011). [CrossRef]

] – all holographic techniques encrypt phase information during the recording process as the photons scattered from the sample interfere with an undisturbed reference wave. As consequence, phase information is encoded in the fringes of the interference pattern on the detector. This allows a direct reconstruction without the need for iterative phase retrieval. Especially attractive but experimentally more demanding are hybrid approaches, which extend the accessible range of spatial frequencies such as Fresnel coherent diffractive imaging (FCDI) [29

29. G. J. Williams, H. M. Quiney, A. G. Peele, and K. A. Nugent, “Fresnel coherent diffractive imaging: treatment and analysis of data,” N. J. Phys. 12(3), 035020 (2010). [CrossRef]

]. An overview of current experiments on soft X-ray imaging at FLASH can be found in [30

30. R. Treusch and J. Feldhaus, “FLASH: new opportunities for (time-resolved) coherent imaging of nanostructures,” N. J. Phys. 12(3), 035015 (2010). [CrossRef]

].

In order to take full advantage of the potentially radiation-damage-free imaging of biological samples, one has to optimize sample preparation to minimize any alteration of internal structures. This can be done by studying organic material in its natural hydrated, yet frozen, environment. Wavelengths within 2.3-4.3 nm are especially suitable to probe such hydrated samples. In this so-called water window, which is framed by the K-edges of carbon at 284 eV and oxygen at 540 eV respectively, the biologically relevant elements like potassium, calcium and carbon have a significantly shorter absorption length than water [31

31. J. Kirz, C. Jacobsen, and M. Howells, “Soft X-ray microscopes and their biological applications,” Q. Rev. Biophys. 28(1), 33–130 (1995). [CrossRef] [PubMed]

]. Due to this relative contrast the elemental distribution [32

32. A. Rosenhahn, R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, and M. Grunze, “Digital in-line soft x-ray holography with element contrast,” J. Opt. Soc. Am. A 25(2), 416–422 (2008). [CrossRef]

] and concentration within cells can be revealed. At the time of the experiment, FLASH was not yet capable of delivering radiation at fundamental wavelengths in the water window, and as such we used the 3rd harmonic (λ 3 = 2.68 nm) of the fundamental (λ = 8 nm) to explore this region. In this paper we present the first digital X-ray holograms of biological samples that have been recorded in the water window at a free-electron laser using FLASH’s 3rd harmonic at λ 3 = 2.68 nm. Since higher harmonics come at the cost of a considerably reduced photon flux, this experimental setup was based on zone plates rather than following our earlier attempts with pinholes [23

23. A. Rosenhahn, F. Staier, T. Nisius, D. Schäfer, R. Barth, C. Christophis, L.-M. Stadler, S. Streit-Nierobisch, C. Gutt, A. Mancuso, A. Schropp, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, M. Martins, B. Faatz, N. Guerassimova, K. Honkavaara, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, I. Vartanyants, G. Grübel, M. Grunze, and T. Wilhein, “Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH,” Opt. Express 17(10), 8220–8228 (2009). [CrossRef] [PubMed]

]. Creating the required divergent light cone with a zone plate increases the total flux seen by the sample by a factor of 102-104 compared to an experimental approach based on pinholes [33

33. R. Heine, T. Gorniak, T. Nisius, C. Christophis, M. E. Pettitt, F. Staier, T. Wilhein, S. Rehbein, M. Grunze, and A. Rosenhahn, “Digital in-line X-ray holography with zone plates,” Ultramicroscopy (in press, uncorrected proof).

]. This improved efficiency virtually outweighs the reduced photon flux mentioned above and therefore opens up the water window for X-ray in-line holography at FLASH.

2. Experimental setup

The experiments have been carried out at FLASH’s high-resolution plane-grating monochromator beamline PG2 [34

34. M. Martins, M. Wellhöfer, J. Hoeft, W. Wurth, J. Feldhaus, and R. Follath, “Monochromator beamline for FLASH,” Rev. Sci. Instrum. 77(11), 115108 (2006). [CrossRef]

,35

35. M. Wellhöfer, M. Martins, W. Wurth, A. Sorokin, and M. Richter, “Performance of the monochromator beamline at FLASH,” J. Opt. A, Pure Appl. Opt. 9(7), 749–756 (2007). [CrossRef]

], where we flange-mounted our dedicated vacuum chamber HORST (holographische Röntgenstreuapparatur) [36

36. F. Staier, “Entwicklung, Bau und Test einer UHV Röntgenstreukammer für die digitale In-Line Holographie,” PhD Thesis (University of Heidelberg, 2009).

]. The FEL operated with a 5 Hz pulse train repetition rate with 30 pulses per train and provided an average of 2x109 photons per pulse at the 3rd harmonic. This corresponds to the wavelength λ 3 = 2.68 nm, which is well inside the water window. As this wavelength was beyond the designed range of operation of the beamline, its transmittance was only 3.5x10−3 (optics, pre-mirror cut and grating efficiency) resulting in 7x106 photons per pulse in average arriving at our experiment with an energy of E = 462 eV. Compared to the 0th order beam (transmittance of 7.5x10−2 and FEL intensity of 2.0x109 photons/pulse), this higher harmonic provides a lower flux by a factor of 1.3x104 [37

37. N. Guerassimova, (personal communication, 2009).

]. The nominal width of the beamline focus is 50 µm full width at half maximum (FWHM) in the horizontal and 1 mm in the vertical direction, meaning that the transmittance of a pinhole with 150 nm in diameter (given the wavelength of 2.68 nm and the distance between focal spot and CCD of 600 nm, one would have to use a 150 nm pinhole in order to achieve a full illumination of the detector) would be about 2x10−7. Using a pinhole with a diameter of 100 µm (equal to the size of our zone plate) under the same conditions improves the usable flux to 9x10−2 of the photons available for imaging. The efficiency of an unsupported Fresnel zone plate can be estimated to have a value of approximately 9% considering the relevant 1st diffraction order only [38

38. D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications (Cambridge University Press, 2007).

]. Taking into account the geometrical and experimental constraints described above, this evaluation shows that our zone plate is roughly 4 orders of magnitude more efficient than an adequate pinhole, compensating for the lower flux when switching from the fundamental wavelength to the 3rd harmonic.

The experimental setup is depicted schematically in Fig. 1
Fig. 1 Schematic drawing of the experimental setup. A zone plate (ZP) is creating the divergent light cone, which is required for digital X-ray holography. An order sorting aperture (OSA) is filtering the direct beam as well as higher diffraction orders from the ZP. To preserve clarity only the 0th (yellow), 1st (orange) and 3rd (blue) diffraction orders are depicted here.
. The zone plate consists of 715 zones arranged within a diameter of D zp = 100 µm. The outermost zone has a width of Δr = 35 nm. This leads to the focal length f = 1.3 mm given a wavelength of 2.68 nm. The direct beam was blocked by a central stop with diameter D cs = 20 µm. In the focus of the zone plate’s first diffraction order, an order-sorting aperture (OSA) with a diameter of 2 µm was used to obstruct the higher diffraction orders and the directly transmitted X-ray beam.

Downstream of the OSA, the samples – the marine bacterium Cobetia marina and a rat fibroblast cell – were positioned at distances of 2 and 3 mm, respectively.

The holograms were recorded by a CCD detector (Andor DODX436-BN, 2048x2048 pixels, pixel size: 13.5x13.5 µm2), which was placed 600 mm behind the zone plate’s first diffraction order focus. In this geometry the acquisition time for full saturation of the CCD chip was approximately 600 s. Considering the estimates regarding pinhole transmittances, experiments in the standard pinhole geometry would not have been feasible at the 3rd harmonic. Only the use of zone plate-illumination has enabled these experiments to be carried out.

3. Materials and methods

To reconstruct the holograms we applied the Kirchhoff-Helmholtz transformation, allowing a direct reconstruction of arbitrary image planes between the source of the X-ray cone and the detector without further assumptions about the phase and the sample or iterative refinement [39

39. J. Garcia-Sucerquia, W. B. Xu, S. K. Jericho, P. Klages, M. H. Jericho, and H. J. Kreuzer, “Digital in-line holographic microscopy,” Appl. Opt. 45(5), 836–850 (2006). [CrossRef] [PubMed]

]:
K(r)=screenI(ζ)exp[krζζ]dxdy .
(1)
The integration extends over the two-dimensional surface of the detector with coordinates ζ = (x,y,L), where L is the distance from the source (focal spot created by ZP) to the center of the CCD-chip, k is the norm of the wave vector k, and I(ζ) is the measured intensity distribution of the hologram. The wave front K(r) at position r can be reconstructed at any plane between detector and source in analogy to scanning the focal depth of an optical microscope to display the desired imaging plane within the object. For the numerical implementation of the transformation, a fast algorithm was used that evaluates K(r) analytically. A more detailed overview about reconstruction and resolution in digital in-line holographic microscopy can be found in [39

39. J. Garcia-Sucerquia, W. B. Xu, S. K. Jericho, P. Klages, M. H. Jericho, and H. J. Kreuzer, “Digital in-line holographic microscopy,” Appl. Opt. 45(5), 836–850 (2006). [CrossRef] [PubMed]

].

All samples were prepared on Si3N4-membrane windows purchased from Silson Ltd, Northampton. Rat embryonic fibroblasts REF52WT cells were cultivated on fibrinogen coated silicon nitride membranes (75 nm thick, 1x1 mm2 window size) for 24 h in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), both purchased at Gibco. After fixation in 2% paraformaldehyde for 15 min, the cell water was slowly exchanged against ethanol by six different ethanol/water concentrations and the cells were finally critical point dried (Bal-Tec CPD 030). Marine biofouling bacteria Cobetia marina were cultivated on membranes with a thickness of 50 nm and a window size of 1x1 mm2. After immersing the membranes into artificial seawater, Cobetia marina bacteria were added and allowed to adhere for 30 min. The adhered organisms were fixed with 2% paraformaldehyde for 15 min and the seawater exchanged against distilled water in six steps. The water was subsequently exchanged against ethanol by six different ethanol/water concentrations and the cells were finally critical point dried (Bal-Tec CPD 030). All samples used in the experiments were characterized by optical microscopy and overview images were recorded. For comparison with the digital in-line X-ray holography images, the corresponding image sections were additionally investigated by reflective and transmission light micrographs (Nikon TE2000, 40x Plan Fluor Ph2, NA = 0.6 and 100x Plan Fluor EPI, NA = 0.9).

The zone plate [40

40. J. M. Byrd, T. J. Shea, P. Denes, P. Siddons, D. Attwood, F. Kaertner, L. Moog, Y. Li, A. Sakdinawat, and R. Schlueter, “Enabling instrumentation and technology for 21st century light sources,” Nucl. Instrum. Methods Phys. Res. A 623(3), 910–920 (2010). [CrossRef]

] was prepared using several nanofabrication processes. It was fabricated on a 100 nm thin Si3N4-membrane. 5 nm of chromium and 7 nm of gold were evaporated onto the membrane and used as plating base during the gold electroplating process. Polymethyl methacrylate (PMMA) was then spun onto the substrate, and electron-beam lithography was used for generating the zone plate pattern. Then, the PMMA mold was developed and 100 nm thick gold was electroplated to create the zone plate. Afterwards the mold was removed using an oxygen plasma etch. The central beam stop was fabricated with a similar technique in a subsequent step. The theoretical diffraction efficiency of this zone plate in the first order of diffraction is approximately 9% [38

38. D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications (Cambridge University Press, 2007).

]. Taking into account the transmission of the support membrane covered by the chromium and gold layer, approximately 5% of the incoming photons from the beamline were found in the first order focal spot.

4. Results and discussion

Figure 2
Fig. 2 Imaging the marine bacteria Cobetia marina in the water window at λ 3 = 2.68 nm using digital in-line holography. (a) SEM-image of used zone plate with clearly visible central beam stop. (b) Close-up of the zone plate’s outermost zones. (c) X-ray hologram with Cobetia marina in the lower right corner. (d) Reconstruction of hologram (c). (e) Sample Cobetia marina under an optical microscope in bright field illumination (100x, NA = 0.9). (f) Magnified ROI of the reconstructed image as indicated by rectangle in (d).
shows the first coherent microscopy results of dehydrated biological samples in the water window at a photon energy of E = 462 eV using free-electron laser radiation. Figures 2(a) and 2(b) show scanning electron microscopy images (SEM) of the zone plate, which was used to create the divergent light cone following the schematic drawing of the experiment in Fig. 1. The zone plate’s central beam stop is surrounded by periodically arranged virtual Moiré-artifacts due to insufficient sampling of the image. The distance between the zone plate’s focal spot and the sample was l = 2 mm. Given the OSA-camera distance of L = 600 mm, this results in a magnification of m = 300.

Figure 2(c) shows an X-ray hologram of the marine bacteria Cobetia marina at λ 3 = 2.68 nm. The depicted image is a drift-corrected accumulation of four holograms with an exposure time of 600 s each. As pointed out in the materials and methods section, this is 10−4 of the exposure time which would have been required using a pinhole to create a point source with comparable performance. Near the center of the image one can clearly see the dark round shaped spot, which originates from the zone plate’s central beam stop. The dashed lines mark the border of regions where the CCD image is dominated by noise. Dividing the pixel-diameters of the inner black spot and the partly visible outer dashed circle we obtain R px = 2750/570 = 4.8. This meets the expectation R = 5 of the ratio of the diameters of the zone plate D zp and the diameter of the central beam stop D cs in real space. Thus the zone plate projects the beam profile out of the ZP-plane onto the CCD. This is why, contrary to our former experimental results, which were based on a setup with pinholes [23

23. A. Rosenhahn, F. Staier, T. Nisius, D. Schäfer, R. Barth, C. Christophis, L.-M. Stadler, S. Streit-Nierobisch, C. Gutt, A. Mancuso, A. Schropp, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, M. Martins, B. Faatz, N. Guerassimova, K. Honkavaara, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, I. Vartanyants, G. Grübel, M. Grunze, and T. Wilhein, “Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH,” Opt. Express 17(10), 8220–8228 (2009). [CrossRef] [PubMed]

], the illumination of the detector does not have the shape of an Airy pattern and also lacks rotational symmetry.

The theoretically achievable resolution is restricted by the experimental setup and the detection geometry. The focus of the zone plate is limited by the outermost zone width of Δr = 35 nm [38

38. D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications (Cambridge University Press, 2007).

]. This determines a theoretical resolution limit of δ zp = 43 nm, as the achievable resolution in point source holography is directly linked to the size of the source of the divergent light cone [43

43. R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, M. Grunze, and A. Rosenhahn, “Soft X-ray holographic microscopy of chromosomes with high aspect ratio pinholes,” J. Biotechnol. 149(4), 238–242 (2010). [CrossRef] [PubMed]

]. The numerical aperture NAgeo, which is defined by the sample-detector geometry by the ratio of the size of the CCD over the distance L-l, gives a second, geometrical limit to the achievable spatial resolution. This restriction can be calculated as
δgeo=0.61λ3NAgeo=71 nm .
(2)
In consequence, as the latter exceeds the theoretical limit, the size of the CCD and its distance to the sample sets the relevant resolution limit in the used geometry rather than the focus of the zone plate. The resolution achieved in our experiment was determined by line scans using the 10%/90% edge criterion [41

41. A. Rosenhahn, R. Barth, X. Cao, M. Schürmann, M. Grunze, and S. Eisebitt, “Vacuum-ultraviolet Gabor holography with synchrotron radiation,” Ultramicroscopy 107(12), 1171–1177 (2007). [CrossRef] [PubMed]

] to be δ edge = 485 ± 88 nm. This value is the average over the three steepest line plots. They have been measured perpendicular to the edges of an imaged dirt particle, which is situated well above the shadow of the central beam stop. Interestingly, almost every line scan in the vertical direction led to a noticeably poorer resolution. Assuming that this dirt particle does not have perfectly steep knife-edges, the determined value δ edge can be considered as an upper limit of the de facto achieved resolution. Nevertheless, δ edge considerably deviates from the theoretically possible sub-100 nm region. The most likely reason for this is a combined effect of limited coherence, low signal-to-noise ratio (SNR), and poor scattering from the samples. As consequence, coherently small-angle-scattered photons, which are important for high spatial resolution in the reconstruction, were not able to generate a signal strong enough to be interpreted by the reconstruction algorithm. This leads to a reduced effective numerical aperture NAeff. A coarse estimation of NAeff based on the visibility of interference fringes along a line plot across an object leads to a radius of about 160 pixels where one is still able to distinguish the interference signal from the noisy background. This radius translates in our experimental geometry into an effective numerical aperture of NAeff = 3.3x10−3, which corresponds to the noise-limited resolution
δeff=0.61λ3NAeff=453 nm .
(3)
Besides the limited data quality due to a low SNR, insufficient temporal coherence can restrict the experimental resolution. A Gaussian fit to the sum of 1857 single shot spectral measurements of the FEL which were recorded just prior to our experiment shows that the distribution of the 3rd harmonic radiation had a maximum at 463 eV with a FWHM of 8 eV. The spatial energy dispersion along the vertical axis in the focal plane was 5.3 eV/mm. Taking into account the zone plate’s geometry and the arrangement of the experimental elements, the provided bandwidth corresponds to a coherence length of 2.4 µm and thus should theoretically lead to a temporal coherence-limited resolution of δ coh = 584 nm [44

44. S. Lindaas, M. Howells, C. Jacobsen, and A. Kalinovsky, “X-ray holographic microscopy by means of photoresist recording and atomic-force microscope readout,” J. Opt. Soc. Am. A 13(9), 1788–1800 (1996). [CrossRef]

]. While δ eff lies well within the error bar of δ edge, δ coh does not. This difference can be explained by a direction-selective effect, which originates from the orientation of the grating in the monochromator. The calculated value δ coh is only strictly valid in the vertical direction, which resembles the axis of energy dispersion due to the horizontally mounted grating. Thus, temporal coherence should influence the resolution less in the horizontal direction. The aforementioned measurement of the achieved resolution using the edge-criterion already hinted that there may be a direction-selective effect influencing the resolution. Both the line plot for the coarse estimation of the visibility of fringes and the line plots for applying the edge-criterion were not taken in the vertical direction. They rather point to an angle of about 45° against the vertical axis. In consequence, the mismatch of δ coh and δ edge is not astonishing. Since it is rather unlikely that the underlying test object has uniform edges, it is impossible to discriminate between their influence and the impact from the direction-selective coherence. Thus, these results should be considered as a first estimate. According to a study conducted by Vartanyants et al. [21

21. I. A. Vartanyants, A. P. Mancuso, A. Singer, O. M. Yefanov, and J. Gulden, “Coherence measurements and coherent diffractive imaging at FLASH,” J. Phys. At. Mol. Opt. Phys. 43(19), 194016 (2010). [CrossRef]

] the influence of the transverse coherence of 3rd harmonic radiation at PG2 does not further decrease the achievable resolution limit set by the temporal counterpart.

Intensity measurements are consistent with the theoretical prediction of a 99.5% transmittance in the case of a 1 nm thick carbon film at E = 155 eV. Compared to a typical 30 nm Si3N4-membrane, this leads to a reduction of the exposure time by a factor of two. These preliminary results show that it is possible to holographically image samples, which are placed on carbon nanosheets. One of the main advantages of such molecular sheets is their small roughness. For imaging of macromolecules or organelles with future X-ray free-electron lasers supported by solid substrates, the roughness of the support will become an increasing challenge for the reconstruction of holographic and CXDI data, as the information lies in the same frequency range as the details to be imaged. Thus, molecular sheets seem to be an ideal support for such experiments including coherent imaging of single proteins, organelles or ordered 2D structures such as membrane systems [51

51. A. P. Mancuso, A. Schropp, B. Reime, L.-M. Stadler, A. Singer, J. Gulden, S. Streit-Nierobisch, C. Gutt, G. Grübel, J. Feldhaus, F. Staier, R. Barth, A. Rosenhahn, M. Grunze, T. Nisius, T. Wilhein, D. Stickler, H. Stillrich, R. Frömter, H.-P. Oepen, M. Martins, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, E. Weckert, and I. A. Vartanyants, “Coherent-pulse 2D crystallography using a free-electron laser x-ray source,” Phys. Rev. Lett. 102(3), 035502 (2009). [CrossRef] [PubMed]

].

5. Conclusions

Acknowledgments

References and links

1.

C. A. Brau, “Free-electron lasers,” Science 239(4844), 1115–1121 (1988). [CrossRef] [PubMed]

2.

J. Feldhaus, J. Arthur, and J. Hastings, “X-ray free-electron lasers,” J. Phys. B: At. Mol. Opt. Phys. 38(9), S799–S819 (2005). [CrossRef]

3.

W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, J. T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, H. T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, C. Gerth, M. Görler, N. Golubeva, H. J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, J. R. Schneider, E. A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, A. V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, M. V. Yurkov, I. Zagorodnov, and K. Zapfe, “Operation of a free-electron laser from the extreme ultraviolet to the water window,” Nat. Photonics 1(6), 336–342 (2007). [CrossRef]

4.

K. Tiedtke, A. Azima, N. von Bargen, L. Bittner, S. Bonfigt, S. Düsterer, B. Faatz, U. Frühling, M. Gensch, C. Gerth, N. Guerassimova, U. Hahn, T. Hans, M. Hesse, K. Honkavaar, U. Jastrow, P. Juranic, S. Kapitzki, B. Keitel, T. Kracht, M. Kuhlmann, W. B. Li, M. Martins, T. Núñez, E. Plönjes, H. Redlin, E. L. Saldin, E. A. Schneidmiller, J. R. Schneider, S. Schreiber, N. Stojanovic, F. Tavella, S. Toleikis, R. Treusch, H. Weigelt, M. Wellhöfer, H. Wabnitz, M. V. Yurkov, and J. Feldhaus, “The soft x-ray free-electron laser FLASH at DESY: beamlines, diagnostics and end-stations,” N. J. Phys. 11(2), 023029 (2009). [CrossRef]

5.

C. Gutt, L. M. Stadler, S. Streit-Nierobisch, A. P. Mancuso, A. Schropp, B. Pfau, C. M. Günther, R. Könnecke, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, I. A. Vartanyants, O. Hellwig, F. Staier, R. Barth, M. Grunze, A. Rosenhahn, D. Stickler, H. Stillrich, R. Frömter, H. P. Oepen, M. Martins, T. Nisius, T. Wilhein, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. Schneidmiller, M. Yurkov, S. Eisebitt, and G. Grübel, “Resonant magnetic scattering with soft x-ray pulses from a free-electron laser operating at 1.59 nm,” Phys. Rev. B 79(21), 212406 (2009). [CrossRef]

6.

P. Emma, R. Akre, J. Arthur, R. Bionta, C. Bostedt, J. Bozek, A. Brachmann, P. Bucksbaum, R. Coffee, F. J. Decker, Y. Ding, D. Dowell, S. Edstrom, A. Fisher, J. Frisch, S. Gilevich, J. Hastings, G. Hays, P. Hering, Z. Huang, R. Iverson, H. Loos, M. Messerschmidt, A. Miahnahri, S. Moeller, H. D. Nuhn, G. Pile, D. Ratner, J. Rzepiela, D. Schultz, T. Smith, P. Stefan, H. Tompkins, J. Turner, J. Welch, W. White, J. Wu, G. Yocky, and J. Galayda, “First lasing and operation of an ångstrom-wavelength free-electron laser,” Nat. Photonics 4(9), 641–647 (2010). [CrossRef]

7.

M. Altarelli, R. Brinkmann, M. Chergui, W. Decking, B. Dobson, S. Düsterer, G. Grübel, W. Graeff, H. Graafsma, J. Hajdu, J. Marangos, J. Pflüger, H. Redlin, D. Riley, I. Robinson, J. Rossbach, A. Schwarz, K. Tiedtke, T. Tschentscher, I. Vartanyants, H. Wabnitz, H. Weise, R. Wichmann, K. Witte, A. Wolf, M. Wulff, and M. Yurkov, “The European X-Ray Free-Electron Laser. Technical Design Report” (2006), retrieved http://xfel.desy.de/tdr/tdr/.

8.

H. N. Chapman, “X-ray imaging beyond the limits,” Nat. Mater. 8(4), 299–301 (2009). [CrossRef] [PubMed]

9.

N. Patel, “Shorter, brighter, better,” Nature 415(6868), 110–111 (2002). [CrossRef] [PubMed]

10.

E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov, The Physics of Free Electron Lasers (Springer, 1999).

11.

R. Neutze, R. Wouts, D. van der Spoel, E. Weckert, and J. Hajdu, “Potential for biomolecular imaging with femtosecond X-ray pulses,” Nature 406(6797), 752–757 (2000). [CrossRef] [PubMed]

12.

J. Miao, P. Charalambous, J. Kirz, and D. Sayre, “Extending the methodology of X-ray crystallography to allow imaging of micrometre-sized non-crystalline specimens,” Nature 400(6742), 342–344 (1999). [CrossRef]

13.

J. Miao, K. O. Hodgson, and D. Sayre, “An approach to three-dimensional structures of biomolecules by using single-molecule diffraction images,” Proc. Natl. Acad. Sci. U.S.A. 98(12), 6641–6645 (2001). [CrossRef] [PubMed]

14.

I. A. Vartanyants, I. K. Robinson, I. McNulty, C. David, P. Wochner, and T. Tschentscher, “Coherent X-ray scattering and lensless imaging at the European XFEL Facility,” J. Synchrotron Radiat. 14(6), 453–470 (2007). [CrossRef] [PubMed]

15.

H. N. Chapman, A. Barty, M. J. Bogan, S. Boutet, M. Frank, S. P. Hau-Riege, S. Marchesini, B. W. Woods, S. Bajt, W. H. Benner, R. A. London, E. Plönjes, M. Kuhlmann, R. Treusch, S. Düsterer, T. Tschentscher, J. R. Schneider, E. Spiller, T. Möller, C. Bostedt, M. Hoener, D. A. Shapiro, K. O. Hodgson, D. Van der Spoel, F. Burmeister, M. Bergh, C. Caleman, G. Huldt, M. M. Seibert, F. R. N. C. Maia, R. W. Lee, A. Szöke, N. Timneanu, and J. Hajdu, “Femtosecond diffractive imaging with a soft-X-ray free-electron laser,” Nat. Phys. 2(12), 839–843 (2006). [CrossRef]

16.

J. Miao, J. Kirz, and D. Sayre, “The oversampling phasing method,” Acta Crystallogr. D Biol. Crystallogr. 56(10), 1312–1315 (2000). [CrossRef] [PubMed]

17.

V. Elser, “Phase retrieval by iterated projections,” J. Opt. Soc. Am. A 20(1), 40–55 (2003). [CrossRef]

18.

J. R. Fienup, “Iterative method applied to image reconstruction and to computer-generated holograms,” Opt. Eng. 19, 297–305 (1980).

19.

S. Marchesini, “A unified evaluation of iterative projection algorithms for phase retrieval,” Rev. Sci. Instrum. 78(1), 011301–011310 (2007). [CrossRef] [PubMed]

20.

A. P. Mancuso, T. Gorniak, F. Staier, O. M. Yefanov, R. Barth, C. Christophis, B. Reime, J. Gulden, A. Singer, M. E. Pettit, T. Nisius, T. Wilhein, C. Gutt, G. Grübel, N. Guerassimova, R. Treusch, J. Feldhaus, S. Eisebitt, E. Weckert, M. Grunze, A. Rosenhahn, and I. Vartanyants, “Coherent imaging of biological samples with femtosecond pulses at the free-electron laser FLASH,” N. J. Phys. 12(3), 035003 (2010). [CrossRef]

21.

I. A. Vartanyants, A. P. Mancuso, A. Singer, O. M. Yefanov, and J. Gulden, “Coherence measurements and coherent diffractive imaging at FLASH,” J. Phys. At. Mol. Opt. Phys. 43(19), 194016 (2010). [CrossRef]

22.

D. Gabor, “A new microscopic principle,” Nature 161(4098), 777–778 (1948). [CrossRef] [PubMed]

23.

A. Rosenhahn, F. Staier, T. Nisius, D. Schäfer, R. Barth, C. Christophis, L.-M. Stadler, S. Streit-Nierobisch, C. Gutt, A. Mancuso, A. Schropp, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, M. Martins, B. Faatz, N. Guerassimova, K. Honkavaara, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, I. Vartanyants, G. Grübel, M. Grunze, and T. Wilhein, “Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH,” Opt. Express 17(10), 8220–8228 (2009). [CrossRef] [PubMed]

24.

C. Fuhse, C. Ollinger, and T. Salditt, “Waveguide-based off-axis holography with hard X rays,” Phys. Rev. Lett. 97(25), 254801 (2006). [CrossRef]

25.

I. McNulty, J. Kirz, C. Jacobsen, E. H. Anderson, M. R. Howells, and D. P. Kern, “High-resolution imaging by Fourier transform X-ray holography,” Science 256(5059), 1009–1012 (1992). [CrossRef] [PubMed]

26.

G. W. Stroke, “Lensless Fourier-transform method for optical holography,” Appl. Phys. Lett. 6(10), 201–203 (1965). [CrossRef]

27.

S. Eisebitt, J. Lüning, W. F. Schlotter, M. Lörgen, O. Hellwig, W. Eberhardt, and J. Stöhr, “Lensless imaging of magnetic nanostructures by X-ray spectro-holography,” Nature 432(7019), 885–888 (2004). [CrossRef] [PubMed]

28.

C. M. Günther, B. Pfau, R. Mitzner, B. Siemer, S. Roling, H. Zacharias, O. Kutz, I. Rudolph, D. Schondelmaier, R. Treusch, and S. Eisebitt, “Sequential femtosecond X-ray imaging,” Nat. Photonics 5(2), 99–102 (2011). [CrossRef]

29.

G. J. Williams, H. M. Quiney, A. G. Peele, and K. A. Nugent, “Fresnel coherent diffractive imaging: treatment and analysis of data,” N. J. Phys. 12(3), 035020 (2010). [CrossRef]

30.

R. Treusch and J. Feldhaus, “FLASH: new opportunities for (time-resolved) coherent imaging of nanostructures,” N. J. Phys. 12(3), 035015 (2010). [CrossRef]

31.

J. Kirz, C. Jacobsen, and M. Howells, “Soft X-ray microscopes and their biological applications,” Q. Rev. Biophys. 28(1), 33–130 (1995). [CrossRef] [PubMed]

32.

A. Rosenhahn, R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, and M. Grunze, “Digital in-line soft x-ray holography with element contrast,” J. Opt. Soc. Am. A 25(2), 416–422 (2008). [CrossRef]

33.

R. Heine, T. Gorniak, T. Nisius, C. Christophis, M. E. Pettitt, F. Staier, T. Wilhein, S. Rehbein, M. Grunze, and A. Rosenhahn, “Digital in-line X-ray holography with zone plates,” Ultramicroscopy (in press, uncorrected proof).

34.

M. Martins, M. Wellhöfer, J. Hoeft, W. Wurth, J. Feldhaus, and R. Follath, “Monochromator beamline for FLASH,” Rev. Sci. Instrum. 77(11), 115108 (2006). [CrossRef]

35.

M. Wellhöfer, M. Martins, W. Wurth, A. Sorokin, and M. Richter, “Performance of the monochromator beamline at FLASH,” J. Opt. A, Pure Appl. Opt. 9(7), 749–756 (2007). [CrossRef]

36.

F. Staier, “Entwicklung, Bau und Test einer UHV Röntgenstreukammer für die digitale In-Line Holographie,” PhD Thesis (University of Heidelberg, 2009).

37.

N. Guerassimova, (personal communication, 2009).

38.

D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications (Cambridge University Press, 2007).

39.

J. Garcia-Sucerquia, W. B. Xu, S. K. Jericho, P. Klages, M. H. Jericho, and H. J. Kreuzer, “Digital in-line holographic microscopy,” Appl. Opt. 45(5), 836–850 (2006). [CrossRef] [PubMed]

40.

J. M. Byrd, T. J. Shea, P. Denes, P. Siddons, D. Attwood, F. Kaertner, L. Moog, Y. Li, A. Sakdinawat, and R. Schlueter, “Enabling instrumentation and technology for 21st century light sources,” Nucl. Instrum. Methods Phys. Res. A 623(3), 910–920 (2010). [CrossRef]

41.

A. Rosenhahn, R. Barth, X. Cao, M. Schürmann, M. Grunze, and S. Eisebitt, “Vacuum-ultraviolet Gabor holography with synchrotron radiation,” Ultramicroscopy 107(12), 1171–1177 (2007). [CrossRef] [PubMed]

42.

S. Flewett, H. M. Quiney, C. Q. Tran, and K. A. Nugent, “Extracting coherent modes from partially coherent wavefields,” Opt. Lett. 34(14), 2198–2200 (2009). [CrossRef] [PubMed]

43.

R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, M. Grunze, and A. Rosenhahn, “Soft X-ray holographic microscopy of chromosomes with high aspect ratio pinholes,” J. Biotechnol. 149(4), 238–242 (2010). [CrossRef] [PubMed]

44.

S. Lindaas, M. Howells, C. Jacobsen, and A. Kalinovsky, “X-ray holographic microscopy by means of photoresist recording and atomic-force microscope readout,” J. Opt. Soc. Am. A 13(9), 1788–1800 (1996). [CrossRef]

45.

W. Eck, A. Küller, M. Grunze, B. Völkel, and A. Gölzhäuser, “Freestanding nanosheets from crosslinked biphenyl self-assembled monolayers,” Adv. Mater. (Deerfield Beach Fla.) 17(21), 2583–2587 (2005). [CrossRef]

46.

C. T. Nottbohm, A. Beyer, A. S. Sologubenko, I. Ennen, A. Hütten, H. Rösner, W. Eck, J. Mayer, and A. Gölzhäuser, “Novel carbon nanosheets as support for ultrahigh-resolution structural analysis of nanoparticles,” Ultramicroscopy 108(9), 885–892 (2008). [CrossRef] [PubMed]

47.

A. Turchanin, M. El-Desawy, and A. Gölzhäuser, “High thermal stability of cross-linked aromatic self-assembled monolayers: nanopatterning via selective thermal desorption,” Appl. Phys. Lett. 90(5), 053102 (2007). [CrossRef]

48.

A. Küller, W. Eck, V. Stadler, W. Geyer, and A. Gölzhäuser, “Nanostructuring of silicon by electron-beam lithography of self-assembled hydroxybiphenyl monolayers,” Appl. Phys. Lett. 82(21), 3776–3778 (2003). [CrossRef]

49.

C. T. Nottbohm, A. Turchanin, A. Beyer, and A. Gölzhäuser, “Direct e-beam writing of 1 nm thin carbon nanoribbons,” J. Vac. Sci. Technol. B 27(6), 3059–3062 (2009). [CrossRef]

50.

A. Turchanin, A. Beyer, C. T. Nottbohm, X. Zhang, R. Stosch, A. Sologubenko, J. Mayer, P. Hinze, T. Weimann, and A. Gölzhäuser, “One nanometer thin carbon nanosheets with tunable conductivity and stiffness,” Adv. Mater. (Deerfield Beach Fla.) 21(12), 1233–1237 (2009). [CrossRef]

51.

A. P. Mancuso, A. Schropp, B. Reime, L.-M. Stadler, A. Singer, J. Gulden, S. Streit-Nierobisch, C. Gutt, G. Grübel, J. Feldhaus, F. Staier, R. Barth, A. Rosenhahn, M. Grunze, T. Nisius, T. Wilhein, D. Stickler, H. Stillrich, R. Frömter, H.-P. Oepen, M. Martins, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, E. Weckert, and I. A. Vartanyants, “Coherent-pulse 2D crystallography using a free-electron laser x-ray source,” Phys. Rev. Lett. 102(3), 035502 (2009). [CrossRef] [PubMed]

OCIS Codes
(030.1640) Coherence and statistical optics : Coherence
(110.7440) Imaging systems : X-ray imaging
(090.1995) Holography : Digital holography
(260.6048) Physical optics : Soft x-rays

ToC Category:
X-ray Optics

History
Original Manuscript: March 10, 2011
Revised Manuscript: April 30, 2011
Manuscript Accepted: May 3, 2011
Published: May 23, 2011

Citation
T. Gorniak, R. Heine, A. P. Mancuso, F. Staier, C. Christophis, M. E. Pettitt, A. Sakdinawat, R. Treusch, N. Guerassimova, J. Feldhaus, C. Gutt, G. Grübel, S. Eisebitt, A. Beyer, A. Gölzhäuser, E. Weckert, M. Grunze, I. A. Vartanyants, and A. Rosenhahn, "X-ray holographic microscopy with zone plates applied to biological samples in the water window using 3rd harmonic radiation from the free-electron laser FLASH," Opt. Express 19, 11059-11070 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-12-11059


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. C. A. Brau, “Free-electron lasers,” Science 239(4844), 1115–1121 (1988). [CrossRef] [PubMed]
  2. J. Feldhaus, J. Arthur, and J. Hastings, “X-ray free-electron lasers,” J. Phys. B: At. Mol. Opt. Phys. 38(9), S799–S819 (2005). [CrossRef]
  3. W. Ackermann, G. Asova, V. Ayvazyan, A. Azima, N. Baboi, J. Bähr, V. Balandin, B. Beutner, A. Brandt, A. Bolzmann, R. Brinkmann, O. I. Brovko, M. Castellano, P. Castro, L. Catani, E. Chiadroni, S. Choroba, A. Cianchi, J. T. Costello, D. Cubaynes, J. Dardis, W. Decking, H. Delsim-Hashemi, A. Delserieys, G. Di Pirro, M. Dohlus, S. Düsterer, A. Eckhardt, H. T. Edwards, B. Faatz, J. Feldhaus, K. Flöttmann, J. Frisch, L. Fröhlich, T. Garvey, U. Gensch, C. Gerth, M. Görler, N. Golubeva, H. J. Grabosch, M. Grecki, O. Grimm, K. Hacker, U. Hahn, J. H. Han, K. Honkavaara, T. Hott, M. Hüning, Y. Ivanisenko, E. Jaeschke, W. Jalmuzna, T. Jezynski, R. Kammering, V. Katalev, K. Kavanagh, E. T. Kennedy, S. Khodyachykh, K. Klose, V. Kocharyan, M. Körfer, M. Kollewe, W. Koprek, S. Korepanov, D. Kostin, M. Krassilnikov, G. Kube, M. Kuhlmann, C. L. S. Lewis, L. Lilje, T. Limberg, D. Lipka, F. Löhl, H. Luna, M. Luong, M. Martins, M. Meyer, P. Michelato, V. Miltchev, W. D. Möller, L. Monaco, W. F. O. Müller, O. Napieralski, O. Napoly, P. Nicolosi, D. Nölle, T. Nuñez, A. Oppelt, C. Pagani, R. Paparella, N. Pchalek, J. Pedregosa-Gutierrez, B. Petersen, B. Petrosyan, G. Petrosyan, L. Petrosyan, J. Pflüger, E. Plönjes, L. Poletto, K. Pozniak, E. Prat, D. Proch, P. Pucyk, P. Radcliffe, H. Redlin, K. Rehlich, M. Richter, M. Roehrs, J. Roensch, R. Romaniuk, M. Ross, J. Rossbach, V. Rybnikov, M. Sachwitz, E. L. Saldin, W. Sandner, H. Schlarb, B. Schmidt, M. Schmitz, P. Schmüser, J. R. Schneider, E. A. Schneidmiller, S. Schnepp, S. Schreiber, M. Seidel, D. Sertore, A. V. Shabunov, C. Simon, S. Simrock, E. Sombrowski, A. A. Sorokin, P. Spanknebel, R. Spesyvtsev, L. Staykov, B. Steffen, F. Stephan, F. Stulle, H. Thom, K. Tiedtke, M. Tischer, S. Toleikis, R. Treusch, D. Trines, I. Tsakov, E. Vogel, T. Weiland, H. Weise, M. Wellhöfer, M. Wendt, I. Will, A. Winter, K. Wittenburg, W. Wurth, P. Yeates, M. V. Yurkov, I. Zagorodnov, and K. Zapfe, “Operation of a free-electron laser from the extreme ultraviolet to the water window,” Nat. Photonics 1(6), 336–342 (2007). [CrossRef]
  4. K. Tiedtke, A. Azima, N. von Bargen, L. Bittner, S. Bonfigt, S. Düsterer, B. Faatz, U. Frühling, M. Gensch, C. Gerth, N. Guerassimova, U. Hahn, T. Hans, M. Hesse, K. Honkavaar, U. Jastrow, P. Juranic, S. Kapitzki, B. Keitel, T. Kracht, M. Kuhlmann, W. B. Li, M. Martins, T. Núñez, E. Plönjes, H. Redlin, E. L. Saldin, E. A. Schneidmiller, J. R. Schneider, S. Schreiber, N. Stojanovic, F. Tavella, S. Toleikis, R. Treusch, H. Weigelt, M. Wellhöfer, H. Wabnitz, M. V. Yurkov, and J. Feldhaus, “The soft x-ray free-electron laser FLASH at DESY: beamlines, diagnostics and end-stations,” N. J. Phys. 11(2), 023029 (2009). [CrossRef]
  5. C. Gutt, L. M. Stadler, S. Streit-Nierobisch, A. P. Mancuso, A. Schropp, B. Pfau, C. M. Günther, R. Könnecke, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, I. A. Vartanyants, O. Hellwig, F. Staier, R. Barth, M. Grunze, A. Rosenhahn, D. Stickler, H. Stillrich, R. Frömter, H. P. Oepen, M. Martins, T. Nisius, T. Wilhein, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. Schneidmiller, M. Yurkov, S. Eisebitt, and G. Grübel, “Resonant magnetic scattering with soft x-ray pulses from a free-electron laser operating at 1.59 nm,” Phys. Rev. B 79(21), 212406 (2009). [CrossRef]
  6. P. Emma, R. Akre, J. Arthur, R. Bionta, C. Bostedt, J. Bozek, A. Brachmann, P. Bucksbaum, R. Coffee, F. J. Decker, Y. Ding, D. Dowell, S. Edstrom, A. Fisher, J. Frisch, S. Gilevich, J. Hastings, G. Hays, P. Hering, Z. Huang, R. Iverson, H. Loos, M. Messerschmidt, A. Miahnahri, S. Moeller, H. D. Nuhn, G. Pile, D. Ratner, J. Rzepiela, D. Schultz, T. Smith, P. Stefan, H. Tompkins, J. Turner, J. Welch, W. White, J. Wu, G. Yocky, and J. Galayda, “First lasing and operation of an ångstrom-wavelength free-electron laser,” Nat. Photonics 4(9), 641–647 (2010). [CrossRef]
  7. M. Altarelli, R. Brinkmann, M. Chergui, W. Decking, B. Dobson, S. Düsterer, G. Grübel, W. Graeff, H. Graafsma, J. Hajdu, J. Marangos, J. Pflüger, H. Redlin, D. Riley, I. Robinson, J. Rossbach, A. Schwarz, K. Tiedtke, T. Tschentscher, I. Vartanyants, H. Wabnitz, H. Weise, R. Wichmann, K. Witte, A. Wolf, M. Wulff, and M. Yurkov, “The European X-Ray Free-Electron Laser. Technical Design Report” (2006), retrieved http://xfel.desy.de/tdr/tdr/ .
  8. H. N. Chapman, “X-ray imaging beyond the limits,” Nat. Mater. 8(4), 299–301 (2009). [CrossRef] [PubMed]
  9. N. Patel, “Shorter, brighter, better,” Nature 415(6868), 110–111 (2002). [CrossRef] [PubMed]
  10. E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov, The Physics of Free Electron Lasers (Springer, 1999).
  11. R. Neutze, R. Wouts, D. van der Spoel, E. Weckert, and J. Hajdu, “Potential for biomolecular imaging with femtosecond X-ray pulses,” Nature 406(6797), 752–757 (2000). [CrossRef] [PubMed]
  12. J. Miao, P. Charalambous, J. Kirz, and D. Sayre, “Extending the methodology of X-ray crystallography to allow imaging of micrometre-sized non-crystalline specimens,” Nature 400(6742), 342–344 (1999). [CrossRef]
  13. J. Miao, K. O. Hodgson, and D. Sayre, “An approach to three-dimensional structures of biomolecules by using single-molecule diffraction images,” Proc. Natl. Acad. Sci. U.S.A. 98(12), 6641–6645 (2001). [CrossRef] [PubMed]
  14. I. A. Vartanyants, I. K. Robinson, I. McNulty, C. David, P. Wochner, and T. Tschentscher, “Coherent X-ray scattering and lensless imaging at the European XFEL Facility,” J. Synchrotron Radiat. 14(6), 453–470 (2007). [CrossRef] [PubMed]
  15. H. N. Chapman, A. Barty, M. J. Bogan, S. Boutet, M. Frank, S. P. Hau-Riege, S. Marchesini, B. W. Woods, S. Bajt, W. H. Benner, R. A. London, E. Plönjes, M. Kuhlmann, R. Treusch, S. Düsterer, T. Tschentscher, J. R. Schneider, E. Spiller, T. Möller, C. Bostedt, M. Hoener, D. A. Shapiro, K. O. Hodgson, D. Van der Spoel, F. Burmeister, M. Bergh, C. Caleman, G. Huldt, M. M. Seibert, F. R. N. C. Maia, R. W. Lee, A. Szöke, N. Timneanu, and J. Hajdu, “Femtosecond diffractive imaging with a soft-X-ray free-electron laser,” Nat. Phys. 2(12), 839–843 (2006). [CrossRef]
  16. J. Miao, J. Kirz, and D. Sayre, “The oversampling phasing method,” Acta Crystallogr. D Biol. Crystallogr. 56(10), 1312–1315 (2000). [CrossRef] [PubMed]
  17. V. Elser, “Phase retrieval by iterated projections,” J. Opt. Soc. Am. A 20(1), 40–55 (2003). [CrossRef]
  18. J. R. Fienup, “Iterative method applied to image reconstruction and to computer-generated holograms,” Opt. Eng. 19, 297–305 (1980).
  19. S. Marchesini, “A unified evaluation of iterative projection algorithms for phase retrieval,” Rev. Sci. Instrum. 78(1), 011301–011310 (2007). [CrossRef] [PubMed]
  20. A. P. Mancuso, T. Gorniak, F. Staier, O. M. Yefanov, R. Barth, C. Christophis, B. Reime, J. Gulden, A. Singer, M. E. Pettit, T. Nisius, T. Wilhein, C. Gutt, G. Grübel, N. Guerassimova, R. Treusch, J. Feldhaus, S. Eisebitt, E. Weckert, M. Grunze, A. Rosenhahn, and I. Vartanyants, “Coherent imaging of biological samples with femtosecond pulses at the free-electron laser FLASH,” N. J. Phys. 12(3), 035003 (2010). [CrossRef]
  21. I. A. Vartanyants, A. P. Mancuso, A. Singer, O. M. Yefanov, and J. Gulden, “Coherence measurements and coherent diffractive imaging at FLASH,” J. Phys. At. Mol. Opt. Phys. 43(19), 194016 (2010). [CrossRef]
  22. D. Gabor, “A new microscopic principle,” Nature 161(4098), 777–778 (1948). [CrossRef] [PubMed]
  23. A. Rosenhahn, F. Staier, T. Nisius, D. Schäfer, R. Barth, C. Christophis, L.-M. Stadler, S. Streit-Nierobisch, C. Gutt, A. Mancuso, A. Schropp, J. Gulden, B. Reime, J. Feldhaus, E. Weckert, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, M. Martins, B. Faatz, N. Guerassimova, K. Honkavaara, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, I. Vartanyants, G. Grübel, M. Grunze, and T. Wilhein, “Digital in-line holography with femtosecond VUV radiation provided by the free-electron laser FLASH,” Opt. Express 17(10), 8220–8228 (2009). [CrossRef] [PubMed]
  24. C. Fuhse, C. Ollinger, and T. Salditt, “Waveguide-based off-axis holography with hard X rays,” Phys. Rev. Lett. 97(25), 254801 (2006). [CrossRef]
  25. I. McNulty, J. Kirz, C. Jacobsen, E. H. Anderson, M. R. Howells, and D. P. Kern, “High-resolution imaging by Fourier transform X-ray holography,” Science 256(5059), 1009–1012 (1992). [CrossRef] [PubMed]
  26. G. W. Stroke, “Lensless Fourier-transform method for optical holography,” Appl. Phys. Lett. 6(10), 201–203 (1965). [CrossRef]
  27. S. Eisebitt, J. Lüning, W. F. Schlotter, M. Lörgen, O. Hellwig, W. Eberhardt, and J. Stöhr, “Lensless imaging of magnetic nanostructures by X-ray spectro-holography,” Nature 432(7019), 885–888 (2004). [CrossRef] [PubMed]
  28. C. M. Günther, B. Pfau, R. Mitzner, B. Siemer, S. Roling, H. Zacharias, O. Kutz, I. Rudolph, D. Schondelmaier, R. Treusch, and S. Eisebitt, “Sequential femtosecond X-ray imaging,” Nat. Photonics 5(2), 99–102 (2011). [CrossRef]
  29. G. J. Williams, H. M. Quiney, A. G. Peele, and K. A. Nugent, “Fresnel coherent diffractive imaging: treatment and analysis of data,” N. J. Phys. 12(3), 035020 (2010). [CrossRef]
  30. R. Treusch and J. Feldhaus, “FLASH: new opportunities for (time-resolved) coherent imaging of nanostructures,” N. J. Phys. 12(3), 035015 (2010). [CrossRef]
  31. J. Kirz, C. Jacobsen, and M. Howells, “Soft X-ray microscopes and their biological applications,” Q. Rev. Biophys. 28(1), 33–130 (1995). [CrossRef] [PubMed]
  32. A. Rosenhahn, R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, and M. Grunze, “Digital in-line soft x-ray holography with element contrast,” J. Opt. Soc. Am. A 25(2), 416–422 (2008). [CrossRef]
  33. R. Heine, T. Gorniak, T. Nisius, C. Christophis, M. E. Pettitt, F. Staier, T. Wilhein, S. Rehbein, M. Grunze, and A. Rosenhahn, “Digital in-line X-ray holography with zone plates,” Ultramicroscopy (in press, uncorrected proof).
  34. M. Martins, M. Wellhöfer, J. Hoeft, W. Wurth, J. Feldhaus, and R. Follath, “Monochromator beamline for FLASH,” Rev. Sci. Instrum. 77(11), 115108 (2006). [CrossRef]
  35. M. Wellhöfer, M. Martins, W. Wurth, A. Sorokin, and M. Richter, “Performance of the monochromator beamline at FLASH,” J. Opt. A, Pure Appl. Opt. 9(7), 749–756 (2007). [CrossRef]
  36. F. Staier, “Entwicklung, Bau und Test einer UHV Röntgenstreukammer für die digitale In-Line Holographie,” PhD Thesis (University of Heidelberg, 2009).
  37. N. Guerassimova, (personal communication, 2009).
  38. D. Attwood, Soft X-Rays and Extreme Ultraviolet Radiation: Principles and Applications (Cambridge University Press, 2007).
  39. J. Garcia-Sucerquia, W. B. Xu, S. K. Jericho, P. Klages, M. H. Jericho, and H. J. Kreuzer, “Digital in-line holographic microscopy,” Appl. Opt. 45(5), 836–850 (2006). [CrossRef] [PubMed]
  40. J. M. Byrd, T. J. Shea, P. Denes, P. Siddons, D. Attwood, F. Kaertner, L. Moog, Y. Li, A. Sakdinawat, and R. Schlueter, “Enabling instrumentation and technology for 21st century light sources,” Nucl. Instrum. Methods Phys. Res. A 623(3), 910–920 (2010). [CrossRef]
  41. A. Rosenhahn, R. Barth, X. Cao, M. Schürmann, M. Grunze, and S. Eisebitt, “Vacuum-ultraviolet Gabor holography with synchrotron radiation,” Ultramicroscopy 107(12), 1171–1177 (2007). [CrossRef] [PubMed]
  42. S. Flewett, H. M. Quiney, C. Q. Tran, and K. A. Nugent, “Extracting coherent modes from partially coherent wavefields,” Opt. Lett. 34(14), 2198–2200 (2009). [CrossRef] [PubMed]
  43. R. Barth, F. Staier, T. Simpson, S. Mittler, S. Eisebitt, M. Grunze, and A. Rosenhahn, “Soft X-ray holographic microscopy of chromosomes with high aspect ratio pinholes,” J. Biotechnol. 149(4), 238–242 (2010). [CrossRef] [PubMed]
  44. S. Lindaas, M. Howells, C. Jacobsen, and A. Kalinovsky, “X-ray holographic microscopy by means of photoresist recording and atomic-force microscope readout,” J. Opt. Soc. Am. A 13(9), 1788–1800 (1996). [CrossRef]
  45. W. Eck, A. Küller, M. Grunze, B. Völkel, and A. Gölzhäuser, “Freestanding nanosheets from crosslinked biphenyl self-assembled monolayers,” Adv. Mater. (Deerfield Beach Fla.) 17(21), 2583–2587 (2005). [CrossRef]
  46. C. T. Nottbohm, A. Beyer, A. S. Sologubenko, I. Ennen, A. Hütten, H. Rösner, W. Eck, J. Mayer, and A. Gölzhäuser, “Novel carbon nanosheets as support for ultrahigh-resolution structural analysis of nanoparticles,” Ultramicroscopy 108(9), 885–892 (2008). [CrossRef] [PubMed]
  47. A. Turchanin, M. El-Desawy, and A. Gölzhäuser, “High thermal stability of cross-linked aromatic self-assembled monolayers: nanopatterning via selective thermal desorption,” Appl. Phys. Lett. 90(5), 053102 (2007). [CrossRef]
  48. A. Küller, W. Eck, V. Stadler, W. Geyer, and A. Gölzhäuser, “Nanostructuring of silicon by electron-beam lithography of self-assembled hydroxybiphenyl monolayers,” Appl. Phys. Lett. 82(21), 3776–3778 (2003). [CrossRef]
  49. C. T. Nottbohm, A. Turchanin, A. Beyer, and A. Gölzhäuser, “Direct e-beam writing of 1 nm thin carbon nanoribbons,” J. Vac. Sci. Technol. B 27(6), 3059–3062 (2009). [CrossRef]
  50. A. Turchanin, A. Beyer, C. T. Nottbohm, X. Zhang, R. Stosch, A. Sologubenko, J. Mayer, P. Hinze, T. Weimann, and A. Gölzhäuser, “One nanometer thin carbon nanosheets with tunable conductivity and stiffness,” Adv. Mater. (Deerfield Beach Fla.) 21(12), 1233–1237 (2009). [CrossRef]
  51. A. P. Mancuso, A. Schropp, B. Reime, L.-M. Stadler, A. Singer, J. Gulden, S. Streit-Nierobisch, C. Gutt, G. Grübel, J. Feldhaus, F. Staier, R. Barth, A. Rosenhahn, M. Grunze, T. Nisius, T. Wilhein, D. Stickler, H. Stillrich, R. Frömter, H.-P. Oepen, M. Martins, B. Pfau, C. M. Günther, R. Könnecke, S. Eisebitt, B. Faatz, N. Guerassimova, K. Honkavaara, V. Kocharyan, R. Treusch, E. Saldin, S. Schreiber, E. A. Schneidmiller, M. V. Yurkov, E. Weckert, and I. A. Vartanyants, “Coherent-pulse 2D crystallography using a free-electron laser x-ray source,” Phys. Rev. Lett. 102(3), 035502 (2009). [CrossRef] [PubMed]