T heory predicts 1-4 that, with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft-X-ray free-electron laser. An intense 25 fs, 4 × 10 13 W cm −2 pulse, containing 10 12 photons at 32 nm wavelength, produced a coherent diffraction pattern from a nanostructured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single-photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling 5-9 , shows no measurable damage, and is reconstructed at the diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one 10 .X-ray free-electron lasers (FELs) are expected to permit diffractive imaging at high resolutions of nanometre-to micrometre-sized objects without the need for crystalline periodicity in the sample [1][2][3][4] . Structural studies within this size domain are particularly important in materials science, biology and medicine. Radiation-induced damage and sample movement prevent the accumulation of high-resolution scattering signals for such samples in conventional experiments 11,12 . Damage is caused by energy deposited into the sample by the very probes used for imaging, for example photons, electrons or neutrons. At X-ray frequencies, inner-shell processes dominate the ionization of the sample; photoemission is followed by Auger or fluorescence emission and shake excitations. The energies of the ejected photoelectrons, Auger electrons and shake electrons differ from each other, and these electrons are released at different times, but within about ten femtoseconds, following photoabsorption 1,13 . Thermalization of the ejected electrons through collisional electron cascades is completed within 10-100 fs (refs 14,15). Heat transport, diffusion and radical reactions take place over some picoseconds to milliseconds.The effect of X-ray-induced sample damage on the recorded image or diffraction pattern could be substantially reduced, if we could collect diffraction data faster than the relevant damage processes 1,16 . This approach requires very short and very bright X-ray pulses, such as those expected from a short-wavelength FEL. However, the large amount of energy deposited into the sample by a focused FEL pulse will ultimately turn the sample into a plasma. The question is when exactly would this happen. There are no experiments with X-rays in the relevant time and intensity nature physics VOL 2 DECEMBER 2006 www.nature.com/naturephysics

In nanotechnology, strategies for the creation and manipulation of nanoparticles in the gas phase are critically important for surface modification and substrate-free characterization. Recent coherent diffractive imaging with intense femtosecond X-ray pulses has verified the capability of single-shot imaging of nanoscale objects at suboptical resolutions beyond the radiation-induced damage threshold. By intercepting electrospray-generated particles with a single 15 femtosecond soft-X-ray pulse, we demonstrate diffractive imaging of a nanoscale specimen in free flight for the first time, an important step toward imaging uncrystallized biomolecules.

We used a combination of dip-pen nanolithography and scanning optical confocal microscopy to fabricate and visualize luminescent nanoscale patterns of various materials on glass substrates. We show that this method can be used successfully to push the limits of dip-pen nanolithography down to controlled deposition of single molecules. We also demonstrate that this method is able to create and visualize protein patterns on surfaces. Finally, we show that our method can be used to fabricate polymer nanowires of controlled size using conductive polymers. We also discuss the factors that influence the size of these nanowires.

We have developed a multistep route to the fabrication of virus assembled nanostructures with chemoselective protein-to-surface linkers synthesized by an efficient solid-phase method. These linkers were used to create patterns of 30-to-50-nm-width-lines by scanning probe nanolithography. Genetically modified cow pea mosaic virus with unique cysteine residues at specific locations on their capsomers were assembled through covalent linkage on these patterns. The morphology of the assembled structures on these line patterns characterized by atomic force microscopy was found to be strongly influenced by the intervirion interactions.

No abstract

The transient nanoscale dynamics of materials on femtosecond to picosecond timescales is of great interest in the study of condensed phase dynamics such as crack formation, phase separation and nucleation, and rapid fluctuations in the liquid state or in biologically relevant environments. The ability to take images in a single shot is the key to studying non-repetitive behaviour mechanisms, a capability that is of great importance in many of these problems. Using coherent diffraction imaging with femtosecond X-ray free-electron-laser pulses we capture time-series snapshots of a solid as it evolves on the ultrafast timescale. Artificial structures imprinted on a Si 3 N 4 window are excited with an optical laser and undergo laser ablation, which is imaged with a spatial resolution of 50 nm and a temporal resolution of 10 ps. By using the shortest available free-electronlaser wavelengths 1 and proven synchronization methods 2 this technique could be extended to spatial resolutions of a few nanometres and temporal resolutions of a few tens of femtoseconds. This experiment opens the door to a new regime of time-resolved experiments in mesoscopic dynamics.To date, optical pulses have made it possible to resolve dynamics on the femtosecond timescale, but the spatial resolution of these studies has been limited to a few micrometres 3 . On the other hand, femtosecond X-ray pulses have been used to detect Å ngstrom-scale atomic motions in extended crystalline materials with long-range order through time-resolved diffraction experiments 4,5 . An entirely different methodology is needed to investigate the ultrafast dynamics of non-crystalline materials at nanometre length scales. Applications at these scales can be found in the study of fracture dynamics, shock formation, spallation, ablation, and plasma formation under extreme conditions. In the solid state it is desirable to directly image dynamic processes such as nucleation and phase growth, phase fluctuations and various forms of electronic or magnetic segregation.Electron microscopes can provide nanometre to atomic resolution, and have recently been demonstrated with ultrafast pulses 6 . However, they have limited penetrating power and struggle to obtain high-quality single-shot images due to space-charge issues 7 . Synchrotron beams from third-generation sources have comparatively long pulse lengths of 10-100 ps, as determined by the shortest electron bunch length possible in a given storage ring. Synchrotron sources can produce short-pulse ($100 fs) X-rays when operated as femtosecond slicing sources 8 , but produce comparatively weak X-ray beams of 1 Â 10 7 photons per second. Along with X-ray pulses from femtosecond laser plasma sources 9,10 and high-harmonic-generation sources 11 this limits their use to non-destructive phenomena where weak signals can be accumulated over many repeatable excitations of the sample.The intense femtosecond X-ray pulses from free-electron-laser (FEL) sources provide the penetrating power, spatial resolution and single-shot imaging c...

We discuss the design and fabrication of 80-cm-diameter random phase plates for target-plane beam smoothing on the Nova laser. Random phase plates have been used in a variety of inertial confinement fusion target experiments, such as studying direct-drive hydrodynamic stability and producing spatially smooth x-ray backlighting sources. These phase plates were produced by using a novel sol-gel dip-coating technique developed by us. The sol-gel phase plates have a high optical damage threshold at the second- and third-harmonic wavelengths of the Nd:glass laser and have excellent optical performance.

Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft x-ray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7-32 nm x-rays with 10 12 photons per pulse. The high brightness, short wavelength, and high repetition rate (>500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of Address correspondence to Michael J. Bogan, Stanford PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road MS59, Menlo Park, CA 94025, USA. E-mail: mbogan@slac.stanford.edu fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatial-and time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science.