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X-ray microscopy makes for super resolution
RESEARCH NEWS
X-ray microscopy makes for super resolution CHARACTERIZATION
oversampled, and the team Researchers from the Paul Scherrer have developed a novel image Institut and the École Polytechnique reconstruction method to make sense Fédérale de Lausanne in Switzerland of both the phase and the intensity in have unveiled the next best thing in the thousands of diffraction patterns. X-ray microscopy by combining the The team ran the microscope through advantages of two well-established its paces by imaging a Fresnel techniques. zone plate buried beneath a gold In scanning transmission X-ray layer. They employed a 6.8 keV microscopy, a sample is raster scanned X-ray source focused to a 300 nm and the transmitted X-ray intensity spot size, collecting a 201 by 201 at each point is recorded to build up array of diffraction patterns. While an absorption image. However, the conventional scanning electron resolution of the approach is limited microscopy yields a high-resolution to the spot size of the focused X-ray Left: Representative diffraction images used for reconstructing a surface image, the SXDM image beam. scanning X-ray diffraction micrograph. Right: Scanning X-ray diffraction micrograph of the gold-coated Fresnel zone plate. (Courtesy of Pierre reveals the structure beneath in great On the other hand, a family of Thibault and Franz Pfeiffer (PSI/EPFL)) detail. techniques under the rubric of The authors note that the approach coherent diffraction imaging have diffraction patterns [Thibault et. al., Science is noninvasive and can be carried been developed, in which a number (2008) 321, 379]. out at ambient conditions using both hard of overlapping diffraction patterns of an At the heart of the experiment is the Megapixel and soft X-rays, depending on the sample. illuminated sample are deconvoluted to provide Pilatus detector, developed at the Paul Scherrer The team intends to extend the method to an image. While the resolution of the approach Institut. It is the world’s first array detector that 3-dimensional imaging, and expects that with is higher, the data analysis is difficult. counts single photons with no readout noise, coming improvements in coherent X-ray sources The new approach, dubbed scanning X-ray acquiring images with frame rates up to 100 Hz. and focusing optics, the resolution limit of the diffraction microscopy or SXDM, uses the core With step sizes smaller than the size of approach will reach 10 nm. ideas of both methods by raster scanning a the focused X-ray beam, the image is thus sample and collecting tens of thousands of D. Jason Palmer
A glimpse of carrier pairing in superconductors ELECTRONIC MATERIALS A peek into the inner workings of high temperature superconductors has been provided by new work by an international collaboration reporting in Nature. A fuller understanding of the transition to superconducting could open new research lines into room temperature superconductors—leading to lossless power transmission and a host of other applications. The new research comes from a team comprised of researchers at the University of Cambridge in the UK, the National High Magnetic Field Laboratories at Los Alamos National Laboratory and Florida State University in the US, and the University of British Columbia and the Canadian Institute for Advanced Research in Canada. The team focused their efforts on samples of YBa2Cu3O6.51. Copper oxides such as this behave as insulating magnets before doping, but on the addition of charge carriers become high-temperature superconductors as the carriers pair up. The
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microscopic physics of that transition, however, has remained a mystery. While superconductors are difficult to investigate using common techniques, the application of high external magnetic fields creates ‘vortices’—regions where the superconductivity is destroyed but whose electronic structure can be studied. To investigate that, the team studied the oscillations of the magnetization of the samples in the presence of an externally applied magnetic field. Such oscillations occur as a result of the de Haas-van Alphen effect, a quantum mechanical phenomenon that arises due to the quantization of electron energies. Prior experimental results have shown a prominent oscillation that occurs at around 500 T, suggesting a small ‘pocket’ in the Fermi surface for carriers. The new work, however, demonstrates an oscillation at 1 650 T, some 30 times weaker but corresponding to more than three times as many charge carriers, each
SEPTEMBER 2008 | VOLUME 11 | NUMBER 9
with twice the effective particle mass as the 500 T pocket [Sebastian et. al., Nature (2008) 454, 200]. “We have been able to shed light on the location in the electronic structure where ‘pockets’ of doped carriers gather,” said lead author Suchitra E. Sebastian of the University of Cambridge—a crucial step toward understanding how the carriers pair up for superconducting. As with many findings in superconductivity research, however, the results have raised many questions, in particular about the implied interplay between magnetism and superconductivity. The two may be separate, competing effects, so that in regions of the material where superconductive behavior is quenched, magnetism takes over. Alternatively, the non-superconducting vortices might work together to create a macroscopic magnetization while the remainder of the structure superconducts.
D. Jason Plamer
X-ray microscopy makes for super resolution CHARACTERIZATION
oversampled, and the team Researchers from the Paul Scherrer have developed a novel image Institut and the École Polytechnique reconstruction method to make sense Fédérale de Lausanne in Switzerland of both the phase and the intensity in have unveiled the next best thing in the thousands of diffraction patterns. X-ray microscopy by combining the The team ran the microscope through advantages of two well-established its paces by imaging a Fresnel techniques. zone plate buried beneath a gold In scanning transmission X-ray layer. They employed a 6.8 keV microscopy, a sample is raster scanned X-ray source focused to a 300 nm and the transmitted X-ray intensity spot size, collecting a 201 by 201 at each point is recorded to build up array of diffraction patterns. While an absorption image. However, the conventional scanning electron resolution of the approach is limited microscopy yields a high-resolution to the spot size of the focused X-ray Left: Representative diffraction images used for reconstructing a surface image, the SXDM image beam. scanning X-ray diffraction micrograph. Right: Scanning X-ray diffraction micrograph of the gold-coated Fresnel zone plate. (Courtesy of Pierre reveals the structure beneath in great On the other hand, a family of Thibault and Franz Pfeiffer (PSI/EPFL)) detail. techniques under the rubric of The authors note that the approach coherent diffraction imaging have diffraction patterns [Thibault et. al., Science is noninvasive and can be carried been developed, in which a number (2008) 321, 379]. out at ambient conditions using both hard of overlapping diffraction patterns of an At the heart of the experiment is the Megapixel and soft X-rays, depending on the sample. illuminated sample are deconvoluted to provide Pilatus detector, developed at the Paul Scherrer The team intends to extend the method to an image. While the resolution of the approach Institut. It is the world’s first array detector that 3-dimensional imaging, and expects that with is higher, the data analysis is difficult. counts single photons with no readout noise, coming improvements in coherent X-ray sources The new approach, dubbed scanning X-ray acquiring images with frame rates up to 100 Hz. and focusing optics, the resolution limit of the diffraction microscopy or SXDM, uses the core With step sizes smaller than the size of approach will reach 10 nm. ideas of both methods by raster scanning a the focused X-ray beam, the image is thus sample and collecting tens of thousands of D. Jason Palmer
A glimpse of carrier pairing in superconductors ELECTRONIC MATERIALS A peek into the inner workings of high temperature superconductors has been provided by new work by an international collaboration reporting in Nature. A fuller understanding of the transition to superconducting could open new research lines into room temperature superconductors—leading to lossless power transmission and a host of other applications. The new research comes from a team comprised of researchers at the University of Cambridge in the UK, the National High Magnetic Field Laboratories at Los Alamos National Laboratory and Florida State University in the US, and the University of British Columbia and the Canadian Institute for Advanced Research in Canada. The team focused their efforts on samples of YBa2Cu3O6.51. Copper oxides such as this behave as insulating magnets before doping, but on the addition of charge carriers become high-temperature superconductors as the carriers pair up. The
10
microscopic physics of that transition, however, has remained a mystery. While superconductors are difficult to investigate using common techniques, the application of high external magnetic fields creates ‘vortices’—regions where the superconductivity is destroyed but whose electronic structure can be studied. To investigate that, the team studied the oscillations of the magnetization of the samples in the presence of an externally applied magnetic field. Such oscillations occur as a result of the de Haas-van Alphen effect, a quantum mechanical phenomenon that arises due to the quantization of electron energies. Prior experimental results have shown a prominent oscillation that occurs at around 500 T, suggesting a small ‘pocket’ in the Fermi surface for carriers. The new work, however, demonstrates an oscillation at 1 650 T, some 30 times weaker but corresponding to more than three times as many charge carriers, each
SEPTEMBER 2008 | VOLUME 11 | NUMBER 9
with twice the effective particle mass as the 500 T pocket [Sebastian et. al., Nature (2008) 454, 200]. “We have been able to shed light on the location in the electronic structure where ‘pockets’ of doped carriers gather,” said lead author Suchitra E. Sebastian of the University of Cambridge—a crucial step toward understanding how the carriers pair up for superconducting. As with many findings in superconductivity research, however, the results have raised many questions, in particular about the implied interplay between magnetism and superconductivity. The two may be separate, competing effects, so that in regions of the material where superconductive behavior is quenched, magnetism takes over. Alternatively, the non-superconducting vortices might work together to create a macroscopic magnetization while the remainder of the structure superconducts.
D. Jason Plamer