Showing papers by "Howard A. Padmore published in 2012"
TL;DR: Of special interest is the development of a higher harmonic rejection system that improves the spectral purity of the x-ray beam.
Abstract: We present the development and characterization of a dedicated resonant soft x-ray scattering facility. Capable of operation over a wide energy range, the beamline and endstation are primarily used for scattering from soft matter systems around the carbon K-edge (∼285 eV). We describe the specialized design of the instrument and characteristics of the beamline. Operational characteristics of immediate interest to users such as polarization control, degree of higher harmonic spectral contamination, and detector noise are delineated. Of special interest is the development of a higher harmonic rejection system that improves the spectral purity of the x-ray beam. Special software and a user-friendly interface have been implemented to allow real-time data processing and preliminary data analysis simultaneous with data acquisition.
419 citations
TL;DR: The effect of a faceted surface geometry on controlling the direction of well-defined line patterns of block copolymer (BCP) microdomains over macroscopic areas is reported.
Abstract: The effect of a faceted surface geometry on controlling the direction of well-defined line patterns of block copolymer (BCP) microdomains over macroscopic areas is reported. Facets with asymmetric base angles can control the direction of BCP microdomains oriented either parallel or perpendicular to the facets depending on BCP film thickness.
38 citations
TL;DR: This work demonstrates how a nanometerthick alumina deposition inside such a cavity can be used to gain an exquisite control over the resonance wavelength, allowing achieving a precise controlover the spectral response.
Abstract: Nanocavities fabricated in a metallic surface have important and technologically useful properties of complete light absorption and strong field enhancement. Here, we demonstrate how a nanometerthick alumina deposition inside such a cavity can be used to gain an exquisite control over the resonance wavelength. This process allows achieving a precise control over the spectral response and is completely reversible allowing many tuning attempts to be made on a single structure until the optimum performance is achieved.
37 citations
TL;DR: In this article, an ion-beam sputtering machine with a highly collimated atomic flux was used to deposit Mo/Si multilayers on saw-tooth substrates.
Abstract: Deposition of multilayers on saw-tooth substrates is a key step in the fabrication of multilayer blazed gratings (MBG) for extreme ultraviolet and soft x-rays. Growth of the multilayers can be perturbed by shadowing effects caused by the highly corrugated surface of the substrates, which results in distortion of the multilayer stack structure and degradation of performance of MBGs. To minimize the shadowing effects, we used an ion-beam sputtering machine with a highly collimated atomic flux to deposit Mo/Si multilayers on saw-tooth substrates. The sputtering conditions were optimized by finding a balance between smoothening and roughening processes in order to minimize degradation of the groove profile in the course of deposition and at the same time to keep the interfaces of a multilayer stack smooth enough for high efficiency. An optimal value of energy of 200 eV for sputtering Kr+ ions was found by deposition of test multilayers on flat substrates at a range of ion energies. Two saw-tooth substrates we...
26 citations
TL;DR: This model gives a straightforward way to design systems for optimum light trapping performance and gives fundamental insights into the interaction of light with metals at the nanoscale.
Abstract: Nanometer sized cavities arranged as a subwavelength metallic grating can provide omni-directional and complete absorption of light. We present an explanation of this extraordinary phenomenon as a collective resonant response of a system based on a surface impedance model. This model gives a straightforward way to design systems for optimum light trapping performance and as well gives fundamental insights into the interaction of light with metals at the nanoscale.
24 citations
TL;DR: This work reports on a way to optimize growth of sputter-deposited Mo/Si multilayers on sawtooth substrates through variation of the sputtering gas pressure and believes a new record for diffraction efficiency was achieved.
Abstract: Diffraction efficiency of multilayer-coated blazed gratings (MBG) strongly depends on the perfection of the sawtooth-shaped layers in the overall composite structure. Growth of multilayers on sawtooth substrates should be carefully optimized to reduce groove profile distortion and, at the same time, to avoid significant roughening of multilayer interfaces. In this work, we report on a way to optimize growth of sputter-deposited Mo/Si multilayers on sawtooth substrates through variation of the sputtering gas pressure. We believe a new record for diffraction efficiency of 44% was achieved for an optimized MBG with groove density of 5250 lines/mm at the wavelength of 13.1 nm.
24 citations
TL;DR: In this article, a methodology for the optimal in situ configuration of bendable Kirkpatrick-baez mirrors is presented. Butler et al. demonstrate a comprehensive and broadly applicable methodology for a bendable x-ray mirror configuration.
Abstract: We demonstrate a comprehensive and broadly applicable methodology for the optimal in situ configuration of bendable
soft x-ray Kirkpatrick-Baez mirrors. The mirrors used for this application are preset at the ALS Optical Metrology
Laboratory prior to beamline installation. The in situ methodology consists of a new technique for simultaneously setting
the height and pitch angle of each mirror. The benders of both mirrors were then optimally tuned in order to minimize
ray aberrations to a level below the diffraction-limited beam waist size of 200 nm (horizontal) × 100 nm (vertical). After
applying this methodology, we measured a beam waist size of 290 nm (horizontal) × 130 nm (vertical) with 1 nm light
using the Foucault knife-edge test. We also discuss the utility of using a grating-based lateral shearing interferometer
with quantitative wavefront feedback for further improvement of bendable optics.
9 citations
TL;DR: After 19 years of round-the-clock operations, the ALS continues to serve a broad community of about 2,000 users, providing an average of 5,300 operating hours per year, resulting in roughly 600 pee...
Abstract: After 19 years of round-the-clock operations, the ALS continues to serve a broad community of about 2,000 users, providing an average of 5,300 operating hours per year, resulting in roughly 600 pee...
5 citations
TL;DR: In this paper, the in-situ X-ray scattering measurements, including XRD and XRR, were used to study the growth process of the K-Cs-Sb photocathode.
2 citations
TL;DR: In this article, a case study of a gold grating with rectangular grooves is presented, where the resonance is shifted from original 720 nm to 960 nm by filling the grooves with an n = 1.4 immersion oil.
Abstract: A subwavelength plasmonic grating with rectangular grooves on the metal surface is an efficient light trapper with
designer resonance position and angular bandwidth. In this work, a new method is presented, where the grooves are
filled with a dielectric resulting in a large shift of the resonance wavelength. A case study of a gold grating with grooves
18 nm wide and 47 nm deep is presented, where the resonance is shifted from original 720 nm to 960 nm by filling the
grooves with an n = 1.4 immersion oil.