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New diamond nanofabrication process for hard x-ray zone plates
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
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2011 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 29, no 6, 06FG03-1-06FG03-4 p.Article in journal (Refereed) Published
Abstract [en]

The authors report on a new tungsten-hardmask-based diamond dry-etch process for fabricating diamond zone plate lenses with a high aspect ratio. The tungsten hardmask is structured by electron-beam lithography, together with Cl2/O2 and SF6/O2 reactive ion etching in a trilayer resist-chromium-tungsten stack. The underlying diamond is then etched in an O2 plasma. The authors demonstrate excellent-quality diamond gratings with half-pitch down to 80 nm and a height of 2.6 μm, as well as zone plates with a 75 μm diameter and 100 nm outermost zone width. The diffraction efficiency of the zone plates is measured to 14.5% at an 8 keV x-ray energy, and the imaging properties were investigated in a scanning microscope arrangement showing sub-100-nm resolution. The imaging and thermal properties of these lenses make them suitable for use with high-brightness x-ray free-electron laser sources.

Place, publisher, year, edition, pages
2011. Vol. 29, no 6, 06FG03-1-06FG03-4 p.
Keyword [en]
zone plate; reactive ion etching; electron beam lithography; diamond; tungsten; nanofabrication; aspect ratio; x-ray free-electron laser; x-ray optics
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-47402DOI: 10.1116/1.3656055ISI: 000298538800086Scopus ID: 2-s2.0-84255168525OAI: oai:DiVA.org:kth-47402DiVA: diva2:454937
Note
QC 20111114Available from: 2011-11-08 Created: 2011-11-08 Last updated: 2017-12-08Bibliographically approved
In thesis
1. High-Resolution Nanostructuring for Soft X-Ray Zone-Plate Optics
Open this publication in new window or tab >>High-Resolution Nanostructuring for Soft X-Ray Zone-Plate Optics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diffractive zone-plate lenses are widely used as optics in high-resolution x-ray microscopes. The achievable resolution in such microscopes is presently not limited by the x-ray wavelength but by limitations in zone-plate nanofabrication. Thus, for the advance of high-resolution x-ray microscopy, progress in zone-plate nanofabrication methods are needed.

 

This Thesis describes the development of new nanofabrication processes for improved x-ray zone-plate optics. Cold development of the electron-beam resist ZEP7000 is applied to improve the resolution of soft x-ray Ni zone plates. The influence of developer temperature on resist contrast, resolution, and pattern quality is investigated. With an optimized process, Ni zone plates with outermost zone widths down to 13 nm are demonstrated. To enhance the diffraction efficiency of Ni zone plates, the concept of Ni-Ge zone plates is introduced. The applicability of Ni-Ge zone plates is first demonstrated in a proof-of-principle experiment, and then extended to cold-developed Ni zone plates with outermost zone widths down to 13 nm. For 15-nm Ni-Ge zone plates a diffraction efficiency of 4.3% at a wavelength of 2.88 nm is achieved, which is about twice the efficiency of state-of-the-art 15-nm Ni zone plates. To further increase both resolution and diffraction efficiency of soft x-ray zone plates, a novel fabrication process for W zone plates is developed. High resolution is provided by salty development of the inorganic electron-beam resist HSQ, and cryogenic RIE in a SF6 plasma is investigated for high-aspect-ratio W structuring. We demonstrate W zone plates with 12-nm outermost zone width and a W height of 90 nm, resulting in a 30% increase in theoretical diffraction efficiency compared to 13-nm efficiency-enhanced Ni-Ge zone plates. In addition to soft x-ray zone plates, some lenses for hard x-ray free-electron-laser applications were also fabricated during this Thesis work. Fabrication processes for the materials W, diamond, and Pt were developed. We demonstrate Pt and W-diamond zone plates with 100-nm outermost zone width and respective diffraction efficiencies of 8.2% and 14.5% at a photon energy of 8 keV.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xii, 70 p.
Series
Trita-FYS, ISSN 0280-316X ; 2011:55
Keyword
zone plates; x-ray optics; x-ray microscopy; high resolution; nanofabrication; electron beam lithography; reactive ion etching; tungsten; nickel; germanium
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-47409 (URN)978-91-7501-175-2 (ISBN)
Public defence
2011-12-02, FA31, Roslagstullsbacken 21, KTH/Albanova, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111114Available from: 2011-11-14 Created: 2011-11-08 Last updated: 2011-11-14Bibliographically approved
2. Nanofabrication of Zone Plates for Hard X-Ray Free-Electron Lasers
Open this publication in new window or tab >>Nanofabrication of Zone Plates for Hard X-Ray Free-Electron Lasers
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis describes the development of hard X-ray zone plates intended for focusing radiation at X-ray free-electron lasers (XFELs). XFELs provide unprecedented brightness and zone plates which are put in the intense X-ray beam are at risk of being damaged. Therefore, it is crucial to perform damage tests in order to design zone plates which can survive the XFEL beam.

Zone plates are diffractive nanofocusing optics and are regularly used at high brightness synchrotron beamlines in the soft and hard X-ray regime. The resolution of a zone plate is proportional to its outermost zonewidth and thus depends on the smallest feature that can be fabricated. State-of-the-art nanofabrication processes developed for zone plates are able to produce zonewidths down to 10 nm. However, for hard X-rays, the zone plates need to be of sufficient thickness to efficiently focus the radiation. Thus, the limit in the fabrication of hard X-ray zone plates lies in the high aspect-ratios. This Thesis describes two processes developed for high aspect-ratio nanostructuring. The first process uses tungsten as diffractive material. Aspect-ratios up to 1:15 have been accomplished. Furthermore, a mounting method of a central stop directly on the zone plate is also presented. The other fabrication process uses diamond, in which aspect-ratios of 1:30 have been demonstrated. Both processes rely on thin-film deposition techniques, electron-beam lithography, and reactive ion etching. Thanks to the materials’ excellent thermal properties these types of zone plates should be suitable for XFEL applications. Tungsten and diamond diffractive optics have been tested at an XFEL at Stanford (LCLS), and damage investigations were performed in order to determine the maximum fluence that could be imposed on the optics before degradation occured. The conclusion of these damage tests is that tungsten and diamond diffractive optics can survive the XFEL beam and could potentially be used in beamline experiments relying on nanofocused X-ray beams. Finally in this Thesis, characterization of two zone plates using an interferometer is presented, where it is also shown that the interferometric method can be used to pin-point beamline instabilities.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xiii, 69 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2014:77
Keyword
X-ray optics, Zone plates, Nanofabrication, X-ray free-electron lasers
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-158121 (URN)978-91-7595-406-6 (ISBN)
Public defence
2015-01-23, FA31, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

QC 20150112

Available from: 2015-01-12 Created: 2014-12-22 Last updated: 2015-01-12Bibliographically approved

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Vogt, UlrichHertz, Hans M.Holmberg, Anders

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