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Compact Zernike phase contrast x-ray microscopy using a single-element optic
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.ORCID iD: 0000-0003-2745-6289
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2008 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 9, 932-934 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate Zernike phase contrast in a compact soft x-ray microscope using a single-element optic. The optic is a combined imaging zone plate and a Zernike phase plate and does not require any additional alignment or components. Contrast is increased and inversed in an image of a test object using the Zernike zone plate. This type of optic may be implemented into any existing x-ray microscope where phase contrast is of interest.

Place, publisher, year, edition, pages
2008. Vol. 33, no 9, 932-934 p.
Keyword [en]
spatial-resolution, zone plates
National Category
Biomedical Laboratory Science/Technology
Identifiers
URN: urn:nbn:se:kth:diva-17561ISI: 000256166900014Scopus ID: 2-s2.0-44949260817OAI: oai:DiVA.org:kth-17561DiVA: diva2:335605
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2012-03-19Bibliographically approved
In thesis
1. Phase-Contrast and High-Resolution Optics for X-Ray Microscopy
Open this publication in new window or tab >>Phase-Contrast and High-Resolution Optics for X-Ray Microscopy
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray microscopy is a well-established technique for nanoscale imaging. Zone plates are used as microscope objectives and provide high resolution, approaching 10 nm, currently limited by fabrication issues. This Thesis presents zone plate optics that achieve either high resolution or phase contrast in x-ray microscopy. The high-resolution optics use high orders of the zone plate, which alleviates the demands on fabrication, and the phase-contrast optics are single-element diffractive optical elements that produce contrast by Zernike or differential-interference contrast methods. The advantage of phase contrast in x-ray microscopy is shorter exposure times, and is crucial in the hard x-ray regime. Microscopy in the absorption‑contrast region of the water-window (2.34 - 4.37 nm) also benefits from these optics. The development of the optics for a laboratory soft x-ray microscope spans from theoretical and numerical analysis of coherence and stray light to experimental implementation and testing. The laboratory microscope uses laser-produced plasma-sources in the water-window and is unique in its design and performance. It will be shown that the laboratory microscope in its current form is a user-oriented and stable instrument, and has been used in a number of applications. The implementation of a cryogenic sample stage for tomographic imaging of biological samples in their natural environment has enabled applications in biology, and 3D x-ray microscopy of cells was performed for the first time with a laboratory instrument.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. x, 61 p.
Series
Trita-FYS, ISSN 0280-316X ; 72
Keyword
Microscopy, X-ray optics, X-ray microscopy, Soft X-ray physics
National Category
Atom and Molecular Physics and Optics Physical Sciences
Identifiers
urn:nbn:se:kth:diva-26781 (URN)978-91-7415-834-2 (ISBN)
Public defence
2010-12-17, FD5, Roslagstullsbacken 21, Stockholm, 15:42 (English)
Opponent
Supervisors
Note
QC 20101130Available from: 2010-11-30 Created: 2010-11-26 Last updated: 2010-11-30Bibliographically approved
2. Laboratory soft x-ray microscopy and tomography
Open this publication in new window or tab >>Laboratory soft x-ray microscopy and tomography
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Soft x-ray microscopy in the water-window (λ = 2.28 nm – 4.36 nm) is based on zone-plate optics and allows high-resolution imaging of, e.g., cells and soils in their natural or near-natural environment. Three-dimensional imaging is provided via tomographic techniques, soft x-ray cryo tomography. However, soft x-ray microscopes with such capabilities have been based on large-scale synchrotron x‑ray facilities, thereby limiting their accessibility for a wider scientific community.

This Thesis describes the development of the Stockholm laboratory soft x-ray microscope to three-dimensional cryo tomography and to new optics-based contrast mechanisms. The microscope relies on a methanol or nitrogen liquid-jet laser-plasma source, normal-incidence multilayer or zone-plate condenser optics, in-house fabricated zone-plate objectives, and allows operation at two wavelengths in the water-window, λ = 2.48 nm and λ = 2.48 nm. With the implementation of a new state-of-the-art normal-incidence multilayer condenser for operation at λ = 2.48 nm and a tiltable cryogenic sample stage the microscope now allows imaging of dry, wet or cryo-fixed samples. This arrangement was used for the first demonstration of laboratory soft x-ray cryo microscopy and tomography. The performance of the microscope has been demonstrated in a number of experiments described in this Thesis, including, tomographic imaging with a resolution of 140 nm, cryo microscopy and tomography of various cells and parasites, and for studies of aqueous soils and clays. The Thesis also describes the development and implementation of single-element differential-interference and Zernike phase-contrast zone-plate objectives. The enhanced contrast provided by these optics reduce exposure times or lowers the dose in samples and are of major importance for harder x-ray microscopy. The implementation of a high-resolution 50 nm compound zone-plate objective for sub-25-nm resolution imaging is also described. All experiments are supported by extensive numerical modelling for improved understanding of partially coherent image formation and stray light in soft x-ray microscopes. The models are useful tools for studying effects of zone plate optics or optical design of the microscope on image formation and quantitative accuracy in soft x-ray tomography.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. x, 76 p.
Series
Trita-FYS, ISSN 0280-316X ; 2011:03
Keyword
Microscopy, X-ray optics, Diffractive optics, Zone plates, X-ray microscopy, Soft X-ray physics, Tomography
National Category
Atom and Molecular Physics and Optics Physical Sciences
Identifiers
urn:nbn:se:kth:diva-29950 (URN)978-91-7415-874-8 (ISBN)
Public defence
2011-02-25, FB42, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110221Available from: 2011-02-21 Created: 2011-02-18 Last updated: 2011-02-21Bibliographically approved
3. Nanofabrication of Diffractive Soft X-ray Optics
Open this publication in new window or tab >>Nanofabrication of Diffractive Soft X-ray Optics
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis summarizes the present status of the nanofabrication of diffractive optics, i.e. zone plates, and test objects for soft x-ray microscopy at KTH. The emphasis is on new and improved fabrication processes for nickel and germanium zone plates. A new concept in which nickel and germanium are combined in a zone plate is also presented. The main techniques used in the fabrication are electron beam lithography for the patterning, followed by plasma etching and electroplating for the structuring of the optical materials. The process for fabricating nickel zone plates has been significantly improved. The reproducibility of the electroplating step has been increased by the implementation of an in-situ rate measurement and an end-point detection method. We have also shown that pulse plating can be used to obtain zone plates with a uniform height profile. New plating mold materials have been introduced and electron-beam curing of the molds has been investigated and implemented to increase their mechanical stability so that pattern collapse in the electroplating step can be avoided. The introduction of cold development has improved the achievable resolution of the process. This has enabled the fabrication of zone plates with outermost zone widths down to 16 nm. The nickel process has also recently been adapted to fabrication of gold structures intended for test objects and hard x-ray zone plates. For the fabrication of germanium zone plates we developed a highly anisotropic plasma-etch process using Cl2 feed and sidewall passivation. Germanium zone plates have been fabricated with zone widths down to 30 nm. The diffraction efficiency is comparable to that of nickel zone plates, but the process does not involve electroplating and thus has for potential for highyield fabrication. The combination of nickel and germanium is a new fabrication concept that provides a means to achieve high diffraction efficiency even for thin nickel. The idea is to fabricate a nickel zone plate on a germanium film. The nickel zone plate itself is then used as etch mask for a highly selective CHF3- plasma etch into the germanium layer. Proof of principle experiments showed an efficiency increase of about a factor of two for nickel zone plates with a 50- nm nickel thickness.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. vii, 71 p.
Series
Trita-FYS, ISSN 0280-316X ; 2008:57
Keyword
Nanofabrication, Zone plate, x-ray, diffractive x-ray optics, x-ray microscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-9800 (URN)978-91-7415-205-0 (ISBN)
Public defence
2009-02-06, FR4, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100728Available from: 2009-01-13 Created: 2009-01-07 Last updated: 2011-10-20Bibliographically approved

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Holmberg, AndersVogt, Ulrich

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