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Compact Soft X-Ray Microscopy: Sources, Optics and Instrumentation
KTH, School of Engineering Sciences (SCI), Applied Physics.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis describes the development of a sub-60-nm full-period resolution compact soft x-ray microscope operating in the water-window region (2.3-4.4 nm). Soft x-ray water-window microscopy is a powerful technique for high-resolution imaging of organic materials exploiting the natural contrast mechanism between carbon and oxygen, cf. Sect. 4.1. The thesis discusses the components of, as well as the integration of the microscope, including liquid-jet laser-plasma x-ray sources, optics, simulations, and image-processing tools.

Liquid-jet-target laser-plasma sources for generation of soft x-rays and extreme-ultraviolet radiation are compact sources with high brightness. The work focused on improved target stability, decreased debris, and accurate source characterization. For x ray microscopy applications a liquid-jet target delivery system allowing cryogenic liquids was developed. Source characterization was performed for two different liquid-jet targets: Methanol and liquid nitrogen. For extreme-ultraviolet lithography applications, the potential use of a liquid-tin-jet laser-plasma source was explored including conversion efficiency and debris measurements.

High quality optics are essential in the development of compact x-ray microscopes. For soft x-ray wavelengths, zone plates and multilayer mirrors are used to focus or redirect radiation. This thesis describes the development and characterization of a condenser zone plate suitable for use in a compact soft x-ray microscope operating at λ = 2.478 nm. It also investigates the possibility to perform differential interference contrast microscopy in the water window using a single diffractive optical element. An arrangement for rapid and accurate determination of absolute and local diffraction efficiency of soft x-ray zone plates using a compact laser-plasma source has been developed. The instrument is used to characterize the zone plates fabricated at the Biomedical & X-Ray Physics division at KTH. Through a collaboration with the Fraunhofer-Institut in Jena, Germany, a large diameter spherical Cr/Sc multilayer mirror, suitable as condenser in the compact x-ray microscope, was developed and characterized. The mirror is designed for λ = 3.374 nm and shows a high, and uniform reflectivity of 3%. This increases the photon flux by an order of magnitude compared to the W/B4C mirrors previously used.

The thesis describes the development of a compact soft x-ray microscope with sub-60-nm full-period resolution. It can operate at two different wavelengths in the water window using the soft x-ray laser-plasma sources combined with the condenser optics described above. Imaging is performed by zone plate objectives. The microscope is capable of imaging hydrated biological samples with thicknesses up to ~10 μm. Improvements made to the mechanical design has turned it into a user friendly instrument allowing daily operation. A numerical method was developed to study the effects of partially coherent illumination on 2D imaging. To stimulate experiments on functional imaging in x-ray microscopy an image-analysis algorithm for identifying colloidal-gold particles was developed. Size selective identification and localization of single gold particles down to a diameter of 50 nm was demonstrated.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , x, 59 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:25
Keyword [en]
soft x-ray microscopy, water window, compact, laser plasma, liquid jet, zone plate optics
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4342ISBN: 978-91-7178-613-5 (print)OAI: oai:DiVA.org:kth-4342DiVA: diva2:11899
Public defence
2007-05-04, FD 5, Albanova, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100819Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-20Bibliographically approved
List of papers
1. Liquid-tin-jet laser-plasma extreme ultraviolet generation
Open this publication in new window or tab >>Liquid-tin-jet laser-plasma extreme ultraviolet generation
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2004 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, no 13, 2556-2258 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate the applicability of liquid-metal jets in vacuum as regenerative targets for laser-plasma generation of extreme ultraviolet (EUV) and soft x-ray radiation. This extends the operation of liquid jet laser-plasma,sources to high-temperature, high-Z, high-density, low-vapor-pressure materials with new spectral signatures. The system is demonstrated using tin (Sn) as the target due to its strong emission around lambdaapproximate to13 nm, which makes the material suitable for EUV lithography. We show a conversion efficiency of 2.5% into (2% BW x 2pi x sr) and report quantitative measurements of the ionic/atomic as well as particulate debris emission.

Keyword
Calibration; Charge coupled devices; Electron beams; Electron transitions; Jets; Light emission; Light reflection; Liquid metals; Photolithography; Scanning electron microscopy; Tin; Ultraviolet radiation; X rays; Extreme ultraviolet (EUV) lithography; High-repetition-rate lasers; Liquid-metal jets; Particulate debris emission; Laser produced plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7013 (URN)10.1063/1.1690874 (DOI)000220591500012 ()2-s2.0-2142714542 (Scopus ID)
Note
QC 20100819Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
2. High-resolution spatial characterization of laser produced plasmas at soft x-ray wavelengths
Open this publication in new window or tab >>High-resolution spatial characterization of laser produced plasmas at soft x-ray wavelengths
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2004 (English)In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 78, no 1, 53-58 p.Article in journal (Refereed) Published
Abstract [en]

In this article, we describe the setup and application of a system for the spatial characterization of laser-produced plasma x-ray sources. While pinhole cameras are normally used for this purpose, we employed a zone plate to act as the x-ray lens. Together with an x-ray CCD camera as the detector, a spatial resolution of up to 2 mum was achieved. Due to the wavelength-dependent focal length of a zone plate, the monochromaticity of the image was better than lambda/Deltalambda=150, and the large aperture of the zone plate allowed single-laser-shot images to be collected. Methanol and ethanol were used as liquid-jet target systems. Two different Nd:YAG lasers with pulse durations of 3 ns and 10 ns produced the plasmas. Our measurements concentrated on the line emission of carbon in the soft x-ray spectral range, namely, the hydrogen-like alpha-line at 3.37 nm and the helium-like alpha-line at 4.03 nm. We investigated the influence of different nozzle sizes, laser energies, and pulse durations on the source size of the plasma. Depending on the experimental conditions, plasma diameters of 17-60 mum were measured.

Keyword
Ethanol; Image quality; Lenses; Light emission; Light sources; Methanol; Neodymium lasers; Nozzles; X rays; High resolution spatial characterization; Liquid jet target systems; Plasma diameters; Soft x ray wavelengths; Laser produced plasmas
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6200 (URN)10.1007/s00340-003-1338-9 (DOI)000187014400011 ()2-s2.0-0742321216 (Scopus ID)
Note
QC 20100819Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-12-14Bibliographically approved
3. Liquid-nitrogen-jet laser-plasma source for compact soft x-ray microscopy
Open this publication in new window or tab >>Liquid-nitrogen-jet laser-plasma source for compact soft x-ray microscopy
2005 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 76, no 4, 043503- p.Article in journal (Refereed) Published
Abstract [en]

We describe a liquid-nitrogen-jet laser-plasma source with sufficient brightness, uniformity, stability, and reliability to be suitable for compact water-window soft x-ray transmission microscopy. A cooled capillary nozzle arrangement allows long-term operation and avoids previously reported jet instabilities. The source is quantitatively characterized by calibrated slit-grating spectroscopy and zone-plate imaging. The absolute photon number in the major spectral lines (lambda=2.48 nm and lambda=2.88 nm) is 1.0x10(12) photons/(pulsexsrxline). The source diameter is similar to 20 mu m (full width at half maximum) and the spatial stability is better than +/- 2 mu m. Within an area with uniformity of 20%, the average source brightness is 4x10(8) photons/(pulsexsrx mu m(2)xline), which allows operation of a compact soft x-ray transmission microscope with exposure times of a few minutes.

Keyword
Liquid-nitrogen-jet laser-plasma sources; Slit-grating spectroscopy; Soft x-ray microscopy; Zone-plate imaging; Imaging techniques; Laser beams; Laser produced plasmas; Neodymium lasers; Photons; Plasma stability; Synchrotron radiation; X ray microscopes; Plasma sources
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7015 (URN)10.1063/1.1884186 (DOI)000228362200016 ()2-s2.0-17644395629 (Scopus ID)
Note
QC 20100820Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
4. Fabrication and characterization of a condenser zone plate for compact x-ray microscopy
Open this publication in new window or tab >>Fabrication and characterization of a condenser zone plate for compact x-ray microscopy
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2004 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 22, no 3, 1118-1122 p.Article in journal (Refereed) Published
Abstract [en]

We describe the in-house fabrication and characterization of a condenser zone plate for a compact laser-plasma-based soft x-ray microscope operating at 2.478 nm wavelength. The fabricated condenser has a diameter of 4.53 mm and an outermost zone width of 49 nm. The pattern is generated by a small-write-field e-beam lithography system and 656 single, 100 mum wide write fields are stitched together to obtain the whole pattern. An in-house method based on a laser-plasma source was developed to characterize the condenser zone plate with regards to diffraction efficiency and imaging properties. The measured groove efficiency of the fabricated condenser zone plate was determined to 11%+/-2% and the imaging properties were found to follow the expectations concerning the object field illumination purpose in the x-ray microscope. The in-house characterization method allows faster process improvement in the small-scale laboratory compared to presently used synchrotron-based methods.

Keyword
Charge coupled devices; Diffraction; Lasers; Lithography; Microscopic examination; Plasmas; Plates (structural components); Scanning electron microscopy; Statistical methods; X ray microscopes; Condenser zone plates (CZP); Multilayer mirrors; Synchrotron radiation sources; Capacitors
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7016 (URN)10.1116/1.1738671 (DOI)000222481400043 ()2-s2.0-3242657331 (Scopus ID)
Note
QC 20100616Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
5. Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source
Open this publication in new window or tab >>Single-optical-element soft-x-ray interferometry with a laser-plasma x-ray source
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2005 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 15, 2167- p.Article in journal (Refereed) Published
Abstract [en]

We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda = 2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.

Keyword
Diffraction; Imaging techniques; Interferometers; Light propagation; Plasmas; X rays; Compact interferometer; Focal spots; Laser-plasma source; Liquid nitrogen; Interferometry
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7017 (URN)10.1364/OL.30.002167 (DOI)000231072700039 ()2-s2.0-24344492433 (Scopus ID)
Note
QC 20100616Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
6. Laboratory arrangement for soft x-ray zone-plate efficiency measurements
Open this publication in new window or tab >>Laboratory arrangement for soft x-ray zone-plate efficiency measurements
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2007 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 78, no 2, 026103- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate a laboratory-scale arrangement for rapid and accurate measurements of the absolute and local efficiency of soft x-ray micro zone plates in the water window. This in-house instrument is based on a single-line lambda=2.88 nm liquid-jet laser-plasma source. Measurements are performed by a simultaneous comparison of first diffraction-order photon flux with the flux in a calibrated reference signal. This arrangement eliminates existing source emission fluctuations. The performance of the method is demonstrated by the result from measurements of two similar to 55 mu m diameter nickel micro zone plates, showing a groove efficiency of 12.9%+/- 1.1% and 11.7%+/- 1.0%. Furthermore, we show that spatially resolved efficiency mapping is an effective tool for a detailed characterization of local zone plate properties. Thus, this laboratory-scale instrument allows rapid feedback to the fabrication process which is important for future improvements.

Keyword
Electron diffraction; Laser beams; Photons; Plasma theory; X rays; Emission fluctuations; Micro zone plates; Reference signals; Plates (structural components)
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7018 (URN)10.1063/1.2472590 (DOI)000244531600057 ()2-s2.0-33847677594 (Scopus ID)
Note
QC 20100820Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
7. High-reflectivity Cr/Sc multilayer condenser for compact soft x-ray microscopy
Open this publication in new window or tab >>High-reflectivity Cr/Sc multilayer condenser for compact soft x-ray microscopy
2006 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, no 12, 123101- p.Article in journal (Refereed) Published
Abstract [en]

The condenser is a critical component in compact water-window x-ray microscopes as it influences the exposure time via its efficiency and the resolution via its numerical aperture. Normal-incidence multilayer mirrors can reach large geometrical collection efficiencies and match the numerical aperture of the zone plate but require advanced processing for high total reflectivity. In the present article we demonstrate large-diameter normal-incidence spherical Cr/Sc multilayer condensers with high and uniform reflectivity. Dc-magnetron sputtering was used to deposit 300 bilayers of Cr/Sc with a predetermined d-spacing matching the lambda=3.374 nm operating wavelength on spherical substrates. The mirrors show a uniform reflectivity of similar to 3% over the full 58 mm diameter condenser area. With these mirrors an improvement in exposure time by a factor of 10 was achieved, thereby improving the performance of the compact x-ray microscope significantly.

Keyword
Chromium compounds; Magnetron sputtering; Multilayers; Numerical analysis; Optical microscopy; Reflection; d-spacing matching; Multilayer mirrors; Water-window x-ray microscopes; Capacitors
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6202 (URN)10.1063/1.2400665 (DOI)000243159100001 ()2-s2.0-33846081459 (Scopus ID)
Note
QC 20100820. Uppdaterad från Submitted till Published 20100820.Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-12-14Bibliographically approved
8. Simulation of partially coherent image formation in a compact soft x-ray microscope
Open this publication in new window or tab >>Simulation of partially coherent image formation in a compact soft x-ray microscope
2007 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 107, no 8, 604-609 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, we describe a numerical method of simulating two-dimensional images in a compact soft X-ray microscope using partially coherent illumination considerations. The work was motivated by recent test object images obtained by the latest generation inhouse compact soft X-ray microscope, which showed diffraction-like artifacts not observed previously. The numerical model approximates the condenser zone plate as a secondary incoherent source represented by individually coherent but mutually incoherent source points, each giving rise to a separate image. A final image is obtained by adding up all the individual source point contributions. The results are compared with the microscope images and show qualitative agreement, indicating that the observed effects are caused by partially coherent illumination.

Keyword
Image formation; Partial coherence; X-ray microscopy; Zone plates; Computer simulation; Light sources; Mathematical models; X ray diffraction; X ray microscopes; Incoherent sources; Partial coherence; X ray microscopy; Zone plates; Image processing; article; diffraction; illumination; image analysis; mathematical model; microscopy; qualitative analysis; separation technique; simulation; X ray analysis
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7020 (URN)10.1016/j.ultramic.2006.12.001 (DOI)000246937000006 ()2-s2.0-34247139671 (Scopus ID)
Note
QC 20100820. Uppdaterad från In press till Published 20100820.Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
9. Size-selective colloidal-gold localization in transmission x-ray microscopy
Open this publication in new window or tab >>Size-selective colloidal-gold localization in transmission x-ray microscopy
2007 (English)In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 225, no 1, 80-87 p.Article in journal (Refereed) Published
Abstract [en]

Colloidal gold is a useful marker for functional-imaging experiments in transmission X-ray microscopy. Due to the low contrast of gold particles with small diameters it is necessary to develop a powerful algorithm to localize the single gold particles. The presented image-analysis algorithm for identifying colloidal gold particles is based on the combination of a threshold with respect to the local absorption and shape discrimination, realized by fitting a Gaussian profile to the identified regions of interest. The shape discrimination provides the possibility of size-selective identification and localization of single colloidal gold particles down to a diameter of 50 nm. The image-analysis algorithm, therefore, has potential for localization studies of several proteins simultaneously and for localization of fiducial markers in X-ray tomography.

Keyword
Colloidal gold; Image analysis; Soft X-ray microscopy; algorithm; article; image analysis; microscopy; normal distribution; particle size; priority journal; protein localization; transmission X ray microscopy; X ray microanalysis
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6201 (URN)10.1111/j.1365-2818.2007.01717.x (DOI)000243974000008 ()2-s2.0-33846829091 (Scopus ID)
Note
QC 20100820. Uppdaterad från Accepted till Published 20100820.Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-12-14Bibliographically approved
10. Towards compact x-ray microscopy with liquid-nitrogen-jet laser-plasma source
Open this publication in new window or tab >>Towards compact x-ray microscopy with liquid-nitrogen-jet laser-plasma source
2006 (English)In: Proceedings of 8th International Conference on X-ray Microscopy, 2006, 12-14 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this contribution we present source properties and design considerations for a compact x-ray microscope operating in the water-window spectral region at 2.48 nm. The microscope will use a liquid-nitrogen-jet laser-plasma source with sufficient brightness, uniformity, stability and reliability for microscopy operation. The source is quantitatively characterized by calibrated slitgrating spectroscopy and zone-plate imaging to determine absolute photon numbers and source size and stability. Calculations including sources parameters as well as characteristics of available x-ray optics indicate that high-quality microscope images can be obtained with exposure times in the range of few minutes.

Series
IPAP Conf. series, 7
Keyword
X-ray microscopy, laser-plasma x-ray source
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7022 (URN)
Conference
8th International Conference on X-ray Microscopy
Note
QC 20100820Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-20Bibliographically approved
11. High-resolution compact x-ray microscopy
Open this publication in new window or tab >>High-resolution compact x-ray microscopy
Show others...
2007 (English)In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 226, no 2, 175-181 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate compact full-field soft X-ray transmission microscopy with sub 60-nm resolution operating at λ= 2.48 nm. The microscope is based on a 100-Hz regenerative liquid-nitrogen-jet laser-plasma source in combination with a condenser zone plate and a micro-zone plate objective for high-resolution imaging onto a 2048 × 2048 pixel CCD detector. The sample holder is mounted in a helium atmosphere and allows imaging of both dry and wet specimens. The microscope design enables fast sample switching and the sample can be pre-aligned using a visible-light microscope. High-quality images can be acquired with exposure times of less than 5 min. We demonstrate the performance of the microscope using both dry and wet samples.

Keyword
Compact; Laser plasma; Liquid-jet; Soft x-ray microscopy; Water window; Zone plate optics
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-9810 (URN)10.1111/j.1365-2818.2007.01765.x (DOI)000245744400008 ()17444946 (PubMedID)2-s2.0-34247246221 (Scopus ID)
Note
QC 20100728Available from: 2009-01-07 Created: 2009-01-07 Last updated: 2017-12-14Bibliographically approved

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