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Nanofabrication of Zone Plate Optics for Compact Soft X-Ray Microscopy
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0003-2745-6289
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This Thesis describes the development of the KTH/Stockholm nanofabrication process for diffractive soft x-ray optics. The effort is motivated by the need for and requirement of specially designed diffractive optics and test objects for compact x-ray microscopy as well as optics for other applications such as phase imaging. The optics have been fabricated in-house, in the KTH Nanofabrication Laboratory.

The nanofabrication process is based on electron-beam lithography in combination with reactive ion etching (RIE) and nickel electroplating. This process has successfully been used for the fabrication of micro zone plates, condenser zone plates, diffractive optical elements for differential-interference microscopy, and different test structures. Optics with electroplated feature sizes down to 25 nm have been fabricated with high aspect-ratios. Special consideration has been given the reproducibility and optimization of the process parameters. This is essential for improving the yield and quality of the fabricated optics. The work includes, e.g., improved e-beam writing strategies and controlled electroplating. Furthermore, a high diffraction efficiency is necessary for our applications, which are based on compact low-power sources. This requires the fabrication of optics with a high and uniform aspect ratio. For this purpose the electroplating process step has been improved with an in-situ light-transmission-based thickness control method for optimum mold filling, and pulse and pulse-reverse techniques for uniform plating.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006.
Series
Trita-FYS, ISSN 0280-316X ; 2006:41
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4045ISBN: 91-7178-390-3 (print)OAI: oai:DiVA.org:kth-4045DiVA: diva2:10544
Public defence
2006-06-16, Sal FD5, AlbaNova univ centrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100616Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-06-16Bibliographically approved
List of papers
1. Design and performance of a laser-plasma based compact soft x-ray microscope
Open this publication in new window or tab >>Design and performance of a laser-plasma based compact soft x-ray microscope
2002 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 73, no 3, 1193-1197 p.Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5980 (URN)
Note
QC 20100616Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-06-16Bibliographically approved
2. Wavelet-based image restoration for compact x-ray microscopy
Open this publication in new window or tab >>Wavelet-based image restoration for compact x-ray microscopy
2003 (English)In: Journal of Microscopy, ISSN 0022-2720, E-ISSN 1365-2818, Vol. 211, no 2, 154-160 p.Article in journal (Refereed) Published
Abstract [en]

Compact water-window X-ray microscopy with short exposure times will always be limited on photons owing to sources of limited power in combination with low-efficency X-ray optics. Thus, it is important to investigate methods for improving the signal-to-noise ratio in the images. We show that a wavelet-based denoising procedure significantly improves the quality and contrast in compact X-ray microscopy images. A non-decimated, discrete wavelet transform (DWT) is applied to original, noisy images. After applying a thresholding procedure to the finest scales of the DWT, by setting to zero all wavelet coefficients of magnitude below a prescribed value, the inverse DWT to the thresholded DWT produces denoised images. It is concluded that the denoising procedure has potential to reduce the exposure time by a factor of 2 without loss of relevant image information.

Keyword
compact X-ray microscopy, image restoration, wavelet denoising
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6199 (URN)000184468300006 ()
Note
QC 20100616Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2010-09-20Bibliographically approved
3. Nano-fabrication of condenser and micro zone plates for compact X-ray microscopy
Open this publication in new window or tab >>Nano-fabrication of condenser and micro zone plates for compact X-ray microscopy
2004 (English)In: Microelectronic Engineering, ISSN 0167-9317, Vol. 73/74, 639-643 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate nano-fabrication of high-aspect ratio and high-spatial frequency diffractive X-ray optics with high uniformity for use in a laser-plasma-based compact water-window X-ray microscope. The structures are fabricated on 50 nm thin Si3N4-membranes using a three-layer resist scheme and 30 keV e-beam lithography in combination with reactive ion etching and nickel electroplating. The process is developed on solely commercially available resists and instruments. As examples, we demonstrate fabrication of micro-zone plates with outermost linewidths of 30 nm and an uniform zone height of 160 nm, and a 4.5 mm diameter condenser zone plate with 50-60 nm lines, fabricated by using stitched fields.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5982 (URN)10.1016/j.mee.2004.03.006 (DOI)000222145400113 ()2-s2.0-2542479378 (Scopus ID)
Note
QC 20100616, QC 20111017. 29th International Conference on Micro and Nano Engineering (MNE 2003), Cambridge, ENGLAND, SEP 22-25, 2003 Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2011-10-18Bibliographically 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
Show others...
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: 2012-03-20Bibliographically 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
Show others...
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: 2012-03-21Bibliographically approved
6. Nickel Zone Plates for Compact Soft X-Ray Microscopy
Open this publication in new window or tab >>Nickel Zone Plates for Compact Soft X-Ray Microscopy
2006 (English)In: Proc. 8th Internat. Conference on X-Ray Microscopy, 2006Conference paper, Published paper (Other academic)
Series
IPAP Conference Series, 7
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5985 (URN)
Conference
8th Internat. Conference on X-Ray Microscopy
Note
QC 20100616Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-06-16Bibliographically approved
7. High-resolution differential-interference-contrast x-ray zone plates: Design and Fabrication
Open this publication in new window or tab >>High-resolution differential-interference-contrast x-ray zone plates: Design and Fabrication
Show others...
2007 (English)In: Spectrochimica Acta Part B - Atomic Spectroscopy, ISSN 0584-8547, E-ISSN 0031-6987, Vol. 62, no 6-7, 539-543 p.Article in journal (Refereed) Published
Abstract [en]

Differential interference contrast is a potentially powerful technique for contrast enhancement in soft X-ray microscopy. We describe the design and fabrication of single-element diffractive optical elements suitable as objectives for high-resolution differential interference contrast microscopy in the water-window spectral range. A one-dimensional pattern calculation followed by an extension to two dimensions results in a pattern resolution of 1 nm, which is well below fabrication accuracy. The same fabrication process as for normal zone plates is applicable, but special care must be taken when converting the calculated pattern to a code for e-beam lithography.

Keyword
Differential interference contrast, Diffractive optics, X-ray microscopy
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5986 (URN)10.1016/j.sab.2007.03.005 (DOI)000249213700005 ()2-s2.0-34547643613 (Scopus ID)
Note

QC 20100616

Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2014-11-10Bibliographically approved
8. Controlled electroplating for high-aspect-ratio zone plate fabrication
Open this publication in new window or tab >>Controlled electroplating for high-aspect-ratio zone plate fabrication
2006 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 24, no 6, 2592-2596 p.Article in journal (Refereed) Published
Abstract [en]

The authors report a method for monitoring, control, and end-point detection of electroplating in nanostructures. The method is demonstrated on nickel plating into polymer molds, which is an important process in the fabrication of soft x-ray zone-plate diffractive optics. The lack of reproducibility presently limits the achievable nickel aspect ratio and, thus, reduces the zone-plate diffraction efficiency. The reported method provides reproducible plating via real-time control of the plating rate. It combines in situ light transmission measurements with current measurements to determine the thickness of the growing layer. The accuracy of the thickness prediction was better than ±4% (1) for 100–300  nm nickel layers. Furthermore, a slight change in the light transmission signal indicates when a gratinglike zone-plate structure is slightly overplated and the plating should be stopped. This end-point detection provides the optimal filling of high-aspect-ratio molds for improved diffraction efficiency.

Keyword
X-RAY MICROSCOPY; HIGH-EFFICIENCY; CONDENSER; OPTICS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-5987 (URN)10.1116/1.2362761 (DOI)000243324400017 ()2-s2.0-33845257285 (Scopus ID)
Note
QC 20100616Available from: 2006-06-08 Created: 2006-06-08 Last updated: 2010-12-06Bibliographically approved

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Citation style
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  • harvard1
  • ieee
  • modern-language-association-8th-edition
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  • en-GB
  • en-US
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  • nn-NO
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