Transmission Diffraction Gratings for Soft X-ray Spectroscopy and Spatial Period Division PDF Download
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Author: Andrew Michael Hawryluk
Publisher:
ISBN:
Category : Diffraction gratings
Languages : en
Pages : 162
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Author: Andrew Michael Hawryluk
Publisher:
ISBN:
Category : Diffraction gratings
Languages : en
Pages : 162
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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This subcontract was initiated in order to facilitate the development at MIT of technologies for fabricating the very fine diffraction grating required in x-ray spectroscopy at Lawrence Livermore Laboratory (LLL). These gratings are generally gold transmission gratings with spatial periods of 200 nm or less. The major focus of our efforts was to develop a means of fabricating gratings of 100 nm period. We explored two approaches: e-beam fabrication of x-ray lithography masks, and achromatic holographic lithography. This work was pursued by Erik Anderson as a major component of his Ph. D. thesis. Erik was successful in both the e-beam and holographic approaches. However, the e-beam method proved to be highly impractical: exposure times of about 115 days would be required to cover an area of 1 cm2. The achromatic holography, on the other hand, should be capable of exposing areas well in excess of 1 cm2 in times under 1 hour. Moreover, 100 nm-period gratings produced by achromatic holography are coherent over their entire area whereas gratings produced by e-beam lithography are coherent only over areas (approximately)100 .mu.m. The remainder of this report consists of portions excerpted from Erik Anderson's thesis. These contain all the details of our work on 100 nm period gratings. 26 refs., 17 figs.
Author: Erwin G. Loewen
Publisher: CRC Press
ISBN: 9780824799236
Category : Technology & Engineering
Languages : en
Pages : 632
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"Offers and up-to-date assessment of the entire field of diffraction gratings, including history, physics, manufacture, testing, and instrument design. Furnishes--for the first time in a single-source reference--a thorough review of efficiency behavior, examining echelles as well as concave, binary, transmission, fiber, and waveguide gratings."
Author: John Paul Caldwell
Publisher:
ISBN:
Category :
Languages : en
Pages : 78
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Author: M.C. Hutley
Publisher: Academic Press
ISBN:
Category : Science
Languages : en
Pages : 348
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Author: Alexander Robert Bruccoleri
Publisher:
ISBN:
Category :
Languages : en
Pages : 249
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The development of the critical-angle transmission (CAT) grating seeks both an order of magnitude improvement in the effective area, and a factor of three increase in the resolving power of future space-based, soft x-ray spectrometers. This will enhance further studies of the universe's make-up, such as the composition of the intergalactic medium, black holes, neutron stars and other high energy sources. Conceptually, x-rays are reflected in the device off nanoscale silicon grating bars at shallow angles, such that the diffraction orders are at the specular reflection angle, which is designed to be less than the critical-angle for total external reflection. This blazing effect boosts the efficiency of the device; however, the grating bars are required to form very deep channels to reflect all the incoming x-rays at shallow angles. Previous attempts to fabricate the grating were done with wet potassium hydroxide (KOH) etching of silicon. This process successfully fabricated small areas of grating and enabled a successful demonstration of the soft x-ray diffraction efficiency. However, the open-area fraction was limited to below 20 percent for four micron-tall CAT grating bars due to diagonal etch stops in the silicon crystal lattice. This limitation prevents the past fabrication technique from achieving the desired open-area fraction for a future x-ray observatory. New nanofabrication techniques are presented that can lead to CAT gratings with an open-area fraction in excess of 50 percent. Specifically, three major nanofabrication processes were developed and are described in detail; a two-dimensional, thermal, silicon dioxide mask, an integrated plasma-etch process to create free-standing, ultra-high aspect ratio gratings, and a polishing process to smooth the grating sidewalls. The two-dimensional mask was used to develop a record-performance deep reactive-ion etch (DRIE) for ultra-high aspect ratio gratings. The mask is the integration of a 5 micron and 200 nanometer-pitch grating into a single layer of 300 nanometer-thick thermal silicon dioxide. It spans 5 centimeters on a side, with vertical sidewalls, and is cleanable which enables consistent high quality etches. Experiments with chrome and polymer masking materials for DRIE are also presented. The DRIE was critical for the integrated process, which combined two plasma-etch processes on the front and back side of a silicon-on-insulator wafer. DRIE is not significantly affected by the silicon crystal orientation and therefore avoids the open-area restrictions of wet etching. The result of the process was a free-standing grating with a period of 200 nanometers, a depth of four microns, and a span of three centimeters. These free-standing gratings exceed the state-of-the-art by more than a factor of two in aspect ratio at the nanoscale. The sidewall roughness is one shortcoming of DRIE, which is often greater than 4 nanometers RMS, and it needs to be approximately one nanometer to efficiently reflect soft x-rays. To address this, the world's first reported nanoscale polishing process has been developed to smooth the sidewalls of DRIE'd, ultra-high aspect ratio silicon. This process utilizes potassium hydroxide etching, an anisotropic etch of single crystal silicon. Specifically, the [111] planes etch approximately 100 times slower than the non-[111] planes. A novel alignment technique is presented to align the CAT grating pattern to the [111] silicon planes to within 0.2 degrees. This precise alignment enables KOH to etch away sidewall roughness and slowly widen the channels without fully destroying the structure. The result of polishing was a reduction in sidewall roughness to approximately 1 nm RMS, while decreasing the widths of the grating bars. In addition to the nanofabrication developments, this work provides a preliminary analysis of launching and deploying CAT gratings in space. The nanofabrication developments are focused towards the CAT grating; however, they have other applications as well. High quality masks have applications in MEMS structures and photonic devices. The free-standing structure as a stand-alone device has applications such as neutral mass spectroscopy, ultraviolet filtration, and x-ray phase contrast imaging. The polishing process is valuable to numerous optical applications where smooth sidewalls are critical, as well as filtration techniques which seek to maximize open-area.
Author: Hiroaki Aritome
Publisher:
ISBN:
Category :
Languages : en
Pages : 13
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Author: Wayne R. McKinney
Publisher: SPIE-International Society for Optical Engineering
ISBN:
Category : Science
Languages : en
Pages : 146
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Gold transmission diffraction gratings used for x-ray spectroscopy must sometimes be rotationally aligned to the axis of a diagnostic instrument to within sub-milliradian accuracy. We have fabricated transmission diffraction gratings with high line-densities (grating period of 200 and 300 nm) using uv holographic and x-ray lithography. Since the submicron features of the gratings are not optically visible, precision alignment is time consuming and difficult to verify in situ. We have developed a technique to write an optically visible alignment pattern onto these gratings using a scanning electron microscope (SEM). At high magnification (15000 X) several submicron lines of the grating are observable in the SEM, making it possible to write an alignment pattern parallel to the grating lines in an electron-beam-sensitive coating that overlays the grating. We create an alignment pattern by following a 1-cm-long grating line using the SEM's joystick-controlled translation stage. By following the same grating line we are assured the traveled direction of the SEM electron beam is parallel to the grating to better than 10 .mu.radian. The electron-beam-exposed line-width can be large (5 to 15 .mu.m wide) depending on the SEM magnification, and is therefore optically visible. The exposed pattern is eventually made a permanent feature of the grating by ion beam etching or gold electroplating. The pattern can be used to accurately align the grating to the axis of a diagnostic instrument. More importantly, the alignment of the grating can be quickly verified in situ.
Author: Jeremy M. Lerner
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 260
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