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Dokumentenidentifikation EP1399927 06.09.2007
EP-Veröffentlichungsnummer 0001399927
Titel MEHRSCHICHTGITTER FÜR DIE MONOCHROMATISIERUNG UND SPEKTROSKOPIE
Anmelder Osmic, Inc., Auburn Hills, Mich., US
Erfinder MARTYNOV, Vladimir V., Troy, MI 48084, US;
PLATONOV, Yuriy, Troy, MI 48098, US
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60221394
Vertragsstaaten DE, FR, GB, NL
Sprache des Dokument EN
EP-Anmeldetag 27.06.2002
EP-Aktenzeichen 027467794
WO-Anmeldetag 27.06.2002
PCT-Aktenzeichen PCT/US02/20751
WO-Veröffentlichungsnummer 2003003380
WO-Veröffentlichungsdatum 09.01.2003
EP-Offenlegungsdatum 24.03.2004
EP date of grant 25.07.2007
Veröffentlichungstag im Patentblatt 06.09.2007
IPC-Hauptklasse G21K 1/06(2006.01)A, F, I, 20051017, B, H, EP

Beschreibung[en]
BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to multi-layer gratings/mirrors and their application in analyzing systems.

Discussion of Related Art

It is well known in the art to use large d-spacing artificially grown crystals, e.g. PET crystals, for x-ray fluorescence spectroscopy. Such artificial crystals are very sensitive to the environment and degrade quickly under the influence of radiation, heat, moisture, etc. Accordingly, the artificial crystals do not last long and are difficult to use. In hard x-rays region (wavelength less than 0.2nm) ordinary crystals, e.g. Si or Ge crystals, when used in monochromators and spectrometers in some cases have resolving powers that are too high (∼ 104) and cut out too much useful flux. Accordingly, the measurement times become longer.

While reflective gratings can be used in place of the artificial crystals, such gratings suffer from low diffraction efficiency in the softer x-ray region (wavelengths ranging from about 0.2nm to about 1.2nm). Multilayer mirrors, while improving reflection efficiency relative to the gratings in a wide wavelengths range (from 1nm to 20nm), have a resolving power that is too low ∼ &lgr;/&Dgr;&lgr; ∼ 10 - 100.

Multilayer gratings/mirrors are well known in the art and are very stable, durable and are easy in use. Examples of such multilayer gratings / mirrors are described in U.S. Patents Nos. 4,727,000 ; 5,646,976 and 5,757,882 . It is well known that the bandpass of such multilayer gratings/mirrors is defined by the number of bilayers in which the incident wave penetrates. This number of bilayers in the multilayer grating/mirror is limited by the factor that due to interference in the periodical structure of the multiple layers stacked upon one another, the radiation wave incident on the multilayer grating/mirror is reflected back and does not penetrate any deeper than a so-called extinction depth. The extinction depth is determined by the wavelength of the incident radiation and the materials of the multilayer grating/mirror. The bandpass and correspondingly the resolution of a spectrometer or a monochromator that uses a multilayer grating/mirror is proportional to: &Dgr;&lgr; / &lgr; 1 / N , wherein N is the number of multilayer periods present within the extinction depth. In many instances, the resolution of a spectrometer or a monochromator is required to be better than that as determined by the extinction depth in the manner described above.

Based on the above relationship, one way to increase the resolution of a multilayer grating/mirror is to increase the extinction depth and thus the number N of multilayer periods within the extinction depth. One known way to increase the extinction depth is to etch grooves in the multilayer grating/mirror and remove part of the reflection planes so as to allow the incidence radiation wave to penetrate deeper into the multilayer grating. As a result, the number of layer N in the extinction depth increases and the bandpass, or the resolution, increases in accordance with equation (1) above. Such a multilayer grating/mirror is discussed in the paper entitled " Lamellar Multilayer Gratings with Very High Diffraction Efficiency," V.V. Martynov et al., SPIE Vol. 3150 0277-786X/97, pp. 2-8 .

By changing the groove/period ratio of the multilayer grating/mirror, the amount of removed material can be continuously varied and, thus, the extinction depth and resolution can be continuously varied. The maximum practical factor in the bandpass variation is defined by technological limits and, for different wavelength, can be as from 1 to 100. While such a multilayer grating/mirror provides increased resolution, the multilayer grating/mirror with periodically spaced lands also may generate many diffraction orders, which contribute in making the detector signal to have a small signal to noise ratio. The generation of multiple diffraction orders is shown by analogy to the single layer periodic transmission grating diffraction intensity distribution shown in FIG. 3. Obviously, if a single layer transmission grating with a periodic structure generates multiple diffraction orders, then a multi-layer transmission grating with a periodic structure will also generate multiple diffraction orders.

Hudek, P. et al, Advanced semiconductor devices and microsystems, 5 October 1998, pages 171-174 shows a tungsten/silicon multilayer grating.

Accordingly, it is an objective of the present invention to provide a multilayer grating/mirror that for a wide range of wavelengths has increased resolution and diffraction efficiency while at the same time contributing in making the detector signal having a large signal to noise ratio.

SUMMARY OF THE INVENTION

One aspect of the present invention regards an analyzing system as claimed.

An advantage of the present invention is to provide a multilayer grating/mirror that has increased resolution and diffraction efficiency while at the same time contributing in making the detector signal having a large signal to noise ratio.

Additional objects and advantages of the invention will become apparent from the following description and the appended claims when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

  • FIG. 1 schematically shows an embodiment of an x-ray fluoroscopy system according to the present invention;
  • FIG. 2 schematically shows a side cross-sectional view of a multilayer grating/mirror to be used with the x-ray fluoroscopy system of FIG. 1;
  • FIG. 3 shows a diffraction intensity distribution from a periodical grating, giving many diffraction orders; and
  • FIG. 4 shows a diffraction intensity distribution from a single layer grating with random line spacing where all diffraction orders are suppressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an x-ray fluoroscopy analyzing system 10 includes a radiation generator or source, such as x-ray tube 12, that generates a beam of radiation along a first direction, such as a beam of x-rays 14. The x-rays 14 have a wavelength that ranges from 0.3 -1.0 nm. The x-rays 14 generated from x-ray tube 12 are received by and interact with the object or sample 16 so that x-ray fluorescence radiation 18 is generated from the object 16. The x-rays 18 are directed through a slit 19 and received by a multilayer grating/mirror 20, which reflects only a zeroth order of diffraction of x-rays 22 of a particular wavelength, such as 0.71nm. The x-rays 22 are then received by a detector system 24, such as a proportional counter detector. The detected radiation is then analyzed in a well known manner.

As shown in FIG. 2, the multilayer grating/mirror 20 includes a multilayer structure 26 deposited on a substrate 28. The multilayer structure 26 is made out of alternating layers of materials with large and small atomic numbers. The material with large atomic number can be selected from the materials W, Ni, Fe, Mo, V, Cr and the material with small atomic numbers can be selected from the materials C, Si, B4C. For example, the multilayer structure 26 can be made out of alternating layers of W (10Å) and C (10Å) layers. Thus, the period, d, of the alternating W and C layers is 20Å. In this embodiment, the number of periods, d, of alternating W/C bi-layers in the multilayer structure 26 is 500. Note that the number of bi-layer depends on a spectral resolution/bandpass requirements. For 500 bi-layers, the bandpass &lgr;/&Dgr;&lgr; ∼ N ∼ 500. The period of the multilayer depends on a required Bragg angle and typically ranges from 15A to 100A for different wavelengths. In addition, other materials and thicknesses for the layers of materials with large and small atomic numbers are possible depending on the specific needs for wavelength and Bragg angle.

As shown in FIG. 2, a plurality of grooves 30 are formed randomly on the multilayer grating/mirror 20. The grooves 30 are positioned between lands 32 of the multilayer structure 26, wherein each land 32 has a width of approximately 1 micrometer and contains 500 periods of alternating W/Si bilayers. The starting points or positions xi of the lands 32 can be determined by a formula given below: xi = d * i + ki * d - Wland ,

where d = effective period of the grating/mirror 20, i =1,2, 3, ..,; Wland = width of land and ki = a random number from 0 to 1. Note that the widths of the lands and depths of the grooves are constant for the entire area of the grating. Furthermore, the lands are placed randomly inside each period according to the formula (2) above.

One of the benefits of using a multilayer grating/mirror 20 with a random pattern of grooves is that all diffraction orders, except the zeroth order, are suppressed. In other words, only the direct beam is reflected by the grating/mirror 20. The suppression of diffraction orders is shown by analogy to the single layer random structure transmission grating diffraction intensity distribution shown in FIG. 4. Obviously, if a single layer transmission grating with a random structure suppresses multiple diffraction orders, then a multi-layer transmission grating with a random structure will also suppress multiple diffraction orders.

In the above-described mode of randomizing the grating/mirror 20, the land widths and the grooves depths are selected so that a desired width of the peak of the rocking curve of the grating/mirror 20, which is the same as an energy bandpass or spectral resolution of the grating/mirror 20, is achieved. Thus, the ability to change the bandpass allows the spectral resolution to be adjusted to specific requirements and so as to optimize flux and resolution.

While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible of modification, variation and change without departing from the scope of the accompanying claims. For example, the grating 20 can also be used as a monochromator.


Anspruch[de]
Analysesystem, umfassend: einen Strahlungsgenerator (12), der einen Strahlungsstrahl (14) entlang einer ersten Richtung erzeugt; ein Objekt (16), das den Strahlungsstrahl (14) empfängt und einen zweiten Strahlungsstrahl (18) erzeugt; ein Gitter (20), das eine Struktur aufweist zum Empfangen des zweiten Strahlungsstrahls und zum Erzeugen eines nur eine nullte Beugungsordnung bildenden dritten Strahlungsstrahls (22); und ein Detektorsystem (24), das den dritten Strahlungsstrahl empfängt, und wobei das Gitter (20) eine Mehrschichtstruktur (26) umfaßt, und wobei die Mehrschichtstruktur mehrere zwischen mehreren Stegen (32) ausgebildete Nuten (30) umfaßt, wobei jeder Steg (32) Perioden von abwechselnden Doppelschichten der Mehrschichtstruktur umfaßt, und wobei

die mehreren Stege (32) zufällig in der Mehrschichtstruktur (26) ausgebildet sind, und wobei

die Startpositionen xi der mehreren Stege (32) durch die unten angegebene Formel bestimmt sind: xi = d * i + ki * d - Wland , wobei d= Periode des Gitters, i=1, 2, 3, ...; Wland= Breite des Stegs und ki= eine Zufallszahl zwischen 0 und 1.
Analysesystem nach Anspruch 1, wobei der Strahlungsgenerator (12) eine Röntgenquelle umfaßt, die einen Strahl von Röntgenstrahlen erzeugt. Analysesystem nach Anspruch 1, wobei die Mehrschichtstruktur (26) Perioden abwechselnder Doppelschichten aus Materialien mit großen und kleinen Ordnungszahlen umfaßt, wobei das Material mit großer Ordnungszahl unter den Materialien W, Ni, Fe, Mo, V, Cr ausgewählt sein kann und Material mit kleinen Ordnungszahlen unter den Materialien C, Si, B4C ausgewählt sein kann. Analysesystem nach Anspruch 3, wobei das Material mit einer großen Ordnungszahl Wolfram ist und das Material mit einer kleinen Ordnungszahl Silizium ist. Analysesystem nach Anspruch 1, wobei jeder der Stege (32) eine gleiche Anzahl von Schichten der Mehrschichtstruktur (26) aufweist. Analysesystem nach Anspruch 1, wobei die Tiefe jeder der mehreren Nuten (30) konstant ist.
Anspruch[en]
An analyzing system comprising: a radiation generator (12) that generates a beam of radiation (14) along a first direction; an object (16) that receives said beam of radiation (14) and generates a second beam of radiation (18); a grating (20) that has a structure to receive said second beam of radiation and to generate only a zeroth-order of diffraction forming a third beam of radiation (22); and a detector system (24) that receives said third beam of radiation, and wherein said grating (20) comprises a multilayer structure (26), and wherein said multilayer structure comprises a plurality of grooves (30) formed between a plurality of lands (32), wherein each land (32) comprises periods of alternating bilayers of said multilayer structure (26), and wherein

said plurality of lands (32) are formed randomly in said multilayer structure (26), and where the starting positions xi of said plurality of lands (32) are determined by the formula given below: xi = d * i + ki * d - Wland , where d=period of said grating, i= 1, 2, 3, ...; Wland=width of land; and ki= a random number from 0 to 1.
The analyzing system of claim 1, wherein said radiation generator (12) comprises an x-ray source that generates a beam of x-rays. The analyzing system of claim 1, wherein said multiplayer structure (26) comprises periods of alternating bilayers of materials with large and small atomic numbers whereby the material with large atomic number can be selected from the materials W, Ni, Fe, Mo, V, Cr and material with small atomic numbers can be selected from the materials C, Si; B4C. The analyzing system of claim 3, wherein said material with a large atomic number is tungsten and said material with a small atomic number is silicon. The analyzing system, of claim 1, wherein each of said lands (32) has an equal number of layers of said multilayer structure (26). The analyzing system of claim 1, wherein the depth of each of said plurality of grooves (30) is constant.
Anspruch[fr]
Système d'analyse comprenant : un générateur de rayonnement (12) générant un faisceau de rayonnement (14) le long d'une première direction ; un objet (16) qui recevant ledit faisceau de rayonnement (14) et générant un deuxième faisceau de rayonnement (18) ; une mire (20) comprenant une structure permettant de recevoir ledit deuxième faisceau de rayonnement et de générer seulement un ordre zéro de diffraction constituant un troisième faisceau de rayonnement (22) ; et un système de détecteur (24) qui recevant ledit troisième faisceau de rayonnement, et dans lequel ladite mire (20) comprend une structure multicouche (26), et dans laquelle ladite structure multicouche comprend une pluralité de sillons (30) situés entre une pluralité de surépaisseurs (32), dans laquelle chaque surépaisseur (32) comprend des périodes alternant des bicouches de ladite structure multicouche (26)

et dans laquelle

ladite pluralité de surépaisseurs (32) est générée de façon aléatoire dans ladite structure multicouche (26), et où

les positions commençantes xi de ladite pluralité de surépaisseurs (32) sont déterminées par la formule donnée ci-dessous : où d=période de ladite mire, i= 1, 2, 3,... ; Wland=épaisseur de la surépaisseur ; et ki= un nombre aléatoire compris entre 0 et 1.
Système d'analyse selon la revendication 1, dans lequel ledit générateur de rayonnement (12) comprend une source de rayon X qui génère un faisceau de rayons X. Système d'analyse selon la revendication 1, dans lequel ladite structure multicouches (26) comprend des périodes alternant des bicouches de matériaux comprenant des grands et des petits nombres atomiques où le matériau ayant un grand nombre atomique peut être sélectionné à partir des matériaux W, Ni, Fe, Mo, V, Cr et où le matériau ayant un petit nombre atomique peut être sélectionné à partir des matériaux C, Si, B4C. Système d'analyse selon la revendication 3, dans lequel ledit matériau ayant un grand nombre atomique est le tungstène et ledit matériau avec un petit nombre atomique est le silicium. Système d'analyse selon la revendication 1, dans lequel chacune desdites surépaisseurs (32) comprend un nombre égal de couches de ladite structure multicouche (26). Système d'analyse selon la revendication 1, dans lequel la profondeur de chacune de ladite pluralité de sillons (30) est constante.






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