JP3643866B2 - X-ray focusing method and X-ray focusing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used in an analysis or measurement apparatus using X-rays, and typical examples include an X-ray microscope and an X-ray microprobe. When X-rays are finely condensed and irradiated onto an object, local information can be obtained and quantitative analysis can be performed. The physical quantity to be measured is transmitted X-ray, fluorescent X-ray, photoelectron and the like. Furthermore, each element has its own X-ray absorption edge, and before and after the absorption edge, there is a property that the absorption coefficient (or transmittance) differs by an order of magnitude even with a slight energy difference. This invention is particularly effective for analysis.
[0002]
[Prior art]
As a conventional technique for condensing X-rays, there is a two-dimensional Fresnel zone plate using Fresnel diffraction. As shown in FIG. 2, in the case of the intensity modulation type, this is a disk shape in which an opaque zone and a transparent zone are alternately repeated with respect to the X-ray. The radius rn of the _nth zone is approximately the X-ray of wavelength λ,
r _n ² = nfλ
In this relationship, the optical path difference of X-rays transmitted from adjacent transparent zones is λ (phase difference is 2π), strengthening each other at the focal point and serving as a lens. Here, f is a focal length.
[0003]
As is apparent from this equation, the focal length f is inversely proportional to the wavelength λ, that is, proportional to energy.
[0004]
[Problems to be solved by the invention]
An element has a characteristic X-ray absorption edge, and there is a property that the absorption coefficient (or transmittance) differs by an order of magnitude even with a slight energy difference before and after the absorption edge. It becomes possible to select and analyze only, and precise analysis becomes possible. However, when the zone plate is used as a light condensing element, the focal length f varies inversely proportional to the wavelength λ (proportional to energy) as shown in the above equation, so the sample position changes each time the wavelength is changed. There was a problem of having to.
[0005]
[Means for Solving the Problems]
In the present invention, two one-dimensional Fresnel zone plates are used, and the focal position is fixed by adjusting the inclination of the one-dimensional Fresnel zone plate in response to fluctuations in X-ray energy. As shown in FIG. 1, the two zone plates are arranged orthogonally, and are held on a turntable that can freely set the incident angle. They are used for light collection in the horizontal and vertical directions, respectively. In the case of oblique incidence, if the incident angle is θ (θ = 90 degrees for vertical incidence),
r _n = (nfλ) ^1/2 / sin θ
Therefore, even if the wavelength is shortened, the focal length f of the same length can be obtained by reducing the incident angle θ.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
For example, X-rays having a wavelength between 2.3 nm and 4.4 nm are hardly absorbed by water, but are absorbed by proteins more than an order of magnitude. By using X-rays in this wavelength range, it is possible to observe the internal tissues of living organisms and organisms containing water with high contrast. Furthermore, although the wavelength at the absorption edge of carbon is 4.48 nm, X-rays with a wavelength of 4.4 nm have the property that they are more easily absorbed in carbon by about one digit than X-rays with a wavelength of 4.5 nm. Similarly, the wavelength at the absorption edge of nitrogen is 3.16 nm, and if the wavelength range from 3.1 nm to 4.5 nm can be collected and analyzed by one element, the component ratio of carbon and nitrogen can also be analyzed. According to the present invention, the same can be done for all elements.
[0007]
The zone plate can be produced by ultraviolet holographic lithography or electron beam lithography. Ultraviolet holographic lithography is a technique developed at the University of Goettingen, Germany. Using two lasers with a wavelength of about 400 nm as the light source, the pattern of the zone plate is directly created by the interference fringes, and the photoresist is exposed. In addition, this is a method of manufacturing by reactive ion etching or the like.
[0008]
Electron beam lithography is the most widely used method for the production of X-ray zone plates, and scans the zone plate pattern with a finely focused electron beam to expose resist such as polymethyl methacrylate. This is a method of processing by reactive ion etching or the like.
[0009]
As the material of the zone plate, gold, silver, nickel, tantalum, germanium, or the like is used according to the energy of the X-ray used. In the zone plate produced so far, the smallest outermost zone width is several tens of nm.
[0010]
【Example】
If the target wavelength λ is 4.5 nm and the focal length f is 20 mm in the one-dimensional zone plate, n = about 3000 and the line width is about 86 nm. In this case, the size of the entire zone plate is about 1 mm. If nickel is used as the material of the zone plate, in this case, a light collection efficiency of about 15% is obtained with a thickness of about 80 nm. When the wavelength was scanned while tilting this, the condensing point changed continuously with a constant, and when tilted 34 degrees, the wavelength was 3.1 nm.
[0011]
【The invention's effect】
Conventional condensing of X-rays has been performed by a concentric two-dimensional zone plate, but in this case, the focal position varies depending on the wavelength λ (energy) of incident X-rays. Therefore, it is not necessary to change the focal position even if the wavelength of the X-ray changes.
[Brief description of the drawings]
FIG. 1 is a layout diagram of a one-dimensional zone plate according to the present invention. FIG. 2 is a diagram of a conventional disk-shaped Fresnel zone plate.

Claims (2)

  In an X-ray condensing method using a one-dimensional Fresnel zone plate, two one-dimensional Fresnel zone plates are orthogonally arranged on an X-ray line, and the plate is used as an X-ray line according to the wavelength of incident X-rays. An X-ray condensing method characterized in that the focal position is fixed by tilting with respect to the surface.   In an X-ray concentrator using a one-dimensional Fresnel zone plate, two one-dimensional Fresnel zone plates are arranged orthogonally to the X-ray line, and the plate adjusts the inclination angle of the plate with respect to the X-ray line. An X-ray condensing device, which is held on a rotating table.

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