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Claims  |
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What is claimed is:
1. An X-ray optical apparatus having, in combination, an X-ray optical
system which is capable of projecting an enlarged sample image by soft
X-rays and a visible optical system which enables observation of said
sample with visible radiation,
said X-ray optical system comprising:
a soft X-ray generator;
a condenser zone plate for converging soft X-rays so as to cast them on
said sample, including a zone plate for converging soft X-rays from said
X-ray generator, and a base plate supporting said zone plate and having a
first soft X-ray passing opening at the center thereof; and
an objective zone plate including a base plate having a second soft X-ray
passing opening at the center thereof to pass said soft X-rays which have
passed through said sample and having a visible radiation passing section
to the outside of said second soft X-ray passing opening, and a zone plate
supported centrally of said base plate for converging soft X-rays which
have passed through said sample and forming said sample image at a
predetermined position;
said visible optical system comprising:
a visible radiation source displaced from the optical axis of said X-ray
optical system;
sample illumination means comprising a condenser lens having a soft X-ray
passing opening at the center thereof to pass said X-rays converged by
said condenser zone plate, said condenser lens condensing light from said
visible radiation source so as to illuminate said sample;
an objective lens having a soft X-ray passing opening at the center thereof
for passing said X-rays converged by said condenser zone plate, the
optical axis of said objective lens being arranged to coincide with the
optical axis of said X-ray optical system in order that visible radiation
which has passed through said sample passes through said visible radiation
passing section of the base plate of said objective zone plate; and
an eyepiece displaced from the optical axis of said X-ray optical system
for observing a sample image formed with said objective lens; and
wherein said visible radiation passing section of said objective zone plate
is generally squarely formed by four rectangular openings with each of
said four openings having a long side substantially opposed to a short
side of another of said four openings at a predetermined distance, said
second soft X-ray passing opening being surrounded substantially by said
four rectangular openings.
2. An X-ray optical apparatus having, in combination, an X-ray optical
system which is capable of projecting an enlarged sample image by soft
X-rays and a visible optical system which enables observation of said
sample with visible radiation,
said X-ray optical system comprising:
a soft X-ray generator;
a condenser zone plate for converging soft X-rays so as to cast them on
said sample, including a zone plate for converging soft X-rays from said
X-ray generator, and a base plate supporting said zone plate and having a
first soft X-ray passing opening at the center thereof; and
an objective zone plate including a base plate having a second soft X-ray
passing opening at the center thereof to pass said soft X-rays which have
passed through said sample and having a visible radiation passing section
to the outside of said second soft X-ray passing opening, and a zone plate
supported centrally of said base plate for converging soft X-rays which
have passed through said sample and forming said sample image at a
predetermined position;
said visible optical system comprising:
a visible radiation source displaced from the optical axis of said X-ray
optical system;
sample illumination means comprising a condenser lens having a soft X-ray
passing opening at the center thereof to pass said X-rays converged by
said condenser zone plate, said condenser lens condensing light from said
visible radiation source so as to illuminate said sample;
an objective lens having a soft X-ray passing opening at the center thereof
for passing said X-rays converged by said condenser zone plate, the
optical axis of said objective lens being arranged to coincide with the
optical axis of said X-ray optical system in order that visible radiation
which has passed through said sample passes through said visible radiation
passing section of the base plate of said objective zone plate; and
an eyepiece displaced from the optical axis of said X-ray optical system
for observing a sample image formed with said objective lens; and
wherein the base plate of said objective zone plate is formed from a square
silicon plate having sides of 14 mm and a thickness of 0.2 to 0.4 mm, and
said zone plate of said objective zone plate comprises a silicon nitride
membrane provided to cover said second soft X-ray passing opening and a
Fresnel's zone pattern formed on said membrane.
3. An X-ray microscopic apparatus which enables observing an enlarged
sample image by the use of soft X-rays and visible radiation, the
apparatus comprising:
a soft X-ray generator;
a soft X-ray projecting optical element to converge soft X-rays from said
soft X-ray generator so as to cast them on said sample;
a soft X-ray image formation optical element to converge soft X-rays which
pass through said sample, so as to form said sample image in a
predetermined position;
a camera element to transfer photoelectrically said sample image formed by
said soft X-ray image forming optical element;
a visible radiation source displaced from an X-ray optical axis extending
from said soft X-ray generator to said camera element;
sample illumination means comprising a condenser lens having a soft X-ray
passing opening at the center thereof to pass said soft X-rays converged
by said soft X-ray projection optical element, said condenser lens
condensing light from said visible radiation source so as to irradiate
said sample;
a base plate having an opening for passing soft X-rays which have passed
through said sample, and including a central section supporting said soft
X-ray image formation optical element and a visible light passing section
having a plurality of visible light passing openings substantially
surrounding said soft X-ray passing opening of said base plate;
an objective lens having a soft X-ray passing opening at the center thereof
for passing said X-rays converged by said soft X-ray image formation
optical element, and having an optical axis arranged to coincide with said
X-ray optical axis in order that visible radiation which has passed
through said sample passes through said visible radiation passing openings
of said base plate; and
an eyepiece displaced from said X-ray optical axis for observing a sample
image formed with said objective lens; and
wherein said visible light passing section of said base plate is generally
squarely formed by four rectangular openings with each of said four
openings having a long side substantially opposed to a short side of
another of said four openings at a predetermined distance, said soft X-ray
passing opening of said base plate formed in the center of said base plate
and substantially surrounded by said four rectangular openings.
4. An X-ray microscopic apparatus which enables observing an enlarged
sample image by the use of soft X-rays and visible radiation, the
apparatus comprising:
a soft X-ray generator;
a soft X-ray projecting optical element to converge soft X-rays from said
soft X-ray generator so as to cast them on said sample;
a soft X-ray image formation optical element to converge soft X-rays which
pass through said sample, so as to form said sample image in a
predetermined position;
a camera element to transfer photoelectrically said sample image formed by
said soft X-ray image forming optical element;
a visible radiation source displaced from an X-ray optical axis extending
from said soft X-ray generator to said camera element;
sample illumination means comprising a condenser lens having a soft X-ray
passing opening at the center thereof to pass said soft X-rays converged
by said soft X-ray projection optical element, said condenser lens
condensing light from said visible radiation source so as to irradiate
said sample;
a base plate having an opening for passing soft X-rays which have passed
through said sample, and including a central section supporting said soft
X-ray image formation optical element and a visible light passing section
having a plurality of visible light passing openings substantially
surrounding said soft X-ray passing opening of said base plate;
an objective lens having a soft X-ray passing opening at the center thereof
for passing said X-rays converged by said soft X-ray image formation
optical element, and having an optical axis arranged to coincide with said
X-ray optical axis in order that visible radiation which has passed
through said sample passes through said visible radiation passing openings
of said base plate; and
an eyepiece displaced from said X-ray optical axis for observing a sample
image formed with said objective lens; and
wherein said base plate is formed from a square silicon plate having side
of 14 mm and a thickness of 0.2 to 0.4 mm said soft X-ray passing opening
of said base plate is formed at the center of said base plate, and said
soft X-ray image formation optical element supported by said base plate
comprises a silicon nitride membrane provided to cover said soft X-ray
passing opening formed at the center of said base plate and a Fresnel's
zone pattern formed on said membrane. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an X-ray optical apparatus, and more
particularly, to an optical apparatus in which a part of an X-ray optical
system and a part of a visible optical system are provided with the same
optical axis.
2. Related Background Art
There is known an X-ray microscopic apparatus employing approximately 2 to
5 nm of wavelength and which can observe a living biological sample and
the like enclosed in a sample capsule under higher power in comparison
with an optical microscope.
Soft X-rays are those of which have normally not less than 200 pm of
wavelength among X-rays having 1 pm to 10 nm of wavelength. Such soft
X-rays are electromagnetic waves which are roughly two orders of magnitude
shorter than a visible radiation having 400 to 800 nm of wavelength. Such
X-rays can transmit through a substance surface without being reflected
thereby. However, they can be well absorbed by the substance and have a
property of being rapidly decayed even in the air. Accordingly, a
transmission observation by the use of soft X-rays is generally conducted
in an X-ray apparatus employing soft X-rays, wherein the optical path of
the soft X-rays is maintained in a high degree of vacuum. The optical
element employs Fresnel's zone pattern and extremely thin samples are
generally used. FIG. 4 is a view illustrating an example of a conventional
X-ray microscopic optical system equipped with an X-ray optical system and
a visible optical system. In this optical microscope, a sample set in the
microscope can be observed by the use of both optical systems, so that low
power preliminary observation by a visible radiation or a combination of
high resolution observation by soft X-rays and a color information
observation by visible radiation can be conducted before observation under
high power is conducted by soft X-rays.
In FIG. 4, an X-ray optical system 11, an observation sample S held in
holder H and a part of visible optical system 12 are placed in a vacuum
vessel 13. A part of an optical axis of the visible optical system 12 is
constituted to coincide with an optical axis of the X-ray optical system
which passes through the observation sample. The X-ray optical system 11
includes a soft X-ray generator G, a condenser zone plate R11, an
objective zone plate R12 and a camera element C. The soft X-rays from the
soft X-ray generator G can be converged on the observation sample S with
condenser zone plate R11. An image of the observation sample S irradiated
with the soft X-rays is formed on the image element C by the objective
zone plate R12. The objective zone plate R12 is structurally similar to
the condenser zone plate R11 and is shown in FIG. 5. This objective zone
plate R12 is attached releasably on the optical axis and comprises a base
plate W having a generally square aperture P at the center thereof for
passing the soft X-rays, a thin silicon nitride membrane N covering the
aperture P of the base plate W and the Fresnel's zone pattern (not shown)
formed on this silicon nitride membrane N.
The visible optical system 12 includes a lamp B, a first condenser L11, a
first mirror M11 and a second condenser lens L12 each having an aperture
at the center thereof for passing the soft X-rays, an objective lens L13
and a second mirror M12 each having an aperture at the center thereof for
passing the soft X-rays, a reticule r10 and an eyepiece L14. A luminous
flux for illumination from a lamp B will be projected on the observation
sample S through the first condenser lens L11, the first mirror M11 and
the second condenser lens L12. The image of the observation sample S is
provided by the luminous flux for illumination. This image is formed on
the reticule r10 through the objective lens L13 and the second mirror M12
and can be observed through the eyepiece L14.
Conventional known objective zone plate R12, as shown in FIG. 5, can
scarcely transmit the visible radiation. In the X-ray microscope in FIG.
4, the objective zone plate R12 is, therefore, attached to a slide frame
for taking it into and from a visible radiation path, and which is
retracted from the visible radiation path during observation by the
visible optical system 12. Accordingly, such arrangement has the
disadvantage of complex structure. In addition, in the X-ray optical
system 11, there is provided a long light path with a fine soft X-ray
beam. Positioning the objective zone plate R12 and angle adjusting thus
require a relatively high precision. This, coupled with the fact that the
mechanism of the objective zone plate must effect retracting and resetting
of the zone plate R12 in a highly evacuated vessel 13, substantially
increases the cost of the X-ray optical apparatus.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to solve the disadvantages of
the above conventional X-ray microscopic apparatus, and more particularly
to provide an apparatus in which an objective zone plate is not required
to retract from an optical axis during sample observation by visible
optical system, which apparatus is readily operated and provides precise
setting of the soft X-ray projection position of a sample.
This object is attained by providing an X-ray optical apparatus which
comprises an X-ray optical system which is capable of projecting an
enlarged sample image by soft X-rays, and a visible optical system which
can observe the sample with a visible radiation, the X-ray optical system
comprising:
a soft X-ray generator;
a condenser zone plate including a zone plate for converging soft X-rays
from the X-ray generator and a base plate supporting the zone plate and
having a soft X-ray passing opening at the center thereof; and
an objective zone plate including a base plate having an opening at the
center thereof to pass soft X-rays which have passed through the sample
and having a visible radiation passing section to the outside of the
opening, and a zone plate supported at the center of the base plate for
converging soft X-rays which have passed through the sample and forming
the sample image to a predetermined position;
the visible optical system comprising:
a visible radiation source displaced from the optical axis of the X-ray
optical system;
a sample illumination means comprising a condenser lens having a soft X-ray
passing opening at the center thereof to pass the X-rays converged by the
condenser zone plate and condensing light from the visible radiation
source so as to illuminate the sample;
an objective lens having a soft X-ray passing opening at the center thereof
for passing the X-rays converged by the condenser zone plate, the optical
axis thereof being arranged to coincide with the optical axis of the
visible radiation in order that the visible radiation which passes through
the sample also passes through the visible radiation passing section
formed on the base plate of the objective zone plate; and
an eyepiece displaced from the optical axis of the X-ray optical system for
observing the sample image formed with the objective lens.
The X-ray optical apparatus is constructed as described above so that the
objective zone plate is not necessary to retract from the optical axis of
the X-ray optical system during sample observation and the soft X-ray
projection position on the sample can be precisely defined. Accordingly,
this invention has more simple construction, high positioning precision
maintained for relatively long periods, and yet the treatment thereof is
easy.
Other and further objects, and advantages of the invention will appear more
fully from the following description referring to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating a soft X-ray microscopic apparatus
of an embodiment of the present invention;
FIG. 2 is a plan view of an objective zone plate constituting a main part
of the apparatus of the embodiment of the present invention;
FIG. 3 is an expanded sectional view taken on line III--III of FIG. 2;
FIG. 4 is a schematic view of a conventional soft X-ray microscopic
apparatus; and
FIG. 5 is a plan view of a conventional zone plate provided for the soft
X-ray microscopic apparatus as shown in FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, FIG. 1 shows a schematic sectional view of a
soft X-ray microscopic apparatus of an embodiment of the present
invention. FIG. 2 is a plan view of an objective zone plate incorporated
into the soft X-ray microscopic apparatus as illustrated in FIG. 1.
In FIG. 1, an observation sample S is provided in a central holder H. An
X-ray optical system 1 is received in a vacuum vessel 3 in order to avoid
attenuation of soft X-rays by the atmosphere. This optical system has a
soft X-ray generator G, a condenser zone plate R1, an objective zone plate
R2 which will be described in further detail, and a camera element C such
as a CCD. The soft X-rays generated from the soft X-ray generator G are
converged by the condenser plate R1 by the use of diffraction and are cast
on the sample S. The soft X-rays diverge after transmission through the
sample S and are converged on the camera element C by the objective zone
plate R2 by the use of diffraction. The image of the portion of the sample
S on which the soft X-rays are cast is projected on the camera element C.
The respective zone plates R1 and R2 are not large size and convergence
efficiencies to the soft X-rays are also low, so that the beam size of the
soft X-rays on the sample S is approximately .phi.0.2 mm. The light path
from the soft X-ray generator to the camera element C attains 2 m.
A visible optical system 2 is superposed on part of the X-ray optical
system 1 by the use of mirrors M1 and M2 having soft X-ray passing
openings A1 and A4. This optical system 2 comprises a lamp B, a first
condenser lens L1, a first mirror M1, a second condenser lens L2, an
objective lens L3, a second mirror M2, a reticule r1 and an eyepiece L4.
Soft X ray passing openings A2 and A3 are provided for the centers of the
second condenser lens L2 and the objective lens L3 respectively.
In the second optical system 2, an optical lens has a large bore diameter
and highly effective convergence in comparison with zone plates R1 and R2.
The use of mirrors M1 and M2 notably allows for greater freedom of design
as compared with the X-ray optical system including the zone plates R1 and
R2. Lenses with their center portion open such as the condenser lens L2
and the objective lens L3 can be manufactured quite readily by those of
ordinary skill.
An illumination light from the lamp B becomes a parallel light flux at the
first condenser lens L1 and is reflected by the first mirror M1 provided
at the optical axis of the X-ray optical system 1. Then, this illumination
light is converged at the second condenser lens L2 and is cast on the
sample S. The sample S lit by this illumination light is imaged on the
reticule r1 through the objective lens L3 and the second mirror M2 and can
be observed by the observer through the eyepiece L4.
The objective zone plate R2 has a soft X-ray passing opening P, as
illustrated in FIG. 2 and FIG. 3, the zone plate comprising: a base plate
W having four visible radiation passing openings T1 to T4 which surround
this opening P; a thin membrane N to cover the central opening P; and
Fresnel's zone pattern FP.
In FIG. 2, a base plate W is a square silicon plate having a thickness of
0.2 to 0.4 mm and respective sides of 14 mm. The plate W is provided with
the square opening P having respective sides 0.2 mm for transmitting the
soft X-rays at the center portion thereof. This opening P is covered with
the thin silicon nitride membrane N. Fresnel's zone pattern FP is, as
shown in FIG. 3, formed on the thin membrane. Visible radiation passing
windows T1 to T4 of 5 mm.times.5.5 mm are formed around the periphery of
the opening P. As shown in FIG. 2, each window T1 to T4 is arranged with a
long side thereof substantially opposed to a short side of another of the
windows. The surface widths of the illustrative sides K1 to K4 are
different at the front and rear surfaces thereof because sectional
configuration of the sides is trapezoidal. The larger width is 0.5 mm.
In the objective zone plate R2 in this embodiment, Fresnel's zone pattern
FP and visible radiation passing windows T1 to T4 are made integral with a
sheet of silicon plate, so that positioning precision during formation of
Fresnel's zone pattern FP enables achievement of the required optical
system alignment precision during locating the objective zone plate R2.
Furthermore, the objective zone plate R2 is fixed and not movable inside
the X-ray microscopic apparatus, whereby the assembly and adjusting of the
X-ray optical system becomes easy and initial alignment precision of the
optical system is always maintained.
In the soft X-ray microscopic apparatus in FIG. 1 constructed as described
above, the soft X-rays from the soft X-ray generator G are converged at
the condenser zone plate R1, and are cast on the sample S through the soft
X-ray passing openings A1 and A2 formed at the centers of the first mirror
M1 and the second condenser lens L2 respectively. The X-rays which are
transmitted through the sample S are converged at Fresnel's zone pattern
F.sub.p formed at the center of the objective zone plate R2. These X-rays
reach the camera element C through the soft X-ray passing openings A3 and
A4 formed at the objective lens 3 and the second mirror M2 respectively.
Accordingly, the portion of sample S image cast by the soft X-rays is
formed on the camera element C.
In the visible optical system, the illumination light from the lamp B is
converged at the first condenser lens L1 and reflected by the first mirror
M1. This illumination light is further converged at the second condenser
lens L2 and is cast on the sample S, so that the sample S is illuminated.
Visible radiation from the illuminated sample S can pass four visible
radiation passing openings T1 to T4 formed in the objective zone plate R2.
The objective lens L3 converges the visible radiation which passes through
the openings T1 to T4. Then, the objective lens L3 forms the sample S
image on the reticule r1 through the second mirror M2. The sample image
formed on this reticule r1 is observed through the eyepiece L4.
In the observational optical system ranging from the objective lens L3 to
the eyepiece L4, the main optical axis passing the objective lens L3 is
arranged to coincide with the main optical axis of the X-ray optical
system 1. The soft X-ray projecting position can be readily located by
moving the holder H in a plane perpendicular to the main axis while
observing the sample through the eyepiece L4. The soft X-ray projecting
image of the sample S located at such position can be readily formed on
the camera element C.
A method of making objective zone plate R2 in this embodiment is now
explained.
First, thin silicon nitride membranes (Si.sub.3 N.sub.4) having a width of
0.05 to 0.1 .mu.m are formed on the respective surfaces of the base plate
W. The membrane producing method may be selected not only chemical methods
such as LP-CVD (Low Pressure-Chemical Vapor Deposition) method, ECR-CVD
(Electron Cyclotron Resonance-(Chemical Vapor Deposition)) method and the
like, but also physical methods such as sputtering and the like. An
internal stress of the membrane (pulling stress) is maintained in the
range of 10.sup.9 to 10.sup.11 dyn/cm.sup.2 in order to avoid slackening
of the thin membrane N of the soft X-ray transmitting section and to
maintain sufficient strength thereof.
Second, a photo resist layer is formed on the thin silicon nitride
membrane. A mask exposure transfer, developing, and etching of the thin
silicon nitride membrane are performed to remove thin silicon nitride
membrane corresponding to one side of the opening P (bottom side in FIG.
3) and respective one sides of the windows T1 to T4 (bottom sides in FIG.
3). Either surface of the thin silicon nitride membranes N of the windows
of T1 to T4 may be removed; however, a transparent silicon nitride
membrane N remains at the windows of T1 to T4 in the finished zone plate.
Third, wet etching of the base plate W starts from the portion with thin
silicon nitride membrane removed. The opening P and the windows of T1 to
T4 are formed. The etching solution may employ a mixture of
ethylenediamine, pyrocatechol and water, or potassium hydroxide solution.
The silicon crystal board (100) employed as the base plate W can conduct
anistropic etching and form a suitable tapering section automatically (a
tapering surface is a surface 111 made of Si crystal) around the opening
P.
Metal thin membranes such as Au, Cr, N and the like are formed on the thin
silicon nitride membrane which remains on the opening P. The thin metal
membrane is formed into the Fresnel's zone pattern, and the objective zone
plate R2 is completed. Fresnel's zone pattern FP may be formed before the
wet etching of the base plate W.
In the X-ray optical apparatus according to this invention, the visible
radiation can freely pass through the objective zone while objective zone
plate R2 is maintained in its predetermined position on the optical axis
of the X-ray optical system. Therefore, both the X-ray optical system and
the visible optical system can be used simultaneously, and the objective
zone plate fixed inside the X-ray microscope maintains an initial
positioning precision and does not require a mechanism for retraction and
resetting thereof. Consequently, reliability of the X-ray optical system
in this X-ray microscope increases and cost of production of the X-ray
optical system decreases. The entire X-ray microscope can become smaller
and operability thereof can be significantly improved.
Because the X-ray optical system and the visible optical system are
simultaneously operative to obtain multiple information and the like, the
invention offers a significantly enhanced range of application.
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