U.S. patent application number 15/616453 was filed with the patent office on 2017-11-09 for hybrid energy conversion and processing detector.
The applicant listed for this patent is Gatan, Inc.. Invention is credited to Alexander Jozef Gubbens, Matthew Lent, Paul Mooney.
Application Number | 20170322322 15/616453 |
Document ID | / |
Family ID | 54249560 |
Filed Date | 2017-11-09 |
United States Patent
Application |
20170322322 |
Kind Code |
A1 |
Gubbens; Alexander Jozef ;
et al. |
November 9, 2017 |
HYBRID ENERGY CONVERSION AND PROCESSING DETECTOR
Abstract
A hybrid arrangement of more than one electron energy conversion
mechanism in an electron detector is arranged such that an image
can be acquired from both energy converters so that selected
high-illumination parts of the electron beam can be imaged with an
indirectly coupled scintillator detector and the remainder of the
image acquired with the high-sensitivity/direct electron portion of
the detector without readjustments in the beam position or
mechanical positioning of the detector parts. Further, a mechanism
is described to allow dynamically switchable or simultaneous linear
and counted signal processing from each pixel on the detector so
that high-illumination areas can be acquired linearly without
severe dose rate limitation of counting and low-illumination
regions can be acquired with counting.
Inventors: |
Gubbens; Alexander Jozef;
(Palo Alto, CA) ; Mooney; Paul; (Pleasanton,
CA) ; Lent; Matthew; (Livermore, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gatan, Inc. |
Pleasanton |
CA |
US |
|
|
Family ID: |
54249560 |
Appl. No.: |
15/616453 |
Filed: |
June 7, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14688081 |
Apr 16, 2015 |
9696435 |
|
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15616453 |
|
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61981138 |
Apr 17, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 2237/2441 20130101;
G01T 1/2018 20130101; H01J 37/244 20130101; H01J 2237/2446
20130101; H01J 2237/2443 20130101; H01J 2237/24485 20130101 |
International
Class: |
G01T 1/20 20060101
G01T001/20; H01J 37/244 20060101 H01J037/244 |
Claims
1. A hybrid processing directly illuminated two-dimensional
detector (HPDD) comprising: a processor configured to:
simultaneously perform linear read-out and event-counting read-out
of at least a portion of pixels in an array, wherein when
performing the event-counting readout, the processor is configured
to identify a centroid with respect to event energy associated with
a pixel and adjacent pixels.
2. The HPDD detector of claim 1, wherein the processor is further
configured to allow simultaneous linear read-out and event counting
readout from every pixel of the pixel array.
3. The HPDD detector of claim 1, wherein the processor is further
configured to adjust signal levels of said linearly read-out pixels
and said event-counted read out pixels to minimize image merge
artifacts.
4. A hybrid processing directly illuminated two dimensional
electron detector (HPDD) comprising: a processor configured to:
linearly read-out a portion of pixels, and event-count read-out a
portion of pixels, wherein said event-count readout includes a
super-resolution computation readout based on identifying a
centroid with respect to event energy associated with a pixel.
5. The HPDD of claim 4, wherein said linear read out and event
counting read-out are dynamically configurable.
6. The HPDD of claim 5, wherein said dynamic configuration of which
pixels are read out linearly and which pixels are read out by
counting is based on an overall dose rate received by the
detector.
7. The HPDD of claim 4, wherein said processor is further
configured to adjust signal levels of said linearly read-out pixels
and said event-counted read out pixels to minimize image merge
artifacts.
8. A hybrid energy-conversion detector (HECD) for receiving a beam
of electron radiation having predetermined high and low
illumination intensity portions, the detector comprising: an energy
converting scintillator exposed to the high illumination intensity
portion of the beam of electron radiation, said scintillator
generating light from said high illumination intensity portion of
the beam of electron radiation; an image sensor that includes: a
first image sensor portion arranged and adapted for receiving said
light from said energy converting scintillator and for processing a
first image portion; and a second image sensor portion arranged and
adapted for directly receiving the low illumination intensity
portion of the beam of electron radiation and for processing a
second image portion, wherein said scintillator is exposed to the
high illumination intensity portion of the beam of electron
radiation, wherein said second sensor portion is exposed to said
low intensity portion of the beam of electron radiation, wherein
said exposure of said first image sensor portion to said light and
said exposure of said second sensor portion to the low illumination
intensity portion of the beam of electron radiation occurs at least
in part simultaneously; and a processor configured to perform a
linear read-out and an event-counting read-out of at least a
portion of pixels in the second image sensor portion, wherein said
event-counting readout includes a super-resolution computation
readout including identification of a centroid with respect to
event energy associated with a pixel and adjacent pixels.
9. The HECD of claim 8, wherein said processor is further
configured to allow simultaneous linear read-out and event counting
readout from every pixel of the second sensor portion.
10. The HECD pixel array of claim 8, wherein said processor is
further configured to adjust signal levels of said linearly
read-out pixels and said event-counted read out pixels to minimize
image merge artifacts.
11. The HECD of claim 8, comprising a linearly read-out portion of
pixels and an event-counted read-out portion of pixels, wherein
said event-counted readout includes the super-resolution
computation readout including identifying the centroid with respect
to event energy associated with the pixel and adjacent pixels.
12. The HECD of claim 11, wherein which pixels are read out
linearly and which pixels are read out by event counting is
dynamically configurable.
13. The HECD of claim 12, wherein said dynamic configuration of
which pixels are read out linearly and which pixels are read out by
counting is based on overall dose rate to said second image sensor
portion.
14. The HECD pixel array of claim 11, wherein said processor is
further configured to adjust signal levels of said linearly
read-out pixels and said event-counted read out pixels to minimize
image merge artifacts.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This non-provisional utility application claims priority as
a divisional application of non-provisional application Ser. No.
14/688,081 filed Apr. 16, 2015 and to provisional application No.
61/981,138, filed Apr. 17, 2014, both applications being entitled
"High Energy Conversion and Processing Detector." The entire
disclosures of both applications are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The invention relates generally to the field of electron
microscopy image detection.
BACKGROUND OF THE INVENTION
[0003] For much of the history of electron microscopy up until the
1990s, sheet film was the main image recording medium. In 1990,
electronic detectors based on scintillators coupled to scientific
semiconductor image sensors with either fused fiber or lens optics
were introduced and began to replace film for most image recording
applications. One of the main advantages of these sensors was for
the applications of electron energy loss spectroscopy (EELS) and
electron diffraction (ED) due the dramatically increased dynamic
range of these scintillator-optics-semiconductor sensor. Both of
these applications involve the use of a focused beam, with specimen
information derived from electrons which are diverted from the main
path either due to energy loss (subsequently made manifest with a
bending magnet) or due to electron diffraction. The deflected beams
can be several to many orders of magnitude weaker than the
un-deflected beam as shown in FIGS. 1A, 1B, 2A and 2B. The graph in
FIG. 1B shows that the diffraction spots in FIG. 1A have dynamic
range of several orders of magnitude. FIGS. 2A and 2B show the
dynamic range needed in EELS. Semiconductor sensors, typically CCDs
for imaging and photodiode arrays and CCDs for spectroscopy, have
significantly higher dynamic range than film, especially scientific
sensors which were made with larger pixels. Dynamic ranges of up to
20,000 have been shown possible in single exposures with merged
multiple exposures extending that limit even further. In addition,
scintillators coupled optically to the sensor protect the sensor
from the radiation damage effects that can results from either
direct exposure of the sensor to the beam or from exposure to
x-rays generated at the scintillator which can then travel to the
sensor. In the case of lens coupling, the glass of the lens and the
distance the lens allows to be created between scintillator and
sensor confer the protective effect. In the case of fused fiber
optic plates, the high density glass provides the x-ray protection.
In both cases, the beam is stopped long before it can hit the
sensor and cause damage directly. For both these reasons, the
scintillator/optic/semiconductor sensor has replaced film in 100%
of diffraction applications and made possible the parallel
acquisition of spectra, which wasn't an option at all before these
sensors made it possible.
[0004] FIG. 3A shows a prior art lens-coupled scintillator indirect
detector having a scintillator 301, a glass prism 302, optical
lenses 303, 304 and a CCD detector 305. FIG. 3B shows a prior art
fused fiber-optic plate coupled indirect detector having a
scintillator 311, an optical fiber bundle, 312 and a CCD detector
313.
[0005] Certain imaging applications, most notably cryo-electron
microscopy of proteins and cellular cryo-tomography drove a need
for a replacement of film which did not have a dynamic range
requirement but rather a sensitivity and resolution requirement. In
the last few years, a class of detectors has been developed using
radiation hardened silicon active pixel detectors which is now
successfully replacing film and extending the resolution limits
attainable in structural biology. This technology is usually
referred to as direct detection technology and cameras using this
technology as direct detectors. In contradistinction to these
detectors, the scintillator/optic/sensor detectors described above
are now commonly referred to as indirect detectors.
[0006] Direct detectors make these improvements in structural
biology resolution in a number of ways. First, silicon, being
lighter than typical scintillator and optical materials, scatters
the electron beam less giving a finer point spread function.
Second, the directly detected incoming electron makes a much
stronger signal. Third, it is possible to thin the device to allow
the beam to pass through without additional noisy backscatter.
While thinning is possible with lens coupled scintillators (see,
for example, U.S. Pat. No. 5,517,033 all references cited herein
are incorporated by reference), thinning comes with a severe loss
of signal strength. FIG. 3C shows a prior art non-thinned ("bulk")
direct detector 320 and FIG. 3D shows a prior art back-thinned
direct detector 330. In a direct detector there is no sensitivity
penalty for thinning.
[0007] Finally, as a result of the first three benefits described
above, (improved point spread function, higher signal strength and
reduced backscatter from thinning), the signal from a direct
detector can be processed to result in a counting mode analogous to
that often used with a photomultiplier tube and with the same
benefit. When an incoming electron is counted as a 1 and added into
a frame buffer, the variations in energy deposited by the incoming
electron are stripped off and not summed as they would be in the
case for a linear, integrating detector, whether direct or
indirect. Because the acquired image no longer contains that
variation in energy, a nearly noise-free acquisition is
possible.
[0008] A second variant of counting is possible in which the
position of entry of the electron is estimated to sub-pixel
accuracy by centroiding the deposited energy. This method is
commonly referred to a super-resolution. FIG. 4 shows the detection
of a single incident electron with a super-resolution detector.
FIG. 4A shows an electron landing on an arbitrary location within a
pixel on a multipixel detection device. FIG. 4B shows scatter from
incoming electrons in a localized region near the point of entry to
the electron. FIG. 4c shows how the amount of scattered detected
signal in nearby pixels is related to the location of the
electron's entry point. FIG. 4d shows that selection of the pixel
with the highest scattered signal locates the point of entry to the
nearest pixel. FIG. 4e shows that finding the center of mass of the
distribution of scattered charge allows location of the entry point
to sub-pixel accuracy.
[0009] Counting and super-resolution dramatically improve the
sensitivity performance as measured by detective quantum efficiency
(DQE), the ratio of detected signal to noise ratio to incoming
signal to noise ratio over the performance of a silicon direct
detection imager.
[0010] FIG. 5 shows the sensitivity improvement summarized: of
direct detection over indirect detection (A), of counting direct
detection over just direct detection (B) and of the effect that
super-resolution adds signal over the Nyquist frequency (C) of the
physical pixel. Part of the DQE benefit comes from the additional
benefit of counting of dramatically reducing detection of
background noise. It is clear that indirect detectors have a
serious disadvantage in terms of sensitivity. This is both in terms
of DQE as shown in the graph in FIG. 5, but also in terms of the
background noise. Both Electron energy loss spectroscopy (EELS) and
electron diffraction (ED) have a strong need for high sensitivity
and good background rejection for the weak parts of the signal.
[0011] Direct detectors (DD) have the drawback that the electron,
while deposing signal energy in the pixel, will also damage it due
to charge injected into insulators, as well as knock-on damage to
the silicon crystal structure. This gives direct detectors a
lifetime dose limit. While this dose limit has been dramatically
increased by improvements to pixel design layout, reductions in
feature sizes which reduce oxide thickness and thereby allow
trapped electrons to diffuse out more readily, and thinning, which
eliminates the energy deposited by backscatter, total lifetime dose
is still limited to significantly lower levels than that of
fiber-optically or lens-optically coupled scintillators. This fact
would be severely limiting in applications like EELS and ED for
which the undeflected beam is often many orders of magnitude higher
than the low intensity part of the signal and would reduce the
sensor lifetime, which is measured in years for cyro-electron
microscopy, to hours.
[0012] For a DD detector to count electron arrival events they must
be spatially and temporally separated on the detector. DQE is only
modestly affected for 300 kV electrons at event densities up to
about 0.025 per pixel (.about.40 pixels per electron event). This
is accomplished by an extreme speedup in frame-rate. A framerate of
400 fps as used on the Gatan K2 Counting direct detection camera
allows a dose rate of 10 electrons per pixel per second at that
event density. While that dose rate is adequate for low-dose
imaging in cryo-microscopy for which it was developed, it is too
low for use in higher-dose and in high-dynamic range applications
such as EELS and ED as described in FIGS. 1 and 2. While it is
conceivable that frame rates could be increased enough to handle
medium dose ranges as shown in FIG. 2B, it is unrealistic to think
that counting could be used for the high intensity parts of either
the EELS or the ED signals. For the current generation of K2
counting direct detector, a commercial camera developed by Gatan,
Inc. which uses the prior art detector arrangement of FIG. 3D in
conjunction with extremely fast readout to separate the incoming
electron events into different frames and a fast processor to count
or centroid the electron events and sum them, the useable dose rate
is 400 times lower in counting mode than in linear mode. FIG. 6
shows the sparsification by speed needed to allow counting. On the
left, the actual signal generated by a sparse beam is shown,
illustrating that each event covers multiple pixels, with varying
size. Sparsification needs to be sufficient to prevent miscounting
or poor centroiding due to overlap of scatter from one event onto
another. The image on the right of FIG. 6 shows the results of
counting the frame on the left. It also illustrates the extent to
which the variability both in event intensity and in event size is
reduced through the counting process.
[0013] Relevant patents in the field include U.S. Pat. No.
7,952,073 ("Bilhorn") and U.S. Pat. No. 8,334,512 ("Luecken"). All
references cited herein are incorporated by reference in their
entirety.
[0014] The inadequacy of indirect detectors in resolution and
sensitivity for dealing with the weak parts of EELS and ED signals
and the inadequacy of direct detection to deal with the strong
parts of EELS and ED signals coupled with the lack of any
workaround in the prior art for acquiring both strong and weak
signals simultaneous with high quality creates a need for a new
solution.
[0015] Electron energy loss spectroscopy (EELS) and electron
diffraction (ED) would stand to benefit significantly if the
capability to read the weakest signals were added to existing
capability. This is especially true for scanning transmission
electron microscope spectrum imaging (STEM SI), for which a
spectrum is taken at each of a N.times.M raster of scanned specimen
pixels and used to derive elemental and electronic contrast images.
See Gatan datasheet, "GIF Quantum", published March 2014. This
technique, which requires high speed to cover a reasonable number
of pixels over a reasonable area of a specimen requires high
sensitivity to very weak signals in the regions used for elemental
contrast and yet still needs to be able to acquire and digitize the
un-deflected beam for normalization. Similar applications are being
developed for electron diffraction with STEM with similar
requirements.
[0016] U.S. Pat. No. 8,334,512 is a patent in the field and
discusses use of a fast detector positioned below the thinned
imaging detector at some distance as a zero-loss beam position
detector but due to the poor resolution associated with its
position, cannot be used as a detector for low-loss spectroscopic
information.
[0017] In addition, EELS and ED signals in their most general
application can, and especially in these STEM applications, do vary
rapidly in time, making serial illumination first of a
low-sensitivity, high-robustness detector and second of a
high-sensitivity low-robustness detector an impractical solution
for the high dynamic range application.
[0018] Therefore there exists a need in the prior art for a
technology which would allow simultaneous robust and high-quality
imaging of high-intensity and weak signals in the same field of
view.
DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1A is an image relating to the prior art;
[0020] FIG. 1B is a graph of intensity for the image in FIG.
1B;
[0021] FIG. 2A is a graph relating to the prior art;
[0022] FIG. 2B is a graph relating to the prior art;
[0023] FIG. 3A is a prior art indirect detector coupling
design;
[0024] FIG. 3B is a prior art indirect detector coupling
design;
[0025] FIG. 3C is a prior art direct detector design;
[0026] FIG. 3D is a prior art direct detector design;
[0027] FIG. 4A is a diagram of electron detection;
[0028] FIG. 4B is a diagram of electron detection
[0029] FIG. 4C is a diagram of electron detection
[0030] FIG. 4D is a diagram showing electron detection event signal
processing;
[0031] FIG. 4E is a diagram showing electron detection event signal
processing;
[0032] FIG. 5 is a graph describing use of detective quantum
efficiency (DQE) as a measure of sensitivity;
[0033] FIG. 6 are two images showing the effect of high speed
readout to separate events into different frames (left) and the
effect of counting those events (right);
[0034] FIG. 7A shows a hybrid detector design using a
fiber-optically coupled scintillator on part of the monolithic
detector array;
[0035] FIG. 7B shows a hybrid detector design using a
fiber-optically coupled scintillator on part of the monolithic
thinned detector array;
[0036] FIG. 7C shows a hybrid detector design using a
fiber-optically coupled scintillator on part of the monolithic
back-illuminated thinned detector array;
[0037] FIG. 7D shows a hybrid detector design using a lens-coupled
scintillator on part of the monolithic front- (or back-)
illuminated thinned detector array;
[0038] FIG. 7E shows a hybrid detector design using a
fiber-optically coupled scintillator on part of the monolithic
thinned detector array with coordinated simultaneous readout of
both optically-coupled and direct detection portions of the
detector;
[0039] FIG. 7F shows a hybrid detector design using a
fiber-optically coupled scintillator on part of the monolithic
thinned detector array with independent simultaneous readout of
both optically-coupled and direct detection portions of the
detector;
[0040] FIG. 8A shows a dual detector having a scintillator in
contact with and on top of a direct detector with the scintillator
being optically coupled to a second detector;
[0041] FIG. 8B shows a dual detector having a scintillator in
contact with and below a direct back-illuminated detector with the
scintillator being coupled by a skewed fiber bundle to a second
detector;
[0042] FIG. 8C shows a dual detector having a scintillator in
contact with and below a direct thinned back-illuminated detector
with the scintillator being coupled by a mirror and optical lenses
to a second detector;
[0043] FIG. 9A shows a dual detector having a scintillator not in
contact with and in front of a direct detector, lens coupled to a
separate optical sensor with means for synchronizing the two
detectors;
[0044] FIG. 9B shows a dual detector having a scintillator-coupled
indirect detector next to and in close proximity to a direct
back-illuminated detector with the scintillator being coupled by a
skewed fiber bundle to enable the very close juxtaposition of the
electron detection planes of the two detectors, with means for
synchronizing the two detectors;
[0045] FIG. 10A shows an exemplary hybrid energy conversion
detector with three types of data read out simultaneously from
three separate regions of the detector; and
[0046] FIG. 10B shows a further exemplary hybrid energy conversion
detector with three types of data read out simultaneously from
three separate regions of the detector in such a way that both the
counted and the linearly read direction detection data is merged to
allow optimal integration of both types of data.
DETAILED DESCRIPTION OF THE INVENTION
[0047] In an embodiment of the invention, there is disclosed a
hybrid arrangement of more than one electron energy conversion
mechanism in a detector arranged physically such that the electron
image can be acquired from both energy converters in such a manner
that selected high-illumination parts of the image can be imaged
with an indirectly coupled scintillator detector and the remainder
of the image acquired with the high-sensitivity/direct electron
portion of the detector without readjustments in the beam position
or mechanical positioning of the detector parts.
[0048] Further, a mechanism is included in the signal processor to
allow dynamic switching between counted and linear readout modes so
that high-illumination areas can be acquired linearly without the
severe dose rate limitation of counting and low-illumination
regions can be acquired with counting to provide the very high
signal quality needed for low dose and long exposures.
Alternatively or in addition, the ability to perform simultaneous
linear and counted signal processing from each pixel of the image
is provided to allow subsequent selection or combination of linear
and counted signals offline after acquisition. Both methods would
make use of a switchover illumination intensity above which the
transition from counted to linear would be made. The switchover
would be the illumination intensity at which the signal quality was
the same for counted and linear modes. Signal quality would
typically be measured using detective quantum efficiency (DQE), as
used in FIG. 5 to compare different detectors. DQE of a counting
detector begins to degrade as illumination rate grows above the
level of 1 electron per 40 pixels and reaches the level of a linear
detector at a dose rate between 1 electron per 20 pixels and 1
electron per 10 pixels. In this manner, each pixel in the image can
be read out and processed in the most optimal fashion.
[0049] Further, because counted and linear modes have different
transfer curves (the functional relationship of illumination to
counts) and frequency response or modulation transfer function
(MTF), signal processing will be provided to remove the intensity
and resolution differences between the linear and counted
signals.
[0050] Hybrid detector realizations can be categorized by location
of scintillator (in contact with the detector or not, above direct
detector or below) by coupling means (fused fiber optic plate or
lens-coupling), by which side of the direct detection device is
coupled to (front side or back side), by whether the direct
detection device is thinned or not, by readout means
(single-sensor, all read out together, single sensor with
integrated split readout, and dual sensor configurations), by
processing means (linear, counted or both). Many combinations of
these factors can be envisioned. A number of representative
combinations are shown in FIGS. 7-10. FIG. 7A-7D show various
options for coupling a scintillator to the direct detection device
with the scintillator not in contact with the direct detection
device. FIG. 7A shows a scintillator 701 above the device coupled
by a fiber optic plate 702 to the front side 703 of a non-thinned
bulk silicon direct detection device 704. FIG. 7B show the same
arrangement as FIG. 7A but coupled to the front side 705 of a
thinned direct detection device 706. FIG. 7C shows a scintillator
701 fiber-optically coupled 702 to the backside 707 of a
back-thinned direct detection device 706. And FIG. 7D shows a
scintillator 702 lens-optically coupled 708 to a frontside thinned
direct detection device. FIGS. 7E and 7F illustrate two
possibilities for readout of the direct detection device 706 which
could apply to any coupling type or position but are here shown in
conjunction with the same fiber-optically coupled scintillator
arrangement of FIG. 7B. FIG. 7E shows the detector 706 being read
out via a unified and coordinated mechanism 710 that reads out the
whole of the device, optically coupled and direct-detection in the
same way. FIG. 7F shows a device with the readout split in to two
sections 711, 712 at the location of the transition from optical
coupling to direct detection. This arrangement would allow for the
high-intensity low-loss and zero loss beams to be read out
independently and potentially faster than the direct detection
portion of the detector. Faster readout would then attenuate the
signal strength in each readout of the high-intensity signal and
allow a greater dynamic range as a result.
[0051] FIGS. 8A through 8C show example configurations which place
the scintillator 801 in contact with the direct detection device
802. In these configurations it is necessary to couple the light to
a second detector 804 which must be placed out of the way of the
incident beam. This is because while light generated in the
scintillator can be detected by the direct detector the signal will
be overwhelmed by the scattered electron beam which will still be
detected by the direct detection device under the scintillator.
FIG. 8A shows a possible lens-optical 805 arrangement including a
shield 803 to prevent scattered electrons from reaching the optical
detector 804. A synchronizer 806 controls readout of the directly
exposed detector 803 and the optical detector 804. FIG. 8B shows a
fiber-optically coupled arrangement with the scintillator 801
beneath the detector 802. The scintillator 801 is coupled to the
second detector 804 by a skewed fiber optic plate 807 FIG. 8C shows
a lens-optically 805 coupled arrangement with the scintillator 804
beneath the detector 802 and using a mirror 812 to redirect the
scintillator image to the second detector. A means of
synchronization is provided to allow the outputs of the two
detectors to be merged into a single hybrid image. The embodiments
shown in FIGS. 7A-F and 8A-C are only representative and do not
constitute all possible arrangements using this concept. An example
of an extension not shown would be to move the in-contact
scintillator to the center of the device for the application of
diffraction (FIGS. 1A and 1B) using lens-coupling to avoid
occluding any part of the electron image or the creation of
backscatter if located under the device.
[0052] FIGS. 9A and 9B show arrangements of two detectors arranged
without physical contact of either the scintillator 901 or the
detector 904. FIG. 9A shows a lens-coupled camera 902 located in
front of the direct detection sensor 904 and with optical design
903, 905 so as to minimize dead pixels between optically-coupled
902 and direct-detection sensor 904 s. This design would also serve
to minimize scatter of electrons from the scintillator onto the
direct-detection portion of the hybrid detector. FIG. 9B shows a
possible arrangement of two detectors 902, 904 with detection
surfaces in the same plane. The embodiment in Figure B includes a
detector 904 designed to minimize dead area, and a shield 907. The
scintillator 901 is coupled to the light sensor 902 by a skewed
fiber optic bundle. As for the previous cases shown in FIGS. 8A-8C,
FIG. 9A shows a synchronizer 906 to control readout of the directly
exposed detector 904 and the optical detector comprised of
scintillator 901, image sensor 902 and optics 905 and 903.
[0053] FIGS. 10A and 10B concern image processing options and the
extension of the hybrid concept to cover a combination of both
linearly detected and counted data. FIG. 10A shows linear indirect,
linear direct and counted direct-detection data being read out by
the detector 1001, from the high, medium and low-dose portions of
the image or spectrum. The embodiment shown here includes a
scintillator 1002 coupled to the detector by a fiber optic bundle
1003. The position of transition from linear direct detection to
counted direct detection would be determined by the illumination
pattern and the switchover illumination intensity and would
therefore vary from one image to the next--and might happen more
than once in an image. FIG. 10B shows an arrangement that processes
every pixel in the direct detection area both as a linear pixel and
with counting or centroiding. While this increases the amount of
data which needs to be saved, it creates the possibility of
selecting or merging the data offline for a more highly optimized
synthesis of data. It should be clear that the above combinations
are just representative of a much larger set of combinations.
[0054] With respect to FIG. 8, Separate detectors could be operated
with or without synchronization. Exposure times could be the same
or different for the indirect and direct portions of the detector.
With the scintillator in direct contact with the direct detector,
the direct detector will be exposed to the intense beam and so will
age quickly. However, since that part of the detector is not needed
due to the presence of the indirectly coupled sensor, it can be
allowed to become non-functional.
[0055] With respect to FIG. 9, Separate detectors could be operated
with or without synchronization. Exposure times could be the same
or different for the indirect and direct portions of the
detector.
* * * * *