U.S. patent number 3,812,288 [Application Number 05/308,522] was granted by the patent office on 1974-05-21 for television display system.
This patent grant is currently assigned to Edax International Inc.. Invention is credited to Morris W. Barnhart, Charles J. Walsh.
United States Patent |
3,812,288 |
Walsh , et al. |
May 21, 1974 |
TELEVISION DISPLAY SYSTEM
Abstract
A television display system for a scanning electron microscope
provides a spatially correlated area map display of X-ray events
emitted from a specimen within one or more predetermined energy
ranges as the specimen is scanned at standard television scanning
rates by an electron beam. The X-ray area map display can be
presented alone, or in combination with a conventional micrograph
magnified image of the specimen. Provision is made for displaying
X-ray events falling within different energy ranges in different
colors on the area map television display to facilitate determining
the distribution of selected elements within the specimen, and for
color coding the distribution peaks on an associated X-ray energy
distribution television display to facilitate correlation with the
elements displayed in the area map display.
Inventors: |
Walsh; Charles J. (Deerfield,
IL), Barnhart; Morris W. (Buffalo Grove, IL) |
Assignee: |
Edax International Inc.
(Prairie View, IL)
|
Family
ID: |
23194308 |
Appl.
No.: |
05/308,522 |
Filed: |
November 21, 1972 |
Current U.S.
Class: |
378/98.6;
250/399; 250/311; 850/10; 348/E9.028 |
Current CPC
Class: |
H04N
9/43 (20130101); H01J 37/28 (20130101); H01J
2237/2807 (20130101) |
Current International
Class: |
H01J
37/28 (20060101); H04N 9/00 (20060101); H04N
9/43 (20060101); H04n 007/18 () |
Field of
Search: |
;178/6.8,7.2,DIG.5,DIG.1
;340/324AD ;250/307,310,311,397,399 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Britton; Howard W.
Assistant Examiner: Masinick; Michael A.
Attorney, Agent or Firm: Wetzel; James M.
Claims
1. In a scanning electron microscope of the type wherein a series
of X-ray emission events are produced as a specimen is cyclically
scanned by an electron beam, a display system comprising:
a detector for detecting said X-ray events and producing output
pulses indicative of the energy level thereof;
means for converting at least some of said output pulses to
energy-indicative information signals, said information signals
following their respective output pulses by random unpredictable
time intervals;
correlation means responsive to said information signals for
correlating said information signals with limits corresponding to a
predetermined energy range and for producing a display pulse
responsive to said correlation after a predetermined time interval
following each of said respective output pulses;
a television monitor having a viewing screen scanned in synchronism
with said specimen;
and means for applying said display pulses to said television
monitor to obtain a spatially correlated X-ray area map display of
said X-ray events.
2. A display system as defined in claim 1 wherein said correlation
means comprise a single channel window circuit for producing a
control effect when one of said information signals falls within
said limits, and a timer responsive to said control effect for
producing said display pulse after a predetermined delay period
following the output pulse associated with said
3. A display system as defined in claim 2 wherein said specimen is
scanned in a line raster and said delay period comprises an
integral number of
4. A display system as defined in claim 2 wherein said electron
microscope includes a detector for detecting secondary electrons
and wherein means are provided for applying the output of said
electron detector to said television monitor to display a
micrograph of said specimen thereon in
5. A display system as described in claim 2 wherein said display
pulse includes a color subcarrier signal, said television monitor
is a color video monitor and said spatially correlated display is a
color display.
6. A display system as described in claim 1 wherein said
information signals are digitally coded signals, and said
correlation means include a digital window circuit for determining
whether said coded signals fall
7. In a scanning elctron microscope of the type wherein a series of
X-ray emission events are produced as a specimen is cyclically
scanned by an electron beam, a display system comprising:
a detector for detecting said X-ray events and producing output
pulses indicative of the energy level thereof;
means for converting at least some of said output pulses to
energy-indicative information signals, said information signals
following their associated events by random unpredictable time
intervals;
a first single-channel window circuit for analyzing said
information signals to produce a first control effect when one of
said signals falls within limits corresponding to a first
predetermined energy range;
a second single-channel window circuit for analyzing said
information signals to produce a second control effect when one of
said signals falls within limits corresponding to a second
predetermined energy range;
means including a timer responsive to said first control effect for
producing a first display pulse and responsive to said second
control effect for producing a second display pulse, each of siad
pulses being produced after a predetermined delay period following
the X-ray event associated with the respective control effect;
a television monitor having a viewing screen scanned in synchronism
with said specimen;
and means for applying said first and second display pulses to said
television monitor to obtain a spatially correlated display of said
X-ray events having energy levels within said first and second
predetermined
8. A display system as defined in claim 7 wherein said specimen is
scanned in horizontal and vertical directions and said delay period
comprises an
9. A display system as defined in claim 7 wherein said television
monitor is a color monitor, and wherein said first display pulses
appear on said monitor with a first distinguishing color, and said
second display pulses
10. In a scanning electron microscope of the type wherein a series
of X-ray emission events are produced as a specimen is cyclically
scanned by an electron beam, a display system comprising:
a detector for detecting said X-ray events and producing output
pulses indicative of the energy level thereof;
means for converting at least some of said output pulses to
energy-indicative information signals, said information signals
following their associated events by random unpredictable time
intervals;
a color television monitor;
an energy distribution analyzer for developing said television
monitor from said information signals a histogram-type display of
the energy levels of said X-ray events versus their cumulative
occurrence over a period of time;
a first single channel window for analyzing said information
signals to generate a first control effect when said signals fall
within limits corresponding to a first predetermined energy
range;
and means for varying the color of said histogram display to
identify that portion of the display falling within said first
predetermined energy
11. A display system as defined in claim 10 which further comprises
a second single channel window for analyzing said information
signals to generate a second control effect when said signals fall
within limits corresponding to a second predetermined energy range,
and means for futher varying the color of said histogram display to
identify that portion of the display falling within said second
predetermined energy range.
Description
BACKGROUND OF THE INVENTION
This invention pertains to video display systems, and more
particularly to a display system for a scanning electron
microscope.
Scanning type electron microscope (SEM) systems, wherein a narrow
electron beam is caused to periodically scan across the surface of
a specimen, have come into wide use for the examination of rough
specimens, such as a fracture or a particle in a substrate. In such
systems a detector, mounted adjacent the specimen, detects the
incidence of secondary electrons as the specimen is scanned to
develop a video signal indicative of the electron density of the
specimen. This video signal, after amplification, is utilized to
intensity-modulate the electron beam of a cathode-ray tube. When
this electron beam is caused to scan in synchronism with the
electron beam of the SEM, an output display is formed on the face
of the cathode-ray tube showing the threedimensional surface
features of the specimen with magnifications typically from 20 to
20,000 times.
The usefulness of a SEM system is greatly enhanced if an elemental
analysis can be made of the specimen at the same time the specimen
is being scanned. This is accomplished by detecting and measuring
the X-rays emitted from the specimen as it is scanned. The energy
level of these X-rays is proportional to the atomic number of the
element emitting the X-rays, and thus can be used to unequivocably
identify the element. Furthermore, the relative number of X-rays of
various energies can be used to calculate the relative abundance of
the different elements in the specimen. Energy-dispersive analysis
systems commonly used in conjunction with SEM systems for elemental
analysis employ a highly purified silicon diode detector for
developing current pulses proportional to the energy level of the
X-ray events. After amplification, these pulses are sorted and
tabulated according to their energy level in a multichannel energy
distribution analyzer to ascertain the complete energy spectrum of
the specimen. All or portions of this spectrum can then be
displayed as a histogram on a cathode-ray tube, or can be
printed-out by means of a teletype terminal or data plotter.
Energy-dispersive analysis systems can also be equipped to single
out specific energy level pulses, and hence specific elements. This
is accomplished by means of a single channel window circuit which
is set to recognize only signals within a predetermined energy
range, or window, and to ignore all others. All X-ray events
falling within this window can be separately processed and
tabulated, allowing the presence of a selected element to be
accurately determined.
One particularly useful application for the single channel window
is to provide an area map of the selected element on the output
display of the SEM system. This may be done by intensity-modulating
the electron beam of the cathode-ray display tube, either so that
only the selected element will be displayed, or so that the
selected element will be made to stand out in some manner from the
rest of the display.
Unfortunately, there is an inherent delay of from 20 to 100
microseconds in energy-dispersive analysis systems in detecting and
identifying the X-ray emissions frm the specimen. In the case of a
slow scan SEM system this delay presents no problem, since the
horizontal sweep is very slow, typically in the order of 100
milliseconds, and the spatial resolution error of the 100
microsecond delay is only 0.1 percent. However, in the case of
television-type SEM system displays, the X-ray detection delay has
heretofore made X-ray mapping impossible. This is because in
systems of this type the horizontal sweep is typically only 63.5
microseconds, so that the horizontal spatial error resulting from
the X-ray detection delay ranges from 30 percent to 150 percent.
Since the actual delay is variable, depending on the energy of the
X-ray event, the X-ray area map of an element resulting from direct
application of a single-channel window output to the SEM system
display is spatially distorted and of no practical value.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to
provide a new and improved display system for a scanning-type
electron microscope wherein elemental identification from an
energy-dispersive X-ray analysis system is displayed in spatial
correlation to the micrographic output display of the
microscope.
It is a more specific object of the present invention to provide a
new and improved television display system for a scanning-type
electron microscope which provides an elemental area map with
reduced horizontal spatial error.
The usefulness of an energy-dispersive X-ray analysis system is
further enhanced by being able to identify and display the location
of two or more elements at one time. While it is possible to
provide more than one single-channel window to identify multiple
elements, heretofore no satisfactory means has been known for
differentiating between different elements in the SEM system
display.
Accordingly, it is another general object of the present invention
to provide a display system for a scanning-type electron microscope
which provides a simultaneous X-ray area-map of multiple
elements.
It is another more specific object of the present invention to
provide a television display system for a scanning-type electron
microscope which provides a means for correlating elements
displayed on a multiple-element area map display with those
represented on a simultaneous energy histogram display.
It is another more specific object of the present invention to
provide a television display system for a scanning-type electron
microscope wherein individual ones of multiple elements are
uniquely identified and displayed in spatial correlation to the
micrograph output display of the microscope.
Accordingly, the invention is directed to a display system for a
scanning electron microscope of the type wherein a series of X-ray
emission events are produced as a specimen is cyclically scanned by
an electron beam. The system comprises a detector for detecting the
X-ray events and producing output pulses indicative of the energy
level thereof, and means for converting at least some of the output
pulses to energy indicative information signals, the information
signals following their respective output signals by random
unpredictable time intervals. Correlation means responsive to the
information signals are provided for producing a display pulse
after a predetermined time interval following each of the output
signals. The system further includes a television monitor having a
viewing screen scanned in synchronism with the specimen, and means
are provided for applying the display pulses to the television
monitor to obtain a spatially correlated display of the X-ray
events.
The invention is further directed, in a scanning electron
microscope of the type wherein a series of X-ray emission events
are produced as a specimen is cyclically scanned by an electron
beam, to a display system comprising a detector for detecting the
X-ray events and producing output pulses indicative of the energy
level thereof, and means for converting at least some of the output
pulses to energy-indicative information signals, the information
signals following their associated events by random unpredictable
time intervals. The display system further comprises a first
single-channel window circuit for analyzing the information signals
to produce a first control effect when one of the signals falls
within limits corresponding to a first predetermined energy range,
and a second single-channel window circuit for analyzing the
information signal to produce a second control effect when one of
the signals falls within limits corresponding to a second
predetermined energy range. Further included are means including a
timer responsive to the first control effect for producing a first
display pulse and responsive to said second control pulse for
producing a second display pulse, each of the pulses being provided
after a predetermined delay period following the X-ray event
associated with the respective control effect. The display system
further comprises a television monitor having a viewing screen
scanned in synchronism with the specimen, and means for applying
the first and second display pulses to the television monitor to
obtain a spatially correlated display of the X-ray events having
energy levels within the first and second predetermined energy
ranges.
The present invention is further directed, in a scanning electron
microscope of the type wherein a series of X-ray emission events
are produced as a specimen is cyclically scanned by an electron
beam, to a display system comprising a detector for detecting the
X-ray events and producing output pulses indicative of the energy
level thereof, and means for converting at least some of the output
pulses to energy-indicative information signals, the information
signals following their associated events by random unpredictable
time intervals. The display system further comprises a color
television monitor, and an energy distribution analyzer for
developing on the television monitor from the information signals a
histogram-type display of the energy levels of the X-ray events
versus their cumulative occurrence over a period of time. Also
included are a first single channel window for analyzing the
information signals to generate a first control effect when the
signals fall within limits corresponding to a first predetermined
energy range, and means for varying the color of the histogram
display to identify that portion of the display falling within the
first predetermined energy range.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the present invention which are believed to be
novel are set forth with particularity in the appended claims. The
invention, together with further objects and advantages thereof,
may best be understood by reference to the following description
taken in connection with the accompanying drawings, in the several
figures of which like reference numerals identify like elements,
and in which:
FIG. 1 is a simplified functional block diagram of a scanning-type
electron microscope television display system constructed in
accordance with the invention to present a spatially correlated
X-ray area map;
FIG. 2 is a spectral histogram of the energy levels of X-ray events
helpful in understanding the operation of the display system of
FIG. 1;
FIG. 3 is a vertically expanded depiction of a television scanning
sequence helpful in understanding the operation of the display
system of FIG. 1;
FIG. 4 is a vertically expanded depiction of another television
scanning sequence helpful in understanding the operation of the
display system of FIG. 1;
FIG. 5 depicts an SEM system micrographic output display helpful in
understanding the operation of the display system of FIG. 1;
FIG. 6 depicts an elemental X-ray area map helpful in understanding
the operation of the display system of FIG. 1;
FIG. 7 is a simplified functional block diagram of a scanning-type
electron microscope display system constructed in accordance with
the invention to simultaneously present X-ray area maps for two
different elements;
FIG. 8 depicts a simultaneous elemental X-ray area map display for
two different elements helpful in understanding the operation of
the display system of FIG. 7; and
FIG. 9 is a spectral histogram of the energy levels of X-ray events
helpful in understanding the operation of the display system of
FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, the display system of the invention is shown
in conjunction with a scanning-type electron microscope 10 which
may be entirely conventional in design and operation. The
microscope may include an electron gun 11, an electro-magnetic
condensing lens 12, and an electro-magnetic objective lens 13 for
establishing and focusing an electron beam 14 onto the surface of a
specimen 15. Because the scanning electron microscope is intended
primarily for high resolution imaging, the electron beam is of
relatively low intensity, typically in the order of 10.sup..sup.-12
amperes, to obtain the smallest possible contact point with the
specimen. As mentioned previously, the specimen for this type of
microscope will ordinarily have a rough surface and may consist of
a plurality of tiny particles to be individually analyzed.
The electron beam 14 is caused to scan specimen 15 by means of an
electromagnetic scanning coil 16. This scanning action may be two
dimensional and like that of a television system wherein a
relatively fast horizontal scan is utilized in conjunction with a
much slower vertical scan. While the scanning rate is to some
extent a matter of choice, in the present system it is purposely
selected to be identical to the present United States standard,
namely a 15,750 Hz line scanning rate and a 60 Hz field scanning
rate. This permits conventional television monitors to be used,
singly or in parallel, to display the output of the microscope and
permits direct interface with other types of video equipment.
Scanning coil 16 is driven by scanning circuits 17, which may
include both horizontal and vertical circuits for establishing the
necessary deflection currents in coil 16. These circuits are
synchronized by means of a sync generator 18, which also has an
output for synchronizing associated output display monitors.
As the electron beam scans specimen 15 low energy secondary
electrons are given off at a rate dependent upon the electron
density of the specimen at the incident point of the beam. These
electrons are detected by a detector 19, which develops an output
signal indicative of the electron density. This signal is applied
to a high gain amplifier 20 wherein it is amplified to a level
suitable for application to video processing circuits 21. The
synchronizing output signals from sync generator 18 are combined
with the amplied detector output signal from amplifier 20 by video
processing circuits 21 to form a composite television signal. This
signal may be applied to one or more conventional television
monitors 22 to obtain an output display showing the
three-dimensional surface features of the specimen as they would
appear to the human eye at magnifications of from 20 to over 20,000
times.
Electron microscope 10 also has associated with it an X-ray
energy-dispersive analysis system for analyzing the elemental
composition of specimen 15. Data for this system is obtained by
means of X-ray detector 23 positioned adjacent to the specimen.
This detector may consist of a lithium-drifted silicon
semiconductor, which when appropriately biased develops a charge
proportional to the energy of the incident X-ray. This charge is
integrated into a current pulse by a field effect transistor (FET)
preamplifier. The silicon detector and its FET preamplifier are
cooled with liquid nitrogen from an adjacent dewar 24 to stabilize
the detector and to reduce the dark current (noise).
The signal from the preamplifier is amplified in a linear amplifier
25. The gain of this amplifier is variable but stable over extended
time periods, thereby providing a means of calibrating the system
and accommodating variations in detector efficiency. The amplified
current pulses from amplifier 25 are applied to a data gate 26,
which allows only those pulses which the system is prepared to
analyze to enter the system. That is, while the system is
processing one or more previous pulses it may not have the capacity
to process a closely following subsequent pulse, and therefore the
subsequent pulse is ignored. Since the occurrence of X-ray events,
and hence pulses, is random over any given period of time, this in
no way affects the accuracy of the final elemental analysis.
The output pulses from data gate 26 are applied one at a time to an
analog to digital converter 27 wherein each is converted to a
binary number information signal indicative of its magnitude, and
hence the energy level of the X-ray event. This information signal
is applied to an energy distribution analyzer 28, wherein it is
used in constructing an energy distribution spectrum of the
specimen. Specifically, analyzer 28 contains a memory unit having a
large number of locations each corresponding to a possible X-ray
event energy level. A number stored in each such memory location
indicates the number of X-ray events which have been received at
that energy level. By adjusting the gain of amplifier 25, the
binary number developed by converter 27 in response to an X-ray
event is made to correspond to the address of the memory location
corresponding to the energy level of the event. Then, by utilizing
the digital number from converter 27 as an address to locate a
particular memory location, and up-dating the contents of that
location by adding one count, it is possible to develop within the
memory a complete energy spectrum for the specimen being analyzed.
In practice, 400 or more such memory locations may be utilized in
developing the final energy distribution spectrum. An output from
analyzer 28 is also provided for controlling data gate 26.
If desired the information contained in the various memory
locations can be read out into a teletypewriter or into a two-axis
plotter to provide an indication of the energy spectrum of the
specimen. However, it is often desirable to provide a real-time
video display, and to this end a television display generator 29
and television monitor 30 are provided in conjunction with analyzer
28. Generator 29 systematically scans the memory locations of the
analyzer at the line scanning rate of monitor 30, and in each case
converts the stored counts of the memory locations to a
proportional field intensification on the monitor. In practice this
is facilitated by rotating the deflection yoke of monitor 30 by
90.degree. so that the slower 60 Hz field scan is horizontal and
the faster 15,750 Hz line scan is vertical. This makes the entire
525 scanning lines of the U.S. standard, now displayed vertically,
available for assignment to memory locations in analyzer 28. It
will be appreciated that when each of these lines is extended up in
proportion to the number or count stored in its corresponding
memory location, a spectral display or histogram of the energy
levels of the specimen results. A grid and additional alphanumeric
information may be provided on the display by incorporating
appropriate circuitry in generator 29.
It is often desirable to analyze a certain energy level or range of
energy levels to determine the presence of a particular element or
group of elements. To this end, the X-ray analysis system of FIG. 1
includes a single channel window 31 which can be set to recognize
and display one particular energy level, or centroid, or
alternatively a range of energy levels. It accomplishes this by
comparing an applied digital number with an internally stored
digital number, and producing an output only when the numbers agree
or are within the selected range. The stored number and the
permissible range can be set by means of switches, or can be
externally selected and retained in a portion of the memory of
analyzer 28.
The input to window 31 is alternately switched between the output
of analog to digital converter 27 and the read-out address output
of television display generator 29 by means of a multiplexer 32. It
will be recalled that analyzer 28 periodically scans the memory
locations of its core storage unit for the purpose of forming a
spectral display. In so doing, it periodically generates addresses
of these memory locations, and it is these addresses that are
applied one at a time by multiplexer 32 to window 31 during one
portion of its operating cycle. If the addresses, which correspond
to discrete energy levels, fall within the range of window 31 an
output pulse is produced. This pulse is utilized by analyzer 28 to
enhance or brighten the video signal generated by display generator
29 so that the selected window will appear as a brightened area to
the operator. It can also be used for statistical purposes, as for
example, determining the total number of pulses within the
window.
The histogram-type energy spectrum display produced on monitor 30
is shown in FIG. 2. Energy levels appear on the horizontal scale
(10 electron volts per channel) and total events (10,000 per
division) appear on the vertical scale. The window is shown as
extending over and brightening an energy peak 33. A grid 34 is
provided for operator convenience and an alphanumeric readout of
the window centroid and display scale factors is provided at the
top. In this case the window is centered at 4,510 electron volts,
an energy level corresponding to the element titanium.
During the other portion of its operating cycle, multiplexer 32
applies the digital output signals from converter 27, representing
energy-levels of occurring X-ray events, to single channel window
31, wherein they are compared with the internally stored number to
determine whether the events fall within the window limits. If they
do, an output pulse is produced by window 31 for the purpose of
producing an X-ray area map indicating the spatial distribution of
the selected element, in this case titanium, on the SEM system
display monitor 22.
However, it will be recalled that the processing time between the
actual X-ray event and the completion of the window analysis is
relatively long, in the order of 20 to 100 microseconds, so that
the output pulse of window 31, if applied directly to monitor 22,
would result in a large horizontal spatial error. Therefore, and in
accordance with one aspect of the invention, a display delay timer
35 is provided for delaying the display of the X-ray event for a
predetermined period of time equal to an integral multiple of the
duration of one line scanning period. Specifically, delay timer 35
is triggered by the leading edges of pulses passed by data gate 26.
After being so triggered, it produces an output after a
predetermined period of time, in this case two line scanning
periods, or 127 microseconds. This output is connected to one input
of an AND gate 36, the other input of which is connected to the
output of window 31. Thus, an output from AND gate 36 is possible
only if the timer has run and the analyzed X-ray event falls within
the limits of the window.
The functioning of this delay circuit can be better appreciated by
reference to FIGS. 3 and 4. In FIG. 3 two X-ray events, X.sub.1 and
X.sub.2 are shown, as they might occur during a portion of a
scanning cycle. As a result of the delay in detecting and analyzing
the X-ray events, it is seen that Y.sub.1 and Y.sub.2 displays of
X.sub.1 and X.sub.2 respectively, are laterally displaced by
substantial amounts and provide no useful correlation with the true
position of the events. In FIG. 4, the displays Y.sub.1 and Y.sub.2
have each been delayed by two horizontal scanning periods, or 127
microseconds, so that the displays fall immediately below their
X-ray event. The resulting vertical spatial error, 2 lines in 525
lines, is less than 0.5 percent and can therefore be ignored.
The output of AND gate 36 is applied to a pulse forming circuit 37
wherein a pulse of predetermined amplitude and duration is
generated for application to video processing circuits 21. A mode
select or switch 38 is provided at the input of processing circuits
21 to permit the operator to select between a micrograph display
mode and and X-ray area map mode. With the latter selection the
X-ray events which have energy levels within the limits of window
31 will be displayed on the screen as momentary bright dots
spatially aligned with their actual origin on the specimen as
displayed in the micrograph mode. Since the dots appear at random
throughout the display, it is contemplated that time lapse
photography would be utilized in recording the X-ray area map. In
practice, shutter openings of from 2 to 4 minutes have been
employed. Because of the spatial correlations made possible by the
invention, it is possible to superimpose an area map display on a
micrograph by taking a double exposure; first of one, then of the
other. It is also possible to generate a composite display by
electronically combining the two signals with appropriate additive
levels.
The SEM system output displays made possible by the invention can
better be appreciated by reference to FIGS. 5 and 6. In FIG. 5 a
micrograph is seen which displays five particles 39-43 greatly
magnified. In FIG. 6, a time-lapse photographed X-ray area map is
shown of the same five particles with the window adjusted to an
energy level corresponding to one element, say titanium. Now only
those particles composed of titanium, namely 39 and 42, appear.
This indicates to the operator that titanium is present, and what
the relative quantity and size of the titanium particles might be.
It will be appreciated that by setting other window limits, other
elements could be displayed instead, and that a simultaneous
comparison is available with the histogram display to determine the
energy level and relative concentration of the selected
element.
In accordance with another aspect of the invention, a plurality of
single channel windows is provided, the outputs of which can be
simultaneously displayed in individual identifying colors on a
single X-ray area map. Referring to FIG. 7, two single channel
windows 44 and 45 are connected to the output of multiplexer 32.
These channels simultaneously receive and process the applied
digital address, although they would normally be adjusted to have
different window centroids. The output of window 44 is connected to
one input of AND gate 46, and the output of window 45 is connected
to one input of an AND gate 47. The remaining inputs of AND gates
46 and 47 are connected to the output of display delay timer 35,
and the outputs of gates 46 and 47 are connected to respective
modulating signal inputs of a color modulator 48. A 3.58 MHz
continuous-wave color oscillator 49 is connected to the unmodulated
signal input of modulator 48.
When the energy level of a pulse processed by analog to digital
converter 27 falls within one of the two windows, an output is
produced from that window. Then, when display delay timer 35
completes its cycle and provides an enabling output, the AND gate
associated with the particular window provides an output pulse.
This pulse is applied to color modulator 48, which responds by
phase-modulating the 3.58 MHz signal from generator 49 to provide a
color subcarrier to accompany the luminance signal. The phase of
the subcarrier thus generated is individually adjustable for the
two inputs, and may be made to change automatically as the energy
centroid of the window is changed. Since the color of the X-ray
area map ultimately displayed on the SEM system output monitor
depends on the phase of the 3.58 MHz subcarrier, the output of each
window can be displayed in a different color. Modulator 48 also
includes a burst gate for periodically generating the reference
burst required during each horizontal retrace interval by U.S.
color television standards.
The output of modulator 48 is amplified by an amplifier 50 before
application to video processing circuits 51. A mode switch 52 may
be connected in series with the inputs of processing circuits 51 to
provide either a micrograph display, a multi-color X-ray area map,
or a composite micrograph and multi-color elemental area map. Video
processing circuits 51 include necessary clamping and matrixing
circuitry for combining the three input signals to form a composite
signal suitable for application to one or more standard color
monitors 53.
The effect of this arrangement can be seen in FIG. 8, which depicts
a multi-color X-ray area map. In this case window 44 is set at 4510
electron-volts, which corresponds to titanium, and window 45 is set
at 5410 electron-volts, which corresponds to the element chromium.
Again, titanium particles 39 and 42 activate the 4,510
electron-volt window, but this time they produce a colored display,
say green. Particles 40 and 41 activate the 5,410 electron-volt
window, identifying themselves as chromium and being displayed in
red. Particle 43, which is neither of these elements, would not be
displayed in the X-ray area map display and would be displayed
without color in the composite display.
The resulting display on monitor 57 comprises a histogram-type
energy spectrum display similar to that shown in FIG. 9. By
displaying the energy levels falling within a particular single
channel window in the same color as in the X-ray area map display;
e.g., green for the titanium peak 58 at 4,510 electron-volts and
red for the chromium peak 59 at 5,410 electron-volts, correlation
between the two displays is easily accomplished. As in the
previously described monochrome display, the actual energy
centroids of the single channel windows can be displayed in
alphanumerics above the graphical data.
Thus, a novel television display system for an electron microscope
has been described which permits elemental identification by means
of an X-ray area map spatially correlated to the micrographic
output of the microscope. Identification of the elemental energy
level under analysis is also made on a simultaneously presented
histogram-type energy spectral display to permit positive
identification of the element and its relative composition in the
specimen. A more advanced system has also been shown which permits
simultaneous identification of multiple windows by color coding the
electron microscope and energy distribution displays.
While particular embodiments of the invention have been shown and
described, it will be obvious to those skilled in the art that
changes and modifications may be made without departing from the
invention in its broader aspects, and, therefore, the aim in the
appended claims is to cover all such changes and modifications as
fall within the true spirit and scope of the invention.
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