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Thin films of triglycine sulfate by laser evaporation
Mat. Res. Bull. Vol. 9, pp. 14Z7-1434, Printed in the United States.
1974.
Pergamon
Press, Inc.
THIN FILMS OF TRIGLYCINE SULFATE BY LASER EVAPORATION
A. W. Stephens, T. J. Zrebiec, and V. S. Ban RCA Laboratories, Princeton, New Jersey 08540
(Received August 28, 1974; Communicated by J. J. Tietjen)
ABSTRACT Thin films of triglycine sulfate were prepared by laser evaporation. The properties of these films were evaluated by electrical measurements, x-ray diffraction and IR spectrometry. The deposited material was found to be essentially triglycine sulfate with some glycine present as a decomposition product. The deposited material was also found to be highly oriented with the pyroelectric direction lying in the plane of the film.
Introduction Triglycine sulfate,
(NH2CH2COOH)3H2S04,
organic ferroelectric material (1,2).
is a well known and studied
This material possesses a high pyro-
electric coefficient and as a result has been a very useful material for pyroelectric infrared detectors. To obtain maximum performance, as an infrared detector, it is necessary that the triglycine sulfate (TGS) be prepared in the form of a wafer some i0 ~m in thickness.
Single crystal TGS is very brittle and cleaves with
ease, thus making the fabrication of thin detector elements of large area (greater than i cm 2) extremely difficult. TGS decomposes at 230°C and does not lend itself to conventional evaporation techniques.
Growth of thin film layers of single crystal material is
also not practical. It has been found that TGS can be successfully evaporated by laser radiation under high vacuum.
Thin films of TGS can be deposited on a substrate
with thickness varying from 0.i to 50 ~m or thicker.
This paper will describe
the method of laser evaporation and the properties of the laser evaporated films. 1427
14Z8
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
I0
Experimental Procedure The laser evaporation system is shown in Fig.
i.
The CO 2 laser is a
laboratory built unit consisting of a 2-1/2 meter cavity with external mirrors.
The tube is continuously pumped and is operated at partial
pressures of 2.2 torr N2, 2.1 torr C02 and 3.5 tort He.
The laser output
is approximately 40 watts cw.
LASER
J
irv~'~R R O R
ROTOR
CO 2
\
NeC~
I
I
-
I
LENS I L,L".
I
VACUUM CHAMBER ALUMINUM BELL JAR '~ I O - 7 T O R R .
•
FIG.
I
I
I
~
~o R
TARGET
I
Diagram of Laser Evaporation Apparatus. The laser beam is deflected
in an x-y scan by means of a movable mirror.
A sodium chloride lens focuses the beam on the target, the spot size on the target being approximately
i ~m in diameter.
The target and substrates are
located in a vacuum chamber which can be evacuated to 10 -7 torr.
The focused
laser beam enters the chamber through a sodium chloride window and strikes the target at a 45 ° angle.
Substrate
to target distance is maintained at 8 cm.
The targets of TGS were prepared by grinding the material into a fine powder and then pressing it into disks 3/4 inch in diameter and 1/4 inch thick, using a Pressure of 45,000 psi.
Attempts
to evaporate from single crystal
targets of TGS resulted in fracture of the target and severe spalling of the crystal surface. The films were evaporated on glass microscope cover slides 18 mm square and 0.22 n~n thick (see Fig. 2).
Four 1.6 mm square metal electrode pads
were evaporated for the bottom electrodes.
A common top electrode,
13 ram in
diameter, was then evaporated over the laser deposited TGS, giving four test elements per sample.
V o l . 9, No.
10
VAPOR EVAPORATED
BOTTOM
-
ELECTRODE
14Z9
F-I
_~4111F
L_J
"S"TSLIGDEGLASS --2' ' II
TRIGLYCLNE SULFATE
:
L_J
TOP COMMON
-- ql /--'---'] ELECTRoDEBOTToMELECTRODE CONTACT
FIG. 2 Detail of Sample Substrate. Glass Slide Dimensions are 18 m x 18 m x 0.22 ~m Thick. Bottom Electrodes have an Area of 0.16 cm 2. TGS evaporations at 10.6 ~m.
respectively.
Pulse repetition
rate was six pulses per
The pulse shape of the laser output was examined with a pyroelectric
detector
and found to be essentially
Specimens fr~
the C02 laser in a pulsed mode emitting
The pulse duration was 0.266 or 0.533 sec for a pulse energy of
i0 and 23 joules, min.
were made using
a square wave.
were poled at 60°C for 2 hrs.
50 to 200 kV/cm.
under an applied
The field was maintained
during
field ranging
slow cooling to room
temperature. The pyroelectric by Byer and Roundy dT/dt
coefficient
(3):
(T = temperature;
was measured
the ~ j o r
modification
t = time) constant
we cycle + 3°C about a mean
temperature
during both heating and cooling.
by means
of a thertnoelectric
supply.
419A microamp meter. by a t h e ~ i s t o r dual channel
Capacitance Radio
and
Resistivity operating voltage
brid~e,
the current.
of time
with three
The
by a temperature
were made using a Hewlett-Packard unit was monitored
and current were plotted on a (see Fig. 3). were obtained
terminal
using a General
connections,
operating
were made at 27°C.
measurements
in the fast mode,
source.
temperature
loss tangent measurements
Measurements
cycling was accomplished
of the t h e ~ o e l e c t r i c
Temperature
as functions
1615-A Capacitance
at 1 kHz.
Temperature
Current measurements
bridge circuit.
recorder
that instead of holding
unit with a timer to reverse
The temperature
to that used
over a wide range of temperatures,
junction was held at constant
regulated water
being
similar
of 27°C with dT/dt being almost
constant
thermoelectric
by a method
were made using a Keithley
as an ampmeter
Sample connections
in conjunction
610C electrometer, with an external
are made so that the leakage resistance
1430
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol.
9, N o .
10
(.} m
+50
r~
tu° z N ~ w oe¢ >. o
O I K
-60
' I'O' : : : ' 1 .... ' , . . . . .
32 -
ill mi, n, ',,,
::
',l
~min : ', I I
Ill:',
TIM E
w
e¢ o IE w
I-
22-
FIG. 3
Plot of Pyroelectric Current and Temperature as a Function of Time for Laser-Evaporated Triglycine Sulfate. of the leads was cancelled out. Results and Discussion X-ray diffraction data show that the laser evaporated TGS is crystalline and has a structure identical to that of the starting material. of several additional
The presence
lines in the laser evaporated material, however,
that there is some decomposition occurring during laser evaporation.
indicates It was
possible to identify the second phase as glycine. Diffractometer traces taken of material deposited on glass substrates showed a high degree of preferred orientation. was found to be deposited
The laser evaporated material
in a highly textured manner.
The greatly reduced
intensity of the (040) reflection (which is the strong reflection in a randomly oriented sample) axis
indicates that very little material is oriented with the b
(pyroelectric direction)
perpendicular to the plane of the sheet.
Most
of the material seems to be oriented with the c axis in the plane of the sheet and the a axis perpendicular to the plane of the sheet. The electrical properties are given in Table I. agreement with published values coefficient.
Values are in good
(1,4,5), with the exception of the pyroelectric
The greatly reduced value of the pyroelectric coefficient is
due to the high degree of preferred orientation which is present in the laser deposited film.
The lower values of dielectric constant are also consistent
with the orientation of the film since the values of ~/~
in the a and c O
directions are i0 and 7, respectively. The infrared spectrum of laser evaporated TGS (Fig. 4) shows the presence of at least two phases, glycine and TGS.
A comparison of the IR spectra of
Vol. 9, No.
VAPOR
i0
EVAPORATED
TRIGLYCINE
SULFATE
1431
TABLE 1 Properties of Laser Evaporated TGS Laser Evaporated TGS Pyroelectric Coefficient (coul/cm 2 OK)
5.5 x i0
Dielectric Constant Resistivity
-i0
30 1013
(ohm-cm)
Curie Temperature
48
Single Crystal TGS
Polycrystalline TGS
3 x 10 -8
1.5 x 10 -8
40 1012 _ 1013
27
47
the starting material with that of the laser evaporated material shows dif-i ferences in the band structure at 3180, 2120, 1335, 1130, and 910 cm These differences are all due to absorption modes associated with glycine. The amount of glycine can be estimated at about 10%.
Infrared data also
confirmed that the glycine in laser evaporated TGS is not due to thermal decomposition.
Step-wise heating of TGS produced broadened and distorted
bands, due to thermal decomposition, without producing bands characteristic of glycine. The exact mechanism of laser evaporation is not presently completely understood.
Laser evaporation using Q switched lasers causes very rapid
heating as a result of the high power density of the beam (6), 108 ~o 1012 watts/cm 2.
The boiling point of the material is believed to be reached in
approximately
10 -7 sec or less.
However, only a very small region is heated
and therefore, very large thermal gradients exist. completely vaporized,
leaving a crater.
The heated material is
The vapor escapes in the form of a
plume with velocities of 105 to 107 cm/sec, exerting recoil pressures of 103 to 105 atm (7). The C02 laser used in these experiments was operated in a pulsed mode with pulse lengths of 0.266 and 0.533 sec duration, 4 kW/cm 2.
for a power density of
TGS is highly absorbing at 10.6 ~m (see Fig. 4) and the thermal
conductivity is low (6.8 x 10 -3 joules/cm-sec OK).
These two factors aid
in the vaporization of TGS although the power density is low.
The high power
densities and temperatures obtained in Q switched lasers are not reached in this case, but the power absorbed is sufficient to vaporize TGS along with decomposition and some expulsion of solid material.
The exact form in
which the material is transported is not presently known.
It is suspected
that the TGS is vaporized and transported as the molecular species. It has been shown that large organic salt molecules can be laser
143Z
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
i0
evaporated without fragmentation (8). A thickness distribution profile of the laser evaporated film is given in Fig. 5.
The thickness was found to obey a cos 6 @ relationship instead
WAVELENGTH,~m
ZO
8.0
I0
9.0
12
14
16 18 20
25 30
40 50
T G S STARTING MATERIAL ON Si 1
NH IN PLANE DEFORMATION/III,II~
,...,(LASERTGsoNEVAPORATEDsi SULFATE
L/ GLYCINE
SULFATE v I
[
CH 2 WAG SULFATE v 5 (not present in TGS) 1 I I
1600
1400
1200
I000
SI
I 800
600
400
200
WAVENUMBER (cm -I) FIG. 4
IR Spectra of Laser-Evaporated Triglycine Sulfate Compared with Starting Material. DISTANCE
I0
I
2
I
I
,,,,.4
~.
•
%%
9 S
E
:L cO CO w Z Y 0
( Cm ) 3
4 I
i
EXPERIMENTAL
POINTS %%
oS o % o ok
5 I
%%~ % o
-----%
T=TO COS6 8 NORMAL COSINE DISTRIBUTION
FIG. 5 6
Thickness Distribution Profile for Laser Evaporated Triglycine Sulfate.
4 3 2
-X o ;\°
\
\ \
TI"X-
~TT
o
Vol.
9, N o .
I0
VAPOR
EVAPORATED
of the usual cos @ law encountered TGS is evaporated,
TRIGLYCINE
SULFATE
1433
in other types of evaporations.
When the
a large volume of material is removed forming a deep
crater with steep sides.
The shape of the cavity is more than likely respon-
sible for the higher power cosine function since the walls of the cavity tend to direct the evaporated material. The film quality of laser evaporated TGS is quite variable.
Approxi-
mately 10% of the TGS is deposited as glycine and free sulfuric acid. shows a scanning electron micro~raph of laser evaporated TGS.
Fig. 6
The crater-
like protuberances are thought to be caused by the reaction of the sulfuric acid with the al~ninum top electrode.
Considerable reaction does occur between
the aluminum electrodes and the acid present.
The aluminum electrodes
(approxi
mately i000~ thick) have been found to be completely dissolved when allowed to stand for a period of several weeks.
Exposure to a moist atmosphere also
causes considerable degradation of the sample.
FIG. 6 Scanning Electron Microscope Micrograph of Laser Evaporated Triglycine Sulfate, 500X Magnification. Conclusions It was found possible to fabricate thin films of triglycine sulfate by laser evaporation.
The electrical properties of the evaporated films were
found to be very similar to bulk material.
IR spectra of the evaporated
1434
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
material indicated that there was some decomposition and that glycine was deposited along with the triglycine sulfate. X-ray diffraction data confirmed that the laser deposited film was highly oriented.
The orientation was such that the pyroelectric direction
lay in the plane of the film.
As a result of this preferential orientation,
the pyroelectric coefficient of the film (measured normal to the film plane) was much smaller than that obtained from single crystal material. Acknowledgments We are most grateful to R. T. Smith and R. J. Paff for x-ray diffraction results, P. J. Zanzucchi and D. A. Kramer for IR spectroscopy, and D. Riehman for his continued interest and encouragement. References I.
B. T. Matthias, C. E. Miller, and J' P. Remeika, Phys. Rev. 104, 849 (1956).
2.
E. A. Wood and A. N. Holden, Acta C~yst. iO, 145 (1975).
3.
R. L. Byer and C. B. Roundy, Ferroelectrics ~, 333 (1972).
4.
S. Hoshino, T. Mitsui, F. Jona, and R. Pepinsky, Phys. Rev. I07, 1255 (1956).
5.
E. H. Putley, Semiconductors & Semimetals, Vol. 5, 260 (Academic Press, New York, 1970).
6.
J.F.
7.
V. S. Ban and B. E. Knox, Int. J. of Mass Spectrum. and Ion Phys. ~, 131 (1969).
8.
F. J. Vastola, A. J. Pirone and R. O. Mumma, Proc. 16th Annual Conf. on Mass Spec. and Allied Topics, ASTM Committee E-14, Pittsburgh, Pa., 300 (1968).
Ready, J. Appl. Phys. 36, 462 (1965).
i0
1974.
Pergamon
Press, Inc.
THIN FILMS OF TRIGLYCINE SULFATE BY LASER EVAPORATION
A. W. Stephens, T. J. Zrebiec, and V. S. Ban RCA Laboratories, Princeton, New Jersey 08540
(Received August 28, 1974; Communicated by J. J. Tietjen)
ABSTRACT Thin films of triglycine sulfate were prepared by laser evaporation. The properties of these films were evaluated by electrical measurements, x-ray diffraction and IR spectrometry. The deposited material was found to be essentially triglycine sulfate with some glycine present as a decomposition product. The deposited material was also found to be highly oriented with the pyroelectric direction lying in the plane of the film.
Introduction Triglycine sulfate,
(NH2CH2COOH)3H2S04,
organic ferroelectric material (1,2).
is a well known and studied
This material possesses a high pyro-
electric coefficient and as a result has been a very useful material for pyroelectric infrared detectors. To obtain maximum performance, as an infrared detector, it is necessary that the triglycine sulfate (TGS) be prepared in the form of a wafer some i0 ~m in thickness.
Single crystal TGS is very brittle and cleaves with
ease, thus making the fabrication of thin detector elements of large area (greater than i cm 2) extremely difficult. TGS decomposes at 230°C and does not lend itself to conventional evaporation techniques.
Growth of thin film layers of single crystal material is
also not practical. It has been found that TGS can be successfully evaporated by laser radiation under high vacuum.
Thin films of TGS can be deposited on a substrate
with thickness varying from 0.i to 50 ~m or thicker.
This paper will describe
the method of laser evaporation and the properties of the laser evaporated films. 1427
14Z8
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
I0
Experimental Procedure The laser evaporation system is shown in Fig.
i.
The CO 2 laser is a
laboratory built unit consisting of a 2-1/2 meter cavity with external mirrors.
The tube is continuously pumped and is operated at partial
pressures of 2.2 torr N2, 2.1 torr C02 and 3.5 tort He.
The laser output
is approximately 40 watts cw.
LASER
J
irv~'~R R O R
ROTOR
CO 2
\
NeC~
I
I
-
I
LENS I L,L".
I
VACUUM CHAMBER ALUMINUM BELL JAR '~ I O - 7 T O R R .
•
FIG.
I
I
I
~
~o R
TARGET
I
Diagram of Laser Evaporation Apparatus. The laser beam is deflected
in an x-y scan by means of a movable mirror.
A sodium chloride lens focuses the beam on the target, the spot size on the target being approximately
i ~m in diameter.
The target and substrates are
located in a vacuum chamber which can be evacuated to 10 -7 torr.
The focused
laser beam enters the chamber through a sodium chloride window and strikes the target at a 45 ° angle.
Substrate
to target distance is maintained at 8 cm.
The targets of TGS were prepared by grinding the material into a fine powder and then pressing it into disks 3/4 inch in diameter and 1/4 inch thick, using a Pressure of 45,000 psi.
Attempts
to evaporate from single crystal
targets of TGS resulted in fracture of the target and severe spalling of the crystal surface. The films were evaporated on glass microscope cover slides 18 mm square and 0.22 n~n thick (see Fig. 2).
Four 1.6 mm square metal electrode pads
were evaporated for the bottom electrodes.
A common top electrode,
13 ram in
diameter, was then evaporated over the laser deposited TGS, giving four test elements per sample.
V o l . 9, No.
10
VAPOR EVAPORATED
BOTTOM
-
ELECTRODE
14Z9
F-I
_~4111F
L_J
"S"TSLIGDEGLASS --2' ' II
TRIGLYCLNE SULFATE
:
L_J
TOP COMMON
-- ql /--'---'] ELECTRoDEBOTToMELECTRODE CONTACT
FIG. 2 Detail of Sample Substrate. Glass Slide Dimensions are 18 m x 18 m x 0.22 ~m Thick. Bottom Electrodes have an Area of 0.16 cm 2. TGS evaporations at 10.6 ~m.
respectively.
Pulse repetition
rate was six pulses per
The pulse shape of the laser output was examined with a pyroelectric
detector
and found to be essentially
Specimens fr~
the C02 laser in a pulsed mode emitting
The pulse duration was 0.266 or 0.533 sec for a pulse energy of
i0 and 23 joules, min.
were made using
a square wave.
were poled at 60°C for 2 hrs.
50 to 200 kV/cm.
under an applied
The field was maintained
during
field ranging
slow cooling to room
temperature. The pyroelectric by Byer and Roundy dT/dt
coefficient
(3):
(T = temperature;
was measured
the ~ j o r
modification
t = time) constant
we cycle + 3°C about a mean
temperature
during both heating and cooling.
by means
of a thertnoelectric
supply.
419A microamp meter. by a t h e ~ i s t o r dual channel
Capacitance Radio
and
Resistivity operating voltage
brid~e,
the current.
of time
with three
The
by a temperature
were made using a Hewlett-Packard unit was monitored
and current were plotted on a (see Fig. 3). were obtained
terminal
using a General
connections,
operating
were made at 27°C.
measurements
in the fast mode,
source.
temperature
loss tangent measurements
Measurements
cycling was accomplished
of the t h e ~ o e l e c t r i c
Temperature
as functions
1615-A Capacitance
at 1 kHz.
Temperature
Current measurements
bridge circuit.
recorder
that instead of holding
unit with a timer to reverse
The temperature
to that used
over a wide range of temperatures,
junction was held at constant
regulated water
being
similar
of 27°C with dT/dt being almost
constant
thermoelectric
by a method
were made using a Keithley
as an ampmeter
Sample connections
in conjunction
610C electrometer, with an external
are made so that the leakage resistance
1430
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol.
9, N o .
10
(.} m
+50
r~
tu° z N ~ w oe¢ >. o
O I K
-60
' I'O' : : : ' 1 .... ' , . . . . .
32 -
ill mi, n, ',,,
::
',l
~min : ', I I
Ill:',
TIM E
w
e¢ o IE w
I-
22-
FIG. 3
Plot of Pyroelectric Current and Temperature as a Function of Time for Laser-Evaporated Triglycine Sulfate. of the leads was cancelled out. Results and Discussion X-ray diffraction data show that the laser evaporated TGS is crystalline and has a structure identical to that of the starting material. of several additional
The presence
lines in the laser evaporated material, however,
that there is some decomposition occurring during laser evaporation.
indicates It was
possible to identify the second phase as glycine. Diffractometer traces taken of material deposited on glass substrates showed a high degree of preferred orientation. was found to be deposited
The laser evaporated material
in a highly textured manner.
The greatly reduced
intensity of the (040) reflection (which is the strong reflection in a randomly oriented sample) axis
indicates that very little material is oriented with the b
(pyroelectric direction)
perpendicular to the plane of the sheet.
Most
of the material seems to be oriented with the c axis in the plane of the sheet and the a axis perpendicular to the plane of the sheet. The electrical properties are given in Table I. agreement with published values coefficient.
Values are in good
(1,4,5), with the exception of the pyroelectric
The greatly reduced value of the pyroelectric coefficient is
due to the high degree of preferred orientation which is present in the laser deposited film.
The lower values of dielectric constant are also consistent
with the orientation of the film since the values of ~/~
in the a and c O
directions are i0 and 7, respectively. The infrared spectrum of laser evaporated TGS (Fig. 4) shows the presence of at least two phases, glycine and TGS.
A comparison of the IR spectra of
Vol. 9, No.
VAPOR
i0
EVAPORATED
TRIGLYCINE
SULFATE
1431
TABLE 1 Properties of Laser Evaporated TGS Laser Evaporated TGS Pyroelectric Coefficient (coul/cm 2 OK)
5.5 x i0
Dielectric Constant Resistivity
-i0
30 1013
(ohm-cm)
Curie Temperature
48
Single Crystal TGS
Polycrystalline TGS
3 x 10 -8
1.5 x 10 -8
40 1012 _ 1013
27
47
the starting material with that of the laser evaporated material shows dif-i ferences in the band structure at 3180, 2120, 1335, 1130, and 910 cm These differences are all due to absorption modes associated with glycine. The amount of glycine can be estimated at about 10%.
Infrared data also
confirmed that the glycine in laser evaporated TGS is not due to thermal decomposition.
Step-wise heating of TGS produced broadened and distorted
bands, due to thermal decomposition, without producing bands characteristic of glycine. The exact mechanism of laser evaporation is not presently completely understood.
Laser evaporation using Q switched lasers causes very rapid
heating as a result of the high power density of the beam (6), 108 ~o 1012 watts/cm 2.
The boiling point of the material is believed to be reached in
approximately
10 -7 sec or less.
However, only a very small region is heated
and therefore, very large thermal gradients exist. completely vaporized,
leaving a crater.
The heated material is
The vapor escapes in the form of a
plume with velocities of 105 to 107 cm/sec, exerting recoil pressures of 103 to 105 atm (7). The C02 laser used in these experiments was operated in a pulsed mode with pulse lengths of 0.266 and 0.533 sec duration, 4 kW/cm 2.
for a power density of
TGS is highly absorbing at 10.6 ~m (see Fig. 4) and the thermal
conductivity is low (6.8 x 10 -3 joules/cm-sec OK).
These two factors aid
in the vaporization of TGS although the power density is low.
The high power
densities and temperatures obtained in Q switched lasers are not reached in this case, but the power absorbed is sufficient to vaporize TGS along with decomposition and some expulsion of solid material.
The exact form in
which the material is transported is not presently known.
It is suspected
that the TGS is vaporized and transported as the molecular species. It has been shown that large organic salt molecules can be laser
143Z
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
i0
evaporated without fragmentation (8). A thickness distribution profile of the laser evaporated film is given in Fig. 5.
The thickness was found to obey a cos 6 @ relationship instead
WAVELENGTH,~m
ZO
8.0
I0
9.0
12
14
16 18 20
25 30
40 50
T G S STARTING MATERIAL ON Si 1
NH IN PLANE DEFORMATION/III,II~
,...,(LASERTGsoNEVAPORATEDsi SULFATE
L/ GLYCINE
SULFATE v I
[
CH 2 WAG SULFATE v 5 (not present in TGS) 1 I I
1600
1400
1200
I000
SI
I 800
600
400
200
WAVENUMBER (cm -I) FIG. 4
IR Spectra of Laser-Evaporated Triglycine Sulfate Compared with Starting Material. DISTANCE
I0
I
2
I
I
,,,,.4
~.
•
%%
9 S
E
:L cO CO w Z Y 0
( Cm ) 3
4 I
i
EXPERIMENTAL
POINTS %%
oS o % o ok
5 I
%%~ % o
-----%
T=TO COS6 8 NORMAL COSINE DISTRIBUTION
FIG. 5 6
Thickness Distribution Profile for Laser Evaporated Triglycine Sulfate.
4 3 2
-X o ;\°
\
\ \
TI"X-
~TT
o
Vol.
9, N o .
I0
VAPOR
EVAPORATED
of the usual cos @ law encountered TGS is evaporated,
TRIGLYCINE
SULFATE
1433
in other types of evaporations.
When the
a large volume of material is removed forming a deep
crater with steep sides.
The shape of the cavity is more than likely respon-
sible for the higher power cosine function since the walls of the cavity tend to direct the evaporated material. The film quality of laser evaporated TGS is quite variable.
Approxi-
mately 10% of the TGS is deposited as glycine and free sulfuric acid. shows a scanning electron micro~raph of laser evaporated TGS.
Fig. 6
The crater-
like protuberances are thought to be caused by the reaction of the sulfuric acid with the al~ninum top electrode.
Considerable reaction does occur between
the aluminum electrodes and the acid present.
The aluminum electrodes
(approxi
mately i000~ thick) have been found to be completely dissolved when allowed to stand for a period of several weeks.
Exposure to a moist atmosphere also
causes considerable degradation of the sample.
FIG. 6 Scanning Electron Microscope Micrograph of Laser Evaporated Triglycine Sulfate, 500X Magnification. Conclusions It was found possible to fabricate thin films of triglycine sulfate by laser evaporation.
The electrical properties of the evaporated films were
found to be very similar to bulk material.
IR spectra of the evaporated
1434
VAPOR
EVAPORATED
TRIGLYCINE
SULFATE
Vol. 9, No.
material indicated that there was some decomposition and that glycine was deposited along with the triglycine sulfate. X-ray diffraction data confirmed that the laser deposited film was highly oriented.
The orientation was such that the pyroelectric direction
lay in the plane of the film.
As a result of this preferential orientation,
the pyroelectric coefficient of the film (measured normal to the film plane) was much smaller than that obtained from single crystal material. Acknowledgments We are most grateful to R. T. Smith and R. J. Paff for x-ray diffraction results, P. J. Zanzucchi and D. A. Kramer for IR spectroscopy, and D. Riehman for his continued interest and encouragement. References I.
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