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nz.sbnd;dependence of superconducting properties in Bi2Sr2Can−1CunOy thin films prepared by in-situ MBE technique
PHYSiCA
Physica C 185-189 (1991) 2011-2012 North-Holland
n - D E P E N D E N C E OF S U P E R C O N D U C T I N G P R O P E R T I E S IN BijSr~.Ca~_iCu~O~ T H I N FILMS P R E P A R E D B Y I N - $ I T U M B E T E C H N I Q U E I. T S U K A D A , H. W A T A N A B E , I. T E R A S A K I , A. M A E D A and K. U C H I N O K U R A Department of Applied Physics, The University of Tokyo, 7-3.1 Hongo, Bunkyo.kn, Tokyo I15, Japan. Thin films of BbSrjCa,~_lCu,~O~ (n = 1 .,~ 4) grown with a sequential deposition technique in properties, Hall coefficient and electron energy spectra were systematically changed from n = l
were prepared in sitn by molecular beam epitaxy. All films were an identical condition. To investigate the n dependence of physical loss spectroscopy were measured. Hall coefficient and energy loss to 3, but the results of the n=4 phase showed different behavior.
In BijSrjCan_lCu~Oy compounds, the number of
and 75 K for the n = l , 2, 3 and 4 phases, respectively.
CuO~ layers in a primitive cell (represented by n)
The normal state resistivities are low and comparable
mainly determines superconducting properties. Recent
to those of single crystals.
progress in thin film processing technique allows us to prepare in situ the metastable phases with n > 4.1
In BijSrjCa~_xCu,~Oy
compounds,
the mecha-
nism of doping holes is not so obvious as that of
To investigate the n dependence in Bi2 SrjCa,~_ 1Cu,~O~
(La, Sr)jCuO4 or YBajCusOr-s, but the excess oxy-
crystals, it is required that the samples are prepared in
gen plays an important role as a charge reservoir. ~,3
the same oxidizing conditions. Superconducting prop-
Hall coefficient provides us useful information about
erties of high-T~ cuprates are very sensitive to the oxy-
charge carriers.
Figure 2 shows the temperature de-
gen partial pressure during growth. Thin film process-
pendence of the Hall coefficient of the n = 1 ~ 4 phase
ing technique has an advantage of the precise control of
films. The measurement is carried out by an ordinary
the oxidizing conditions.
six-probe method under 1.8-T magnetic field parallel
In
this
paper
we
report
the
preparation
of
to the c axis.
RH values in the temperature range
BijSrjCan_lCunO~ superconductors with n up to 4. Hall coefficient (R//) and electron energy loss spec-
2.0
,
,
,
,
,
16.0
I
...." ...." L#,"
troscopy (EELS) were measured and the results are discussed. o 1.5-
The preparation technique of the n = 1 ~ 4 phases is the same as the previously reported one. 1 All films were prepared in situ by modified molecular beam epitaxy machine with pure ozone gas. The substrate tempera-
........
~
- ~ - - W - | .,.~...'"
~
.,
y.''"" --
~1.0 ~.~ ~.
.. ... ,-
..." ......
o,¢" .¢e,z
3 . 0 " " ~'b
,/ .... ...."
ture was kept around 780°C . The ozone pressure was kept around 2
x
i 0 °r'3
Pa during deposition, and ~'" LIiiS
O.
"~ "~"
1.:3
pressure was also kept until the substrate was cooled down to 235 ° C. Films were prepared in the same conditions except for the deposition sequence of each molecular beams.
!
0
Figure 1 shows the temperature dependence of the resistivity of the n=i ~ 4 phase films in an as-grown state. All films show superconductivity beloi~ 7, 65, 71
I
I
.
0
100 200 300 Temperature (K)
FIGUR]~ 1 The temperature dependence of the resistivity of the n = 1 ~ 4 phase films.
0921-4534/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserve0.
L T~,kad, et al / n-Dependence of s~emonducting properaes in Bi2$r2Ca..zCu.Oy thin films
2012
4.0 I
I
I
I
!
I
EELS Ep-lO00 eV 600
g
3.0
....
~,600
,~400
~m
.2 2.0 .m,
.~
"'.::".:
,
~-oo
t,d
= a
1.0
n=4]'<'-,..-"'--i "'~'-q
m
~200 "1
0(n=4) (n=3)0
0.0 0
I
!
!
100
200
300
FIGURE
2
The temperature dependence of the Hall coefficient of the n = 1 ~ 4 phase films. of 100 ~ 5G0 K increase with increasing , up to 3,
O(n=2)
,oo
("=')°0
Temperature (K)
100 I
I
I
I
!
10 2'0 3'0 Energy (eV)
4O
FIGURE 3 Electron energy loss spectra of the n = 1 ~ 4 phase films.
which suggests that the carrier density in the unit cell decreases. In this experiment, oxidized state is thought
crystal structures. The spectrum of the n=4 phase is
to be the same in all samples because of the prepara-
quite similar to that of the n=3 phase. It is, however,
tion in the same oxidizing conditions. Thus the above
not clear whether the n=4 phase has the same elec-
results suggest that the definite numbers of holes are
tronic structure as that of the n=3 phase, because the
distributed to n sheets of Cue2 layers, and as a re-
energy of the primary electron is relatively weak and
sult the cattier density decreases.
the probing depth is not sufficiently long to detect the
Hall coefficient of
the n=4 phase, however, shows quite different behav-
difference between the n=3 and 4 phases.
ior. RH value of the n=4 phase is quite low, which can-
In summary we prepared the superconducting
not be explained in the extrapolation from the n <_ 3
Bi2Sr2Ca,_tCu, Ot ( n = l ~, 4) thin films in zitu by
phases.
Such a low value has not been observed in
molecular beam epitaxy. Hall coefficient and electron
Bi=Sr2C~_xCu,~O~ compounds before. The origin of the low value is not evident, and further experiments are requited.
energy loss spectroscopy were measured. The system-
To investigate the electronic structures, EELS were
films. The behavior of the n=4 phase film cannot be explained in the extrapolation from the n _< 3 phases.
also measured. The energy of the primary electron is 1000 eV. The observed spectra, shown in Fig. 3, are obtained in a reflection mode, where because of a short
atic change of Hall coefficient and the the electron energy loss spectra were observed in the n = 1 ~., 3 phase
REFERENCES
probing depth the spectra for thin films should be equivalent to those for single crystals . The spectra of the
n=l and 2 phases are the same as those of the bulk single-crystal samples. 4 In the spectra of the n=2 and 3 phases, the peak due to Ca is only observed as the intra-atomic transition (C), which supports the oxygen vacancy in the Ca layer. Thus the obtained spectra of the films are consistent with the electronic structures of the n = 1 ~ 3 phases expected from their
1. I. Tsukada and K. Uchinokura, Jpn. J. Appl. Phys. 30 (1991) Lll14. 2. G. Briceno and A. Zettl, Phys. Rev. B 40 (1989) 11354. 3. T. Ishida and T. Sakuma, Physica C 167 (1990) 258. 4. I. Terasaki e~ M., Supercond.
(1991) S397.
Sci.
Technol.
4
Physica C 185-189 (1991) 2011-2012 North-Holland
n - D E P E N D E N C E OF S U P E R C O N D U C T I N G P R O P E R T I E S IN BijSr~.Ca~_iCu~O~ T H I N FILMS P R E P A R E D B Y I N - $ I T U M B E T E C H N I Q U E I. T S U K A D A , H. W A T A N A B E , I. T E R A S A K I , A. M A E D A and K. U C H I N O K U R A Department of Applied Physics, The University of Tokyo, 7-3.1 Hongo, Bunkyo.kn, Tokyo I15, Japan. Thin films of BbSrjCa,~_lCu,~O~ (n = 1 .,~ 4) grown with a sequential deposition technique in properties, Hall coefficient and electron energy spectra were systematically changed from n = l
were prepared in sitn by molecular beam epitaxy. All films were an identical condition. To investigate the n dependence of physical loss spectroscopy were measured. Hall coefficient and energy loss to 3, but the results of the n=4 phase showed different behavior.
In BijSrjCan_lCu~Oy compounds, the number of
and 75 K for the n = l , 2, 3 and 4 phases, respectively.
CuO~ layers in a primitive cell (represented by n)
The normal state resistivities are low and comparable
mainly determines superconducting properties. Recent
to those of single crystals.
progress in thin film processing technique allows us to prepare in situ the metastable phases with n > 4.1
In BijSrjCa~_xCu,~Oy
compounds,
the mecha-
nism of doping holes is not so obvious as that of
To investigate the n dependence in Bi2 SrjCa,~_ 1Cu,~O~
(La, Sr)jCuO4 or YBajCusOr-s, but the excess oxy-
crystals, it is required that the samples are prepared in
gen plays an important role as a charge reservoir. ~,3
the same oxidizing conditions. Superconducting prop-
Hall coefficient provides us useful information about
erties of high-T~ cuprates are very sensitive to the oxy-
charge carriers.
Figure 2 shows the temperature de-
gen partial pressure during growth. Thin film process-
pendence of the Hall coefficient of the n = 1 ~ 4 phase
ing technique has an advantage of the precise control of
films. The measurement is carried out by an ordinary
the oxidizing conditions.
six-probe method under 1.8-T magnetic field parallel
In
this
paper
we
report
the
preparation
of
to the c axis.
RH values in the temperature range
BijSrjCan_lCunO~ superconductors with n up to 4. Hall coefficient (R//) and electron energy loss spec-
2.0
,
,
,
,
,
16.0
I
...." ...." L#,"
troscopy (EELS) were measured and the results are discussed. o 1.5-
The preparation technique of the n = 1 ~ 4 phases is the same as the previously reported one. 1 All films were prepared in situ by modified molecular beam epitaxy machine with pure ozone gas. The substrate tempera-
........
~
- ~ - - W - | .,.~...'"
~
.,
y.''"" --
~1.0 ~.~ ~.
.. ... ,-
..." ......
o,¢" .¢e,z
3 . 0 " " ~'b
,/ .... ...."
ture was kept around 780°C . The ozone pressure was kept around 2
x
i 0 °r'3
Pa during deposition, and ~'" LIiiS
O.
"~ "~"
1.:3
pressure was also kept until the substrate was cooled down to 235 ° C. Films were prepared in the same conditions except for the deposition sequence of each molecular beams.
!
0
Figure 1 shows the temperature dependence of the resistivity of the n=i ~ 4 phase films in an as-grown state. All films show superconductivity beloi~ 7, 65, 71
I
I
.
0
100 200 300 Temperature (K)
FIGUR]~ 1 The temperature dependence of the resistivity of the n = 1 ~ 4 phase films.
0921-4534/91/$03.50 © 1991 - Elsevier Science Publishers B.V. All rights reserve0.
L T~,kad, et al / n-Dependence of s~emonducting properaes in Bi2$r2Ca..zCu.Oy thin films
2012
4.0 I
I
I
I
!
I
EELS Ep-lO00 eV 600
g
3.0
....
~,600
,~400
~m
.2 2.0 .m,
.~
"'.::".:
,
~-oo
t,d
= a
1.0
n=4]'<'-,..-"'--i "'~'-q
m
~200 "1
0(n=4) (n=3)0
0.0 0
I
!
!
100
200
300
FIGURE
2
The temperature dependence of the Hall coefficient of the n = 1 ~ 4 phase films. of 100 ~ 5G0 K increase with increasing , up to 3,
O(n=2)
,oo
("=')°0
Temperature (K)
100 I
I
I
I
!
10 2'0 3'0 Energy (eV)
4O
FIGURE 3 Electron energy loss spectra of the n = 1 ~ 4 phase films.
which suggests that the carrier density in the unit cell decreases. In this experiment, oxidized state is thought
crystal structures. The spectrum of the n=4 phase is
to be the same in all samples because of the prepara-
quite similar to that of the n=3 phase. It is, however,
tion in the same oxidizing conditions. Thus the above
not clear whether the n=4 phase has the same elec-
results suggest that the definite numbers of holes are
tronic structure as that of the n=3 phase, because the
distributed to n sheets of Cue2 layers, and as a re-
energy of the primary electron is relatively weak and
sult the cattier density decreases.
the probing depth is not sufficiently long to detect the
Hall coefficient of
the n=4 phase, however, shows quite different behav-
difference between the n=3 and 4 phases.
ior. RH value of the n=4 phase is quite low, which can-
In summary we prepared the superconducting
not be explained in the extrapolation from the n <_ 3
Bi2Sr2Ca,_tCu, Ot ( n = l ~, 4) thin films in zitu by
phases.
Such a low value has not been observed in
molecular beam epitaxy. Hall coefficient and electron
Bi=Sr2C~_xCu,~O~ compounds before. The origin of the low value is not evident, and further experiments are requited.
energy loss spectroscopy were measured. The system-
To investigate the electronic structures, EELS were
films. The behavior of the n=4 phase film cannot be explained in the extrapolation from the n _< 3 phases.
also measured. The energy of the primary electron is 1000 eV. The observed spectra, shown in Fig. 3, are obtained in a reflection mode, where because of a short
atic change of Hall coefficient and the the electron energy loss spectra were observed in the n = 1 ~., 3 phase
REFERENCES
probing depth the spectra for thin films should be equivalent to those for single crystals . The spectra of the
n=l and 2 phases are the same as those of the bulk single-crystal samples. 4 In the spectra of the n=2 and 3 phases, the peak due to Ca is only observed as the intra-atomic transition (C), which supports the oxygen vacancy in the Ca layer. Thus the obtained spectra of the films are consistent with the electronic structures of the n = 1 ~ 3 phases expected from their
1. I. Tsukada and K. Uchinokura, Jpn. J. Appl. Phys. 30 (1991) Lll14. 2. G. Briceno and A. Zettl, Phys. Rev. B 40 (1989) 11354. 3. T. Ishida and T. Sakuma, Physica C 167 (1990) 258. 4. I. Terasaki e~ M., Supercond.
(1991) S397.
Sci.
Technol.
4