Physica 143B (1986) 189-191 North.Holland, Amsterdam
ELECTRONIC
189
STRUCTURE OF K0.30MoO 3 STUDIED BY ULTRAVIOLET
PHOTOEMISSION
H. MATSUOKA, K. OHTAKE, R. YAMAMOTO, M. DOYAMA, H. SAKAMOTO*, M. FUJISAWA*, K. SODA*, and S. SUGA*
SPECTROSCOPY
T. MORI*, H. NAMATAME*.
Department of Metallurgy and Materials Science, Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan *Synchrotron Radiation Laboratory, Institute for Solid State Physics, The University of Tokyo, Tanashi-shi, Tokyo 188, Japan
Ultraviolet photoemission (UPS) spectra of K~ ~^MoO. have been obtained using synchrotron U.J radiation from 32 to 100 eV. The conduction any valence bands are observed in the binding energy (E~) range of 0-2 eV and 2-10 eV. The photoemission intensity of these structures resonantly increases around the photon energy (hv) of 49 eV, which is much higher than E of Me 4p levels. The angle-resolved UPS measurements have been also performed to revealBthe band structure of K 0.30MOO3 .
were done at room temperature.
i. INTRODUCTION In the class of the compounds potassium molybdenum bronzes,
called
the blue bronze
An angle-integrated
KO.30MoO 3 is well known to be a quasi onedimensional
conductor.
experiments
to reveal the electronic
3. RESULTS AND DISCUSSION
We have performed UPS structure
eV is shown in Figure i.
respectively.
Single crystals
used in the present study
were grown by the electrolytic performed photoemission vacuum ultraviolet
spectroscopy
from SOR-RING,
GeV electron storage ring. the monochromator
the 0.4
The resolution of
The energy distribution
UPS
I
!
i
;
!
i
KQ3MoO3 ( h~'= 100eV)
from
curves
VB
02sK3pA
The
([010]
0 was changed from -6 ° to -I-6° from
was employed
(XPS) measured by
We measured UPS spectra for various hv
UPS
at hv = 54 eV at various polar
the surface normal.
spectra
(ARUPS) were measured along
the F-X direction in the k space
angle 0.
The present
G.K. Wertheim et al. (1985)i
to 0.2 or 0.3 eV at the photon
(EDC) were normalized by the photon flux. angle-resolved
the peaks with E B smaller than 2 eV is assigned to the conduction bands.
x-ray photoemission
The angle-integrated
to the valence bands, while
results are in good agreement with these of
in the
for various photon energies
32 to i00 eV.
We
was set to 0.2 eV and that
energy hv = 50 eV. were measured
reduction,
region by use of
radiation
of the analyzer
The peaks in the region of E B =
2-10 eV correspond
2. EXPERIMENTAL
direction)
The p e a k s at E B =
18.1, 22.5, 34.2 and around 40 eV correspond to K 3p, O 2s, K 3s and Me 4p orbitals,
of K0.30MoO 3.
synchrotron
spectrum for hv = i00
A full acceptance
for ARUPS.
of i0 °
All the measurements
0378 - 4363/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) and Yamada Science Foundation
l
60
I
I
I
I
I
40 20 0 BINDING ENERGY (eV)
FIGURE I UPS spectrum for hv = i00 eV
H. Matsuoka et al. / Electronic structure o / Ko.3oMo03
190
between are
32 and i00 eV
resolved
(Figure
at E B = ].8,
2)•
Structures
4.6 and 6.7 eV•
'-
Noticable
enhancement
of the p h o t o e m i s s i o n
intensity
is o b s e r v e d
a r o u n d h~ = 50 eV.
constant-initial-state structures
have
(CIS)
shown
the Mo 4p core e x c i t a t i o n This
resonance
effect
channels:
excitation
and
a direct
photoemission resonance
U w m
pbotoemissior~
After
=.
two
~
t
U
decay
I
I
I
~i
the inner
I
= 1.8eV
take place,
from the Mo 4d state.
with
3).
is the same as the direct
peak o b s e r v e d
in a g r e e m e n t
the
the A u g e r process
final state
I
above
(Figure
Coster-Kronig
of the Mo 4p core states.
whose
threshold
between
the super
core excitation,
for these
behavior
can be q u a l i t a t i v e l y
e x p l a i n e d by c o n s i d e r i n g excitation
spectra
resonance
The
1]~e
40 5O 6O 70 80 PHOTON ENERGY (eY)
a r o u n d h> = 49 eV is
the c o r r e s p o n d i n g
absorption
F[GURE 5 peak
(not shown here).
higher
than the b i n d i n g
The energy energy
the Mo 4p level by 9 eV, w h i c h attributed
to the delay
is much
E B = 40 eV of
(?IS spectra 6.7 eV
In Figure spectra
[ Ko3MoO3
~..,~, h v :
angle
4 is present
ill the conduction
at various
corresponds
Brillouin
~ 6OeV
I/,-,,"
to the
curves
as shown
s h a l l o w bands
of the usual
band•
Since
in a unit
there
Then we have
of K O . 3 0 M o O 3.
consisting
of ten
cell of the
structure there
exist
(1985) 2
of K0 30Mo03 and is one c o n d u c t i o n
two clusters
unit ceil of K0.30MoO3,
tt is natural
consider
two c o n d u c t i o n
band
8 4 0 BINDING ENERGY (eV)
observed
in the present
measurements.
FIGURE 2 dependence of the a n g l e - i n t e g r a t e d
upper band
It can be seen
Actually,
from the
does not cut
by use
formula•
cluster
calculation
the
derivative
5 (b),
and P. Waci~ter
crystallographical
oi
We determined
5 (a).
the band s t r u c t u r e
MoO 6 octahedra
from their
•
in Figure
kinematic
measured
-X direction
in Figure
{;. T r a v a g l i n i
region
Tile azimuthal
from the second
mapped
calculated
..'..~.':; 40eVl
band
zone of KO.3oMOt)
l]~ey treated one
~-~
a set of ARUPS
@ for hv = 54 eV.
ti~e peak p o s i t i o n s
P h o t o n energy UPS s p e c t r a
4.6 and
can be
of the a b s o r p t i o n
peak.
Z
to E B : 1•8,
corresponding
in the to
structures
figures
the Fermi
the upper b a n d should
that
as
the
level•
cut the Fermi
H. Matsuoka et al. / Electronic structure Of Ko.3oMoOa
191
Ko3MoO3 hv=54eV •
.
•
•.-.:........•
......
,.,
,•
h~'=S&eV :
.
•
.
"" :"" . . . . ~ " ...'.. . . .
•
i
1.0
,".¢
~
• wi i w
~2.0
-3 " ..@
r'
?=,-y."..I
X
MOMENTUM
3210 BINDING ENERGY(eV)
1:8 1.'2 0:6 BINDING ENERGY (eV) FIGURE 4 ARUPS spectra in the conduction band region
(a)
(b) FIGURE 5
(a) Second derivative curves of the spectra level since K0.3oMOO 3 is a quasi onedimensional conductor•
This disagreement
might be due to some experimental reasons•
in Figure 4 (b) Experimental band structure of the conduction band region along the F-X direction
The total resolution of the whole system was about 0.4 eV.
The acceptance angle of the
angle-resolved measurements was i0 = , which
channels:
a direct excitation of the Mo 4d
state and the final state realized through the
was rather wide, more than half of the
super Coster-Kronig decay of the Mo 4p core
Brillouin zone in the F-X direction.
excited state.
From the measurements of the
ARUPS, we have observed two structures of the 4. CONCLUSION
conduction band.
These UPS measurements have provided much information about the electronic structure of K0.3oMoO 3.
The inner core levels of K 3p, O
2s, K 3s and Mo 4p are observed at 18.1, 22.5, 34.2 and around 40 eV, respectively.
The
conduction bands extend down to 2 eV below the Fermi level and the valence bands are observed in the region between 2 and i0 eV.
The
resonance enhancement of the photoemission intensity of the valence and conduction bands around hv = 49 eV is considered to be due to an interference between two excitation
REFERENCES i. G.K. Wertheim, L.F. Schneemeyer and D.N.E. Buchanan, Phys. Rev. B32 (1985) 3568. 2. G. Travaglini and P. Wachter, CDW Phase Mode Investigation in the FIR in K n qnMOOq and Band Calculation, in: L e c t u r e V ~ e s ~n Physics, 217, Charge Density Wave in Solids, Proceedings of the International Comference Held in Budapest, Hungary, September 3-7, 1984, eds. Gy. Hutiary and J. Solyom (Springer-Verlag, Berlin, Heidelberg, New York and Tokyo, 1985) pp. 115- 120.