Electronic structure of K0.30MoO3 studied by ultraviolet photoemission spectroscopy

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.