Resonant photoemission at the 2p edge in
compounds containing Mn with different valencies
M. C. Richter1, J. M. Mariot2, O. Heckmann1, L. Kjeldgaard3, B. S. Mun4 , C. S. Fadley4,
K. Hricovini1
1 LMPS, Univers ité
de Cergy-Pontois e, Neuville/Ois e, 95031 C ergy-Pontois e, France, 2 LCPMR (UMR 7614), Univers ité Pierre et Marie Curie, 75231 Paris Cedex 05, France
3 M AX-lab, Lund, Sweden, 4 M aterials Sciences Divis ion, LBNL, Berkeley, CA 94720, USA
R esonant phot oemi ssi on permi t s t o probe hybri di zat i on and l ocal i zat i on of
phot o-exci t ed el ect rons. Two di fferent behavi ors are observed: i n t he
radi at i onl ess R aman regi me, t he ki net i c energy of t he out goi ng el ect rons
fol l ows t he i ncomi ng phot on energy, whi l e i n t he Auger regi me t he
el ect rons are det ect ed at const ant ki net i c energy.
The compari son bet ween t he phot on energy Ec at whi ch R aman and Auger
behavi ors cross and t he energy EX at whi ch absorpt i on i s at a maxi mum
(resonance energy) cont ai ns i nformat i on not onl y on t he el ect roni c band
st ruct ure but al so on t he dynami cs of i t s el ect rons as an answer t o t he
phot on creat ed core hol e. We report here on a st udy of manganese i n vari ous
envi ronment s, i . e. wi t h di fferent nomi nal val enci es. The purpose of our
st udy i s t o l i nk t he i nfluence of t he M n val ency and i nsul at i ng/ met al l i c
charact er of t he compound t o t he R aman/ Auger behavi or and t o search for
some general t rends i n order t o use resonant phot oemi ssi on i n a more
powerful way for el uci dat i ng t he el ect roni c st ruct ure of mat t er.
( b eam l i ne I511-1
3
of t he M AX-l ab, Sweden )
( b eam l i ne I511-1
of t he M AX-l ab, Sweden )
relative photon energy (eV):
MnO
Mn 2p3p3p
100x10
The experi ment s on bul k M nO were performed on t he beam l i ne I511-1 of t he
M AX-l ab st orage ri ng (Lund) usi ng a modi fied SX-700 monochromat or, whi ch
gi ves a flux of 10 1 2 p hot ons/ s at a t ypi cal resol vi ng power of 5000. Therefore
t he wi dt h of t he i ncomi ng radi at i on i s smal l compared t o t hat of t he resonance.
Anneal i ng t o 800 K cl eaned t he M nO surface, as checked by phot oemi ssi on,
whi ch show t hat no carbon was present on t he surface. The M n 2 p absorpt i on
spect rum was t ypi cal of manganese i n a d 5 configurat i on. The LSM O sampl e was
measured on t he beam l i ne 9. 3. 2 of t he Advanced Li ght Source (ALS) at t he
Lawrence Berkel ey Nat i onal Laborat ory usi ng a SGM monochromat or w i t h 10 1 1 10 1 2 p hot ons/ s at a resol vi ng power of about 5000. Thi n-fil m sampl es of
LSM O (~1000 Å t hi ckness) deposi t ed on SrTi O 3 (STO) were produced by l aser
abl at i on i n t he C R ISM AT l aborat ory, C aen, France.
+160
+14.3
80
The M n 2 p 3 d 3 d decay does have t he
shape of
t he di rect
val ence band
phot oel ect ron spect rum, whi ch has been
recorded at 9. 5 eV b el ow resonance.
Approachi ng t he resonance t he domi nant
peak i n t hi s feat ure i ncreases st ronger
t han t he ot her t ransi t i ons. It t akes t he
shape, wi t h t he same proport i ons of
feat ures cont ai ned i n i t , of t he di rect
phot oemi ssi on from t he val ence band
onl y at about 20 eV above EX . At
phot on energy of about 5 eV above
resonance,
one
cl earl y
det ect s
t he
appearance of t he cl assi cal 2p 3 d 3 d Auger
t ransi t i on, t he shape of whi ch i s
di fferent from t hat of t he R aman
t ransi t i on but has t he same ki net i c
energy as t he resonance spect ra.
+5.5
+3.4
Intensity (arb. units)
60
+2.7
+1.7
3
+1.3
40
+0.9
+0.2
20
(resonance) 0
2
-0.3
0
In b) we pl ot t he ki net i c energy of each of
t he t hree 2p 3 p 3 p feat ures i ndi cat ed i n fig. a)
as a funct i on of t he i ncomi ng phot on
energy. In t hi s represent at i on a l i ne wi t h
sl ope uni t y i ndi cat es R aman behavi or and a
hori zont al l i ne corresponds t o a cl assi cal
Auger t ransi t i on. Onl y from ≈ 4 . 2 eV
above EX on we find a cl assi cal Auger
behavi or.
-0.5
-1.1
-20
-1.5
Mn3s
1
540
545
550
-2
555
a)
560
565
Kinetic Energy (eV)
543
MnO: Mn 2p3p3p
3s2
3s1
Kinetic Energy (eV)
542
541
160 eV
1
MnO
Mn 2p3d3d
relative photon energy (eV):
+160
+17.5
+5.5
+12.5
+2.7
Intensity (arb. units)
a) raw spect ra
b)
ki net i c energy
of
t he di fferent
t ransi t i ons as a funct i on of t he phot on
energy
t he dot t ed st rai ght l i nes have a sl ope of
one, i ndi cat i ng pure R aman b ehavi our.
+1.7
+0.5
0 (resonance)
-0.5
-1.5
-2
-5.5
-9.5
540
2
625
630
635
640
645
650
655
Kinetic Energy (eV)
539
b)
3
538
-2
0
2
4
6
8
Relative Photon Energy (eV)
MnO, peak 1: R aman behavi or up t o ≈ 5 eV
above resonance. Peaks 2 and 3 appear i n t he
spect ra approxi mat el y at ≈ 5 eV above
resonance. They seem t o be t he final cl assi cal
Auger t ransi t i ons whi ch we find far above
(160 eV) resonance at t he same ki net i c energy
as t he resonance spect ra. The 2p 3 p 3 d resonance
feat ure i s broad and has t he same st ruct ure at
resonance as what we have found for 0. 2 M L
M n/ C u (M . C . R i cht er et al , Phys. R ev. B 63
(2001) 205416. )
MnO
Mn 2p3p3d
0.2 ML Mn/Cu thin film:
“p ure“
2p 3 p 3 d
Auger
el ect rons onl y from about 1
eV above resonance on, wi t h
qui t e
a
l arge
area
of
t ransi t i on around resonance .
MnO/Cu
thin
film:
R aman behavi or st ops
j ust bel ow resonance,
t he met al l i c subst rat e
under t he oxi de t hi n
fil m
al l ows
fast er
del ocal i zat i on
of
t he
phot on-exci t ed
3d
el ect rons,
expl ai ni ng
t he di fference from t he
bul k M nO cryst al .
a)
3
relative photon
energy (eV):
2
MnO crystal
+160
6
60x10
0.2 ML Mn/Cu thin film
Mn t hick film: t he 3d band i s
i mpl i ed i n t he aut o-i oni zat i on
process and pl ays an i mport ant
rol e. for t he met al l i c sampl e
t he decay
feat ure i s l ess
st ruct ured (not shown) t han
for t he M n t hi n fil m or t he
i nsul at i ng M nO cryst al . Al so
t he
R aman/ Auger
behavi or
i ndi cat i ng t he degree of 3 d
el ect ron l ocal i zat i on on t he
t i mescal e of aut o-i oni zat i on i s
charact eri st i c
for
met al l i c/ i nsul at i ng
syst ems
wi t h more or l ess l ocal i zed 3 d
el ect rons. For t he M n t hi ck
fil m we found a cl assi cal
Auger behavi or from 1. 65 eV
bel ow resonance on.
La 0 .7 Sr0 .3 MnO3 (LSMO) perovskite,
(M n i n mi xed val ence 3+ / 4+):
R aman-Auger crossi ng at Ec =
1. 3 eV b el ow resonance. The shape
of t he 2p 3 p 3 d feat ure i s si mi l ar t o
t hat observed for M nO, i . e. , i t
shows
at omi c charact er.
Three
t ransi t i ons, pl us t he di rect M n 3 p
phot oel ect ron
peak,
can
be
di st i ngui shed. The pecul i ari t y of
t he R aman-Auger curves i s t he
osci l l at i on
about
t he st rai ght
l i nes. We expl ai n i t qual i t at i vel y
by a vari at i on of i nt ensi t y of t he
di fferent mul t i pl et t erms.
Mn/Cu thick film
MnO/Cu thin film
652.6
a
-1.5
0
570
580
590
Kinetic Energy (eV)
588
586
3
160 eV
655
b
652.2
656
654
652.0
652
651.8
66
64
62
60
58
56
54
610
5
10
Relative Photon Energy (eV)
9
586.5
633.5
11
cross-over at - 1.65 eV
633.0
653
15
651.2
57.0
LSMO
Mn 2p3p3d
!hv=0 eV
10
12
13
14
15
651.4
0
634.0
651.6
16
! hv= -2.25 eV
586.0
resonance
585.5
!hv= -2.1 eV
!hv= -2.7 eV
585.0
17
652
-5.5
600
slope 1
654
! hv=+0.7 eV
587.0
632.5
584
LSMO
634.5
MnxOy/Cu 2p3p3d
658
Kinetic Energy (eV)
+1.5
(resonance) 0
Mn 3p
Photon energy (eV)
+2.5
20
1
660
a
photon energy (eV)
590
+4.5
652.4
b)
MnO: Mn 2p3p3d
Mn0530_025
Photon energy (eV)
+7.5
1
40A Mn/Cu
635.0
662
b
40
Kinetic Energy (eV)
Intensity (arb. units)
Ve11Sep98
(ALS, Berkl ey )
+12.5
0.2 ML Mn/Cu
56.5
56.0
55.5
Binding Energy (eV)
55.0
54.5
54.0
62
60
58
56
54
632.0
56.0
55.5
55.0
binding energy (eV)
54.5
Mn3p direct
584.5
644
645
646
647
Photon Energy (eV)
648
649
650
580
585
590
595
Kinetic Energy (eV)
Binding energy (eV)
In concl usi on, t he R aman-Auger charact eri zat i on of t hree mai n radi at i onsl ess decays consecut i ve t o t he creat i on of a M n 2 p hol e i s compl i cat ed by t he appearance and di sappearance of di fferent
t ransi t i ons. The l ong persi st ence of a R aman behavi or above resonance for bul k M nO sampl es i s a surpri si ng resul t meani ng t hat t he phot o-exci t ed 3d el ect ron st ays i n t he vi ci ni t y of t he core
hol e and gi ves i t s surpl us energy t o t he out goi ng el ect ron. The compari son of t he resul t s obt ai ned for vari ous M n compounds underl i nes t he i nt erpl ay of t he v al ency and t he
met al l i c/ i nsul at i ng charact er of t he mat eri al i n t he det ermi nat i on of t he spect ral response. The val ency u nderst ood i n t erms of t he number of el ect rons i n t he M n 3 d orbi t al i nfluences t he
screeni ng dynami cs of t he M n 2 p core hol e and t he i nsul at i ng charact er of t he mat eri al rei nforces t he at omi c charact er of t he t ransi t i ons.
600