日本分析化学会中国四国支部愛媛地区講演会
愛媛大学工学部 ２００７．１．３１

金属内包フラーレンの紫外光電子分光
ー内包金属とフラーレンケージの相互作用ー

愛媛大学大学院理工学研究科
日 野 照 純

目次
• Introductory– 光電子分光– アルカリメタル・フラーレン錯体– フラーレンの光電子スペクトル• 単原子内包フラーレン– M@C82• 多原子内包フラーレン– C82 cage
– C78 cage

• まとめ光電子分光法とは？

• 原理はEinsteinの光電効果（１９０５）光（紫外線・X線）
ｈν

電子
KE

KE = h ν – BE
BE は電子の結合エネルギー

自由原子・分子からの光電子放出

E
入射光のエネルギー

真空準位
R• 各軌道の結合エネルギーに応じて放出される電子の運動エネルギーが異なる

固体からの光電子放出
原則的には気体からの光電子放出と同じ
ただし、エネルギーの基準点はFermi Level

固体からの光電子分光で分かること• 電子状態
内殻準位の結合エネルギー
価電子帯の電子の状態密度• さらに．．．
金属・半導体の判定(hν = 20 eV)WFof Au

Fermi edge
of Au

UPS of C2-C82

15105BE / eV

Cut-off

まず、金のスペクトルを測定してFermi levelを決める

0-5EFOnsethν(= 20 eV)

次に試料を蒸着して測定

IP

Ionization
Potential

Vacuum Level〜〜〜〜

WorkFunction

Fermi Level

Photoelectron Intensity (arb. units)

紫外光電子スペクトルの見方

光電子分光装置の概要

Electronanalyzer

Sublimation
gunThickness
monitor• Superconductivity in alkali metal – C60 complex
From 18 K ( K3C60)
to 33K (Cs2RbC60)

expectation of hightemperaturesuperconductor
on higher fullerenes

As for AxC60,Stable phases : A1C60, A3C60, A4C60, A6C60
Metallic AxC60 complexes
A = K, Rb, Cs

Semiconductive AxC60
complex
A = Li, Na, Mg

J.Phys.Chem.Solids 53, 1321

• Alkali (alkali earth) metal C60 complexes– Metallic (superconducting*) phase :A1C60, A3C60* (A = K, Rb, Cs)
Ca5C60*, Ba6C60*• Not all electron accepting fullerenes become
metallic or superconducting.
• Electron donation to C60 is the key.
• They are unstable to the ambient air !

Enclosure of donor in the cage

C60-O2, H2O
Encapsulation of electron donating atom(s)prohibits degrading of donor

Metallofullerenes synthesized so far

Sc@C82

La@C82Isolated pentagon rule (IPR) satisfying C82 cages
M3+@C823C2v (major),Cs
No.1 C2(b)No.2 Cs(b)No.3 C2(a)M2+@C822C2v, C2
Cs, C3v
No.4 Cs(c)No.5 C2(c)No.6 Cs(a)C2 ×3Cs×3C3v×2
No.7 C3v

No.8 C3v

No.9 C2v

One of the issues on M@C82• 電子状態を決めているものはなにか?
– ケージ構造 ? 内包原子種 ?

• 決定方法– 内包原子種を変える– ケージ構造を変化させる

Summary of Mono-metal atom entrapped C82HG

Principally metallofullerenes withthe same C2v cage give
essentially the same spectra.

FIECDB
ATbLaScTm
108

642Binding Energy / eV

That is,Small or no interaction between
the fullerene cage and theentrapped atom0

Difference only in upper band dueto the difference in the amount ofelectrons transferredMultiple atoms encapsulated metallofullerenes
Examples ;Er2@C82,
La2@C78, La2@C80, La2@C84
Sc@C66,Sc3@C82, Sc3N@C82, Sc2@C82(Sc2@C84), Sc2C2@C84
Ti2C2@C78(Ti2@C80), Ti2@C82, Ti2C2@C82
Y2@C82, Y2C2@C82

etc. etc….

IssuesAny special difference from M@C82 ?
Entrapped atoms play differently or not?

Cage structure of three isomers : (I) Cs(6), (II) C2v(9), (III) C3v(8?)

hν = 40 eV

Y2C2@C82(III)Y2C2@C82(II)Y2C2@C82(I)1614121086420Binding Energy / eV

T. Inoue et al.

Different electronic structure, particularly
in upper valence band region

C82 cage also contains metal atoms without carbon atoms.
Y2C2@C82 and Y2@C82 give analogous absorption and havethe same C3v cage structure

Do they have analogous electronic structure ?

Comparison of Y2@C82 and Y2C2@C82 (III)the same cage structure and entrapped metal atoms
difference is additional two carbon atoms.
4Ionization Potential ( eV )3 2 1 0 -1 -2 -3 -4 -5

Cage symmetry seems todominate
the electronic structure !

C3v-C82 (No.8)
charge = - 4

Difference spectrum indicates
additional two electron transferin Y2@C82hν = 30 eV

Y2C2@C82(YC)24+@C824- and Y3+2@C826-Y2@C82

Y2@C82 - Y2C2@C8208642Binding Energy ( eV )0 =EF

Because Y3+ is the oxidation states ofboth fullerenes, carbon atoms accept
two electrons or bonds is formed in(Y2C)2@C82

when different species, Lu3+ and Y3+, entrappedhν = 40 eV

Lu2C 2@C 82
Y2C 2@C 82(III)Y2C 2@C 82(II)Y2C 2@C 82(I)16141210864Binding Energy / eV20

The UPS of the same
C3v (8) cages
Ti2C2@C82 andY2C2@C82 are not
identical !

C3v cages

B2 B1

Oxidation state of Ti in
Ti2C2@C82 is +2,Y in Y2C2@C82 is +3 !

Oxidation state ofentrapped atoms
seems to be the key !

GTi2C2F E

HDY2C2C

10

8A2
A1

64BAY2

20Binding Energy / eVElectronic structure change might be introduced by strong
interaction between the cage and entrapped species.

IPR satisfying C78 cages
One of the important Issues
No.1-D3

No.2-C2v

No.3-C2v

There are two D3h structures.
Are the structure of(TiC)2@C78 and La@C78 thesame or not ?

No.4-D3hNo.5-D3h10864

20LDA-DFT calculation on two
D3h cage structures withencapsulated La2 and (TiC)2(TiC)2@C78

Good agreement on D3h (5)cage structure

La2@C78Ti(5)Ti(4)

Although they have thesame cage structure,but have the different
electronic structures

La(5)

La(4)

864

20-2

Oxidation states of entrapped
atoms may be the key !

Wave function distribution

Hybridization is observed in HOMO-1 of Ti2C2@C78

Summary(as for the effect of entrapped atoms to theelectronic structure of the cage)• Mono metal atom encapsulated fullerenes– Cage dominate the electronic structure– Entrapped species have few influence– weak interaction between the cage and entrappedatom• Multiple atoms encapsulated fullerenes– Fullerenes with metals of the same oxidation state
and the same cage give analogous electronicstructure– Upper π-valence band depends on different oxidation
states of entrapped species– Strong interaction is expected thanks to narrow innerspace of fullerenes