Surface electronic structure of ordered alkali- and noble metal-overlayers on Si(111)

ap~ieO surface science ELSEVIER

Applied Surface Science 121 / 122 (1997) 89-97

Surface electronic structure of ordered alkali- and noble metal-overlayers on Si(111) Taichi Okuda a,*, Hiroshi Daimon a, Shigemasa Suga a, Yoshihiro Tezuka

b

Shozo Ino b a Department of Material Physics, Faculty of Engineering Science, Osaka Unit,ersit~, Toyonaka, Osaka 560, Japan b Department of Physics, Faculty of Science, Unit,ersio'of Tokyo, Hongo, Bun~,o-ku, Tokyo 113, Japan Received 1 November 1996; accepted 21 February 1997

Abstract Some progresses of our photoemission studies for ordered metal/Si(11 l) surfaces are reviewed. The 5-6-7 model having ~--bonded chain structure on the alkali metal (AM) induced Si(l 11)3 × 1 surfaces is strongly suggested from the comparison between our results of angle resolved photoelectron spectroscopy (ARPES) and recently reported theoretical calculations. We also focus on the difference of the Si 2p surface core level shifts (SCLS) between Ag induced- and AM inducedSi(111)3 × 1 surfaces. Finally, we discuss the electronic and geometric structures of the Si(111)5 X 2, c~-~J- X ~ - , /3- f3X ~3- and 6 X 6-Au surfaces from our ARPES and SCLS studies. © 1997 Elsevier Science B.V. PACS: 79.60; 73.20; 68.35 Keywords: Surface electronic structure; ARPES; Surface core level shift

1. Introduction The investigation of the electronic and geometric structures of reconstructed surfaces is one of the most important subjects of surface physics. Among various reconstructed surfaces the m e t a l / s e m i c o n ductor surfaces have been studied most intensively from the industrial and academic requirements. Photoelectron spectroscopy is one of the most powerful and suitable tools to investigate surfaces, especially when we use synchrotron radiation (SR) as an excita-

Corresponding author. Tel.: +81-6-8506422; fax: +81-68454632; e-mail: [email protected].

tion light source. W e applied ARPES and Si 2p core level spectroscopy (CLS) to investigate the surface electronic and geometric structures of several metal ordered reconstructions on Si(l 11) surface. First, we report the electronic structures of the Si(111)3 × 1-AM surfaces. Their surface state band dispersions obtained by the ARPES measurement are compared with those of recently reported theoretical calculations. From the results of the SCLS and the ARPES measurements we discuss about the possibility of the ~'-bonded chain structure on this 3 X 1-AM surface. Next, the comparison between Ag- and AM-induced Si(11 I)3 X 1 surfaces is given by the results of their SCLS. Finally, we discuss the electronic and geometric structures of the Au induced

0169-4332/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PH S01 6 9 - 4 3 3 2 ( 9 7 ) 0 0 2 6 3 - 8

90

T. Okuda et al. / A p p l i e d Surface Science 121 / 122 (1997) 8 9 - 9 7

various reconstructions on S i ( l l l ) surface such as 5 X 2 (=5Xl), c~-ffX~J-, /3-~-X~(abbreviated to c~- ~ - and /3- f 3 hereafter) and 6 x 6 surfaces from the results of ARPES and SCLS measurements. All the experiments other than ARPES of A u / S i ( l l l ) surfaces were performed at the ISSP beamline, BL-18A, of the Photon Factory at the National Laboratory for High Energy Physics using VG-CLAM(II) and ADES 500 systems. The ARPES measurements of the Au/Si(111) surfaces were done using the VG ADES 400 system with a He lamp.

spite of the simple electronic state of the adsorbate, the electronic and geometric structures of the AM induced S i ( l l l ) 3 × I surfaces are controversial [1]. For these 3 X 1-AM surfaces the coverage of 2 / 3 ML was estimated by a scanning tunneling microscopic (STM) image and the semiconducting character was derived from the STM I - V measurement [1]. The semiconducting character in spite of the odd number of electrons in the unit cell was explained as the Mott-Habbard model at first. Recent studies [2-4] of this surface, however, revealed that the coverage is 1 / 3 ML and the inconsistency between the electric character and geometric structure has been almost wiped away. The complete understanding of electronic and the geometric structures of these surfaces, however, has not been archived yet and strongly required. For this purpose we have performed precise ARPES measurements on the Si(111)3 X 1-K [3] and Na [5] surfaces. The measurements were done along the [101] and [112] directions which correspond to

2. Alkali metal (AM) induced S i ( l l l ) 3 X 1 surfaces A M / s e m i c o n d u c t o r surfaces are prototype systems for the study of the metal adsorbed semiconductor surfaces because of the simple electronic state of the adsorbate which has one s valence electron. In

0-

]~ G a) ij '- - , .

.

~.~..... 1

• ..

..--

.

-~ . . . . . . . .

. , J 2 .......

.c: "l~

i:51

,

~

,'

'

', i I

i

k

,

...................r............... $1 [

'

~

0

.

~

.

,

[112]

[10]]

1"------/,, K~

, ~ -.,. j

, , - ~ i ~

.~,.~'.,~

~

',. . , . . , . .

,

i E

L

,

iSl

./~~!a/. .~,.,) "

-~

..

~

!"

J

..................

I

,

I I

,

'

'

,

. ..............+.... .........• i .............. i

i

.......

"

I

i

DC ,, i I '

.

,

I

, 3AE ,

t

i

"'"

-

......

.

...r-,-.,-,,~

I

¢-

E

.

4-1

I~ ¢II

1

~

, d z ~ - . ~

~.

W O-Irb~'

.

I

".,

,~

.

;-c.~S1

' "'"'..,

I

HAFB ~ Ii ,' ,

.

I

Ii

i

0.5

ii

i

I

I

I

~l

i,

1 Wave

Number

i

1.5

I

I

~J

,I

I

i

~

2

(]k-1)

Fig. 1. Surface state dispersions along the symmetry points of 3 :x: 1 surface Brillouin zone (the right hand of the figure) derived from the ARPES measurement. In (a) theoretical results of the Jeong and Kang (dashed curves) [9] for bulk terminated surface and Erwin (dotted curves) [10] for the 5-6-7 model are also plotted. In (b) recently reported Jeong and Kang's calculated dispersions [11] for 5-membered model (dotted curves) and for 5-6-7 model (dashed curves) are incorporated with our experimental ones.

Z Okuda et al./Applied Surface Science 121 / 122 (1997) 89-97

F - K and F - M directions of the 1 X 1 symmetry as seen in the right hand of Fig. 1. In the figure the surface Brillouin zone (SBZ) of the 3 × 1(1 × 1) surface is indicated by solid (broken) lines. The symbols A to H are symmetry points of the 3 × 1 SBZ which we named in this paper tentatively. The summary of the surface state dispersions of the S i ( l l l ) 3 × l-Na surface is shown in Fig. l(a). The data points are indicated by filled or empty circles, triangles, asterisks and crosses corresponding to different h u and direction measurements (see Ref. [5]). As the results, at least four surface states (S~-S 4) are found on the 3 X 1-Na surface and these states do not cross the Fermi level indicating that the surface electronic state is semiconducting. One of the most interesting results is the dispersion feature of the S~ state which disperses upward by about 0.47 eV from F to H the point. This dispersion width and the curvature are very much similar to those derived for the 7r-bonded chain structure on the Si(111)2 × 1 clean surface [6]. On the other hand, the dispersion of the S 2 state is similar to that of the Na 3s-Si 3p bonding state on the S i ( l l l ) with 1 ML of Na adsorption [7]. From these results, we conclude that there are ~--bonded chain like structures and N a - S i bonds on the Si(111)3 × 1-Na surface. The surface dispersions of the 3 × 1-K surface were almost the same as those of the 3 X l-Na surface indicating the similar surface structures on both surfaces. This similarity between 3 x l-Na and -K is consistent with the similarity o f the low energy electron diffraction(LEED) 1 - V curves of the 3 × 1 surfaces with different adsorbates [8]. Considering the results of the ARPES and SCLS measurement described below, we have proposed three types of models for the 3 X 1-AM with parallel It-bonded chains along the [101] direction and 1,/3 ML coverage of AM [4]. Two of these models named (a) a 5-membered ring and (b) 5-6-7 models are shown in Fig. 2. In Fig. l(a) we plotted the results of the theoretically calculated dispersions which were recently reported. The dashed curves represent the dispersions which are derived from the Na adsorbed bulk terminated Si(111) surface calculated by Jeong and Kang [9]. The dotted curves are the results of the Erwin's calculation [10] for the 5-6-7 model (Fig. 2(b)). Erwin concluded that this model is the most stable one among the several models including the 5-mem-

91

[1013 [1123 7g-bonded chain I

~.I.<]

(a)

.......•-.~

~"--"-':~i0

?,... :.

..... ' },'6J

"~...

. ... :'..0 ....

~ -bonded chain

(b) , : : ~ :

6..)1:.

,t ?-. t. ,i,. tTop

view

Side view

Fig. 2. Models for the 3 × l structure, (a) 5-membered ring model, (b) 5-6-7 model. Both models have parallel 7r-bonded chain structures and 1 / 3 ML of alkali metal.

bered ring and bulk terminated ones. Comparing these calculated dispersions to the obtained S~ and S 2 states (connected by solid curves), Jeong and Kang's calculated dispersions (dashed curves) are too flat and do not reproduce the experimental results suggesting that the bulk terminated surface is not appropriate for the 3 × 1-AM surface. On the other hand the surface state corresponding to the 7r-bonded chain state (labeled p) of the 5-6-7 model of Erwin's calculation (dotted curve) has upward dispersion from F to the H point and the other state corresponding to the S i - N a bonding has downward dispersion from F to the H point. These two states cross each other at the point marked by the arrow. The results of Erwin's calculation seem to reproduce our experimental dispersions qualitatively, implying that the 5-6-7 model is one of the likeliest candidates for the 3 × 1-AM surface, although the dispersion width of the calculation (0.60 eV for S l and 0.69 eV for S 2) are a little bit larger than the experimental ones (0.47 and 0.40 eV for S 1 and S 2, respectively). Very recently, Jeong and Kang [ 11 ] have reported the results of another calculation for the 5-6-7 and

92

T. Okuda et al. /Applied Su.rface Science 121 / 122 (1997) 89 97

5-membered ring models. Contrary to Erwin's results, they concluded that the most stable model is the 5-membered ring model. In Fig. l(b) their calculated dispersions of the 5-membered ring and 5-6-7 models are plotted by dotted and dashed curves with our experimental results. Their result for the 5-6-7 model has crossing points similar to the Erwin's calculation, although the EB's of the surface states at point are higher than those of Erwin's. Because of these high EB's their dispersion widths become much larger than the experimental ones and the results led the authors to conclude that the 5-membered ring model is more suitable to explain the experimental results [11]. The double crossing feature of their calculation for the 5-6-7 model contrast to the parallel feature of that for the 5-membered ring model, however, it is qualitatively consistent with our experimental results. From these results we believe that the 5-6-7 model is the nearest structure to the real 3 × 1 surface at present, although there are some quantitative disagreement between experiments and both Erwin's and recent Jeong and Kang's calculations. Our SCLS result for the 3 × 1-Na surface [4] also supports the 7r-bonded chain structure. Fig. 3(a) shows the results of the surface sensitive ( h u = 130 eV) Si 2p spectrum of the Si(111)3 × l-Na surface. The spectrum is well fitted by a non-linear least squares method (see Ref. [4]) with one bulk (dotted curve; B) and two surface (dashed curves; S 1 and S 2) components, which are spin-orbit split doublets convoluted with Gaussian and Lorentzian functions. The two surface components shift to lower and higher EB's from the bulk peak position, reflecting the negatively and positively charged surface Si atoms comparing to the bulk Si atoms. The almost the same intensities of the two surface components indicate the existence of almost the same numbers of positively and negatively charged surface Si atoms on the 3 × 1-Na surface. According to Erwin's calculation, the total energy of the surface becomes lower when the surface Si atoms form the asymmetric 7r-bonded chain as ' A ' and ' B ' atoms in Fig. 2(b). In this case the charge of the ' A ' atoms transfers to the ' B ' atoms due to the same mechanism as the famous Haneman backling model [12] and the atoms ' B ' and ' A ' are charged negatively and positively. The atom ' C ' which connects with the Na atom is also consid-

(a)3xl-Na hv=130eV ,~, T~=~R T. ~

=.. ~;~ (b)3xl-Rb hv=133eV ,~ T~=75K

.~

oH

IllJ

J l l L l l ~ l

~ lIRI

I

¢} .(c)3xl-Ag I~ hv=-125eV m j ~

101

100

99

98

Binding Energy (eV) Fig. 3. Si 2p core spectra of (a) 3 × 1-Na, (b) 3 × l-Rb and (c) 3 × l-Ag surfaces. Empty circles are the experimental data. From the curve fitting bulk (B) and two or three surface (Si, Se and S3) components are deconvoluted.

ered to be charged negatively. Therefore, the existence of positively and negatively charged Si is consistent with the 7r-bonded chain structure. From the above discussion, however, it is expected that three surface components exist on the 3 × 1 surface, contradicting to the results of the two surface components. In addition, the numbers of surface Si atoms corresponding to S 1 and S 2 components estimated from the intensity ratios using well-known layer attenuation model analysis (for example Ref. [13]) are 2 and 2 in the 3 × 1 unit cell. This result means there is another surface atom besides ' A ' , ' B ' and ' C ' although these numbers may have some errors

T. Okuda et al. /Applied Surface Science 121 / 122 (1997) 89-97

because we did not consider the photoelectron diffraction effect. The high resolution surface Si 2p core spectrum (described in Section 3) of Si(111)3 X 1-Rb surface was fitted well with one bulk and three surface components rather than one bulk and two surface components as shown in Fig. 3(b). In this surface two of the three surface states are shifted to lower E B's. The estimated numbers corresponding to these three surface components, S~, S 2 and S 3, are 2, 1.6 and 1.33 in the unit cell, which means there are about 2, 1 or 2 and 1 or 2 surface Si atoms, which are positively-, negatively- and slightly negativelycharged, respectively. These results can be explained by the 5-6-7 model if we assign the S 2 component to the electrons from 'B' and 'C' atoms which are negatively charged, the S~ component to those from 'A' and other atoms which are positively charged and the S 3 component to those from bulk-like 'D', 'E' or 'F' atoms which may be slightly negatively charged. In the case of the 3 X 1-Na surface the S 3 component may merge into the bulk component because of the finite energy resolution of the experiment.

93

Contrary to the 3 × 1-AM surfaces there are no surface components shifted largely to lower Eg's from bulk component on the 3 × 1(6 × l)-Ag surface. On the other hand, one surface component shifted remarkably to higher Eg's than the bulk component. The existence of only two surface components on the 3 × 1(6 × 1)-Ag surface is not inconsistent with the 5-6-7 model if we assume that the S 2 component of the 3 × 1(6 × l)-Ag contains two surface components corresponding to S 2 and S 3 of the 3 × l-Rb surface. The estimated numbers of the surface atoms of 2.8 and 4.2 for S 1 and S 2 components arc roughly consistent with this assignment. On the basis of this assignment the small energy difference between S 1 and S 2 suggests that the asymmetry of the 7r-bonded chain on Si(lll)3 × 1(6 × 1)-Ag surface is smaller than that of the 3 × I-AM. In addition to the Si 2p core, we also measured the core spectra of the adsorbates such as Rb 4p and Ag 4d. The observed Rb 4p and Ag 4d core spectra showed simple spectral shape without any shifted components. These results indicate the single adsor-

~B ( a ) 7 x..S 7

3. Silver induced S i ( l l l ) 3 × 1(6 × 1) surface A Si(lll)3 × 1 surface also appears when we adsorb Ag onto the Si(111) surface. The structure is considered to be similar to the Si(lll)3 × 1-AM surface from the LEED I - V curve measurement [8]. The electronic structure, however, has hardly been investigated so far. We performed Si 2p SCLS measurement of the Ag induced 3 X 1(6 × 1) surface in order to compare with the SCLS of the 3 × 1-AM surfaces. Fig. 3(c) shows the result of the surface sensitive Si 2p core photoemission of the 3 × 1(6 × 1)-Ag measured at h u = 125 eV. The spectrum was recorded at the sample temperature of about 75 K to reduce the phonon broadening effect to achieve high energy resolution. By cooling the sample the FWHM of the spectrum becomes smaller and the Si 2p core of the 7 × 7 surface were deconvoluted into one bulk and four surface components as reported by recent SCLS measurements [14] of 7 × 7 surface. As seen in Fig. 3(c) the spectrum of the 3 × 1(6 × l)-Ag can be fitted by one bulk and two surface components.

:"

!

." -.. i f

hv=130eV I

I

I

I

I

I

I

.

•

~ :. ',: .% /

¢.

,*

,,

"-

~

. . . . . -,~.r.-..~ | , . _ . , I

I

I

|

I

~2.-"1

100

I

I

•

-.

I

1---

"

99

Binding Energy (eV)

tTQ-;

100

~

"-,

99

Binding Energy (eV)

Fig. 4. Si 2p core spectra of the Au induced (b) 5 × 2, (c) a-~/3-, (d) /3-x~-, and (e) 6 × 6 surfaces as well as (a) 7 X 7 surface.

94

T. Okuda et al. /Applied SurJhce Science 121 / 122 (19971 89-97

bate site on these surfaces and are consistent with the 1/3 ML coverage.

/3- ~3--Au and 6 × 6-Au surfaces [15]. We have performed SCLS and ARPES measurements of these Au induced reconstructions. Fig. 4 is the Si 2p core spectra of the (b) 5 × 2-Au, (c)o~-f3--Au, (d)/3-v~3-Au, (e) 6 X 6-Au surfaces as well as (a) 7 X 7 clean Si surface measured at room temperature. Every spectrum is well fitted with one bulk and two surface components. One important result is the large bulk core level shifts to lower EB'S from the 7 × 7 surface on these Au induced reconstructed surfaces due to

4. Au induced various S i ( l l l ) reconstructions Noble metal/semiconductor surface is another major subject of the surface science. On the Au adsorbed Si(111) surface a variety of reconstructions has been observed so far; 5 X 2 ( = 5 X 1)-Au, c~- and

m

(a)

5X2 [:2il] M

r

o

R[11

"'i~

,. ""

4

A .

1

0.5

..

~

,b4

• 8

,q~E

-

0 0.5 1 Wave Number ( A -1)

0

0.5

1

E

(b)

1vr K' o~-f-3[2][] M

K'

lvr M[11~

F

E

F' K[101]

F"

"'

L

I1"'

~'

1

r

'

'

h-; i

I

a

•"

I

1

I I

_

ee* ,

t

I .s

1

,

¢Ii

I

0.5

,

,

I

i

~,

,

,

,

.I

sI

,

I

I. I. ]

I

•

b

i

i

0 0.5 1 Wave Number ( A "1)

0

0.5

1

Fig. 5. Band maps of(a) 5 X 2-Au, (b) o~-~--Au, (c) /3- f3--Au and (d) 6 × 6-Au surfaces along [101], [112] and [211] directions.

95

Z Okuda et al./Applied Surface Science 121 / 122 (1997) 89-97 E

(c)

1vr K' fl-~-3 [2IT] M I

K'

F'

I~10]]

F

I

I

•

I

I

I

I

I

I

..b,,*

2

i

'

i

lit

I

I

I

I

~

]

2%,: •

I

lVI'

M'

I

4

.g ¢n

C'

'

C'

I

[

1

I

--

0.5

--

0

I

0.5

,

I

1

0

i,,, 0.5

i,.I 1

Wave Number ( A 4 )

(c:l) 6x6 [211] M

1

F

0.5

M[ll2]

0

0.5

1

Wave Number ()~-~)

F

~10]]

=1

0

0.5

Fig. 5 (continued).

their band bending of the valence bands toward the Fermi level• The stronger electronegativity of Au than Si may be the reason for the large band bending to lower EB's [16]. The SCLS to higher EB's than the bulk component for all surface reconstructions can also be explained by the electronegativity difference between Au and Si [16]. In spite of the charge transfer from Si to Au, the E B of Au 4f, however, shifts to higher EB'S on these surfaces (not shown here). These strange results can be explained as

follows. The net number of Au electrons increases when Au bonds to Si but the number of the localized 5d electron decreases to make a bonding state with the Si 3s3p band. Since the Coulomb interaction energy of F°(4f, 5d) is larger than that of F°(4f, cond), the E B of the 4f electron becomes larger although the net number of electrons increases. Other important results are the spectral dissimilarity between a-f3--Au and /3-f3-Au and the spectral resemblance between /3-~--Au and 6 × 6-Au sur-

96

T. Okuda et aL /Applied Surface Science 121 / 122 (1997) 89-97

faces. From this result it can be said that the chemical environments of surface Si of the c~- and /3-f3-Au are different from each other and the distinction of these two ~ f surfaces is necessary and the local structures of the /3-v/-3--Au and 6 X 6-Au surfaces are almost the same. The large and small intensities of S~ and S 2 states of 5 × 2-Au indicate the large number of the surface Si atoms which are almost uniformly influenced by Au and a small amount of the surface Si influenced by Au more strongly. Considering the small amount of Au on the 5 × 2-Au surface (0.4-0.5 ML [16]), Au atoms should sit at the position surrounded by many Si atoms at an equal distance like a T~ or H 3 site, where a small amount of gold can influence many Si atoms equally. As for the c~-~--Au surface, the ratio of two surface Si atoms is about 3 : 1 and this ratio cannot be explained successfully so far by the proposed models [16]. Assuming one of the surface components (S 2) as the contribution of the Si atoms at domain walls, the slight change of the ratio of S 2 on the 6 X 6-Au surface from the /3-v/3--Au surface is consistent with the picture that the ordering of domain walls leads the transition to the 6 X 6-Au from /3- ~ - A u [17]. The results of the ARPES measurement of these reconstructed surfaces are presented in Fig. 5 as the band mappings. The states around E B = 4 - 8 eV labeled A, B, C, D, C', C" and D' are thought to be Au 5d components and other states E v < E~ < ~ 4 eV labeled S, s, V, E, S' and V' are considered to be the bonding states of Au 6s-Si 3s3p. Some bulk band states labeled b estimated from the comparison with the band structure of the 7 × 7 surface are also shown. The A states have almost no dispersion for all surfaces and are considered to be the non-bonding Au 5d states. These states seem to accompany relatively weak states labeled B in each surface. The states B are almost parallel to the states A suggesting that the B and A are the same states split into two states by the spin-orbit interaction. The energy difference between A and B is about 0.6-1.0 eV and comparable to the energy of the spin-orbit splitting of Au 5d states (about 0.7 eV) expected by theoretical and experimental studies of bulk Au crystal (for example Ref. [18]).

In contrast to A and B, the states labeled C have relatively large and complex dispersions and split into some parts of C', C", D and D' suggesting that these states are composed of bonding 5d electrons. The existence of the bonding 5d states is consistent with the SCLS results in which the hybridization between Au 5d and Si 3s3p electrons is suggested. Spin-orbit splitting of C and D states are not clear implying that the orbital angular momentum is not a good quantum number for bonding electrons. In the bulk band gap of the [10~] direction the surface states (S) are shown on every surface. On every surface there are faint states (s) lying under the Fermi level. On the /3-f3--Au and 6 × 6-Au surfaces the states are seen in every wave number and strongly implying the metallic characters of these surfaces. The s states of the ~-~f3--Au surface, however, were only observed at several region in the momentum space and their density of states (DOS) are very small. Assuming that the domain wall structure of the ce-, / 3 - f 3 - A u and 6 × 6-Au surfaces has metallic character the result of the weak metallic states on the o~-f3-Au surface is consistent with the smaller density of the domain wall on the oL-f 3 - A u surface than / 3 - f 3 - A u and 6 × 6-Au surfaces which is suggested by STM measurement [17]. Except for the difference of the metallic s states the electronic structures of o~f3--Au, /3-~/3--Au and 6 X 6-Au surfaces are similar to each other, which suggests the local structure of these surfaces inside the domain wall are almost the same. According to the ARPES study of the single domain surface by Collins et al. [19], the 5 × 2-Au surface is one dimensional metal along the [110] direction. Thus, our results of metallic character along [10-[] and non-metallic character along [112] for the three domain 5 X 2-Au surface is consistent with their results. The states labeled V have similar dispersion curves to the edge of valence band maximum and may not be surface states. Karlsson et al. [20], however, also found these states V on the ~ - X ~ - - A u surface and assigned them as surface states from their independence from hr. On the 5 X 2-Au surface other surface states, S' and V', are seen suggesting its complex surface structure compared with other surfaces. For the accurate assignment of these surface states, however, further theoretical band calculations and experiments are required.

T. Okuda et al. /Applied Surface Science 121 / 122 (1997) 89-97

5. Conclusion Surface sensitive Si 2p CLS and ARPES measurements were applied to clarify the surface electronic and geometric structures of the AM and Ag induced Si(lll)3 × 1 and Au induced various reconstructions. As for the 3 X 1 reconstructed surface induced by AM, the 5-6-7 model is strongly suggested by ARPES and recent theoretical studies and also partly supported by the SCLS results. The SCLS results of the Ag induced 3 X 1 surface showed different shift from AM induced 3 × 1 surface suggesting that the different surface bonding character of the 3 X 1-Ag surface even though the geometric structure may be similar to that of the 3 X 1-AM surfaces. Regarding the Au induced reconstructions, the SCLS and ARPES results implies that the main difference between oL-, and /3-f3-Au and 6 X 6-Au surfaces is the domain wall densities and structures of these surfaces. In addition, the electronic structure of the 5 × 2-Au surface is different from other surfaces. The evidence of the hybridization of a part of Au 5d electrons with Si 3s3p electrons has been found on these surfaces by ARPES and SCLS measurements.

Acknowledgements We are obliged to the staff of the Photon Factory and Professor T. Ishii, Miss A. Harasawa, T. Kinoshita and A. Kakizaki of SRL/ISSP for their support of our experiment. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Sports, Science and Culture of Japan.

97

References [I] D. Jeon, T. Hashizume, T. Sakurai, R.F. Willis, Phys. Rev. LeU. 69 (1992) 1419. [2] T. Hashizume, M. Kayama, D. Jeon, M. Aono, T. Sakurai, Jpn. J. Appl. Phys. 32 (1993) L1263, for example. [3] K. Sakamoto, T. Okuda, H. Nishimoto, H. Daimon, S. Suga, T. Kinoshita, A. Kakizaki, Phys. Rev. B 50 (1995) 1725. [4] T. Okuda, H. Shigeoka, H. Daimon, S. Suga, T. Kinoshita, A. Kakizaki, Surf. Sci. 321 (1995) 105. [5] T. Okuda, K. Sakamoto, H. Nishimoto, H. Daimon, S. Suga, T. Kinoshita. A. Kakizaki, Phys. Rev. B 55, in print. [6] K.C. Pandey, Phys. Rev. Lett. 47 (1981) 1913. [7] J.E. Northrup, J. Vac. Sci. Technol. A 4 (1986) 1404. [8] W.C. Fan, A. Ignatiev, Phys. Rev. B 41 (1990) 3592. [9] S. Jeong, M.tt. Kang, Phys. Rev. B 51 (1995) 17635. [10] S.C. Erwin, Phys. Rev. Lett. 75 (1995) 1973. [11] S. Jeong, M.H. Kang, Phys. Rev. B 54 (1996) 8196. [12] Haneman, Phys. Rev. 121 (1961) 1093. [13] D.H. Rich, A. Samsavar, T. Miller, H.F. Lin, T.-C. Chiang, J.-E. Sundgren, J.E. Greene, Phys. Rev. Lett. 58 (1987) 579, and references therein. [14] C.J. Karlsson, E. Landemark, Y.-C. Chao, R.I.G. Uhrberg, Phys. Rev. B 50 (1994) 5767, for example. [15] S. Ino, in: P.K. Larsen, P.J. Dobson (Eds.), Proc. NATO Advanced Research Workshop on RHEED and Reflection Electron Imaging of Surfaces, June 15-19, Netherlands, NATO ASI Series B 188, Plenum, New York, 1988, p. 3. [16] Y. Okuda, H. Shigeoka, H. Daimon, S. Suga, T. Kinoshita, A. Kakizaki, J. Electron Spectrosc. Rel. Phen. 80 (1996)229. [17] J. Nogami, A.A. Baski, C.F. Quate, Phys. Rev. Lett. 65 (1990) 1611. [18] K.A. Mills, R.F. Davis, S.D. Kevan, G. Thornton, D.A. Shirley, Phys. Rev. B 22 (1980) 581, and references therein. [19] I.R. Collins, J.T. Moran, P.T. Andrews, R. Cosso, J.D. O'Mahony, J.F. McGilp, G. Margaritondo, Surf. Sci. 325 (1995) 45. [20] C.J. Karlsson, E. Landemark, L.S.O. Johansson, R.I.G. Uhrberg, Phys. Rev. B 42 (1990) 9546.