第3300回無機材料に関する最近の研究成果発表会

JJaann  2288,,  22001133

可溶性有機ケイ素高分子の新展開：酸素や水に極めて安定な  紫外・可視発光材料化と熱分解法による結晶シリコンへの物質変換  

奈良先端科学技術大学院大学  
物質創成科学研究科 藤木道也  

謝辞：川本義樹•･加藤雅彦•･藤本雄士•･斉藤知来•･細島進一•･川部琢磨•･郭起燮  ((財))日本板硝子材料工学助成会  ((22000099年度))  
1

Background: Importance of Polymers in Science and Industry
高分子とは？  
四大基幹素材の一つ  
•  幅広い分野と領域で利用  

高分子  •  人類の現代生活を支える必需物資  
•  産業の基幹となる資材  •  化学・繊維から医療や電子産業、      航空宇宙分野まで豊かな社会と  導電性
高分子  

無機
高分子    先端技術を  実現する機能材料  
セラミックスITO/SnO2
InGaZnO
SSiiOO22  
SSii33NN44  

有機ケイ素高分子  （シリコーン）  

金属  金属シリサイド(CaSi2, MoSi2)

固体Si

2

Background: Importance of Silicon in Science and Industry
４族半導体  

Si	

シリコンが用いられる主な理由  
11..  資源的に豊富（地殻中に2277%%))  
22..  環境下において無害((低毒性//無毒）  
33..  単結晶基板加工・薄膜化が容易  
44..  ppnn制御が容易  

33族--55族化合物半導体  
22族--66族化合物半導体  

55..  高純度化が容易  
66..  良好な透明・絶縁膜  ((SSiiOO22))  
77..  室温で適当なバンドギャップ((11..11eeVV))  

SSii以外の元素（特に第３周�期以降）では  ・高い電子・正孔移動度  ・毒性    ・資源に乏しく、高価  ・安全管理に多大なコスト  
・発火性  

短所  
11..  バルクSSii結晶は非発光性（間接遷移）  
22..  電子  ((~~660000ccmm22//VVss))・正孔((~~110000  ccmm22//VVss))    移動度が比較的低い  
33..  電子、光電変換デバイスに用途が限定  
44..  電界発光デバイス//レーザー????  
rreeff))  11..5555μmm光通信帯域で誘導RRaammaannレーザー          ((IInntteell,,  NNaattuurree  22000055))            緑色・赤色発光ポーラスSSii  
（LL..TT..  CCaannhhaamm,,  AAPPLL  11999900,,  JJAAPP  11999977,,  NNaattuurree11999911）引用回数  55000000,,  11000000,,  660000回  
3

Importance of Silicon both Science and Industry
アモルファスシリコン  ((aa--SSii))  （結晶SSiiと比較して))  
高分子::  SSiiHH44,,  SSii22HH66  ((ガス状モノマー）の３次元架橋重合体  
特徴  
11..  自由な形状加工が可能  
22..  大面積化が可能  
33..  単純工程のため、低コスト化  
44..  製造温度が比較的低温((330000--335500℃))  

aa--SSii  ::  iinnssoolluubbllee  SSii--SSii  bboonnddeedd  ppoollyymmeerrss  AA  mmiixxttuurree  ooff  11DD,,  22DD,,  nneettwwoorrkkss  
wwiitthh  HH--tteerrmmiinnii  短所  
11..  SSiiHH44,,  SSii22HH66など自然発火性ガスの使用  
22..  非発光性欠陥準位((ffrreeee  rraaddiiccaall))の形成  
33..  電子・正孔移動度((~~1100  ccmm22//VVss))がかなり低い  
多結晶SSii  ((ppoollyy--SSii))  
現状：アモルファスシリコン  ((aa--SSii))  のSSii--SSii吸収帯にエキシマーレーザー照射  SSii--HH結合の解裂//脱水素反応（化学的はフラッシュ熱分解法))  
4

新概念//革新プロセスによる有機・無機ハイブリッド材料  
--  設計・創成・手法・要素技術の確立  --

安全な新しい工業化プロセスを視野に入�れて  •  危険なSSiiHH44,,  SSii22HH66ガスの代替ソース  •  頻繁に保守を必要とする高価でエキシマーレーザの不使用  •  大気下で安定で、溶媒可溶な固体SSiiソースは可能か？  

5

Break-through of Si-Based Materials and Devices
1954: Pearsonら(ATT Bell研究所)
c-Siを用いた太陽電池の発明→1958: バンガード1号(米国海軍:人工衛星)に搭載  
1975: Spear, LeComberら(Dundee大学)不可能とされていた水素終端a-Si:Hのpn制御に成功  
1976: Carson, Wronski (RCA)
a-Si:Hを用いた太陽電池を試作    
1979: Spear, LeComberら(Dundee大学)
a-Si:HをTFT試作に成功    
1970: IBM Esaki-Tsu ら
半導体超格子の基本概念の提唱と実証  

6

Break-through of Si-Based Materials and Devices
1970s–90s: III-V族 GaAs/InGaAs 研究が活発化

SiO2石英系ファイバー用LD光源  (1975-1980)   

1988: 古川  ((九工大）

Siにおける量子サイズ効果：Egの増大nc-Si:H  

1990: 高木ら(キャノン)

SiH4のCVD法で作製したnc-Si:Hが量子サイズ効果により室温で赤色発光    

1990: Canham (Royal Signals and Raders)

ポーラスシリコン (por-Si)から量子細線�効果により室温で強く赤色発光

1991: Lehmann, Gösele (Duke Univ)

por-Siが量子細線�化によりEgがc-Siより0.5eV以上ブルーシフト    

1980–1990: 空気中で安定で、溶媒可溶性の鎖状シリコン高分子:
Organopolysilane
量子細線�効果により室温で強く紫外発光77  

Silicon shines on

Heisenberg uncertainty

Δp・Δx ≥ (1/2)	ΔE・Δt ≥ (1/2)"rB	

Γ	Band gap

3-D type

Direct type

3.4 eV (365nm)

Indirect type

1.1 eV (1127nm)

L. Brus, J. Phys. Chem., 1994, 98, 3575

殆どのパイ共役高分子  Bohr radius (4.9nm)∝ ε (~11.7) x 1/eeff8

Crossovers between 0-D, 1-D, 2-D, and 3-D. How Silicon shines onBand gap

3-D

2-D

1-D

Direct gap

3.4eV (365nm)

2.61eV (475nm)

Indirect gap

1.1eV (1127nm)

2.48eV (500nm)

3.89eV (319nm)

L. Brus, J. Phys. Chem., 1994, 98, 3575
Light-emission from•loss of k-selection rule (Heisenberg principle)•In Physics…

•decrease in dimensionality (3D→2D, 1D, 0D)•inversion dissymmetry by polar structure (O,F)•inversion dissymmetry by TO phonon•In Chemistry…
9

1144族元素の骨格次元性とバンドギャップ  ((EEgg))	

Question: Is it possible to tailor optical band gap between 0.1 and 5.5 eV ?
Possible approaches: network Si, Si-Ge alloy, 2D-3D meso-structure, 0D (nano cluster) 	

(eV)

14 Group元素の階層性    骨格の階層性  
3D
iinnddiirreecctt  ggaapp  ((非発光性))

2D-3D

2D0D
1D-2D
1D
((発光性)) ddiirreecctt  ggaapp    ((発光性))  

–

ca. 8

C

5.5

Si

1.1

1.8-2.3

2.3

ca. 3–4

Ge

0.7

1.35

–

ca. 3–4

Sn

0.1 (direct gap)

–Pb(0)

–

ca. 3
–10

Silicon shines onIn Physics•a-Si:Hx by plasma CVD of SiH4 and Si2H6
D. J.Wolford et al, Appl. Phys. Lett., 1983, 42, 369

In Chemistry
4NaA. Watanabe, J. Organomet. Chem., 2003, 685, 122.

•Porous Si by electrochemical etching
L. T. Canham, Appl. Phys. Lett., 1990, 57, 1046

•nc-Si by sputtering Si in H2 gas
S. Furukawa, Phys. Rev. B, 1988, 38, 5726

•nc-Si into SiO2 by ion implantation

3Na

Y. Kanemitsu, Phys. Rev. B, 1994, 49, 16845

K. Furukawa et al, Jpn. J. Appl. Phys., 1994, 33, L413

•1-D ~ R2SiCl2 2Na→ polysilane•2-D ~ CaSi2 → siloxene
HCl aq

M. Stützmann et al, Phys. Rev. B, 1993, 47, 4806.
3Na

RSiCl3 → polysilyne

H. Takagi et al, Appl. Phys. Lett., 1990, 56, 2379

•a-Si/SiO2 superlattice
D. J. Lockwood et al. Nature, 1995, 378, 258

Δ

t-BuSiCl3 → octasilacubane → a-Si

Brongersma et al, Appl. Phys. Lett., 2000, 76, 351•nc-Si by plasma CVD of SiH4RBrΔ•0-D ~ SiCl4 → (Si)n → (R)m(Si)n →a-Si

K. Furukawa et al, Macromolecules, 1990, 23, 3423.
Δ→ a-Si like [O2] (by XPS, EDX, IR)
M. Fujiki et al, Chem. Mater., 2009, 21, 2459.

11温故知新. Kipping (1924), Gilman (1961), Hengge (1975), Shimoda (2006)  
Solution Processable Poly-Si for TFT   
T. Shimoda et al. (Seiko-Epson & JSR groups), Nature, 2006, 440, 783-786   
Phliquid  

Ph

Ph
ClSi
PhPh

Cl

Ph

Li/THF

Si

Si
photo-induced
ring opening
reaction upon
405 nmirradiationin GloveBox

PhSi

PhClPh
Si

Si Si

~1920
Kipping反応  
Hliquid bp 190°C  

PhCl

PhPh

Cl
AlCl3/Bz

in CPSSiSi

Si SiClClClHClH

Cl

LiAlH4Si
HHSiSiSi Si
HH
H
H

H1975 Hengge  CPS
Si–H結合: C–H結合と違ってO2やH2Oに敏感 : 変質・分解  a-Si:HnHClSiH

Clpyrolysis
1. 300°C, 10min
2. a-Si 300-400°C
3. 540°C 2h

poly-Si
308nm
XeCl laser
spin coat µ ~ 108 cm2V-1s-1
ink jet µ ~ 6.5 cm2V-1s-1

in GloveBox

cf.
>> µ (高分子半導体)>µ (分子性半導体)  

12

New Approach of 2D-Si nanosheets  
H. Okamoto, Y. Sugiyama, H. Nakano (Toyota R&D). Chem. Eur. J., 2011, 17, 9864-9887. 	

3 CaSi2 + 6HCl + 3 H2O	Si2H3(OH)3 + 3CaCl2 + 3 H2	

Shaken with surfactants (SDS) for 10 days	

3 CaSi2 + 6HCl → (Si6H6) + 3 CaCl2	–30 °C	

(Si6H6)n	 treated with n-decylamine	

13

Reaction mechanism of polycarbosilane : Precursor for ceramics

矢島プロセス	 R = Me → β-SiC	
C. A. Burkhard, J. Am. Chem. Soc., 1945, 67, 2173-2174.
Yajima, S.; Hasegawa, Y.; Hayashi, J.; Okamura, K. J. Mater. Sci. 1978, 13, 2569-2576.
Interrante, L. V. et al. Chem. Mater. 1999, 11, 2038–2048.
CH3 CH3SiSiCH3Si

CH3 CH3CH3SiH
CH3CH2CH3+H3C Si
CH3CH3+fastHSiSi

CH3CH3slow

CH3SiCH3CH3CH3CH2Si
CH3CH3CH2Si
CH3+H2β-SiC	

H. Ichikawa, Development of Organosilicon Polymers, CMC, 1989, 187-196.

14

Hypothesis: A possible production of (Si)n from soluble Si-containing
polymer due to ß-H elimination reaction by flash pyrolysis in vacuo

R = Me → β-SiC	

矢島プロセス	

素朴な疑問そして作業仮説  
R =>> Et → β-SiC (?)	HC H

β-水素を有するRが自己還元剤  RCHSiSiSiSiSiRSiHH2Sin15

One-pot synthesis of soluble polysilyne : (RSi)nK. Furukawa et al, Macromolecules, 1990, 23, 3423.
16

Pyrolytic properties of (n-BuSi)n in N2
2020°C /min, in N2

100i-Bu
n-Bu

90

15

1040i-Bu
n-Bu

52080
TG [%]

60

DTG [%/min]

TG [%]

80

n-Bu

100

250
300
350
400
450
500

7060
50
40050

SNP

150

250
350
Temp. [00550

450

20406080
Time [100120

Isothermal TGA (20°C /min, in N2)

Weight loss (%)
obscalc (R/RSi)

i-Bu

56.9

67.0n-Bu43.3

67.0

250°C
Pyrolytic timedependency

500°C
Pyrolytic temp.
dependency
17

Pyrolytic properties of (n-CnH2n+1Si)n in N218

Broad change in PL spectra of pyrolitic n-Bu-polysilyne : (n-BuSi)nSi∆ (≤ 450°C)

in vacuo

350
400
450

Intensity (normalize)

n-Bu

as-prep250
300

400 450 500 550 600 650 700 750 800
Wavelength /nm∆ (500°C)

in vacuoc-Si(very week PL)

λex = 360nm (500°C:λex = 390nm), 77K

19

Photoluminescence from pyrolyzed (n-BuSi)n (77K, 0.5mW/cm2)
Ex= 360nm

Ex= 360nm

as-prep
500-10min500-90min

400-90min
450-90min
Intensity (normalize)

as-prep
350-90min
Intensity (normalize)

Intensity (normalize)

as-prep
250-10min250-90min
30010min
300-90min

Ex= 390nm

1

6

3
400 450 500 550 600 650 700 750 800

400 450 500 550 600 650 700 750 800

400 450 500 550 600 650 700 750 800

Wavelength /nm

Wavelength /nm

Wavelength /nm

250°C

300°C

as-prep

350°C

400°C

450°C

500°C (10min)

500°C
20

Absorption spectra of pyrolyzed (n-BuSi)n films (r.t.)

500°C (10min)

500°C
21

The origin of red-shift at 350–450°C•Nanocrystal(n-BuSi)nEg ~ Egbulk + 29.6 (eVÅ)/DEgbulk =1.1 eV

D =Si diameter

L. E. Ramos et al.
Phys. Stat. Sol. (b), 242 (2005) 3053

Photon energy /eV

3.0
as-prep
250
300
350
400
450
500

150

2.5

250
410

700

2.0
1000
1480
2120
1.50

12

34Diameter /nm

5622

The origin of red-shift at 350–450°C•Superlattice

EPL (eV) = 1.6+0.7/dSi2
dSi =Si film thickness

a-Si
SiO2n-Bu

Lockwood, D. J. et al. Nature, 378 (1995) 258

23

The origin of marked decrease in deep red emission band at 500°C

amorphouscrystal

25µm

Polysilyne

Δ500°C -90min

25µm

Si crystal
Eg~1.1eV
No emissive

PL intensity (~850nm)
markedly decreased

Exposed to air
Functional Groups

Region /cm-1

Si-Si~480 (a-Si)

Si-H

985-800

Highly emissive Si-based particle
Dispersed in various solvents
24

Intense blue emission particles dispersed in various solvents
λex 365nm,
1.0mW/cm2, r.t.

100µm

cast on quartz

ΦF = 23% (DMF)
21% (THF)
14% (Hexane)
1% (Water)τ = 4.8 nsec, > 10nsec (THF)(in hexane)

Region /cm-1

400

Si-Si

~480 (this work)

7350

Si-O-Si

1090-1010 (ref)

6300

5250

cf Si-Si (c-Si)(a-Si)

508cm-1 (this work)~ 460cm-1 (this work)

4200

3UV

PL

21500±150cm-1100
PLE

1050000

150

Intensity (a.u.)

Functional Groups

Wavelength /nm
300
400 500 600

2008Absorbance

λex= 360nm

40000

5030000

Wavenumber /cm

20000
-10

electron-phonon
Si-Si and Si-O-Si coupling ?
25

Nanometer-size Baumküchen of pyrolized (n-BuSi)n exposed to air

TEM and EDX

3.8 Å spacing~1.9Å (~0.19 nm)

SiO

Si

~3.8Å (~0.38 nm)

alike nm-size Baumküchen ?

26

Nanometer-size Baumküchen of pyrolized (n-BuSi)n exposed to air
Highly elongated by 10-23% with highly opened angle (~180°)

SiO

Si

Si:O = 1 :3 (EDX)

R(SiOSi): 3.24-3.64 Å~ (1.62-1.82 Å ) x2 ÅR(SiOSi) : 4 Å~ 2 x2 Å by forcing polysiloxane

OSi108°SiR(SiOSi): 2.6 Å = sin(108°/2) x 1.6 Å x2Ref)
1. J. S. Nicoll et al. Phys. Chem. Min., 20, 617-624 (1994)
2. E. M. Lupton et al., NIC Symp., 32, 57-64 (2006)
27

Schematic explanation by chemists
Baumküchen Silicon (pyrolized (n-BuSi)n exposed to air)

σ-electronn-electronlone pairSiOSi

σ-n mixing (conjugation)
cf. σ-phπ mixing (conjugation)

SiO
Si

SiO
SiSi

ν1 ~
500cm-1
ν2 ~1100cm-1

OSi

lattice~ 4 Å

Puckered 2D-Si planes

2-D Si electronic structure
coupled with (ν1 + ν2)

To design light-emission silicon materials•loss of k-selection rule (decrease in size, introduction of disorder)•dimensionality decrease (3D→ 2.5D, 2D)•introduction of dissymmetry by polar oxygen•introduction of dissymmetry by electron-phonon coupling (Si-Si / Si-O-Si)
28

Band-gap engineering from organo (Si/Ge/Sn) polymers

3NaClSiClCl

3Na
Cl

Ge C lCl

Sn C lCl∆≤ 150°C~250°C∆∆≤ 300°C

350°C

c-Si ?

c-Ge ?

3Na
Cl

∆

∆
≤ 200°C∆
250°C
c-Sn ?

29

PL spectra of [(n-BuSi)x-block-(n-BuGe)1-x]n30

Thermogravimetric (TG), Differential TG (DTG), Raman analyses

TG/DTG diagrams (5°C /min, in N2)

Raman spectraa-Ge
c-Ge

X=0.00as-prep

Intensity (normalize)

200-90min
250-90min

300-90min

350-90min
400-90min
450-90min
500-90min

1000

800

600

400

200

400

500 ()-1

Wavenumber (cm )X＝0.00 
!
 

0100

Polymer

200300

Polymer

(-R)

a-Ge

a-Ge(-H)c-Ge

c-Ge31

Raman, HR-TEM, EELS of pyrolitic [(n-BuSi)x-block-(n-BuGe)1-x]n film
EELS
X=0.50, 500 °C-90min

TEM
X=0.50,500°C-90min

Raman spectra

Intensity (normalize)

a-Si

X=1.00 500-90min

c-Si
a-Ge

X=0.50 500-90minc-Ge

X=1.00 500-90min
1000

800

600400Amorphous

200Ge map

-1

Wavenumber (cm )CH3CH3Δ
SixGeSi1-xnx

Ge1-xn32

Next Ideas to Solve Problematic Issues

アルキルポリシリン	

Δ(200–500°C)	
熱分解物	

n-Bu	i-Bu	

欠点	Φ < 1% （at RT）	耐酸化性 → 低い	
耐水性 → 低い	
熱分解物も同様	
33

Hypothesis and Design

元素周期表�
13�14�15�16�17�18B

CNOAl SiPS Cl Ar

高耐久・高効率可視発光材料の設計指針�

フッ化アルキル基の導入�

F Ne・撥水性, 撥油性	

安定性	・電子吸引性	

耐酸化性	

・2DSi電子構造の制御	
・発光波長の制御	
・アルキルポリシリンとの共重合	
34

Structure and some propertiesPolymer Chemistry, 3, 3256-3265（2012)35

HR-TEM and EELS images and nano-structures
BSNP	

FSNP	

HR-TEM images of (left) BSNP and (right) FSNP cast onto
a carbon micro grid (scale bar = 20 nm).	

Si mapping (left) and F mapping (right) images in EELS ofFSNP on a carbon micro-grid (scale bar = 0.1 µm).	

36

Calculation (TD-DFT/3-21G)– 0.025 au	
– 0.027 au	

– 0.036 au	
– 0.041 au	– 0.247 au	
– 0.253 au	– 0.265 au	– 0.274 au	

perhydro-trans-siladecaline	

37

Calculation (TD-DFT/3-21G)

R = 	38

UV-Vis Calculation (TD-DFT/3-21G)
fwhm (0.025 eV)	39

Change in UV-Vis spectra with PL spectrum
Direct-type transition !	
allowed	A comparison of UV–vis absorption spectra of
FSNP, BSNP, and FBSNP (x = 0.25, 0.50, 0.75) in
THF at 25 °C.	

PL spectra (excited at 360 nm) and PLE
monitored at 500 nm of FSNP in THF at 25 °C.	

H. Okamoto, Y. Sugiyama, H. Nakano. Chem. Eur. J.,
2011, 17, 9864-9887 	

40

No change in IR spectra to air exposure

Changes in the IR spectra (3500–400 cm-1) of (a) FSNP and (b) BSNP films cast onto KBr(as-prepared fresh sample and sample left in air for one month).	
41

Change in PL spectra (Film)

Changes in the normalized PL spectra of
FSNP, BSNP, and FBSNP (x = 0.50) films
after different air-exposure times.	

42

A comparison of three PL spectra (THF, RT)

ΦF / 3.0 % 	
ΦF / 1.9 % 	
ΦF / 1.0 % 	

43Change in PL spectra in THF-H2O solution

Changes in the PL spectra of FSNP, BSNP, andFBSNP (x = 0.50) in a THF–water (90/10 (v/v))
solution after different storage times. 	

44

Effects of Fluoroalkyl Groups

vs	
1. Excellent stability toward air and THF-water (film, solution) upto 300 °C
from IR, Raman, PL, Calculation (TD-DFT, 3-21G, B3LYP) 	
2. Direct-type transition from dual indirect-and-direct transitions
from UV, PL, PLE, Calculation 	3. Quantum efficiency ~3% at RT (cf. 1% of (n-BuSi)n)	
4. Loss of such the stability of pyrolytic products at 500 °C
due to release of trifluoropropyl group	45

環境影響最小化を視野に入�れ、機能材料をシンプルプロセス技術でhttp://panasonic.co.jp/eco/products/chemical_substance/	

欧米ではno more new polymers
no more toxic materials
既存材料 +新プロセスの組合わせ技術で...  

46

Conclusion
λex 365nm, 1.0 mW/cm2 (77K)

λex 365nm,1.0 mW/cm2 (RT)Eg =3 eVVis

near IR

3NaClM ClClSi∆∆≤ 450°C

500°C

Air (O2,H2O)

c-Si

アルキル  
フッ化アルキル  Geアルキル  47