ru(0001)表面およびco/ru(0001)表面における ナノクリスタル氷...
TRANSCRIPT
-
ナノクリスタル氷の成長ダイナミクス
Ru(0001)表面およびCO/Ru(0001)表面における
川合真紀 (東京大学新領域 教授、独立行政法人理化学研究所 主任研究員)
加藤浩之 (独立行政法人理化学研究所 川合表面化学研究室 先任研究員)Mischa Bonn(オランダ国ライデン大学教授、FOMディレクター)
近藤剛弘
27 April 2007 研究室セミナー
T. Kondo, et al., J. Chem. Phys. 127 (2007) 094703, 1-14.T. Kondo, et al., J. Chem. Phys. 126 (2007) 181103, 1-5.
T. Kondo, et al., Surf. Sci. 600 (2006) 3570-3574.T. Kondo, et al., Chem. Phys. Lett. 448 (2007) 121-126.
-
M.Chaplin,“Water structure and behavior”http://www.lsbu.ac.uk/water/
Phase diagram of water
triple point: 273.16 K, 610.6 Pa
Typical earth
Typical Venus
Typical Mars
Critical point
2nd Critical point
研究背景
-
“Physics of ice” Edited by V. F. Petrorenko et al. (1999) Oxford University press
M.Chaplin,“Water structure and behavior”
HGW : hyperquenched glassy water (if rapidly cooled)I. Kohl, et al., Phys. Chem. Chem. Phys. 7 (2005) 3210. V. Velikov, et al., Science 294 (2001) 2335.
Metastable phase: Supercooled-water and glassy-water 研究背景
O. Mishima, Nature 396 (1998) 329O. Mishima, 高圧力の科学と技術, 13 (2003) 165.
-
研究背景
Both amorphous solid water(ASW) and crystalline ice (CI) are observed.
Interstellar medium (Cosmic dust clouds )
Planetesim (Astroid, comet)
Proto planetary disk
Planetary atmosphere (stratosphere)
氷表面が化学反応の舞台となっている!
Formation of prebiotic organic molecule
P. Ehrenfreund, et al., Rep. Prog. Phys. 65 (2002) 1427.
分子進化(生命の起源)
オゾン層破壊Halogen chemistry
J.Abbatt, Chem. Rev. 103 (2003) 4783.
基礎科学的に氷表面での化学反応を明らかにする:Well-definedな氷表面の作成が必要
アモルファス氷の結晶化や氷表面のモフォロジーの理解が重要!
-
Vapor
Background
ASW : amorphous solid waterC. A. Angell, Ann. Rev. Phys. Chem. 55 (2004) 559.T. Loerting, et al. J. Phys.: Cond. Matt. 18 (2006) R919. HDA : high density amorphous ice
(1.17 g cm-3 at 0.1 Mpa, many dangling bonds)
O. Mishima, et al. Nature 396 (1998) 329.
HDG : high density glassy water(1.1 g cm-3)
A. H. Narten, et al., J. Chem. Phys. 64 (1976) 1106.M. E. Palumbo, J. Phys.: Conf. Ser. 6 (2005) 211.
LDA : low density amorphous ice(0.94 g cm-3)
O. Mishima, et al. Nature 396 (1998) 329.
VHDA : very high density amorphous ice (1.26 g cm-3 at 0.1 Mpa, many dangling bonds)
T. Loerting, et al. Phys. Chem. Chem. Phys. 3 (2001) 5355.
アモルファス氷の結晶化
ex) LDA (10~130K, UHV)
Dosing on solid at
-
Amorphous Solid Water
amorphous
crystalline
ener
gy結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
-
Amorphous Solid Water
amorphous
crystalline
ener
gy
crystalline nucleus
3 24( ) ( ) 43 cryst amorph
G r r r
* 2( )cryst amorph
r
( ) 0G rr
Change in free energy when a nucleus forms:
Classical nucleation theory
Surface termpositive
Bulk termnegative
Barrier at: ; Barrier height: G(r*)
Nucleus size at maximum:
: the material density: the chemical potential: the surface tension between the phase
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
e.g. : Backus et al., J. Chem. Phys. 121, 1038 (2004)
-
Amorphous Solid Water
amorphous
crystalline
ener
gy
crystalline nucleus
* /2( )
CI ASW
cryst amorph
r
( ) 0G rr
Change in free energy when a nucleus forms:
Classical nucleation theory
Surface termpositive
Bulk termnegative
Barrier at: ; Barrier height: G(r*)
Nucleus size at maximum:
3 2/
4( ) ( ) 43 cryst amorph CI ASW
G r r r
: the material density: the chemical potential: the surface tension between the phase
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
e.g. : Backus et al., J. Chem. Phys. 121, 1038 (2004)
-
amorphous
crystalline
ener
gy
Amorphous Solid Watercrystalline nucleus
3 2/
1 4( ) ( ) 42 3 cryst amorph CI ASW
G r r r
Change in free energy when a nucleus forms:
Classical nucleation theory
Surface termpositive
Bulk termnegative
: the material density: the chemical potential: the surface tension between the phase
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
e.g. : Backus et al., J. Chem. Phys. 121, 1038 (2004)
-
amorphous
crystalline
ener
gy
Amorphous Solid Watercrystalline nucleus
Change in free energy when a nucleus forms:
Classical nucleation theory
Surface termpositive
Bulk termnegative
3 2/
1 4( ) ( ) 42 3 cryst amorph CI ASW
G r r r
: the material density: the chemical potential: the surface tension between the phase
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
e.g. : Backus et al., J. Chem. Phys. 121, 1038 (2004)
-
amorphous
crystalline
ener
gy
Amorphous Solid Watercrystalline nucleus
3 2/
2 "/ /
1 4( ) ( ) 42 3
( ) ( )
cryst amorph CI ASW
CI air ASW air
G r r r
r f r
Change in free energy when a nucleus forms:
Classical nucleation theory
Surface terms
Bulk termnegative Line tension
: the material density: the chemical potential: the surface tension between the phase
Additional terms affect for positive/negative??
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
バルク、表面のどちらからもありうる
e.g. : Backus et al., J. Chem. Phys. 121, 1038 (2004)
-
Side-view
Top-view
( 3 3) 30R
D. L. Doering et al.,Surf. Sci. 123, 305 (1982).
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
Ru(0001)
氷の結晶をそのまま乗せた構造
Ru(0001)でのエピタキシャル成長の期待
下地が及ぼす“template effect”の期待
Modified Bernal-Fowler-Pauling rules に従う:(1) water is bound to the surface through oxygen lone pair orbital(2) tetrahedral bonding configuration is maintained for water(3) O has two H attached at 0.96 Åwith an H-O-H bond angle of 105o(4) there is one hydrogen atom on each O-O axis
D. L. Doering et al.,Surf. Sci. 123, 305 (1982). P. A. Thiel et al., Surf. Sci. Rep. 7, 211 (1987).
M. A. Henderson, Surf. Sci. Rep. 46, 1 (2002).
Z. Dohnálek, et al, J. Chem. Phys. 110, 5489 (1999).
Z. Dohnálek, et al., J. Chem. Phys. 112, 5932 (2000).
界面からの成長も十分に考えられるD. L. Doering et al.,Surf. Sci. 123, 305 (1982).
-
E. H. G. Backus, M. L. Grecea, A. W. Kleyn, and M. Bonn, Phys. Rev. Lett. 92 (2004) 236101.
P. Ahlström, P. Löfgren, J. Lausma, B. Kasemo and D. Chakarov, Phys.Chem.Chem.Phys. 6 (2004) 1890.
Z. Dohnálek et al., J. Chem. Phys. 112 (2000) 5932.P. Löfgren et al., Surf. Sci. 367 (1996) L19.
P. Löfgren et al., Langmuir 19 (2003) 265.
Crystalization initiates from Interface and/or bulk of ASW
Crystalization initiates from surface of ice
Crystalization initiates from Interface and/or bulk
V. Buch et al., J. Phys. Chem. 100 (1996) 3732.B. Rowland et al., J. Chem. Phys. 102 (1995) 8328.
Different case
Denied by
No direct evidence was reported up to now!本研究により詳細が明らかになった。
結晶化はどこから起こるのか(表面?バルク?界面)?
研究背景 結晶化のメカニズム
-
R. S. Smith et al. Surf. Sci, 367 (1996) L13.
(Isothermal temperature-programmed desorption, ITPD)160K
“” has been used to analyzethe crystallization kinetics!
CrystallineASW
85K
研究背景: どうやって結晶化したことを判断するのか ?
等温脱離種計測 (ITPD)
-
R. Souda, Chem. Phys. Lett. 415 (2005) 146.
液体状態の相変化
異なるITPDの解釈が提案されている…
R. Souda, Phys. Rev. Lett. 93 (2004) 235502.
モフォロジーの変化
R. Souda, J. Phys. Chem. 122 (2005) 134711.
モフォロジーの変化
脱離率の違いは結晶化を示してはいない ???
最近になり…
-
R. Souda, J. Phys. Chem. 125 (2006) 181103.
ガラスー液体 (or 液体ー液体) 相変化とモフォロジーの変化
R. Souda, J. Phys. Chem B. 110 (2006) 17524.
過冷却水状態の生成過程
モフォロジーの変化
R. Souda, J. Phys. Chem B. 110 (2006) 14787.
どちらのITPD解釈が正しいのかを明らかにするためには
(1) 結晶性とモフォロジー両方のモニターが必要 !!!
(2) 非破壊に計測することが重要 !!!
研究動機(1)
-
R. S. Smith et al. Surf. Sci, 367 (1996) L13.
等温脱離種計測 (ITPD)
160K
“” has been used to analyzethe crystallization kinetics!
CrystallineASW
85K
研究背景: ITPDによるモフォロジーの解釈
-
CrystallineASW Crystalline Appearance of substrate
P. Löfgren et al., Langmuir 19 (2003) 265.
P.Ahlstrom et al., Phys.Chem.Chem.Phys. 6 (2004) 1890.
下地表面の“濡れ性”によって解釈されてきた
Zero-order desorption
Morphological change
研究背景 ITPDによるモフォロジーの解釈
-
CrystallineASW Crystalline Appearance of substrate
G. Kimmel et al., Phys. Rev. Lett. 95 (2005) 166102.(also by G. Zimbitas et al., J. Chem. Phys. 123 (2005) 174701.)
appearance of the first-water-layer
Morphological changes AFTER crystallization
結晶化の最中および結晶化後のモフォロジー
研究動機(2)
?結晶化の最中のモフォロジーは ?
Bulk state (surely crystallize??) Morphology ??
-
ヘリウム原子線散乱 (HAS) 表面の結晶性とモフォロジー
ITPD
反射赤外吸収分光法 (IRAS)
バルクの状態
Ru(0001)のアモルファス氷(ASW)の結晶化過程を明らかすること (いつ, どこから, and どのように ?)
研究目的
Combination of ITPD, HAS and IRAS
非破壊・無擾乱に同時計測!!
COの伸縮振動のエネルギー 界面の状態
COASW
-
b
c
1
2
34
5
d
e
ghi
jf
・Y
X
Z
Skimmer
Chopper
Nozzle 0.05 or 0.02
0.2 6.1
33.9
43Aperture
[mm]
Aperture
Aperture
1.5107.5
201372
115
SampleSurface
Detector
3.4 1.2
a
(B)
(A)
1 Source chamber : < 3x10-7 Torr
2 Chopper chamber : < 2x10 -8 Torr
3 Scattering chamber : < 1x10 -10 Torr
4 Second chopper chamber: < 1x10 -10 Torr
5 Detector chamber : < 9x10 -11 Torr
実験装置
T. Kondo, et al. Eur. Phys. J D 38 (2006) 129.
NozzleSkimmer
Aperture
Aperture
Q-mass (MSQ-400)
MCT detector
Ru(0001)
Q-mass (HAL201)
Aperture
ZnSe polarizer
BaF view port
BaF view port
Pre-amplifier
Discriminator
Pulse counterMirror
MirrorMirror
Mirror
Mirror
Mirror
TC (K-type)
TC (C-type)
PCGPIB
GPIB RS-232C
Digital multimeter
IR source Pre-amplifier
PC
HAS ITPD
IRAS
He
(B)
(A)
-
4
3
2
1
0In
tens
ity (x
106
)[ar
b.un
its]
7065605550454035302520
Scattering angle [deg.]
Ru(0001)Ts= 800KEHe=60meV
清浄化Ar ion bombardment (0.5keV, 20min.)Annealing (1000K a few min.)O2 treatment (RT)Flashing (up to 1560K)
清浄性の確認
He atom scatteringLow Energy Electron Diffraction
Clean Ru(0001) surface
-
CO/Ru(0001)Ts=155K
103
104
105
106
107
He
inte
nsity
[cou
nts]
350300250200150100500
Time [s]
3.53.02.52.01.51.00.50.0
CO Exposure [L]
(2 3 2 3) 30R ( 3 3) 30R
(5 3 5 3) 30R
2100
2080
2060
2040
2020
2000
Wav
enum
ber [
cm-1
]
350300250200150100500
CO exposure time [s]
14121086420
Absorbance [x10
-3 ]
Adsorption of CO on Ru(0001)
He beam
He beam
CO exposure
Lateral dipole interaction
CO> 0.33
CO< 0.33
Lateral dipole interactionWeakening of the Ru-CO bond
(S. H. Payne, et al., Surf. Sci. 594, 240 (2005). and references therein)
on-top
-
Preparation of D2O/Ru(0001)
-
102
103
104
105
106
107
He
inte
nsity
[cou
nts/
s]
16001400120010008006004002000
D2O exposure time [s]
876543210
D2O exposure [L]
D2O / Ru(0001)EHe = 63 meV0.005 L/s
Ts= 111 K Ts= 118 K
T. Kondo, et al., Surf. Sci. 600 (2006) 3570
He散乱で観るRu(0001)表面へのD2O吸着
He beam
He beam
D2O exposure
1.5 L (corresponding to =0.67, = 1.0ML)
3 3 30R
4
68
103
2
4
68
104
2
He
inte
nsity
[cou
nts]
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6
Momentum transfer K [Å-1]
D2O / Ru(0001)[1100] directionAfter 1.5 L exposureEHe = 63 meVTs = 118 ± 2 K
x10-
9
200180160140
2.75 L
2.0 L
1.5 L0.75 L0.5 L
D2O TPD
1.5 L 3 3 30R
Temperature [K]
disorder
1022
4
1032
4
1042
4
105
He
inte
nsity
[cou
nts/
s]
86420-2-4-6-8
K [Å-1]
~50ML~90 K[1100]
ASW/Ru(0001)
dosing
dosing
-
Ice Ih H-up Half-dissociated H-down
これまでに提案されてきた Ru(0001) における水分子吸着形態
D. L. Doering and T. E. Madey.,Surf. Sci. 123 (1982) 305.
TPDLEED
G. Held and D. Menzel, Surf. Sci. 316 (1994) 92.
LEED I-VP. J. Feibelman, Science. 295 (2002) 99. A. Michaelides, et al. J. Am. Chem. Soc. 125 (2003) 2746.
DFT
Side-view
Top-view
( 3 3) 30R
D. N. Denzler, et al. Chem. Phys. Lett. 376 (2003) 618.
TPD, SFG
P. J. Feibelman, Chem. Phys. Lett. 389 (2004) 92.
H-side ? dissociated ?Space for H
Many possibilities
-
S. Meng, Chem. Phys. Lett. 402 (2005) 384.
H-up and H-down mixing structure
For satisfying the experimentally observed work function and SFG
Proposed by DFT
Short chain(flat and upright sequence)
Chain structure models are proposed !
Short chain
S. Haq, et al. Phys. Rev. B 73 (2006) 115414.
LEED, IRAS, DFT, work function
( N. S. Faradzhev, et al., Surf. Sci. 415 (2005) 165. and references therein)Exceptionally high dissociation probability by the electron or x-rayMost stable structure is “dissociated phase” but essentially water is intact on Ru
これまでに提案されてきた Ru(0001) における水分子吸着形態
M. Thiam, T. Kondo, et al., J. Phys. Chem B 109 (2005) 16024.T. Kondo, et al., Surf. Sci. 600 (2006) 3570
Our HAS, IRAS and TPD supports this view
-
Preparation of D2O/CO/Ru(0001)
-
CO=~0.65 MLCO=~0.33 MLCO=0 ML
COの被覆率によってRu(0001)でのD2Oとの相互作用が大きく異なる!
102
103
104
105
106
107
1400120010008006004002000
D2O dosing time [s]
3.53.02.52.01.51.00.50.0
D2O exposure [L]
102
103
104
105
106
107
1400120010008006004002000
D2O dosing time [s]
3.53.02.52.01.51.00.50.0
D2O exposure [L]
2800
2600
2400
2200
2000
1800
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O dosing time [s]
15
10
5
0
Absorbance x10
-3
2100
2050
2000
1950
1900
1850
1800
1750
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O dosing time [s]
10
8
6
4
2
0
Absorbance x10
-3
2800
2600
2400
2200
2000
1800
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O dosing time [s]
2800
2600
2400
2200
2000
1800
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O dosing time [s]2100
2050
2000
1950
1900
1850
1800
1750
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O dosing time [s]
CO = 0.33Ts=~95 K
CO = 0.65Ts=~95 K
(c)
(d) (e) (f)
(h) (i)
102
103
104
105
106
107
He
inte
nsity
[cou
nts/
s]
1400120010008006004002000
3.53.02.52.01.51.00.50.0
D2O exposure [L]
CO = 0Ts=~95 K
(b)(a)
HAS
IRAS(OD)
IRAS(CO)
25
20
15
10
5
0
Abs
orba
nce
[x10
-3 ]
120010008006004002000
D2O dosing time [s]
CO=0 CO=0.33 CO=0.65
Absorbance at 2535 cm-1(g)
Free-OD水素結合OD
H. Ibach and D. L. Mills, “Electron energy loss spectroscopy and surface vibrations”, (Academic Press, New York, 1982).
on-top
bridge
hollow
CO at
Assignment wasbased on
-
100
80
60
40
20
0
Abs
orba
nce
[x10
-3 ]
2200 2100 2000 1900 1800
Wavenumber [cm-1]
2060CO/Ru(0001)
~90 K
2
4
1032
4
1042
4
105
He
inte
nsity
[cou
nts/
s]
86420-2-4-6-8
K [Å-1]
-CO/Ru(0001)
5 3 5 3 30R -CO/Ru(0001)
5 3 5 3 30R
Preparation
[1100] direction
~ 90 K
Exposing the Ru(0001) surface to ~20 L CO at ~120 K Helium diffraction
IRAS
CO=~0.65 ML:
Accords with the literature:J. Braun, et al., J. Chem. Phys. 106, 8262 (1997).
Accords with the literature:H. Pfnür, et al.,Surf. Sci. 93, 431 (1980)
-
2800
2600
2400
2200
2000
Wav
enum
ber [
cm-1
]
1400120010008006004002000
D2O exposure time [s]
403020100
D2O adsorption layer [BL]
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Absorbance
102
103
104
105
106
107
He
inte
nsity
[cou
nts]
1400120010008006004002000
Time [s]
D2O/CO/Ru(0001)Ts=125 KD2O/CO/Ru(0001)Ts=125 K
Shift !
D2O dosing followed with IRAS and He scatteringA
bsor
banc
e
3000 2800 2600 2400 2200 2000
Wavenumber [cm-1]
2%
OD str.
CO str.
Water exposure
D2O coverage [ML]
1022
4
1032
4
1042
4
105H
e in
tens
ity [c
ount
s/s]
86420-2-4-6-8
K [Å-1]
disorder
~90 K~50 ML[1100]
100
80
60
40
20
0
Abs
orba
nce
[x10
-3 ]
2200 2100 2000 1900 1800
Wavenumber [cm-1]
2060
2042
CO/Ru(0001)
D2O/CO/Ru(0001)
~90 K
-CO/Ru(0001) 5 3 5 3 30R D2O/
ASW/CO/Ru(0001)
50 ML
-
Crystallization of ASW(D2O) on Ru(0001)
T. Kondo, et al., J. Chem. Phys. 126 (2007) 181103, 1-5.
-
Abs
orba
nce
2800 2700 2600 2500 2400 2300 2200
Wavenumber [cm-1]
Abs
orba
nce
[arb
.uni
ts]
3000 2800 2600 2400 2200 2000
Wavenumber [cm-1]
100
80
60
40
20
0
Converted [%
]
300025002000150010005000Time [s]
10
8
6
4
2
0
Tota
l wei
ghte
d ab
sorb
ance
Absorption intensity( ) ( ) ( )Cryst Cryst ASW ASWI a I b I
0.67ASW Cryst
Converted fraction0.67
0.67aFraction
a b
Total weighted absorbance0.67
(0.67 )initial
a ba b
a
b
a : Crystalline iceb : Amorphous solid water
Analysis of IRAS spectra
timeOD stretch mode
Converted fraction [%
]2800
2700
2600
2500
2400
2300
2200
Wav
enum
ber [
cm-1
]
3500300025002000150010005000
Time [s]
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Absorbance
2800
2700
2600
2500
2400
2300
2200
Wav
enum
ber [
cm-1
]
3500300025002000150010005000
Time [s]
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Absorbance
Experimental result
Fitting result
c.f. E. Backus, et al., Phys. Rev. Lett. 92 (2004) 236101.
-
103
104
105
He
inte
nsity
[cou
nts/
s]
103
104
105H
e intensity [counts/s]
Verifying the original interpretation !
152.5 K
Crystallization of ASW on Ru(0001)
156.5 K
バルク内からのランダム核生成を示唆している!
ITPD
HAS
IRAS
2000150010005000
Time [s]
0.30
0.20
0.10
0.00
Absorbance
4
3
2
1
0
Mass 20 [arb. units]x10
-9
2.0
1.5
1.0
0.5
0.0Mas
s 20
[arb
. uni
ts]x10 -9
2800270026002500240023002200W
aven
umbe
r [cm
-1]
500040003000200010000
Time [s]
10
8
6
4
2
0
Tota
l abs
orba
nce
[arb
.uni
ts]
100
80
60
40
20
0
Converted fraction [%
]
Crystallization Crystallization
( OD:バルクの状態)
(脱離水分子の数)
(表面の状態)
ヘリウム原子線散乱
等温脱離種計測
反射赤外吸収分光
103
104
105 d{ln(IHe )}/dt[arb.units]
D2O/Ru(0001) 48 ML
Ru(0001) 58 ML
下地Ru(0001)からの“template effect”がないことを示している結晶化中における下地露出を伴うモフォロジー変化を示唆!
-
M. J. Avrami, J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941).
: converted fraction [%]t: time [s]k: crystallization rate constantn : parameter (mechanism of the crystallization)
Classical nucleation and growth model of isothermal solid-state phase transformation kinetics
100 1 exp ( ) [%]nt kt
n = ~4.0 :Random nucleationand homogeneous growth
検証:理論モデルを用いた結晶化メカニズムの解析
n = 1.4 :Heterogeneous growth
Our result is well fitted byn = ~3.5 :ランダム核形成、実効的等方成長
Water in Confining Geometries, edited by V. Buch and J. P. Devlin (Springer-Verlag, Berlin, 2003)
100
80
60
40
20
0Con
verte
d fr
actio
n [%
]
40003000200010000
Time [s]
experiment:Avrami equation n = 5: n = 4: n =3.5: n = 3: n = 2:
D2O / Ru(0001)153 K
-
(1) 結晶化時の脱離(2) 形成核の有限サイズ(3) 表面、界面、バルクそれぞれからの成長
更に進んだ理論モデルを用いることが可能になる
E. H. G. Backus et al., J. Chem. Phys. 121, 1038 (2004).
検証:理論モデルを用いた結晶化メカニズムの解析
バルク内でのランダム核形成、実効的等方成長である
考慮する3要素
100
80
60
40
20
0Con
verte
d fr
actio
n [%
]
6000500040003000200010000
Time [s]
160.5 K 156 K 153 K 152.5 K 152 K Model
ASW / Ru(0001)Nucleation grain diameter is selected as 3 ML
P. Ahlström, et al., Phys. Chem. Chem. Phys. 6, 1890 (2004).
ランダム核形成、等方成長メカニズムであることが確認された
For the model, “bulk nucleation” is applied
導出したGrowth-rateとnucleation-rate
-
101
102
103
104
105
Cry
stal
lizat
ion
time
[s]
6.66.56.46.36.26.16.05.95.8
1000/T [1/K]
Crystallization time of ASW (~50 ML)deposited on Ru(0001)
Ecrystallize=650 ± 25 meV
Activation energy of the ASW (~50 ML) crystallization on Ru(0001)
exp Ek ART
Arrhenius equation
k : rate coefficient of the reaction
T : temperature
A : pre-exponential factor (frequency factor)
E : activation energy of the reaction
R : gas constant (or Boltzmann constant)
1ln( ) ln( )Ek AR T
T. Kondo, et al., J. Chem. Phys. 126 (2007) 181103, 1-5.
-
まとめ:Ru(0001)表面におけるアモルファス氷の結晶化
Ru(0001)
first-water-layer
Amorphous solid water
Crystalline ice grain
“” in ITPD“Random nucleation”“effectively homogeneous growth”
“appearance of the first-water-layer”
Morphological change
Ecrystallize=650 ± 25 meV
Time for the ASWcrystallization:
T. Kondo, et al., J. Chem. Phys. 126 (2007) 181103, 1-5.
-
形成される結晶氷のIRASスペクトルにおける違いA
bsor
banc
e
3000 2800 2600 2400 2200 2000
Wavenumber [cm-1]
A (168 K)A (166.5 K)A (160.5 K)A (156.5 K)
アモルファス氷
90 KD2O / Ru(0001)
T結晶氷
結晶氷間の差スペクトル
T. Kondo, et al., Chem. Phys. Lett. 448 (2007) 121-126.
-
46
10
2
46
Gra
in si
ze [M
L]
170165160155150Aneealing temperature [K]
(b)
D2O / Ru(0001)
100
80
60
40
20
0Con
verte
d fr
actio
n [%
]
6000500040003000200010000
Time [s]
160.5 K 156 K 153 K 152.5 K 152 K BB-model
D2O / Ru(0001)
(a)
13
00.5 ( ) (1 ( ))CI NR J T t dt
平均的氷結晶グレインサイズの見積もり
: the fraction of the conversion from ASW to CI at the time t
( )t
( )NJ T : the crystalline nucleation rate derived from model analysis
: the isothermal annealing temperature
T
T. Kondo, et al., Chem. Phys. Lett. 448 (2007) 121-126.
-
Abs
orba
nce
3000 2800 2600 2400 2200 2000Wavenumber [cm-1]
ASW A (168 K) A (166.5 K) A (160.5 K) A (156.5 K)
33
3
4 3 ( * ) 4 3 ( * ) 0.54 3 ( * )
CI CI
CI
r R r RS
r R
: critical nuclei size*r
スペクトル成分量がグレインサイズの面積に対応している
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Frac
tion
of g
rain
bou
ndar
y sp
ectru
m
35302520151050Average crystal growth [ML]
experimental data model calculation
Frac
tion
of g
rain
bou
ndar
y
氷グレインー氷グレイン界面の水分子振動に対応
赤外分光による初の観測T. Kondo, et al., Chem. Phys. Lett. 448 (2007) 121-126.
-
Crystallization of ASW(D2O) on CO/Ru(0001)
T. Kondo, et al., J. Chem. Phys. 127 (2007) 094703, 1-14.
-
103
104
105
He intensity [arb.units]
103
104
105
He
inte
nsity
[cou
nts/
s]
x10-
9
4
3
2
1
0
Mass 20 [arb.units]x10
-9
2.0
1.5
1.0
0.5
0.0Mas
s 20
[arb
. uni
ts]x1
0-9
0.30
0.20
0.10
0.00
Absorbance
100
80
60
40
20
0
Converted fraction [%
]
2000150010005000
Time [s]
20151050
Absorbance [x10
-3 ]
2800270026002500240023002200W
aven
umbe
r [cm
-1]
D2O/CO/Ru(0001)152.5 K
2080
2060
2040
2020
2000
1980Wav
enum
ber [
cm-1
]
500040003000200010000
Time [s]
[arb
.uni
ts]10
8
6
4
2
0To
tal a
bsor
banc
e
2000150010005000
Time [s]
CO
abs
orba
nce
500040003000200010000
Time [s]
Integral absorbance of the peak at ~2050cm-1
Integral absorbance of the peak at ~2040cm-1
50 ML55 ML156.5 K
D2O/CO/Ru(0001)
ITPD
HAS
IRAS( OD:バルクの状態)
(脱離水分子の数)
(表面の状態)
ヘリウム原子線散乱
反射赤外吸収分光
IRAS(CO:界面の状態)
反射赤外吸収分光
-
103
104
105
He intensity [arb.units]
103
104
105
He
inte
nsity
[cou
nts/
s]
x10-
9
4
3
2
1
0
Mass 20 [arb.units]x10
-9
2.0
1.5
1.0
0.5
0.0Mas
s 20
[arb
. uni
ts]x1
0-9
0.30
0.20
0.10
0.00
Absorbance
100
80
60
40
20
0
Converted fraction [%
]
2000150010005000
Time [s]
20151050
Absorbance [x10
-3 ]
2800270026002500240023002200W
aven
umbe
r [cm
-1]
D2O/CO/Ru(0001)152.5 K
2080
2060
2040
2020
2000
1980Wav
enum
ber [
cm-1
]
500040003000200010000
Time [s]
[arb
.uni
ts]10
8
6
4
2
0To
tal a
bsor
banc
e
2000150010005000
Time [s]
CO
abs
orba
nce
500040003000200010000
Time [s]
Integral absorbance of the peak at ~2050cm-1
Integral absorbance of the peak at ~2040cm-1
50 ML55 ML156.5 K
D2O/CO/Ru(0001)
(1) Ru(0001)の場合と同じ結晶化メカニズム及びキネティックス
(2) 極初期に界面が変化
(3) 結晶化中における下地表面の曝露を伴うモフォロジー変化
新たに分かる主な事柄:
(4) HASのみが捉えたポテンシャル凹凸の違い
-
2000150010005000
103
104
105 d{ln(IHe )}/dt[arb.units]
検証:下地表面が露出するタイミングの比較
500040003000200010000
2000150010005000
Time [s]
20151050
Absorbance [x10
-3 ]
2080
2060
2040
2020
2000
1980Wav
enum
ber [
cm-1
]
500040003000200010000
Time [s]
CO/Ru(0001)でのIRAS
152.5 K 156.5 K
crystallizationAppear !!!
非常に似たタイミングで下地が析出している
Appear !!!crystallization
結晶グレインのサイズや分布が似ていることを示唆している
Ru(0001)でのHAS
-
101
102
103
104
105
Cry
stal
lizat
ion
time
[s]
6.66.56.46.36.26.16.05.95.8
1000/T [1/K]
50 ML Ru(0001)50 ML CO/Ru(0001)50 ML O/Ru(0001)50 ML (2×1)-O/Ru(0001) Exposure to the vacuum
Ecrystallize= 650 ± 25 meV
Activation energy of the ASW (~50 ML) crystallization on Ru(0001)
exp Ek ART
Arrhenius equation
k : rate coefficient of the reaction
T : temperature
A : pre-exponential factor (frequency factor)
E : activation energy of the reaction
R : gas constant (or Boltzmann constant)
1ln( ) ln( )Ek AR T
(1) 活性化エネルギーが下地に依らない(2) 結晶化中の下地露出と結晶化の競争が起きている
-
結論
first-water-layer
Crystalline ice grain
(1) オリジナルのITPD解釈が正しい(脱離率の変化が結晶化の変化と対応)
Morphological change
Ecrystallize= 650 ± 25 meV
Time for the ASW crystallization: “” in ITPD
ASW
(2) アモルファス氷の結晶化は下地によらずバルク内からのランダム核形成および 実効的等方成長である(Ru(0001)からのtemplate effectはおきない)
(3) 結晶化の最中に下地の露出を伴うモフォロジーの変化が起きている
非破壊同時計測によりRu(0001)でのアモルファス氷(ASW)結晶化を調べた結果、以下のことが分かった:
(4) ポテンシャル凹凸は下地によって異なる(よく定義された氷表面作成に際して
極めて重要ーHASのみが捉えた!!)
T. Kondo, et al., J. Chem. Phys. 127 (2007) 094703, 1-14.T. Kondo, et al., J. Chem. Phys. 126 (2007) 181103, 1-5.
T. Kondo, et al., Surf. Sci. 600 (2006) 3570-3574.T. Kondo, et al., Chem. Phys. Lett. 448 (2007) 121-126.