448
23 Sized Crystals
same substance. The DPS not only determines the skin-shell thickness but also distinguishes the performance of bonds in terms of length and stiffness and electrons in
the skin shells in terms of binding energy shift.
Figure 23.1 insets show the peak-area normalized Raman spectra collected from
the sized CeO 2 nanocrystals [1] and from the H 2 O(95%) + D 2 O(5%) droplets [2]
under the ambient conditions. At the ambient, water nanodroplet is in the supersolid
state of higher melting point and lower freezing and evaporation temperature [3]. The
measurements were focused on the D–O mode (centered at 2500 cm
−1 ) for the liquid
water and the vibration mode centered at 464 cm
−1 for the CeO 2 . The spectral peak
area normalization to one unit aims to minimizing the experimental artifacts. Insets c
and d illustrate the core-shell structure and its potential well, which shows the BOLS
effect on bond contraction and potential well depression in the undercoordinated skin
region up to three atomic layers [4].
The DPS thus resolves the phonons transiting their population from the bulk
(valley) to the skin (peak). The DPS blueshift from the valley to the peak represents
-0.06
-0.04
-0.02
0.00
0.02
380 400 420 440 460 480 500 520
Raman shift (cm -1 )
pellet
25 nm
15 nm
10 nm
7.4 nm
6.1 nm
I (arbitrary unit)
Δω (cm
-1
)
25 nm
15 nm
10 nm
7.4 nm
6.1 nm
CeO 2
(a)
(b)
(c)
(d)
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
I (arbituray unit)
Δω DO (cm
-1
)
1.7 nm
2.3
4.0
H 2 O droplet
0.1
0.2
0.3
0.4
0.5
1/D (nm
-1
)
Fraction
CeO 2
F = 2.995D
-1
400
420
440
460
480
500
2300
2400
2500
2600
2700
0.04
0.08
0.12
0.16
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
1/D (nm
-1
)
Fraction
f(D) = 0.54D
-1
H 2 O
Fig. 23.1 DPS verification of the core-shell configuration for the sized a CeO 2 nanocrystals and
b H 2 O nanodroplets with insets a and b showing the spectral area normalized peaks (original spectral
data are sourced from [1, 2]). Insets c and d illustrate the core-shell structure and its BOLS defined
potential well that turns to be deeper in the skin covering shells. The fraction coefficient f(D) =
= 3R/R = 6 defines the skin-shell thickness b = 0.5 nm for CeO 2 nanocrystals
and d = 0.09 nm of the H–O dangling bond length for H 2 O nanodroplets. Reprinted with
permission from [7]
23 Sized Crystals
same substance. The DPS not only determines the skin-shell thickness but also distinguishes the performance of bonds in terms of length and stiffness and electrons in
the skin shells in terms of binding energy shift.
Figure 23.1 insets show the peak-area normalized Raman spectra collected from
the sized CeO 2 nanocrystals [1] and from the H 2 O(95%) + D 2 O(5%) droplets [2]
under the ambient conditions. At the ambient, water nanodroplet is in the supersolid
state of higher melting point and lower freezing and evaporation temperature [3]. The
measurements were focused on the D–O mode (centered at 2500 cm
−1 ) for the liquid
water and the vibration mode centered at 464 cm
−1 for the CeO 2 . The spectral peak
area normalization to one unit aims to minimizing the experimental artifacts. Insets c
and d illustrate the core-shell structure and its potential well, which shows the BOLS
effect on bond contraction and potential well depression in the undercoordinated skin
region up to three atomic layers [4].
The DPS thus resolves the phonons transiting their population from the bulk
(valley) to the skin (peak). The DPS blueshift from the valley to the peak represents
-0.06
-0.04
-0.02
0.00
0.02
380 400 420 440 460 480 500 520
Raman shift (cm -1 )
pellet
25 nm
15 nm
10 nm
7.4 nm
6.1 nm
I (arbitrary unit)
Δω (cm
-1
)
25 nm
15 nm
10 nm
7.4 nm
6.1 nm
CeO 2
(a)
(b)
(c)
(d)
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
I (arbituray unit)
Δω DO (cm
-1
)
1.7 nm
2.3
4.0
H 2 O droplet
0.1
0.2
0.3
0.4
0.5
1/D (nm
-1
)
Fraction
CeO 2
F = 2.995D
-1
400
420
440
460
480
500
2300
2400
2500
2600
2700
0.04
0.08
0.12
0.16
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
1/D (nm
-1
)
Fraction
f(D) = 0.54D
-1
H 2 O
Fig. 23.1 DPS verification of the core-shell configuration for the sized a CeO 2 nanocrystals and
b H 2 O nanodroplets with insets a and b showing the spectral area normalized peaks (original spectral
data are sourced from [1, 2]). Insets c and d illustrate the core-shell structure and its BOLS defined
potential well that turns to be deeper in the skin covering shells. The fraction coefficient f(D) =
= 3R/R = 6 defines the skin-shell thickness b = 0.5 nm for CeO 2 nanocrystals
and d = 0.09 nm of the H–O dangling bond length for H 2 O nanodroplets. Reprinted with
permission from [7]