Electron source

Probe-forming lens

Sample (clusters)

DF-STEM detector

Aperture

HAADF-STEM detector

BF-STEM (EELS) detector

STEMimage x–y scan q

FIGURE 5.1 A schematic diagram of the operating principle of STEM, showing BF-STEM,

DF-STEM and HAADF-STEM detectors.

Gauss focus

Simple thin lens

Paraxial ray

Peripheral ray

Opticalaxis

Objective plane

Longitudinalaberration

Transverseaberration

Circle ofleast confusion

Drt

Dz

Drs

FIGURE 5.2 Ray diagram for a round lens with spherical aberration. Because of spherical aber-

ration, rays entering a round lens system away from the optical axis are refracted more strongly

than those entering closer to the optical axis.

Radius (nm)

Tem

pera

ture

(K

)

Cubic crystal

Decahedral

Icosahedral

Liquid

A

B

Quasi-molten

Quasi-molten

Decahedral

Icosahedral

Melt

Surface roughening

ROUGHFCCDECAICOS

00

200

400

600

800

1000

1200

1400

2 4 6 8 10

Nanoparticle diameter, D (nm)

Tem

pera

ture

, T (

K)

0300

400

500

600

700

800

900

1000

1100

1200

1300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

*

*

FIGURE 5.3 Phase diagrams of the structure of Au nanoparticles, presented in (A) by Marks in

19942 and (B) Barnard et al.49 in 2009. In (A), the dashed lines were extrapolated from the exper-

imental results shown in the solid lines. In (B), The solid lines were from the simulation whiles

the different symbols were experimental data. It is apparent that the general trend is similar in

both studies, though the actual phase boundaries are slightly different. In both cases, experimental

data were missing for nanoparticles smaller than 5nm in diameter.

Cluster size (nm)

Cluster size (nm)

0

0 0.5 1 1.5 2

0 0.5 1 1.5 2

0.2

0.4

0.6

0.8

1

B

A

C

0

0.2

0.4

0.6

0.8

1

HA

AD

F in

tens

ity (

a.u.

)H

AA

DF

inte

nsity

(a.

u.)

FIGURE 5.6 Three-dimensional atomic structure of an Au309 cluster. (A) 3D intensity profile

plot of Au309 derived from Figure 5.5A. A hard-sphere model for an Ino-decahedral structure is

shown with the electron beam (arrow) parallel to the fivefold axis. (B) Experimental intensity line

profile taken from the central atom column of the cluster to one of the corners. (C) Simulated

HAADF-STEM image (inset), obtained with a simple kinematical approach, of an Au309 cluster

with Ino-decahedral geometry. An intensity profile (solid curve) across one ridge is compared

with the result from a full dynamical multislice calculation (dashed line).8

Number of gold atoms along the column

0 2 4 6 8 10 12 14 16 18 20

AD

F in

tens

ity (

70–2

00m

rad)

Au309

Au[001]Au[111]

FIGURE 5.7 HAADF intensity as a function of number of Au atoms along the column, by mul-

tislice simulation.58

Lateral gold island size (nm)

Num

ber

of g

old

isla

nds

Coherent interface

Incoherent interface

1

5

5

0

2 3 4 5

Au

A <110>

C D

1 nm

B

E

G

F

5 Å

FIGURE 5.8 (A–E) HAADF-STEM images of Au nanoparticles on TiO2(110) arranged in the

order of projected particle size. The lattice coherency between Au nanoparticles and TiO2 sub-

strate changes according to the Au particle size. Panels (A) and (B) are coherent and (C)–(E)

are incoherent. (F) Magnified image of the epitaxial Au structure shown in (A). Here, two types

of Au sites are identified: on top of Ti–O columns and on top of O columns in the troughs of Ti-

containing columns (along the arrows). (G) A histogram of the formation of coherent or incoher-

ent interfaces as a function of Au nanoparticle lateral size.59

AWidth = 10.9 nm

Width = 4.3 nmB

1 nm

C

D W

2 nm

2h−Dh

FIGURE 5.9 Cross-sectional HAADF-STEM images of Au nanoparticles, supported on

TiO2(110), with width (A) 10.9 and (B) 4.3nm. (C) An atomistic model of Au nanoparticle on

TiO2. (D) A schematic Au nanoparticle showing measurements of nanoparticle dimensions.60

Hemisphericalclusters

Sphericalclusters

10

N1/3

500

2

4

6

8

10A

Dia

met

er (

nm

)D

iam

eter

(n

m)

Dia

met

er (

nm

)

15 20

10

N1/3

500

2

4

6

8

10B

15 20

10

N1/3

500

2

4

6

8

10C

15 20

FIGURE 5.12 Relationship between particle diameter and N1/3 for Au nanoparticles prepared by

three different methods: (A) colloidal nanoparticles, (B) nanoparticles by thermal evaporation and

(C) size-selected clusters performed in gas phase and soft-landed on the surface. Spherical cluster

approximation (the blue solid line) and hemispherical cluster approximation (the red dashed line)

are shown to allow comparison of overall particle geometry.64

Integrated HAADF intensity (a.u.)Integrated HAADF intensity (a.u.)

Num

ber

of p

artic

les

Num

ber

of p

artic

les

00

5

10

15

20

MP-Au38MP-Au38

0

5

10

15

20

D E

2 4 6 80 2 4 6

Au38

Au25

A

B

5 nm 5 nm

C

FIGURE 5.14 Weighing monolayer-protected (MP) Au38 clusters using size-selected Au clus-

ters. (A) Schematics showing that both types of clusters are co-deposited on the same TEM grid.

(B and C) Typical HAADF images of size-selected Au38 clusters and MP-Au38 clusters (with a

monomer arrowed). (D and E) Integrated HAADF intensities of MP-Au38 monomers are com-

pared with size-selected Au38 and Au25 clusters, respectively.65

A

B

C

D

FIGURE 5.15 Schematic representation of some possible atomic structures of bimetallic nano-

particles. (A) Core–shell, (B) sub-cluster segregation, (C) mixed and (D) three shells.66

Inte

nsity

Position (nm)

A B

0.0 0.2 0.4 0.6 0.8 1.0 1.2

4278

385Diameter = 4.5nm Diameter = 3.5nm

FIGURE 5.20 (A) One-dimensional HAADF-STEM (black) and EELS (red) intensity profiles

across a PdcorePtshell nanoparticle, showing that the Pt shell is two layer thick. The EELS signal

is the background-subtracted Pd core loss around 420eV. (B) Two-dimensional mapping using

HAADF-STEM (left) and Pd EELS signals (right) with 0.27nm per pixel resolution.83

B

A C

40,000

35,000

30,000

25,000

20,000

15,000

10,000

50000 10 20 30 40

60 70 80 90

70

60

50

40

3020100

50,000

45,000

40,000

35,000

30,000

25,000

20,000

15,000

10,000

5000

x

z

z

y50

FIGURE 5.21 (A) HAADF image of a RhIr cluster adsorbed on a MgO(110) surface. (B) Inten-

sity surface plot of the image in (A). (C) Three-dimensional model showing the cluster structure

determined by quantitative analysis.9