Chemistry Reference
In-Depth Information
Table 1 Key parameters for Rh, Pd, Pt and Au
Rh Pd Pt Au Reference
Atomic number 45 46 78 79 [
36
]
Lattice constant (
Å
)
3.80 3.89 3.92 4.08 [
36
]
Average surface energy (J m
2
) 2.7 2.0 2.5 1.5 [
72
]
Bulk cohesive energy (eV atom
1
) 5.75 3.89 5.84 3.81 [
36
]
Au-M diatomic binding energy (eV) 2.03 1.90 1.81 1.55 This study
a
a
The Au-M diatomic binding energies have been calculated at the LDA-DFT (PAW) level using
the VASP package [
73
,
74
]
expressed in terms of the so-called hopping integrals,
, between atom
i
and its
neighbours. This term incorporates the many-body nature of the interaction. All
interactions are assumed to decay exponentially with the interatomic distance
r
ij
.
The parameters {
A
,
ξ
,
p
,
q
} depend on the nature of the two atoms. Three parameter
sets are thus needed for a binary system: two sets for the two homonuclear
interactions and one for the heteronuclear interaction.
Typically, the parameters of the homonuclear interactions are fitted to reproduce
the experimental values of the cohesive energy of the metal and its elastic constants.
As a first approximation, the parameters of the heteronuclear interaction can be
taken as the mean values of the corresponding parameters of the two elements.
Although, in many cases, this has proved to be a successful strategy [
70
], a better
representation of the mixing properties of the two elements can be achieved by
fitting the heteronuclear parameters to the dissolution energies of each element into
a bulk matrix of the other [
71
].
ξ
6 Case Studies of AuM Nanorods (M
¼
Rh, Pd or Pt)
Gaining a fundamental understanding of the origin of the nanoscale properties of
bimetallic nanoparticles is a challenging issue. We describe our recent work
on three AuM systems, where M is Rh, Pd or Pt, to illustrate how the application
of experimental structural characterisation, computer simulation and chemical
synthesis techniques is possible to gain an understanding of, and control over, the
factors that drive the formation of the interfacial structure in core-shell nanorods.
Key structural and energetic parameters for the elements Rh, Pd, Pt and Au are
summarised in Table
1
. These parameters, and the relative differences between
them for the constituent metals of each system, underpin the metal-metal interac-
tions that are instrumental in the formation and stability of structure through
metal-on-metal growth.
