Hanoi Tower-like Multilayered Ultrathin Palladium
Nanosheets
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Abstract
This paper describes the synthesis,
formation mechanism, and mechanical
property of multilayered ultrathin Pd nanosheets. An anisotropic,
Hanoi Tower-like assembly of Pd nanosheets was identified by transmission
electron microscopy and atomic force microscopy (AFM). These nanosheets
may contain ultrathin Pd layers, down to single unit cell thickness.
Selected area electron diffraction and scanning transmission electron
microscopy data show the interconnected atomically thick layers stacking
vertically with rotational mismatches, resulting in unique diffractions
and Moiré patterns. Density functional theory (DFT) calculation
with van der Waals correction (DFT+vdW) shows the adsorption of Pd<sub>4</sub>(CO)<sub>4</sub>(OAc)<sub>4</sub> on Pd(110) surface (<i>E</i><sub>ad</sub> = −5.68 eV) is much stronger than
that on Pd(100) (<i>E</i><sub>ad</sub> = −4.72 eV)
or on Pd(111) (<i>E</i><sub>ad</sub> = −3.80 eV).
The adsorption strength of this Pd complex is significantly stronger
than that of CO on the same Pd surfaces. The DFT+vdW calculation results
suggest a new mechanism for the observed anisotropic growth of nanosheets
with unusually high aspect ratio, in which the competitive adsorptions
between Pd<sub>4</sub>(CO)<sub>4</sub>(OAc)<sub>4</sub> complex and
CO on various surfaces result in a favored growth along the ⟨110⟩
directions and inhibition along ⟨111⟩ directions. The
mechanical property of these multilayered Pd nanosheets was studied
using AFM and nanoindentation techniques, which indicate multilayered
nanosheets show more plastic deformation than the bulk in response
to an applied force