How Can We Make Stable Linear Monoatomic Chains? Gold-Cesium Binary Subnanowires as an Example of a Charge-Transfer-Driven Approach to Alloying

On the basis of first-principles calculations of clusters and one dimensional infinitely long subnanowires of the binary systems, we find that alkali-noble metal alloy wires show better linearity and stability than either pure alkali metal or noble metal wires. The enhanced alternating charge buildup on atoms by charge transfer helps the atoms line up straight. The cesium doped gold wires showing significant charge transfer from cesium to gold can be stabilized as linear or circular monoatomic chains.

Figure 1

HOMO and LUMO of 1D hexamer clusters: (a) ${\mathrm{Na}}_6$, (b) ${\mathrm{Cs}}_6$, (c) ${\mathrm{Au}}_6$, (d) $(\mathrm{CsAu}{)}_3$. Charges on each atom are 0.86, $-0.86$ for Cs-Au (0.70, $-0.70$ for Na-Au), and 0.92, $-0.90$, 0.91, $-0.90$, 0.86, $-0.88$ for CsAuCsAuCsAu (0.86, $-0.82$, 0.80, $-0.79$, 0.70, $-0.74$ for NaAuNaAuNaAu).

Figure 2

Schematic diagram of a unit cell projected onto the $yz$ plane (circles are for atoms) (a), and plots of cohesive energies and bond angles as a function of the chain length for pure $\mathrm{Au}/\mathrm{Na}/\mathrm{Cs}$ and binary $\mathrm{Na}/\mathrm{Cs}\mathrm{\text{−}}\mathrm{Au}$ atomic chains: (b) Au, (c) Na, (d) Cs, (e) Na-Au, and (f) Cs-Au (where solid and open circles indicate cohesive energy and bond angle, respectively).

Figure 3

Schematic diagram of electrostatic force on atoms constituting infinitely long atomic chain, disfavoring the zigzag structure. (A circle denotes an atom with positive or negative charge, and the arrow denotes the net electrostatic force on atom.)

Figure 4

Electronic band structures of pure $\mathrm{Au}/\mathrm{Na}/\mathrm{Cs}$ and binary $\mathrm{Na}/\mathrm{Cs}\mathrm{\text{−}}\mathrm{Au}$ chains for the minimum energy structures.