Strain Relief Guided Growth of Atomic Nanowires in a ${\mathrm{Cu}}_3\mathbf{N}\mathrm{\text{−}}\mathrm{Cu}(110)$ Molecular Network

A self-corrugated ${\mathrm{Cu}}_3\mathrm{N}\mathrm{\text{−}}\mathrm{Cu}(110)$ molecular network shows the potential to overcome the element dependence barrier as demonstrated by epitaxial growth of atomic nanowires ($\sim 1\mathrm{nm}$ in width) among various $3d$, $4d$, and $5d$ elements. Scanning tunneling microscopy shows that all of the investigated atomic nanowires share an identical structure, featuring uniform width, height, orientation and the same minimum separation distance. Ab initio study reveals that the formation mechanism of atomic nanowires can be directly attributed to a strain relief guided asymmetric occupation of atoms on the originally symmetric crest zone of the corrugated network.

Figure 1

(a) High-resolution room temperature STM image ($60\AA \times 60\AA$, 0.37 nA, 750 mV) with line profile along $x{x}^{\prime }$. (b) Schematic view of the atomic structure for one corrugation unit on the ${\mathrm{Cu}}_3\mathrm{N}$ network from ab initio calculations. ${\mathrm{N}}_t$, ${\mathrm{N}}_m$, and ${\mathrm{N}}_b$ represent the top, middle, and bottom positions, respectively, for N atoms. (c) STM image ($14\AA \times 20\AA$) magnified from image (a), superimposed upon N atoms based on the structural model. Blue, dark brown, and light brown spheres denote N atoms including ${\mathrm{N}}_t$, ${\mathrm{N}}_m$, and ${\mathrm{N}}_b$ in the top layer of the ${\mathrm{Cu}}_3\mathrm{N}$, Cu atoms in the top layer of the ${\mathrm{Cu}}_3\mathrm{N}$, and Cu atoms below the ${\mathrm{Cu}}_3\mathrm{N}$ network, respectively.

Figure 2

(a) STM image ($570\AA \times 570\AA$, 0.45 nA, 860 mV) of atomic nanowires after deposition of 0.05 ML of Fe and the line profile along $x{x}^{\prime }$. (b),(c) and (d) show STM images of atomic nanowires after deposition of 0.2 ML of Fe, Pd, and Au, respectively (all three STM images are sized $700\AA \times 700\AA$).

Figure 3

(a) The top view shows three different fourfold hollow sites of the ${\mathrm{Cu}}_3\mathrm{N}$ network which are designated as 1, 3, and 5, for the top, intermediate, and bottom Fe atoms, respectively, and two different threefold bridge sites 2 and 4, for top and bottom Fe atoms. The side view shows that the positions of the Fe adatoms at sites 2 and 4, according to the results of ab initio calculation, are higher than the ones at other sites. (b) Schematic view of the atomic structure of a single Fe nanowire from ab initio calculations. Each nanowire is five atomic rows in width. Fe atoms at the top (1), intermediate (3) and bottom (5) adsorption sites are shown in side view. (c) STM image of the Fe atomic nanowire ($39\AA \times 48\AA$, 0.46 nA, 500 mV) superimposed upon the Fe atom positions from ab initio study. The structural model is placed to the right for better understanding. In (a), (b), and (c); blue, dark brown, light brown, and light green colors denote all N atoms in the top layer of the ${\mathrm{Cu}}_3\mathrm{N}$, Cu atoms in the top layer of the ${\mathrm{Cu}}_3\mathrm{N}$, Cu atoms below ${\mathrm{Cu}}_3\mathrm{N}$ network, and Fe atoms, respectively. Note: The bottom Fe atoms (5) are shown in gray color since they are deeply embedded into the ${\mathrm{Cu}}_3\mathrm{N}$ network and hence hardly visible in the STM image.

Figure 4

(a) STM image ($700\AA \times 700\AA$, 0.5 nA, 860 mV) of Fe atomic nanowires at coverage of 0.4 ML with line profile (right side) along $x{x}^{\prime }$. The inset magnified image clearly shows that the occupation at the trough nearest to the atomic nanowire is strictly forbidden. The structural model below the line profile is shown to demonstrate the existence of a minimum separation distance. (b) The left and right figures show the structure obtained from ab initio studies before and after relaxation. Atoms on the crest region become unstable due to the increased Fe-Fe bond distance once both sides of the crest are symmetrically occupied. Here, colors of the atoms are exactly the same as in Fig. 3.