Pulling gold nanowires with a hydrogen clamp: Strong interactions of hydrogen molecules with gold nanojunctions

In this paper an experimental study of the interaction of hydrogen molecules with gold nanowires is presented. Our results show that chains of Au atoms can also be pulled in hydrogen environment; however, in this case the conductance of the chain is strongly reduced compared to the perfect transmission of pure Au chains. The comparison of our experiments with recent theoretical prediction for the hydrogen welding of Au nanowires implies that a hydrogen molecule can even be incorporated in the gold nanocontact, and this hydrogen clamp is strong enough to pull a chain of gold atoms.

Figure 1

(Color online) Panel (a) is the conductance histogram of pure gold in high vacuum, exhibiting a sharp peak in the $1G_0$ region. This peak arises due to flat conductance plateaus at $1G_0$ corresponding to single atom Au contacts or monoatomic Au wires (the latter is shown in the inset, an interatomic Au-Au distance in the chain is $2.5\mathrm{\AA }$). The area graph in panel (b) is the histogram of gold in hydrogen environment, showing the appearance of new atomic configurations in the low-$G$ region. The inset shows an example for a trace with a well-structured periodic behavior in the low-conductance region, which is attributed to the pulling of a gold chain with an incorporated ${\mathrm{H}}_2$ molecule. The line graph in panel (b) is the histogram for the hydrogen affected traces (see text).

Figure 2

(Color online) Plateau-length histograms for gold junctions in hydrogen environment. Panel (a) shows the plateau-length histogram for the traces that are not affected by hydrogen. Panel (b) contains plateau-length histograms for the hydrogen-affected traces ($\sim 50\%$ of all curves). The line graph shows the distribution of the lengths in the $1G_0$ region, the dashed line shows the distribution of the lengths in the low-$G$ region, whereas the area graph presents the distribution of the summed lengths of the low-$G$ and $1G_0$ regions.

Figure 3

(Color online) The figure shows the determination of the lengths in the different conductance regions for an individual conductance trace. The length of a trace is measured by the number of data points in a certain region. The summed length means the length in the entire $1G_0$ and low-$G$ region, i.e., $G∕G_0∊[0.05,1.1]$.

Figure 4

(Color online) Analysis of the plateau-length histogram for the summed length region. The area graph presents the measured distribution of the summed lengths of the low-$G$ and $1G_0$ regions. The dashed line shows the calculated distribution of the summed length which means the convolution of the plateau-length histograms for the low-$G$ region and $1G_0$ region assuming that the lengths in these two regions are independent. The appearance of the peaks demonstrates the correlations indicating the chain formation in the entire low-$G$ and $1G_0$ regions.

Figure 5

(Color online) The average returning length as a function of the pulling length for the hydrogen-affected traces (circles) and the non-affected traces (diamonds). The pulling length is the length of the plateau in the [0.05, 1.1] region before break, whereas the returning length is the length measured from point of breakage back to point, where a contact with $G>0.05G_0$ is reestablished.

Figure 6

(Color online) Conductance traces showing a well-defined periodic structure in the low-$G$ region. The bottom curve is on true scale, while the other curves are artificially shifted on the conductance axis for the sake of visibility (the corresponding zeros are signed on the right axis). The interatomic distance in the pure gold chain is indicated by grid lines. Approximately 5% of the traces shows this special behavior.

Figure 7

(Color online) The average of all the traces that have a length $>8.8\mathrm{\AA }$ in the low-$G$ region. The averaging was done as a function of the length measured backward from the point of breakage.

Figure 8

(Color online) Plateau-length analysis for different types of hydrogen-affected traces. The plateau-length histograms shown by the dashed/solid lines are built from the traces that have longer (shorter) than 30% section with positive plateaus’ slope. In panel (a) the distribution of the summed length in the entire $1G_0$ and low-$G$ region is plotted, while panel (b) shows the distribution of the lengths in the tail region, $G∕G_0∊[0.05,0.3]$.

Figure 9

(Color online) Illustration for the weakly bound hydrogen molecule (a) and the mechanism of pulling an atomic gold chain with a hydrogen molecule (b).