Figure 1

Distance tunneling spectroscopy of the physically adsorbed hydrogen molecules on the surface of Ta [(1)–(3)], W (4), and Mo (5). Curve 3 displays the presence of two hydrogen molecules. All curves were taken while the electrodes approached each other.Reuse & Permissions

Figure 2

(Color online) Conductance histograms for Ta measured during the chemisorption process. All histograms were taken within 1 h. Inset: Upper panel—conductance histogram made of the first 2000 traces of histogram 1 and lower panel—conductance histogram made of the last 2000 conductance traces of the original histogram 1.Reuse & Permissions

Figure 3

(Color online) Effect of hydrogen adsorption on the conductance histograms of tungsten. Upper panel: histogram for W MCBJ with an etched neck show no distinct features. Inset: For this type of junctions, peaks close to integers of $G_0$ were repeatedly observed in vacuum due to the surface states. Lower panel: conductance histograms for W samples with a mechanically produced neck display a peak at $2.6G_0$, corresponding to the conductance through an one-atom contact (inset). Adsorption of hydrogen results in an emerging peak at $\sim 1G_0$ related to the conductance through the bridge of chemically adsorbed hydrogen atoms.Reuse & Permissions

Figure 4

(Color online) Conductance histogram for Mo in vacuum (inset) and in the case of dissociative adsorption of hydrogen. Time evolution (histograms 1, 2, and 3 were taken within 2–3 h) results in the smearing of the conductance peak at $1G_0$.Reuse & Permissions

Figure 5

(Color online) Upper panel: $R\left(z\right)$ dependencies for ${\text{TaH}}_x$ electrodes. Transition from tunneling to direct mechanical contact (onset of a steplike behavior) occurs in the conductance range of $0.1-0.001G_0$. Lower panel: $R\left(z\right)$ dependencies for Mo and W MCBJs with hydrogen dissolved into the electrodes.Reuse & Permissions

Figure 6

(Color online) Dependence of the position of the one-atom contact conductance peak on bias voltage for ${\text{TaH}}_x$. From the bottom to top, $V_b$ is equal to 400, 300, 250, 200, and 175 mV. All histograms were scaled and shifted for clarity.Reuse & Permissions

Figure 7

Typical pattern of conductance fluctuations for ${\text{TaH}}_x$ junctions for $G=6.5G_0$ and $G=140.5G_0$ (upper panel). The noise power spectra for the same junctions display $1/f^{\alpha }$ law at $f\le 1\text{Hz}$ with $\alpha =1.3$ (curve 1) and 1.7 (curve 2), respectively (lower panel). Curve 3 represents the noise power spectra for ${\text{WH}}_x$ measured after saturation. In all cases, $V_b=10\text{mV}$.Reuse & Permissions

Figure 8

(Color online) Bias dependence of the conductance of the low-Ohmic W point-contacts measured before admittance of 0.1 mM of hydrogen into the vessel (curve 1), after 4 h (curve 2), and after 10 h of exposition (curve 3).Reuse & Permissions

Figure 9

(Color online) Bias dependence of the conductance of Mo contacts of different diameters after 1 h exposure to 0.1 mM of hydrogen.Reuse & Permissions

Figure 10

(Color online) Asymmetric conductance curve for a ${\text{TaH}}_x$ point contact. The arrows indicate the direction of $G\left(V\right)$ recording. For this curve (double and fully reproducing itself), the recording time was $\sim 60\text{min}$. Inset: Conductance of the ${\text{TaH}}_x$ point contact at different temperatures. From top to bottom: $T=4.2$, 4.5, 4.7, 4.9, and 5.1 K. The four last curves are shifted and equally spaced for clarity. All measurements were done in a two-probe configuration.Reuse & Permissions