Fabrication of stable Pd nanowire assisted by hydrogen in solution

Abstract

We have mechanically fabricated a Pd nanowire in solution under electrochemical potential control. A clear feature appeared in the conductance histogram when the electrochemical potential of the Pd wire was kept at the hydrogen evolution potential. Conductance traces showed the Pd wire was stretched 0.4 nm in length just before breaking, suggesting that at least two Pd atoms might contribute to the formation of the Pd wire. The results indicate that a certain atomic configuration of the Pd nanowire is stabilized by hydrogen. We discuss the stabilization mechanism due to changes in bond strengths caused by hydrogen adsorption or incorporation.Fabrication and characterization of metal atomic wires have attracted attention due to their potential applications in future electronic devices [1]. Recently, Ir, Pt, Au mono atomic wires have been fabricated by pulling nano contacts using a scanning tunneling microscope (STM) or a mechanically controllable break junction (MCBJ) in ultra high vacuum (UHV) at low temperatures [1][2][3]. In addition to methods in UHV, the electrochemical method has been recognized as another powerful approach in the fabrication of metal nanowires [4][5][6][7][8]. Recently, we have demonstrated that Fe, Co, and Ni metal nanowires were stabilized in solution at room temperature via the hydrogen evolution reaction [6,7]. Furthermore, we observed results suggesting the formation of a mono atomic Ni wire in solution, while mono atomic wires of 3d and 4d metals have not been prepared in UHV up to now.In the present study, we have studied the hydrogen assisted stabilization of the Pd (4d metal) nanowire in the fabrication of a mono atomic wire. A mono atomic Pd wire is predicted to be ferromagnetic [9], and to test this hypothesis it is useful to fabricate this wire. In addition to the stabilization of the Pd nanowire by hydrogen, the interaction between hydrogen and the Pd nanowire should be interesting. Since the interaction between hydrogen and Pd is large, the nanowire of the palladium hydride formed in solution should have electrical properties [10].In our study of the Pd nanowire, we have chosen to measure the conductance. Electrical conductance through a metal nanowire on an atomic scale is expressed by G = 2e 2 /h T i where T i is the transmission probability of the i-th conductance channel, e is the electron charge, and h is Plank's constant [1]. Since conductance quantization depends on the atomic structure of a nanowire and the inherent properties of metals, we can study the atomic and electronic structures of metal nanowires by the conductance measurements. We have already studied conductance quantization of a Pd nanowire in solution [8]. The conductance histogram displayed a clear feature peak at 1 G 0 , while conductance quantization was not observed in UHV at room temperature [11]. At low temperatures in UHV, the appearance of the 1 G 0 and 0.5 G 0 features were reported in the conductance histogram for Pd under hydrogen dosing [12]. At the present stage, it is clear that hydrogen sta...

Fabrication of stable metal nanowire showing conductance quantization in solution

“…The present results showed that the stable Cu mono atomic contact was fabricated in the solution with thiourea. To evaluate the stability of the Cu mono atomic contact quantitatively, the distribution of lengths was examined for the last conductance plateau [7]. Improved the stability of the Cu nanowire by thiourea could be explained by adsorption of the thiourea molecule on the Cu surface [8,9].…”

“…Recently, the electrochemical method has been recognized to be a powerful approach to fabricate stable metal nanowires [3][4][5][6][7]. Electrochemical potential determines the potential energy of the electrons of the nanowires, resulting in the control of the bonding strength between the metal atoms, and the interaction of the metals with molecules of surrounding medium.…”

“…These facts make possible to fabricate very stable metal nanowires, which has not been prepared in UHV. Fabrication of stable Au, Ag, Cu, Pb, Fe, Co, Ni, and Pd nanowires and interesting phenomena characteristic of the electrochemical system have been reported in solution at room temperature [3][4][5][6][7]. Although a Cu nanowire in a solution was more stable than that in UHV at room temperature, the stretched length of the nanowire was still rather short, typically less than 0.1 nm.…”

Electric conductance of metal nanowires at mechanically controllable break junctions under electrochemical potential control

“…Recently, preparation of metal nanowires under electrochemical potential control has attracted wide attention [9][10][11][12][13]. Electrochemical potential determines the potential energy of electrons in metal nanowires, resulting in control of the bonding strength between the metal atoms in the wires and the interaction between the metals and molecules in the surrounding medium.…”

“…These characteristics lead to successful fabrication of very stable metal nanowires, which cannot be prepared in UHV. Relatively stable Au [9], Ag, Cu, Pb [10], Fe, Co, Ni [11], and Pd [12] metal nanowires were fabricated in solution at room temperature with the aid of electrochemical potential control. Furthermore, the stability and structure of Au mono atomic wires was controlled by the electrochemical potential [13].…”