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The electrical conductance through an atomic-size metal nanoconstriction is quantized as a unit of Go (Go = 2e2 / h). Recently, the quantized conductance of ferromagnetic metals has attracted much attention, because of the expectation for the spin-dependent electron transport. Despite of their interest, previously documented data was less consistent each other due to chemical instability of the ferromagnetic metals nanoconstriction. Here, we pay attention to in-situ preparation of ferromagnetic metals nanoconstriction in solution. In solution, the electrochemical potential determines the potential energy of the electrons of the nanoconstrictions, resulting in the control of the bonding strength between the metal atoms, and the interaction of the nanoconstrictions with molecules of surrounding medium. These facts make possible to fabricate very stable metal nanoconstrictions, which can not be stabilized in air or ultra high vacuum. In the present study, we mechanically fabricated ferromagnetic metals, Ni, Co, Fe, Pd nanoconstrictions in solution, and investigated their conductance under the electrochemical potential control.
Electrochemical scanning tunneling microscope (EC-STM) was used to fabricate ferromagnetic metal nanoconstrictions. First, the electrochemical potential of both the STM tip and substrate were maintained at lower than the potential where bulk deposition proceeds. After sufficient deposition of the metals onto the surfaces of the STM tip and the substrate, the tip was driven into and out of contact with the substrate. During the contact breaking, a ferromagnetic metal nanoconstriction was formed between the tip and substrate.
In the case of the Pd nanoconstrictions, a featureless histogram was observed at 100 mV vs Ag/AgCl. As the potential was scanned to -300mV where hydrogen evolution reaction proceeded, the conductance histogram showed a clear feature around 1 Go. The adsorbed hydrogen would stabilize a certain atomic configuration showing 1 Go. Conductance histograms also depended upon electrochemical potential for other ferromagnetic metals.
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