Evidence for a Single Hydrogen Molecule Connected by an Atomic Chain

Abstract

Stable, single-molecule conducting-bridge configurations are typically identified from peak structures in a conductance histogram. In previous work on Pt with H 2 at cryogenic temperatures it has been shown that a peak near 1G 0 identifies a single-molecule Pt-H 2 -Pt bridge. The histogram shows an additional structure with lower conductance that has not been identified. Here, we show that it is likely due to a hydrogen decorated Pt chain in contact with the H 2 molecular bridge. DOI: 10.1103/PhysRevLett.98.146802 PACS numbers: 73.63.Rt, 63.22.+m, 73.23.ÿb, 85.65.+h The interest in chains of single metal atoms bridging between two electrodes is largely due to their unique properties as ideal one-dimensional systems [1]. For clean metals, only Au, Pt, and Ir form atomic chains [2,3]. However, atomic or molecular adsorption on metal surfaces can widen this scope. Recently, 2 nm long Ag atomic chains have been created in the presence of oxygen at ultralow temperature, while clean Ag only forms short chains [4]. Atomic chains have been imaged by transmission electron microscope for the noble metals Cu, Ag, and Au [5][6][7][8].In the first experiments contacting molecules by Pt atomic leads it was shown that a single hydrogen molecule H 2 can be contacted and there appeared to be no indication for atomic chain formation [9,10]. By use of point contact spectroscopy and shot noise measurements, the system was characterized in detail and close agreement with atomistic model calculations was obtained [9,10]. The Pt-H 2 -Pt junction was first identified by its conductance. It shows up as a recurring plateau in the conductance when controllably breaking a contact, and in a histogram of conductance values collected for many such breakings it gives rise to a sharp peak near 1G 0 , where 1G 0 2e 2 =h is the conductance quantum. This main peak at 1G 0 for the Pt=H 2 system is therefore well understood. However, there is more structure in the conductance histogram for the Pt=H 2 junctions, which has not been explained. In particular, a strong peak is found at about 0:1-0:2G 0 , suggesting that other configurations of hydrogen between Pt leads may be formed. In the present study we focus on those structures, having a conductance below 1G 0 , and we present evidence that they can be attributed to the formation of a hydrogen decorated Pt atomic chain that forms one of the leads contacting a hydrogen molecule.The measurements have been performed using the mechanically controllable break junction technique (see Ref.[11] for a detailed description). Once under vacuum and cooled to 4.2 K a fine Pt wire was broken. Atomicsized contacts between the wire ends can be formed using a piezoelement for fine adjustment. H 2 was admitted via a capillary. dc two-point voltage-biased conductance measurements were performed by applying a voltage in the range from 10 to 150 mV. Every statistical data set was built from a large number (over 3000) of individual digitized conductance traces. ac voltage bias conductance measurements were performed ...

Atomic configuration, conductance, and tensile force of platinum wires of single-atom width

“…29,32,54,55 As previously reported, peaks are observed at 1.3-1.8G 0 in conductance histograms when pure Pt NCs are retracted in ultrahigh vacuum. 32,36,37 On the other hand, peaks near 0.2 and ϳ0.9G 0 are observed beside a trough near 0.5G 0 when Pt NCs are examined in a hydrogen atmosphere.…”

“…32,36,37 On the other hand, peaks near 0.2 and ϳ0.9G 0 are observed beside a trough near 0.5G 0 when Pt NCs are examined in a hydrogen atmosphere. 32,55 In accordance with these previous results, we classified the Pt ASWs observed in this study, since a hydrogen molecules is not imaged by HRTEM ͑Ref. 52͒; pure Pt ASWs exhibiting conductances exceeding 1.3G 0 and hydrogen-incorporated Pt ASWs exhibiting conductances less than ϳ0.9G 0 .…”

Molecular signature of highly conductive metal-molecule-metal junctions

“…For Pt/ H 2 it is attributed to molecular junctions that involve molecules connected to a chain of Pt atoms, 34 while for Pt/ C 6 H 6 it is was argued to be associated with the conductance of the stretched molecular junction. 7 The origin of the 0.2G 0 conductance peak in the histograms of Pt/ H 2 O and Pt/ C 2 H 2 has not been studied.…”

Interaction of a CO molecule with a Pt monatomic wire: Electronic structure and ballistic conductance

“…For instance, in Pt nanocontacts the presence of H 2 causes the suppression of the peak at 1.5 G 0 and the formation of new peaks at 1 G 0 and 0.1 G 0 . 10,12,13 In presence of CO instead, the lowest conductance peak is replaced by two new peaks, a major one just above 1 G 0 and a smaller one at 0.5 G 0 . 8,9 Such adsorption-induced modifications are usually rationalized by guessing a few possible adsorption geometries and calculating, via density functional theory, their Landuaer-Büttiker ballistic conductance.…”