Stable single-atom contacts of zinc whiskers

Abstract

We report low-temperature measurements of the electrical transport properties of single-atom and tunnel contacts of Zn. We present a variant of the mechanically controllable break-junction technique that comprises a whisker as the central part. This technique combines the possibility to fabricate reproducibly single-atom contacts and well-characterized electronic and lattice properties of the electrodes. From tunneling current-voltage characteristics, we deduce a well-pronounced quasiparticle spectrum for whiskers, while for standard "notched-wire" and thin-film break junctions the spectrum is smeared out. The tunneling density of states 1 is usually deduced from electronic transport measurements through tunneling contacts , fabricated by different methods. However, although discovered many years ago, for several elementary supercon-ductors direct transport measurements are still lacking because of the difficulty to fabricate suitable tunneling contacts. The divalent metal Zn is an example for this situation where, besides the metallurgical problems that hinder the creation of tunneling contacts with standard methods, the superconducting properties are anisotropic. Single-atom or few-atom contacts are model systems to investigate the electronic transport properties on the atomic scale because the electronic conduction can be regarded as a fully quantum-mechanical scattering problem, i.e., the con-ductance G can be attributed to independent nicknamed conduction channels which contribute to the total conduc-tance with a weight given by their transmission coefficients i : G = G 0 i=1 N i G 0 =2e 2 / h is the conductance quantum and N the number of channels. 2 An atomic-size contact between two metallic electrodes can accommodate only a small number of conduction channels the number and i of which depend on the chemical properties of the atoms forming the contact and on their geometrical arrangement. The latter information has been deduced from the fact that the transport properties change when rearranging the contact region. 3,4 The use of a hexagonal metal allows to establish different configurations of the few-atom contacts in contrast to the cubic metals that have been studied so far. In principle, all physical properties that depend on the channel ensemble i could be used to determine the transport channels. However, independent determination of all i s with arbitrary values has so far only successfully been performed by analyzing current-voltage characteristics I-Vs of superconducting contacts. The analysis relies on the quantitative agreement between the calculated I-Vs for BCS super-conductors and the experimental data. 4,5 Consequently, the superconducting properties of the electrodes forming the atomic-size contact have to be of high quality. In the present work the measurement of the i s is accomplished for Zn, a metal not explored so far, by using mechanically controllable break junctions MCB Refs. 3 and 6 of whiskers glued on top of a prepatterned flexible substrate see Fig. 1. Zn whiskers grow with a p...

Mechanically controllable break-junctions for use as electrodes for molecular electronics

“…For Zn samples in only a few cases three channels are present, most of the contacts transmit only one or two channels. A detailed discussion of the transport properties of Zn single-atom contacts will be published elsewhere [25]. Experiments with Au lithographic break-junctions (with Al leads for inducing superconductivity via the proximity effect) show a single channel in a single-atom configuration [28,29].…”

“…The data have been recorded on a lithographic break-junction. Figure 3(B) displays three I -V characteristics with G 0.9 G 0 for contacts from different, but consecutive opening procedures of a Zn whisker break-junction without closing the whisker thoroughly between the openings (for more details see [25]). The measuring temperature was 270 mK.…”

Correlation between transport properties and atomic configuration of atomic contacts of zinc by low-temperature measurements

“…The superconducting properties of the lithographic breakjunctions allowed to determine the transport channels of contacts with up to two channels but failed for larger contacts since the superconducting density of states deviates markedly from the BCS shape. 20 The sample preparation of the whisker MCBs and the results of these investigations together with a detailed theoretical analysis have been reported before. 14,20 However, the limited lifetime of those contacts hindered the recording of a histogram.…”

Thiol and thiolate bond formation of ferrocene-1,1-dithiol to a Ag(111) surface

“…No inclinations were found for the less asymmetric S-bonding configurations. [4][5][6][7][8][9] As a second example, and in order to demonstrate the variability of the bonding configurations formed, we show in Fig. 3 the relaxed structure resulting from starting configuration 7.…”

“…A method that has come closest to this goal is the use of molecular break junctions. 3,4 While conductance through single atoms 3 and also through molecules inserted into open break junctions 5 has been demonstrated, the local configuration cannot be controlled in these junctions, so that only indirect conclusions by comparison with theoretical simulations can be drawn. 6 Therefore, alternative contacts are currently developed.…”