Atomic discreteness and the nature of structural equilibrium in conductance histograms of electromigrated Cu nanocontacts

Pfender-Siedle, Robert; Hauser, Julia; Hoffmann‐Vogel, Regina

doi:10.1103/physrevb.95.235418

Cited by 3 publications

(10 citation statements)

References 20 publications

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“…Therefore, we conclude that already at values around 15G 0 it is essentially only one junction that is conducting. Such instabilities seem to be characteristic to the EM process, since they are commonly not observed in MCBJ experiments but have also been found in recent EM experiments with Cu nanocontacts [24]. Since a distribution of contacts of various sizes exist, there is still a small probability for conductance through more than one channel that is reflected by the small number of counts in the range between 14G 0 and 5G 0 .…”

Section: Resultsmentioning

confidence: 63%

“…Peaks at 2.1G 0 , 2.6G 0 , 3.0G 0 , 3.8G 0 , 4.2G 0 , 4.6G 0 , 14.5G 0 and 15G 0 are observed. At this point it is not clear whether these values are the result of several contacts in parallel or stem from a single contact, since non-integer values of conductance are commonly observed also for single contacts [24,29,30], mainly due to asymmetric and slightly irregular shapes of the contact, in agreement with theoretical simulations [7].…”

Section: Resultsmentioning

confidence: 86%

“…This information is obtained from Fourier transforms (FTs) of the conductance histograms. It also contains information about the structural thinning process, as demonstrated previously for several metallic systems [21][22][23][24], since, depending on the metal (fcc or bcc structure), the calculated ratios of frequencies in the FTs were compatible with a preferential growth in certain crystallographic high-symmetry directions. Our study also uses these tools for data analysis.…”

Section: Introductionmentioning

confidence: 71%

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Electromigration-induced directional steps towards the formation of single atomic Ag contacts

Chatterjee

Tegenkamp

Pfnür

2020

Beilstein J. Nanotechnol.

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Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G 0 and 15G 0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

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Section: Resultsmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 71%

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Electromigration-induced directional steps towards the formation of single atomic Ag contacts

Chatterjee

Tegenkamp

Pfnür

2020

Beilstein J. Nanotechnol.

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“…Compared to low temperature studies, a larger number of sharp relevant peaks were observed in the same conductance interval with only limited broadening by thermal effects or by the change of the applied voltage. Different periodicities in the conductance have been observed and have been assigned to different crystallographic orientations of the nanocontacts [7,10]. Both work-hardening and electromigration lead to enhanced local heating increasing the probability of the nanocontact to find structural equilibrium [10].…”

Section: Introductionmentioning

confidence: 98%

“…Different periodicities in the conductance have been observed and have been assigned to different crystallographic orientations of the nanocontacts [7,10]. Both work-hardening and electromigration lead to enhanced local heating increasing the probability of the nanocontact to find structural equilibrium [10]. In this way the structural properties of the nanocontacts are enhanced compared to methods based on pulling at low temperature.…”

Section: Introductionmentioning

confidence: 99%

Shell effects and free-electrons in electromigrated oxidized Cu-nanocontacts

et al. 2023

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Electromigration in interconnects continues to be an important field of study in integrated circuits as the interconnects are planned to shrink in size at comparable pace as the semiconductor functional elements. Through shrinking the interconnects approach the regime where quantum size effects become important. The observation of quantum size and shell effects is usually restricted either to low-temperatures or vacuum conditions or to chemically inert materials such as Au. Here, we show that in electromigrated Cu nanocontacts such effects can be observed at room temperature and room pressure even in the presence of oxidation. Our data provide evidence that the nanocontacts are nearly spherical objects with a triangular-cylindrical symmetry of their electronic wave functions with a stronger free-electron-like character compared to previous results. We do not observe a detrimental effect of oxygen. The presence of shell effects has implications for the technological use of Cu nanocontacts as interconnects in integrated circuits and could lead to the use of electronic wave functions of shells in such interconnects.

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Shaping single atomic junctions in ultra-thin Ag structures by electromigration

Chatterjee

Heidenblut

Edler

et al. 2018

Applied Physics Letters

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By characterizing and manipulating the conductive properties of single Ag nano-grain boundaries with electromigration—originally considered only as a detrimental effect for metallic nanostructures—we show that atomic point contacts can be generated at well-defined locations with extreme reliability in ultra-thin (5 nm) and ultra-small (minimum width 16 nm) Ag nanostructures, deposited on hydrogen terminated low-doped Si(100) samples. Single contacts were always obtained once the smallest constriction of the structures was below the average grain size of the Ag films and competing thermal migration was suppressed. These ultra-thin and laterally open structures on Si provide complete accessibility for local characterisation of the molecular junction.

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Atomic discreteness and the nature of structural equilibrium in conductance histograms of electromigrated Cu nanocontacts

Cited by 3 publications

References 20 publications

Electromigration-induced directional steps towards the formation of single atomic Ag contacts

Electromigration-induced directional steps towards the formation of single atomic Ag contacts

Shell effects and free-electrons in electromigrated oxidized Cu-nanocontacts

Shaping single atomic junctions in ultra-thin Ag structures by electromigration

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