Connective neck evolution and conductance steps in hot point contacts

Halbritter, András; Csonka, Szabolcs; Kolesnychenko, O. Yu.; Mihály, G.; Shklyarevskiǐ, O. I.; Kempen, H. van

doi:10.1103/physrevb.65.045413

Cited by 37 publications

(40 citation statements)

References 36 publications

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“…As to Joule heating, the temperature rise in a nanocontact due to electron energy dissipation is still a matter of controversy [1], and no definite results have been established on the contact temperature under high-bias/high-current conditions. On the other hand, electromigration of atoms have been experimentally observed in atom-sized contacts under high biases [8,9], and two-level fluctuations (TLF) in conductance were reported on some metal nanocontacts at low temperatures [8,10,11]. Although these previous observations of TLF suggest that our conductance fluctuations are likely due to electromigration, no detailed analyses can be made at this time since electromigration is a thermally activated process but we lack information on the contact temperature.…”

Section: Discussionmentioning

confidence: 50%

Stability of Atom-sized Metal Contacts under High Biases

Fujii

Mizobata

Kurokawa

et al. 2004

e-J. Surf. Sci. Nanotechnol.

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Conductance and its bias dependence have been measured on Au and Ag breaking nanocontacts for biases up to 3.0 V at room temperature in ultrahigh vacuum. Under high-bias/high-current conditions, both Au and Ag contacts often show a characteristic conductance fluctuation when the conductance attains a certain critical value Gth. This critical conductance ranges from ∼ 10G0 to ∼ 50G0 (G0 ≡ 2e 2 /h is the quantum unit of conductance) and increases with the bias. When Gth is plotted against the contact current I, we obtained a linear I − Gth plot for Au contacts. Since Gth is in a semiclassical regime and hence should be proportional to the cross sectional area of the contact, the slope of the I − Gth plot represents a critical current density for the onset of the conductance fluctuation. These observations indicate that the conductance fluctuation is due to certain current-induced contact instability. When the current density exceeds the critical value, a contact becomes unstable and tends to be ruptured, leaving small chances of further necking deformation down to a single-atom contact.

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Section: Discussionmentioning

confidence: 50%

Stability of Atom-sized Metal Contacts under High Biases

Fujii

Mizobata

Kurokawa

et al. 2004

e-J. Surf. Sci. Nanotechnol.

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“…The most important result is that the conductance histogram shows peaks close to integer multiples of the conductance quantum. 8,27,28 Here, the peak-to-valley ratio is smaller than in experimental conductance histograms, but this could be caused by the relatively small number of configurations used in our calculations. Also, the statistical analysis could improve by taking into account different orientations of the nanowire main axis.…”

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confidence: 65%

Ballistic resistivity in aluminum nanocontacts

et al. 2005

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We perform a representative series of semiclassical molecular dynamics simulations of aluminum nanocontact breakages, coupled to full quantum conductance calculations. This approach allows to obtain realistic conductance histograms of polyvalent species and understand the origin of their peaked structures. The results show that the conductance depends linearly on the contact minimum cross section for the geometrically favored nanocontact configurations. Valid in a broad range of conductance values, such relation suggests the definition of a transport parameter for the nanoscale, that represents the novel concept of ballistic resistivity. One of the major industrial challenges is to profit from some fascinating physical features present at the nanoscale. The production of dissipationless nanoswitches ͑or nanocontacts͒ is one of such attractive applications. 1 The inelastic electron mean free path is usually larger than nanocontact typical cross sections ͑of the order of few atoms in controlled experimets͒ even at room temperature, and, therefore, the electronic transport through these nanoconstrictions is expected to be ballistic. Nevertheless, the lack of knowledge of the real efficiency of this electronic ballistic/nondissipative transport limits future innovations.For contact sizes of the order of a few Fermi wavelengths F , well defined modes ͑channels͒ appear associated with the transversal confinement of electrons. For this situation, the conductance G is given by the Landauer formula G = G 0 ͚ n=1 N T n , where G 0 =2e 2 / h is the conductance quantum ͑e being the electron charge and h Planck's constant͒, T n is the transmission probability of the nth channel, and N is the number of propagating modes with energies below the Fermi energy. 2 It has been shown that the number of conducting channels is determined by the number of valence electrons of the respective chemical element. 3 For monovalent noble metals such as Cu, Ag and Au, the transmission probability T has been estimated to be approximately equal to 1 ͑i.e., each noble-metal atom contact contributes with G 0 to the conductance value 4,5 ͒. But for monovalent alkali metals or polyvalent chemical species, single-atom contact studies revealed that this channel transmittivity can have a result smaller than one. 3,6,7 Nowadays, there exist several experimental techniques to characterize the electronic transport through nanocontacts. Among them, the measurement of the conductance histogram during nanocontact breakages 8-10 is one of the most used. By putting in contact two opposite electrodes and then separating them, one observes a stepwise decrease in the electrical conductance ͑i.e., a conductance scan͒, until the breakpoint is reached. [11][12][13][14] It has been shown that each scan of the conductance dependence on the electrode retraction differs from one another, since the nanocontact structural evolutions during breakages are not identical. 15 Notwithstanding for fixed experimental parameter conditions ͑such as temperature and applied voltage...

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“…8,[10][11][12] The latter two properties, in particular, are of key importance in understanding the stability of atomic wires under current flow. 12 Halbritter et al 13 and, more recently, Mizobata et al 14,15 have explored the mechanical stability of atom-sized Al wires. These authors found that the probability of forming single-atom contacts decreases with increasing bias and that it vanishes at a critical bias of about 1 V. 16,17 In addition, several samples exhibited low-bias instabilities ͑typically at biases of 100 mV or less͒ leading to breakup of the atomic wires.…”

mentioning

confidence: 99%

Role of heating and current-induced forces in the stability of atomic wires

et al. 2005

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We investigate the role of local heating and forces on ions in the stability of current-carrying aluminum wires. For a given bias, we find that heating increases with wire length due to a redshift of the frequency spectrum. Nevertheless, the local temperature of the wire is relatively low for a wide range of biases provided good thermal contact exists between the wire and the bulk electrodes. On the contrary, current-induced forces increase substantially as a function of bias and reach bond-breaking values at about 1 V. These results suggest that local heating promotes low-bias instabilities if dissipation into the bulk electrodes is not efficient, while current-induced forces are mainly responsible for the wire breakup at large biases. We compare these results to experimental observations. Atomic wires are an ideal testbed to study transport properties at the nanoscale. 1,2 Physical phenomena that have been investigated in these systems include their quantized conductance, 3 conductance and noise oscillations as a function of the wire length, 4-7 heating, 1,8,9 and current-induced atomic motion. 8,[10][11][12] The latter two properties, in particular, are of key importance in understanding the stability of atomic wires under current flow. 12Halbritter et al. 13 and, more recently, Mizobata et al. 14,15 have explored the mechanical stability of atom-sized Al wires. These authors found that the probability of forming single-atom contacts decreases with increasing bias and that it vanishes at a critical bias of about 1 V. 16,17 In addition, several samples exhibited low-bias instabilities ͑typically at biases of 100 mV or less͒ leading to breakup of the atomic wires. Similar trends have been reported in the case of Pb ͑Ref. 13͒ and Au ͑Ref. 4͒ point contacts, suggesting that the mechanisms leading to such instabilities are material independent. These low-bias instabilities have typically been attributed to inadequate dissipation of heat into the bulk electrodes. 4,8,9 However, additional forces on ions due to current flow may also contribute, since both effects are present at any given bias.In this paper, we explore the relative role of local heating and current-induced forces in the stability of aluminum wires at different biases. We study these effects perturbatively, i.e., we first calculate current-induced forces on ions while neglecting local heating; second, we assume current-induced forces are negligible and evaluate the local temperature of the wires. This perturbative approach is supported a posteriori: we find that local heating is substantial at very low biases if poor thermal contacts exist between the wire and the bulk electrodes, 8,9,18 while current-induced forces ͑in particular, the average force per atom, see below͒ are small at low biases but increase substantially with increasing external voltage. In addition, if the heat in the wire can be dissipated efficiently into the electrodes, the local temperature in the junction will be quite low at biases for which currentinduced forces reach bond-brea...

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Connective neck evolution and conductance steps in hot point contacts

Cited by 37 publications

References 36 publications

Stability of Atom-sized Metal Contacts under High Biases

Stability of Atom-sized Metal Contacts under High Biases

Ballistic resistivity in aluminum nanocontacts

Role of heating and current-induced forces in the stability of atomic wires

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