Fast and accurate current-voltage curves of metallic quantum point contacts

Abstract

We present an experimental setup for measuring the electrical conductance through metallic quantum point contacts (QPCs) under constant or time-dependent bias voltage conditions. The response time of the setup is as short as 25 ns and typical bias voltages range from 10 mV to 2 V. A function generator is used as bias voltage supply. With this, voltage bursts with a frequency of up to 100 kHz can be applied to the QPCs, whereby current-to-voltage (I–V) curves can be acquired using a homebuilt, 30 MHz bandwidth I–V converter, and a 100 Msamples/s digital storage oscilloscope. Test experiments on resistors show that nonlinear contributions to the I–V curves are always less than 1% of the current for all applied voltages. From the slope of the I–V curves, the conductance can be determined with an accuracy better than 1%. The QPCs are formed between a single-crystal metal sample and the tip of a scanning tunneling microscope under clean ultrahigh vacuum conditions. We demonstrate how the setup can be used to capture the I–V curves of several metastable states in a Au QPC, as it breaks during a period of 200 μs at room temperature.

Exploring the conduction in atomic-sized metallic constrictions created by controlled ion etching

“…With the available data, it is not possible to discard that, due to the moderate vacuum level (10 −6 Torr) and the Ga-assisted etching process, some impurity could be in the surroundings of the nanoconstriction and could exert some influence in the conduction properties. However, the obtained linearity in the I -V curves in the metallic regime seems to confirm the presence of clean contacts, because only the presence of adsorbates and contaminants produces non-linear curves in the low-voltage regime [23,24]. In our case, the use of low ion energy (5 kV) and current (2 pA) is expected to minimize the role of Ga damage and implantation.…”

Atomic configuration and mechanical and electrical properties of stable gold wires of single-atom width

“…This low probability is consistent with the results obtained by STM. 72,73 Since this growth occurs during retraction, a tensile force acts on the contact in Fig. 1.…”

“…76 Thus, these two states cannot be distinguished from the analysis of the Au atom positions. It is noted that the duration of pure Au ASWs, which are measured by SPM, is, at most, ϳ2 ms at a retraction speed of ϳ10 m / s. 69,72,73,88 According to ab initio calculations, pure Au ASWs with longer interatomic distances occurring at dimerization are unstable because the distances are similar to or exceed the fracture length. 33,40,77,83 In contrast, Au ASWs are strengthened owing to the incorporation and absorption of hydrogen, boron, carbon, oxygen, and sulfur atoms.…”

Current-voltage curves of gold quantum point contacts revisited

“…Previous measurements of I -V curves on Au contacts 2,5,9 were done over a time scale of 0.1-50 s, thus restricting the measurements to contacts which are stable over relatively long time scales. Instead, we use a setup, 10 whereby an I -V curve can be acquired within only 20 s, and transient contact geometries can be studied. The contacts are formed between a polycrystalline Au tip mounted in a scanning tunneling microscope ͑STM͒ and a Au͑110͒ singlecrystal surface under ultra-high-vacuum ͑UHV͒ conditions in two different ways: ͑i͒ Hard indentations.…”