The continuing miniaturization of microelectronics raises the prospect of nanometre-scale devices with mechanical and electrical properties that are qualitatively different from those at larger dimensions. The investigation of these properties, and particularly the increasing influence of quantum effects on electron transport, has therefore attracted much interest. Quantum properties of the conductance can be observed when 'breaking' a metallic contact: as two metal electrodes in contact with each other are slowly retracted, the contact area undergoes structural rearrangements until it consists in its final stages of only a few bridging atoms [1][2][3]. Just before the abrubt transition to tunneling occurs, the electrical conductance through a monovalent metal contact is always close to a value of 2e 2 /h(≈ (12.9kΩ) −1 ), where e is the charge on an electron and h is Plack's constant [4][5][6]. This value corresponds to one quantum unit of conductance, thus indicating that the 'neck' of the contact consists of a single atom [7]. In contrast to previous observations of only single-atom necks, here we describe the breaking of atomic-scale gold contacts, which leads to the formation of gold chains one atom thick and at least four atoms long. Once we start to pull out a chain, the conductance never exceeds 2e2 /h, confirming that it acts as a one-dimensional quantized nanowire. Given their high stability and the ability to support ballistic electron transport, these structures seem well suited for the investigation of atomic-scale electronics.Previous studies on metallic contacts of atomic dimensions have shown remarkable properties of such structures, including conductance quantisation and superior mechanical strength compared to the bulk. Experimental techniques, most common being scanning tunnelling microscopy (STM) and mechanically controllable break-junctions (MCB), are all based on piezoelectric transducers which allow fine positioning of two metal electrodes with respect to each other. STM, in which the tip is driven into contact with a metal surface and the conductance is measured during subsequent retraction, has been widely used for this purpose [4,5,8,9]. In the alternative method of MCB one starts with a macroscopic notched wire [10], or a nanofabricated metal bridge [11] mounted on a flexible substrate. The wire (or bridge) is broken at low temperatures in vacuum, and contact is re-established between the fracture surfaces by piezoelectric control of substrate bending. In this work we have used both MCB and a very stable STM at liquid helium temperatures to produce and study chains of single gold atoms. In each case, high purity (99.99 + %) gold was used. Conductance was measured at a 10 mV DC voltage bias with 1% accuracy.An example of a conductance curve obtained while stretching a gold nanocontact is presented in Fig. 1. The curve reflects the evolution of some particular atomic configuration, during which the conductance decreases in a series of sharp vertically descending steps, with a gradual slop...

The transmission of conductance modes in atom-size gold contacts is investigated by simultaneously measuring conductance and shot noise. The results give unambiguous evidence that the current in the smallest gold contacts is mostly carried by nearly fully transmitted modes. In particular, for a singleatom contact the contribution of additional modes is only a few percent. In contrast, the trivalent metal aluminum does not show this property. [S0031-9007(99)08411-2] PACS numbers: 72.70. + m, 72.15.Eb, 73.23.Ad, 73.40.Jn In 1918, Schottky mentioned shot noise as a fundamental shortcoming of vacuum diodes. He realized that the discreteness of electron charge e causes the current to be a Poisson process, and calculated the corresponding mean square current fluctuations to be equal to the product of e and the average current I divided by the total time of averaging [1]. This type of noise is present in all kinds of devices, including microscopic conductors. In the last decade, it has become clear that it can actually be used to obtain information on the electron transport mechanism [2-12]. For example, in a ballistic quantum point contact (QPC) in a two-dimensional electron gas (2DEG), the conductance G as a function of contact diameter shows a stepwise increase by integer multiples of the conductance quantum, G 0 ϵ 2e 2 ͞h [13]. Recent 2DEG experiments showed that shot noise was strongly suppressed at quantized conductance values [2,3], in accordance with theoretical predictions [4][5][6][7][8]. In this Letter, measurements of shot noise are performed for the first time to analyze the electronic transport properties of atom-size metallic contacts.For a metal, the size of an atom is comparable to half the Fermi wavelength l F of the conduction electrons. Therefore, the equivalence of electronic properties of QPCs in a 2DEG and in a metal is far from trivial. In particular, it inhibits a direct observation of the effect of the formation of discrete electron modes in a metallic QPC, i.e., quantization of the conductance. In fact, using a combined scanning tunneling microscopy and atomic force microscopy setup [14] it has been shown that steps in the conductance, observed when stretching the contact, are the result of atomic rearrangements (see also [15]). Primarily, evidence for quantization of the conductance in metals is derived from histograms of the conductance values, which, for gold [16] and sodium [17], show peaks close to integer multiples of G 0 . However, this evidence is not unambiguous, as demonstrated for aluminum, which shows clear peaks near quantized conductance values in the histograms [18], while up to three modes contribute to the conductance near G G 0 [19].In a ballistic QPC with perfect transmission of electrons there are no fluctuations in the occupation numbers of left and right moving electrons, suppressing all shot noise [4][5][6][7][8]. For a contact of size comparable to the Fermi wavelength l F , electron transport is described using the Landauer-Büttiker formalism. In this formalism, the...

We present measurements on a pulse-driven ac Josephson voltage standard (ACJVS) for frequencies up to 1 MHz. By automating our setup we were able to perform a systematic study of the frequency dependence of the ACJVS output. We show that the error caused by the voltage leads is the major error source when measuring at frequencies up to 1 MHz. The squared frequency dependence of the error, which is caused by a resonance in the circuit, allows us to make a correction that results in an uncertainty on the µV V−1 level for frequencies up to at least 20 kHz.

Over the last 15 years, research in ac Josephson voltage metrology has focused on two fundamentally different systems: the programmable and the pulse-driven Josephson voltage standards (JVSs). This paper reports the first high precision comparison between the two types of JVS. The METAS programmable voltage standard was moved from Switzerland to the Netherlands to be compared with the Dutch pulse-driven system during four days in November 2010. After a careful investigation of the systematic sources of errors, the comparison was made at a frequency of 500 Hz and an rms amplitude of 104 mV. At that level, the voltage difference measured between the fundamental frequency components of the two standards was −0.18 ± 0.26 µV V−1 (k = 2), showing an excellent agreement between the two systems.

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Recent studies showed that static electricity meters can generate wrong metering results when exposed to conducted electromagnetic inference caused by electronic appliances, consisting of waveforms with very steep rising edges in combination with large peak amplitudes. To identify more waveforms that can cause errors, we captured a large series of waveforms of common household appliances, and after analyzing these waveforms we selected a number of waveforms for testing a static electricity meter.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Sampling current ratio bridge for calibration of current transducers up to 10 kA with 5 ppm uncertainty van den Brom, Helko E.; Rietveld, Gert; So, Eddy NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21272619&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21272619&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Previous studies regarding static energy meter errors under non-sinusoidal load conditions have shown that these meters can produce erroneous readings. This paper describes an investigation done using loads consisting of a commercial lighting dimmer in combination with either a resistive heater or an array of various energy-saving lamps. Dimmer impedance and phase firing angle were gradually adjusted to change load conditions. Several meters showed dramatic variations in metering error under different load conditions. In the most extreme case, metering errors ranged from five times the energy consumed by the load to registering almost no energy. Though perhaps not typically found in households, the load combinations used in this study were able to highlight sensitivities of different static energy meters to changes in load conditions.