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Plasmonics is a powerful tool to miniaturize photonics. In this review, we introduce memristive plasmonics as a technique to shrink photonic devices to the atomic scale. We show atomic-scale plasmonic switches, detectors and emitters.

After decades of continuous scaling, further advancement of complementary metal-oxide-semiconductor (CMOS) technology across the entire spectrum of computing applications is today limited by power dissipation, which scales with the square of the supply voltage. Here, an atomic-scale tin transistor is demonstrated to perform conductive switching between bistable configurations with on/off potentials, Advanced Electronic Materials, 8 (10), ISSN:2199-160X

Plasmonics allows for an unmatched miniaturization. Along with the shrinking comes power efficient operation. Here, we show how plasmonics allows for an unprecedented downscaling of the classical MEMS and even of emerging memristive approaches. Ultimately, we will demonstrate optical elements at the atomic scale., 2020 European Conference on Optical Communications (ECOC), ISBN:978-1-7281-7361-0, ISBN:978-1-7281-7362-7

One focus of nanoelectronics research is to exploit the physical limits in size and energy efficiency. Here, we demonstrate a device in the form of a fully metallic atomic-scale transistor based on a lead (Pb) single-atom quantum point contact. The atomic configuration of the point contact determines the conductance of the Pb atomic-scale transistor. The conductance multiplicity of the Pb single-atom transistor has been confirmed by performing switching between an electrically nonconducting ``off-state'' and conducting ``on-states'' at $1{\mathrm{G}}_{0}({\mathrm{G}}_{0}=2{e}^{2}/h$, where $e$ is the electron charge, and $h$ Planck's constant), $2.0{\mathrm{G}}_{0}$, $3.0{\mathrm{G}}_{0}$, $1.5{\mathrm{G}}_{0}$, $2.4{\mathrm{G}}_{0}$, $2.7{\mathrm{G}}_{0}$, $2.8{\mathrm{G}}_{0}$, and $5.4{\mathrm{G}}_{0}$, respectively. Our density-functional calculations for various ideal Pb single-atom contacts explain the atomic-configuration-related conductance multiplicity of the Pb single-atom transistor. The performance of the Pb single-atom transistors indicates that both the signatures of atomic valence and conductance quantization play roles in electron transport and bistable reconfiguration. The bistable reconfiguration of the electrode tips is an underlying mechanism in the switching of the Pb atomic-scale transistors. The absolute value of the electrochemical potential applied to the gate electrode is less than 30 mV. This merit suggests Pb [besides silver (Ag)] atomic-scale transistors as potential candidates for the development of electronic circuits with low power consumption. The dimension of the switching unit in the Pb single-atom transistor is in the range of 1 nm, which is much smaller than the projected scaling limit of the gate lengths in silicon transistors (5 nm). Therefore, the metallic single-atom transistors may provide perspectives for electronic applications beyond silicon.

Motivated by recent experiments on electrochemically controlled Pb atomic-scale switches we have studied the self-diffusion of Pb on flat and stepped surfaces since diffusion processes play an important role in the growth of metal substrates. Kinetic modelling based on Monte-Carlo simulations using a model potential suggests that exchange processes play an important role in the contact formation at the nanoscale. Periodic density functional theory indeed find that the barriers for exchange diffusion across the steps are significantly lower than for hopping diffusion. The consequences for the contact formation in electrochemically controlled switches are discussed.

We report on the electronic transport through nanoscopic metallic contacts under the influence of external light fields. Various processes can be of relevance here, whose underlying mechanisms can be studied by comparing different kinds of atomic contacts. For this purpose two kinds of contacts, which were established by electrochemical deposition, forming a gate-controlled quantum switch (GCQS), have been studied. We demonstrate that in these kinds of contacts thermal effects resulting from local heating due to the incident light, namely thermovoltage and the temperature dependences of the electrical resistivity and the electrochemical (Helmholtz) double layer are the most prominent effects.

The single-atom transistor represents a quantum electronic device at room temperature, allowing the switching of an electric current by the controlled and reversible relocation of one single atom within a metallic quantum point contact. So far, the device operates by applying a small voltage to a control electrode or "gate" within the aqueous electrolyte. Here, the operation of the atomic device in the quasi-solid state is demonstrated. Gelation of pyrogenic silica transforms the electrolyte into the quasi-solid state, exhibiting the cohesive properties of a solid and the diffusive properties of a liquid, preventing the leakage problem and avoiding the handling of a liquid system. The electrolyte is characterized by cyclic voltammetry, conductivity measurements, and rotation viscometry. Thus, a first demonstration of the single-atom transistor operating in the quasi-solid-state is given. The silver single-atom and atomic-scale transistors in the quasi-solid-state allow bistable switching between zero and quantized conductance levels, which are integer multiples of the conductance quantum G0 = 2e2 /h. Source-drain currents ranging from 1 to 8 µA are applied in these experiments. Any obvious influence of the gelation of the aqueous electrolyte on the electron transport within the quantum point contact is not observed.

The demonstration of a multi-atom quantum point contact relay is reported, which can be reversibly switched between a quantized conducting ‘on-state’ and an insulating ‘off-state’ by applying an electrochemical control potential to a separate, third electrode, the control or gate electrode. The transition occurs directly from the conducting ‘on-state’ at 5 G 0 ( G 0 =2 e 2 / h being the conductance quantum) to the insulating ‘off-state’. No stable intermediate levels are observed during the switching process, indicating a reproducible bistable reconfiguration of one single multi-atom contact rather than a deposition and dissolution of different parallel contacts. The results at the same time demonstrate the feasibility and reproducible operation of a configurable electronic device based on a multi-atom contact, which exhibits the functionality of an atomic relay or a transistor, opening intriguing perspectives for electronics and logics on the atomic scale.

Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from 'electrochemical' to 'mechanical', which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

Atomic-sized lead (Pb) contacts are deposited and dissolved in an electrochemical environment, and their transport properties are measured. Due to the electrochemical fabrication process, deformation-induced mechanical strain is largely avoided, and we obtain conductance histograms with sharply resolved, individual peaks. Charge transport calculations based on density-functional theory for various ideal Pb contact geometries are in good agreement with the experimental results. Depending on the atomic configuration, single-atom-wide contacts of one and the same metal yield very different conductance values.

The controlled fabrication of actively switchable atomic-scale devices, in particular transistors, has remained elusive to date. Here, we explain the operation of an atomic-scale three-terminal device by a novel switching mechanism of bistable, self-stabilizing reconstruction of the electrode contacts at the atomic level: While the device is manufactured by electrochemical deposition, it operates entirely on the basis of mechanical effects of the solid-liquid interface. We analyze mechanically and thermally stable metallic junctions with a predefined quantized conductance of 1-5 G0 in experiment and atomistic simulation. Atomistic modeling of structural and conductance properties elucidates bistable electrode reconstruction as the underlying mechanism of the device. Independent room temperature operation of two transistors at low voltage demonstrates intriguing perspectives for quantum electronics and logics on the atomic scale.

Single-atom transistors are a novel approach opening intriguing perspectives for quantum electronics and logics at room temperature. They are based on the stable and reproducible operation of atomic-scale switches, which allow us to open and close an electrical circuit by the controlled reconfiguration of silver atoms within an atomic-scale junction. We demonstrate the operation of such atomic quantum switches, and discuss in more detail the process during which these switches are formed by repeated electrochemical deposition and dissolution. Only after repeated deposition/dissolution cycles, a bistable contact is formed on the atomic scale, which allows to switch between a configuration where the contact is closed, the conducting state or “on”-state, and a configuration where the contact is open, the nonconducting state or “off”-state. The controlled fabrication of these well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at noninteger multiples of the conductance quantum G 0 = 2e 2 ∕ h( ≈ 1 ∕ 12. 9 kΩ) in conventional experiments with simple metals is correlated with defects resulting from the fabrication process. Our combined electrochemical deposition and annealing method allows the controlled fabrication of point contacts with preselectable integer quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms.

Spin valve multilayers exhibiting enhanced giant magnetoresistive (GMR) effect and weak interlayer coupling as well as strong exchange biasing were fabricated by a two-step deposition procedure. The down sublayers (i.e., buffer layer Ta/free layer NiFe/interlayer Cu) were deposited at a lower argon pressure, then the upper sublayers (i.e., pinned layer NiFe/pinning layer FeMn/cover layer Ta) were deposited at a higher argon pressure. The former promoted formation of the strong (111) textures, smooth interfaces, and dense Cu film, resulting in a weak interlayer coupling. The latter promoted small domains and less diffusive interfaces, resulting in a strong exchange biasing and an enhanced GMR ratio. This shows that independent control of magnetoresistance, interlayer coupling, and exchange biasing is possible. (C) 1999 American Institute of Physics. [S0021-8979(99)06518-4].

The controlled fabrication of well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at non-integer multiples of the conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects resulting from the fabrication process. Here we demonstrate a combined electrochemical deposition and annealing method which allows the controlled fabrication of point contacts with pre-selectable integer quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms.

An atomic-scale quantum conductance switch is demonstrated that allows us to open and close an electrical circuit by the controlled and reproducible reconfiguration of silver atoms within an atomic-scale junction. The only movable parts of the switch are the contacting atoms. The switch is entirely controlled by an external electrochemical voltage applied to an independent third gate electrode. Controlled switching was performed between a quantized, electrically conducting "on state" exhibiting a conductance of G(0)=2e(2)/h ( approximately 1/12.9 kOmega) or preselectable multiples of this value and an insulating "off state."

We report on conductance quantization at room temperature in atomic-scale silver point contacts electrochemically fabricated within a nanoscale gap between two gold electrodes on a glass substrate. The formation of stable contacts exhibiting quantized conductance at integer multiples of the conductance quantum G0 = 2e2/h (≈ 1/12.9 kΩ) was observed. While transient contacts with other conductance values were also found, a clear preference for values close to integer multiples of G0 was observed for contacts stable for up to several hours. Stable conductance levels were observed not only at 1G0, but also at higher integer multiples of G0 (up to 8G0). When applying electrochemical deposition or dissolution potentials, sharp transitions were induced between different quantized conductance levels while between these transitions, horizontal plateaus of constant conductance were found.

Karlsruher Wissenschaftlern ist es erstmals gelungen, einen Transistor auf atomarer Skala zu entwickeln. Durch das gezielte Umlagern eines einzigen Silberatoms in einem winzigen metallischen Kontakt lasst sich ein elektrischer Stromkreis kontrolliert offnen und schliesen. Die atomaren Schalter werden dabei durch ein elektrisches Kontrollpotential gesteuert, das an eine unabhangige dritte Elektrode, die Gate-Elektrode, angelegt wird. Das Bauelement, das reproduzierbar bei Raumtemperatur funktioniert, stellt die erstmalige Realisierung eines atomaren Relais oder Transistors dar und eroffnet faszinierende Perspektiven fur die Gebiete der Quantenelektronik und der Logikschaltungen auf atomarer Skala.

Electrochemical gating permits the observation of few-atom processes in contact reconstruction. We monitor the junction conductance during the opening and closing of an atomic-scale metallic contact and use this as an instantaneous probe of the atomic-scale structural switching process. We observe clear correlations in the quantum conductance of a contact in subsequent switching events, demonstrating memory effects at the atomic scale. These experimental observations are supported by numerical simulations which show a conservation of the contact reconstruction process across several switching cycles. These results open a route to electrochemically control few-atom surface reconstruction events with present-day detection capabilities.

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