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Chirality-induced spin selectivity has been reported in many experiments, but a generally accepted theoretical explanation has not yet been proposed. Here, we introduce a simple model system of a straight cylindrical free-electron wire containing a helical string of atomic scattering centers with spin–orbit interaction. The advantage of this simple model is that it allows deriving analytical expressions for the spin scattering rates, such that the origin of the effect can be easily followed. We find that spin-selective scattering can be viewed as resulting from the constructive interference of partial waves scattered by the spin–orbit terms. We demonstrate that forward scattering rates are independent of spin, while back scattering is spin dependent over wide windows of energy. Although the model does not represent the full details of electron transmission through chiral molecules, it clearly reveals a mechanism that could operate in chiral systems. [ABSTRACT FROM AUTHOR]

Biopolymer sequencing with graphene edge-based tunnel junctions has the potential to overcome current limitations with the third generation of sequencing based on biological nanopores. Detection of nucleotides via (recognition) tunneling with noble metal break junctions shows promising results; however, the bulky nature and a range of physical and chemical instabilities of the electrodes prevent advancing toward long-read sequencing with single base-calling accuracy. Graphene edges as tunnel electrodes may overcome these limitations, with the possibility to reach true single-molecule readout, thanks to their 2D nature. Currently, the development of graphene tunnel sequencers faces challenges in terms of targeted chemical functionalization of the graphene edge to enable recognition tunneling and the eventual integration in a nanopore configuration to realize long-read sequencing of biopolymers. Herein, we discuss the current developments that encourage active research toward graphene edge junctions for single-molecule detection, recognition, and sequencing applications with nucleotides and deoxyribonucleic acid as example. [ABSTRACT FROM AUTHOR]

It is possible to fabricate structures at the atomic scale using state of the art techniques to manipulate single atoms. It is shown that the chemical valence determines the conduction properties of a one-atom contact between two metallic banks. It is assumed that the number of current-carrying modes of a one atom contact is determined by the available valence orbitals, and should differ for metallic elements in the periodic table.

For the technological integration of molecular switches in electronic devices, self‐assembling nanomaterials of such switches are highly sought after. The syntheses of a new tetrapyridyl ligand bearing a C12 alkyl chain and two N−H bridges (compound 1) and of its iron(II) complex [Fe(1)(NCS)2] (compound 2), are described. Magnetic susceptibility data for bulk samples of 2 confirmed their gradual spin‐crossover properties. The self‐assembly of 1 and 2 on highly ordered pyrolytic graphite surfaces (HOPG) was investigated by Scanning Tunneling Microscopy (STM). Both compounds 1 and 2 formed ordered monolayers after deposition by drop casting. The patterns of the two compounds are very different, which is attributed to the fundamentally different hydrogen bonding networks before and after coordination of Fe(NCS)2 to the tetradentate chelate. Two possible models for the self‐assembly of 1 and 2 are provided. This work suggests that it is possible to design molecular switches that self‐assemble on surfaces in highly ordered monolayer films. This is a significant step in the development of spin‐switching materials, which may streamline the integration of molecular switches in for example memory and sensing devices. [ABSTRACT FROM AUTHOR]

We demonstrate that it is possible to distinguish two conductance switching mechanisms in silver sulfide devices at room temperature. Experiments were performed using a Ag2S thin film deposited on a wide Ag bottom electrode, which was contacted by the Pt tip of a scanning tunneling microscope. By applying a positive voltage on the silver electrode, the conductance is seen to switch to a state having three orders of magnitude higher conductance, which is related to the formation of a conductive path inside the Ag2S thin film. We argue this to be composed of a metallic silver nanowire accompanied by a modification of the surrounding lattice structure. Metallic silver nanowires decaying after applying a negative voltage allow observing conductance steps in the breaking traces characteristic for atomic-scale contacts, while the lattice structure deformation is revealed by gradual and continuously decreasing conductance traces. [ABSTRACT FROM AUTHOR]

Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2-xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to -2 V. A non-electrostatic mechanism takes over for gate voltages below -2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7-x and La2-xSrxCuO4 [ABSTRACT FROM AUTHOR]

Shot noise measurements on atomic and molecular junctions provide rich information about the quantum transport properties of the junctions and on the inelastic scattering events taking place in the process. Dissipation at the nanoscale, a problem of central interest in nano-electronics, can be studied in its most explicit and simplified form. Here, we describe a measurement technique that permits extending previous noise measurements to a much higher frequency range, and to much higher bias voltage range, while maintaining a high accuracy in noise and conductance. We also demonstrate the advantages of having access to the spectral information for diagnostics. [ABSTRACT FROM AUTHOR]

We demonstrate that the notched-wire mechanically controllable break junction technique can be exploited for the study of single molecule junctions. We have developed a protocol for deposition of thiol-coupled molecules onto Au electrodes from solution. We find surprisingly sharp conductance historgrams at low temperatures, which suggest that the commonly observed large width of the peaks in conductance historgams is the result of inhomogeneous broadening. [ABSTRACT FROM AUTHOR]

Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and undoped Nd2CuO4. We find major resistance drops of the bilayer coupled to observations of the presence of a considerable Faradeic component in the gate current and of the appearance of charge transfer peaks in the cyclic voltammetry data. This leads us to propose a mechanism of gating based on irreversible electrochemical reactions, likely due to trace amounts of contaminations present in the ionic liquid. This work is therefore in line with previous reports confirming the presence of irreversible electrochemistry in ionic liquid gated electron- doped cup-rates. [ABSTRACT FROM AUTHOR]

Metal/organic interfaces critically determine the characteristics of molecular electronic devices, because they influence the arrangement of the orbital levels that participate in charge transport. Studies on self-assembled monolayers show molecule-dependent energy-level shifts as well as transport-gap renormalization, two effects that suggest that electric-field polarization in the metal substrate induced by the formation of image charges plays a key role in the alignment of the molecular energy levels with respect to the metal's Fermi energy. Here, we provide direct experimental evidence for an electrode-induced gap renormalization in single-molecule junctions. We study charge transport through single porphyrin-type molecules using electrically gateable break junctions. In this set-up, the position of the occupied and unoccupied molecular energy levels can be followed in situ under simultaneous mechanical control. When increasing the electrode separation by just a few ångströms, we observe a substantial increase in the transport gap and level shifts as high as several hundreds of meV. Analysis of this large and tunable gap renormalization based on atomic charges obtained from density functional theory confirms and clarifies the dominant role of image-charge effects in single-molecule junctions. [ABSTRACT FROM AUTHOR]

We present a modular high-vacuum setup for the electrical characterization of single molecules down to liquid helium temperatures. The experimental design is based on microfabricated mechanically controllable break junctions, which offer control over the distance of two electrodes via the bending of a flexible substrate. The actuator part of the setup is divided into two stages. The slow stage is based on a differential screw drive with a large bending range. An amplified piezoceramic actuator forms the fast stage of the setup, which can operate at bending speeds of up to 800 μm/s. In our microfabricated break junctions this is translated into breaking speeds of several 10 nm/s, sufficient for the fast acquisition of large statistical datasets. The bandwidth of the measurement electronics has been optimized to enable fast dI/dV spectroscopy on molecular junctions with resistances up to 100 MΩ. The performance of the setup is demonstrated for a π-conjugated oligo(phenylene-ethynylene)-dithiol molecule. [ABSTRACT FROM AUTHOR]

Keywords: Iron; Molecular materials; Scanning tunneling microscopy; Self-assembly; Surface chemistry EN Iron Molecular materials Scanning tunneling microscopy Self-assembly Surface chemistry 2801 2801 1 08/25/21 20210726 NES 210726 B The Front Cover b shows an artist's impression of the self-assembly of spin-crossover complexes modified with alkyl tails. Iron, Molecular materials, Scanning tunneling microscopy, Self-assembly, Surface chemistry Front Cover: Highly Ordered, Self-Assembled Monolayers of a Spin-Crossover Complex with In-Plane Interactions (Eur. J. Inorg. [Extracted from the article]

In article number 1700449, Jan M. Van Ruitenbeek and co‐workers study the time evolution of the conduction of SrTiO3 near the glass‐transition temperature of an ionic liquid. The top surface of the crystalline SrTiO3 insulator can be converted into a good conductor by application of a gate potential, mediated by the ionic liquid. The process by which the conducting layer forms can be followed by cooling the ionic liquid to a temperature close to the glass transition, here about 185 K. [ABSTRACT FROM AUTHOR]

Ionic‐liquid gating has become a popular tool for tuning the charge carrier densities of complex oxides. Among these, the band insulator SrTiO3 is one of the most extensively studied materials. While experiments have succeeded in inducing (super)conductivity, the process by which ionic‐liquid gating turns this insulator into a conductor is still under scrutiny. Recent experiments have suggested an electrochemical rather than electrostatic origin of the induced charge carriers. Here, experiments probing the time evolution of conduction of SrTiO3 near the glass transition temperature of the ionic liquid are reported. By cooling down to temperatures near the glass transition of the ionic liquid, the process develops slowly and can be seen to evolve in time. The experiments reveal a process characterized by waiting times that can be as long as several minutes preceding a sudden appearance of conduction. For the conditions applied in our experiments, a consistent interpretation in terms of an electrostatic mechanism for the formation of a conducting path at the surface of SrTiO3 is found. The mechanism by which the conducting surface channel develops relies on a nearly homogeneous lowering of the surface potential until the conduction band edge of SrTiO3 reaches the Fermi level of the electrodes. The time evolution of conduction of SrTiO3 near the glass transition temperature of the ionic liquid is recorded. The experiments reveal waiting times that can be as long as several minutes preceding a sudden appearance of conduction. For the conditions applied, a consistent interpretation is found in terms of a purely electrostatic mechanism for the formationof a conducting path at the surface of SrTiO3. [ABSTRACT FROM AUTHOR]

Molecular electronics saw its birth with the idea to build electronic circuitry with single molecules as individual components. Even though commercial applications are still modest, it has served an important part in the study of fundamental physics at the scale of single atoms and molecules. It is now a routine procedure in many research groups around the world to connect a single molecule between two metallic leads. What is unknown is the nature of this coupling between the molecule and the leads. We have demonstrated recently (Tewari, 2018, Ph.D. Thesis) our new setup based on a scanning tunneling microscope, which can be used to controllably manipulate single molecules and atomic chains. In this article, we will present the extension of our molecular dynamic simulator attached to this system for the manipulation of single molecules in real time using a graphics processing unit (GPU). This will not only aid in controlled lift-off of single molecules, but will also provide details about changes in the molecular conformations during the manipulation. This information could serve as important input for theoretical models and for bridging the gap between the theory and experiments. [ABSTRACT FROM AUTHOR]

One dimensional systems strongly enhance the quantum character of electron transport. Such systems can be realized in 5d transition metals Au, Pt, and Ir, in the form of suspended monatomic chains between bulk leads. Atomic chains between ferromagnetic leads would open up many perspectives in the context of spin-dependent transport and spintronics, but the evidence suggests that for pure metals only the mentioned three 5d metals are susceptible to chain formation. It has been argued that the stability of atomic chains made up from ferromagnetic metals is compromised by the same exchange interaction that produces the local moments. Here we demonstrate that magnetic atomic chains can be induced to form in break junctions under the influence of light molecules. Explicitly, we find deuterium assisted chain formation in the 3d ferromagnetic transition metals Fe and Ni. Chain lengths up to eight atoms are formed upon stretching the ferromagnetic atomic contact in deuterium atmosphere at cryogenic temperatures. From differential conductance spectra vibronic states of D2 can be identified, confirming the presence of deuterium in the atomic chains. Shot noise spectroscopy indicates the presence of weakly spin polarized transmission channels. [ABSTRACT FROM AUTHOR]

Using remarkably simple experimental techniques it is possible to gently break a metallic contact and thus form conducting nanowires. During the last stages of the pulling a neck-shaped wire connects the two electrodes, the diameter of which is reduced to single atom upon further stretching. For some metals it is even possible to form a chain of individual atoms in this fashion. Although the atomic structure of contacts can be quite complicated, as soon as the weakest point is reduced to just a single atom the complexity is removed. The properties of the contact are then dominantly determined by the nature of this atom. This has allowed for quantitative comparison of theory and experiment for many properties, and atomic contacts have proven to form a rich test-bed for concepts from mesoscopic physics. Properties investigated include multiple Andreev reflection, shot noise, conductance quantization, conductance fluctuations, and dynamical Coulomb blockade. In addition, pronounced quantum effects show up in the mechanical properties of the contacts, as seen in the force and cohesion energy of the nanowires. We review this research, which has been performed mainly during the past decade, and we discuss the results in the context of related developments. [Copyright &y& Elsevier]

Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2-xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to -2 V. A non-electrostatic mechanism takes over for gate voltages below -2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7-x and La2-xSrxCuO4 [ABSTRACT FROM AUTHOR]

Pt is known to show spontaneous formation of monatomic chains upon breaking a metallic contact. From model calculations, these chains are expected to be spin polarized. However, direct experimental evidence for or against magnetism is lacking. Here, we investigate shot noise as a potential source of information on the magnetic state of Pt atomic chains. We observe a remarkable structure in the distribution of measured shot-noise levels, where the data appear to be confined to the region of nonmagnetic states. While this suggests a nonmagnetic ground state for the Pt atomic chains, from calculations we find that the magnetism in Pt chains is due to "actor" electron channels, which contribute very little to ballistic conductance and noise. On the other hand, there are weakly polarized "spectator" channels, which carry most of the current and are only slightly modified by the magnetic state. [ABSTRACT FROM AUTHOR]

We present shot noise measurements on Au nanowires showing very pronounced vibration-mode features. In accordance to recent theoretical predictions the sign of the inelastic signal, i.e., the signal due to vibration excitations, depends on the transmission probability becoming negative below a certain transmission value. We argue that the negative contribution to noise arises from coherent two-electron processes mediated by electron-phonon scattering and the Pauli exclusion principle. These signals can provide unique information on the local phonon population and lattice temperature of the nanoscale system. [ABSTRACT FROM AUTHOR]

The article analyzes a study on fullerene-based molecular electronics anchoring. Stable chemical anchoring is an important step in the formation of single-molecule junctions. Thiol moieties have been extensively used to bind single molecules to gold electrodes however it exhibits variations that are reflected in the electronic properties of molecular junctions. To achieve junction stabilities, fullerenes is being considered because of its high symmetry and affinity for noble metals.