Atomic Wires Research Articles

Ab initio study of highly tunable charge transfer in β−RuCl3 /graphene heterostructures

Heterostructures of graphene in proximity to magnetic insulators open the possibility to investigate exotic states emerging from the interplay of magnetism, strain and charge transfer between the layers. Recent reports on the growth of self-integrated atomic wires of β−RuCl3 on graphite suggest these materials as versatile candidates to investigate these effects. Here we present detailed first-principles calculations on the charge transfer and electronic structure of β−RuCl3/graphene heterostructures and provide a comparison with the work function analysis of the related honeycomb family members α−RuX3 (X = Cl,Br,I). We find that proximity of the two layers leads to a hole-doped graphene and electron-doped RuX3 in all cases, which is sensitively dependent on the distance between the two layers. Furthermore, strain effects due to lattice mismatch control the magnetization which itself has a strong effect on the charge transfer. Charge accumulation in β−RuCl3 strongly drops away from the chain making such heterostructures suitable candidates for sharp interfacial junctions in graphene-based devices. Published by the American Physical Society 2024

Electronic structure, absorption spectra and oxidation dynamics in polyynes and dicyanopolyynes.

The advent of femtosecond to attosecond experimental tools has made now possible to study such ultrafast carrier dynamics, e.g., the spatial and temporal charge density evolution, after an initial oxidation or reduction in molecules, candidates for atomic wires like polyynes and dicyanopolyynes. Here, we study the electronic structure and hole transfer in symmetric molecules containing carbon, nitrogen and hydrogen, the first members in the series of polyynic carbynes and dicyanopolyynes, using methods based on density functional theory (DFT): constrained DFT (CDFT), time-dependent DFT (TDDFT) and real-time TDDFT (RT-TDDFT), with Löwdin population analysis, comparing many levels of theory and obtaining convergence of the results. For the same purposes, we develop a tight binding (TB) variant using all valence orbitals of all atoms. This TB variant is applied here in linear molecules, but it is also adequate for electronic structure, charge transfer and charge transport of non-linear molecules and clusters of molecules. We calculate the electronic structure, the time-dependent dipole moment and the probabilities of finding the hole at each site, their mean over time values, the mean transfer rates from the oxidation site to other sites and the frequency content (using charge as well as dipole moment oscillations). We take into account zero-point motion. The initial conditions for RT-TDDFT are obtained by CDFT. For TB, we explore different initial conditions: we place the hole at a particular orbital or distribute it among a number of orbitals; it is also possible to include phase differences between orbitals. Finally, we compare with available experimental data.

Exploring the Growth Dynamics of Size-Selected Carbon Atomic Wires with In Situ UV Resonance Raman Spectroscopy.

Short carbon atomic wires, the prototypes of the lacking carbon allotrope carbyne, represent the fundamental 1D system and the first stage in carbon nanostructure growth, which still exhibits many open points regarding their growth and stability. An in situ UV resonance Raman approach is introduced for real-time monitoring of the growth of carbon atomic wires during pulsed laser ablation in liquid without perturbing the synthesis environment. Single-chain species' growth dynamics are tracked, achieving size selectivity by exploiting the peculiar optoelectronic properties of carbon wires and the tunability of synchrotron radiation. Diverse solvents are systematically explored, finding size- and solvent-dependent production rates linked to the solvent's C/H ratio and carbonization tendency. Carbon atomic wires' growth dynamics reveal a complex interplay between formation and degradation, leading to an equilibrium. Water, lacking in carbon atoms and reduced polyynes solubility, yields fewer wires with rapid saturation. Organic solvents exhibit enhanced productivity and near-linear growth, attributed to additional carbon from solvent dissociation and low relative polarity. Exploring the dynamics of the saturation regime provides new insights into advancing carbon atomic wires synthesis via PLAL. Understanding carbon atomic wires' growth dynamics can contribute to optimizing PLAL processes for nanomaterial synthesis.

Impact of Halogen Termination and Chain Length on π-Electron Conjugation and Vibrational Properties of Halogen-Terminated Polyynes.

We explored the optoelectronic and vibrational properties of a new class of halogen-terminated carbon atomic wires in the form of polyynes using UV-vis, infrared absorption, Raman spectroscopy, X-ray single-crystal diffraction, and DFT calculations. These polyynes terminate on one side with a cyanophenyl group and on the other side, with a halogen atom X (X = Cl, Br, I). We focus on the effect of different halogen terminations and increasing lengths (i.e., 4, 6, and 8 sp-carbon atoms) on the π-electron conjugation and the electronic structure of these systems. The variation in the sp-carbon chain length is more effective in tuning these features than changing the halogen end group, which instead leads to a variety of solid-state architectures. Shifts between the vibrational frequencies of samples in crystalline powders and in solution reflect intermolecular interactions. In particular, the presence of head-to-tail dimers in the crystals is responsible for the modulation of the charge density associated with the π-electron system, and this phenomenon is particularly important when strong I··· N halogen bonds occur.

Titanium-Based Metasurfaces for Optoelectronics.

We report on the fabrication method that enables the development of transparent conductive metasurfaces capable of the resonant absorption of light in specific frequency bands. The approach is based on embedding linear sp-carbon chains and metallic nanoparticles in a porous matrix of titanium dioxide (TiO2). We develop a blading technique for the formation of a periodical grating of TiO2 microtubes at the macroscale. The method allowed us to maintain the periodicity of an array of microtubes with an accuracy of ±5%. Tuning the diameter of the tubes and the concentration of metallic nanoparticles, we achieved the regime of strong resonant absorption of the fabricated complex metasurface in the visible range. Computer simulations helped revealthe regime of TE/TM-polarized laser pumping that allowed for the most efficient transformation of light energy into electric current flow. In the studied structures, the sp-carbon clusters embedded inside transparent titanium dioxide tubes play the role of atomic wires. The interplay between efficient conductivity through carbon wires and the plasmon-enhanced absorption of light allows the design of photodiode structures based on periodical metasurfaces and characterized by highly selective optical sensitivity.

Computational study of conductance through Cu, Ag, Au and Pt atomic chain contacts

Atomic size wires are basic devices of molecular electronics and a common model for simulation of transport properties of other molecular devices, where hypothetical semi-infinite equidistant atomic chains are considered as electrodes. In this work, structure of infinite linear Cu, Ag, Au and Pt atomic chains was studied at nonrelativistic, scalar and spin–orbit zeroth order relativistic approximation levels. Bonds in chains were characterized within Quantum Theory of “Atoms In Molecules” approach. Conductance through finite chains of six atom length between bulk leads for bias voltage range of 0.0–1.0 V was calculated within non-equilibrium Green’s function approach combined with density functional theory. Chain conductance at high bias voltages correlates with product of Jenkins’ metallicity and positively defined kinetic energy density at bond critical points of corresponding infinite atomic chains. Variation of number of atoms in finite Au and Pt chains showed weak “odd-even” oscillations of chain conductance at some bias voltages.

Electronic structure and intrinsic mobilities of one-dimensional CuO2 atomic wires: A first-principles study

Herein, the electronic structure and intrinsic carrier mobility of the one-dimensional CuO2 atomic chain were studied by first-principles calculations. The band structure of the CuO2 atomic chain was obtained using the HSE06 hybrid functional with spin polarization. The results show that the band gap and hole effective mass of antiferromagnetic (ferromagnetic) CuO2 were 1.42 (0.38) eV and 1.53 (0.81) m0, respectively. The magnetism in CuO2 mainly originates from O atoms, consistent with the experiment, and the magnetic moment of these O atoms in the antiferromagnetic (ferromagnetic) state was ±0.58 (+0.41) μB. The intrinsic carriers of CuO2 have relatively high hole mobility (318 cm2 V−1 s−1) and extremely low electron mobility. Combined with the phonon dispersion calculation, the CuO2 atomic chain is an excellent and structurally stable p-type one-dimensional semiconductor material. Our work is expected to provide useful guidance for thermal transport materials containing CuO2 atomic chain substructure.

Phonon and Magnon Jets above the Critical Current in Nanowires with Planar Domain Walls.

We show through nonequilibrium nonadiabatic electron-spin-lattice simulations that above a critical current in magnetic atomic wires with a narrow domain wall (DW), a couple of atomic spaces in width, the electron flow triggers violent stimulated emission of phonons and magnons with an almost complete conversion of the incident electron momentum flux into a phonon and magnon flux. Just below the critical levels of the current flow, the DW achieves maximal velocity of about 3×10^{4} m/s, entering a strongly nonadiabatic regime of DW propagation, followed by a breakdown at higher biases. Above this threshold, a further increase of the current with the applied bias is impossible-the electronic current suffers a heavy suppression and the DW stops. This poses a fundamental limit to the current densities attainable in atomic wires. At the same time it opens up an exciting way of generating the alternative quasiparticle currents, described above, once the requisite electronic-structure properties are met.

Alteration of the inter-chain distance between Au atomic wires on Si(111) induced by Tl adsorption

Thallium (Tl) deposition onto the Au/Si(111)5 × 2 reconstruction followed by annealing at about 300 °C has been found to result in the formation of the surface structure having 4 × 2 periodicity. Similar to the most reconstructions in the (Au, Tl)/Si(111) system, Au and Tl do not intermix uniformly. While Au chains preserve their inner structure, Tl atoms being highly mobile at room temperature continuously migrate over the Si chains. Thallium donates electrons into the surface, that results in the two consequences: (i) filling the originally partially filled surface-state band, thus converting the metallic surface into an insulating state; (ii) transforming Si chains, which separate Au atomic rows, from the honeycomb-like to the zigzag according to the electron counting rule. The latter alters the inter-chain distance within the array of Au atomic wires. Au and/or Si chains contain point defects, which are masqueraded by the mobile Tl atoms producing peculiar “wavy” STM images.

Synchrotron-based UV resonance Raman spectroscopy probes size confinement, termination effects, and anharmonicity of carbon atomic wires

Vibrational and electronic properties and anharmonicity of sp-carbon atomic wires (i.e., polyynes) have been studied using resonance Raman spectroscopy, focusing on the confinement effects connected to their structure (length and termination). We exploited the fine tunability of the synchrotron radiation to resonantly excite short H-, CH3-, and CN-capped carbon atomic wires at their vibronic transitions in the deep UV. We report for the first time the resonance Raman spectra of size-selected CH3-capped polyynic wires (HCnCH3, n = 8–12) and CN-capped wires (HC6CN and HC12CN). We observed that the degree of π-electron conjugation increases with the wire length and is related to the specific termination. The analysis of multiple quanta Raman overtone bands shows that the anharmonic correction of the vibrational potential energy becomes increasingly relevant as the wire length increases. Finally, studying the vibronic lines of the UV absorption spectra allows the determination of an effective displacement parameter between the minima of the ground and the low-lying excited state, proving that the strong electron-phonon coupling of these systems is sensitive to chain length and termination.

Intrinsic Atomic-Scale Antiferroelectric VOF3 Nanowire with Ultrahigh-Energy Storage Properties.

Antiferroelectrics with antiparallel dipoles are receiving tremendous attention for their technological importance and fundamental interest. However, intrinsic one-dimensional (1D) materials harboring antiferroelectric ordering have rarely been reported despite the promise of novel paradigms for miniaturized and high-density electronics. Herein, based on first- and second-principles calculations, we demonstrate the VOF3 atomic wire, exfoliated from an experimentally synthesized yet underexplored 1D van der Waals (vdW) bulk, as a new 1D antiferroelectric material. The energetic, thermal, and dynamic stabilities of the nanowire are confirmed theoretically. Moreover, the temperature-dependent phase transitions and double-hysteresis polarization-field loops are computed for the VOF3 nanowire by constructing the second-principles model. According to the hysteresis loops, high energy densities and efficiencies can be obtained simultaneously at room temperature in the VOF3 nanowire under moderate applied fields. Our identified 1D atomic wire not only expands the family of antiferroelectricity but also holds potential for novel high-power energy storage nanodevices.

Topological soliton molecule in quasi 1D charge density wave

Soliton molecules, bound states of two solitons, can be important for the informatics using solitons and the quest for exotic particles in a wide range of physical systems from unconventional superconductors to nuclear matter and Higgs field, but have been observed only in temporal dimension for classical wave optical systems. Here, we identify a topological soliton molecule formed spatially in an electronic system, a quasi 1D charge density wave of indium atomic wires. This system is composed of two coupled Peierls chains, which are endowed with a Z4 topology and three distinct, right-chiral, left-chiral, and non-chiral, solitons. Our scanning tunneling microscopy measurements identify a bound state of right- and left-chiral solitons with distinct in-gap states and net zero phase shift. Our density functional theory calculations reveal the attractive interaction of these solitons and the hybridization of their electronic states. This result initiates the study of the interaction between solitons in electronic systems, which can provide novel manybody electronic states and extra data-handling capacity beyond the given soliton topology.

Growth of self-integrated atomic quantum wires and junctions of a Mott semiconductor.

Continued advances in quantum technologies rely on producing nanometer-scale wires. Although several state-of-the-art nanolithographic technologies and bottom-up synthesis processes have been used to engineer these wires, critical challenges remain in growing uniform atomic-scale crystalline wires and constructing their network structures. Here, we discover a simple method to fabricate atomic-scale wires with various arrangements, including stripes, X-junctions, Y-junctions, and nanorings. Single-crystalline atomic-scale wires of a Mott insulator, whose bandgap is comparable to those of wide-gap semiconductors, are spontaneously grown on graphite substrates by pulsed-laser deposition. These wires are one unit cell thick and have an exact width of two and four unit cells (1.4 and 2.8 nm) and lengths up to a few micrometers. We show that the nonequilibrium reaction-diffusion processes may play an essential role in atomic pattern formation. Our findings offer a previously unknown perspective on the nonequilibrium self-organization phenomena on an atomic scale, paving a unique way for the quantum architecture of nano-network.

Controllable dimensionality conversion between 1D and 2D CrCl3 magnetic nanostructures

The fabrication of one-dimensional (1D) magnetic systems on solid surfaces, although of high fundamental interest, has yet to be achieved for a crossover between two-dimensional (2D) magnetic layers and their associated 1D spin chain systems. In this study, we report the fabrication of 1D single-unit-cell-width CrCl3 atomic wires and their stacked few-wire arrays on the surface of a van der Waals (vdW) superconductor NbSe2. Scanning tunneling microscopy/spectroscopy and first-principles calculations jointly revealed that the single wire shows an antiferromagnetic large-bandgap semiconducting state in an unexplored structure different from the well-known 2D CrCl3 phase. Competition among the total energies and nanostructure-substrate interfacial interactions of these two phases result in the appearance of the 1D phase. This phase was transformable to the 2D phase either prior to or after the growth for in situ or ex situ manipulations, in which the electronic interactions at the vdW interface play a nontrivial role that could regulate the dimensionality conversion and structural transformation between the 1D-2D CrCl3 phases.

Intrinsic ferroelectrics and carrier doping-induced metallic multiferroics in an atomic wire

Low-dimensional multiferroic metals characterized by the simultaneous coexistence of ferroelectricity, conductivity, and magnetism hold tremendous potential for scientific and technological endeavors. However, the mutually exclusive mechanisms among these properties impede the discovery of multifunctional conducting multiferroics, especially at the atomic-scale. Here, based on first-principles calculations, we design and demonstrate intrinsic one-dimensional (1D) ferroelectrics and carrier doping-induced metallic multiferroics in an atomic WOF4 wire. The WOF4 atomic wire that can be derived from a 1D van der Waals crystal exhibits pronounced ferroelectricity manifested in the form of large cooperative atomic displacements. By performing Monte Carlo simulations with an effective Hamiltonian method, we obtain the nanowire that can sustain a high Curie temperature, indicating its potential for room-temperature applications. Moreover, doping with electrons is found to induce magnetism and metallic conductivity that coexists with the ferroelectric distortion in the nanowire. These appealing properties in conjunction with the experimental feasibility enable the doped WOF4 nanowire to act as a promising atomic-scale multifunctional material.

Theoretical Investigations on the Plasmon-Mediated Dissociation of Small Molecules in the Presence of Silver Atomic Wires.

Plasmonic nanoparticles can promote bond activation in adsorbed molecules under relatively benign conditions via excitation of the nanoparticle's plasmon resonance. As the plasmon resonance often falls within the visible light region, plasmonic nanomaterials are a promising class of catalysts. However, the exact mechanisms through which plasmonic nanoparticles activate the bonds of nearby molecules are still unclear. Herein, we evaluate Ag8-X2 (X = N, H) model systems via real-time time-dependent density functional theory (RT-TDDFT), linear response time-dependent density functional theory (LR-TDDFT), and Ehrenfest dynamics in order to better understand the bond activation processes of N2 and H2 facilitated by the presence of the atomic silver wire under excitation at the plasmon resonance energies. We find that dissociation is possible for both small molecules at high electric field strength. Activation of each adsorbate is symmetry- and electric field-dependent, and H2 activates at lower electric field strengths than N2. This work serves as a step toward understanding the complex time-dependent electron and electron-nuclear dynamics between plasmonic nanowires and adsorbed small molecules.

Some Properties of Motion of Atoms near a Charged Wire

We are concerned with the classical approach to atomic motions in the vicinity of a wire charged by an oscillating voltage. This mechanism has been proposed to serve for trapping cold neutral atoms. We prove that, under some conditions, the atom must either collide with the wire or escape to infinity in the radial direction. The presented results for the atom–wire problem extend and complement some earlier ones in the literature.

Machine-learning prediction of the formation of atomic gold wires by mechanically controlled break junctions.

One of the challenging issues in the formation of atomic wires in break-junction experiments is the formation of stable monoatomic chains of reasonable length. To address this issue, in this study, we present a combination of unsupervised and supervised machine learning models trained on the experimentally measured conductance traces, with a goal to develop a microscopic understanding. Applying a machine learning model to two independent data sets from two different samples containing 72 000 and 90 000 conductance-displacement traces of single-atomic junctions, respectively, we first obtain the optimum conditions of bias and the stretching rate for the formation of chains of length > 4 Å. A deep learning method is subsequently applied for the classification of individual breaking traces, leading to the identification of trace features related to long-chain formation. Further investigation by ab initio molecular dynamics simulations provides a molecular-level understanding of the problem.

Scale-Free Distribution of Oxygen Interstitial Wires in Optimum-Doped HgBa2CuO4+y

Novel nanoscale probes are opening new venues for understanding unconventional electronic and magnetic functionalities driven by multiscale lattice complexity in doped high-temperature superconducting perovskites. In this work, we focus on the multiscale texture at supramolecular level of oxygen interstitial (O-i) atomic stripes in HgBa2CuO4+y at optimal doping for the highest superconducting critical temperature (TC) of 94 K. We report compelling evidence for the nematic phase of oxygen interstitial O-i atomic wires with fractal-like spatial distribution over multiple scales using scanning micro- and nano-X-ray diffraction. The scale-free distribution of O-i atomic wires at optimum doping extending from the micron down to the nanoscale has been associated with the intricate filamentary network of hole-rich metallic wires in the CuO2 plane. The observed critical opalescence provides evidence for the proximity to a critical point that controls the emergence of high-temperature superconductivity at optimum doping.

Electronic transport properties of atomic wires on monolayers

In recent years, several scientific organizations have focused on the electrical characteristics of atomic wires on monolayers. The usage of MoS2 in many technologies requires contacts between metallic atomic wires and MoS2. Using first-principles density functional theory, we investigate the interaction of a variety of metallic atomic wires on MoS2, including Al and Pt. The electronic properties of atomic wire sandwiches containing MoS2 monolayers such as aluminium (Al) and platinum (Pt) have been thoroughly investigated using density functional theory calculations. Despite significant lattice deformation, structural investigations show that all sandwich systems almost maintain the original MoS2 structure type. By inserting flat impurity bands within the band gap, the electronic transport property is improved. The electrical structure of the system reveals the binding processes and trends in binding energy. On MoS2, we show that monitoring monomer adhesion energy and mobility on the substrate may be used to predict metal nanoparticle growth morphologies. The indirect bandgap of layered atomic wires sandwiched with MoS2 becomes a direct band gap in the visible spectrum, making them appropriate for optoelectronics devices.