Low-dimensional Nanostructures Research Articles

Crucial Role of Metal Coordination Number in Optimizing Electrocatalyst Activity of Holey Large-Area 2D Ru Nanosheets.

Low-dimensional metal nanostructures have attracted considerable research attention, owing to their potential as catalysts. A controlled reductive phase transition of monolayer RuO2 nanosheets could provide an effective way to produce holey large-area 2D Ru nanosheets with tailored defect structures and metal coordination number. The locally optimized holey Ru metal nanosheet, with a metal coordination number of ∼10.2, exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) with a reduced overpotential of 38 mV in a 1 M KOH electrolyte. The creation of a highly anisotropic holey nanosheet morphology with optimization of local structure was quite effective in developing efficient catalyst materials. The universal importance of controlling the coordination number was confirmed through a comparative study of Ru nanoparticles, which showed optimized HER activity with an identical metal coordination number. The coordination number plays a pivotal role in governing electrocatalytic activity, which could be ascribed to the formation of the most active structure for HER at most 2 defects near active sites (2,2'), resulting in the stabilization of a dihydrogen Ru-(H2) intermediate and the increased contribution of Volmer-Tafel mechanism.

Revealing the Influence of Molecular Chemisorption Direction on the Reaction Selectivity of Dehalogenative Coupling on Au(111): Polymerization versus Cyclization.

The control of reaction selectivity is of great interest in chemistry and depends crucially on the revelation of key influencing factors. Based on well-defined molecule-substrate model systems, various influencing factors have been elucidated, focusing primarily on the molecular precursors and the underlying substrates themselves, while interfacial properties have recently been shown to be essential as well. However, the influence of molecular chemisorption direction on reaction selectivity, as a subtle interplay between molecules and underlying substrates, remains elusive. In this work, by a combination of scanning tunneling microscopy imaging and density functional theory calculations, we report the influence of molecular chemisorption direction on the reaction selectivity of two types of dehalogenative coupling on Au(111), i.e., polymerization and cyclization, at the atomic level. The diffusion step of a reactive dehalogenated intermediate in two different chemisorption directions was theoretically revealed to be the key to determining the corresponding reaction selectivity. Our results highlight the important role of molecular chemisorption directions in regulating the on-surface dehalogenative coupling reaction pathways and products, which provides fundamental insights into the control of reaction selectivity by exploiting some subtle interfacial parameters in on-surface reactions for the fabrication of target low-dimensional carbon nanostructures.

The effect of pressure on the thermodynamic properties of hydrogenic impurity in the GaAs semiconductor quantum well

ABSTRACT Studying the thermodynamic properties of hydrogen impurity in low-dimensional nanostructures under high-pressure environment is crucial for understanding the optical property and thermal excitation behaviour of semiconductor material. Here, we extensively explore the effect of pressure on thermodynamic properties, specifically, the average energy, free energy, entropy, and heat capacity of one-dimensional (1-D) hydrogenic impurity in GaAs semiconductor quantum well. Our findings reveal some novel phenomenon in the thermodynamic properties of hydrogenic impurity as pressure increases in the GaAs quantum well. Remarkably, at a constant temperature, both the average energy and free energy of hydrogenic impurity decrease as pressure rises, while entropy increases with increasing pressure. Intriguingly, the heat capacity shows distinct behaviour with varying pressure for different sizes of the quantum well. For very small size of the quantum well, the heat capacity increases with increasing pressure. However, for larger size of the quantum wells, the variation of heat capacity with pressure becomes irregular, showing a changeover from an increase to a decrease in response to increasing pressure. This research presents a pioneering method that employs pressure as a versatile tool for modulating the thermodynamic properties of hydrogenic impurity states in the nanostructures, and has some guidance for the preparation and synthesis of semiconductor devices.

Role of Pyramidal Low-Dimensional Semiconductors in Advancing the Field of Optoelectronics

Numerous optoelectronic devices based on low-dimensional nanostructures have been developed in recent years. Among these, pyramidal low-dimensional semiconductors (zero- and one-dimensional nanomaterials) have been favored in the field of optoelectronics. In this review, we discuss in detail the structures, preparation methods, band structures, electronic properties, and optoelectronic applications (photocatalysis, photoelectric detection, solar cells, light-emitting diodes, lasers, and optical quantum information processing) of pyramidal low-dimensional semiconductors and demonstrate their excellent photoelectric performances. More specifically, pyramidal semiconductor quantum dots (PSQDs) possess higher mobilities and longer lifetimes, which would be more suitable for photovoltaic devices requiring fast carrier transport. In addition, the linear polarization direction of exciton emission is easily controlled via the direction of magnetic field in PSQDs with C3v symmetry, so that all-optical multi-qubit gates based on electron spin as a quantum bit could be realized. Therefore, the use of PSQDs (e.g., InAs, GaN, InGaAs, and InGaN) as effective candidates for constructing optical quantum devices is examined due to the growing interest in optical quantum information processing. Pyramidal semiconductor nanorods (PSNRs) and pyramidal semiconductor nanowires (PSNWRs) also exhibit the more efficient separation of electron-hole pairs and strong light absorption effects, which are expected to be widely utilized in light-receiving devices. Finally, this review concludes with a summary of the current problems and suggestions for potential future research directions in the context of pyramidal low-dimensional semiconductors.

Impact of intermittent sputtering on the ordering of triangular surface topography

It is demonstrated that the quality of nanoscale triangular structures on Si (100) surfaces can be improved by applying intermittent ion beam sputtering. This investigation is conducted along the work of Rakhi et al. (2023), which introduces an additional physical parameter space related to intermittent sputtering. Through this approach, we have observed the minimum surface defect density associated with higher-order surface structures, particularly at tT = 8 min. This can have large potential applications in modern cutting-edge technology demands of controlled growth of nanostructures, especially the low dimensional high aspect ratio nanostructures.

Soft Nanofluidic Machinery.

Soft devices integrating flexible structures and versatile material functionalities offer platform technologies for the healthcare, information, and communication industries. The flexibility can be achieved by constructing devices from low-dimensional nanostructures or nanoporous soft materials. By pushing the limits of fabrication and structuring down to the nanometer and Ångstrom scales, nanofluidics with extreme spatial confinement has recently been actively explored for energy-, environment-, and human-friendly device applications as alternative solutions to electronics and mechanotronics. Soft nanofluidic machinery enables ultrafast and selective fluidic transport, efficient energy conversion, and information processing, offering unconventional dimensions of design. The physics behind the design is introduced, followed by discussions on their implementations and performance and an outlook on the opportunities and challenges.

Atomic Scale Structure of Self-Assembled Lipidated Peptide Nanomaterials.

β-Peptides have great potential as novel biomaterials and therapeutic agents, due to their uniqueability to self-assemble into low dimensional nanostructures,and their resistance to enzymatic degradationin vivo. However, the self-assembly mechanisms of β-peptides, which possess increased flexibility due to the extra backbone methylene groups present within the constituent β-amino acids, are not well understood due to inherent difficulties of observing their bottom-up growth pathway experimentally. A computational approach is presented for the bottom-up modelling of the self-assembledlipidated β3-peptides, from monomers, to oligomers, to supramolecular low-dimensional nanostructures, in all-atom detail. The approach is applied to elucidate the self-assembly mechanisms of recently discovered, distinct structural morphologies of low dimensional nanomaterials, assembled from lipidated β3-peptide monomers. The resultant structures of the nanobelts and the twisted fibrils are stable throughout subsequent unrestrained all-atom molecular dynamics simulations, and these assemblies display good agreement with the structural features obtained from X-ray fiber diffraction and atomic force microscopy data.This is the first reported, fully-atomistic model of a lipidated β3-peptide-based nanomaterial, and the computational approach developed here, in combination with experimental fiber diffraction analysis and atomic force microscopy, will be useful in elucidating the atomic scale structure of self-assembled peptide-based and other supramolecular nanomaterials.

Light-Controlled Multiconfigurational Conductance Switching in a Single 1D Metal-Organic Wire.

Precise control of multiple spin states on the atomic scale presents a promising avenue for designing and realizing magnetic switches. Despite substantial progress in recent decades, the challenge of achieving control over multiconfigurational reversible switches in low-dimensional nanostructures persists. Our work demonstrates multiple, fully reversible plasmon-driven spin-crossover switches in a single π-d metal-organic chain suspended between two electrodes. The plasmonic nanocavity stimulated by external visible light allows for reversible spin crossover between low- and high-spin states of different cobalt centers within the chain. We show that the distinct spin configurations remain stable for minutes under cryogenic conditions and can be nonperturbatively detected by conductance measurements. This multiconfigurational plasmon-driven spin-crossover demonstration extends the available toolset for designing optoelectrical molecular devices based on SCO compounds.

A CsPbBr3/CdS-based hybrid bidirectional optoelectronic device with light-emitting, modulation, and detection functions

Optoelectronic integrated circuits, with a broad photonic transportation bandwidth, have emerged as a promising solution to fulfill the escalating demands for high-volume information transportation and processing. However, challenges persist in developing optoelectronic integrated circuits based on low-dimensional nanostructures, including limited integration density and high energy consumption. Here, we demonstrate a bidirectional optoelectronic device by integrating a light-emitting/harvesting CsPbBr3 nanoplate with a waveguiding/modulating/detecting CdS nanobelt. By configuring the CsPbBr3 nanoplate in a Schottky-type device structure with a metal electrode, bright electroluminescence was attained at a bias voltage of 18 V. Thanks to the electric field-tuned phonon-coupling effect, the waveguided light in the CdS nanobelt exhibited a high modulation depth of up to 94%, rendering it an excellent building block as optical modulators and optical switches. Moreover, the integrated nanostructure device showcased functionality in the photodetection mode. The proposed device architecture holds promise for broader applications, potentially extending to other perovskite-coupled II–VI semiconductor optoelectronic integrated circuits for expanding integration capacity and enhancing optoelectronic performance.

Separation of Halogen Atoms by Sodium from Dehalogenative Reactions on a Au(111) Surface.

On-surface dehalogenative reactions have been promising in the construction of nanostructures with diverse morphologies and intriguing electronic properties, while halogen (X), as the main byproduct, often impedes the formation of extended nanostructures and property characterization, and the reaction usually requires high C-X activation temperatures, especially on relatively inert Au(111). Enormous efforts in precursor design, halogen-to-halide conversion, and the introduction of extrinsic metal atoms have been devoted to either eliminating dissociated halogens or reducing reaction barriers. However, it is still challenging to separate halogens from molecular systems while facilitating C-X activation under mild conditions. Herein, a versatile halogen separation strategy has been developed based on the introduction of extrinsic sodium (Na) into dehalogenative reactions on Au(111) as model systems that both isolates the dissociated halogens and facilitates the C-Br activation under mild conditions. Moreover, the combination of scanning tunneling microscopy imaging and density functional theory calculations reveals the formation of sodium halides (NaX) from halogens in these separation processes as well as the reduction in reaction temperatures and barriers, demonstrating the versatility of extrinsic sodium as an effective "cleaner" and "dehalogenator" of surface halogens. Our study demonstrates a valuable strategy to facilitate the on-surface dehalogenative reactions, which will assist in the precise fabrication of low-dimensional carbon nanostructures.

Nano1D: An accurate computer vision software for analysis and segmentation of low-dimensional nanostructures

Nanoparticles in microscopy images are usually analyzed qualitatively or manually and there is a need for autonomous quantitative analysis of these objects. In this paper, we present a physics-based computational model for accurate segmentation and geometrical analysis of one-dimensional deformable overlapping objects from microscopy images. This model, named Nano1D, has four steps of preprocessing, segmentation, separating overlapped objects and geometrical measurements. The model is tested on SEM images of Ag and Au nanowire taken from different microscopes, and thermally fragmented Ag nanowires transformed into nanoparticles with different lengths, diameters, and population densities. It successfully segments and analyzes their geometrical characteristics including lengths and average diameter. The function of the algorithm is not undermined by the size, number, density, orientation and overlapping of objects in images. The main strength of the model is shown to be its ability to segment and analyze overlapping objects successfully with more than 99 % accuracy, while current machine learning and computational models suffer from inaccuracy and inability to segment overlapping objects. Benefiting from a graphical user interface, Nano1D can analyze 1D nanoparticles including nanowires, nanotubes, nanorods in addition to other 1D features of microstructures like microcracks, dislocations etc.

On-surface cyclization of vinyl groups on poly-para-phenylene involving an unusual pentagon to hexagon transformation

On-surface synthesis relies on carefully designed molecular precursors that are thermally activated to afford desired, covalently coupled architectures. Here, we study the intramolecular reactions of vinyl groups in a poly-para-phenylene-based model system and provide a comprehensive description of the reaction steps taking place on the Au(111) surface under ultrahigh vacuum conditions. We find that vinyl groups successfully cyclize with the phenylene rings in the ortho positions, forming a dimethyl-dihydroindenofluorene as the repeating unit, which can be further dehydrogenated to a dimethylene-dihydroindenofluorene structure. Interestingly, the obtained polymer can be transformed cleanly into thermodynamically stable polybenzo[k]tetraphene at higher temperature, involving a previously elusive pentagon-to-hexagon transformation via ring opening and rearrangement on a metal surface. Our insights into the reaction cascade unveil fundamental chemical processes involving vinyl groups on surfaces. Because the formation of specific products is highly temperature-dependent, this innovative approach offers a valuable tool for fabricating complex, low-dimensional nanostructures with high precision and yield.

Thermal transport characterization of monolayer GaN nanoribbon doped with group IV materials: An equilibrium molecular dynamics study

Bulk gallium nitride (GaN) has been considered as one of the prominent materials for a long time in the application of laser, LED and transistors. Due to its superior electrical characteristics, its low-dimensional hexagonal counterpart is currently drawing attention like graphene. In this study, we have investigated the effect of impurity atoms on the heat energy conduction within this honeycomb nanostructure of GaN to explore its scope of applications. The room temperature thermal conductivity of zigzag GaN nanoribbon (ZGaNNR) is found to be ∼ 11 Wm−1K−1 using the molecular dynamics approach with the Green-Kubo formulation. Various group IV elements namely- carbon, silicon, germanium and tin, have been incorporated within the pristine structure in four distinct doping patterns; like- point (Type-I and Type-II), pair and delta doping, to explore the thermal transport in chemically doped nanostructures. A gradual enhancement in the thermal conductivity is observed for the increasing concentration of carbon and silicon as dopants. On the other hand, selection of germanium and tin as impurity atoms suppresses the heat conduction within the crystal due to the increased low frequency phonon scattering. In all cases, Type-I point doping affects the thermal transport of ZGaNNR significantly. The narrower ribbons impede the phonon transportation due to the strong boundary effects resulting in a lower thermal conductivity. Moreover, phonon transportation is largely suppressed, and heat energy is observed to flow at a slower rate as the temperature of the ribbon rises. We have also studied these doped structures under the influence of point, edge and pair vacancies and observed a decreasing trend in thermal conductivity for each type of vacancy defect patterns introduced in the crystal. Such a study would promote the rising interest in properly characterizing the heat transport of low dimensional nanostructures and it can be an effective technique to tune the thermal conductivity of ZGaNNR for improving thermoelectric performance and thermal management in nanoscale devices.

Thermally Driven Field Emission from Zinc Oxide Wires on a Nanomembrane Used as a Detector for Time-of-Flight Mass Spectrometry.

Mass spectrometry is a crucial technology in numerous applications, but it places stringent requirements on the detector to achieve high resolution across a broad spectrum of ion masses. Low-dimensional nanostructures offer opportunities to tailor properties and achieve performance not reachable in bulk materials. Here, an array of sharp zinc oxide wires was directly grown on a 30 nm thin, free-standing silicon nitride nanomembrane to enhance its field emission (FE). The nanomembrane was subsequently used as a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry detector. When ionized biomolecules impinge on the backside of the surface-modified nanomembrane, the current-emitted from the wires on the membrane's front side-is amplified by the supplied thermal energy, which allows for the detection of the ions. An extensive simulation framework was developed based on a combination of lateral heat diffusion in the nanomembrane, heat diffusion along the wires, and FE, including Schottky barrier lowering, to investigate the impact of wire length and diameter on the FE. Our theoretical model suggests a significant improvement in the overall FE response of the nanomembrane by growing wires on top. Specifically, long thin wires are ideal to enhance the magnitude of the FE signal and to shorten its duration for the fastest response simultaneously, which could facilitate the future application of detectors in mass spectrometry with properties improved by low-dimensional nanostructures.

One-Pot Facile Synthesis of a Cluster of ZnS Low-Dimensional Nanoparticles for High-Performance Supercapacitor Electrodes.

To maximize the use of ZnS low-dimensional nanoparticles as high-performance supercapacitor electrodes, this work describes a simple one-pot synthesis method for producing a cluster of these particles. The ZnS nanoparticles fabricated in this work exhibit a cluster with unique low-dimensional (0D, 1D, and 2D) characteristics. Structural, morphological, and electrochemical investigations are all part of the thorough characterization of the produced materials. An X-ray diffraction pattern of clustered ZnS nanoparticles reflects the phase formation with highly stable cubic blende sphalerite polymorph. The confirmation of nanoparticle cluster formation featuring multiple low-dimensional nanostructures was achieved through field emission scanning electron microscopy (FE-SEM), while the internal structure was assessed using transmission electron microscopy (TEM). Systematically assessing the ZnS nanoparticles' electrochemical performance reveals their prospective qualities as supercapacitor electrode materials. The electrode assembled with this material on Ni foam demonstrates elevated specific capacitance (areal capacitance) values, reaching 716.8 F.g⁻1 (2150.4 mF.cm-2) at a current density of 3 mA.cm⁻2. Moreover, it reflects 69.1% capacitance retention with a four times increase in current density, i.e., 495.5 F.g-1 (1486.56 mF.cm-2) capacitance was archived at 12 mA.cm-2 with 100% Coulombic efficiency. Furthermore, the electrode exhibits prolonged cycling capability with 77.7% capacitance retention, as evidenced by its charge-discharge measurements sustained over 15,000 cycles at a current density of 25 mA cm⁻2.

Deciphering the Mechanism of On-Surface Dehydrogenative C-C Coupling Reactions.

On-surface synthesis has proven to be a powerful approach for fabricating various low-dimensional covalent nanostructures with atomic precision that could be challenging for conventional solution chemistry. Dehydrogenative Caryl-Caryl coupling is one of the most popular on-surface reactions, of which the mechanisms, however, have not been well understood due to the lack of microscopic insights into the intermediates that are fleetingly existing under harsh reaction conditions. Here, we bypass the most energy-demanding initiation step to generate and capture some of the intermediates at room temperature (RT) via the cyclodehydrobromination of 1-bromo-8-phenylnaphthalene on a Cu(111) surface. Bond-level scanning probe imaging and manipulation in combination with DFT calculations allow for the identification of chemisorbed radicals, cyclized intermediates, and dehydrogenated products. These intermediates correspond to three main reaction steps, namely, debromination, cyclization (radical addition), and H elimination. H elimination is the rate-determining step as evidenced by the predominant cyclized intermediates. Furthermore, we reveal a long-overlooked pathway of dehydrogenation, namely, atomic hydrogen-catalyzed H shift and elimination, based on the observation of intermediates for H shift and superhydrogenation and the proof of a self-amplifying effect of the reaction. This pathway is further corroborated by comprehensive theoretical analysis on the reaction thermodynamics and kinetics.

Single-Walled Cluster Nanotubes for Single-Atom Catalysts with Precise Structures.

Spatially confining isolated atomic sites in low-dimensional nanostructures is a promising strategy for preparing high-performance single-atom catalysts (SACs). Herein, fascinating polyoxometalate cluster-based single-walled nanotubes (POM-SWNTs) with atomically precise structures, uniform diameter, and single-cluster wall thickness are constructed by lacunary POM clusters (PW11 and P2W17 clusters). Isolated metal centers are accurately incorporated into the PW11-SWNTs and P2W17-SWNTs supports. The structures of the resulting MPW11-SWNTs and MP2W17-SWNTs are well established (M = Cu, Pt). Molecular dynamics simulations demonstrate the stability of POM-SWNTs. Furthermore, the turnover frequency of PtP2W17-SWNTs is 20 times higher than that of PtP2W17 cluster units and 140 times higher than that of Pt nanoparticles in the alcoholysis of dimethylphenylsilane. Theoretical studies indicate that incorporating a Pt atom into the P2W17 support induces straightforward electron transfer between them, combining the nanoconfined environment to enhance the catalytic activity of PtP2W17-SWNTs. This work shows the feasibility of using subnanometric POM clusters to assemble single-walled cluster nanotubes, highlighting their potential to prepare superior SACs with precise structures.

Highly Responsive Switchable Broadband DUV-NIR Photodetector and Tunable Emitter Enabled by Uniform and Vertically Grown III-V Nanowire on Silicon Substrate for Integrated Photonics.

Low-dimensional semiconductor nanostructures, particularly in the form of nanowire configurations with large surface-to-volume-ratio, offer intriguing optoelectronic properties for the advancement of integrated photonic technologies. Here, a bias-controlled, superior dual-functional broadband light detecting/emitting diode enabled by constructing the aluminum-gallium-nitride-based nanowire on the silicon-platform is reported. Strikingly, the diode exhibits a stable and high responsivity (R) of over 200mAW-1 covering an extremely wide operation band under reverse bias conditions, ranging from deep ultraviolet (DUV: 254nm) to near-infrared (NIR: 1000nm) spectrum region. While at zero bias, it still possesses superior DUV light selectivity with a high off-rejection ratio of 106. When it comes to the operation of the light-emitting mode under forward bias, it can achieve large spectral changes from UV to red simply by coating colloid quantum dots on the nanowires. Based on the multifunctional features of the diodes, this study further employs them in various optoelectronic systems, demonstrating outstanding applications in multicolor imaging, filterless color discrimination, and DUV/NIR visualization. Such highly responsive broadband photodetector with a tunable emitter enabled by III-V nanowire on silicon provides a new avenue toward the realization of integrated photonics and holds great promise for future applications in communication, sensing, imaging, and visualization.

Constructing Two-Dimensional Distorted Kagome Lattices on Ag(111).

Two-dimensional (2D) tessellation of organic species acquired increased interest recently because of their potential applications in physics, biology, and chemistry. Herein, we successfully synthesized the chiral distorted Kagome lattice p3 (333) with bicomponent precursors on Ag(111). Scanning tunneling microscopy and density functional calculation studies reveal that the networks are formed by multiple intermolecular hydrogen bonds. The network structures can be rationally tuned by adjusting the stoichiometric ratio of the reaction precursors. Our study provides new strategies to synthesize complex low-dimensional nanostructures on metal surfaces.

Synthesis of a Porous [14]Annulene Graphene Nanoribbon and a Porous [30]Annulene Graphene Nanosheet on Metal Surfaces.

The electrical and mechanical properties of graphene-based materials can be tuned by the introduction of nanopores, which are sensitively related to the size, morphology, density, and location of nanopores. The synthesis of low-dimensional graphene nanostructures containing well-defined nonplanar nanopores has been challenging due to the intrinsic steric hindrance. Herein, we report the selective synthesis of one-dimensional (1D) graphene nanoribbons (GNRs) containing periodic nonplanar [14]annulene pores on Ag(111) and two-dimensional (2D) porous graphene nanosheet containing periodic nonplanar [30]annulene pores on Au(111), starting from a same precursor. The formation of distinct products on the two substrates originates from the different thermodynamics and kinetics of coupling reactions. The reaction mechanisms were confirmed by a series of control experiments, and the appropriate thermodynamic and kinetic parameters for optimizing the reaction pathways were proposed. In addition, the combined scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations revealed the electronic structures of porous graphene structures, demonstrating the impact of nonplanar pores on the π-conjugation of molecules.