Nanoscale Width Research Articles

Observing Weak Interchain Coupling in 1D vdWs Ternary Mo6Se2I8 to Achieve Probe Exfoliation of Ultrathin Molecular Chains

Abstractvan der Waals (vdWs) interchain coupling is a unique feature of 1D vdWs materials, where strong vdWs coupling in 1D vdWs materials leads to the thickness‐dependent physical properties, while weak vdWs coupling can preserve the single‐chain property even in their thick counterparts. Different from 2D vdWs materials, due to their nanoscale widths, identifying and producing ultrathin 1D molecular chains are challenging, severely limit their device applications. Thus, looking for novel 1D vdWs materials with weak interchain coupling is crucial. In this paper, the authors report that the 1D ternary vdWs material, Mo6Se2I8 with non‐centrosymmetric characteristic and strong optical anisotropy, exhibits weak interchain coupling. On one hand, the density functional theory (DFT) calculations theoretically demonstrate its thickness‐independent electronic structure, negligible interchain differential charge density, and weak cleavage energy as low as 0.256 J m−2. On the other hand, the thickness‐independent work function and low first‐order temperature coefficient of −0.0030 cm−1 K−1 further experimentally confirm its weak interchain coupling. Moreover, taking advantage of this weak vdWs coupling characteristic, the in situ exfoliation of the Mo6Se2I8 nanowires is achieved by using a nanoprobe in a scanning electron microscope (SEM), obtaining ultrathin molecular chains with a thickness of ≈1.2 nm.

The Nanoscale Wetting Parameter and Its Role in Interfacial Phenomena: Phase Transitions in Nanopores.

Through analysis of the statistical mechanical equations for a thin adsorbed film (gas, liquid, or solid) on a solid substrate or confined within a pore, it is possible to express the equilibrium thermodynamic properties of the film as a function of just two dimensionless parameters: a nanoscale wetting parameter, αw, and pore width, H*. The wetting parameter, αw, is defined in terms of molecular parameters for the adsorbed film and substrate and so is applicable at the nanoscale and for films of any phase. The main assumptions in the treatment are that (a) the substrate structure is not significantly affected by the adsorbed layer and (b) the diameter of the adsorbate molecules is not very small compared to the spacing of atoms in the solid substrate. We show that different surface geometries of the substrate (e.g., slit, cylindrical, and spherical pores) and various models of wall heterogeneity can be accounted for through a well-defined correction to the wetting parameter; no new dimensionless variables are introduced. Experimental measurements are reported for contact angles for various liquids on several planar substrates and are shown to be closely correlated with the nanoscale wetting parameter. We apply this approach to phase separation in nanopores of various geometries. Molecular simulation results for the phase diagram in confinement, obtained by the flat histogram Monte Carlo method, are reported and are shown to be closely similar to experimental results for capillary condensation, melting, and the triple point. The value of the wetting parameter, αw, is shown to determine the qualitative behavior (e.g., increase vs decrease in the melting temperature, capillary condensation vs evaporation), whereas the pore width determines the magnitude of the confinement effect. The triple point temperature and pressure for the confined phase are always lower than those for the bulk phase for all cases studied.

Microstructure Evolution of the Ti-46Al-8Nb-2.5V Alloy during Hot Compression and Subsequent Annealing at 900 °C.

TiAl alloys are high-temperature structural materials with excellent comprehensive properties, and their ideal service temperature range is about 700-950 °C. High-Nb containing the Ti-46Al-8Nb-2.5V alloy was subjected to hot compression and subsequent annealing at 900 °C. During hot compression, work-hardening and strain-softening occurred. The peak stresses during compression are positively correlated with the compressive strain rates and negatively correlated with the compression temperatures. The α2 phase exhibited a typical (0001)α2 basal plane texture after hot compression, while the β0 and γ phases did not show a typical strong texture. Subsequent annealing at 900 °C of the hot-compressed samples resulted in significant phase transformations, specifically the α2 → γ and β0 → γ phase transformations. After 30 min of annealing, the volume fraction of the α2 phase decreased from 39.0% to 4.6%. The microstructure characteristics and phase fraction after 60 min of annealing were similar to those after 30 min. According to the calculation of Miller indexes and texture evolution during annealing, the α2 → γ phase transformation did not follow the Blackburn orientation relationship. Multiple crystal-oriented α2 phases with nanoscale widths (20~100 nm) precipitate within the γ phase during the annealing process, which means the occurrence of γ → α2 phase transformation. Still, the γ → α2 phase transformation follows the Blackburn orientation relationship.

Development of Dewatering Concentration Method for Cellulose-Nanofibers Slurry by Using Multi Wires

Cellulose nanofibers (CNFs) which are extremely small fibers with a width of several nm comprising mainly crystalline cellulose. They are a promising material with many superior characteristics in a wide range of industrial fields, and have been developed by domestic and foreign paper mill companies. CNF slurry with a high water content (> 98%) is usually supplied because CNFs are generally produced through pulp nanofibrillation in a relatively large volume water. Dewatering of CNF slurry is an important issue because this process affects various processes such as shipping, drying, and product developments. To dehydrate and concentrate CNF with a high-water retention efficiently, the original dewatering CNF method with multiple wires was used in this study. First, the CNFs obtained by mechanical nanofibrillation were prepared using a grinder from Laubholz bleached kraft pulp (LBKP). The fibers with a nano-scale width and a micro-scale fiber network were observed in the prepared CNF slurry. Furthermore, flocculation and dispersion in CNF slurry occurred. Second, the initial solid concentration of CNF slurry, wire opening, and number of wire stacks affected the CNF dewatering in the static and batch tests. In this test, a recovery yield (retention) of 87.7% and concentration to 9.5% were achieved using three stacked wires from CNF slurry of 1.7%. Third, the laboratory-scale apparatus for dynamic CNF dewatering was constructed assuming the practical continuous manufacturing machine, and applied. The gradual suction; combining weaker suction (5 kPa) with multiple wires in the early stage and stronger suction with a single wire in the later stage, was the most effective for dewatering CNF using metal wires. However, multiple wires and the combination of weaker suction in the early stage and stronger suction in the later stage were suitable for dewatering CNF using plastic wires. Ultimately, 98% retention a solid concentration of 9.9% were achieved in the dynamic tests using multiple plastic wires.

Friction dependence on the textured structure of an amorphous carbon surface: A reactive molecular dynamics study

Amorphous carbon (a-C) film provides ultralow friction when combined with lubricating oil. However, it is unclear how textured surfaces affect the friction behavior of a-C at atomic scale, specifically the transformation of interfacial structure and the flow of lubricating oil, owing to the limitations of experimental characterization. Here, a-C films with different textured surfaces were fabricated, and the friction behaviors of mating a-C surfaces with textured parameters, including nanoscale depth and width, were examined by reactive molecular dynamics simulation. Results indicate that compared to that under dry condition, the introduction of a textured surface reduces the friction coefficient of a-C under oil lubrication condition. However, its efficiency highly depends on the depth and width of textured surface, exhibiting different effects on hydrodynamic lubrication. The increase in textured depth causes the friction coefficient decreased first and then increased, attributing to the lubrication from hydrodynamic to boundary state as primary mechanism. The regional aggregation of lubricant atoms with a textured width on the a-C surface occurs at the friction interface following the increased friction coefficient. These results provide insights into the underlying friction mechanism of a-C films induced by surface texturing and enable the development of highly efficient lubrication systems for applications.

Additive effect of micro-damage zones from nano-scale crack tip and nano-grains for fracture toughness measurements of 3Y-TZP zirconia ceramics

A nano-scale crack tip around 500 nm wide introduced by femtosecond laser still affects the accuracy of fracture toughness KIC measurements of 3Y-TZP zirconia ceramics with average grain size G from 200 to 500 nm. A simple formula was proposed to estimate the additive effect of crack-tip damage zones from an infinitely sharp crack to a nano-scale blunt notch. The error in fracture toughness measurements is less than 8 % if the nano-scale crack-tip width < 0.5·G. The intrinsic KIC can be deduced from the simple formula if the nano-scale crack tip > 0.5·G. This study shows the same KIC was deduced from two different sets of 3Y-TZP measurements with nano- and micro-scale notches of 500 nm and 18 µm wide. Furthermore, the simple formula specifies the relation between the fracture toughness KIC and intrinsic strength ft via grain size G, which means KIC can also be estimated from ft and G without testing pre-cracked specimens. KIC values of 3Y-TZP from specimens with and without pre-cracks were compared.

Visualizing Line Defects in non-van der Waals Bi2O2Se Using Raman Spectroscopy.

Atomic-layered materials, such as high-quality bismuth oxychalcogenides, which are composed of oppositely charged alternate layers grown using chemical vapor deposition, have attracted considerable attention. Their physical properties are well-suited for high-speed, low-power-consumption optoelectronic devices, and the rapid determination of their crystallographic characteristics is crucial for scalability and integration. In this study, we introduce how the crystallographic structure and quality of such materials can be projected through Raman spectroscopy analysis. Frequency modes at ∼55, ∼78, ∼360, and ∼434 cm-1 were detected, bearing out theoretical calculations from the literature. The low-frequency modes positioned at 55 and 78 cm-1 were activated by structural defects, such as grain boundaries and O-rich edges in the Bi2O2Se crystals, accompanied by sensitivity to the excitation energy. Furthermore, the line defects at ∼55 cm-1 exhibited a strong 2-fold polarization dependence, similar to graphene/graphite edges. Our results can help illuminate the mechanism for activating the Raman-active mode from the infrared active mode by defects, as well as the electronic structures of these two-dimensional layered materials. We also suggest that the nanoscale width line defects in Bi2O2Se can be visualized using Raman spectroscopy.

Improved water solubility, chemical stability, antioxidant and anticancer activity of resveratrol via nanoencapsulation with pea protein nanofibrils

Fabricated pea protein isolate (PPI) nanofibrils were used as nanocarriers to encapsulate, stabilize and deliver resveratrol (RES). PPI nanofibrils possessed a dramatically higher surface hydrophobicity than PPI (native), and PPI nanofibrils exhibited nanoscale widths of 10 nm and average lengths of 1.0 μm. Fluorescence analyses demonstrated PPI nanofibrils had high binding constant with RES. Compared with RES (free), the aqueous solubility of RES was improved by approximately 1000-fold with PPI nanofibrils complex. DPPH and ABTS radical scavenging activity assays showed that the antioxidant capacity of RES was pronouncedly enhanced through the nanocomplexation with PPI nanofibrils. RES-PPI nanofibrils complexes exhibited higher antiproliferative activities than RES (free), with the cell viabilities of 52.6% and 38.5% for RES (free) and RES-PPI nanofibrils complex at 20 μg/mL. This study demonstrates that PPI nanofibrils can be utilized as novel nanocarriers for improvements of the water solubility, chemical stability and in vitro biological activities of hydrophobic nutraceuticals.

Evolution of Graphene Patterning: From Dimension Regulation to Molecular Engineering.

The realization that nanostructured graphene featuring nanoscale width can confine electrons to open its bandgap has aroused scientists' attention to the regulation of graphene structures, where the concept of graphene patterns emerged. Exploring various effective methods for creating graphene patterns has led to the birth of a new field termed graphene patterning, which has evolved into the most vigorous and intriguing branch of graphene research during the past decade. The efforts in this field have resulted in the development of numerous strategies to structure graphene, affording a variety of graphene patterns with tailored shapes and sizes. The established patterning approaches combined with graphene chemistry yields a novel chemical patterning route via molecular engineering, which opens up a new era in graphene research. In this review, the currently developed graphene patterning strategies is systematically outlined, with emphasis on the chemical patterning. In addition to introducing the basic concepts and the important progress of traditional methods, which are generally categorized into top-down, bottom-up technologies, an exhaustive review of established protocols for emerging chemical patterning is presented. At the end, an outlook for future development and challenges is proposed.

Ultralong phase-correlated networks of plasmonic nanoantennas coherently driven by photonic modes

We study coherently-stimulated plasmonic dipoles and their phase-correlated coupling, offering ultralong coherent networks of metallic nanoantennas. This is done by considering Au nanoislands with random sizes and shapes placed in close vicinity of each other in a strip with long length and nanoscale width. The positions of the nanoislands in such a strip fluctuate, forming a one-dimensional disordered array. We demonstrate that once such a structure is periodically repeated such that the Rayleigh anomaly condition is satisfied, the photonic lattice modes can drive the plasmon modes of the nanoislands at frequencies dictated by such modes. This allows the nanoislands to act as nano-scale antennas that are excited in phase and are coupled to the neighboring nanoantennas coherently over distances far larger than the sizes of the individual nanoislands. Under these conditions the disordered array acts as a network wherein coherent specifications are distributed in scales far longer than those of the individual nanoislands.

Nanoscale profiling of multilayer graphene films on silicon carbide by a focused ion beam

The controlled and reproducible formation of a nanoscale interelectrode gap is crucial for the development of next-generation nanoelectronics devices, such as nano-electromechanical systems or field emission structures. This paper reports an etching of multilayer graphene (MLG) film on silicon carbide using focused ion beam (Ga+). The main task is to obtain nanoscale width trenches for the formation of isolated planar nanostructures based on MLG. MLG were obtained by thermal decomposition of silicon carbide in vacuum. We used 6H-SiC as a substrate. The analysis of the Raman spectrum showed the presence of about 10 layers of graphene in the film. The influence of the focused ion beam (FIB) parameters on the distribution of the Ga+ ions concentration in the SiC substrate was estimated by the Monte Carlo method. We revealed the maximum concentration of Ga+ ions in the SiC substrate is at a depth of 19 nm at the ion energy of 30 keV and the incidence angle of the ion beam on the substrate relative to the normal 0°. The results of local nanoscale etching of MLG on SiC by using FIB are presented. The AFM-studies confirm the dependence of the geometric dimensions of the etching area on the FIB etching parameters. The resolving power of the method is determined on the basis of a number of detectable nanoscale trenches at various currents of the FIB.

Negative differential resistance effect in different structures of armchair graphene nanoribbon

Graphene is a one-atom-thick stable covalently bonded carbon layer ordered in a honeycomb lattice. Single layer graphene of nanoscale width (including a few numbers of atoms across the width) is known as Graphene Nanoribbon, GNR. Armchair chirality of GNR provides appropriate value of band gap (in the range of that of common semiconductors), whereas its bandgap is tunable by only changing the width of ribbon. These two properties in addition to availability in two-dimension and very high carrier mobility made GNR a unique semiconductor substance in recent years. Therefore, in the past few years it has gained lots of attention for its interesting properties and applications such as: sensors, filters, detectors and switches. On the other hand, passivation of edges of GNR plays a fantastic role in its electrical behavior, where by implementing some special configuration for passivation Negative-Differential-Resistance (NDR) can be created. Graphene-based NDR behavior creates a great potential for providing some new devices in electronics. This work is focused on armchair graphene nanoribbons (AGNR) for its semiconducting behavior, where the edges of ribbon have significant effects on the current-voltage characteristic of the device. We report a theoretical investigation and numerical simulation of the effect of passivating the edges on the carrier transport in AGNRs. The number of carbon atoms across the ribbon width is an important parameter that we selected ten atoms to have a suitable size for simulation and appropriate band gap energy as a semiconductor material. Calculations are done based on density functional theory (DFT) and using Green's function of atomic structure of the device. Four types of edge terminations as: H-edged-AGNR, O-edged-AGNR, homo H-O-edged-AGNR and hetero H-O-edged-AGNR terminations are investigated in detail. It is shown that the edge termination of graphene nanoribbons by a special arrangement of both hydrogen and oxygen atoms causes NDR behavior which can have interesting applications in nanoelectronics and nanosensors. In addition, the oxygen atoms edge termination demonstrates NDR behavior, while such a behavior is not observed by only hydrogen atoms edge termination.

Towards the ultrafast optical nanopore platform for single molecule sensing

Abstract Recently there have been significant interests about fabrication of optical nanopore with its diameter range of 5 nm–10 nm for single molecule analysis and manipulation. However, due to very small amount of the optical intensity through the tiny size of the nano-aperture much smaller than the optical wavelength, the optical intensity enhancement via plasmonic effect by using pore array or periodic groove patterns have been tried. Also, the double slits with nanoscale width are reported to provide the constructive periodic modulation for the transverse-magnetic (TM) wave mode. In this report, the Au aperture arrays sidelined with the nanoscale double slit, and surrounded by 4 nanoscale slits have been fabricated with optical characterization in the visible range.

Fabrication of Plasmonic Optical Nanopore Platform for Single Molecule Sensing

Recently there have been significant interests about fabrication of optical nanopore with its diameter range of 5 nm to 10 nm for single molecule analysis and manipulation. However, due to very small amount of the optical intensity through the tiny size of the nano-aperture much smaller than the optical wavelength, the optical intensity enhancement via plasmonic effect by using pore array or periodic groove patterns have been tried. Also, the double slits with nanoscale width are reported to provide the constructive periodic modulation for the transverse-magnetic (TM) wave mode. In this report, the nanoscale double slit with an Au aperture array have been fabricated and optically characterized.

The effect of discontinuous γ' precipitation on the mechanical properties of Al-Co-Ni alloys

Discontinuous precipitation (DP) produces precipitate plates that have a distinct orientation relationship with the matrix and nanoscale widths and spacings. For structural alloys a DP structure limited to the grain boundary regions is undesirable since it degrades the mechanical properties due to the inhomogeneity of the microstructure. In Al-Co-Ni alloys, the DP transformation can go to completion and the mechanical properties of such structures have been studied in this work. The hardness, tensile and creep properties of alloy samples with DP structure were investigated. The results imply that the occurrence and complete transformation of DP will have a favorable effect on the hardness and tensile strength of the sample while lowering the ductility. A method to generate serrated grain boundaries based on the DP transformation is demonstrated. Such structures are found to increase the creep resistance in a limited temperature and loading range.

Gate-tuned conductance of graphene-ribbon junctions with nanoscale width variations.

To utilize graphene as interconnection electrodes in high-density nanoelectronic structures, the electrical stability of graphene should be guaranteed under nanometer-scale deviations. Graphene-ribbon (GR) junctions with accessible dimensions (i.e., sub-micrometer widths) are used in diverse interconnection electrode applications and should be characterized properly if they are to be applied in high-density nanoelectronics. Analyzing the effects of nanoscale GR width variations on the conductance of the entire graphene electrode is necessary for their proper characterization. Here, we diagnose the conductance and thermal effect of graphene electrode junctions constructed from GRs of various widths and directions under gate-tuned voltages. On applying partial gate voltages, we identify the effect of local potential variance on the entire graphene electrode junction. As a result, we were able to perceive precise and minute conductance variations for the entire graphene electrode, arising mainly from different sub-micrometer-scale widths of the GRs, which could not be distinguished using conventional global gating methods.

Characterization of a Nanocrystalline Structure Formed by Crystal Lattice Transformation in a Bulk Steel Material

The formation of nanocrystalline structures in bulk metal materials is of great significance for both investigating the structural features of nanocrystalline materials and enhancing the value of bulk metal materials in engineering applications. Herein, we report a nanocrystalline structure formed by lattice transformation in a three-dimensional bulk metal material. We characterized its phase composition, three-dimensional features, and boundary structure. This nanocrystalline structure had microscale length and height and nanoscale width, which gave it a “nanoplate” structure in three-dimensional space. We observed edge dislocations in the interior of the nanocrystalline structure. A unique transitional boundary that contributed to maintaining its nanoscale size was found at the border between the parent phase and the nanocrystalline structure.

Quantum plasmonic hot-electron injection in lateral WSe2/MoSe2 heterostructures

Lateral two-dimensional (2D) transitional metal dichalcogenide (TMD) heterostructures have recently attracted a wide attention as promising materials for optoelectronic nanodevices. Due to the nanoscale width of lateral heterojunctions, the study of their optical properties is challenging and requires using subwavelength optical characterization techniques. We investigated the photoresponse of a lateral 2D WSe2/MoSe2 heterostructure using tip-enhanced photoluminescence (TEPL) with nanoscale spatial resolution and with picoscale tip-sample distance dependence. We demonstrate the observation of quantum plasmonic effects in 2D heterostructures on a non-metallic substrate, and we report the nano-optical measurements of the lateral 2D TMD heterojunction width of ~ 150 nm and the charge tunneling distance of ~ 20 pm. Controlling the plasmonic tip location allows for both nano-optical imaging and plasmon-induced hot electron injection into the heterostructure. By adjusting the tip-sample distance, we demonstrated the controllability of the hot-electron injection via the competition of two quantum plasmonic photoluminescence (PL) enhancement and quenching mechanisms. The directional charge transport in the depletion region leads to the increased hot electron injection, enhancing the MoSe2 PL signal. The properties of the directional hot-electron injection in the quantum plasmonic regime make the lateral 2D MoSe2/WSe2 heterostructures promising for quantum nanodevices with tunable photoresponse.

Epitaxial Lateral Overgrowth of InP on Nanopatterned GaAs Substrates by Metal–Organic Chemical Vapor Deposition

Epitaxial lateral overgrowth (ELO) of 1.8-μm InP films was performed on nanopatterned GaAs (001) substrates via metal–organic chemical vapor deposition. Parallel SiO2 trenches with a nano-scale width (∼ 170 nm) and various seed line orientations of [110], [410], [010] and [4–10] were first adopted to optimize the growth in our work. Scanning electron microscopy, atomic force microscopy and double-crystal x-ray diffraction were used to characterize the as-grown InP/GaAs heterostructures. The results reveal that the surface morphology and crystalline quality are strongly affected by the seed line orientations, and both of these parameters are optimized under the orientation of the [4–10] direction. A low average full width at half maximum of 285.1 arcsec and a root mean square surface roughness of 2.95 nm are obtained for the 1.8-μm InP film. To clearly observe the initial coalescence stage during the growth processes, thinner (500 nm) ELO InP films were also grown. We found that the seed line orientation has a significant effect on the lateral growth rate and affects the quality of the final InP/GaAs epilayer.

Broadband Ultra-Deep Sub-Diffraction-Limit Optical Focusing by Metallic Graded-Index (MGRIN) Lenses.

The development of techniques for efficiently confining energy in the visible and infrared spectral regions to the deep subwavelength spatial scale with dimensions as small as a few nanometers would have great significance for scientific research and engineering practices. Such an ability to manipulate light is impossible for conventional dielectric lenses due to the diffraction limit. Here, we propose a metallic graded-index (MGRIN) lens formed by an array of coupled metallic waveguides with identical nanoscale widths embedded by index-varying dielectrics to enable the optical nanofocusing. The focusing mechanism of the MGRIN lens is theoretically investigated based on Hamiltonian optics, which are verified by the finite-difference time-domain (FDTD) method. Numerical results reveal that an ultra-deep subwavelength focus of 8 nm (λ/500) with a long focal depth (1.93λ) and enhanced field intensity can be achieved. Moreover, the nanofocusing capability of the MGRIN lens without redesigning the structure can be well kept when the incident wavelength changes over a broad range from visible to infrared. Our design of optical nanofocusing shows great potential for use in nano-optics and nanotechnology.