Nanoscale Modulation Research Articles

Entropy stabilized form chirality in curved rod nematics: structure and symmetries.

Monte Carlo molecular simulations of curve-shaped rods show the propensity of such shapes to polymorphism revealing both smectic and polar nematic phases. The nematic exhibits a nanoscale modulated local structure characterized by a unique, polar, C2-symmetry axis that tightly spirals generating a mirror-symmetry-breaking organization of the achiral rods-form chirality. A comprehensive characterization of the polarity and its symmetries in the nematic phase confirms that the nanoscale modulation is distinct from the elastic deformations of a uniaxial nematic director in the twist-bend nematic phase. Instead it is shown that, analogous to the isotropic-to-nematic transition, entropy stabilizes the roto-translating polar director in the polar-twisted nematic phase. The conflation of macroscale form chirality in ferroelectric nematics with that in the twist-bend nematic stems from the misattribution of the nanoscale modulation in the lower temperature nematic "NX phase" found in CB7CB dimers.

Dynamical control of nanoscale electron density in atomically thin n-type semiconductors via nano-electric pulse generator.

Controlling electron density in two-dimensional semiconductors is crucial for both comprehensive understanding of fundamental material properties and their technological applications. However, conventional electrostatic doping methods exhibit limitations, particularly in addressing electric field-induced drift and subsequent diffusion of electrons, which restrict nanoscale doping. Here, we present a tip-induced nanospectroscopic electric pulse modulator to dynamically control nanoscale electron density, thereby facilitating precise measurement of nano-optoelectronic behaviors within a MoS2 monolayer. The tip-induced electric pulse enables nanoscale modulation of electron distribution as a function of electric pulse width. We simultaneously investigate spatially altering photoluminescence quantum yield at the nanoscale region. We model the extent of electron depletion region, confirming a minimum doping region with a radius of ∼265 nanometers for a 30-nanosecond pulse width. Our approach paves the way for engineering local electron density and in situ nano-optical characterization in two-dimensional materials, enabling an in-depth understanding of doping-dependent nano-optoelectronic phenomena.

Micro- and nano-scale spindle perpendicularity modulation method to enhance the quality of milled surfaces

Micro- and nano-scale spindle perpendicularity modulation method to enhance the quality of milled surfaces

Dynamic control of the directional scattering of single Mie particle by laser induced metal insulator transitions.

Interference between the electric and magnetic dipole-induced in Mie nanostructures has been widely demonstrated to tailor the scattering field, which was commonly used in optical nano-antennas, filters, and routers. The dynamic control of scattering fields based on dielectric nanostructures is interesting for fundamental research and important for practical applications. Here, it is shown theoretically that the amplitude of the electric and magnetic dipoles induced in a vanadium dioxide nanosphere can be manipulated by using laser-induced metal-insulator transitions, and it is experimentally demonstrated that the directional scattering can be controlled by simply varying the irradiances of the excitation laser. As a straightforward application, we demonstrate a high-performance optical modulator in the visible band with high modulation depth, fast modulation speed, and high reproducibility arising from a backscattering setup with the quasi-first Kerker condition. Our method indicates the potential applications in developing nanoscale optical antennas and optical modulation devices.

Mechanical and Tribological Properties of CrWN/MoN Nano-Multilayer Coatings Deposited by Cathodic Arc Ion Plating

CrWN/MoN nano-multilayer coatings were deposited in pure N2 by multi-arc ion plating using CrW and Mo targets, with the cathode co-controlled by a permanent magnet combined with an electromagnet. The effects of the thickness modulation period on the microstructure and mechanical and tribological performance were systematically analyzed by grazing-incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM), Nanoindentation, scanning electron microscope (SEM) and profilometry using a Talysurf profilometer. The local coherent interfaces and nanoscale modulation period were confirmed by TEM, while the coatings were confirmed to be composed of fcc-CrWN and hexagonal δ-MoN by GIXRD. With the increase in the modulation period, the hardness of the CrWN/MoN nano-multilayer coatings decreased, and the values of the H/E ratio and friction coefficient showed the same variation trend. At an 8.0 nm modulation period, the CrWN/MoN nano-multilayer coating showed the maximum hardness (30.2 GPa), the lowest H/E value (0.082) and an H3/E*2 value of 0.16. With the decrease in the modulation period, the average friction coefficient of the CrWN/MoN nano-multilayer coatings gradually decreased from 0.45 to 0.29, while the wear rate decreased from 4.2 × 10−7 mm3/Nm to 3.3 × 10−7 mm3/Nm.

Accelerating redox kinetics of sulfurized polyacrylonitrile nanosheets by trace doping of element

“Solid-solid” conversion mechanism of sulfurized polyacrylonitrile (SPAN) could eliminate the “shuttle effect” of polysulfides intermediate in LiS batteries, but it leads to poor redox reaction kinetics. Herein, traces of high conductivity elements Se and Te are doped in two-dimensional SPAN nanosheets (NS) by co-heating method. This synergistic effect enhances the conductivity of SPAN while affording a larger contact area with the electrolyte and shortening the electron/ion transport path. As a result, both the energy barrier for redox reaction and polarization for battery are decreased. At a high current density of 3 A g−1, Te0.052S0.948PAN NS and Se0.071S0.929PAN NS exhibit significantly enhanced discharge capacities of 485 mA h g−1composite and 457 mA h g−1composite, respectively, while SPAN nanoparticles (NP) only delivers a capacity of 417 mA h g−1composite. At 0.2 A g−1 current density, the capacity retention rates of Te0.052S0.948PAN NS and Se0.071S0.929PAN NS are 92.20 % and 56.10 % after 200 cycles, respectively, both higher than the 40.10 % of SPAN NP. When the loading amount is further increased, Te0.052S0.948PAN NS and Se0.071S0.929PAN NS still maintain excellent electrochemical performance. In-situ Raman and XPS analysis confirms the reversible breaking and formation of CS/SS bonds during the first cycle. Additionally, XPS and SEM analysis after 100 cycles demonstrate the stable nanostructure and molecular structure of Se0.071S0.929PAN NS and Te0.052S0.948PAN NS throughout the cycling process. These results herald a new approach to high redox kinetics of SPAN by the synergistic effect of elements doping and nanoscale modulation.

The nanoscale modulation of interlayer space in two-dimensional nanoclay membranes for osmotic energy conversion

The harvest of osmotic energy based on two-dimensional (2D) nanochannel membranes has been attracting wide attentions for addressing the energy issues. Here, we report the nanoscale modulation of interlayer space in 2D nanochannel membranes based on montmorillonite (MMT) for osmotic energy conversion. Cationic surfactants with different alkyl chain lengths are intercalated between MMT nanosheets to regulate the interlayer spacing of 1.74 and 2.49 nm, thus achieving the modulation of ion flux through the nanoclay membranes. A high power density of ∼4.13 W/m2 can be attained in 300-fold concentration gradient. The mechanism of the influence of nanochannel sizes on osmotic energy conversion performance is investigated by experiments and theoretical simulations. Realizing the nanoscale modulation of interlayer space in 2D nanochannels provides new insights for designing nanofluidic membranes toward clean energy harvesting.

High temperature decomposition and age hardening of single-phase wurtzite Ti1−xAlxN thin films grown by cathodic arc deposition

Wurtzite TmAlN (Tm=transition metal) themselves are of interest as semiconductors with tunable band gap, insulating motifs to superconductors, and piezoelectric crystals. Characterization of wurtzite TmAlN is challenging because of the difficulty to synthesize them as single-phase solid solution and such thermodynamic, elastic properties, and high temperature behavior of wurtzite Ti1−xAlxN is unknown. Here, we investigated the high temperature decomposition behavior of wurtzite Ti1−xAlxN films using experimental methods combined with first-principles calculations. We have developed a method to grow single-phase metastable wurtzite Ti1−xAlxN (x=0.65, 0.75, 085, and 0.95) solid-solution films by cathodic arc deposition using low duty-cycle pulsed substrate-bias voltage. We report the full elasticity tensor for wurtzite Ti1−xAlxN as a function of Al content and predict a phase diagram including a miscibility gap and spinodals for both cubic and wurtzite Ti1−xAlxN. Complementary high-resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950∘C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semicoherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1–2 GPa. Published by the American Physical Society 2024

Plasmonic signal modulation at sub-GHz frequency via on-chip integration of tunnel junctions.

Plasmonic technology offers one of the most promising solutions to achieve on-chip integration of nanoscale and fast modulation circuits using surface plasmon polaritons (SPPs) as the information carriers. However, the potential of modulation speed of plasmonic signals has not been fully tapped. In this paper, we have demonstrated the plasmonic signal can be modulated at the bandwidth of sub-GHz (>100 MHz) via the on-chip integration of tunnel junctions. We also find that the lifetime of tunnel junctions under AC conditions can be improved significantly compared with the DC counterparts, which allows us to investigate and visualize the real-time breakdown process of tunnel junctions. Our implementation of plasmonic signal modulation at sub-GHz frequency paves the way toward potential industrial applications of on-chip plasmonic circuits.

Effect of nanoheterogeneities on the fracture toughness and tensile ductility of CuTa metallic glass thin films

Nanoheterogenenous metallic glasses (MG) can offer improved ductility through a nanoscale modulation in their mechanical properties. However, the relationship between the modulation parameters and the mechanical behavior is not well understood. Physical vapor deposition can directly control the compositional and morphological parameters of nanoheterogeneous MGs and enables the systematic investigation of this problem. This work explores the microstructure and mechanical properties of a range of CuTa-based nanolayered amorphous/amorphous (A/A) and amorphous/semi-crystalline (A/SC) nanoheterogeneous MGs and MG composites. The first step was the identification of three microstructural regimes in CuTa, namely, a fully amorphous form (23–65 at.% Ta), a Ta-rich amorphous-crystalline composite (65–75 at.% Ta), and a Cu-rich amorphous-crystalline composite (16–23 at.% Ta). The hardness of the films increased from 6 GPa to 17 GPa with increasing Ta content. Next, a range of CuxTa1−x/CuyTa1−y nanolayers composed of A/A and A/SC nanolayers were investigated. The hardness of all nanolayers follows the rule of mixture. A/A structures do not provide a significant increase in fracture toughness and only a minor increase in tensile ductility despite the high amplitude modulation of hardness between layers. A/SC nanolayers’ hardness and toughness was higher than A/A nanolayers as well as monolithic amorphous films, but still remained below the monolithic Cu25Ta75 SC film. The results show that the design of nanoheterogeneities in MGs requires careful optimization to achieve a useful improvement in mechanical properties.

Nano-assembled modified graphene composites based on rapid microwave fabrication for thermal management

Carbon materials are commonly considered as the main wave-absorbing material for radar stealth in conventional stealth materials. In fact, nanoscale modulation can adequately exploit their superior properties to develop their potential as infrared stealth. In this paper, an ingenious strategy is proposed for rapidly preparing carbon-based materials through simple microwave radiation. Graphene oxide is modified by a “defect/ion matching” mechanism to accomplish the structural construction of the carbon chessboard/silver chess pieces (CCB-SCP). Additionally, inexpensive chitosan has been introduced via topological bonding without using binders. Due to the delicate structural design, CCB-SCP/Chitosan has low density (0.064 g cm−3), ultra-low thermal conductivity (0.018 W m−1 K−1), and significant thermal shielding temperature difference (ΔT ∼ 50℃). The cost-effective composite material can be applied to thermal management in medium–high temperature sections (∼200℃). At a heating platform of 190 °C, CCB-SCP/Chitosan can provide a temperature drop of up to 46℃. In addition, CCB-SCP/Chitosan exhibits good electrical conductivity, thermal insulation stability, and relatively low infrared emissivity. An innovative approach to the delicate design of carbon-based materials utilizing microwaves, including carbon layers encapsulation, three-dimensional structures, and five-fold twinned particles, is proposed, which opens a new avenue for nanostructure-based thermal camouflage applications in the medium to high temperature region.

A sequential template electrodeposition anodization and in situ aniline electropolymerization-based facile electrochemical synthesis strategy

Herein, we propose a facile continuous electrochemical synthesis strategy to build 3D hierarchical hybrid conductive networks based on sequential template electrodeposition-anodization and in-situ aniline electropolymerization. It was implemented in a tin system to prepare a 3D tin skeleton with micron-scale features using the hydrogen bubble dynamic template method, followed by electrochemical anodization to achieve nanoscale modulation. This well-designed 3D hierarchical metal oxide framework was used for the in-situ electropolymerization of aniline, preserving the hierarchical morphological features while establishing large conductive networks for ultrafast electron transport and enhancing the structural stability of tin dendrites. Regulation of the hierarchical morphologies promotes material surface reactivity, increases the electrochemically active sites, and improves the ion diffusion kinetics, thus solving the “dead surface” problem in the energy storage process. Such multifaceted synergistic strategies of structural modulation and functional hybridization have opened up new ways to design efficient binder-free hybrid electrode materials.

Flexo-Pyrophotronic Effect Modulated Giant Near Infrared Photoresponse from VO2 -Based Heterojunction for Optical Communication.

The flexoelectric phenomenon, which occurs when materials undergo mechanical deformation and cause strain gradients and a related spontaneous electric polarization field, can result in wide variety of energy- and cost-saving mechano-opto-electronics, such as night vision, communication, and security. However, accurate sensing of weak intensities under self-powered conditions with stable photocurrent and rapid temporal response remains essential despite the challenges related to having suitable band alignment and high junction quality. Taking use of the flexoelectric phenomena, it is shown that a centrosymmetric VO2 -based heterojunction exhibits a self-powered (i.e., 0V), infrared (λ = 940nm) photoresponse. Specifically, the device shows giant current modulation (103 %), good responsivity of >2.4mA W-1 , reasonable specific detectivity of ≈1010 Jones, and a fast response speed of 0.5ms, even at the nanoscale modulation. Through manipulation of the applied inhomogeneous force, the sensitivity of the infrared response is enhanced (> 640%). Ultrafast night optical communication like Morse code distress (SOS) signal sensing and high-performing obstacle sensors with potential impact alarms are created as proof-of-concept applications. These findings validate the potential of emerging mechanoelectrical coupling for a wide variety of novel applications, including mechanoptical switches, photovoltaics, sensors, and autonomous vehicles, which require tunable optoelectronic performance.

All Structures Great and Small: Nanoscale Modulations in Nematic Liquid Crystals.

The nature of the nanoscale structural organization in modulated nematic phases formed by molecules having a nonlinear molecular architecture is a central issue in contemporary liquid crystal research. Nevertheless, the elucidation of the molecular organization is incomplete and poorly understood. One attempt to explain nanoscale phenomena merely “shrinks down” established macroscopic continuum elasticity modeling. That explanation initially (and mistakenly) identified the low temperature nematic phase (NX), first observed in symmetric mesogenic dimers of the CB-n-CB series with an odd number of methylene spacers (n), as a twist–bend nematic (NTB). We show that the NX is unrelated to any of the elastic deformations (bend, splay, twist) stipulated by the continuum elasticity theory of nematics. Results from molecular theory and computer simulations are used to illuminate the local symmetry and physical origins of the nanoscale modulations in the NX phase, a spontaneously chiral and locally polar nematic. We emphasize and contrast the differences between the NX and theoretically conceivable nematics exhibiting spontaneous modulations of the elastic modes by presenting a coherent formulation of one-dimensionally modulated nematics based on the Frank–Oseen elasticity theory. The conditions for the appearance of nematic phases presenting true elastic modulations of the twist–bend, splay–bend, etc., combinations are discussed and shown to clearly exclude identifications with the nanoscale-modulated nematics observed experimentally, e.g., the NX phase. The latter modulation derives from packing constraints associated with nonlinear molecules—a chiral, locally-polar structural organization indicative of a new type of nematic phase.

Dynamically tunable perfect absorber based on VO2–Au hybrid nanodisc array

The nanoscale modulation of light can be achieved by integrating plasmonic nanostructures with phase change materials. A dynamic and tunable perfect absorber is designed by combining VO2–Au hybrid nanodisc array with metal–insulator–metal structure. The finite-difference time-domain method is used to simulate the absorption curves under different structural parameters and temperatures. In the near-infrared band of 700 to 1800 nm, the average absorption rate and absorption bandwidth of the absorber in the insulating phase of VO2 are 87.6% and 939 nm, respectively. And the maximum absorption modulation depth before and after phase transition of VO2 reaches 63.8%. The absorber can tolerate a wide range of incident angles and exhibits polarization-independent features. We envisage that the overall advantages of this absorber will open new opportunities for optical modulation and optoelectronics.

Atomically-Precise Texturing of Hexagonal Boron Nitride Nanostripes.

Monolayer hexagonal boron nitride (hBN) is attracting considerable attention because of its potential applications in areas such as nano‐ and opto‐electronics, quantum optics and nanomagnetism. However, the implementation of such functional hBN demands precise lateral nanostructuration and integration with other two‐dimensional materials, and hence, novel routes of synthesis beyond exfoliation. Here, a disruptive approach is demonstrated, namely, imprinting the lateral pattern of an atomically stepped one‐dimensional template into a hBN monolayer. Specifically, hBN is epitaxially grown on vicinal Rhodium (Rh) surfaces using a Rh curved crystal for a systematic exploration, which produces a periodically textured, nanostriped hBN carpet that coats Rh(111)‐oriented terraces and lattice‐matched Rh(337) facets with tunable width. The electronic structure reveals a nanoscale periodic modulation of the hBN atomic potential that leads to an effective lateral semiconductor multi‐stripe. The potential of such atomically thin hBN heterostructure for future applications is discussed.

Probing the optimal refractive index profile of disordered silicon nanowires for photon management applications

Controlling the light transport using photonic structures is essential for the deterministic control of light trapping and that depends on the nano-scale spatial modulation of refractive index. Here, we study the optimal effective refractive index profile ( n eff ) of vertically-aligned disordered silicon nanowires using the measured spatial-and wavelength-dependent micro-reflectivity values across the nanowire length. A multi-layer model for the nanowire sample is employed to calculate the reflectivity values using the different n eff profiles. The calculated reflectivity values are compared with the measured reflectivity values for different polarization states of light. The results validate that the silicon nanowires with an exponential n eff profile suppress more than 90% reflectivity over a wide angular range for both polarization states of light. Moreover, the nanowires sample with an exponential n eff profile shows a significant enhancement in light trapping and Raman scattering. • Spatial mapping of reflectivity values across the nanowire length using micro-reflectivity setup. • The optimal refractive index profiles of disordered silicon nanowires are estimated which are supported with simulations. • The nanowire sample with an exponential index profile shows enhanced antireflection, light trapping, and Raman scattering. • Our results are useful for applications involving solar cells, photo-detectors, and sensing.

Anisotropy-induced spin reorientation in chemically modulated amorphous ferrimagnetic films

The ability to tune the competition between the in-plane and out-of-plane orientation of magnetization provides a means to construct thermal sensors with a sharp spin re-orientation transition at specific temperatures. We have observed such a tuneable, temperature driven spin re-orientation in structurally amorphous, ferrimagnetic rare earth-transition metal (RE-TM) alloy thin films using scanning transmission X-ray microscopy (STXM) and magnetic measurements. The nature of the spin re-orientation transition in FeGd can be fully explained by a non-equilibrium, nanoscale modulation of the chemical composition of the films. This modulation leads to a magnetic domain pattern of nanoscale speckles superimposed on a background of in-plane domains that form Laudau configurations in micron-scale patterned elements. It is this speckle magnetic structure that gives rise to a sharp two step-reversal mechanism that is temperature dependent. The possibility to balance competing anisotropies through the temperature opens opportunities to create and manipulate topological spin textures.

Structural colours in diverse Mesozoic insects.

Structural colours, nature's most pure and intense colours, originate when light is scattered via nanoscale modulations of the refractive index. Original colours in fossils illuminate the ecological interactions among extinct organisms and functional evolution of colours. Here, we report multiple examples of vivid metallic colours in diverse insects from mid-Cretaceous amber. Scanning and transmission electron microscopy revealed a smooth outer surface and five alternating electron-dense and electron-lucent layers in the epicuticle of a fossil wasp, suggesting that multilayer reflectors, the most common biophotonic nanostructure in animals and even plants, are responsible for the exceptional preservation of colour in amber fossils. Based on theoretical modelling of the reflectance spectra, a reflective peak of wavelength of 514 nm was calculated, corresponding to the bluish-green colour observed under white light. The green to blue structural colours in fossil wasps, beetles and a fly most likely functioned as camouflage, although other functions such as thermoregulation cannot be ruled out. This discovery not only provides critical evidence of evolution of structural colours in arthropods, but also sheds light on the preservation potential of nanostructures of ancient animals through geological time.

Displacive Order–Disorder Behavior and Intrinsic Clustering of Lattice Distortions in Bi‐Substituted NaNbO3

AbstractPerovskite‐like NaNbO3‐Bi1/3NbO3 solid solutions are studied to understand the interactions between octahedral rotations, which dominate the structural behavior of NaNbO3 and displacive disorder of Bi present in Bi1/3NbO3. Models of instantaneous structures for representative compositions are obtained by refining atomic coordinates against X‐ray total scattering and extended X‐ray‐absorption fine structure data, with additional input obtained from transmission electron microscopy. A mixture of distinct cations and vacancies on the cuboctahedral A‐sites in Na1−3xBixNbO3 (x ≤ 0.2) results in 3D nanoscale modulations of structural distortions. This phenomenon is determined by the inevitable correlations in the chemical composition of adjacent unit cells according to the structure type—an intrinsic property of any nonmolecular crystals. Octahedral rotations become suppressed as x increases. Out‐of‐phase rotations vanish for x > 0.1, whereas in‐phase tilts persist up to x = 0.2, although for this composition their correlation length becomes limited to the nanoscale. The loss of out‐of‐phase tilting is accompanied by qualitative changes in the probability density distributions for Bi and Nb, with both species becoming disordered over loci offset from the centers of their respective oxygen cages. Symmetry arguments are used to attribute this effect to different strengths of the coupling between the cation displacements and out‐of‐phase versus in‐phase rotations. The displacive disorder of Bi and Nb combined with nanoscale clustering of lattice distortions are primarily responsible for the anomalous broadening of the temperature dependence of the dielectric constant.