Multilayer Nanostructures Research Articles

The effect of van der Waals force on the vibrational properties of low-dimensional nanostructure

On nanoscale, van der Waals (vdW) force has a very important influence on physical, chemical, electrical and mechanics properties of low-dimensional nanostructures. vdW force is an important factor affecting constitutive relation, boundary condition of low-dimensional nanostructures, and then affecting its natural frequency and nonlinear dynamics property. The nanostructures have wide applications in fabricating the nanoresonator and nanosensor, such as mass sensing, optical sensing, signal-processing, et al. In this paper, the latest research progress about the effect of vdW force on the vibrational properties of low-dimensional nanostructures is introduced. The main contents of this paper are as follows. The vdW force is introduced in the first part of this paper. The source of vdW force and the expression to describe vdW force are presented. The research progress on the basic development history of vdW force is discussed. In the second part, the effect of vdW force on the mechanical property of nanomaterials is discussed, including buckling, stretching, fracture, et al. vdW force is weak in resisting interlayer shear or sliding. However, it can affect the buckling and fracture behavior of nanomaterials, and can especially affect the deformation of nanomaterials. The effect of vdW force on the vibrational behavior of nanomaterials is presented in the third part. Different from the macro structure, vdW force has a significant influence on the vibrational behavior of low-dimensional nanoscale structures. The experimental method, molecular dynamic simulations method and continuum mechanics method are usually used for studying the influence of vdW force on the vibrational behavior of low-dimensional nanostructure. Due to the existence of vdW force between interlayer of low-dimensional nanostructures, the vibration of double-layered low-dimensional nanostructures appear anti-phase vibration mode and in-phase vibration mode. The frequency of anti-phase vibration mode is much higher than that of in-phase vibration mode, but the vdW force cannot affect the first order natural frequency. However, the existence of the vdW force between the interlayer of multi-layered low-dimensional nanostructure can cause the interlayer shear force. The vdW force can affect the vibrational behavior of low-dimensional nanostructure, e.g., the natural frequency is affected by vdW force. Some latest researches about the interlayer shear force caused by vdW force on the vibration property are discussed in this paper. The vdW force can also affect the boundary condition of the vibrational problems for low-dimensional nanostructure. For one-dimensional nanostructures, they are usually bridged on the substrate. But for two-dimensional nanostructures, they are usually suspended on the circular hole. The vdW force between the substrate and low-dimensional nanostructure is a very important factor that can affect the boundary conditions of vibrational property of these low-dimensional nanostructures. Some open problems and future researches in the dynamic behaviors of low-dimensional nanostructure with vdW force are presented. To study the effect of vdW force on the vibration characteristics of nanoscale structures by quantum mechanics method or semi quantum mechanics method is a prodigious challenge. The effect of nonlinear vdW force and long-range nonlocal vdW force on the vibration characteristics of nanoscale structures should be an interesting problem to be solved. The influence of vdW force on the vibration characteristics of nanostructures needs to be verified by experiments.

SIMULATION OF HYSTERESIS PHENOMENA IN MULTILAYER MAGNETIC NANOSTRUCTURES

The Monte Carlo simulation of magnetic properties of artificial multilayer nanostructures, where ultrathin ferromagnetic films divided by layer of nonmagnetic metal are coupled antiferromagnetically, is realized. The anisotropic Heisenberg model is applied for de-scription of magnetic properties. Dependence of hysteresis phenomena on thickness of ferromagnetic films and various values of interlayer exchange interaction is revealed.

Inhibiting tumor oxygen metabolism and simultaneously generating oxygen by intelligent upconversion nanotherapeutics for enhanced photodynamic therapy

Hypoxia is one of the hallmarks of solid tumor, which heavily restricts the clinical cancer therapy treatments, especially for the oxygen (O2) -dependent photodynamic therapy (PDT). Herein, an intelligent multi-layer nanostructure was developed for decreasing the O2-consumption and elevating the O2-supply simultaneously. The cell respiration inhibitor –atovaquone (ATO) molecules were reserved in the middle mesoporous silicon layer, and thus were intelligently released at the tumor site after the degradation of gatekeeper of MnO2 layer, which effectively inhibit tumor respiration metabolism to elevate oxygen content. Meanwhile, the degradation of MnO2 layer can generate O2, further boosting oxygen content. Moreover, the inner upconversion nanostructures as the near infrared (NIR) light-transducers enable to activate photosensitizers for deep-tissue PDT. Systematic experiments demonstrate that this suppressing O2-consumption and O2-generation strategy improved oxygen supply to boost the singlet oxygen generation to eradicate cancer cells under NIR light excitation. Better still, superior trimodality imaging capabilities (computed tomography (CT), NIR-II window fluorescence, and tumor microenvironment-responsive T1-weighted magnetic resonance (MR) imaging) of the nanoplatform were evaluated. Our findings offer a promising aproach to conquer the serious hypoxia problem in cancer therapy by turning down the O2 metabolism aveneue and simultaneously generating O2.

Design of high-efficiency all-dielectric polymer meta-surfaces beam deflection blazed grating

Optical meta-surface element is a kind of two-dimensional ultra-thin device based on the regular arrangement of single-layer or multi-layer sub-wavelength nanostructure array. It can realize the sudden operation of optical amplitude, phase, polarization, the wavelength in a subwavelength scale. In this paper, we design a Huygens meta-surface based on low loss all-dielectric, which can approach the phase control of the outgoing beam after the parallel beam incident on the meta-surface. By the single-layer dielectric nanostructure array, so called Huygens surface, the abnormal transmission without reflection and low loss meta-atoms are realized. Five different beam deflectors were design by these meta-atoms. The different performance of five beam deflectors were discussed, and the effect of wavelength for different beam deflector was investigated next. The highest efficiency of beam deflector is around 85%. The largest deflection angle is 13.248˚ for one polymer grating. These silicon-based beam deflection meta-surfaces may be applied as blazed grating in the monochromator r, precision measurement, and laser shaping.

Narrowing of filters and laser mirror in tilt-modulated chiral sculptured thin films

Helicoidal multi-layered nanostructures obsess intriguing optical properties to develop various optical and photonic devices. The optical properties of such spiral materials are adjacent with helical rotation. Tilt-modulated chiral sculptured thin film (STF) can totally reflect or transmit light in the Bragg regime for varying amplitudes of oscillation angles. Particularly, twist defect chiral STFs of same handedness creating spectral hole for circularly polarized light at different oscillation amplitudes. A narrow bandstop or wide bandpass filters and Bragg reflectors are created in defect modulated chiral STF. While, increasing the number of oscillations in a structural half period of chiral STF, the filters are flattering and narrower having blue shift. For large number of oscillation, the modulated chiral STF behave as laser mirror and creating Bragg fringes in the Bragg regime. Similarly, for different angles of incidence light the spectral holes and optical filters are become narrowing and shifted to lower wavelength regime, eventually die out in the Bragg regime, with maximum reflection for large angle of incident light. Therefore, it is suggested that such chiral STF are very useful in optical devices which operating in different wavelength regime.

Properties of renormalized spectrum of interacting with polarization phonons localized quasiparticle with degenerated excited state

The quantum theory of renormalized energy spectrum of the system of localized two-level quasiparticle, with degenerated spectrum, interacting with polarization phonons, being the model of multilayered nanostructure, is developed within the modified Feynman-Pines diagram technique. Effectively taking into account the multi-phonon processes, the theory is valid in a wide range of energies which contains the main states and the satellite groups of energies produced by the resonant bound-to-phonons states of quasiparticle in the vicinity of the threshold energies of their radiation. The properties of renormalized spectrum of the system are analyzed and dependences of the widths of groups of energy levels (main and satellite) on the magnitudes of inter-level coupling constants are obtained.

Acoustic phonons in multilayer nitride-based AlN/GaN resonant tunneling structures

The study of physical processes associated with acoustic phonons in nitride-based nanosystems is of great importance for the effective operation of modern nanoscale devices. In this paper, a consistent theory of acoustic phonons arising in multilayer nitride-based semiconductor resonant tunneling structures, that can function as a separate cascade of a quantum cascade laser or detector is proposed. Using the physical and geometric parameters of a typical nanostructure, the spectrum of various types of acoustic phonons and the corresponding normalized components of the elastic displacement vector are calculated. It has been established that the spectrum of acoustic phonons of a multilayer nanostructure consists of two groups of the shear phonons dependencies and three groups of dependencies for a mixed spectrum of flexural and dilatational phonons. The dependencies of the acoustic phonons spectrum of the nanostructure and the components of the elastic displacement vector on its geometric parameters are studied. It has been established that for the components of the displacement vector u2 for shear phonons have a decrease in the absolute values of their maxima with increasing of energy level number. The components u1 and u3 of flexural and dilatational phonons behave respectively as symmetric and antisymmetric functions relatively the center of an separate selected layer of the nanostructure. The proposed theory can be further applied to study the interaction of electrons with acoustic phonons in multilayer resonant tunneling structures.

Size-dependent mechanical-diffusion responses of multilayered composite nanoplates

ABSTRACT Multi-cell storage devices (e.g. lithium-ion batteries (LIBs)) stand as one of the most important components which are widely used in battery energy storage technology for renewable energy power system, hybrid electric vehicles and portable electronic devices due to its high energy density and low manufacturing cost. In recent years, there has been an explosion of developing new and multifunctional nanomaterials with particular interest to electrode nanomaterials (nano-MnO2, nano-LiMn2O4, etc.). In such case, size-dependent mechanical-diffusion responses analysis of multilayered composite nanostructure under non-uniform concentration in-service environment will become significantly important. To address the problem, a multilayered composite nanoplates account for diffusion impedance and elastic wave impedance at the interface is considered in this research. Governing equations involving with size-dependent characteristic lengths and material constant ratio of each two adjacent layers are formulated, and then, a semi-analytical approach via the Laplace transformation is applied. Then, the obtained solutions are applied to bilayered composite nanoplates, and the influences of size effects and material constants ratio on structural responses are emphatically discussed to provide guidelines on and new insights into the optimal design and management of mechanical responses and vibration control of nano-sized multi-cell storage devices under non-uniform concentration environment, especially for the nano-coating.

Spectrum and normalized modes of acoustic phonons in multilayer nitride-based nanostructure

Using the model of an elastic continuum, precise analytical solutions of the equations of motion are established and a theory of the spectrum and components of the displacement field of acoustic phonons is developed for a two-well resonant-tunneling nanostructure with AlN – quantum barriers and GaN∕Alx Ga1−x N – quantum wells. For the experimentally realised nanostructure – the active zone of a quantum cascade detector – depending on its geometric parameters, the spectrum of acoustic phonons and normalized components of the displacement fields were calculated.

Functionalization of multilayer fullerenic nanostructures with l-lysine for supercapacitor applications: Comparing oxidation against diazonium salt methods

The functionalization of pristine carbon nano-onions (p-CNOs), obtained by thermal annealing of nanodiamonds, with l-lysine was carried out through two synthetic routes: i) amidation of previously oxidized p-CNOs (lys-CNOs); and ii) by formation of diazonium salts to produce the corresponding aliphatic carbocation that is added to the outer shell of the nanomaterial (slys-CNO). Characterization was carried out by ATR-FTIR and Raman spectroscopy. Additionally, the degree of functionalization was estimated by TGA. The specific capacitance of the functionalized nanomaterials was determined by cyclic voltammetry, using the method of the linearization of the peak current as a function of the sweep rate, obtaining values of 16.49 F g−1, 4.03 F g−1 and 32.72 F g−1 for p-CNOs, lys-CNOs and slys-CNOs, respectively. Finally, an evaluation of the electrochemical system was carried out through EIS. Our results show that the oxidation method has a great influence on the electrical properties of CNOs as evidenced in the capacitance.

Carbon–titanium nanostructures: synthesis and characterization

C–Ti multilayer nanostructures were deposed by thermionic vacuum arc technology. The layers consisting of about 100 nm Carbon base layer and seven 40 nm alternatively Ti and C layers were deposed on Silicon substrates. On the other hand, in order to obtain C–Ti multilayer structures with variable thickness and different percentages in C and Ti of layers, a 20 nm thick C layer was first deposed on Si substrate and then seven Ti–C layers, each of these having thickness of up to 40 nm were deposed. To perform the successively layers with various thickness were changed the discharge parameters for C and Ti plasma sources to obtain the desirable thickness. By changing of substrate temperature between room temperature and 300 °C and on the other hand the bias voltage up to −700 V, different batches of samples were obtained for this study. To characterize properties of as prepared C–Ti multilayer structures were used electron microscopy techniques (TEM, STEM), Raman spectroscopy, RBS techniques and tribological measurements. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured, and then the electrical conductivity. Using the Wiedemann–Frantz law was calculated the thermal conductivity.

The effect of microstructure on corrosion behavior of a novel AlCrTiSiN ceramic coating

A novel AlCrTiSiN ceramic coating was deposited on 316L austenitic stainless steel (ASS) to enhance its anti-corrosion against 10 vol% HCl solution. Meanwhile, an AlCrN coating was selected for comparison. The results show the AlCrTiSiN consists entirely of single-phase fcc-AlCrTiSiN solid solution, showing nano-multilayered structure. While the AlCrN coating is composed of single-phase fcc-AlCrN solid solution, revealing a typical columnar structure. Growth-related micro-particles (MPs) induce the transformation of growth behavior of the AlCrTiSiN coating over MPs from nano-layered structure to columnar structure, resulting in a reduction in coating densification. Corrosion mechanisms of AlCrTiSiN-coated sample are: pitting corrosion first arrives from surface defects and columnar GBs, and then propagate towards coating subsurface until steel substrate, leading to local corrosion. Subsequently, the galvanic corrosion between coating and substrate happens, resulting in the rapid dissolution of steel substrate beneath the coatings. The combination of pitting corrosion, local corrosion and galvanic corrosion further induces the corrosion cracking, and finally results in coating delamination. In addition, layered interfaces induce the deflection of corrosion cracks along layered interfaces, and further retard the dissolution of coating. Electrochemical and immersion tests confirm that the AlCrTiSiN-coated sample shows a superior corrosion resistance compared with AlCrN-coated one. Superior anti-corrosion of AlCrTiSiN ceramic coating is mainly related to its lower MP number density, denser structure and high-density layered interfaces parallel to coating surface.

Effect of Ni doping on the microstructure and toughness of CrAlN coatings deposited by magnetron sputtering

This study determines the effects of nickel (Ni) doping on the composition, phase structure, chemical valence state, hardness, and toughness of CrAlNiN coatings. CrAlNiN coatings with various Ni contents (0.00 at%–27.71 at%) were deposited on the surfaces of M2 tool steel and monocrystalline silicon (Si) using unbalanced magnetron sputter ion plating. The results showed that the CrAlNiN coatings possess a nanomultilayer structure, maintaining the face centered cubic crystal structure of the chromium aluminum nitride (CrAlN) coatings. The Ni in the coatings acts as a toughening phase to ease stress, to increase resistance to crack growth, and to delay the generation of cracks, thereby having an obvious toughening effect. At an Ni content of approximately 20.33%, the Ni toughening phase in the modulation layer tends to saturate and the effect of continuing the increase in Ni content is limited from the viewpoint of improving the toughness.

Microstructure and Rutherford Backscattering Spectrometry of Hard/Lubricant Mo-Ti-Al-N Multilayered Coatings Prepared by Multi-Arc Ion Plating at Low Substrate Rotation

To develop the hard and self-lubricating coatings applied for the industrial dry-cutting and die-casting machining tool fields, a series of MoTiAlN/MoN/Mo multilayered coatings were deposited on Si substrates under low substrate rotation by cathodic multi-arc ion plating. XRD, SEM, TEM, RBS, nanoindentation, and tribology tester were used to monitor the phase structure, morphology, component, nanohardness, and friction coefficient of the coatings. It was found that the coatings deposited at various substrate rotations comprised paramount cubic B1 structure TiAlN and Mo2N phases. The micrographs confirmed that the mean modulation period and total physical thickness of multilayered TiAlN/Mo2N coatings with a sharp interface fabricated at 2 revolutions per minute (rpm) were 26 nm and 1.15 μm. The mean nanohardness and friction coefficient were ca. 30 GPa and 0.4, respectively. RBS results along with the SIMNRA code allowed to estimate the total atomic concentrations and the physical thickness of individual sublayer as well as the modulation period of multilayered coatings, which demonstrated an efficiency of this approach for characterization of nano-multilayered structures.

Effects of the Van der Waals Force on the Vibration of Typical Multi-layered Two-dimensional Nanostructures

Recently, two-dimensional nanostructures have caught much attention because of their magnificent physical characteristics. The vibrational behavior of typical multi-layered two-dimensional nanostructures (TMLTNs) is extraordinary significant to TMLTN-based nanoresonantors. In this investigation, the vibrational behavior of TMLTNs, taking black phosphorus (BP), graphene and BN as examples, is studied adopting molecular dynamics (MD) simulations and the sandwich plate model (SPM). The MD results show that the fundamental resonant frequency of multi-layered BP (MLBP) and multi-layered BN (MLBN) increase obviously with the number of layers. However, the fundamental resonant frequency of a multi-layered graphene sheet (MLGS) rise slightly when the number of layers increases. This phenomenon is caused by the shear modulus in the xz-plane and yz-plane resulted by the vdW force. Hence, an SPM considering the shear modulus in the xz-plane and yz-plane caused by the vdW force is used to investigate the vibration of the TMLTN. Compared with the MD results, it is shown that the SPM can better predict the vibration of the TMLTN.

Novel bio-based core-shell organic-inorganic nanohybrid from embedding aspartic acid-guanine ionic liquid on the hydroxylated nano silica surface (nano [(Asp-Gua) IL@PEG-SiO2]): A versatile nanostructure for the synthesis of bis(2,3-dihydroquinazolin-4(1H)-one) derivatives and tricarboxamides under green media

A new multi-layered nano structure has been prepared using hydroxylated nano silica (as core) and novel guaninium aspartate ionic liquid (as shell) (nano [(Asp-Gua) IL@PEG-SiO2]). It characterized by FT-IR, 1H NMR, FESEM, EDAX, XRD, TGA/ DTG, and BET analysis. This bio-based organic-inorganic hybrid catalyzed synthesis of peptide-like tricarboxamides though the pseudo five-component condensation of aromatic aldehydes, aromatic amines, tert-butyl isocyanide, and Meldrum's acid under green solventless conditions at room temperature successfully. Its efficacy affirmed in the preparation of bis(2,3-dihydroquinazolin-4(1H)-one) derivatives via one-pot pseudo five-component reaction of aldehydes, amines, and isatoic anhydride in 70 °C aqueous media. The protocol contains several advantages such as relatively short reaction times, simple work-up procedure, economic and environmentally-friend because of performing the two class of MCRs under green media, utilizing wide-range of substrates, and reusability and recoverability of the core-shell nano-promoter for 3 runs without significant activity loss.

Nonlinear resonance of FG multilayer beam-type nanocomposites: Effects of graphene nanoplatelet-reinforcement and geometric imperfection

In this paper, the nonlinear dynamic response of a FG multilayer beam-type nanocomposite reinforced with graphene nanoplatelet (GNP) by considering the initial geometric imperfection is investigated on the basis of nonlocal strain gradient Euler-Bernoulli beam theory. Four patterns of GNP distribution incorporating the uniform distribution (UD) and O-, X-, and A- FG pattern distributions are taken into account and the effective elastic properties of the beam-type nanocomposite are evaluated in the framework of Halpin-Tsai scheme. The first-order vibrational mode is employed to represent the initial geometric imperfection of the nonlinear FG beam-type nanocomposite. Correspondingly, the nonlinear amplitude-frequency response of the imperfect FG multilayer beam-type nanostructures subjected to the excitation resonance is analyzed with the aid of multiple scale method. Firstly, the present model is validated with a comparison of two previous works. Then, a comprehensive investigation is conducted to evaluate the effects of GNP distributed pattern, weight fraction of GNPs, geometric imperfection amplitude, boundary condition, excitation amplitude, nonlocal and strain gradient size scale parameters on the nonlinear frequency-response of FG multilayer beam-type nanostructures. The current work is beneficial for the application of GNP as reinforcement to enhance mechanical performances of nanostructures.

Accelerating the discovery of multilayer nanostructures with analytic differentiation of the transfer matrix equations

The authors describe a novel theoretical methodology for the design of multilayer nanostructures that is based upon analytical differentiation of the transfer matrix equations, and demonstrate this methodology provides an efficient route to optimizing the geometries of structures for applications including incandescent light sources, anti-reflective solar coatings, and light-harvesting structures coupled to molecular chromophores.

Insertion of Iron Decorated Organic-Inorganic Cage-Like Polyhedral Oligomeric Silsesquioxanes between Clay Platelets by Langmuir Schaefer Deposition.

Tuning the architecture of multilayer nanostructures by exploiting the properties of their constituents is a versatile way to develop multifunctional films. Herein, we report a bottom-up approach for the fabrication of highly ordered hybrid films consisting of dimethyldioctadecylammonium (DODA), iron decorated polyhedral oligomeric silsesquioxanes (POSS), and montmorillonite clay platelets. Clay platelets provided the template where Fe/POSS moieties were grafted by the use of the surfactant. Driven by the iron ions present, DODA adopted a staggered arrangement, which is essential to realize the controllable layer-by-layer growth of the film. The elemental composition of the film was studied by X-ray photoelectron spectroscopy and X-ray reflectivity confirmed the existence of smooth interfaces between the different layers.

Improving External Quantum Efficiency by Subwavelength Nano Multi-Layered Structures for Optoelectronic Devices

Based on thin film optics (TFO) and finite element method (FEM), we have theoretically investigated improving external quantum efficiency (EQE) by anti-reflection (AR) films constructed from subwavelength nano multi-layers (NML) of low and high index materials, where the low and high index materials are MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> , respectively. This kind of NML dielectric structures have the advantages of low-cost and flexible. Three kinds of substrates have been studied here, which are glass, polyethylene naphthalate (PEN), and polyethylene terephthalate (PET), respectively. TFO theory has been used to obtain the transmittance and reflectance, which agrees well with FEM results. For NML structure, TFO is more efficient than FEM in terms of calculation time and accuracy. The average AR effects (AAREs) are about 3.69%, 3.46% and 3.07% on glass substrate, about 6.15%, 5.56% and 5.02% on PEN substrate, and about 5.06%, 4.62% and 4.17% on PET substrate, for AR bands (ARBs) 350~800 nm, 350~1100 nm and 350~1500 nm, respectively. The results also reflect that wider AR bandwidth needs more NML layers. In practice, this kind of AR films can be widely applicable to enhance the EQE of the optoelectronic devices (OEDs).