Nanolayer Thickness Research Articles

Thermal conductivity enhancement of phase change material with charged nanoparticle: A molecular dynamics simulation

The present work investigates the effects of charged nanoparticles on thermal properties of phase change material (PCM). Nanoparticles (CuO) with different electrical charges were dispersed into paraffin (octadecane) to prepare nanocomposite phase change material (NPCM). Molecular dynamics method was used to study the thermal conductivity of NPCM and reveal the effect of the charged nanoparticle. The results show that the thermal conductivity of NPCM is promoted with increasing nanoparticle charges. Coulomb energy is nonlinearly increased with the increasing charge. Furthermore, the local density of atoms is also affected by the charged nanoparticle. The peak value of local density increases with increasing nanoparticle charges. Phonon density of state (PDOS) is calculated to study the phonon transport in NPCM. Phonon scattering is weakened around the nanoparticle due to the existence of nanolayer. Moreover, the thickness of nanolayer is increased with the increasing charge, resulting in weaker phonon scattering and contributing to more thermal conductivity enhancement of NPCM. It can be a good way to control the thermal properties of NPCM by adjusting the nanoparticle charge.

Linear dispersion of Dirac fermions in (Cd1–x–yZnxMny)3As2, х+y = 0.2, у = 0.02, 0.04, 0.06, 0.08 solid solutions

Based on the results of the Shubnikov-de Haas oscillations study in single-crystalline diluted magnetic semiconductors (Cd1−x−yZnxMny)3As2 (CZMA) with х + y = 0.2 and Mn content (у = 0.02, 0.04, 0.06, 0.08) at temperatures T = 4.2 to 30 K and magnetic fields B = 0 to 12 T under hydrostatic pressure p = 0 and 10 kbar, the values of the phase shift β, indicating the existence of the Berry phase in all samples were determined. Thickness of two-dimensional surface topological nanolayers in CZMA (х + y = 0.2) single crystals was defined. The rise in Mn concentration led to an increase in the concentration of charge carriers in the 2D surface layers n 2D and a decrease in its mobility μ 2D. The reduced cyclotron mass m с (0)/m 0, depending on the Fermi wave vector k F , experimentally observed from the Shubnikov-de Haas oscillations, which was in a good agreement with the prediction theory of linear dependence and experimental results in topological insulator single crystals Bi2Se3 indicated that Dirac fermions were present in a diluted magnetic semiconductor CZMA system with х + y = 0.2. The damping of the Shubnikov-de Haas oscillations for pressures p = 0 and 10 kbar in the CZMA sample (х + y = 0.2; y = 0.2) was found to be associated with an amplitude decrease by spin splitting (Zeeman effect). From the analysis of experimental data, the effective Lande factor g = 7.63 and 7.87 and the band gap Δ =35.3 and 9.7 meV at p = 0 and 10 kbar, respectively, were obtained.

Determination of heat transport mechanism using nanoparticle property and interfacial nanolayer in a nanofluidic system

Elucidation of heat transport mechanism is the key for the preparation and application of nanofluids with high thermal conductivity. However, the effect of microscopic parameters on nanoparticle property, especially thermal conductivity of nanofluids has limited studied. To establish the relationship between nanolayer structure characteristics and thermal conductivity, Al2O3, CuO, and Cu nanoparticles were dispersed in deionized water (W). The thermal conductivity of nanofluids was measured at various temperatures (293–333 K) and volume fractions (0.5–2.0 vol%). The thermal conductivity of nanofluids decreased in the following order: CuO/W > Al2O3/W > Cu/W nanofluids. Nanoparticles with a high thermal conductivity do not always exhibit a high thermal conductivity of nanofluids. Then, number density (N), nanolayer structure, and its thickness (δ) were obtained from a molecular dynamics simulation. The simulation results show that two obvious interfacial nanolayers exist around the central nanoparticle; however, the interfacial potential of the first layer is much higher than that of the second layer. Therefore, the morphology of the first layer mainly determines the thermal conductivity in a nanofluidic system. However, the trend of number density differs from that of thermal conductivity. Moreover, the thickness of interfacial nanolayer is similar for different nanofluids. Thus, only the number density or thickness of nanolayer is not a determined parameter to evaluate the thermal conductivity. A new parameter, N/δ (ratio of number density and thickness), is described to quantitatively evaluate the relationship between nanolayer structure and thermal conductivity. The high value of N/δ indicates that denser and more ordered liquid molecules arrange around the nanoparticles, creating a higher heat transfer channel than other regions and thus exhibiting a higher thermal conductivity of nanofluids.

Hole Injection Role of p-Type Conjugated Polymer Nanolayers in Phosphorescent Organic Light-Emitting Devices

Here, we report the hole injection role of p-type conjugated polymer layer in phosphorescent organic light-emitting devices (OLEDs). Poly(3-hexylthiophene) (P3HT) nanolayers (thickness = ~1 nm thick), which were subjected to thermal annealing at 140 °C by varying annealing time, were inserted between indium tin oxide (ITO) anodes and hole transport layers (N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine, NPB). The 1 nm-thick P3HT layers showed very weak absorption in the visible light range of 500~650 nm. The device results disclosed that the presence of P3HT layers were just able to improve the charge injection of OLEDs leading to an enhanced luminance irrespective of thermal annealing condition. The highest luminance and efficiency were achieved for the OLEDs with the P3HT layers annealed at 140 °C for 10 min. Further annealing for 30 min resulted in turn-down of device performances. The emission color was almost unchanged by the presence of P3HT layers even though the color coordinates were marginally fluctuated according to the annealing time. The present result delivers the possibility to use p-type conjugated polymers (i.e., P3HT) as a hole injection layer in OLEDs.

Change of Bandgap Energy in Quantum System of Nanolayer on Silicon

In the quantum system of nanolayer (NL) on silicon, the bandgap energy obviously increases with the decrease of NL thickness, where the quantum confinement (QC) effect plays the main role as the thickness of Si NL changes along with (100), (110) and (111) directions, respectively. And the simulation result demonstrated that the direct bandgap can be obtained as the NL with (001) direction is thinner than 10 nm on Si surface. However, it is discovered in the simulated calculation that the QC effect disappears as the NL thickness arrives at the size of the monoatomic layer, in which its bandgap sharply decreases, where the abrupt change effect in bandgap energy occurs near-ideal 2D-layer. In the experiment, we fabricated the Si NL structure by using electron beam irradiation and laser deposition methods, in which a novel way was used to control the NL thickness by modulating irradiation time of the electron beam. The new effect should have a good application on a photonic-electronic chip of silicon.

Investigation of the properties of Ti-TiN-(Ti,Al,Nb,Zr)N composite coating and its efficiency in increasing wear resistance of metal cutting tools

The paper investigates the structure and the elemental and phase composition of Ti-TiN-(Ti,Al,Nb,Zr)N coatings, deposited using Filtered Cathodic Vacuum Arc Deposition (FCVAD) technology. The coating under study has a nanolayer architecture of outer (wear-resistant) material with a nanolayer thickness of 2–10 nm and ternary period of λ = 180 nm. The experiments found that the wear-resistant coating layer was composed of a main cubic phase of (Ti,Nb,Zr,Al)N with the space group -Fm3m, as well as very small amounts of a h-AlN phase with the space group P6.3mc. The distribution of elements within the ternary period varies in a wide range due to the planetary rotation of the substrate (Al varies within 1–20 at.%, Ti – 5-70 at.%, Zr – 3-30 at.%, and Nb – 3-40 at.%). The investigation includes comparative cutting tests of tools with the coating under study, as well as tools with Ti-TiN-TiAlN coatings with high (55 at.%) and low (16 at.%) aluminum content, and uncoated tools. The study considers the specifics of the wear patterns on carbide tools during the turning of workpieces made of AISI 1045 steel. The investigation is focused on the specifics of diffusion processes in the area of the interface of the coating and the material being machined. Both the diffusion of iron into the coating structure (to a depth not exceeding 100 nm) and the diffusion of coating elements (primarily titanium) into the structure of the material being machined (to a depth not exceeding 200 nm) are detected.

A novel model for predicting the effective specific heat capacity of molten salt doped with nanomaterial for solar energy application

In order to establish instructions for high-performance molten salt preparation, this paper focuses on accurate prediction method on the effective heat capacity of nanomaterial-enhanced molten salt (NMS). With carbon nanotube (CNT) enhanced carbonate eutectic (Li2CO3-K2CO3) taken as the study subject, the microscopic mechanism of nanomaterial on the effective specific heat capacity enhancement of molten salt is revealed. The nanolayer content is calculated, and the specific heat capacity of CNT and nanolayer is quantified. Accordingly, the effective heat capacity prediction model is completed. In addition, the CNT-enhanced carbonate eutectic is experimentally prepared with a high-energy ball milling method. Its effective specific heat capacity is measured and used to validate the prediction model. The results show that, firstly, the thickness of nanolayer is 0.65 nm and 0.98 nm in the single-walled CNT case and multi-walled CNT case, respectively. Secondly, the specific heat capacity of CNT is 1.613 J·g−1·K−1 at 800 K, and the specific heat capacity of nanolayer increases with increasing the surface atom ratio. Finally, the effective specific heat capacity of CNT-enhanced carbonate salt is predicted and validated with experimental results. It is revealed that, in the cases of well-dispersed nanomaterial-enhanced molten salt, the prediction method presented in this research has considerable accuracy (error < 2.90%). Furthermore, the effective specific heat capacity of NMS doped with CNT of various diameter is given.

Bioactive Functional Nanolayers of Chitosan-Lysine Surfactant with Single- and Mixed-Protein-Repellent and Antibiofilm Properties for Medical Implants.

Medical implant-associated infections resulting from biofilm formation triggered by unspecific protein adsorption are the prevailing cause of implant failure. However, implant surfaces rendered with multifunctional bioactive nanocoatings offer a promising alternative to prevent the initial attachment of bacteria and effectively interrupt biofilm formation. The need to research and develop novel and stable bioactive nanocoatings for medical implants and a comprehensive understanding of their properties in contact with the complex biological environment are crucial. In this study, we developed an aqueous stable and crosslinker-free polyelectrolyte–surfactant complex (PESC) composed of a renewable cationic polysaccharide, chitosan, a lysine-based anionic surfactant (77KS), and an amphoteric antibiotic, amoxicillin, which is widely used to treat a number of infections caused by bacteria. We successfully introduced the PESC as bioactive functional nanolayers on the “model” and “real” polydimethylsiloxane (PDMS) surfaces under dynamic and ambient conditions. Besides their high stability and improved wettability, these uniformly deposited nanolayers (thickness: 44–61 nm) with mixed charges exhibited strong repulsion toward three model blood proteins (serum albumin, fibrinogen, and γ-globulin) and their competitive interactions in the mixture in real-time, as demonstrated using a quartz crystal microbalance with dissipation (QCM-D). The functional nanolayers with a maximum negative zeta potential (ζ: −19 to −30 mV at pH 7.4), water content (1628–1810 ng cm–2), and hydration (low viscosity and elastic shear modulus) correlated with the mass, conformation, and interaction nature of proteins. In vitro antimicrobial activity testing under dynamic conditions showed that the charged nanolayers actively inhibited the growth of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria compared to unmodified PDMS. Given the ease of fabrication of multifunctional and charged biobased coatings with simultaneous protein-repellent and antimicrobial activities, the limitations of individual approaches could be overcome leading to a better and advanced design of various medical devices (e.g., catheters, prosthetics, and stents).

The effect of gain-assisted silica separate layer on the plasmonic local field enhancement of Ag-Si-Ag coaxial-cable type silver nanotube

The plasmonic local electric field enhancement characters of gain-assisted coaxial-cable type Ag-Si-Ag nanotube have been investigated computationally. The calculation results based on quasi-static analysis indicate that the three surface plasmon resonance (SPR) hybridization modes depend on the gain medium of the silica separate layer in different ways. The SPR band from antisymmetric coupling between bonding tube plasmon mode and the wire plasmon mode (denoted as peak3) is mostly sensitive to the gain assist, and the greatest local field enhancement factor of 104 could be achieved with a critical gain coefficient. The physical mechanism has been attributed to the appearance of the local field hot spot in silica separate layer, in which the gain medium has been dropt. The critical gain coefficient could be tuned by altering the geometry factors of the nanostructure. It has been found that the thickness of the middle silica nanolayer with gain medium greatly affect the critical gain coefficient. For peak3, the maximum plasmonic field enhancement could be easily achieved with a small gain coefficient and within a slight change region. Whereas for SPR band from the symmetric coupling between the bonding tube plasmon mode and the wire plasmon mode (denoted as peak2), the local field hot spot appears in the inner Ag nanowire without gain medium. Thus the maximum plasmonic field enhancement could only be achieved with a large gain coefficient when the middle nanolayer with gain medium has a thin thickness.

Tuning the Magnetically Segregated Nanolayering in Mn–Ni–As Intermetallics

2D materials exhibiting alternating ferro- and non-ferromagnetic layers are highly sought due to their potential for applications. In this work, we demonstrate, through the use of robust methodology, the existence of single-phase, Mn1–xNixAs (0.25 ≤ x ≤ 0.50), with a unique intrinsic nanostructuring where the thickness of MnAs and NiAs nanolayers can be tuned via the composition, x. We describe a periodic variation of nanolayers of edge-sharing MnAs6 and NiAs6 octahedra layers with thicknesses ranging from 1 to 6 octahedra, 2–16 Å. These crystalline structures are modulated and fully described based on 3D electron diffraction and neutron diffraction. Moreover, by X-ray magnetic circular dichroism, an elemental and orbital-specific technique, we probe the 3d magnetic moments of Mn and Ni. We unveil that the nanosegregated MnAs and NiAs layers behave very differently, with the magnetic moment of manganese being one order of magnitude greater than that of nickel. This study opens the path to a completely new class of materials with intrinsic layers of high and low magnetization with potential applications within spintronics.

Molecular dynamic simulation on the density of titanium dioxide and silver water-based nanofluids using ternary mixture model

This study utilizes molecular dynamics (MD) simulations to scrutinize the influence of type and volume fraction of nanoparticle on the density of nanofluids, i.e. silver (as a hydrophilic case) and titanium dioxide (as a hydrophobic case) water-based nanofluids. Ionic structure of TiO2 distinguishes the solid–liquid interactions with those in silver-water nanofluid. The thickness of nanolayer is estimated from density profile formed around the nanoparticle and is included in the density calculation. It is found that the type of interatomic potential between the nanoparticle and surrounding water can highly affect the thickness of nanolayer. The hydrophobicity/hydrophilicity of nanoparticle is of great importance in nanolayer density and its thickness. It is observed that the difference between the traditional binary mixture and the ternary mixture formula for calculating the density of nanofluid increases by increasing the volume fraction of nanoparticle. This indicates that the effect of nanolayer gets more considerable at high volume fractions.

Using molecular dynamics simulations to investigate the effect of the interfacial nanolayer structure on enhancing the viscosity and thermal conductivity of nanofluids

To understand the remarkable enhancements in viscosity and thermal conductivity of nanofluids, a molecular dynamics (MD) simulation approach was used to investigate the structure and thickness of the interfacial layer and obtain values for radial distribution function, g(r), viscosity, and thermal conductivity of Cu/water nanofluids with volume fractions and temperatures ranging from 0.5–2 vol% and 293–333 K, respectively. The results revealed that value of g(r) was much higher in the first molecular nanolayer compared to the second layer, indicating that greater numbers of water molecules are present in the first layer, which reduces contact thermal resistance and improves thermal conductivity of nanofluids. Moreover, while value of g(r) increased with increasing Cu volume fraction and decreased with temperature, nanolayer thickness was unchanged with temperature at each volume fraction, indicating that intermolecular forces intensify in the first nanolayer. Macroscopically, viscosity and thermal conductivity of the nanofluids increased at higher volume fractions, showing increases of 71.7% and 75% for viscosity, and 41.7% and 53.3% for thermal conductivity at 0.5 and 2 vol%, respectively, compared to water at 333 K. These results, although obtained for Cu/water systems, can provide useful insights into structural and transport properties of nanofluids in general.

Thermal Conductivity Calculations for Nanoparticles Embedded in a Base Fluid

The Prasher analytical model was used for calculating the thermal conductivity of the embedded nanoparticles of Al2O3, CuO, ZnO, and SiO2 in conventional fluids, such as water and ethylene glycol. The values that were obtained were used in the nanofluid theoretical models for comparison with experimental data, where good agreement was obtained. Liang and Li’s theoretical model was also used to calculate the thermal conductivity of these nanoparticles, where the results agreed with those obtained using the Prasher model. The effect of the liquid nanolayer thickness around the nanoparticles that was used to enhance the effective thermal conductivity of nanofluids was explained. The role of the nanoparticles’ surface specularity parameter, which was size-dependent, was clarified. This theoretical trend provides a simple method for estimating the thermal conductivity of nanoparticles and nanofluids.

Influence of the thickness of nanolayers in wear-resistant layer of Ti-TiN-(Ti,Cr,Al)N coating on the tool life and wear pattern of the carbide cutting tools in steel turning

The paper discusses the influence of the thickness of nanolayers in a wear-resistant layer of the Ti-TiN-(Ti,Cr,Al)N multilayered composite coating on the coating and tool cutting properties in turning 1045 steel. The coatings with nanolayer thickness in the range of 10–302 nm were investigated. The studies showed that with a decrease in the nanolayer thickness, the cutting tool life increased. The tests revealed an optimal nanolayer thickness with regard to the tool life under the given cutting conditions, and it was 16 nm. With a further decrease in the nanolayer thickness to 10 nm, the tool life reduced.

Heat enhancement analysis in a differentially heated inclined square enclosure with water and ethylene glycol based Al2O3 nanofluid

This paper investigates the analysis of natural-convection heat enhancement in an inclined square enclosure when filled with water-based nanofluids with left edge wall undergoing heating with consistent heat flux while the right edge wall being cold and other remaining walls are kept adiabatic. The parameters used in this analysis include: solid fraction volume (range from 0-20%), length of the heaters (0.25 cm, 0.50 cm, and 1.0 cm from the left edge), and Rayleigh number (range from 104 to 106 ). The nanolayer thickness ratio was kept at a constant value of 1.0 throughout the analysis. The heat source is found at the center of the left wall. Polynomial differential quadrature equations have been adopted for this analysis for various angles range from 0-90?. As the Rayleigh numbers and particle volume fraction got the much-needed raise, the average count of the heat transfer rate improved too. The length of the heat flux heater has become more prominent parameter that has been affecting the calculated temperature and the flow fields. When the heat flux heater length is pushed to an increasing limit, the heat enhancement rate essentially starts to decline. This happens at the smaller inclination angle, though.

Influence of the nanostructure of the functional layers of a multilayer coating on the wear of a carbide tool

The results of studies of the effect of nanolayer thickness on the wear of carbide tools are presented. The effect of nanolayer thicknesses on microhardness and fracture resistance of a multilayer coating during scratch testing is shown. The role of nanostructure in the processes of crack formation in multilayer coatings during cutting is revealed.

Physical impact of nano-layer on nano-fluid flow due to dispersion of magnetized carbon nano-materials through an absorbent channel with thermal analysis

The current study intends to analyze the significance of the nano-layer on Newtonian fluid consisting of carbon nano-materials has been considered. The special absorbent channel with moving porous walls under the effect of external MHD is manifested. Mathematical modeling of the concerning problem is done in the form of the partial differential structure under the boundary layer theory with effective structures of thermophysical properties. The core features of capitalized induced carbon nano-particles along with base fluid are presented by empirical relations and utilized during the formulation of work. Attained expressions are transmuted because of dimensionless ODE's by obliging transformation approach. The solution of attained ODE's is heeded with the R-K method along with the shooting procedure. Using applicable similarity transforms, the governing equations are converted into a system of nonlinear ordinary differential equations which are solved by using the 4th-order R-K (Runge-Kutta) technique together with shooting methodology. The phenomena of nano-layer have been also modeled mathematically. The motivation behind this section is to demonstrate the behavior of involved parameters on velocity and temperature profiles. A meticulous table is presented in which the effects of involved parameters on shear stress and heat transfer rate are discussed. Specially presented the impact of the thickness of the nano-layer and radius of the particle on the temperature profile. Heat transfer rate increases due to an increase in the thickness of nano-layer. Inverse proportionality exists between the radius of nano-particle and thermal conductivity. The consequences of this research may be advantageous to the applications of biotechnology and industrial motive.

A printed-circuit heat exchanger consideration by exploiting an Al2O3-water nanofluid: Effect of the nanoparticles interfacial layer on heat transfer

Supercritical carbon dioxide (S-CO2) Brayton cycle is an encouraging power conversion technology pertaining to waste heat recovery applications, because of the high compactness and efficiency it presents. A key technological challenge for the commercialization of this technology is the improvement of the cooling process of these cycles. In this study, an analytical investigation of a printed-circuit heat exchanger (PCHE) used as precooler for S-CO2 Brayton cycles and employing an Al2O3-water nanofluid is presented. In particular, the heat exchanger is modeled as segments in series to investigate the nanofluid impact on the PCHE’s thermal-hydraulic performance. Regarding the nanoparticles consideration, the selected theoretical model for the estimation of the thermal conductivity takes into account the radius of the nanoparticles and the nanolayer thickness which is formed around it. In brief, the maximum used nanoparticle volume fraction of 5% results in an improvement of 75% for the heat transfer coefficient leading, in turn, to a reduction of 1% for the heat exchanger length and a pressure drop increase of 8%. Finally, the increase of nanoparticle radius results in a reduced effective thermal conductivity, while the nanolayer thickness of 2 nm showed an improved heat transfer coefficient by 43% compared to the minimum nanolayer thickness of 0.5 nm.

Epitaxial TiN/MgO multilayers with ultrathin TiN and MgO layers as hyperbolic metamaterials in visible region

Multilayers with metal-dielectric stacks are considered as an effective approach to produce hyperbolic metamaterials (HMMs). However, fabricating ultrathin metal layers with high crystallinity for low-loss HMMs is very challenging. In this work, TiN has been applied as an alternative candidate to the noble metals, and TiN/MgO multilayers with varied numbers of layers and layer thicknesses have been designed. The microstructure study reveals that the thickness of TiN nanolayer is controlled as thin as 2.9 nm, 1.26 nm and 0.9 nm by varying the total number of layers, and the epitaxial quality of the multilayer films is high even with such ultrathin layers. Extraordinary optical properties have been achieved, such as plasmonic resonance in visible range, as well as strong optical anisotropy. In addition, the real part of dielectric permittivity (ε′) shows opposite optical anisotropy in different wavelength ranges, i.e. ε∥′>0, ε⊥′<0 in the range of 350 nm–450 nm, and <0, ε⊥′>0 under higher wavelength, which is a novel property realized in a multilayer system.

Effect of Ge nanolayer stacking order on performance of CZTSSe thin film solar cells

In the present work, the effect of germanium (Ge) stacking order on optoelectronic properties of Cu2ZnSn(S, Se)4 (CZTSSe) thin films are investigated. It was found that the addition of the Ge nanolayer significantly improved the CZTSSe absorber quality, elemental distribution, and reduced secondary phases. The Ge nanolayer deposited on top and bottom of the precursor improved open-circuit voltage (Voc) and short-circuit current density (Jsc) in the device respectively. The device with optimum position and thickness of the Ge nanolayer improved device efficiency from 6.91% to 7.87%. Further, these experimental results suggest that the optimum amount of Ge nanolayer and their position can further improve optoelectronic properties of kesterite CZTSSe absorbers which can be used to achieve high-efficiency in kesterite based solar cells.