Research

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9 pages, 1971 KiB

Open AccessArticle

Temperature Dependence of Dielectric Properties of Ferroelectric Heterostructures with Domain-Provided Negative Capacitance

by Maksim A. Pavlenko, Yuri A. Tikhonov, Anna G. Razumnaya, Valerii M. Vinokur and Igor A. Lukyanchuk

Nanomaterials 2022, 12(1), 75; https://doi.org/10.3390/nano12010075 - 28 Dec 2021

Cited by 8 | Viewed by 1776

Abstract

It is well known that the ferroelectric layers in dielectric/ferroelectric/dielectric heterostructures harbor polarization domains resulting in the negative capacitance crucial for manufacturing energy-efficient field-effect transistors. However, the temperature behavior of the characteristic dielectric properties, and, hence, the corresponding behavior of the negative capacitance, [...] Read more.

It is well known that the ferroelectric layers in dielectric/ferroelectric/dielectric heterostructures harbor polarization domains resulting in the negative capacitance crucial for manufacturing energy-efficient field-effect transistors. However, the temperature behavior of the characteristic dielectric properties, and, hence, the corresponding behavior of the negative capacitance, are still poorly understood, restraining the technological progress thereof. Here we investigate the temperature-dependent properties of domain structures in the SrTiO₃/PbTiO₃/SrTiO₃ heterostructures and demonstrate that the temperature–thickness phase diagram of the system includes the ferroelectric and paraelectric regions, which exhibit different responses to the applied electric field. Using phase-field modeling and analytical calculations we find the temperature dependence of the dielectric constant of ferroelectric layers and identify the regions of the phase diagram wherein the system demonstrates negative capacitance. We further discuss the optimal routes for implementing negative capacitance in energy-efficient ferroelectric field-effect transistors. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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9 pages, 3269 KiB

Open AccessArticle

Numerical Study on Broadband Antireflection of Moth-Eye Nanostructured Polymer Film with Flexible Polyethylene Terephthalate Substrate

by Jun Lan, Yong Yang and Song Hu

Nanomaterials 2021, 11(12), 3313; https://doi.org/10.3390/nano11123313 - 06 Dec 2021

Cited by 4 | Viewed by 2171

Abstract

The application of moth-eye nanostructured polymer film on the flexible polyethylene terephthalate (PET) substrate is an effective way to improve its antireflection (AR) performance. However, many factors affect the AR properties of the moth-eye structure in the actual manufacturing process. Moreover, the antireflection [...] Read more.

The application of moth-eye nanostructured polymer film on the flexible polyethylene terephthalate (PET) substrate is an effective way to improve its antireflection (AR) performance. However, many factors affect the AR properties of the moth-eye structure in the actual manufacturing process. Moreover, the antireflection research based on PET substrate has been relatively lacking compared with the silicon substrate. In this paper, we simulate and analyze the AR performance of the moth-eye nanostructured polymer film on PET substrate by using the finite-difference time-domain method within the wavelength range of 400–1100 nm. Simulation results show that the parabola-shaped moth-eye structure (PSMS) can suppress the Fresnel reflection significantly. Moreover, the height and filling ratios are the dominant factors that affect the AR performance of PSMS. Additionally, the base diameter, residual layer thickness, and the refractive index of PSMS polymer film also affect the reflectivity of PET slightly. As a result, an optimal PSMS with base diameter of 400 nm, height of 300 nm, and the hexagonal close-packed arrangement is appropriate, and the solar-weighted reflectivity of PET can be suppressed to 0.21%, which shows a prominent advantage over the bare PET (≈6%). Therefore, this research has promising potential for improving the optical performance of optoelectronic devices by using nanostructured polymer materials. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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29 pages, 5883 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Quantitative Assessment of Chirality of Protein Secondary Structures and Phenylalanine Peptide Nanotubes

by Alla Sidorova, Vladimir Bystrov, Aleksey Lutsenko, Denis Shpigun, Ekaterina Belova and Ilya Likhachev

Nanomaterials 2021, 11(12), 3299; https://doi.org/10.3390/nano11123299 - 05 Dec 2021

Cited by 11 | Viewed by 1947

Abstract

In this study we consider the features of spatial-structure formation in proteins and their application in bioengineering. Methods for the quantitative assessment of the chirality of regular helical and irregular structures of proteins are presented. The features of self-assembly of phenylalanine (F) into [...] Read more.

In this study we consider the features of spatial-structure formation in proteins and their application in bioengineering. Methods for the quantitative assessment of the chirality of regular helical and irregular structures of proteins are presented. The features of self-assembly of phenylalanine (F) into peptide nanotubes (PNT), which form helices of different chirality, are also analyzed. A method is proposed for calculating the magnitude and sign of the chirality of helix-like peptide nanotubes using a sequence of vectors for the dipole moments of individual peptides. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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19 pages, 23637 KiB

Open AccessArticle

Iron in Hydroxyapatite: Interstitial or Substitution Sites?

by Leon Avakyan, Ekaterina Paramonova, Vladimir Bystrov, José Coutinho, Sandrine Gomes and Guillaume Renaudin

Nanomaterials 2021, 11(11), 2978; https://doi.org/10.3390/nano11112978 - 05 Nov 2021

Cited by 13 | Viewed by 2100

Abstract

Iron-doped hydroxyapatite (Fe-HAp) is regarded as a promising magnetic material with innate biocompatibility. Despite the many studies reported in the literature, a detailed theoretical description of Fe inclusions is still missing. There is even no consensual view on what kind of Fe defects [...] Read more.

Iron-doped hydroxyapatite (Fe-HAp) is regarded as a promising magnetic material with innate biocompatibility. Despite the many studies reported in the literature, a detailed theoretical description of Fe inclusions is still missing. There is even no consensual view on what kind of Fe defects take place in Fe-HAp—iron interstitial or calcium substitutions? In order to address these questions, we employ modern first-principles methodologies, including hybrid density functional theory, to find the geometry, electronic, magnetic and thermodynamic properties of iron impurities in Fe-HAp. We consider a total of 26 defect configurations, including substitutional (phosphorus and calcium sites) and interstitial defects. Formation energies are estimated considering the boundaries of chemical potentials in stable hydroxyapatite. We show that the most probable defect configurations are: Fe

^{3 +}

and Fe

^{2 +}

substitutions of Ca(I) and Ca(II) sites under Ca-poor conditions. Conversely, Fe interstitials near the edge of the hydroxyl channel are favored in Ca-rich material. Substitutional Fe on the P site is also a probable defect, and unlike the other forms of Fe, it adopts a low-spin state. The analysis of Fe K-XANES spectra available in the literature shows that Fe-HAp usually contains iron in different configurations. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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12 pages, 4423 KiB

Open AccessArticle

Dual-Spectral Plasmon-Induced Transparent Terahertz Metamaterial with Independently Tunable Amplitude and Frequency

by Tong Wu, Guan Wang, Yang Jia, Yabin Shao, Chen Chen, Jing Han, Yang Gao and Yachen Gao

Nanomaterials 2021, 11(11), 2876; https://doi.org/10.3390/nano11112876 - 28 Oct 2021

Cited by 8 | Viewed by 1529

Abstract

A bifunctional tunable metamaterial composed of pattern metal structure, graphene, and strontium titanate (STO) film is proposed and studied numerically and theoretically. The dual plasmon-induced transparency (PIT) window is obtained by coupling the bright state cut wire (CW) and two pairs of dark [...] Read more.

A bifunctional tunable metamaterial composed of pattern metal structure, graphene, and strontium titanate (STO) film is proposed and studied numerically and theoretically. The dual plasmon-induced transparency (PIT) window is obtained by coupling the bright state cut wire (CW) and two pairs of dark state dual symmetric semiring resonators (DSSRs) with different parameters. Correspondingly, slow light effect can also be realized. When shifting independently, the Fermi level of the graphene strips, the amplitudes of the two PIT transparency windows and slow light effect can be tuned, respectively. In addition, when independently tuning the temperature of the metamaterial, the frequency of the dual PIT windows and slow light effect can be tuned. The physical mechanism of the dual-PIT was analyzed theoretically by using a three-harmonic oscillator model. The results show that the regulation function of the PIT peak results from the change of the oscillation damping at the dark state DSSRs by tuning conductivity of graphene. Our design presents a new structure to realize the bifunctional optical switch and slow light. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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9 pages, 2098 KiB

Open AccessArticle

Low Resistance Asymmetric III-Nitride Tunnel Junctions Designed by Machine Learning

by Rongyu Lin, Peng Han, Yue Wang, Ronghui Lin, Yi Lu, Zhiyuan Liu, Xiangliang Zhang and Xiaohang Li

Nanomaterials 2021, 11(10), 2466; https://doi.org/10.3390/nano11102466 - 22 Sep 2021

Cited by 4 | Viewed by 2304

Abstract

The tunnel junction (TJ) is a crucial structure for numerous III-nitride devices. A fundamental challenge for TJ design is to minimize the TJ resistance at high current densities. In this work, we propose the asymmetric p-AlGaN/i-InGaN/n-AlGaN TJ structure for the first time. P-AlGaN/i-InGaN/n-AlGaN [...] Read more.

The tunnel junction (TJ) is a crucial structure for numerous III-nitride devices. A fundamental challenge for TJ design is to minimize the TJ resistance at high current densities. In this work, we propose the asymmetric p-AlGaN/i-InGaN/n-AlGaN TJ structure for the first time. P-AlGaN/i-InGaN/n-AlGaN TJs were simulated with different Al or In compositions and different InGaN layer thicknesses using TCAD (Technology Computer-Aided Design) software. Trained by these data, we constructed a highly efficient model for TJ resistance prediction using machine learning. The model constructs a tool for real-time prediction of the TJ resistance, and the resistances for 22,254 different TJ structures were predicted. Based on our TJ predictions, the asymmetric TJ structure (p-Al_0.7Ga_0.3N/i-In_0.2Ga_0.8N/n-Al_0.3Ga_0.7N) with higher Al composition in p-layer has seven times lower TJ resistance compared to the prevailing symmetric p-Al_0.3Ga_0.7N/i-In_0.2Ga_0.8N/n-Al_0.3Ga_0.7N TJ. This study paves a new way in III-nitride TJ design for optical and electronic devices. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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12 pages, 3143 KiB

Open AccessArticle

Modeling of Self-Assembled Peptide Nanotubes and Determination of Their Chirality Sign Based on Dipole Moment Calculations

by Vladimir Bystrov, Alla Sidorova, Aleksey Lutsenko, Denis Shpigun, Ekaterina Malyshko, Alla Nuraeva, Pavel Zelenovskiy, Svitlana Kopyl and Andrei Kholkin

Nanomaterials 2021, 11(9), 2415; https://doi.org/10.3390/nano11092415 - 16 Sep 2021

Cited by 11 | Viewed by 2038

Abstract

The chirality quantification is of great importance in structural biology, where the differences in proteins twisting can provide essentially different physiological effects. However, this aspect of the chirality is still poorly studied for helix-like supramolecular structures. In this work, a method for chirality [...] Read more.

The chirality quantification is of great importance in structural biology, where the differences in proteins twisting can provide essentially different physiological effects. However, this aspect of the chirality is still poorly studied for helix-like supramolecular structures. In this work, a method for chirality quantification based on the calculation of scalar triple products of dipole moments is suggested. As a model structure, self-assembled nanotubes of diphenylalanine (FF) made of L- and D-enantiomers were considered. The dipole moments of FF molecules were calculated using semi-empirical quantum-chemical method PM3 and the Amber force field method. The obtained results do not depend on the used simulation and calculation method, and show that the D-FF nanotubes are twisted tighter than L-FF. Moreover, the type of chirality of the helix-like nanotube is opposite to that of the initial individual molecule that is in line with the chirality alternation rule general for different levels of hierarchical organization of molecular systems. The proposed method can be applied to study other helix-like supramolecular structures. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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21 pages, 6539 KiB

Open AccessArticle

Investigation on Plastic Flow Behaviors of FCC Polycrystalline Aluminum under Pre-Cyclic Tension-Compression Loading: Experiments and Crystal Plasticity Modeling

by Damin Lu, Keshi Zhang and Guijuan Hu

Nanomaterials 2021, 11(9), 2397; https://doi.org/10.3390/nano11092397 - 14 Sep 2021

Viewed by 2264

Abstract

The plastic flow behaviors of FCC polycrystalline aluminum after pre-cyclic tension-compression deformation are mainly investigated in tension–torsion stress space by the physically based crystal plasticity model introducing a back-stress. A global finite element model (GFEM) constructed of sufficient grains was established to simulate [...] Read more.

The plastic flow behaviors of FCC polycrystalline aluminum after pre-cyclic tension-compression deformation are mainly investigated in tension–torsion stress space by the physically based crystal plasticity model introducing a back-stress. A global finite element model (GFEM) constructed of sufficient grains was established to simulate the same-size thin-walled tube specimen constrained and loaded as the experiments of yield surfaces. The computational results showed that the shape of subsequent yield surfaces and the plastic flow directions directly depended on the given offset strain levels and the applied re-loading paths under different pre-cyclic deformations. The angle deviation between the plastic flow direction and the theoretical orthogonal direction further indicated that there was a large difference between them in the inverse pre-straining direction, but the difference was negligible in the pre-straining direction. From the influence of the anisotropic evolution of the subsequent yield surfaces on plastic flow, we found that the plastic normality rule followed the smooth yield locus; conversely, the significant non-associated flow was attributed to the distorted yield locus. Furthermore, it was also demonstrated that the anisotropic evolution and the plastic flow trend of the subsequent yield surfaces obtained by experiments can be better reproduced by the crystal plasticity model. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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11 pages, 3396 KiB

Open AccessArticle

Tunable Transmissive Terahertz Linear Polarizer for Arbitrary Linear Incidence Based on Low-Dimensional Metamaterials

by Zhenyu Yang, Dahai Yu, Huiping Zhang, Anqi Yu, Xuguang Guo, Yuxiang Ren, Xiaofei Zang, Alexei V. Balakin and Alexander P. Shkurinov

Nanomaterials 2021, 11(7), 1851; https://doi.org/10.3390/nano11071851 - 18 Jul 2021

Cited by 4 | Viewed by 2133

Abstract

In this work, we propose a structure consisting of three metamaterial layers and a metallic grating layer to rotate the polarization of arbitrary linearly polarized incidence to the y-direction with high transmissivity by electrically tuning these metamaterials. The transfer matrix method together with [...] Read more.

In this work, we propose a structure consisting of three metamaterial layers and a metallic grating layer to rotate the polarization of arbitrary linearly polarized incidence to the y-direction with high transmissivity by electrically tuning these metamaterials. The transfer matrix method together with a harmonic oscillator model is adopted to theoretically study the proposed structure. Numerical simulation based on the finite difference time-domain method is performed assuming that the metamaterial layers are constituted by graphene ribbon arrays. The calculation and simulation results show that the Drude absorption is responsible for the polarization rotation. Fermi level and scattering rate of graphene are important for the transmissivity. For a polarization rotation of around 90°, the thickness of either the upper or lower dielectric separations influences the transmission window. For a polarization rotation of around 45° and 135°, the lower dielectric separations decide the frequency of the transmission window, while the upper dielectric separations just slightly influence the transmissivity. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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12 pages, 1527 KiB

Open AccessArticle

Magnetic Simulations of Core–Shell Ferromagnetic Bi-Magnetic Nanoparticles: The Influence of Antiferromagnetic Interfacial Exchange

by Juan A. Ramos-Guivar, Carlo A. Tamanaha-Vegas, Fred Jochen Litterst and Edson C. Passamani

Nanomaterials 2021, 11(6), 1381; https://doi.org/10.3390/nano11061381 - 24 May 2021

Cited by 9 | Viewed by 2598

Abstract

Magnetic properties of ferromagnetic nanostructures were studied by atomistic simulations following Monte Carlo and Landau–Lifshitz–Gilbert approaches. First, we investigated the influence of particle size and shape on the temperature dependence of magnetization for single cobalt and gadolinium nanoparticles and also in bi-magnetic Co@Gd [...] Read more.

Magnetic properties of ferromagnetic nanostructures were studied by atomistic simulations following Monte Carlo and Landau–Lifshitz–Gilbert approaches. First, we investigated the influence of particle size and shape on the temperature dependence of magnetization for single cobalt and gadolinium nanoparticles and also in bi-magnetic Co@Gd core–shell nanoparticles with different sizes. The Landau–Lifshitz–Gilbert approach was subsequently applied for inspecting the magnetic hysteresis behavior of 2 and 4 nm Co@Gd core–shell nanoparticles with negative, positive, and zero values of interfacial magnetic exchange. We were able to demonstrate the influence of finite-size effect on the dependence of the Curie temperature of Co and Gd nanoparticles. In the Co@Gd core–shell framework, it was possible to handle the critical temperature of the hybrid system by adjusting the Co core size. In addition, we found an improvement in the coercive field values for a negative interfacial exchange energy and for a different core size, suggesting an exchange spring behavior, while positive and zero values of interfacial exchange constant showed no strong influence on the hysteresis behavior. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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12 pages, 4807 KiB

Open AccessArticle

The Adsorption and Sensing Performances of Ir-modified MoS₂ Monolayer toward SF₆ Decomposition Products: A DFT Study

by Hongcheng Liu, Feipeng Wang, Kelin Hu, Tao Li, Yuyang Yan and Jian Li

Nanomaterials 2021, 11(1), 100; https://doi.org/10.3390/nano11010100 - 04 Jan 2021

Cited by 35 | Viewed by 2917

Abstract

In this paper, the Ir-modified MoS₂ monolayer is suggested as a novel gas sensor alternative for detecting the characteristic decomposition products of SF₆, including H₂S, SO₂, and SOF₂. The corresponding adsorption properties and sensing [...] Read more.

In this paper, the Ir-modified MoS₂ monolayer is suggested as a novel gas sensor alternative for detecting the characteristic decomposition products of SF₆, including H₂S, SO₂, and SOF₂. The corresponding adsorption properties and sensing behaviors were systematically studied using the density functional theory (DFT) method. The theoretical calculation indicates that Ir modification can enhance the surface activity and improve the conductivity of the intrinsic MoS₂. The physical structure formation, the density of states (DOS), deformation charge density (DCD), molecular orbital theory analysis, and work function (WF) were used to reveal the gas adsorption and sensing mechanism. These analyses demonstrated that the Ir-modified MoS₂ monolayer used as sensing material displays high sensitivity to the target gases, especially for H₂S gas. The gas sensitivity order and the recovery time of the sensing material to decomposition products were reasonably predicted. This contribution indicates the theoretical possibility of developing Ir-modified MoS₂ as a gas sensor to detect characteristic decomposition gases of SF₆. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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21 pages, 6292 KiB

Open AccessArticle

Structures and Properties of the Self-Assembling Diphenylalanine Peptide Nanotubes Containing Water Molecules: Modeling and Data Analysis

by Vladimir Bystrov, Jose Coutinho, Pavel Zelenovskiy, Alla Nuraeva, Svitlana Kopyl, Olga Zhulyabina and Vsevolod Tverdislov

Nanomaterials 2020, 10(10), 1999; https://doi.org/10.3390/nano10101999 - 10 Oct 2020

Cited by 19 | Viewed by 2544

Abstract

The structures and properties of the diphenylalanine (FF) peptide nanotubes (PNTs), both L-chiral and D-chiral (L-FF and D-FF) and empty and filled with water/ice clusters, are presented and analyzed. DFT (VASP) and semi-empirical calculations (HyperChem) to study these structural and physical properties of [...] Read more.

The structures and properties of the diphenylalanine (FF) peptide nanotubes (PNTs), both L-chiral and D-chiral (L-FF and D-FF) and empty and filled with water/ice clusters, are presented and analyzed. DFT (VASP) and semi-empirical calculations (HyperChem) to study these structural and physical properties of PNTs (including ferroelectric) were used. The results obtained show that after optimization the dipole moment and polarization of both chiral type L-FF and D-FF PNT and embedded water/ice cluster are enhanced; the water/ice cluster acquire the helix-like structure similar as L-FF and D-FF PNT. Ferroelectric properties of tubular water/ice helix-like cluster, obtained after optimization inside L-FF and D-FF PNT, as well of the total L-FF and D-FF PNT with embedded water/ice cluster, are discussed. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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22 pages, 3654 KiB

Open AccessArticle

Tuning the Magnetic Moment of Small Late 3d-Transition-Metal Oxide Clusters by Selectively Mixing the Transition-Metal Constituents

by Rodrigo H. Aguilera-del-Toro, María B. Torres, Faustino Aguilera-Granja and Andrés Vega

Nanomaterials 2020, 10(9), 1814; https://doi.org/10.3390/nano10091814 - 11 Sep 2020

Cited by 2 | Viewed by 1913

Abstract

Transition-metal oxide nanoparticles are relevant for many applications in different areas where their superparamagnetic behavior and low blocking temperature are required. However, they have low magnetic moments, which does not favor their being turned into active actuators. Here, we report a systematical study, [...] Read more.

Transition-metal oxide nanoparticles are relevant for many applications in different areas where their superparamagnetic behavior and low blocking temperature are required. However, they have low magnetic moments, which does not favor their being turned into active actuators. Here, we report a systematical study, within the framework of the density functional theory, of the possibility of promoting a high-spin state in small late-transition-metal oxide nanoparticles through alloying. We investigated all possible nanoalloys A

_{n - x}

B

_{x}

O

_{m}

(A, B = Fe, Co, Ni; n = 2, 3, 4;

0 \leq x \leq n

) with different oxidation rates, m, up to saturation. We found that the higher the concentration of Fe, the higher the absolute stability of the oxidized nanoalloy, while the higher the Ni content, the less prone to oxidation. We demonstrate that combining the stronger tendency of Co and Ni toward parallel couplings with the larger spin polarization of Fe is particularly beneficial for certain nanoalloys in order to achieve a high total magnetic moment, and its robustness against oxidation. In particular, at high oxidation rates we found that certain FeCo oxidized nanoalloys outperform both their pure counterparts, and that alloying even promotes the reentrance of magnetism in certain cases at a critical oxygen rate, close to saturation, at which the pure oxidized counterparts exhibit quenched magnetic moments. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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12 pages, 2744 KiB

Open AccessArticle

Off-Resonant Absorption Enhancement in Single Nanowires via Graded Dual-Shell Design

by Wenfu Liu, Xiaolei Guo, Shule Xing, Haizi Yao, Yinling Wang, Liuyang Bai, Qi Wang, Liang Zhang, Dachuan Wu, Yuxiao Zhang, Xiao Wang and Yasha Yi

Nanomaterials 2020, 10(9), 1740; https://doi.org/10.3390/nano10091740 - 02 Sep 2020

Cited by 6 | Viewed by 2137

Abstract

Single nanowires (NWs) are of great importance for optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that, [...] Read more.

Single nanowires (NWs) are of great importance for optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that, with appropriate thickness and refractive index of the inner shell, the DSNW exhibits significantly enhanced light trapping compared with the bare NW (BNW) and the NW only coated with the outer shell (OSNW) and the inner shell (ISNW), which can be attributed to the optimal off-resonant absorption mode profiles due to the improved coupling between the reemitted light of the transition modes of the leak mode resonances of the Si core and the nanofocusing light from the dual shells with the graded refractive index. We found that the light absorption can be engineered via tuning the thickness and the refractive index of the inner shell, the photocurrent density is significantly enhanced by 134% (56%, 12%) in comparison with that of the BNW (OSNW, ISNW). This work advances our understanding of how to improve off-resonant absorption by applying graded dual-shell design and provides a new choice for designing high-efficiency single NW photovoltaic devices. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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Review

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30 pages, 5667 KiB

Open AccessReview

Simulation and Computer Study of Structures and Physical Properties of Hydroxyapatite with Various Defects

by Vladimir Bystrov, Ekaterina Paramonova, Leon Avakyan, José Coutinho and Natalia Bulina

Nanomaterials 2021, 11(10), 2752; https://doi.org/10.3390/nano11102752 - 17 Oct 2021

Cited by 23 | Viewed by 3039

Abstract

Simulation and computer studies of the structural and physical properties of hydroxyapatite (HAP) with different defects are presented in this review. HAP is a well-known material that is actively used in various fields of medicine, nanotechnology, and photocatalytic processes. However, all HAP samples [...] Read more.

Simulation and computer studies of the structural and physical properties of hydroxyapatite (HAP) with different defects are presented in this review. HAP is a well-known material that is actively used in various fields of medicine, nanotechnology, and photocatalytic processes. However, all HAP samples have various defects and are still insufficiently studied. First of all, oxygen and OH group vacancies are important defects in HAP, which significantly affect its properties. The properties of HAP are also influenced by various substitutions of atoms in the HAP crystal lattice. The results of calculations by modern density functional theory methods of HAP structures with these different defects, primarily with oxygen and hydroxyl vacancies are analyzed in this review. The results obtained show that during the structural optimization of HAP with various defects, both the parameters of the crystallographic cells of the HAP change and the entire band structure of the HAP changes (changes in the band gap). This affects the electronic, optical, and elastic properties of HAP. The review considers the results of modeling and calculation of HAP containing various defects, the applied calculation methods, and the features of the effect of these defects on the properties of HAP, which is important for many practical applications. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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13 pages, 3357 KiB

Open AccessReview

Polarization Switching in 2D Nanoscale Ferroelectrics: Computer Simulation and Experimental Data Analysis

by Ekaterina Paramonova, Vladimir Bystrov, Xiangjian Meng, Hong Shen, Jianlu Wang and Vladimir Fridkin

Nanomaterials 2020, 10(9), 1841; https://doi.org/10.3390/nano10091841 - 15 Sep 2020

Cited by 6 | Viewed by 2756

Abstract

The polarization switching kinetics of nanosized ferroelectric crystals and the transition between homogeneous and domain switching in nanoscale ferroelectric films are considered. Homogeneous switching according to the Ginzburg-Landau-Devonshire (LGD) theory is possible only in two-dimensional (2D) ferroelectrics. The main condition for the applicability [...] Read more.

The polarization switching kinetics of nanosized ferroelectric crystals and the transition between homogeneous and domain switching in nanoscale ferroelectric films are considered. Homogeneous switching according to the Ginzburg-Landau-Devonshire (LGD) theory is possible only in two-dimensional (2D) ferroelectrics. The main condition for the applicability of the LGD theory in such systems is its homogeneity along the polarization switching direction. A review is given of the experimental results for two-dimensional (2D) films of a ferroelectric polymer, nanosized barium titanate nanofilms, and hafnium oxide-based films. For ultrathin 2D ferroelectric polymer films, the results are confirmed by first-principle calculations. Fitting of the transition region from homogeneous to domain switching by sigmoidal Boltzmann functions was carried out. Boltzmann function fitting data enabled us to correctly estimate the region sizes of the homogeneous switching in which the LGD theory is valid. These sizes contain several lattice constants or monolayers of a nanosized ferroelectrics. Full article

(This article belongs to the Special Issue Simulation and Modeling of Nanomaterials)

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