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Estudo da aplicação de hidróxidos duplos lamelares na remoção e liberação lenta de pesticidas; Study of aplication of Layered Double Hydroxides in removal and slow release of pesticides

Cardoso, Lucelena Patricio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/09/2006 PT
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A extensa utilização de pesticidas na agricultura moderna tem contribuído para um aumento na contaminação do meio ambiente. Os Hidróxidos Duplos Lamelares (HDLs) ou argilas aniônicas, apresentam uma estrutura lamelar na qual uma variedade de ânions podem ser intercalados entre as lamelas através de interações eletrostáticas. Estes materiais lamelares podem ser utilizados em processos de adsorção/sorção e como suporte para a liberação lenta de compostos químicos. Assim, os principais objetivos deste trabalho foram: o estudo da sorção de ânions orgânicos de herbicidas ácidos 2,4-D, MCPA e Picloram utilizados na agricultura nacional, pela regeneração de HDLs de Mg-Al-CO3 calcinado e por troca aniônica em HDLs de Mg-Al-Cl. Para isso foram investigados a cinética do processo de sorção, além da determinação das isotermas em dois valores diferentes de pH. Assim, estes herbicidas foram intercalados em HDLs de Mg-Al, utilizando dois métodos de síntese indireta: regeneração do material calcinado e troca aniônica em solução, além do método de síntese direta por coprecipitação, sendo os materiais devidamente caracterizados. Todos os materiais obtidos, intercalados com cada um dos herbicidas, foram utilizados para o estudo da cinética de liberação dos mesmos em água. Os materiais obtidos por regeneração contendo cada um dos três herbicidas foram utilizados também no estudo da lixiviação em colunas de solo e no estudo de bio-ensaio com plantas...

Nanocompósitos orgânico-inorgânicos de polímero biodegradável e estruturas lamelares; Organic-inorganic nanocomposites based on biodegradable polymer and layered structures

Perotti, Gustavo Frigi
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/05/2013 PT
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O presente trabalho de Doutorado tem como objetivo investigar a influência de materiais lamelares prístinos e modificados e a influência de diferentes rotas sintéticas nas propriedades físico-químicas do amido termoplástico, utilizando glicerol como plastificante. Para tanto, empregou-se para a produção dos materiais híbridos uma argila sintética da família das hectoritas (Laponita RD) na forma prístina e também modificada com íons berberine e carnosina, além de um hidróxido duplo lamelar (HDL) constituído por íons Zn2+/Al3+ intercalado com carboximetilcelulose (CMC). O amido e o material lamelar foram combinados, utilizando as metodologias de casting e extrusão, nas concentrações de 2,5 e 5,0 % (m/m) de argila ou HDL com relação ao polissacarídeo. Já quantidade de plastificante empregada foi variável, dependendo da rota de preparação empregada, sendo de aproximadamente 20 % (m/m) via casting e 30 % (m/m) via extrusão com relação ao amido. Conforme mostram os difratogramas de raios X dos filmes obtidos pelo método casting, todos os filmes contendo argila em sua composição exibem um sinal largo de difração na região de baixo ângulo de 2θ, embora pouco intenso, indica a existência de certa quantidade de nanocompósito do tipo intercalado. Já para os materiais obtidos via extrusão...

Síntese e pilarização de ácidos silícicos lamelares; Syntheses and pilarization of layered silicic acids

Cléo Thomas Gabriel Vilela Menegaz Teixeira Pires
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 03/08/2010 PT
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Nos últimos anos tem sido observado um crescente interesse na obtenção de materiais lamelares modificados, devido as suas propriedades únicas e consequentes aplicações científicas e tecnológicas possíveis. Ácidos silícicos como a magadeíta, a kaneíta e a ilerita são compostos extremamente versáteis, podendo-se variar os seus espaçamentos basais a partir de intercalações com grupos de cadeia carbônica longa ou troca iônica. Outras alterações possíveis são as substituições isomórficas do silício por átomos tri- ou tetravalentes como alumínio e titânio respectivamente, modificando as propriedades químicas da lamela. Neste trabalho os ácidos silícicos lamelares magadeíta, ilerita e kaneíta foram sintetizados pelo método hidrotérmico, contendo também átomos de Al e Ti inseridos na estrutura. Em todos os casos observou-se que conforme aumenta-se a quantidade de metal adicionado ou o tempo de tratamento hidrotérmico, ocorrem transições de fase que seguem a ordem: amorfa, fase lamelar de interesse, cristobalita e tridimita, bem como suas misturas em situações intermediárias. Diferentes métodos de pilarização com TiO2 foram exaustivamente testados, variando-se uma série de parâmetros. O método que se mostrou mais eficiente consistiu na utilização de CTAB e TBAOH como agentes espaçadores sob refluxo a 353 K...

Síntese e caracterização de nanocompósitos de poli(estireno) com materiais lamelares - hidróxido duplo lamelar e hidroxissal lamelar - via polimerização in situ; Synthesis and characterization of poly(styrene) layered materials nanocomposites - layered double hydroxide and layered hydroxide salt - via in situ polimerization

Rodrigo Botan
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 29/01/2014 PT
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Ao longo da última década, nanocompósitos poliméricos vêm atraindo grande atenção da comunidade científica e industrial. Este fato se deve à notável melhora em inúmeras propriedades destes novos materiais, proporcionado pelo uso de uma pequena quantidade de nanoreforços. Entre as propriedades melhoradas é possível citar com maior destaque as propriedades mecânicas e térmicas. Buscando alcançar melhores propriedades para o poli(estireno) (PS), o objetivo deste trabalho foi o de sintetizar nanocompósitos in situ de PS com hidróxidos duplos lamelares (HDLs) e hidroxissal lamelar (HSL). Para isto, foram sintetizados dois tipos de HDLs e um tipo de HSL, os HDLs foram modificados com ácido láurico, ácido palmítico e uma mistura destes dois ácidos e o HSL foi modificado com ácido palmítico. Os HDLs e HSL sintetizados foram caracterizados por difração de raios x (DRX), microscopia eletrônica de varredura (MEV), espectroscopia no infravermelho por transformada de Fourier (FTIR) e análise termogravimétrica (TGA). Os nanocompósitos foram sintetizados in situ por polimerização em massa e foram caracterizados por DRX, FTIR, TGA, calorimetria exploratória diferencial (DSC), microscopia eletrônica de transmissão (MET)...

Materiales laminares pilareados: preparación y propiedades

Pergher,Sibele B. C.; Corma,Avelino; Fornes,Vicente
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/1999 ES
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The structure of several types of layered materials will be described. These include clays, layered double hydroxides, group IV metal phosphates and other layered materials. The preparation of the pillared materials and pillaring agents will be presented along with a description of the properties and applications of the products.

Vertically stacked multi-heterostructures of layered materials for logic transistors and complementary inverters

Yu, Woo Jong; Li, Zheng; Zhou, Hailong; Chen, Yu; Wang, Yang; Huang, Yu; Duan, Xiangfeng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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The layered materials such as graphene have attracted considerable interest for future electronics. Here we report the vertical integration of multi-heterostructures of layered materials to enable high current density vertical field-effect transistors (VFETs). An n-channel VFET is created by sandwiching few-layer molybdenum disulfide (MoS2) as the semiconducting channel between a monolayer graphene and a metal thin film. The VFETs exhibit a room temperature on-off ratio >103, while at same time deliver a high current density up to 5,000 A/cm2, sufficient for high performance logic applications. This study offers a general strategy for the vertical integration of various layered materials to obtain both p- and n-channel transistors for complementary logic functions. A complementary inverter with larger than unit voltage gain is demonstrated by vertically stacking the layered materials of graphene, Bi2Sr2Co2O8 (p-channel), graphene, MoS2 (n-channel), and metal thin film in sequence. The ability to simultaneously achieve high on-off ratio, high current density, and logic integration in the vertically stacked multi-heterostructures can open up a new dimension for future electronics to enable three-dimensional integration.

Highly efficient gate-tunable photocurrent generation in vertical heterostructures of layered materials

Yu, Woo Jong; Liu, Yuan; Zhou, Hailong; Yin, Anxiang; Li, Zheng; Huang, Yu; Duan, Xiangfeng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Layered materials of graphene and MoS2, for example, have recently emerged as an exciting material system for future electronics and optoelectronics. Vertical integration of layered materials can enable the design of novel electronic and photonic devices. Here, we report highly efficient photocurrent generation from vertical heterostructures of layered materials. We show that vertically stacked graphene–MoS2–graphene and graphene–MoS2–metal junctions can be created with a broad junction area for efficient photon harvesting. The weak electrostatic screening effect of graphene allows the integration of single or dual gates under and/or above the vertical heterostructure to tune the band slope and photocurrent generation. We demonstrate that the amplitude and polarity of the photocurrent in the gated vertical heterostructures can be readily modulated by the electric field of an external gate to achieve a maximum external quantum efficiency of 55% and internal quantum efficiency up to 85%. Our study establishes a method to control photocarrier generation, separation and transport processes using an external electric field.

A rational design of cosolvent exfoliation of layered materials by directly probing liquid–solid interaction

Halim, Udayabagya; Zheng, Chu Ran; Chen, Yu; Lin, Zhaoyang; Jiang, Shan; Cheng, Rui; Huang, Yu; Duan, Xiangfeng
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Exfoliation of layered materials such as graphite and transition metal dichalcogenides into mono- or few-layers is of significant interest for both the fundamental studies and potential applications. Here we report a systematic investigation of the fundamental factors governing the liquid exfoliation process and the rational design of a cosolvent approach for the exfoliation of layered materials. We show that Young’s equation can be used to predict the optimal cosolvent concentration for the effective exfoliation of graphite and molybdenum disulphide in water mixtures with methanol, ethanol, isopropanol and t-butyl alcohol. Moreover, we find that the cosolvent molecular size has an important role in the exfoliation yield, attributed to the larger steric repulsion provided by the larger cosolvent molecules. Our study provides critical insight into the exfoliation of layered materials, and defines a rational strategy for the design of an environmentally friendly pathway to the high yield exfoliation of layered materials.

Ab-initio study of cathode materials for lithium batteries

Reed, John Stuart, 1968-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 311 p.; 13157589 bytes; 23099591 bytes; application/pdf; application/pdf
ENG
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Using first principles calculations the effect of electronic structure on the stability of positive electrode materials for lithium rechargeable batteries is investigated. The investigation focuses upon lithiated α-NaFeO₂ type 3d transition metal oxide structures. It is found that the ligand field stabilization energy (LFSE) is of particular importance in stabilizing the α-NaFeO₂ type layered structure with general formula Li[sub]x MO₂ (0 <[or equal to] x <[or equal to] 1 and M = Co, Fe, Mn, Ni, ...) at partial lithiation. The key quantity is found to be the difference in LFSE between the 3d metal ion in tetrahedral coordination and octahedral coordination in the cubic close packed (CCP) oxygen framework. If the change in LFSE is small, then the migration of 3d transition metal ions between tetrahedral and octahedral sites generally involves less variation in energy, and hence is easier. This facilitates diffusion of the 3d transition metal ions through the CCP oxygen framework and tends to destabilize the layered structure at partial lithiation. Layered lithium manganese oxide is given particular attention as a material that rapidly transforms to a spinel-like structure with electrochemical cycling. Focus is also placed upon layered lithium cobalt oxide as a material that remains stable in the layered structure with electrochemical cycling. The differing stability of these compounds in the layered structure is explained in terms of LFSE. Spin pairing energy (SPE) is also found to make an important contribution to the energetics of low spin transition metal oxides like lithium cobalt oxide. The influence of SPE on structural stability...

Designing new electrode materials for energy devices by integrating ab initio computations with experiments

Kang, Kisuk
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 161 p.
ENG
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Utilization of Ni2+/Ni4+ double redox couple in electrochemical reactions has been tested as a way to gauge useful properties such as high capacity in electrode materials. The feasibility of a Ni2+/Ni4+ active redox couple is confirmed in a new layered electrode material, Lio.gNi045Ti5502. First principles calculations combined with experiments show that the degree of cation disordering in the material arising from both synthesis conditions and the electrochemical reaction is critical in performance of this material as the electrode. In an attempt to fully utilize Ni2+/Ni4+ double redox couple, Li2NiO2 in the Immm structure was successfully synthesized and its electrochemical behavior upon delithiation was evaluated. The material shows a high specific charge capacity of about 320 mAh/g and discharge capacity of about 240 mAh/g at the first cycle. The stability of Li2NiO2 in the Immm structure is attributed to the more favorable Li arrangement possible as compared to a Li2NiO2 structure with octahedral Ni. The electrochemical data, first principles calculation and EXAFS analysis all indicate that the orthorhombic Immm structure is rather prone to phase transformation to a close-packed layered structure during the electrochemical cycling.; (cont.) The possibility of stabilizing the orthorhombic Immm structure during the electrochemical cycling by partial substitution of Ni is also evaluated. First principles computations of some chemically substituted materials identified Pt substitution as a way of stabilizing the Li2(Ni...

Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials – A general bond polarizability model

Luo, Xin; Lu, Xin; Cong, Chunxiao; Yu, Ting; Xiong, Qihua; Ying Quek, Su
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 15/10/2015 EN
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2D layered materials have recently attracted tremendous interest due to their fascinating properties and potential applications. The interlayer interactions are much weaker than the intralayer bonds, allowing the as-synthesized materials to exhibit different stacking sequences, leading to different physical properties. Here, we show that regardless of the space group of the 2D materials, the Raman frequencies of the interlayer shear modes observed under the typical configuration blue shift for AB stacked materials, and red shift for ABC stacked materials, as the number of layers increases. Our predictions are made using an intuitive bond polarizability model which shows that stacking sequence plays a key role in determining which interlayer shear modes lead to the largest change in polarizability (Raman intensity); the modes with the largest Raman intensity determining the frequency trends. We present direct evidence for these conclusions by studying the Raman modes in few layer graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles calculations and Raman spectroscopy. This study sheds light on the influence of stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D layered materials in general...

Wannier Function Approach to Realistic Coulomb Interactions in Layered Materials and Heterostructures

Rösner, M.; Şaşıoğlu, E.; Friedrich, C.; Blügel, S.; Wehling, T. O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/04/2015
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We introduce an approach to derive realistic Coulomb interaction terms in free standing layered materials and vertical heterostructures from ab-initio modelling of the corresponding bulk materials. To this end, we establish a combination of calculations within the framework of the constrained random phase approximation, Wannier function representation of Coulomb matrix elements within some low energy Hilbert space and continuum medium electrostatics, which we call Wannier function continuum electrostatics (WFCE). For monolayer and bilayer graphene we reproduce full ab-initio calculations of the Coulomb matrix elements within an accuracy of $0.2$eV or better. We show that realistic Coulomb interactions in bilayer graphene can be manipulated on the eV scale by different dielectric and metallic environments. A comparison to electronic phase diagrams derived in [M. M. Scherer et al., Phys. Rev. B 85, 235408 (2012)] suggests that the electronic ground state of bilayer graphene is a layered antiferromagnet and remains surprisingly unaffected by these strong changes in the Coulomb interaction.; Comment: 12 pages, 8 figures

Quantifying the Stacking Registry Matching in Layered Materials

Hod, Oded
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/09/2010
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A detailed account of a recently developed method [Marom et al., Phys. Rev. Lett. 105, 046801 (2010)] to quantify the registry mismatch in layered materials is presented. The registry index, which was originally defined for planar hexagonal boron-nitride, is extended to treat graphitic systems and generalized to describe multi-layered nanotubes. It is shown that using simple geometric considerations it is possible to capture the complex physical features of interlayer sliding in layered materials. The intuitive nature of the presented model and the efficiency of the related computations suggest that the method can be used as a powerful characterization tool for interlayer interactions in complex layered systems.; Comment: 8 pages, 8 figures. To be published in a special issue of the Israel Journal of Chemistry regarding "Inorganic Nanotubes and Nanostructures"

Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties

Liu, Bilu; Köpf, Marianne; Abbas, Ahmad A.; Wang, Xiaomu; Guo, Qiushi; Jia, Yichen; Xia, Fengnian; Weihrich, Richard; Bachhuber, Frederik; Pielnhofer, Florian; Wang, Han; Dhall, Rohan; Cronin, Stephen B.; Ge, Mingyuan; Fang, Xin; Nilges, Tom; Zhou, Chong
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/05/2015
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Two-dimensional (2D) layered materials with diverse properties have attracted significant interest in the past decade. The layered materials discovered so far have covered a wide, yet discontinuous electromagnetic spectral range from semimetallic graphene, insulating boron nitride, to semiconductors with bandgaps from middle infrared to visible light. Here, we introduce new layered semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into long-wavelength infrared (LWIR) regime and cannot be readily reached by other layered materials. Moreover, polarization-resolved infrared absorption and Raman studies reveal in-plane anisotropic properties of b-AsP. This family of layered b-AsP materials extend the electromagnetic spectra covered by 2D layered materials to the LWIR regime, and may find unique applications for future all 2D layered material based devices.; Comment: 31 pages, 13 figures (4 in main text and 9 in Supporting Information), 2 Tables. To appear in Advanced Materials, 2015

LayerOptics: Microscopic modeling of optical coefficients in layered materials

Vorwerk, Christian; Cocchi, Caterina; Draxl, Claudia
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/10/2015
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Theoretical spectroscopy is a powerful tool to describe and predict optical properties of materials. While nowadays routinely performed, first-principles calculations only provide bulk dielectric tensors in Cartesian coordinates. These outputs are hardly comparable with experimental data, which are typically given by macroscopic quantities, crucially depending on the laboratory setup. Even more serious discrepancies can arise for anisotropic materials, e.g., organic crystals, where off-diagonal elements of the dielectric tensor can significantly contribute to the spectral features. Here, we present LayerOptics, a versatile and user-friendly implementation, based on the solution of the Maxwell's equations for anisotropic materials, to compute optical coefficients in anisotropic layered materials. We apply this tool for post-processing full dielectric tensors of molecular materials, including excitonic effects, as computed from many-body perturbation theory using the exciting code. For prototypical examples, ranging from optical to X-ray frequencies, we show the importance of combining accurate ab initio methods to obtain dielectric tensors, with the solution of the Maxwell's equations to compute optical coefficients accounting for optical anisotropy of layered systems. Good agreement with experimental data supports the potential of our approach...

Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials - A general bond polarizability model

Luo, Xin; Cong, Chunxiao; Lu, Xin; Yu, Ting; Xiong, Qihua; Quek, Su Ying
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/04/2015
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57.720757%
2D layered materials have recently attracted tremendous interest due to their fascinating properties and potential applications. The interlayer interactions are much weaker than the intralayer bonds, allowing the as-synthesized materials to exhibit different stacking sequences (e.g. ABAB, ABCABC), leading to different physical properties. Here, we show that regardless of the space group of the 2D material, the Raman frequencies of the interlayer shear modes observed under the typical configuration blue shift for AB stacked materials, and red shift for ABC stacked materials, as the number of layers increases. Our predictions are made using an intuitive bond polarizability model which shows that stacking sequence plays a key role in determining which interlayer shear modes lead to the largest change in polarizability (Raman intensity); the modes with the largest Raman intensity determining the frequency trends. We present direct evidence for these conclusions by studying the Raman modes in few layer graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles calculations and Raman spectroscopy. This study sheds light on the influence of stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D layered materials in general...

Mechanics of freely-suspended ultrathin layered materials

Castellanos-Gomez, Andres; Singh, Vibhor; van der Zant, Herre S. J.; Steele, Gary A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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The study of atomically thin two-dimensional materials is a young and rapidly growing field. In the past years, a great advance in the study of the remarkable electrical and optical properties of 2D materials fabricated by exfoliation of bulk layered materials has been achieved. Due to the extraordinary mechanical properties of these atomically thin materials, they also hold a great promise for future applications such as flexible electronics. For example, this family of materials can sustain very large deformations without breaking. Due to the combination of small dimensions, high Young's modulus and high crystallinity of 2D materials, they have attracted the attention of the field of nanomechanical systems as high frequency and high quality factor resonators. In this article, we review experiments on static and dynamic response of 2D materials. We provide an overview and comparison of the mechanics of different materials, and highlight the unique properties of these thin crystalline layers. We conclude with an outlook of the mechanics of 2D materials and future research directions such as the coupling of the mechanical deformation to their electronic structure.; Comment: Review article. 11 figures, 2 tables

Van der Waals bonding in layered compounds from advanced first-principles calculations

Björkman, T.; Gulans, A.; Krasheninnikov, A. V.; Nieminen, R. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/04/2012
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Although the precise microscopic knowledge of van der Waals interactions is crucial for understanding bonding in weakly bonded layered compounds, very little quantitative information on the strength of interlayer interaction in these materials is available, either from experiments or simulations. Here, using many-body perturbation and advanced density-functional theory techniques, we calculate the interlayer binding and exfoliation energies for a large number of layered compounds and show that, independent of the electronic structure of the material, the energies for most systems are around 20 meV/\AA$^2$. This universality explains the successful exfoliation of a wide class of layered materials to produce two-dimensional systems, and furthers our understanding the properties of layered compounds in general.; Comment: Accepted for publication in Physical Review Letters. Includes Supplementary Material

A Gaussian Treatment for the Friction Issue of Lennard-Jones Potential in Layered Materials: Application to Friction between Graphene, MoS2 and Black Phosphorus

Jiang, Jin-Wu; Park, Harold S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/01/2015
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The Lennard-Jones potential is widely used to describe the interlayer interactions within layered materials like graphene. However, it is also widely known that this potential strongly underestimates the frictional properties for layered materials. Here we propose to supplement the Lennard-Jones potential by a Gaussian-type potential, which enables more accurate calculations of the frictional properties of two-dimensional layered materials. Furthermore, the Gaussian potential is computationally simple as it introduces only one additional potential parameter that is determined by the interlayer shear mode in the layered structure. The resulting Lennard-Jones-Gaussian potential is applied to compute the interlayer cohesive energy and frictional energy for graphene, MoS2, black phosphorus, and their heterostructures.; Comment: 9 figures, 3 tables

First principles calculations of surfaces and layered materials

Machado Charry, Fabio Eduardo
Fonte: Bellaterra : Universitat Autònoma de Barcelona, Publicador: Bellaterra : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2008 ENG; ENG
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Descripció del recurs: el 21-08-2008; Consultable des del TDX; Títol obtingut de la portada digitalitzada; En este trabajo se han realizado cálculos de primeros principios para estudiar las propiedades físicas de superficies y materiales laminares. Los cálculos se basan en la obtención de las propiedades electrónicas por medio de la Teoría del Funcional de la Densidad, con la que se obtienen la energía y fuerzas atómicas para cada sistema estudiado. De esta forma, se realizaron cálculos de optimización estructural y de dinámica molecular, que proporcionan información sobre las estructuras de equilibrio y la dinámica atómica en función de las condiciones externas (tales como presión y temperatura). Los cálculos realizados se han centrado en diferentes sistemas con interés experimental, siempre en estrecha colaboración con distintos grupos experimentales. En el campo de superficies, se han estudiado problemas relacionados con el crecimiento de láminas delgadas de Cobre para metalización de circuitos microelectrónicos, la adsorción de fullerenos sobre superficies de Germanio, y la medición de ondas de densidad de carga mediante microscopía de efecto túnel en bronces azules. En materiales laminares, el trabajo se ha centrado en comprender el efecto de la presión sobre las propiedades estructurales y electrónicas de semiconductores laminares III-VI...