Nanomaterials

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3 pages, 181 KiB

Open AccessEditorial

Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry

by Jelle Vekeman and Frederik Tielens

Nanomaterials 2020, 10(3), 540; https://doi.org/10.3390/nano10030540 - 17 Mar 2020

Cited by 2 | Viewed by 1681

Abstract

For a few years now, quantum chemical modeling of materials has experienced a tremendous boost due to the increasing computational power [...] Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

Research

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16 pages, 360 KiB

Open AccessArticle

Computational Modeling of Tensile Stress Effects on the Structure and Stability of Prototypical Covalent and Layered Materials

by Hocine Chorfi, Álvaro Lobato, Fahima Boudjada, Miguel A. Salvadó, Ruth Franco, Valentín G. Baonza and J. Manuel Recio

Nanomaterials 2019, 9(10), 1483; https://doi.org/10.3390/nano9101483 - 18 Oct 2019

Cited by 7 | Viewed by 2613

Abstract

Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials [...] Read more.

Understanding the stability limit of crystalline materials under variable tensile stress conditions is of capital interest for technological applications. In this study, we present results from first-principles density functional theory calculations that quantitatively account for the response of selected covalent and layered materials to general stress conditions. In particular, we have evaluated the ideal strength along the main crystallographic directions of 3C and 2H polytypes of SiC, hexagonal ABA stacking of graphite and 2H-MoS

_{2}

. Transverse superimposed stress on the tensile stress was taken into account in order to evaluate how the critical strength is affected by these multi-load conditions. In general, increasing transverse stress from negative to positive values leads to the expected decreasing of the critical strength. Few exceptions found in the compressive stress region correlate with the trends in the density of bonds along the directions with the unexpected behavior. In addition, we propose a modified spinodal equation of state able to accurately describe the calculated stress–strain curves. This analytical function is of general use and can also be applied to experimental data anticipating critical strengths and strain values, and for providing information on the energy stored in tensile stress processes. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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17 pages, 6874 KiB

Open AccessArticle

Understanding the Role of Rutile TiO₂ Surface Orientation on Molecular Hydrogen Activation

by Baohuan Wei, Frederik Tielens and Monica Calatayud

Nanomaterials 2019, 9(9), 1199; https://doi.org/10.3390/nano9091199 - 26 Aug 2019

Cited by 23 | Viewed by 5257

Abstract

Titanium oxide (TiO₂) has been widely used in many fields, such as photocatalysis, photovoltaics, catalysis, and sensors, where its interaction with molecular H₂ with TiO₂ surface plays an important role. However, the activation of hydrogen over rutile TiO₂ [...] Read more.

Titanium oxide (TiO₂) has been widely used in many fields, such as photocatalysis, photovoltaics, catalysis, and sensors, where its interaction with molecular H₂ with TiO₂ surface plays an important role. However, the activation of hydrogen over rutile TiO₂ surfaces has not been systematically studied regarding the surface termination dependence. In this work, we use density functional theory (PBE+U) to identify the pathways for two processes: the heterolytic dissociation of H₂ as a hydride–proton pair, and the subsequent H transfer from Ti to near O accompanied by reduction of the Ti sites. Four stoichiometric surface orientations were considered: (001), (100), (110), and (101). The lowest activation barriers are found for hydrogen dissociation on (001) and (110), with energies of 0.56 eV and 0.50 eV, respectively. The highest activation barriers are found on (100) and (101), with energies of 1.08 eV and 0.79 eV, respectively. For hydrogen transfer from Ti to near O, the activation barriers are higher (from 1.40 to 1.86 eV). Our results indicate that the dissociation step is kinetically more favorable than the H transfer process, although the latter is thermodynamically more favorable. We discuss the implications in the stability of the hydride–proton pair, and provide structures, electronic structure, vibrational analysis, and temperature effects to characterize the reactivity of the four TiO₂ orientations. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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10 pages, 1572 KiB

Open AccessArticle

Dibenzyl Disulfide Adsorption on Cationic Exchanged Faujasites: A DFT Study

by Etienne Paul Hessou, Miguel Ponce-Vargas, Jean-Baptiste Mensah, Frederik Tielens, Juan Carlos Santos and Michael Badawi

Nanomaterials 2019, 9(5), 715; https://doi.org/10.3390/nano9050715 - 08 May 2019

Cited by 16 | Viewed by 3190

Abstract

Although dibenzyl disulfide (DBDS) is used as a mineral oil stabilizer, its presence in electrical transformer oil is associated as one of the major causes of copper corrosion and subsequent formation of copper sulfide. In order to prevent these undesirable processes, MY zeolites [...] Read more.

Although dibenzyl disulfide (DBDS) is used as a mineral oil stabilizer, its presence in electrical transformer oil is associated as one of the major causes of copper corrosion and subsequent formation of copper sulfide. In order to prevent these undesirable processes, MY zeolites (with M = Li, Na, K, Cs, Cu or Ag) are proposed to adsorb molecularly DBDS. In this study, different MY zeolites are investigated at the DFT+D level in order to assess their ability in DBDS adsorption. It was found that CsY, AgY and CuY exhibit the best compromise between high interaction energies and limited S-S bond activation, thus emerging as optimal adsorbents for DBDS. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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19 pages, 1766 KiB

Open AccessArticle

Thermal Boundary Characteristics of Homo-/Heterogeneous Interfaces

by Koen Heijmans, Amar Deep Pathak, Pablo Solano-López, Domenico Giordano, Silvia Nedea and David Smeulders

Nanomaterials 2019, 9(5), 663; https://doi.org/10.3390/nano9050663 - 26 Apr 2019

Cited by 6 | Viewed by 3674

Abstract

The interface of two solids in contact introduces a thermal boundary resistance (TBR), which is challenging to measure from experiments. Besides, if the interface is reactive, it can form an intermediate recrystallized or amorphous region, and extra influencing phenomena are introduced. Reactive force [...] Read more.

The interface of two solids in contact introduces a thermal boundary resistance (TBR), which is challenging to measure from experiments. Besides, if the interface is reactive, it can form an intermediate recrystallized or amorphous region, and extra influencing phenomena are introduced. Reactive force field Molecular Dynamics (ReaxFF MD) is used to study these interfacial phenomena at the (non-)reactive interface. The non-reactive interfaces are compared using a phenomenological theory (PT), predicting the temperature discontinuity at the interface. By connecting ReaxFF MD and PT we confirm a continuous temperature profile for the homogeneous non-reactive interface and a temperature jump in case of the heterogeneous non-reactive interface. ReaxFF MD is further used to understand the effect of chemical activity of two solids in contact. The selected Si/SiO₂ materials showed that the TBR of the reacted interface is two times larger than the non-reactive, going from

1.65 \times 10^{- 9}

to

3.38 \times 10^{- 9}

m²K/W. This is linked to the formation of an intermediate amorphous layer induced by heating, which remains stable when the system is cooled again. This provides the possibility to design multi-layered structures with a desired TBR. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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20 pages, 4439 KiB

Open AccessArticle

Investigation of the Impact of Cross-Polymerization on the Structural and Frictional Properties of Alkylsilane Monolayers Using Molecular Simulation

by Jana E. Black, Andrew Z. Summers, Christopher R. Iacovella, Peter T. Cummings and Clare McCabe

Nanomaterials 2019, 9(4), 639; https://doi.org/10.3390/nano9040639 - 19 Apr 2019

Cited by 11 | Viewed by 3585

Abstract

Cross-linked chemisorbed n-alkylsilane (CH₃(CH₂)_n₋₁Si(OH)₃) monolayers on amorphous silica surfaces have been studied and their structural properties and frictional performance were compared to those of equivalent monolayers without cross-linkages. The simulations isolated for the [...] Read more.

Cross-linked chemisorbed n-alkylsilane (CH₃(CH₂)_n₋₁Si(OH)₃) monolayers on amorphous silica surfaces have been studied and their structural properties and frictional performance were compared to those of equivalent monolayers without cross-linkages. The simulations isolated for the first time the effects of both siloxane cross-linkages and the fraction of chains chemisorbed to the surface, providing insight into a longstanding fundamental question in the literature regarding molecular-level structure. The results demonstrate that both cross-linkages and the fraction of chemisorbed chains affect monolayer structure in small but measurable ways, particularly for monolayers constructed from short chains; however, these changes do not appear to have a significant impact on frictional performance. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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9 pages, 2454 KiB

Open AccessArticle

Raman Study of Strain Relaxation from Grain Boundaries in Epitaxial Graphene Grown by Chemical Vapor Deposition on SiC

by Laiyuan Chong, Hui Guo, Yuming Zhang, Yanfei Hu and Yimen Zhang

Nanomaterials 2019, 9(3), 372; https://doi.org/10.3390/nano9030372 - 05 Mar 2019

Cited by 14 | Viewed by 3619

Abstract

Strains in graphene play a significant role in graphene-based electronics, but many aspects of the grain boundary effects on strained graphene remain unclear. Here, the relationship between grain boundary and strain property of graphene grown by chemical vapor deposition (CVD) on the C-face [...] Read more.

Strains in graphene play a significant role in graphene-based electronics, but many aspects of the grain boundary effects on strained graphene remain unclear. Here, the relationship between grain boundary and strain property of graphene grown by chemical vapor deposition (CVD) on the C-face of SiC substrate has been investigated by Raman spectroscopy. It is shown that abundant boundary-like defects exist in the graphene film and the blue-shifted 2D-band frequency, which results from compressive strain in graphene film, shifts downward linearly as 1/L_a increases. Strain relaxation caused by grain boundary diffusion is considered to be the reason and the mechanism is analyzed in detail. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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9 pages, 3171 KiB

Open AccessArticle

Tunable Electronic Properties of Nitrogen and Sulfur Doped Graphene: Density Functional Theory Approach

by Ji Hye Lee, Sung Hyun Kwon, Soonchul Kwon, Min Cho, Kwang Ho Kim, Tae Hee Han and Seung Geol Lee

Nanomaterials 2019, 9(2), 268; https://doi.org/10.3390/nano9020268 - 15 Feb 2019

Cited by 40 | Viewed by 5605

Abstract

We calculated the band structures of a variety of N- and S-doped graphenes in order to understand the effects of the N and S dopants on the graphene electronic structure using density functional theory (DFT). Band-structure analysis revealed energy band upshifting above the [...] Read more.

We calculated the band structures of a variety of N- and S-doped graphenes in order to understand the effects of the N and S dopants on the graphene electronic structure using density functional theory (DFT). Band-structure analysis revealed energy band upshifting above the Fermi level compared to pristine graphene following doping with three nitrogen atoms around a mono-vacancy defect, which corresponds to p-type nature. On the other hand, the energy bands were increasingly shifted downward below the Fermi level with increasing numbers of S atoms in N/S-co-doped graphene, which results in n-type behavior. Hence, modulating the structure of graphene through N- and S-doping schemes results in the switching of “p-type” to “n-type” behavior with increasing S concentration. Mulliken population analysis indicates that the N atom doped near a mono-vacancy is negatively charged due to its higher electronegativity compared to C, whereas the S atom doped near a mono-vacancy is positively charged due to its similar electronegativity to C and its additional valence electrons. As a result, doping with N and S significantly influences the unique electronic properties of graphene. Due to their tunable band-structure properties, the resulting N- and S-doped graphenes can be used in energy and electronic-device applications. In conclusion, we expect that doping with N and S will lead to new pathways for tailoring and enhancing the electronic properties of graphene at the atomic level. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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11 pages, 2157 KiB

Open AccessArticle

Drain Current Model for Double Gate Tunnel-FETs with InAs/Si Heterojunction and Source-Pocket Architecture

by Hongliang Lu, Bin Lu, Yuming Zhang, Yimen Zhang and Zhijun Lv

Nanomaterials 2019, 9(2), 181; https://doi.org/10.3390/nano9020181 - 01 Feb 2019

Cited by 12 | Viewed by 4227

Abstract

The practical use of tunnel field-effect transistors is retarded by the low on-state current. In this paper, the energy-band engineering of InAs/Si heterojunction and novel device structure of source-pocket concept are combined in a single tunnel field-effect transistor to extensively boost the device [...] Read more.

The practical use of tunnel field-effect transistors is retarded by the low on-state current. In this paper, the energy-band engineering of InAs/Si heterojunction and novel device structure of source-pocket concept are combined in a single tunnel field-effect transistor to extensively boost the device performance. The proposed device shows improved tunnel on-state current and subthreshold swing. In addition, analytical potential model for the proposed device is developed and tunneling current is also calculated. Good agreement of the modeled results with numerical simulations verifies the validation of our model. With significantly reduced simulation time while acceptable accuracy, the model would be helpful for the further investigation of TFET-based circuit simulations. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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18 pages, 3012 KiB

Open AccessArticle

Tin, The Enabler—Hydrogen Diffusion into Ruthenium

by Chidozie Onwudinanti, Ionuţ Tranca, Thomas Morgan and Shuxia Tao

Nanomaterials 2019, 9(1), 129; https://doi.org/10.3390/nano9010129 - 21 Jan 2019

Cited by 20 | Viewed by 5907

Abstract

Hydrogen interaction with ruthenium is of particular importance for the ruthenium-capped multilayer reflectors used in extreme ultraviolet (EUV) lithography. Hydrogen causes blistering, which leads to a loss of reflectivity. This problem is aggravated by tin. This study aims to uncover the mechanism via [...] Read more.

Hydrogen interaction with ruthenium is of particular importance for the ruthenium-capped multilayer reflectors used in extreme ultraviolet (EUV) lithography. Hydrogen causes blistering, which leads to a loss of reflectivity. This problem is aggravated by tin. This study aims to uncover the mechanism via which tin affects the hydrogen uptake, with a view to mitigation. We report here the results of a study of hydrogen interaction with the ruthenium surface in the presence of tin using Density Functional Theory and charge density analyses. Our calculations show a significant drop in the energy barrier to hydrogen penetration when a tin atom or a tin hydride molecule (SnH_x) is adsorbed on the ruthenium surface; the barrier has been found to drop in all tested cases with tin, from 1.06 eV to as low as 0.28 eV in the case of stannane (SnH₄). Analyses show that, due to charge transfer from the less electronegative tin to hydrogen and ruthenium, charge accumulates around the diffusing hydrogen atom and near the ruthenium surface atoms. The reduced atomic volume of hydrogen, together with the effect of electron–electron repulsion from the ruthenium surface charge, facilitates subsurface penetration. Understanding the nature of tin’s influence on hydrogen penetration will guide efforts to mitigate blistering damage of EUV optics. It also holds great interest for applications where hydrogen penetration is desirable, such as hydrogen storage. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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17 pages, 4796 KiB

Open AccessArticle

Quantum-Mechanical Study of Nanocomposites with Low and Ultra-Low Interface Energies

by Martin Friák, David Holec and Mojmír Šob

Nanomaterials 2018, 8(12), 1057; https://doi.org/10.3390/nano8121057 - 15 Dec 2018

Cited by 13 | Viewed by 2972

Abstract

We applied first-principles electronic structure calculations to study structural, thermodynamic and elastic properties of nanocomposites exhibiting nearly perfect match of constituting phases. In particular, two combinations of transition-metal disilicides and one pair of magnetic phases containing the Fe and Al atoms with different [...] Read more.

We applied first-principles electronic structure calculations to study structural, thermodynamic and elastic properties of nanocomposites exhibiting nearly perfect match of constituting phases. In particular, two combinations of transition-metal disilicides and one pair of magnetic phases containing the Fe and Al atoms with different atomic ordering were considered. Regarding the disilicides, nanocomposites MoSi

_{2}

/WSi

_{2}

with constituents crystallizing in the tetragonal C11

_{b}

structure and TaSi

_{2}

/NbSi

_{2}

with individual phases crystallizing in the hexagonal C40 structure were simulated. Constituents within each pair of materials exhibit very similar structural and elastic properties and for their nanocomposites we obtained ultra-low (nearly zero) interface energy (within the error bar of our calculations, i.e., about 0.005 J/m

^{2}

). The interface energy was found to be nearly independent on the width of individual constituents within the nanocomposites and/or crystallographic orientation of the interfaces. As far as the nanocomposites containing Fe and Al were concerned, we simulated coherent superlattices formed by an ordered Fe

_{3}

Al intermetallic compound and a disordered Fe-Al phase with 18.75 at.% Al, the

α

-phase. Both phases were structurally and elastically quite similar but the disordered

α

-phase lacked a long-range periodicity. To determine the interface energy in these nanocomposites, we simulated seven different distributions of atoms in the

α

-phase interfacing the Fe

_{3}

Al intermetallic compound. The resulting interface energies ranged from ultra low to low values, i.e., from 0.005 to 0.139 J/m

^{2}

. The impact of atomic distribution on the elastic properties was found insignificant but local magnetic moments of the iron atoms depend sensitively on the type and distribution of surrounding atoms. Full article

(This article belongs to the Special Issue Modeling of Complex Interfaces: From Surface Chemistry to Nano Chemistry)

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