Search

Detection of pollutant gases, such as formaldehyde (HCHO), in our homes and surrounding environment is of high importance for our health and safety. The effect of surface defects and specifically pre-adsorbed oxygen on the gas sensing reaction of HCHO with ZnO nanostructures is largely unknown. Using density functional theory, nonequilibrium Green's function method and

The ferroelectric material In2Se3 is currently of significant interest due to its built-in polarisation characteristics that can significantly modulate its electronic properties. Here we employ density functional theory to determine the transport characteristics at the metal-semiconductor interface of the two-dimensional multiferroic In2Se3/Fe3GeTe2 heterojunction. We show a significant tuning of the Schottky barrier height as a result of the change in the intrinsic polarisation state of In2Se3: the switching in the electric polarization of In2Se3 results in the switching of the nature of the Schottky barrier, from being n-type to p-type, and is accompanied by a change in the spin polarization of the electrons. This switchable Schottky barrier structure can form an essential component in a two-dimensional field effect transistor that can be operated by switching the ferroelectric polarization, rather than by the application of strain or electric field. The band structure and density of state calculations show that Fe3GeTe2 lends its magnetic and metallic characteristics to the In2Se3 layer, making the In2Se3/Fe3GeTe2 heterojunction a potentially viable multiferroic candidate in nanoelectronic devices like field-effect transistors. Moreover, our findings reveal a transfer of charge carriers from the In2Se3 layer to the Fe3GeTe2 layer, resulting in the formation of an in-built electric field at the metal-semiconductor interface. Our work can substantially broaden the device potential of the In2Se3/Fe3GeTe2 heterojunction in future low-energy electronic devices.

Systematic structural changes to the functional groups of sulfonimide anions can be used to improve the calculated oxidation potential, reductive stability, lithium binding energy and lithium-anion coordination for application in lithium-metal batteries.

Antimicrobial resistance has rendered many conventional therapeutic measures, such as antibiotics, ineffective. This makes the treatment of infections from pathogenic micro-organisms a major growing health, social, and economic challenge. Recently, nanomaterials, including two-dimensional (2D) materials, have attracted scientific interest as potential antimicrobial agents. Many of these studies, however, rely on the input of activation energy and lack real-world utility. In this work, we present the broad-spectrum antimicrobial activity of few-layered black phosphorus (BP) at nanogram concentrations. This property arises from the unique ability of layered BP to produce reactive oxygen species, which we harness to create this unique functionality. BP is shown to be highly antimicrobial toward susceptible and resistant bacteria and fungal species. To establish cytotoxicity with mammalian cells, we showed that both L929 mouse and BJ-5TA human fibroblasts were metabolically unaffected by the presence of BP. Finally, we demonstrate the practical utility of this approach, whereby medically relevant surfaces are imparted with antimicrobial properties via functionalization with few-layer BP. Given the self-degrading properties of BP, this study demonstrates a viable and practical pathway for the deployment of novel low-dimensional materials as antimicrobial agents without compromising the composition or nature of the coated substrate.

Synthesizing two dimensional (2D) nanomaterials with controlled sub-nanometer thicknesses from non-layered crystals presents both significant challenges and vast opportunities. However, mechanical exfoliation techniques and physical/wet chemical deposition processes are widely disadvantageous for applicability to non-layered structures. Here we have utilized a simple self-limiting approach to prepare large sheets of 2D zinc oxide (ZnO) at the metal-melt/air interface. These ultra-thin sheets demonstrated highly crystalline hexagonal structures. The specific ZnO hexagonal sheet thickness and its interaction with the substrate were found to have a critical impact on d33. This unusual structure resulted in an exceptionally high out of plane piezoelectricity, yielding a giant value of 80 ± 0.8 pm/V at 2.5 unit-cell thickness for d33, which is 5 Zn-O layers in the wurtzite crystal. This out of plane piezoelectricity value is approximately 8 times larger than that of the value for bulk ZnO. Theoretical studies were carried out to elucidate the impact of the thickness and the substrate’s role on the polarization of the layers. The existence of a large piezoelectricity offered by the synergy of the substrate and specific thickness of ultrathin films offers the opportunity for other groups of potentially piezoelectric materials to be explored.

Ionic liquids are versatile solvents that can be tailored through modification of the cation and anion species. Relatively little is known about the corrosive properties of protic ionic liquids. In this study, we have explored the corrosion of both zinc and copper within a series of protic ionic liquids consisting of alkylammonium or alkanolammonium cations paired with nitrate or carboxylate anions along with three aprotic imidazolium ionic liquids for comparison. Electrochemical studies revealed that the presence of either carboxylate anions or alkanolammonium cations tend to induce a cathodic shift in the corrosion potential. The effect in copper was similar in magnitude for both cations and anions, while the anion effect was slightly more pronounced than that of the cation in the case of zinc. For copper, the presence of carboxylate anions or alkanolammonium cations led to a notable decrease in corrosion current, whereas an increase was typically observed for zinc. The ionic liquid-metal surface interactions were further explored for select protic ionic liquids on copper using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to characterize the interface. From these studies, the oxide species formed on the surface were identified, and copper speciation at the surface linked to ionic liquid and potential dependent surface passivation. Density functional theory and ab initio molecular dynamics simulations revealed that the ethanolammonium cation was more strongly bound to the copper surface than the ethylammonium counterpart. In addition, the nitrate anion was more tightly bound than the formate anion. These likely lead to competing effects on the process of corrosion: the tightly bound cations act as a source of passivation, whereas the tightly bound anions facilitate the electrodissolution of the copper.

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS2 nanosheets comprising 4-10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on MoS2 nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS2 surface are coupled with the electron-rich nitrogen center of ODA and yield ODA-functionalized MoS2 (MoS2-ODA). The MoS2-ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL-1) to mineral oil. It is shown that even at low concentration, MoS2-ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS2-based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO3 and WO3 are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO3-x-based electrically activated ultraviolet (UV) filters. The MoO3-x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H+ injection/extraction in MoO3-x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325-800 nm), with a peak of ∼60% in the UV-A range (350-392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm2 C-1 are achieved.

Boron nitride nanotubes (BNNTs) represent a relatively new class of materials that provides alternative electrical and thermal properties to the carbon analogue. The high chemical and thermal stability and large band gap combined with high electrical resistance make BNNTs desirable in several thin-film applications. In this study, stable BNNT and hexagonal boron nitride (hBN) particle dispersions have been developed using environmentally friendly advanced oxidation processing (AOP) that can be further modified for electrophoretic deposition (EPD) to produce thin films. The characterization of the dispersions has revealed how the hydroxyl radicals produced in AOP react with BNNT/hBN and contaminant boron nanoparticles (BNPs). While the radicals remove the carbon contaminant present on BNNT/hBN and increase dispersion stability, they also oxidize the BNPs and the boron oxide produced, which, conversely, reduces the dispersion stability. The use of high- or low-powered ultrasonication in combination with the AOP affects the rate of the competing reactions, with low-powered sonication and AOP providing the best combination for producing stable dispersions with high concentrations. BNNT/hBN dispersions were functionalized with polyethyleneimine to facilitate EPD, where films of several micrometer thickness were readily deposited onto stainless steel and glass-fiber fabrics. BNNT/hBN films produced on glass fabrics by EPD exhibited a consistent through-thickness macroporosity that was facilitated by platelet and nanotube stacking. The film macroporosity present on the coated fabrics was suitable for use as separator layers in supercapacitors and provided improved device robustness with a minimal impact on electrochemical performance.

Metal chalcogenides are important members of the two-dimensional (2D) materials family and have been extensively investigated for high-performance electronic device applications. However, when they are produced on a large-scale, their carrier mobilities are strongly influenced by the surface conditions. Here, we print indium sulphide (In2S3) with the thickness down to the single unit cell limit on wafer-scale out of metallic indium liquid, in which structural indium vacancies are formed in an orderly fashion. First principles investigations reveal that the unique ordered-vacancy structure results in a highly dispersive conduction band with low effective electron mass, forming multiple band-like electronic transport channels sandwiched within the crystal structure which are less influenced by the surface conditions. Back-gated field effect transistors are fabricated, and the measured mobility is up to 58 cm2 V-1 s-1 with a high degree of reproducibility, which is amongst one of the highest reported for wafer-scale-grown ultra-thin metal chalcogenides. This establishes ordered-vacancy-enabled semiconductors in the 2D geometry as suitable alternatives for new generation high-performance electronic devices.

Two-dimensional (2D) ferroelectric materials are providing promising platforms for creating future nano- and opto-electronics. Here we propose new hybrid van der Waals heterostructures, in which the 2D ferroelectric material CuInP2S6 (CIPS) is layered on a 2D semiconductor for near-infrared (NIR) memory device applications. Using density functional theory, we show that the band gap of the hybrid bilayers formed with CIPS can be tuned and that the optical and electronic properties can be successfully modulated via ferroelectric switching. Of the 3712 heterostructures considered, we identified 19 structures that have a type II band alignment and commensurate lattice matches. Of this set, both the CuInP2S6/PbSe and CuInP2S6/Ge2H2 heterostructures possess absorption peaks in the NIR region that change position and intensity with switching polarisation, making them suitable for NIR memory devices. The CuInP2S6/ISSb, CuInP2S6/ISbSe, CuInP2S6/ClSbSe and CuInP2S6/ZnI2 heterostructures had band gaps which can be switched from direct to indirect with changing the polarisation of CIPS making them suitable for optoelectronics and sensors. The heterostructures formed with CIPS are exciting candidates for stable ferroelectric devices, opening a pathway for tuning the band alignment of van der Waal heterostructures and the creation of modern memory applications that use less energy.

Lithium metal batteries (LMBs) require an electrolyte with high ionic conductivity as well as high thermal and electrochemical stability that can maintain a stable solid electrolyte interphase (SEI) layer on the lithium metal anode surface. The borate anions tetrakis(trifluoromethyl)borate ([B(CF3)4]−), pentafluoroethyltrifluoroborate ([(C2F5)BF3]−), and pentafluoroethyldifluorocyanoborate ([(C2F5)BF2(CN)]−) have shown excellent physicochemical properties and electrochemical stability windows, however, the suitability of these anions as high-voltage LMB electrolytes components that can stabilise the Li anode is yet to be determined. In this work, density functional theory calculations show high reductive stability limits and low anion–cation interaction strengths for Li[B(CF3)4], Li[(C2F5)BF3], and Li[(C2F5)BF2(CN)] that surpass popular sulfonamide salts. Specifically, Li[B(CF3)4] has a calculated oxidative stability limit of 7.12 V vs. Li+/Li0 which is significantly higher than the other borate and sulfonamide salts (≤6.41 V vs. Li+/Li0). Using ab initio molecular dynamics simulations, this study is the first to show that these borate anions can form an advantageous LiF-rich SEI layer on the Li anode at room (298 K) and elevated (358 K) temperatures. The interaction of the borate anions, particularly [B(CF3)4]−, with the Li+ and Li anode, suggests they are suitable inclusions in high-voltage LMB electrolytes that can stabilise the Li anode surface and provide enhanced ionic conductivity.

Imprinting vision as memory is a core attribute of human cognitive learning. Fundamental to artificial intelligence systems are bioinspired neuromorphic vision components for the visible and invisible segments of the electromagnetic spectrum. Realization of a single imaging unit with a combination of in-built memory and signal processing capability is imperative to deploy efficient brain-like vision systems. However, the lack of a platform that can be fully controlled by light without the need to apply alternating polarity electric signals has hampered this technological advance. Here, a neuromorphic imaging element based on a fully light-modulated 2D semiconductor in a simple reconfigurable phototransistor structure is presented. This standalone device exhibits inherent characteristics that enable neuromorphic image pre-processing and recognition. Fundamentally, the unique photoresponse induced by oxidation-related defects in 2D black phosphorus (BP) is exploited to achieve visual memory, wavelength-selective multibit programming, and erasing functions, which allow in-pixel image pre-processing. Furthermore, all-optically driven neuromorphic computation is demonstrated by machine learning to classify numbers and recognize images with an accuracy of over 90%. The devices provide a promising approach toward neurorobotics, human-machine interaction technologies, and scalable bionic systems with visual data storage/buffering and processing.

Multifunctional electronic memories capable of demonstrating both analog and digital switching on-demand are extremely attractive for miniaturization of electronics without significant drain on energy consumption. Simultaneously translating functionality onto mechanically conformable platforms will further enhance their suitability. Here, we demonstrate the ability to engineer multifunctionality in strontium titanate (STO)-based resistive random-access memories (ReRAM) on a flexible polyimide platform. By utilizing different bottom electrodes of various work functions while the top electrode is fixed, differential work functions are induced in STO, to induce bipolar or complementary switching behaviors whenever required. This work-function difference-induced bifunctional switching on the flexible platform reveals a streamlined route for achieving flexible artificial neural networks, high density integration, and logic operation using a single ReRAM.

Mono-elemental two-dimensional (2D) crystals (graphene, silicene, germanene, stanene, and so on), termed 2D-Xenes, have been brought to the forefront of scientific research. The stability and electronic properties of 2D-Xenes are main challenges in developing practical devices. Therefore, in this review, we focus on 2D free-standing group-IV graphene analogs (graphene quantum dots, silicane, and germanane) and the functionalization of these sheets with organic moieties, which could be handled under ambient conditions. We highlight the present results and future opportunities, functions and applications, and novel device concepts.

Graphitic nanoplatelets (GNPs) have been treated using an ultrasonicated ozonolysis procedure to produce stable aqueous dispersions that facilitate deposition of thin films using electrophoretic deposition. The thin GNP films were then coated with zero valence (ZV) iron nanocubes using a pulsed electrodeposition technique. Characterization of the ZV-iron coating with deposition time revealed that the changing magnetic character of the ferromagnetic-graphitic hybrid material was related to the nucleation density and growth of the ZV-iron nanocubes. Density functional theory calculations show a preference for ZV-iron adsorption at the oxygen sites of the GNPs, with ZV-iron displacement of oxygen groups favored in some configurations. Transmission electron microscopy studies confirm ZV-iron growth nucleates preferentially at the graphite nanoplatelet edges and the hybrid material magnetism is affected by the convergent crystalline grain boundaries formed between adjacent ZV-iron nanocubes.

The adsorption of formaldehyde (HCHO) gas on different one-dimensional ZnO nanostructures is examined using density functional theory calculations. The effects of nanostructure shape and gas concentration are investigated to determine how these factors may influence the surface reaction of HCHO for sensing applications. The binding energies, vibrational frequencies, charge transfer and density of states were determined. We show that HCHO associatively chemisorbs in multiple sites and orientations on the ZnO nanowire and facetted-nanotube. The facetted-nanotube offers a greater number of adsorption sites due to its larger surface area and hollow centre where HCHO can also adsorb. HCHO is able to form one or two bonds to the surface, where structures in the latter configuration show greater stability, with HCHO behaving as a charge acceptor. Conversely, HCHO acts as a charge donor in the singly coordinated structures. As the adsorption mechanism of HCHO gas on the surface of ZnO nanostructure is not well understood, this study provides useful insights into the gas-surface reaction that may assist future experimental development of ZnO nanostructures for gas sensing of formaldehyde.

Nitrogen dioxide (NO2) is a toxic gas that contributes to photochemical pollution and can cause adverse effects to human and environmental health. Monitoring this gas is therefore important to warn of potential exposure. Nanostructures of zinc oxide (ZnO) have been studied for the sensing of NO2 gas, however, the effect of nanostructure morphology on the gas-sensor reaction mechanism is not understood. We examine the NO2 sensing mechanism for three different ZnO nanostructures, namely a nanowire, a facetted nanotube and a single walled (8,0) nanotube using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The effect of gas concentration and oxygen vacancies is also determined. It was shown that NO2 adsorbs on all nanostructures in multiple configurations, with the bonding being strongest on the nanowire and weakest on the single walled nanotube. NO2 behaves as a charge acceptor, consistent with adsorption on the thin film and desorbs intact from the nanostructures at simulation temperatures of 300 K and 700 K, providing new surface sites for detection of other molecules. The presence of surface oxygen vacancies was found to enhance the binding, with NO2 chemisorbing on all 3 nanostructures via two bonds to the surface. The AIMD simulations showed that at a simulation temperature of 500 K, NO2 dissociates on the nanowire and facetted nanotube defect surfaces resulting in a surface bound oxygen atom which fills the defect site, with the remaining NO desorbing from the surface. The single walled nanotube was shown to be unstable at these simulation temperatures. These findings provide important information for the experimental development of ZnO nanostructure-based gas sensors.

Anelasticity of nanowires has recently attracted attention as an interesting property for high efficiency mechanical damping materials. While the mechanism of anelasticity has so far been analysed using continuum mechanical models based on defect diffusion, the mechanisms behind anelasticity have not yet been determined on an atomic level. Such information is needed in order to be able to design and synthesise new nanomaterials having desired mechanical properties. Here we determine the potential mechanism of anelasticity in narrow zinc oxide nanowires by analyzing the bond stretching and compression within the nanowire structure based on density functional theory. Our approach shows that different local minimum structures are created when different strain patterns are applied which give rise to the anelastic behavior. These findings can be applied for the prediction of potential anelasticity of other nanowire materials.

Atomically thin materials face an ongoing challenge of scalability, hampering practical deployment despite their fascinating properties. Tin monosulfide (SnS), a low-cost, naturally abundant layered material with a tunable bandgap, displays properties of superior carrier mobility and large absorption coefficient at atomic thicknesses, making it attractive for electronics and optoelectronics. However, the lack of successful synthesis techniques to prepare large-area and stoichiometric atomically thin SnS layers (mainly due to the strong interlayer interactions) has prevented exploration of these properties for versatile applications. Here, SnS layers are printed with thicknesses varying from a single unit cell (0.8 nm) to multiple stacked unit cells (≈1.8 nm) synthesized from metallic liquid tin, with lateral dimensions on the millimeter scale. It is reveal that these large-area SnS layers exhibit a broadband spectral response ranging from deep-ultraviolet (UV) to near-infrared (NIR) wavelengths (i.e., 280-850 nm) with fast photodetection capabilities. For single-unit-cell-thick layered SnS, the photodetectors show upto three orders of magnitude higher responsivity (927 A W-1 ) than commercial photodetectors at a room-temperature operating wavelength of 660 nm. This study opens a new pathway to synthesize reproduceable nanosheets of large lateral sizes for broadband, high-performance photodetectors. It also provides important technological implications for scalable applications in integrated optoelectronic circuits, sensing, and biomedical imaging.

In your life, you are fortunate indeed to be able to count a close friend as someone who has been your teacher and mentor; Ian Snook was such a friend. He was a talented and internationally recogni...

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Few-layer black phosphorous (BP) has emerged as a promising candidate for next-generation nanophotonic and nanoelectronic devices. However, rapid ambient degradation of mechanically exfoliated BP poses challenges in its practical deployment in scalable devices. To date, the strategies employed to protect BP have relied upon preventing its exposure to atmospheric conditions. Here, an approach that allows this sensitive material to remain stable without requiring its isolation from the ambient environment is reported. The method draws inspiration from the unique ability of biological systems to avoid photo-oxidative damage caused by reactive oxygen species. Since BP undergoes similar photo-oxidative degradation, imidazolium-based ionic liquids are employed as quenchers of these damaging species on the BP surface. This chemical sequestration strategy allows BP to remain stable for over 13 weeks, while retaining its key electronic characteristics. This study opens opportunities to practically implement BP and other environmentally sensitive 2D materials for electronic applications.

Gas sensor devices have traditionally comprised thin films of metal oxides, with tin oxide, zinc oxide and indium oxide being some of the most common materials employed. With the recent discovery of novel metal oxide nanostructures, sensors comprising nano-arrays or single nanostructures have shown improved performance over the thin films. The improved response of the nanostructures to different gases has been primarily attributed to the highly single crystalline surfaces as well as large surface area of the nanostructures. In this paper the properties of clean and defected quasi one-dimensional ZnO nanostructures, including hexagonal and triangular nanowires, nanotubes and facetted nanotubes are reviewed. The adsorption of atoms and molecules on the ZnO nanostructures are also reviewed and the findings are compared to studies examining similar reactions on nanostructured metal oxide surfaces for sensing purposes. While both experimental and theoretical approaches have been employed to examine gas sensor reactions, this review focuses on studies that employ electronic structure calculations, which primarily concentrate on using density functional theory. Computational studies have been useful in elucidating the reaction mechanism, binding strength, charge transfer as well as other electronic and structural properties of the nanomaterials and the gas-sensor interaction. Despite these studies there are still significant areas of research that need to be pursued that will assist in the link between theoretical and experimental findings, as well as advancing the current chemical and physical understanding of these novel materials. A summary and outlook for future directions of this exciting area of research is also provided.

Black phosphorus (BP) exhibits fascinating thickness dependent optical and electronic characteristics. However, photoluminescence (PL) emission in the visible spectrum does not exist for multilayer BP and requires the achievement of single layer, which are highly environmentally sensitive. This poses significant challenges in realizing the true potential of BP as multilayer BP exhibits exciting optical properties for a range of applications. Here, for the first time we reveal visible range room-temperature photoluminescence (PL) in multi-layered black phosphorus (BP) via chemical doping using organic molecules. We find the drastic enhancement of PL originates from the adsorption of p-type dopants and offer further insight using density functional theory (DFT) calculations. The reported non-destructive method creates a pathway to precisely control optical and electronic properties thereby expanding the application horizon for multilayer BP that is environmentally robust compared to monolayer.

Density functional theory calculations were used to model the structure and properties of ZnO ( 1 0 1 ¯ 0 ) and ( 2 1 ¯ 1 ¯ 0 ) surfaces. Our calculations of the clean ( 1 0 1 ¯ 0 ) surface indicate that the Zn atom moves towards the surface, while the O atom moves away from the surface slightly, resulting in a tilting and shortening of the Zn–O bond. On the clean ( 2 1 ¯ 1 ¯ 0 ) surface, the movements are similar but smaller in magnitude. Surface energy calculations indicate that the ( 1 0 1 ¯ 0 ) surface is more stable than the ( 2 1 ¯ 1 ¯ 0 ) surface. The clean surface models were used to investigate the adsorption of N 2 O on these surfaces. More than one minimum energy structure was found for each surface, all showing relatively small binding energy values that reflect physisorbed surface species. Even though the geometry of N 2 O was little changed after adsorption, small surface relaxations and adsorbate-induced reconstructions were observed, resulting in a further tilting of the Zn–O surface bond so that the O atoms sit even higher on the surface. On both surfaces N 2 O prefers to adsorb to a surface Zn atom, via the O atom on the ( 1 0 1 ¯ 0 ) surface and via the N atom on the ( 2 1 ¯ 1 ¯ 0 ) surface. Charge density differences, electron localisation function plots, Bader charges and vibrational frequency values were also calculated, with all these properties reflecting the weak interaction between the adsorbate and surface. Adsorption mainly leads to charge polarisation within the adsorbate molecule and the surface, resulting in a small transfer of at most 0.02 e from the surface to the adsorbate.

The electronic properties of thiol-functionalized 2D MoS2 nanosheets are investigated. Shifts in the valence and conduction bands and Fermi levels are observed while bandgaps remain unaffected. These findings allow the tuning of energy barriers between 2D MoS2 and other materials, which can lead to improved control over 2D MoS2 -based electronic and optical devices and catalysts.

A geometry optimisation of the perovskite and hexagonal phases of BaTiO3 has been conducted using Density Functional Theory (DFT) within the Local Density Approximation (LDA) and Generalised Gradient Approximation (GGA) schemes. The LDA was found to give lattice parameters closer to experiment than the GGA. A study of oxygen vacancies in the hexagonal phase has been performed and the results suggest an O(1) type (face sharing) vacancy is more stable than an O(2) type (corner sharing) vacancy in the octahedral structure. In addition, the effect of different Ru doping concentrations on the structure and stability of the hexagonal phase has been investigated.

Density Functional Theory (DFT) calculations using gaussian 98 have been performed on hydrogen adsorbed on clusters representing the (110) and (111) surfaces of Cu. Clusters were constructed to model different adsorption sites, and at least two different size clusters were used for each site. On the (111) surface, hydrogen prefers to adsorb in a hollow site, though with the hcp variant being favoured by the adsorption energy, and the fcc alternative by the vibrational frequencies. On the (110) surface, the "fcc" site on a (1 2 2) reconstructed surface is preferred.

This issue of Molecular Simulation is dedicated to the memory of our dear friend, teacher and colleague Professor Ian Keith Snook who passed away on 7 April 2013 after succumbing to cancer followin...

The development of lightweight, long lasting Li-ion batteries is of great technological importance for hybrid and plug-in hybrid electric vehicles, as well as for power grid applications. Here we report an alternative approach to the use of Li cations, based on the fabrication of BF4 anion rocking-chair-type secondary batteries. For the anode material, we report a Si-based compound, [Si10H8(OCH2CH2NH(CH3)2)2](BF4)2, which is capable of reacting with two BF4 anions per formula unit at a potential of 1.8 V, giving a reversible capacity of 80mA h g−1. This anion battery also showed superior performance under thermal abuse compared with Li-ion batteries. Furthermore, the anion battery is operable at −30 °C, a temperature at which Li-ion batteries are generally not operable because Li-ions are solvated by coordination with basic organic molecules around this temperature.

Surface defects are commonly believed to be fundamentally important to gas-sensor performance. We examine the effect of gas coverage and ethanol orientation on its adsorption on the stoichiometric and oxygen deficient (101(-)0) nanowire surface. Our density functional theory calculations show that ethanol adsorbs in multiple stable configurations at coverages between 1/4 and 1 ML, highlighting the ability of ZnO to detect ethanol. Ethanol prefers to bind to a surface Zn via the adsorbate oxygen atom and, if a surface oxygen atom is in close proximity, the molecule is further stabilized by formation of a hydrogen bond between the hydrogen of the hydroxyl group and the surface oxygen. Two primary adsorption configurations were identified and have different binding strengths that could be distinguished experimentally by the magnitude of their OH stretching frequency. Our findings show that ethanol adsorbed on the oxygen deficient ZnO(101(-)0) surface has a reduced binding strength. This is due to either the lack of a hydrogen bond (due to a deficiency in surface oxygen) or to surface reconstruction that occurs on the defect surface that weakens the hydrogen bond interaction. This reduced binding on the oxygen deficient surface is in contrast to the defect enhanced gas-sensor interaction for other gases. Despite this difference, ethanol still acts as a reducing gas, donating electrons to the surface and decreasing the band gap. We show that multiple adsorbed ethanol molecules prefer to be orientated parallel to each other to facilitate the hydrogen bonding to the defect-free surface for enhanced interaction.

We have shown, using density functional theory calculations, that the properties of Si nanosheets change as a function of thickness. While Si(111) oriented nanosheets that are 0.56 nm thick (2-layers) display a novel reconstruction, classified as Si(111)-2 × 2 on both surface layers (T. Morishita, M. J. S. Spencer, S. P. Russo, I. K. Snook and M. Mikami, Chem. Phys. Lett., 2011, 506, 221), nanosheets that are up to a thickness of 1.42 nm show the Si(111)-2 × 1 surface reconstruction, that is seen on the bulk Si(111) surface, on both sides of the nanosheet. For these thicker nanosheets, the relative orientation of the π-chain structure on each surface of the nanosheet can either be the same or different, resulting in unique electronic properties. When the orientation is the same, there is a widening of the band gap, indicating that the interaction between the surface π-chains is not present when they are oriented in different directions. The electronic properties of the nanosheets approach those of the bulk by 1.42 nm thick. The variation in structural and electronic properties of Si nanosheets with different thicknesses, as shown in this study, highlights the novelty of these materials and their significance for applications in electronic device technologies.

There have been many investigations to reveal the nature of the hydrogen gas and ZnO nanopowder interaction at elevated temperatures, while at present no conclusive description of such an interaction has been confidently reported. In this work, we demonstrate that a hydroxyl group is formed during this interaction, depending on size and relative crystallinity of nanopowders. Our in situ Raman spectroscopy investigations show that the interaction directly affects the intensity of the Raman signal at 483 cm(-1), relative to the peak at 519 cm(-1). Ex situ x-ray diffraction (XRD) and infrared spectroscopy also show extra peaks at 44° and 1618 cm(-1), respectively, after hydrogenation. These peaks were all identified as surface hydroxyl groups, which can be related to the formation of water on the ZnO nanopowder surfaces.

Hydrothermally grown ZnO nanorods show high interaction rates with H2 when the spacing between adjacent nanorods decreases. Density functional theory calculations showed the interaction between nanorod surfaces in-registry is attractive at separations < 5??, while it is repulsive for out-of-registry alignments, indicating that uniform nanorods grown with their faces aligned out-of-registry are not likely to fuse due to the repulsion between the surfaces. The separation of 5?? was found to be sufficient for H2 to adsorb between the surfaces, resulting in a transfer of charge from H2 to the surface, consistent with the measured increase in conductivity. This explains the ability of hydrogen to adsorb on closely spaced nanorods.

The adsorption of atomic nitrogen and oxygen on the (2110) crystal face of zinc oxide (ZnO) was studied. Binding energies, workfunction changes, vibrational frequencies, charge density differences and electron localization functions were calculated. It was elucidated that atomic oxygen binds more strongly than nitrogen, with the most stable O/ZnO(2110) structure exhibiting a binding energy of -2.47 eV, indicating chemisorption onto the surface. Surface reconstructions were observed for the most stable minima of both atomic species. Positive workfunction changes were calculated for both adsorbed oxygen and nitrogen if the adsorbate interacted with zinc atoms. Negative workfunction changes were calculated when the adsorbate interacted with both surface oxygen and zinc atoms. Interactions between the adsorbate and the surface zinc atoms resulted in ionic-type bonding, whereas interactions with oxygen atoms were more likely to result in the formation of covalent-type bonding. The positive workfunction changes correlate with an experimentally observed increase in resistance of ZnO conductometric sensor devices.