Half-metallic ferromagnetism in Ag-doped ZnO: An ab initio study

The spin-resolved electronic structures of ZnO doped with 6.25% Ag have been studied with the first-principles calculations based on the spin density functional theory. The substitutional Ag impurities and their nearest neighbor O atoms are shown to be in a spin polarized state with a global magnetization of 1.0μ_B. Ag-doped ZnO is in a ferromagnetic ground state which can be explained by Zener's double exchange mechanism. Furthermore, band structure calculations show a half-metallic behavior of the Ag-doped ZnO. These results indicate that Ag-doped ZnO shows promise as a dilute magnetic semiconductor free of magnetic precipitation and may find applications in the field of spintronics.     

Nanostructure Synthesis at the Solid–Water Interface: Spontaneous Assembly and Chemical Transformations of Tellurium Nanorods

Bottom‐up synthesis offers novel routes to obtain nanostructures for nanotechnology applications. Most self‐assembly processes are carried out in three dimensions (i.e. solutions); however, the large majority of nanostructure‐based devices function in two dimensions (i.e. on surfaces). Accordingly, an essential and often cumbersome step in bottom‐up applications involves harvesting and transferring the synthesized nanostructures from the solution onto target surfaces. We demonstrate a simple strategy for the synthesis and chemical transformation of tellurium nanorods, which is carried out directly at the solid–solution interface. The technique involves binding the nanorod precursors onto amine‐functionalized surfaces, followed by in situ crystallization/oxidation. We show that the surface‐anchored tellurium nanorods can be further transformed in situ into Ag₂Te, Cu₂Te, and SERS‐active Au–Te nanorods. This new approach offers a way to construct functional nanostructures directly on surfaces.     

Atmospheric pressure chemical vapour deposition of selenium and tellurium films by UV laser photolysis of diethyl selenium and diethyl tellurium

Excimer laser‐induced photolysis of gaseous diethyl selenium and diethyl tellurium (C₂H₅)₂M (M = Se, Te) is controlled by cleavage of both M? C bonds, it yields C₁–C₄ hydrocarbons (ethene as major product) and results in chemical vapour deposition of selenium films and nanosized tellurium powder. The selenium and tellurium properties were characterized by X‐ray photoelectron spectroscopy and Scanning electron Microscopy techniques. Copyright © 2001 John Wiley & Sons, Ltd.     

Polymerization of Tellurophene Derivatives by Microwave‐Assisted Palladium‐Catalyzed ipso‐Arylative Polymerization

We report the synthesis of a tellurophene‐containing low‐bandgap polymer, PDPPTe2T, by microwave‐assisted palladium‐catalyzed ipso‐arylative polymerization of 2,5‐bis[(α‐hydroxy‐α,α‐diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC₇₁BM show PCE values of up to 4.4 %. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 µm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon–carbon bonds between the tellurophene and thiophene rings, which results in the red‐shift in absorption upon substitution of tellurium for sulfur.     

Tailoring Transition‐Metal Hydroxides and Oxides by Photon‐Induced Reactions

Controlled synthesis of transition‐metal hydroxides and oxides with earth‐abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition‐metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺, Mn²⁺, and Co²⁺ ion‐containing aqueous solution undergoes photo‐induced reactions and produces hollow metal‐oxide nanospheres (Ni_0.18Mn_0.45Co_0.37O_x) or core–shell metal hydroxide nanoflowers ([Ni_0.15Mn_0.15Co_0.7(OH)₂](NO₃)_0.2?H₂O), depending on the laser wavelengths. We propose two reaction pathways, either by photo‐induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon‐induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.     

Computational Study of Cage Like (ZnO)12 Cluster Using Hybrid and Hybrid Meta Functionals

Density Functional Theory employing hybrid and M06 functionals in combination with three different basis sets is used to calculate the ground state of a cage like (ZnO)₁₂ nanocluster which has been consistently reported as the more stable cluster for its particular size. B3LYP and B3PW91 hybrid functionals combined with 6‐31+G*, Lanl2dz and SDD basis sets are employed to treat the ZnO molecular system. Alternatively, three M06 functionals in combination with three basis sets are employed in the nanostructure calculations. Results obtained by treating ZnO sodalite cage nanocluster with M06 functionals demonstrated comparable quality to results obtained with hybrid functionals. Within this study, efficient theoretical DFT methods with the widely known hybrid and the recently created M06 meta‐hybrid functionals are employed to study nanostructured ZnO. Our resulting parameters provide a fresh approach performance wise on the different theoretical methods to treat transition metal nanostructures, particularly, ZnO nanoclusters geometry and electronic structure.     

Photomagnetic and nonlinear optical properties in cis‐trans green fluoroprotein chromophore coupled Bis‐imino nitroxide diradicals

The current study extends an earlier investigation (Bhattacharya, et al., Phys. Chem. Chem. Phys. 2012, 14, 6905) to further explore various photomagnetic and optical properties of bis‐imino nitroxide, that is, (IN)₂‐based green fluorescent protein (GFP) chromophore coupled diradicals revealing new significant features. The conversion mechanisms of selected trans‐isomers into their corresponding cis‐conformers are discussed in detailed using a number of recently‐developed density functional theory (DFT) functionals based on the Minnesota suite of DFT‐models as well as using some other DFT functionals developed earlier. To provide a more in‐depth analysis of variations in magnetic properties as trans‐conformers (singlet ground‐state) convert into their cis‐analogues (triplet ground‐state), the changes in exchange magnetic coupling constants J are compared with the variation of the selected aromaticity indices. The aromaticity indices include the nuclear independent chemical shift [NICS(0)] values calculated at the center of ring structures and the harmonic oscillator model of aromaticity. Furthermore, the investigation of static nonlinear optical response properties in the (IN)₂‐based GFP chromophore coupled diradicals reveal unusually large static first hyperpolarizabilities for these systems which is highly significant for practical applications in optics and optoelectronics. © 2015 Wiley Periodicals, Inc.     

Structure and opto-electrochemical properties of ZnO nanowires grown on n-Si substrate

Zinc oxide (ZnO) nanostructures have attracted great attention as a promising functional material with unique properties suitable for applications in UV lasers, light emitting diodes, field emission devices, sensors, field effect transistors, and solar cells. In the present work, ZnO nanowires have been synthesized on an n-type Si substrate using a hydrothermal method where surfactant acted as a modifying and protecting agent. The surface morphology, electrochemical properties, and opto-electrochemical properties of ZnO nanowires are investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry, and impedance spectroscopy techniques. The cycling characteristics and rate capability of the ZnO nanowires are explored through electrochemical studies performed under varying electrolytes. The photo response is observed using UV radiation. It is demonstrated that crystallinity, particle size, and morphology all play significant roles in the electrochemical performance of the ZnO electrodes.     

Structural and optical properties of ZnMgO nanostructures formed by Mg in-diffused ZnO nanowires

ZnMgO nanostructures with wurtzite phase were prepared by thermal diffusion of Mg into the ZnO nanowires. As ZnO light-emitting devices have been operated by using ZnMgO layers as energy barrier layers to confine the carriers, it is essential to realize the characterization of ZnMgO particularly. In this work, the Mg content in Zn_1−xMg_xO alloy determined by X-ray diffraction (XRD) and photoluminescence (PL) shows a good coincidence. The variation of lattice constant and the blueshift of near-band-edge emission indicate that Zn²⁺ ions are successfully substituted by Mg²⁺ ions in the ZnO lattice. In Raman-scattering studies, the change of E₂(high) phonon line shape in ZnO:Mg nanostructures reveals the microscopic substitutional disorder. In addition to the host phonons of ZnO, two additional bands around 383 and 510 cm⁻¹ are presumably attributed to the Mg-related vibrational modes.     

An ab-initio study of structural,opto-electronic and thermoelectric aspects of zinc sulfide and zinc telluride

In this study, structural, electronic, optical and thermoelectric aspects of Zinc Sulfide (ZnS) and Zinc Telluride (ZnTe) have been explored in detail. These calculations have been done by utilizing FP-LAPW method via Density Functional Theory (DFT). In order to attain accurate band gaps, opto-electronic properties are evaluated with modified Becke Johnson potential (mBJ). From band structure plots, both ZnS and ZnTe reveals direct (Γ_v–Γ_C) band gap semiconductors in nature with bandgap value equal to 3.5 and 2.3 eV while in Density Of States (DOS) major influence is observed due to p states of S/Te and d state of Zn. Prominent variation of optical responses such as high values of imaginary dielectric constants 𝜀1 (ω) and n (ω) refractive index suggests that ZnS and ZnTe are applicant materials for future photonics and microelectronic devices. The thermoelectric aspects were explored by Boltz Trap code to determine electrical and thermal conductivities, Seebeck coefficients, power factors and figure of merit. The figure of merits is closer to 1 while compared with p-type ZnS and ZnTe, n-type ZnS and ZnTe has good thermoelectric properties, which are attributed to low thermal conductivity of the hole and larger effective mass. The goal of this research is to investigate not only the detailed physical aspects but also to provide an overview of its future applications in optoelectronics, displays, sensors and microelectronic industry.     

Green Synthesis and Applications of ZnO and TiO2 Nanostructures

Over the last two decades, oxide nanostructures have been continuously evaluated and used in many technological applications. The advancement of the controlled synthesis approach to design desired morphology is a fundamental key to the discipline of material science and nanotechnology. These nanostructures can be prepared via different physical and chemical methods; however, a green and ecofriendly synthesis approach is a promising way to produce these nanostructures with desired properties with less risk of hazardous chemicals. In this regard, ZnO and TiO₂ nanostructures are prominent candidates for various applications. Moreover, they are more efficient, non-toxic, and cost-effective. This review mainly focuses on the recent state-of-the-art advancements in the green synthesis approach for ZnO and TiO₂ nanostructures and their applications. The first section summarizes the green synthesis approach to synthesize ZnO and TiO₂ nanostructures via different routes such as solvothermal, hydrothermal, co-precipitation, and sol-gel using biological systems that are based on the principles of green chemistry. The second section demonstrates the application of ZnO and TiO₂ nanostructures. The review also discusses the problems and future perspectives of green synthesis methods and the related issues posed and overlooked by the scientific community on the green approach to nanostructure oxides.     

Computational Study of the Interactions between Benzene and Crystalline Ice Ih: Ground and Excited States

Ground‐state geometries of benzene on crystalline ice cluster model surfaces (I_h) are investigated. It is found that the binding energies of benzene‐bound ice complexes are sensitive to the dangling features of the binding sites. We used time‐dependent DFT to study the UV spectroscopy of benzene, ice clusters, and benzene–ice complexes, by employing the M06‐2X functional. It is observed that the size of the ice cluster and the dangling features have minor effects on the UV spectral characteristics. Benzene‐mediated electronic excitations of water towards longer wavelengths (above 170 nm) are noted in benzene‐bound ice clusters, where the cross‐section of photon absorption by water is negligible, in good agreement with recent experimental results (Thrower et al., J. Vac. Sci. Technol. A, 2008, 26 , 919–924). The intensities of peaks associated with water excitations in benzene–ice complexes are found to be higher than in isolated ice clusters. The π→π* electronic transition of benzene in benzene–ice complexes undergoes a small redshift compared with the isolated benzene molecule, and this holds for all benzene‐bound ice complexes.     

Be2C Monolayer with Quasi‐Planar Hexacoordinate Carbons: A Global Minimum Structure

The design of new materials is an important subject in order to attain new properties and applications, and it is of particular interest when some peculiar topological properties such as reduced dimensionality and rule‐breaking chemical bonding are involved. In this work, we designed a novel two‐dimensional (2D) inorganic material, namely Be₂C monolayer, by comprehensive density functional theory (DFT) computations. In Be₂C monolayer, each carbon atom binds to six Be atoms in an almost planar fashion, forming a quasi‐planar hexacoordinate carbon (phC) moiety. Be₂C monolayer has good stability and is the lowest‐energy structure in 2D space confirmed by a global minima search based on the particle‐swarm optimization (PSO) method. As a semiconductor with a direct medium band gap, Be₂C monolayer is promising for applications in electronics and optoelectronics.     

Reactivity of molecular oxygen with aluminum clusters: Density functional and Ab Initio molecular dynamics simulation study

Dissociative adsorption of molecular oxygen (O₂) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O₂ with Al clusters using density functional theory (DFT) and atom‐centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O₂ and Al clusters to estimate the barrier energy of this reaction. The M06‐2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06‐2X functional predicts the reactivity of O₂ with the Al cluster in agreement with the experimental findings, that is, singlet O₂ readily reacts with Al clusters but triplet O₂ is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O₂ with Al clusters. The M06‐2X functional is relevant for investigating chemical reactions involving Al and O₂. © 2016 Wiley Periodicals, Inc.     

Challenges in the simulation of dye-sensitized ZnO solar cells: quantum confinement, alignment of energy levels and excited state nature at the dye/semiconductor interface

We report a first principles density functional theory/time-dependent density functional theory (DFT/TDDFT) computational investigation on a prototypical perylene dye anchored to realistic ZnO nanostructures, approaching the size of the ZnO nanowires used in dye-sensitized solar cells devices. DFT calculations were performed on (ZnO)(n) clusters of increasing size, with n up to 222, of 1.3 × 1.5 × 3.4 nm dimensions, and for the related dye-sensitized models. We show that quantum confinement in the ZnO nanostructures substantially affects the dye/semiconductor alignment of energy levels, with smaller ZnO models providing unfavourable electron injection. An increasing broadening of the dye LUMO is found moving to larger substrates, substantially contributing to the interfacial electronic coupling. TDDFT excited state calculations for the investigated dye@(ZnO)(222) system are fully consistent with experimental data, quantitatively reproducing the red-shift and broadening of the visible absorption spectrum observed for the ZnO-anchored dye compared to the dye in solution. TDDFT calculations on the fully interacting system also introduce a contribution to the dye/semiconductor admixture, due to configurational excited state mixing. Our results highlight the importance of quantum confinement in dye-sensitized ZnO interfaces, and provide the fundamental insight lying at the heart of the associated DSC devices.     

Physicochemical Interaction of ZnO Fine Particles with 5‐Mono‐(4‐carboxyphenyl)‐10,15,20‐Triphenylporphyrin

This study deals with an investigation on the preparation and physicochemical interactions of ZnO nanoparticles with acid functionalized porphyrin [5‐mono‐(4‐carboxyphenyl)‐10,15,20‐triphenylporphyrin (CPTPP)] for photovoltaic applications in a detailed manner. Zinc acetate and sodium hydroxide were used as the starting materials for the synthesis of ZnO nanoparticles at 60 °C in an alcoholic medium. The freshly prepared fine particles were then functionalized with CPTPP. Both the virgin and pregnant ZnO particles were characterized by using UV‐Visible spectrophotometry (UV), fluorescence emission (PL), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The band gap energy obtained for ZnO particles, having a value of 3.47 eV, shows significant quantum confinement effect and enhanced photophysical activity. FTIR analysis of the doped ZnO nanostructures showed the presences of some chemical species. SEM analysis revealed a clear change in the surface morphologies of undoped ZnO. The average crystallite size of nanoparticles, calculated from XRD peaks, was found in the nano regime. The lattice parameters calculated for ZnO nanocrystals were also found in good agreement with those given in the literature. From the enhancement in the red shift of the UV‐Vis spectra, it is concluded that hybridization of acid functionalized porphyrin can cause a significant expansion in the total absorption region of ZnO semiconductor for photovoltaic applications.     

Local‐Curvature‐Controlled Non‐Epitaxial Growth of Hierarchical Nanostructures

Site‐selective growth on non‐spherical seeds provides an indispensable route to hierarchical complex nanostructures that are interesting for diverse applications. However, this has only been achieved through epitaxial growth, which is restricted to crystalline materials with similar crystal structures and physicochemical properties. A non‐epitaxial growth strategy is reported for hierarchical nanostructures, where site‐selective growth is controlled by the curvature of non‐spherical seeds. This strategy is effective for site‐selective growth of silica nanorods from non‐spherical seeds of different shapes and materials, such as α‐Fe₂O₃, NaYF₄, and ZnO. This growth strategy is not limited by the stringent requirements of epitaxy and is thus a versatile general method suitable for the preparation of hierarchical nanostructures with controlled morphologies and compositions to open up a verity of applications in self‐assembly, nanorobotics, catalysis, electronics, and biotechnology.     

Polytellurides and Polyselenides – Compounds Containing $_{\infty}^{1}\rm [Te_{6}-Te_{4}]^{4-}$ and [Sn(Se4)3]2− Anions

The reactions of the Zintl phase K₂Cs₂Sn₉ with elemental tellurium and selenium in ethylenediamine have been investigated. From the reaction of K₂Cs₂Sn₉ with elemental tellurium [K‐(2,2,2‐crypt)]₄Te₆Te₄ ( 2 ) and [K‐(2,2,2‐crypt)]₂Sn₂Te₃ ( 3 ) were obtained, whereas the reaction of K₂Cs₂Sn₉ with elemental selenium led to the formation of [K‐(2,2,2‐crypt)]₂Sn(Se₄)₃ ( 4 ) and [K‐(2,2,2‐crypt)]₂Cs₂Sn₂Se₆·2en ( 5 )¹⁾. Compounds 2 , 4 , 5 have been characterized by single crystal X‐ray structure determination.     

Walking Down the Chalcogenic Group of the Periodic Table: From Singlet to Triplet Organic Emitters

The synthesis, X‐ray crystal structures, ground‐ and excited‐state UV/Vis absorption spectra, and luminescence properties of chalcogen‐doped organic emitters equipped on both extremities with benzoxa‐, benzothia‐, benzoselena‐ and benzotellurazole ( 1_X and 2_X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal‐structure analyses provide evidence of similar packing for 2_O – 2_Se , in which the benzoazoles are engaged in π–π stacking and, for the heavier atoms, in secondary X???X and X???N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium‐doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters.