Electrodeposition of hierarchical ZnO nanorod-nanosheet structures and their applications in dye-sensitized solar cells

We present a two-step electrochemical deposition process to synthesize hierarchical zinc oxide (ZnO) nanorod-nanosheet structures on indium tin oxide (ITO) substrate, which involves electrodeposition of ZnO nanosheet arrays on the conductive glass substrate, followed by electrochemical growth of secondary ZnO nanorods on the backbone of the primary ZnO nanosheets. The formation mechanism of the hierarchical nanostructure is discussed. It is demonstrated that annealing treatment of the primary nanosheets synthesized by the first-step deposition process plays a key role in synthesizing the hierarchical nanostructure. Photovoltaic properties of dye-sensitized solar cells (DSSCs) based on hierarchical ZnO nanostructures are investigated. The hierarchical ZnO nanorod-nanosheet DSSC exhibits improved device performance compared to the DSSC constructed using photoelectrode of bare ZnO nanosheet arrays. The improvement can be attributed to the enhanced dye loading, which is caused by the enlargement of internal surface area within the nanostructure photoelectrode. Furthermore, we perform a parametric study to determine the optimum geometric dimensions of the hierarchical ZnO nanorod-nanosheet photoelectrode through adjusting the preparation conditions of the first- and second-step deposition process. By utilizing a hierarchical nanostructure photoelectrode with film thickness of about 7 μm, the DSSC with an open-circuit voltage of 0.74 V and an overall power conversion efficiency of 3.12% is successfully obtained.     

Mathematical formulation for zero reflection from multilayer metamaterial structures and their notable applications

The behaviour of bilayer structures composed of common materials and metamaterials (MTMs) under oblique incidence of plane waves is investigated by exact analytical methods. The TE, TM and elliptical polarisations are analysed. There are several combinations of double positive (DPS), double negative (DNG), epsilon negative (ENG) and mu negative (MNG) media for the bilayer structures, but only DPS?DPS, DPS?DNG and ENG?MNG bilayers with TE, TM and circular polarisations are analysed in detail. For homogeneous and isotropic MTM media, exact mathematical relations are derived for the design of reflectionless bilayer structures as a function of their geometry (thickness) and electric and magnetic parameters. Frequency dispersion is included in the formulations. It is shown that bilayers composed of common materials are not effective for the construction of zero reflection bilayer surfaces, whereas the application of MTMs is required to realise reflectionless phenomena. For the design of zero reflection bilayer structures, their thicknesses and values of ε and μ are determined. Finally, the performance of forward and backward notch filters observed by MTM bilayer structures are studied in detail and their designs and applications are investigated. The bandwidth of lossy MTMs increases considerably.     

Extensions of Kronecker product algebra with applications in continuum and computational mechanics

Summary Kronecker product algebra is widely applied in control theory. However, it does not appear to have been commonly applied to continuum and computational mechanics (CCM). In broad terms the goal of the current investigation is to extend Kronecker product algebra so that it can be broadly applied to CCM. Many CCM quantities, such as the tangent compliance tensor in finite strain plasticity, are very elaborate or difficult to derive when expressed in terms of tensor indicial or conventional matrix notation. However, as shown in the current article, with some extensions Kronecker product algebra can be used to derive compact expressions for such quantities. In the following, Kronecker product algebra is reviewed and there are given several extensions, and applications of the extensions are presented in continuum mechanics, computational mechanics and dynamics. In particular, Kronecker counterparts of quadratic products and of tensor outer products are presented. Kronecker operations on block matrices are introduced. Kronecker product algebra is extended to third and fourth order tensors. The tensorial nature of Kronecker products of tensors is established. A compact expression is given for the differential of an isotropic function of a second-order tensor. The extensions are used to derive compact expressions in continuum mechanics, for example the transformation relating the tangent compliance tensor in finite strain plasticity in undeformed to that in deformed coordinates. A compact expression is obtained in the nonlinear finite element method for the tangent stiffness matrix in undeformed coordinates, including the effect of boundary conditions prescribed in the current configuration. The aforementioned differential is used to derive the tangent modulus tensor in hyperelastic materials whose strain energy density is a function of stretch ratios. Finally, block operations are used to derive a simple asymptotic stability criterion for a damped linear mechanical system in which the constituent matrices appear explicitly.Appendix: Notation A, Â, a_ij matrix, second-order tensor - a, a_i vector, VEC (A) - a vector - â scalar - B, b_ij matrix, second-order tensor - b, b_i VEC (B) - b vector - block permutation matrix - C, C, c_ijkl fourth-order tensor - right Cauchy Green strain tensor - c VEC () - c_i eigenvalues of - C _a,C _b third-order tensors - C ₁,C ₂,C ₃ outer product functions - D deformation rate tensor - D damping matrix - d VEC (D) - E boundary stiffness matrix - e VEC () - Eulerian strain - F isotropic tensor-valued function ofA - deformation gradient tensor - f VEC - f scalar valued counterpart ofF - G coordinate transformation tensor - G strain-displacement matrix - g VEC (G) - g consistent force vector - H dynamic system matrix - h_n lowest eigenvalue ofH - I,I _n,I ₉ identity matrix/tensor - i VEC (I) - I₁ TRACE () - I index - i index - J determinant of - J matrix relating d to da - J index - j index - J matrix relating d to da - K,K _T,K _b,K stiffness matrices - K index - k index - L velocity gradient tensor - L index - l index - M mass matrix - strain-displacement matrix - M matrix arising from Ogden model - M index - m index - N shape function matrix - N matrix arising from Ogden model - n, n₀ exterior normal vectors - n n² - N index - n index - P, dynamic system matrix - p VEC (P) - p_n eigenvalue ofP - Q rotation tensor - R,r _ij tensor used with outer products - r rank, index - r VEC (R) - S,s _ij tensor used with outer products - s VEC (S) - S, S₀ surface area - S matrix diagonalizingA - s index - T unitary matrix - t₀, t traction - t VEC () - VEC ( ) - t time - T time interval - U _n ,U ₉,U _M permutation matrices - u displacement vector - V matrix appearing in linear system stability criterion - V projection matrix - W,W _i multipliers d - w, w₁ vectors - strain energy function - X undeformed position - x deformed position - Y,Y coordinate system - y, y_j vectors - z, z_j vectors - _j eigenvalue ofA - _j eigenvalue ofB - , ₁, ₂ nodal displacement vectors - _j eigenvalue of - matrix - , ₁, ₂, _a, _b diagonal matrices - _ij entries of the Kronecker tensor (I) - Lagrangian strain - _ijk permutation tensor - _i coefficient of Ogden model - parameter in linear system stability criterion - _i eigenvalue - Lamé coefficient - matrix - surface area factor - Lamé coefficient - _j eigenvalue ofA - _i coefficient of Ogden model - matrix - second Piola-Kirchhoff stress - Cauchy stress - Truesdell stress flux - matrix/tensor - matrix/tensor - matrix/tensor - TEN22 (C) - d rotation vector - d rotation tensor - TRACE(.) trace of a matrix - left Kronecker function - right Kronecker function - VEC(.) vectorization operator - VECB(.) block vectorization operator - TEN22(.) tensor operator - TEN12(.) tensor operator - TEN21(.) tensor operator - _x, _y divergence operator - d(.) differential operator - (.) variational operator - (right) Kronecker product - Kronecker sum - Kronecker difference - block Kronecker product - left Kronecker product - AsB block Kronecker sum ofA andB - AdB block Kronecker difference ofA and      

On the development of colloidal nanoparticles towards multifunctional structures and their possible use for biological applications

In this Review, we describe the synthesis of high-quality colloidal nanoparticles in organic solvents, the mechanisms by which they can be transferred into aqueous solution, and some of their applications in biology. In particular, we will place emphasis on the creation of multifunctional nanoparticles or nanoparticle assemblies.     

Piezotensegritic structures for transducer applications

Piezoelectricity and tensegrity have been coupled into an electrically active device. This concept, hereby known as piezotensegrity, can be used to sense or actuate. A composite sensor has been tested using compression elements stabilized with tensioning bands. The piezoelectric elements are arranged on the face diagonals with perimeter tension bands. Experimental piezoelectric response from this design was 1200 pC/N in air testing with peak hydrostatic response of 700 pC/N. The good device sensitivity as compared to properties of the base piezoelectric material is attributed to the internal arrangement of the piezoelectric elements and the tensioning system. Received: 28 April 1999 / Reviewed and accepted: 6 August 1999     

Magnetic sensors and their applications

Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented.     

Nanofluidic devices and their applications

Recent developments in micro- and nanotechnologies made possible the fabrication of devices integrating a deterministic network of nanochannels, i.e., with at least one dimension in a range from 1 to 100 nm. The proximity of this dimension and the Debye length, the size of biomolecules such as DNA or proteins, or even the slip length, added to the excellent control on the geometry gives unique features to nanofluidic devices. This new class of devices not only finds applications wherever less well-defined porous media, such as electrophoresis gels, have been traditionally used but also give a new insight into the sieving mechanisms of biomolecules and the fluid flow at the nanoscale. Beyond this, the control on the geometry allows smarter design resulting, among others, in new separation principles by taking advantage of the anisotropy. This perspective gives an overview on the fabrication technologies of nanofluidic devices and their applications. In the first part, the current state of the art of nanofluidic fabrication is presented. The second part first discusses the key transport phenomena in nanochannels. Current applications of nanofluidic devices are next discussed. Finally, future challenges and possible applications are highlighted.     

Antenna applications of negative-refractive-index transmission-line structures

A number of new antenna-related applications that have recently been developed at the University of Toronto based on the concept of negative-refractive-index transmission-line metamaterials are reviewed. These include non-radiating phase-shifting lines that can produce either a positive or a negative phase-shift while exhibiting a broadband linear phase response, as well as compact and broadband series power dividers and associated planar series-fed printed dipole arrays with reduced beam-squinting. Moreover, a fully printed electrically small ring antenna featuring vertical polarisation and good radiation efficiency is also described     

Electrical properties and applications of carbon nanotube structures

The experimentally verified electrical properties of carbon nanotube structures and manifestations in related phenomena such as thermoelectricity, superconductivity, electroluminescence, and photoconductivity are reviewed. The possibility of using naturally formed complex nanotube morphologies, such as Y-junctions, for new device architectures are then considered. Technological applications of the electrical properties of nanotube derived structures in transistor applications, high frequency nanoelectronics, field emission, and biological sensing are then outlined. The review concludes with an outlook on the technological potential of nanotubes and the need for new device architectures for nanotube systems integration.     

Extensions of the U* theory for applications on orthotropic composites and nonlinear elastic materials

To improve the performance and the efficiency of a structure, it is essential to understand how the applied loads are transferred through the structure. The U* index was introduced as one of the methods for identifying the load transfer paths within structures. It has increasingly been used by industry due to its unique capability in structural analysis and design. However, the feasibility of the U* theory for composite materials has not been demonstrated yet. Meanwhile, the U* index was only arisen for linear elastic materials, as a result it is invalid for materials with nonlinear elasticity. In this paper, two modified load transfer indexes for orthotropic composites (\(U_{O}^{*}\)) and nonlinear elastic materials (\(U_{NL}^{*}\)) are proposed based on the basic U* theory, respectively. The computational process of both the \(U_{O}^{*}\) and the \(U_{NL}^{*}\) indexes is presented. The effectiveness of the proposed indexes on load transfer analysis is demonstrated through four case studies.     

Language-based access control approach for component-based software applications

Security in component-based software applications is studied by looking at information leakage from one component to another through operation calls. Components and security specifications about confidentiality as regular languages are modelled. Then a systematic way is provided to synthesise an access control mechanism, which not only guarantees all specifications to be obeyed, but also allows each user to attain maximum permissive behaviours.     

Ceramic-based layer structures for biomechanical applications

A survey of recent advances in the analysis of ceramic-based layer structures for biomechanical applications is presented. Data on model layer systems, facilitating development of explicit fracture mechanics relations for predicting critical loads to produce lifetime-threatening damage, form the basis of the work.     

Ferroelectric films and their device applications

Recent reseach on ferroelectric films is discussed, with emphasis on preparative problems, optimization of film structure and of electrical properties and application in devices. Rapid progress has been made in each of these research areas and this fact, together with the emergence of certain new materials such as polyvinylidene fluoride (PVF₂), is increasing the variety of possible applications to solid state devices. Typical examples considered here include microwave capacitors, thermistor bolometers, pyroelectrics, piezoelectric transducers, memories and optical display devices. The present state of the art for these applications and materials development needed for further progress are reviewed.     

Lithium solid electrolytes and their applications

The preparation, characterisation and applications of two systems of lithium ion conductors, lithium zinc germanate (Lisicon) and lithium germanate vanadate are described. Ionic conductivity studies include ac conductivity, thermopower andnmr which provide complementary information. High pressure studies and fabrication of a solid-state cell are also reported. An erratum to this article is available at .     

Soluble carbon nanotubes and their applications

Carbon nanotubes (CNTs) have been the forefront of nanoscience and nanotechnology due to their unique electrical and mechanical properties and specific functions. However, due to their poor solubility in solvents, the applications using the materials have been limited. Therefore, strategic approaches toward the solubilization of CNTs are important in wide fields including chemistry, physics, biochemistry, biology, pharmaceuticals, and medical sciences. In this article, we summarize: (i) the strategic approaches toward the solubilization of CNTs using chemical and physical modifications, (ii) nanocomposites of CNTs and biological molecules including DNA, (iii) formation of CNTs with topological structures, (iv) separation of metallic and semiconducting nanotubes, (v) the preparations of films and fibers of CNTs and hybrid materials of CNTs and organic and inorganic molecules.     

Nanocellulose-stabilized Pickering emulsions and their applications

Abstract

Pickering emulsion, which is an emulsion stabilized by solid particles, offers a wide range of potential applications because it generally provides a more stable system than surfactant-stabilized emulsion. Among various solid stabilizers, nanocellulose may open up new opportunities for future Pickering emulsions owing to its unique nanosizes, amphiphilicity, and other favorable properties (e.g. chemical stability, biodegradability, biocompatibility, and renewability). In this review, the preparation and properties of nanocellulose-stabilized Pickering emulsions are summarized. We also provide future perspectives on their applications, such as drug delivery, food, and composite materials.