Solid State Phenomena Vols. 121-123

Abstract: Recent experiment showed that nano-fibers composite ceramics, fabricated through SHS process, can acquire high toughening and strengthening. Composite ceramics are mainly composed of fiber eutectic structures with random orientation, in which nanometer sized zirconia fibers are dispersed within the alumina matrix. First, it can be visualized that tensile force is transmitted from the matrix to the nano-fiber by means of shear stress that develop along the fiber- matrix interface. Then the mesomechanical strength model of the fiber eutectic structure is built. The longitudinal tensile stress of the fiber eutectic structure and shear stress on the surface of the fiber eutectic structure are obtained. They related to the volume fraction and slenderness ratio of the nano-fibers, and external strain of the fiber eutectic structure. Then considering random orientation of the fiber eutectic structure, as composite ceramics is subjected to tensile stress, external strain of the fiber eutectic structure can be determined. Finally, theoretical expression for the strength prediction of composite ceramics is gotten.

Abstract: Configurations of single-walled carbon nanotubes (SWCNTs) with randomly distributed vacancies were generated by numerical method. Molecular dynamics (MD) method was used to investigate the compressive mechanics properties of SWCNTs with vacancies. The simulation results show that the SWCNTs with vacancies have more complicated deformation procedures and the Young’s modulus is lower than the corresponding perfect SWCNTs. The Young’s modulus of the SWCNTs with no more than 20 vacancies ranges from 940Gpa to 620Gpa, and its value is approximately linearly proportional to the number of vacancies. It is found that local buckling first appears in the surface region having high density of vacancies of (10, 10) SWCNTs under axial compression. As the loading increases, SWCNTs with more vacancies have more complicated buckling configuration and sluggish energy variation. Under a case of the same displacement load the more vacancies the SWCNT has, the more complicated the mechanical behavior is. SWCNTs with 20 vacancies can still maintain self structure stabilization, this validates that SWCNTs have good spacial stabilization.

Abstract: 3D layer-by-layer photonic crystals possess a full photonic band gap. Simulation of 3D layer-by-layer photonic crystals can optimize the parameters of the photonic crystals to get useful photonic band gap by solving Maxwell’s equations using the plane-wave-based transfer-matrix method. The relations between the parameters (rod pitch a, rod width w, rod thickness h and rod refractive index n) and the photonic band gap have been simulated. We also have fabricated a 3D layer-by-layer photonic crystal with femtosecond laser microfabrication technique through two-photon-absorption photopolymerization of resin. Its reflection spectra have been detected which agree with the simulation result.

Abstract: Nano-fibers composite ceramics were mainly composed of fiber eutectics with random orientation, in which nanometer sized second fibers are dispersed within the ceramic matrix. First, Mori-Tanaka method was used to predict the stiffness of the fiber eutectic structure. The fiber eutectic structure is transverse isotropy and has five independent elastic constants. Then considering random orientation of the fiber eutectic structure, the Young’s modulus and Poisson’s ratio of composite ceramics is determined by mean strain. Composite ceramics is isotropy. When the volume fraction of nano-fibers increase, the Young’s modulus of composite ceramics decrease and are little smaller than the volume average value, the Poisson’s ratio of composite ceramics decrease and are little bigger than the volume average value.

Abstract: Electrons impinging or escaping from a solid surface undergo surface electronic excitations which are competitive in nature to other electron-solid interaction channels. The detailed information about electron inelastic scattering probability for surface excitations at solid surface is also important in reflection electron energy loss spectroscopy. A self energy formalism based on quantum mechanical treatment of interaction of electrons with a semi-infinite medium, which uses the optical dielectric function is considered to study surface boundary effect for planar surfaces of Cu and Ni for various conditions of electron-solid interactions. The total surface excitation probability of an electron while crossing the surface boundary once is numerically computed by integrating surface term of spatial and angular dependent differential inelastic cross sections over energy loss and distance from the surface. It is found that surface effect is prominent for low energy electrons and large oblique angles with respect to surface normal and confined to the close vicinity of surface boundary.

Abstract: The cohesive energy is the energy to divide the crystal into isolated atoms, and the direct result of cohesive energy is to create new surface. The increased surface energy should equal the cohesive energy of the crystal, which results from the surface area difference between the total atoms and the crystal. This is the basic concept of Surface-Area-Difference (SAD) model. The SAD model has been extended to account for the melting temperature of metallic nanocrystals with non-free surface (embedded in a matrix) in the present work. It is shown if the melting temperature of the matrix must be much higher than that of the bulk value of the nanocrystals, and the nanocrystals has coherent or semi-coherent interface with the matrix, the nanocrystals may be superheated. The present results are supported by the available experimental values.

Abstract: The size-dependent electronic structures of metal clusters Cun (n=2-20) have been calculated using density functional theory method. The results reveal that their electronic properties are almost the same as bulk material if the cluster size larger than a critical value. The properties can be understood by a surface-noncrystalline-layer model that composed of an interior crystalline-like core and an outer surface noncrystalline layer.

Abstract: Large area coatings containing nanoparticulate metal oxides dispersed in polymers are manufactured at high speed (up to 200 m2 /min.) by curtain- or cascade coating on flexible substrates near room temperature. Simultaneously coated multilayers, which may contain different metal oxides, show interesting new properties for industrial applications. Thick (40 $m) coatings with rare-earth doped aluminum oxide nanoparticles have been commercialized for waterfast ink-jet media which are dry to touch after printing, show photo-parity and are very stable towards water, light and environment if appropriate inks are used. Strong capillary forces due to nanoporosity allow instant ink-absorption. Experimental techniques used to develop these materials and results related to imaging parameters are discussed. Thin layers (1-10 $m) of nanoparticulate, nanoporous TiO2 and LiMn2O4, dispersed in non-electroactive polymers such as polyethylene glycols, can be used as electrodes for rechargeable Li-ion batteries with very fast charge-discharge cycles and high power performance. The excellent ion-conducting properties of unsintered, nanoparticulate coatings of these metal oxides were unexpected and allow applications of temperature sensitive substrates and organic addenda. By coating very thin, almost or totally polymer-free layers of highly-porous, monodisperse aluminum-oxides with minimum particle size, display devices with improved optical efficiency were prepared. These layers have a low refractive index thus allowing for higher intensities of light emitted by organic electro-luminescers in OLED’s and PLED’s. This property is useful for mobile devices as phones and PDA’s. A hitherto unknown, photo-catalytic chemical reaction of the classical green emitter tris-(8-hydroxychinolino)-aluminum (Alq3) has been discovered in coatings of such optically efficient devices after exposing them to daylight in air. An efficient blue-emitting species of Alq3 with another stereochemical structure was directly formed within these layers at room temperature by photolysis in ambient atmosphere. Interesting new applications of specially designed, large-area coated and transparent nanostructured matrices on flexible substrates for optical gas sensors are discussed in more detail in this paper.

Abstract: Nano-structured carbon nitride film, which is a new sensor material, has been prepared by facing target magnetron sputter for microsensor applications. Surface morphology, surface roughness and bonding structures of the films were investigated by EDS, SEM, AFM and FTIR spectroscopy. The growth rate of film is about 2.2 um/hr, and grain size and RMS roughness are about 320 nm and 0.9 nm, respectively. The impedance of micro-humidity-sensor, which was fabricated by the conventional semiconductor fabrication process including lift-off technique, changed 95.4 kΩ to 2 kΩ in the relative humidity range of 5 % to 95 %.

Abstract: Piezoelectric motors have been successfully developed for various applications like autofocus drives in camera lenses and manufacturing equipment for semiconductor production. Their high speed and accurate positioning capability, combined with a moderate holding torque, make piezo motors also very attractive for actuation purposes in spacecraft mechanisms. However, these motors require high driving voltage and have only a small driving torque. In this paper, the authors have developed a novel magnetostrictive rotary motor using Terfenol-D (Tb0.3Dy0.7Fe1.9) material as the driving elements. The small movement of the magnetostrictive actuator is scaled to 3 times by using flexible flexure hinges, a special designed mechanism is used to combine 3 such actuators to form a pure rotation movement and this movement is used to drive the rotor of the motor. Prototype of this research is made and a commonly 3-phase alternating current is used to drive the motor. Experiments are also carried on in the lab of School of Mechanical and Electrical Engineering of Hangzhou Dianzi University.