In-house synthesized copolymers Polystyrene-co-glycidyl methacrylate (PSt-co-GMA) are electrospun as mat of surface modified nanofibers with and without multi walled carbon nanotubes (MWCNTs). Composites are then formed by embedding layers of the nanofiber mats into epoxy resin. Interfacial bonding between polymer matrix and the nanofibers, and surface modification driven enhancement in mechanical response is assessed under flexural loads. Results indicate that at elevated temperture storage modulus of epoxy reinforced by PSt-co-GMA nanofibers and PSt-co-GMA/ MWCNTs composite nanofibers is about 10 and 20 times higher than the neat epoxy, respectively, despite weight fraction of the nanofibers being as low as 2%. Interfacial interaction is revealed by the storage modulus comparison of unmodified Polystyrene (PSt) and modified PSt-co-GMA nanofiber reinforced composite. To enhance further the resulting “crosslinked” structure, crosslinking agent ethylenediamine is also sprayed on the nanofibrous mats. Increased crosslinking density improves mechanical response of sprayed-over PSt-co-GMA nanofibers reinforced composites which is about 4 times higher than plain PSt-co-GMA nanofibers.

Superlattices with an ultra-low thermal conductivity were extensively studied to design thermoelectric materials. However, since they are made up of superposed materials showing lattice mismatches, they often show cracks and dislocations. Therefore, it is challenging to fabricate superlattices with a thermoelectric figure of merit ZT higher than unity. Moreover, like nanowires, they decrease heat transport in only one main direction. Self-assembly from epitaxial layers on a Si substrate is a major bottom-up technology to fabricate 3D Ge quantum-dot (QD) arrays in Si, which have been used for 3D quantum-device applications. Using the model of the atomic-scale 3D phononic crystal, we showed that 3D high-density arrays of self-assembled Ge QDs in Si can also show an ultra-low thermal conductivity in 3D, which can be several orders of magnitude lower than that of bulk Si. As a result, they can be considered to design novel 3D thermoelectric devices showing CMOS compatibility. In an example QD crystal, the thermal conductivity can be decreased below only 0.2 W/m/K. The main objective of this paper is to show the size dependence of the thermal conductivity versus the supercell lattice parameter d. For a constant QD-crystal filling ratio x = 12.5 at%, a decrease of the thermal conductivity is observed for an increasing d. This analysis enables us to predict that the optimal d-value will be of the order of 11 nm for the given filling ratio. At this optimum, the thermal conductivity decreases to the global minimum value of 0.9 W/m/K. The presented results are a first step towards the optimal design of thermoelectric devices with a maximal ZT obtained by global optimization of the size parameters.

Activated carbon is widely used for its attractive diffusion, adsorption and reaction properties. However, its mechanical behavior has received much less attention. We present a molecular dynamics simulation study on the elastic properties of activated carbon with nanometer-sized pores. The nanoporous carbon sample is composed of curved and defected graphene sheets, which is synthesized using quench molecular dynamics (QMD) method [1]. One unique feature of the current model is the mechanical stability, thus the bulk modulus, Young’s modulus, shear modulus and Poisson’s ratio can be obtained from simulated mechanical tests. By varying the density of the nanoporous carbon model, it was further found that the bulk modulus vs. density relation follows Gibson-Ashby type power law with exponents of 2.80 at low densities and 1.65 at high densities.

Pure ZnO, and Al doped ZnO, 120 -300 nm thin films on glass substrates, were synthesized by inkjet printing technique using zinc and aluminum acetate solution as precursors and a two stage heat treatment process to obtain polycrystalline hexagonal wurtzite structure with the mean grain size of 25 and 30 nm respectively. All films exhibit a transmittance above 85-90% in the visible wavelength range below 700 nm. In the Al doped films the UV absorption spectra show a strong absorption onset below 380nm followed by shoulders centered around 325 nm depending on the film thickness. The electrical conductivity of Al doped ZnO thin films is larger by two orders of magnitude than that for pure ZnO films while the photoconductivity increases by about three orders of magnitude under UV irradiation. The photoresponse of the films with UV irradiation in terms of the rise and decay times in the frequency range from 5 to 500 Hz is also presented and discussed.

Future CMOS technologies will require the use of substrate material with a very high mobility. Therefore, the combination of Ge pMOS with GaAs nMOS devices is investigated for its possible use in advanced CMOS applications. In this work, the physical, chemical and electrical properties of a-GeO2 interfacial passivation layer (IPL) for n-Ge(001) and p-GaAs(001) have been investigated, using Molecular Beam Epitaxy (MBE) technique. The efficient electrical passivation of Ge/GeO2 will be demonstrated, and in the case of GaAs, the use of a thin a-GeO2 interlayer reduces the defects at the interface.

We present generalized theoretical analysis and experimental realization of active quality factor control for the self-oscillating quartz tuning-fork (QTF). The quality factor Q and resonance frequency can be controlled by adding a phase shifted signal of proper gain with respect to the QTF motion. It is demonstrated that the analysis of QTF can be extended to other quartz resonators which are analyzed by an equivalent circuit-a combination of a parallel circuit of an harmonic L-R-C and a stray capacitance C0 . Finally, we suggest the prospect of several applications by using the active Q control of QTF such as increasing force sensitivity, reducing scanning time in scanning probe microscopy, and feedback cooling of electromechanical resonator.

Efficient methodologies for synthesis of nanocrystals (NC) are a crucial component for creation of nanostructured electronic components. Physical vapor deposition (PVD) is one of the most flexible techniques to fabricate self-assembled arrangements of nanoclusters. Controllable fabrication of such assemblies can improve reliability of nanocapacitors, enhance performance of magnetic memories, and has many applications in opto-electronics devices, etc. However, size, shape and density of nanocrystals are highly sensitive to the process conditions such as duration of deposition, temperature, substrate material, etc. To efficiently synthesize nanocrystalline arrays by PVD, the process control factors should be understood in greater detail. In this work, we present a kinetic Monte Carlo (KMC) model and report simulations that explicitly represent the PVD synthesis of nanocrystals on substrates. Here we study how varying the most important process parameters affects the morphologies of self-assembled metallic islands on substrates. We compare our results with experimentally observed surface morphologies generated by PVD and demonstrate that KMC models like this are an efficient tool for computer-aided design of PVD processes for synthesis of nanocrystals.

Degradation of In2O3-Ga2O3-ZnO (IGZO) thin-film transistors (TFTs)) was studied. We evaluated degradation caused by applying gate voltage and drain voltage stress. A parallel shift of the transfer curve was observed under gate voltage stress. Joule heating caused by the drain current was observed. We tried to reproduce this degradation of the transfer curve change by device simulation. When we assumed the trap level as the density of state (DOS) model and increased two kinds of trap density, we obtained properties that show the same trends as the experimental results. We concluded that two degradation mechanisms occur under gate and drain voltage stress conditions. And then, we tried to improve the TFT characteristics using high pressure water vapor (HPV) annealing. We also found that the cooling conditions after HPV annealing affect the IGZO TFT characteristics.

Electrochemomechanical deformations (ECMD) of conducting polymer, polyaniline, films are studied to investigate the creeping and the memory effects. During electrochemical cycling under high tensile stresses up to 5 MPa, the films showed a remarkable creeping, resulting in the one dimensional anisotropic deformation. However, the creeping was recovered by release of the tensile stress, restoring from the anisotropic deformation. It was also found that the strain of ECMD after applying high tensile stresses increased compared with that before applying the large tensile stress. The result indicates that the artificial muscles are strengthened in strain by the experience of large tensile loads, and discussed taking the rheology of electrochemical cycles, viz., electrostatic crosslinking of polymer chains by oxidation and release of crosslinking by reduction.

This contribution reports static ionic displacements in ferromagnetic disordered Fe70Pd30 alloys obtained by relaxation of the ionic positions of a 108-atom supercell within the framework of density functional theory. Comparison with a simple statistical model based on Lennard-Jones pair interactions reveals that these displacements are significantly larger than can be explained by the different sizes of the elemental constituents. The discrepancies are presumably related to collective displacements of the Fe atoms. Corresponding distortions are experimentally observed for ordered Fe3Pt and predicted by first-principles calculations for all ordered Fe-rich L12 alloys with Ni group elements and originate from details of the electronic structure at the Fermi level.

We report the experimental observation of a very strong cavity polariton dispersion in a multi-axial mode GaN microcavity. The linewidth of photoluminescent (PL) spectrum covers a few cavity axial modes. The resonant photoluminescent peaks have a strong dispersion. The frequency spacing between adjacent peaks decreases by almost a factor of five from 470nm to 370nm. The strong dispersion can be well described by cavity polariton dispersion, but not by the dispersion of the refractive index of GaN. The measured exciton-photon interaction constant is 260 meV. It is an order of magnitude higher than the typically reported values for GaN microcavities

Tensile deformation of individual electrospun polyvinyl alcohol (PVA) nanofibres was performed using a novel combination atomic force microscope (AFM)- scanning electron microscope (SEM) technique. The AFM was used to provide manipulation and mechanical testing of individual PVA nanofibers while the SEM was used to observe the deformation process. Resultant stress-strain curves show how the elastic modulus shows comparable, or even slightly increased, values to isotropic films. In addition, the electrospun fibers were tested to failure to measure their tensile strength.

In this paper three multilayered architectures based on a-SiC:H with voltage controlled spectral selectivity in the visible spectrum range are analyzed. Multiple simultaneous modulated communication channels (red, green and blue or their polychromatic mixtures) were transmitted together at different frequencies. The combined optical signal was analyzed by reading out the photocurrent signal generated by the devices, under different applied voltages. Results show that the multiplexed signal depends on the device architecture and is balanced by the wavelength and transmission speed of each input channel, keeping the memory of the incoming optical carriers. In the single graded p-i’i-n configuration the device acts mainly as an optical switch while in two stacked p-i’-n-(ITO)-p-i-n configurations, the input channels are selectively tuned by shifting between forward and reverse bias. An electrical model, supported by a numerical simulation gives insight into the device operation.

The formation of nanocrystal-molecule-nanocrystal nanostructures via controlled mixing of Au nanocrystals and bifunctional Re linkers is reported. UV-visible absorbance data, coupled with histogram analysis of nanostructures measured using Scanning Electron Microscopy has shown a characteristic optical response at wavelengths close to 600 nm following formation of dimer and trimer nanostructures. Directed assembly processes based on dielectrophoretic trapping have also been developed for electrical interfacing of these nanostructures between top-down nanoelectrode pairs for electrical characterization.

We have synthesized W and Mo doped VO2 nanoclusters embedded in 200 nm thick thermally grown SiO2 on 4-inch silicon wafers by sequential ion implantation of the elements V, W, Mo and O. The implantation energies have been chosen to locate the mean projected range in the centre of the SiO2 thin film. A post implantation rapid thermal annealing step in flowing Ar at 1000°C for 10 min leads to the growth of doped VO2 nanoclusters. The optical properties of the nanoclusters were analyzed by temperature dependent spectral ellipsometry in the spectral range of 320 to 1700 nm. It will be shown, that the semiconductor-metal phase transition hysteresis width starting at 50K in the undoped case can be systematically closed by increasing dopand concentration.

To investigate the feasibility of a 3D integrated all-solid-state micro-battery, the deposition of several battery materials was investigated. Deposition techniques where used that are in principle able to deposit step conformally in 3D structures: ALD was used to create a conductive Pt current collector, and LPCVD was applied for the deposition of poly-silicon anodes and LiCoO2 cathodes.The layers, initially deposited on planar substrates, showed the expected physical and electrochemical behavior and are in principle suitable for solid state micro-batteries.

We report on microstructure analysis of aluminum nitride (AlN) epilayers by transmission electron microscopy (TEM). AlN epilayer samples were grown on sapphire substrates by metal organic chemical vapor deposition. Cross section and plan view images were taken by TEM to investigate the threading dislocations. Edge type threading dislocations dominate the total dislocation density. The threading dislocations are greatly reduced by inserting an intermediate layer prior to the growth of high temperature AlN epilayer. The dislocations further reduce with increasing thickness. Our results correlate with the dislocation density estimated from x-ray diffraction analysis.

Calculated results for spin injection, transport, and magneto-resistance (MR) in organic semiconductors sandwiched between two ferromagnetic contacts are presented. The carrier transport is modeled by spin dependent device equations in drift-diffusion approximation. In agreement with earlier results, spin injection from ferromagnetic contacts into organic semiconductors can be greatly enhanced if (spin-selective) tunneling is the limiting process for carrier injection. Modeling the tunnel processes with linear contact resistances yields spin currents and MR that tend to increase with increasing bias. We also explore the possibility of bias dependent contact resistances and show that this effect may limit MR to low bias.

A series of binary to hexanary alloys (Ni, Co, Mo, Al, Fe, Cu) are produced by mechanical alloying. Formation of an FCC solid solution is observed in the binary system. For ternary to quinary systems the presence of an amorphous phase and a BCC solid solution is identified, and for the hexanary system a combination of BCC and FCC solid solutions is detected. There is a very small change in the lattice parameter of Mo, reflecting the limited solid solubility of other element in this structure. However, Mo induces the fast amorphization of other elements and the reduction of crystallite size.

Indium tin oxide (ITO) is widely used for opto-electronic products such as organic light-emitting diodes, organic photovoltaic devices and liquid crystal displays due to its high transparency and electrical conductivity. Since there is a trade-off between the conductivity and transparency of ITO, it is necessary to optimize performances of opto-electronic products by balancing the sheet resistance and transmittance. Both sheet resistance and transmittance are affected by a number of factors such as working temperature, working pressure, oxygen-to-argon ratio during the fabricating process, and thickness. In our study, ITO thin films were deposited on glass substrates by dc sputtering. Effects of ITO with different thicknesses, sheet resistances, and transmission spectra on the performance of bulk heterojunction photovoltaic devices were investigated.