MEMS vibration energy harvesting has been investigated to provide energy to low-power micro-electronic systems and potentially to enable batteryless autonomous systems. While enjoying the small footprint hence the ability to be embedded in other systems, MEMS vibration energy harvesters are working at much higher frequencies and input vibration amplitudes. The mechanical resonator based energy harvesters seem inherently have such high frequency due to the scaling of the device dimension. Lower the working frequency range and input vibration amplitude are possible by optimizing the dimensions of the device. However, we are viewing the problem from a different perspective and proposing a solution based on employing the common material property of the micro-fabricated thin film – residual stress. We found that by taking advantage of the compressive residual stress, a bi-stable mechanical resonator could be built and a new spectrum of dynamics can be brought into energy harvesting, which could lower the working frequency range and input g value. The concepts have been analytically simulated and experimentally verified by a meso-scale model.

The present study explores the burning of microscale porous silicon channels with sodium perchlorate. These on-chip porous silicon energetics were embedded in crystalline silicon, and therefore surrounded on three sides by an efficient thermal conductor. For slow burning systems, this presents complications as heat loss to the crystalline silicon substrate can result in inconsistent burning or flame extinction. We investigated <100 μm wide porous silicon strips, sparsely filled with sodium perchlorate (NaClO4), to probe the limits of on-chip combustion. Four different etch times were attempted to decrease the dimensions of the porous silicon strips. The smallest size achieved was 12 x 64 µm, and despite the small dimensions, demonstrated the same flame speed as the larger porous silicon strips of 6-7 m/s. We predict that unreacted porous silicon acts as a thermal insulator to aid combustion for slow burning porous silicon channels, and SEM images provide evidence to support this. We also investigated the small scale combustion of a rapidly burning sample (∼1200 m/s). Despite the rapid flame speed, the propagation followed a designed, winding flame path. The use of these small scale porous silicon samples could significantly reduce the energetic material footprint for future microscale applications.

In order to understand enhanced mechanical properties of magnesium-yttrium (Mg-Y) alloys, applied stresses which were required to operate independent plastic deformation mechanisms on various stress axes were evaluated. Moreover, for this analysis, mechanical tests including newly-established testing method “pure-shear test” were conducted to evaluate Critical Resolved Shear Stresses (CRSSes) for various plastic deformation mechanisms of Mg-Y solid solution alloy single crystals with various Y concentration. Relatively higher solid solution strengthening of dominant plastic deformation mechanisms such as basal slip and extension twin at room temperature, results in increase in the activation of non-basal slip system. By a simple analysis based on von-Mises criterion with experimental CRSS values, it is revealed that enhanced mechanical properties of Mg-Y alloys might be attributed to the decrease of difference in the activity of plastic deformation mechanisms by Y addition.

The present work focuses on the polyol-mediated synthesis of pure and Mg-doped ZnO nanoparticles. The synthesized samples were characterized via X-ray diffraction, Fourier transformed infrared spectroscopy, ultraviolet visible spectroscopy and photoluminescence techniques. The Standard Plate Count was used to assess the bactericidal properties of the nanoparticles against E. coli at 1000 ppm and 1500 ppm of concentration. The capacity of the Zn-Mg oxides to generate singlet oxygen (SO) species was also evaluated. X-ray diffraction information evidenced the formation of ZnO-wurtzite; no diffraction peaks corresponding to isolated Mg-phases were detected. The average crystallite size of the Zn-Mg oxide nanocrystals was estimated in the 6nm - 7nm range. Infrared spectroscopy measurements confirmed the formation of the oxide with a Metal-Oxygen band centered on 536 cm-1; other bands associated to the functional groups of polyol by product were also observed. The exciton peak of UV spectrum suggests similarity in the particle size with the dopant addition. The effect of particle composition (i.e. doping level) on the corresponding generation of SO and bactericidal capacity is presented and discussed.

MscL, a large-conductance mechanosensitive channel, is a ubiquitous osmolyte release valve that aids bacteria in surviving abrupt hypo-osmotic shocks. The large scale of its tension-driven opening transition makes it a strong candidate to serve as a transducer in novel stimuli-responsive biomolecular materials. In the previous work, a low-threshold gain-of-function V23T mutant of MscL produced a reliable activation behavior in a droplet interface bilayer (DIB) with applied axial droplet compression. Near the maximal compression, the aqueous droplets deform and the resulting increase in surface area leads to an increase in tension in the water-lipid-oil interface. This increase in tension is the product of the relative change in the droplet surface area and the elastic modulus of the DPhPC lipid monolayer (∼120 mN/m). This paper, presents a study of the physical processes that cause MscL gating in the DIB. Analysis of video during compression and relaxation of the droplets is utilized to estimate the change in the surface area of the droplet and the variation on monolayer surface tension. The monolayer surface tension is proportional to the area change of the droplet normalized to the original surface area. The results demonstrate that the area change in the droplet is negligible at frequencies above 1 Hz, but is approximately 2% at frequencies in the range of 100 mHz. In addition, at low frequencies (∼0.2 Hz) bilayer thinning occurs at maximum compression, proving an increase in bilayer tension. However, this study also shows that gating at frequencies higher than 0.2 Hz could be achieved through the application of high duty cycle oscillation (∼75%). The relative change in monolayer area increases significantly at higher duty cycle oscillations where the compression stroke is much faster than the relaxation stroke.

We present the first quantitative assessment of combustion dynamics of on-chip porous silicon (PS) energetic material using sulfur and nitrate-based oxidizers with potential for improved moisture stability and/or minimized environmental impact compared to sodium perchlorate (NaClO4). Material properties of the PS films were characterized using gas adsorption porosimetry, and profilometry to calculate specific surface area, porosity and etch depth. The PS/sulfur energetic composite was formed using three pore loading techniques, where the combustion speeds ranged from 2.9 – 290 m/s. The nitrate-based oxidizers were solution-deposited using different compatible solvents, and depending on the metal-nitrate yielded combustion speeds of 3.1 – 21 m/s. Additionally, the combustion enthalpies from bomb calorimetry experiments are reported for the alternative PS/oxidizer systems in both nitrogen and oxygen environments.

Nano-graphite oxide has been synthesized from graphite flakes using modified Hummer’s method. Fourier transform infrared (FT-IR) data, x-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed functionalization of the synthesised nano-graphitic platelets with oxygenated bonds. Using thermal embedding technique for the fabrication of self-assembled films, electrodes of nano-graphite oxide have been fabricated for enzyme free detection of cholesterol electrochemically. The electrodes provided a linear response for the enzyme less detection in the range of 50mg/dl to 500mg/dl with a correlation coefficient, R, of 0.99784 and sensitivity of 1.0587 µA/mg.

The role of ferroelectric LiNbO3 (LNB) in altering the frequency dependence of the capacitance of CaCu3Ti4O12 (CCTO) thin films has been investigated. A cost effective spin coating deposition process was used to integrate the oxide heterostructures onto silicon substrates. This study showed that the frequency stability of the CCTO/LNB structure was much improved when the crystallization conditions and physical dimension of each layer were optimized. To integrate this structure with current silicon technology, heterostructures of CCTO and LNB thin films were fabricated on HF terminated Si using chemical solution deposition. It was found that the order of deposition of the two layers was important for the structural quality of the heterostructures with the CCTO layer followed by the LNB layer being the preferred structure. In addition to improvement of the capacitance variation with frequency, the heterostructures also provide a path to tuning the frequency of operation.

Atomic force microscopy is employed to study the structural changes in the morphology and physical characteristics of asphaltene aggregates as a function of temperature. The exotic fractal structure obtained by evaporation-driven asphaltene aggregates shows an interesting dynamics for a large range of temperatures from 25°C to 80°C. The changes in the topography, surface potential and adhesion are unnoticeable until 70°C. However, a significant change in the dynamics and material properties is displayed in the range of 70°C - 80°C, during which the aspahltene aggregates acquire ‘liquid-like’ mobility and fuse together. This behaviour is attributed to the transition from the pure amorphous phase to a crystalline liquid phase which occurs at approximately 70°C as shown by using Differential Scanning Calorimetry (DSC). Additionally, the charged nature of asphaltenes and bitumen is also explored using kelvin probe microscopy. Such observations can lead to the development of a rational approach to the fundamental understanding of asphaltene aggregation dynamics and may help in devising novel techniques for the handling and separation of asphaltene aggregates using dielectrophoretic methods.

Thiophene small novel branched structures have been proposed as candidates for dopant agents transporting holes-electron in organic solar cell (OSC). Low-band gap of these branched oligotiophene have been obtained to be used in organic solar cells. Two branched thiophene oligomers, a sexithienylene vinylene (E)-Bis-1,2-(5,5´´-Dimethyl-(2,2´:3´,2´´-terthiophene) vinylene, (BSTV) and octathienylene vinylene (BOTV) (E)-Bis-1,2-(5,5´´´-Dimethyl-(2,2´:5´,2´´:3´,2´´´-tetrathiophene) vinylene oligomers, have been synthesized and used as electron donor or dopant in a bulk heterojunction poly(3-hexylthiophene) (P3HT), /[6,6]-phenyl C61-butyric acid methylester (PCBM), Organic Photovoltaic cell.

We consider energy transfer between non-equal nanoparticles mediated by a quantum system. The nanoparticles are considered as thermal reservoirs described as ensembles of finite numbers of harmonic oscillators within the Drude-Ullersma model having mode spacings Δ1 and Δ2. Our approach is based on the generalized quantum Langevin equation. The quasi-static energy transport between the thermal reservoirs is investigated. As is shown, the double degeneracy of the mode frequencies, which occurred in the previously considered case when Δ1 = Δ2, is removed in the present case of non-equal mode spacings. Equations describing long-time (t ∼1/Δ1,2) relaxation for the mode temperatures (or the ensemble averaged mode energies) are solved and the resulting expression for the total energy current between the nanoparticles is derived and explored.

We have been interested in the plasmonic properties of alternative conducting materials to metals, such as conducting oxides, and we have recently expanded our studies to include highly correlated oxides, such as vanadium dioxide (VO2) thin films. VO2 exhibits a metal-insulator transition (MIT) just above ambient temperature at ∼ 340K. Interestingly, this transition can be induced thermally, optically or applying electric fields. Across the MIT, the optical properties are completely modified over a broad frequency range. We will present our recent optical investigations on the photon induced transition studies on such films, as well as the surface plasmon resonance (SPR) modulation in nanopatterned Au gratings by the thermally induced MIT in VO2 thin films, addressing possibilities of ultrafast SPR modulation with VO2.

Porous coatings at the surface of living cells have application in human cell transplantation by controlling the transport of biomolecules to and from the cells. Sol-gel-derived mesoporous silica materials are good candidates for such coatings, owing to their biocompatibility, facile solution-based synthesis conditions, and thin film formation. Diffusion and transport across the coating correlates to long-range microstructural properties, including pore size distribution, porosity, and pore morphology. Here, we investigated collagen-fibril matrices with known biocompatibility to serve as templating systems for directed silica deposition. Type 1 collagen oligomers derived from porcine skin are extensively characterized such that we can predict and customize the final collagen-fibril matrix with respect to fibril density, interfibril branching and viscoelasticity. We show that these matrices template and direct the deposition of mesoporous silica at the level of individual collagen fibrils. We varied the fibril density, silicic acid concentration, and time of exposure to silicifying solution and characterized the resulting hybrid materials by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and rheology. Microstructural properties of the collagen-fibril template are preserved in the silica surface of hybrid materials. Results for three different collagen fibril densities, corresponding to shear storage moduli of 200 Pa, 1000 Pa, and 1600 Pa, indicate that increased fibril density increases the absolute amount of templated silica when all other silica synthesis conditions are kept constant. Additionally, mechanical properties of the hybrid material are dominated by the presence of the silica coating rather than the starting collagen matrix stiffness.

We study the thermodynamical properties and lattice dynamics of two-dimensional crystalline membranes, such as graphene and related compounds, in zero temperature limit, where quantum effects are dominant. We find out that, just as in the high temperature classical limit, a fundamental role is played by the anharmonic coupling between in-plane and out-of plane lattice modes, which leads to a strong reconstruction of the dispersion relation of the out-of-plane mode. We identify a crossover temperature, T *, bellow which quantum effects are dominant. We estimate that for graphene T * ∼ 70 - 90 K. Inclusion of anharmonic effects makes the thermal expansion finite in the thermodynamic limit, and below T * it tends to zero as a power law as T→0 as required by the third law of thermodynamics. The specific heat also goes to zero as a power law as T→0, but with a exponent that differs from the one predicted by the harmonic theory.

In this paper, we describe unique thermally responsive polymer system based on nanotube-elastomers dispersed with core-shell expanding microspheres (phase-change material). Upon thermal or infrared stimuli, liquid hydrocarbon cores encapsulated within the microspheres vaporize, expanding the surrounding shells and stretching the matrix. Microsphere transformation resulted in visible dimensional changes associated with macroscopic volume increase (>500%), reduction in density (>80%), and increase in elastic modulus (>675%). Additionally, electrically conductive nanotubes allowed for expansion dependent electrical responses. We present our new findings on expansion dependent superhydrophobicity in these materials and present some outlook and comparison of our stimuli responsive polymers with other material systems for future origami based applications.

Poly(vinyl alcohol) (PVA) is a synthetic polymer which has been used in a wide variety of applications. This polymer has been extensively investigated by a large number of techniques to shed light about its physical and chemical properties. In this work, for fist time, high frequency (1x109-3x109 Hz) relaxation process has been observed in the PVA films in the temperature range of -100C to +1200C. This relaxation exhibits negative activation energy below glass transition temperature Tg and at higher temperature positive activation energy with subsequent saturation. Upon cooling the activation energy was negative again. This high frequency relaxation process and its temperature dependence can be attributed to the interaction of the bounded water and the changes of energy and freedom of movement of OH side molecular chains groups. This conclusion has been supported by in situ FTIR measurements. A possible scenario of this relaxation and dynamics of molecular motion has been proposed.

Functionalization of gelatin with desaminotyrosine (DAT) and desamino tyrosyl tyrosine (DATT) has been demonstrated to allow network formation based on non-covalent interactions of the aromatic moieties. Based on the observation that the DAT(T) groups furthermore could interact with hydroxyapatite fillers, here it was investigated whether such interactions of DAT(T) could also be employed to stabilize composites formed by functionalized gelatins and bioactive glass (BG) particles. Because of sedimentation of the BG microparticles during the gelification, anisotropic composites with two distinct layers were formed. The characterization of mechanical properties by tensile tests and rheology showed that all composites of non-functionalized and DAT(T) functionalized gelatins with BG microparticles showed an increased Young’s modulus (E) up to 3 MPa, an increased storage modulus (G’) up to 100 kPa, increased tensile strength (σ max) up to 3.4 MPa, and increased loss modulus (G’’) compared to the pure matrices. As the observed effects were more pronounced in the DAT(T) functionalized gelatins compared to non-functionalized gelatins, and a much increased thermal stability of these composites was found, it is likely that there are binding interactions between the aromatic moieties and the BG microparticles. This effect open opportunities for the further development of this type of gelatin-based composites for bone regeneration applications.