Improved solar spectrum optical absorption in multilayered nanostructures consisting of metal, semiconductor and dielectric layers increase their potential for efficient photon to electron conversion. In this work, we analyze the influence of different nanostructure shapes and dimensions on the optical absorption in the vacuum wavelength range of 400 nm to 1500 nm based on Finite Domain Time Difference (FDTD) method. A periodic metallic photonic crystal composed of nanorods of gold, titanium oxide, and alumina is proposed by optimizing thickness of Au and TiO2, aspect ratio, sidewall angle, and geometry of the elemental shape. A high aspect ratio structure consisting of elliptical nose cone elements with optimized dimensions is seen to absorb more than 90% of the solar spectrum in the range considered.

We have demonstrated the NiO/ZnO based rectifying diode for LED application for substituting GaN for optoelectronics applications. We have systematically studied the current-voltage (I-V) characteristics of NiO based Metal-Insulator-Semiconductor (MIS) devices under forward and reverse bias for its use in LED applications. The results obtained show that the current increases exponentially with the voltage after a critical turn-on-voltage. The mechanism of carrier transport responsible for the rectifying behavior of the MIS structure as well as the light emission is discussed in relation to the experimental results.

Reversible changes in the conductivity of HfO2 dielectric film betweenhigh and low resistive states of a metal-insulator-metal memory cell wereattributed to the formation of oxygen vacancies and their clustering across theinsulator layer. In this study we present an innovative model which includesgeneration of two-charged states of oxygen vacancies at the anode, theirdiffusion to the cathode, transformation to one-charged state, and then toneutral vacancies. Vacancy clusters in the insulator layer are built from onlyneutral vacancies, while the kinetics of the clustering process is controlled bydiffusion of mobile one-charged state vacancies. Resistive switching is treatedas the formation of critical size vacancy cluster which provides continuousconductive path through the dielectric layer. Good agreement between theexperimental data and the theoretical bias and temperature dependences for thedelay time was obtained.

The influence of deep level defects (DLs) on the conversion efficiency of multicrystalline Si-based standard solar cells (SCs) is investigated. Multicrystalline p-type Si wafers with 156×156 mm dimensions and 200 μm thickness were used for SCs preparation. Three types of SCs with conversion efficiency 10%, 16.8% and 20.4% were studied using capacitance voltage characteristics method (C-V) and by current deep level transient spectroscopy (I-DLTS). The correlation between the total concentration of DLs and the values of the SCs conversion efficiency is found.

In Belgium, the preferred long-term management option for Eurobitum bituminized ILW is its final disposal in a geologically stable clay formation such as the Boom Clay, which is studied as a reference host formation. After disposal, clay pore water will infiltrate the secondary concrete waste containers filled each with ten Eurobitum drums. Eurobitum contains hygroscopic salts, mostly NaNO3 (20-30 wt%) and CaSO4 (4-6 wt%), and thus will take up water and swell. If swelling is hindered, a pressure will be exerted on the concrete container and ultimately on the surrounding Boom Clay, possibly inducing stresses in the clay close to the disposal galleries. To improve our understanding of these processes, water uptake tests are ongoing in which inactive Eurobitum is contacted with 0.1 M KOH (representing young cement water). These tests suggest that the swelling is mainly driven by osmosis. This understanding was validated in the presented research by varying the water activity of the leachant in water uptake tests in both constant stress and constant volume conditions. After a stable swelling rate was reached in contact with 0.1 M KOH, the leachant was switched in the following order: nearly saturated (∼7.8 M) NaNO3 – 0.1 M KOH – nearly saturated NaNO3 – 4 M NaNO3 – 0.1 M KOH. The changes in swelling rate and pressure evolution correlated nicely to the changes in water activity. This confirms that osmosis is the key process governing the swelling of Eurobitum.

The goal of this work is to study the properties of magnetically aligned CNT/PC nanocomposites towards the development of hydrogen gas separation membranes. A fraction (0.1 weight %) of synthesized carbon nanotubes (CNTs) have been dispersed homogeneously throughout polycarbonate (PC) matrix by ultrasonication. The alignment of CNT in PC matrix has been accomplished by applying an external magnetic field of 1200 Gauss. These nanocomposites have been studied by gas permeation using H2, N2 and Co2 electrical and dielectric constant measurements. Experimental results of gas permeability measurements exhibit here that H2 is more selective than N2 and Co2 in magnetically aligned nanocomposite membranes which can be used as good hydrogen separating media. I-V characteristics show the electron hopping like behavior and dielectric constant shows the enhancement in permittivity of these nanocomposites.

Stretchable and flexible electronic devices have gained significant attention in recent years, as they can be integrated into many systems such as medical sensors, displays, and robots. One of the primary areas of research is designing stretchable interconnects which provide adequate conductivity and mechanical robustness. Metal-based interconnects have been reported to have the highest conductivity, but are not stretchable enough, while elastomer interconnects are not conductive enough. In this paper we report on a silver polymer blend composite that provides excellent conductivity, stretchability and flexibility for use as a stretchable interconnect. The composite was prepared by dispersing silver flakes in a Polyvinyl alcohol (PVA), Phosphoric acid (H3PO4) and poly(3,4-ethyl-ene-dioxythiophene) (PEDOT):Poly(styrene sulfonic acid) (PSS) polymer mixture. Silver was chosen as it has the highest conductivity of all metals, while the PEDOT:PSS/PVA- H3PO4 blend was chosen as the blend offers a practical trade-off between conductivity and stretchability for the composite matrix. The polymer blend provides conductive pathways between the silver flakes, leading to the blend’s superior electrical properties, even at large deformations. The synthesis process of the composite material, along with the observed electrical and mechanical properties under various straining conditions of the composite will be presented in detail.

One main difference between practical device and ideal design for subwavelength grating structure is the tapered sidewall profile of grating, which is normally obtained by the practical CMOS-compatible fabrication and etching process. Our work has investigated the impacts of tapered sidewall profile on the subwavelength grating wideband reflector characteristics. Both zero-contrast gratings (ZCG) and high- contrast gratings (HCG) are numerically investigated in detail and the results show a distinct differences of the impacts of tapered sidewall profile of grating. The simulation results reveal that this factor play a critical role in determining the reflection bandwidth, average reflectance, and the band edge. Our study has potential in guiding the utilization of subwavelength grating wideband reflector on application of a variety of nanophotonic devices and their integration, as well as to facilitate the design of the fabrication process on the control of tapered sidewall profile.

Since the isolation of graphene, a monolayer of sp2-bonded carbon atoms arranged in a hexagonal lattice, two-dimensional (2D) layered materials have attracted a great deal of attention due to their outstanding mechanical, optical and electronic properties. The research areas of interest for these new materials include exploring their novel properties, developing scalable approaches to synthesize these materials, and integrating them into a new generation of nanodevices. The utilization of 2D materials in devices has many advantages, which includes scaled materials to the limit of atomic-scale membranes, and the potential to form device structures on flexible and transparent substrates, among others. Transition metal dichalcogenides (TMDs) monolayers in particular, have received increasing attention in recent years, especially molybdenum disulfide (MoS2), which is one of the most well explored semiconducting materials in the 2D materials system. In this work we present the synthesis of MoS2 using chemical vapor deposition (CVD), where we have varied the synthesis parameters and compared the structure and quality of the CVD synthesized MoS2. At the same time, we have compared the characteristics with those obtained for mechanically exfoliated flakes from the bulk MoS2 crystal. The MoS2 quality has been analyzed using Raman spectroscopy.

Sonication is a commonly used method for particle removal from various surfaces. There has been a growing interest in the use of combination of two or more acoustic frequencies for cleaning as it is expected to achieve better particle removal efficiency and lower feature damage compared to a single frequency acoustic system. In this study, stable and transient cavitation characteristics in de-ionized water subjected to dual-frequency irradiation have been illustrated using experimentally obtained absolute values of cavitation pressures and pressure-frequency spectra. Comparison of the calculated ratio of stable cavitation pressure to transient cavitation pressure suggests that dual-frequency mode has the potential to reduce feature damage while maintaining the particle removal efficiency compared to low frequency ultrasonic field. These observations are further confirmed from the results of damage studies conducted on aluminum coated glass samples.

A number of electrical components and devices work in extreme environment such as high temperature, high pressure, strong vibration, corrosive chemicals, etc. A common practice to protect them is to shield them in materials that are mechanically and chemically resistant to these harsh conditions. In this scenario, epoxy bonding is preferred and it is crucial to have high bonding strength. One example is the acoustic transducers used in oil drilling. The temperature can reach 200 °C and the pressure can reach 140 MPa. The piezoelectric ceramic parts cannot withstand these conditions so different packaging materials are used such as polyether ether ketone (PEEK).

Here an epoxy bonding apparatus is presented that has demonstrated ultrahigh bonding strength. Though epoxy resin is degassed before applying, which gets rid of air bubbles generated in the mixing process, there is trapped air when two surfaces are closed together. This trapped air has minuscule effect for applications in ambient environment, but under extreme environment, it compromises the bonding strength majorly. We devised a vacuum system that contains a motorized stage with the bonding parts attached. After the epoxy is applied and the system is pumped to 1% vacuum, a computer controls the motor to move the bonding parts into contact. Since the entire operation is in vacuum, it leaves no trapped air and results in increased bonding strength. This apparatus confirmed the importance of surface preparation, including removal of air by starting the cure in vacuum (5 mm Hg) and subsequently releasing the vacuum [1].

Another technique to improve the bonding strength utilizes the finding that a uniform epoxy resin layer between 50 µm and 150 µm [2] results in the optimal bonding strength. Here we applied spacers such as optic fiber (125 µm in diameter) or glass fiber fabric (150 µm in thickness) in between the bonding surfaces. These spacers ensure that the epoxy resin layer is of uniform thickness. It also utilizes the principle of glass-epoxy compositing to increase mechanical strength by fiber reinforcement and load distribution [3, 4].

The above bonding apparatus has been proven to increase the bonding strength by experiments. Acoustic transducers bonded with this technique passed the high pressure, high temperature tests resembling the oil drilling conditions.

Thin films of TiO2/SnO2:F multilayers were prepared by spray pyrolysis technique on glass substrate. The samples were prepared using titanium (IV) isopropoxide 98%, ammonium fluoride and tin(II) chloride dehydrate extra pure as precursor materials. Thus, a TiO2 thickness dependence optical study of TiO2/SnO2:F/glass system is presented. The optical property was characterized by UV-Visible transmittance spectroscopy. For all the samples, the average transmissions in the visible wavelength region (400-800 nm) were between 69 and 84%. The optical parameters, such as the real part dielectric function ε1 and the imaginary part dielectric function ε2, of TiO2 and SnO2:F in the TiO2/SnO2:F thin films structure, determined by fitting the measured optical transmittance spectra, are presented and analyzed. Among the various classical dispersion relations for the dielectric function, the Drude model combined with the Lorentzian oscillators was used to get a good fit of transmittance in the measured spectral range. Results on related parameters such as high frequency dielectric constant, plasma frequency, film thickness and band gap are presented.

Nanostructures tend to comprise distinct and measurable forms, which can be referred to in this context as nanopatterns. Far from being random, these patterns reflect the order of well-understood chemical and physical laws. Under the aegis of said physical and chemical laws, atoms and molecules coalesce and form discrete and measurable geometric structures ranging from repeating lattices to complicated polygons. Rules from several areas of pure mathematics such as graph theory can be used to analyze and predict properties from these well-defined structures. Nanocarbons have several distinct allotropes that build upon the basic honeycomb lattice of graphene. Because these allotropes have clear commonalities with respect to geometric properties, this paper reviews some approaches to the use of graph theory to enumerate structures and potential properties of nanocarbons. Graph theoretic treatment of the honeycomb lattice that forms the foundation of graphene is completed, and parameters for further analysis of this structure are analyzed. Analogues for modelling graphene and potentially other carbon allotropes are presented.

The interface between the adhesive toes of geckos and a substrate consists of an array of regularly sized, densely packed, and elastically coupled nanoscopic contacts. The velocity-dependent friction exhibited by this system hints at a convolution of various material and structural effects. We explore the dynamics of frictional sliding in these materials using models based on arrays of coupled masses driven by external forces that can become pinned and unpinned to a potential energy landscape. The model system is driven at normalized velocities spanning 6 orders of magnitude, and the output of this model captures both the low-V and high-V behavior of the actual gecko materials. We explore modifications to the essential model that incorporate features more representative of the structure and behavior of the natural gecko system. These results have implications in the design of materials with custom frictional properties.

Calcium phosphate cements show self-hardening reaction upon mixing with liquids to form calcium-deficient hydroxyapatite (CDHA) or dicalcium phosphate dihydrate. The effects of particle sizes, crystallinities, and natural polymers such as tilapia scale collagen (Col) and hyaluronic acid as a dispersant on the mechanical properties of alpha tricalcium phosphate (TCP) cements mixed with citric acid (CA) as an additive were investigated. Three types of alpha TCP particles were fabricated with spray-dry (SD; 14 μm), freeze-dry (FD; 45 μm), and cold isostatic press (CIP; 134 μm) methods, followed by sintering at 1300°C and ground/crushed. The amounts of Ca dissolution from these particles were in the order of SD > FD > CIP. The CA liquid was added to the powders of SD-FD or SD-CIP, and kneaded under different liquid/powder ratios. The cements containing CIP particles showed lower compressive strength at 22.9 ± 1.5 MPa than those containing FD particles at 28.3 ± 2.5 MPa, even though the apparent densities of the cements containing CIP material was higher. Although the packing density of powders is an important factor on the mechanical properties of cements, the dissolution of Ca ion has a greater impact on the mechanical properties. The addition of Col into the cements increased the mechanical properties at 33.6 ± 2.5 MPa at 1 day to enhance the re-precipitation of CDHA.

We report a simple and scalable process to synthesize the core–shell nanostructure of MoS2@N-doped carbon nanosheets (MoS2@C), in which polydopamine is coated on the MoS2 surface and then carbonized. Transmission electron microscopy reveals that the as-synthesized MoS2@C possesses a nanoscopic and ultrathin layer of MoS2 sheets with a thin and conformal coating of carbon layers (∼5 nm). The MoS2@C demonstrates a superior electrochemical performance as an anode material for lithium ion batteries compared to exfoliated MoS2 sample. This unique core–shell structure is capable of excellent delivery of Li+ ion in charging–discharging process: a specific capacity as high as 1239 mA h g−1, a high rate of charging-discharging capability even at a high current rate of 10 A g−1 while retaining 597 mA h g−1, and a good cycle stability over 70 cycles at a high current rate of 2 A g−1.

The functionalization of biosilica shells (frustules) of diatoms microalgae with a tailored luminescent molecule is a convenient, scalable and biotechnological approach for obtaining new light emitting silica nanostructures with promising applications in photonics. In particular, here we report the synthesis of a red emitting organic fluorophore and its covalent linking to the surface of mesoporous biosilica extracted from Thalassiosira weissflogii diatoms cultured in our laboratories. The organic dye has a conjugated skeleton composed of thienyl, benzothiadiazolyl and phenyl units and a peripheral triethoxysilyl group which enables its stable binding onto the frustules surface. The protocol to extract the biosilica shells from living diatoms preserving their natural ornate nanostructured morphology is also discussed.

The study of on-body energy harvesting is most often focused on improving and optimizing the energy harvester. However, other factors play a critical factor in the energy harvesting integration techniques of the harvester to close-to body materials of the wearable device. In addition, one must recognize the wide array of human factors and ergonomic factors that lead a variation of the energy harvesting. In this work, key affecting variables at varying on-body locations are investigated for commercial thermoelectric generators (TEGs) integrated within a textile-based wearable platform. For this study, a headband and an armband is demonstrated with five TEGs connected in series in a flexible form factor via Pyralux®. These platforms enable comparison of the amount of energy harvested from the forehead versus the upper arm during various external conditions and movement profiles, e.g. running, walking, and stationary for periods of up to 60 minutes. During these tests, ambient temperature, ambient humidity, accelerometry, and instantaneous power are recorded live during the activity and correlated to the energy harvested. Human factors such as skin temperature and application pressure were also analyzed. Our analysis demonstrates that vigorous movement can generate over 100 μW of instantaneous power from the headband and up to 35 μW from the armband. During the stationary movement profile, the instantaneous power levels of both the headband and the armband decreased to a negligible value. Our studies show that for higher intensities of movement, air convection on the cool side of the TEG is the dominating variable whereas the temperature gradient has a significant effect when the subject is stationary. This work demonstrates key materials and design factors in on-body thermoelectric energy harvesting that allows for a strategic approach to improving the integration of the TEGs.

Sodium bismuth titanate (Na0.5Bi0.5TiO3: NBT) a lead free piezoelectric; exhibits promising features such that it could be an alternate to lead based piezoelectrics. In this work, we report the microstructural influence on piezoelectric and leakage current behavior of NBT thin films grown by pulsed laser ablation (PLD). Various microstructural features like coarse faceted grains and fine spherical grains was achieved by effective optimization of substrate temperature and oxygen partial pressures. The studies reveals that, leakage current of NBT thin films were dominated by interface limited modified Schottky emission type of conduction. The piezoelectric domain studies reveal that for NBT thin films with fine spherical grain the domain pattern was highly dominated by the morphology and in the case of coarse faceted grains the domains were relatively large and the domains were extending beyond the grain boundaries.

The control of ferromagnetic properties by external stimuli is of great interest in the electronics community. One method of producing such a control is through proximity of a ferromagnetic film with a material that has a semiconductor-to-metal transition (SMT). In order for these magnetic heterostructures to be beneficial, they must consist of high-quality, crystalline films. Epitaxial films increase the reproducibility of both devices and properties. We have investigated the trend in magnetic coercivity in epitaxial nickel films on VO2. We show that not only does the interaction between the Ni and VO2 change the normal coercivity trend found in Ni M-H curves with no proximity to VO2, but that the crystalline growth mode of the Ni film also impacts the magnetic coercivity as a function of temperature.