Poly(N-isopropylacrylamide) (PNIPAM) is a thermosensitive polymer that is well-known for its behavior at a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water, and above this temperature, polymer chains collapse and transform into a globule state. The conformational dynamics of single chains of polymer in a solution is known to be different from those of grafted structures that comprise of an ensemble of such single chains. In this study, we have carried out MD simulations of a mesoscopic nanostructure of PNIPAM polymer chains consisting of 60 monomer units grafted onto gold nanoparticles of different diameters, to study the effect of temperature and core particle size on the polymer conformations. Additionally, we have also studied the effect of grafting density on the coil-to-globule transition exhibited by PNIPAM through the LCST. The systems investigated consisted of ∼3 and ∼6 million atoms. Simulations were carried out below and above the LCST of PNIPAM, at 275K and 325K. Simulation trajectories were analyzed for radius of gyration of PNIPAM chains.

An actual trend to enhance solar cells efficiency is to build multijunction cells, creating a bandshape wavelength collection. However, the best multijuction cells are actually made of III-V compounds when silicon and its alloys don’t lead to high efficiency devices. In this article, we study a 3C-SiC/Si heterojunction as a first step for 3C-SiC/Si tandem cells. Four samples were fabricated by depositing 3C-SiC on Si wafers with different SiC doping levels. Simulations of the structures are performed, as well as optical and electrical characterizations of the heterojunction cells.

A solution-processed method is developed to fabricate fully transparent resistive random access memory (RRAM) devices with a configuration of FTO/ZrO2/ITO, where the zirconium dioxide (ZrO2) layer was firstly deposited on fluorine tin oxide (FTO) substrate by sol-gel and then indium tin oxide (ITO) films were deposited on ZrO2 layer by sol-gel as the top electrodes.The solution processed FTO/ZrO2/ITO based RRAM devices show the fully transparency and excellent bipolar resistance switching behaviors. The resistance ratio between high and low resistance states was more than 10, and more than 100 switching cycles and good data retention and multilevel resistive switching have been demonstrated.

One of promising photorechargeable electrode, which has two functions of photovoltaic and electrical energy storage, is a composite film of mesoporous TiO2 and conducting polymer polyaniline. Galvanostatic charge/discharge characteristics of the TiO2-polyaniline composite were examined to reveal how fast the film was charged. The film with a specific capacity 60-120 mAh g–1 was found to be fully charged at high charging rate 20 mA cm–2 which is comparable to high performance solar cells. Such high charging rate was achieved by the compact polyaniline layer covering the large specific surface area of mesoporous TiO2 film.

Flexible electronics and microsystems are an emerging technology with a tremedous impact to the future electronics and information technology and widespread applications. Various devices and microsystems have been developed. Surface acoustic wave (SAW) devices are a type of essential device for electronics, microsensors and microsystems; however there is no activity on the development of flexible SAW devices yet. This paper reports the development of flexible SAW devices on cheap, bendable and disposable plastic films. Flexible SAW devices with resonant frequency of 198.1 MHz and 447 MHz for the Rayleigh and Lamb waves respectively have been obtained with a large transmission signal up to 18dB. The flexible SAW devices have also demonstrated their ability for acoustic streaming with a velocity up to 3.4 cm/s and for particle concentration. The results have clearly demonstrated that the flexible SAW devices have great potential for applications in electronics and microsystems.

Herein, we detail the fabrication of atomic force microscope (AFM) probes that have two and three coaxial electrodes at their tips. This fabrication strategy leverages the availability of conductive AFM probes and encompasses a general method for processing their complex and delicate structure through the deposition of insulating and conductive layers by shadow masked chemical and physical vapor deposition, respectively. Focused ion beam milling is used to expose the two electrode (coaxial) or three electrode (triaxial) structures at the tip of the AFM probe. Finally, we discuss new imaging modalities enabled by these probes including electrically-driven contact resonance imaging for nanoscale mechanical characterization, imaging the local dielectric constant by quantifying the dielectrophoretic force, and trapping functional particles at the tip of a probe using dielectrophoresis. These imaging techniques illustrate the generality and utility of this fabrication approach and suggest that such probes could be widely applied to image many nanoscale materials.

Hexagonal boron nitride (hBN) crystals enriched in 10B and 11B isotopes were synthesized using a high temperature (1500° C) Ni-Cr-B reactive-precipitation growth under a N2 atmosphere. Two growth mechanisms were observed: conventional defect-facilitated bulk growth which produced crystals with a platelet-like habit with width and thickness of 20-30 μm and 5 μm, respectively, and vapor-liquid-solid interface growth of hBN whiskers with lengths and diameters as large as 70 μm and 5 μm, respectively. Similar growth mechanisms were seen for samples enriched in either isotope. Isotopic analysis via secondary-ion mass spectrometry showed boron concentrations of 84.4 at% and 93.0 at% for the majority isotopes in the 10B-rich and 11B-rich samples, respectively. Raman spectroscopy showed an increase in peak Raman shift for the 10B-rich sample, having two barely resolved peaks at 1393.5 and 1388.8 cm-1, and a decrease for the 11B-rich sample, having peak at 1359.5 cm-1 (FWHM of 9.4 cm-1), compared to that of natural hBN, with its peak at 1365.8 cm-1 (FWHM of 10.3 cm-1). Raman shift showed a linear trend with increasing 10B concentration allowing for a calibration curve to be developed to estimate 10B enrichment in hBN using non-destructive methods.

Nanomaterials engineered in novel multi-modular systems in which every component works in a synergistic way with others could potentially lead to a completely new type of tools for nanomedicine. The development of nanostructures able to release drugs directly within the target after a stimulus can drastically improve the therapeutics efficiency by reducing side effects. Gold nanoparticles offer one of the most suitable platforms for the development of modular nano-devices. On the one hand, their surface properties enable effective coating by peptides containing at least one cysteine, thus yielding stable and non-cytotoxic systems. On the other, their intriguing photophysics, characterized by the surface plasmon resonance, can be exploited for novel excitation schemes. Doxorubicin is a widely used, but toxic, cancer chemotherapeutic agent. In order to localize its therapeutic action while minimizing its side effects, doxorubicin was covalently conjugated to 30 nm peptide-encapsulated gold nanospheres by click-chemistry and then it was photo-released in a controlled fashion through the cleavage of the 1,2,3-triazolic ring by a multiphoton process using 561 nm irradiation at µW power. Selective apoptosis of human osteosarcoma (U2OS) cells was observed only in the irradiated 100x100 micron area in less than six minutes after the stimulus. Notably, the apoptotic effect of doxorubicin was completely inhibited for at least eight hours until its release “on demand” was externally light-triggered.

There has been a recent resurgence in interest in developing ohmic switches to complement transistors in order to address challenges associated with electrical current leakage. A critical limitation in ohmic switches remains the reliability of their electrical contacts. These contacts are prone to hydrocarbon induced contamination which progressively inhibits signal transmission, eventually leading to device failure. We report on progress made towards controlling the contamination phenomenon. We discuss how contact materials and operating environment affect device performance, showing that RuO2 coated microswitch contacts operating in the presence of O2 experience very limited contaminant accumulation even in hydrocarbon-rich environments. We then demonstrate that devices which have experienced contamination can recover their original performance by being operated in clean N2:O2 environment. Finally, we suggest that this resistance recovery is associated with the chemical transformation of the contaminant as opposed to its removal and that the transformed contaminant may shield the Pt coating from oxidation.

Silicon carbide (SiC) has long been known as a robust semiconductor with superior properties to silicon for electronic applications. Consequently a tremendous amount of international activity has been on-going for over four decades to develop high-power solid state SiC electronics. While this activity has focused on the hexagonal polytypes of SiC, the only form that can be grown directly on Si substrates, 3C-SiC (or cubic SiC), has been researched for non-electronic applications such as MEMS and biosensors. In particular in our group we have pioneered several biomedical devices using 3C-SiC grown on Si substrates, and recently have been investigating the use of this novel material for clean energy applications. This paper first reviews progress made in the area of 3C-SiC electronic devices. Next a review of nearly a decade of biomedical activity is presented, with particular emphasis on the most promising applications: in vivo glucose monitoring, biomedical implants for connecting the human nervous system to advanced prosthetics, and MEMS/NEMS research aimed at allowing for in vivo diagnostic and therapeutic systems for advanced biomedical applications. Recent published work in the area of hydrogen production via electrolysis using 3C-SiC closes the paper as this last application is extremely promising for the burgeoning hydrogen economy and demonstrates a third important application of 3C-SiC on Si – its potential use in clean energy systems.

Recently, major advances have been made in electrolytic and solid state DSSCs through the use of perovskite nanocrystals as a sensitizing agent where power conversion efficiencies of over 12% have been realized [1–3]. Moreover the planar DSSC/PV devices with perovskites used as photoactive absorbers sandwiched between selective electron and hole transport layers have demonstrated record performances. Additionally, the uses of carbon nanotubes (CNTs) as a flexible, transparent, lightweight and robust electrode material have been demonstrated in both DSSC as well as OPV devices. The application of CNTs as a charge collector with perovskite sensitized solid state planar PV and DSSCs is discussed. Performance characteristics of CNTs within perovskite based hybrid OPVs are investigated and the role of CNTs as an efficient charge collector is extended to the inverted geometry.

Assembly of nanowires into ordered macroscopic structures has attracted great scientific interests in the past decade. In this work, we report a rapid low-cost scalable oil-water interfacial self assembly process for fabricating aligned Ag nanowires (AgNWs) films on solid substrates. This process is much simpler than the traditional Langmuir-Blodgett (LB) techniques and allows the assembly of one–dimensional Ag nanowires onto any solid substrates without extra pretreatment of the surface of silver nanowires or the solid substrate. The present aligned AgNW films can serve as robust surface-enhanced Raman scattering (SERS) sensors for chemical and bimolecular detection with improved spectra quality and demonstrated uniformity of SERS signal using R6G dye as probe.

We have been developing a collection of low-cost experiments for exploring the science of glassy materials through hands-on activities with sucrose based glass (a.k.a. hard candy). These form a mini-curriculum of glass science, consisting of inter-related experiments and home built apparatuses. It provides an environment to develop an understanding of glassy materials through active, prolonged engagement. Some of our earlier experiments were reported four years ago[1]. Since that report we have made substantial improvements and added new topics, including electrical and thermal conductivity, an improved DTA apparatus, and improved methodology for crystallization kinetics. All of our experiments are designed to be low-cost (typically <$100) and the apparatuses are designed for construction by students or teachers.

Several strategies have been explored from viewpoint of biomimetics to accomplish artificial photosynthesis by using macromolecules as a medium such as liposomes, supramolecules, and hydrogels.1 Differing from disordered solution systems in which multiple components such as photosensitizer and catalytic nanoparticle are diffusively mixed, the photochemical reactions occur efficiently in medium due to maintenance of the dipersibility of the components and specific molecular arrangement. Here we attempt to clarify the effect of medium hierarchy for photoinduced electronic transmission among multiple components. By conjugating each component on tubulin and integrating them via self-assembly to microtubules, ideal component arrangements with optimum distance for the electronic transmission will be possible.

A new approach for functionalising oxidised MWCNTs using hydroxylated imidazolium bromide via esterification reaction is reported. The bromide anion of a functionalised MWCNTs was exchanged with bis(trifluoromethanesulfonyl) imide (TFSI) through a metathesis reaction to improve its solubility in the IL medium. Composite was characterized with IR, XPS, EDX and TGA analysis, which clearly confirmed that the MWCNTs were functionalized with IL. For potential application as lubricant, the tribological properties of the IL-functionalised MWCNTs (MWCNT-IL) were also evaluated. It was confirmed that even low concentrations of MWCNT-IL composite in ILs causes a significant improvement in the anti-wear and friction properties.

Here we investigate how charge transport properties scale down to the nanoscale regime, comparing the properties to standard semiconductor materials and providing a perspective on what it means to device manufacturing. Strontium titanate - the prototypical oxide material - has been widely studied for applications in thermoelectrics, nanoelectronics, catalysis, and other uses. We investigated how charge transport is effected at interfaces to strontium titanate under a wide range of conditions - by varying contact size, interface shape, dopant concentration, surface structures and in various combinations and relate the results to experiments utilizing standard semiconducting materials such as silicon and gallium arsenide. Also, the results of the analysis has wide ranging implications, especially for ferroelectric perovskite materials and serves as the basis for understanding and controlling switching effects - both polarization and oxygen migration based switching.

Ce3+ is known to show broad optical emission peaking in the green spectral range. For the stabilization of 3-valent cerium in ceramic phosphors such as calcium scandate CaSc2O4, often co-doping with sodium for charge compensation is performed (Na+, Ce3+ ↔ 2 Ca2+). At the melting point of CaSc2O4 (≈2110°C), however, alkaline oxides evaporate completely and co-doping is thus no option for crystal growth from the melt. It is shown that even without co-doping Ce3+:CaSc2O4 crystal fibers can be grown from the melt by laser-heated pedestal growth (LHPG) in a suitable reactive atmosphere. Reactive means here that the oxygen partial pressure is a function of temperature and p O2(T) rises for this atmosphere in such a way that Ce3+ is kept stable for all T. Crystal fibers with ≈1 mm diameter and ≤50 mm length were grown and characterized. Differential thermal analysis (DTA) was performed in the pseudo-binary system CaO–Sc2O3, and the specific heat capacity c p (T) of CaSc2O4 was measured up to 1240 K by differential scanning calorimetry (DSC). Near and beyond the melting point of calcium scandate significant evaporation of calcium tends to shift the melt composition towards the Sc2O3 side. Measurements and thermodynamic calculations reveal quantitative data on the fugacities of evaporating species.

Water-soluble associative polyelectrolytes of methacrylic acid [MAA] and ethyl acrylate [EA] (1:1 molar ratio), hydrophobically modified with small amounts of stearyl metacrylate [MM18], were synthesized by means of solution polymerization. Polyelectrolytes with two different molecular structures: multisticker, with hydrophobic groups randomly distributed along the hydrophilic chain and combined, with the hydrophobic groups along the chain and as terminal groups of the backbone, were obtained. Steady shear behavior and linear viscoelastic properties were studied as a function of polymer microstructure and hydrophobic group concentrations on salt-free aqueous solution using a cone-and-plate rheometer. Concentration regimes were obtained for each synthetized polymer. Viscoelastic study shows that the maximum thickening effect corresponds to the combined structure followed by multisticker structure. These polyelectrolytes exhibit high thickening power on aqueous solutions due to the synergy between the hydrophobic attractive interactions and coil expansion phenomena.

The BiFeO3 (BFO) / PbTiO3 (PT) multiferroic ceramic composites with multilayered structure were prepared from orderly laminated BFO and PT tapes by tape casting method. The dielectric constant ε r , loss tanδ, remnant polarization P r and field-induced strain of BFO/PT ceramic composites were 140 (1 kHz), 5% (1 kHz), 12 µC/cm2 (at 80 kV/cm) and 0.06% (at 80 kV/cm) respectively, which were comparable to those pure BFO ceramics and BFO-based solid solutions

Effect of residual stresses of multiple welding repairs on API 5L X52 pipeline steel on stress corrosion cracking (SCC) in a simulated acidic soil solution was studied. Four conditions of repairs of the girth weld were evaluated. The residual stresses were measured through X-ray diffraction (XRD) on the internal side of the pipe in longitudinal and circumferential direction. The circumferential and longitudinal residual stresses values are compressive on the inner surface of the welding joints. The highest residual stresses were measured in the hoop direction reaching values of about 98% of the yielding strength (360 MPa). It was observed that its magnitude increases as move away from weld center line. The effect of residuals stresses in the SCC susceptibility of X52 pipeline steel was evaluated through slow strain rate tests (SSRT) in a simulated acidic soil solution. Relation between mechanical properties obtained from SSRT and residual stresses on the SCC susceptibility was analyzed. Results of SCC index taking account the ratios obtained from the mechanical properties of the welding joints evaluate, showed good SCC resistance in acidic soil solution at low pH. Scanning electron microscopy (SEM) observations showed that the region with high residual stresses prior to generate cracks in the steel due to the combination of soil solution and the strain exerted, should favor pitting formation and not cracking.