Novel multi-stage adaptive morphing of a hydrogel cube has been achieved by combining multi-metal ionoprinting and redox chemistry of iron. A demonstration of the two-stage deployment has been shown for (1) the selective opening and closing of the cube’s lid, where the hinge point has been ionoprinted with iron, and (2) the full unfolding and folding of the cube into its cruciform net, with remaining hinges ionoprinted with vanadium. The selective unfolding and folding is achieved by alternating the oxidation state of iron between +2 and +3. This is achieved using redox chemistry selective for iron. This approach could be applied, in principle, to more degrees of staging by adding additional redox responsive ionoprinted cations and appropriate selection of reducing agents.

We studied nonlinear absorption characteristics of exfoliated Molybdenum disulphide (MoS2) dispersion in 1-Methyl-2-pyrrolidinone and demonstrate a dual absorption characteristic at 532nm nanosecond pulsed laser wavelength. A number of recent reports demonstrate a saturable absorption in MoS2 and other 2D materials at low fluences and a deviation from this saturable absorption at higher fluence using open aperture Z scan (OZ scan) technique. It has been suggested that this deviation at higher fluences is due to nonlinear optical scattering. We have recently developed a new technique which combines OZ scan and photoacoustic Z-scan (PAZ-scan). It can measure photoacoustic and optical transmission signals simultaneously. The data obtained from both signals are employed to find nonlinear absorption parameters in non-linear optical materials. Our results reveal that non-linear scattering is not the cause of deviation of 2D materials from saturable absorption at higher fluences. We propose that the optical limiting behavior at higher fluence in these 2D materials is dominated by free carrier absorption.

Finite element modelling has been used to optimise the current/ voltage (I/V) characteristics of metal/ n-SiC and metal/ n-Si diodes incorporating a thin interfacial layer. The electrical properties of the diodes have been examined in relation to the polytype of SiC (3H, 4H or 6C), the doping level, NA, (1015 - 1018cm3) of the substrate, the defect state density, Dit and the work function of the Schottky metal, Φm. The modelling by Technology Computer-Aided Design (TCAD) has shown that the presence of an interfacial insulating layer with a thickness of 1.0 nm has reduced the reverse leakage current of the diode by a factor of ∼102 in Si and 1013 (from 10-19 A to 10-6 A) for SiC with only a minor reduction (∼ 0.8 times) in the forward current in SiC. The properties of the diodes have been modelled at room temperature without thermal annealing.

In search for effective negative electrodes for Mg- and K-ion batteries, we investigate the potential of glassy amorphous carbon by means of density functional theory calculations. Specifically, we provide the energetics for Mg and K insertion in two different structures of amorphous carbon. The insertion sites are found to be well distributed in energy, with insertion energies E f vs. the cohesive energies of respectively Mg and K ranging from -1.1 to 2.8 eV for Mg and from -1.0 to 3.7 eV for K. To compare amorphous carbon to the most common structure of carbon (graphite), we study in addition the energetics associated with the insertion of Mg and K in graphite, for which two different stackings are considered for the two layers intercalating the Mg/K atom: the AB stacking which is most stable at the initial state of charge (in pure graphite) and the AA stacking which is most stable at the known final state of charge of K (K x C, x = 1/8). Already at the low concentration considered (x = 1/128), the insertion of Mg and K in graphite is found to favor the AA stacking, and to be thermodynamically unfavored (E f positive with E f = 1.9 eV for Mg and E f = 0.7 eV for K). Amorphization appears therefore to provide insertion sites for Mg and K of lower (and negative) energies. The effect is of larger extent for Mg than for K, so much so that the insertion of Mg becomes more favored than that of K in amorphous carbon, although in graphite K is more easily inserted than Mg.

Microstructured polymeric surfaces capable of a thermally-induced shape-memory effect (SME) can perform on demand changes of surface properties such as wettability or adhesion.

In this study, we explored the influence of the applied compression direction during programming, i.e. vertical compression and tilted compression, on the SME of microstructured crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) films comprising arrays of micro-cylinders with a height of 10 µm and different diameters of 10 µm, 25 µm, and 50 µm. The shape recovery of the microstructures during heating was visualized online by optical microscopy, while atomic force microscopy (AFM) was utilized to investigate the temperature-induced shape change of single micro-cylinders. Here, the changes in micro-cylinder height and the characteristic angle θ were followed and analyzed for quantification of the shape-memory performance. Both compression modes resulted in almost flat programmed surfaces as indicated by high shape fixity ratios of Rf ≥ 93±1%. A nearly complete recovery of the micro-cylinders was obtained for all investigated cPEVA samples documented by high shape recovery values of Rr ≥ 97±1%, while the obtained shape change of the micro-cylinders during recovery almost reversely recalled the applied deformation during programming. The presented capability of SMP microstructured substrates to memorize the way of deformation during programming could be a new tool for controlling particular shape changes of microstructures during recovery and in such a way the generated local recovery forces can be adjusted.

In the present work, sodium titanate nanotubes doped with potassium were synthesized by the Kasuga method and tested as catalysts for biodiesel production. Potassium was added to the nanotubes in order to increase their basicity and, consequently, improve their performance in the transesterification of soybean oil with methanol. In the synthesis, the NaOH:KOH molar ratio was changed from 9:1 to 7:3 in order to increase potassium loadings in the obtained nanotubular solids. Synthesized catalysts were characterized by N2 physisorption, powder XRD, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), FT-IR, FT-Raman and CO2 temperature-programmed desorption (CO2-TPD). Obtained results showed that sodium trititanate nanotubes containing 1.5 wt. % of potassium were obtained when 10 M alkali solution with NaOH:KOH molar ratio of 9:1 was used. In this case, the proportion of sodium and potassium in the synthesized material was similar to that used in the synthesis. An increase in the proportion of KOH to 20 and 30 molar % in the NaOH-KOH solutions used in the synthesis allowed obtaining titanate nanotubes with larger potassium loadings (3.2 and 3.3 wt. %, respectively). As it was expected, potassium addition to the sodium titanate nanotubes resulted in an increase in the amount of medium and strong basic sites. Potassium-containing nanotubes showed higher catalytic activity in the transesterification reaction than the pure sodium counterpart used as a reference. The best results were obtained with the samples containing 3.2-3.3 wt. % of potassium where a biodiesel yield of about 94-96 % was obtained at 80 °C and 1 h reaction time.

Polyphenol in mango seed kernel extraction has been demonstrated to show benefits against skin disorders. In this study, micro-cellulose sponges (MCS) from waste cotton are used as the carrier for polyphenol to produce a controlled release system. Polyphenol loaded micro-cellulose sponges were produced by acid hydrolysis and a freeze drying method. The microparticles were characterized in terms of size and morphology, total polyphenol loading, and physical state of the encapsulated polyphenol. Polyphenol release from the microparticles was assessed by dissolution tests. The particles had spherical shapes with amorphous form. The controlled drug release was tested by using different polyphenol concentration. The results showed that the structure of micro-cellulose sponges, the media type and the solubility of the polyphenol influenced the polyphenol-release behavior. Since the release of the polyphenol is controlled by the structure and interactions between the microparticles and the cellulose matrix, modulation of the matrix formers enable a control of the drug release rate. These structures of micro-cellulose sponges can be very useful in many pharmaceutical micro-particle applications.

A variety of Titanium dioxide (TiO2) phases and nanostructures have been explored for their applications in photoelectrochemical cells (PECs) for solar-driven water splitting. In this case, anatase phase and TiO2 nanotubes offer significant advantages especially for PEC-based applications. Though, significant efforts have already been engaged to combine the advantages from both the fields, poor activation and the high electron-hole pair recombination rate of TiO2 electrodes, originating from intrinsic physicochemical properties, limits its practical use. As an alternative, we report directly grown TiO2 nanotubes (synthesized on Fluorine doped Tin Oxide (FTO) via facile electrospinning technique) on carbon nanofibers, using hydrothermal method. The hierarchical branch type configuration has an intimate contact between the TiO2 nanotube and carbon nanofiber backbone and offers higher photocatalytic activity than their respective individual components (namely TiO2 nanotubes and carbon nanostructures).

Ferromagnetic (FM) electrodes chemically anchored with thiol functionalized molecules can yield novel molecular spintronics devices (MSDs). However, significant challenges lie in developing commercially viable MSD fabrication approach utilizing FM electrodes. A practical MSD fabrication approach should consider FM electrodes’ susceptibility to oxidation, chemical etching, and stress induced deformations during fabrication and usage. This paper will discuss NiFe, an alloy used in the present day memory devices and high-temperature engineering applications, as a candidate for FM electrode and for the fabrication of MSDs. Our spectroscopic reflectance studies show that NiFe starts oxidizing aggressively beyond ∼90 ⁰C. The NiFe surfaces, aged for several months or heated for several minutes below ∼90 ⁰C, were suitable for chemical bonding with the thiol-functionalized molecules. NiFe also demonstrated excellent etching resistance in widely used dichloromethane solvent for dissolving molecular device elements. NiFe also reduced the mechanical stress induced deformities in other FM metals like cobalt. This paper also discusses the successful utilization of NiFe electrodes in the magnetic tunnel junction based molecular device fabrication approach. This research is expected to address the knowledge gap blocking the experimental development of FM based MSDs.

Molybdenum based alloy having a nominal composition Mo–0.5Ti–0.1Zr–0.02C (wt%) popularly known as TZM alloy possess high temperature strength, high creep resistance, low coefficient of thermal expansion and high thermal conductivity. Processed TZM alloy contains TiC, ZrC and complex carbides which inhibit recrystallization at high temperatures and also improve the working conditions. In this study, the effect of sintering temperature, holding time and pressure on densification, microstructure and hardness of the spark plasma sintered TZM alloys were investigated. The sample sintered at 1575 °C for 150 second under 40 MPa exhibited the highest relative density, ∼98%. Microstructural characterization was performed by using FESEM and it was observed that TiC and ZrC dispersed through the microstructure. The average size of precipitates were measured as 7.5 and 3.5 µm for TiC and ZrC, respectively.

Transition metal oxide thin film heterostructures have garnered increasing research interest in the last decade due to their multifunctional properties, such as ferromagnetism and ferroelectricity, which may be utilized in next generation device applications. Many previous works reported on the deposition of such structures on oxide substrates such as SrTiO3, which are not compatible with CMOS applications where Si(100) is the mainstay substrate material. BiFeO3 (BFO) is a room temperature insulating ferroelectric and antiferromagnet, a well-known multiferroic material. SrRuO3 (SRO) is a ferromagnetic metal with the Curie temperature (TC) of 165K. Unexpected properties emerge when these two dissimilar materials are conjoined. However, there has been no report on exploring the magnetic properties of BFO when it is in contact with SRO, and particularly when they are integrated with Si(100) substrates, which is the subject of present study. BFO/SRO thin films have been epitaxially grown on Si (100) substrates by introducing MgO/TiN epitaxial buffer layers using pulsed laser deposition. BFO thin films show room temperature ferroelectricity as observed from piezo force microscopy (PFM) measurements. The magnetic data collected from BFO thin films show typical antiferromagnetic features as expected. The TC of SRO in all the samples studied was found be ∼ 170K, close to the reported value of 165K. Interestingly, we have noticed that the coercive field of SRO layer increased from 4 kOe to 15 kOe (nearly fourfold) by reducing its thickness from 180 to 23nm, while keeping the thickness of BFO layer constant at 100nm. Pinning of Ru ions by ferroelectric domain walls in BFO, strong interfacial exchange coupling and SRO layer thickness could cause the observed enhancement in coercivity. Our near future work will address the precise underlying mechanisms in greater detail.

TDDFT in real-space and real-time approach has been applied to study the optical property of poly(9,9'-dioctyl-fluorene) in the gas phase and in the solid state in order to clarify the effect of aggregation on the spectrum. We show that the spectrum of polymer chain is basically the same in linear and helical shape when it is in the gas phase, however, in solid state phase, the spectrum of aligned aggregate model is different from the spectrum sum of its constituent single chains, suggesting the existence of inter-chain interaction and its effect on the spectrum.

Intrinsically conductive polymers have received increased attention in the biomedical field due to their mechanical flexibility, electronic and ionic conductivity. On the other hand, bio-derived polymers such as silk proteins (fibroin and sericin) are an important set of materials to realize mechanically deformable, biocompatible and biodegradable systems. Here, we show a ‘green’ approach to fabricate micropatterned, flexible biosensors using photoreactive silk proteins in conjunction with conductive polymers. A functional ink comprised of poly(3,4-ethylene dioxythiophene: poly(styrene sulfonate) (PEDOT:PSS) with silk sericin as a carrier enables the formation of high resolution conducting micropatterns on a silk fibroin substrate via photolithography. The flexible and conformable organic device formed can be used to sense biomolecules with high sensitivity and selectivity. The micropatterned functional silk composites are made using an all water-based fabrication approach, and shown to be cell friendly and degradable. Such systems can find applications in implantable optical devices, bio-sensors, and bio-optoelectronic devices.

Multilayered film stacks, with length scales less than 10 nm are commonly used in a variety of devices, but present significant challenges to mechanical testing and evaluation. This is due to property convolution of the different layers. Both the properties of the individual layers and the combined response of the film stack are important input for design optimization. Here, we present ex-situ nanoindentation of a film stack representative of a perpendicular magnetic recording (PMR) hard disc drive (HDD), with more than 10 layers. We then compare this with in-situ transmission electron microscopy indentation to visualize deformation of individual layers of the stack. The ex-situ testing reveals early plastic deformation, with an initially high contact pressure (13 GPa) and modulus ( >160 GPa), followed by significant softening (8 GPa contact pressure and 140 GPa modulus), then slight hardening to 9 GPa. From in-situ testing, it is revealed that the metallic layer directly under the diamond like carbon (DLC) contributes the majority of the deformation and plastic flow, which is in turn constrained by a metallic oxide.

Contact metallization is an essential obstacle for utilizing low temperature achievable polycrystalline ZnO in any discrete devices and integrated circuits. To develop ZnO based semiconductor devices with advanced feature of flexibility, transparency and compatibility with low temperature processing, rectifying junctions must be fully developed. In this work, nanoscale polycrystalline ZnO thin films are fabricated with via low temperature (<200 °C) by atomic layer deposition (ALD). A vertical structure of bottom Schottky metallized diode is developed with copper (Cu) sputtered in room temperature. A control of Cu surface oxidation is realized with an in-situ remote plasma treatment. The results indicate that preparation of the copper surface substantially affects the electrical behavior of the diode. Thermal reliability of Cu metallized Schottky diode is subsequently carried out by annealing up to a maximum temperature of 300 °C before it breaks. This work considers the current transport mechanism evolved deviating current vs voltage (I-V) characteristics from conventional thermionic emission theory.

We describe a simple and inexpensive method to enhance the sensitivity or improve the detection limit of solution-phase localized surface plasmon (LSPR) sensors of metallic nanoparticles. The substrate surface contains metallic nanostructures which are replicated from DVD disks via the standard soft lithography. By mixing BSA molecules with nanoparticle solution, we demonstrate that the wavelength shift due to the absorption of BSA molecules on nanoparticle surfaces is amplified by more than an order of magnitude in comparison to that over a smooth flat surface.

Resistive Random Access Memory (RRAM) is a novel form of non-volatile memory that is expected to play a major role in future computing and memory solutions. It has been shown that the resistance of RRAM devices can be precisely tuned by modulating switching voltages, by limiting peak current, and by adjusting the switching pulse duration. This enables the realization of novel applications such as memristive neuromorphic computing and neural network computing. The RRAM devices described in this work utilize an inert tungsten bottom electrode, hafnium oxide based active switching layer, a titanium oxygen exchange layer, and an inert titanium nitride top electrode. Linear sweep and controlled pulse (down to 10 ns) based electrical characterization of RRAM devices was performed in a 1 transistor 1 RRAM (1T1R) configuration to determine endurance, reliability, retention and threshold voltage parameters. We demonstrated endurance values above 108 cycles with an average on/off ratio of 15 and pulse voltages for set/reset operation of ±1.5V. The on-chip 1T1R structures show an excellent controllability with respect to the low and high resistive state by manipulating the peak current from 75 up to 350µA we were able to achieve 10 discrete resistive states. Our results demonstrate that the set operation (which shifts the RRAM device from the high to the low resistance state) is only dependent on the voltage of the switching pulse and the peak current limit. The reset operation, however, occurs in an analog fashion and appears to be dependent on the total energy of the applied switching pulse. Pulse energy was modulated by varying the peak voltage which resulted in a larger relative change of the RRAM device resistance.

Detection of volatile organic compounds (VOCs) emitted from cancerous tumor cells in exhaled human breath allows for early diagnosis of various types of cancers. 3D graphene with a large surface area is considered a suitable material for creating novel sensitive VOCs sensors. In this study, 3D graphene and 3D graphene oxide were synthesized from graphene oxide suspension, hydroquinone and formaldehyde by employing polymerization and reduction. The capability of VOC gas sensing was evaluated by measuring the electrical current response in flowing N2 gas over a range of concentrations of acetone or 1-butanol at room temperature. It was observed that the device current correlated well with the VOC concentration. The adsorption of acetone decreased the current, but the adsorption of 1-butanol increased the current during sensing. 3D graphene oxide device was more sensitive than 3D graphene device because of the high concentration of oxygen-containing functional groups on the surface. These results indicated that 3D graphene and 3D graphene oxide may be the suitable materials for VOCs sensing devices.