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Organic materials are always viewed as promising electrochromic (EC) materials due to their synthetic versatility, color tunability, ready processability, and derivability from sustainable feedstocks. Most organic materials, however, are prone to undesirable redox side reactions in the presence of oxygen and water. As such, redox–active organic layers are often used in tandem with organic electrolytes to preserve their electrochemical stability. With the growing interest in electronics that are environmentally sustainable and biologically safe, developing aqueous‐compatible organic materials is gaining growing interest. Herein, a rationally designed iron terpyridyl coordination polymer (CP) is prepared by controlled electropolymerization for realization of aqueous compatible EC and energy storage applications. Detailed analysis is established, showing that the CP grows in a 1D fashion and exhibits a predominant capacitive behavior which is reflected from its rapid charge–transfer kinetics. Taking this as an advantage, an integrated hybrid electrochromic zinc battery device is demonstrated with high color contrast, fast response time, and good endurance., Electropolymerization of rationally designed iron–terpyridyl complexes forms 1D growth coordination polymer with the ability to electrochemically switch between the initial purplish‐blue state and the bleached transparent state in an aqueous electrolyte. The modified electrode is used to construct an integrated hybrid electrochromic zinc battery exhibiting both electrochromic and energy‐storage abilities with good endurance in the aqueous environment.

Pollution caused by nondegradable plastics has been a serious threat to environmental sustainability. Natural polymers, which can degrade in nature, provide opportunities to replace petroleum-based polymers, meanwhile driving technological advances and sustainable practices. In the research field of soft electronics, regenerated natural polymers are promising building blocks for passive dielectric substrates, active dielectric layers, and matrices in soft conductors. Here, the natural-polymer polymorphs and their compatibilization with a variety of inorganic/organic conductors through interfacial bonding/intermixing and surface functionalization for applications in various device modalities are delineated. Challenges that impede the broad utilization of natural polymers in soft electronics, including limited durability, compromises between conductivity and deformability, and limited exploration in controllable degradation, etc. are explicitly inspected, while the potential solutions along with future prospects are also proposed. Finally, integrative considerations on material properties, device functionalities, and environmental impact are addressed to warrant natural polymers as credible alternatives to synthetic ones, and provide viable options for sustainable soft electronics. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was supported by the NRF Investigatorship (Award No. NRF-NRFI2016-05) under the National Research Foundation, Prime Minister’s Office, Singapore, and the Ministry of Education AcRF Tier 1 Award RT15/20, Singapore.

The design and construction of 3D architectures enabled by stimuli-responsive soft materials can yield novel functionalities for next generation soft-bodied actuating devices. Apart from additive manufacturing processes, origami inspired technology offers an alternative approach to fabricate 3D actuators from planar materials. Here we report a class of near-infrared (NIR) responsive 3D active origamis that deploy, actuate and transform between multistable structural equilibria. By exploiting the nonlinear coefficient of thermal expansion (CTE) of graphene oxide (GO), graphene oxide/ethylene cellulose (GO/EC) bilayers are readily fabricated to deliver precise origami structure control, and rapid low-temperature-triggered photothermal actuation. Complexity in 3D shapes is produced through heterogeneously patterning GO domains on 2D EC thin films, which allows us to customize 3D architectures that adapt to various robotic functions. The strategy also enables the construction of material systems possessing naturally inaccessible properties, such as remotely controlled mechanical metamaterials with auxetic behavior and bionic flowers with a rapid blooming rate. Harnessing deformability with multiple degrees of freedom (DOF) upon light irradiation, this work leads to breakthroughs in the design and implementation of shape-morphing functions with soft origamis. National Research Foundation (NRF) Accepted version This work was supported by the Competitive Research Program (NRF-CRP13-2014-02) and NRF Investigatorship (Award No. NRF-NRFI2016-05) under the National Research Foundation, Prime Minister’s Office, Singapore. D. Gao acknowledge the research scholarships awarded by Nanyang Technological University, Singapore.

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d₃₃ = −1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Nanyang Technological University Published version This research was funded by Ministry of Education-Singapore, grant MOE2016-T2-2-108; Nanyang Technological University, CHAIR PROFESSORSHIPS grant; Agency for Science, Technology, and Research, grant AMBM, A18A8b0059.

Coordination polymers (CPs) and coordination network solids such as metal–organic frameworks (MOFs) have gained increasing interest during recent years due to their unique properties and potential applications. Preparing 3D printed structures using CP would provide many advantages towards utilization in fields such as catalysis and sensing. So far, functional 3D structures were printed mostly by dispersing pre-synthesized particles of CPs and MOFs within a polymerizable carrier. This resulted in a CP active material dispersed within a 3D polymeric object, which may obstruct or impede the intrinsic properties of the CP. Here, we present a new concept for obtaining 3D free-standing objects solely composed of CP material, starting from coordination metal complexes as the monomeric building blocks, and utilizing the 3D printer itself as a tool to in situ synthesize a coordination polymer during printing, and to shape it into a 3D object, simultaneously. To demonstrate this, a 3D-shaped nickel tetra-acrylamide monomeric complex composed solely of the CP without a binder was successfully prepared using our direct print-and-form approach. We expect that this work will open new directions and unlimited potential in additive manufacturing and utilization of CPs. National Research Foundation (NRF) Published version This research was supported by the grants from the National Research Foundation, Prime Minister's Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) Programme, Nanomaterials for Energy and Water-Energy Nexus, and by the Hebrew university fund for PhD students.

Smart sensing electronic devices with good transparency, high stretchability, and self-powered sensing characteristics are essential in wearable health monitoring systems. This paper innovatively proposes a stretchable nanocomposite nanogenerator with good transparency that can be conformally attached to the human body to harvest biomechanical energy and monitor physiological signals. The work reports an innovative device that uses sprayed silver nanowires as transparent electrodes and sandwiches a nanocomposite of piezoelectric BaTiO3 and polydimethylsiloxane as the sensing layer, which exhibits good transparency and mechanical transformability with stretchable, foldable, and twistable properties. The highly flexible nanogenerator affords a good input–output linearity under the vertical force and the sensing ability to detect lateral stretching deformation up to 60% strain under piezoelectric mechanisms. Furthermore, the proposed device can effectively harvest touch energies from the human body as a sing...

Molybdenum trioxide is an interesting inorganic system in which the empty 4d states have potential to hold extra electrons and therefore can change states from insulating opaque (MoO3) to colored semimetallic (HxMoO3). Here, we characterize the local electrogeneration and charge transfer of the synthetic layered two-dimensional 2D MoO3-II (a polymorph of MoO3 and analogous to α-MoO3) in response to two different redox couples, i.e., [Ru(NH3)6]3+ and [Fe(CN)6]3- by scanning electrochemical microscopy (SECM). We identify the reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+ at the microelectrode that leads to the reduction of MoO3-II to conducting blue-colored molybdenum bronze HxMoO3. It is recognized that the dominant conduction of the charges occurred preferentially at the edges active sites of the sheets, as edges of the sheets are found to be more conducting. This yields positive feedback current when approaching the microelectrode toward 2D MoO3-II-coated electrode. In contrast, the [Fe(CN)6]4-, which is reduced from [Fe(CN)6]3-, is found unfavorable to reduce MoO3-II due to its higher redox potential, thus showing a negative feedback current. The charge transfer on MoO3-II is further studied as a function of applied potential. The results shed light on the charge transfer behavior on the surface of MoO3-II coatings and opens the possibility of locally tuning of their oxidation states. National Research Foundation (NRF) We acknowledge financial support from the National Research Foundation Investigatorship Award, NRF-NRFI-2016-05. Part of this work was also supported by the Nanomaterials for Energy and Water Management Programme under the Campus for Research Excellence and Technological Enterprise (CREATE) that is supported by the National Research Foundation, Prime Minister’s Office, Singapore.

The rational design of previously unidentified materials that could realize excellent electrochemical‐controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D π–d conjugated coordination polymer (Ni‐BTA) is reported, consisting of metal (Ni)‐containing nodes and organic linkers (1,2,4,5‐benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni‐BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm2 C−1), and high gravimetric capacity (168.1 mAh g−1). In particular, the Ni‐BTA film can maintain its electrochemical recharge‐ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni‐BTA films present a great promise for Ni‐BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows., A 1D π–d conjugated coordination polymer (CCP) is successfully fabricated in which specific organic linker and metal ions are selected with the aim of increasing the density of redox active centers and enabling conductive paths for charge transport. Moreover, this CCP enables dual electrochromic and energy storage functionalities in an integrated smart device.

This is the peer reviewed version of the following article: Advanced Functional Materials 29.15 (2019): 1808424, which has been published in final form at https://doi.org/10.1002/adfm.201808424. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions, This work presents the fabrication of 3D-printed composite objects based on copper(II) 1D coordination polymer (CP1) decorated with thymine along its chains with potential utility as an environmental humidity sensor and as a water sensor in organic solvents. This new composite object has a remarkable sensitivity, ranging from 0.3% to 4% of water in organic solvents. The sensing capacity is related to the structural transformation due to the loss of water molecules that CP1 undergoes with temperature or by solvent molecules' competition, which induces significant change in color simultaneously. The CP1 and 3D printed materials are stable in air over 1 year and also at biological pHs (5–7), therefore suggesting potential applications as robust colorimetric sensors. These results open the door to generate a family of new 3D printed materials based on the integration of multifunctional coordination polymers with organic polymers, N.M. and V.G.V. contributed equally to this work. The authors thank financial support from the Spanish Ministerio de Economía y Competitividad (MAT2016‐77608‐C3‐1‐P, MAT2016‐75883‐C2‐2‐P) and the National Research Foundation, Prime Minister's Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. O.H. acknowledges the support for Ph.D. students from The Hebrew University of Jerusalem. J.I.M. acknowledges the financial support by the “Ramón y Cajal” Program of MINECO (Grant RYC‐2015‐17730) and the EU via the ERC‐Synergy Program (Grant ERC‐2013‐SYG‐610256 NANOCOSMOS). A.E.P.‐P. acknowledges a TALENTO grant (2017‐T1/IND5148) from Comunidad de Madrid. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at beamline P02.1 PETRA III under the proposal I‐20170717 EC. V.G.V. thanks to the Ministry of Education, Youth and Sports, the Madrid Community and the European Social Fund. The authors thank Deseada Diaz Barrero, from Autonoma University of Madrid, Applied Physics Department, for the study of diffuse reflectance of the compound presented here

A simple and low-cost process of embedding metal nanocrystals as charge storage centers within a dielectric is demonstrated to address leakage issues associated with the scaling of the tunnelling oxide in flash memories. Metal nanocrystals with high work functions (nickel, platinum and palladium) were prepared as embedded species in methyl siloxane spin-on-glass (SOG) films on silicon substrates. Sub-10 nm-sized, well-isolated, uniformly distributed, multi-layered nanocrystals with high particle densities (1011–1012 cm−2) were formed in the films by thermal curing of the spin-coated SOG films containing the metal precursors. Capacitance-Voltage measurements performed on metal-insulator-semiconductor capacitors with the SOG films show that the presence of metal nanocrystals enhanced the memory window of the films to 2.32 V at low operating voltages of ±5 V. These SOG films demonstrated the ability to store both holes and electrons. Capacitance-time measurements show good charge retention of more than 75% after 104 s of discharging. This work demonstrates the applicability of the low-cost in-situ sol-gel preparation in contrast to conventional methods that involve multiple and expensive processing steps.

With the advancement of wearable electronics, stretchable energy harvesters are attractive to reduce the need of frequent charging of wearable devices. In this work, a stretchable kirigami piezoelectric nanogenerator (PENG) based on barium titanate (BaTiO ) nanoparticles, Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) matrix, and silver flakes-based electrode is fabricated in an all-3D printable process suited for additive manufacturing. The 3D printable extrusion ink is formulated for facile solvent evaporation during layer formation to enable heterogenous multilayer stacking. A well-designed modified T-joint-cut kirigami structure is realized to attain a non-protruding, high structural stretchability performance, overcoming the out-of-plane displacement of the typical kirigami structure and therefore enabling the pressing-mode of a kirigami-structured PENG. This PENG can be stretched to more than 300% strain, which shows a great potential for application in wearable electronic systems. Furthermore, a self-powered gait sensor is demonstrated using this PENG. 3 National Research Foundation (NRF) Published version This research is supported by the grant from the National Research Foundation, Prime Minister’s Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) programme.

The interaction site of phthalocyanine (Pc) with nitrogen dioxide (NO2) has been characterized using different methods and found to be conflicting. By knowing the interaction site, the Pc molecule can be better customized to improve the gas sensitivity. In this article, the interaction sites of copper phthalocyanine (CuPc) with oxidizing NO2 or with reducing gas (ammonia, NH3) were identified using in situ X-ray absorption spectroscopy (XAS). The sensitivity of CuPc to sub-ppm levels of the tested gases was established in the CuPc chemoresistive gas sensors. The analyte-sensor interaction sites were identified and validated by monitoring the Cu K-edge XAS before and during gas exposure. From the X-ray absorption near-edge structure and its first derivative, a low or lack of axial coordination on the Cu metal center of CuPc is evident. Using the extended X-ray absorption fine structure with molecular orbital information of the involved molecules, the macrocycle interaction between CuPc and NO2 or NH3 was proposed to be the dominant sensing mechanism on CuPc sensors. EDB (Economic Devt. Board, S’pore) Published version

Dielectric elastomer actuators (DEAs) have shown great potential in the field of robotics, energy harvesting, or haptics for wearables. However, existing DEA materials typically require prestretching and exhibit time-dependent deformations due to their inherent viscoelastic properties. In this work, we address these issues by designing and synthesizing a polyurethane acrylate (PUA) DEA copolymerized with a polar crosslinker, polyethylene glycol diacrylate (PEGDA), to reduce viscoelastic effects through chemical crosslinking. We realized a buckling-mode actuator that displays out-of-plane deformations triggered by an electric field without the need for prestretching. Copolymerization with PEGDA showed improved dynamic response actuation performances compared to pristine PUA, wherein the former reached 90% of its maximum actuation in

Ferroelectric materials have attracted interest in recent years due to their application in energy harvesting owing to its piezoelectric nature. Ferroelectric polymers are flexible and can sustain larger strains compared to inorganic counterparts, making them attractive for harvesting energy from mechanical vibrations. Herein, we report, for the first time, the enhanced piezoelectric energy harvesting performance of the bilayer films of poled poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] and graphene oxide (GO). The bilayer film exhibits superior energy harvesting performance with a voltage output of 4 V and power output of 4.41 μWcm(-2) compared to poled PVDF-TrFE films alone (voltage output of 1.9 V and power output of 1.77 μWcm(-2)). The enhanced voltage and power output in the presence of GO film is due to the combined effect of electrostatic contribution from graphene oxide, residual tensile stress, enhanced Young's modulus of the bilayer films, and the presence of space charge at the interface of the PVDF-TrFE and GO films, arising from the uncompensated polarization of PVDF-TrFE. Higher Young's modulus and dielectric constant of GO led to the efficient transfer of mechanical and electrical energy.

Here we demonstrate the effect of the concentration of hydrogen peroxide solution on the generation of various kinds of oxygen ions, mainly peroxide (O22−) and superoxide (O2−) ions, on the surface of molybdenum trioxide (MoO3) nanobelts. Due to O22− and O2− ions, the mechanism of charge storage shows an interplay between surface-controlled and diffusion-controlled redox reactions. The concentration of H2O2 is indicative of the strength of hydrogen bonding, which significantly affects the concentration or coordination of the surface species (O2−, O22−, Mo5+ and Mo6+) that are available to interact with the electrolyte ions. By altering the concentration of the surface species (IO2−/IO22−, IMo5+/IMo6+), a specific capacitance as high as 210 F g−1 is achieved for MoO3 nanobelts at an applied current density of 0.5 A g−1, with relatively good cycling stability (≈85 %) after 2000 cycles.

Combinatorial approaches in preparing nanocomposites of transition metal oxides with conductive polymers have gained enormous attention due to their outstanding pseudocapacitive properties which are mainly associated with the solid-state diffusion of electrolyte ions as well as surface or near-surface reversible redox reactions. Here, we elaborate on the interplay of surface-controlled and diffusion-controlled redox reactions based on polyaniline and hexagonal molybdenum trioxide (h-MoO3) hollow nanorods to realize improved electrochemical performance of the nanocomposite electrode. The cationic species (Ferric ions) were used as the oxidants to polymerize aniline monomers and assist in the formation of h-MoO3 hollow nanorods. The formation of h-MoO3 hollow nanorods was realized through the cation exchange-assisted Kirkendall effect driven by ferric ions. The resultant core–shell architecture of the polymerized h-MoO3 showed improved pseudocapacitive performance (270 F/g) when compared to the pristine h-M...

Solar-blind photodetectors based on Zn2GeO4 (ZGO) nanowires (NWs) with high transparency and good flexibility were successfully fabricated on a polyethylene terephthalate (PET) substrate using a facile all solution-processible method. The electrodes and functional channels are constructed with silver NWs (Ag NWs) and ZGO NWs, respectively, using a spray coating method. The spray-coated all-NW device exhibited high transparency, good mechanical bending stability, high photoresponse, and short cutoff wavelength. The Schottky barrier between the Ag–ZGO NWs together with the junction barrier between interconnecting ZGO NWs contributed to a high photoresponse and improved switching time in the devices. We propose that the unique energy band structure of the ZGO NW networks provides an additional mechanism to further reduce the cutoff wavelength in solar-blind photodetectors.

The crystallographic structure and morphology of redox active transition metal oxides have a pronounced effect on their electrochemical properties. In this work, h-MoO3 nanostructures with three distinct morphologies, i.e., pyramidal nanorod, prismatic nanorod and hexagonal nanoplate, were synthesized by a facile solvothermal method. The morphologies of h-MoO3 nanostructures were tailored by a controlled amount of hexamethylenetetramine. An enhanced specific capacitance about 230 F g−1 at an applied current density of 0.25 A g−1 was achieved in h-MoO3 pyramidal nanorods. Electrochemical studies confirmed that the h-MoO3 pyramidal nanorods exhibit superior charge-storage ability. This improved performance can be ascribed to the coexistence of its well exposed crystallographic planes with abundant active sites, i.e., hexagonal window (HW), trigonal cavity (TC) and four-coordinated square window (SW). The mechanism of charge-storage is likely facilitated by the vehicle mechanism of proton transportation due to the availability of the vehicles, i.e., NH4+ and H2O. The promising, distinct and unexploited features of h-MoO3 nanostructures reveal a strong candidate for pseudocapacitive electrode materials. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

A new tetraazatetracene derivative, 2,3-[4,4'-bis(N,N-diphenylamino)benzyl]-5,12-bis[(triisopropylsilyl)ethynyl]-1,4,6,11-tetraazatetracene (TPAs-BTTT), displays rewritable multilevel memory behavior, which is probably induced by multielectron intramolecular charge transfer (CT).

This study reports a novel strategy to obtain a layered metastable phase of molybdenum trioxide (MoO3). The metastable phase in the layered framework, i.e., MoO3-II, was a result of the topotactic phase transformation of hexagonal-MoO3 (h-MoO3) into MoO3-II. This transformation was realized through the removal of the water and ammonium molecules from the framework of h-MoO3. Next, a facile exfoliation strategy was adopted to prepare MoO3-II nanosheets, consisting of double-layers of MoO6 octahedra. The as-exfoliated MoO3-II nanosheets had measured thicknesses of 1.4, 2.4, and 11.2 nm, as quantified using atomic force microscopy (AFM), equivalent to 2, 3, and 16 double-layers of the MoO6 octahedra in MoO3-II, respectively, after taking into account their respective van der Waals gaps (thickness of a MoO3-II double-layer ∼0.709 nm). This work is the first attempt to synthesize MoO3-II nanosheets and shed light on their formation mechanism.

N-substituted heteroacenes have been widely used as electroactive layers in organic electronic devices, and only a few of them have been investigated in organic resistive memory devices. Here, a novel N-substituted heteroacene 2-(4′-(diphenylamino)phenyl)-4,11-bis((triisopropylsilyl)ethynyl)-1H-imidazo[4,5-b]phenazine (DBIP) has been designed, synthesized, and characterized. Sandwich-structure memory devices based on DBIP have been fabricated and the devices show non-volatile and stable memory character with good endurance performance.

In this work, we present the formation of porous NiCo oxide nanowires from single crystal nickel cobalt bimetallic carbonate hydroxide nanowires (NiCo cNW) for supercapacitor applications. High aspect ratio NiCo cNWs are found to evolve from highly crystalline nickel cobalt layered double hydroxides through a dodecyl anion assisted crystallization–dissolution–recrystallization process. The porous nickel cobalt oxide (NixCo3−xO4) nanowire array is formed by the heat treatment of nickel cobalt bimetallic carbonate hydroxide nanowires on nickel foam (NF) for the assembly of supercapacitors. This binder free electrode shows a high specific capacitance of 1479 F g−1 at 1 A g−1 and 792 F g−1 at 30 A g−1, indicating an excellent rate capability. Asymmetric device is constructed from NixCo3−xO4 on NF and activated carbon (AC) with an operation potential from 0 to 1.6 V. It shows a high specific capacitance of 105 F g−1 at a current density of 3.6 mA cm−2, while it maintains 58.7 F g−1 at 89.4 mA cm−2. In addition, the asymmetric device shows good stability towards long time charge–discharge cycles.

A “nano to nano” electrodeposition approach for preparing nano-structured thin films from the dispersion of nano-objects is reported. A typical WO3 system is demonstrated, where nanocrystalline films are electrodeposited onto transparent conductive electrodes such as ITO and Ag grid printed PET (Ag grid/PET) from the water dispersion of WO3 nanoparticles without applying high potential, adding surfactants or polymers. The process is based on the reduction of WO3, which eliminates the electrostatic repulsion between the nanoparticles causing film deposition on the cathode. The reduced WO3 (HWO3) is conductive, thus it allows further film growth towards higher thickness and coverage. The electrodeposited films consist of stacked crystalline nanoparticles, which provide a highly active surface area, facilitate the penetration of electrolyte and the intercalation/deintercalation of Li+ in the nanocrystals and therefore result in outstanding electrochromic performance and stability (92% contrast, 9 s coloring and 15 s bleaching, retaining 76% contrast after 1000 coloring–bleaching cycles). The thickness, electrochromic performance and surface coverage of the films are well tuned by potential and time. This novel “nano to nano” electrodeposition approach based on the electrochemical redox of nano-objects can be extended to various transition metal oxide nano-objects with different sizes and shapes.

WO3 and electrochemical reduced graphene oxide (WO3/rGO) nanocomposites were prepared by one-step facile electrochemical deposition in an aqueous electrolyte containing tungsten species and graphene oxide. The WO3 in the as-prepared WO3/rGO composite is amorphous and exists in the form of nanostructure. Raman spectra confirm the co-existence of WO3 and the reduction of the graphene oxide sheets in the WO3/rGO composite. The electrochromic properties of the WO3/rGO film show significant improvement compared to WO3 films. The WO3/rGO film shows faster switching time, longer cycle life and larger coloration efficiency at the wavelength of 632.8 nm. These enhancements are mainly due to the synergistic incorporation of rGO into WO3.

Hybrid thin films composed of multilayer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) and tungsten trioxide (WO3) were electrochemically deposited on indium tin oxide (ITO) from a one-pot solution using a square-wave galvanostatic method. The morphology of the hybrid thin films could be easily manipulated to optimize their electrochromic properties by adjusting deposition conditions. In the hybrids, both components can be simultaneously switched to coloured or bleached states. The hybrid film obtained with very short deposition times of PEDOT:PSS and WO3 in each cycle exhibits significantly enhanced electrochromic properties. The optical contrast of the hybrid film is higher than that of PEDOT:PSS or WO3 films of the same thickness. Moreover, the stability of the hybrid film is also drastically enhanced. The enhancement may be attributed to the favourable interactions between the two components, i.e., PEDOT:PSS may enter the defect sites in electrodeposited WO3, preventing surface-defect-induced anodic dissolution during cycling, while the surface functional groups of WO3 may act as dopants to inhibit over-oxidation of PEDOT, as well as the large interfacial area created using this unique one-pot multilayer deposition method. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

Stretchable devices with good transparency offer exciting new applications over the existing technologies, but remarkable difficulties remain in the fabrication of transparent and stretchable devices. In this paper, we report an effective method to fabricate transparent elastic photodetectors which combines the merits of the transparent polydimethylsiloxane (PDMS) polymer with its stretchability and the Zn₂SnO₄ nanowire (NW) with its photodetection functionality. Zonyl fluorosurfactant is found to be critical which improves the bonding between the functional NWs and the PDMS matrix, thus enabling the high efficient transfer of NW structures into PDMS. Highly conductive and thin percolating AgNW films were successfully embedded into PDMS mixed with ∼11% Zonyl which are otherwise not achievable with pure PDMS. Transparent and stretchable photodetectors were fabricated with the developed method. The photocurrent was found to be reciprocal to the square of the channel length, Iph∼ 1/l(2). The chemically bonded sensing materials in the PDMS matrix allow more NW exposure to air. This lead to a fast switching operation of the photodetectors with a response time below 0.8 s and a reset time around 3 s, which is significantly improved compared to reported stretchable NW photodetectors fully embedded in the polymer matrix.

Electronics with multifunctionalities such as transparency, portability, and flexibility are anticipated for future circuitry development. Flexible memory is one of the indispensable elements in a hybrid electronic integrated circuit as the information storage device. Herein, we demonstrate a transparent, flexible, and transferable hexagonal boron nitride (hBN)-based resistive switching memory with indium tin oxide (ITO) and graphene electrodes on soft polydimethylsiloxane (PDMS) substrate. The ITO/hBN/graphene/PDMS memory device not only exhibits excellent performance in terms of optical transmittance (∼85% in the visible wavelength), ON/OFF ratio (∼480), retention time (∼5 × 104 s) but also shows robust flexibility under bending conditions and stable operation on arbitrary substrates. More importantly, direct observation of indium filaments in an ITO/hBN/graphene device is found via ex situ transmission electron microscopy, which provides critical insight on the complex resistive switching mechanisms.

Many organisms and animals have sensing abilities that are different from those of human beings; for example, snakes have strong smell-, vibration-, touch- and heat-sensing abilities. A nature-mimicking sensing platform capable of sensing multiple stimuli, such as strain, pressure, temperature and other uncorrelated conditions, is highly desirable to broaden the applications of sensors. Here, we construct a semitransparent intelligent skin-like sensing platform based on polyaniline (PANI) nanowire arrays that can act as a bionic component by simultaneously sensing tactile stimuli and detecting colorless, odorless gas. Our multifunctional bionic sensing strategy is remarkably adaptive for versatile applications. The strain-sensing performance is superior to that of most conducting polymer-based sensors reported so far and is comparable to or even better than traditional metal and carbon nanowire/nanotube-based strain sensors. The highest gauge factor demonstrated is 149, making our system a remarkable candidate for strain-sensing applications. The sensor can accurately detect a wide range of human motions. We also demonstrate the simultaneous controlled olfaction ability for the detection of methane with high sensitivity and a fast response time. These results enable the realization of multifunctional and uncorrelated sensing capabilities, which will afford a wide range of applications to augment robotics, treatment, simulated skin, health monitoring and bionic systems. A wearable sensor can track full-range human motion and sniff out toxic gases using polymer nanowires with features similar to snakeskin. The device, which was developed by Pooi See Lee and co-workers at Nanyang Technological University, is based on polyaniline, a conducting polymer with natural flexibility and chemical sensitivity. Polyaniline often becomes unworkably rigid when deposited as a thin film, but the Singapore-based team avoided this issue by growing a vertical forest of polymer nanowires on a thin silicone support. Scanning electron microscopy revealed that when stretched, the nanowires formed scale-like islands and cracks that alter the resistance of the thin film. The researchers demonstrated that these electrical changes were sensitive enough to use for forehead sensors of breathing and eye movement and as a ‘smelling skin’ for detecting methane–an odorless and explosive gas. A semitransparent intelligent skin-like sensor platform based on polyaniline nanowire arrays was constructed, which can act as bionic component by simultaneously sensing tactile stimuli and detecting colorless odorless gas. The highest gauge factor demonstrated is 149, making it a remarkable candidate in strain sensing applications. Simultaneously, we demonstrate the controlled olfaction ability of the sensor with the detection of methane with high sensitivity and fast response time. These results enable the realization of multifunctional and uncorrelated sensing capabilities that will have wide range applications to augment robotics, treatment, simulate skin, health and bionic system.

Reversible electrochemical mirror (REM) device can be electrochemically tuned to exhibit dual transmittance and reflectance modulations in a single device. Conventional REM devices reversibly switched between transparent and mirror states. However, it is of great challenge to maintain the mirror state of the REM devices due to the diffusion of anions into the metallic film at the open-circuit state. In this work, we report a Cu-based REM device which offers reversible switching between transparent, blue and mirror states with judicious selection of electrolyte and controllable electrodeposition. The blue state can be obtained through the formation of copper (I) chloride, CuCl, when copper (II) chloride CuCl2 undergoes electrochemical reduction. The polymer host, PVA (poly(vinyl alcohol)) plays an important role in reducing the surface roughness of the electrodeposited mirror film, improving film uniformity and sustaining the mirror state of the device during the voltage-off state. NRF (Natl Research Foundation, S’pore) Accepted version

Sodium ion battery (SIB) as a next‐generation battery has been drawing much attention due to the abundance and even distribution of sodium source. Metal sulfides with high theoretical capacity and good electrical conductivity are promising anode candidates for SIB, however, the structural collapse caused by severe volume change during the de/sodiation process typically results in a fast capacity decay, limited rate capability, and cycling stability. In this work, by careful composition and structure design, polydopamine coated Prussian blue analogs derived carbon coated bimetallic sulfide hollow nanocubes (PBCS) are prepared with distinguished morphology, higher surface area, smaller charge transfer resistance, and higher sodium diffusion coefficient than the uncoated bimetallic sulfides. An optimum carbon coated bimetallic sulfide hollow nanocube anode delivers a specific capacity of ≈500 mA h g−1 at 50 mA g−1 with ethylene carbonate/dimethyl carbonate (1:1, vol%) electrolyte in the presence of fluoroethylene carbonate additives. A capacity of 122.3 mA h g−1 can be realized at 5000 mA g−1, showing good rate performance. In addition the carbon coated bimetallic sulfide hollow nanocubes can maintain capacity of 87 mA h g−1 after being cycled at 500 mA g−1 for 150 times, indicating its good cycling stability. The structure integrity, high specific capacity, good rate performance, and cycling stability of PBCS render it a promising anode material for advanced SIB. NRF (Natl Research Foundation, S’pore) Accepted version

In this work, the coexistence of Write Once Read Many Memory (WORM) and memristor can be achieved in a single device of Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) and Polyvinyl Alcohol (PVA) blend organic memory system. In memristor mode, the bistable resistance states of the device can be cycled for more than 1000 times. Once a large negative bias of −8V was applied to the device, it was switched to permanent high resistance state that cannot be restored back to lower resistance states. The mechanism of the memristor effect can be attributed to the charge trapping behaviour in PVA while the WORM effect can be explained as the electrochemical characteristic of PEDOT: PSS which harnesses the percolative conduction pathways. The results may facilitate multipurpose memory device with active tunability. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

Chemiresistors of varying Copper Phthalocyanine sensing layer thickness, from 10 to 350 nm, have been fabricated and tested for sensing to sub-ppm levels of Nitrogen Dioxide. The results obtained were analyzed and the kinetics was shown to correlate well with first order kinetics, rather than with Elovich model. In explaining the sensitivity trend to thickness variation, gas diffusion into the layer was found to play a role and should be taken into consideration.

This work reports a versatile approach utilizing covalent assembly of functionalized gold nanoparticles for organic field-effect transistor (OFET) based memory devices. 11-Mercapto-1-undecanol functionalized gold nanoparticles (AuNPs) having size of 5 ± 0.5 nm were synthesized and immobilized onto SiO(2) substrate through covalent binding using a functionalized polymer as a surface modifier. The pentacene OFET-based memory devices utilizing such covalently bound gold nanoparticles with nanoparticle density of 5 × 10(11) cm(-2) exhibited a large memory window (7.7 V), high on/off ratio between memory states (10(5)), and long retention time (10,000 s). The present synthetic route for memory devices incorporating covalently immobilized gold nanoparticles has several advantages such as solution processable, enhanced device stability, low-cost, and low-temperature process and will be a step toward realization for low-cost, lightweight, flexible, logic display driver, and flash memory applications.

Indium tin oxide (ITO) nanowires array was used as current collector and building block for polyaniline based supercapacitor. Thin polyaniline coating was deposited on the nanowires and resulted in the formation of polyaniline ITO coaxial nanowires. This hybrid heterostructure design improved the specific capacitance, rate capability, and cycling stability of the supercapacitor electrode. Good conductivity harnessed by these directly grown ITO nanowires is useful to improve the charge transport during the charge discharge processes which were confirmed by the electrochemical impedance spectroscopy measurement. Electrochemical test in 1 M H2SO4 at 4 A g−1 delivered specific capacitance as high as 738 F g−1. In addition, sub-micron size of the intercoaxial nanowires spacing ensures the fast penetration of electrolyte ions which resulted in the superior rate capability (98% capacitance retention when applied current was varied from 4 to 25 A g−1). The capacitance retention is significantly higher as compared to other polyaniline composite electrodes and it is one of the best reported performances to date for polyaniline based supercapacitor electrodes. This work illustrates a promising platform that can be adopted for other redox nanocomposite materials while reaping the benefit as low cost and binder free electrode material for supercapacitor application.

Stretchable and self-healing (SH) energy storage devices are indispensable elements in energy-autonomous electronic skin. However, the current collectors are not self-healable nor intrinsically stretchable, they mostly rely on strain-accommodating structures that require complex processing, are often limited in stretchability, and suffer from low device packing density and fragility. Here, an SH conductor comprising nickel flakes, eutectic gallium indium particles (EGaInPs), and carboxylated polyurethane (CPU) is presented. An energy storage device is constructed by the two SH electrodes assembled with graphene nanoplatelets sandwiching an ionic-liquid electrolyte. An excellent electrochemical healability (94% capacity retention upon restretching at 100% after healing from bifurcation) is unveiled, stemming from the complexation modulated redox behavior of EGaIn in the presence of the ligand bis(trifluoromethanesulfonyl)imide, which enhances the reversible Faradaic reaction of Ga. Self-healing can be achieved where the damaged regions are electrically restored by the flow of liquid metal and mechanically healing activated by the interfacial hydrogen bonding of CPU with an efficiency of 97.5% can be achieved. The SH conductor has an initial conductivity of 2479 S cm-1 that attains a high stretchability with 700% strain, it restores 100% stretchability even after breaking/healing with the electrical healing efficiency of 75%. National Research Foundation (NRF) S.P. and G.T. contributed equally to this work. This research was financially supported by the Competitive Research Programme Award No. NRF-CRP-13-2014-02, NRF-Investigatorship Award No. NRF-NRFI2016-05, and the Campus for Research Excellence and Technological Enterprise (CREATE) programme, under the National Research Foundation, Prime Minister’s Office, Singapore.

Light-emitting electrochemical cell (LEEC) performance is drastically affected by the selection of suitable electrolyte. With the limited n-type doping in MEH-PPV near the cathodic interface, we hypothesized that anions in the electrolyte are critical to attain a higher conductivity p-doped area. Poly(ethylene oxide)-lithium salts electrolyte systems have been investigated in the LEEC devices to determine the influence of anions on device turn-on voltage and operation. The TFSI anions showed higher resonance states, low turn-on voltages near the optical bandgap of the emissive conjugated polymer, high ionic conductivity in solid state (1.05 × 10 S cm ), and larger electrochemical stability window compared to conventional CF SO anion. Device maximal brightness (∼100 cd/m ) can be achieved. Modulated differential scanning calorimetry (mDSC) studies of the polymer blend films correlate the thermal stability and doping effectiveness during operation and delineate the onset of degradation that entails burnout of the devices. National Research Foundation (NRF) K.J.C., V.K., C.V.N., and J.W. acknowledge the research scholarship provided by Nanyang Technological University in Singapore. This work is supported by the Institute for Sports Research and the NRF Investigatorship, Award No. NRFNRFI2016-05.

A novel multilayer system via layer-by-layer (LbL) self-assembly by alternatively packing polyethylene glycol (PEG)-α-cyclodextrin (αCD) complex and poly(acrylic acid) (PAA) via hydrogen-bonding is designed and investigated in this work. The PEG-αCD inclusion complex is obtained by supramolecular interaction. Multilayer films with different ratios of αCD are fabricated, and the growth behavior, morphology, thermal properties and electrical properties of the resultant LbL films are systematically characterized. The films with PEG-αCD complex and PAA as building blocks show high ionic conductivity reaching up to 2.5×10-5 S cm-1 under room temperature (52%RH), which is almost two orders magnitude higher than the PEG/PAA films under the same conditions. The PEG-αCD15/PAA films also possess high water retention due to the large amount of hydroxyl groups carried by αCD, which enables the films, after exposed to a high humidity environment, to maintain a high ionic conductivity under low humidity environment. This PEG-αCD/PAA LbL system provides an insight for designing polymer based solid state electrolyte and its application towards electrochemical devices. NRF (Natl Research Foundation, S’pore) Accepted version

In this work, a synaptic transistor based on the indium gallium zinc oxide (IGZO)–aluminum oxide (Al2O3) thin film structure, which uses ultraviolet (UV) light pulses as the pre-synaptic stimulus, has been demonstrated. The synaptic transistor exhibits the behavior of synaptic plasticity like the paired-pulse facilitation. In addition, it also shows the brain's memory behaviors including the transition from short-term memory to long-term memory and the Ebbinghaus forgetting curve. The synapse-like behavior and memory behaviors of the transistor are due to the trapping and detrapping processes of the holes, which are generated by the UV pulses, at the IGZO/Al2O3 interface and/or in the Al2O3 layer. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Published version

In this invited talk, we first review various methods for the formation of p+/n junctions of depth of less than 40nm using excimer pulsed laser annealing technique of 248nm wavelength. The characteristics of junctions formed using single and multiple-pulsed shallow melt and non-melt laser annealing on amorphous and single crystalline Si substrate would be compared. To overcome the defect-related enhanced diffusion during pulsed laser annealing, novel junction engineering methodology using implantation generated defects such vacancies is illustrated. Methods employing ultra-low energy implants with laser annealing for junctions less than 25 nm are proposed. In addition, we will also talk briefly about the potential application of the laser annealing to be used for an ultra-low thermal budget silicide formation.

The effects of thermal annealing on amorphous silicon deposited using low-pressure chemical vapour deposition (LPCVD) are presented in this paper. The amorphous silicon film is being subjected to different annealing conditions ranging from 600 to 900 °C for a varying period of 30 to 90 min holding time in nitrogen ambient. X-Ray diffraction (XRD) shows that crystallization of amorphous silicon to poly-silicon starts to occur after 30 min of thermal cycle at 600 °C. Atomic force microscope (AFM) has been used to study the surface roughness and grain size of the films after different annealing times and temperatures. The nanocrystalline grains result in photoluminescence behavior. Stress measurement, using curvature analysis, shows that the stress magnitude reduces with decreasing annealing temperature and time. This is likely due to stress relief during grain growth and crystallization at higher temperatures. The detailed study of the structural, morphology and property changes in amorphous silicon upon annealing will be presented.

The impact of etch-stop layers (ESLs) of borderless contact (BLC) on transistor characteristics, especially for NMOSFETs, was studied concerning on the ESL-induced mechanical stress. Two new ESL schemes using dual etch-stop layers: (scheme A) SiON (bottom)/SiN (top) and (scheme B) SiN (bottom)/SiON (top) were studied and implemented into device fabrication. The electrical performance of the N- and PMOSFETs was characterized. It has been found that by using scheme A, a 2.7% improvement of I on versus I off margin as compared with the single-layer process is achieved on NMOSFETs. The scheme A results in a loss of the PMOS margin by 1.4%, which is still within the specifications. However, scheme B, which uses a SiN as the bottom layer, presents a slightly less improvement of process margin (1.7%) on NMOSFETs with much larger loss of process margin (2.3%) on PMOSFETs. Our results suggest that optimization of ESL for borderless contact could play an important role in determining transistor performance for deep submicron CMOS.

A method for analyzing sub-micron devices by Rutherford backscattering spectrometry is presented. Using simplifying assumptions, we are able to simulate the backscattering spectrum of laterally non-uniform samples. The method has been verified with Ni/Pt laterally non-uniform layers on (1 0 0)Si substrate and has been applied to characterize the formation of Ni silicide in structures similar to metal oxide semiconductor (MOS) transistors. It is shown that the analysis of devices with a linewidth as low as 0.25 μm is possible using micro RBS and the method of simulation that we have developed.

Developing high energy density supercapacitors is of great importance to the transportation, consumer electronics, and micro-grid energy storage sectors. Recently, the development of high voltage organic electrolyte based supercapacitor devices has been gaining much attention. Among them, there is an on-going intense interest in investigating high capacity lithium ion storage anode materials in hybrid supercapacitors. However, developing high capacity cathode materials for high voltage organic electrolyte supercapacitor devices is rarely investigated. The low electrical double layer capacitances of carbon cathode electrodes, which are widely used in current supercapacitor devices, are often the limiting bottleneck. In this contribution, we investigated the electrochemical energy storage behavior of a polyaniline (PANI)-single wall carbon nanotube (SWCNT) composite material in an organic electrolyte as a supercapacitor cathode. The PANI-SWCNT composite exhibits a high specific capacitance of 503 F/g, of which 58.8% of the total capacitance is attributed to the pseudocapacitive and electrical double layer energy storage. The cycling stability of the PANI-SWCNT composite could be further improved by polydopamine (PDA) modification. The PDA with strong adhesion properties is able to prevent mechanical degradation. The PDA modified PANI-SWCNT shows excellent stability with only 5% degradation after 2000 cycles. NRF (Natl Research Foundation, S’pore) Published version

Two organic small molecule memory materials, TPA-2BIPs and TPA-3BIPs, containing triphenylamine (TPA) as a donor and 4,11-bis((triisopropylsilyl)ethynyl)-1 H-imidazo[4,5-b]phenazine (BIP) units as acceptors have been synthesized and characterized. Sandwich-structure memory devices based on these two molecules have been fabricated and the as-fabricated devices displayed similar switching behavior but different ON/OFF ratios. The analysis of AFM images indicates that increasing the numbers of acceptors changes the stacking of molecules in the solid state, which results in different morphology and microstructures in films. Although the switching behavior is not significantly different with increasing acceptor moieties, more acceptor groups do help to enhance the stacking of the molecules in the solid state to generate more consistent switching performance.

Few-layered phosphorene is exfoliated through a liquid phase exfoliation in ethanol, acting as an additive to mix with tempo-oxidized cellulose nanofibrils (CNF), forming a transparent, flexible nanogenerator paper. The gas barrier property of CNF protects phosphorene against oxidation in ambient condition. The phosphorene in the hybrid paper is stable over six months even with exposure to ambient condition (23 °C, 70% RH) in air. The hybrid paper is used as an active layer to construct a triboelectric energy nanogenerator (TENG). This hybrid paper shows an open-circuit voltage of 5.2 V with a current density of 1.8 µA cm−2, which is five and nine times higher than that of the pure CNF paper device, respectively. This work reveals the role of phosphorene in acting as a charge carrier in the hybrid paper and demonstrates a new way to attain stable functional phosphorene hybrids in ambient condition. The resultant phosphorene hybrid paper could be used as a building block for TENG with enhanced output performance.

This communication describes the co-assembly of polydopamine spheres, either bare or coated with Fe3O4 magnetic nanoparticles, with the short aromatic peptide diphenylalanine. The combination of polydopamine particles and diphenylalanine generated tubular structures decorated with adhesive spherical particles, while the co-assembly of the polydopamine spheres coated with magnetic Fe3O4 nanoparticles with diphenylalanine resulted in the formation of a magnetic hydrogel. These new architectures may be useful as new vehicles for several applications including tissue regeneration and drug delivery.