Thermal decomposition is a promising route for the synthesis of magnetic nanoparticles. The simplicity of the synthesis method is counterbalanced by the complex chemistry of the system such as precursor decomposition and surfactant-reducing agent interactions. Control over nanoparticle size is achieved by adjusting the reaction parameters, namely, the precursor concentration. The results, however, are conflicting as both an increase and a decrease in nanoparticle size, as a function of increasing concentration, have been reported. Here, we address the issue of size-controlled synthesis via the precursor concentration. We synthesized iron oxide nanoparticles with sizes from 6 nm to 24 nm with narrow size distributions. We show that the size does not monotonically increase with increasing precursor concentration.After an initial increase, the size reaches a maximum and then shows a decrease with increasing precursor concentration. We argue that the observation of two different size regimes is closely related to the critical role of the amount of surfactant. We confirm the effect of surfactant amount on nucleation and growth and explain the observed trend. Furthermore, we show that the nanoparticles show size-dependent but superior superparamagnetic properties at room temperature.

A highly efficient VOC sensor based on N-doped graphene quantum dots (N-GQDs)/poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) was fabricated at room temperature.

We herein report an investigation of ultralarge graphene oxide (UL-GO) sheet/poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin composite layers fabricated by spin coating on an indium-tin-oxide (ITO) anode as hole transport layer (HTL) in polymer light-emitting diodes (PLEDs), as well as polymer solar cells (PSCs). Monolayer UL-GOs were first synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes which were then mixed into the PEDOT:PSS solution in various specific amounts. The PEDOT:PSS composite film mixed with 0.04 wt% UL-GO by weight exhibits a conductivity of 749.4 S cm À1 and a transmittance of 88.6% at 550 nm.The PEDOT:PSS/GO HTL shows enhanced charge carrier transport because of improved conductivity by the weakening of the coulombic attraction between PEDOT and PSS by the functional groups on GO nanosheets, and the formation of an extended conductive network. Moreover, it can effectively block electrons and reduce resistance in the HTL, leading to better injection and transport of holes and lower turn-on voltage and resulting in a higher overall efficiency in PLEDs. Similarly, it remarkably increases the short circuit current (J sc ), and PSC efficiency because of a remarkable reduction of exciton quenching that results in higher charge extraction in PSCs. The optimized PLEDs and PSCs with a PEDOT:PSS/GO composite HTL layer show a maximum luminosity of 725.6 cd m À2 (at 10.6 V) for PLEDs, as well as a power conversion efficiency of 3.388% for PSCs, which were improved by $11% and 12%, respectively, compared to reference PLEDs and PSCs with a PEDOT:PSS layer.

Iron oxide magnetic nanoparticles produced by chemical synthesis are usually composed of both magnetite and maghemite phases. Information about the phase composition is typically obtained using Mössbauer spectroscopy. A method that can provide information about the magnetite versus maghemite phase composition of the nanoparticles and the organization of the phases simply from magnetization curve is still missing. Here we present a simple and elegant method that for nanoparticles with a known size distribution can give information about the magnetite and maghemite phase composition and suggests a magnetite core and a maghemite shell structure for all the nanoparticles sizes. The method is based on fitting of the room-temperature magnetization curve using a Brillouin function, while considering dipolar interactions. The model predicts that the nanoparticles are composed of a single magnetic domain for sizes below 14 nm. The model is validated by Mössbauer spectroscopy.

Ferroelectricity, a bistable ordering of electrical dipoles in a material, is widely used in sensors, actuators, nonlinear optics, and data storage. Traditional ferroelectrics are ceramic based. Ferroelectric polymers are inexpensive lead-free materials that offer unique features such as the freedom of design enabled by chemistry, the facile solution-based low-temperature processing, and mechanical flexibility. Among engineering polymers, odd nylons are ferroelectric. Since the discovery of ferroelectricity in polymers, nearly half a century ago, a solution-processed ferroelectric nylon thin film has not been demonstrated because of the strong tendency of nylon chains to form hydrogen bonds. We show the solution processing of transparent ferroelectric thin film capacitors of odd nylons. The demonstration of ferroelectricity, as well as the way to obtain thin films, makes odd nylons attractive for applications in flexible devices, soft robotics, biomedical devices, and electronic textiles.

Thermal decomposition is a promising route for the synthesis of highly monodisperse magnetite nanoparticles. However, the apparent simplicity of the synthesis is counterbalanced by the complex interplay of the reagents with the reaction variables that determine the final particle size and dispersity. Here, we present a combined experimental and theoretical study on the influence of the heating rate on crystal growth, size, and monodispersity of iron oxide nanoparticles. We synthesized monodisperse nanoparticles with sizes varying from 6.3 to 27 nm simply by controlling the heating rate of the reaction. The nanoparticles show sizedependent superparamagnetic behavior. Using numerical calculations based on the classical nucleation theory and growth model, we identified the relative time scales associated with the heating rate and precursor-to-monomer (growth species) conversion rate as a decisive factor influencing the final size and dispersity of the nanoparticles.

Non-volatile memories—providing the information storage functionality—are crucial circuit components. Solution-processed organic ferroelectric memory diodes are the non-volatile memory candidate for flexible electronics, as witnessed by the industrial demonstration of a 1 kbit reconfigurable memory fabricated on a plastic foil. Further progress, however, is limited owing to the lack of understanding of the device physics, which is required for the technological implementation of high-density arrays. Here we show that ferroelectric diodes operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge accumulation are the fundamental mechanisms governing the device operation. Surprisingly, thermionic emission can be disregarded and the on-state current is not space charge limited. The proposed model explains and unifies a wide range of experiments, provides important design rules for the implementation of organic ferroelectric memory diodes and predicts an ultimate theoretical array density of up to 1012 bit cm−2.

A highly efficient gas sensor is described based on the use of a nanocomposite fabricated from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) and ultra-large graphene oxide (UL-GO). The nanocomposite was placed by drop casting in high uniformity on interdigitated gold electrodes over a large area of silicon substrate and investigated for its response to volatile organic compounds (VOCs) at room temperature. Monolayers of ULGOs were synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes. The nanocomposite was optimized in terms of composition, and the resulting vapor sensor (containing 0.04 wt% of UL-GO) exhibits strong response to various VOC vapors. The improved gas-sensing performance is attributed to several effects, viz. (a) an enhanced transport of charge carriers, probably a result of the weakening of columbic attraction between PEDOT and PSS by the functional groups on the UL-GO sheets; (b) the increase in the specific surface area on adding UL-GO sheets; and (c) enhanced interactions between the sensing film and VOC molecules via the network of π-electrons. The sensitivity, response and recovery times of the PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% of UL-GO are 11.3 %, 3.2 s, and 16 s, respectively. At a methanol vapor concentration as low as 35 ppm, this is an improvement by factors of 110, 10, and 6 respectively, compared to a PEDOT-PSS reference gas sensor without UL-GO.