Functional Materials Letters

One-dimensional (1D) nanostructures are of great interest due to the promise of enhanced properties and improved device performance such as increased efficiency in solar cells by improved charge separation. There are many means of producing 1D nanostructures including chemical synthesis, lithography, template assisted growth and gas phase reaction. While all of these have their advantages and disadvantages, growth by gas phase reaction has the benefit of low cost and scalability to be used in mass production. This work outlines several of the more common growth mechanisms which utilize gas phase reactions to produce 1D nanostructures. The similarities and differences between the different mechanisms are discussed with an emphasis on the confinement of growth to 1D.

The Sn₂P₂S₆ compound is a member of a large isomorphous ferroelectric family. This compound exhibits a strong piezoelectric effect, combining large photorefractive coefficients with a fast holographic response, a high pyroelectric coefficient and a bulk piezoelectric modulus, which make them promising materials in a wide temperature and pressure range for optical and acoustical applications and also interesting materials for sensor applications in modern electronics.

The volume expansion of palladium by electrochemical hydrogen absorption and desorption is used as an actuating mechanism. Palladium films are obtained by electrodeposition from aqueous solution. Actuation based on potentiostatic and galvanostatic signals is investigated in acid and alkaline solutions. Performance characteristics of the actuator are determined. The reversibility of the actuator is hindered by the embrittlement of the Pd layer. The response time strongly depends on the layer thickness (increases for thicker films) and potential (decrease for more cathodic values). The maximum theoretical energy density of the Pd–H actuator is about 5000 kJ/m³. In this work, it is experimentally determined to be around 100–200 kJ/m³.

In this study, polyvinylidene fluoride (PVDF) membranes with various structures ranging from dense to highly asymmetric morphologies were obtained by changing the effective parameters in the phase inversion process. The effect of some important processing parameters such as solution concentration, harshness of the precipitation bath, exposure time before immersion in coagulation bath and bath temperature was studied and the mentioned parameters were optimized. The membranes were then modified with nano-sized alumina powder in order to improve the hydrophilicity of the PVDF membranes. The surface morphology, surface and cross-sectional structures of the membranes were examined by scanning electron microscope (SEM) and atomic force microscope (AFM). The specific surface area of the membranes was determined using the Brunauer–Emmett–Teller (BET) method. The contact angles between water and the membranes' surfaces were measured in order to study the hydrophilicity changes of the membrane surface. The results indicated that the addition of nano-sized alumina to the casting dope increased the hydrophilicity of the PVDF membrane surface.

Solid polymer electrolytes comprising a blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) with different concentration of potassium hydroxide (KOH) as ionic dopant were prepared using a solution–casting technique. The conductivity was enhanced to (1.5 ± 1.1) × 10^-4S cm^-1 when 40 wt.% KOH was added. The highest conductivity exhibited when 20 wt.% ethylene carbonate (EC) and 30 wt.% propylene carbonate (PC) was added into the PVA/PVP–KOH sample electrolytes. Conductivity–temperature dependence of the plasticized samples was established to obey an Arrhenian relationship with the activation energy of the order of 0.08–0.4 eV, depending on the plasticizer concentration. Electrochemical cells of Zn|PVA/PVP–KOH + EC|MnO₂ and Zn|PVA/PVP–KOH + PC|MnO₂ have been fabricated. The discharge characteristics of the cells are considered under a constant current of 1 mA. The open circuit voltage (OCV) and discharge capacity of the cells are measured.

With in glass forming region of Li₂O–WO₃–B₂O₃ glass system, a particular composition 40Li₂O–5WO₃–(55–x) B₂O₃: xV₂O₅ (with x ranging from 0.2 to 0.8, all are in mol.%) is chosen. The DSC traces are obtained to identify the glass transition temperature (T_g) and the glass forming ability of all the glass samples. The ESR and IR spectra portray the local structure of the glass system and valance states of the vanadium ions in the glass matrix. As the content of V₂O₅ increases up to 0.6 mol.% in the glass system, a gradual conversion of vanadium ions from V⁵⁺ state to V⁴⁺ state is observed, causing the depolymerization in the glass matrix by the transformation of several glass forming units BO₄ → BO₃ and WO₄ → WO₆.

Yttria nanoparticles are synthesized by co-precipitation method and as-prepared nanoparticles are annealed at various temperatures. The as-prepared and annealed particles are characterized by X-ray diffraction and transmission electron microscope (TEM). Here we estimated the lattice strain, crystallite size, deformation stress, and deformation energy density for annealed (800°C) yttrium oxide nanoparticles by Williamson-Hall-Isotropic Strain Model (W-H-ISM), W-H-Anisotropic Strain Model (W-H-ASM) and W-H-Energy Density Model (W-H-EDM) based on W-H plot from powder X-ray diffraction data. The shape and size of the nanoparticles are determined using TEM. The results of the estimated crystallite size of yttria nanoparticles by various methods agreed with the TEM results.

A hierarchical carbon material containing nanopores (micropores and mesopores) and micrometric sized capillaries (macropores) is produced using a combination of hard and soft templates. The hard template is a polypropylene (PP) cloth which decomposes during pyrolysis leaving a macroporous structure. The soft template is a cationic polyelectrolyte which stabilizes the resorcinol/formaldehyde (RF) resin porous structure during drying to give a nanoporous RF resin. The method produces a nanocomposite of the porous RF resin with an imbibed PP cloth. The composite is then pyrolyzed in a inert gas atmosphere to render a carbon material having macropores as well as micro/mesopores. The material exhibits both a large surface area (S_BET = 742 ± 2 m²/g) due to nanopores and goof fluid permeability due to micrometric sized pores. The macropores can be oriented during fabrication. The nanoporous surface can be used to support metal nanoparticles for fuel cell while the macropores allow easy flux of gas and liquids through the monolithic material.

A new way to open the temperature window for the growth of SWCNTs is reported. With little water induced, high quality SWCNTs without amorphous carbons have been produced at 1000°C in Ar. The water opens the temperature window for the growth of SWCNTs to the high temperature side. The high growth temperature improves the crystallinity of SWCNTs. The water impedes the progress of the self-decomposition of CH₄. The results have been studied by transmission electron microscopy (TEM) and Raman spectroscopy.

Nickel oxide films were coated onto FTO substrate at optimum conditions. The coated NiO films exhibited nanopore structure. The cyclic stability of the NiO films was studied using cyclic voltammetry. An electrochromic device has been built with the structure G/FTO/NiO/PMMA–PC–H⁺/WO₃/FTO/G. The device exhibits a change in optical transmission of 47.7% (colored 19.7% and bleached 67.4%) and optical density of 0.54 at 550 nm. The response time for coloration/bleaching of the device is 22.8 s/11.4 s. The device goes from transparent orange in the bleached state to gray color in the colored state.