Nuruzzaman Noor

Enhanced transparent-conducting fluorine-doped tin oxide films formed by Aerosol-Assisted Chemical Vapour Deposition

We report a systematic study into the importance of carrier solvent on the Aerosol-Assisted Chemical Vapour Deposition (AACVD) of fluorine-doped tin oxide (FTO) films. In particular, the resultant effects on both the optical transparency and electrical conductivity properties are reported with optimised films showing figures-of merit significantly beyond commercial products. Depositions were carried out at substrate temperatures of 500, 550 and 600 °C using either N2 or air as the carrier gas. The carrier solvent was found to have a marked effect on film quality and performance characteristics. Hall Effect results indicate that use of propan-2-ol as carrier solvent and air as carrier gas gave the best performing n-type FTO thin films overall that exhibited high optical transparency (>80% at 550 nm) and resistivity values of 4 × 10−4 Ω cm, with charge carrier density and carrier mobility values of 4 × 1020 cm−3 and 39 cm2 V−1 s−1 respectively, in addition to haze values of 10–15%. Such parameters are ideal for thin film solar cell applications and have significantly higher figures of merit compared to current commercial materials. Success of this method of deposition is attributed, in part, to a halide transfer reaction in which part fluorine substitution of the tin precursor occurs in the solvent resulting in a direct tin–fluorine bond. The work shows the key role carrier solvents play in AACVD in directing the system chemistry.

One pot synthesis of nickel foam supported self-assembly of NiWO4 and CoWO4 nanostructures that act as high performance electrochemical capacitor electrodes

In this work, we report a facile one-step hydrothermal approach to synthesize NiWO4 and CoWO4 nanostructures on nickel foam as binder-free electrodes for use as supercapacitors. The as-synthesized materials showed excellent electrochemical performance, with a high specific capacitance of 797.8 F g−1 and 764.4 F g−1 at a current density of 1 A g−1 after 3000 cycles. On increasing the current density by 20 times, the rate capabilities still maintained 55.6% and 50.6% of the original value for NiWO4/Ni foam and CoWO4/Ni foam, respectively. Moreover, both of these materials exhibited outstanding cycling stability, the 6000th cycle at 50 mV s−1 demonstrated 2.06 and 2.81 times better capacitance than the initial cycles for NiWO4/Ni foam and CoWO4/Ni foam, respectively. To our knowledge, this capacitance performance is better than any previously reported value for these materials and is a consequence of the highly evolved surface area/microstructure of the materials formed by this technique.

A bioinspired solution for spectrally selective thermochromic VO 2 coated intelligent glazing

We present a novel approach towards achieving high visible transmittance for vanadium dioxide (VO(2)) coated surfaces whilst maintaining the solar energy transmittance modulation required for smart-window applications. Our method deviates from conventional approaches and utilizes subwavelength surface structures, based upon those present on the eyeballs of moths, that are engineered to exhibit broadband, polarization insensitive and wide-angle antireflection properties. The moth-eye functionalised surface is expected to benefit from simultaneous super-hydrophobic properties that enable the window to self-clean. We develop a set of design rules for the moth-eye surface nanostructures and, following this, numerically optimize their dimensions using parameter search algorithms implemented through a series of Finite Difference Time Domain (FDTD) simulations. We select six high-performing cases for presentation, all of which have a periodicity of 130 nm and aspect ratios between 1.9 and 8.8. Based upon our calculations the selected cases modulate the solar energy transmittance by as much as 23.1% whilst maintaining high visible transmittance of up to 70.3%. The performance metrics of the windows presented in this paper are the highest calculated for VO(2) based smart-windows.

TiO2-based transparent conducting oxides; the search for optimum electrical conductivity using a combinatorial approach

A series of Nb, W, N and F:TiO2 thin-film systems were grown by a combinatorial atmospheric pressure chemical vapour deposition (APCVD) process. Conditions were varied in each experiment to produce a series of films with compositional gradient. For each system, the electrical resistivity at a number of positions (up to 200 on each film) was screened using a high-throughput tool. This allowed easy identification of the material with the lowest electrical resistivity across a reservoir of combinatorially produced samples. The most conductive material within each system was analysed in depth by X-ray photoelectron spectroscopy, wavelength dispersive X-ray analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-visible-NIR spectroscopy and Hall effect measurements. The most electrically conductive materials are found in the F:TiO2 [Fs ≈ 4–5%, ρ = 0.21 Ω cm, μ = 3.6 cm2 V−1 s−1, n = 8.1 × 1018 cm−3] and Nb:TiO2 [Nb = 0.07 ± 0.03%, ρ = 0.22 Ω cm, μ = 3.4 cm2 V−1 s−1, n = 8.3 × 1018 cm−3] systems. The electrical resistivities reported for Nb:TiO2 and W:TiO2 are the best to date for materials grown by APCVD. Extensive comparisons with the literature are made and summarised in this report.

Temperature and thickness-dependent growth behaviour and opto-electronic properties of Ga- doped ZnO films prepared by aerosol-assisted chemical vapour deposition

Ga-doped ZnO thin films were deposited onto glass substrates by aerosol-assisted chemical vapour deposition of zinc and gallium acetylacetonates in methanol. The effect of deposition temperature and thickness on the film growth behaviour and functional properties was investigated. It is found that the films preferred deposition and growth sites on the glass surface change with the substrate temperature. The resulting ZnO:Ga coatings are mainly composed of c-axis oriented crystallites and this (002) texture tends to be weakened by increasing thickness, although their crystallinity exhibits a continuous improvement associated with the emergence of columnar grain structures. The increase of deposition temperature transforms the wedge-shaped film morphology into round-shaped particles and enhances the specimen charge carrier density from 1.263–2.790 × 1020 cm−3 to 4.095–5.282 × 1020 cm−3. Due to the improved carrier mobility with system crystallinity, the film resistivity reduces with thickness and the minimum value obtained is 6.51 × 10−3 Ω cm. High visible transmittance (≈70–90% at 550 nm) and favourable infrared reflection (up to 45.5% at 2500 nm) are also observed in these ZnO:Ga coatings, arising from their wide band gaps and high carrier densities, as well as carrier numbers.

Influencing FTO thin film growth with thin seeding layers: a route to microstructural modification

We report on the seeded growth of fluorine doped tin oxide (FTO) polycrystalline transparent conducting oxide (TCO) thin films on float glass using a novel two-step chemical vapour deposition (CVD) method. Aerosol-assisted CVD (AACVD) was used to grow a seed layer to direct and promote full film growth via an atmospheric pressure CVD (APCVD) overlay. The method allowed for reproducible control over morphology and denser, rougher, higher-performing TCO at a relatively low growth temperature (500 °C). Growth promotion depended on seeding time with an optimal seeding time being present, below which morphology control and conformal coverage was unavailable. The film properties and functional characteristics were characterised by SEM, AFM, XRD, XPS, UV-Vis-Near IR transmittance-reflectance and Hall Effect probe measurements. Highly transparent and electrically conductive films, comparable to commercial materials and with high roughness and low transmission haze values indicate the process yields high quality films with a controllable morphology that can be tuned to desired application. The versatile method provides a route towards the morphological control of high-quality FTO thin films with high optical clarity and low-emissivity properties and can be readily extended to a variety of different substrates and metal oxide materials.

Incorporation of crystal violet, methylene blue and safranin O into a copolymer emulsion; the development of a novel antimicrobial paint

Crystal violet, methylene blue, safranin O and 2 nm gold nanoparticles were incorporated into a copolymer emulsion paint and three separate paint systems were prepared; a three-dye system (crystal violet, methylene blue, safranin O and 2 nm gold nanoparticles), a two-dye system (crystal violet, methylene blue and 2 nm gold nanoparticles) and a one dye system (safranin O and 2 nm gold nanoparticles). The modified polymers were characterised by UV-Vis absorbance spectroscopy, IR spectroscopy and X-ray photoelectron spectroscopy. The three paint systems were moderately stable under aqueous conditions, with a limited amount of leaching of the dyes from the paint polymer into the surrounding aqueous solution. Exposure of the three paint systems to a 28 W white light source induced the lethal photosensitisation of both Staphylococcus aureus and Escherichia coli. Moreover, both the three-dye and two-dye systems resulted in a 4 log kill against S. aureus under dark conditions, and a 1.5 log dark kill was obtained by the safranin O and 2 nm gold nanoparticle system.

Superhydrophobic Au/polymer nanocomposite films via AACVD/swell encapsulation tandem synthesis procedure

A synthetic route is presented for creating well-attached Au/polymer nanocomposite thin films on glass which exhibit superhydrophobicity. Such films have been demonstrably difficult to synthesise by established means. The synthetic route devised here affords great control over the functional, physical and chemical properties of the end product. A superhydrophobic PDMS thin film is deposited on a glass substrate by aerosol-assisted chemical vapour deposition (AACVD), then gold nanoparticles are incorporated by swelling the polymer film in a dispersion of the nanoparticles in toluene, which diffuse into the polymer and become embedded upon drying. Characterisation of the nanoparticles and resultant composite films are carried out using electron microscopy (SEM and TEM), UV-visible spectroscopy, X-ray photoelectron spectroscopy (XPS) and water droplet contact angle measurements.

Graphene-based two-dimensional Janus materials

Two-dimensional (2D) Janus materials with opposing components and properties on two sides have recently attracted fevered attention from various research fields for use as, for example, oil/water separating membranes, interfacial layers for mass transfer, 2D sensors and actuators. The Janus structure allows for a unidirectional transportation system and programmed response to certain stimuli to be achieved. Graphene, the 2D honeycomb network formed from one atomic layer of carbon atoms, has also received substantial research interest because of its intriguing structure and fascinating properties. The high mechanical strength, flexibility and optical transparency make graphene a unique candidate as a building block of 2D Janus materials through asymmetric modification with different functional groups on the graphene surfaces. This article reviews graphene-based 2D Janus materials, starting with a theoretical understanding of the behavior of Janus graphene. Then, different strategies for fabricating Janus graphene and its derivatives are reviewed in detail according to the chemical strategies of the modification methods. The applications of graphene-based Janus materials are discussed with a specific focus on the Janus structures that lead to bandgap engineering, as well as the construction of a responsive system on graphene.Two-dimensional materials: two-faced materials head in the right directionThe two-dimensional material graphene could find use as a one-way permeable membrane that improves the performance of batteries. Asymmetry has practical advantages in that it supports an action or motion in one direction while suppressing it in the other. Zijian Zheng and co-workers from The Hong Kong Polytechnic University review the different techniques developed to produce such asymmetric materials using graphene. These so-called Janus materials, named after the two-faced Roman god, can be fabricated by adding another substance to one side of the graphene. The authors summarize techniques for adding hydrogen or halogen atoms, small molecules, metal nanoparticles, or layers of a metal or polymer. These Janus materials could improve the efficiency of batteries, transistors and solar cells.Graphene has received enormous research interest in recent years owing to its intriguing structure and fascinating properties. Its high mechanical strength, flexibility and optical transparency make it a desire building block of 2D Janus materials. Through asymmetric surface modifications on target graphene derivatives, including hydrogenation and halogenation, grafting of organic molecules and polymers, and deposition of metal/metal oxides, different graphene-based Janus materials have been achieved with various shapes, sizes, and compositions. This review presents and discusses the development, fabricating strategies and applications of these 2D Janus materials, starting with the theoretical understanding of the behavior of Janus graphene.

Layer-by-Layer Assembly of Polyelectrolyte Multilayer onto PET Fabric for Highly Tunable Dyeing with Water Soluble Dyestuffs

Poly(ethyleneterephthalate) (PET) is a multi-purpose and widely used synthetic polymer in many industrial fields because of its remarkable advantages such as low cost, light weight, high toughness and resistance to chemicals, and high abrasion resistance. However, PET suffers from poor dyeability due to its non-polar nature, benzene ring structure as well as high crystallinity. In this study, PET fabrics were firstly treated with an alkaline solution to produce carboxylic acid functional groups on the surface of the PET fabric, and then was modified by polyelectrolyte polymer through the electrostatic layer-by-layer self-assembly technology. The polyelectrolyte multilayer-deposited PET fabric was characterized using scanning electron microscopy SEM, contact angle, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The dyeability of PET fabrics before and after surface modification was systematically investigated. It showed that the dye-uptake of the polyelectrolyte multilayer-deposited PET fabric has been enhanced compared to that of the pristine PET fabric. In addition, its dyeability is strongly dependent on the surface property of the polyelectrolyte multilayer-deposited PET fabric and the properties of dyestuffs.