Woon Ming Lau

Synthesis of Ag?TiO2 composite nano thin film for antimicrobial application

TiO2 photocatalysts have been found to kill cancer cells, bacteria and viruses under mild UV illumination, which offers numerous potential applications. On the other hand, Ag has long been proved as a good antibacterial material as well. The advantage of Ag-TiO2 nanocomposite is to expand the nanomaterials antibacterial function to a broader range of working conditions. In this study neat TiO2 and Ag-TiO2 composite nanofilms were successfully prepared on silicon wafer via the sol-gel method by the spin-coating technique. The as-prepared composite Ag-TiO2 and TiO2 films with different silver content were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) to determine the topologies, microstructures and chemical compositions, respectively. It was found that the silver nanoparticles were uniformly distributed and strongly attached to the mesoporous TiO2 matrix. The morphology of the composite film could be controlled by simply tuning the molar ratio of the silver nitrate aqueous solution. XPS results confirmed that the Ag was in the Ag(0) state. The antimicrobial effect of the synthesized nanofilms was carried out against gram-negative bacteria (Escherichia coli ATCC 29425) by using an 8 W UV lamp with a constant relative intensity of 0.6 mW cm(-2) and in the dark respectively. The synthesized Ag-TiO2 thin films showed enhanced bactericidal activities compared to the neat TiO2 nanofilm both in the dark and under UV illumination.

Highly efficient fullerene/perovskite planar heterojunction solar cells via cathode modification with an amino-functionalized polymer interlayer

A new amino-functionalized polymer, PN4N, was developed and applied as an efficient interlayer to improve the cathode interface of fullerene/perovskite (CH3NH3PbIxCl3−x) planar heterojunction solar cells. The PN4N polymer is soluble in IPA and n-BuOH, which are orthogonal solvents to the metallohalide perovskite films, and therefore they can be spuncast on the heterojunction layer before the deposition of the metal cathode. This simple modification of the cathode interface showed a remarkable enhancement of power conversion efficiency (PCE) from 12.4% to 15.0% and also reduced the hysteresis of photocurrent. We also found that conventional water–methanol-soluble polymer interlayer, such as PFN, was incompatible with the perovskite films because of the small molecular size of aprotic solvent such as MeOH, which could decompose the perovskite films to PbI2, resulting in considerably lower solar cell performance. This study provides new design guidelines for efficient interfacial materials and also demonstrates that interface engineering could be a key strategy to improve perovskite solar cells.

Shewanella oneidensis MR-1 Bacterial Nanowires Exhibit p-Type, Tunable Electronic Behavior

The study of electrical transport in biomolecular materials is critical to our fundamental understanding of physiology and to the development of practical bioelectronics applications. In this study, we investigated the electronic transport characteristics of Shewanella oneidensis MR-1 nanowires by conducting-probe atomic force microscopy (CP-AFM) and by constructing field-effect transistors (FETs) based on individual S. oneidensis nanowires. Here we show that S. oneidensis nanowires exhibit p-type, tunable electronic behavior with a field-effect mobility on the order of 10(-1) cm(2)/(V s), comparable to devices based on synthetic organic semiconductors. This study opens up opportunities to use such bacterial nanowires as a new semiconducting biomaterial for making bioelectronics and to enhance the power output of microbial fuel cells through engineering the interfaces between metallic electrodes and bacterial nanowires.

In situ growth of epitaxial lead iodide films composed of hexagonal single crystals

Lead iodide (PbI2) films composed of single crystals with regular hexagonal microstructures have been in situ fabricated on lead foils through a one-step solution-phase chemical route under solvothermal conditions. X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM) were employed to characterize the resulting PbI2 crystals. The orientation of the hexagonal planes can be controlled via the adjustment of the concentration of iodine and the types of solvents. It is expected to be a simple way for in situ fabricating PbI2 crystals/films for future utilizing in radiation detection.

3D hierarchical porous SnO2 derived from self-assembled biological systems for superior gas sensing application,

Mother Nature has always taught us lots about the arcanum of Gods creation, which primarily ties to the wonderful and complex self-assembly of biomolecules even in a mild condition. In the present work, we put forward a bio-inspired strategy, that is, directly bring in biological systems capable of self-assembly to fabricate functionalized hierarchical structures for effective gas sensing. For advanced pollination, biomolecules in pollen coats could self assemble to form bio-structures with effective mass transportablity, and herein were used to guide the self assembly of SnO2-precusors, which finally transferred to SnO2 materials by calcination. Gaining the 3D hierarchical porous structrues formed in the self-assembly of biomolecules, the as-fabricated SnO2 has high connective porous networks from macro- to micro-, and even nanoscale. The specific structures could facilite target gases to quickly transport towards, and then fully react with, the SnO2 nanoparticles, and thus endow the SnO2 with excellent gas response to both reducing gases (C2H5OH and CH3CH2CH3) and oxidising gas (Cl2). This present strategy provides a novel and facile way towards the development of functionallized hierarchical structures by learning from natural self-assembled systems. The resultant hierarchical structures can be extended to other applications in filters, adsorbents, catalysis, thermal, acoustic and electrical insulators, and so on.

Design and growth of dendritic Cu2−xSe and bunchy CuSe hierarchical crystalline aggregations

Dendritic nanocrystals of copper selenide were fabricated in situ for the first time by using alcohol as the solvent. Cu2−xSe films composed of hierarchically ordered dendritic nanostructures were prepared on Cu substrates at a rather moderate temperature of 190–200 °C for just 1–3 h, while bunchy CuSe nanostructures could be further constructed above the Cu2−xSe dendrites by prolonging the reaction time of solvothermal growth with ethanol as the solvent. The resulting Cu2−xSe nanodendrites display highly symmetric corolitic morphology while the bunchy CuSe aggregations show particular nanostructures with a pronounced trunk and actinomorphic multi-branches. It is also found that the dendritic structures of crystalline Cu2−xSe could never be obtained when the reaction temperature is less than 190 °C, while the temperature needed is 160 °C for Ag2Se nanodendrites and higher than 220 °C for CdSe nanodendrites. These copper selenide nanostructures with hierarchically ordered 3-dimensional (3D) framework exhibited good absorbance and photoluminescence (PL) property and could bear potential applications in solar cell devices in the future.

Growth of highly oriented (110) γ-CuI film with sharp exciton band

The growth of highly oriented (110) γ-CuI films on copper substrates with the best photoluminescence properties among all known CuI films are demonstrated, in the context of improving the current techniques in the preparation of CuI films for electronic and optoelectronic applications. The comparison of the photoluminescence spectra of CuI films with different growth orientations shows that the highly oriented (110) films prepared are less defective and give only a sharp exciton band.

One-pot electrodeposition, characterization and photoactivity of stoichiometric copper indium gallium diselenide (CIGS) thin films for solar cells

Herein we report the one-pot electrodeposition of copper indium gallium diselenide, CuIn(1-x)Ga(x)Se(2) (CIGS), thin films as the p-type semiconductor in an ionic liquid medium consisting of choline chloride/urea eutectic mixture known as Reline. The thin films were characterized by scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman microspectroscopy, and UV-visible spectroscopy. Based on the results of the characterizations, the electrochemical bath recipe was optimized to obtain stoichiometric CIGS films with x between 0.2 and 0.4. The chemical activity and photoreactivity of the optimized CIGS films were found to be uniform using scanning electrochemical microscopy and scanning photoelectrochemical microscopy. Low-cost stoichiometric CIGS thin films in one-pot were successfully fabricated.

Construction and applications of a dual mass‐selected low‐energy ion beam system

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass‐resolved low‐energy ion beams which merge at the target with an incident energy range 50–25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100 μA/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3–0.5×2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1×10−7 Pa and a typical pressure of 5×10−6 Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the tar...

Preparation of antibacterial surfaces by hyperthermal hydrogen induced cross-linking of polymer thin films

The covalent immobilization of polymers on surfaces has the potential to impart new properties and functions to surfaces for a wide range of applications. However, most current methods for the production of these surfaces involve multiple chemical steps or do not impart a high degree of control over the chemical functionalities at the surface. Described here is the preparation of surfaces covalently functionalized with quaternized poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), a known antibacterial polymer. PDMAEMA was coated onto octadecyltrimethoxysilane modified silicon wafers and was then cross-linked by the selective cleavage of C–H bonds using a hyperthermal hydrogen treatment. The surfaces were then quaternized with ethyl bromide. At each step the surfaces were characterized extensively using techniques including atomic force microscopy, contact angle measurements and X-ray photoelectron spectroscopy. These results demonstrated a high degree of functional group retention throughout the process. The antibacterial properties of the surfaces against Gram-positive S. aureus and Gram-negative E. coli were investigated using a “drop test” assay. Furthermore, the process was successfully applied to produce antibacterial butyl rubber surfaces, demonstrating the versatility of the method for grafting onto unfunctionalized hydrocarbon surfaces.