Inside Front Cover: Preparation of Porous Poly(dimethylsiloxane)‐Based Honeycomb Materials with Hierarchal Surface Features and Their Use as Soft‐Lithography Templates (Adv. Mater. 22/2006)

The inside cover shows a library of hierarchically patterned poly(dimethylsiloxane) surfaces, with a schematic view in the background. These materials are prepared by the ‘breath figure' technique, in work reported by Qiao and Connal on p. 3024, that utilizes a low glass transition temperature star polymer that can form ordered honeycomb materials and contour to nonflat TEM grids. These surfaces are also used as soft lithography masters to create the inverse pattern.     

A novel patterning technique using super-hydrophobic PTFE thin films by Cat-CVD method

Super-hydrophobic poly-tetrafluoroethylene (PTFE) films, with a water contact angle of over 160°, are formed by catalytic chemical vapor deposition (Cat-CVD) under high catalyzer temperature or pressure. Hydrophobicity of the PTFE films is maintained even after annealing up to 300 °C. We demonstrate a novel method for forming metal lines using super-hydrophobic PTFE films. Water-based functional liquid containing silver nanoparticles dropped on the patterned PTFE film localizes only on hydrophilic regions, resulting in formation of metal lines after annealing up to 150 °C.     

Synthesis of anisotropic gold nanoparticles in a water-soluble polymer

Anisotropic gold nanoparticles have been synthesized by a UV irradiation technique through the interaction of HAuCl₄ and a stabilizing agent, poly (vinyl pyrrolidone) (PVP). The effect of irradiation time on the size and shape of gold nanoparticles was investigated by UV-visible spectroscopy and Transmission Electron Microscopy (TEM). The absorption spectra of all samples show a broad band with the characteristic surface plasmon resonance (SPR) peak visible at around 530 nm. The presence of an additional low intensity absorption peak at a longer wavelength suggests the presence of non-spherical nanoparticles. The TEM measurements show evidence of particle shapes such as spheres, hexagons, decahedrons and truncated triangles as the reaction proceeded from 5 min to 24 h. The variation in particle shape is probably due to the effect of the reduced gold to PVP ratio as the reaction proceeds.     

Development and characterization of fluorine tin oxide electrodes modified with high area porous thin films containing gold nanoparticles

Different electrode materials are prepared using fluoride doped tin oxide (FTO) electrodes modified with high area porous thin films of metal oxides containing gold nanoparticles. Three different metal oxides (TiO₂, MgO and SnO₂) have been assayed to this end. The effect of the metal oxide nature and gold loading on the structure and performance of the modified electrodes was examined by Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy and electrochemical techniques. XRD measurements reveal that MgO electrodes present the smallest gold nanoparticles after the sintering step however, the electrochemical response of these electrodes shows important problems of mass transport derived from the high porosity of these materials (Brunauer Emmett Teller area of 125 m²/g). The excellent sintering properties of titania nanoparticles result in robust films attached to the FTO electrodes which allow more reliable and reproducible results from an electroanalytical point of view.     

X-ray image resolution of carbon nanotube emitters grown with resist-assisted patterning process

We obtained X-ray images using carbon nanotube arrays. The electron emitter was fabricated using the resist-assisted patterning (RAP) process. The X-ray image was obtained with a current of 300 μA at an anode bias of 30 kVp. The emitter had a pattern width of 5 μm and a pitch of 40 μm producing a turn-on field of 1.5 V/μm with a field emission current of 10 μA/cm². The resulting X-ray image clearly shows micrometer scale lines on an integrated circuit chip bonded in a printed circuit board.     

Formation of gold nanoparticles in silicon suboxide films prepared by plasma enhanced chemical vapour deposition

Nanostructured materials fabricated by dispersing metal particles on the dielectric surface have potential application in the field of nanotechnology. Interfacial metal particles/dielectric matrix interaction is important in manipulating the structural and optical properties of metal/dielectric films. In this work, a thin layer of gold (Au) was sputtered onto the surface of silicon oxide, SiO_x (0.38 < x < 0.68) films which was deposited at different N₂O/SiH₄ flow rate ratios of 5 to 40 using plasma enhanced chemical vapor deposition (PECVD) technique prior to the annealing process at 800 °C. FTIR spectra demonstrate the intensity and full-width at half-maximum (FWHM) of Si-O-Si stretching peaks are significantly dependent on the N₂O/SiH₄ flow-rate ratio, η. The films deposited at low and high N₂O/SiH₄ flow rate ratios are dominated by the oxygen and silicon contents respectively. The size and concentration of Au particles distributed on the surface of SiO_x films are dependent on the N₂O/SiH₄ flow-rate ratio. High concentrations of Au nanoparticles are distributed evenly on the surface of the film deposited at N₂O/SiH₄ flow-rate ratio of 30. Crystallinity and crystallite sizes of Au are enhanced after the thermal annealing process. Appearance of surface plasma resonance (SPR) absorption peaks at 524 nm for all samples are observed as a result of the formation of Au particles. The annealing process has improved SPR peaks for all the as-deposited films. The energy gap of the as-deposited Au/SiO_x films are in the range of 3.58 to 4.38 eV. This energy gap increases after the thermal annealing process except for the film deposited at η = 5.     

Laser patterning with beam shaping on indium tin oxide thin films of glass/plastic substrate

In this research the laser beam shaper component has been used to obtain top-hat intensity distribution laser beam to perform line scribing and to perform electrode patterning on Indium thin oxide (ITO) thin films deposited on glass and plastic substrate. ITO films were removed with third harmonic Nd:YAG laser processing system. The pulse duration, laser output power, pulse repetition rate and scanning speed parameters of straight line patterning and electrode patterning on different types of substrates were discussed, respectively. The experimental results are measured by optical microscope and scanning electron microscope to evaluate the processing parameters and surface properties of ITO thin films.     

Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

Characterization of 6PV phenylene vinylene oligomer thin films

Investigations of phenylene vinylene oligomer thin films with 7 phenyl, 6 vinyl units (6PV) have been performed by optical and electrical measurements. The optical characterizations including infrared, Raman and UV-VIS spectroscopies were discussed by comparing the results with those obtained in poly(p-phenylene vinylene) (PPV). The electrical properties of oligomer based diodes were studied by measuring the current-voltage-temperature characteristics and the thermally stimulated currents (TSC). At high fields, tunneling of carriers through the interfacial barrier would occur while at lower fields, two distinct temperature ranges were observed. In the high temperature range (> 250 K), a field assisted mechanism occurs involving localized states in the oligomer bulk whereas in the low temperature range, hopping conduction is probable. The TSC spectrum shows two relaxation peaks at 219 and 261 K which correspond to trap depths of 0.4 and 0.55 eV. The deep traps appeared as a characteristic of phenylenevinylene oligomers.     

Fabrication of self-assembled polyaniline films by doping-induced deposition

The ultrathin films of polyaniline (PAni)/poly (styrenesulfonic acid)(PSSA) were fabricated via a novel self-assembling process by alternately immersing the substrates into dilute PAni solution in N-methylpyrrolidinone (NMP) and the aqueous solution of PSSA. The process was characterized by UV–Vis absorption spectroscopy. It was found that the oxidation state of polyaniline in single monolayers was dependent on the thickness of the film. The self-assembling mechanism was based on the acid-base reaction between PAni and PSSA. The thickness of the films can be easily manipulated at nanometer scale by controlling the solution chemistry and recycling times. The resulting films are uniform and adhere strongly to the substrates.     

Microdisk laser emission and electrical properties of composite films based on poly(3-hexylthiophene)s with different stereoregularity

The optical and electrical properties of composite thin films of poly(3-hexylthiophene)s (PAT6s), processing different stereo-regularity originating from side-chain regio orders have been studied. The laser emission properties of PAT6 composite thin films in microdisk structure have been observed by pulsed photopumping. From the electrical and optical measurements, the electrical conductivity and the quantum efficiency of the PAT6 composite films were estimated. The emission and conductivity depending on the mixture ratios were discussed by taking the stereo-regularity of the molecular structure into consideration.     

Photoinduced charge transfer through films containing poly(hexylthiophene), phthalocyanine, and porphyrin-fullerene layers

Efficient photoinduced interlayer electron transfer from a phthalocyanine derivative, ZnPH4, to porphyrin cation of a porphyrin-fullerene donor-acceptor dyad was demonstrated by using time-resolved photovoltage technique. Multicomponent thin films with desired layer arrangements were constructed by the Langmuir-Blodgett and spin-coating methods in order to study charge transfer in solid state. As a contradiction to the photovoltage experiments, the dyad monolayer in the film structure did not enhance the current amplitude in electrochemical photocurrent measurements. This is associated with a weak electronic interaction between fullerene and aqueous electrolyte, reducing the photocurrent generation. The use of poly(3-hexylthiophene) as a hole conducting layer was shown to improve photocurrent yield of the device by forming efficient heterojunction together with the ZnPH4 layer.     

Preparation and characterization of bacterial cellulose-poly(vinyl alcohol) films with antimicrobial properties

Antimicrobial composites from poly(vinyl alcohol) and bacterial cellulose containing potassium sorbate as antimicrobial agent were obtained by film casting method. The obtained films were tested against Escherichia coli and showed a good antimicrobial activity.     

The use of nanoimprint lithography to improve efficiencies of bilayer organic solar cells based on P3HT and a small molecule acceptor

Nanoimprint lithography (NIL) was carried out on bilayer organic photovoltaics (OPVs) based on regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) as electron donor and 4,7-bis(2-(1-ethylhexyl-4,5-dicyano-imidazol-2-yl)vinyl)benzo[c]1,2,5-thiadiazole (EV-BT) as electron acceptor. The power conversion efficiency of the devices after nanoimprinting increased from 0.20% to 0.30%, closer to that of the bulk heterojunction device at 0.37%. As a result, NIL proved to be a feasible method for improving the bilayer OPV performance by increasing the donor/acceptor interfacial area.     

Crystallization of amorphous silicon thin films: The effect of rapid thermal processing pretreatment

In the present work, the effect of low temperature short-time rapid thermal processing (RTP) pretreatment on the average grain size and the crystallinity of the polycrystalline silicon thin films, fabricated by subsequent solid phase crystallization (SPC) of amorphous silicon (a-Si) thin films grown by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at high temperature has been studied. The average grain size and the crystallinity results were estimated using X-ray diffraction (XRD) and Raman spectroscopy, respectively. It was found that RTP at 800 °C for 60 s resulted in slightly larger average grain size and higher crystallinity than those without the RTP pretreatment after SPC at 800 °C for 5, 10 and 22 h. The results suggest that the low-temperature short-time RTP pretreatment can promote the crystallization process of the as-deposited a-Si thin films during the following SPC and then improve their crystallinity. Finally, the mechanism is also discussed in detail in the paper.     

Preparation of composite nanofibers containing gold nanoparticles by using poly(N-vinylpyrrolidone) and β- cyclodextrin

We report a new method for preparing β-cyclodextrin/poly(N-vinylpyrrolidone) composite nanofibers containing gold nanoparticles by electrospinning. β-Cyclodextrin is mixed into fibers as a new material, and it acts as stabilized reagent and reducing reagent in the synthesis of gold nanoparticles. TEM observation confirms that the gold nanoparticles are completely encapsulated within the composite nanofibers.     

Self-doped polyaniline films prepared by electropolymerization in the presence of sulfonated nickel phthalocyanine

It is shown that the addition of tetrasulfonated nickel phthalocyanine (NiTSPc) to an acidic solution of aniline results in an accelerated deposition of polyaniline (PANI) from such a solution using the electrochemical potential cycling method. The electrodeposited polyaniline includes NiTSPc to form a composite film that retains its electroactivity in a wide pH range due to the self-doping effect. The thus formed composite PANI-NiTSPc film exhibits catalytic activity toward the electrooxidation of ascorbic acid in a nearly neutral buffer (pH 7.4).     

High-throughput dynamic impact characterization of polymer films

An instrumented falling weight impact apparatus has been designed and constructed for high-throughput characterization of polymer films in the 5–100 m thickness range. The primary intended use of the instrument is rapid and accurate characterization of the dynamic impact response of multiple (100) positions on a combinatorial library film. This will allow future exploration of the dependence of mechanical response on polymer composition, thickness, and annealing temperature using combinatorial synthesis and characterization methods. This paper describes the instrument and presents validation measurements using polyethylene films of uniform thickness (25 m) and poly(urethaneurea) elastomers of thicknesses from 10–30 m. Measurements on the polyethylene film demonstrate the reproducibility and lack of interaction effects for multiple measurements on the same film. Poly(urethaneurea) elastomer impact measurements are used to indicate the instrument sensitivity to controlled variations in polymer chemistry and structure. In particular, the results from force-deformation profiles indicate an optimum curing temperature and the expected trend in mechanical response with respect to polyurethaneurea diamine chain extender composition.     

Synthesis of YAG:Ce/TiO2 nanocomposite films

Our work is devoted to the development of YAG:Ce³⁺ phosphor nanoparticle-based converter layer for white LEDs. To avoid losses due to scattering effects, the strategy is to control separately the down-conversion and the extraction of light instead of using micron-sized luminescent particles acting simultaneously as both converter and scatterer. YAG:Ce nanoparticles were synthesized by a glycothermal method in autoclave at low temperature (300 °C). Y₃Al₅O₁₂ garnet phase with a crystallite size of 25 nm was obtained, as verified by X-ray diffraction and electron microscopy. The quantum yield of nanoparticles is 55%. The colloidal nanoparticles are finally incorporated into a sol-gel matrix of TiO₂. The small difference in refractive index between particles and matrix and the nanosize of the particles contribute to the transparency of the converter films. The surface of these layers can be periodically patterned by soft nano-imprint lithography. The diffraction due to the obtained photonic crystal at the surface may offer the opportunity to compensate the absence of scattering to extract the converted light.