Low-cost micro-lens arrays fabricated by photosensitive sol–gel and multi-beam laser interference

In this paper, we introduce a low-cost approach for fabricating micro-lens arrays that is based on photosensitive sol–gel and multi-beam laser interference. UV photosensitive ZrO₂ gel films are prepared with Zr(O(CH₂)₃CH₃)₄ and BzAcH as the precursor and chemical modifier, respectively. With UV laser irradiation via different dose, nonlinear photodecomposition occurs in this film. Large scale 2D micro lens arrays with the sizes of 830 nm × 830 nm and 280 nm × 280 nm are fabricated by four-beam laser interference. The surface profile modeling shows that the micro lens is plano convex lens, and the effective focal lengths are 812.0 nm and 317.6 nm, respectively.     

A high (0 0 1)-oriented CoPt/Ag film deposited on glass substrate

The magnetic properties and structures of CoPt_15 nm/Ag_0−100 nm films deposited by DC magnetron sputtering on glass substrates have been studied. The (0 0 1) texturing was improved by introducing an Ag underlayer. As the Ag underlayer thickness was 100 nm, a nearly perfect (0 0 1)-textured CoPt film was obtained.     

Characterization of the channel walls roughness in photonic crystal fibers

We present electron microscope (FEI NanoSEM) and atomic force microscopy measurements of surface roughness in nanochannels in photonic crystal fibers (PCF). A method was invented to cleave the PCF along the axis without damaging the surface structure in the nanochannels allowing us to characterize the morphology of the nanochannels in the PCF. A multi-wall carbon nanotube mounted onto commercial AFM probes and super sharp silicon non-contact mode AFM probes were used to characterize the wall roughness in the nanochannels. The roughness is shown to have a Gaussian distribution, and has an amplitude smaller than 0.5 nm. The height–height correlation function is an exponential correlation function with an autocorrelation length of 13 nm, and 27 nm corresponding with scan sizes of 200×100 nm², and 1600×200 nm², respectively.     

A new carbon nitride synthesized by shock compression of organic precursors

A series of shock recovery experiments up to ∼50 GPa were carried out on three nitrogen-rich materials of a C–N–O amorphous precursor, dicyandiamide and melamine. The powder X-ray diffractions (XRD) of recovered samples show that carbon nitride phases are formed. They are β-C₃N₄ and a new crystalline phase. The new phase is indexed as a monoclinic cell with a=0.981 nm, b=0.723 nm, c=0.561 nm, β=95.2° and V_cell=0.3966 nm³. Melamine was very stable and did not decompose up to ∼37 GPa. This new phase is considered to form during the adiabatic release process with an extremely high quenching rate (∼10⁹ K/s) and shock compression may provide a novel synthesis route for various C–N phases from appropriate organic materials.     

Mesopore size dependence of the ionic diffusivity in alumina based composite lithium ionic conductors

Ordered-mesoporous Al₂O₃ was synthesized by a sol–gel method using neutral copolymer surfactants as structure-directing agents. The pore size was controlled over the 3–15 nm range by the use of various surfactants. Composites composed of the synthesized mesoporous Al₂O₃ and a lithium ion conductor (LiI) were prepared. The maximum dc electrical conductivity, 2.6 × 10^− 4 S cm^− 1 at 298 K, was observed for 50 LiI·50 Al₂O₃ composite with 4.2 nm average mesopore size, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which conductivity increased with decreasing pore size, except for samples with a pore size of 2.8 nm. The lithium ion diffusion coefficient determined by the ⁷Li pulsed field gradient nuclear magnetic resonance (PFG-NMR) showed excellent agreement with the measured conductivity calculated by the Nernst-Einstein equation. On the other hand, lithium migration activation energies obtained by quasielastic neutron scattering (QENS) and ⁷Li NMR spin-lattice relaxation time (T₁) were considerably smaller than those obtained from electrical conductivity and PFG-NMR. This could be explained by the ion migration mechanism in heterogeneous composites and a possible enhancement of conductivity in mesoscopically confined spaces.     

Magnetic properties of Ni nanoparticles on microporous silica spheres

Ni nanoparticles (~32 nm particle diameter) have been synthesized on the walls of microporous (~1 nm pore diameter) silica spheres (~2.6 μm sphere diameter) and characterised magnetically to potentially produce a new class of core (silica micro-spheres)-shell (nanometallic)-type nanocomposite material. These magnetic nanocomposite materials display a characteristic increase in coercivity with reducing temperature. The average particle size has been used to calculate the anisotropy constant for the system, K. The discussion postulates the potential mechanisms contributing to the difference between the calculated K value and the magnetocrystalline anisotropy constant of bulk Ni. Various factors such as surface anisotropy and interparticle interactions are discussed as possible contributing factors to the anisotropy values calculated in the paper.     

A new design of low-loss and ultra-flat zero dispersion photonic crystal fiber using hollow ring defect

New hollow ring defect structure is introduced in photonic crystal fiber design for ultra- flat zero dispersion with very low waveguide losses. The hollow ring defect consisted of a central hole surrounded by a doped silica ring provides highly flexible defect engineering capabilities in photonic crystal fibers to achieve precise control of dispersion value and dispersion slope while independently maintaining low waveguide losses, which was not attainable in previous designs. A nearly flat zero dispersion of D=0±0.51 ps/nm km was obtained in the wavelength range of 1.44–1.61 μm with the maximum slope of ?2.7×10^?2 ps/nm² km. The confinement loss was less than 5.75×10^?8 dB/m along with the bending loss of 2.8×10^?6 dB/m for the radius of 10 mm, and splice loss of less than 1.57 dB to conventional single mode fiber at 1.55 μm.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

Interface characterization of a [Pt/Co)]3/IrMn multilayer by laser-assisted tomographic atom probe

A sputtered Ta_3 nm/[[Pt_2 nm/Co_0.4 nm)]₃/IrMn_7 nm]₇/Pt_10 nm multilayer has been analyzed by laser-assisted tomographic atom probe, allowing to perform three-dimensional reconstructions of the layers and to determine their chemical composition at the atomic scale. From the concentration profiles, we show that the Co layer in contact with IrMn is strongly mixed. The Co/IrMn and IrMn/Pt interfaces are thus non-symmetric, the Co/IrMn interface being more diffuse than the IrMn/Pt one. This study demonstrates that the LATAP technique is extremely well suited for atomic scale structural and chemical characterizations of magnetic multilayers in relationship with their magnetic properties.     

Structural and optical properties of La-doped BaSnO3 thin films grown by PLD

In this study the structural and optical properties of lanthanum-doped BaSnO₃ powder samples and thin films deposited on fused silica were investigaed using laser ablation. Under an oxygen pressure of 5×10⁻⁴ mbar, phase pure BaSnO₃ films with a lattice constant of 0.417 nm and grain size of 21 nm were prepared at 630 °C. The band gap of BaSnO3 powder sample and thin films was calculated to be 3.36 eV and 3.67 eV, respectively. There was a progressive increase in conductivity for thin films of BaSnO₃ doped with 0~7 at% of La. The highest conductivity, 9 Scm⁻¹, was obtained for 7 at% La-doped BaSnO₃. Carrier concentration, obtained from Burstein-Moss (B-M) shift, nearly matches the measured values except for 3 at% and 10 at% La-doped BaSnO₃ thin films.     

Investigating gate metal induced reduction of surface donor density in GaN/AlGaN/GaN heterostructure by electroreflectance spectroscopy

The internal field of GaN/AlGaN/GaN heterostructure on Si-substrate was investigated by varying the thickness of an undoped-GaN capping layer using electroreflectance spectroscopy. The four samples investigated are AlGaN/GaN heterostructure without a GaN cap layer (reference sample) and three other samples with GaN/AlGaN/GaN heterostructures in which the different thickness of GaN cap layer (2.7 nm, 7.5 nm, and 12.4 nm) has been considered. The sheet carrier density (n_s) of a two-dimensional electron gas has decreased significantly from 4.66 × 10¹² cm⁻² to 2.15 × 10¹² cm⁻² upon deposition of a GaN capping layer (12.4 nm) over the reference structure. Through the analysis of internal fields in each GaN capping and AlGaN barrier layers, it has been concluded that the undiminished surface donor states (n_s) of a reference structure and the reduced n_s caused by the Au gate metal are approximately 5.66 × 10¹² cm⁻² and 1.08 × 10¹² cm⁻², respectively.     

Preparation of enzyme nanoparticles and studying the catalytic activity of the immobilized nanoparticles on polyethylene films

Using high-intensity ultrasound, in situ generated α-amylase nanoparticles (NPs) were immobilized on polyethylene (PE) films. The α-amylase NP-coated PE films have been characterized by E-SEM, FTIR, DLS, XPS and RBS. The PE was reacted with HNO₃ and NPs of the α-amylase were also deposited on the activated PE. The PE impregnated with α-amylase (4 μg per 1 mg PE) was used for hydrolyzing soluble potato starch to maltose. The immobilization improved the catalytic activity of α-amylase at all the reaction conditions studied. The kinetic parameters, K_m (5 and 4 g L^?1 for the regular and activated PE, respectively) and V_max (5 × 10^?7 mol ml^?1 min^?1, almost the same numbers were obtained for the regular and activated PEs) for the immobilized amylase were found to slightly favor the respective values obtained for the free enzyme (K_m = 6.6 g L^?1, V_max = 3.7 × 10^?7 mol ml^?1 min^?1). The enzyme remained bound to PE even after soaking the PE in a starch solution for 72 h and was still found to be weakly active.     

Synthesis and characterization of a Ni/Ba2In0.6Ti1.4O5.7□0.3 cermet for SOFC application

Ni-based cermets were prepared and reduced from mixtures of NiO and Ba₂In_0.6Ti_1.4O_5.7□_0.3. A cermet containing 18.7 vol.% of Ni exhibits promising characteristics: 40% of open porosity and a lower DC resistivity than a Ni/YSZ cermet with a larger Ni content (30 vol.%). Its thermal expansion coefficient is 11.4 × 10^− 6 K^− 1 whereas that measured for Ba₂In_0.6Ti_1.4O_5.7□_0.3 is 9.9 × 10^− 6 K^− 1. Electrical measurements vs. the Ni content have shown that the percolation threshold corresponds to 15.7 vol.% of Ni. By using saccharose as a pore former, the porosity of the electrode can be tuned. It is shown that the pore size is controlled by the particle size distribution of the pore former.     

Preparation and electrochemical properties of mesoporous Co3O4 crater-like microspheres as supercapacitor electrode materials

Mesoporous Co₃O₄ microspheres with unique crater-like morphology were obtained by utilizing the mesoporous silica material MCM-41 as a template. The analysis results of N₂ adsorption–desorption measurement indicate that the product has a large Brunauer–Emmett–Teller (BET) surface area of 60 m² g⁻¹ and a narrow pore size distribution centering around 3.7 nm. Its electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The findings reveal that this novel morphology material has a smaller inner resistance of about 0.4 Ω and a higher onset frequency of 550 Hz. This material can provide a high specific capacitance of 102 F g⁻¹ and a large capacity retention of 74% in 500 continuous cycles test at a sweep rate of 3 mV s⁻¹. More significantly, the mass loading of electroactive species can reach as large as 2 mg cm⁻², which is one order of magnitude larger than common amount used.     

Ultrasonic-assisted ultra-rapid synthesis of monodisperse meso-SiO2@Fe3O4 microspheres with enhanced mesoporous structure

A core–shell-type of meso-SiO₂@Fe₃O₄ microsphere was synthesized via an ultrasonic-assisted surfactant-templating process using solvothermal synthesized Fe₃O₄ as core, tetraethoxysilane (TEOS) as silica source, and cetyltrimethyl ammonium bromide (CTAB) as templates. The samples were characterized by FT-IR, XRD, TEM, N₂ adsorption–desorption technology, and vibrating sample magnetometer (VSM). The results show that as-prepared meso-SiO₂@Fe₃O₄(E) and meso-SiO₂@Fe₃O₄(C) microspheres, treated by acetone extraction and high temperature calcination, respectively, still maintain uniform core–shell structure with desirable mesoporous silica shell. Therein, the meso-SiO₂@Fe₃O₄(E) microspheres possess a distinct pore size distribution in 1.8–3.0 nm with large specific surface area (468.6 m²/g) and pore volume (0.35 cm³/g). Noteworthily, the coating period of this ultrasonic-assisted method (40 min) is much shorter than that of the conventional method (12–24 h). The morphology of microspheres and the mesoporous structure of silica shell are significantly influenced by initial concentration of CTAB (C_CTAB), ultrasonic irradiation power (P) and ultrasonic irradiation time (t). The acceleration roles of ultrasonic irradiation take effect during the whole coating process of mesoporous silica shell, including hydrolysis-condensation process of TEOS, co-assembly of hydrolyzed precursors and CTAB, and deposition of silica oligomers. In addition, the use of ultrasonic irradiation is favorable for improving the homogeneity of silica shell and the monodispersity of meso-SiO₂@Fe₃O₄ microspheres.     

Growth of the Au-induced c(8 × 2) structure on vicinal Ge(001)

We have studied the formation of Ge(001) c(8 × 2)–Au surfaces on vicinal samples by scanning tunneling microscopy. The vicinal samples are tilted 1° toward [110]. The c(8 × 2)–Au surface is prepared by depositing 0.75 ± 0.05 ML of Au onto a germanium surface held at 800 K. The anisotropy introduced by the atomic steps of the vicinal surface and the preferential etching of S_B steps during Au deposition is sufficient to introduce a preferred growth direction for the c(8 × 2)–Au phase. The result is a sample on which 78% of the surface is populated by Au-induced chains oriented parallel to the step direction. These parallel Ge(001) c(8 × 2)–Au domains are separated by single or multiple height D_A steps (0.28 nm high).     

Ohmic contact and space-charge-limited current in molybdenum oxide modified devices

The effect of indium-tin oxide (ITO) surface treatment on hole injection of devices with molybdenum oxide (MoO₃) as a buffer layer on ITO was studied. The Ohmic contact is formed at the metal/organic interface due to high work function of MoO₃. Hence, the current is due to space charge limited when ITO is positively biased. The hole mobility of N, N′-bis-(1-napthyl)-N, N′-diphenyl-1, 1′biphenyl-4, 4′-diamine (NPB) at various thicknesses (100–400 nm) has been estimated by using space-charge-limited current measurements. The hole mobility of NPB, 1.09×10⁻⁵ cm²/V s at 100 nm is smaller than the value of 1.52×10⁻⁴ cm²/V s at 400 nm at 0.8 MV/cm, which is caused by the interfacial trap states restricted by the surface interaction. The mobility is hardly changed with NPB thickness for the effect of interfacial trap states on mobility which can be negligible when the thickness is more than 300 nm.     

In-situ imaging of the nucleation and growth of epitaxial anatase TiO2(001) films on SrTiO3(001)

The growth of TiO₂ anatase films on Nb‐doped SrTiO₃(001) molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski–Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO₂. The epitaxial islands subsequently nucleate and coalesce into large commonly oriented crystallites. The reconstruction observed by reflection high-energy electron diffraction (RHEED) is shown to result from the coexistence of individual (4 × 1) and (1 × 4) reconstructions present on different crystallite surfaces. The anatase grows in units of bilayers, resulting in a step height of 2 ML (~ 0.5 nm). This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4 × 1) and (1 × 4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Sonochemical synthesis and rheological properties of shear thickening silica dispersions

A sonochemical method has been developed to synthesize shear thickening fluid. This shear thickening fluid (STF) is composed of hard silicon dioxide nanoparticles and polyethylene glycol (PEG) liquid polymer. The combination of flow-able and hard components at a particular composition, results a material with remarkable rheological properties that is suitable for liquid body armor applications. In the present study nine types of STF’s have been synthesized with two different types of silica nanoparticles (15 nm and 200 nm) and polyethylene glycol at various weight fractions using a high intensity ultrasonic irradiation. The resultant STF samples were tested for their rheological and thermal properties. The advantages and disadvantages of this process have been discussed.