Mechanistic insight into sonochemical biodiesel synthesis using heterogeneous base catalyst

The beneficial effect of ultrasound on transesterification reaction is well known. Heterogeneous (or solid) catalysts for biodiesel synthesis have merit that they do not contaminate the byproduct of glycerol. In this paper, we have attempted to identify the mechanistic features of ultrasound–enhanced biodiesel synthesis with the base–catalyst of CaO. A statistical design of experiments (Box–Behnken) was used to identify the influence of temperature, alcohol to oil molar ratio and catalyst loading on transesterification yield. The optimum values of these parameters for the highest yield were identified through Response Surface Method (with a quadratic model) and ANOVA. These values are: temperature = 62 °C, molar ratio = 10:1 and catalyst loading = 6 wt.%. The activation energy was determined as 82.3 kJ/mol, which is higher than that for homogeneous catalyzed system (for both acidic and basic catalyst). The experimental results have been analyzed vis–à–vis simulations of cavitation bubble dynamics. Due to 3–phase heterogeneity of the system, the yield was dominated by intrinsic kinetics, and the optimum temperature for the highest yield was close to boiling point of methanol. At this temperature, the influence of cavitation bubbles (in terms of both sonochemical and sonophysical effect) is negligible, and ultrasonic micro–streaming provided necessary convection in the system. The influence of all parameters on the reaction system was found to be strongly inter–dependent.     

Investigation on the microscopic features of layered oxide Li[Ni1 / 3Co1 / 3Mn1 / 3]O2 and their influences on the cathode properties

Three kinds of samples of Li[Ni_1 / 3Co_1 / 3Mn_1 / 3]O₂ were prepared respectively from direct solid-state reaction method, combustion method and co-precipitation route and their microscopic structural features have been investigated using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), magnetic susceptibility measurement and X-ray photoelectron spectroscopy (XPS). The microscopic features such as uniform distribution of transition metal ions at 3b-site and the site-exchange ratio between lithium and nickel were found to be significantly dependent on the synthetic routes. The electrochemical properties of three samples were monitored using 2016 coin-cell by galvanostatic charge–discharge cycling test and cyclic voltammetry, which showed that the microscopic structural features are deeply related with the electrochemical performance. The obtained results also suggested that the combustion method may become a much simple alternative synthetic route to the complicate co-precipitation method.     

Pt-chain induced formation of Ge nanowires on the Ge(001) surface

A new reconstructed Pt/Ge(001)–4 × 2 surface structure of 0.25 ML Pt deposition is suggested based on density functional theory. The Ge dimers form nanowire arrays on a Pt-chain modified Ge(001) surface in which the chain is located between the two quasi-dimer rows and below the Ge nanowire. The simulated scanning tunneling microscope (STM) images of the surface are in excellent agreement with the previously observed STM features and sample bias dependence. It is the nanowire Ge dimers and not the Pt atoms that contribute to the STM images for occupied states at high sample biases, contrary to what has always been assumed in experiments. The surface bands of the Pt chain and quasi-dimer rows exhibit quasi-one-dimensional metallic behavior in the direction of the nanowire. When changing from the 4 × 2 to the 4 × 4 structure, there are likely pseudogaps opened at the new surface Brillouin zone boundary, which simultaneously reduce the metallicity. This may be related to the Peierls instability. The interaction between the Pt chain and the quasi-dimer row, as well as the inter-quasi-dimer row interaction, is of essential importance for stabilization.     

The adsorption and reaction of 2-butanol on clean and oxygen-covered Pd(100)

The surface chemistry of 2-butanol is explored on clean Pd(100), c(2 × 2)-O/Pd(100) and p(2 × 2)-O/Pd(100) surfaces by means of temperature-programmed desorption, reflection–absorption infrared and X-ray photoelectron spectroscopies. 2-Butanol adsorbs molecularly on clean and oxygen-covered Pd(100) below ～ 190 K, but then appears to react to form 2-butoxide species at ～ 200 K. Both 2-butanone and 2-butanol desorb from the clean surface at ～ 226 K, by β-hydride elimination from the 2-butoxide species and rehydrogenation of the 2-butoxide, respectively. In contrast, almost exclusively 2-butanone is formed on oxygen-covered surfaces. Butanone desorbs at ～ 195 K and ～ 260 K from c(2 × 2)-O/Pd(100) with the 195 K peak being the most intense. However, on p(2 × 2)-O/Pd(100), 2-butanone desorbs at ～ 195 K and ～ 295 K, and the latter peak is the most intense. The ～ 195 K, 2-butanone state is proposed to occur due to abstraction by adsorbed atomic oxygen and the change in relative intensity of these features is ascribed to the lower ability of surface hydroxyl groups to facilitate β-hydride elimination on oxygen-covered surfaces. Further heating results in the formation of hydrogen and carbon monoxide and leaves a small amount of carbon deposited on the surface.     

Evolution of interface properties of the Pentacene/Bi(0001) system

Using angle-resolved photoemission spectroscopy we measured the evolution of the electronic properties of the Pentacene (Pn)/Bi(0001) interface. From thickness dependent photoemission spectra of the substrate and Pn film we conclude that Pn growth is epitaxial. Pentacene highest occupied molecular orbital (HOMO) valence band features are identical for sub-monolayer (ML) as well as for thick films which suggests a thickness independent film morphology. The Pn/Bi interaction is weak and results in a lowering of the HOMO binding energy by 180 ± 5 meV and 80 ± 5 meV for the first and second MLs respectively. The interface dipole (ID) is fully developed over the first ～ 1.2 ML of Pn coverage and has a value of ID = 310 ± 10 meV. The hole injection barrier across the interface is Φ_h = 1.03 ± 0.01 eV.     

Design and experiment of spectrometer based on scanning micro-grating integrating with angle sensor

A compact, low cost, high speed, non-destructive testing NIR (near infrared) spectrometer optical system based on MOEMS grating device is developed. The MOEMS grating works as the prismatic element and wavelength scanning element in our optical system. The MOEMS grating enables the design of compact grating spectrometers capable of acquiring full spectra using a single detector element. This MOEMS grating is driven by electromagnetic force and integrated with angle sensor which used to monitored deflection angle while the grating working. Comparing with the traditional spectral system, there is a new structure with a single detector and worked at high frequency. With the characteristics of MOEMS grating, the structure of the spectrometer system is proposed. After calculating the parameters of the optical path, ZEMAX optical software is used to simulate the system. According the ZEMAX output file of the 3D model, the prototype is designed by SolidWorks rapidly, fabricated. Designed for a wavelength range between 800 nm and 1500 nm, the spectrometer optical system features a spectral resolution of 16 nm with the volume of 97 mm × 81.7 mm × 81 mm. For the purpose of reduce modulated effect of sinusoidal rotation, spectral intensity of the different wavelength should be compensated by software method in the further. The system satisfies the demand of NIR micro-spectrometer with a single detector.     

Lateral inhomogeneity of unoccupied states for PbPc films

Micro-spot two-photon photoemission (micro-2PPE) spectroscopy is used to probe unoccupied electronic levels at sub-monolayer (ML) films of lead phthalocyanine (PbPc) on graphite (HOPG). The high-energy resolution (30 meV) 2PPE spectra with high-lateral resolution (0.4 μm) show well-resolved features due to molecule-derived occupied/unoccupied levels and the image potential state (IPS). The surface images based on photoemission from the highest occupied molecular orbital (HOMO) become laterally uniform after an annealing procedure. By contrast, the images based on the peak due to the lowest unoccupied molecular orbital (LUMO) and the next LUMO (LUMO + 1) are laterally inhomogeneous even after the annealing. The IPS peak is broadened to higher energy by 0.3 eV for sub-ML films and becomes sharp when a 1 ML film is formed. The broadening indicates that the electron in the IPS is scattered by molecules within the mean free path in the range from 1 to 10 nm. PbPc molecules are randomly distributed including nm-clusters. The LUMO and LUMO + 1 levels are stabilized as the cluster size increases. The inhomogeneity of the surface image due to the LUMO + 1 peak arises from the size distribution of the nm-clusters. The present results demonstrate that the unoccupied levels are more sensitive to the environment than the occupied levels.     

Robust automatic facial expression detection method based on sparse representation plus LBP map

Recently the sparse representation based classification (SRC) is successfully used to automatically recognize facial expression, well-known for its ability to solve occlusion and corruption problems. The results of those methods which using different features conjunction with SRC framework show state of the art performance on clean or noised facial expression images. Therefore, the role of feature extraction for SRC framework will greatly affect the success of facial expression recognition (FER). In this paper, we select a new feature which called LBP map. This feature is generated using local binary pattern (LBP) operator. It is not only robust to gray-scale variation, but also extracts sufficient texture information for SRC to deal with FER problem. Then we proposed a new method using the LBP map conjunction with the SRC framework. Firstly, we compared our method with state of the art published work. Then experiments on the Cohn–Kanade database show that the LBP map + SRC can reach the highest accuracy with the lowest time-consuming on clean face images than those methods which use different features such as raw image, Downsample image, Eigenfaces, Laplacianfaces and Gabor conjunction with SRC. We also experiment the LBP map + SRC to recognize face image with partial occluded and corrupted, the result shows that this method is more robust to occlusion and corruption than existing methods based on SRC framework.     

Diffusion of a Ga adatom on the GaAs(001)‐c(4 × 4)‐heterodimer surface: A first principles study

The adsorption and diffusion behavior of a Ga adatom on the GaAs (001)‐c(4 × 4)-heterodimer surface were studied by employing ab initio density functional theory (DFT) computations in the local density approximation. Structural and bonding features of the c(4 × 4)-heterodimer reconstruction surface were examined. A comparison with the c(4 × 4)-ss reconstruction was performed. Minimum energy sites (MES) on the c(4 × 4)-heterodimer surface were located by mapping the potential energy surface for a Ga adatom. Barriers for diffusion of a Ga adatom between the neighboring MES were calculated by using top hopping- and exchange-diffusion mechanisms. We proposed two unique diffusion pathways for a Ga adatom diffusing between the global minimums of two neighboring unit cells. Signature differences between electronic structures of top hopping- and exchange‐diffusion mechanisms were studied for relevant atoms. We observed a higher diffusion barrier for exchange mechanism compared to top hopping.     

Reversible and irreversible reactions of three oxygen precursors on InAs(0 0 1)-(4 × 2)/c(8 × 2)

The substrate reactions of three common oxygen sources for gate oxide deposition on the group III rich InAs(0 0 1)-(4 × 2)/c(8 × 2) surface are compared: water, hydrogen peroxide (HOOH), and isopropyl alcohol (IPA). Scanning tunneling microscopy reveals that surface atom displacement occurs in all cases, but via different mechanisms for each oxygen precursor. The reactions are examined as a function of post-deposition annealing temperature. Water reaction shows displacement of surface As atoms, but it does not fully oxidize the As; the reaction is reversed by high temperature (450 °C) annealing. Exposure to IPA and subsequent low-temperature annealing (100 °C) show the preferential reaction on the row features of InAs(0 0 1)-(4 × 2)/c(8 × 2), but higher temperature anneals result in permanent surface atom displacement/etching. Etching of the substrate is observed with HOOH exposure for all annealing temperatures. While nearly all oxidation reactions on group IV semiconductors are irreversible, the group III rich surface of InAs(0 0 1) shows that oxidation displacement reactions can be reversible at low temperature, thereby providing a mechanism of self-healing during oxidation reactions.     

Vibration spectroscopy of water on stepped gold surfaces

The vibration spectrum of H₂O (ice) adsorbed at low temperatures on Au(1 0 0), Au(1 11 1), and Au(1 1 5) is studied using electron energy loss spectroscopy. On the Au(1 0 0) surface, the spectra show the presence of the typical H-bonded network of water molecules for all coverages from the submonolayer into the multilayer range. The absence of a non-H-bonded OH-stretching mode is indicative for the “H-down bilayer”. On stepped surfaces, on the other hand, a considerable fraction of the H-atoms remains in the non-H-bonded state; surprisingly even in the multilayer range, and even after annealing. The fraction of non-H-bonded hydrogen atoms scales with the step density. Spectral features of water adsorbed at step-sites are isolated after annealing a surface exposed to small doses of H₂O. The results are discussed in the context of recent theoretical studies as well as in conceivable relation to the experimentally found reduction of the Helmholtz-capacitance on stepped Au(1 1 n) electrodes.     

Ultrasonic assisted dispersive solid-phase microextraction of Eriochrome Cyanine R from water sample on ultrasonically synthesized lead (II) dioxide nanoparticles loaded on activated carbon: Experimental design methodology

The present research focus on designing an appropriate dispersive solid-phase microextraction (UA-DSPME) for preconcentration and determination of Eriochrome Cyanine R (ECR) in aqueous solutions with aid of sonication using lead (II) dioxide nanoparticles loaded on activated carbon (PbO-NPs-AC). This material was fully identified with XRD and SEM. Influence of pH, amounts of sorbent, type and volume of eluent, and sonication time on response properties were investigated and optimized by central composite design (CCD) combined with surface response methodology using STATISTICA. Among different solvents, dimethyl sulfoxide (DMSO) was selected as an efficient eluent, which its combination by present nanoparticles and application of ultrasound waves led to enhancement in mass transfer. The predicted maximum extraction (100%) under the optimum conditions of the process variables viz. pH 4.5, eluent 200 μL, adsorbent dosage 2.5 mg and 5 min sonication was close to the experimental value (99.50%). at optimum conditions some experimental features like wide 5–2000 ng mL⁻¹ ECR, low detection limit (0.43 ng mL⁻¹, S/N = 3:1) and good repeatability and reproducibility (relative standard deviation, <5.5%, n = 12) indicate versatility in successful applicability of present method for real sample analysis. Investigation of accuracy by spiking known concentration of ECR over 200–600 ng mL⁻¹ gave mean recoveries from 94.850% to 101.42% under optimal conditions. The procedure was also applied for the pre-concentration and subsequent determination of ECR in tap and waste waters.     

Role of electronic structure in magnetic tunneling

To assess the effect of electronic structure of magnetic electrodes on the magnetoresistance of tunnel junctions (JMR) we made ab initio calculations of the electronic structure of BCC(1 0 0) Fe, and FCC(1 0 0) Co and Ni electrodes. We treat hopping to and propagation in the barrier as adjustable parameters and discuss features of the JMR attributable to the electronic structure of the electrodes.     

The electronic properties of Co nanowires on Cu(110)-p(2 × 3)N

We present the first measurements of the differential conductance of Co wires grown on top of Cu(110)-p(2 × 3)N (Cu₃N). We apply scanning tunneling spectroscopy (STS) in constant height and constant current mode to access the electronic density of states of the sample over a wide energy range. All measurements have been performed at 7 K. Our study reveals that the differential conductance of the Co wires is very similar to that of Cu₃N. Spectra of the differential conductance measured on the Co wires and on Cu₃N reveal that both systems exhibit the same characteristic features near + 1.8V and + 3.5 V.     

Ga induced 2D superstructural phase diagram on trenched Si(5 5 12) surface

The high index Si(5 5 12) surface offers morphological trenches, which can be interesting for epitaxial growth. In this study, the evolution of Ga adsorption at a very low flux rate of 0.03 ML/min on high index trenched Si(5 5 12) ? 2 × 1 reconstructed surface at various substrate temperatures ranging from room temperature (RT) to 600 °C has been investigated using in-situ AES, LEED and EELS. The Auger uptake curves, which plot the Ga(LMM)/Si(LVV) Auger intensity ratio with Ga adsorption time, show that Ga grows in layer plus islands mode for substrate temperatures in the RT to 350 °C range, while it grows in Volmer–Weber (3D islands) for higher substrate temperatures (> 350 °C). We also arrive at a complete 2D superstructural phase diagram for Ga/Si(5 5 12) interfacial system that shows the pathways to attain the different superstructural phases. The formation of Ga nanowires as (2 2 5), (3 3 7) phase and Ga 3D islands in the (1 1 2) ? 6 × 1, (1 1 2) ? 6 × 2 phases and other Ga induced superstructural phases like (7 7 17) + 2x(1 1 3), (2 2 5) + (3 3 7), 1 × 1 has been carefully followed. The electronic structures of each of the observed phases have been probed by EELS and each of them is shown to have characteristic features.     

Synthesis of superhydrophobic PTFE-like thin films by self-nanostructuration in a hybrid plasma process

Superhydrophobic poly(tetrafluoro-ethylene) (PTFE) like thin films were grown on silicon wafers using a plasma-based hybrid process consisting on sputtering a carbon target in an Ar/CF₄ atmosphere. The influence of the bias voltage applied to the substrate (V_Bias) as well as of the gas mixture composition (%CF₄) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated.The chemical composition measured by X-ray Photoelectron Spectroscopy (XPS) has revealed that the F/C atomic ratio is always lower than for conventional PTFE (F/C = 2) and that it decreases when V_Bias increases (from F/C = 1 for V_Bias = ? 100 V to F/C = 0.75 for V_Bias = ? 200 V). This behavior is associated with the preferential sputtering of the fluorine atoms during the plasma-assisted growth of the films. Consecutively, a self-nanostructuration enhanced when increasing V_Bias is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine concentration and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCAs, a small hysteresis between the advancing and receding WCAs is observed (< 10°) allowing these films to fulfill completely the requirements of superhydrophobicity. The nanostructuration is probably due to the chemical etching by fluorine atoms of the fluorinated group.In order to get more understanding on the wettability mechanisms of these surfaces, the topography of the films has been evaluated by atomic force microscopy (AFM). The data have revealed, for all films, a dense and regular structure composed by conic objects (A_vH is their average height and A_vD is the average distance between them) for which the dimensions increase with V_Bias. A correlation between A_vH/A_vD, defined as the “morphological ratio”, with the WCA was established. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin film surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations.     

Fabrication of broadband poly(vinylidene difluoride-trifluroethylene) line-focus ultrasonic transducers for surface acoustic wave measurements of anisotropy of a (1 0 0) silicon wafer

This paper investigates a new method for fabrication of broadband line-focus ultrasonic transducers by sol–gel spin-coating the poly(vinylidene difluoride-trifluroethylene) [P(VDF-TrFE)] copolymer film on a concave fine-polished beryllium copper backing. The ferroelectric hysteresis loops of the P(VDF-TrFE) films spin-coated from different molar ratios of VDF/TrFE, 77/23 and 55/45, were measured to select the better mixture. Owing to the better acoustic matching to water, compared with lead zirconate titanate (PZT), the fabricated transducers show relatively wide bandwidth of approximately 50 MHz with high central frequency of 60 MHz obtained at the focal plane when a fused-quartz acts as a reflecting target. Each one of the two finished transducers has a focal length of 5 mm and a full aperture angle of 90°. After applying the specially developed digital signal processing algorithm to the defocusing experiment data, which is called V(f,z) analysis method based on two-dimensional fast Fourier transform (2-D FFT), the operating frequency can extend from several MHz to over 90 MHz. Surface acoustic wave (SAW) velocities of a typical (1 0 0) silicon wafer was measured along various directions between [1 0 0] and [0 1 0] to represent the anisotropic features.     

Magnetic behaviour of nanocrystalline Ni–Cu ferrite and the effect of irradiation by 100 MeV Ni ions

The effects of 100 MeV Ni ion irradiation on magnetic properties of nanoparticles of Ni_0.8Cu_0.2Fe₂O₄ with average particle sizes of 40 Å and 60 Å, synthesized by chemical co-precipitation method have been studied. The spinel cubic structures were confirmed by XRD. The average particle size estimated by XRD and by Langevin function fitting are in good agreement for both the pristine and irradiated samples. The blocking temperature increases with particle size and does not change after irradiation. On irradiation by 100 MeV Ni ions, significant changes in the hysteresis loop features are observed, which may be attributed to formation of cluster of defects in the nanocrystalline samples due to swift heavy ion (SHI) irradiation. It is also found that SHI irradiation produces more dominant changes in the hysteresis loop of smaller particle size of 40 Å as compared to that of 60 Å.     

Raman gain in modified tellurite glasses and thin films

We report the tailoring of Raman spectra of the tellurite glass by varying molar concentrations of phosphates, fluorides in phosphate modified tellurite glasses to analyze the Raman gain. From the measured Raman spectrum, the Raman gain and gain bandwidth in these glasses were calculated and compared. The structural features that give rise to the observed spectra and its dependence on glass composition are identified and reported. Raman gain as high as 170 × 10^? 13 m/W is obtained for glass modified by zinc oxide. Glass thin films prepared by pulsed laser deposition show a Raman gain of 5.0 × 10^? 13 m/W suggesting their importance in short waveguide Raman amplifier fabrication.