Study of boron doping in MPCVD grown homoepitaxial diamond layers based on cathodoluminescence spectroscopy, secondary ion mass spectroscopy and capacitance-voltage measurements

Boron incorporation from the gas phase was achieved in MPCVD grown (100)-oriented homoepitaxial diamond layers, either with or without a small fraction of oxygen in the gas phase, in addition to hydrogen, methane and diborane. From secondary Ion Mass Spectroscopy (SIMS), it is shown that the 0.25% of oxygen decreases the Boron concentration [B] by two orders of magnitude. In this way, we demonstrate that it becomes possible to control [B] with low levels of compensation and passivation down to the 10¹⁵ cm^− 3 range. Cathodoluminescence spectroscopy is systematically performed in seventeen samples under a 10 kV acceleration voltage at 5 K and the exciton bound to boron (BE_TO) intensity to the free exciton (FE_TO) intensity ratio is evaluated (I_BETO/I_FETO). A linear relationship between I_BETO/I_FETO and [B] with a coefficient of 3.5 × 10¹⁶ cm^− 3 is demonstrated for [B] < 3 × 10¹⁷ cm^− 3 in single crystalline diamond, irrespective of the gas phase composition during growth.     

Ionic conductivity, infrared and Raman spectroscopic studies of 1-methyl-3-propylimidazolium iodide ionic liquid with added iodine

Polyiodides (I_x⁻, x = 3 and 5) and 2I⁻…I₂ adducts were established from the Raman spectra study of 1-methyl-3-propylimidazolium iodide (MPIm⁺I_x⁻; 1 ≤ x ≤ 5) ionic liquids containing various amounts of iodine (0 mol ≤ I₂ ≤ 2 mol). The existence of I₃⁻ and 2I⁻…I₂ was established for 1 ≤ x ≤ 2.5, symmetric I₃⁻ ions for x = 3, while linear and discrete I₅⁻ was substantiated for 3 ≤ x ≤ 5. The presence of polyiodide species in MPIm⁺I_x⁻ (1 ≤ x ≤ 5) was correlated with an enhanced ionic conductivity, attributed to the established relay-type Grotthus mechanism. Two-step conductivity increase was also reflected in decrease of the hydrogen bond interactions between the CH ring groups and polyiodides. While in the concentration range 1 ≤ x ≤ 3 (triiodides and tetraiodides) IR bands changed only slightly in intensity, in the concentration range x > 3 the CH stretching bands (3040-3170 cm⁻¹) split and the new band at 1585 cm⁻¹ appeared in the IR spectra beside the already existing Im⁺ ring stretching mode at 1566 cm⁻¹.     

Orientation of graphitic planes during annealing of “dip deposited” amorphous carbon film: A carbon K-edge X-ray absorption near-edge study

Annealing effect of amorphous carbon thin films on Si(1 0 0) substrates is studied by normal incidence and angle dependent carbon K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The angle dependence of the XANES signal shows that the graphitic basal planes are oriented perpendicular to the surface when the film is annealed at 1000 °C. Micro-Raman spectroscopy reveals two well-separated bands the D band at 1355 cm⁻¹ and G band at ∼1600 cm⁻¹, and their I_D/I_G intensity ratio indicates the formation of more graphitic film at higher annealing temperatures. X-ray diffraction pattern of 1000 °C temperature annealed film confirms the formation of graphite structure.     

Application of poly(acrylic acid-g-gelatin)/polypyrrole gel electrolyte in flexible quasi-solid-state dye-sensitized solar cell

A novel gel polymer electrolyte based on poly(acrylic acid-g-gelatin)/polypyrrole with conductivity of 14.1 mS cm⁻¹ was prepared. Based on the gel electrolyte, a flexible quasi-solid-state dye-sensitized solar cell was fabricated by using a low-temperature filming technique. Owing to high conductivity and the catalytic function of polypyrrole for I⁻/I₃⁻ redox reaction for the gel electrolyte, the flexible quasi-solid-state dye-sensitized solar cell showed a light-to-electric energy conversion efficiency of 1.28%, under a simulated solar light irradiation with intensity of 100 mW cm⁻² (AM 1.5).     

A polyblend electrolyte (PVP/PEG+KI+I2) for dye-sensitized nanocrystalline TiO2 solar cells

A novel polyblend electrolyte consisting of KI and I₂ dissolved in a blending polymer of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) was prepared. The formation of ⁻I₃ in the polymer electrolyte was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Due to the coordinating and plasticizing effect by PVP, the ionic conductivity of the polyblend electrolyte is enhanced. The highest ionic conductivity of 1.85 mS cm⁻¹ for the polyblend electrolyte was achieved by optimizing the compositions as 40 wt.% PVP + 60 wt.% PEG + 0.05 mmol g⁻¹ I₂ + 0.10 mmol g⁻¹ KI. Based on the polyblend electrolyte, a DSSC with fill factor of 0.59, short-circuit density of 9.77 mA cm⁻², open-circuit voltage of 698 mV and light-to-electricity conversion efficiency of 4.01% was obtained under AM 1.5 irradiation (100 mW cm⁻²).     

Rapid formation of high-quality self-assembled monolayers of dodecanethiol on polycrystalline gold under ultrasonic irradiation

Self-assembled monolayers of dodecanethiol (C₁₂SH-SAMs) on polycrystalline gold were prepared under ultrasonic irradiation at 100 W (the actual ultrasonic power intensity is about 0.1 W cm⁻² including the heat loss) for different time and investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV experiments show that the differential capacitance C_d values of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min are independent of the scan rate, the thickness d value of this monolayer is 17.5 Å, the tilt angle φ value of the molecules in this monolayer from the gold surface normal was calculated to be 30° and the difference value of the current density at −0.2 and 0.5 V (Δi_p) is only 0.69 μA cm⁻². From the EIS experiments, we find that the phase angle value at 1 Hz Φ_1 Hz of the C₁₂SH-SAM prepared under ultrasonic irradiation at 100 W (0.1 W cm⁻²) for 15 min is 89°, the charge transfer resistance R_ct value of this monolayer is 1.40 × 10⁶ Ω cm² and the surface coverage θ value of this monolayer was calculated to be 99.997% from R_ct. These results indicate that the C₁₂SH-SAM of almost defect-free structure and very low ionic permeability can be formed under ultrasonic irradiation at 100 W (0.1 W cm⁻²) in a short time (15 min).     

A solar regenerable cathodic electron acceptor for microbial fuel cells

In this study, a high performance and solar regenerable cathodic electron acceptor, I₃⁻, was incorporated into a microbial fuel cell (MFC). Linear sweep voltammetry showed that a current density of 4.2 mA cm⁻² can be obtained from the electroreduction of I₃⁻. This value was approximately twice that of ferricyanide (Fe(CN)₆³⁻) and was independent of the pH of the electrolyte. The effect of regeneration conditions, such as the pH of the KI solution, KI concentration, oxygen flow rate and the Xe light intensity, on the I₃⁻ yield and performance of the MFC was investigated. A sufficient supply of I₃⁻ was achieved when the concentration of an air-saturated KI solution was greater than 0.2 M and its pH was around 2.0, under an irradiation higher than 300 mW cm⁻². Extended operation of the MFC showed that I₃⁻ is capable of supporting the MFC for long-term electricity generation. The maximum power output of the MFC using a catholyte containing 1.2 mM I₃⁻ + 0.2 M KI solution was 484.0 mW m⁻². This performance was greater than that (307.1 mW m⁻²) when using a catholyte containing 1.2 mM Fe(CN)₆³⁻ + 0.2 M KCl solution under the same conditions.     

The role of textural characteristics and oxygen-containing surface groups in the supercapacitor performances of activated carbons

It is suggested that the specific capacitance C₀ of activated carbons at low current densities (d ∼ 1 mA cm⁻²) consists, to a good first approximation, of two contributions. For the H₂SO₄ electrolyte they correspond to approximately 0.080 F m⁻² from the total accessible surface area and an additional pseudo-capacitance of 63 F mmol⁻¹ from the surface species generating CO in thermally programmed desorption (TPD). The new correlation proposed here is an alternative to Shi's earlier approach which considered contributions from the microporous and the external surface areas. Furthermore, it appears that the variation of the specific capacitance C at high current densities d (up to 100-150 mA cm⁻²) depends essentially on the CO₂-generating surface groups and on 1/L₀, the inverse of the average micropore width.     

Pulsed electrodeposition of bismuth telluride films: Influence of pulse parameters over nucleation and morphology

Pulsed electrodeposition methods were applied to the preparation of bismuth telluride films. Over the potential ranges from −170 mV to −600 mV, the formation of Bi₂Te₃ nuclei proceeded through a three-dimensional instantaneous nucleation mode. The nuclei densities for several values of potential were ranged between ∼10⁶ nuclei cm⁻² and ∼10⁸ nuclei cm⁻². For a pulsed galvanostatic electroplating, the best covering percentage and a stoichiometry close to the desired Bi₂Te₃ were obtained with the parameters t_on, t_off and J_c, respectively, equal to 10 ms, 1000 ms and −100 mA cm⁻².     

Regeneration of a solid waste from an edible oil refinery

This work presents a valorization of a solid waste originating from an edible oil refinery called spent bleaching earth (SBE). The SBE material is first impregnated with an ammonium chloride solution (3 M), then treated directly in furnace at 400 °C during an hour followed by a washing in the cold by HCl 1 M. To elucidate the changes in its crystalline structure, induced by the regeneration method, the obtained material (RSBE) is characterized by several physicochemical methods (X-ray diffraction, FTIR, thermal analysis, BET and SEM). The characterization results show that the heat treatment in furnace and the chemical treatment (decomposition of NH₄Cl) don’t affect the structure of montmorillonite of regenerated material (RSBE). The study of porous texture by the nitrogen adsorption technique at −196 °C shows that the specific surface area S_BET and the pore volume increased in the RSBE material compared to those of virgin bleaching earth VBE (unused) and their values are respectively of 145.68 against 115.5 m² g⁻¹ and of 0.287 against 0.234 cm³ g⁻¹. Calculations by the adsorption equations using BJH method, applied to both materials, show that the treatment generate an increase in the micropores in the RSBE material. We belonged the values of the micropores area of S_mic = 41.98 cm² g⁻¹ and of V_mic = 0.074 cm³ g⁻¹ for the volume.     

Raman spectroscopy studies of carbide derived carbons

The Raman spectra of a number of carbide derived carbons (CDCs) synthesised from TiC at 700, 800, 900, 1000, 1100 and 1200 °C and from VC, WC, TaC, NbC, HfC and ZrC made at 1000 °C have been recorded using laser excitation wavelengths of 514 and 785 nm. The spectra show two main features, the D- and G-peaks situated around 1350 cm⁻¹ and 1600 cm⁻¹, respectively. The peak positions, their intensities (I_D/I_G) and full width at half maximum (FWHM), as well as their wavelength dependent dispersion, were used to obtain information about the degree of disorder in CDCs. The increasing ordering with synthesis temperature was confirmed by lower FWHM values obtained from CDCs made at higher synthesis temperatures. However, this parameter was not very sensitive to variation in ordering in CDCs made at 1000 °C from different carbides. The I_D/I_G was used for determination of the in-plane correlation length, which has shown to be independent of synthesis temperature and more sensitive to the choice of the precursor carbide. However, the changes in in-plane correlation length were small and barely accounted for the size of one sixfold ring.     

Preparation, characterization and electrocatalytic properties of an iodine|lignin-modified gold electrode

Hydrolytic lignin (HL) was adsorbed from an aqueous/organic solution on bare and iodine-modified gold electrode. Subsequent electrooxidation of the lignin adsorbate generated redox-active quinone-based groups in the biopolymer structure, exhibiting high reversibility during potential cycling and fast electron transfer kinetics. The presence of the chemisorbed iodine layer on the supporting gold electrode had a pronounced effect on the electrochemical properties of the final modified electrode in terms of double-layer capacitance (C_dl) and the observed surface coverage (Γ_obs). The high electrochemical activity in connection with low C_dl made it possible to apply the Au|I_(ads)|HL electrode as a fast-responding and sensitive electrochemical sensor for NADH. When tested in the amperometric mode at a constant potential of +0.4 V vs. Ag/AgCl, the modified electrode showed a linear current-concentration response over the range of 5-120 μM with a sensitivity of 2.39 nA μM⁻¹ cm⁻² and a detection limit of 1.0 μM (S/N = 3). Kinetic studies using the rotating disk electrode revealed that the mediated oxidation of NADH on the Au|I_(ads)|HL electrode was limited by the second order reaction of the analyte molecules with o-quinone moieties with a rate constant of ca. 4.7 × 10² M⁻¹ s⁻¹ (C_NADH → 0). The modified electrode showed high resistivity against fouling and retained ca. 65% activity after storage in phosphate buffer (pH 7.4) at room temperature for 1 week.     

Facile in situ template synthesis of sulfonated polyimide/mesoporous silica hybrid proton exchange membrane for direct methanol fuel cells

Highly conductive and hydration retentive organic-inorganic hybrid proton exchange membranes for direct methanol fuel cells were synthesized by in situ sol-gel generation of mesoporous silica (mSiO₂) in sulfonated polyimide (SPI) via self-assembly route of organic surfactant templates for the tuning of the architecture of silica. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The mesopores of about 3 nm in silica dispersion phase were formed in the SPI matrix. The existence of the mesoporous structure of silica improved the thermal stability, water-uptake and proton conductivity as well as methanol resistance of the hybrid membranes. The hybrid membrane with 30 wt.% mSiO₂ exhibited the water-uptake of 44.8% at 25 °C, and proton conductivity of 0.214 S cm⁻¹ at 80 °C at RH = 100%, while pure SPI exhibited the values of 40.6% and 0.179 S cm⁻¹ in the same test conditions, respectively. The results suggested that the highly hydrophilic character of Si-OH groups and the large surface area of mSiO₂ should contribute to the improvement of the water-uptake, meanwhile the mesoporous channels may supply the continuous proton conductive pathway in the hybrid membranes.     

Influence of halides on the dissolution and passivation behavior of AZ91D magnesium alloy in aqueous solutions

The electrochemical behavior of AZ91D in various aqueous sodium halide solutions was investigated using open-circuit potential (E_oc), potentiodynamic polarization and ac impedance (EIS) techniques. Generally, the results reveal that during immersion a protective layer of a salt film is formed on the alloy surface whose passivation performance depends on the halide nature, its concentration and temperature. E_oc shifts positively with time until attaining a steady (E_st) value, which becomes less noble with increasing concentration or temperature of the test solution. At any given conditions, self-passivation was found to be favored in the order F⁻ > I⁻ > Br⁻ > Cl⁻. This sequence is consistent with that for surface film resistance (R_T) and its relative thickness (1/C_T). Nevertheless, in F⁻ medium each of the above parameters increases with [F⁻] up to a critical value of 0.3 M then decreases. Increasing concentration above 0.3 M induces large change in the microstructure of the outermost layer of the fluorinated extremely protective film and depassivation behavior predominates. In Br⁻ and I⁻ solutions, as well as the lower Cl⁻ concentrations (≤0.01 M), AZ91D exhibits pseudo-passive state over the polarization range from the corrosion potential (E_corr) to the knee point (E_pt) in the anodic scan, at which passivity breakdown occurs with rapid increase in the anodic current and hydrogen gas reaction. At Cl⁻ concentrations >0.01 M the negative difference effect (NDE) occurs under cathodic polarization where E_pt lies negative to E_corr. Addition of F⁻ to the Cl⁻ solution can induce large changes in the behavior of AZ91D. Equal concentration addition (1:1) produces the highest propensity of the surface to form passivating layer that can afford better protection.     

Detection of N-methyladenosine in urine samples by electrochemiluminescence using a heated ITO electrode

A sensitive and rapid electrochemiluminescence (ECL) method for the detection of N⁶-Methyladenosine (m6A) in urine samples on a heated indium-tin-oxide (ITO) electrode is presented. The ECL intensity of Tris(2,2′-bipyridyl) dichlororuthenium(II)hexahydrate (Ru(bpy)₃²⁺) can be enhanced by the presence of m6A. Experimental results showed that the change of ECL intensities (ΔI) of the Ru(bpy)₃²⁺ between before and after addition of m6A was affected by the working electrode surface temperature (T_e); the highest ΔI occurred at 31 °C. Under optimum conditions, the ΔI had a linear relationship with the m6A concentration in the range of 1.9 × 10⁻⁹-3.9 × 10⁻⁶ mol/L and a detection limit of 7.7 × 10⁻¹⁰ mol/L (S/N = 3) at T_e = 31 °C. The recovery of m6A standards added to urine samples verified the accuracy of the proposed method.     

XPS and flow-cell EQCM study of albumin adsorption on passivated chromium surfaces: Influence of potential and pH

The adsorption of albumin (BSA: bovine serum albumin) on passivated chromium surfaces was studied in deaerated sulphate solutions as a function of potential (in the passive state) and pH (from 4 to 10). In situ switch-flow cell EQCM measurements were coupled to ex situ XPS analyses. EQCM results showed that (i) the initial adsorption rate is about 3.3 ng cm⁻² s⁻¹ which corresponds to 3 × 10¹⁰ molecules cm⁻² s⁻¹, irrespective of the passive potential and pH, and (ii) the passive potential as well as the pH have no influence on the amount of adsorbed BSA (Δm = 440 ± 70 ng cm⁻² on the adsorption plateau). From the XPS N 1s and C 1s signals, which provide a fingerprint for the protein, it can be concluded that BSA is adsorbed on the Cr surface and is chemically intact. The XPS results show that (i) when increasing the passive potential, the oxide layer thickness increases (mean value: d_ox = 2.2 ± 0.2 nm), and (ii) the passive film is not modified by the adsorption of protein. From combined EQCM and XPS data, a full coverage of the Cr surface by the adsorbed proteins (γ = 1) is demonstrated at pH 4 (whatever the passive potential). The thickness of the continuous BSA layer (h_BSA) is 3.3 ± 0.3 nm, which corresponds to one monolayer “side-on”, i.e. oriented parallel to the surface. At pH 5.5 and 10, the adsorbed proteins form islands. The surface coverage is much lower (γ ∼ 0.5), and the height of the protein islands is significantly higher (h_BSA ∼ 6.5 nm). The results suggest a strong interaction (partially covalent) between the protein and the passivated chromium surface.     

Structural and electrochemical characterization of SnOx thin films for Li-ion microbattery

SnO_x thin films were prepared by reactive radio frequency magnetron sputtering with different sputtering powers. X-ray photoelectron spectroscopy suggested that all the films have similar chemical stoichiometry as SnO_1.5. X-ray diffraction and transmission electro microscopy results showed that crystal size of the SnO_x thin films gradually increases with increase of sputtering power from 50 to 150 W. Cyclic voltammetry and galvanostatic charge/discharge cycling measurements indicated that the electrochemical properties of SnO_x films strongly rely on their crystal sizes as well as surface morphologies. The SnO_x film deposited at sputtering power of 120 W exhibits the best electrochemical performances. It could deliver a reversible capacity of 670 μAh cm⁻² μm⁻¹ at 50 μA cm⁻² in the voltage range of 0.1-1.2 V up to 50 cycles.     

Influence of ionic additives NaI/I2 on the properties of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

The ionic additives NaI/I₂ in polymer gel electrolyte not only provide cations, but also affect the liquid electrolyte absorbency of the poly(acrylic acid)-poly(ethylene glycol) hybrid, which results in the change of ionic conductivity of polymer gel electrolyte and the photovoltaic performance of quasi-solid-state dye-sensitized solar cell. With the optimized components of liquid electrolyte containing 0.5 M NaI, 0.05 M I₂, 0.4 M pyridine, 70 vol.% γ-butyrolactone and 30 vol.% N-methylpyrrolidone, a 4.74% power conversion efficiency of quasi-solid-state dye-sensitized solar cell was obtained under 100 mW cm⁻² (AM 1.5) irradiation.     

Recovery of triglycerides from used frying oil by extraction with liquid and supercritical ethane

The extraction of triglycerides from used frying oil with liquid and supercritical ethane has been studied in a semibatch system at different temperatures (25-80 °C) and pressures (150-250 kg/cm²). It has been found that isobaric decreases of temperature and isothermal increases of pressure lead to both increasing extraction yields and decreasing separation efficiencies. Lipid fractions recovered in the high density region had acceptable concentrations of polar compounds.Results with ethane have been compared to those reported for CO₂ in earlier works. At similar reduced densities of the solvents, oil solubility in ethane was higher than in CO₂, being the separation efficiency of polar fractions slightly better when using ethane.The extraction process was further analyzed in a packed countercurrent column. At optimum conditions (250 kg/cm², 25 °C, and solvent-to-oil ratio 45 g:g) about 85% of the triglycerides were recovered, being 11.2% the polar content of the triglyceride fraction recovered.     

Redox and photochemical behaviour of a porphyrin monolayer on an indium-tin oxide electrode

In order to investigate photoluminescence behaviour of an ordered molecular porphyrin monolayer and its quenching properties by oxygen gas, a porphyrin with long alkyl chains, 5,10,15,20-tetrakis[4-(11-carboxylundecane-1-oxy)phenyl]porphyrin (4), was synthesized and adsorbed onto an indium-tin oxide (ITO) substrate by a chemical dipping method. Cyclic voltammetry was used to analyze the ITO electrode coated with 4. The peak current of the first oxidation was proportional to the sweep rate, and the surface coverage was estimated to be 2.3-2.5 × 10⁻¹⁰ mol cm⁻². The UV-vis spectrum of the monolayer showed a broadened Soret band, which shifted to longer wavelength. These features suggest that the porphyrin moieties of 4 are packed to form a J-type structure. The oxygen quenching ratio of the porphyrin 4 monolayer on the ITO electrode, I₀/I₁₀₀, was estimated to be 1.25, where I₀ and I₁₀₀ are, respectively, luminescence intensity values in 100% argon and 100% oxygen. On repeated step cycling between 100% argon and 100% oxygen atmospheres, the response times of luminescence quenching were 10 s (argon to oxygen) and 23 s (oxygen to argon). These findings suggest that a monolayer of sensing dye is applicable for oxygen sensing system without deterioration of size-accuracy of models.