X-ray photoelectron spectroscopy investigation of magnetron sputtered Mg–Ti–H thin films

Thin film samples of Mg₈₀Ti₂₀ (Mg–Ti) and Mg, both with and without H, were investigated in a series of X-ray photoelectron spectroscopy (XPS) measurements. The samples were covered with a thin protective layer of Pd, which was removed by Ar⁺ sputtering prior to data acquisition. This sputtering was found to reduce both oxides and hydrides. A distinct, previously unknown peak was revealed in the Mg KLL spectrum of the Mg–Ti–H samples, located between the metallic and the MgO component. This peak was attributed to trapping of H in very stable interstitial sites at the interface between Ti nano-clusters and the Mg matrix, based on earlier density functional theory calculations and supported by so-called Bader analysis. The latter was performed in order to study the theoretical charge distribution between Mg, Ti and H, establishing a link between the position of the previously unknown peak and the effect of H on the valence state of Mg. The composition of the samples was studied both by energy dispersive spectroscopy using transmission electron microscopy and by quantitative XPS analysis. Final state Auger parameters (AP) were obtained for metallic Mg, MgO and MgH₂, as well as Mg affected by trapped H. No difference between the AP values from the metallic components was found between the Mg and the Mg–Ti samples. The AP values for MgO and MgH₂ were consistent with previous reports in literature; several eV lower than the metallic value. Mg in the vicinity of trapped hydrogen, on the other hand, showed a more metallic character, with its corresponding AP value less than 1 eV below the AP for pure Mg.     

CdS thin film post-annealing and Te–S interdiffusion in a CdTe/CdS solar cell

Small area CdTe/CdS solar cells were fabricated using chemical bath deposited CdS and CSS deposited CdTe thin films to investigate the interface properties related to the CdS processing. The effect of post deposition annealing of CdS on the junction properties and the possible interdiffusion at the interface is discussed. The hypothesis of hardening of CdS due to annealing against the diffusion of “S” and “Te” is discussed using the quantum efficiency data in the blue and red regions. Devices prepared using as-deposited CdS films exhibited evidences of higher “S” and “Te” diffusion compared to devices made using CdS films annealed in oxygen. The maximum efficiency of the devices used in this study was 9.8%.     

Physical properties of disordered chalcogenide solar cell from Pb20Ge x Se80 − x thin films

The preparation and study of homogeneous p-n junctions from amorphous chalcogenide Pb₂₀Ge _x Se_{80 ? x} by thermal evaporation are presented. Such p-n junction is a novel module since no one had fabricated such homogeneous cell from these amorphous compounds yet. The p-type layer is Pb₂₀Ge₂₀Se₆₀ and the n-type is Pb₂₀Ge₂₅Se₅₅ elemental analysis of n- and p-types of Pb₂₀Ge _x Se_{80 ? x} is confirmed by energy dispersive X-ray analysis. Optical energy gaps were determined from transmission spectra in the range of 300 to 2500 nm; these values was 1.9 eV for p-Pb₂₀Ge₂₀Se₆₀ and 2.0 eV for n-Pb₂₀Ge₂₅Se₅₅ thin films. The J-V characteristics in the dark are exhibited rectification in the reverse voltage resulting from junction. The reverse current under illumination shows no saturation with voltage. From I-V characteristics under illumination and the spectral response the open circuit voltage V _oc and I _sc were measured. Capacitance measurements are the main method to evaluate doping concentration through the solar cell. The distribution of charged carriers across the depletion region was calculated and interpreted.     

Experimental and thermodynamic evaluation of La1−xSrxMnO3±δ and La1−xSrxCo1−yFeyO3−δ cathodes in Cr-containing humidified air

Chemical and structural stability of strontium doped lanthanum manganite (LSM) and lanthanum cobalt ferrite (LSCF) cathodes in Cr-containing humidified air has been studied by a combination of experimental and thermodynamic approaches. During 100 h tests performed in flowing air (3% H₂O) at 1023 K, the electrochemical performance of LSM/yttria doped zirconia (YSZ)/Pt half-cells exhibited a relatively faster degradation in current (I–t) at 0.5 V applied bias than the LSCF/gadolinium-doped ceria (GDC)/Pt half-cells. Cr species from the gas phase deposited predominantly at LSM/YSZ interface while LSCF showed mainly surface deposition throughout the electrode. Raman spectra indicate SrCrO₄ formation on the post tested LSCF cathode but not on the post tested LSM cathode. The polarization resistance of the LSM cathode also increased significantly compared to that of the LSCF cathode. A linear programming approach coupled with first-principles thermodynamics suggests that the stoichiometric LSM remains stable and unreacted for the whole range of experimental P_CrO3 and temperature conditions whereas the formation of SrCrO₄ on LSC cathode is energetically favored at 1023 K supporting the experimental findings.     

Cu–Ga–Se thin films prepared by a combination of electrodeposition and evaporation techniques

Cu–Ga–Se thin films were prepared using a combination of electrodeposition and evaporation techniques. A Cu–Se/Mo/glass precursor thin film was first prepared by galvanostatic electrodeposition. On top of this film three different thicknesses of Ga were deposited by evaporation. The Cu–Ga–Se thin films were formed by annealing the Ga/Cu–Se/Mo/glass thin film configuration in a tubular chamber with Se powder, at different temperatures. Thin films were characterized by X-ray diffraction (XRD), photocurrent spectroscopy (PS), inductively coupled plasma (ICP) analysis, and scanning electron microscopy (SEM). The detailed analysis from X-ray reveals that after annealing at 550 °C the CuGaSe₂ phase is formed when the thickness of Ga is 0.25 μm, however at 0.5 μm and 1.0 μm Ga the formation of CuGa₃Se₅ and CuGa₅Se₈ phases is observed respectively. Band gap values were obtained using photocurrent spectroscopy.     

Deposition of μc-Si and μc-SiC thin films by remote plasma-enhanced chemical-vapor deposition

This paper describes properties of microcrystalline silicon (μc-Si), and microcrystalline silicon-carbon (μc-SiC) thin films formed by the process of remote plasma-enhanced chemical-vapor deposition (PECVD). We discuss: (i) the way that the remote PECVD deposition process is applied to the deposition of μc-Si and μc-SiC thin films; (ii) the characterization and properties of the intrinsic and doped μc-Si thin film materials; (iii) the characterization and properties of the intrinsic and doped μc-SiC thin film materials; and (iv) the application of remote PECVD μc-Si and μc-SiC thin films in device structures.     

Chemical solution deposition and characterization of the La1-хSrxScO3-α thin films on La1-xSrxMnO3-α substrate

The development of solid oxide fuel cells (SOFC) is one of the priority directions for the creation of alternative energy sources. High operating temperatures of these devices are lead to the complexity of the constructions and active diffusion processes between the functional materials. The use of thin-film proton electrolytes is a promising way to reduce the operating temperature of SOFC, while the conductivity level and, as a result, the effective power, may be maintained due to the smaller thickness of the film.Based on LaScO₃ proton-conducting oxides with a perovskite structure, having high chemical stability to water vapor, are promising proton electrolytes for SOFC, but they are poorly studied in the form of thin films. Lanthanum-strontium manganite is one of the most common materials for the SOFC cathode. The aim of this work is to study the effect of the La_0.6Sr_0.4MnO_3-α cathode substrate composition on the properties, including the electrical conductivity of La_1-xSr_xScO₃ (0.01, 0.05 and 0.10) thin-film proton electrolytes, obtained by simple centrifugation of the film-forming solution. The properties of La_1-xSr_xScO₃ in the form of ceramic and thin-film samples are compared.The experiment showed that the films La_1-xSr_xScO₃ at 5 ÷ 30-fold deposition on cathode substrates form continuous coatings with a grain size of 50–200 nm, which do not contain transverse pore. These results have a fundamental importance for the development of SOFC with ultra-thin film electrolyte on a supporting electrode. It is established that under dry and wet air the electrical conductivity of La_0.6Sr_0.4MnO_3-α/La_1-xSr_xScO₃/Pt cells is bulk conductivity and it rises with increasing atmospheric humidity, which indicates an increase in the contribution of proton conductivity. In this case, the grain-boundary resistance of the material and the polarization resistance of the electrodes are practically not realized. The conductivity of LSS films is 1–2 orders of magnitude higher than the bulk conductivity of ceramic samples of similar composition and has a low activation energy. The observed differences in the conductive properties of films are explained by the interaction of related perovskites of the scan date and lanthanum manganite.The data obtained may be of interest to specialists in the fields of hydrogen energy, electrochemistry, materials science, the development of electrochemical devices: sensors, fuel cells.     

Physical properties of the CNT:TiO2 thin films prepared by sol–gel dip coating

Uniform and highly adherent thin films of CNT:TiO₂ were synthesized by sol–gel dip coating method. Both TiO₂ and CNT:TiO₂ films showed very identical structural characteristics and no significant changes in the lattice values were observed. The crystalline size decreased from 20 nm for TiO₂ film to 17 nm for the 4%CNT:TiO₂ film. The film surface was very smooth and compact, as indicated by the roughness data obtained from AFM measurements; the root mean square (rms) average of the roughness was as low as 3 nm. The HRTEM showed that the CNTs are embedded in the matrix of TiO₂ indicating the formation of a composite. In Raman spectra the characteristic vibrations of the TiO₂ are identified, the increase in the FWHM of main anatase peak (144 cm^?1) in the case of the 4%CNT:TiO₂ film is interpreted as due to the incorporation of CNTs in the film. At the wavelength of 600 nm the refractive index of pure TiO₂ was 2.07 and the 4%CNT:TiO₂ showed a value of 2.29. The photoresponse curves showed typical features of charge trapping centers in the band gap of the films.     

Novel high temperature proton conducting fuel cells: Production of La0.995Sr0.005NbO4−δ electrolyte thin films and compatible cathode architectures

For breakthrough development in solid oxide fuel cells, novel cell architectures integrating better performing materials and cost-effective manufacturing processes with potential for mass production must be realised. The present work addresses this on the basis of the recent discovery of acceptor doped rare-earth ortho-niobate proton conductors and the development of a versatile fabrication process. La_0.995Sr_0.005NbO_4−δ/NiO anodes are produced by tape-casting and co-lamination of green layers. Their porosity is finely tuned by using a pyrolyzable pore former. La_0.995Sr_0.005NbO_4−δ electrolytes are spin-coated using ceramic-based suspensions. Fully dense electrolytes with thickness ranging from 9 μm to 26 μm are obtained after sintering in air at 1350 °C. The cathode layers are then screen-printed. To match thermal expansion and to avoid chemical reaction between the functional layers, special attention is paid to the design of cathode architectures. CaTi_0.9Fe_0.1O_3−δ, La₂NiO_4+δ and La₄Ni₃O₁₀ mixed oxygen ion and electron conducting oxides are investigated as either monophase or La_0.995Sr_0.005NbO_4−δ-based composite electrodes. The latter gives the whole cell an innovative “semi-monolithic” concept, which can take advantage of the chemical and mechanical stability of La_0.995Sr_0.005NbO_4−δ, as well as of inherent material integration. Most promising cell architectures are finally selected based on thermo-mechanical and chemical compatibility of all functional layers.     

The effective light-harvesting performance of graded compositional AlxGa1−xN nano-cone arrays photocathode for ultraviolet detector—A numerical investigation and simulation

A graded compositional Al_xGa_1−xN nanomaterial with a built-in electric field has been proposed to improve the quantum efficiency of the negative electronic affinity photocathode. When the graded compositional Al_xGa_1−xN nano-cone array is applied to the ultraviolet (UV) detector, it is necessary to improve the effective light absorption, which is high absorption in the UV short-wavelength and high sensitivity in the threshold wavelength. Therefore, the light absorption of nano-cone arrays with different feature sizes and geometrical properties is accurately calculated innovatively based on the finite-difference time-domain method. Studies show that a non-close-packed six-sided pyramid structure with a fill factor of 42.44% and a height of 1000 nm has an absorption spectrum that better satisfies the response characteristics of the UV detector. Surface reflection depends to a large extent on the transformation of the angle of incidence. The optical absorption properties of the graded compositional Al_xGa_1−xN nano-cone array provide flexibility and reference value for the improvement of the absorption coefficient and other parameters in the actual quantum efficiency experiment of the UV photocathode with built-in electric field, which can realize the highest sensitivity of various designed UV detector optical system.     

Fabricating NixCo1−xO@C cocatalysts sensitized by CdS through electrostatic interaction for efficient photocatalytic H2 evolution

Exploiting efficient and stable noble metal-free hydrogen evolution catalysts for water splitting is of great importance. In this work, Ni_xCo_1-xO@C/CdS hybrid is successfully fabricated through an electrostatic interaction of oppositely charged nanoparticles on their surfaces. The resulting Ni_xCo_1-xO@C nanoboxes cocatalysts which were derived from NiCo-LDH@ZIF-67 with Ni–Co layered double hydroxides (LDH) decorated with ZIF-67 precursor exhibited improved hydrogen production rate compared with bare CdS semiconductor from 0.7 mmol g⁻¹ h⁻¹ to 56 mmol g⁻¹ h⁻¹. It is demonstrated that the electrostatic interaction between the two surface charged nanoparticles of Ni_xCo_1-xO@C and CdS play an important role in migrating and separating of photogenerated charge carriers. The synthesized Ni_xCo_1-xO@C as excellent candidates for cost-effective cocatalysts is aimed to substitute for noble metals in photocatalytic H₂ evolution.     

Wavelength-dependent photoactivity of ZnxCd1−xS and ZnCo2O4/ZnxCd1−xS for H2 and H2O2 production

Zinc cadmium sulfide (Zn_xCd_1?xS) is a good photocatalyst for hydrogen evolution reaction (HER), but an optimum x (x_m) at which a maximum HER rate is reached varies from one report to another. In this work, we examine the effect of light wavelength, not only for the HER to H₂ in the presence of Na₂S and Na₂SO₃, but also for oxygen reduction reaction (ORR) without addition of any sacrifices. For the HER under a 365 and 420 nm LED lamp, the x_m were 0.9 and 0.7, respectively. For the HER under a 330 and 395–515 nm cut-off xenon lamp, the x_m were 0.7 and 0.5, respectively. For the ORR under a 420 nm cut-off halogen lamp, a maximum production of H₂O₂ was observed at x = 0.3. Furthermore, after 4% ZnCo₂O₄ loading, Zn_xCd_1?xS had an increased activity and stability, either for the HER or for the ORR. Through a (photo)electrochemical measurement, it is proposed that the photocatalytic activity of Zn_xCd_1?xS is determined by its light absorptivity and electron reactivity. The improved performance of n-type Zn_xCd_1?xS by p-type ZnCo₂O₄ is due to formation of a p-n junction, promoting the HER (ORR) on Zn_xCd_1?xS, and the sulfide (water) oxidation on ZnCo₂O₄. This work highlights that Zn_xCd_1-xS is a promising photocatalyst for H₂ and H₂O₂ production, respectively.     

LiN1 − xCoxCoxO2 prepared at low temperature using β-Ni1 − xCox OOH and either LiNO3 or LiOH

LiNi_{1 − y}Co_yO₂ has been prepared at 400 °C by using β-Ni_{1 − y}Co_yOOH and either LiNO₃ or LiOH. The mechanism of these reactions was clarified by differential thermal and thermogravimetric analyses. The material prepared with LiNO₃ is well crystallized because LiNO₃ melts and then reacts with the oxyhydroxide in a viscous state. However, when LiOH is used, a solid-solid diffusion reaction takes place and leads to a material with broad X-ray diffraction peaks. The electrochemical characteristics of these materials were evaluated and compared with those prepared by the usual processes at high temperature.     

Production of syngas from carbon dioxide reforming of methane by using LaNixFe1−xO3 perovskite type catalysts

A series of bulk and supported LaNixFe1-xO3 catalysts were synthesized, characterized and studied for dry reforming of methane (DRM) reaction. The catalysts were synthesized using sol-gel, incipient wetness impregnation (IWI) and co-precipitation methods. The catalysts were characterized by BET, XRD, FE-SEM, H2-TPR, and FTIR spectroscopy. A specific type of perovskite phase was obtained while changing the ratio of Ni to Fe for the synthesis of LaNixFe1-xO3 perovskite catalyst. The addition of supports increased the dispersion of perovskite phase, surface area and pore volume of the bulk perovskite catalysts. The support silica destroyed the perovskite features of the catalysts at higher calcinations temperature. The most active catalyst was found to be 40LaNi0.75Fe0.25O3/SiO2 calcined at 973 K for the DRM reaction with ratio of CH4:CO2:N2 as 1:1:2. The highest conversion corresponded to the catalyst calcined at 1073 K. However, the highest products yields and selectivity obtained while the catalyst was calcined at 773 K for 1 h. Thus, the choice of Ni to Fe ratio, support, method of synthesis and catalyst calcination temperature were crucial factors while synthesizing and designing a perovskite catalyst for dry reforming of methane reaction.