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In this study, density functional theory has been used to investigate the structural and electronic properties of lead selenide (PbSe) and lead sulfide (PbS) semiconductors and their alloys PbSe1-xSx using the virtual crystal approximation (VCA) and random structure (RS) generations. The generalized gradient approximation (GGA) has been used to obtain lattice parameters which are compared with theory and experimental results. The generalized gradient approximation (MGGA) of TB09LDA has been used to calculate the electronic bands, for different sulfur compositions (0≤x≤1, ∆x=0.1). It has been observed that the transition from the valence band to the conduction band takes place at the L point, which agrees with previous theoretical investigations. It has been observed that both the bandgap and lattice parameters of the alloys obey Vegard's law. Effective band diagrams obtained from the unfolding of supercell band diagrams, reported for the first time for this system, show that the impacts of alloy disorder are low in the vicinity of the L point, indicating that the alloy composition do not appear to influence the transport phenomena. This work shows the suitability of the VCA approximation and the band unfolding method, to deal and describe the composition-dependent properties of the PbSe1-xSx pseudo binary alloys.

The electrical and mechanical properties of carbon fiber-reinforced polymer (CFRP) composites have a close dependence on the use of modifiers like polyvinylpyrrolidone (PVP), as well as on the processing techniques to disperse functional charges such as graphene-related materials into the epoxy base. In the present work, reduced graphene oxide (RGO), prepared by a natural antioxidant agent, astaxanthin, was used as a filler material in the epoxy matrix of the carbon fiber composites. The astaxanthin reduction leads to an increase in the sp2 ordering in RGO; some residual epoxy and C-O groups that enhance the interaction with the epoxy matrix remain after reduction. The effects of RGO and PVP-modified RGO (PVP-RGO) fillers with different contents (0.05, 0.1, and 0.15% wt.) on the electrical conductivity, bending properties, and dynamic mechanical properties of CFRP were investigated. The incorporation of 0.15 wt.% RGO with and without PVP-modification, leads to through-the-thickness (Z-direction testing) conductivity values 7.4 and 9.6 times higher than those of the neat composite, respectively. The conductivity tests indicate that the RGO/epoxy composite behaves as a continuous conductor due to the formation of agglomerates of RGO within the matrix, while at the added contents of the PVP-RGO filler, the composite is below the percolation threshold, then conducting by electron tunneling, due to a better dispersion of the PVP-RGO filler within the epoxy matrix. The dynamic mechanical analysis shows that the glass transition temperature is indicative of the interactions among the filler, the epoxy matrix, and the carbon fiber, that is, the PVP-RGO filler increases the chain mobility due to its higher dispersion in the matrix. While Tg of the neat epoxy/CFRP composite is 92.5°C, a minimum Tg of 88.5°C was achieved with a 0.10 % wt. PVP-RGO filler contents, and a maximum Tg of 94.5°C with a 0.15 % wt. of RGO filler amount. For constant filler content (0.15 wt.%), CFRP composite containing RGO and PVP-modified RGO exhibited 9.73% and 13.87% increase in flexural strength values, respectively, compared to the neat composite. The bending test revealed that PVP modification to RGO is beneficial to improve flexural strength of CFRP composites.

Catharanthus roseus (Apocynaceae family) extract is rich in organic phytochemicals such as alkaloids, polyphenolic compounds, and flavonoids. It contains several functional entities such as fused heterocycles, and hydroxyl and carbonyl groups, which could be useful for corrosion inhibition of mild steel in NaCl environments. In the present work, ultrasonic energy was used to obtain the ethanolic extracts of root and stem which were then tested as corrosion inhibitors for mild steel in the presence of 3.5% NaCl. The corrosion inhibition process was studied by UV-visible spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, weight loss, and electrochemical methods. After immersing in the corrosive medium, the microstructures of mild steel were investigated by scanning electron microscopy, X-ray diffraction, and ellipsometry. The extract of C. roseus showed excellent adsorption on mild steel surface as confirmed by DFT calculations. The results indicate that the extract of C. roseus acts as a mixed type corrosion inhibitor, where the stem extract is the most efficient inhibitor in 3.5% NaCl solution possibly due to the higher active area of stem phytochemicals.

We report the synthesis of AlN hexagonal thin films by pulsed laser ablation, using Al target in nitrogen ambient over natively-oxidized Si (111) at 600°C. Composition and chemical state were determined by X-ray photoelectron spectroscopy (XPS); while structural properties were investigated using X-ray diffraction (XRD). High-resolution XPS spectra present a gradual shift to higher binding energies on the Al2ppeak when nitrogen pressure is incremented, indicating the formation of the AlN compound. At 30 mTorr nitrogen pressure, theAl2p peak corresponds to AlN, located at 73.1 eV, and the XRD pattern shows a hexagonal phase of AlN. The successful formation of the AlN compound is corroborated by UV-Vis reflectivity measurements.

The local atomic structure of multilayer films of graphene oxide, cadmium sulfide, and cadmium sulfide–selenide was analyzed by X-ray absorption fine structure spectroscopy. The films were prepared...

Ti6Al4V alloy is light weight and is used in construction, oil industries and airbus, automobile, and bio implant materials. The native oxide layers of the alloy are not stable at high temperatures and strong mineral acid environments. The conventional epoxy-based layers are porous and the alloy finally fails in the harsh environment in the long term. Therefore, the carbon-based functional materials are being proposed as coating materials to overcome the alloy degradation. In the present contribution, we have used the neodymium-decorated graphene oxide as the corrosion inhibiting barrier for the Ti6Al4V alloy. As a novelty, we found that the few-layer graphene decorated with neodymium acts as a self-cleaning coating. The Nd-decorated graphene oxide were studied by XRD, TEM, FESEM, FTIR, UV, and Raman spectroscopy. The corrosion inhibition efficiency was studied by electrochemical methods.

ZnO: Al thin films were deposited by spray pyrolysis onto glass substrates with 0, 0.5, 1.0, 2.0, 5.0 and 10.0% [Al3+/Zn2+] ratios in the deposition solution. Films were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, UV–vis transmittance, conductive atomic force microscopy and the sheet resistance was measured. Aluminum contents in the films increases with the Al3+/Zn2+ ratio in the bath while the film deposition rate decreases due to the lower Al3+ surface mobility. Films were crystalline and display a varied morphology that evolves from flakes to mixtures between flakes and pencils and finally between triangles and hexagonal columns with increasing Al contents. Al3+ inclusion at the different sites within the ZnO lattice is proposed to direct the crystal habit and therefore the observed morphology and film texture. The optical band gap evolution and carrier density are related by the Burstein-Moss effect. The results show that film texture influences carrier mobility: increased presence of (112) planes originate a mobility increase while a predominant (110) or (100) texture reduces it. By Current sensing Atomic Force Microscopy (CAFM) the local surface current distribution was related with the observed film texture.

Copper aluminum oxide (CuAlO2) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2H-CuAlO2 and Al2O3 impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl2O4 (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K−1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m−1 K−1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10−8 to 4.94 × 10−4 in the order of the literature reports. From the Arrhenius plot ln(σT) versus 1000/T, an activation energy E a = 0.32 eV for the electrical conductivity was calculated.

The local atomic structure in non-stoichiometric Cu 2 ZnSnS 4 (CZTS) thin films was investigated using X-ray absorption fine structure spectroscopy (XAFS). From the XAFS spectra we infer the presence of disorder in the Cu-Zn plane suggesting that this characteristic might be intrinsic of non-stoichiometric CZTS. This disorder increases with the Cu/(Zn+Sn) ratio. Structural parameters derived from fits to the data show a contraction in the Cu-S bond length and an expansion in the Sn-S bond length, compared to distances obtained from diffraction, for all samples. X-ray absorption near edge spectroscopy (XANES) indicates presence of secondary phases not observed by X-ray diffraction. In Cu-poor samples, ZnS and SnS were identified as secondary phases. The amount of those phases correlates with the Cu deficit and were quantified by a linear combination fit of the XANES of standard materials. This work provides direct evidence of intrinsic disorder in CZTS, which must be considered to generate a realistic atomic structural model, in addition to lattice relaxations and secondary phases.

Graphene oxide (GO) was used as an additive to the anode, to modify the electrochemical properties of polymer fuel cells (PEMFC) based on Nafion. GO was obtained by modified Hummers method and fully characterized by Raman, FTIR, X-ray, TEM, electrochemically (CV) and Surface Area and Porosity Analyzer. PEMFC with a GO-based anode containing about 30% less Pt, was constructed and compared with a cell with standard anodes. The electrodes were electrochemically tested at 25 and 60 °C. A maximum power density of 134 mW/cm 2 with a current density of 374 mA/cm 2 was achieved for PEMFC with GO-based anode at 60 °C. The electrochemical surface area (ECSA) of the PEMFC with GO-based anode was about two times higher than that of the reference device. The electrochemical characterization as well as the Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) analysis indicate that GO in the anode reduced Pt agglomeration, as a consequence of the increased surface area and decreased average pore width, compared with the reference electrode. Well-fitted equivalent circuits were proposed and discussed after an electrochemical impedance spectroscopy study of the constructed devices.

In this paper, chemically synthesized graphene oxide (GO) was added to modify the performance and electrochemical properties of bulk heterojunction polymer solar cells (PSCs) with different architectures. GO was obtained by modified Hummers method and fully characterized by Raman spectroscopy, Fourier Transform Infrared Spectroscopy, X-ray diffraction as well as with cyclic voltammetry (CV). Bulk heterojunction PSCs with P3HT:PC61BM or PTB7:PC71BM active layers and PEDOT:PSS as hole transport layers (HTL) were constructed and investigated relative to: (i) concentration of GO in HTL, (ii) acidity of GO, (iii) type of polymer used in active layer, (iv) annealing temperature of the active layer and (v) place where GO is incorporated in the devices. For PSCs, the best performance was obtained for device with the ITO/PEDOT:PSS:GO/PTB7:PC71BM/Al architecture when the volume ratio of PEDOT:PSS to GO was 1:1. Under these conditions, a power conversion efficiency (PCE) of 5.22% with open circuit voltage Voc = 0.654 V, short circuit current density Jsc = 15.17 mA/cm2, and fill factor FF = 0.53 were achieved. It is shown that for devices with P3HT:PC61BM active layer, a better performance of device was achieved for the active layer annealed at 130 °C instead of 75 °C. For the ITO/(PEDOT:PSS):GO (1:1)/P3HT:PC61BM (75 °C)/Al device about 75% higher PCE was found compared with reference device (PCE for device without GO = 0.64%, while PCE for device with GO = 1.07%). The influence of GO on energy gap and HOMO-LUMO levels in PEDOT:PSS was investigated by CV method. The observed effect of GO in the HTL is to reduce the HOMO-LUMO gap and to shift the LUMO position downwards in energy, with the GO contents. The devices were additionally tested by electrochemical impedance spectroscopy (EIS) and well-fitted equivalent circuits were proposed.

This chapter discusses the basic principles of microbial fuel cell (MFC), various prototypes proposed for the conversion of waste materials either to fuel or energy, and their future prospects. It provides readers access to information in a simplified form for better understanding. A microbial fuel cell comprises a simple electrochemical setup whereby biocatalyst functions lead to reactions at the anode. The MFC setup is composed of minimal components usually possessing an anodic chamber containing microorganisms and wastewater, while an oxidant at the cathode is connected to an external circuit to generate electricity. A microbial electrolytic cell is a modified form of MFCs where the main motive is the conversion of organic matter into value-added products like hydrogen, methane, acetate, and hydrogen peroxide from which electricity can be produced indirectly. The collaborative analysis of biological and electrochemical influences will definitely help in the prediction of MFC output.

Energy and environmental crisis are two major challenges in present-day life. The advent usage of fossil fuels for electricity and transportation had resulted in global warming with deadly repercussions. Photocatalysis could be a good alternative to solve the present-day problems. Engineering the material for maximum solar irradiation harvesting, efficient charge generation, its transport to reaction centers, and high catalytic properties are the main priorities; in this sense, two-dimensional materials could be suitable for photocatalysis because of its physical, electrical, and chemical properties and the possibility to chemically tailor them. Photoinduced charge carriers could catalyze various chemical reactions for crucial applications. Hydrogen fuel could be used for hydrogen fuel cell to generate the electricity and power the electric vehicles. Major greenhouse gas, such as CO2 emitted by various industries and conventional automobiles, could be reduced to high-energy fuel such as methanol, ethanol, or formate. Photodegradation could decompose toxic organic substances from water-polluted sources. Human effort and expenditures could be saved by self-cleaning photocatalysis in offices, hospitals, or photovoltaic panels. Photocatalytic materials may play a critical role in effective cancer therapy for its sensitizing property and ability to produce reactive oxygen species which kills cancer.

Every year, the leather tanning industry produces substantial quantities of residues such as chrome-tanned leather shavings (CTLS), which contain considerable amounts of Cr(III) salts. The residues have no particular value and under natural conditions can transform into toxic Cr(VI) wastes. The objective of the present work is to evaluate the transformation of these residues into carbon adsorbents at low temperatures (

Non-stoichiometric $${\mathrm{{Cu}}_2\mathrm{{ZnSnS}}_4}$$ (CZTS) thin films were prepared using a closed-space sulfurization process of vacuum-evaporated stacks of ZnS, Cu and Sn in a custom-designed Joule-heated graphite reactor. In the first sulfurization step, at 250 °C, Cu and Sn transform into CuS and SnS. In a second sulfurization step, at 510 °C, the stack finally transforms into CZTS. Sample compositions were determined by energy-dispersive X-ray spectroscopy. Three different Cu-poor/Zn-rich samples and one slightly Cu-rich/Zn-poor sample were obtained, with Cu/(Zn$$\,+\,$$Sn) ratios of 0.64, 0.85, 0.91 and 1.02. The effect of the closed-space sulfurization process in the morphology was analyzed by scanning electron microscopy, allowing to obtain estimates of grain sizes in the range from 0.50 to 0.75 $$\upmu \mathrm{{m}}$$. X-ray diffraction confirmed the polycrystalline structure of the kesterite CZTS thin films with crystallite sizes that vary from 48 to 64 nm as the Cu content increases in the samples. An estimate of lattice microstrain indicates larger values for samples with larger grains and higher Cu/(Zn$$\,+\,$$Sn) ratios. Raman spectroscopy reveals the characteristic kesterite structure with the main peak shifted to a lower wave number, a signature associated with partially disordered kesterite. Optical characterization shows a decreasing bandgap from 1.47 to 1.39 eV and an increasing Urbach energy from 77 to 200 meV as the relation Cu/(Zn$$\,+\,$$Sn) increases, indicating a decrease in the localized states in the bandgap for Cu-poor samples. Results indicate that CZTS thin films obtained from the custom-made Joule-heated graphite reactor have similar characteristics to the films obtained from more conventional methods like sulfurization in a tubular furnace with the advantage of a precise and fast-response temperature control that could allow novel sulfurization strategies.

Production of a ZnO–rGO composite, using a novel one-pot method consisting in continuously flowing argon into a GO aqueous suspension heated at 80 °C, in the presence of galvanized iron steel scrap is presented. FTIR shows the complete disappearance of GO functional groups and only the C=C band remained, indicating extensive GO reduction. Raman spectra indicated sp2 character increase after reaction and the presence of the E2h mode of ZnO. SEM showed submicron crystals identified by XRD as ZnO in the hexagonal phase, while TEM images indicate ZnO nanoparticles decorate mainly the rGO borders. Optical band gap of 3.5 eV corresponding to ZnO, and optical transitions at 4.1 and 5.5 eV related with n → π and π → π* were observed. Electrochemical characterization by cyclic voltammetry shows an specific capacitance of 4.7 F g−1 at a scan rate of 5 mVs−1, which drops to ca. 0.8 F g−1 at 200 mVs−1. By electrochemical impedance spectroscopy, the relaxation time was ca. 5 ms. The proposed mechanism for the materials‘ synthesis includes Zn dissolution from scrap, galvanic displacement of oxygen moieties at the GO sheet, Zn deposition onto the carbon surface, and further oxidation and growth of ZnO nanocrystals.

Polycarbonate (PC) was reinforced with pristine and chemically modified graphene oxide (GO) to assess its effect on the PC mechanical properties. Commercial graphene with oxygen contents of 4.7 at %, was used as reference to corroborate the affinity of a GO with oxygen content of 25.6 at. % with PC. GO was modified with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDAC). Commercial graphene, unmodified and modified GO were characterized by FTIR, Raman, XRD and XPS to determine the effects of their structure on the mechanical properties of the reinforced PC. The concentration of graphene oxides in the PC nanocomposites was 0.25, 0.50 and 0.75 wt %. The nanocomposites were characterized by tensile and impact resistance tests as well as by TGA. The distribution of graphene oxides within the PC matrix was evaluated by optical microscopy and scanning electron microscopy. Samples with unmodified GO and commercial graphene showed better dispersion into the polymer matrix than EDAC-modified GO. The unmodified GO increased show increased impact resistance with respect to PC as well as a 291% increment in the elongation at break, with an optimal content of 0.25 wt % of the filler. The EDAC-modified graphene oxide as well as commercial graphene did not increase the impact resistance at any used concentration. The structural and chemical analysis of the EDAC-GO indicate GO reduction during its modification, suggesting that the oxygen functional groups in pristine GO, particularly carboxyl moieties are the responsible for the dispersion and interactions with the polymer and the improvement in mechanical properties.

A novel procedure based on the use of the Boltzmann equation to model the x parameter, the film deposition rate, and the optical band gap of BaxSr1−xTiO3 thin films is proposed. The BaxSr1−xTiO3 films were prepared by RF cosputtering from BaTiO3 and SrTiO3 targets changing the power applied to each magnetron to obtain different Ba/Sr contents. The method to calculate x consisted of fitting the angular shift of (110), (111), and (211) diffraction peaks observed as the density of substitutional Ba2+ increases in the solid solution when the applied RF power increases, followed by a scale transformation from applied power to x parameter using the Boltzmann equation. The Ba/Sr ratio was obtained from X-ray energy dispersive spectroscopy; the comparison with the X-ray diffraction derived composition shows a remarkable coincidence while the discrepancies offer a valuable diagnosis on the sputtering flux and phase composition. The proposed method allows a quick setup of the RF cosputtering system to control film composition providing a versatile tool to optimization of the process.

In this work, conductive reduced graphene oxide films onto glass substrates were prepared by immersion of the substrate at room temperature in a suspension of graphene oxide and antioxidant commercial supplements such as resveratrol, omega-3, triple-dosed omega-3 and astaxanthin. The films prepared with triple-dosed omega-3 and astaxanthin showed a defined diffraction peak at the graphite 2 theta position and the lower oxygen contents. Raman spectra indicate the restoring of the sp2 character and increase in the crystallite size, which increased the electron mobility from 0.009 cm2V−1s−1 in the GO film to 68 cm2V−1s−1 and decreased sheet resistance from 4.6 × 1010 ohm/sq in the graphene oxide film to the lowest achieved sheet resistance of 92.5 O/sq in the film reduced with astaxhantin.

Thin films of nanometric order of a solid solution of barium-strontium titanate Ba x Sr1−x TiO3 (BSTO), in the entire 0 ≤ x ≤ 1 range, were deposited at 495 °C on quartz by RF reactive co-sputtering. The composition was controlled through the RF power (P) applied to the targets. X ray diffractograms (XRD) reveal that all the samples show the cubic perovskite crystalline structure. The percentage of elements (x) in the films were evaluated by usingof electron dispersion spectroscopy, also through the change of the (110) lattice interplanar spacing determination of BSTO by means of XRD patterns. Experimental data points of concentration of Ba (x) and Sr (1−x) as a function of P describe a symmetric sigmoidal curve. The average crystal size for the whole composition is around 20 nm as estimated from XRD data. Raman measurements in the 100–900 cm−1 range show that optic phonons experience local hardening in the x interval 0.6–0.8. Around this region of x it is, in general, expected in BSTO a crystalline cubic-tetragonal phase transition when is prepared at low substrates temperatures. Distortion of the unit cell is observed in that interval, which probably originates the local hardening of phonons.

In the present work, Pr-decorated graphene oxide was synthesized and tested as a corrosion barrier layer in acidic media for the magnesium AZ31 alloy. The morphology, composition and structure of Pr-decorated graphene oxide sheets were characterized via HRTEM, FESEM, Raman, XRD, DLS, UV and FTIR studies. The corrosion inhibition efficiency on the alloy surface was monitored via microstructural and electrochemical methods. The results indicate that Pr-decorated graphene oxide provides improved protection for the Mg AZ31 alloy compared to conventional epoxy coatings. The proposed mechanism arises from a combination of the barrier activities of the composite, GO + Pr, and the epoxy coating on the Mg alloy in acidic media.

• The amorphous and crystalline fractions in raw corn pericarp were obtained by sequential extraction.

Graphene oxide (GO) powders with different oxidation degree estimated through the relative intensity of the infrared absorption bands related to oxygen containing groups were prepared through variations of the Hummers method. The GO powders were analyzed by Transmission Electron Microscopy, Energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, Raman spectroscopy, X-ray Diffraction, UV–VIS spectroscopy and Electrical Resistance measurements. Several square micron GO sheets with low wrinkling were obtained. Oxygen to carbon ratio is around 0.2 in all the samples although a strong variance in the relative intensity of the oxygen related infrared bands is evident. Thus, the oxidation degree was estimated from the FTIR measurements using the quotient between the C–O related bands area to the total area under the spectra. FTIR shows presence of hydroxyl (–OH), epoxy (C–O–C), carboxyl (–COOH) and carbonyl (C O) moieties and evidence of intermolecular interactions between adjacent groups. These interactions influence the exfoliation degree, the absorbance of the GO suspensions, as well as the electrical resistance, while the crystalline domain sizes, estimated from XRD and Raman do not show a noticeable behavior related with the composition and molecular structure. The results indicate that the electrical resistance is influenced mainly by the surface chemistry of the GO powders and not only by the O/C ratio. The control of the surface chemistry of GO powders would allow their use as additives in organic bulk heterojunction solar cells with enhanced photoconversion efficiency.

Using Ca K-edge X-ray absorption spectroscopy the calcium uptake and species in alkaline corn have been studied and compared with corn starch and crystalline cellulose as main compounds in corn endosperm and pericarp. XANES data showed that calcium binds preferably to hemicelluloses in the pericarp. The main calcium species found by EXAFS in cellulose and starch is calcium carbonate although some protein-calcium species could be formed within the starch granules. From X-ray diffraction and microscopy techniques, pericarp dissolution, mainly at the amorphous hemicellulose fraction was inferred. The hemicellulose dissolution during steeping increases the apparent pericarp crystallinity, while the relative calcium content determined by XANES absorption edges reduces. XANES and EXAFS spectroscopies showed to be a valuable tool in order to determine the calcium species and to make a semiquantitative determination of calcium in the different nixtamalized corn fractions.

In the present work selenium films were electrodeposited onto fluorine-doped SnO2 substrates, departing from a Se4+ aqueous electrolyte. The temperature and deposition potential were varied; the structure, morphology and band gap were studied by Atomic Force Microscopy, Raman Spectroscopy and optical absorption. The voltammetry study showed two reduction peaks that shift towards positive potentials as the deposition temperature increases from 25 to 75 °C: the first one shifts between −925 mV and −1120 mV versus Pt and the second between −1060 mV to −1250 mV versus Pt A black/greyish selenium film of a-Se and trigonal Se was deposited at −925 mV@75 °C and a deep red monoclinic Se one at −960 mV@50 °C; in the other conditions the film color indicate a mixture of the red a-Se and trigonal phases confirmed by Raman and optical spectroscopy. Trigonal phase has a calculated band gap of 1.6 eV, red and black a-Se band gap value of 1.83 eV, and monoclinic Se of 2.0 eV, respectively. From Electrochemical Impedance Spectroscopy, the films were found to be n-type, with carrier densities around 1018–1019 cm−3, and Flat Band Potentials between 0.6–1.0 V in dependence of the deposition conditions. The results point out the feasibility of controlling the phase of Se layers using a single aqueous bath and mild temperature conditions.

In the current work, we present a new self-organizing anodization approach of metallic Sn layers to obtain vertically aligned tin oxide nanochannel structures. For this, we use a sulphide-containing electrolyte and a set of optimized anodizing parameters. The resulting high aspect ratio nanochannel morphologies can be converted into crystalline SnO2 by high temperature annealing and show highly promising H2 sensing properties. We show that these anodic layers can operate at relatively low temperatures (∼80 °C), detecting concentrations as low as 9 ppm, and with extremely fast response and recovery times. This excellent gas-sensing performance is ascribed to the advanced structure, characterized by a crack-free, straight and top-open nanochannel geometry.

An estimation of climatological fields of incident solar energy in Tamaulipas State, northeastern Mexico, is presented. Monthly mean evolution of solar energy in 7 automatic meteorological stations distributed along the State shows that the maximum values generally exceed 500 ± 200 W m−2 during fall-winter (Nov–Feb), and 700 ± 200 W m−2 during spring-summer (May–Aug). An empirical model, which estimates the solar energy as function of other climatic variables (minimum temperature, maximum temperature, evaporation, and precipitation) recorded in 165 climatological conventional stations, is used to extend the climatological solar-energy estimate in the study area. The mean values of both measured and estimated solar energy are objectively mapped to fill the observation gaps and reduce the noise associated with inhomogeneous statistics and estimation errors. The highest values of solar energy ( ∼ 6.7 kW h m−2 during the summer and ∼ 4.0 kW h m−2 during the winter) are observed in the highlands, southwestern part of the State, whereas the lowest values ( ∼ 5.7 kW h m−2 during the summer and ∼ 2.8 kW h m−2 during the winter) are observed in the south-central part of the State.

The mechanism of the electrochemical passivation on Tin electrodes in 0.1 M NaOH is studied at low scan rates in a wide potential range. To this aim, tin oxide layers were grown on a polycrystalline tin surface under potentiostatic conditions in both the active and passive electrochemical potential ranges, and characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The results show that the first anodic process in the active region corresponds to the formation of a SnO·nH2O prepassive layer that is removed upon increasing the applied potential due to surface etching occurring at the metal/oxide interface. During the etching process, Sn2+ ions supersaturate at the electrode vicinity thus forming a SnO crystalline phase on top of the electrode surface in the presence of the alkaline medium. At higher anodic potentials, near the passive plateau, the etching process ceases and the current drops due to the formation of a n-type Sn(IV)-based oxide at the metal/SnO interface that provides an efficient electronic passivation of the electrode.

ZnO:Al films were deposited at 70 °C at a fixed −1.1 V potential onto ITO substrates from a 0.01 M Zn(NO3)2 + x Al(NO3)3·9H2O electrochemical bath, with Al3+ concentrations between 0 and 2 mM. Electrodeposition conditions were optimized to remove bubbles, increase grain size homogeneity and ensure adherence. Films were characterized by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis transmittance, electrochemical impedance spectroscopy and photocurrent spectroscopy. Films were crystalline with the wurtzite structure and present a morphology made of hexagonal nano-pillars. It was found that Al incorporation increases gradually up to ∼11 at% for samples prepared within the concentration range 0.0–0.3 mM Al3+ in the bath. For higher Al3+ contents (>0.4 mM) an amorphous Al2O3-like compound develops on top of the films. In the grown films with Al contents up to 11 at%, changes in the optical band gap from 2.88 eV to 3.45 eV and in the carrier densities from 1019 to 1020 cm−3 were observed. The blue shift in the band gap energy was attributed to the Burstein-Moss effect. Changes in the photocurrent response and the electronic disorder were also discussed in the light of Al doping. Optical transmittances up to 60% at 550 nm were obtained, thus making these films suitable as transparent and conductive oxide films.