Raman Investigation Research Articles

Facile architecture of highly effective nanofibrous membrane adsorbent via electrospun followed by hydrothermal carbonization for potential application in dye removal from water.

Rapid removal of toxic dye pollutants in water by conventional materials is ineffective and expensive that warrants the necessity for the architecture of hybrid nanofibrous membrane through layer by layer deposition using electrospinning method. In order to achieve this, here we demonstrated the electrospun fabrication of graphene/ferrocene intercalated polyacrylonitrile nanofibrous (GFPN) membrane through hydrothermal carbonization (HTC) method and studied its potential adsorption properties for the removal of environmental pollutants. An aqueous dispersion of graphene/ferrocene (1mg/mL) stabilized by the polymeric backbone was prepared by the solvent homogenization method and electrospun to yield nanofibrous membrane and further characterized by several analytical and spectroscopic techniques. Raman and XPS investigations corroborated the intercalation of graphene/Fe decorated onto the nanofibrous network. Adsorption experiments found that the GFPN membrane achieved more than 90% removal of anionic Congo red (CR) dye within 30min in the aqueous phase irrespective of the concentration and takes some additional time for attaining the equilibrium. The longevity and stability of the membrane was studied by conducting successive adsorption-desorption cycles for the regeneration of its adsorption properties. The de-coloration mechanism was comprehensively investigated through the mathematical approaches using the kinetic and intraparticle diffusion studies and confirmed with the experimental findings through IR and XPS spectroscopic techniques. In a nutshell, this work focuses on the fabrication of hybrid nanofibrous membrane and studied its adsorption properties through varying concentrations of dye (20 to 150mg/L). Moreover, this work extensively explored the mechanism associated with the adsorption process and specifically emphasize the existence of combined phenomena during the process, i.e., anion-cation interactions, hydrogen bonding, and successive stages of intraparticle diffusion through the comparative elucidation of both theoretical and experimental approaches.

Low-Temperature Raman Investigations and Photoresponse of a Detector Based on High-Quality WSe2 Crystals

The WSe2 single crystals were grown by a high-yield vapor-phase synthesis technique. The grown crystals have 2H-hexagonal lattice structure with a P63/mmc space group. Excitonic resonances A′ and B′ are observed due to splitting of the ground and excited states of A and B transitions, respectively, resulting from inter- and intralayer perturbation of the d-electron band of the W atom by p orbitals of the Se atom. Raman spectroscopy over the temperature range of 77 to 298 K shows that the A1g and E2g modes exhibit a linear dependence on temperature. The shifting of frequency from 251.46 to 253.71 cm–1 follows the first-order temperature coefficient of 9.8 × 10–3 cm–1 K–1. The width of the Raman peaks at half maxima also exhibits a systematic linear dependence on temperature. On the basis of the semiquantitative model, it is stated that the thermal expansion contribution mainly dominates in WSe2 single crystals. Subsequently, the photodetector was analyzed in the temperature range of 200 to 298 K under periodic exposure of 670 nm light of 5 mW/cm2 power intensity. The device exhibits a photoresponsivity of 43.92 mA/W and a response time of 0.85 s.

Effect of Potassium Nitrate in ZnO Nanoparticle Synthesis to Study the Performance of Dye Sensitized Solar Cell

X-ray diffraction, Raman investigations, band gap energy of zinc oxide nanoparticles (ZnO NPs) along with current-voltage characteristic curves of an assembled dye-sensitized solar cell (DSSC) are presented in this article. ZnO NPs were first synthesized with and without potassium nitrate (KNO3) salt by precipitation method from precursor solutions of zinc acetate and sodium hydroxide. Then, their thin films were deposited on FTO substrates from the paste made with acetic-acid glacial, and Triton X-100 in ethanol by doctor blade method. The X-ray diffraction (XRD) pattern of ZnO NPs prepared without KNO3 annealed at 500°C showed a hexagonal wurtzite structure with preferred orientation along (101) planes and crystallite size of 25 nm. Very similar XRD pattern was found for ZnO NPs prepared with KNO3. The crystallite size was found decreased to 17 nm for ZnO NPs made with KNO3 salt. Raman spectrum of ZnO NPs showed the presence of E2 high or E2 (2) peak at 437 cm-1. The optical band gaps of the ZnO thin films prepared from ZnO NPs with and without KNO3 were measured to be of 3.16 eV and 3.26 eV, respectively. After sensitizing the above-prepared ZnO films by dye extract of Artocarpus lakoocha, the dye-sensitized solar cells were prepared, and their performance was tested by measuring I-V curves under light illumination of the power density of 1000 W/m2. The measurement showed highest Isc and Voc of 44 μA and 326 mV, respectively.

Laboratory Raman and VNIR spectroscopic studies of jarosite and other secondary mineral mixtures relevant to Mars

AbstractJarosite is an indicator of ephemeral, acidic fluids in Martian history, which often occurs with some other secondary minerals based on Mars in situ and remote sensing detections. However, detailed Raman and visible and near‐infrared (VNIR) spectroscopic studies of jarosite and other secondary mineral mixtures relevant to Mars still lack, which are essential for jarosite identifications and hence a better understanding of Martian aqueous history. In this study, we prepared 44 binary mixtures of jarosite with four other secondary minerals (alunite, gypsum, kaolinite, and montmorillonite), and characterized their detailed Raman and VNIR spectral features. We find the Raman spectral patterns of jarosite, alunite and gypsum are distinctive and ready for their identification in mixtures, although mixtures with montmorillonite and kaolinite show high fluorescence background and their Raman spectral features are obscured by strong and sharp peaks of jarosite. The normalizing strengths of their characteristic Raman spectral features (e.g., ν1 for jarosite) change with jarosite mass fractions, and mineral distribution maps and volume percentages of endmembers are acquired using Raman imaging method. The band depths of absorption features in VNIR spectra are also correlated with jarosite mass proportions, and four models are proposed to evaluate jarosite mass fractions in the mixtures using a partial least squares algorithm. These detailed spectral properties of mixtures and models would provide valuable information for in situ Raman investigations on Mars (e.g., ExoMars and Mars 2020) and orbital VNIR remote sensing detections (e.g., Compact Reconnaissance Imaging Spectrometer for Mars).

Structure and low energy vibrations in silver borate glasses with low silver content

Structural changes of (Ag2O)x(B2O3)1-x glasses, over the range between X = 0.0 and X = 0.14, have been monitored by Raman spectroscopy. Low temperature heat capacity measurements have been also performed between 0.4 K and 25 K to investigate along with low frequency Raman scattering the behavior of the low-energy vibrational dynamics. A progressively decreasing intensity of the main band at 808 cm−1 and the appearance of a band at about 775 cm−1 with increasing Ag2O content have been observed and analyzed in detail. The strongly polarized band at 808 cm−1 is ascribed to the breathing vibration of boroxol rings and the decrease of its intensity indicates the reduction of the number of these units in the network. The band at 775 cm−1 is assigned to vibrations of pentaborate units, formed from two boroxol rings linked by a tetrahedral BO4 group. The rate of formation of BO4 groups appears to increase as X/(1-X). Raman investigation has been extended to very low frequencies, where a broad intense band, the Boson peak (BP), dominates the spectrum of all the samples below 100 cm−1. Addition of Ag2O shifts the BP position from 26 cm−1 up to 33 cm−1 and gives rise to a decrease of its intensity up to X = 0.09 and a sudden increase for X = 0.14, which has been explained as due to rattling motion of silver ions whose contribution is added to that of localized vibrations. The formation of tetrahedral BO4 groups stiffens the network and leads to a decrease of the excess heat capacity over the Debye prediction below 20 K, which is not taken into account by the simple hardening of the elastic continuum but seems to follow the reduction of boroxol rings. This result contrasts the observations on borate glasses with high Ag content and emphasizes the crucial role of the network continuity on the vibrational dynamics of a glass.

Natural gas partial oxidation process as a way to synthesize onion-like carbon

Onion-like carbon (OLC) particles were produced as a byproduct of thermal partial oxidation of methane under different O2/Natural Gas (NG) ratio. It was established that the particles have quasi-spherical morphology and concentric shell structure. The particles have an outer diameter of 20–60 nm while the inner cage is rather typical for onions and has a diameter below 1 nm. The concentric graphitic structure and spherical symmetry along with the absence of amorphous carbon were confirmed by transmission electron microscopy, electron diffraction, EDX spectroscopy and Raman investigation. Variation of O2/NG ratio was proved a powerful tool for controlling OLC particles yield and structure. The formation of single-core or multicore OLC can be controlled by thermal partial oxidation process.

How water-mediated hydrogen bonds affect chlorophyll a/b selectivity in Water-Soluble Chlorophyll Protein

The Water-Soluble Chlorophyll Protein (WSCP) of Brassicaceae is a remarkably stable tetrapyrrole-binding protein that, by virtue of its simple design, is an exceptional model to investigate the interactions taking place between pigments and their protein scaffold and how they affect the photophysical properties and the functionality of the complexes. We investigated variants of WSCP from Lepidium virginicum (Lv) and Brassica oleracea (Bo), reconstituted with Chlorophyll (Chl) b, to determine the mechanisms by which the different Chl binding sites control their Chl a/b specificities. A combined Raman and crystallographic investigation has been employed, aimed to characterize in detail the hydrogen-bond network involving the formyl group of Chl b. The study revealed a variable degree of conformational freedom of the hydrogen bond networks among the WSCP variants, and an unexpected mixed presence of hydrogen-bonded and not hydrogen-bonded Chls b in the case of the L91P mutant of Lv WSCP. These findings helped to refine the description of the mechanisms underlying the different Chl a/b specificities of WSCP versions, highlighting the importance of the structural rigidity of the Chl binding site in the vicinity of the Chl b formyl group in granting a strong selectivity to binding sites.

Role of strontium substitution in spray drying of hydroxyapatite: A comparative study on physical properties

AbstractSpray drying (SD) has the ability to tailor granule size and morphology, thus, it is used for producing hydroxyapatite (HA) granules. Recently, Sr functionalized HA (SrHA) has been recommended owing to its improved biological properties. The aim of this article was to produce SrHA granules with the combination of nanoparticle synthesis and spray‐drying. The effects of substitution on the physical properties of SrHA nanoparticles and spray‐dried granules were investigated. TEM analyzes revealed that Sr substitution reduced the mean size of HA nanoparticles from 4.59 nm to 2.31 nm. Besides, Sr substitution increased the viscosity of the prepared slurry for spray drying, which may be attributed to the smaller nanoparticle sizes. The reduced nanoparticle size caused to the agglomeration of the SrHA more than the pure HA nanoparticles. Moreover the 16 mol % Sr substituted HA (16SrHA) slurry were quickly hardened, which hampered the feeding of the slurry to the SD system; eventually the atomizer was blocked. The increase in the viscosity increased the mean granule size of HA from 41.53 µm to 49.18 µm. HA and 8SrHA granules presented HA phase dominantly after the heat treatment at 1000°C, while, 16SrHA decomposed to TCP according to RAMAN and XRD investigations.

Growth and characterisation of ZnO micro/nanostructures doped with cerium for photocatalytic degradation applications

ZnO:Ce structures have been obtained by a vapour-solid method. Different dopant concentrations have been used, and the incorporation of cerium in the crystalline structure of zinc oxide has been verified by means of Energy Dispersive Spectroscopy and Raman investigations. The morphology of the structures varies depending on the initial content of Ce in the samples, changing from long and thin rods and wires to “bottle-like” and truncated hexagonal pyramids as the Ce content increases. Cathodoluminescent properties have also been studied, the near band edge and deep level emissions change depending on both Ce content and morphology of the structures. Photocatalysis investigations show that an increase above 5 wt % of cerium oxide in the material causes a slight decrease in the efficiency of these structures in the degradation of the contaminant.

Determination of bulk residual stresses in superhard diamond-SiC materials

Superhard silicon carbide bonded diamond materials can be produced by liquid silicon infiltration of diamond containing preforms. These materials can be produced as bulk materials and as layered materials with the SiC bonded diamond only in areas where it is required. In order to understand the behaviour of the materials it is necessary to know the internal stresses in the different phases and at the interface. These stresses were determined by Raman spectroscopy and in the bulk by neutron diffraction using the SALSA instrument in the ILL. In the SiC bonded diamond material the diamond and the remaining Si are under compressive stresses. The SiC-phase is under tensile stresses up to 500 MPa. The Raman investigations and the neutron diffraction resulted in similar results. At the interface between the SiC-bonded diamond and the SiSiC no significant additional stresses could be observed.

Intrinsic and Extrinsic Responses of ZIF-8 under High Pressure: A Combined Raman and X-ray Diffraction Investigation

ZIF-8 is a prototypical porous material in the family of zeolitic imidazolate frameworks, and its structural stability is of great significance for a wide range of practical applications. Here, the intrinsic and extrinsic structural and mechanical responses of nanosized ZIF-8 perturbed by high external pressure have been comparatively investigated based on our in situ Raman measurements in different pressure environments, accompanied by synchrotron X-ray diffraction measurements and results from previous reports. An improvement of both the chemical and crystallographic stability of ZIF-8, rather than an intrinsic quick deterioration, can be observed when penetrating guest molecules get into the pores. Spectral evidence demonstrates that the C═C section of the imidazolate ring is an optimal interaction site for the penetrating methanol, water, and nitrogen molecules. We further find that water molecules can cleave Zn–N bonds to bring linker-associated defects to ZIF-8. When compressed in the nonpenetrating silicone oil as a pressure transmitting medium (PTM) or when no PTM is used, irreversibility is observed, while samples show a highly reversible transformation both in the short-range and long-range regions upon decompression from a partially or entirely amorphous state in penetrating PTM. Furthermore, the released samples transform to a dense bulk state in the absence of penetrating PTM instead of preserving the original nanosized particles when penetrating pressure transmitting fluids is present. Moreover, the compressible behavior of ZIF-8 varies and is found to be strongly influenced by the size and polarity of molecules in the pores. The present results indicate that the stability, compressibility, and reversibility of ZIF-8 under pressure are closely related to the pressure environments and the characteristics of the guest molecules in the PTM. Thus, this study sheds light on the available mechanical modifications and selectable applications of ZIF-8 as gas absorbents for the future.

Stretchability of PMMA-supported CVD graphene and of its electrical contacts

The remarkable mechanical robustness and excellent electrical/thermal properties make graphene a promising candidate for future flexible, stretchable and bio-integrated electronics. In practice, many soft electronics such as the graphene electronic tattoos (GETs) demand the chemical vapor deposited (CVD) graphene to be supported by a deformable substrate. Moreover, various conductive overlayers need to directly laminate on graphene to make electrical contacts. To investigate the mechanical reliability of CVD graphene in these situations, we fabricated CVD monolayer graphene supported by ultrathin poly(methyl methacrylate) (PMMA) substrate and also placed gold/polyethylene terephthalate (Au/PET) and graphene/PMMA (Gr/PMMA) overlayers on graphene. The stretchability of the Gr/PMMA and the overlayer-Gr/PMMA interface was characterized by electrical resistance change during uniaxial tensile tests. Combined with in situ microstructure and Raman investigation, we identified four deformation/fracture stages of Gr/PMMA—pre-cracking elastic deformation, limited micro-cracking in graphene, extensive cracking in graphene, and macro-cracking in PMMA. While micro-cracks emerged in graphene at very small strain (~0.9%), the electrical conductivity of the Gr/PMMA specimen remained up to tensile strains of ~14.5%. In contrast, 100 nm-thick Au film supported by the same PMMA substrate fully ruptured after tensile strains of ~1%. When laminating Au/PET and Gr/PMMA over Gr/PMMA, we found that the Au/PET- Gr/PMMA interface is very vulnerable but the Gr/PMMA- Gr/PMMA interface behaves very similar to intact Gr/PMMA electromechanically. The cyclic behaviour of Gr/PMMA, the effects of PMMA thickness and adhesion are also briefly discussed. The present experimental study provides fundamental insight into the failure of ultrathin polymer-supported graphene and its electrical contacts, which is critical for designing future graphene-based soft electronics.

Investigation of Photophysical Properties of Ternary Zn-Ga-S Quantum Dots: Band Gap versus Sub-Band-Gap Excitations and Emissions.

Highly luminescent ternary Zn–Ga–S quantum dots (QDs) were synthesized via a noninjection method by varying Zn/Ga ratios. X-ray diffraction and Raman investigations demonstrate composition-dependent changes with multiple phases including ZnGa2S4, ZnS, and Ga2S3 in all samples. Two distinct excitation pathways were identified from absorption and photoluminescence excitation spectra; among them, one is due to the band-gap transition appearing at around 375 and 395 nm, whereas another one observed nearby 505 nm originates from sub-band-gap defect states. Photoluminescence (PL) spectra of these QDs depict multiple emission noticeable at around 410, 435, 461, and 477 nm arising from crystallographic point defects formed within the band gap. The origin of these defects including zinc interstitials (IZn), zinc vacancies (VZn), sulfur interstitials (IS), sulfur vacancies (VS), and gallium vacancies (VGa) has been discussed in detail by proposing an energy-level diagram. Further, the time-dependent PL decay curve strongly suggests that the tail emission (appear around 477 nm) in these ternary QDs arises due to donor–acceptor pair recombination. This study enables us to understand the PL mechanism in new series of Zn–Ga–S ternary QDs and can be useful for the future utilization of these QDs in photovoltaic and display devices.

Vibrational and computational analysis for molecular structure properties of N-(2-(trifluoromethyl)phenyl)acetamide: Density functional theory approach

The conformational study using Potential Energy Surface analysis was performed and its minimum energy conformer has been obtained for N-(2-(Trifluoromethyl)phenyl)acetamide. Fourier Transform Infrared and Fourier Transform Raman investigation have been done experimentally and theoretically. Nuclear Magnetic Resonance analysis has been performed to obtain 1H and 1C chemical shifts. Ultraviolet-Visible analysis has been performed to obtain maximum absorption wavelength. The molecular orbital diagram with different energies has been obtained and compared with the band gap of Ultraviolet-Visible data. Wave function analysis has been discussed to know the electronic properties. Thus, this present study reports the structural, electrical, chemical activities of the title compound.

Pseudocapacitive behaviour of FeSx grown on stainless steel up to 1.8 V in aqueous electrolyte

Abstract Iron sulfide was synthesized for 4 h, 7 h and 12 h by a hydrothermal process directly on stainless steel current collectors. The synthesis time determined the material morphology and electrochemical response. The shortest synthesis time promoted the formation of randomly oriented nanowires that evolved to nanosheets decorated with nanoflakes, organized in a cuboidal-like morphology upon longer synthesis times. XRD, Raman, FTIR and XPS investigations confirmed the formation of FeSx. The electrochemical activity was studied in a potential window ranging from −0.95 to 0 V and the material obtained after 7 h of synthesis stored the maximum specific capacitance of 730 mF cm−2 at the current density of 1 mA cm−2. This material also retained approximately 34% of its initial capacitance at 10 mA cm−2 and showed very good cycling stability, keeping around 95% of the specific capacitance after 2000 galvanostatic charge-discharge (GCD) cycles. The kinetic analysis of the electrochemical results revealed the predominance of diffusional controlled processes. An asymmetric cell was assembled using FeSx as negative electrode and carbon nanofoam (CNF) as positive electrode. The FeSx||CNF cell showed enhanced capacitive response in a potential window of 1.8 V in 1 M Na2SO4 electrolyte and delivered specific capacitance of 236 mF cm−2 at 0.5 mA cm−2 with good rate capability. The FeSx||CNF cell stored maximum energy density of 0.11 mW h cm−2 at the power density of 0.45 mW cm−2. The cell showed very good stability by retaining 83% of the initial capacitance after 2000 cycles of consecutive charge discharge.

Raman and FT-IR investigation of neutron and fission-fragment irradiated DAP polymer

The polymer Diallyl Phthalate (DAP), commonly used as solid-state nuclear track detector (SSNTD), has been characterized via optical microscopy and Raman and FT-IR spectroscopies in three distinct processes: i) without irradiation; ii) irradiated by neutrons and induced fission fragments and iii) as a function of the chemical etching time. The detectors were exposed to fission fragments from the induced fission of 235U and to the neutrons themselves. The optical microscopy provides information about the morphological changes, while the spectroscopic techniques provide physical and chemical information over the detector molecular structure. The irradiation and chemical etching induces molecular degradation and cross-linking of the detector chemical structure as observed in the Raman and FT-IR analyses. According to the spectral profile analyses, the strength of the functional groups OCOO, CH, CHCH, CCH, COC, CCH3, C(CH3)2, CCH3, CO, CH2 decrease and additional CO2 gases and OH groups are produced. Therefore, the characterization process performed in this work is essential to better comprehend the behavior of the DAP molecular structure under irradiation and chemical etching and also to better understand the track formation process which is related to the etching kinetics.

In operando Raman investigation of Fe doping influence on catalytic NiO intermediates for enhanced overall water splitting

Transition metal iron (Fe)-incorporated Ni oxide and oxyhydroxide compounds generally show an enhanced activity for alkaline water splitting. However, the role of Fe for this enhanced activity is not fully elucidated, especially under hydrogen evolution reaction (HER). Herein, we combine electrochemical and spectroscopic techniques to investigate the Fe doping effect on self-standing NiO nanosheets for enhanced activities for both HER and oxygen evolution reaction (OER) in overall water splitting. The results show that the presence of Fe suppresses Ni self-oxidation and adjusts the Ni–O local environment and its ability to form surface phases. In operando Raman spectroscopy is utilized to explore the active intermediates present under catalytic conditions. Apart from a slight suppression of grain size, our results show that Fe incorporation into NiO enhances in-situ formation of active layered intermediates NixFe1-xOOH with a phase transformation of FeOOH layers into γ-NiOOH layers containing Ni4+ at potentials approaching OER in contrast to undoped NiO electrodes with a dominating conversion of NiO to β-NiOOH, with persisting Ni3+. In addition, the work function on the electrode surface is reduced by 90 meV upon Fe doping, revealing a higher intrinsic Fermi-level and thus a lower requirement for added bias during HER. Together with the lower resistance for electron transport beneficial for both HER and OER, this leads to improved OER and HER efficiency upon Fe-doping. The study shows how Fe doping influences the active catalytic NiO intermediates for both HER and OER. Specifically, in operando vibrational spectroscopy utilized in parallel with electrochemical characterization can shed light on enhancement mechanisms and influence of doping for catalytic intermediates under any chosen bias at the respective electrode under full water splitting.

Raman investigation of N‐implanted ZnO: Defects, disorder and recovery

AbstractUnderstanding defects, disorder and doping due to N implantation in ZnO is one of the most debated issues for the last few years. In the present work, a comprehensive investigation has been carried out using Raman, photoluminescence (PL) spectroscopy and grazing‐incidence X‐ray diffraction on 50 keV N ions implanted granular ZnO with different fluence (approximately up to 6.5% atomic concentration) along with postimplantation annealing. Raman investigation suggests that 275, 510, 643, and 857 cm−1 modes are directly related to nitrogen. Additionally, VZn may have some role in stabilizing 275 cm−1 mode. The broadening (or tailing) of E2low mode is related to vibration of distorted Zn sublattice, which may be a product of ion implantation generated defect cluster like VZn–VO. The distortion starts to reduce with annealing at elevated temperatures. Direct correlation between 555 cm−1 Raman mode and the tailing of E2low mode has been found. More defect clustering is vivid from the reduced PL of the ZnO samples with increasing implantation fluence. So, tailing of E2low Raman mode, increasing intensity of 555 cm−1 mode and nonradiative defect centers are of common origin. Both the ratios E1(2LO)/E1(LO) and E2high/E1(LO) can be used as parameters to measure the defective nature of ZnO after ion implantation/irradiation. Low temperature PL (selected samples) suggests absence of shallow acceptor states, although negative thermal quenching above 175 K has been observed (implantation fluence 1 × 1016 ions/cm2 and annealed at 500°C) which can be a signature of deep acceptors.

Ellipsometry and Raman Investigations into the Influence of Chloride on Steel Corrosion Rates in Alkaline Environments

The contribution to pitting corrosion from chloride is a well-accepted agreement, however, the mechanism and the relationship between the presence of chloride and the generation of pitting corrosion in different cases is still remains to be studied. Likewise, the study of the inhibition mechanism of corrosion inhibitors is also deficient. Spectroscopic methods such as Raman and ellipsometry have the advantage of being surface sensitive and non-destructive characterization processes. It gives one a chance to investigate the dynamics of localized corrosion on steel in high alkaline solution (pH=12.5) in the presence of chloride ions. An industrial example of such an environment is reinforced concrete. In this study, these spectroscopic techniques are combined with electrochemical measurements such as open circuit potential (OCP; Figure 1) and electrochemical impedance spectroscopy (EIS; Figure 2) to analyze the corrosion tendency of attack by chloride at different concentrations at pH12.5. It is found that for chloride concentrations higher than 50mM the OCP spontaneously decreases, indicating an irreversible destruction of the passive film formed in the alkaline solution. The EIS data could be fitted to a simple one time constant equivalent circuit in either the Bode or Nyquist formats (Figure 3). The constant phase element CPE is linked the capacitance by: ZCPE=[Cox(jω)n]-1 It is shown that the capacitance, Cox, increased with the increasing chloride concentration, possibly indicating a thicker oxide layer on the carbon steel sample surface. EIS also revealed that the corrosion rate increased with increasing chloride content, as indicated by a reduction in the charge transfer resistance, R ct (Figure 3). SEM, Raman spectroscopy and ellipsommetry were applied for surface characterization, with the in-situ Raman and ellipsometry cells shown in the Figure 4. SEM revealed that when NaCl was introduced to the alkaline solution, the sample surface obtained a higher roughness after 24 h immersion test. For Raman, because of the thinness of the corrosion product layer, it was first necessary to electrochemically deposit to induce the surface enhanced Raman (SERS) in order to collect spectra from the carbon steel in pH=12.5 alkaline solution with or without NaCl (Figures 5 & 6). The locations of Raman peaks i of selected iron oxides, hydroxides and oxyhydroxides are listed in the table (Ref 1 & 2), with the most intense peak being bold. ComponentRaman shift (cm-1)α-FeOOH 290 β-FeOOH400 720 γ-FeOOH 252 380526650δ-FeOOH663(braod)Fe(OH)2 460 545 Fe(OH)3 692(broad)Fe3O4 550 670 It was found that in the absence of chloride the main components of the passive are Fe(OH)2, Fe3O4, γ & δ – FeOOH. However, on addition of chloride, the γ - FeOOH in the oxide layer is converted to β-FeOOH. The in-situ ellipsometry data allowed the thicknesses of the films to be determined and it was found that the oxide layer thicken by around 20% on the addition of chloride to the alkaline solution. It those concluded that as the chloride ions convert γ - FeOOH converted to β-FeOOH this both thickens and destabilizes the passive film. Figure 1

Growth dynamics of CBD-assisted CuS nanostructured thin-film: optical, dielectric and novel switchable device applications

The microcrystal structure of copper sulfide (CuS) nano-structured ultra-thin film was prepared on glass substrate from aqueous ammonia solution and sodium hydroxide at 60 °C using a simple and cost-effective chemical bath deposition (CBD). The powder X-ray diffraction method was used to characterize the hexagonal structure of the prepared CuS thin-film. While, surface morphology and surface topology were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optical properties were investigated by using UV–visible absorption spectrum. The electronic properties including average energy gap (Penn gap), Fermi energy, electronic polarizability and valence electron plasma energy of CuS thin films were determined. Semiconductor characterization of CuS film was confirmed using temperature dependent conductivity analysis. To prove the positive photoconductivity of nano-structured CuS nano-structured thin film, photoconductivity measurements were performed. I–V characteristics result, and Hall Effect measurements were also evaluated. Our results showed that the prepared CuS nano-structured thin films have higher crystallinity, purity and higher content of copper (Cu: 89.6%) as confirmed by XRD and EDX elemental analysis, respectively. While, their optical band gap energy is about 2.2 eV. Polarization-dependent Raman investigations allowed sample identification by dominant peaks at 265 cm−1 and 474 cm−1, proving the formation of CuS. Moreover, stimulating energy was found to be 0.028 eV by employing DC conductivity measurements. The estimated surface roughness was about (115 nm) with an average thickness of about (16.3 nm) as obtained from AFM analysis. Finally, remarkable smooth multi-colored marble like textural patterns have been recorded confirming the novel switching as recorded by the polarizing optical microscopy.