UV Vis Absorption Edge Research Articles

Characterization of Cu2−xSe thin films synthesized from electrochemical deposition

• Cu 2− x Se films were electrodeposited on Mo substrate with CuSO 4 and H 2 SeO 3 . • The deposited films were near-stoichiometric Cu 2− x Se with FCC structure. • The direct band gap for Cu 2− x Se thin films are in the range of 2.14–2.18 eV. Copper selenide (Cu 2− x Se) thin films were potentiostatically deposited on molybdenum substrate with an aqueous solution of CuSO 4 and H 2 SeO 3 . The effect of the deposition potential on the microstructure and electrical properties of the thin films were studied using FESEM, HRTEM, and two probe conducting measurements. The morphologies of the films changed from densely packed nanoparticles to the plate-like grains growing perpendicular to the substrate. In addition, these plates were composed of nanoparticles of about 100–200 nm in size. The nanoparticles were verified to be the face centered cubic (FCC) Cu 2− x Se from XPS and HRTEM analysis. The direct band gap for the Cu 2− x Se thin films was in the range of 2.14–2.18 eV measured from UV–vis absorption edge. The electrical conductivity of the thin films increased from 4.51 × 10 −3 to 7.08 × 10 −3 (Ω m) −1 as the Cu/Se ratio decreased from 1.92 to 1.89.

Efficiency enhancement of CuInS2 quantum dot sensitized TiO2 photo-anodes for solar cell applications

Two-step process had been employed to enhance the photovoltaic performance of CuInS2 quantum dot sensitized solar cells. 3.5nm MPA-capped CuInS2 quantum dots were firstly adsorbed on the TiO2 nanoparticle films by assembly linking technique. And then large amount of CuInS2 quantum dots were deposited on the photo-anodes by SILAR technique. The UV–Vis absorption edge of the photo-anodes from two-step process had greatly expanded from 400nm to 800nm. These solar cells exhibited the IPCE peak value of 36% and photovoltaic efficiency of 1.85%, which was much higher than that from individual assembly linking and SILAR technique.

Syntheses, crystal structures, and properties of two new one-dimensional heterometallic selenides: [DBNH]4[M3Sn4Se11(Se2)2] (M=Cd, Hg)

Two new one-dimensional ternary selenides, [DBNH]4[M3Sn4Se11(Se2)2] (M = Cd (1), Hg (2); DBN = 1,5-diazabicyclo[4.3.0]non-5-ene), have been prepared under solvothermal conditions by the reactions of Sn, CdCl2/HgCl2, Se, DBN, and H2O at 160 °C for 6 days. Single crystal X-ray analyses reveal that compounds 1 and 2 are isostructural and crystallize in the monoclinic space group C2/c (for 1, a = 22.236(4) Å, b = 12.623(3) Å, c = 21.756(4) Å, β = 109.91(3)°; for 2, a = 22.137(4) Å, b = 12.663(3) Å, c = 21.780(4) Å, β = 109.48(3)°). Both compounds contain the similar wave-like ribbon (which is built up by SnSe4 tetrahedra, CdSe4/HgSe4 tetrahedra, and Se22− ions) and the protonated DBNH+ cations (which are located in the inter-ribbon spaces). A pseudo-3D network is formed through C–H⋅⋅⋅Se and N–H⋅⋅⋅Se hydrogen bonds with adjacent ribbons. The sharp UV-Vis absorption edges suggest band gaps of 2.13 eV for 1 and 2.18 eV for 2, respectively.

Diffusion mediated agglomeration of CdS nanoparticles via Langmuir–Blodgett technique

We have reported a diffusion mediated agglomeration of cadmium sulphide (CdS) nanoparticles within cadmium arachidate (CdA2) film matrix. The structural morphology and formation of CdS nanoparticles are characterized by X-ray diffraction (XRD), X-ray reflectivity (XRR), atomic force microscopy (AFM) and ultraviolet-visible spectroscopy techniques. X-ray diffraction (XRD) results show a change in bilayer difference from 53.04Å to 43Å after the sulphidation. An epitaxial growth of the films by ∼5Å after sulphidation is confirmed from atomic force microscopy studies. The particle size calculated form UV–vis absorption edges are found to be varying from 2.6nm to 3.3nm for the different layers. A lateral dimension of 72–80nm from AFM measurements and a size of 2.6–3.3nm have confirmed one side flat pseudo two-dimensional disk-like nanoparticles. UV–vis reflectivity peak at E1 (A) confirms the formation of hexagonal CdS nanoparticles along the c-axis.

Redox properties of α2-K8P2W17(M·OH2)O61 (M = MnII, ZnII, FeII, CoII, and NiII) Wells–Dawson heteropolyacids probed by scanning tunneling microscopy and tunneling spectroscopy

Abstract Scanning tunneling microscopy (STM) and tunneling spectroscopy investigations of α 2 -K 8 P 2 W 17 (M·OH 2 )O 61 (M = Mn II , Zn II , Fe II , Co II , and Ni II ) Wells–Dawson heteropolyacids (HPAs) were conducted. HPAs formed self-assembled and well-ordered arrays on graphite surface. Negative differential resistance (NDR) phenomena were observed in the tunneling spectra of the HPAs. NDR peak voltage of the HPAs appeared at less negative voltage with increasing reduction potential and with decreasing UV–visible absorption edge energy. HPAs were then applied to the electro-oxidation of methanol as a redox mediator. The oxidation activity for residual intermediates in the reaction increased as NDR peak voltage of HPA appeared at less negative voltage.

Electrical, dielectric and optical properties of Sb2O3–PbCl2–MoO3 glasses

Electrical, dielectric, and optical properties of lead molybdenum antimonoxychloride glasses, (90−x)Sb2O3–10PbCl2–xMoO3 (x ∈ {10,15,…35} mol%), are reported and discussed. DC conductivity is measured in the temperature range from −50°C up to 160°C. At higher temperatures, temperature dependences of the dc conductivity are Arrhenius-like with conduction activation energies equal to 1.00±0.06eV. With increasing concentration of MoO3 the dc conductivity increases. At lower temperatures, the activation energy slightly decreases; this decrease is more pronounced at higher concentration of MoO3. It is probable that electron hopping between Mo5+ and Mo6+ contributes to the dc conductivity, at low temperature. Frequency dependences (100Hz to 100kHz) of ac conductivity and relative permittivity are measured at a constant temperature in the range (20–200°C). Modular analysis gives static relative permittivity ranging from 20.2 up to 24. Infrared spectra and UV–VIS spectra are measured. Strong extrinsic absorption bands in infrared region originate from hydroxyl groups, CO2 and Si–O vibrations. The slope of UV–VIS absorption edge edge decreases and the optical gap shifts to longer wavelengths with increasing MoO3 content.

Photoluminescence and optical dispersion parameters of N-doped ZnO nano-fiber thin films

N-doped ZnO (NZO) nanocrystalline thin films were successfully synthesized via sol–gel method. The structural and optical properties of the films were characterized by various techniques including X-ray diffraction, atomic force microscopy (AFM), UV–vis absorption and photoluminescence. The UV–vis absorption edge was changed with increasing N-doping concentration. X-ray diffraction (XRD) results clearly showed that the zinc oxide doped with nitrogen (5 to 20 wt.%) were identified with phases of hexagonal ZnO and N-doped ZnO nanocrystalline thin films. The refractive index dispersion mechanism obeys the Single oscillator model. The dispersion parameters E o and E d of the thin films were determined. The dispersion parameters were changed by N dopant. It is evaluated that the structural, optical constants, photoluminescence properties of Zinc oxide film can be controlled by N dopants.

Optical properties of copper modified sol–gel SiO2 thin films

Copper modified SiO2 thin films have been synthetized by sol–gel/dip coating process and annealed at 450°C. The presence of crystallized CuO is only detected for the highest level of introduced Cu [Cu/(Cu+Si)=0.2]. UV–Visible absorption edge increases with the copper content in the film. Optical gap (Eg) and Urbach energy (Eu) extracted from the UV–Visible absorption curves evidence the large effect of the presence of copper species on silica optical properties. The decrease of the optical gap agrees with the lowering of the UV–Visible absorption peak energy calculated at the Time Dependent Density Functional Theory (TD-DFT) level for silica clusters without and with a copper atom.

Synthesis of soluble and autophotosensitive hyperbranched polyimides with good optical properties and thermal properties

A series of autophotosensitive hyperbranched polyimides based on a new triamine, 1,3,5-tri(3-aminophenoxy-4′-benzoyl)benzene (TABB), various aromatic dianhydride monomers, and endcapped with ortho-alkyl aniline was synthesized by two-step chemical imidization methods. UV–vis spectra indicated high optical transparency of the hyperbranched polymer (HBPI) films with a UV–vis absorption edge of 342–353 nm. The spin-coated films of HBPIs presented a minimum birefringence value as low as 0.0026 at 650 nm and low dielectric constants of 2.74–3.09 (at 1 MHz). The HBPI films also showed high glass-transition temperatures between 190 and 238 °C, good thermal stabilities with 5 wt % loss temperatures ranged from 506 to 525 °C and excellent organosolubilities even in acetone and chloroform. Photolithographic property of the polymer was examined by UV exposure. SEM analysis revealed that highly resolved pattern with a line width of 20 µm were obtained. A series of soluble and autophotosensitive hyperbranched polyimides were successfully prepared. The hyperbranched polymer (HBPI) films showed excellent solubility, low dielectric constant and a minimum birefringence value as low as 0.0026 at 650 nm. In addition, HBPI-1 and 3, exhibited excellent optical properties and good photolithographic properties, may be considered as promising processable high-temperature materials for applications in microelectronic and optical devices.

Photodecomposition of H<sub>2</sub>S to H<sub>2</sub> over Cu<sup>2+</sup> Doped Cd<sub>0.3</sub>In<sub>2</sub>S<sub>4</sub>-Zn<sub>0.7</sub>In<sub>2</sub>S<sub>4</sub> Composite Photocatalysts

The Cd0.3In2S4-Zn0.7In2S4 composite photocatalyst doped with transition metal Cu2+ has been synthesized by hydrothermal method. The physical and photophysical properties of the above-prepared photocatalysts were characterized by XRD, UV-Vis, SPS, SEM and XPS. The XRD peaks of Cu2+ doped Cd0.3In2S4-Zn0.7In2S4 were almost the same as the crystal structure of Cd0.3In2S4-Zn0.7In2S4. The UV-Vis absorption edge of Cu2+ doped Cd0.3In2S4-Zn0.7In2S4 shifted monotonically to long wavelength. The photocatalytic activity of Cu2+ doped photocatalysts had been improved as a result of the enhancement of the charge separation efficiency. The results indicated that the photocatalyst of Cu2+(2wt %)-Cd0.3In2S4/Zn0.7In2S4 exhibited the highest photocatalytic activity with the rate of H2 evolution to be 1141 μmol/(h·g) under visible light irradiation.

ZnFe2O4-TiO2Nanoparticles within Mesoporous MCM-41

A novel nanocomposite ZnFe2O4-TiO2/MCM-41 (ZTM) was synthesized by a sol-gel method and characterized through X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption-desorption, Raman spectroscopy, and ultraviolet visible (UV-vis) spectrophotometry. The results confirmed the incorporation of ZnFe2O4-TiO2 nanoparticles inside the pores of the mesoporous MCM-41 host without destroying its integrity. ZnFe2O4 nanoparticles can inhibit the transformation of anatase into rutile phase of TiO2. Incorporation of ZnFe2O4-TiO2 within MCM-41 avoided the agglomeration of nanoparticles and reduced the band gap energy of TiO2 to enhance its visible light photocatalytic activity. UV-vis absorption edges of ZTM nanocomposites redshifted with the increase of Zn/Ti molar ratio. The nanocomposite approach could be a potential choice for enhancing the photoactivity of TiO2, indicating an interesting application in the photodegradation and photoelectric fields.

Study on Stability of AgI/TiO<sub>2</sub> Visible Light Photocatalysts in Solutions of Various pH Values

Nanostructured AgI/TiO2 photocatalysts exhibit highly efficient visible light photocatalytic activity. Though there have been extensive investigations on AgI/TiO2 photocatalysts, study on their stablity is still very limited. So in this paper, such a study is designed and conducted. AgI/TiO2 nanostructured photocatalysts were prepared and separately immersed in HCl solutions, DI water and NaOH solutions with pH value of 0, 4, 7, 10 and 14, respectively. X-ray diffraction and diffusive reflectance UV-vis spectroscopy analyses reveal that the immersion in acidic solutions led to the formation of AgCl and a blue shifting to 450nm for the absorption edge of AgI/TiO2, while the alkaline treatment had no significant effect on the composite structure of AgI/TiO2 or on the UV-vis absorption edge. Photocatalytic tests show that immersion in acidic solutions had more significant influence on AgI/TiO2 photocatalytic degradation of methyl orange (MO). At pH = 4, photocatalytic efficiency was dropped nearly 30%. At pH = 10, no significant change was observed. AgI/TiO2 nanostructured photocatalysts have thus been found to display a higher stability in alkaline solutions than in acidic solutions.

Effect of Structural Parameters of TiO2 Nanotube Arrays upon Their Photocatalytic/Photoelectrocatalytic Performance

AbstractThe effect of structural parameters of TiO2 nanotube arrays (TNAs) upon their photocatalytic/photoelectro‐catalytic performance is studied by comparing the morphological characteristics and physicochemical properties with different tube lengths prepared from three kinds of electrolytes. The results show that the UV‐Vis absorption edge of TNAs red‐shifted with the increment of tube length and the short TNAs possess higher bandgap energy. The variation tendency of electrochemical window of TNAs is DMSO (5.5 V)>Cit (3.2 V)>HF (1.8 V). The long TNAs possess higher photocatalytic (PC) reactivity suggesting the surface roughness factor is the main determinant of PC efficiency, although, there is obvious recombination effects for the long TNAs. Evidenced by the positive correlation between tube length and photoelectrocatalytic (PEC) efficiency for TNAs from the same electrolyte, the enhancement of the tube length could lead to better PEC reactivity, but when the tube length is over a certain value, the PEC degradation rate no longer increases but decreases. The long TNAs with large surface roughness factor prepared from Cit and DMSO electrolytes exhibit comparative or even lower PEC performance compared with the short TNAs prepared from HF electrolyte, indicating that the PEC performance of TNAs was dominated by charge separation and photoelectron transfer properties rather than surface roughness coefficient and the tube length.

Towards atomic level vanadium doping of TiO 2 via liquid-phase atomic layer deposition

Vanadium-doping of TiO 2 at the atomic level was achieved via a liquid phase atomic layer deposition (L-ALD) method. UV–vis absorption edge of vanadium-doped TiO 2 has been red-shifted ∼55 nm into visible light region. Photocatalytical assessment reveals that the degradation rate of methylene blue (MB) for vanadium-doped TiO 2 under visible light illumination was enhanced by up to 500% compared to the undoped TiO 2. This improvement was believed to be attributed to the atomic level doping of the L-ALD method.

Effects of an Intercalation Nanocomposite at the Photoanode/Electrolyte Interface in Quasi-Solid Dye-Sensitized Solar Cells

In this paper, interface effects of N-methyl-benzimidazole (NMBI) and a novel intercalation composite of NMBI and montmorillonite (MMT) were studied. The intercalation composite showed better interface modification effects than NMBI individually. The FTIR spectra results showed interaction between N3 and NMBI could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. However, the results of cyclic voltammograms and UV–vis absorption edge revealed the interaction between NMBI and dye molecules could cause the lowest unoccupied molecular orbital (LUMO) level of the dye molecule to drop, decreasing the electron injection efficiency. It decreased the Jsc of dye-sensitized solar cells (DSCs). The intercalation composite could remedy the disadvantage of NMBI and obtain strengthened interface effects. The photocurrent–voltage (I–V) curve showed that, with the modification of this intercalation nanocomposite, the Jsc of the devices increased, showing that the disadvantage caused by NMBI was improved. Besides, results of the dark current curve and transient photovoltage spectra showed the NMBI–MMT intercalation composite modification retarded charge recombination more effectively than using NMBI individually. An electrochemical impedance spectroscopy (EIS) test also indicated that modification of the NMBI–MMT intercalation composite showed a strengthened effect of retarding the charge recombination. Furthermore, the results of intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) tests also showed that the interface modification of the NMBI–MMT intercalation composite enhanced the electron transportation and lifetime in DSCs more than using NMBI individually.

Synthesis of hydroxyphenylglycine-derived novel poly(silylenevinylenephenyleneethynylene)s

The hydrosilylation polymerization of d-(−)- p-hydroxyphenylglycine-derived diethynyl monomers 1 p and 1 m with dihydrosilanes Si1 and Si2 was carried out using RhI(PPh 3) 3 as a catalyst to give optically active novel poly(silylenevinylenephenyleneethynylene)s [( E)-poly( 1 p - Si1), ( E)-poly( 1 p - Si2), ( E)-poly( 1 m - Si1), ( E)-poly( 1 m - Si2), and ( Z)-poly( 1 p - Si1)] with number-average molecular weights ranging from 2800 to 17,000 in 41–92% yields. Polymers having ( E)- and ( Z)-olefin moieties were obtained, wherein the ( E)-/( Z)-ratios depended on the reaction conditions. The UV–vis absorption edge of ( E)-poly( 1 p - Si1) was positioned at a wavelength longer than that of ( Z)-poly( 1 p - Si1), indicating that ( E)-vinylene-linkage extends the conjugation more largely than the ( Z)-counterpart. This was also confirmed by fluorescence spectroscopy. Alkaline hydrolysis of ester moieties of these polymers gave the corresponding polymers having carboxy groups. The ( E)-polymers showed different solubility in hydrophobic solvents before and after hydrolysis, but the non-hydrolyzed and hydrolyzed ( Z)-polymers exhibited the same solubility.

Interface modification effects of 4-tertbutylpyridine interacting with N3 molecules in quasi-solid dye-sensitized solar cells

In this paper, the interface modification effects of 4-tertbutylpyridine (TBP), especially the interaction with dye molecules, were discussed. The results of FTIR showed that TBP interacted with dye molecules, in addition to its interaction with the TiO(2) film. Reaction between N3 and TBP by the interaction force of the H atom in the -COOH group of N3 and the N atom of TBP could retard the aggregation of dye molecules, decreasing the electron quenching and charge recombination. Furthermore, the results of cyclic voltammograms and UV-vis absorption edge revealed the interaction between TBP and dye molecules could cause the energy level of the dye molecules to change, influencing the electron injection efficiency in DSCs. The IPCE results indicated that with TBP modification, the injection efficiency decreased, but the electron collection efficiency was enhanced.

Structure and optical property of CdS/niobate composite synthesized by exfoliation/self-assembly processing

CdS/niobate composite synthesized by exfoliation/self-assembly processing was first reported. The processing presents two steps, namely (i) restacking of [Ca 2Nb 3O 10] n n− nanosheets in Cd(NH 3) 4 2+ solution and (ii) forming of CdS/niobate composite by adding Na 2S to the (i) reacting system. The as-prepared composite of CdS/niobate can be indexed to tetrahedral symmetry (lattice parameters, a 5.462(5) Å; c 17.3303(1) Å) on basis of X-Ray powder diffraction result. The scanning electron microscope and energy dispersive spectrometer observation demonstrates the uniform distributions of Ca, Nb, O, Cd, and S elements in the particles. The UV–vis absorption edge of the CdS/niobate composite (CdS coated with host niobate) shows blue shift (shifts to high energy) compared with that of the uncoated CdS particles.

Redox properties and oxidation catalysis of group 5 metal (V, Nb, Ta)-containing Keggin and Wells–Dawson heteropolyacid (HPA) catalysts

Group 5 metal-containing H 4PW 11M 1O 40 (M = V, Nb, Ta) Keggin heteropolyacids (HPAs) and H 7P 2W 17M 1O 62 (M = V, Nb, Ta) Wells–Dawson HPAs were prepared in this work. Reduction potentials and UV–visible absorption edge energies of H 4PW 11M 1O 40 (M = V, Nb, Ta) and H 7P 2W 17M 1O 62 (M = V, Nb, Ta) HPA catalysts in solution were measured by an electrochemical method and UV–visible spectroscopy, respectively. It was observed that reduction potentials of H 4PW 11M 1O 40 (M = V, Nb, Ta) and H 7P 2W 17M 1O 62 (M = V, Nb, Ta) HPA catalysts increased with decreasing absorption edge energies of the HPA catalysts. In order to correlate the redox properties (reduction potential and absorption edge energy) with the oxidation catalysis of H 4PW 11M 1O 40 (M = V, Nb, Ta) and H 7P 2W 17M 1O 62 (M = V, Nb, Ta) HPA catalysts, we carried out vapor-phase benzyl alcohol oxidation as a model reaction. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalysts. Reduction potentials of H 4PW 11M 1O 40 (M = V, Nb, Ta) and H 7P 2W 17M 1O 62 (M = V, Nb, Ta) HPA catalysts measured by an electrochemical method and absorption edge energies of the HPA catalysts measured by UV–visible spectroscopy could be utilized as probes of oxidation catalysis of the HPA catalysts.

Large-scale synthesis of CuS hexaplates in mixed solvents using a solvothermal method

Large-scale covellite CuS hexaplates were successfully synthesized by the 200 °C solvothermal reactions of CuCl 2.2H 2O and (NH 4) 2S in C 2H 5OH–H 2O mixed solvents containing HCOOH as a pH stabilizer, including different amounts and molecular weights (MWs) of polyethylene glycol (PEG). By using XRD and SAED, CuS (hcp) was detected. XRD peaks of the product, synthesized in a solution containing 5 g PEG6000 and 1.5 ml HCOOH for 5 h, are in accordance with those of the simulation and database. The (110) peak shows the preferential growth, corresponding to the hexaplates, characterized using SEM, TEM and HRTEM. CuS hexaplates with the (100) and (010) lattice planes at an angle of 120° were detected on the flat surface, and the (002) lattice plane on the edge. UV–vis absorption edge was detected at 610 nm (2.03 eV), and the PL emission at 361 nm (3.43 eV). Phase and morphology formations were also explained according to the experimental results.