Surfactant modified deoxyribonucleic acid films: synthesis,interaction with acridine orange and luminescent properties

Dye-doped deoxyribonucleic acids (DNA)–tetradecyltrimethylammonium (TTA) films have been prepared. Acridine orange, known as a DNA-binding molecule, can be spontaneously doped by immersing the DNA–TTA film in an acetonitrile solution of the dye. Dye-doped samples exhibit two characteristic absorption bands corresponding to the dye monomer and aggregate, respectively. With the elapse of time after immersion, dye molecules undergo an unusual transformation from the aggregate state to the monomer state, and photoluminescence intensity also increases. Dye molecules in the sample exhibit a pronounced enhancement in their photoluminescence intensity than those in PMMA. The photoluminescence intensity of the samples strongly correlates to both of the dye concentration and monomer/(monomer + aggregates) ratio. Not only the hydrophobic interaction but also the electrostatic force between DNA and dyes play important roles in the formation of the dye-doped samples. It is surmised that monomers and aggregates disperse within the hydrophobic TTA sites in the early stage, and then a part of monomers presumably intercalate between adjacent base pairs of DNA with the elapse of time.     

ZnO nanocrystalline thin films: a correlation of microstructural,optoelectronic properties

The compositional, structural, microstructural, dc electrical conductivity and optical properties of undoped zinc oxide films prepared by the sol–gel process using a spin-coating technique were investigated. The ZnO films were obtained by 5 cycle spin-coated and dried zinc oxide films followed by annealing in air at 600 °C. The films deposited on the platinum coated silicon substrate were crystallized in a hexagonal wurtzite form. The energy-dispersive X-ray (EDX) spectrometry shows Zn and O elements in the products with an approximate molar ratio. TEM image of ZnO thin film shows that a grain of about 60–80 nm in size is really an aggregate of many small crystallites of around 10–20 nm. Electron diffraction pattern shows that the ZnO films exhibited hexagonal structure. The SEM micrograph showed that the films consist in nanocrystalline grains randomly distributed with voids in different regions. The dc conductivity found in the range of 10⁻⁵–10⁻⁶ (Ω cm)⁻¹. The optical study showed that the spectra for all samples give the transparency in the visible range.     

Sol–gel derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript> thin films: effect of annealing on structural,morphological and optoelectronic properties

Nanocrystalline Co₃O₄ thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co₃O₄ thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co₃O₄ films is improved by annealing. The dc electrical conductivity of Co₃O₄ thin films were increased from 10⁻⁴ to 10⁻² (Ω cm)⁻¹ with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 10¹⁹ cm⁻³ and 5.2–7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹ respectively. It is observed that Co₃O₄ thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.     

Electrical and optical properties of one-dimensional metallophthalocyanine (M?=?Fe) thin films grown by thermal evaporation

Semiconducting molecular materials based on iron phthalocyanine and diamine ligands have been successfully used to prepare thin films by a thermal evaporation technique. The samples were deposited on corning glass substrates and crystalline silicon wafers and were characterized by FT-IR, UV–Vis, SEM and EDS. The optical parameters have been investigated using spectrophotometric transmission measurements in the 200–1,150 nm wavelength range. The UV–VIS spectra of the films show two well defined absorption bands, namely, the Soret and the Q-band. The values of the optical band gap E_g (direct transitions) calculated from the absorption spectra, ranged between 3.30 and 4.38 eV. The effect of temperature on the conductivity of the films was also evaluated and the electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.04–0.64 eV, were calculated from Arrhenius plots.     

Undoped tin oxide thin films obtained by the sol gel technique,starting from a simple precursor solution

In this work, we report the synthesis and the structural, optical and electrical properties of undoped tin oxide thin films obtained by the sol–gel technique. The films have been prepared from a simpler precursor solution than other ones reported; it is based on stannous chloride (SnCl₂·2H₂O), ethanol, glycerol and triethylamine. The films are deposited on glass slide substrates and sintered at temperatures in the 300–550 °C range, in an open atmosphere. A second thermal treatment in vacuum is made in order to decrease the resistivity of the films. The X-ray diffraction patterns show the tetragonal phase of SnO₂ with a small preferential orientation in the (110) plane. All films show high optical transmission (~85%) and a direct band gap value around of 3.8 eV. The minimum resistivity value, 2 × 10⁻¹ Ohm-cm, is obtained for the films sintered at 300 and 350 °C and thermal treated in vacuum at 500 °C for 1 h. The decrease of the resistivity with the thermal treatment in vacuum is associated with an increase in the oxygen vacancies concentration.     

Investigation of structural,electrical and optical properties of nickel substituted CdSe thin films

The technologically important Cd_1−xNi_xSe thin films with variable compositions (0 ≤ x ≤ 1) have been developed by a chemical deposition method. The structural, compositional, optical and electrical properties were studied by X-ray diffraction, Scanning electron microscopy, Atomic absorption spectroscopy, UV–visible double beam spectrophotometer and d.c. two probe method. XRD studies indicate polycrystalline in nature with hexagonal phase for all the samples. The lattice constants decrease with increase in nickel content in CdSe host lattice. The surface morphology study of all samples reveals uniform and spherical grains. An optical study of the samples shows that band gap value decreases with nickel content. Electrical measurements depict semiconducting properties of all samples.     

Colored microporous polyethylene films: effect of porous structure on dye adsorption

Microporous polyethylene (PE) films with good mechanical properties have been produced by high-speed extrusion from the melt followed by annealing, uniaxial stretching and thermal fixation. The films have pores of 0.15–0.45 μm size and relief on the scale of 1–2 μm. Coloration of the films with fluorescent dyes, 3-aminobenzanthrone and derivatives of 1,8-naphthalimide, was performed at the room temperature. The quantity of adsorbed dye depends upon the spin draw ratio of PE membranes and has an influence upon their color shade. The color effect is not observed in the case of only extruded or annealed PE films treated in the same way. The enhanced adhesion of the dyes on porous films is related to their high surface area. Specifically, the interactions between dye and polymer at pore walls provide color stability of the microporous films. The effect of relevant properties of both PE membranes (pores relief and lamellar thickness) and dye molecules (aspect ratio and cohesion) is discussed. Electronic Publication     

Influence of gamma radiation on the optical properties of ZnSe nanocrystalline thin films

The effect of gamma (γ) irradiation on the absorption spectra and the optical energy bandwidth of ZnSe nanocrystalline thin films have been studied. Thin films of different thicknesses from 20 to 120 nm were deposited by Inert gas condensation technique at constant temperature of 300 K and under pressure 2 × 10⁻³ Torr of Argon gas flow. The optical transmission (T) and optical reflection (R) in the wavelength range 190–2,500 nm of ZnSe nanocrystalline thin films were measure for unirradiated and irradiated films. The dependence of the absorption coefficient α on photon energy hν was determined for different γ-doses irradiated films. The ZnSe thin films show direct allowed interband transition by γ-doses. Both the absorption coefficient (α) and optical energy bandwidth were found to be γ-dose dependent. The optical energy band width has been decreased by irradiated of γ-doses. The E_gn values of irradiated thin films by 34.5 Gy of γ-doses were recovered to nearly their initial values after 100 days at 300 K.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

The effects of temperature on the molecular orientation of zinc phthalocyanine films

Phthalocyanine compounds have been widely investigated as candidate materials for technological applications, which is mainly due to their thermal stability and possibility of processing in the form of thin films. In most applications, the controlled growth of thin films with high crystalline quality is essential. In this study, zinc phthalocyanine (ZnPc) thin films were prepared by evaporation on glass and Au-coated glass substrates with subsequent annealing at different temperatures in ambient atmosphere. The morphological and structural features of 80 nm thick zinc phthalocyanine films were investigated, evidencing an α → β phase transformation after annealing the films at 200 °C, as indicated by UV–Vis spectroscopy and FTIR analyses. A better uniformity of the annealed films was also evidenced via AFM analysis, which may be of importance for applications where film homogeneity and excellent optical quality are required.     

Novel process for low temperature crystallization of a-SiC:H for optoelectronic applications

Metal-induced crystallization (MIC) process was employed to crystallize hydrogenated amorphous silicon carbide (a-SiC:H) films deposited by PECVD on n-type Si substrate. To optimize the crystallization process, Aluminum thin films of different thicknesses were deposited on a-SiC:H films which were then annealed at 600 °C in N₂ environment for 1 h. UV–visible spectrophotometer, atomic force microscopy (AFM) and hall measurement system were used to characterize the films. It was observed from the UV–visible spectrum that the films crystallized using higher Al thickness show absorption in the visible range whereas the samples crystallized with lower Al thickness did not show absorption in the visible range but shows large absorption above the bandgap of the material. Considering UV–visible and Hall measurement data it can be concluded that the sample crystallized with 50 nm of Al can be a good candidate for SiC–Si hetero-junction solar cells.     

Investigations on the structural, optical and electrical properties of Nb-doped SnO2 thin films

Niobium-doped tin oxide thin films were deposited on glass substrates by the chemical spray pyrolysis method at a substrate temperature of 400 °C. Effects of Nb doping on the structural, electrical and optical properties have been investigated as a function of niobium concentration (0–2 at.%) in the spray solution. X-ray diffraction patterns showed that the films are polycrystalline in nature and the preferred growth direction of the undoped film shifts to (200) for Nb-doped films. Atomic force microscopy study shows that the surface morphology of these films vary when doping concentration varies. The negative sign of Hall coefficient confirmed the n-type conductivity. Resistivity of ~4.3 × 10⁻³ Ω cm, carrier concentration of ~5 × 10¹⁹ cm⁻³, mobility of ~25 cm² V⁻¹ s⁻¹ and an average optical transmittance of ~70% in the visible region (500–800 nm) were obtained for the film doped with 0.5 at.% niobium.     

Fabrication and ferroelectric properties of sol–gel derived 1–1 intergrowth-superlattice-structured Bi<Subscript>3</Subscript>TiNbO<Subscript>9</Subscript>-Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

1–1 intergrowth-superlattice-structured Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT) ferroelectric thin films have been prepared on p-Si substrates by sol-gel processing. The precursor films are crystallized in the desired intergrown BTN–BIT superlattice structures by optimizing the processing conditions. Synthesized BTN–BIT thin films annealed below 750 °C are polycrystalline, uniform and crack-free, no pyrochlore phase or other second phase, and exhibited good ferroelectric properties. As the annealing temperature increases from 600 to 700 °C, both remanent polarization P _r and coercive electric field E _c of BTN–BIT thin films increase, but the pyrochlore phase in BTN–BIT films annealed above 750 °C will impair the ferroelectric properties. The BTN–BIT thin films annealed at 700 °C have a P _r value ~19.1μC/cm² and an E _c value ~135 kV/cm.     

Boron-doped zinc oxide thin films prepared by sol-gel technique

Multilayer transparent conducting boron-doped zinc oxide films have been prepared on glass substrates by the sol gel dip coating process. Zinc acetate solutions of 0.4 M in isopropanol stabilized by diethanolamine and doped with boron tri-i-propoxide were used. Each layer was fired at 400–650^∘C in a conventional furnace for 30 min. Selected samples were vacuum annealed at 400–450^∘C for 1 h to improve their electrical properties. The electrical resistivity curve with doping shows a minimum around 0.8 at.%. Excess boron caused a drop of the carrier mobility without acting as donors. Post-deposition annealing sequence was crucial for dopant partial regeneration. Films with an average optical transmittance exceeding 90% can be achieved reproducibly.     

Electrodeposition of CuInSe2 in citrate-containing electrolytes

CuInSe₂ is a frequent constituent of solar cells. Low-cost solar cells can be prepared by electrodeposition from a single bath, provided that the multiple variables affecting the process can be properly tuned. Our design includes an n-layer of TiO₂ (dense and/or nanoporous), on top of which a p-layer of CuInSe₂ is electrodeposited. The TiO₂ layer is supported on conductive glass. When CuInSe₂ is applied onto TiO₂, a p–n junction is formed by which sunlight could be transformed into electricity. CuInSe₂ films have been prepared by electrodeposition from a single bath aqueous solution. Citrate has been used as complexing agent, so as to shift the copper deposition potential in the negative direction, bringing it closer to the In deposition potential. Films are obtained potentiostatically at −0.8 V (vs. standard calomel electrode) for 1 h. The electrolyte consisted of 0.4 mol/L sodium citrate containing 3 mmol/L CuCl₂, 6 mmol/L InCl₃, and 5 mmol/L SeO₂. Different pH values between 4 and 6 are investigated. The samples are annealed in a furnace under flowing Ar at 350 °C for 15 min, which proves to be essential to improve the crystallinity of the CuInSe₂ films. TiO₂ and CuInSe₂ have been characterized using scanning electron microscopy, X-ray diffraction, and optical absorption spectroscopy. The morphology and the physical and optical properties are in good agreement with those reported in the literature. In order to investigate the photoresponse of the cells, current–voltage curves of prototype devices are performed in the dark and under light.     

Low temperature synthesis of sol–gel derived Al-doped ZnO thin films with rapid thermal annealing process

A series of sol–gel derived Al-doped ZnO (AZO) thin films with rapid thermal annealing process at low temperature were studied to examine the influence of annealing temperature and the Al doping concentration on their microstructure, electrical and optical transport properties. Crystalline AZO thin films were obtained following an annealing process at temperatures between 400 and 600 °C for 10 min in argon gas ambient. AZO thin films with Al doping of 1 at% were oriented more preferentially along the (002) direction, and have larger grain size and lower electrical resistivity, while the highest average optical transmittances of 92% were observed in AZO films with Al doping of 2 at%. With the annealing temperature increasing from 400 to 600 °C, the grain size of AZO films increased, the optical transmittance became higher, and the electrical resistivity decreased to a lowest value of 1.2 × 10⁻⁴ Ω cm resulting from the increase of the carrier concentration and the mobility.     

Structural, optoelectronic and electrochemical properties of nickel oxide films

Thin nickel oxide (NiO) films were deposited by the electron beam evaporation technique. The films were post annealed in air at 450–500 °C for 5 h and the effect of annealing on the structural, microstructural, electrical and optical properties were studied. X-ray diffraction studies indicated the polycrystalline nature of the films. The microstructural parameters were evaluated. The band gap of the films was found to be about 3.60 eV. Electrical resistivity of the films was 4.5 × 10⁻⁴ Ω cm. FTIR studies indicated a broad spectrum centered at 461.6 cm⁻¹. Cyclic voltammetry studies in 1 M KOH solution revealed good electronic electrochromic behaviour.     

Comparative investigation on nanocrystal structure,optical, and electrical properties of ZnO and Sr-doped ZnO thin films using chemical bath deposition method

This paper reports on the comparative investigation of structural and optical properties of nano thin films of ZnO and Sr-doped ZnO (SZO) onto glass substrates synthesized by a two-step chemical bath deposition (CBD) technique. The mode of crystallization, structural properties, and morphologies have been investigated. The films are polycrystalline in nature with hexagonal phase having (002) preferential orientation. The typical crystallite size is also estimated and found to be around 30–80 nm. The shifts in optical band gap of the SZO films are estimated to be ∼3.25–3.27 eV with respect to the ZnO film and the refractive index is 2.35. The room temperature resistivity is of the order of ∼2,000 Ωcm. Thermoemf measurements show that films are of n-type. The sensitivity of the films was studied as a function of their temperature 275–575 K for a fixed ethanol concentration (400 ppm). The films have been tested for cross sensitivity for different gases and it has been confirmed that these are highly sensitive and selective for ethanol vapors around 200 °C in air atmosphere.     

Nanocrystalline TiO2 thin films for NH3 monitoring: microstructural and physical characterization

Nanocrystalline titanium oxide thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH₃ gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by X ray diffraction, Scanning microscopy, high resolution electron microscopy and selected area electron diffraction. The X-ray diffraction measurements confirmed that the films grown by this technique have good crystalline tetragonal mixed anatase and rutile phase structure. The HRTEM image of TiO₂ thin film showed grains of about 50–60 nm in size with aggregation of 10–15 nm crystallites. Selected area electron diffraction pattern shows that the TiO₂ films exhibited tetragonal structure. The surface morphology (SEM) of the TiO₂ film showed that the nanoparticles are fine with an average grain size of about 50–60 nm. The optical band gap of TiO₂ film is 3.26 eV. Gas sensing properties showed that TiO₂ films were sensitive as well as fast in responding to NH₃. A high sensitivity for ammonia indicates that the TiO₂ films are selective for this gas.     

Optical and electrical properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O thin films by sol–gel method

Mg _x Zn_1−x O (0 ≤ x ≤ 0.35) thin films have been deposited by sol–gel technique and the composition related structural, electrical, and optical properties are investigated. All the films have hexagonal wurtzite structure and the separation of MgO phase occurs when x = 0.3 and 0.35. With the increase of Mg content, the densification of the films decrease and band gap values increase. The maximum band gap value reaches 3.56 eV when x = 0.15. After Mg doping the conductivities of the Mg _x Zn_1−x O films are reduced greatly and the electrical current–voltage (I–V) characteristics show nonlinearity for x > 0.15.