Enhancement of photosensitivity by annealing in Bi2S3 thin films grown using SILAR method

Bi₂S₃ thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi₂S₃ thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi₂S₃ thin film gives good photoresponse as compared to as deposited thin film and Bi₂S₃ thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi₂S₃ thin films revealed n-type electrical conductivity.     

Preparation and characterization of CdS–Bi2S3 nanocomposite thin film by successive ionic layer adsorption and reaction (SILAR) method

CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. These films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrical measurement systems. A comparative study was made between CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin films. The XRD patterns reveal that CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin film have hexagonal, orthorhombic and mixed phase of hexagonal CdS and orthorhombic Bi₂S₃ crystal structure, respectively. SEM images showed uniform deposition of the material over the entire glass substrate. The energy band gap for CdS, Bi₂S₃ and CdS–Bi₂S₃ thin films were revealed from the optical studies and were found to be 2.4, 1.6 and 1.69 eV, respectively. The thermoemf measurements of CdS–Bi₂S₃ nanocomposite thin film revealed n-type electrical conductivity, while the I–V measurement of CdS, Bi₂S₃ and CdS–Bi₂S₃ nanocomposite thin film under dark and illumination condition (100 mW/cm²) exhibited photoconductivity phenomena suggesting its applicability in photosensors devices.     

Sb2S3:C/CdS p-n junction by laser irradiation

In this paper, we report laser irradiated carbon doping of Sb₂S₃ thin films and formation of a p-n junction photovoltaic structure using these films. A very thin carbon layer was evaporated on to chemical bath deposited Sb₂S₃ thin films of approximately 0.5 μm in thickness. Sb₂S₃ thin films were prepared from a solution containing SbCl₃ and Na₂S₂O₃ at 27 °C for 5 h and the films obtained were highly resistive. These C/Sb₂S₃ thin films were irradiated by an expanded laser beam of diameter approximately 0.5 cm (5 W power, 532 nm Verdi laser), for 2 min at ambient atmosphere. Morphology and composition of these films were analyzed. These films showed p-type conductivity due to carbon diffusion (Sb₂ S₃:C) by the thermal energy generated by the absorption of laser radiation. In addition, these thin films were incorporated in a photovoltaic structure Ag/Sb₂S₃:C/CdS/ITO/Glass. For this, CdS thin film of 50 nm in thickness was deposited on a commercially available ITO coated glass substrate from a chemical bath containing CdCl₂, sodium citrate, NH₄OH and thiourea at 70 °C. On the CdS film, Sb₂S₃/C layers were deposited. This multilayer structure was subjected to the laser irradiation, C/Sb₂S₃ side facing the beam. The p-n junction formed by p-Sb₂S₃:C and n-type CdS showed V_oc = 500 mV and J_sc = 0.5 mA/cm² under illumination by a tungsten halogen lamp. This work opens up a new method to produce solar cell structures by laser assisted material processing.     

Properties of BGO thin films under the influence of gamma radiation

It is important to know the behaviour of materials under the influence of radiation for the effective design of novel sensor systems. Optical properties of bismuth germinate (Bi₄Ge₃O₁₂—BGO) thin films were investigated in terms of their perception to gamma radiation exposure. An Edwards E306A vacuum thermal coating system was used for thin films deposition. BGO films with a thickness of 200 nm were exposed to a disk-type ¹³⁷Cs gamma radiation source with an activity of 370 kBq. Optical properties of the films were investigated using CARY IE UV-Visible Spectrophotometer. Calculated optical band gap for as-deposited BGO thin film was 1.95 eV. Gamma radiation induced changes in the optical properties of thin films, which could be explained by the variation in the degree of disorder. From the density-of-state model, it is known that optical band gap decreases with an increasing degree of disorder of the amorphous phase.Electrical properties of BGO thin films were recorded in real time using a low power capacitive interface system with a high resolution, which is based on Delta-sigma modulator. At doses from 0 to 1.5 mGy little if any changes in the capacitance were measured. This could be explained by co-existence of two processes, namely creation and annihilation of defects under the influence of radiation. After a threshold dose of 1.5 mGy creation of defects becomes more prevailing and the BGO film capacitance has gradually increased in value from 2.97 pF to 7.09 pF after irradiation with a 2.44 mGy dose.     

Physical properties of Bi2 (Te,Se)3 and Bi2Se1.2Te1.8 prepared using solid-state microwave synthesis

Bi₂(Te, Se)₃ and Bi₂Se_1.2Te_1.8 bulk products were synthesised using standard solid-state microwave synthesis. The Bi₂(Te, Se)₃ and Bi₂Se_1.2Te_1.8 were then deposited thermally onto glass substrates at a pressure of 10^? 6 Torr. The structure of the samples was analysed using X-ray diffraction (XRD), and the powders and thin films were observed to be polycrystalline and rhombohedral in structure. The surface morphology of the samples was determined using scanning electron microscopy (SEM). From the measurements of optical properties, the energy gap values for the Bi₂Te₃, Bi₂Se₃, and Bi₂Se_1.2Te_1.8 thin films were 0.43, 0.73, and 0.65 eV, respectively.     

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.     

Preparation of mixed (Cd,Bi)S composite thin films via surfactant facilitated electrodeposition process and their photoelectrochemical characterization

In the present investigation we explored possibilities of preparing mixed CdS–Bi₂S₃ composite thin films of nanodimensions using a single step surfactant facilitated electrochemical process from aqueous solutions containing different colloidal concentrations of CdS and Bi₂S₃ particles. As deposited composite thin films has been characterized on the basis of SEM, AFM and XRD studies for determination of their surface morphology, surface roughness and grain size. Photoelectrochemical characterization of these composite materials has been carried out on the basis of photopotential, current–voltage (I–V) characteristics under dark and illumination conditions and photoaction spectral studies. Attempt has also been made to estimate the resistance of these composite materials towards their electrochemical corrosion. As prepared mixed (Cd,Bi)S composite semiconductor film exhibits substantial improvement in their photoelectrochemical properties.     

Structure evolution and ferroelectric properties of Bi3.4Yb0.6Ti3O12 thin films crystallized under a moderate temperature

Ytterbium-doped Bi₄Ti₃O₁₂ (Bi_3.4Yb_0.6Ti₃O₁₂, BYT) ferroelectric thin films were successfully deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by chemical solution deposition (CSD). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. Structure evolution and ferroelectric properties of the as-prepared thin films annealed under different temperatures (600 °C-750 °C) were studied in detail. Additionally, the mechanism concerning the dependence of electrical properties of the BYT ferroelectric thin films on the annealing temperature was discussed.     

Effect of gamma radiation on electrical and optical properties of (TeO<Subscript>2</Subscript>)<Subscript>0·9</Subscript> (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0·1</Subscript> thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO₂)_0·9 (In₂O₃)_0·1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 μGy/μA/cm². These values are far superior to any presently available real-time gamma radiation dosimeter.     

Electrodeposition of nano-grain sized Bi-Co thin films in organic bath and their magnetism

In this paper we report the preparation of nano-grain sized Bi_1−xCo_x thin films containing different percentages of bismuth and cobalt by galvanostatic electrodeposition on Cu substrates in organic baths, and provided a good procedure to prepare nano-grain sized Bi-based alloy thin films. The prepared Bi_1−xCo_x thin films consisted almost entirely of nanograins with sizes of 20-80 nm, and they were very compact. The results of X-ray diffraction (XRD) indicated that the nano-grain sized Bi_1−xCo_x thin films were amorphous. After heat treatment of crystallization at 280 °C for 1 h in a protecting atmosphere, Bi(110), Cu(111), Bi₁₀Co₁₆O₃₆(532), Co(102) and Co(110) phases could be found in XRD patterns, respectively. The magnetic measurements showed that the nano-grain sized Bi_1−xCo_x thin films had a superparamagnetism-like behavior with the magnetization increasing rapidly and then reaching saturation, and a clear enlargement of deposit coercivity was obtained by increasing Co content.     

Preparation of Bi2S3 nanorods via a hydrothermal approach

Large-scale bismuth sulfide (Bi₂S₃) nanorods with uniform size have been prepared by hydrothermal method using bismuth chloride (BiCl₃) and sodium sulfide (Na₂S·9H₂O) as raw materials at 180 °C and pH = 1-2 for 12 h. The powder X-ray diffraction (XRD) pattern shows the Bi₂S₃ crystal belongs to the orthorhombic phase with calculated lattice constants a = 1.1187 nm, b = 1.1075 nm and c = 0.3976 nm. Furthermore, the quantification of X-ray photoelectron spectra (XPS) analysis peaks gives an atomic ratio of 1.9:3.0 for Bi:S. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopic (TEM) studies reveal that the appearance of the as-prepared Bi₂S₃ is rod-like with typical lengths in the range of 2-5 μm and diameters in the range of 10-30 nm. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of Bi₂S₃ nanorods is proposed.     

Preparation and properties of Bi2−x As x S3 thin films by solution-gas interface technique

The solution gas interface technique by which thin films of Bi_2−x As _x S₃ were deposited is described in this paper. The semiconducting properties of the interface grown Bi_2−x As _x S₃ thin films are studied. The optical absorption, dark resistivity and thermoelectric power of the films were studied and results are reported.     

Photoelectrochemical characterization of Bi2Se3 thin films deposited by SILAR technique

Bi₂Se₃ thin films have been deposited by simple and less investigated successive ionic layer adsorption and reaction (SILAR) technique onto fluorine-doped tin oxide (FTO) coated glass substrates at room temperature (27 °C). The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies indicate that Bi₂Se₃ thin films are nanocrystalline. These films are used for photoelectrochemical (PEC) characterization in cell with configuration as n-Bi₂Se₃/0.1 M polysulfide/C. The studies such as current–voltage characteristics in dark and light, photovoltaic power output, transient photoresponse, and capacitance–voltage have been carried out. The study reveals that fill factor and power conversion efficiency of the cell are low (0.43 and 0.032%, respectively).The flat bond potential is found to be −0.04 V (SCE).     

Luminescence of Bi3+ in the orthorhombic perovskites CaB4+O3 (B4+=Zr,sn): Crossover from localized to D-state emission

The optical properties of Bi³⁺ in the orthorhombic perovskites CaZrO₃ and CaSnO₃ are investigated. The Stokes shift of Bi³⁺ emission in CaZrO₃ is small (∼0.80 eV) with the peak wavelength of the emission band occurring in the ultraviolet. This emission is attributed to the localized ³P_0,1 → ¹S₀ optical transition. In contrast, the Stokes shift of the Bi³⁺ emission in CaSnO₃ is large (>1 eV) with the emission band peaking in the visible. The emission band is also considerably broadened in CaSnO₃. It is claimed that Bi³⁺ luminescence in CaSnO₃ corresponds with the Bi³⁺ (6s²) -Sn⁴⁺ (5s^°) charge transfer emission (D-state emission). The energy of the ¹S₀→³P₁ (A-band) excitation band in both perovskites are very nearly the same. Physical reasoning is advanced for the occurrence and lack thereof of the D-state emission in these perovskites.     

In situ fabrication of Bi2S3 nanocrystal film for photovoltaic devices

A facile wet-chemical method to prepare Bi₂S₃ thin films with flake nanostructures directly on ITO glass substrate is presented in this paper for the first time. The product was characterized by X-ray powder diffractometer (XRD), Raman spectrometer, scanning electron microscope (SEM), and atomic force microscope (AFM). The one-step solvothermal elements treatment on the ITO substrate spare time to form film by spin-coating process and the film could be tightly attached to the ITO electrode. A conjugated polymer, poly 3-hexylthiophene (P3HT), was then spin-coated on the as-prepared Bi₂S₃ film to form an inorganic-organic hybrid thin film. The photovoltaic performance of the resulting solar cell device was also investigated.     

Photo-sensing properties of Cd-doped In2S3 thin films fabricated via low-cost nebulizer spray pyrolysis technique

In this study, we report the fabrication of cadmium-doped indium sulfide thin films (In₂S₃:Cd) using a low-cost nebulizer-aided spray pyrolysis process at 350 °C on glass substrates for photo-sensing applications. The impact of 0, 2, 4, and 8 wt% cadmium concentrations on the structure, morphology, optical properties, and photo-sensing capabilities of In₂S₃ thin films were examined systematically. From X-ray diffraction (XRD) analysis, the major peak is located in the (103) plane for all Cd-doped In₂S₃ thin film samples, and the maximum crystallite size for the 4 wt% sample is 59 nm. The field emission scanning electron microscope (FESEM) image revealed a homogenous large-grained surface of Cd-doped In₂S₃ film that completely covered the substrate. UV–Vis absorption analysis demonstrated good absorption for all thin film samples in the visible and ultraviolet regions of the electromagnetic spectrum, particularly, the 4% Cd-doped concentration showed excellent absorption as is observed from Tauc relation. The highest PL intensity at 680 nm was observed for the sample coated with 4 wt% of Cd. Under UV light, the I–V behavior depicts a light current of 1.06?×?10^–6 A for a 5 V bias voltage. The In₂S₃: Cd (4%) sample had the highest responsivity of 2.12?×?10^?1A/W and a detectivity of 1.84?×?10¹¹ Jones, with a high EQE of 50%. The study manifests that the developed Cd (4%)-doped In₂S₃ thin film sample might be better suited for the application of photodetectors.

     

Solar cells with Sb2S3 absorber films

CdS/Sb₂S₃/PbS structures were prepared by sequential chemical deposition of CdS, Sb₂S₃ and PbS thin films on TEC-8 (Pilkington) transparent electrically conductive SnO₂ (TCO) coatings. CdS thin films (100 nm) were deposited with hexagonal structure from Cd-citrate bath and of cubic structure from Cd-ammine/triethanolamine bath. Sb₂S₃ thin films were deposited at 40 °C from a solution mixture of potassium antimony tartrate, triethanolamine, ammonia and thioacetamide(TA) or at 1 to 10 °C from a mixture of antimony trichloride and thiosulfate (TS). These films were made photoconductive by heating at temperatures 250 to 300 °C. When heated in the presence of a chemically deposited Se thin film of 300 nm, a solid solution Sb₂S_1.8Se_1.2 resulted. PbS thin films of 100-200 nm thickness were deposited on the TCO/CdS/Sb₂S₃ or TCO/CdS/Sb₂S_1.8Se_1.2 structure. Graphite paint was applied on the PbS film prior to applying a silver epoxy paint. The cell structures were of area 0.4 cm². The best results reported here is for a cell: TCO/CdS(hex-100 nm)/Sb₂S₃(TS-100 nm)/PbS(200 nm) with open circuit voltage (V_oc) 640 mV, short circuit current density 3.73 mA/cm², fill factor 0.29, and conversion efficiency 0.7% under 1000 Wm^− 2 sunlight. Four series-connected cells of area 1 cm² each gave V_oc of 2 V and short circuit current of 1.15 mA.     

Synthesis of novel photocatalytic InVO4-TiO2 thin films with visible light photoactivity

Novel InVO₄-TiO₂ thin films were synthesized by introducing nano InVO₂ into the TiO₂ thin films via a sol-gel method. The photocatalytic efficiency of InVO₄-TiO₂ thin films was investigated by photodegrading of methyl orange in aqueous solution under visible light irradiation. A wide range of characterization techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV-vis absorption spectroscopy (UV-vis), were applied to characterize the obtained thin films. The results indicated that the InVO₄-TiO₂ thin films consist of uniform anatase TiO₂ crystals of 70-80 nm with highly dispersed orthorhombic InVO₄ nanocrystals. The decoloration of methyl orange results illustrated that the InVO₄-TiO₂ thin films with 0.5 wt.% InVO₄ showed the best photoactivities under visible light irradiation, the decoloration rate reached 32.5% after irradiated for 15 h. The InVO₄-TiO₂ thin films exhibited photoactivity under visible light after doped InVO₄ in the TiO₂ films.     

Microstructure and ferroelectric properties of dysprosium-doped bismuth titanate thin films

Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films with Dy³⁺ substitution (Bi_4−xDy_xTi₃O₁₂, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) were grown on Pt(111)/Ti/SiO₂/Si(100) substrates using sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that after annealing at 710 °C for 10 min, all Bi_4−xDy_xTi₃O₁₂ films became polycrystallites. Among all the deposited thin films, the Bi_3.4Dy_0.6Ti₃O₁₂ specimen exhibits improved ferroelectric properties with the largest average remanent polarization (2Pr) of 53.06 μC/cm² under applied field of 400 kV/cm and fatigue free characteristics (16% loss of 2Pr after 1.5 × 10¹⁰ switching cycles), indicating that it is suitable for non-volatile ferroelectric random access memories applications.     

Spray pyrolysed bismuth oxide thin films and their characterization

Uniform, adherent and reproducible bismuth oxide thin films have been deposited on glass substrates from aqueous Bi(NO₃)₃ solution, using the solution spray technique. Their structural, surface morphological, optical, and electrical properties were investigated by XRD, AFM, optical absorption, electrical resistivity and thermo-emf measurements. The structural analysis from XRD pattern showed the formation of mixed phases of monoclinic Bi₂O₃ (predominant), tetragonal β-Bi₂O₃ and nonstiochiometric Bi₂O_2.33. The surface morphological studies on atomic force micrographs revealed round grain morphology of bismuth oxide crystallites. The optical studies showed a direct band gap of 2.90 eV for as-prepared bismuth oxide films. The electrical resistivity measurements of bismuth oxide films indicated a semiconducting behavior with the room temperature electrical resistivity of the order of 10⁷ Ω cm. From thermo-emf measurements, the electrical conductivity was found to be of n-type.