K. Mohanraj

Electrical and optical properties of CZTS thin films prepared by SILAR method

Abstract In the present work, Cu2ZnSnS4 (CZTS) thin film was deposited onto the glass substrate by simple and economic SILAR method and its structural, morphological, optical and electrical properties were analyzed. X-ray diffraction (XRD) analysis confirms the formation of CZTS with kesterite structure and the average crystallite size is found to be 142 nm. Scanning electron microscope (SEM) image shows that the film has homogeneous, agglomerated surface without any cracks. The prepared CZTS film shows good optical absorption (104 cm−1) in the visible region and the optical band gap energy is found to be quite close to the optimum value of about 1.54 eV for solar cell application. The refractive index of the prepared film is found to be 2.85. The electrical resistivity of the film is found to be ∼10−2 Ω cm at room temperature.

Structural and optical properties of SnS nanoparticles and electron-beam-evaporated SnS thin films

SnS nanoparticles were synthesised by the precipitation method using SnCl2.2H2O and Na2S.xH2O and the nanoparticles were characterised by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. From the particles’ XRD pattern, a strong peak at 2θ = 31.5˚ was observed, which confirms the Herzenbergite orthorhombic crystal structure of SnS. The FTIR result also confirmed the SnS nanoparticles at 2354 cm−1 and 615 cm−1. Second, thin SnS films were prepared on a glass substrate by the electron beam evaporation technique at room temperature and annealed at 100°C, 200°C and 300°C. The effect of the annealing temperature on structural and optical properties of the SnS films was characterised by XRD and ultraviolet–visible (UV–Vis) analysis. From the experimental studies, optical absorption of SnS films increases with respect to the annealing temperature, while the values of band gap energy (Eg) get reduced from 1.77 to 1.57 eV.

Electrochemical and fluorescence properties of SnO2 thin films and its antibacterial activity

Nanocrystalline SnO2 thin films were deposited by a simple and inexpensive sol-gel spin coating technique and the films were annealed at two different temperatures (350°C and 450°C). Structural, vibrational, optical and electrochemical properties of the films were analyzed using XRD, FTIR, UV-Visible, fluorescence and cyclic voltammetry techniques respectively and their results are discussed in detail. The antimicrobial properties of SnO2 thin films were investigated by agar agar method and the results confirm the antibacterial activity of SnO2 against Escherichiacoli and Bacillus.

Microwave-assisted Bi2Se3 nanoparticles using various organic solvents

Microwave assisted Bi2Se3 nanoparticles were synthesized from five different solvents DMF, EG, EG+H2O, EDA+dil.HNO3 and N2H4+H2O+Ethanol. The influence of solvents on purity of the compound was analysed by using X-ray diffraction patterns. The result indicates pure rhombohedral Bi2Se3 nanoparticles formed for N2H4+H2O+Ethanol. The presence of vibrational bands in the range of 400-800 cm(-1) is confirmed the formation of Bi2Se3. The maximum optical absorption observed around 450 nm and the band gap values are found in the range of 1.5 eV-2.17 eV for all the solvents. The nanostructure of the Bi2Se3 particles change with solvents. From the experimental results, the solvent N2H4+H2O+Ethanol produces pure nanosize Bi2Se3 particles under the microwave assisted method.

Shape-dependent optoelectrical investigation of Cu2+xCd1−xSnS4 thin films for solar cell applications

Cu2+xCd1−xSnS4 thin films were prepared with excess Cu concentrations (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) by a successive ionic layer adsorption and reaction (SILAR) method. The deposited films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-visible spectroscopy and I–V analysis. XRD analysis confirms the formation of tetragonal structured Cu2CdSnS4 thin films for all the excess Cu concentrations, while the corresponding FESEM images showed microstructural change. It may be attributed to the injection of excess Cu atoms into the Cd sites of the Cu2CdSnS4. The absorption coefficient is found to be greater than 104 cm−1 in the visible region and the bandgap energy is slightly tuned from 1.68 eV to 1.58 eV when compared to Cu2CdSnS4. The Cu2.1Cd0.9SnS4 film showed the highest photoresponse.

Structural, optical and electrical characterization of nanostructured porous silicon: Effect of current density

In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150mA/cm(2)) with constant time (30min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I-V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100mA/cm(2) and decrease for 125mA/cm(2). It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150mA/cm(2), the average pore diameter increase as in the case of first layer (40-100mA/cm(2)) of c-Si wafer. The result is reflected in PL emission band (at 708nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2θ=69.3° belongs to (400) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S-H2 and Si-O-Si at 2109cm(-1), 915cm(-1) and 615cm(-1) and 1107cm(-1), respectively. The I-V characteristic of PS exhibited rectifying behavior with different values of ideality factor (η) and barrier height (ϕb). It is concluded from the experimental results that the formed pores developed up to 100mA/cm(2) in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100mA/cm(2)).

MORPHOLOGICAL AND OPTOSTRUCTURAL STUDIES ON HYDRAZINE HYDRATE ASSISTED Zr(SeO3)2 NANOPARTICLES

Zirconium diselenite (Zr(SeO 3 ) 2 ) nanoparticles have been prepared by precipitation method using ZrO(NO 3 ) 2 .xH 2 O and SeO 2 with Hydrazine hydrate and vary the temperature. The obtained samples were characterised by using XRD, FTIR, FESEM and optical analysis. The XRD study shows the orthorhombic crystalline structure and particle sizes is found to be 78.06, 42.13 and 27.17 nm for 0.25:1, 0.5:1 and 0.75:1M respectively. FTIR results are confirmed the Zr(SeO 3 ) 2 at 885 cm-1, 739 cm-1 and 491 cm-1. FESEM images provide different shapes such as cubic and hexagonal of Zr(SeO 3 ) 2 . Maximum absorption is found around 387 nm and the percentage of optical absorption is increased in the entire visible region when the molar concentration of zirconium decreases. The average band gap energy of the samples are found to be 3.95±2 eV. It is observed that the optical absorption is higher in the hydrazine hydrate assisted samples.

Sonochemically prepared PbWO4 tetragonal-bipyramidal microcrystals and their photoluminescence properties.

Lead tungstate (PbWO4) microcrystals were synthesized for the first time, via different concentrations of PVA assisted sonochemical process. The concentration of PVA acts as a structure directing agent and played an important role in the morphological control of resulting PbWO4 microcrystals. The product PbWO4 composing of Pb, W and O and WO stretching vibration band of WO4 tetrahedrons were confirmed through XRD, FTIR, FESEM and EDS. The TG/DTA curves showed that the particles are crystallized at room temperature itself and the thermal stability of the product is really good. The optical properties of the product shows extraordinarily high room temperature photoluminescence intensity compared to without PVA assisted product.

Synthesis of selenium nanorods with assistance of biomolecule

Nanorods of one-dimensional (1D) trigonal selenium (t-Se) are synthesized using biomolecule substances for five different aging times (1 h, 2 h, 3 h, 1 day and 4 days) by precipitation method. XRD analysis indicates a shift of the (1 0 1) plane towards higher diffraction angle for 1 day aging time. It is observed that the crystallite size decreases with increase in aging time except for an aging period of 4 days. FTIR analysis confirmed that the presence of stretching and bending vibrations of Se–O in both synthesized and commercial selenium samples at 465, 668 and 1118 cm −1. The FESEM micrographs are evident for the changes of rod size as a function of aging time. It is observed that the optical band gap energy is increased with aging time up to 1 day, whereas it decreases in 4 days aging time.

Solvothermal-Assisted Synthesis of Cu3XS3 (X = Bi and Sb) Chalcogenide Nanoparticles

Cu3BiS3 and Cu3SbS3 nanoparticles were obtained for three different copper concentration (500, 1000, 1500 mmol) via facile solvothermal route at 180°C for 20 h. Phase purity, homogeneity, surface morphology, elemental distribution, optical absorption, and emission characteristics of the obtained samples were carried out by using XRD, FTIR, SEM, FESEM, EDS, UV-Visible, and photoluminescence spectroscopic techniques. From the experimental data, Cu3SbS3 renders good optical property than Cu3BiS3 due to lower bandgap energy (2.1 eV).