S. Tripathi

Investigation of Fe doped ZnO thin films by X-ray absorption spectroscopy

Fe doped ZnO thin films with varying Fe doping concentrations have been deposited by rf magnetron sputtering technique on c-Si substrates. X-ray Diffraction (XRD) measurements show the pure wurtzite structure of all the samples. X-ray near edge spectroscopy (XANES) measurements confirm that Fe is present in the samples in Fe2+ and Fe3+ oxidation states. Extended X-ray Absorption Fine Structure (EXAFS) measurements at Zn and Fe K edges prove that Zn atoms are being substituted by Fe dopants, Zn vacancies are created in the samples near the dopant sites and also support the presence of mixed oxidation states obtained by XANES measurements. Oxygen K-edge XANES results support the conjecture that Fe goes to Zn sites in tetrahedral symmetry. Magnetization measurements show the presence of room temperature ferromagnetism (RTFM) in the samples and saturation magnetization is found to increase as Fe doping concentration increases. The observed ferromagnetism seems to be intrinsic in nature and it is explained in the light of XANES and EXAFS observations.

Study of interface correlation in W/C multilayer structure by specular and non-specular grazing incidence X-ray reflectivity measurements

W/C/W tri-layer thin film samples have been deposited on c-Si substrates in a home-built Ion Beam Sputtering system at 1.5 × 10−3 Torr Ar working pressure and 10 mA grid current. The tri-layer samples have been deposited at different Ar+ ion energies between 0.6 and 1.2 keV for W layer deposition and the samples have been characterized by specular and non-specular grazing incidence X-ray reflectivity (GIXR) measurements. By analyzing the GIXR spectra, various interface parameters have been obtained for both W-on-C and C-on-W interfaces and optimum Ar+ ion energy for obtaining interfaces with low imperfections has been found. Subsequently, multilayer W/C samples with 5-layer, 7-layer, 9-layer, and 13-layer have been deposited at this optimum Ar+ ion energy. By fitting the specular and diffused GIXR data of the multilayer samples with the parameters of each interface as fitting variables, different interface parameters, viz., interface width, in-plane correlation length, interface roughness, and interface d...

EXAFS studies on Gd-doped ZrO 2 thin films deposited by RF magnetron sputtering

ZrO2 thin films with 0%, 7%, 9%, 11%, and 13% Gd doping have been prepared by RF magnetron sputtering and have been characterized by grazing incidence x-ray diffraction, spectroscopic ellipsometry, and optical transmission measurements to probe their structural and optical properties. Extended x-ray absorption fine structure (EXAFS) measurements have also been carried out on the samples at the Zr K- and Gd L3-edges. It has been observed that Gd goes to Zr sites up to 9%-11% doping concentration, and for Gd doping concentrations beyond 11%, Gd precipitates out as a separate Gd2O3 phase. The local structure information surrounding the Zr and Gd sites obtained from the analysis of the EXAFS studies have also been used to explain the macroscopic optical properties of the samples.

Refractive index tailoring of morphology engineered SiO2 thin films by collimated glancing angle RF magnetron sputtering

Conventional RF magnetron sputtering system was modified for collimated glancing angle deposition geometry at fixed vapour flux angle of 86° by employing a collimating plate designed and located parallel to the substrate. With this geometry, refractive index (RI) of morphologically engineered silica films ∼1.28 could be achieved against 1.48 @550 nm in conventional sputtered geometry along with the significant transmission (antireflection) of ∼93.7%, which makes this thin film suitable to be used in anti-reflection coatings for solar cell applications.

The effect of pulse width on asymmetric bipolar pulse DC sputtered tantalum pentoxide thin films

The effect of pulse width in asymmetric bipolar pulse DC (ABPDC) sputtering technique is studied by depositing a set of Ta2O5 dielectric thin films under varying pulse widths from 496-1616 ns. Structural studies showed no distinction among the deposited samples. Optical properties of the samples have been characterized by transmission spectrophotometry and spectroscopic ellipsometry which reveal that with increase in pulse width, the deposition rate and hence total thickness of the samples decreases while the percentage of substrate-film interface thickness increases. The void percentage in interface layers were found to be almost constant up to 1296 ns pulse width and increases substantially beyond this. The study is important from the point of pulse width optimization for depositing Ta2O5 thin films by ABPDC sputtering technique for optical multilayer thin film application.The effect of pulse width in asymmetric bipolar pulse DC (ABPDC) sputtering technique is studied by depositing a set of Ta2O5 dielectric thin films under varying pulse widths from 496-1616 ns. Structural studies showed no distinction among the deposited samples. Optical properties of the samples have been characterized by transmission spectrophotometry and spectroscopic ellipsometry which reveal that with increase in pulse width, the deposition rate and hence total thickness of the samples decreases while the percentage of substrate-film interface thickness increases. The void percentage in interface layers were found to be almost constant up to 1296 ns pulse width and increases substantially beyond this. The study is important from the point of pulse width optimization for depositing Ta2O5 thin films by ABPDC sputtering technique for optical multilayer thin film application.

Oxygen partial pressure dependent optical properties of glancing angle deposited (GLAD) Ta2O5 films deposited by magnetron sputtering

Experiments were carried out on Ta2O5 oxide thin films by asymmetric bipolar pulsed DC magnetron sputtering using a new hybrid combination of conventional (normal incidence) deposition and glancing angle deposition (GLAD) geometries. The films were prepared with varying O2 partial pressure. The ellipsometry characterization reveals a systematic variation in refractive index, which decreased from 2.2 in the normal films to an average 1.78 in the GLAD films. The bandgap of these GLAD films is slightly higher as compared to normal films. Overall transmission of the GLAD films is increased is by ~ 15 % implying a reduction in the refractive index for potential optical filtering device applications. The results were further supported by X-ray reflectivity measurements which show an effective double layer structure in GLAD consisting of layers with different densities of the same Ta2O5 material.

Effect of sputtering power on MgF2 thin films deposited by sputtering technique under fluorine trapping

A non-conventional magnetron sputtering technique was explored to deposit magnesium fluoride thin films using the concept of fluorine gas trapping without the introduction of additional fluorine gas flow inside the chamber. The effect of magnetron power from 50 W to 250 W has been explored on structural, optical and physical properties of the samples. Polycrystalline nature with tetragonal crystallinity of the films has been confirmed by GIXRD measurements along with thickness dependency. Monotonic increase of attenuation coefficient (k) with RF power has been explained in terms of target compound dissociation probability. In conclusion, with fluorine trapping method, the samples deposited at lower RF powers (<100 W) are found to be more suitable for optical applications.

Investigation on optical properties of spin coated TiO2/Co composite thin films

The optical properties of spin coated Co doped TiO2 composite films have been studied in the present communication based on the suitability of such materials for possible application in solar cell windows. Before deposition, raw materials of the nanoparticles (NPs) were examined by X-ray diffraction technique for the analysis of their crystal structure. Both the NPs were found to be polycrystalline in nature with mean crystallite sizes of ∼17 and ∼70 nm for TiO2 and Co respectively. The composite films were prepared by adding different concentrations of Co nanoparticles (1-4 wt %) in TiO2 nanoparticles solution. Transmission measurements revealed a strong dependency of film transmission with Co doping concentration with maximum transmission ∼85% @ 550 nm for 4% doping. The optical energy band gap evaluated from Tauc’s law for the films has been found to be blue-shifted with doping with a maximum value of 4.04 eV for 4% doping concentration. Overall results suggest that the thin film composite prepared by ...

Annealing induced morphological modifications in PTFE films deposited by magnetron sputtering

As grown RF magnetron sputtered polytetrafluoroethylene (PTFE) thin films were subjected to vacuum annealing at optimized elevated temperature of 200° C for varying time duration and corresponding surface morphological changes were recorded. The columnar structures appearing after an annealing duration of 2 hours are interesting for fabrication of rough PTFE surfaces towards possible applications in hydrophobicity along with high transmission. Supported by transmission data, the AFM images show a transformation of smooth PTFE surface with less than 2 nm rms roughness to a very rough surface. The results are interpreted in terms of thermal energy induced modifications only at the surface without any change in the original bonding structure on the surface and inside the sample. Preliminary studies indicate that the optimization of roughness and transmission together on such surfaces may lead to high water contact angles.As grown RF magnetron sputtered polytetrafluoroethylene (PTFE) thin films were subjected to vacuum annealing at optimized elevated temperature of 200° C for varying time duration and corresponding surface morphological changes were recorded. The columnar structures appearing after an annealing duration of 2 hours are interesting for fabrication of rough PTFE surfaces towards possible applications in hydrophobicity along with high transmission. Supported by transmission data, the AFM images show a transformation of smooth PTFE surface with less than 2 nm rms roughness to a very rough surface. The results are interpreted in terms of thermal energy induced modifications only at the surface without any change in the original bonding structure on the surface and inside the sample. Preliminary studies indicate that the optimization of roughness and transmission together on such surfaces may lead to high water contact angles.

Temperature dependent optical characterization of Ni-TiO2 thin films as potential photocatalytic material

Along with other transition metal doped titanium dioxide materials, Ni-TiO2 is considered to be one of the most efficient materials for catalytic applications due to its suitable energy band positions in the electronic structure. The present manuscript explores the possibility of improving the photocatalytic activity of RF magnetron sputtered Ni-TiO2 films upon heat treatment. Optical, structural and morphological and photocatalytic properties of the films have been investigated in detail for as deposited and heat treated samples. Evolution of refractive index (RI) and total film thickness as estimated from spectroscopic ellipsometry characterization are found to be in agreement with the trend in density and total film thickness estimated from grazing incidence X-ray reflectivity measurement. Interestingly, the evolution of these macroscopic properties were found to be correlated with the corresponding microstructural modifications realized in terms of anatase to rutile phase transformation and appearance of a secondary phase namely NiTiO3 at high temperature. Corresponding morphological properties of the films were also found to be temperature dependent which leads to modifications in the grain structure. An appreciable reduction of optical band gap from 2.9 to 2.5 eV of Ni-TiO2 thin films was also observed as a result of post deposition heat treatment. Testing of photocatalytic activity of the films performed under UV illumination demonstrates heat treatment under atmospheric ambience to be an effective means to enhance the photocatalytic efficiency of transition metal doped titania samples.Along with other transition metal doped titanium dioxide materials, Ni-TiO2 is considered to be one of the most efficient materials for catalytic applications due to its suitable energy band positions in the electronic structure. The present manuscript explores the possibility of improving the photocatalytic activity of RF magnetron sputtered Ni-TiO2 films upon heat treatment. Optical, structural and morphological and photocatalytic properties of the films have been investigated in detail for as deposited and heat treated samples. Evolution of refractive index (RI) and total film thickness as estimated from spectroscopic ellipsometry characterization are found to be in agreement with the trend in density and total film thickness estimated from grazing incidence X-ray reflectivity measurement. Interestingly, the evolution of these macroscopic properties were found to be correlated with the corresponding microstructural modifications realized in terms of anatase to rutile phase transformation and appearance...