SK MAIDUL HAQUE
@barc.gov.in
SCIENTIFIC OFFICER
Bhabha Atomic Research Centre
Scopus Publications
Scholar Citations
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Scopus Publications
Rajnarayan De, S. Augustine, B. Das, M. K. Sikdar, M. Ranjan, P. K. Sahoo, S. Maidul Haque, C. Prathap, and K. Divakar Rao
Springer Science and Business Media LLC
Rajnarayan De, Bujagouni Karthik Goud, Chinmaya Kar, Sk Maidul Haque, Anil Krishna Debnath, Mrinal Kanti Sikdar, Pratap Kumar Sahoo, and Kompalli Divakar Rao
Wiley
Postdeposition heat treatment‐induced modifications of nanoplasmonic response in glancing angle‐deposited (GLAD) Ag nanostructures are systematically investigated. The as‐deposited GLAD Ag thin films are annealed at various temperatures namely 200, 250, 300, and 350 °C in air atmosphere. The reduction in localized surface plasmon resonance (LSPR) absorption peak width is detected with annealing. Morphological characterization of the as‐deposited and annealed films reveals reduction in grain size and shape distributions responsible for narrowing of the LSPR peak width. The refractive index sensitivities of the as‐deposited and annealed films are measured using an in‐house‐developed optical setup and figure of merit (FOM) of the sensors is also estimated. An increase in FOM of the sensors is observed upon annealing while sensitivity is found to be reduced. E‐field profile surrounding the Ag nanoparticles is also simulated to explain the experimental observations on refractive index sensitivity of the films.
S. Maidul Haque, Rajnarayan De, J.S. Misal, C. Prathap, and K. Divakar Rao
Elsevier BV
S. Maidul Haque, S.D.V.S. Jagannadha Raju, Rajnarayan De, C. Prathap, M.K. Sikdar, Pratap K. Sahoo, and K. Divakar Rao
Elsevier BV
S D V S Jagannadha Raju, S Maidul Haque, B Karthik Goud, Rajnarayan De, J S Misal, and K Divakar Rao
IOP Publishing
Abstract Fiber Bragg grating sensors are used to monitor physical parameters like temperature even in inaccessible, unconventional environments. One such application is monitoring the temperature of a substrate from the back surface like any conventional thermocouple sensor and simultaneously monitoring the temperature on the front surface, which is in contact with ion plasma in a magnetron sputtering system. Since thin film parameters depend on substrate temperature, precise measurement plays an important role and thermocouple-like sensors are erroneous when placed on the front side of a substrate exposed to ion plasma. The lateral variation of temperature on the front side for larger substrates also has been established at four different locations, exploiting the multiplexing capability of FBGs. In this report, we demonstrate and utilise the versatility and capability of fiber Bragg grating sensors for online monitoring of substrate temperatures during thin film deposition, for the first time to the best of our knowledge, on different types of substrates. FBG based approach is expected to significantly aid in better control of thin film devices.
Rajnarayan De, S. Maidul Haque, M.K. Sikdar, P.K. Sahoo, S. Kesari, Ch Kishan Singh, S. Augustine, M. Ranjan, R. Rao, and K. Divakar Rao
Elsevier BV
S. Maidul Haque, Rajnarayan De, C. Prathap, S. K. Srivastava, and K. Divakar Rao
Wiley
S. Maidul Haque, Rajnarayan De, C. Prathap, Sanjiv Kumar, G.L.N. Reddy, Shobhna Mishra, and K. Divakar Rao
Elsevier BV
Abstract CW laser (532 nm) induced damage mechanism has been studied on Ag/TiO2 bilayer thin films exhibiting diffused silver mediated plasmonic absorption. The thin films were deposited by e-beam evaporation technique under various O2 flow conditions in the range of 0–20 sccm. The required exposure time (tD) for onset of damage under irradiance of 37 W/cm2 has been measured to be in the range from 118 to 1244 s. Standing Wave Electric Field (SWEF) distribution has been simulated for all the Ag/TiO2 bilayer thin films based on the film optical constants retrieved from spectroscopic ellipsometry analysis. It has been observed that tD is mainly governed by two primary factors (in 2–16 sccm range) visualizing the shift of SWEF peak position with respect to Ag/TiO2 interface and the possible increase in thermal conductivity of TiO2 controlled by diffused Ag concentration across the interface. The SWEF magnitude and light absorbance seems to have relatively lesser bearing on laser withstanding time. Beyond 16 sccm, tD slightly decreases due to increase in surface roughness of the film. The required exposure time, tD is the highest for 0 sccm sample of which there is negligible interfacial Ag diffusion. All these results suggest that interfacially diffused plasmonic silver nanoparticles play an important role in deciding laser dose withstandability of Ag/TiO2 bilayer thin film system through control of electric field distribution and possibly thermal conductivity of TiO2 layer.
Rajnarayan De, S Maidul Haque, M K Sikdar, P K Sahoo, and K Divakar Rao
IOP Publishing
Single-sided TiO2 thin films were prepared using a modified glancing angle deposition (GLAD) technique. An additional flux collimation plate was introduced into the GLAD arrangement to enhance the degree of collimation of depositing vapour flux. Enhancement in the ballistic growth of film on the substrate was observed with increasing distance from the vapour source. The substrate position near to the vapour source (i.e. bottom region) showed a high refractive index (RI, ∼1.336 @ 550 nm wavelength) and lower average film transmittance (∼94.5% in 400–900 nm wavelength range) compared to the others. In contrast, the TiO2 coating deposited at a distant position from the source (i.e. top region) showed a remarkably low RI (∼1.190 @ 550 nm wavelength) and excellent anti-reflection over a broad spectral region with a maximum average transmittance (∼95.3% in 400–900 nm wavelength) compared to the other substrate positions. The reduction in film RI was correlated qualitatively with the morphological alterations in the coating for different substrate positions. With a further increase in distance from the vapour source, an ultimate reduction in the RI of TiO2 to ∼1.101 was observed, which was ∼50% lower than the bulk TiO2 value (∼2.221 @ 550 nm wavelength). The present study reports the lowest RI of TiO2 together with fabrication of a TiO2-based broadband single-layer anti-reflection coating.
Rajnarayan De, S. Maidul Haque, Ranveer Singh, C. B. Basak, S. Jena, J. S. Misal, D. D. Shinde, Tapobrata Som, and K. Divakar Rao
Springer Science and Business Media LLC
E-beam evaporation equipped with glancing angle deposition arrangement (GLAD) was used to fabricate nanostructured polytetrafluoroethylene (PTFE) films in a single-step coating process. Three sets of PTFE coatings were prepared using various oblique angles, e-beam currents, and deposition times to explore the effects of deposition parameters on the properties of PTFE nanostructured coatings. Water contact angle (WCA) of the coatings was found to be enhanced with the increase in all the above process parameters. Optical transmittance of the coatings was also found to be improved with the above parameters except for in the case of an increase in thickness of the films (in very high thickness region), where the transmittance was degraded due to light scattering from the sample surface. After all the optimizations, the ~ 130-nm-thick GLAD PTFE sample prepared with highest e-beam current was found to be more suitable for antireflection and self-cleaning applications. The single-sided coating demonstrates a very high average transmittance of ~ 95.6% (with a wideband transmittance spectrum among the others) in the visible and NIR wavelength range with excellent self-cleaning nature (WCA ~ 156°, sliding angle ~ 10°). The trend of measured WCA with respect to surface roughness follows the Cassie–Baxter model. Overall, the study demonstrates the possibility of fabricating highly transparent self-cleaning coatings using the GLAD technique, which is potentially useful for fabricating protecting cover glasses in solar panels.
A.K. Yadav, S. Maidul Haque, D.K. Shukla, D.M. Phase, S.N. Jha, and D. Bhattacharyya
Elsevier BV
Abstract The present study deals with the local structure of amorphous TiO2 and Fe-doped TiO2 thin films deposited on Si substrate using magnetron sputtering. The absence of long range order is confirmed by grazing incidence x-ray diffraction and the short range order is studied using x-ray absorption near edge structure (XANES) measurements at Ti, Fe and O K-edges and Fe and Ti L3-edge. The XANES provides understanding about the electronic transition induced from the short range ordering and dependence of electronic hybridization of the central Ti-p orbitals with the Ti-d orbitals. The XANES measurements also show that maximum Fe doping concentration allowed to replace Ti is 2 at.% and after that separate phase starts appearing, which is consistent with simulation by ab-initio multiple scattering theory based code FEFF9. Ellipsometry measurements show gradual decrease in band-gap energy upto 2 at.% Fe doping from pristine TiO2, however a drastic decrease in band-gap energy is observed at 4 at.% or higher doping concentration due to formation of other phases.
S. Maidul Haque, Rajnarayan De, Shilpa Tripathi, R.K. Sharma, S.R. Polaki, and K. Divakar Rao
Elsevier BV
Abstract Oxygen pressure mediated interfacial diffusion of silver up to top surface of thick (∼120 nm) TiO2 layer in e-beam evaporated Ag/TiO2 bilayer thin films has been observed. This effect has been investigated in oxygen pressure range of 5.9 × 10−5-5.8 × 10−4 mbar during evaporation. The amount of Ag diffusion (5–24%) has been found to be correlated with the induced porosity of TiO2 layer. Both compositional and structural characterizations confirm Ag0 chemical state of diffused silver. Scanning Electron Microscopy revealed Ag aggregates having an approximate average diameter of ∼4 nm and ∼24 nm on top surface. Spectroscopic ellipsometry analysis demonstrates that plasmonic absorption caused by these Ag nanoparticles manifests significant modulation of effective complex refractive indices (ECRI) of TiO2 layer. Specifically, the imaginary part of ECRI of TiO2 exhibits substantial non-zero value (∼6.5 × 10−2) in the visible wavelength range which is otherwise close to zero (
Rajnarayan De, S Maidul Haque, M K Sikdar, P K Sahoo, Tapobrata Som, and K Divakar Rao
IOP Publishing
Low thickness Silver (Ag) coatings (thickness ~25 nm) were fabricated by electron beam evaporation technique equipped with glancing angle deposition (GLAD, 86o) arrangement at varrying substrate heating temperatures (viz. 30oC, 75oC, 125oC and 150oC). Although all the GLAD-Ag films prepared up to 125oC temperature were found to be plasmonic in nature, the localized surface plasmon resonance (LSPR) band was more prominent at 125oC and disappeared at 150oC temperature. The dielectric contribution in the overall dispersion of sample structure was maximum for 125oC with dominating metallic contribution observed for 150oC. Detailed investigation of 125oC deposited GLAD-Ag sample revealed sharpening of the LSPR band with reduction in film thickness. The ultra-thin coating (~5 nm) was found to be purely dielectric in nature with the most prominent LSPR band among the others. Overall, the substrate heating temperature of 125oC was found to be the threshold for fabricating plasmonic GLAD-Ag films with the best result observed for the ultra-thin (~5 nm) specimen.
S. Maidul Haque, Rajnarayan De, D.D. Shinde, C. Prathap, J.S. Misal, and K. Divakar Rao
Elsevier BV
Abstract The sputtering target re-deposit grown by cumulative sputtering has been investigated in this work by studying both fresh and rigorously sputtered zirconium oxide target by Fourier Domain Optical Coherence Tomography (FDOCT), a depth resolved optical imaging modality. The Optical Coherence Tomography (OCT) depth profiles have further been analysed to extract optical attenuation coefficient of sputtered target surface as well as fresh target surface. Re-deposited sputtered target surface shows larger optical attenuation coefficient in the range of 1.5–4.4 mm−1 as opposed to that of 1.1 mm−1 for fresh ZrO2 target. The same sputtered target surfaces have also been looked into by using grazing incident X-ray diffraction technique with an optimised grazing angle of incidence. A strong correlation between structural changes of re-deposited surface and the extent of light depth penetration obtained by analysing OCT depth profiles at different locations of the sputtered target was observed. The results indicate, that FDOCT can be considered to be an effective tool to probe sputtering target re-deposits, with the advantage of being faster and non-contact method.
S. Maidul Haque, Rajnarayan De, Arijit Mitra, J.S. Misal, C. Prathap, Parlapalli V. Satyam, and K. Divakar Rao
Elsevier BV
Abstract In glancing angle electron beam evaporation technique, the deposition geometry has been engineered in a novel manner in this work to produce extensive tunablity of Ag morphology. A physical plate (collimator) parallel to the substrate has been suitably placed in order to constrain the angle of incoming deposition vapor flux. The distance between substrate and this collimator as well as the distance between substrate to crucible orifice has been optimized for maximum variation in Ag morphology which resulted in the discussed tunability. SEM images acquired across the sample surface on the best optimized sample show variation of Ag morphology from nearly continuous film to Ag nanocolumns (dia-135 nm) and then to Ag nanoislands of varying size (26–83 nm) with the variation in height from substrate bottom edge. Surface plasmon resonance (SPR) peak of this Ag nanostructure has been found to shift to longer wavelength and to broaden with the increase of thickness across the substrate surface. The estimated band gap values of the Ag nanostructure are non-zero which reveals its dielectric like dispersion behavior. Thickness and optical constants at various locations on the best optimized sample have been estimated through spectroscopic ellipsometry measurements and the obtained results have been validated with measured transmission spectrophotometry spectra. Three different ellipsometry models have been tried to fit the ellipsometry data of such grown ultrathin film consisting of Ag nanoislands/nanocolumns. An effective media consisting of the mixture of bulk Ag, dielectric media represented by Lorentz oscillator and air was found to be the best to describe the disperision behavior of the deposited Ag film. The dielectric like dispersion behavior of Ag ultrathin film has been ascribed to localized surface Plasmon resonance (LSPR) effect of Ag nanoislands in optical wavelength region. Due to the gradual variation of thickness and optical constants across the film, the optimized film exhibits variation in average optical transmittance (600–1000 nm) from 1.1% to 91% across 40 mm distance which demonstrates its potential for application as variable optical transmission attenuator. Finally, this novel deposition flux constrainment technique has been regarded as an effective method for fabrication of tunable Ag nano-morphologies for optical and surface plasmonic applications.
Rajnarayan De, S. Maidul Haque, Jitendra S. Misal, Deepak D. Shinde, Chilakala Prathap, Shyam R. Polaki, Ranveer Singh, Tapobrata Som, and K. Divakar Rao
Wiley
S. Maidul Haque, Rajnarayan De, S. Tripathi, C. Mukherjee, S.N. Jha, and D. Bhattacharyya
Elsevier BV
Abstract Study of laser induced damage mechanism and effort to increase the damage threshold of oxide thin films is of immense technological importance because as improved laser-damage resistant optical materials and better fabrication technologies are developed, laser designers can increase the system operating energies and powers to the limits of these new materials. Although, many efforts have been made to investigate how stoichiometry or long range order structure plays a role in describing the laser damage process, to the best of our knowledge, efforts to understand the local structural changes in the materials due to laser irradiation around the damage threshold has not been made so far. In this communication, a set of RF sputter deposited dielectric refractory oxide thin film samples have been subjected to laser irradiation across their damage threshold. In case of TiO2, Ta2O5, and HfO2 thin films, the samples were irradiated with optimized laser fluence and different locations on the samples were irradiated with varying number of pulse shots, while in case of Gd2O3 films, different locations of the samples were irradiated with fixed number of pulse shots and with varying laser fluence. The irradiated samples have subsequently been subjected to X-ray absorption spectroscopy (XAS) studies to find out change in the local structure of the samples under laser irradiation. Apart from XAS measurements, various other characterization techniques such as optical microscopic imaging, grazing incidence X-ray reflectivity and grazing incidence X-ray diffraction have also been employed to study the laser irradiated zones. The results indicate interesting local structural evolution in oxide thin films with the onset of laser induced damage which gives novel insight about the laser damage mechanism.
Shilpa Tripathi, Rajnarayan De, Kompalli D. Rao, Sheikh M. Haque, Bhujagouni K. Goud, Chillakala Prathap, Jitendra S. Misal, Manju M. Patidar, Vedachalaiyer Ganesan, and Naba K. Sahoo
Wiley
A. K. Yadav, S. M. Haque, R. De, Md. A. Ahmed, V. Srihari, M. Gupta, D. M. Phase, S. Bandyopadhyay, S. N. Jha, and D. Bhattacharyya
Author(s)
Ashok Kumar Yadav, S. Maidul Haque, Rajnarayan De, Nimai Pathak, D.K. Shukla, R.J. Choudhary, D.M. Phase, S.N. Jha, and D. Bhattacharyya
Elsevier BV
Abstract Radio Frequency magnetron sputtering technique has been used to prepare Ni doped ZnO thin films with varying Ni doping concentration of upto 10 at.%. Grazing Incidence X-ray Diffraction results show wurtzite structure of the samples throughout the Ni concentration range while X-ray Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure results at Zn and Ni K edges show that Ni is substituting Zn in ZnO lattice and no other extra phase is present in the samples. The substitution of Zn by Ni is further confirmed by O K-edge XANES measurements. Photoluminescence measurements on the samples and theoretical simulations of the XANES spectra at Ni and O K-edges have been used to explain the room temperature ferromagnetic character on the basis of the presence of oxygen vacancies in the samples.
S Tripathi, Rajnarayan De, S Maidul Haque, K Divakar Rao, J S Misal, C Prathap, S C Das, Manju M Patidar, V Ganesan, and N K Sahoo
IOP Publishing
Ashok Kumar Yadav, Sk. Maidul Haque, Rajnarayan De, Md. Azaharuddin Ahmed, Velaga Srihari, Mukul Gupta, Deodatta M. Phase, Sudipta Bandyopadhyay, Shambu Nath Jha, and Dibyendu Bhattacharyya
Wiley
Rajnarayan De, S. Maidul Haque, S. Tripathi, K. Divakar Rao, Ranveer Singh, T. Som, and N. K. Sahoo
AIP Publishing
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...
S. Maidul Haque, Rajnarayan De, S. Tripathi, C. Mukherjee, A. K. Yadav, Dibyendu Bhattacharyya, S. N. Jha, and N. K. Sahoo
The Optical Society
Gadolinium oxide is an excellent optical material that offers high transmission in a wide wavelength range of 200-1600 nm and exhibits a high bulk refractive index of ∼1.80 at 550 nm. In the present study, a set of Gd2O3 thin films has been deposited on fused silica substrates by RF sputtering of a Gd2O3 target under various O2 to Ar flow ratios. The samples have been characterized by grazing incidence x-ray diffraction (GIXRD) to study the long range structural behavior, by GIXR to study density and surface roughness of the films, by atomic force microscopy measurements to study morphological properties, by Rutherford backscattering measurements for compositional studies, and by transmission spectrophotometry and spectroscopic ellipsometry techniques to study their optical properties. It has been observed that the films deposited with 10% oxygen partial pressure have low density, high surface roughness, and high void content, which results in a low value of refractive index of this film, and film quality improves as oxygen partial pressure is further increased. Extended x-ray absorption fine structure measurement with synchrotron radiation has also been employed to extract local structural information around Gd sites, which has in turn been used to explain some of the observed macroscopic properties of the films.
S. Maidul Haque, K. Divakar Rao, S. Tripathi, Rajnarayan De, D.D. Shinde, J.S. Misal, C. Prathap, Mohit Kumar, T. Som, U. Deshpande,et al.
Elsevier BV
Abstract A novel deposition flux collimation technique has been explored in combination with glancing angle deposition geometry in radio frequency magnetron sputtering deposition technique with a motive to tailor the refractive index of silicon di-oxide thin film. In this technique, a collimating plate has been placed in parallel to the substrate at variable substrate to collimator distances (D SC = 4 mm, 6 mm and 9 mm) and the effect of D SC on various properties of the deposited film at different spatial locations on the substrate has been investigated. The use of such collimator was found to be highly effective in reducing the refractive index of the deposited film. A lowest refractive index of ~ 1.31 @ 550 nm of SiO 2 was achieved by using this novel collimation technique in combination with glancing angle deposition geometry which is not possible by glancing angle deposition geometry alone in the framework of non-directional deposition flux in magnetron sputtering technique. Variable angle spectroscopic ellipsometry (VASE) has been employed to accurately determine thickness and refractive index of the deposited films at various spatial locations of the sample. Ellipsometry data fitting model at different spatial locations has been verified by simulating the transmission spectrum based on the layer structure model obtained from ellipsometry modeling and then comparing it with that of the experimentally measured transmission spectra. For a given D SC an optimum location on the substrate surface was obtained to exhibit lowest refractive index. FTIR measurement showed no significant difference in bonding behavior of Si O among different representative spots of the deposited SiO 2 samples. AFM measurement on various spatial locations indicates a possible strong correlation between variation of refractive index and the grain size which is again affected by the degree of collimation and ad atom kinetic energy at various spatial locations.