Saikiran Vadavalli
@gitam.edu
Assistant Professor of Physics
GITAM Deemed to be University
RESEARCH INTERESTS
Laser Matter Interaction, Nano structuring with ion beams, ion solid interaction, SERS, Photonics
Scopus Publications
Scopus Publications
V. Saikiran, B. Mohanarao, P. Surya Lakshmi, P. Babuji, A.P. Pathak, L. Jyothi, P. Gopala Krishna, and S.A. Khan
Elsevier BV
Ponnada Tejeswara Rao, Nodagala Rama Kumar, and V. Saikiran
Elsevier BV
Sh. Soumya, Sattibabu Bhumireddi, K. Ugendar, Durga Rao Tadisetti, Manish K. Niranjan, Arvind Kumar Yogi, Vadavalli Saikiran, and R. J. Choudhary
AIP Publishing
This study investigates the structural, dielectric, and magnetodielectric properties of indium-doped TbMnO3 (Tb1−xInxMnO3, x = 0.00, 0.05, 0.075) synthesized via the solid-state method. Low-temperature x-ray diffraction (XRD) measurements reveal a temperature-driven phase transition from the centrosymmetric orthorhombic Pnma space group at 300 K to the non-centrosymmetric Pna21 space group at 11 K, indicative of ferroelectric behavior. Below the transition temperature, sudden changes in lattice parameters, unit cell volume, Mn–O bond lengths, and Mn–O–Mn bond angles with varying temperature may be associated with spin–lattice coupling that underlies magnetoelectric behavior. The optical bandgap, as estimated from UV–visible absorption spectra, slightly decreases with In3+ substitution. This experimental observation is well supported by DFT + U calculations. Dielectric and magnetodielectric measurements confirm ferroelectric transitions at ∼22 ± 0.5, 20 ± 0.5, and 20 ± 0.5 K for x = 0.00, 0.05, and 0.075, respectively. An enhanced magnetodielectric effect is observed with In doping, peaking at 3.49% for x = 0.05 under a 5 T magnetic field. The findings highlight the role of non-magnetic A-site doping in tuning the multiferroic behavior of TbMnO3, making it a promising candidate for multifunctional device applications.
B. Mohanarao, P. Babuji, M. Venkaiah, and V. Saikiran
Springer Science and Business Media LLC
Brahma Swamulu Atchukola, Rajasekhar Vesalapu, Hamad Syed, Saikiran Vadavalli, and G Krishna Podagatlapalli
Springer Science and Business Media LLC
Putiki Babuji and Vadavalli Saikiran
AIP Publishing
T.V. Sai Suresh, V. Saikiran, and A.P. Pathak
Elsevier BV
Twinkle J, Sailaja M, Dipanjan B, Babuji P, Rajasekhar V, Hamad S, Saikiran V, Chandrasekhar A, Kanaka Raju P, and G Krishna Podagatlapalli
Springer Science and Business Media LLC
G. Neelima, P. Babuji, A.P. Pathak, D. Narayana Rao, P. Gopala Krishna, and V. Saikiran
Elsevier BV
P. Babuji, Md Abu Taher, Mudasir H. Dar, D. Narayana Rao, P. Gopala Krishna, and V. Saikiran
MDPI AG
Here, we present a simple and green method of preparing Au-Ag bimetallic nanoparticles (NPs) with a tunable surface plasmon resonance (SPR) wavelength by using picosecond laser irradiation. Au-Ag alloy NPs have been produced by irradiating the solutions containing respective metallic salts in a polyvinyl alcohol (PVA) matrix using a picosecond laser in a single-step process. The SPR wavelength of the Au-Ag bimetallic NPs is observed to be shifted/changed with the Au-Ag concentration and the laser irradiation parameters. The Au-Ag NPs embedded in the PVA matrix are advantageous for Surface-Enhanced Raman scattering (SERS) applications. The estimated enhancement factors (EFs) were observed to vary as a function of conditions of the Au-Ag bimetallic alloy NPs synthesis and also on the concentration of Au at a fixed input fluence of irradiation. The SERS active platforms of Au-Ag bimetallic NPs showed EFs as high as of the order of 108 for Crystal Violet (CV) dye samples at nano molar concentrations. The present study demonstrates a simple, single-step, and green method that fabricates Au-Ag alloy-based nanocomposites suitable for SERS investigations with significantly higher orders of EFs.
V. Saikiran, G. Neelima, N. Srinivasa Rao, and A. P. Pathak
Springer Nature Singapore
G. Neelima, T. Mahesh, N. Manikanthababu, A.P. Pathak, and V. Saikiran
Elsevier BV
R. Kuladeep, L. Jyothi, Chakradhar Sahoo, D. Narayana Rao, and V. Saikiran
Springer Science and Business Media LLC
We report here a detailed analysis of the ultrashort laser pulse irradiation effects on a single crystalline silicon surface. A systematic study has been performed to understand the surface morphological changes under irradiation with ultrashort laser pulses by changing different input laser parameters such as laser fluence, laser pulse number, and incident laser polarization. Field emission scanning electron microscopy images reveal the formation of laser induced periodic sub-wavelength surface structures directly on bulk surface. The orientation of the formed sub-wavelength surface structures is perpendicular to the incident laser polarization and their morphology and spatial periodicity strongly depend on the applied laser fluence and laser pulse number. The sub-wavelength surface structures are accompanied by the formation of a large density of silicon nanoparticles which possess broad visible photoluminescence ranging from 410 to 680 nm which is due to superficial oxidation of silicon during laser irradiation. The amount of oxygen incorporated into silicon strongly depends on laser parameters such as laser fluence and number of laser pulses.
Nabil A. Saad, E. Ramya, V. Saikiran, Sri Ram G. Naraharisetty, and D. Narayana Rao
Elsevier BV
Abstract We introduce a simple and eco-friendly synthesis of multiwalled carbon nanotubes with silver nanoparticles as a MWCNT-Ag hybrid. A solution is made of MWCNTs and AgNO3 in polyethylene glycol, where the silver nitrate gets reduced into AgNPs in the presence of MWCNTs. We have studied the effect of concentration and temperature on the hybrid nanostructure formation. Formation of MWCNT-Ag composite was confirmed through UV–Vis, transmission electron microscope images, and the Raman studies. The nonlinear optical properties of the hybrids were examined using Z-scan technique using the second harmonic at 532 nm of Nd:YAG laser operated at 10 Hz and pulse duration of 6 ns. The experimental results also revealed that surface enhanced Raman scattering enhancement depends on the temperature during synthesis of hybrid nanoparticles, size, and concentration of AgNPs. The nonlinear absorption exhibits reverse saturable absorption behaviour due to the excited state absorption process.
P.V. Prakash Madduri, N. Manikanthababu, I. Sameera, Ravi Bhatia, A.P. Pathak, and V. Saikiran
Elsevier BV
Abstract Effects of irradiation with swift heavy ions at different fluences on the structural and magnetic properties of multi-walled carbon nanotubes filled with Fe nanorods and nanoparticles (Fe-MWCNTs) are investigated. An up-shift in the ‘G’- band of the Raman spectra with the increasing fluence designates the development of stresses in Fe-MWCNTs. During the ion-irradiation, the disorder parameter that signifies the defect concentration initially decreases at lower fluence and then picks-up with a further rise in fluence. Structural characterization by electron microscopy reveals damaged walls and formation of defects in Fe-MWCNTs irradiated at the highest fluence. The average diameter of Fe-MWCNTs inferred from high-resolution TEM shows a reduction from 56 (±2) nm to 36 (±2) nm upon increasing the irradiation fluence from 5 × 1012 to 1 × 1014 ions/cm2. The ferromagnetic character of Fe nanoparticles/nanorods embedded in the MWCNTs swamps the diamagnetic nature of bare MWCNTs and hence a saturation behaviour in magnetization is seen for the Fe-MWCNTs. A significant reduction in the saturation magnetization (≈20%) is observed in the ‘irradiated’ Fe-MWCNTs when compared to their ‘as-prepared (pristine)’ counterparts and is attributed to the increase in surface disorder and weakening of exchange interactions upon irradiation. The coercive field follows a monotonous thermal decline in both ‘pristine’ and ‘irradiated’ Fe-MWCNTs. Contrary to the expectation, the coercivity of the ‘irradiated’ Fe-MWCNTs is less than nearly half the value for ‘pristine’ samples, in the entire temperature range 2 K–300 K.
N. Manikanthababu, V. Saikiran, T. Basu, K. Prajna, S. Vajandar, A.P. Pathak, B.K. Panigrahi, T. Osipowicz, and S.V.S. Nageswara Rao
Elsevier BV
Abstract The influence of 120 MeV Ag ion irradiation on the structural and electrical properties of HfO2 (3 nm)/SiON (1 nm)/Si (n-type), grown by atomic layer deposition, has been investigated. X-ray Reflectivity and X-ray Photoelectron Spectroscopy measurements suggested the formation of a mixed interlayer of HfSiON above a critical fluence of 1 × 1012 ions/cm2. The observed irradiation induced changes in the leakage current have been attributed to the defects and structural changes caused by ion irradiation. The influence of various quantum tunneling mechanisms on the leakage current has been investigated as a function of ion fluence. The structural changes, defects dynamics and the consequent effects on leakage current have been explained within the framework of ion induced annealing, creation of defects and intermixing effects.
V. Saikiran, Mudasir H. Dar, R. Kuladeep, L. Jyothi, and D. Narayana Rao
Elsevier
Abstract Nanostructures and nanoparticles of various kinds of materials are fabricated by using laser irradiation of the respective bulk targets in air and liquids. In this chapter the formation of nanostructures and nanoparticles of different semiconductor materials like silicon, germanium, graphite and metals such as aluminum, titanium, indium, and Au–Ag alloy using femtosecond (fs) laser irradiation in different media such as air and water is discussed. The laser beam was focused on the sample surface and scanning of the sample was done along and normal to the laser polarization direction. The fabricated nanostructures on the surface and the formed nanoparticles in the ablated liquid are characterized by different methods to understand the characteristics of the synthesized nanostructures. The morphology, orientation, and spatial periodicity of the surface nanostructures depends upon various parameters such as laser pulse energy, number of pulses per focal spot, laser polarization, surrounding dielectric medium, and the nature of the material. These fabricated nanomaterials have applications in different photonics-related studies like surface-enhanced Raman scattering (SERS), optical limiting, and low reflective surfaces. The basic physics and mechanism behind the formation of nanostructures and nanoparticles under fs laser irradiation are discussed in view of the nanostructures formed on different materials.
Raghavendra Rao Juluri, Sathyavathi Ravulapalli, Saikiran Vadavlli, and Satyam Venkata Parlapalli
Wiley
V. Saikiran, P. Bazylewski, I. Sameera, Ravi Bhatia, A.P. Pathak, V. Prasad, and G.S. Chang
Elsevier BV
Abstract Multi-wall carbon nanotubes (MWCNT) filled with Fe nanorods were shown to have contracted and deformed under heavy ion irradiation. In this study, 120 MeV Ag and 80 MeV Ni ion irradiation was performed to study the deformation and defects induced in iron filled MWCNT under heavy ion irradiation. The structural modifications induced due to electronic excitation by ion irradiation were investigated employing high-resolution transmission electron microscopy, micro-Raman scattering experiments, and synchrotron-based X-ray absorption and emission spectroscopy. We understand that the ion irradiation causes modifications in the Fe nanorods which result in compressions and expansions of the nanotubes, and in turn leads to the buckling of MWCNT. The G band of the Raman spectra shifts slightly towards higher wavenumber and the shoulder G′ band enhances with the increase of ion irradiation fluence, where the buckling wavelength depends on the radius ‘r’ of the nanotubes as exp[(r)0.5]. The intensity ratio of the D to G Raman modes initially decreases at the lowest fluence, and then it increases with the increase in ion fluence. The electron diffraction pattern and the high resolution images clearly show the presence of ion induced defects on the walls of the tube and encapsulated iron nanorods.
V. Saikiran, Mudasir H. Dar, and D. Narayana Rao
Elsevier BV
Abstract Here we have experimentally studied ultrafast femtosecond laser ablation of graphite in air and water environments for the fabrication of promising nanostructures on the graphite surface and also nanographite flakes, graphene quantum dots in water. After the fs laser irradiation in air quasi-periodic nanogratings were found on the graphite surface and when the irradiation is done in water we observed graphene quantum dots (GQDs) and graphitic flakes dispersed in the solution. The sheets consist of few layers of spongy kind of porous graphene, which form an irregular 3D porous structure. The field emission scanning electron microscopy reveals the formation of fluence dependent quasi-periodic deep-subwavelength nanogratings (Ʌ = 130–230 nm) on the surface. Several characterization methods have confirmed the formation of layered graphene and quantum dots. The studies on the solution confirmed the presence of GQDs with dimensions ranging about 2–4 nm. It is found that the formation of subwavelength structures and GQDs depends on the fs-laser energy and vary with different laser parameters such as fluence, energy, laser polarization.
N. Manikanthababu, T. K. Chan, S. Vajandar, V. Saikiran, A. P. Pathak, T. Osipowicz, and S. V. S. Nageswara Rao
Springer Science and Business Media LLC
Atomic layer deposited (ALD) samples with layer stacks of HfO2 (3 nm)/SiO2 (0.7 nm)/ Si were subjected to 120 MeV Au ion irradiation at different fluences to study intermixing effects across the HfO2/SiO2 interface. High-resolution Rutherford backscattering spectrometry (HRBS) and X-ray reflectivity (XRR) measurements confirm an increase in the interlayer thickness as a result of SHI induced intermixing effects. Current–voltage (I–V) measurements reveal an order of magnitude difference in the leakage current density between the pristine and irradiated samples. This can be explained by considering the increased physical thickness of interlayer (HfSiO). Furthermore, the samples were subjected to rapid thermal annealing (RTA) process to analyze annealing kinetics.
Mudasir H. Dar, R. Kuladeep, V. Saikiran, and Narayana Rao D.
Elsevier BV
Abstract We investigated experimentally the formation of laser induced periodic surface structures (LIPSS) on titanium (Ti) metal upon irradiation with linearly polarized Ti:Sapphire femtosecond (fs) laser pulses of ∼110 fs pulse width and 800 nm wavelength in air and water environments. It is observed that initially formed random and sparsely distributed nano-roughness (nanoholes, nanoparticles and nanoprotrusions) gets periodically structured with increase in number of laser pulses. In air at lower fluence, we observed the formation of high spatial frequency-LIPSS (HSFL) oriented parallel to the laser polarization direction, whereas at higher fluence formation of low spatial frequency-LIPSS (LSFL) were observed that are oriented perpendicular to the incident laser polarization. In water two types of subwavelength structures were observed, one with spatial periodicity of ∼λ/15 and oriented parallel to laser polarization, while the other oriented perpendicular to laser polarization with feature size of λ/4. The optimal conditions for fabricating periodic sub-wavelength structures are determined by controlling the fluence and pulse number. The fs laser induced surface modifications were found to suppress the specular reflection of the Ti surface over a wide wavelength range of 250–2000 nm to a great extent.
Nabil A. Alraymi
OSA
Simple and biocompatible synthesis of silver nanodots using thermal etching of silver nanoparticles in polyethylene glycol at different temperatures is presented. Etching at 100°C –170°C temperatures leads to the formation of broad and strong fluorescent Ag nanodots in the band (300–550nm) with a reduced plasmon peak. At 200°C–250°C temperatures, the nanodots size increases with a red-shift absorption. Leading to a narrow fluorescence in (510–580nm) region.
V. Saikiran, Mudasir H. Dar, R. Kuladeep, and Narayana Rao Desai
Springer Science and Business Media LLC
In this manuscript a simple approach is discussed to fabricate uniform periodic surface structures on semiconductor surfaces by femtosecond laser irradiation for surface-enhanced Raman spectroscopy (SERS) applications. Gold films having different thickness are first deposited on semiconductor silicon (Si) surfaces and then periodic surface structures are fabricated by femtosecond laser irradiation. The periodic structures are observed to be uniform over a large area with chain type structure formation of gold and Si. We have studied the formation of these surface structures on Si surface by having different thickness gold films deposited on Si substrates. This approach of the fabrication of surface structures with the assistance of gold film is found to help in local field enhancement and hence work as suitable substrate for the SERS experiments. The conditions for achieving high enhancement factor in SERS with different gold film thicknesses are explored in detail. We also present here the formation of low frequency ripples on Silicon (Si) and high frequency as well as low frequency ripples on titanium (Ti) surface in air and water environments by irradiation with fs laser pulses. Different morphologies were observed on Ti surface depending upon the laser irradiation parameters and the surrounding dielectric medium.