The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Satyaprakash Sahoo - One of the best experts on this subject based on the ideXlab platform.
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influence of li ion implantation on lo Phonon broadening and bandgap opening in zno thin films
Journal of Alloys and Compounds, 2019Co-Authors: Gopal K Pradhan, Satyaprakash Sahoo, Sanjeev K Gupta, Prabal Dev BhuyanAbstract:Abstract Doping of nonmagnetic impurities in technologically important ZnO has opened a new window for achieving room temperature ferromagnetism, p-type carrier conduction, and enhancement of ferroelectric properties. Here, we report on the confined optical Phonon and bandgap engineering in highly oriented Li implanted ZnO thin films. Using resonance Raman scattering condition, the confined longitudinal optical Phonon lineshapes in uniaxial hexagonal wurtzite crystal are analyzed in detail using the Phonon Confinement model. We have demonstrated that Phonon Confinement model can yield a meaningful result for the interpretation of resonance Raman lineshapes if one considers the contribution of both the E1 (LO) and A1 (LO) modes, particularly while dealing with oriented ZnO thin films. Furthermore, with the increase in Li dose, the bandgap of ZnO is found to show a blue shift, and such blue shift in bandgap is explained using first principles calculation.
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titanium dioxide synthesized using titanium chloride size effect study using raman spectroscopy and photoluminescence
Journal of Raman Spectroscopy, 2009Co-Authors: Sanjeev K Gupta, Satyaprakash Sahoo, Prafulla K Jha, Rucha Desai, Davor KirinAbstract:Titanium dioxide nanocrystals were prepared by the wet chemical method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering (RS) and photoluminescence techniques. The XRD pattern shows the formation of single phase anatase structure of average sizes ∼7 nm (sample A) and ∼15 nm (sample B) for two samples. Additionally, TEM and RS were used to confirm the anatase crystal structure for both samples. The PL spectra show that the intensity of the sample A is more than that of sample B, which has been attributed to defect(s) and particle size variation. A modified Phonon Confinement model incorporating particle size distribution function and averaged dispersion curves for two most dispersive Phonon branch (Γ-X direction) have been used to interpret the size effect in Raman spectra. The obtained Raman peak shift and full width at half-maximum agree well with the experimental data. Our observations suggest that the Phonon Confinement effects are responsible for a significant shift and broadening for the Raman peaks. Copyright © 2009 John Wiley & Sons, Ltd.
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raman line shapes of optical Phonons of different symmetries in anatase tio2 nanocrystals
Journal of Physical Chemistry C, 2009Co-Authors: Satyaprakash Sahoo, A K Arora, V SridharanAbstract:Raman spectroscopic investigations of Phonons of different symmetries in anatase TiO2 nanocrystals synthesized by the sol−gel method are carried out. Out of six Raman active Phonons, the line shapes of two Eg modes and one B1g mode have been analyzed quantitatively to distinguish between the contributions of laser-induced local heating, Phonon Confinement effects, and defects to the line broadening. The line shape asymmetry arising from Confinement of optical Phonons in the 397 cm−1 B1g mode is found to be of opposite nature than those in the 144 and 639 cm−1 Eg modes. This arises due to the negative dispersion of the 397 cm−1 B1g Phonon dispersion curve. The measured spectra show larger broadening than those predicted by a Phonon Confinement model. The excess broadening, attributed to intrinsic defects, is found to be least for the 144 cm−1 Eg mode and largest for the 397 cm−1 B1g mode. In addition, finite laser power of the excitation wavelength is found to raise the temperature of the nanocrystals, wit...
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Phonon Confinement in stressed silicon nanocluster
Journal of Nanoscience and Nanotechnology, 2009Co-Authors: Satyaprakash Sahoo, Sandip Dhara, S Mahadevan, A K AroraAbstract:Confined acoustic and optical Phonons in Si nanoclusters embedded in sapphire, synthesized using ion-beam implantation are investigated using Raman spectroscopy. The l=0 and l=2 confined acoustic Phonons, found at low Raman shift, are analyzed using complex frequency model and the size of the nanoparticles are estimated as 4 and 6 nm. For the confined optical Phonon, in contrast to expected red shift, the Raman line shape shows a substantial blue shift, which is attributed to size dependent compressive stress in the nanoparticles. The calculated Raman line shape for the stressed nanoparticles fits well to data. The sizes of Si nanoparticles obtained using complex frequency model are consistent with the size estimated from the fitting of confined optical Phonon line shapes and those found from X-ray diffraction and TEM.
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Phonon Confinement and substitutional disorder in cd1 xznxs nanocrystals
Journal of Raman Spectroscopy, 2009Co-Authors: Satyaprakash Sahoo, V. Sivasubramanian, Sandip Dhara, S Kalavathi, A K AroraAbstract:1-longitudinal optical (LO) Phonons in free-standing mixed Cd1−xZnxS nanocrystals, synthesized using chemical precipitation, are investigated using Raman spectroscopy. As expected for the nanocrystals, the 1-LO modes are found to appear at slightly lower wavenumbers than those in the bulk mixed crystals and exhibit one-mode behavior. On the other hand, the line broadening is found to be much more than that can be accounted on the basis of Phonon Confinement. From the detailed line-shape analysis it turns out that the substitutional disorder in the mixed crystals contributes much more to the line broadening than the Phonon Confinement. The linewidth arising from these mechanisms are also extracted from the analysis. Copyright © 2009 John Wiley & Sons, Ltd.
Kang L Wang - One of the best experts on this subject based on the ideXlab platform.
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optical and acoustic Phonon modes in self organized ge quantum dot superlattices
Applied Physics Letters, 2000Co-Authors: Jianlin Liu, G Jin, Y S Tang, Yi Luo, Kang L WangAbstract:Raman scattering measurements were carried out in self-organized Ge quantum dot superlattices. The samples consisted of 25 periods of Ge quantum dots with different dot sizes sandwiched by 20 nm Si spacers, and were grown using solid-source molecular-beam epitaxy. Optical Phonon modes were found to be around 300 cm−1, and a dependence of the Raman peak frequency on the size of dots was evidenced in good agreement with a prediction based on Phonon Confinement and strain effects. Acoustic Phonons related to the Ge quantum dots have also been observed.
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effect of Phonon Confinement on the thermoelectric figure of merit of quantum wells
Journal of Applied Physics, 1998Co-Authors: Alexander A Balandin, Kang L WangAbstract:Recently, it has been shown that the thermoelectric figure of merit is strongly enhanced in quantum wells and superlattices due to two-dimensional carrier Confinement. We predict that the figure of merit can increase even further in quantum well structures with free-surface or rigid boundaries. This additional increase is due to spatial Confinement of acoustic Phonons and corresponding modification of their group velocities. The latter leads to an increase of the Phonon relaxation rates and thus, a significant drop in the lattice thermal conductivity.
Shun Ito - One of the best experts on this subject based on the ideXlab platform.
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Phonon Confinement and self limiting oxidation effect of silicon nanowires synthesized by laser ablation
Journal of Applied Physics, 2006Co-Authors: Naoki Fukata, T Oshima, Naoya Okada, Tokushi Kizuka, Takao Tsurui, Kouichi Murakami, Shun ItoAbstract:The Phonon Confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs’ surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical Phonon peak due to Phonon Confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.
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Phonon Confinement in silicon nanowires synthesized by laser ablation
Physica B-condensed Matter, 2006Co-Authors: Naoki Fukata, T Oshima, Naoya Okada, Tokushi Kizuka, Takao Tsurui, Shun Ito, Kouichi MurakamiAbstract:Abstract The Phonon Confinement effect was investigated by Raman measurements for Si nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) catalyst and for SiNWs thermally oxidized at 700–1000 °C. The Si optical Phonon peak for SiNWs, unlike that for bulk Si, showed a downshift and an asymmetric broadening. Thermal oxidation caused a further downshift and broadening. These phenomena can be explained by the Phonon Confinement effect due to the decrease in the diameter of the Si core of the SiNWs. It was additionally found that excess oxidation caused an upshift of the optical Phonon peak due to compressive stress.
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Phonon Confinement effect of silicon nanowires synthesized by laser ablation
Applied Physics Letters, 2005Co-Authors: Naoki Fukata, T Oshima, Tokushi Kizuka, Takao Tsurui, Kouichi Murakami, Shun ItoAbstract:A gradual downshift and asymmetric broadening of the Si optical Phonon peak were observed by Raman scattering measurements of continuously thermally oxidized silicon nanowires (SiNWs) synthesized by laser ablation. This downshift and broadening can be interpreted by the Phonon Confinement effect. Further thermal oxidation produced a reverse change; namely, an upshift of the optical Phonon peak. This is considered to be due to compressive stress since this stress was relieved by removing the oxide layers formed around the SiNW cores, resulting in a downshift of the optical Phonon peak.
A K Arora - One of the best experts on this subject based on the ideXlab platform.
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raman line shapes of optical Phonons of different symmetries in anatase tio2 nanocrystals
Journal of Physical Chemistry C, 2009Co-Authors: Satyaprakash Sahoo, A K Arora, V SridharanAbstract:Raman spectroscopic investigations of Phonons of different symmetries in anatase TiO2 nanocrystals synthesized by the sol−gel method are carried out. Out of six Raman active Phonons, the line shapes of two Eg modes and one B1g mode have been analyzed quantitatively to distinguish between the contributions of laser-induced local heating, Phonon Confinement effects, and defects to the line broadening. The line shape asymmetry arising from Confinement of optical Phonons in the 397 cm−1 B1g mode is found to be of opposite nature than those in the 144 and 639 cm−1 Eg modes. This arises due to the negative dispersion of the 397 cm−1 B1g Phonon dispersion curve. The measured spectra show larger broadening than those predicted by a Phonon Confinement model. The excess broadening, attributed to intrinsic defects, is found to be least for the 144 cm−1 Eg mode and largest for the 397 cm−1 B1g mode. In addition, finite laser power of the excitation wavelength is found to raise the temperature of the nanocrystals, wit...
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Phonon Confinement in stressed silicon nanocluster
Journal of Nanoscience and Nanotechnology, 2009Co-Authors: Satyaprakash Sahoo, Sandip Dhara, S Mahadevan, A K AroraAbstract:Confined acoustic and optical Phonons in Si nanoclusters embedded in sapphire, synthesized using ion-beam implantation are investigated using Raman spectroscopy. The l=0 and l=2 confined acoustic Phonons, found at low Raman shift, are analyzed using complex frequency model and the size of the nanoparticles are estimated as 4 and 6 nm. For the confined optical Phonon, in contrast to expected red shift, the Raman line shape shows a substantial blue shift, which is attributed to size dependent compressive stress in the nanoparticles. The calculated Raman line shape for the stressed nanoparticles fits well to data. The sizes of Si nanoparticles obtained using complex frequency model are consistent with the size estimated from the fitting of confined optical Phonon line shapes and those found from X-ray diffraction and TEM.
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Phonon Confinement and substitutional disorder in cd1 xznxs nanocrystals
Journal of Raman Spectroscopy, 2009Co-Authors: Satyaprakash Sahoo, V. Sivasubramanian, Sandip Dhara, S Kalavathi, A K AroraAbstract:1-longitudinal optical (LO) Phonons in free-standing mixed Cd1−xZnxS nanocrystals, synthesized using chemical precipitation, are investigated using Raman spectroscopy. As expected for the nanocrystals, the 1-LO modes are found to appear at slightly lower wavenumbers than those in the bulk mixed crystals and exhibit one-mode behavior. On the other hand, the line broadening is found to be much more than that can be accounted on the basis of Phonon Confinement. From the detailed line-shape analysis it turns out that the substitutional disorder in the mixed crystals contributes much more to the line broadening than the Phonon Confinement. The linewidth arising from these mechanisms are also extracted from the analysis. Copyright © 2009 John Wiley & Sons, Ltd.
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Phonon Confinement and substitutional disorder in cd1 xznxs nanocrystals
arXiv: Materials Science, 2009Co-Authors: Satyaprakash Sahoo, V. Sivasubramanian, Sandip Dhara, S Kalavathi, A K AroraAbstract:1LO optical Phonons in free-standing mixed Cd1-xZnxS nanocrystals, synthesized using chemical precipitation, are investigated using Raman spectroscopy. As expected for the nanocrystals, the 1-LO modes are found to appear at slightly lower wavenumbers than those in the bulk mixed crystals and exhibit one mode behavior. On the other hand, the line broadening is found to be much more than that can be accounted on the basis of Phonon Confinement. From the detailed line shape analysis it turns out that the substitutional disorder in the mixed crystals contributes much more to the line broadening than the Phonon Confinement. The linewidth arising from these mechanisms are also extracted from the analysis.
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raman spectra of cds nanocrystals in nafion longitudinal optical and confined acoustic Phonon modes
Physica E-low-dimensional Systems & Nanostructures, 2001Co-Authors: P Nandakumar, M. Rajalakshmi, A K Arora, C Vijayan, Y V G S MurtiAbstract:Abstract Quantum Confinement effects on the longitudinal optical and acoustic Phonons in CdS nanocrystals in the strongly confined regime in the polymer matrix Nafion are studied using Raman spectroscopy. The LO-Phonon modes show size-dependent asymmetric broadening though the broadening and asymmetry are less than those predicted by the Phonon Confinement models. Two types of confined acoustic modes corresponding to n =1, l =0 and n =1, l =2 spheroidal vibrations are observed. Softening of the spheroidal modes is observed in the strongly confined regime.
L Donetti - One of the best experts on this subject based on the ideXlab platform.
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hole mobility in ultrathin double gate soi devices the effect of acoustic Phonon Confinement
IEEE Electron Device Letters, 2009Co-Authors: L Donetti, F Gamiz, Noel Rodriguez, A GodoyAbstract:We show that the effect of Phonon Confinement in ultrathin double-gate silicon-on-insulator (DGSOI) transistors on hole mobility is weaker than that predicted for electron mobility. To do so, confined Phonon modes in SOI devices are computed, employing an elastic continuum model of acoustic Phonons in a three-layer structure. A self-consistent k middot p-Poisson solver has been developed for the valence-band structure calculation, and Kubo-Greenwood formalism is used to compute the hole mobility in ultrathin DGSOI transistors under the combined effect of confined Phonon and surface-roughness scattering.
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acoustic Phonon Confinement in silicon nanolayers effect on electron mobility
Journal of Applied Physics, 2006Co-Authors: L Donetti, F Gamiz, J B Roldan, A GodoyAbstract:We demonstrate the Confinement of acoustic Phonons in ultrathin silicon layers and study its effect on electron mobility. We develop a model for confined acoustic Phonons in an ideal single-layer structure and in a more realistic three-layer structure. Phonon quantization is recovered, and the dispersion relations for distinct Phonon modes are computed. This allows us to obtain the confined Phonon scattering rates and, using Monte Carlo simulations, to compute the electron mobility in ultrathin silicon on insulator inversion layers. Thus, comparing the results with those obtained using the bulk Phonon model, we are able to conclude that it is very important to include confined acoustic Phonon models in the electron transport simulations of ultrathin devices, if we want to reproduce the actual behavior of electron transport in silicon layers of nanometric thickness.
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influence of acoustic Phonon Confinement on electron mobility in ultrathin silicon on insulator layers
Applied Physics Letters, 2006Co-Authors: L Donetti, F Gamiz, N Rodriguez, F Jimenez, C SampedroAbstract:We show the importance of acoustic Phonon Confinement in ultrathin silicon-on-insulator inversion layers by comparing electron mobility calculated by the Monte Carlo method assuming a bulk acoustic Phonon model (the usual procedure) with that obtained by using a confined acoustic Phonon model developed in this work. Both freestanding and rigid boundary conditions are taken into account for the evaluation of the confined Phonon dispersion in a three-layer structure. Mobility reductions of 30% are observed for silicon thicknesses of around 5–10nm when the confined acoustic Phonon model is used.We show the importance of acoustic Phonon Confinement in ultrathin silicon-on-insulator inversion layers by comparing electron mobility calculated by the Monte Carlo method assuming a bulk acoustic Phonon model (the usual procedure) with that obtained by using a confined acoustic Phonon model developed in this work. Both freestanding and rigid boundary conditions are taken into account for the evaluation of the confined Phonon dispersion in a three-layer structure. Mobility reductions of 30% are observed for silicon thicknesses of around 5–10nm when the confined acoustic Phonon model is used.