Browsing by Author "Lee, J.-H."

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Ceria-samarium binary metal oxides: A comparative approach towards structural properties and soot oxidation activity
(2018) Anantharaman, A.P.; Geethu, J.; P, M.R.; Dasari, Hari Prasad; Lee, J.-H.; Bhaskar, Babu, G.U.; Dasari, H.
Binary metal oxides of CeO2-Sm2O3 (CSx, x varies from 10 to 90 mol%) along with pure CeO2 and Sm2O3 were synthesised successfully by the EDTA-Citrate method. From XRD, Raman spectroscopy and UV vis DRS results, the whole composition of metal oxides exist in three phases: (fluorite phase (F) (CS10-CS30), bi-phase (fluorite (F) + cubic (C)) (CS30-CS90) and cubic phase (C) (Sm2O3)). For CSx samples, the calculated band gap energy values obtained from the UV vis DRS results were in between 3.0 5.1 eV and fluorite phase samples (CS10 CS30) displayed lower band gap energy values (3.04 3.07 eV) than compared to the samples in other phases. Similarly, from XPS analysis, fluorite phase samples (CS10 CS30) showed higher surface oxygen vacancy concentration than compared to samples in other phases. Catalytic activity for soot oxidation is carried out on CSx samples, and the T50 temperature is in between 480 540 C. Fluorite phase samples (CS10 CS30) showed higher surface area, lower degree of agglomeration, lower band gap energy, higher oxygen vacancy concentration and better catalytic activity for soot oxidation. Among all the CSx samples, CS10 sample displayed highest surface area (38 m2/g), lowest degree of agglomeration (0.36), lowest band gap energy (3.04 eV), highest oxygen vacancy concentration (64%) and highest soot oxidation activity (T50 = 480 C). The order of the soot oxidation activity of CSx samples followed the same trend of band gap energy values. 2018 Elsevier B.V.
Ceria-samarium binary metal oxides: A comparative approach towards structural properties and soot oxidation activity
(Elsevier B.V., 2018) Anjana, A.P.; Geethu, J.; P, M.R.; Prasad Dasari, H.P.; Lee, J.-H.; Harshini, H.; Bhaskar Babu, G.U.
Binary metal oxides of CeO2-Sm2O3 (CSx, x varies from 10 to 90 mol%) along with pure CeO2 and Sm2O3 were synthesised successfully by the EDTA-Citrate method. From XRD, Raman spectroscopy and UV–vis DRS results, the whole composition of metal oxides exist in three phases: (fluorite phase (F) (CS10-CS30), bi-phase (fluorite (F) + cubic (C)) (CS30-CS90) and cubic phase (C) (Sm2O3)). For CSx samples, the calculated band gap energy values obtained from the UV–vis DRS results were in between 3.0–5.1 eV and fluorite phase samples (CS10–CS30) displayed lower band gap energy values (3.04–3.07 eV) than compared to the samples in other phases. Similarly, from XPS analysis, fluorite phase samples (CS10–CS30) showed higher surface oxygen vacancy concentration than compared to samples in other phases. Catalytic activity for soot oxidation is carried out on CSx samples, and the T50 temperature is in between 480–540 °C. Fluorite phase samples (CS10 CS30) showed higher surface area, lower degree of agglomeration, lower band gap energy, higher oxygen vacancy concentration and better catalytic activity for soot oxidation. Among all the CSx samples, CS10 sample displayed highest surface area (38 m2/g), lowest degree of agglomeration (0.36), lowest band gap energy (3.04 eV), highest oxygen vacancy concentration (64%) and highest soot oxidation activity (T50 = 480 °C). The order of the soot oxidation activity of CSx samples followed the same trend of band gap energy values. © 2018 Elsevier B.V.
Comparative evaluation of organic contamination sources from roller and pencil type PVA brushes during the Post-CMP cleaning process
(Elsevier Ltd, 2020) Lee, J.-H.; Poddar, M.K.; Han, K.-M.; Ryu, H.-Y.; Yerriboina, N.P.; Kim, T.-G.; Wada, Y.; Hamada, S.; Hiyama, H.; Park, J.-G.
In post-CMP (chemical mechanical polishing) processing, the use of poly vinyl acetal (PVA) brushes to clean the wafer surface is one of the most effective and prominent techniques applied for the removal of CMP contaminants. Recently, organic contaminants induced in different types of PVA brushes during brush manufacturing have been drawing substantial research interest in CMP communities. In this study, investigated the root cause of these residual organic impurities in two different types of PVA brushes was investigated: roller and pencil type brushes. PVA roller brushes have a skin layer due to the brush molding process, but pencil-type PVA brushes do not have the skin layer. Extraction of organic impurities from both types of brushes was accomplished using an ultrasound-assisted technique at a sonication frequency of 40 kHz, and input power of 600 W. Further evaluation of these organic impurities using Field Emission Scanning Electron Microscopy (FE-SEM) revealed a large number of organic impurities in roller brushes and negligible impurities in pencil brushes. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed polydimethylsiloxane (PDMS) as the organic impurities extracted from PVA roller brushes, which were generated during the brush manufacturing process. The PDMS content in PVA roller brushes was further analyzed using FE-SEM micrographs via dissolving the organic impurities in tetramethylammonium hydroxide solution (TMAH). During brush fabrication, the high content of PDMS organic impurities in roller PVA brushes is essentially attributed to the presence of the additional skin layer formed by the mold releasing agent at the mold-cavity interface. © 2020 Elsevier Ltd
Nanocatalyst-induced hydroxyl radical ( OH) slurry for tungsten CMP for next-generation semiconductor processing
(2020) Poddar, M.K.; Ryu, H.-Y.; Yerriboina, N.P.; Jeong, Y.-A.; Lee, J.-H.; Kim, T.-G.; Kim, J.-H.; Park, J.-D.; Lee, M.-G.; Park, C.-Y.; Han, S.-J.; Choi, J.-G.; Park, J.-G.
Chemical mechanical polishing (CMP) is one of the important steps that involves during fabrication of semiconductor devices. This research highlights the importance of tungsten (W) polishing slurries consisting of a novel nonionic, heat-activated FeSi nanocatalyst on the performance of W chemical mechanical polishing. The results obtained from the polishing data showed a higher W removal rate of 5910 /min with a slurry consisting of FeSi nanocatalyst at a polishing temperature of 80 C. The increase in W polishing rate using FeSi slurry was explained on the basis of formation of a thicker oxide layer (WO3) due to the interaction between the W surface and hydroxyl radicals ( OH) generated via the reaction between FeSi and hydrogen peroxide at 80 C. Higher OH generation and increase in oxygen depth profile of W film were confirmed by UV Vis spectrometer and AES analysis, respectively. Compared to Fe(NO3)3 catalyst, the slurry with FeSi showed a higher static etch rate at 80 C. Potentiodynamic polarization results obtained using FeSi slurry showed thicker WO3 passivation layer as compared to the slurry with Fe(NO3)3. The increase in the polishing rate of W CMP using slurry with FeSi nanocatalyst can be essentially attributed to the generation of much stronger oxidant OH due to its increased catalytic effect at a high polishing temperature of 80 C. 2019, Springer Science+Business Media, LLC, part of Springer Nature.
Nanocatalyst-induced hydroxyl radical (·OH) slurry for tungsten CMP for next-generation semiconductor processing
(Springer, 2020) Poddar, M.K.; Ryu, H.-Y.; Yerriboina, N.P.; Jeong, Y.-A.; Lee, J.-H.; Kim, T.-G.; Kim, J.-H.; Park, J.-D.; Lee, M.-G.; Park, C.-Y.; Han, S.-J.; Choi, J.-G.; Park, J.-G.
Chemical mechanical polishing (CMP) is one of the important steps that involves during fabrication of semiconductor devices. This research highlights the importance of tungsten (W) polishing slurries consisting of a novel nonionic, heat-activated FeSi nanocatalyst on the performance of W chemical mechanical polishing. The results obtained from the polishing data showed a higher W removal rate of 5910 Å/min with a slurry consisting of FeSi nanocatalyst at a polishing temperature of 80 °C. The increase in W polishing rate using FeSi slurry was explained on the basis of formation of a thicker oxide layer (WO3) due to the interaction between the W surface and hydroxyl radicals (·OH) generated via the reaction between FeSi and hydrogen peroxide at 80 °C. Higher ·OH generation and increase in oxygen depth profile of W film were confirmed by UV–Vis spectrometer and AES analysis, respectively. Compared to Fe(NO3)3 catalyst, the slurry with FeSi showed a higher static etch rate at 80 °C. Potentiodynamic polarization results obtained using FeSi slurry showed thicker WO3 passivation layer as compared to the slurry with Fe(NO3)3. The increase in the polishing rate of W CMP using slurry with FeSi nanocatalyst can be essentially attributed to the generation of much stronger oxidant ·OH due to its increased catalytic effect at a high polishing temperature of 80 °C. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
Praseodymium doped ceria as electrolyte material for IT-SOFC applications
(2018) Shajahan, I.; Ahn, J.; Nair, P.; Medisetti, S.; Patil, S.; Niveditha, V.; Uday, Bhaskar, Babu, G.; Dasari, Hari Prasad; Lee, J.-H.
Praseodymium-doped ceria (PDC, Ce0.9Pr0.1O2) electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been successfully synthesised by EDTA-citrate method. From X-Ray diffraction (XRD), fluorite structure along with a crystallite size of 5.4 nm is obtained for PDC nanopowder calcined at 350 C/24 h. Raman spectroscopy confirmed the structure, presence of oxygen vacancies with the manifestation of the main peak at 457 cm?1 and with a secondary peak at 550 cm?1. From Transmission Electron Microscopy (TEM) analysis, the average particle size is around 7 10 nm and selected area electron diffraction (SAED) patterns further confirmed the fluorite structure of PDC nanopowder. The PDC nanopowder displayed a BET surface area of 65 m2/g with a primary particle size of ?13 nm (calculated from BET surface area). Dilatometer studies revealed a multi-step shrinkage behaviour with the multiple peaks at 522, 1171 and 1461 C which may be originated due to the presence of multiple size hard agglomerates. The PDC electrolyte pellet sintered at 1500 C displayed an ionic conductivity of 1.213E-03 S cm?1 along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO2) and cubic structure (PrO2). 2018 Elsevier B.V.
Praseodymium doped ceria as electrolyte material for IT-SOFC applications
(Elsevier Ltd, 2018) Shajahan, I.; Ahn, J.; Nair, P.; Medisetti, S.; Patil, S.; Niveditha, V.; Uday Bhaskar Babu, G.; Prasad Dasari, H.P.; Lee, J.-H.
Praseodymium-doped ceria (PDC, Ce0.9Pr0.1O2) electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been successfully synthesised by EDTA-citrate method. From X-Ray diffraction (XRD), fluorite structure along with a crystallite size of 5.4 nm is obtained for PDC nanopowder calcined at 350 °C/24 h. Raman spectroscopy confirmed the structure, presence of oxygen vacancies with the manifestation of the main peak at 457 cm?1 and with a secondary peak at 550 cm?1. From Transmission Electron Microscopy (TEM) analysis, the average particle size is around 7–10 nm and selected area electron diffraction (SAED) patterns further confirmed the fluorite structure of PDC nanopowder. The PDC nanopowder displayed a BET surface area of 65 m2/g with a primary particle size of ?13 nm (calculated from BET surface area). Dilatometer studies revealed a multi-step shrinkage behaviour with the multiple peaks at 522, 1171 and 1461 °C which may be originated due to the presence of multiple size hard agglomerates. The PDC electrolyte pellet sintered at 1500 °C displayed an ionic conductivity of 1.213E-03 S cm?1 along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO2) and cubic structure (PrO2). © 2018 Elsevier B.V.
Record-low sintering-temperature (600 c) of solid-oxide fuel cell electrolyte
(2016) Dasari, Hari Prasad; Ahn, K.; Park, S.-Y.; Hong, J.; Kim, H.; Yoon, K.J.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.
One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (?150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ?1.00 10-2 S cm-1 at 600 C in air and from the conductivity plots the activation energy is found to be 0.53 eV. 2016 Elsevier B.V. All rights reserved.
Record-low sintering-temperature (600 °c) of solid-oxide fuel cell electrolyte
(Elsevier Ltd, 2016) Prasad Dasari, H.P.; Ahn, K.; Park, S.-Y.; Hong, J.; Kim, H.; Yoon, K.J.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.
One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 °C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 °C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 °C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (?150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ?1.00 × 10-2 S cm-1 at 600 °C in air and from the conductivity plots the activation energy is found to be 0.53 eV. © 2016 Elsevier B.V. All rights reserved.
Soot Oxidation Activity of Redox and Non-Redox Metal Oxides Synthesised by EDTA Citrate Method
(2017) Anantharaman, A.P.; Dasari, Hari Prasad; Lee, J.-H.; Babu, G.U.B.; Dasari, H.
Abstract: In the present study, redox (CeO2, SnO2, Pr6O11 and Mn3O4) and non-redox (Gd2O3, La2O3 ZrO2 and HfO2) metal oxides were successfully synthesised using the EDTA citrate complexing method and tested for soot oxidation activity. The characterization of the metal oxides is carried out using FTIR, XRD, BET surface area, pore volume analyser, SEM and TEM. The redox nature and metal oxygen bond information of the metal oxides are obtained from XPS analysis. In redox metal oxides, three critical parameters [lattice oxygen binding energy, reduction temperature and ?r (ionic size difference of the corresponding metal oxide oxidation states)] govern the soot oxidation activity. Among the redox metal oxide samples, Mn3O4 and Pr6O11 samples showed lower binding energy for oxygen (O? 529.4, 528.9 eV respectively), lower reduction temperature (T? 317 and 512 C respectively) and have smaller ?r value (9 pm and 17 pm respectively). Thus, displayed a better soot oxidation activity (T50 = 484 and 482 C respectively) than compared to other redox metal oxides. Among the non-redox metal oxides, HfO2 sample displayed higher BET surface area (21.06 m2/g), lattice strain (0.0157), smaller ionic radius (58.2 pm) and higher relative surface oxygen ratio (58%) and thus resulted in a significantly better soot oxidation activity (T50 = 483 C) than compared to other non-redox metal oxides. Graphical Abstract: [Figure not available: see fulltext.]. 2017, Springer Science+Business Media, LLC.
Soot Oxidation Activity of Redox and Non-Redox Metal Oxides Synthesised by EDTA–Citrate Method
(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Anjana, A.P.; Prasad Dasari, H.P.; Lee, J.-H.; Harshini, H.; Babu, G.U.B.
Abstract: In the present study, redox (CeO2, SnO2, Pr6O11 and Mn3O4) and non-redox (Gd2O3, La2O3 ZrO2 and HfO2) metal oxides were successfully synthesised using the EDTA–citrate complexing method and tested for soot oxidation activity. The characterization of the metal oxides is carried out using FTIR, XRD, BET surface area, pore volume analyser, SEM and TEM. The redox nature and metal–oxygen bond information of the metal oxides are obtained from XPS analysis. In redox metal oxides, three critical parameters [lattice oxygen binding energy, reduction temperature and ?r (ionic size difference of the corresponding metal oxide oxidation states)] govern the soot oxidation activity. Among the redox metal oxide samples, Mn3O4 and Pr6O11 samples showed lower binding energy for oxygen (O?—529.4, 528.9 eV respectively), lower reduction temperature (T?—317 and 512 °C respectively) and have smaller ?r value (9 pm and 17 pm respectively). Thus, displayed a better soot oxidation activity (T50 = 484 and 482 °C respectively) than compared to other redox metal oxides. Among the non-redox metal oxides, HfO2 sample displayed higher BET surface area (21.06 m2/g), lattice strain (0.0157), smaller ionic radius (58.2 pm) and higher relative surface oxygen ratio (58%) and thus resulted in a significantly better soot oxidation activity (T50 = 483 °C) than compared to other non-redox metal oxides. Graphical Abstract: [Figure not available: see fulltext.]. © 2017, Springer Science+Business Media, LLC.
Synthesis of GDC electrolyte material for IT-SOFCs using glucose & fructose and its characterization
(2017) Medisetti, S.; Ahn, J.; Patil, S.; Goel, A.; Bangaru, Y.; Sabhahit, G.V.; Babu, G.U.B.; Lee, J.-H.; Dasari, Hari Prasad
Nano-powder of gadolinium-doped-ceria (GDC, Ce0.9Gd0.1O2) has been synthesized using a novel sol gel method with glucose and fructose as organic additives. The main objective of the present study is to find the suitability of this synthesis method in synthesizing ceria-based SOFC electrolyte materials and evaluate its performance. The average crystallite/particle size obtained from XRD, TEM, BET surface area was found to be 4 12 nm. The phase was found to be cubic fluorite from XRD and further the structure and the nature of oxygen vacancies was confirmed using Raman spectroscopy. Dilatometer studies illustrated two shrinkage maxima (450 C and 1450 C). The ionic conductivity measurements were done using DC four-probe method on the GDC electrolyte sintered at 1500 C. The sintered sample showed an ionic conductivity of 1.13E?02 Scm?1 at a temperature of 700 C in the air, and the activation energy is 1.02 eV. The present study reveals that this synthesis method can be adaptable for synthesizing SOFC electrolyte materials. 2017 Elsevier B.V.
Synthesis of GDC electrolyte material for IT-SOFCs using glucose & fructose and its characterization
(Elsevier B.V., 2017) Medisetti, S.; Ahn, J.; Patil, S.; Goel, A.; Bangaru, Y.; Sabhahit, G.V.; Babu, G.U.B.; Lee, J.-H.; Prasad Dasari, H.P.
Nano-powder of gadolinium-doped-ceria (GDC, Ce0.9Gd0.1O2) has been synthesized using a novel sol–gel method with glucose and fructose as organic additives. The main objective of the present study is to find the suitability of this synthesis method in synthesizing ceria-based SOFC electrolyte materials and evaluate its performance. The average crystallite/particle size obtained from XRD, TEM, BET surface area was found to be 4–12 nm. The phase was found to be cubic fluorite from XRD and further the structure and the nature of oxygen vacancies was confirmed using Raman spectroscopy. Dilatometer studies illustrated two shrinkage maxima (450 °C and 1450 °C). The ionic conductivity measurements were done using DC four-probe method on the GDC electrolyte sintered at 1500 °C. The sintered sample showed an ionic conductivity of 1.13E?02 Scm?1 at a temperature of 700 °C in the air, and the activation energy is 1.02 eV. The present study reveals that this synthesis method can be adaptable for synthesizing SOFC electrolyte materials. © 2017 Elsevier B.V.
Ultrafast dynamics of autoionizing states in O2 probed by laser-field-assisted XUV photoionization
(2013) Zhu, C.; Ko, D.H.; Kang, K.S.; Lee, J.; Lee, J.-H.; Umesh, G.; Krishnakumar, E.; Nam, C.H.
Dynamics of the autoionizing states in O2 was investigated using the method of laser-field-assisted extreme-ultraviolet photoionization. Harmonics, ranging from 9th to 21st orders generated in Kr with 25 fs laser pulses at 820 nm, were employed to carry out photoionization of O2. Distinct autoionization features in the photoelectron spectrum, stemming from the resonant excitation of superexcited states of O2 by the 11th harmonic, were observed. The superexcited states, referred to as autoionizing states, were identified to be the ?? = 0, n = 5 Rydberg states converging to the b 4?g- state of O 2+. Infrared laser pulses were utilized as the probe to monitor time-varying characteristics of photoionization and autoionization of O2. A decay time of 21 fs was obtained for the autoionizing states of O2 by deconvoluting the pump-probe results in O2 and Ar. � 2013 American Physical Society.
Ultrafast dynamics of autoionizing states in O2 probed by laser-field-assisted XUV photoionization
(2013) Zhu, C.; Ko, D.H.; Kang, K.S.; Lee, J.; Lee, J.-H.; Umesh, G.; Krishnakumar, E.; Nam, C.H.
Dynamics of the autoionizing states in O2 was investigated using the method of laser-field-assisted extreme-ultraviolet photoionization. Harmonics, ranging from 9th to 21st orders generated in Kr with 25 fs laser pulses at 820 nm, were employed to carry out photoionization of O2. Distinct autoionization features in the photoelectron spectrum, stemming from the resonant excitation of superexcited states of O2 by the 11th harmonic, were observed. The superexcited states, referred to as autoionizing states, were identified to be the ?? = 0, n = 5 Rydberg states converging to the b 4?g- state of O 2+. Infrared laser pulses were utilized as the probe to monitor time-varying characteristics of photoionization and autoionization of O2. A decay time of 21 fs was obtained for the autoionizing states of O2 by deconvoluting the pump-probe results in O2 and Ar. © 2013 American Physical Society.