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566 results on '"Mandal, Soumen"'

162. GaN-on-diamond technology platform: Bonding-free membrane manufacturing process

Author

Smith, Matthew D., primary, Cuenca, Jerome A., additional, Field, Daniel E., additional, Fu, Yen-chun, additional, Yuan, Chao, additional, Massabuau, Fabien, additional, Mandal, Soumen, additional, Pomeroy, James W., additional, Oliver, Rachel A., additional, Uren, Michael J., additional, Elgaid, Khaled, additional, Williams, Oliver A., additional, Thayne, Iain, additional, and Kuball, Martin, additional

Published
2020
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163. Effect of slurry composition on the chemical mechanical polishing of thin diamond films

Author

Werrell, Jessica M., Mandal, Soumen, Thomas, Evan L. H., Brousseau, Emmanuel B., Lewis, Ryan, Borri, Paola, Davies, Philip R., and Williams, Oliver A.

Subjects
Chemical mechanical polishing, chemical vapour deposition, lcsh:Biotechnology, lcsh:TP248.13-248.65, surface roughness, lcsh:TA401-492, nanocrystalline diamond, lcsh:Materials of engineering and construction. Mechanics of materials, Optical, Magnetic and Electronic Device Materials, QC, Article, QB
Abstract

Nanocrystalline diamond (NCD) thin films grown by chemical vapour deposition (CVD) have an intrinsic surface roughness, which hinders the development and per-\ud formance of the films' various applications. Traditional methods of diamond polishing are not effective on NCD thin films. Films either shatter due to the combination\ud of wafer bow and high mechanical pressures or produce uneven surfaces, which has led to the adaptation of the chemical mechanical polishing (CMP) technique for\ud NCD films. This process is poorly understood and in need of optimisation. To compare the effect of slurry composition and pH upon polishing rates, a series of NCD\ud thin films have been polished for three hours using a Logitech Tribo CMP System in conjunction with a polyester/polyurethane polishing cloth and six different slurries. The reduction in surface roughness was measured hourly using an atomic force microscope. The nal surface chemistry was examined using X-ray photoelectron\ud spectroscopy and a scanning electron microscope. It was found that of all the various properties of the slurries, including pH and composition, the particle size was\ud the determining factor for the polishing rate. The smaller particles polishing at a greater rate than the larger ones.

Published
2017

172. Thick, Adherent Diamond Films on AlN with Low Thermal Barrier Resistance

Author

Mandal, Soumen, primary, Yuan, Chao, additional, Massabuau, Fabien, additional, Pomeroy, James W., additional, Cuenca, Jerome, additional, Bland, Henry, additional, Thomas, Evan, additional, Wallis, David, additional, Batten, Tim, additional, Morgan, David, additional, Oliver, Rachel, additional, Kuball, Martin, additional, and Williams, Oliver A., additional

Published
2019
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177. Microwave Permittivity of Trace sp² Carbon Impurities in Sub-Micron Diamond Powders

Author

Cuenca, Jerome Alexander, Thomas, Evan, Mandal, Soumen, Morgan, David John, Lloret Vieira, Fernando Manuel, Araújo Gay, Daniel, Williams, Oliver Aneurin, Porch, Adrian, and Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica

Subjects
Condensed Matter::Materials Science, Physics::Atomic and Molecular Clusters
Abstract

Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.

Published
2018

178. Positive zeta potential of nanodiamonds

Author

Gines, Laia, Mandal, Soumen, Ahmed, Ashek-I, Cheng, Chia-Liang, Sow, Maabur, and Williams, Oliver A.

Subjects
QC
Abstract

In this paper, the origin of positive zeta potential exhibited by nanodiamond particles is explained. Positive zeta potentials in nano-structured carbons can be explained by the presence of graphitic planes at the surface, which leave oxygen-free Lewis sites and so promotes the suppression of acidic functional groups. Electron Microscopy and Raman Spectroscopy have been used to show that positive zeta potential of nanodiamond is only exhibited in the presence of sp2 carbon at the surface.

Published
2017

179. Slow electron–phonon cooling in superconducting diamond films

Author

Titova, Nadezhda, Kardakova, Anna I., Tovpeko, Nina, Ryabchun, Sergey, Mandal, Soumen, Morozov, Dmitry, Klemencic, Georgina M., Giblin, Sean R., Williams, Oliver A., Goltsman, Gregory N., and Klapwijk, T. M.

Subjects
Condensed Matter::Materials Science, Condensed Matter::Superconductivity, Condensed Matter::Strongly Correlated Electrons, QC
Abstract

We have measured the electron-phonon energy-relaxation time, τeph, in superconducting boron-doped diamond films grown on silicon substrate by chemical vapor deposition. The observed electron-phonon cooling times vary from 160 ns at 2.70 K to 410 ns at 1.8 K following a T -2-dependence. The data are consistent with the values of τeph previously reported for single-crystal boron-doped diamond films epitaxially grown on diamond substrate. Such a noticeable slow electron-phonon relaxation in boron-doped diamond, in combination with a high normal-state resistivity, confirms a potential of superconducting diamond for ultrasensitive superconducting bolometers.

Published
2017

182. Production of Metal-Free Diamond Nanoparticles

Author

Ginés, Laia, primary, Mandal, Soumen, additional, Morgan, David John, additional, Lewis, Ryan, additional, Davies, Philip R., additional, Borri, Paola, additional, Morley, Gavin W., additional, and Williams, Oliver A., additional

Published
2018
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190. Dielectric properties of diamond using an X-band microwave split dielectric resonator.

Author

Cuenca, Jerome A., Mandal, Soumen, Stritt, Jaspa, Zheng, Xiang, Pomeroy, James, Kuball, Martin, Porch, Adrian, and Williams, Oliver A.

Subjects
*DIELECTRIC resonators, *DIELECTRIC properties, *DIELECTRIC measurements, *DIELECTRIC loss, *MICROWAVES
Abstract

This work presents an easy-to-use microwave split dielectric resonator (MSDR) for X-band dielectric measurements of free-standing unpolished poly-crystalline diamond (PCD). PCD grown with varying CH 4 /H 2 and O 2 / CH 4 /H 2 in the gas phase show stark differences in dielectric loss. Low microwave dielectric loss PCD is found for CH 4 /H 2 concentrations of less than 5% while PCD grown with O 2 show very high loss tangents. Vacuum annealing introduces non-diamond carbon (NDC) impurities which increases the loss, however, even after significant discolouration the loss is still lower than the O 2 grown PCD. The loss mechanism of O 2 grown PCD is likely due to a high concentration of grain boundaries and grain boundary hopping conduction mechanisms as opposed to high concentrations of NDC impurities. [Display omitted] [ABSTRACT FROM AUTHOR]

Published
2024
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194. Surface Zeta Potential and Diamond Seeding on Gallium Nitride Films

Author

Mandal, Soumen, primary, Thomas, Evan L. H., additional, Middleton, Callum, additional, Gines, Laia, additional, Griffiths, James T., additional, Kappers, Menno J., additional, Oliver, Rachel A., additional, Wallis, David J., additional, Goff, Lucy E., additional, Lynch, Stephen A., additional, Kuball, Martin, additional, and Williams, Oliver A., additional

Published
2017
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196. Investigating the broadband microwave absorption of nanodiamond impurities

Author

Cuenca, Jerome A., Thomas, Evan L. H., Mandal, Soumen, Williams, Oliver Anuerin, and Porch, Adrian

Abstract

Broadband microwave complex permittivity measurements of nanodiamond powders are presented. Previous studies show that measurements of dielectric loss strongly correlate with the presence of nondiamond surface impurities. In this study, the frequency dependence of these losses is investigated using the microwave cavity perturbation (MCP) and broadband coaxial probe (BCP) methods. This allowed further understanding as to what mechanisms contribute to the microwave absorption (free electron conduction or dielectric loss from the disordered surfaces). A multimode MCP system is used which utilizes ${rm TM}_{0np}$ modes to provide partial spectral characterization. The MCP results revealed minimal frequency dependence, unlike any static conduction-related mechanism. The BCP measurements corroborate the MCP results with much higher spectral resolution, and further demonstrate that disorder related loss may dominate over free electron conduction from 1–10 GHz. From 0.1–1 GHz, free electron conduction has a greater influence with a characteristic $1/f$ dependence implying that conduction may dominate at lower frequencies. However, the BCP method, while repeatable, lacks in precision compared to the cavity method. Nonetheless, the major conclusion in this paper is that through simple microwave permittivity measurements, nondiamond carbon impurities in nanodiamond powders are measurable most likely because of disorder related losses as opposed to free electron conduction.

Published
2015

197. Electrochemical Behavior of Cu60Zr25Ti15 Bulk Metallic Glass with the Addition of Nb and Mo.

Author

Mandal, Soumen, Sivakumar, B., Singhbabu, Y. N., Bandyopadhyay, N. R., Chattopadhyay, P. P., and Kailath, Ansu J.

Subjects
METALLIC glasses, OPEN-circuit voltage, X-ray photoelectron spectroscopy, SCANNING electron microscopes, CORROSION resistance, AQUEOUS solutions
Abstract

This paper reports the changes in the electrochemical behavior of Cu60Zr25Ti15 bulk metallic glass (BMG) with the addition of 1 at.% Mo and Nb in 3.5 wt.% NaCl aqueous solution. Electrochemical methods employed for the study are open-circuit potential (OCP) and potentiodynamic polarization. The OCP values of the parent BMG and minor-alloyed BMGs differ only marginally. However, potentiodynamic studies show slightly higher corrosion resistance for the minor-alloyed BMGs than that of the parent alloy. Polarized surfaces of all the samples, examined under a scanning electron microscope (SEM), reveal pits formed due to corrosion. Corrosion products are analyzed by energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Higher corrosion resistance observed for Nb- or Mo-added BMGs is attributed to the formation of NbO2/Nb2O5 and MoO2, respectively, besides the oxides of other constituent elements. [ABSTRACT FROM AUTHOR]

Published
2019
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199. Silver and molybdenum disulfide nanoparticles synthesized in situ in dimethylformamide as dielectric for micro-electro discharge machining.

Author

Mandal, Soumen, Vinod Kumar, Rajulapati, and Nagahanumaiah

Abstract

The research focuses on the applicability of silver (Ag) and molybdenum disulfide (MOS2) nanoparticle synthesized in situ in dimethylformamide solution as dielectric material for micro-electro discharge machining. Ag nanoparticles (~120 nm size) and MOS2 nanoparticles (~20 nm size) were synthesized in dimethylformamide solution using a combination of nanoparticle solution synthesis routes. A setup for micro-electro discharge machining was developed in-house with an arrangement to generate spark at varying voltages. The setup was integrated with a precise linear height gauge to measure the spark gap during the experiments where Ag and MOS2 nanoparticles in dimethylformamide solution served as dielectric. The debris was collected and was characterized for each of the experiments. The feature size of the crater generated during the micro-electro discharge machining was also studied. The experiments were repeated with silver and MOS2 nanoparticle powder mixed with dimethylformamide as dielectric. It was observed that in situ prepared nanoparticles in dimethylformamide offered much better machining performance in terms of process stability, crater size and material removal rates. On use of in situ synthesized nanoparticle dielectric, the material removal rate increased by nearly two to three times whereas the spark gap increased by about two times. [ABSTRACT FROM AUTHOR]

Published
2019
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200. Time-varying process model for intelligent prediction of strain and temperature in micro-turning process.

Author

Mandal, Soumen, Pal, Aniruddha, and Nagahanumaiah

Abstract

Time-varying process models for micro-machining processes are important as they aid in control of machining parameters. In this research, a state-space-based process model for the temperature and strain generated near the cutting edge of the tool tip is identified using system identification approach. Fiber Bragg grating sensors were placed rigidly near the cutting edge of the tool tip in a micro-turning setup. Subsequently, micro-turning operations were carried out on aluminum and mild steel. The computer numerically controlled program was such that the machining parameters (feed velocity, depth of cut and RPM) change with machining time. The time-varying machining parameters act as inputs to the model, and the dynamic values of strain and temperature serve as model output. A state-space model was generated using the experimental data. Subsequently, a Kalman filter was used to intelligently predict the values of strain and temperature at the cutting edge of tool tip in advance using the model parameters identified by state-space modeling. Experimental results confirm that the time-varying model and the Kalman filter proposed in this research are effective in predicting the strain and temperature in advance with high accuracy. The maximum error in prediction of temperature was 0.4 °C, whereas for strain prediction, the maximum error was 0.3µ∈. [ABSTRACT FROM AUTHOR]

Published
2019
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