Study on the Effects of H+ and He+ Implantation in Semi-Insulating GaAs by Using Raman Spectroscopy

Santhakumar, K.,Kim, J. S.,Lee, C. R.,Kesavamoorthy, R.,Nair, K. G. M.,Jayavel, P.,Hayakawa, Y.,Soga, T. Korean Physical Society 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2

Study on the Effects of H+ and He+ Implantation in Semi-Insulating GaAs by Using Raman Spectroscopy

santhakumar kannappan,Cheul-Ro LEE,Hayakawa Y,Jayavel P,Jin soo Kim,Kesavamoorthy R,Muraleedaran Nair,Tetsuo soga 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I

Fifty-keV hydrogen-ion (H$^+$) and 70-keV helium-ion (He$^+$) implantation with doses from 10$^{13}$ to 10$^{16}$ cm$^{-2}$ in semi-insulating (100) gallium-arsenide (GaAs) single- crystal substrates have been carried out. Raman spectra of as-grown, implanted, and post-implantation-annealed GaAs samples are analyzed. Two LO phonon modes have been observed for all the samples. The lower wavenumber peak is attributed to the strained surface layer whereas the higher wavenumber peak is due to bulk GaAs crystal. For H$^+$ implantation, the peak positions of both peaks shift towards lower wavenumber up to a dose of 10$^{14}$ cm$^{-2}$ due to passivation of charge carriers. For higher doses, the peak positions shift towards higher wavenumber due to hydrogen-filled vacancy loops. On the other hand, for He$^+$-implanted samples, the peak positions increase for doses up to 10$^{13}$ cm$^{-2}$ and then decrease at higher doses. The immiscible nature of helium at low doses causes the increase in the peak positions. In contrast, implantation-induced damage is dominant at higher doses. Implantation-induced defects are partially annealed by post-implantation annealing, causing a blueshift of the peak positions for the H$^+$-implanted samples. In He$^+$-implanted samples, the peak positions redshift due to annealing of He interstitials at low doses and blueshift due to annealing of implantation-induced defects at high doses.

Robust Adaptive Tracking Control of Autonomous Underwater Vehicle-Manipulator Systems

Santhakumar, M.,Kim, J. AMERICAN SOCIETY MECHANICAL ENGINEERS 2014 Journal of Dynamic Systems, Measurement and Contro Vol.136 No.5

On the Study of the Atomic Structures of Nitrogen-Ion-Implanted InP

santhakumar K,이철로,아소칸,Hayakawa Y,Jayavel p,Tetsuo soga 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I

Nitrogen ions at doses of 1 $\times$ 10$^{13}$ -- 1 $\times$ 10$^{15}$ cm$^{-2}$ have been implanted in semi-insulating (SI) InP (100) single-crystal substrates. The surface topography of as-grown and implanted samples has been investigated using atomic force microscopy (AFM). The as-grown InP surface has minimum roughness and appears to be smooth. Angstrom-level pits-type defects are seen on the InP surface after the implantation. Root-mean-square roughness values measured for the as-grown and the implanted InP samples. The surface roughness increased with increasing the nitrogen-ion dose monotonically up to 5 $\times$ 10$^{14}$ cm$^{-2}$ and decreased at a dose of 1 $\times$ 10$^{15}$ cm$^{-2}$ the increase in the roughness was due to implantation-induced damages, and the decrease at higher dose 10$^{15}$ cm$^{-2}$ might have been be due to plastic deformation on the surface associated with a surface amorphisation. Post-implantation annealing smoothened the surface. Roughness values decreased relative to the implanted samples up to a dose 5 $\times$ 10$^{14}$ cm$^{-2}$, which indicates that the defects were partially annealed. At a higher dose of 10$^{15}$ cm$^{-2}$, there was no change in roughness value in spite of annealing. This indicates that the InP surface had been plastically deformed leading to amorphization at higher dose. Further, Raman characterization of these implanted samples clearly supports the surface amorphization at higher doses.

A non-linear tracking control scheme for an under-actuated autonomous underwater robotic vehicle

Mohan, Santhakumar,Thondiyath, Asokan Korean Society of Ocean Engineers 2011 International journal of ocean system engineering Vol.1 No.3

This paper proposes a model based trajectory tracking control scheme for under-actuated underwater robotic vehicles. The difficulty in stabilizing a non-linear system using smooth static state feedback law means that the design of a feedback controller for an under-actuated system is somewhat challenging. A necessary condition for the asymptotic stability of an under-actuated vehicle about a single equilibrium is that its gravitational field has nonzero elements corresponding to non-actuated dynamics. To overcome this condition, we propose a continuous time-varying control law based on the direct estimation of vehicle dynamic variables such as inertia, damping and Coriolis & centripetal terms. This can work satisfactorily under commonly encountered uncertainties such as an ocean current and parameter variations. The proposed control law cancels the non-linearities in the vehicle dynamics by introducing non-linear elements in the input side. Knowledge of the bounds on uncertain terms is not required and it is conceptually simple and easy to implement. The controller parameter values are designed using the Taguchi robust design approach and the control law is verified analytically to be robust under uncertainties, including external disturbances and current. A comparison of the controller performance with that of a linear proportional-integral-derivative (PID) controller and sliding mode controller are also provided.

Modelling, Simulation and Model Reference Adaptive Control of Autonomous Underwater Vehicle-Manipulator Systems

Mohan Santhakumar,Jinwhan Kim 제어로봇시스템학회 2011 제어로봇시스템학회 국제학술대회 논문집 Vol.2011 No.10

This paper presents the detailed modelling and simulation of the dynamic coupling in an autonomous underwater vehicle (AUV)-manipulator system, used for deep-sea intervention tasks. The interaction effects due to damping, restoring and inertial effects of a single degree of freedom (DOF) manipulator mounted on an underactuated AUV are analysed. The actuator and sensor dynamics of the system are also considered. The linear and angular position errors of the vehicle and the manipulator due to the interaction effects between them are also investigated and the results are presented. A model reference adaptive control (MRAC) scheme is proposed to compensate the above mentioned errors. The effectiveness of the proposed control scheme is demonstrated using numerical simulations along with comparative study between conventional proportional-integral-derivative (PID) control. The robustness of the proposed control scheme is also illustrated with numerical study in the presence of external disturbances and parameter uncertainties.

High-performance Organic Solar Cells based on a Low-bandgap Poly-thienothiophene-benzodithiophene Polymer and Fullerene Composite Prepared by using the Airbrush Spray-coating Technique

Palanisamy Kumar,Santhakumar Kannappan,Shizuyasu Ochiai,신백균 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8

In the present work, we have demonstrated high-performance organic solar cells with spray coated active layers. The influence of the nanomorphology on the power conversion efficiency of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C71-butyric acid (PC71BM)methyl ester bulk heterojunction solar cells is presented. Active layers were prepared using a chlorobenzene solvent containing a small volume of 1,8-diiodooctane as an additive by spray coating with conventional handheld airbrushes. The surface morphology of the active layers deposited for various spray-coating times was examined using atomic force microscopy. The resulting devices were measured under AM 1.5G (100 mW/cm2) conditions in an ambient atmosphere. The optimized spray-coated PTB7:PC71BM film showed a high solar cell performance with a short-circuit current density of 14.20 ± 0.41 mA/cm2, a fill factor of 56.00 ± 0.02% and a power conversion efficiency of 5.96 ± 0.15%.

A Novel Heterozygous Mutation (F252Y) in Exon 7 of the IRF6 Gene is Associated with Oral Squamous Cell Carcinomas

Melath, Anil,Santhakumar, Gopi Krishnan,Madhavannair, Shyam Sunder,Nedumgottil, Binoy Mathews,Ramanathan, Arvind Asian Pacific Journal of Cancer Prevention 2013 Asian Pacific journal of cancer prevention Vol.14 No.11

Background: Interferon regulatory factor 6 (IRF6) is a transcription factor with distinct and conserved DNA and protein binding domains. Mutations within the protein binding domain have been significantly observed in subjects with orofacial cleft relative to healthy controls. In addition, recent studies have identified loss of expression of IRF6 due to promoter hypermethylation in cutaneous squamous cell carcinomas. Since mutational events occurring within the conserved domains are likely to affect the function of a protein, we investigated whether regions within the IRF6 gene that encodes for the conserved protein binding domain carried mutations in oral squamous cell carcinoma (OSCC). Materials and Methods: Total chromosomal DNA extracted from 32 post surgical OSCC tissue samples were amplified using intronic primers flanking the exon 7 of IRF6 gene, which encodes for the major region of protein binding domain. The PCR amplicons from all the samples were subsequently resolved in a 1.2% agarose gel, purified and subjected to direct sequencing to screen for mutations. Results: Sequencing analysis resulted in the identification of a mutation within exon 7 of IRF6 that occurred in heterozygous condition in 9% (3/32) of OSCC samples. The wild type codon TTC at position 252 coding for phenylalanine was found to be mutated to TAC that coded for tyrosine (F252Y). Conclusions: The present study identified for the first time a novel mutation within the conserved protein binding domain of IRF6 gene in tissue samples of subjects with OSCC.

Determination of Economic Threshold Level of Whitefly, Dialeuropora decempuncta (Quaintance and Baker) in Mulberry, Morus alba L.

Bandyopadhyay, U.K.,Santhakumar, M.V.,Saratchandra, B.,Das, K.K. Korean Society of Sericultural Science 2002 International Journal of Industrial Entomology Vol.4 No.2

Whitefly, Dialeuropora decempuncta (Quaintance rind Baker) (Homoptera: Aleyrodidae) has attained the major pest status in mulberry, causing 24% crop loss by sucking the leaf juice and manifesting leaf curl, chlorosis and sooty mould desease during monsoon season in West Bengal, India. The assessment of economic threshold revel is an essential component for formulating the management practices. Experiments were carried out by inoculating five different densities of whitefly viz.,10, 20, 30, 40 and 50 adults on covered mulberry plants in glass houses. From the findings, it was observed that irrespective of released density, no crop loss was observed in the initial period. But with the passing of days, the percent crop loss was increased rapidly. The linear relationship between percent crop loss and number of adults released was established to highlight the significance of economic threshold. The statistical analysis in the linear form of equation showed that initial population of 10, 20, 30, 40 and 50 whiteflies/plant causes 3%, 12%, 21%, 30% and 40% crop loss in a period of 28 days which is equivalent to 57 kg, 247 kg, 437 kg, 626 kg and 816 kg leaf/acre. Execution of management practices (spray of 0.01% monocrotophos) are economical to the farmer whenever the loss is above 247 kg/acre, but below which application of control measures is not economical. From this study, it can be inferred that the economic threshold level far whitefly is 20 individuals/plant beyond which a farmer has to take appropriate control measures.

Effect of Additives on the Structure, Nanomorphology and Efficiency of PCPDTBT: PC71BM Solar Cells

Shogo Imamura,Kumar Palanisamy,Santhakumar Kannappan,Shizuyasu Ochiai 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3

We investigated the effect of additives on the morphology of a poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b0]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):(6,6)-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) blended onto a surface of poly (3, 4-ethylendioxythiophene): poly(styrensulfonate)(PEDOT:PSS) to form photoactive films. Films of PCPDTBT: PC₇₁BM bulk heterojunctions were prepared by spin-coating from a solution in chlorobenzene (CB) and were processed with and without the addition of 2%, 4%, and 6 vol% 1-chloro naphthalene (CN) or 1, 8-octanedithiol (ODT) as additives. For all samples, the PCPDTBT:PC₇₁BM molar ratio was 1:2 (wt%), and the additives in 1 ml were prepared with a concentration of 30 mg of PCPDTBT:PC₇₁BM. Optical absorption spectroscopy measurements of the films indicated shifts in the absorption peaks in the range from 500 - 800 nm which was attributed to PCPDTBT. XRay diffraction (XRD) was used to investigate the nature of the molecular stacking in the polymer thin films. Topographic images which were obtained by using an atomic force microscope, of the PCPDTBT:PC₇₁BM layers with 2 vol% ODT additive, were found to have the highest surface roughness. The best performing device shows a power conversion efficiency of 2.15% for a 2-vol% ODT additive.