Effect of annealing temperature on the electrical and structural properties of V/p-GaN Schottky structures

Padma, R.,Nagaraju, G.,Rajagopal Reddy, V.,Choi, Chel-Jong Elsevier 2016 THIN SOLID FILMS - Vol.598 No.-

<P><B>Abstract</B></P> <P>The electrical and structural properties of V/p-GaN Schottky barrier diode (SBD) have been investigated as a function of annealing temperature. The Schottky barrier height (SBH) of the as-deposited contact is found to be 0.82eV (<I>I–V</I>) and 1.10eV (<I>C–V</I>). However, it is noted that the SBH increases for the contact annealed at 400°C and the values are 0.94eV (<I>I–V</I>) and 1.21eV (<I>C–V</I>). Further, with increasing annealing temperature up to 500°C, the SBH decreases to 0.92eV (<I>I–V</I>) and 1.19eV (<I>C–V</I>). Also, the rectification ratio of the V/p-GaN SBD is evaluated for as-deposited and annealed contacts. The electrical parameters of the V/p-GaN SBD are also discussed with Cheung's and Norde functions. It is noted that the interface state density decreases upon annealing at 400°C and then slightly increases after annealing at 500°C. Results reveal that the superior electrical characteristics are obtained for the contact annealed at 400°C. The electrical results are also correlated with the interfacial microstructure of the contacts. The AES and XRD results reveal that the formation of nitride phases at the interface may be the reason for the increase of SBH after annealing at 400°C. The formation of gallide phases at the interface may be reason for the decrease in the SBH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Annealing effects on electrical and structural properties of V/p-GaN SBD are studied. </LI> <LI> Maximum barrier height is obtained on V/p-GaN SBD upon annealing at 400°C. </LI> <LI> Interface state density decreases with increasing annealing temperature up to 400°C. </LI> <LI> Electrical results are correlated with the interfacial microstructure of the contacts. </LI> <LI> Nitride interfacial phases are responsible for increase in BH after annealing at 400°C. </LI> </UL> </P>

Influence of traditional medicines on the activity of keratinocytes in wound healing: an in-vitro study

Sushma R. Kotian,Kumar M. R. Bhat,Divya Padma,K. Sreedhara R. Pai 대한해부학회 2019 Anatomy & Cell Biology Vol.52 No.3

Natural medicinal systems such as Ayurveda and folk medicine has remedies for wound management. However, the exact cellular and extracellular mechanisms involved in the healing process and its influence on keratinocytes is less discussed. Therefore, the present study was designed to evaluate the effect of certain natural wound healing medicines on the biology of the keratinocytes/HaCaT cells. Test materials such as honey (H), ghee (G), aqueous extracts of roots of Glycyrrhiza glabra (GG) and leaves of Nerium indicum (NI) were considered. The HaCaT cells were treated with the test materials singly and in combinations (H+G, all combined [Tot]) for a specific period (24, 48, and 72 hours). The cells were then subjected to cytotoxicity/proliferation and migration/scratch assays. All the test materials, except NI, were non-cytotoxic and showed increased cell proliferation at variable concentrations. Significant observations were made in the groups treated with honey (100 µg/ml at 48 hours, P<0.05; 1,000 µg/ml at 72 hours, P<0.05), GG (all concentrations at 48 hours, P<0.05; 750 µg/ml at 72 hours, P<0.05), H+G (250 µg/ml at 24 hours, P<0.001; 500 µg/ml at 48 and 72 hours, P<0.05), and Tot (50 µg/ml at 24, 48 and 72 hours, P<0.01). In the in-vitro wound healing assay, all the treated groups showed significant migration and narrowing of the scratch area by 24 and 48 hours (P<0.001) compared to control. The results obtained from the present study signifies the positive influence of these natural wound healing compounds on keratinocytes/HaCaT cells.

A Survey on Study of Various Machine Learning Methods for Classification

S. Padma,R. Pugazendi 보안공학연구지원센터 2015 International Journal of Database Theory and Appli Vol.8 No.5

This article comprises a review of various sequential algorithms. The review represents the working nature of the learning methods. It also includes the methods such as Minimal Resource Allocation Network (MRAN), Extreme Learning Machine (ELM), Self-regulated Resource Allocation Network (SRAN) and Meta-Cognitive Neural Network (MCNN) for real –valued neural network. Projection Based Learning with Meta-Cognitive Radial Basis Function Network (PBL-McRBFN) for complex valued neural network. Finally about Meta-Cognitive Fuzzy Inference System (MCFIS) using the Neuro - Fuzzy inference system for learning. The previously said SRAN works on the basis of self – regulatory mechanism in order to reduce the huge loss error and to maximize the class – wise significance. The methods such as MCNN, PBL-McRBFN and MCFIS execute on the human learning strategies such as what – to-learn, when –to-learn and how –to – learn. This review helps to select the learning methods suitable for the data that is to be classified.

PERFORMANCE COMPARISON OF p – n JUNCTION DIODES USING ZINC OXIDE AND COPPER PHTHALOCYANINE HYBRID NANOCOMPOSITES AND BILAYER HETEROSTRUCTURES

N. PADMA,MANORANJAN GHOSH,SHASHWATI SEN,R. TEWARI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.6

Nanocomposites of n-type Zinc Oxide (ZnO) and p-type copper phthalocyanine (CuPc) weresynthesized using solution route and the electrical properties of heterojunctions of ZnO and CuPcin the nanocomposite ¯lm was studied. For comparison, electrical properties of bilayer hetero-junction devices using ZnO nanostructure drop cast ¯lm and thermally evaporated CuPc werealso studied. Recti¯cation ratio (RR) of about 28 and 5.5 was obtained at 4 V for devices withnanocomposite ¯lm and bilayer heterojunctions indicating improved formation of p – n junctioncharacteristics for nanocomposite ¯lms. Values of ideality factor, barrier height at the p – njunction interface and series resistance were estimated using di®erent methods like semilog plots,Cheung and Norde's methods. Ideality factor estimated from semilog plots and Cheung'smethods were found to be higher than unity indicating deviation from ideal diode behavior. Barrier height estimated from di®erent methods was about 0.7 eV. Series resistance measuredusing Cheung and Norde's methods were found to be about 92 K ? and 21 K ? , respectively. Bilayer heterojunction devices exhibited much higher series resistance, ideality factor and barrierheight as estimated using all the above-mentioned methods as compared to the devices withnanocomposite ¯lm. The above results indicate intimate mixing and improved interface betweenZnO and CuPc in the in situ synthesized nanocomposite ¯lm thereby o®ering improved p – njunction characteristics.

Dazzling red emission from TiO2 nanoparticles impregnated co-doped Gd3++Eu3+: PVA polymer nanocomposites for photonic applications

K. Naveen Kumar,R. Padma,L. Vijayalakshmi,강미숙 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.45 No.-

Red emission was obtained from rare earth doped polymer nanocomposites, namely, composites ofpolyvinyl-alcohol (PVA) co-doped with Gd3+ and Eu3+ and embedded with TiO2 nanoparticles (TiO2NP),under ultraviolet (UV) excitation. We successfully synthesized Eu3+: PVA, Gd3+: PVA, (Gd3+ + Eu3+): PVA,and (Gd3+ + Eu3+ + TiO2NP): PVAfilms by solution casting method. From X-ray diffraction patterns andFourier-transform infrared spectral profiles, the structural details of thefilms and the ion–polymerinteraction mechanism responsible for their formation were systematically analyzed. The thermalstability and decomposition dynamics of the prepared samples were evaluated by thermogravimetry anddifferential thermal analysis. Pertinent optical absorption bands related to Eu3+ and Gd3+ ions in thepolymer composites were observed and assigned to the corresponding electronic transitions. The PVAfilm containing different concentrations of the Eu3+ dopant displayed red emission at 618 nm (5D0!7F2)under UV excitation at 396 nm (7F0!5L6). Upon co-doping with Gd3+ to form the (Gd3+ + Eu3+): PVAfilm,it exhibited red emission that was stronger than that from the singly doped Eu3+: PVAfilm under 270 nmexcitation because of the energy transfer from Gd3+ to Eu3+ ions. After the TiO2 nanoparticles were evenlydispersed in the co-doped (Gd3+ + Eu3+): PVAfilms, the photoluminescence properties were remarkablyenhanced and prominent red emission was observed under 274 nm excitation. The red emission of Eu3+was significantly enhanced through an efficient energy-transfer process from the Gd3+ ions to Eu3+ ionsand from the TiO2 nanoparticles to Eu3+ ions. A possible energy-transfer mechanism was clearlydemonstrated by severalfluorescent methods and lifetime decay dynamics. Based on the above results,these polymer compositefilms are promising candidates for red luminescent photonic devices.

The values of an Euler sum at the negative integers and a relation to a certain convolution of Bernoulli numbers

Khristo N. Boyadzhiev,H. Gopalkrishna Gadiyar,R. Padma 대한수학회 2008 대한수학회보 Vol.45 No.2

The paper deals with the values at the negative integers ofa certain Dirichlet series related to the Riemann zeta function and withthe expression of these values in terms of Bernoulli numbers.

Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers

Catherine Kanimozhi,Myungwoong Kim,Steven R. Larson,Jonathan W. Choi,Daniel P. Sweat,Padma Gopalan 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

THE VALUES OF AN EULER SUM AT THE NEGATIVE INTEGERS AND A RELATION TO A CERTAIN CONVOLUTION OF BERNOULLI NUMBERS

Boyadzhiev, Khristo N.,Gadiyar, H. Gopalkrishna,Padma, R. Korean Mathematical Society 2008 대한수학회보 Vol.45 No.2

The paper deals with the values at the negative integers of a certain Dirichlet series related to the Riemann zeta function and with the expression of these values in terms of Bernoulli numbers.

Hierarchical nanostructured MnCo₂O₄-NiCo₂O₄ composites as innovative electrodes for supercapacitor applications

Lee, Han-Min,V. V. Muralee Gopi, Chandu,Rana, Prem Jyoti Singh,Vinodh, Rajangam,Kim, Sanghyun,Padma, R.,Kim, Hee-Je The Royal Society of Chemistry 2018 New journal of chemistry Vol.42 No.21

<P>NiCo2O4 (NCO) nanosheet decorated MnCo2O4 (MCO) nanoflakes are successfully prepared on a nickel foam surface using a one-step chemical bath deposition route for supercapacitor applications. The unique nanoflakes with nanosheet structures provide efficient pathways for rapid electron and ion transportation. As a result, the MCO-NCO composite electrode exhibits a higher specific capacitance of 1152 F g<SUP>−1</SUP> at 1 A g<SUP>−1</SUP>, excellent rate capability and superior cycling stability (95.38% retention after 3000 cycles) compared to individual MCO nanoflakes and NCO nanosheets. These results show that the as-fabricated MCO-NCO composites are promising candidates for electrochemical supercapacitors.</P>