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- 저자 : Y. Ashok Kumar Reddy (검색결과 8 건)
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Y. Ashok Kumar Reddy,B. Ajitha,P. Sreedhara Reddy,프라탑 렙디,이정희 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.5
NiO-Ag thin films were deposited on Corning 7059 glass substrates by DC reactive magnetron sputtering technique and investigated the substrate temperature (Ts) dependent properties of NiO-Ag thin films. X-ray diffraction results showed that crystalline films can be obtained at high Ts and all films have a preferred crystal growth texture with face centered cubic (fcc) structure and was also confirmed by Raman studies. The grain size, transmittance, band gap, mobility and carrier concentrations were increased with Ts. Room temperature deposited films have an average roughness around 6.9 nm where as increment of Ts resulted in increased roughness up to 14 nm with nanocrystalline morphology. The optimum substrate temperature to obtain NiO-Ag films was found to be 200°C. It was found that with increasing the Ts, resistivity of the films was significantly decreased.
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Reddy, Y. Ashok Kumar,Shin, Young Bong,Kang, In-Ku,Lee, Hee Chul Springer-Verlag 2018 Journal of electronic materials Vol.47 No.3
<P>The present study directly addresses the improved bolometric properties by means of different Nb doping concentrations into TiO2-x films. The x-ray diffraction patterns do not display any obvious diffraction peaks, suggesting that all the films deposited at room temperature had an amorphous structure. A small binding energy shift was observed in x-ray photo electron spectroscopy due to the change of chemical composition with Nb doping concentration. All the device samples exhibit linear I-V characteristics, which attests to the formation of good ohmic contact with low contact resistance between the Nb:TiO2-x (TNO) film and the electrode (Ti) material. The performance of the bolometric material can be evaluated through the temperature coefficient of resistance (TCR), and the absolute value of TCR was found to be increased from 2.54% to 2.78% with increasing the Nb doping concentration. The voltage spectral density of 1/f noise was measured in the frequency range of 1-60 Hz and found to be decreased with increase of Nb doping concentration. As a result, for 1 at.% Nb-doped TNO sample exhibits improved bolometric properties towards the good infrared image sensor device.</P>
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Reddy, Y Ashok Kumar,Kang, In-Ku,Shin, Young Bong,Lee, Hee Chul IOP 2018 Journal of Physics. D, Applied Physics Vol.51 No.2
<P>In order to reduce the sun-burn effect in a sample of the bolometric material Nb:TiO<SUB>2−<I>x</I> </SUB>, oxygen annealing was carried out. This effect can be examined by comparing thermal stability test results between the as-deposited and oxygen-atmosphere-annealed samples under high-temperature exposure conditions. Structural studies confirm the presence of amorphous and rutile phases in the as-deposited and annealed samples, respectively. Composition studies reveal the offset of oxygen vacancies in the Nb:TiO<SUB>2−<I>x</I> </SUB> samples through oxygen-atmosphere annealing. The oxygen atoms were diffused and seemed to occupy the vacant sites in the annealed samples. As a result, the annealed samples show better thermal stability performance than the as-deposited samples. The universal bolometric parameter (<I>β</I>) values were slightly decreased in the oxygen-annealed Nb:TiO<SUB>2−<I>x</I> </SUB> samples. Although bolometric performance was slightly decreased in the oxygen-annealed samples, high thermal stability would be the most essential factor in the case of special applications, such as the military and space industries. Finally, these results will be very useful for reducing the sun-burn effect in infrared detectors.</P>
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Reddy, Y. Ashok Kumar,Kang, In-Ku,Shin, Young Bong,Lee, Hee Chul Elsevier 2017 CERAMICS INTERNATIONAL Vol.43 No.12
<P><B>Abstract</B></P> <P>The aim of this paper is to investigate the effects of oxygen atmosphere annealing on the bolometric properties of Nb: TiO<SUB>2−x</SUB> samples for infrared detectors. We conducted the structural and composition analyses of as-deposited and annealed samples. The structural properties demonstrate an improvement in the film crystallinity and the composition analysis confirms the compensation of oxygen vacancies though post-deposition annealing in an oxygen atmosphere. A test device was fabricated to find the bolometric properties of the resistivity, temperature coefficient of resistance (TCR), 1/f noise parameter, bolometric parameter (β) and thermal stability. The logarithmic decrement of the resistivity with the temperature confirms that both the as-deposited and annealed test device samples show typical semiconducting behavior. Meanwhile, the annealed samples show lower TCR values while they have high resistivity due to their small changes in resistance with the temperature. The sample annealed for 20min has good thermal stability and is similar in terms of the 1/f noise and β values to the as-deposited samples. The obtained results suggest that the post-deposition annealing of TNO samples in an oxygen atmosphere will lead to much stronger thermal stability compared to that of an as-deposited sample.</P>
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Ajitha, B.,Reddy, Y. Ashok Kumar,Jeon, Hwan-Jin,Ahn, Chi Won VSP 2018 Advanced powder technology Vol.29 No.1
<P><B>Abstract</B></P> <P>In the present study, silver nanoparticles (AgNPs) with a flower-like structure were synthesized through an easy, rapid and eco-friendly pathway using <I>Phyllanthus amarus</I> leaf extract. The obtained AgNPs were characterized using ultraviolet–visible (UV–Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). In addition, the antimicrobial and catalytic activities of the bio-synthesized AgNPs were carried out. Our results indicated that the concentration of the Ag precursor and the volume of the leaf extract played key roles in the formation of the flower-shaped AgNPs. Morphology study confirms the shape of the obtained bio-AgNPs as flower like structure. This study also showed the presence of clear capping layers surrounding and apparently interacting with the nanoparticles. Moreover, our studies indicated this interaction to involve bio-organic capping agents in the leaf extract. UV–Vis absorption spectra confirmed the formation of AgNPs with an optimized size. The zeta (ζ) potential of the AgNPs attests the stability of the nanoparticles. FTIR spectra provided evidence for the presence of biomolecules responsible for the reduction as well as capping of the AgNPs. Finally, the bio-synthesized AgNPs were shown to be an excellent microbial activity against the selected pathogens and enhanced catalyst of the reduction of rhodamine B.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>Phyllanthus amarus</I> is an exceptional sink for biosynthesis of silver nanoparticles. </LI> <LI> Biomolecules of leaf extract are found to play an active role in AgNPs formation. </LI> <LI> Zeta potential value attested the higher stability of biosynthesized AgNPs. </LI> <LI> Excellent antimicrobial and catalytic activities were obtained in an eco-friendly way. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Ajitha, B.,Reddy, Y. Ashok Kumar,Reddy, P. Sreedhara,Suneetha, Y.,Jeon, Hwan-Jin,Ahn, Chi Won Elsevier 2016 Journal of molecular liquids Vol.219 No.-
<P><B>Abstract</B></P> <P>New and innovative strategies are of potential interest for the synthesis of silver nanoparticles (AgNPs), which are used in huge range of consumer products. The present work is focused on bio-fabrication of AgNPs in single step employing <I>Lawsonia inermis</I> and evaluation of their antimicrobial, antioxidant and catalytic properties. The prepared AgNPs are highly stable and monitored through UV–Vis spectrophotometer. X-ray diffraction (XRD) and the selected area electron diffraction (SAED) patterns proved the crystalline nature of AgNPs with face-centered cubic (fcc) geometry. Morphological images confirm the uniform distribution of spherical nanoparticles. Fourier transform infrared spectroscopy (FTIR) result expounds the functional groups of a leaf extract responsible for the bio-reduction of silver ions and their interaction between them. The synthesized AgNPs show potent catalytic activity in the degradation of anthropogenic pollutant (4-nitrophenol) by excess of NaBH<SUB>4</SUB>. The biosynthesized AgNPs seem to exhibit effective antibacterial, antifungal properties and further more possess potent antioxidant and DNA protective activities. At last, the current study illustrated the potential use of <I>L. inermis</I> as a novel source for AgNPs synthesis and their pronounced applicability in biomedical field.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>Lawsonia inermis</I> is an exceptional sink for biosynthesis of silver nanoparticles. </LI> <LI> Biomolecules of leaf extract are found to play active role in AgNPs formation. </LI> <LI> Zeta potential value attested the higher stability of biosynthesized AgNPs. </LI> <LI> Potent catalytic, antimicrobial and antioxidant activities are perceived. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Kang, In-Ku,Reddy, Y. Ashok Kumar,Shin, Young Bong,Kim, Woo Young,Lee, Hee Chul Elsevier 2018 CERAMICS INTERNATIONAL Vol.44 No.7
<P><B>Abstract</B></P> <P>This study aims to investigate the influence of substitutionally incorporated Li on sensing performance of nickel oxide films for bolometer applications by comparing Ni<SUB>1-<I>x</I> </SUB>O and (Li<SUB> <I>y</I> </SUB>Ni<SUB>1-<I>y</I> </SUB>)<SUB>1-<I>x</I> </SUB>O films. From the results of structural analysis, it was confirmed that the film deposited from Li<SUB>0.2</SUB>Ni<SUB>0.8</SUB>O target contained Li which substitutionally occupies the Ni cation site while maintaining a cubic NiO structure. The substitutionally incorporated Li in nickel oxide can serve as an acceptor providing a hole carrier, like as a structural defect. However, in contrast to the structural defect, the substitutional incorporation of Li made it possible to increase the number of hole carriers in nickel oxide film while maintaining excellent film quality. In addition, the contact resistance with electrode was greatly reduced as a result of the substitutionally incorporated Li. These changes in structural and electrical properties lead to a significant reduction of 1/<I>f</I> noise arisen from the (Li<SUB> <I>y</I> </SUB>Ni<SUB>1-<I>y</I> </SUB>)<SUB>1-<I>x</I> </SUB>O film. As a result, the sensing performance of the (Li<SUB> <I>y</I> </SUB>Ni<SUB>1-<I>y</I> </SUB>)<SUB>1-<I>x</I> </SUB>O film as evaluated using the (<I>α</I> <SUB> <I>H</I> </SUB>/<I>n</I>)<SUP>1/2</SUP>/|<I>β</I>| value was nearly 10 times better than that of the Ni<SUB>1-<I>x</I> </SUB>O film. Consequently, it can be concluded that the substitutional incorporation of Li can significantly improve the sensing performance of nickel oxide films for bolometer applications.</P>
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Kang, In-Ku,Kumar Reddy, Y. Ashok,Bong Shin, Young,Young Kim, Woo,Chul Lee, Hee Elsevier 2017 Ceramics international Vol.43 No.12
<P><B>Abstract</B></P> <P>The aim of this study is to investigate the dependence of the sputtering pressure on the bolometric properties of Ni<SUB>1−x</SUB>O films. In order to analyze the structural properties, X-ray diffraction and X-ray photoelectron spectroscopy studies were conducted for Ni<SUB>1−x</SUB>O films deposited at various sputtering pressures. As a result, it was confirmed that all of the films had a Ni-deficient non-stoichiometric structure and that the films deposited at higher sputtering pressures revealed a more crystallized structure with fewer structural defects. The variation of the structural characteristics induced by the sputtering pressure also affected several electrical properties, known as the bolometric properties, including the electrical conductivity, temperature coefficient of resistivity and 1/f noise. With increasing the sputtering pressure from 1mTorr to 10mTorr, the electrical conductivity decreased from 1.0×10<SUP>−2</SUP> S/cm to 2.2×10<SUP>−5</SUP> S/cm while the absolute value of the temperature coefficient of resistivity increased from 2.76%/K to 5.62%/K, respectively. In addition, the magnitude of the 1/f noise also increased with an increase in the sputtering pressure. To evaluate and compare the bolometric performance, we introduced the material figure of merit, (<I>α</I> <SUB> <I>H</I> </SUB>/<I>n</I>)<SUP>1/2</SUP>/|β|, which was determined by both the TCR and the 1/f noise. As a result, the films deposited at a lower sputtering pressure exhibited a lower value of (<I>α</I> <SUB> <I>H</I> </SUB>/<I>n</I>)<SUP>1/2</SUP>/|β|, implying that these films are capable of better bolometric performance. Consequently, this research reveals that the sputtering pressure is an important parameter influencing the bolometer performance capabilities of Ni<SUB>1−x</SUB>O films.</P>
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