Size Effects of MoS₂ on Hydrogen and Oxygen Evolution Reaction

Ghanashyam, Gyawali,Jeong, Hae Kyung The Korean Electrochemical Society 2022 Journal of electrochemical science and technology Vol.13 No.1

Molybdenum disulfide (MoS₂) has been widely used as a catalyst for the bifunctional activities of hydrogen and oxygen evolution reactions (HER and OER). Here, we investigated size dependent HER and OER performance of MoS₂. The smallest size (90 nm) of MoS₂ exhibits the lowest overpotential of -0.28 V at -10 mAcm^-2 and 1.52 V at 300 mAcm^-2 with the smallest Tafel slopes of 151 and 176 mVdec^-1 for HER and OER, respectively, compared to bigger sizes (2 ㎛ and 6 ㎛) of MoS₂. The better HER and OER performance is attributed to high electrochemical active surface area (6 × 10^-4 cm²) with edge sites and low charge transfer resistance (18.1 Ω), confirming that the smaller MoS₂ nanosheets have the better catalytic behavior.

Nitrogen-doped Molybdenum Disulfide to Catalyze Hydrogen and Oxygen Evolution Reactions

Gyawali Ghanashyam,Hae Kyung Jeong 한국물리학회 2022 새물리 Vol.72 No.4

Nitrogen-doped molybdenum disulfide (N-MoS2) was synthesized using melamine as the nitrogen source to be used as a catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-synthesized N-MoS₂ had an atomic nitrogen composition of 13%, and it exhibited a low overpotential of −0.20 V at −10 mA/c㎠ for HER and 1.43 V at 10 mA/㎠ for OER, with small Tafel slope values of 97 and 117 mV/dec for HER and OER, respectively. The enhanced HER and OER performances observed as a result of the nitrogen doping of MoS₂ is attributed to N-MoS₂ being characterized by a higher electrochemical active surface area (9.1 × 10<SUP>−4</SUP> ㎠) and lower charge transfer resistance (8.1 Ω) than its precursor.

A Thermally Reduced Graphite Oxide and Carbon Nanotube Composite for Supercapacitor Applications

Gyawali GHANASHYAM,정혜경 한국물리학회 2018 New Physics: Sae Mulli Vol.68 No.2

A thermally reduced graphite oxide and carbon nanotube (TRGO-CNT) composite is synthesized for supercapacitor applications by using a simple chemical method. The TRGO-CNT composite shows higher capacitance then the precursors (TRGO and CNT), and its impedance is lower than that of CNT, meaning that TRGO of high surface area connected with a CNT could provide highly efficient surface area and good connection for supercapacitor electrodes. Different weight ratios of TRGO to CNT are investigated, and the results show that the composite with more TRGO has better performance in the electrochemical measurements. Based on these findings, the proper TRGO amount is necessary for a high-performance supercapacitor. Neither CNT nor TRGO by itself can give the highest electrochemical performance for the supercapacitor; thus, the synergistic effect of TRGO and CNT is important.

Carbon Nanofiber on Nickel Foam for Flexible Supercapacitors

Gyawali GHANASHYAM,Hae Kyung JEONG 한국물리학회 2023 새물리 Vol.73 No.5

Electric Field Induced Dissociation of SiC Thin Films Leading to the Formation of Nanocrystalline Graphite

Poreddy Chaitanya Akshara,M. Ghanashyam Krishna,G. Rajaram,Y. Rajesh,Nilanjan Basu,Jayeeta Lahiri 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.3

Thin flm Au–SiC–Cu and Au–SiC–Pt crossbar structures of 40μmx40μm size where all three layers are 100 nm thicknesswere fabricated by lithography. Decomposition of the SiC flm is observed under the infuence of an electric feld (104–106 V/cm) applied between the Au bottom electrode and the top metal electrode (Cu or Pt) for a few cycles during the course oftesting as a resistive switching structure. This is evidenced using Raman mapping and Raman spectroscopy techniques. TheRaman spectra reveal peaks corresponding to the D and G bands of nanocrystalline graphite. Raman mapping at diferentlocations indicates that most of the graphite forms at the interface between the metal electrode and SiC. Raman mappingimages reveal the formation of graphite on the surface. This technique is simple and enables site-selective localized growthof nanocrystalline graphite which is expected to impact many nanoscale applications. It could also be extended to formgraphene at the nanoscale.

Tumor-like Presentation of Tubercular Brain Abscess: Case Report

Dan B. Karki,Ghanashyam Gurung,Mohan R. Sharma,Ram K. Shrestha,Gita Sayami,Gopal Sedain,Amina Shrestha,Ram K. Ghimire 대한자기공명의과학회 2015 Investigative Magnetic Resonance Imaging Vol.19 No.4

A 17-year-old girl presented with complaints of headache and decreasing vision ofone month’s duration, without any history of fever, weight loss, or any evidence ofan immuno-compromised state. Her neurological examination was normal, exceptfor papilledema. Laboratory investigations were within normal limits, except for aslightly increased Erythrocyte Sedimentation Rate (ESR). Non-contrast computerizedtomography of her head revealed complex mass in left frontal lobe with a concentric,slightly hyperdense, thickened wall, and moderate perilesional edema with masseffect. Differential diagnoses considered in this case were pilocytic astrocytoma,metastasis and abscess. Magnetic resonance imaging (MRI) obtained in 3.0 Tesla(3.0T) scanner revealed a lobulated outline cystic mass in the left frontal lobe withtwo concentric layers of T2 hypointense wall, with T2 hyperintensity between theconcentric ring. Moderate perilesional edema and mass effect were seen. Postgadolinium study showed a markedly enhancing irregular wall with some enhancingnodular solid component. No restricted diffusion was seen in this mass in diffusionweighted imaging (DWI). Magnetic resonance spectroscopy (MRS) showed increasedlactate and lipid peaks in the central part of this mass, although some areas at thewall and perilesional T2 hyperintensity showed an increased choline peak withoutsignificant decrease in N-acetylaspartate (NAA) level. Arterial spin labelling (ASL) anddynamic susceptibility contrast (DSC) enhanced perfusion study showed decrease inrelative cerebral blood volume at this region. These features in MRI were suggestiveof brain abscess. The patient underwent craniotomy with excision of a grayishnodular lesion. Abundant acid fast bacilli (AFB) in acid fast staining, and epithelioidcell granulomas, caseation necrosis and Langhans giant cells in histopathology, wereconclusive of tubercular abscess. Tubercular brain abscess is a rare manifestationthat simulates malignancy and cause diagnostic dilemma. MRI along with MRS andmagnetic resonance perfusion studies, are powerful tools to differentiate lesions insuch equivocal cases.

Wettability Control and Flow Regulation Using a Nanostructure-Embedded Surface

Tafti, Ehsan Yakhshi,Londe, Ghanashyam,Chunder, Anindarupa,Zhai, Lei,Kumar, Ranganathan,Cho, Hyoung J. American Scientific Publishers 2011 Journal of nanoscience and nanotechnology Vol.11 No.2

<P>This work addresses the synthesis, integration and characterization of a nanostructure-embedded thermoresponsive surface for flow regulation. In order to create a hierarchic structure which consists of microscale texture and nanoscale sub-texture, hybrid multilayers consisting of poly(allylamine hydrochloride) (PAH), poly(acrylic acid) (PAA) and colloidal silica nanoparticles (average diameter = 22 nm and 7 nm) were used. Based on the electrostatic interactions between the polyelectrolytes and nanoparticles, a layer-by-layer deposition technique in combination with photolithography was employed to obtain a localized, conformally-coated patch in a microchannel. Grafted with the thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm), wettability of the surface could be tuned upon heating or cooling. The measurement of differential pressure at various stages of device verified the working conditions of the nanostructure-embedded surface for regulating a capillary flow in the microchannel.</P>

Effect of High Temperature Deposition on the Diffusion of Nickel in Amorphous Silicon Thin Films

Md. Ahamad Mohiddon,M. Ghanashyam Krishna 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.4

The diffusion of nickel into amorphous Si (a-Si) thin films and the growth of different nickel silicides is reported. a-Si and Ni films were deposited on Borosilicate Glass substrates and annealed in vacuum at temperatures from 200 to 500°C. The average grain size of the films increases from 150 nm to 360 nm with deposition temperature. Cross-sectional scanning electron microscopy and energy dispersive x-ray spectroscopy have been used in conjunction to reveal the process of diffusion. It is inferred from x-ray diffraction and Raman spectroscopy analysis on these stacks that Ni3Si is formed at 200°C, NiSi at 300°C and NiSi2 at 400°C. This study reveals that Ni-Si bilayer films deposited at an elevated temperature and subsequently annealed at the deposition temperature formed monophase Ni silicides.

Tumor-like Presentation of Tubercular Brain Abscess: Case Report

Karki, Dan B.,Gurung, Ghanashyam,Sharma, Mohan R.,Shrestha, Ram K.,Sayami, Gita,Sedain, Gopal,Shrestha, Amina,Ghimire, Ram K. Korean Society of Magnetic Resonance in Medicine 2015 Investigative Magnetic Resonance Imaging Vol.19 No.4

A 17-year-old girl presented with complaints of headache and decreasing vision of one month's duration, without any history of fever, weight loss, or any evidence of an immuno-compromised state. Her neurological examination was normal, except for papilledema. Laboratory investigations were within normal limits, except for a slightly increased Erythrocyte Sedimentation Rate (ESR). Non-contrast computerized tomography of her head revealed complex mass in left frontal lobe with a concentric, slightly hyperdense, thickened wall, and moderate perilesional edema with mass effect. Differential diagnoses considered in this case were pilocytic astrocytoma, metastasis and abscess. Magnetic resonance imaging (MRI) obtained in 3.0 Tesla (3.0T) scanner revealed a lobulated outline cystic mass in the left frontal lobe with two concentric layers of T2 hypointense wall, with T2 hyperintensity between the concentric ring. Moderate perilesional edema and mass effect were seen. Post gadolinium study showed a markedly enhancing irregular wall with some enhancing nodular solid component. No restricted diffusion was seen in this mass in diffusion weighted imaging (DWI). Magnetic resonance spectroscopy (MRS) showed increased lactate and lipid peaks in the central part of this mass, although some areas at the wall and perilesional T2 hyperintensity showed an increased choline peak without significant decrease in N-acetylaspartate (NAA) level. Arterial spin labelling (ASL) and dynamic susceptibility contrast (DSC) enhanced perfusion study showed decrease in relative cerebral blood volume at this region. These features in MRI were suggestive of brain abscess. The patient underwent craniotomy with excision of a grayish nodular lesion. Abundant acid fast bacilli (AFB) in acid fast staining, and epithelioid cell granulomas, caseation necrosis and Langhans giant cells in histopathology, were conclusive of tubercular abscess. Tubercular brain abscess is a rare manifestation that simulates malignancy and cause diagnostic dilemma. MRI along with MRS and magnetic resonance perfusion studies, are powerful tools to differentiate lesions in such equivocal cases.

On Semi C-Reducibility of General (α, β) Finsler Metrics

Tiwari, Bankteshwar,Gangopadhyay, Ranadip,Prajapati, Ghanashyam Kr. Department of Mathematics 2019 Kyungpook mathematical journal Vol.59 No.2

In this paper, we study general (${\alpha}$, ${\beta}$) Finsler metrics and prove that every general (${\alpha}$, ${\beta}$)-metric is semi C-reducible but not C2-like. As a consequence of this result we prove that every general (${\alpha}$, ${\beta}$)-metric satisfying the Ricci flow equation is Einstein.