Khem Thapa - Academia.edu (original) (raw)
Papers by Khem Thapa
Materials Science and Engineering: B
Physica Scripta
Effective surface plasmons for dielectric properties of nanocomposite (NC) with spherical silver ... more Effective surface plasmons for dielectric properties of nanocomposite (NC) with spherical silver nanoparticles (Ag-NPs) in a host ZrO2 has investigated at different radii and filling fractions of nanoparticles (NPs) using the Maxwell-Garnett model. The optical properties of one-dimensional ternary periodic structure (1-DTPS) containing SiO2, TiO2, and NC with different parameters has investigated using the transfer matrix method (TMM). Moreover, the absorption properties of the considered structure for transverse electric (TE) and transverse magnetic (TM) have been studied at different incident angles and thicknesses of the NC layer. The dielectric and optical properties of the considered structure has affected by surface waves of dielectric layers as well as surface plasmons of Ag-NPs. The optical properties of the 1-DTPS for TE and TM modes has been studied with varying thicknesses of NC and angles of incidence wave. With the optimum values of the optical parameters of NC and Ag-N...
Advances in Photonic Crystals and Devices
In this present communication we studied the frequency dependence of the effective electromagneti... more In this present communication we studied the frequency dependence of the effective electromagnetic parameters of left-handed and related meta-materials (NIMs) of the split ring resonator (SRR) and wire type. By varying the width of inserted material as well as the host material, we also calculate the effective parameters of NIM like effective permittivity and effective permeability. Using these parameters, we calculate the effective refractive index and impedance of the considered medium. Our results reveal that the negative index of materials can be achieved when the thickness of the host materials should equal to the thickness of the inserted materials. OCIS codes: (350.4238) Photonics; (160.3918) Metamaterial.
Iranian journal of mathematical chemistry, 2020
The liquid crystal (LC) 4-4′-disubstituted biphenyls (HnCBP) of the general line formula HO-(CnH2... more The liquid crystal (LC) 4-4′-disubstituted biphenyls (HnCBP) of the general line formula HO-(CnH2n+1)-O-C6H4-C6H4-CN (n=1-12) shows the odd-even effect under the applied electric field. The odd-even effects are observed in the HOMO-LUMO gap, birefringence, order parameter, and dipole moment. The odd carbon atom number of alkyl chain shows HOMO-LUMO gap, birefringence and order parameter in the upward direction and even carbon atom number of alkyl chain shows in the downward direction; however the dipole moment exhibits a shift of even carbon number of alkyl chain in the upward direction and odd carbon number of alkyl chain in the downward direction.
Jordan Journal of Chemistry, 2020
In this work, different parameters of E7 liquid crystal (LC) have been calculated under the influ... more In this work, different parameters of E7 liquid crystal (LC) have been calculated under the influence of an electric field in THz frequency. The E7 LC parameters have positive as well as negative values of order parameter and birefringence under the influence for an electric field. The director angle of E7 LC shows fast fluctuations above the angle θ=45° and due to rapid change in the orientation of molecules, fast electro-optical switching devices based on E7 LC can be designed. The refractive index of the E7 LC maintains stability in THz frequency.
This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photon... more This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photonic crystal (APC) containing double negative (DNG) metamaterials and air. The proposed annular structure consists of the alternate layers of dispersive DNG material and air immersed in free space. The reflectance properties of the APC by employing the transfer matrix method (TMM) in the cylindrical waves for TE polarization is studied theoretically. In addition of this, we have also studied the effect of plasma frequency on the reflection behavior of the considered annular structure.This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photonic crystal (APC) containing double negative (DNG) metamaterials and air. The proposed annular structure consists of the alternate layers of dispersive DNG material and air immersed in free space. The reflectance properties of the APC by employing the transfer matrix method (TMM) in the cylindrical waves for TE pola...
Due to the potential applications of a negative index material (NIM), the development of the NIM ... more Due to the potential applications of a negative index material (NIM), the development of the NIM has been occurred at an outstanding place in optics. To understand the optical properties of the single NIM layer, we have studied the propagation of electromagnetic wave through a medium of single NIM layer which is sandwiched between two dielectric materials. By using simple translational matrix method, the optical properties of the structure have calculated in the effect of thickness and plasma frequency of the NIM layer. The zero-refractive index, transmittance and dispersion of the structure are controlled by the thickness and the separation between the electric and magnetic plasma frequencies of NIM layer. The study of the electromagnetic wave propagation through the single negative index material may help to study the unusual behavior of the periodic structure containing NIMs. The study reveals that the single NIM layer can be used to make controlled optical devices (like Omni-dir...
Sensors and Actuators B: Chemical
Abstract Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19... more Abstract Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19 nanorods at room temperature under visible light radiation has been thoroughly inspected and reported. The sensing element is observed to be poorly responsive towards LPG in dark conditions at room temperature, while it reveals a good photo response in presence of visible light of 30 mW/cm2, and the visible light aids in improving the LPG sensing response up to a great extent at room temperature. Under the irradiation, the nanorods are found to detect the presence of LPG molecules of concentration as small as 0.5 vol.% at the response and recovery times ~5.02 sec and ~10.10 sec respectively. The sensitivity of the visible-light induced material was evaluated ~ 41.27 sensor response/vol.% with the maximum sensor response as high as 108, whereas, in dark, the same material showed a maximum response of ~6.64 with a sensitivity of merely 1.94 sensor response/vol.%. The photo-generated carriers are suggested to be responsible for achieving a significant, stable, fast response in presence of LPG. This is the first ferrite based visible light-induced LPG sensor.
Journal of Physical Science
Commercially available compound CuInGa (S, Se) can be replaced with emerging quaternary compound ... more Commercially available compound CuInGa (S, Se) can be replaced with emerging quaternary compound Cu2ZnSnS4 (Copper Zinc Tin Sulphur or CZSS) for photovoltaic applications due to the high absorption coefficient and optimum bandgap. Unstable sulphur and the co-existence of binary and ternary phases in CZSS are the main obstacles for a single-phase kesterite quaternary compound. To overcome these issues, the researchers are synthesising the CZSS in presence of sulphur and selenium environment. The sulphurization and selenization are the constraints for the synthesis of CZSS and these processes make it costlier. In the present work, the wet-chemical method (i.e., co-precipitation method) was used to synthesise CZSS without vacuum annealing where the sulphur constituent was controlled by changing the stoichiometric ratio. X-ray diffraction (XRD) and Raman analysis confirm that the synthesised CZSS was in polycrystalline and single-phase kesterite nature. The average crystallite sizes for...
IOP SciNotes
In present work, we report the N-(p-hexyloxy-benzylidene)–p-toluidine (HBT) liquid crystal (LC) m... more In present work, we report the N-(p-hexyloxy-benzylidene)–p-toluidine (HBT) liquid crystal (LC) molecule having maximum absorbance due to the O–C stretching (carbon atom of benzene ring) during the intermolecular interaction. Under the expansion of an external electric field, the HBT LC having nematic to smectic phase stability with adverse (negative values) order parameter and birefringence. The refractive index expresses stability in the nematic, smectic, and isotropic phases. The director angle maintains stability for the nematic phase in the adverse order and smectic phase stable in positive order.
Sensors and Actuators B: Chemical
Abstract In this study, dual-layered self-healable LPG sensor which can successfully re-establish... more Abstract In this study, dual-layered self-healable LPG sensor which can successfully re-establish both of its structural and sensing properties after an external deformation occurred, has been reported. Here Ni0.4Zn0.6Fe2O4 (NZF) works as a highly sensitive LPG sensor which can detect LPG well below the lowest explosion limit (LEL) efficiently. The self-healing phenomenon has been achieved by urea-formaldehyde (U-F) microcapsules encapsulating NZF and linseed oil. The dual-layered self-healable sensing film is prepared by forming a lower layer using urea-formaldehyde (U-F) microcapsules capturing linseed oil and NZF, serving as healing layer, and an upper layer using NZF aiding sensing phenomenon. LPG sensing parameters like sensitivity, sensor response, recovery time and response time were investigated in case of both uncracked sample and healed sample to get a clear idea of how much sensing properties were recovered after healing took place. The minimum response and recovery times of the uncracked film corresponding to 0.5 vol.% LPG concentrations were found to be 28.08 s and 52.46 s respectively, whereas, the same after healing were as 34.39 s and 45.17 s respectively. After healing, ∼ 86.4 % sensitivity was restored. This is the first dual-layered microcapsule-based LPG sensor, which has healing property.
AIP Conference Proceedings
By use of an empirical example from a planned organizational change program within an internation... more By use of an empirical example from a planned organizational change program within an international company, we examine how specific characteristics of objects (forms) used to represent ideas-in interaction with "hard-wired" aspects of human cognition-may contribute to explain outcomes of translation processes and the extent of alteration of the design of the future organization. We argue that a type of syllogism judged as invalid by criteria of formal logics-denoted as Erasmus syllogism-could be rather common in reasoning, and that these logically invalid interferences may contribute to significant innovations. Situations where syllogisms are not recognized as invalid by the involved actors seem to be more prevalent when e.g. the actors are unfamiliar with the semantic content (as e.g. abstract symbols). We argue that understanding of semiotic conditions for occurrence of formal logically invalid syllogism, as well as of the neglect of their invalidity by involved actors in ongoing discourses and reasoning, may contribute to a better understanding of how ideas and objects are translated, within organizations as well as in general. The discussion is a contribution to better understanding of why and how ideas are altered as part of ongoing sense making processes within organizations.
3RD INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC-2019)
AIP Conference Proceedings
AIP Conference Proceedings
Broadband reflector of 1D photonic crystal containing TiO 2 /SiO 2 material at visible region
Journal of Physical Science
To cite this article: Singh, P. et al. (2019). Omnidirectional reflection band of onedimensional ... more To cite this article: Singh, P. et al. (2019). Omnidirectional reflection band of onedimensional periodic structure (1DPS) of Si/SiO 2 with defect mode of nematic liquid crystal (5CB).
Optical and Quantum Electronics
In this article, transmission spectra of multilayer structure of zinc sulfide (ZnS) and titanium ... more In this article, transmission spectra of multilayer structure of zinc sulfide (ZnS) and titanium dioxide (TiO2) with defect of magnetized cold plasma (MCP) have been calculated theoretically by using characteristics transfer matrix method. The transmission spectra versus frequency have been analyzed for symmetric and asymmetric structure. Due to have a multiple band gaps in the asymmetric structure, we have taken the asymmetric structure for analysis with the parameters of MCP and the thicknesses of the dielectric materials. It is well known that magnetized cold plasma is an abnormal material because the permittivity changes with applied external magnetic field, and shows tunable photonic band gap for permittivity of the MCP. Now, the transmission spectra of the asymmetric structure versus frequency by inserting one or two magnetized cold plasma layer were analyzed with the variation of incident angles, the parameters of MCP, and the thicknesses of ZnS and TiO2 material. The analyzed transmission spectra of asymmetric structure with the variation of electron density, thicknesses of dielectric materials were obtained better results with defect of two plasma layers as compare to the defect of one layer of plasma. These obtained results reveal that the defect of two magnetized cold plasma layers of one dimensional asymmetric structure of ZnS, TiO2 may be used for the tunable multichannel filter at microwave region.
Materials Science and Engineering: B
Physica Scripta
Effective surface plasmons for dielectric properties of nanocomposite (NC) with spherical silver ... more Effective surface plasmons for dielectric properties of nanocomposite (NC) with spherical silver nanoparticles (Ag-NPs) in a host ZrO2 has investigated at different radii and filling fractions of nanoparticles (NPs) using the Maxwell-Garnett model. The optical properties of one-dimensional ternary periodic structure (1-DTPS) containing SiO2, TiO2, and NC with different parameters has investigated using the transfer matrix method (TMM). Moreover, the absorption properties of the considered structure for transverse electric (TE) and transverse magnetic (TM) have been studied at different incident angles and thicknesses of the NC layer. The dielectric and optical properties of the considered structure has affected by surface waves of dielectric layers as well as surface plasmons of Ag-NPs. The optical properties of the 1-DTPS for TE and TM modes has been studied with varying thicknesses of NC and angles of incidence wave. With the optimum values of the optical parameters of NC and Ag-N...
Advances in Photonic Crystals and Devices
In this present communication we studied the frequency dependence of the effective electromagneti... more In this present communication we studied the frequency dependence of the effective electromagnetic parameters of left-handed and related meta-materials (NIMs) of the split ring resonator (SRR) and wire type. By varying the width of inserted material as well as the host material, we also calculate the effective parameters of NIM like effective permittivity and effective permeability. Using these parameters, we calculate the effective refractive index and impedance of the considered medium. Our results reveal that the negative index of materials can be achieved when the thickness of the host materials should equal to the thickness of the inserted materials. OCIS codes: (350.4238) Photonics; (160.3918) Metamaterial.
Iranian journal of mathematical chemistry, 2020
The liquid crystal (LC) 4-4′-disubstituted biphenyls (HnCBP) of the general line formula HO-(CnH2... more The liquid crystal (LC) 4-4′-disubstituted biphenyls (HnCBP) of the general line formula HO-(CnH2n+1)-O-C6H4-C6H4-CN (n=1-12) shows the odd-even effect under the applied electric field. The odd-even effects are observed in the HOMO-LUMO gap, birefringence, order parameter, and dipole moment. The odd carbon atom number of alkyl chain shows HOMO-LUMO gap, birefringence and order parameter in the upward direction and even carbon atom number of alkyl chain shows in the downward direction; however the dipole moment exhibits a shift of even carbon number of alkyl chain in the upward direction and odd carbon number of alkyl chain in the downward direction.
Jordan Journal of Chemistry, 2020
In this work, different parameters of E7 liquid crystal (LC) have been calculated under the influ... more In this work, different parameters of E7 liquid crystal (LC) have been calculated under the influence of an electric field in THz frequency. The E7 LC parameters have positive as well as negative values of order parameter and birefringence under the influence for an electric field. The director angle of E7 LC shows fast fluctuations above the angle θ=45° and due to rapid change in the orientation of molecules, fast electro-optical switching devices based on E7 LC can be designed. The refractive index of the E7 LC maintains stability in THz frequency.
This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photon... more This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photonic crystal (APC) containing double negative (DNG) metamaterials and air. The proposed annular structure consists of the alternate layers of dispersive DNG material and air immersed in free space. The reflectance properties of the APC by employing the transfer matrix method (TMM) in the cylindrical waves for TE polarization is studied theoretically. In addition of this, we have also studied the effect of plasma frequency on the reflection behavior of the considered annular structure.This paper presents the reflection bands, photonic band gaps, of the one-dimensional annul photonic crystal (APC) containing double negative (DNG) metamaterials and air. The proposed annular structure consists of the alternate layers of dispersive DNG material and air immersed in free space. The reflectance properties of the APC by employing the transfer matrix method (TMM) in the cylindrical waves for TE pola...
Due to the potential applications of a negative index material (NIM), the development of the NIM ... more Due to the potential applications of a negative index material (NIM), the development of the NIM has been occurred at an outstanding place in optics. To understand the optical properties of the single NIM layer, we have studied the propagation of electromagnetic wave through a medium of single NIM layer which is sandwiched between two dielectric materials. By using simple translational matrix method, the optical properties of the structure have calculated in the effect of thickness and plasma frequency of the NIM layer. The zero-refractive index, transmittance and dispersion of the structure are controlled by the thickness and the separation between the electric and magnetic plasma frequencies of NIM layer. The study of the electromagnetic wave propagation through the single negative index material may help to study the unusual behavior of the periodic structure containing NIMs. The study reveals that the single NIM layer can be used to make controlled optical devices (like Omni-dir...
Sensors and Actuators B: Chemical
Abstract Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19... more Abstract Here, the photo-enhanced behavior in LPG sensing of hydrothermally synthesized BaFe12O19 nanorods at room temperature under visible light radiation has been thoroughly inspected and reported. The sensing element is observed to be poorly responsive towards LPG in dark conditions at room temperature, while it reveals a good photo response in presence of visible light of 30 mW/cm2, and the visible light aids in improving the LPG sensing response up to a great extent at room temperature. Under the irradiation, the nanorods are found to detect the presence of LPG molecules of concentration as small as 0.5 vol.% at the response and recovery times ~5.02 sec and ~10.10 sec respectively. The sensitivity of the visible-light induced material was evaluated ~ 41.27 sensor response/vol.% with the maximum sensor response as high as 108, whereas, in dark, the same material showed a maximum response of ~6.64 with a sensitivity of merely 1.94 sensor response/vol.%. The photo-generated carriers are suggested to be responsible for achieving a significant, stable, fast response in presence of LPG. This is the first ferrite based visible light-induced LPG sensor.
Journal of Physical Science
Commercially available compound CuInGa (S, Se) can be replaced with emerging quaternary compound ... more Commercially available compound CuInGa (S, Se) can be replaced with emerging quaternary compound Cu2ZnSnS4 (Copper Zinc Tin Sulphur or CZSS) for photovoltaic applications due to the high absorption coefficient and optimum bandgap. Unstable sulphur and the co-existence of binary and ternary phases in CZSS are the main obstacles for a single-phase kesterite quaternary compound. To overcome these issues, the researchers are synthesising the CZSS in presence of sulphur and selenium environment. The sulphurization and selenization are the constraints for the synthesis of CZSS and these processes make it costlier. In the present work, the wet-chemical method (i.e., co-precipitation method) was used to synthesise CZSS without vacuum annealing where the sulphur constituent was controlled by changing the stoichiometric ratio. X-ray diffraction (XRD) and Raman analysis confirm that the synthesised CZSS was in polycrystalline and single-phase kesterite nature. The average crystallite sizes for...
IOP SciNotes
In present work, we report the N-(p-hexyloxy-benzylidene)–p-toluidine (HBT) liquid crystal (LC) m... more In present work, we report the N-(p-hexyloxy-benzylidene)–p-toluidine (HBT) liquid crystal (LC) molecule having maximum absorbance due to the O–C stretching (carbon atom of benzene ring) during the intermolecular interaction. Under the expansion of an external electric field, the HBT LC having nematic to smectic phase stability with adverse (negative values) order parameter and birefringence. The refractive index expresses stability in the nematic, smectic, and isotropic phases. The director angle maintains stability for the nematic phase in the adverse order and smectic phase stable in positive order.
Sensors and Actuators B: Chemical
Abstract In this study, dual-layered self-healable LPG sensor which can successfully re-establish... more Abstract In this study, dual-layered self-healable LPG sensor which can successfully re-establish both of its structural and sensing properties after an external deformation occurred, has been reported. Here Ni0.4Zn0.6Fe2O4 (NZF) works as a highly sensitive LPG sensor which can detect LPG well below the lowest explosion limit (LEL) efficiently. The self-healing phenomenon has been achieved by urea-formaldehyde (U-F) microcapsules encapsulating NZF and linseed oil. The dual-layered self-healable sensing film is prepared by forming a lower layer using urea-formaldehyde (U-F) microcapsules capturing linseed oil and NZF, serving as healing layer, and an upper layer using NZF aiding sensing phenomenon. LPG sensing parameters like sensitivity, sensor response, recovery time and response time were investigated in case of both uncracked sample and healed sample to get a clear idea of how much sensing properties were recovered after healing took place. The minimum response and recovery times of the uncracked film corresponding to 0.5 vol.% LPG concentrations were found to be 28.08 s and 52.46 s respectively, whereas, the same after healing were as 34.39 s and 45.17 s respectively. After healing, ∼ 86.4 % sensitivity was restored. This is the first dual-layered microcapsule-based LPG sensor, which has healing property.
AIP Conference Proceedings
By use of an empirical example from a planned organizational change program within an internation... more By use of an empirical example from a planned organizational change program within an international company, we examine how specific characteristics of objects (forms) used to represent ideas-in interaction with "hard-wired" aspects of human cognition-may contribute to explain outcomes of translation processes and the extent of alteration of the design of the future organization. We argue that a type of syllogism judged as invalid by criteria of formal logics-denoted as Erasmus syllogism-could be rather common in reasoning, and that these logically invalid interferences may contribute to significant innovations. Situations where syllogisms are not recognized as invalid by the involved actors seem to be more prevalent when e.g. the actors are unfamiliar with the semantic content (as e.g. abstract symbols). We argue that understanding of semiotic conditions for occurrence of formal logically invalid syllogism, as well as of the neglect of their invalidity by involved actors in ongoing discourses and reasoning, may contribute to a better understanding of how ideas and objects are translated, within organizations as well as in general. The discussion is a contribution to better understanding of why and how ideas are altered as part of ongoing sense making processes within organizations.
3RD INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC-2019)
AIP Conference Proceedings
AIP Conference Proceedings
Broadband reflector of 1D photonic crystal containing TiO 2 /SiO 2 material at visible region
Journal of Physical Science
To cite this article: Singh, P. et al. (2019). Omnidirectional reflection band of onedimensional ... more To cite this article: Singh, P. et al. (2019). Omnidirectional reflection band of onedimensional periodic structure (1DPS) of Si/SiO 2 with defect mode of nematic liquid crystal (5CB).
Optical and Quantum Electronics
In this article, transmission spectra of multilayer structure of zinc sulfide (ZnS) and titanium ... more In this article, transmission spectra of multilayer structure of zinc sulfide (ZnS) and titanium dioxide (TiO2) with defect of magnetized cold plasma (MCP) have been calculated theoretically by using characteristics transfer matrix method. The transmission spectra versus frequency have been analyzed for symmetric and asymmetric structure. Due to have a multiple band gaps in the asymmetric structure, we have taken the asymmetric structure for analysis with the parameters of MCP and the thicknesses of the dielectric materials. It is well known that magnetized cold plasma is an abnormal material because the permittivity changes with applied external magnetic field, and shows tunable photonic band gap for permittivity of the MCP. Now, the transmission spectra of the asymmetric structure versus frequency by inserting one or two magnetized cold plasma layer were analyzed with the variation of incident angles, the parameters of MCP, and the thicknesses of ZnS and TiO2 material. The analyzed transmission spectra of asymmetric structure with the variation of electron density, thicknesses of dielectric materials were obtained better results with defect of two plasma layers as compare to the defect of one layer of plasma. These obtained results reveal that the defect of two magnetized cold plasma layers of one dimensional asymmetric structure of ZnS, TiO2 may be used for the tunable multichannel filter at microwave region.