Eric Ashalley - Academia.edu (original) (raw)

Papers by Eric Ashalley

Advanced Optical Materials

Journal of Physics D: Applied Physics

Electromagnetic wave absorbers with full-spectrum near-unity solar absorption are extremely desir... more Electromagnetic wave absorbers with full-spectrum near-unity solar absorption are extremely desirable for solar energy conversion. Here, we theoretically proposed a broadband refractory plasmonic absorber without refractory metal, which has nearly perfect absorption over the whole solar spectrum. The absorber is supported by a periodic refractory dielectric framework of alumina and exhibits superior solar-selective and omnidirectional absorption. The simulated average absorption efficiency is up to 96% from 300 to 1400 nm, and the solar energy absorption efficiency can reach up to 90.8% over the entire solar spectrum range. Moreover, the steady-state temperature profile indicates that the absorber heats uniformly. The broadband refractory plasmonic absorber paves the way for the selective thermal absorption under high-temperature environment and holds great promise for solar energy harvesting and desalination applications.

Strain analysis has significance both for tailoring material properties and designing nanoscale d... more Strain analysis has significance both for tailoring material properties and designing nanoscale devices. In particular, strain plays a vital role in engineering the growth thermodynamics and kinetics and is applicable for designing optoelectronic devices. In this paper, we present a methodology for establishing the relationship between elastic bond constants and measurable parameters, i.e., Poisson’s ratio ν and systematic elastic constant K. At the atomistic level, this approach is within the framework of linear elastic theory and encompasses the neighbor interactions when an atom is introduced to stress. Departing from the force equilibrium equations, the relationships between ν, K, and spring constants are successfully established. Both the two-dimensional (2D) square lattice and common three-dimensional (3D) structures are taken into account in the procedure for facilitating, bridging the gap between structural complexity and numerical experiments. A new direction for understand...

2017 2nd International Conference on Image, Vision and Computing (ICIVC), 2017

This paper proposes a novel method combining dark channel prior (DCP) and bright channel prior (B... more This paper proposes a novel method combining dark channel prior (DCP) and bright channel prior (BCP) for single image dehazing. The proposed method achieves airlight approximations by implementing numerical proximity of atmospheric light, which use the average value of the DCP and BCP. Meanwhile, in order to reduce computational time, a fast guided filtration method is used for the transmission map refinement. Experimental results on a variety of outdoor hazy images show the effectiveness and robustness of the proposed algorithm.

Journal of Electronic Science and Technology

Chiral metamaterial absorbers (CMMAs), a particular class of chiral metamaterials that refuse the... more Chiral metamaterial absorbers (CMMAs), a particular class of chiral metamaterials that refuse the transmission of incident radiation and exhibit different optical responses upon interactions with left and right circularly polarized (LCP, RCP) light, have gained research traction in recent years. CMMAs demonstrate numerous exotic and specialized applications owing to their achievable compatibility with various physical, chemical, and biomolecular systems. Aside from their wellevolved fabrication modalities for a broad range of frequencies, CMMAs exhibit strong chiroptical effects, making them central to various detection, imaging, and energy harvesting applications. Consequently, within the past decade, studies encompassing the design, optimization, and fabrication, as well as demonstrating the diverse applications of CMMAs have emerged. In this review, the theory, design, and fabrication of CMMAs are discussed, highlighting their top-down fabrication techniques as well as recent algorithmic and machine-learning (ML)-based approaches to their design and optimization. Some of their broad-spectrum applications are also discussed, spanning their roles in enantioselective photodetection, chiral imaging, generation of hot electrons, selective temperature sensing, and active chiral plasmonics.

RSC Advances

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for it... more Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co 3 O 4 nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/ NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm À2 for HER and 342 mV at 50 mA cm À2 for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

Photonics Research

IoT devices are increasingly being implicated in cyber-attacks, raising community concern about t... more IoT devices are increasingly being implicated in cyber-attacks, raising community concern about the risks they pose to critical infrastructure, corporations, and citizens. In order to reduce this risk, the IETF is pushing IoT vendors to develop formal specifications of the intended purpose of their IoT devices, in the form of a Manufacturer Usage Description (MUD), so that their network behavior in any operating environment can be locked down and verified rigorously. This paper aims to assist IoT manufacturers in developing and verifying MUD profiles, while also helping adopters of these devices to ensure they are compatible with their organizational policies and track devices network behavior based on their MUD profile. Our first contribution is to develop a tool that takes the traffic trace of an arbitrary IoT device as input and automatically generates the MUD profile for it. We contribute our tool as open source, apply it to 28 consumer IoT devices, and highlight insights and challenges encountered in the process. Our second contribution is to apply a formal semantic framework that not only validates a given MUD profile for consistency, but also checks its compatibility with a given organizational policy. We apply our framework to representative organizations and selected devices, to demonstrate how MUD can reduce the effort needed for IoT acceptance testing. Finally, we show how operators can dynamically identify IoT devices using known MUD profiles and monitor their behavioral changes on their network.

Nanotechnology

Hot electron photodetection (HEPD) excited by surface plasmon can circumvent bandgap limitations,... more Hot electron photodetection (HEPD) excited by surface plasmon can circumvent bandgap limitations, opening pathways for additional energy harvesting. However, the costly and time-consuming lithography has long been a barrier for large-area and mass production of HEPD. In this paper, we proposed a planar and electron beam lithography-free hot electron photodetector based on the Fabry-Pérot resonance composed of Au/MoS2/Au cavity. The hot electron photodetector has a nanoscale thickness, high spectral tenability, and multicolour photoresponse in the near-infrared region due to the increased round-trip phase shift by using high refractive index MoS2. We predict that the photoresponsivity can achieve up to 23.6 mA/W when double cavities are integrated with the Fabry-Pérot cavity. The proposed hot electron photodetector that has a nanoscale thickness and planar stacking is a perfect candidate for large-area and mass production of HEPD.

Particle & Particle Systems Characterization

Applied Physics Letters

Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic sp... more Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic spintronic nanodevices. Here, using first-principles calculations, we predicted the existence of half-metallicity in porphin-decorated graphene nanoribbons based on the synthesized porphin-decorated graphene [He et al., Nat. Chem. 9, 33–38 (2017)]. The configurations are constructed by coupling porphin molecules to one side of three different graphene nanoribbons: zigzag, sawtooth, and armchair graphene nanoribbons. We found that the porphin-decorated zigzag graphene nanoribbons (ZGNRs) exhibit half-metallicity, where their bandgaps are fixed at ∼0.3 eV for the gapped spin channel regardless of the variation of the ribbon width. Different from ZGNR, porphin-decorated sawtooth graphene nanoribbons exhibit ferromagnetic semiconducting properties, and for the armchair graphene nanoribbons, porphin modification only influences their bandgaps. Our findings open an avenue to the graphene-based electronic and spintronic devices.Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic spintronic nanodevices. Here, using first-principles calculations, we predicted the existence of half-metallicity in porphin-decorated graphene nanoribbons based on the synthesized porphin-decorated graphene [He et al., Nat. Chem. 9, 33–38 (2017)]. The configurations are constructed by coupling porphin molecules to one side of three different graphene nanoribbons: zigzag, sawtooth, and armchair graphene nanoribbons. We found that the porphin-decorated zigzag graphene nanoribbons (ZGNRs) exhibit half-metallicity, where their bandgaps are fixed at ∼0.3 eV for the gapped spin channel regardless of the variation of the ribbon width. Different from ZGNR, porphin-decorated sawtooth graphene nanoribbons exhibit ferromagnetic semiconducting properties, and for the armchair graphene nanoribbons, porphin modification only influences their bandgaps. Our findings open an avenue to the graphene-based electronic and spintroni...

Nanoscale

A hot-electron-enabled route to controlling light with dissipative loss compensation in semicondu... more A hot-electron-enabled route to controlling light with dissipative loss compensation in semiconductor quantum light emitters has been realized for tunable quantum optoelectronic devices via a two-speciesplasmonsystem. Thedualspeciesnano-plasmonicsystemisachievedbycombining UV-plasmonic gallium metal...

Advanced Science

His research interest lies in molecular beam epitaxy of materials with layered structure and expl... more His research interest lies in molecular beam epitaxy of materials with layered structure and exploration of their fundamental physical properties.

Nanotechnology, Jan 8, 2018

Au nanobipyramids (NBPs) with sharp tips and narrow plasmon linewidths are ideal candidates for p... more Au nanobipyramids (NBPs) with sharp tips and narrow plasmon linewidths are ideal candidates for plasmonic applications. In this paper, we investigated the influencing factors of longitudinal plasmon resonance wavelength (LPRW) and scattering properties of single Au NBP by simulation. Compared with the volume, we establish the aspect ratio (length/width) as the dominant factor that affect the LPRW of Au NBPs. Plasmonic nanoparticles have been widely used for light-trapping enhancement in photovoltaics. To give a profound understanding of the superior light harvesting properties of Au NBPs, the near-field localization effect and far-field scattering mechanism of Au NBPs were investigated. Under the light injection at LPRW, the tip area shows near-field enhancement and the maximum scattering intensity appears on the side area of the waist owing to the remarkable optical absorption near the tips. Additionally, we confirm the fraction of light scattered into the substrate and angular dis...

Journal of Physics D: Applied Physics

For most of the reported metamaterial absorbers, the peak absorption only occurs at one single wa... more For most of the reported metamaterial absorbers, the peak absorption only occurs at one single wavelength. Here, we investigated a dual-band absorber which is based on simple gold nano-rings. Two absorption peaks can be readily achieved in 3-5 μm and 8-14 μm via tuning the width and radius of gold nano-rings and dielectric constant. The average maximum absorption of two bands can be as high as 95.1% (-0.22 dB). Based on the simulation results, the perfect absorber with nano-rings demonstrates great flexibility to create dual-band or triple-band absorption, and thus holds potential for further applications in thermophotovoltaics, multicolor infrared focal plane arrays, optical filters, and biological sensing applications.

Vacuum, 2016

Abstract The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absen... more Abstract The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absence of Au catalysts on Si and mica substrates is investigated. In the presence of Au nanodroplets on substrate surfaces, the growth of Bi 2 Se 3 nanostructures in diverse crystallographic orientations is initiated via a catalyst-assisted process at low source flux condition. At elevated flux supply, nearly free-standing vapor-solid growth dominates and an array consisting of dense inclined standing nanoribbons are achieved. The morphologies of the obtained Bi 2 Se 3 nanoribbons can be easily manipulated by changing growth temperature.

Modern Economy, 2016

Revenues generated from taxes constitute a major source of income for governments. However, the e... more Revenues generated from taxes constitute a major source of income for governments. However, the epic display of tax evasion by individuals and firms in most countries has induced researches on the factors accounting for tax evasion in developing countries. Therefore, this study is conducted to investigate the determinants of the informal sector compliance issues and the causality nexus between tax evasion and Gross Domestic Product (GDP). This research solely adopts the theory of planned behavior in analyzing tax compliance issues. The research work is divided into two parts. In analyzing the informal sector compliance issues, questionnaires were submitted to 600 respondents comprising informal sector taxpayers in all the ten regions in Ghana. Regression analysis was employed in our study to depict the results of the informal sector compliance issues. The result revealed that attitudes, subjective norm and perceived behavioral control are the main determinants of the informal sector compliance issues. The second part of this research examined the causality between taxes and GDP in Ghana's economy over the period of 1980-2015. The data were analyzed by employing the Augmented Dickey Fuller Unit Root test, the variables were found to be integrated of the order one and the Johansen test showed the presence of co-integration between the variables. The Granger causality test for the study indicated a unidirectional causality from taxation to GDP. Therefore, the study recommends that efforts should be geared towards the improvement of tax systems in order to augment the GDP of the country.

Open Journal of Business and Management, 2017

Electricity plays a crucial role in the economic development of most economies. The causality nex... more Electricity plays a crucial role in the economic development of most economies. The causality nexus between electricity consumption and economic growth is important in enacting energy consumption policy and environmental policy. Many researchers have studied the causality between energy consumption and economic growth yet no consensus has emerged. Irrespective of the numerous researches conducted between these two variables, less evidence has been recorded in Ghana. Studies establishing the direction of causality between economic growth and energy consumption have concluded mixed result posing stern threat to Ghana's energy policy. It is therefore viable to investigate the direction of causality between electricity consumption and economic growth in Ghana. This study uses the Cobb-Douglas growth model covering time series data from 1970 to 2014. Vector Error Correction Model was also conducted in order to empirically ascertain the error correction adjustment. Granger Causality test was used to determine the direction of causality between electricity consumption and economic growth and the empirical findings obtained herein reveals that there exists a unidirectional causality running from GDP to electricity consumption. This line of causality obtained from the data supports Growth-Led-Energy Hypothesis. Therefore, it is evident that Ghana is a less energy-dependent economy.

Advances in nano research, 2014

The self-assembled strain-induced sub-micrometric islands and nanostructures are grown from In-As... more The self-assembled strain-induced sub-micrometric islands and nanostructures are grown from In-As-Sb-P quaternary liquid phase on InAs (100) substrates in Stranski-Krastanow growth mode. Two samples are under consideration. The first sample consists of unencapsulated islands and lens-shape quantum dots (QDs) grown from expressly inhomogeneous liquid phase. The second sample is an n-InAs/p-InAsSbP heterostructure with QDs embedded in the p-n junction interface. The morphology, size and shape of the structures are investigated by high-resolution scanning electron (SEM) and transmission electron (TEM) microscopy. It is shown that islands, as they decrease in size, undergo shape transitions. Particularly, as the volume decreases, the following succession of shape transitions are detected: sub-micrometric truncated pyramid, {111} facetted pyramid, {111} and partially {105} facetted pyramid, completely unfacetted "pre-pyramid", hemisphere, lens-shaped QD, which then evolves again to nano-pyramid. A critical size of 5±2 nm for the shape transformation of InAsSbP-based lens-shaped QD to nano-pyramid is experimentally measured and theoretically evaluated.

British Journal of Economics, Management & Trade, 2015

ABSTRACT

Journal of Physics D: Applied Physics, 2015

ABSTRACT The InAsSbP composition type-II quantum dots (QDs) are grown on a InAs(1 0 0) substrate ... more ABSTRACT The InAsSbP composition type-II quantum dots (QDs) are grown on a InAs(1 0 0) substrate from In-As-Sb-P quaternary liquid phase at a constant temperature in Stranski–Krastanow growth mode. Device structures in the form of photoconductive cells are prepared for investigation. Magnetospectroscopy and high-precision capacitance spectrometry are used to explore the QDs structure’s electric sheet resistance in a magnetic field and the capacitance (charge) law at lateral current flow. Aharonov–Bohm (AB) oscillations with the period of δB = 0.38 ± 0.04 T are found on the magnetoresistance curve at both room and liquid nitrogen temperatures. The influence of the QDs size distribution on the period of AB oscillations is investigated. The magnetoresistance hysteresis equals to ~50 mΩ and ~400 mΩ is revealed at room and liquid nitrogen temperature, respectively. The capacitance hysteresis (CH) and contra-directional oscillations are also detected. Behavior of the CH versus applied voltage frequency in the range f = 103–106 Hz is investigated. It is shown that the CH decreases with increasing frequency up to 106 Hz. The time constant and corresponding frequency for the QDs R–C parallel circuit (generator) equal to τ = 2.9 × 10−7 s and f 0 = 5.5 × 105 Hz, respectively, are calculated.

Advanced Optical Materials

Journal of Physics D: Applied Physics

Electromagnetic wave absorbers with full-spectrum near-unity solar absorption are extremely desir... more Electromagnetic wave absorbers with full-spectrum near-unity solar absorption are extremely desirable for solar energy conversion. Here, we theoretically proposed a broadband refractory plasmonic absorber without refractory metal, which has nearly perfect absorption over the whole solar spectrum. The absorber is supported by a periodic refractory dielectric framework of alumina and exhibits superior solar-selective and omnidirectional absorption. The simulated average absorption efficiency is up to 96% from 300 to 1400 nm, and the solar energy absorption efficiency can reach up to 90.8% over the entire solar spectrum range. Moreover, the steady-state temperature profile indicates that the absorber heats uniformly. The broadband refractory plasmonic absorber paves the way for the selective thermal absorption under high-temperature environment and holds great promise for solar energy harvesting and desalination applications.

Strain analysis has significance both for tailoring material properties and designing nanoscale d... more Strain analysis has significance both for tailoring material properties and designing nanoscale devices. In particular, strain plays a vital role in engineering the growth thermodynamics and kinetics and is applicable for designing optoelectronic devices. In this paper, we present a methodology for establishing the relationship between elastic bond constants and measurable parameters, i.e., Poisson’s ratio ν and systematic elastic constant K. At the atomistic level, this approach is within the framework of linear elastic theory and encompasses the neighbor interactions when an atom is introduced to stress. Departing from the force equilibrium equations, the relationships between ν, K, and spring constants are successfully established. Both the two-dimensional (2D) square lattice and common three-dimensional (3D) structures are taken into account in the procedure for facilitating, bridging the gap between structural complexity and numerical experiments. A new direction for understand...

2017 2nd International Conference on Image, Vision and Computing (ICIVC), 2017

This paper proposes a novel method combining dark channel prior (DCP) and bright channel prior (B... more This paper proposes a novel method combining dark channel prior (DCP) and bright channel prior (BCP) for single image dehazing. The proposed method achieves airlight approximations by implementing numerical proximity of atmospheric light, which use the average value of the DCP and BCP. Meanwhile, in order to reduce computational time, a fast guided filtration method is used for the transmission map refinement. Experimental results on a variety of outdoor hazy images show the effectiveness and robustness of the proposed algorithm.

Journal of Electronic Science and Technology

Chiral metamaterial absorbers (CMMAs), a particular class of chiral metamaterials that refuse the... more Chiral metamaterial absorbers (CMMAs), a particular class of chiral metamaterials that refuse the transmission of incident radiation and exhibit different optical responses upon interactions with left and right circularly polarized (LCP, RCP) light, have gained research traction in recent years. CMMAs demonstrate numerous exotic and specialized applications owing to their achievable compatibility with various physical, chemical, and biomolecular systems. Aside from their wellevolved fabrication modalities for a broad range of frequencies, CMMAs exhibit strong chiroptical effects, making them central to various detection, imaging, and energy harvesting applications. Consequently, within the past decade, studies encompassing the design, optimization, and fabrication, as well as demonstrating the diverse applications of CMMAs have emerged. In this review, the theory, design, and fabrication of CMMAs are discussed, highlighting their top-down fabrication techniques as well as recent algorithmic and machine-learning (ML)-based approaches to their design and optimization. Some of their broad-spectrum applications are also discussed, spanning their roles in enantioselective photodetection, chiral imaging, generation of hot electrons, selective temperature sensing, and active chiral plasmonics.

RSC Advances

Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for it... more Hydrogen is the most promising renewable energy source to replace traditional fossil fuels for its ultrahigh energy density, abundance and environmental friendliness. Generating hydrogen by water splitting with highly efficient electrocatalysts is a feasible route to meet current and future energy demand. Herein, the effects of Ru doping and phosphorization treatment on Co 3 O 4 nanoarrays for water splitting are systemically investigated. The results show that a small amount of phosphorus can accelerate hydrogen evolution reaction (HER) and the trace of Ru dopant can significantly enhance the catalytic activities for HER and oxygen evolution reaction (OER). Ru-doped cobalt phosphorous oxide/nickel foam (CoRuPO/ NF) nanoarrays exhibit highly efficient catalytic performance with an overpotential of 26 mV at 10 mA cm À2 for HER and 342 mV at 50 mA cm À2 for OER in 1 M KOH solution, indicating superior water splitting performance. Furthermore, the CoRuPO/NF also exhibits eminent and durable activities for alkaline seawater electrolysis. This work significantly advances the development of seawater splitting for hydrogen generation.

Photonics Research

IoT devices are increasingly being implicated in cyber-attacks, raising community concern about t... more IoT devices are increasingly being implicated in cyber-attacks, raising community concern about the risks they pose to critical infrastructure, corporations, and citizens. In order to reduce this risk, the IETF is pushing IoT vendors to develop formal specifications of the intended purpose of their IoT devices, in the form of a Manufacturer Usage Description (MUD), so that their network behavior in any operating environment can be locked down and verified rigorously. This paper aims to assist IoT manufacturers in developing and verifying MUD profiles, while also helping adopters of these devices to ensure they are compatible with their organizational policies and track devices network behavior based on their MUD profile. Our first contribution is to develop a tool that takes the traffic trace of an arbitrary IoT device as input and automatically generates the MUD profile for it. We contribute our tool as open source, apply it to 28 consumer IoT devices, and highlight insights and challenges encountered in the process. Our second contribution is to apply a formal semantic framework that not only validates a given MUD profile for consistency, but also checks its compatibility with a given organizational policy. We apply our framework to representative organizations and selected devices, to demonstrate how MUD can reduce the effort needed for IoT acceptance testing. Finally, we show how operators can dynamically identify IoT devices using known MUD profiles and monitor their behavioral changes on their network.

Nanotechnology

Hot electron photodetection (HEPD) excited by surface plasmon can circumvent bandgap limitations,... more Hot electron photodetection (HEPD) excited by surface plasmon can circumvent bandgap limitations, opening pathways for additional energy harvesting. However, the costly and time-consuming lithography has long been a barrier for large-area and mass production of HEPD. In this paper, we proposed a planar and electron beam lithography-free hot electron photodetector based on the Fabry-Pérot resonance composed of Au/MoS2/Au cavity. The hot electron photodetector has a nanoscale thickness, high spectral tenability, and multicolour photoresponse in the near-infrared region due to the increased round-trip phase shift by using high refractive index MoS2. We predict that the photoresponsivity can achieve up to 23.6 mA/W when double cavities are integrated with the Fabry-Pérot cavity. The proposed hot electron photodetector that has a nanoscale thickness and planar stacking is a perfect candidate for large-area and mass production of HEPD.

Particle & Particle Systems Characterization

Applied Physics Letters

Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic sp... more Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic spintronic nanodevices. Here, using first-principles calculations, we predicted the existence of half-metallicity in porphin-decorated graphene nanoribbons based on the synthesized porphin-decorated graphene [He et al., Nat. Chem. 9, 33–38 (2017)]. The configurations are constructed by coupling porphin molecules to one side of three different graphene nanoribbons: zigzag, sawtooth, and armchair graphene nanoribbons. We found that the porphin-decorated zigzag graphene nanoribbons (ZGNRs) exhibit half-metallicity, where their bandgaps are fixed at ∼0.3 eV for the gapped spin channel regardless of the variation of the ribbon width. Different from ZGNR, porphin-decorated sawtooth graphene nanoribbons exhibit ferromagnetic semiconducting properties, and for the armchair graphene nanoribbons, porphin modification only influences their bandgaps. Our findings open an avenue to the graphene-based electronic and spintronic devices.Realization of the half-metallicity in graphene is of crucial importance in all-carbon organic spintronic nanodevices. Here, using first-principles calculations, we predicted the existence of half-metallicity in porphin-decorated graphene nanoribbons based on the synthesized porphin-decorated graphene [He et al., Nat. Chem. 9, 33–38 (2017)]. The configurations are constructed by coupling porphin molecules to one side of three different graphene nanoribbons: zigzag, sawtooth, and armchair graphene nanoribbons. We found that the porphin-decorated zigzag graphene nanoribbons (ZGNRs) exhibit half-metallicity, where their bandgaps are fixed at ∼0.3 eV for the gapped spin channel regardless of the variation of the ribbon width. Different from ZGNR, porphin-decorated sawtooth graphene nanoribbons exhibit ferromagnetic semiconducting properties, and for the armchair graphene nanoribbons, porphin modification only influences their bandgaps. Our findings open an avenue to the graphene-based electronic and spintroni...

Nanoscale

A hot-electron-enabled route to controlling light with dissipative loss compensation in semicondu... more A hot-electron-enabled route to controlling light with dissipative loss compensation in semiconductor quantum light emitters has been realized for tunable quantum optoelectronic devices via a two-speciesplasmonsystem. Thedualspeciesnano-plasmonicsystemisachievedbycombining UV-plasmonic gallium metal...

Advanced Science

His research interest lies in molecular beam epitaxy of materials with layered structure and expl... more His research interest lies in molecular beam epitaxy of materials with layered structure and exploration of their fundamental physical properties.

Nanotechnology, Jan 8, 2018

Au nanobipyramids (NBPs) with sharp tips and narrow plasmon linewidths are ideal candidates for p... more Au nanobipyramids (NBPs) with sharp tips and narrow plasmon linewidths are ideal candidates for plasmonic applications. In this paper, we investigated the influencing factors of longitudinal plasmon resonance wavelength (LPRW) and scattering properties of single Au NBP by simulation. Compared with the volume, we establish the aspect ratio (length/width) as the dominant factor that affect the LPRW of Au NBPs. Plasmonic nanoparticles have been widely used for light-trapping enhancement in photovoltaics. To give a profound understanding of the superior light harvesting properties of Au NBPs, the near-field localization effect and far-field scattering mechanism of Au NBPs were investigated. Under the light injection at LPRW, the tip area shows near-field enhancement and the maximum scattering intensity appears on the side area of the waist owing to the remarkable optical absorption near the tips. Additionally, we confirm the fraction of light scattered into the substrate and angular dis...

Journal of Physics D: Applied Physics

For most of the reported metamaterial absorbers, the peak absorption only occurs at one single wa... more For most of the reported metamaterial absorbers, the peak absorption only occurs at one single wavelength. Here, we investigated a dual-band absorber which is based on simple gold nano-rings. Two absorption peaks can be readily achieved in 3-5 μm and 8-14 μm via tuning the width and radius of gold nano-rings and dielectric constant. The average maximum absorption of two bands can be as high as 95.1% (-0.22 dB). Based on the simulation results, the perfect absorber with nano-rings demonstrates great flexibility to create dual-band or triple-band absorption, and thus holds potential for further applications in thermophotovoltaics, multicolor infrared focal plane arrays, optical filters, and biological sensing applications.

Vacuum, 2016

Abstract The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absen... more Abstract The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absence of Au catalysts on Si and mica substrates is investigated. In the presence of Au nanodroplets on substrate surfaces, the growth of Bi 2 Se 3 nanostructures in diverse crystallographic orientations is initiated via a catalyst-assisted process at low source flux condition. At elevated flux supply, nearly free-standing vapor-solid growth dominates and an array consisting of dense inclined standing nanoribbons are achieved. The morphologies of the obtained Bi 2 Se 3 nanoribbons can be easily manipulated by changing growth temperature.

Modern Economy, 2016

Revenues generated from taxes constitute a major source of income for governments. However, the e... more Revenues generated from taxes constitute a major source of income for governments. However, the epic display of tax evasion by individuals and firms in most countries has induced researches on the factors accounting for tax evasion in developing countries. Therefore, this study is conducted to investigate the determinants of the informal sector compliance issues and the causality nexus between tax evasion and Gross Domestic Product (GDP). This research solely adopts the theory of planned behavior in analyzing tax compliance issues. The research work is divided into two parts. In analyzing the informal sector compliance issues, questionnaires were submitted to 600 respondents comprising informal sector taxpayers in all the ten regions in Ghana. Regression analysis was employed in our study to depict the results of the informal sector compliance issues. The result revealed that attitudes, subjective norm and perceived behavioral control are the main determinants of the informal sector compliance issues. The second part of this research examined the causality between taxes and GDP in Ghana's economy over the period of 1980-2015. The data were analyzed by employing the Augmented Dickey Fuller Unit Root test, the variables were found to be integrated of the order one and the Johansen test showed the presence of co-integration between the variables. The Granger causality test for the study indicated a unidirectional causality from taxation to GDP. Therefore, the study recommends that efforts should be geared towards the improvement of tax systems in order to augment the GDP of the country.

Open Journal of Business and Management, 2017

Electricity plays a crucial role in the economic development of most economies. The causality nex... more Electricity plays a crucial role in the economic development of most economies. The causality nexus between electricity consumption and economic growth is important in enacting energy consumption policy and environmental policy. Many researchers have studied the causality between energy consumption and economic growth yet no consensus has emerged. Irrespective of the numerous researches conducted between these two variables, less evidence has been recorded in Ghana. Studies establishing the direction of causality between economic growth and energy consumption have concluded mixed result posing stern threat to Ghana's energy policy. It is therefore viable to investigate the direction of causality between electricity consumption and economic growth in Ghana. This study uses the Cobb-Douglas growth model covering time series data from 1970 to 2014. Vector Error Correction Model was also conducted in order to empirically ascertain the error correction adjustment. Granger Causality test was used to determine the direction of causality between electricity consumption and economic growth and the empirical findings obtained herein reveals that there exists a unidirectional causality running from GDP to electricity consumption. This line of causality obtained from the data supports Growth-Led-Energy Hypothesis. Therefore, it is evident that Ghana is a less energy-dependent economy.

Advances in nano research, 2014

The self-assembled strain-induced sub-micrometric islands and nanostructures are grown from In-As... more The self-assembled strain-induced sub-micrometric islands and nanostructures are grown from In-As-Sb-P quaternary liquid phase on InAs (100) substrates in Stranski-Krastanow growth mode. Two samples are under consideration. The first sample consists of unencapsulated islands and lens-shape quantum dots (QDs) grown from expressly inhomogeneous liquid phase. The second sample is an n-InAs/p-InAsSbP heterostructure with QDs embedded in the p-n junction interface. The morphology, size and shape of the structures are investigated by high-resolution scanning electron (SEM) and transmission electron (TEM) microscopy. It is shown that islands, as they decrease in size, undergo shape transitions. Particularly, as the volume decreases, the following succession of shape transitions are detected: sub-micrometric truncated pyramid, {111} facetted pyramid, {111} and partially {105} facetted pyramid, completely unfacetted "pre-pyramid", hemisphere, lens-shaped QD, which then evolves again to nano-pyramid. A critical size of 5±2 nm for the shape transformation of InAsSbP-based lens-shaped QD to nano-pyramid is experimentally measured and theoretically evaluated.

British Journal of Economics, Management & Trade, 2015

ABSTRACT

Journal of Physics D: Applied Physics, 2015

ABSTRACT The InAsSbP composition type-II quantum dots (QDs) are grown on a InAs(1 0 0) substrate ... more ABSTRACT The InAsSbP composition type-II quantum dots (QDs) are grown on a InAs(1 0 0) substrate from In-As-Sb-P quaternary liquid phase at a constant temperature in Stranski–Krastanow growth mode. Device structures in the form of photoconductive cells are prepared for investigation. Magnetospectroscopy and high-precision capacitance spectrometry are used to explore the QDs structure’s electric sheet resistance in a magnetic field and the capacitance (charge) law at lateral current flow. Aharonov–Bohm (AB) oscillations with the period of δB = 0.38 ± 0.04 T are found on the magnetoresistance curve at both room and liquid nitrogen temperatures. The influence of the QDs size distribution on the period of AB oscillations is investigated. The magnetoresistance hysteresis equals to ~50 mΩ and ~400 mΩ is revealed at room and liquid nitrogen temperature, respectively. The capacitance hysteresis (CH) and contra-directional oscillations are also detected. Behavior of the CH versus applied voltage frequency in the range f = 103–106 Hz is investigated. It is shown that the CH decreases with increasing frequency up to 106 Hz. The time constant and corresponding frequency for the QDs R–C parallel circuit (generator) equal to τ = 2.9 × 10−7 s and f 0 = 5.5 × 105 Hz, respectively, are calculated.