2017 2nd International Conference on Image, Vision and Computing (ICIVC)
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.
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...
Journal of Electronic Science and Technology, 2021
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.
Abstract In this work, oxygen‐vacancy‐rich Ni1-xFexS electrocatalyst modified Fe2O3 nanoarrays ph... more Abstract In this work, oxygen‐vacancy‐rich Ni1-xFexS electrocatalyst modified Fe2O3 nanoarrays photoanode (denoted as Ni1-xFexS/Fe2O3) has been prepared firstly through a facile dripping solution method and a sulfurized process. As-prepared Ni1-xFexS/Fe2O3 anode shows a very high photocurrent density of ∼3.48 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) and a saturated photocurrent density of 7.03 mA/cm2 at 1.57 V vs. RHE in PEC water splitting, which is 2.5 times of Fe2O3 (1.38 mA/cm2 at 1.23 V vs. RHE and 2.98 mA/cm2 at 1.57 V vs. RHE, respectively). Moreover, the photocurrent onset potential shows a distinct negative shift of about 272 mV. The Ni1-xFexS/Fe2O3 photoanode is controllable to achieve superior PEC performance because of the synergistic effects of Ni1-xFexS electrocatalyst and oxygen vacancies. Since in situ formed Ni1-xFexS electrocatalyst not only increase electrochemical active surface area of electrode, but also dramatically decrease solid and electrolyte interface resistance as well as dramatically suppresses charge carrier recombination in Fe2O3 photoanodes. In the meanwhile, introduced the oxygen vacancies in a sulfurized process of Ni1-xFexS electrocatalyst serve as active sites for sufficient chemical reaction. Hence, our work testifies oxygen‐vacancy‐rich Ni1-xFexS not only act as a promising OER electrocatalyst, but also offers a new strategy to prepare efficient and low-cost PEC solar energy conversion devices.
The field of chiral plasmonics has registered considerable progress with machine-learning (ML)-me... more The field of chiral plasmonics has registered considerable progress with machine-learning (ML)-mediated metamaterial prototyping, drawing from the success of ML frameworks in other applications such as pattern and image recognition. Here, we present an end-to-end functional bidirectional deep-learning (DL) model for three-dimensional chiral metamaterial design and optimization. This ML model utilizes multitask joint learning features to recognize, generalize, and explore in detail the nontrivial relationship between the metamaterials’ geometry and their chiroptical response, eliminating the need for auxiliary networks or equivalent approaches to stabilize the physically relevant output. Our model efficiently realizes both forward and inverse retrieval tasks with great precision, offering a promising tool for iterative computational design tasks in complex physical systems. Finally, we explore the behavior of a sample ML-optimized structure in a practical application, assisting the s...
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, 2018
three stages. [1,2] First, photogenerated electron-hole pairs migrate to the surface of semicondu... more three stages. [1,2] First, photogenerated electron-hole pairs migrate to the surface of semiconductor. Second, the electron transfer to water molecules while the holes transfer either to water or to other holeacceptor sacrificial agents presented in solution. Third, the electrons reduce H + to H 2 in water. [3,4] Therefore, searching for energetic photocatalysts which first can directly generate electron-hole pairs under visible light-irradiation, second, can efficiently separate and transport photogenerated carriers to water, and last can reduce H + to H 2 in water is a critical mission. Cu 2 ZnSnS 4 is a direct bandgap p-type semiconductor with a high optical absorption coefficient of about 10 5 cm −1. [5] It can directly generate electron-hole pairs under visible light irradiation due to its favorable bandgap (1.5 eV). Furthermore, the conduction band (CB) minimum of Cu 2 ZnSnS 4 is about −0.7 eV (vs Normal hydrogen electrode (NHE), pH = 0), [6] which is more negative than the redox potential of H + /H 2 (0 eV vs NHE, pH = 0). Therefore, in theory, Cu 2 ZnSnS 4 is suitable for water reduction. [7] Accordingly, Cu 2 ZnSnS 4 has been investigated as a potential visible light driven photocatalyst for hydrogen production and showed inspiring results. [8,9] However, as the valence band (VB) mini mum of Cu 2 ZnSnS 4 is ≈0.8 eV (vs NHE, pH = 0), [6] which is less positive than the redox potential of O 2 /H 2 O (1.23 eV vs NHE, pH = 0), the photogenerated holes can only be absorbed by sacrificial agents, not by water. It results in a high charge carrier recombination rate of photogenerated electron-hole pairs, as well as leading to a low photocatalytic efficiency. Up to now, it is still a challenge to improve the photocatalytic efficiency of Cu 2 ZnSnS 4. Some self-assembly of nanoparticle (NP) and diverse single molecule detections are studied. [10,11] Most recently, employing nanosized noble metals, such as Pt and Au, to decorate Cu 2 ZnSnS 4 to form a new Fermi level equilibrium to inhibit the charge carrier recombination has been proved to be a feasible method. [12] Besides introducing noble metals, designing optimal core/shell nanostructure between noble metal and Cu 2 ZnSnS 4 was further studied and greatly improved the photocatalytic efficiency of Cu 2 ZnSnS 4. [13] However, the scarcity and high cost of noble metals may hinder them from being widespread used. Therefore, developing nonnoble metal, abundant and efficient cocatalysts to promote the effective charge carrier transfers becomes an urgent requirement. Hydrogen produced from water splitting is a renewable and clean energy source. Great efforts have been paid in searching for inexpensive and highly efficient photocatalysts. Here, significant enhancement of hydrogen production has been achieved by introducing ≈1 mol% of MoS 2 to Cu 2 ZnSnS 4 nanoparticles. The MoS 2 /Cu 2 ZnSnS 4 nanoparticles showed a hydrogen evolution rate of ≈0.47 mmol g −1 h −1 in the presence of sacrificial agents, which is 7.8 times that of Cu 2 ZnSnS 4 nanoparticles (0.06 mmol g −1 h −1). In addition, the MoS 2 /Cu 2 Z-nSnS 4 nanoparticles exhibited high stability, and only ≈3% of catalytic activity was lost after a long time irradiation (72 h). Microstructure investigation on the MoS 2 /Cu 2 ZnSnS 4 nanoparticles reveals that the intimate contact between the nanostructured MoS 2 and Cu 2 ZnSnS 4 nanoparticles provides an effective oneway expressway for photogenerated electrons transferring from the conduction band of Cu 2 ZnSnS 4 to MoS 2 , thus boosting the lifetime of charge carriers, as well as reducing the recombination rate of electrons and holes.
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 e...
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...
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.
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...
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.
The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absence of Au ... more 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.
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.
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.
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.
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.
2017 2nd International Conference on Image, Vision and Computing (ICIVC)
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.
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...
Journal of Electronic Science and Technology, 2021
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.
Abstract In this work, oxygen‐vacancy‐rich Ni1-xFexS electrocatalyst modified Fe2O3 nanoarrays ph... more Abstract In this work, oxygen‐vacancy‐rich Ni1-xFexS electrocatalyst modified Fe2O3 nanoarrays photoanode (denoted as Ni1-xFexS/Fe2O3) has been prepared firstly through a facile dripping solution method and a sulfurized process. As-prepared Ni1-xFexS/Fe2O3 anode shows a very high photocurrent density of ∼3.48 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) and a saturated photocurrent density of 7.03 mA/cm2 at 1.57 V vs. RHE in PEC water splitting, which is 2.5 times of Fe2O3 (1.38 mA/cm2 at 1.23 V vs. RHE and 2.98 mA/cm2 at 1.57 V vs. RHE, respectively). Moreover, the photocurrent onset potential shows a distinct negative shift of about 272 mV. The Ni1-xFexS/Fe2O3 photoanode is controllable to achieve superior PEC performance because of the synergistic effects of Ni1-xFexS electrocatalyst and oxygen vacancies. Since in situ formed Ni1-xFexS electrocatalyst not only increase electrochemical active surface area of electrode, but also dramatically decrease solid and electrolyte interface resistance as well as dramatically suppresses charge carrier recombination in Fe2O3 photoanodes. In the meanwhile, introduced the oxygen vacancies in a sulfurized process of Ni1-xFexS electrocatalyst serve as active sites for sufficient chemical reaction. Hence, our work testifies oxygen‐vacancy‐rich Ni1-xFexS not only act as a promising OER electrocatalyst, but also offers a new strategy to prepare efficient and low-cost PEC solar energy conversion devices.
The field of chiral plasmonics has registered considerable progress with machine-learning (ML)-me... more The field of chiral plasmonics has registered considerable progress with machine-learning (ML)-mediated metamaterial prototyping, drawing from the success of ML frameworks in other applications such as pattern and image recognition. Here, we present an end-to-end functional bidirectional deep-learning (DL) model for three-dimensional chiral metamaterial design and optimization. This ML model utilizes multitask joint learning features to recognize, generalize, and explore in detail the nontrivial relationship between the metamaterials’ geometry and their chiroptical response, eliminating the need for auxiliary networks or equivalent approaches to stabilize the physically relevant output. Our model efficiently realizes both forward and inverse retrieval tasks with great precision, offering a promising tool for iterative computational design tasks in complex physical systems. Finally, we explore the behavior of a sample ML-optimized structure in a practical application, assisting the s...
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, 2018
three stages. [1,2] First, photogenerated electron-hole pairs migrate to the surface of semicondu... more three stages. [1,2] First, photogenerated electron-hole pairs migrate to the surface of semiconductor. Second, the electron transfer to water molecules while the holes transfer either to water or to other holeacceptor sacrificial agents presented in solution. Third, the electrons reduce H + to H 2 in water. [3,4] Therefore, searching for energetic photocatalysts which first can directly generate electron-hole pairs under visible light-irradiation, second, can efficiently separate and transport photogenerated carriers to water, and last can reduce H + to H 2 in water is a critical mission. Cu 2 ZnSnS 4 is a direct bandgap p-type semiconductor with a high optical absorption coefficient of about 10 5 cm −1. [5] It can directly generate electron-hole pairs under visible light irradiation due to its favorable bandgap (1.5 eV). Furthermore, the conduction band (CB) minimum of Cu 2 ZnSnS 4 is about −0.7 eV (vs Normal hydrogen electrode (NHE), pH = 0), [6] which is more negative than the redox potential of H + /H 2 (0 eV vs NHE, pH = 0). Therefore, in theory, Cu 2 ZnSnS 4 is suitable for water reduction. [7] Accordingly, Cu 2 ZnSnS 4 has been investigated as a potential visible light driven photocatalyst for hydrogen production and showed inspiring results. [8,9] However, as the valence band (VB) mini mum of Cu 2 ZnSnS 4 is ≈0.8 eV (vs NHE, pH = 0), [6] which is less positive than the redox potential of O 2 /H 2 O (1.23 eV vs NHE, pH = 0), the photogenerated holes can only be absorbed by sacrificial agents, not by water. It results in a high charge carrier recombination rate of photogenerated electron-hole pairs, as well as leading to a low photocatalytic efficiency. Up to now, it is still a challenge to improve the photocatalytic efficiency of Cu 2 ZnSnS 4. Some self-assembly of nanoparticle (NP) and diverse single molecule detections are studied. [10,11] Most recently, employing nanosized noble metals, such as Pt and Au, to decorate Cu 2 ZnSnS 4 to form a new Fermi level equilibrium to inhibit the charge carrier recombination has been proved to be a feasible method. [12] Besides introducing noble metals, designing optimal core/shell nanostructure between noble metal and Cu 2 ZnSnS 4 was further studied and greatly improved the photocatalytic efficiency of Cu 2 ZnSnS 4. [13] However, the scarcity and high cost of noble metals may hinder them from being widespread used. Therefore, developing nonnoble metal, abundant and efficient cocatalysts to promote the effective charge carrier transfers becomes an urgent requirement. Hydrogen produced from water splitting is a renewable and clean energy source. Great efforts have been paid in searching for inexpensive and highly efficient photocatalysts. Here, significant enhancement of hydrogen production has been achieved by introducing ≈1 mol% of MoS 2 to Cu 2 ZnSnS 4 nanoparticles. The MoS 2 /Cu 2 ZnSnS 4 nanoparticles showed a hydrogen evolution rate of ≈0.47 mmol g −1 h −1 in the presence of sacrificial agents, which is 7.8 times that of Cu 2 ZnSnS 4 nanoparticles (0.06 mmol g −1 h −1). In addition, the MoS 2 /Cu 2 Z-nSnS 4 nanoparticles exhibited high stability, and only ≈3% of catalytic activity was lost after a long time irradiation (72 h). Microstructure investigation on the MoS 2 /Cu 2 ZnSnS 4 nanoparticles reveals that the intimate contact between the nanostructured MoS 2 and Cu 2 ZnSnS 4 nanoparticles provides an effective oneway expressway for photogenerated electrons transferring from the conduction band of Cu 2 ZnSnS 4 to MoS 2 , thus boosting the lifetime of charge carriers, as well as reducing the recombination rate of electrons and holes.
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 e...
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...
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.
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...
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.
The growth of Bi 2 Se 3 nanostructures by physical vapor deposition in presence or absence of Au ... more 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.
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.
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.
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.
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.
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Papers by Eric Ashalley