Showing papers on "Potential well published in 2015"
TL;DR: In this paper, the structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible (UV-Vis) absorption, and photoluminescence spectrograph.
Abstract: ZnS nanoparticles are prepared by homogeneous chemical co-precipitation method using EDTA as a stabilizer and capping agent. The structural, morphological, and optical properties of as-synthesized nanoparticles are investigated using x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible (UV-Vis) absorption, and photoluminescence spectroscopy. The x-ray diffraction pattern exhibits a zinc-blended crystal structure at room temperature. The average particle size of the nanoparticles from the scanning electron microscopy image is about 50 nm. The ultraviolet absorption spectrum shows the blue shift in the band gap due to the quantum confinement effect. The photoluminescence spectrum of ZnS nanoparticles shows a blue visible spectrum.
107 citations
TL;DR: In this article, a simple, highly efficient, large-scale and low-cost melamine-assisted exfoliation route is reported to obtain quasi-2D carbon nitride using an oil bath.
Abstract: Polymeric graphitic carbon nitride with a two-dimensional (2D) structure has intensive potential applications in hydrogen production from water splitting under visible light irradiation. Searching for an efficient technology is the key to synthesizing 2D materials from bulk powders. Here, a simple, highly-efficient, large-scale and low-cost melamine-assisted exfoliation route is reported to obtain quasi-2D carbon nitride using an oil bath. Quasi 2D carbon nitride possesses a high specific surface area (116.76 m2 g−1), a larger bandgap (by 0.13 eV), an enhanced electronic transport ability in the in-plane direction, a prolonged photo-excited charge carrier lifetime, and a lowered recombination of photo-induced electrons and holes resulting from the quantum confinement effect. These make enormous contributions to the photoactivity for hydrogen production under visible light. Therefore, the melamine-assisted liquid exfoliation route can be applied to large-scale polymeric carbon nitride photocatalyst production and is envisaged to have great promise for the exfoliation of other materials with layered structures.
88 citations
TL;DR: Graphene/Si quantum dot (QD) heterojunction diodes are reported for the first time and the photoresponse is remarkably enhanced in the near-ultraviolet range compared to commercially available bulk-Si photodetectors.
Abstract: Graphene/Si quantum dot (QD) heterojunction diodes are reported for the first time The photoresponse, very sensitive to variations in the size of the QDs as well as in the doping concentration of graphene and consistent with the quantum-confinement effect, is remarkably enhanced in the near-ultraviolet range compared to commercially available bulk-Si photodetectors The photoresponse proves to be dominated by the carriertunneling mechanism
56 citations
TL;DR: It is shown that molecular-sized SiC nanoparticles of 1-3 nm show a relatively strong and broad surface related Luminescence whilst the larger ones exhibit a relatively weak band edge and structural defect luminescence with no evidence of quantum confinement effect.
Abstract: Molecular-sized colloid silicon carbide (SiC) nanoparticles are very promising candidates to realize bioinert non-perturbative fluorescent nanoparticles for in vivo bioimaging. Furthermore, SiC nanoparticles with engineered vacancy-related emission centres may realize magneto-optical probes operating at nanoscale resolution. Understanding the nature of molecular-sized SiC nanoparticle emission is essential for further applications. Here we report an efficient and simple method to produce a relatively narrow size distribution of water soluble molecular-sized SiC nanoparticles. The tight control of their size distribution makes it possible to demonstrate a switching mechanism in the luminescence correlated with particle size. We show that molecular-sized SiC nanoparticles of 1-3 nm show a relatively strong and broad surface related luminescence whilst the larger ones exhibit a relatively weak band edge and structural defect luminescence with no evidence of quantum confinement effect.
45 citations
TL;DR: In this article, a one-step corrosion process was reported to synthesize nanostructured CuO thin films at room temperature, where the reaction time has great effect on the composition and microstructure of products to control the size and shape of the copper compound.
Abstract: We report a one-step corrosion process to synthesize nanostructured CuO thin films at room temperature. The reaction time has great effect on the composition and microstructure of products to control the size and shape of the copper compound. X-ray diffraction studies showed the transformation of nanograins from Cu(OH)2 nanowires to flower-like CuO and to dispersed CuO nanosheets. The optical properties of CuO nanosheets were investigated by using UV-vis spectroscopy with considerable blue-shift in the optical band gap (Eg = 1.8 eV) due to the quantum confinement effect. Additionally, the photocatalytic activities of as-prepared copper compound films were determined by measuring the degradation of methyl blue (MB) to find out their potential application in waste water treatment. The photoluminescence (PL) spectrum showed both UV as well as visible emission peaks, indicating their good optical properties. Moreover, a reasonable growth mechanism for the formation of the CuO nanostructure is proposed by means of a scanning electron microscope (FESEM).
39 citations
TL;DR: In this paper, three new hybrid Iodoargentates (H2pipe)0.5(α-AgI2) (1), (Me2teda)2+ (2), and (H 2dpe)2 + (3) have been synthesized under solvothermal conditions, whereby the aliphatic organic cations (Piperazine, teda, triethylenediamine) and conjugated organic cation(H2dpe), respectively, exhibit different contributions to both the crystal and electronic structures.
Abstract: Three new hybrid iodoargentates (H2pipe)0.5(α-AgI2) (1), (Me2teda)0.5(α-AgI2) (2), and (H2dpe)0.5(β-AgI2) (3) have been synthesized under solvothermal conditions, whereby the aliphatic organic cations (H2pipe)2+ and (Me2teda)2+ (pipe = piperazine, teda = triethylenediamine) and the conjugated organic cation (H2dpe)2+ [dpe = 1,2-di(4-pyridyl)ethylene] exhibit different contributions to both the crystal and electronic structures. The (H2pipe)2+ and (Me2teda)2+ cations direct the formation of α-type (AgI2)– polyanionic chains and influence the bandgaps of 1 and 2 indirectly by modulating the iodoargentate anionic structures. By contrast, the (H2dpe)2+ cation directs the formation of a novel β-type (AgI2)– chain and changes the bandgap of 3 directly to make up the bottom of the conduction band. From 1 and 2 to 3, a direct to indirect bandgap transformation and reduced bandgap can be observed (3.74, 2.88, and 1.99 eV for 1–3, respectively). Relative to the bandgap of bulk AgI2, the bandgaps of 1 and 2 show a blueshift as a result of the quantum confinement effect, whereas the bandgap of 3 shows a redshift owing to the direct participation of the conjugated cation (H2dpe)2+ in adjusting the bandgap.
38 citations
TL;DR: In this article, aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques and the lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum.
Abstract: Aromatic nitrogen doped graphene quantum dots were investigated by steady-state and time-resolved photoluminescence (PL) techniques. The PL lifetime was found to be dependent on the emission wavelength and coincident with the PL spectrum, which is different from most semiconductor quantum dots and fluorescent dyes. This result shows the synergy and competition between the quantum confinement effect and edge functional groups, which may have the potential to guide the synthesis and expand the applications of graphene quantum dots.
36 citations
TL;DR: To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs), scanning tunneling spectroscopy was employed to monitor the electronic structure of individual isolated Ge NCs as a function of their size.
Abstract: To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs) we employed scanning tunneling spectroscopy to monitor the electronic structure of individual isolated Ge NCs as a function of their size. The (single-particle) band gaps extracted from the tunneling spectra increase monotonically with decreasing nanocrystal size, irrespective of the capping ligands, manifesting the effect of quantum confinement. Band-gap widening of ∼1 eV with respect to the bulk value was observed for Ge-NCs 3 nm in diameter. The picture emerging from comparison with theoretical calculations and other experimental results is discussed.
35 citations
TL;DR: Theoretical optical absorbance shows that the largest absorption of this ultrathin single-layer sheet of ZnSe occurs at a wavelength similar to its four-atom-thick double-layer counterpart, suggesting a comparable behavior on incident photon-to-current conversion efficiency for solar water splitting, among a wealth of potential applications.
Abstract: The recently synthesized freestanding four-atom-thick double-layer sheet of ZnSe holds great promise as an ultraflexible and transparent photoelectrode material for solar water splitting. In this work, we report theoretical studies on a novel three-atom-thick single-layer sheet of ZnSe that demonstrates a strong quantum confinement effect by exhibiting a large enhancement of the band gap (2.0 eV) relative to the zinc blende (ZB) bulk phase. Theoretical optical absorbance shows that the largest absorption of this ultrathin single-layer sheet of ZnSe occurs at a wavelength similar to its four-atom-thick double-layer counterpart, suggesting a comparable behavior on incident photon-to-current conversion efficiency for solar water splitting, among a wealth of potential applications. The results presented herein for ZnSe may be generalized to other group II-VI analogues.
34 citations
TL;DR: In this paper, an efficient tuning mechanism of the light harvesting and detection of Ge quantum dots (QDs) was reported, where thin films of SiGeO alloys, produced by rf-magnetron sputtering, were annealed at 600°C in N2 to induce precipitation of small amorphous Ge QDs into the oxide matrix.
33 citations
TL;DR: In this article, the edge passivation effect of phosphorene nanoribbons was systematically investigated using density functional theory, and the new configuration, named Cb, can effectively reduce the effective mass of electrons, which benefits the future design of PHYRON-based electronic devices.
TL;DR: In this article, the formation mechanism of CZTS spherical quantum dots also has been investigated, according to the mechanism, copper sulfide nuclei firstly forms, and serves as the starting point for the nucleation and growth of cZTS.
Patent•
06 Nov 2015TL;DR: In this paper, the perovskite nanocrystalline particle in accordance with the present invention has a crystalline structure in which FCC and BCC are combined, and forms a lamellar structure, in which an organic plane and an inorganic plane are alternately stacked.
Abstract: Provided are perovskite nanocrystalline particle and an optoelectronic device using the same. The perovskite nanocrystalline particle may include a perovskite nanocrystalline structure while being dispersible in an organic solvent. Accordingly, the perovskite nanocrystalline particle in accordance with the present invention has therein a perovskite nanocrystal having a crystalline structure in which FCC and BCC are combined; forms a lamellar structure in which an organic plane and an inorganic plane are alternately stacked; and can show high color purity since excitons are confined to the inorganic plane. In addition, the perovskite nanocrystalline particle have a particle size greater than or equal to a Bohr diameter beyond a quantum confinement effect, and simultaneously can implement high emission efficiency and emission wavelength which is almost not dependent on particle size. Furthermore, the perovskite nanocrystalline particle in accordance with the present invention, as a nanoparticle which is dispersible in an organic solvent, is applicable in various electronic devices such as light emitting devices, lasers, solar cells, etc.
TL;DR: In this paper, the parabolic potential effects on the ground and excited energy states of two-electron quantum dot with impurity inside an infinite spherical confining potential well were investigated, and the wave function and energy eigenvalues were calculated using a modified variational optimization procedure based mainly on quantum genetic algorithm and Hartree-Fock-Roothaan method.
Abstract: In this study, we investigate the parabolic potential effects on the ground and excited energy states of two-electron quantum dot with impurity inside an infinite spherical confining potential well. The wave function and energy eigenvalues were calculated using a modified variational optimization procedure based mainly on quantum genetic algorithm and Hartree–Fock–Roothaan method. The results show that the parabolic potential and impurity charge have a strong effect on the energy states and ionization energies. It is worth pointing out that as impurity charge increases, the ionization energy rises, but the ionization dot radius decreases. On the other hand, as parabolic potential increases, the ionization energy decreases, but the ionization dot radius increases.
TL;DR: In this paper, Li+ co-doped CdS quantum dots (QDs) were synthesized by chemical precipitation method and they showed that they are highly luminescent and emit multiple intense violet (362, 371, 385, 395) and blue (422, 445, 456 and 465) colored peaks with increasing intensity with co-drug concentration.
Abstract: l-Arginine-passivated Nd3+ and Li+ co-doped CdS quantum dots (QDs) were synthesized by chemical precipitation method. Ultraviolet–visible absorption spectra of prepared QDs show absorption in the range of 477–450 nm indicating huge blue shift in energy band gap as compared to the bulk CdS due to quantum confinement effect. The optical band gap is found increasing from 2.44 to 2.97 eV as the doping concentration increased from 1 to 5 wt%. Photoluminescence spectra showed that co-doped CdS QDs are highly luminescent and emit multiple intense violet (362, 371, 385, 395 nm) and blue (422, 445, 456 and 465 nm) coloured peaks with increasing intensity with co-dopant concentration. Fourier transform infrared study confirmed the interaction between CdS nanoparticles and l-arginine ligands. The structural and morphological study revealed the formation of orthorhombic crystal structure. The size of CdS QDs, as analysed by X-ray diffraction and high-resolution transmission electron microscopy, is found reducing with co-dopant concentration. The energy dispersive X-ray analysis shows no impurities present except dopants indicating high purity of the prepared samples. Based on the results, we proposed that this material is a new class of luminescent material suitable for optoelectronics devices’ application, especially in light emitting devices, electroluminescent devices and display devices.
TL;DR: In this paper, the wake potential in a magnetized semiconductor quantum plasma in the presence of an upper hybrid wave which is excited via externally injected electron beam was studied using the non-relativistic quantum hydrodynamic model.
Abstract: Using the non-relativistic quantum hydrodynamic model, wake potential has been studied in a magnetized semiconductor quantum plasma in the presence of upper hybrid wave which is excited via externally injected electron beam. The quantum effect contains electron exchange and correlation potential, Fermi degenerate pressure, and Bohm potential. It is found that the contribution of quantum mechanical electron exchange and correlation potential significantly modifies the amplitude and the effective length of the oscillatory wake potential. In the electron-hole plasma systems, electron exchange-correlation effects tend to increase the magnitude of the wake potential and are much effective at the distances of the order of Debye-length. The application of the work in context of the semiconductor plasmas have also been analyzed graphically.
TL;DR: In this paper, the synthesis of pure, Cobalt (Co) and Iron (Fe) doped CdSe nanoparticles by the wet chemical method has been investigated by using X-ray diffraction (XRD), UV-vis spectroscopy to find the optical direct band gap and estimation of particle size by using Debye-Scherrer formula and HRTEM.
Abstract: The present work aims at the synthesis of pure, Cobalt (Co) and Iron (Fe) doped CdSe nanoparticles by the wet chemical method. The optical properties of synthesized nanoparticles have been characterized by X-ray diffraction (XRD), UV–vis spectroscopy to find the optical direct band gap and estimation of particle size by using Debye–Scherrer formula and HRTEM. The nonlinear optical properties such as nonlinear absorption co-efficient, nonlinear refraction co-efficient and third order nonlinear susceptibility χ (3) are investigated. The calculations have been performed with the help of Z-scan experimental set-up using Nd: YAG laser emitting 532 nm, 5 ns laser pulses with intensity maintained at 2.296 TW/cm 2 . The nanoparticles clearly exhibit a negative value of nonlinear refraction, which is attributed to the two photon absorption and free carrier absorption. Further the optical limiting behavior is determined (figure of merit (FOM)). The presence of RSA in these nanoparticles makes them a potential material for the development of optical limiter.
TL;DR: A generalized energy diagram is proposed to understand the thickness induced MIT in the SnO2:Sb system based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures.
Abstract: A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.
TL;DR: In this article, the frequency dependent dielectric constant of cadmium sulfide nanoparticles was investigated and normal behavior with applied field is seen and the values of real and imaginary part of dielectrics show dispersion at low frequencies and become almost saturated at higher frequencies.
TL;DR: In this article, the role of distribution of Au catalyst nanoparticles on the size and shape of AlGaN nanowires is discussed and a significant blue shift of the band gap, in the absence of quantum confinement effect in the Nanowires with diameter ∼100 nm, is used as a supportive evidence for the AlGAN alloy formation.
Abstract: Growth of monodispersed AlGaN nanowires of ternary wurtzite phase is reported using the chemical vapor deposition technique in the vapor–liquid–solid process. The role of distribution of Au catalyst nanoparticles on the size and shape of AlGaN nanowires is discussed. These variations in the morphology of the nanowires are understood invoking Ostwald ripening of Au catalyst nanoparticles at high temperature followed by the effect of single and multiprong growth mechanism. Energy-filtered transmission electron microscopy is used as an evidence for the presence of Al in the as-prepared samples. A significant blue shift of the band gap, in the absence of quantum confinement effect in the nanowires with diameter ∼100 nm, is used as a supportive evidence for the AlGaN alloy formation. Polarized resonance Raman spectroscopy with strong electron–phonon coupling along with optical confinement due to the dielectric contrast of nanowire with respect to that of surrounding media are adopted to understand the crystall...
TL;DR: According to the measurements and numerical simulation results, the strain relaxation effect is believed to play a dominant role rather than the quantum confinement effect in determining the emission wavelength of nanopillars.
Abstract: Nanopillars with diameters down to 20 nm were fabricated from InGaN/GaN multiple quantum wells (MQWs) by using a nanosphere–SiO2 double mask and inductively coupled plasma (ICP) etching. Clear photoluminescence (PL) signals of the nanopillars were observed at room temperature, and the PL peak energy at 20 K showed a large blueshift of 220 meV compared with that of the original MQWs. The exciton activation energy in the temperature range of 100 ∼300 K increased from 33 meV for MQWs to 83 meV for nanopillars. According to the measurements and numerical simulation results, the strain relaxation effect is believed to play a dominant role rather than the quantum confinement effect in determining the emission wavelength of nanopillars. This work also demonstrates a promising method for obtaining IIInitride quantum dots.
TL;DR: The strong photoluminescence (PL) signal at wavelengths ranging from 1,300 to 1,500 nm was observed in GaAsBi epitaxial layers grown by migration-enhanced epitaxy and annealed at higher temperatures as mentioned in this paper.
Abstract: The strong photoluminescence (PL) signal at wavelengths ranging from 1,300 to 1,500 nm was observed in GaAsBi epitaxial layers grown by migration-enhanced epitaxy and annealed at $$600\,^{\circ }\hbox {C}$$
and higher temperatures. PL measurements at liquid helium temperatures showed two peaks at $$\sim $$
0.9 and $$\sim $$
1 eV. It was found that intensity of the higher energy peak decreases with temperature leaving only the lower energy peak at room temperature. Structural investigations demonstrated that annealing reduces Bi content in GaAsBi lattice by precipitating bismuth in nanometer-scale clusters. It is suggested that PL can be caused by the semimetal–semiconductor transition quantum confinement due to the quantum confinement effect in Bi clusters.
TL;DR: In this article, the growth of PbTe quantum dots embedded in a novel fluorogermante glass matrix was investigated, and the size of the nanoparticles calculated from optical absorption spectra were found to be 3.2, 3.6, 6.1 and 7.3 nm.
TL;DR: In this article, a method of growing the catalyst-free self-organized ZnMgO nanocolumns with single quantum well on Si (1 1/1/1) substrates by plasma assisted molecular beam epitaxy technique (PA-MBE) was reported.
TL;DR: In this paper, the mechanisms of photoluminescence (PL) emission of samples annealed at different temperatures were investigated and it was shown that the PL emission of the as-deposited samples shows little change while that of the annealing samples at 1100°C exhibits an obvious redshift with the increase of excitation wavelength from 325-nm to 532-nm.
TL;DR: In this article, a simple wet chemical method of synthesizing spherical ZnO particles without using any surfactants was reported, which was confirmed using energy dispersive X-ray spectroscopy in situ with FESEM.
TL;DR: ZnO quantum dots embedded in an amorphous SiO2 matrix were examined in depth by using variable-temperature photoluminescence (PL) and optical reflectance spectroscopies and a remarkably reduced long-range Fröhlich interaction was revealed.
Abstract: ZnO quantum dots (QDs) embedded in an amorphous SiO2 matrix were examined in depth by using variable-temperature photoluminescence (PL) and optical reflectance spectroscopies. Compared with ZnO bulk crystals, ZnO quantum dots with an average size of 4 nm exhibit a strong quantum confinement effect, evidenced by a large blue shift in both PL and reflectance peaks of excitons. More interestingly, a remarkably reduced long-range Frohlich interaction was revealed in ZnO QDs. These fascinating effects may make ZnO QDs a very appealing system in the fields of optoelectronics and others.
TL;DR: In this article, ultrathin two-dimensional WS2 nanostructures with various morphologies have been prepared on SiO2/Si and sapphire substrates by vapor phase deposition method.
Abstract: Ultrathin two-dimensional WS2 nanostructures with various morphologies have been prepared on SiO2/Si (300 nm) and sapphire substrates by vapor phase deposition method. Simultaneously, tungsten nanostructures have also been obtained during the growth process. The nanostructures and morphologies of as-prepared products were systematically characterized by employing atomic force microscopy, Raman spectroscopy as well as scanning electron spectroscopy. The electrostatic properties of WS2 nanostructures were investigated exhibiting uniform surface potential and charge distributions. We have also detected the photoluminescence properties of WS2 nanostructures, which are dependent on the thickness and nanostructures of synthesized WS2. These results suggest that the optoelectronic properties of WS2 nanostructures can be effectively tuned by quantum confinement effect and nanostructures.
TL;DR: In this paper, a large amount of atomic hydrogen flux that originates due to the high degree dissociation of the gas molecules in high-density inductively coupled plasma (ICP) is used to grow plenty of ultra-nanocrystallites that demonstrate intense visible photoluminescence.
TL;DR: In this article, the authors reported transition metal doping of CdS nanoparticles with the generic formula Cd1-xTMxS; x = 0.04 and 0.08 synthesized by chemical co-precipitation method.
Abstract: This work reports transition metal (TM = Ni, Mn, Fe, Co and Cr) doping of CdS nanoparticles with the generic formula Cd1-xTMxS; x = 0.04 and 0.08 synthesized by chemical co-precipitation method. Polyvinylpyrrolidone was used as surfactant to prevent agglomeration. The samples were characterized with X-ray diffraction (XRD), UV–Vis absorption spectroscopy, photoluminescence and superconducting quantum interference device (SQUID). XRD confirmed the phase purity of the doped samples. Average crystallite size calculated from Debye–Scherrer formula was 2–9 nm. The UV–Vis spectra of the samples show blue shift, revealing strong confinement effect in the nanoparticles. The band gap calculated from UV–Vis spectroscopy lies in the range of 2.81–2.89 eV. The synthesized samples show luminescent emission ranging from 450 to 600 nm in the visible region of the electromagnetic spectrum. SQUID studies at 300 K reveal that Cd1−xNixS and Cd1−xMnxS show paramagnetic behaviour with small nonlinearity for low magnetic field whereas room temperature ferromagnetism was observed for Cd1−xFexS, Cd1−xCoxS and Cd1−xCrxS nanoparticles.