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Showing papers on "Potential well published in 2016"


Journal ArticleDOI
28 Apr 2016
TL;DR: In this paper, a detailed study on the Raman and photoluminescence spectra of 2D NCs of monolayer WS2 (1L WS2) and 1L WSe2 prepared by ion implantation is presented.
Abstract: Defects strongly modify optical properties in pristine and nanostructured two-dimensional (2D) materials. The ion implantation technique can be used to gradually introduce defects in semiconductor to obtain nanocrystallites (NCs) with different domain sizes. Here, we present a detailed study on the Raman and photoluminescence spectra of 2D NCs of monolayer WS2 (1L WS2) and 1L WSe2 prepared by ion implantation. With increasing ion dosages, both and modes of 1L WS2 exhibit a downshift in frequency and an asymmetrical broadening toward lower frequency, while the mode in 1L WSe2 NCs exhibits an opposite behavior, showing asymmetrical broadening and peak shift toward higher frequency. This behavior is well understood by phonon quantum confinement of the out-of-plane optical branch whose frequency displays a minimum at Γ in pristine 1L WSe2. After the ion implantation, phonons from the Brillouin zone boundary are revealed in the Raman spectra, and the corresponding assignments are identified by resonant Raman spectra at low temperature. The defects can act as trapping centers of free carriers, which result in a sharp decrease of photoluminescence (PL) emission from A exciton with increasing ion dosage. The PL peak from A-exciton in both 1L WS2 and 1L WSe2 NCs blueshifts with increasing the ion dosage due to the quantum confinement effect of smaller NC size. The ion-implantation results in a new emission peak of defect-bound neutral excitons below the A-exciton peak in both 1L WS2 and 1L WSe2 NCs. Its relative intensity to the A exciton increases with increasing the ion dosage and finally vanishes along with the A exciton. These results offer a route toward tailoring the optical properties of 2D materials by controlling the size of 2D NCs.

138 citations


Journal ArticleDOI
TL;DR: In this paper, the size-dependent electronic, optical absorption, and emission properties of black phosphorus quantum dots (BPQDs) were systematically studied by employing time-dependent density functional theory calculations.
Abstract: Understanding electron transitions in black phosphorus nanostructures plays a crucial role in applications in electronics and optoelectronics. In this work, by employing time-dependent density functional theory calculations, we systematically study the size-dependent electronic, optical absorption, and emission properties of black phosphorus quantum dots (BPQDs). Both the electronic gap and the absorption gap follow an inversely proportional law to the diameter of BPQDs in conformity to the quantum confinement effect. In contrast, the emission gap exhibits anomalous size dependence in the range of 0.8–1.8 nm, which is blue-shifted with the increase of size. The anomaly in fact arises from the structure distortion induced by the excited-state relaxation, and it leads to a huge Stokes shift in small BPQDs.

95 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of ZnO/Al2O3 bilayer thickness on the fundamental properties of 1D PAN ZnNOMA has been investigated and the tuning of structural properties and the enhancement of electronic and optical properties of the nanomaterials designed by atomic layer deposition and electrospinning.
Abstract: Nanolaminates are new class of promising nanomaterials with outstanding properties. Here we explored on the tuning of structural properties and the enhancement of electronic and optical properties of 1D PAN ZnO/Al2O3 nanolaminates designed by atomic layer deposition (ALD) and electrospinning. The influence of ZnO/Al2O3 bilayer thicknesses on the fundamental properties of 1D PAN ZnO/Al2O3 nanolaminates has been investigated. Due to the quantum confinement effect, the shift of XPS peaks to higher energies has been observed. Work function of Al2O3 was mostly independent of the bilayers number, whereas the ZnO work function decreased with an increase of the bilayer number. Photoluminescence of the 1D PAN ZnO/Al2O3 nanolaminates corresponded to emission bands in ZnO nanolayers. Due to quantum confinement and surface band bending, no excitonic peaks were observed. The defect emission band was affected by the band bending and defect concentration. The enhanced photoluminescence of the 1D PAN ZnO/Al2O3 nanolamina...

90 citations


Journal ArticleDOI
TL;DR: Multilayer antimonene nanoribbons with room temperature orange light emission uniformly distributed on InSb were synthesized by the plasma-assisted process, creating attractive two-dimensional material that is proper for applications of transistors and light-emitting diodes.

89 citations


Journal ArticleDOI
TL;DR: This work establishes an intimate relation between quantum dot size and even shape and its bandgap energy on a single object level and shows the presence of an effective coupling between proximal dots in an ensemble, leading to band structure modification.
Abstract: We investigate the variation of the bandgap energy of single quantum dots of CsPbBr3 inorganic halide perovskite as a function of size and shape and upon embedding within an ensemble. For that purpose, we make use of valence-loss electron spectroscopy with Z-contrast annular dark-field (ADF) imaging in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope. In the experiment, energy absorption is directly mapped onto individual quantum dots, whose dimensions and location are simultaneously measured to the highest precision. In that way, we establish an intimate relation between quantum dot size and even shape and its bandgap energy on a single object level. We explicitly follow the bandgap increase in smaller quantum dots due to quantum confinement and demonstrate that it is predominantly governed by the smallest of the three edges of the cuboidal perovskite dot. We also show the presence of an effective coupling between proximal dots in an ensemble, leading to band structu...

87 citations


Journal ArticleDOI
TL;DR: A visible-light-sensitive tin sulfide photocatalyst was designed based on a ubiquitous element strategy and density functional theory (DFT) calculations, and the bandgap of the synthesized SnS quantum dots was found to be tunable by adjusting the number of successive ionic layer adsorption and reaction (SILAR) cycles, which controls the magnitude of the quantum confinement effect.

74 citations


Journal ArticleDOI
TL;DR: In this paper, the average particle size calculated from band gap values is in good agreement with the TEM study calculation and it is around 4-5 nm, whereas for CdS:Cr nanoparticles, a broad emission band with a maximum at similar to 587 nm is observed.

66 citations


Journal ArticleDOI
21 Apr 2016-ACS Nano
TL;DR: In this study, a self-consistent theoretical model is proposed to study the piezo-phototronic effect in the framework of perturbation theory in quantum mechanics and its validity and universality are well-proven.
Abstract: With enhancements in the performance of optoelectronic devices, the field of piezo-phototronics has attracted much attention, and several theoretical works have been reported based on semiclassical models. At present, the feature size of optoelectronic devices are rapidly shrinking toward several tens of nanometers, which results in the quantum confinement effect. Starting from the basic piezoelectricity equation, Schrodinger equation, Poisson equation, and Fermi’s golden rule, a self-consistent theoretical model is proposed to study the piezo-phototronic effect in the framework of perturbation theory in quantum mechanics. The validity and universality of this model are well-proven with photoluminescence measurements in a single GaN/InGaN quantum well and multiple GaN/InGaN quantum wells. This study provides important insight into the working principle of nanoscale piezo-phototronic devices as well as guidance for the future device design.

59 citations


Journal ArticleDOI
TL;DR: The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.
Abstract: Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S2–. Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S2– ligand significantly enhances the electronic coup...

58 citations


Journal ArticleDOI
TL;DR: In this article, the complex optical conductivities for monolayer and few-layered MoS2 films were derived from their reflectance and transmittance responses, showing that the excitonic quantum confinement effect significantly modifies both the peak energy and magnitude of their optical conductivity, manifested by a gradual blueshift in energy and exponential attenuation in magnitude with decreasing layer number.
Abstract: Optical conductivity plays an important role in characterizing the optoelectronic properties of two-dimensional materials. Here we derive the complex optical conductivities for monolayer and few-layered MoS2 films from their reflectance and transmittance responses. We show that the excitonic quantum confinement effect significantly modifies both the peak energy and magnitude of their optical conductivity, manifested by a gradual blueshift in energy (consistent with two well-known models for quantum well systems) and exponential attenuation in magnitude with decreasing layer number. More importantly, the C excition induced optical conductivity peak exhibits the strongest dependence on the MoS2 layer number because of its largest Bohr radius among the A, B and C excitons. This unambiguously confirms the strong influence of quantum confinement effect in the optical conductivity of MoS2, shedding important insights into understanding its rich exciton-related optical properties and therefore facilitating potential applications in optoelectronic devices.

55 citations


Journal ArticleDOI
TL;DR: In this paper, a solution-processed near-infrared photodiode ITO/ZnO/PbSxSe1−x/Au, in which ternary PbS xSe 1−x QDs act as the active layer and the ZnO interlayer acts as electron-transporting layer, was demonstrated.
Abstract: Semiconductor quantum dots (QDs) have been the subject for wide research studies owing to their quantum confinement effect. Photodetectors or photodiodes are recognized potential applications for QDs due to their high photosensitivity, solution processability and low cost of production. In this paper, a solution-processed near-infrared photodiode ITO/ZnO/PbSxSe1−x/Au, in which ternary PbSxSe1−x QDs act as the active layer and the ZnO interlayer acts as electron-transporting layer, was demonstrated. The photosensitive spectrum can be broadened by adjusting the molar fraction of ternary PbSxSe1−x QDs. The narrow band edge of absorption and photoluminescence exciton energy of PbSxSe1−x alloyed NCs were blue-shifted from the band edge of the same size PbSe QDs to the band edge of PbS QDs by controlling the S/(Se + S) molar ratio in the synthetic mixture. Efficient electron extraction was carried out by inserting a solution-processed ZnO interlayer between the indium-tin oxide (ITO) electrode and the active layer. Our experimental results show that the solution processing of the ZnO layer can lead to high-performance photodiodes by using photosensitized PbS0.4Se0.6 alloyed nanocrystals as the active layer. The effect of the thickness of the active layer on the device performance was briefly described and a maximum photoresponsivity and specific detectivity of 25.8 A/W and 1.30 × 1013 Jones, respectively, were obtained at a certain thickness under 100 μW cm−2 980 nm laser illumination. The devices are made stably by layer-by-layer ligand exchange treatment.

Journal ArticleDOI
TL;DR: In this paper, the authors achieved electron transfer in a homojunction of branched rutile TiO2 nanorod by quantum confinement effect aroused by the nanoparticle, which is proved by the blue-shifting in UV-vis absorption spectrum of the homjunction.

Journal ArticleDOI
TL;DR: In this article, a layered perovskite (OA)2(MA)n−1PbnBr3n+1 (OA =C8H17NH3) was proposed for light emitting diodes.
Abstract: Air instability and poor exciton recombination of 3D perovskites MAPbX3 (MA = CH3NH3, X = halogens) seriously hinder their applications in light emitting diodes. Herein, we report a promising alternative to solve these two critical drawbacks. Layered perovskite OA2(MA)n−1PbnBr3n+1 (OA = C8H17NH3) has higher binding energy and is passivated by long organic chain, which can be synthesized using a facile method. By increasing the OA+ ratio in layered perovskite, strong quantum confinement effect and obvious features of exciton were observed in photoluminescence and UV-Vis absorption spectra. Notably, the photoluminescence quantum yield (PLQY) of (OA)2(MA)2Pb3Br10 (n = 3 layered perovskite) can be up to 67.3% due to the enhanced exciton recombination, significantly higher than its 3D counterpart. Moreover, layered perovskite exhibits promoted stability in air than that of the 3D perovskite. The layered perovskite (OA)2(MA)2Pb3Br10-based perovskite light emitting diodes (PeLEDs) with a maximum current efficiency, a maximum power efficiency and the external quantum efficiency (EQE) of 1.43 cd A−1, 0.89 lm W−1, and 0.53% was demonstrated, which can be compared with that of the best-reported perovskite quantum dots LEDs so far. The demonstration of layered perovskite renders its bright future in optoelectronic applications, such as displays and photodetections.

Journal ArticleDOI
TL;DR: Fast and stable photodetctors with high photocurrent gain are fabricated with Mn and Cu doped QDs and are found to be faster than pure In2S3 and an indication of the most suitable system forphotodetector devices.
Abstract: Indium sulphide (In2S3) quantum dots (QDs) of average size 6 ± 2 nm and hexagonal nanoplatelets of average size 37 ± 4 nm have been synthesized from indium myristate and indium diethyl dithiocarbamate precursors respectively. The absorbance and emission band was tuned with variation of nanocrytal size from very small in the strong confinement regime to very large in the weak confinement regime. The blue emission and its shifting with size has been explained with the donor-acceptor recombination process. The 3d element doping (Mn(2+) and Cu(2+)) is found to be effective for formation of new emission bands at higher wavelengths. The characteristic peaks of Mn(2+) and Cu(2+) and the modification of In(3+) peaks in the x-ray photoelectric spectrum (XPS) confirm the incorporation of Mn(2+) and Cu(2+) into the In2S3 matrix. The simulation of the electron paramagnetic resonance signal indicates the coexistence of isotropic and axial symmetry for In and S vacancies. Moreover, the majority of Mn(2+) ions and sulphur vacancies (VS ) reside on the surface of nanocrystals. The quantum confinement effect leads to an enhancement of band gap up to 3.65 eV in QDs. The formation of Mn 3d levels between conduction band edge and shallow donor states is evidenced from a systematic variation of emission spectra with the excitation wavelength. In2S3 QDs have been established as efficient sensitizers to Mn and Cu emission centers. Fast and slow components of photoluminescence (PL) decay dynamics in Mn and Cu doped QDs are interpreted in terms of surface and bulk recombination processes. Fast and stable photodetctors with high photocurrent gain are fabricated with Mn and Cu doped QDs and are found to be faster than pure In2S3. The fastest response time in Cu doped QDs is an indication of the most suitable system for photodetector devices.

Journal ArticleDOI
TL;DR: In this article, a simple and controllable sequent electrodeposition method for the functionalization of graphene quantum dots with chitosan and preparation of a thin film on a glassy carbon electrode surface was proposed and further used for the construction of an electrochemical detector.
Abstract: Graphene quantum dot (GQD) with tunable sizes, (2–5 nm) especially displays unique optical and electrical properties due to the quantum confinement effect. Experiments have revealed that the band gap and HOMO/LUMO energy levels of GQDs can be independently controlled by either the lateral size or chemical functionalization. In the present work, a simple and controllable sequent electrodeposition method for the functionalization of graphene quantum dots with chitosan and preparation of a thin film on a glassy carbon electrode surface was proposed and further used for the construction of an electrochemical detector. This novel interface was constructed by two-step electrochemical deposition in solution containing graphene quantum dots and chitosan. This deposited interface possessed excellent stability by the characterization of cyclic voltammetry and wave voltammetry in phosphate buffer with pH 7.4. As the nanostructured sensing film provides plenty of active sites for the direct oxidation of vitamin C, the prepared sensor exhibited excellent electrochemical, catalytical and analytical performance at the pH 7.4. The kinetics of charge transfer and mass transport processes across the nanocomposite/solution interface were studied. The modified electrode showed an efficient electrocatalytic activity toward the oxidation of vitamin C through a surface mediated electron transfer. The catalytic rate constant and the vitamin C diffusion coefficient were reported.

Journal ArticleDOI
TL;DR: A facile single injection Hydrothermal (SIH) method has been developed to synthesize high quality 3-Mercaptopropionic acid (MPA) stabilized aqueous CdTe QDs, entirely in ambient environment as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a nonthiol ligand passivated HgS quantum dot exhibits strong steady-state intraband transition in ambient condition and enables a versatile ligand replacement to oxide, acid, and halide functional ligands.
Abstract: Electron occupation in the lowest quantized state of the conduction band (1Se) in the colloidal quantum dot leads to the intraband transition in steady-state (1Se-1Pe). The intraband transition, solely originating from the quantum confinement effect, is the unique property of semiconducting nanocrystals. To achieve the electron occupation in 1Se state in the absence of impurity ions, nonthiol ligand passivated HgS colloidal quantum dots are synthesized. The nonthiol ligand passivated HgS quantum dot exhibits strong steady-state intraband transition in ambient condition and enables a versatile ligand replacement to oxide, acid, and halide functional ligands, which was not achievable from conventional HgS or HgSe quantum dots. Surprisingly, the atomic ligand passivation to HgS colloidal quantum dot solution efficiently maintains the electron occupation at 1Se of HgS CQDs in ambient condition. The electron occupation in 1Se of HgS CQD solid film is controlled by surface treatment with charged ions, which is ...

Journal ArticleDOI
TL;DR: Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition technique and a dependence of the density of states (DOS) and of the conduction band (CB) on theZnO thickness is observed, with a decreasing of the CB onset energy for increasing thickness.
Abstract: Two-dimensional (2D) ZnO structures have been deposited on the Au(111) surface by means of the pulsed laser deposition technique. In situ scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed to characterize morphological, structural and electronic properties of 2D ZnO at the nanoscale. Starting from a sub-monolayer coverage, we investigated the growth of ZnO, identifying different atomic layers (up to the fifth). At low coverage, we observed single- and bi-layer nanocrystals, characterized by a surface moire pattern that is associated to a graphene-like ZnO structure. By increasing the coverage, we revealed a morphological change starting from the fourth layer, which was attributed to a transition toward a bulk-like structure. Investigation of the electronic properties revealed the semiconducting character of 2D ZnO. We observed a dependence of the density of states (DOS) and, in particular, of the conduction band (CB) on the ZnO thickness, with a decreasing of the CB onset energy for increasing thickness. The CB DOS of 2D ZnO shows a step-like behaviour which may be interpreted as due to a 2D quantum confinement effect in ZnO atomic layers.

Journal ArticleDOI
TL;DR: In this paper, an improved hydrothermal method with water-oil two-phase reaction system was developed to synthesize size-controllable and oil-soluble Cu4SnS4 (CTS) quantum dots (QDs).

Journal ArticleDOI
TL;DR: These nanocrystals exhibit continuously tunable UV-vis absorption and photoluminescence across the visible spectrum, which is attributed to the quantum confinement effect with certain stoichiometry.
Abstract: Organic-inorganic perovskite materials, typically methylammonium lead trihalide (MAPbX3: MA = methylammonium; X = Br, I), are recently attract enormous attention for their distinguished photo-electronic properties. The control of morphology, composition and dispersability of MAPbX3 perovskite nanocrystals is crucial for the property tailoring and still a major challenge. Here we report the synthesis of colloidal MAPbBrxI3−x(0 ≤ x ≤ 3) nanocrystals at room temperature by using alkyl carboxylate as capping ligands. These nanocrystals exhibit continuously tunable UV-vis absorption and photoluminescence (PL) across the visible spectrum, which is attributed to the quantum confinement effect with certain stoichiometry. Their unique exciton recombination dynamics was investigated and discussed.

Journal ArticleDOI
TL;DR: In this paper, the EuO band gap is shown to increase from 1.19ÕeV for bulk-like (d = 32 nm) to ≈1.4 ÔeV in the ultrathin films (dÔ= 1.1Ônm) and the observed band gap widening is a clear sign of a quantum confinement effect.
Abstract: Quantum wells are created from ultrathin single-crystalline EuO layers to study the evolution of the optical band gap down to the single nanometer regime. We find that the EuO band gap is indirect—independent of quantum well thickness—and increases from 1.19 eV for bulk-like (d = 32 nm) to ≈1.4 eV in the ultrathin films (d = 1.1 nm). The observed band-gap widening is a clear sign of a quantum confinement effect, which can be used to control and modify the band gap in EuO-based all-oxide heterostructures.

Journal ArticleDOI
TL;DR: In this article, the electronic structure and the interactions between multiple sized CdSe QDs and single crystal rutile TiO2 with (001), (110), and (111) orientations are described.
Abstract: Semiconductor quantum dots (QDs) have many desirable characteristics for use as sensitizers, such as enabling tuning of the band gap on the basis of the quantum confinement effect, a higher extinction coefficient, and facilitating charge injection as a result of the large dipole moment. Despite these potential advantages, no major advance in the efficiency of quantum-dot-sensitized solar cells (QDSCs) has yet been reported. The poor efficiency can be attributed to electron-transfer (ET) reactions that compete with the ideal energy generation cycle in QDSCs. Despite the great technological significance, the interfacial ET between QDs and inorganic species remains poorly understood. In this paper, we describe the electronic structure and the interactions between multiple sized CdSe QDs and single crystal rutile TiO2 with (001), (110), and (111) orientations. Single crystal TiO2 is well characterized and is not only ideal for comparing the amount and the structure of the QDs but is also useful for studying E...

Journal ArticleDOI
TL;DR: The high luminescence yields in the visible range of the spectrum and size-tunable low-temperature synthesis with plasma and radical control make these quantum dot films good candidates for light emitting applications.
Abstract: The advanced materials process by non-thermal plasmas with a high plasma density allows the synthesis of small-to-big sized Si quantum dots by combining low-temperature deposition with superior crystalline quality in the background of an amorphous hydrogenated silicon nitride matrix. Here, we make quantum dot thin films in a reactive mixture of ammonia/silane/hydrogen utilizing dual-frequency capacitively coupled plasmas with high atomic hydrogen and nitrogen radical densities. Systematic data analysis using different film and plasma characterization tools reveals that the quantum dots with different sizes exhibit size dependent film properties, which are sensitively dependent on plasma characteristics. These films exhibit intense photoluminescence in the visible range with violet to orange colors and with narrow to broad widths (∼0.3–0.9 eV). The observed luminescence behavior can come from the quantum confinement effect, quasi-direct band-to-band recombination, and variation of atomic hydrogen and nitrogen radicals in the film growth network. The high luminescence yields in the visible range of the spectrum and size-tunable low-temperature synthesis with plasma and radical control make these quantum dot films good candidates for light emitting applications.

Journal ArticleDOI
TL;DR: In this paper, the effects of surfactants on the structural and optical properties of nanoparticles were investigated by UV-visible and PL spectroscopy, and the optical band gap values were determined by simple energy wave equation and Tauc plot method.

Journal ArticleDOI
TL;DR: In this paper, a polystyrene (PS)-nanosphere (NS) array is used as an etching mask for a single-layer GQD patterned by reactive ion etching and the size (d) of the GQDs is controlled by varying the etching time.
Abstract: Graphene quantum dots (GQDs) are one of the most attractive graphene nanostructures due to their potential optoelectronic device applications, but it is a challenge to accurately control the size and arrangement of GQDs. In this report, we fabricate well-aligned GQDs on a large area by polystyrene (PS)-nanosphere (NS) lithography and study their structural and optical properties. Single-layer graphene grown on a Cu foil by chemical vapour deposition is patterned by reactive ion etching employing aligned PS-NS arrays as an etching mask. The size (d) of the GQDs is controlled from 75 to 23 nm by varying the etching time, as proved by scanning electron microscopy and atomic force microscopy. This method is well valid for both rigid/flexible target substrates and even for multilayer graphene formed by piling up single layers. The absorption peak of the GQDs is blue-shifted with respect to that of a graphene sheet, and is sequentially shifted to higher energies by reducing d, consistent with the quantum confinement effect (QCE). The Raman D-to-G band intensity ratio shows an almost monotonic increase with decreasing d, resulting from the dominant contribution of the edge states at the periphery of smaller GQDs. The G-band frequency shows a three-step size-dependence: initial increase, interim saturation, and final decrease with decreasing d, thought to be caused by the competition between the QCE and edge-induced strain effect.

Journal ArticleDOI
01 Sep 2016-Optik
TL;DR: In this article, an indium oxide (In 2 O 3 ) nanostructured thin films are prepared by ultrasonic spray technique on glass substrates at 350°C Solution flow rate influence on the structural, morphological, optical and electrical properties of these samples is then studied.

Journal ArticleDOI
TL;DR: In this paper, a new kind of polyaniline/carbon nanotube/CdS quantum dot composites have been developed via in-situ polymerization of aniline monomer in the presence of dispersed CdS and multi-walled carbon nanotubes (CNT), which exhibits enhanced optical and electrical properties.

Journal ArticleDOI
25 Jul 2016
TL;DR: In this paper, the influence of ethylene glycol addition during the first stages of reaction (1-5 min) as a stabilizer, as well as its concentration in 2-propanol were investigated.
Abstract: ZnO quantum dots were prepared via a sol–gel route from zinc acetate and sodium hydroxide. The influence of ethylene glycol addition during the first stages of reaction (1–5 min) as a stabilizer, as well as the influence of its concentration in 2-propanol were investigated. The optimization led to particles with enough stability and homogeneity around 3.7 nm of diameter to allow for quantum confinement effect. Spectroscopic UV–vis absorption measurements allowed to explore the underlying mechanism of nucleation and growth and to have the control of it. The emission of the ZnO nanoparticles was explored under experimental perturbations with addition of small amounts of water to investigate the interplay between surface defects and the excitonic effect. The results suggest that the water interferes directly on the defects first and later on the excitonic recombination. Their morphology was determined with transmission electron microscopy.

Journal ArticleDOI
J. Y. Cui1, K. Y. Li1, L. Ren1, J. Zhao1, Tongde Shen1 
TL;DR: In this paper, the nano-doping mechanism of Cu-doped ZnSe/ZnS/L-cys self-assembled core-shell quantum dots (QDs) is studied by surface photovoltaic (SPV) and photoacoustic (PA) techniques, XRD, HRTEM, FT-IR, UV-VIS adsorption, and Laser Raman spectra.
Abstract: The photoelectron characteristics and nano-doping mechanism of Cu-doped ZnSe/ZnS/L-cys self-assembled core-shell quantum dots (QDs) are studied by surface photovoltaic (SPV) and photoacoustic (PA) techniques, XRD, HRTEM, FT-IR, UV-VIS adsorption, and Laser Raman spectra. The results suggest that the doped copper element prefers to locate at the Zn atom-vacancy of the (111) face of the QDs in the Cu2+ ion form. The defect-state levels are referred to the shallow accepter levels, leading to an obvious quantum confinement effect and a weakened n-type surface photovoltaic characteristic in the Cu-doped QDs. The quantum confinement effect strongly depends on the depth of the quantum well that is buried in the space charge region located in the graded-band-gap and at the side of the core-ZnSe. These electron structures are responsible for the increased lifetime and diffusion length of photogenerated free charge carriers, which significantly enhance the intensity of SPV response, enlarge the range of SPV respons...

Journal ArticleDOI
Q.Y. Zhang1, J.M. Ashfaq1, B.C. Hu1, Jing Wang1, N. Zhou1 
TL;DR: In this article, the authors reported the ZnO/ZnMgO MQWs fabricated under optimized conditions, and the MQW samples, excited by a 325-nm He-Cd laser, exhibited intense ultraviolet photoluminescence (PL) tuned by the quantum confinement effect.