Showing papers on "Potential well published in 2004"
TL;DR: In this paper, the surface photovoltage properties of ZnO nanoparticles were investigated by means of SPS and FISPS, and the results showed that the SPV of different sizes of nanoparticles are greatly different for their different sizes.
Abstract: The ZnO quantum dots (about 3 nm in average size) and the ZnO nanorods (about 80 nm in length and 14 nm in width) were synthesized by the sol−gel method. They were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV−vis spectroscopy, and photoluminescence (PL) spectroscopy. The surface photovoltage (SPV) of ZnO nanoparticles was investigated by means of surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (FISPS), and the bands were identified. The results show that the SPV of ZnO nanoparticles are greatly different for their different sizes as a result of the quantum confinement effect. The ZnO quantum dots exhibit marked quantum confinement properties; that is, FISPS takes a high symmetry in the changes of the response intensity with the strengthening of the two opposed electric fields, and the FISPS response band always appears at about 369 nm, no matter what external electric field is applied. Whereas for the ZnO nanorods a...
248 citations
TL;DR: In this paper, the authors show that the ZnO quantum dots are formed and embedded in the amorphous silicon oxide interfacial layer when annealed at 850°C.
Abstract: ZnO quantum dots (QDs) have been fabricated by the growth of SiO2/ZnO films/Si substrate and subsequent rapid-thermal annealing in a N2 ambient. Transmission electron microscopy (TEM) results show that the ZnO QDs 3–7 nm in size are formed and embedded in the amorphous silicon oxide interfacial layer when annealed at 850 °C. Photoluminescence (PL) at room temperature from the 850 °C-annealed samples reveals only high-energy emission at about 3.37 eV, while PL at 10 K shows a broad spectra with a tail up to about 3.5 eV. The TEM and PL results indicate that the broad spectra are caused by the presence of the ZnO QDs and hence by the quantum confinement effect.
105 citations
TL;DR: Nanosized ZnGa 2 O 4 :Cr 3+ powder is synthesized through hydrothermal method and the average particle size is 20nm and they are spherical in shape as discussed by the authors.
83 citations
TL;DR: In this paper, the concept of quantum scintillators, satisfying both a large light output and a quick response, is proposed, and the temporal behavior of scintillation from (n-C6H13NH3)2PbI4, a natural multiple quantum well structure provided by the lead-halide-based perovskite-type organic-inorganic hybrid compound, was investigated using a short-pulsed electron beam and a streak camera.
Abstract: The concept of a "quantum scintillator", satisfying both a large light output and a quick response, is proposed. The temporal behavior of scintillation from (n-C6H13NH3)2PbI4, a natural multiple quantum well structure provided by the lead-halide-based perovskite-type organic-inorganic hybrid compound, was investigated using a short-pulsed electron beam and a streak camera. A decay component of 390 ps was efficiently observed even at room temperature. This response is notably quicker than conventional Ce3+-activated scintillators because of a quantum confinement effect that increases the overlapping region of electron and hole wavefunctions in the low-dimensional system. This achievement would be the next breakthrough in the development of ultra-fast inorganic scintillators.
78 citations
TL;DR: The first aqueous preparation of luminescent CdS QDs from a single precursor is reported in this paper, where the size of the nanoparticles is tunable by varying the capping agent-to-precursor molar ratio.
Abstract: The first aqueous preparation of luminescent CdS QDs from a single precursor is reported. These water-soluble CdS quantum dots with tunable sizes between 25 and 40 A were produced from a readily prepared [(2,2‘-bipyridine)Cd(SC{O}Ph)2] complex by simply refluxing in an aqueous solution. The as-prepared nanoparticles are fairly uniform in size without the need of size sorting, and exhibit a quantum confinement effect. The size of the nanoparticles is tunable by varying the capping agent-to-precursor molar ratio. The green- and yellow-emitting quantum dots obtained via this simple route are water soluble and have OH functionality that is suitable for further applications. The particle aging kinetics was investigated by monitoring the optical band edge absorption and was found to follow the Ostwald ripening mechanism. When the amount of capping agent used is 10 mmol, unprecedented dimerization of some QDs upon prolong reflux to form nanocrystals double the size is detected. Thus, a common red shift of the ab...
75 citations
TL;DR: In this paper, the photoluminescence properties of ZnO/Zn0.8Mg0.2O nanorod singlequantum-well structures (SQWs) were measured at various temperatures between 10 and 300 K.
Abstract: We report on photoluminescent properties of ZnO/Zn0.8Mg0.2O nanorod single-quantum-well structures (SQWs). Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) was employed for precise controls of well widths and compositions of the nanorod SQWs. Both time-integrated and time-resolved photoluminescence (PL) spectra of ZnO/Zn0.8Mg0.2O nanorod SQWs were measured at various temperatures between 10 and 300 K. From the PL spectra of the nanorod SQWs measured at 10 K, a PL peak blue-shift dependent on ZnO well layer width was observed, resulting from a quantum confinement effect. Further photoluminescent properties of the nanorod SQWs were investigated measuring time-resolved PL (TRPL) and temperature-dependent PL spectra.
63 citations
TL;DR: In this article, photoluminescence (PL) of ZnO-opal structures excited by a 351.1 nm laser line was studied, and strong excitonLO phonon and exciton-Frohlich mode coupling was derived from the analysis of multiphonon excitonic resonant Raman scattering.
Abstract: We study photoluminescence(PL) of ZnO-opal structures excited by a 351.1 nm laser line. The structures were fabricated by infiltration of ZnO from an aqueous solution of zinc nitrate into opal matrices. The emission spectrum of thick ZnO layers grown on the surface of bulk opals exhibits narrow PL bands associated with the recombination of bound and free-excitons. The free-exciton lines are discussed taking into account the polariton phenomena. The width of the excitonic lines (2–3 meV) along with their energy position is indicative of high quality and strain-free state of the layer. The emission from ZnO crystallites embedded into bulk opal is dominated by near band gap luminescence, a weak quantum confinement effect being observed for crystallites with sizes around 50 nm. Thin ZnOfilmsgrown on single-layer opals exhibit enhanced resonant Raman scattering,phonon confinement effects, and surface-related modes. Strong exciton-LO phonon and exciton-Frohlich mode coupling in ZnO nanostructures is deduced from the analysis of multiphonon excitonic resonant Raman scattering.
43 citations
TL;DR: In this article, the lifetime of conduction electron through a preselected single state that is well separated from other states due to the quantum confinement effect is controlled by using magnetic fields comparable to 1 Tesla.
Abstract: The electrical conductance through a ring is sensitive to the threading magnetic flux. It contains a component that is periodic with an Aharonov−Bohm (AB) period equal to the quantum flux. In molecular/atomic loops on the nanometer scale, encircling very small areas, the AB period involves unrealistically huge magnetic fields. We show that despite this, moderate magnetic fields can have a strong impact on the conductance. By controlling the lifetime of the conduction electron through a preselected single state that is well separated from other states due to the quantum confinement effect, we demonstrate that magnetic fields comparable to 1 Tesla can be used to switch a nanometric AB device. Using atomistic electronic structure calculations, we show that such effects can be expected for loops composed of monovalent metal atoms (quantum corrals). Our findings suggest that future fabrication of nanometric magnetoresistance devices based on the AB effect is feasible.
31 citations
TL;DR: In this article, a study of the Raman spectrum of the nanowires showed that the shift to low frequency is due to the quantum confinement effect, which is discussed by using the phonon confinement model.
Abstract: Array-ordered single-crystal silicon nanowires were fabricated by the nanochannel-aluminal and CVD method. The average length and diameter of the nanowires is about 10 μm and 60 nm, respectively. A study of the Raman spectrum of the nanowires shows that the Raman shift to low frequency is due to the quantum confinement effect, which is discussed by using the phonon confinement model. Also we determine the peaks of the Raman spectrum to be corresponding to that of crystal silicon (c-Si).
28 citations
TL;DR: In this paper, the optical and structural properties of mixed ZnO/MgO particles prepared by solution techniques are investigated by the cathodoluminescence and electron microscopy techniques.
26 citations
Patent•
20 Feb 2004TL;DR: In this article, the authors describe nanophotonic materials and devices for both classical and quantum optical signal processing, transmission, amplification, and generation of light, which are based on a set of quantum systems having a discrete energy levels, such as atoms, molecules, or quantum dots, embedded in a frequency bandgap medium.
Abstract: The present invention describes nanophotonic materials and devices for both classical and quantum optical signal processing, transmission, amplification, and generation of light, which are based on a set of quantum systems having a discrete energy levels, such as atoms, molecules, or quantum dots, embedded in a frequency bandgap medium, such as artificial photonic crystals (photonic bandgap materials) or natural frequency dispersive media, such as ionic crystals, molecular crystals, or semiconductors, exhibiting a frequency (photonic) bandgap for propagating electromagnetic modes coupled to optical transitions in the quantum systems. If the frequency of one of optical transitions, called the working transition, lies inside the frequency bandgap of the medium, then spontaneous decay of the working transition into propagating photon modes is completely suppressed. Moreover, the excitation of the working transition and a photon form a photon-quantum system bound state lying inside the photonic bandgap of the medium, in which radiation is localized in the vicinity of the quantum system. In a quantum system “wire” or a quantum system “waveguide”, made of spatially disordered quantum systems, or in a chain quantum system waveguide made of a periodically ordered identical quantum systems, wave functions of the photon-quantum system bound states localized on different quantum systems overlap each other and develop a photonic passband lying inside bandgap of the photonic bandgap medium. Photons with frequencies lying inside the photonic passband propagate along the quantum system waveguide. Since the working transition cannot be excited twice, the passband photons interact with each other extremely strongly both in one waveguide and in different waveguides that are located sufficiently close to each other. These unique nonlinear properties of the quantum system waveguides are proposed to use for engineering key nanophotonic devices, such as all-optical and electro-optical switches, modulators, transistors, control-NOT logic gates, nonlinear directional couplers, electro-optical modulators and converters, generators of entangled photon states, passband optical amplifiers and lasers, as well as all-optical integrated circuits for both classical and quantum optical signal processing, including quantum computing.
TL;DR: In this paper, photoluminescence measurements were obtained at room temperature in silicon-rich,silica-silica multilayers grown by reactive magnetron sputtering, where the silicon nanograin size is controlled via the silicon layer thickness.
Abstract: The increasing interest in photonics in the field of communication has led to intense research work on silicon based nanostructures showing efficient photoluminescence. The present paper reports photoluminescence measurements obtained at room temperature in silicon-rich-silica-silica multilayers grown by reactive magnetron sputtering. The silicon nanograin size is controlled via the silicon layer thickness which can be monitored with high accuracy. We aim to develop a comprehensive understanding of the combined roles played by the quantum confinement effect through the silicon grain size and the existence of an interfacial region between the grain and the surrounding silica matrix. Two bands of photoluminescence are displayed in the 600 nm-900 nm range and correspond to the bands previously observed at 2 K. Their origin is demonstrated through a model based on the solution of the Schrodinger equation of the exciton wavefunction in a one-dimension geometry corresponding to the growth direction of the multilayers. The silicon layer as well as the Si-SiO2 interface thicknesses are the key parameters of the photoluminescence features.
TL;DR: In this article, the effects of both nanocrystal shape and applied magnetic field on the electron energy spectra of colloidal ZnO quantum dots have been investigated in the frame of finite element method, using nonuniform triangular elements.
Abstract: The effects of both nanocrystal shape and applied magnetic field on the electron energy spectra of colloidal ZnO quantum dots have been investigated in the frame of finite element method, using nonuniform triangular elements. Four shapes of quantum dots (spherical, ellipsoidal, rod-shaped, and lens-shaped) were studied. It was found that the physical properties of the semiconductor quantum dots could be manipulated by changing their size and/or their shape. The energies of an electron increase as one reduces the quantum dot shape symmetry from spherical towards the lens-shaped. The magnetic field effect strongly interplays with the nanocrystal size and the nanocrystal shape effects. Such interplay has been attributed to the competition of the quantum confinement effect introduced by the barrier potential and the quantum confinement effect introduced by the applied magnetic field.
TL;DR: In this article, the white light was achieved by controlling only the size distribution without adding any fluorescent ions, and the photoluminescence spectrum covered a wide range of 320 nm-700 nm with a full width at half maximum of approximately 190 nm.
Abstract: White-light-emitting silicon nanoparticles, whose surfaces were passivated with butyl, were prepared using a focused ultrasonic energy. The white light was achieved by controlling only the size distribution without adding any fluorescent ions. The white-light-emitting silicon nanoparticles had a wide size distribution of 1–5 nm and an average size of 2.7 nm, which were sufficiently small to indicate the quantum confinement effect for silicon. The photoluminescence spectrum covered a wide range of 320 nm–700 nm with a full width at half maximum of approximately 190 nm.
TL;DR: In this paper, the growth mechanism of quantum silicon nanowires (SiNWs) without catalyst is discussed based on VLS mechanism, and field emission from SiNWs arrays under various anode-cathode distances are analyzed based on Fowler-Nordheim theory.
Abstract: Quantum silicon nanowires (SiNWs) arrays have been synthesized by chemical vapor deposition template method without catalyst. The results of SEM and TEM reveal clear alignment of the SiNWs and each nanowire with perfect lattices is a single crystal. The growth mechanism of SiNWs without catalyst is discussed based on VLS mechanism. The unusual pattern in the Raman spectrum may be a unique characteristic of low-dimensional nano-scale materials. Enhanced photoluminescence properties may be associated with the quantum confinement effect and the formation of ordered arrays. Field emission from SiNWs arrays under various anode–cathode distances are analyzed based on Fowler–Nordheim theory. The superior field emission behavior is believed to originate from the oriented growth and the sharp tips of SiNWs.
TL;DR: In this paper, room-temperature piezoelectric photothermal spectroscopy (PPTS) measurements were carried out for the single-quantum-well (SQW) structures of GaInNAs.
Abstract: Room-temperature piezoelectric photothermal spectroscopy (PPTS) measurements were carried out for the single-quantum-well (SQW) structures of GaInNAs. Four as-grown samples with thicknesses of 10, 7, 5 and 3 nm were used to investigate the quantum confinement effect in the SQW. The exciton contribution was clearly distinguished from the two-dimensional step like band-to-band transition. The thickness dependence of PPT signal peak energy were well understood by quantum mechanics. The decrease in well thickness results in increases in quantized energy level and exciton binding energy. The present results showed that the newly developed PPT methodology is a unique and powerful tool for investigating the optical absorption spectra of extremely thin quantum well structures.
TL;DR: In this paper, a new synthetic method of HgSe quantum dots has been investigated through template controlling with emulsion liquid membrane system, which consists of kerosene as solvent, span80 as surfactant, N7301 as carrier, and HgCl2 solution as internalaqueous phase containing template of different concentrations, and uses gas-liquid transport on interface of external phase.
TL;DR: In this paper, a cubic phase HgTe nanocrystals with a mean size of 5.35 nm have been synthesized by an electrochemical technique and optical absorption measurements reveal two well resolved excitonic peaks around 578.5 nm and 550 nm attributed to heavy hole valence band (HVB)-conduction band (CB) and light hole value band (LVB) transitions, respectively.
Abstract: Mercury Telluride (HgTe) nanocrystals with a mean size of 5.35 nm have been synthesized by an electrochemical technique. Structural analysis by transmission electron microscopy and glancing angle X-ray diffraction studies indicate the presence of cubic phase HgTe nanocrystals in the deposit. Optical absorption measurements reveal two well resolved excitonic peaks around 578.5 nm and 550 nm attributed to heavy hole valence band (HVB)–conduction band (CB) and light hole valence band (LVB)–CB transitions, respectively, and suggest a band opening of bulk inverted narrow band gap HgTe as a result of strong quantum confinement effect (QCE). Visible photoluminescence (PL) of HgTe nanocrystals indicates free exciton transition around 579.5 nm as observed from the PL measurement at 300 K along with a bound exciton dominated band around 588 nm. Micro-Raman measurements at 300 K indicate the 1LO vibrational mode at 142.6 cm-1 shifted by 6 cm-1 from its standard bulk value and confirm the QCE.
TL;DR: In this paper, an exciton quantum dot in a Gaussian confining potential and an external magnetic field was explored by means of numerical matrix diagonalization within the effective mass approximation.
TL;DR: In this article, the size dependence of the exciton levels and the influence of the depth of the confining potential well in the spherical quantum dots are investigated, and the same calculations performed with the parabolic approximation of the Gaussian potential lead to the results.
Abstract: The exciton L = 0 and L = 1 states of a spherical GaAs quantum dot with a Gaussian confining potential are calculated by using the matrix diagonalization method. The size dependence of the exciton levels and the influence of the depth of the confining potential well in the spherical quantum dots are investigated. The same calculations performed with the parabolic approximation of the Gaussian potential lead to the results, which are qualitatively and quantitatively different.
TL;DR: Growth of CdS0.08Se0.92 nanocrystals embedded in glass is studied through the combinative analysis of optical absorption and photoluminescence (PL) spectroscopy at room temperature.
Abstract: Growth of CdS0.08Se0.92 nanocrystals embedded in glass is studied through the combinative analysis of optical absorption and photoluminescence (PL) spectroscopy at room temperature. The quantum confinement effect is observed in these structures. Average nanocrystal radii are found to be in the range of 2.3?4.2 nm with the help of a quantized state effective mass theory. Photoluminescence spectra are studied by means of the model of Ravindran et al (1999 Nanostruct. Mater. 11 603). The difference between the energies of the deep trap peak and first exciton peak is found to be ~0.2?0.3 eV. The possible sources of the overall shift in these peaks are also discussed.
TL;DR: In this article, the laser annealing effects on the structures and properties of silicon (Si) nanocrystal films fabricated by pulsed-laser deposition in inert argon gas were studied.
Abstract: We studied the laser annealing effects on the structures and properties of silicon (Si) nanocrystal films fabricated by pulsed-laser deposition in inert argon gas. The as-deposited samples show large particles (i.e., droplets) with size ranging from ∼100 nm to several μm on a uniform background film. The strong photoluminescence (PL) was from the background film rather than from the crystalline droplets. The consistency of the PL and crystal size from the background film supports the quantum confinement effect theory. After KrF excimer laser annealing, nanoparticles (NPs) with sizes of 10–50 nm were formed in the as-deposited films. In the vicinity of the droplets, the NPs were aligned together to form incident-light-angle-dependent cylindrical ripples which were caused by the interference of the incident light and the surface-scattered waves. The threshold fluence of surface melting was also reduced due to the interference. The intensity enhancement and blueshift of PL, the correlation between the indirect transition in optical absorption, and the bonding information in infrared spectra, further reveal the oxidation and ablation during the laser annealing process.
TL;DR: In this article, the particle size dependence, especially D-3 dependence of γ was clearly observed for the films which were prepared at different particle generation temperatures and annealed at 170°C, and consisted of particles of 26 to 46 nm in size.
Abstract: Silver particles generated by the evaporation-condensation method were deposited to form a film on a silica glass substrate. The films thus obtained consist of nano-sized silver particles. Nonlinear refractive index, γ and nonlinear absorption coefficient, β determined by using Z-scan technique were both negative, while γ in the literatures for the silver particles-dispersed-glass composites was positive. The absolute value of γ for the as-deposited samples was increased as absorption peak wavelength due to surface plasmon resonance became close to the laser wavelength used in the measurement. The particle size (D) dependence, especially D-3 dependence of γ was clearly observed for the films which were prepared at different particle generation temperatures and annealed at 170°C, and consisted of particles of 26 to 46 nm in size. This dependence was explained in terms of the quantum confinement effect.
TL;DR: In this article, a simple model taking into account the lens shape of ZnSe QDs is introduced to calculate the quantum confinement effects in lens-shaped QDs and obtained excitonic ground state transition energies are in good agreement with the experimental PL peaks.
Abstract: Self-assembled ZnSe quantum dots (QDs) embedded in ZnS were grown by metal-organic chemical vapour deposition and investigated with atomic-force microscopy (AFM) and photoluminescence (PL) measurements. Lens-shaped ZnSe QDs with the height of 1–2.4 nm and the radius of 25–37 nm are observed through the AFM measurements. The size and areal density of QDs increases as ZnSe deposition is increased. PL spectra of ZnSe QDs show consistent blueshifts due to quantum confinement effects. A simple model taking into account the lens shape of ZnSe QDs is introduced to calculate the quantum confinement effects in ZnSe QDs. Obtained excitonic ground state transition energies are in good agreement with the experimental PL peaks, which proposes that the model is adequate to describe the quantum confinement effect in lens-shaped ZnSe QDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the size and structure of silicon nanocrystals were confirmed by high-resolution transmission electron microscopy and the photoluminescence peak energy as E(eV) = 1.16 + 11.8/d2 is an evidence for the quantum confinement effect.
Abstract: Silicon nanocrystals were in situ grown in a silicon nitride film by plasma enhanced chemical vapor deposition. The size and structure of silicon nanocrystals were confirmed by high-resolution transmission electron microscopy. Depending on the size, the photoluminescence of silicon nanocrystals can be tuned from the near infrared (1.38 eV) to the ultraviolet (3.02 eV). The fitted photoluminescence peak energy as E(eV) = 1.16 + 11.8/d2 is an evidence for the quantum confinement effect in silicon nanocrystals. The results demonstrate that the band gap of silicon nanocrystals embedded in silicon nitride matrix was more effectively controlled for a wide range of luminescent wavelengths.
Journal Article•
TL;DR: In this paper, small size, large density and vertical ordering Ge quantum dots (QDs) were grown by ultra-high vacuum chemical vapor deposition (UHV/CVD) system.
Journal Article•
TL;DR: In this article, the quantum confinement effect of ZnO nano-particles and the laser scattering characteristic of particles with different scales, which are irradiated with different rays, are studied.
Abstract: The quantum confinement effect of ZnO nano-particles and the laser scattering characteristic of particles with different scale, which are irradiated with different rays, are studied. The optical characteristics of nano-material are verified from experiments and theories respectively.
TL;DR: In this article, a process of controlling the size of silicon quantum dots in SiO2 layers by Si+ implantation and rapid thermal annealing (RTA) is proposed.
Abstract: In this paper, a process of controlling the size of silicon (Si) quantum dots in SiO2 layers by Si+ implantation and rapid thermal annealing (RTA) is proposed. Through the proposed process, nanoscale Si islands in the range of 2–5 nm have been generated and then analyzed by various techniques including photoluminescence (PL) analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The characterization results are consistent with the results of theoretical computation based on the quantum confinement model by the finite-element method (FEM). The proposed process and results will be helpful in developing single-electron devices.
TL;DR: In this paper, the successful growth of ZnSe and ZnTe quantum dots (QDs) embedded in ZnS on GaAs substrate was reported, and it was found that the size of the QDs is controlled by the growth duration.
Abstract: We report the successful growth of ZnSe and ZnTe quantum dots (QDs) embedded in ZnS on GaAs substrate. These QDs have good optical properties and show quantum confinement effect. High-resolution electron scanning microscope studies show that these QDs are grown in Volmer-Weber mode. It is found that the size of the QDs is controlled by the growth duration. When the growth time is short, high density of QDs could be fabricated, but with a long growth time the small QDs get together to form a large cluster. We also show that with this growth method it is possible to grow both ZnSe quantum and ZnTe QDs on one substrate at the same time. For this dual QDs system, two peaks corresponding to the emission from the ZnSe dots (3.0 eV, blue-violet) and ZnTe dots (2.6 eV, green-blue) could be observed at the same time in the photoluminescence measurement.
TL;DR: In this article, a method based on the calculation of the image charge potential by solving Poisson equation in cylindrical coordinates was proposed to analyze the charging effects on electronic spectrum of Silicon (Si) based quantum wells.
Abstract: In order to analyze the charging effects on electronic spectrum of Silicon (Si) based quantum wells (QW’s), we use a method based on the calculation of the image charge potential by solving Poisson equation in cylindrical coordinates. The numerical results shows that the confined electron ground state energy level can be shifted by more than 50 meV due to the contribution of the image charges to the confinement potential of the graded quantum well.