共查询到20条相似文献,搜索用时 15 毫秒
1.
Shili Hou Huibing Mao Jiqing Wang Ziqiang Zhu Weiping Jing 《Applied Physics A: Materials Science & Processing》2009,94(4):795-797
Cadmium sulfide (CdS) quantum dots (QDs) prepared by a convenient chemical method have been characterized using absorption,
fluorescence, and photoluminescence excitation techniques. The photoluminescence excitation studies show that there is an
electron transfer from the surface adsorbate (thiourea) to CdS QDs in aqueous solution. The excitation band with peak maximum
at 5.8 eV is assigned to the electronic transitions in the chemisorbed thiourea, whereas the excitation band between 3.45
and 3.7 eV corresponds to the band-to-band transition within the nanocrystalline CdS host. The absorption spectroscopy of
the CdS QD solutions shows a strong absorption peak which is generated from thiourea. The band-edge fluorescence of the CdS
QDs has also been investigated. It is shown that the fluorescence property of the CdS QDs can be enhanced by adding cadmium
chloride (CdCl2) solution. 相似文献
2.
Properties of excitons in vertically coupled GaAs/AlGaAs quantum dots were investigated using the variational method within the envelope function and effective mass approximations. It was found that when the thickness of the spacer layer becomes less than about one exciton Bohr radius, both the exciton binding energy and the fundamental optical transition energy are reduced compared to those in isolated quantum dots. This is a result of increased space extension of exciton due to the penetration of carrier wave functions into the spacer layer and corresponding reduction in confinement energy which dominates over the Coulomb interaction between the electron and the hole. 相似文献
3.
Y. Chen D. Yu B. Li X. Chen Y. Dong M. Zhang 《Applied physics. B, Lasers and optics》2009,95(1):173-177
PbS quantum dots (QDs) have been incorporated in a Nafion membrane, where the QD sizes were adjusted by changing the reaction
time due to the steady growing process. The radiative emissions of the samples were investigated by optical absorption, photoluminescence
(PL), and time-resolved PL spectroscopy. Size-tunable emissions are shown by the PL spectrum in a range of 1.84–1.65 eV, and
the emission mechanism was investigated based on a four-band envelope-function model. Possible energy transitions for the
radiative emission are listed. The PL lifetime depending on the particle size is about one microsecond, and PL decay curves
exhibit a trend of decreasing decay time with an increase of the PbS QD size. 相似文献
4.
The photoluminescence correlation from a single CdSe nanocrystal under pulsed excitation is studied, and a single photon is
realized at wavelength 655 nm at room temperature. The single colloidal CdSe quantum dot is prepared on a SiO2/silicon surface by a drop-and-drag technique. The long-term stability of the single-photon source is investigated; it is
found that the antibunching effect weakens with excitation time, and the reason for the weakening is attributed to photobleaching.
The lifetimes of photoluminescence from a single quantum dot are analyzed at different excitation times. By analyzing the
probability distribution of on and off times of photoluminescence, the Auger assisted tunneling and Auger assisted photobleaching models are applied to explain
the antibunching phenomenon. 相似文献
5.
The influence of ligands on the preparation and optical properties of water-soluble CdTe quantum dots 总被引:1,自引:0,他引:1
Yao-hai Zhang 《Applied Surface Science》2009,255(9):4747-4753
In a systematic investigation has been found that ligands play an important role in both the water-phase preparation and optical properties of CdTe quantum dots. Experiments were performed using three typical thioalkyl acids as ligands, namely mercaptoacetic acid (MAA), l-cysteine (Cys) and reduced glutathione (GSH). The growth rate and size-distribution of CdTe quantum dots (QDs) are shown to depend on the type of ligands. A proper choice of ligand enables to make lager nanocrystals with narrower size-distribution. The effects of pH (buffer solution), illumination, heating and cations on the spectroscopic properties of CdTe QDs for the three ligands are reported. In addition, three same-size CdTe QDs were individually characterized by micellar electrokinetic capillary electrophoresis with laser-induced fluorescent detection, which proved their monodisperse size-distribution and different electric charge distribution on the surface for each of the three different type of QDs. 相似文献
6.
M. P. Lumb D. J. Farrell E. M. Clarke M. J. Damzen R. Murray 《Applied physics. B, Lasers and optics》2009,94(3):393-398
We have designed and grown a resonant, low-finesse quantum-dot saturable absorber mirror and subsequently modified the important
parameters using chemical etching. The modulation depth and saturation fluence at the design wavelength of 1064 nm were modified
by etching the sample to tune the cavity resonance. The device properties were characterised using normal incidence spectroscopic
reflectivity measurements, intensity dependent reflectivity measurements and modelled using a transfer matrix approach. The
saturable absorber mirror was used to facilitate self-starting, passively mode locked pulses in a neodymium vanadate laser
operating at 1064 nm. The etching was found to affect the duration of the pulses, leading to temporal width tuning over a
range of 94 ps. The shortest pulse duration of 84 ps was achieved for the cavity resonance close to 1064 nm, with an output
power of 3 W. This method is an effective technique for post-growth engineering of the properties of semiconductor saturable
absorber mirrors (SESAMs) with nanometre precision. 相似文献
7.
G. G. Adamian R. V. Jolos A. K. Nasirov 《Zeitschrift für Physik A Hadrons and Nuclei》1994,347(3):203-210
In the single-particle approach a partition of the excitation energy between the reaction products in deep inelastic collisions of heavy ions are investigated. The role of the particle-hole excitations and the nucleon exchange is considered. The ratio of the projectile excitation energy to the total excitation energy for the reactions238U(1468 MeV)+124Sn,238U(1398 MeV)+110Pd,56Fe(505MeV)+165Ho,74Ge (629 MeV)+165Ho and68Ni(880 MeV)+197Au is calculated. The results of calculations are in good agreement with the experimental data.We are grateful to Dr. N.V. Antonenko for valuable discussions. This work was supported partly by the Russian Minister for Education and Research under the Grant N2-61-13-28. 相似文献
8.
T. V. Kononenko P. Alloncle V. I. Konov M. Sentis 《Applied Physics A: Materials Science & Processing》2009,94(3):531-536
Blister-based laser induced forward transfer (BB-LIFT) is a promising technique to produce surface microstructures of various
advanced materials including inorganic and organic micro/nanopowders, suspensions and biological micro-objects embedded in
life sustaining medium. The transferred material is spread over a thin metal film irradiated from the far side by single laser
pulses through a transparent support. Interaction of the laser pulse with the metal–support interface under optimized conditions
causes formation of a quickly expanding blister. Fast movement of the free metal surface provides efficient material transfer,
which has been investigated for the case of diamond nanopowder and diamond-containing suspension. The unique features of the
given technique are universality, simplicity and efficient isolation of the transferred material from the ablation products
and laser heating. 相似文献
9.
S. Schulz S. Schumacher G. Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(1):51-60
We present an sp
3 tight-binding model for the calculation of the electronic and optical properties of wurtzite semiconductor quantum dots (QDs).
The tight-binding model takes into account strain, piezoelectricity, spin-orbit coupling and crystal-field splitting. Excitonic
absorption spectra are calculated using the configuration interaction scheme. We study the electronic and optical properties
of InN/GaN QDs and their dependence on structural properties, crystal-field splitting, and spin-orbit coupling. 相似文献
10.
Sword-like (diameter ranging from 40 nm to 300 nm) and needle-like zinc oxide (ZnO) nanostructures (average tip diameter ∼40 nm)
were synthesized on annealed silver template over silicon substrate and directly on silicon wafer, respectively via thermal
evaporation of metallic zinc followed by a thermal annealing in air. The surface morphology, microstructure, chemical analysis
and optical properties of the grown samples were investigated by field emission scanning electron microscopy, X-ray diffraction,
energy dispersive X-ray analysis, room temperature photoluminescence and Raman spectroscopy. The sword-like ZnO nanostructures
grown on annealed silver template are of high optical quality compared to needle-like ZnO nanorods for UV emission and show
enhanced Raman scattering. 相似文献
11.
A. A. Sirotkin L. Di Labio A. I. Zagumennyi Yu. D. Zavartsev S. A. Kutovoi V. I. Vlasov W. Lüthy T. Feurer A. A. Onushchenko I. A. Shcherbakov 《Applied physics. B, Lasers and optics》2009,94(3):375-379
The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking
of c-cut Nd:Gd0.7Y0.3VO4, Nd:YVO4, and Nd:GdVO4 lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition
rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results
in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz. 相似文献
12.
We have fabricated a Schottky diode embedding InAs self-assembled quantum dots (QDs) grown by alternately supplying In and As sources. As a function of the electric field, we have investigated the photoluminescence (PL) for the InAs QDs in the Schottky diode at 300 K. We controlled the electric field in order that the QD layer was located in the depletion region of Schottky diode. The relationship between the electric field and the depletion width of the Schottky diode was deduced through the capacitance-voltage measurement. The Stark shift was observed in PL spectra for QDs; the energy of the PL line shifted to the lower energy as the electric field increased. It was also observed that the PL emission intensity gradually decreased. By the fitting to the experimental data, we determined a built-in dipole moment, corresponding to an electron-hole separation. 相似文献
13.
X. Q. Xi J. B. Gong T. Zhang R. H. Yue W. M. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(2):193-199
For the process of electron-electron (e-e) bremsstrahlung the momentum and energy distributions of the recoiling electrons
are calculated in the laboratory frame. In order to get the differential cross section and the photon spectrum for target
electrons which are bound to an atom, these formulae are multiplied by the incoherent scattering function and numerically
integrated over the recoil energy. The effect of atomic binding is most pronounced at low energies of the incident electrons
and for target atoms of high atomic numbers. The results are compared to those of previous calculations. 相似文献
14.
A recent investigation of the possibility of having a
-symmetric periodic potential in an optical lattice stimulated the urge to generalize non-hermitian quantum mechanics beyond
the case of commutative space. We thus study non-hermitian quantum systems in non-commutative space as well as a
-symmetric deformation of this space. Specifically, a
-symmetric harmonic oscillator together with an iC(x
1+x
2) interaction are discussed in this space, and solutions are obtained. We show that in the
deformed non-commutative space the Hamiltonian may or may not possess real eigenvalues, depending on the choice of the non-commutative
parameters. However, it is shown that in standard non-commutative space, the iC(x
1+x
2) interaction generates only real eigenvalues despite the fact that the Hamiltonian is not
-symmetric. A complex interacting anisotropic oscillator system also is discussed. 相似文献
15.
R. Guo J. Nishimura M. Matsumoto M. Higashihata D. Nakamura T. Okada 《Applied physics. B, Lasers and optics》2009,94(1):33-38
Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition
(NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about
2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction
diodes and was intensified by increasing the applied voltage up to 30 V. 相似文献
16.
Temperature dependence of photoconductivity and persistent photoconductivity of single ZnO nanowires 总被引:1,自引:0,他引:1
Zhi-Min Liao Yi Lu Jun Xu Jing-Min Zhang Da-Peng Yu 《Applied Physics A: Materials Science & Processing》2009,95(2):363-366
Photoelectrical properties of single ZnO nanowires have been investigated using photocurrent–voltage characteristics measurements
varying with excitation photon energy and temperature. It is found that persistent photoconductivity (PPC) exists, and the
PPC decreases with decreasing temperature. The temperature dependence of the PPC effect indicates that thermally activated
return of electrons from shallow traps is responsible for the PPC phenomenon. The photosensitivity is found to be linear with
the applied voltage, and it increases with decreasing temperature. A temperature dependence of photoconductivity gain was
introduced to explain the experimental results. 相似文献
17.
Bing Liu Zhendong Hu Yong Che Arnold Allenic Kai Sun Xiaoqing Pan 《Applied Physics A: Materials Science & Processing》2008,93(3):813-818
In this work, we study the application of ultrafast pulsed laser deposition (PLD) in ZnO nanomaterial synthesis, including
nanoparticles and nanorods. PLD using long pulse (nanosecond) lasers has been widely used as a method for growing prototype
materials. The recently-emerged ultrafast PLD is expected to be able to overcome the problem of large liquid droplet formation.
Using near infrared and femtosecond laser pulses in ablation, we first characterize the ablation plume using a Langmuir probe
and plasma optical emission spectroscopy. We then examine the structural properties of the nanoparticles generated during
low-fluence ablation. Finally, we demonstrate that using nanoparticle aggregates as templates, assisted by plume-excited nitrogen
radicals at a high fluence, high quality ZnO nanorods can be grown free of metal catalysts. 相似文献
18.
Germanium (Ge) nanocrystals embedded in silica matrix is an interesting material for new optoelectronic devices. In this paper,
standard silica-on-silicon waveguides with a core doped by Ge nanocrystals were fabricated using plasma enhanced chemical
vapour deposition and reactive ion etching. The cross-sectional waveguide structures were investigated by scanning electron
microscopy. Transmission of the waveguide was measured using a broadband light source covering the wavelength range from 500
nm to 1700 nm, and the results were compared against transmission through a standard waveguide. Strong absorption peaks at
1056.8 nm, 1263.2 nm and 1406 nm were observed. These are assigned to the quantum confinement effect in Ge nanocrystals in
the core. Putting Ge nanocrystals in a waveguide enables easy material characterisation and potential application in an integrated
lightwave circuit device. 相似文献
19.
A. K. Atayan E. M. Kazaryan A. V. Meliksetyan H. A. Sarkisyan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):485-492
The absorption of light in an ensemble of non-interacting cylindrical quantum dots in the presence of a magnetic field is
discussed using a model consisting of dots with rectangular infinitely-high potential barriers. The ensemble’s absorption
coefficient is calculated — as well as the threshold frequency of absorption — as a function of the applied magnetic field
and the quantum dot size. Theoretical results are compared with experimental data on magneto-luminescence in an In0.53Ga0.47As/InP cylindrical quantum dot system. In addition, using a perturbation theory framework, the influence of excitonic effects
on the behaviour of the electron-hole energetic spectrum of said system is discussed. 相似文献
20.
Wei Wu Ekaterina Ponizovskaya Evgenia Kim David Cho Alexander Bratkovsky Zhaoning Yu Qiangfei Xia Xuema Li Y. Ron Shen S. Y. Wang R. Stanley Williams 《Applied Physics A: Materials Science & Processing》2009,95(4):1119-1122
We have studied the geometry dependency of fishnet-like negative refractive index meta-materials (NIMs), and developed a process
to fabricate such NIMs using nanoimprint lithography (NIL) in a controlled way for it to achieve negative refractive index
in the desired frequency range. As an example, we fabricated a fishnet structure with a minimum negative refractive index
of −1.7 at 1560 nm, which was only 10 nm off the targeted wavelength of 1550 nm. 相似文献