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Previous studies of the gold-nanoparticles-covered U-type medical optical fiber sensor with millimeter size were mainly confined to the experimental aspect, while the corresponding theoretical studies were only for bare fibers based on geometrical optics or those for micron level photonic crystal fibers based on wave optics. Combining wave and geometrical optics, the gold-nanoparticles-covered U-type optical fiber sensor was simulated with millimeter size. The localized surface plasmon resonance absorption peak near 540 nm is obtained in the simulation, very close to that (≈560 nm) of the experimental value for the gold nanoparticles of 37 nm size. Compared with the refractive index (RI) sensitivity (≈7.10/RIU) for the plain, U-type optical fiber (≈43.50/RIU) exhibits more than 610% enhancement in the gold-nanoparticles-covered sample. Present studies would be helpful to the further simulation and design for various noble metal nanoparticles covered optical fiber sensors with different shapes.

As an important technology of the quantum detection, the quantum synchronization detection is always used in the detection or measurement of some quantum systems. A probing model is established to describe the probing of a qubit system in the cavity field and to reveal the effect of the environment (cavity) on the quantum synchronization occurrence, as well as the interactions among environment, a qubit system, and probing equipment. By adjusting the frequency of the probe, the in-phase, anti-phase, and out-of-phase synchronization can be achieved. Simultaneously, the effect of γ 3 ${\gamma }_{3}$ which describes the interaction strength between the probe and environments for quantum synchronization is discussed under different Ohmic dissipation index s . Finally, the machine learning method is applied to present an optimization for classification and regression of synchronization transition dependent on s and γ 3 ${\gamma }_{3}$ .

The local structure, d-d transition band as well as spin Hamiltonian parameters (SHPs) are theoretically studied for the V4+ probe in 10Na2 O-30PbO-10Bi2 O3 -(50-x)SiO2 (NPBS) glass ceramics containing V2 O5 dopant with various concentration x (0 ≤ x ≤ 5 mol %) by using the perturbation formulas of the SHPs for tetragonally compressed octahedral 3d1 clusters. The first decreasing (or increasing) and then increasing (or decreasing) d-d transition band (= 10 Dq ) and hyperfine structure constants A// and A⊥ (or g factors g// and g⊥ ) with x can be suitably simulated with the similarly varying Fourier type concentration functions of cubic field parameter Dq , covalence factor N, core polarization constant κ and reduction factor H (or relative tetragonal compression ratio ρ), with the minima (or maxima) at the middle concentration x = 3 mol %, respectively. The above concentration variations of SHPs and the related quantities may originate from the modifications of local crystal-field strength, tetragonal compression and electron cloud distribution near the impurity V4+ with x, corresponding to the highest [V4+ ]/[V5+ ] ratio at 3 mol %. Present studies would be helpful to explore novel sodium lead bismuth silicate glass ceramics by modifying the concentration of V2 O5 dopant.

As a universal quantum character of quantum correlation, the freezing phenomenon is researched by geometry and quantum discord methods, respectively. In this paper, the properties of Rènyi discord is studied for two independent Dimer System coupled to two correlated Fermi-spin environments under the non-Markovian condition. We further demonstrate that the freezing behaviors still exist for Rènyi discord and study the effects of different parameters on this behaviors.

As an important technology of the quantum detection, the quantum synchronization detection is always used in the detection or measurement of some quantum systems. A detection schemes are key to the study of quantum system. The quantum synchronization detection which is presented between the probe and the quantum system is always used in detection application. A probing model is established to describe the probing a qubit system in the cavity field and to reveal the effect of the environment (cavity) on the quantum synchronization occurrence as well as the interactions among environment, a qubit system and probing equipment. By adjusting the frequency of the probe, the in-phase and out-of-phase synchronization can be achieved. So the information of the probe can be used to obtain the quantum system. Simultaneously, the effect of \({\gamma }_{3}\) which describes the interaction strength between the probe and environments for quantum synchronization is discussed under different the values of Ohmic dissipation index s. Finally, the machine learning method is applied to present an optimization for classification and regression of synchronization transition dependent on s and \({\gamma }_{3}\). This opens the way for studying the generalized form of quantum synchronization through machine learning algorithms (Artificial neural network) in the future.

The local structure, d-d transition band, and spin Hamiltonian parameters (SHPs) are theoretically studied for the V

Sensing of whispering-gallery-modes in a microring resonator coated with a fluorescent high-refractive-index film is modeled using finite-difference time-domain method. A short pulse with ultrawide bandwidth in the high-index film spans the circumference of the ring. The spectra of the high-index film and the pulse propagation in time domain were simulated. The results indicate redshifts of the resonance wavelengths with an increasing refractive index inside the ring. A sensitivity of 28.5 nm/RIU is found for the index of 1.48. Considering the effects of scattering and absorption of a single object adhered to the inner surface of the microring, an obvious splitting or broadening of resonance modes is found for sensing. For single particles with a radius of 3 μm, the mode splitting is increased with increasing number of particles from one to nine. The estimation of the size of the particles is also studied based on the mode splitting of the optical field in the ring depends on the scattering of the particles. This work reveals the potential applications of whispering-gallery-modes in a microring resonator coated with a fluorescent high-index film for sensing one or multiple objects and even a single molecule.

The electron paramagnetic resonance parameters and local structures for V4 + in xV2O5-(100 − x)[0.8NaPO3-0.2ZnO] glasses are theoretically investigated by using the perturbation formulas for tetragonally compressed octahedral 3d1 clusters. Polynomial, custom and power law functions are applied to describe the concentration variations of covalency factor N, relatively tetragonal compression ratio ρ, core polarization constant κ and reduction factor H. The concentration dependences of the measured electron paramagnetic resonance parameters are suitably reproduced, and the PL functions are found to be the optimal with the lowest mean absolute percentage deviation from the experimental data. The [VO6]8 − clusters exhibit moderately decreasing N, rapidly increasing ρ, slightly decreasing κ and moderately increasing H with x. The calculated decreasing local optical basicity Λloc also supports the declining trend of covalency factor. The theoretical study of the microscopic mechanisms for the concentration dependences of the relevant quantities are discussed in view of the impurity local behaviors with x due to mixed alkali effect.

The defect structure, d-d transition and EPR parameters for V4+ in 10CaF2-(20-x)Bi2O3-60P2O5-10B2O3-xV2O5 (CBPB) glasses with distinct V2O5 contents x are theoretically investigated from the perturbation formulas for tetragonally compressed octahedral 3d1 clusters. Linearly decreasing cubic field parameter Dq or increasing g|| and g⊥ with x are suitably reproduced by linearly decreasing content function of Dq or decreasing and increasing content functions of covalence factor N and relative tetragonal compression ratio τ. The overall slightly increasing and decreasing average and anisotropy of hyperfine structure constants are illustrated as the cubic increasing content functions of core polarization constant κ and reduction factor H. These content dependences are ascribed to the modulations in local tetragonal compression, crystal-field strength and electron cloud distribution near V4+ with x. V2O5 as strong network modifier inducing depolymerization of phosphate long chains and Bi2O3 as network former and modifier exhibiting discontinuous changes with x may account for these modifications of the local structural properties.

Density functional theory (DFT) calculations of the structures and the Cu2+ g factors (g x , g y and g z ) and hyperfine coupling tensor A (A x , A y and A z ) were performed for the paddle-wheel (PW)-type binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) powder and single crystal. Calculations were carried out with the ORCA software using the functionals BHandHlyp, B3P86 and B3LYP with five different basis sets: 6-311g, 6-311g(d,p), VTZ, def-2 and def2-TZVP. Results were tested by the MPAD analysis to find the most suitable functional and basis sets. The electronic structure and covalency between copper and oxygen were investigated by the electron localisation function and the localised orbital locator as well as the Mayer bond order for the [CuO5] group. The optical spectra were theoretically calculated by the time-dependent DFT module and plotted by the Multiwfn program for the [CuO5] group and reasonably associated with the local structure in the vicinity of the central ion copper. In addition, the interactions between the OCNH2CH3, NH3 and H2O molecules and the uncoordinated PW copper(II) complex were studied, and the corresponding adsorption energies, the frequency shifts with respect to the free molecules and the changes of the Cu–Cu distances were calculated and compared with the relevant systems.

Based on the density functional theory (DFT) method, the geometrical structures, relative stability, electronic, and spectral properties of AuSn (2 ≤ n ≤ 7) clusters are systematically studied, whose sizes are largely in the range of 0.3–0.5 nm. AuS4 and AuS3 show the highest and lowest energy gaps and hence the highest chemical stability and chemical activity, respectively. The total magnetic moment is 3.0 and 1 (or 0) μB for AuS4 and other clusters, respectively, which largely (about 99.9%) arise from the local magnetic moment of S atoms. The average polarization tensor for single atom ( ) generally increases with increasing the number of S atoms, with the maximum 91.72 a.u. for AuS7, corresponding to the most significant delocalization effect. AuS4 cluster exhibits the highest polarizability anisotropic invariant Δα (≈ 350.56 a.u.) and the lowest total dipole moment (≈ 0.06 D) among all systems, corresponding to the strongest anisotropic response to external electric field and the weakest polarization, respectively. The IR, Raman, UV-Vis, and PES spectra are simulated for AuSn (2 ≤ n ≤ 7) clusters with the structures of the lowest isomers. The O–O and O–H bond lengths, adsorption energies, vibration frequencies, and density of states are also calculated for AuS4 and AuS3 adsorbing one O2 and H2O molecules, respectively. The adsorption capacity of AuS3 for both gas molecules is higher than AuS4, and AuSn (n = 3, 4) clusters are more favor to adsorb O2 than H2O.

The defect structures and spin Hamiltonian parameters (SHPs) for V4+ in lead halo borate (xPbX2–(30 − x)PbO–68B2O3, X = F, Cl, Br and x = 5, 10, 15, 20 and 25 mol%) glass composites containing 2 mol% of V2O5 dopant are theoretically studied by applying the perturbation formulas of the SHPs for tetragonally compressed octahedral 3d1 clusters. The experimental SHPs are suitably reproduced by the optimal covalency factor N, relative tetragonal compression ratio ρ, core polarization constant κ and reduction factor H at various x, which are simulated with the corresponding Fourier type content functions. The distinct deviations of these quantities from the relevant simulated Fourier type content functions at 5 mol% of PbCl2 and PbBr2 are reasonably explained from the modifications of compactness and electronic cloud redistributions around V4+ at this content. This is supported by the previous analysis on the content variations of ionic conductivity of the systems.

The quantum correlation in open quantum systems is of fundamental and practical importance for quantum information processing and controllable nanometer devices. And the properties of quantum correlation can be influenced by the information flow between systems and environments. In this study, we investigated the geometric measure discord of quantum correlation of a two qubits system, interacting with two independent and intrinsic interacting spin-environments, respectively. Based on the asymmetry environments with comparable parameters, the different properties of the geometric measure of entanglement and quantum discord are displayed and discussed for initial Bell states.

The electron paramagnetic resonance (EPR) parameters of three copper complexes (Cu(ClO4)2·6H2O, the supported Cu(BOX)(ClO4)2 complex (5) and the surface-functionalized Cu(BOX)(ClO4)2 complex (6j), with BOX = bis(oxazoline)) are systematically investigated from the perturbation formulas of these parameters for a rhombically elongated octahedral 3d9 groups. Cu(ClO4)2·6H2O exhibits the weakest covalency and the largest g anisotropy Δg (=gz - (gx + gy)/2) among these systems. Compared with the octahedral [CuO6] group in Cu(ClO4)2·6H2O, the larger elongation distortions in the two supported Cu-BOX complexes (5) and (6j) can be interpreted as the absence of two apical ligands from an ideal octahedron and the stronger crystal-fields arising from the two planar ligands N−. In consideration of the local elongation distortions, crystal-field strength and covalency, the features of the EPR parameters (i.e., anisotropy Δg, average of g factors and the ratio |gz/Az|) are uniformly discussed for these systems.

As an important resource to realize quantum information, quantum correlation displays different behaviors, freezing phenomenon and non-localization, which are dissimilar to the entanglement and classical correlation, respectively. In our setup, the ordering of quantum correlation is represented for different quantization methods by considering an open quantum system scenario. The machine learning method (neural network method) is then adopted to train for the construction of a bridge between the R\`{e}nyi discord ($\alpha=2$) and the geometric discord (Bures distance) for $X$ form states. Our results clearly demonstrate that the machine learning method is useful for studying the differences and commonalities of different quantizing methods of quantum correlation.

EPR parameters and local structures for V4+ in xNb2O5•(30-x)A2O•69B2O3 (NAB, where A = Li, Na, K; x = 0, 4, 8 mol%) glasses are theoretically studied using the perturbation formulas of EPR parameters for tetragonally compressed octahedral 3d1 clusters. From the quasi-linear concentration variations for covalency factor N, tetragonal compression ratio ρ and core polarization constant κ with only three adjustable coefficients, the concentration dependences of EPR parameters are suitably interpreted. N increases linearly for NLB (0.839–0.864) and NNB (0.801–0.811) with x (0–8 mol%) but shows the quadratic decrease for NKB (0.802, 0.807, 0.801 at 0, 4 and 8 mol%), whereas ρ and κ decrease linearly. For different alkali metal A at the same x, N decreases with increasing ionicity of A, while ρ and κ increase due to declining force constant of V4+–O2– bond and enhancing vanadium 3d-3 s (4 s) orbital admixtures, respectively.

A finite difference technology is applied to the InAs/InGaAs/GaAs quantum dots-in-a-well (DWELL) structures in order to determine their electronic properties. Conventional quantum dots (QDs) sample has a simple structure, i.e., the QDs are imbedded in a GaAs bulk medium. In stead of the conventional structure, we prefer the weak confinement DWELL structure because it can efficiently lower the intersubband transition energy. Thus the DWELL detector is expected to make the longer wavelength detection possible. Present method used in this study is demonstrated to be efficient and flexible for determining the electronic state of the DWELL system. However, to our knowledge there has been no literature reporting so far on the electronic structure of DWELL characterized by the finite difference method.

Based on the quantum master equation which describes the dynamical evolution of a two-level atom interacting with one mode of the quantized photon field in a cavity, we have investigated the systemic dissipative and decoherence properties by use of the development algebraic dynamic method for the automatic and non-automatic condition. Furthermore, using the exact solution of the quantum master equation, we have investigated the asymptotic behaviours of the system.

Based on algebraic dynamics and the concept of the concurrence of the entanglement, we investigate the evolutive properties oft he two-qubit entanglement that formed by Heisenberg XXX models under a time-depending external field. For this system, the property of the concurrence that is only dependent on the coupling constant J and total values of the external field is proved. Furthermore, we found that the thermal concurrence of the system under a static random external field is a function of the coupling constant J, temperature T, and the magnitude of external field.

Using first-principles calculations, the elastic constants, the thermodynamic properties, and the structural phase transition between the B1 (rocksalt) and the B2 (cesium chloride) phases of NaCl are investigated by means of the pseudopotential plane-waves method. The calculations are performed within the generalized gradient approximation to density functional theory with the Perdew-Burke-Ernzerhof exchange-correlation functional. On the basis of the third-order Birch-Murnaghan equation of states, the transition pressure Pt between the B1 phase and the B2 phase of NaCl is determined. The calculated values are generally speaking in good agreement with experiments and with similar theoretical calculations. From the theoretical calculations, the shear modulus, Young's modulus, rigidity modulus, and Poisson's ratio of NaCl are derived. According to the quasi-harmonic Debye model, we estimated the Debye temperature of NaCl from the average sound velocity. Moreover, the pressure derivatives of elastic constants, partial differentialC11/partial differentialP, partial differentialC12/partial differentialP, partial differentialC44/partial differentialP, partial differentialS11/partial differential P, partial differentialS12/partial differentialP, and partial differentialS44/partial differentialP, for NaCl crystal are investigated for the first time. This is a quantitative theoretical prediction of the elastic and thermodynamic properties of NaCl, and it still awaits experimental confirmation.

We study the dynamics evolution of a two-qubit Heisenberg XXX spin chain under a time-dependent rotating magnetic field. Based on the algebraic structure of the non-autonomous system, the exact solution of the Schrodinger equation is obtained by using the method of algebraic dynamics. Based on the time-dependent analytical solution, we further study the entanglement evolution between the two coupled spins For different initial states, and find that the entanglement is determined by the coefficients of the initial state and the Coupling constant J of the system.

Based on the homotrinuclear spin cluster having SU(2)⊗SU(2) symmetry with twofold orbital degeneracy τ = 1/2) and the SU(2) algebraic structures of both ŝ and τˆ subspaces in the external magnetic field, we calculate exactly the non-adiabatic energy levels and the cyclic and non-cyclic non-adiabatic geometric phase of the homotrinuclear spin cluster by making use of the method of algebraic dynamics. The solution will show that the Berry phase is much influenced by the parameters N =γs/γτ (γs and γτ are the magnetic momentums of ŝ and τ̂ subspaces, respectively) in addition to ω/Ω in a rotating magnetic field. The change of the Berry phase in the basis state of the system is demonstrated from the changing diagram.

Using the method of algebraic dynamics, we investigate the h omega(4) non-autonomous quantum system, which is formed by a single molecule within a harmonic potential driven by laser radiation field and obtain the exact solutions of the system. Based on the exact solutions, in particular on the features of the diabatic energy levels, then we proceed to studying the geometric phase of the system. From the above results, we may determine the vibration frequency of the molecule by measuring the changes in the properties of geometric phase. (C) 2007 Elsevier B.V. All rights reserved.

Based on the non-autonomous quantum master equation which describes the collision between a two-level system and other atoms or molecules, we investigate the systemic dissipative and decoherence properties. Using a novel algebraic dynamic method, we found the SU ( 2 ) ⊕ U ( 1 ) dynamical symmetry of this system and obtained the exact solutions. Furthermore, the asymptotic behaviors of the master equation have been investigated.

In this paper, the non-Markovian dynamics of a two spin-qubits system which interacts with two correlated spin-environments have been researched. Using the quantification of quantum features, a trace distance which quantifies the degree of non-Markovian processes, the Concurrence of the entanglement and the Quantum Discord which has been applied to measure quantum correlations, we show that the feedback of information, entanglement and quantum correlation can be affected as a function of the coupling parameter q of the environments and time t for different temperature T and the system initial states. Especially, we show that the quantum correlation between two spin-qubits increases with the strengthening coupling between the environments strengthen and that the entanglement does not account for all nonclassical correlations.

Structural and magnetic characteristics of Fe3-xSnxO4 (x < 0.3) nanoparticles synthesized using the precipitation exchange method have been investigated by X-ray diffraction, transmission electron microscope, Mossbauer spectra, X-ray photoelectron spectroscopy and magnetization measurement. The mean particle dimension decreases from 8 to 6 nm, the lattice parameters enlarge, the saturation magnetization decreases, as well as the magnetization and the coercive field increase, with increasing tin-content. The paramagnetic property of the specimens indicates that the replacement of Fe3+ by Sn4+ on the octahedral sites of Fe3O4 causes a progressive lowering of the Curie temperature and the Curie temperatures of the materials are all lower than that of crystallite tin-doped magnetite. This striking debasing is due to the lessening of the grain size. This is the smallest size reported thus far for paramagnetic tin-doped magnetite particles. (c) 2006 Elsevier B.V. All rights reserved.

By diagonalizing the complete energy matrix of a d4 configuration ion in tetragonal symmetry, the zero-field-splitting parameters a, D and F of InP:Cr2+ have been studied. The local structure distortion parameters ΔR = 0.08 Å and Δθ = 1.01◦ were estimated. They show an expansion distortion around Cr2+ in the InP semiconductor. The Jahn-Teller energy EJT is found to be about 413 cm−1, which agrees well with the experiment. - PACS numbers: 75.10.Dg; 76.30.-v

The complete energy matrix including all the spin states is constructed for d(4) ions in tetragonal symmetry within a strong-field representation. The excitation levels, fine-structure splitting, and EPR parameters in Rb2CrCl4 and CrF2 are studied with the energy matrix. The contributions of the spin singlets to zero-field splitting (ZFS) are investigated for the first time. The results show that the spin-singlet contribution to D is negligible, but the contributions to a and F cannot be neglected.

The role of dislocation scattering in electron mobility in ZnMgO/ZnO heterostructures was studied. It was found that dislocation scattering was dominant in the low-electron concentration region. The total low-temperature mobility was calculated by considering dislocation scattering and interface-roughness scattering (IRS) together. The sheet density of dislocations was chosen as Ndis=1.5 × 108 cm-2 and the IRS parameters were Δ = 5.206 and Λ = 30 Å. We obtained a good fit between our calculated results and experimental data reported in the works referenced.

A two qubits system interacting with two independent spin-environments connecting with the third environment is constructed in order to demonstrate the effect of the multi-environment for quantum correlation. In this process, the freezing phenomenon appears for SCI and X states under Quantum Discord and Geometric Discord measures, respectively, but not for the same initial state measured by different measures. Meanwhile, the properties of the freezing platform, characterized by the collapse, revival and persistent time, are researched by the different parameters. The result of this paper may pave a way to control quantum correlation and design nanospintronic devices.

Deep trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8 x 10(19) cm(-3), but the hole concentration was as low as 1.3x10(17) cm-3 at room temperature. The DLTS spectrum has a dominant peak D-1 with an activation energy of 0.41+/-0.05 eV, accompanied by two additional peaks with activation energies of 0.49+/-0.09 eV (D-2) and 0.59+/-0.05 eV (D-3). It was found that the dominant peak D-1 consists of five peaks, each of which has different activation energy and capture cross section. In order to investigate these deep levels further, we performed heat treatment on the same samples to observe the variations of activation energy, capture cross section, and amplitude of DLTS signals. It was found that the longer the heat treatment duration is, the lower the amplitude of DLTS peaks become. This suggests that the decrease of the DLTS signal originates from hydrogen atom outgoing from the film during the annealing process. The possible originality of multiple trap levels was discussed in terms of the Mg-N-H complex. (C) 2000 American Vacuum Society. [S0734-2101(00)01701-2].

We use a polarizer to investigate quantum-well infrared absorption, and report experimental results as follows. The intrasubband transition was observed in GaAs/AlxGa1-xAs multiple quantum wells (MQWs) when the incident infrared radiation (IR) is polarized parallel to the MQW plane. According to the selection rule, an intrasubband transition is forbidden. Up to now, most studies have only observed the intersubband transition between two states with opposite parity. However, our experiment shows not only the intersubband transitions, but also the intrasubband transitions. In our study, we also found that for light doping in the well (4x10(18) cm(-3)), the intrasubband transition occurs only in the lowest subband, while for the heavy doping (8x10(18) cm(-3)), such a transition occurs not only in the lowest subband, but also in the first excited one, because of the electron subband filling. Further experimental results show a linear dependence of the intrasubband transition frequency on the root of the well doping density. These data are in good agreement with our numerical results. Thus we strongly suggest that such a transition can be attributed to plasma oscillation. Conversely, when the incident IR is polarized perpendicular to the MQW plane, intersubband-transition-induced signals appear, while the intrasubband-transition-induced spectra disappear for both light and heavy well dopings. A depolarization blueshift was also taken into account to evaluate the intersubband transition spectra at different well dopings. Furthermore, we performed a deep-level transient spectroscopy (DLTS) measurement to determine the subband energies at different well dopings. A good agreement between DLTS, infrared absorption, and numerical calculation was obtained. In our experiment, two important phenomena are noteworthy: (1) The polarized absorbance is one order of magnitude higher than the unpolarized spectra. This puzzling result is well explained in detail. (2) When the IR, polarized perpendicular to the well plane, normally irradiates the 45 degrees-beveled edge of the samples, we only observed intersubband transition spectra. However, the intrasubband transition signals caused by the in-plane electric-field component are significantly absent. The reason is that such in-plane electric-field components can cancel each other out everywhere during the light propagating in the samples. The spectral widths of bound-to-bound and bound-to-continuum transitions were also discussed, and quantitatively compared to the relaxation time tau, which is deduced from the electron mobility. The relaxation times deduced from spectral widths of bound-to-bound and bound-to-continuum transitions are also discussed, and quantitatively compared to the relaxation time deduced from electron mobility. [S0163-1829(98)01912-2].

Infrared absorption due to a collective excitation of a two-dimensional electronic gas was observed in GaAs/AlxGa1-xAs multiple-quantum wells when the incident light is polarized parallel to the quantum-well plane. We attribute this phenomenon to a plasma oscillation in the quantum wells. The measured wavelength of the absorption peak due to the plasma oscillation agrees with our theoretical analysis. In addition, in this study the plasma-phonon coupling effect is also fitted to the experimental result. We show that the absorption is not related to the intersubband transitions but to the intrasubband transition, which originates from a plasma oscillation.

Three-dimensional GaN pyramids have been successfully obtained on submicron dot-patterned (0001) sapphire substrates by using the selective metalorganic vapor phase epitaxy (MOVPE) technique. The dot-pattern is a hexagon arranged with a 0.5-mu m width and 1.0-mu m spacing. The GaN structure comprises a hexagonal pyramid covered with six {1 (1) over bar 01} pyramidal facets on the side of a hexagonal pyramid having a (0001) facet on the top. Cathodoluminescence (CL) measurement was carried our. on the hexagonal pyramid at low temperature. Two distinct spectra were observed to occur at about 359 and 329 nm. The higher energy is thought to be related to GaN dot, and the lower one is due to GaN dot band edge emission. The intensities of the two spectra were investigated as a function of temperature in the range of 135-150 K. (C) 2000 Published by Elsevier Science B.V.