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High quality ZnO nanostructures were grown directly on sapphire subtracts by metal organic vapor deposition. By changing the growth conditions, the different nano structures (nanorods,nanotubes, nanowalls, nanonetworks) can be selectively. These nanostructures were all epitaxially grown and had the same epitaxial relationship with respect to the substrate. Mechanisms corresponding to different nanostructures were discussed. The nanostructures exhibited stable excitonic states at room temperature, and the emission due to exciton-exciton scattering was observed

Epitaxial films of ZnO have been synthesized by the sol-gel method using ZnO buffer layers on sapphire (001) substrates. The buffer layers of 50-nm ZnO were epitaxially grown by metal organic chemical vapor deposition prior to the sol-gel process and significantly improved the crystallinity of the sol-gel ZnO. The six-fold symmetry observed in X-ray diffraction φ-scan spectra confirmed the epitaxial nature of the sol-gel ZnO films. Excitonic recombinations were dominant in the photoluminescence, while defect-related emissions around 3.31 to 3.32 eV, which are commonly observed in polycrystalline sol-gel films, were not observed in the sol-gel ZnO with ZnO buffer layers.

We compared the nano-structures of three samples of ZnO thin film on sapphire under different growth temperature conditions. Although disconnected domain structures (on the scale of 100 nm in size) were observed in the samples of high-temperature (450 °C) growth, their crystal quality is generally better than the one grown at a low temperature (200 °C), either near or away from the sapphire interface. Lattice misfits and threading dislocations were observed within a domain with the separation of around 8 nm. The sample grown at the low temperature showed a continuous structure through the ZnO layer although void-like structures might exist inside. However, its crystal quality is relatively poorer. Of the two samples with high-temperature growth, the one with initial low-temperature growth had a larger domain structure (around 150 nm in size) and relatively lower crystal quality. In particular, strong strains existed near the interface of this sample. The samples of high-temperature growth generally have higher photon emission efficiencies. Temperature-dependent integrated photoluminescence intensities of the high-temperature-growth samples show that the exciton trapping by either intrinsic donors or acceptors leads to a higher thermal quenching rate in comparison with free excitons.

Nucleation and growth kinetics of II-O epitaxial layers deposited on SiC substrates have been investigated. ZnO nucleates initially with islands and switches to coalescences and grains with the increase of layer thickness, while MgxZn1−xO alloys grow with two-dimensional growth mode. The strain kinetics due to the driving force Δa/a favors the coherent growth of ZnO for the layer thickness of

Growth of ZnO films on Si (1 1 1) substrates has been carried out at temperatures ranging from 300 to 475 °C by metal organic chemical vapor deposition (MOCVD) technique. A multilayer-tower structure was observed for the film deposited at 300 °C. For the films deposited at higher temperatures, nanorods accompanied with nanotubes were observed. The X-ray diffraction measurement shows that the film deposited at 425 °C has better crystalline quality than the others. Ultraviolet (UV) band edge emissions peaked at 3.27 eV with a full-width at half-maximum (FWHM) of 113–136 meV were observed for all of the films at room temperature. Low-temperature photoluminescence (PL) spectra at 3.5 K are dominated by neutral donor-bound excitons (D0X) and donor–acceptor pair (DAP) emission. For the films deposited at lower temperature, a deep level emission peaked at 2.80 eV were observed. Temperature dependence of PL shows that the free exciton emission increases with increasing temperature and eventually dominates the PL spectra for the temperature higher than 80 K. Time-resolved PL were carried out at room temperature and 77 K. For the film deposited at 425 °C, the decay times of DAP and D0X at 77 K were 293 and 389 ps, respectively, while that of the band edge emission was 190 ps at room temperature.

We compared the nano-structures of three samples of ZnO thin films grown on GaN with different growth temperature conditions. Although disconnected spiral domain structures (of the order of 100?nm in width) were observed in the samples of high-temperature growth, their crystal qualities are generally better than the one grown at low temperature, either near the GaN interface or far away from the interface. In the sample of high-temperature growth through the whole process, the domain structures extend from the interface with a smaller scale and almost vertical sharp boundaries. The sample grown at the low temperature showed a generally continuous structure from the interface. However, its crystal quality is quite poor. In the sample with initial low-temperature growth and then high-temperature growth, the ZnO layer started with a continuous structure, like the sample of low-temperature growth. However, it evolved into domain structures similar to the sample of high-temperature growth beyond about 200?nm in thickness. The samples of high-temperature growth generally have higher photon emission efficiencies. The sample grown at the high temperature through the whole growth process has the highest emission quantum efficiency.

ZnO nucleated initially with two-dimensional (2D) islands on 6H–SiC substrates. With the increase of ZnO layer thickness, however, the 2D islands led to coalescence and grain growths. The aspect ratios of these islands/coalescences/grains were found to be thickness dependence that has been interpreted by a schematic model. The growth mode transition from 2D islands to three-dimensional (3D) grains is the result of strain energy relaxation accumulated by lattice and thermal mismatches. An analog result diffracted in transmission electron microscopy with misfit dislocations that extended into the ZnO epilayers to be ≤150 nm. The secondary ion-mass spectroscopy analysis exhibited anomalous impurities contributed by an interdiffusion in between ZnO and SiC materials.

MgxZn1−xO/MgyZn1−yO multilayers were fabricated by metalorganic chemical vapor deposition (MOCVD) technique and second-harmonic generation (SHG) was carried out by the Maker fringe technique. By comparing the second-harmonic signal generated in ZnO film and Mg0.05Zn0.95O/Mg0.4Zn0.6O multilayers with the same deposition temperature and total thickness, we concluded that a significant enhancement of second-harmonic signal can be achieved in multilayer structure. The second-order susceptibility tensor χ zzz ( 2 ) = 21.2 pm / V was deduced from Mg0.05Zn0.95O/Mg0.4Zn0.6O multilayers deposited at 425 °C with a total thickness ∼1 μm, which was about 2 times that of ZnO film.

ZnO nanocrystallite films were grown on pyrex by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD) measurements revealed that the film was grown with ZnO (0001) surfaces parallel to the substrate. Optical transition due to free excitons was observed from both absorbance and photoluminescence (PL) measurements. The film also showed strong second harmonic generation (SHG). These results demonstrate the high quality of such films.

Thickness-dependent biaxial strain relaxation of epitaxial ZnO layers grown on 6H–SiC substrates has been addressed. The strain ratio under the biaxial stress was estimated to be 0.38, while the c/a ratio changed from 1.593 to 1.608. The biaxial strain was accounted maximum for the ZnO layer thickness of ⩾6–⩾200 nm. Free (FX A ), donor-bound (D 0 X), and neutral acceptor-bound (A 0 X) excitons energies were blue shifted with the increase of layer thickness to be 2.5, 4.8, and 5.8 meV, respectively. The strain-induced band shift for the FX A , FX B , and D 0 X bands was estimated with the corresponding energies of 13.1, 16.4, and 14.6 eV.The strain-induced optical band structure was analyzed using the Hamiltonian for the valence bands under the out-of-plane biaxial strain.

Single-crystalline ZnO tubes were grown on sapphire(0001) substrates by metalorganic chemical vapor deposition at 400 °C. The growth temperature was much lower than that (900–1100 °C) used in previous reports. The tubes were grown along the substrate normal and were characterized by hexagon-shaped cross sections. All of the tubes possessed the same epitaxial relationships with respect to the substrate. Growth pressure was found to play an important role in the formation of ZnO tubes.

High-quality Zn-polar ZnO films were grown on metal-organic chemical-vapor deposition (MOCVD) grown ZnO/a-sapphire templates by plasma-assisted molecular beam epitaxy (MBE). Annealing of the MOCVD-ZnO layer in an O 2 atmosphere improved the surface roughness and crystallinity of the template. Reflection high-energy electron diffraction and atomic force microscopy observations revealed that MBE-ZnO maintained its Zn-polarity, which is the polarity of the underlying MOCVD-ZnO, and that the optimized growth condition is the O-rich flux regime. Structural and optical properties of the MBE-ZnO films were significantly improved by growth under O-rich flux condition and introducing a low-temperature ZnO buffer. The line widths of (0002) and (1010) X-ray ω-rocking curves for MBE-ZnO films were 533 and 582 arcsec, respectively. The ground and excited (n = 2) states of A-exciton were clearly evident at 3.377 and 3.423 eV in low-temperature (4.2 K) photoluminescence of the Zn-polar ZnO film.

Third-harmonic generation (THG) was studied from ZnO thin film deposited by the metalorganic chemical vapor deposition (MOCVD) technique on sapphire substrates at different temperatures. A strong THG signal was obtained from the film deposited at an appropriate temperature. The dependence of THG on the deposition temperatures was discussed. A third-order susceptibility χ(3)=3.77×10-12 esu was deduced for a film deposited at 250 °C. This value is similar to that observed from ZnO nanocrystalline films fabricated by pulse-laser deposition (PLD). We conclude that film structure and the crystalline quality is main factors determined the THG in the film.

Second harmonic generation (SHG) from ZnO thin films fabricated by metalorganic chemical vapor deposition (MOCVD) technique was carried out. By comparing the second harmonic signal generated in a series of ZnO films with different deposition temperatures, we conclude that a significant part of second harmonic signal is generated at the film deposited with appropriate temperature. The second-order susceptibility tensor χ(2)zzz=9.2 pm/V was deduced for a film deposited at 250 °C.

Networks consisting of one-dimensional ZnO nanowires and two-dimensional ZnO nanowalls were synthesized using a catalyst-free low-temperature approach. The size of the nanostructure was much smaller than that obtained by the previous catalyst-assisted method. The nanostructures exhibited stable excitonic states at room temperature, and emission due to exciton-exciton scattering was observed.

This work was supported in part by the Special Postdoctoral Research Fellowship Program, Photodynamics Research Center, The Institute of Physical and Chemical Research, Japan.

ZnO nanorods were epitaxially grown by metalorganic chemical vapour deposition (MOCVD) on sapphire (0001) and substrates. The nanorods were elongated along the ZnO c-axis which was parallel to the substrate normal. Good alignment among the rods was achieved both in the length direction and in the in-plane orientations. The line width of bound exciton emissions was meV at low temperatures. Emissions due to free excitons were observed from low to room temperature. Biexciton emissions were observed up to K. The band edge emission at room temperature was found to be a mixture of emissions due to free excitons and other impurity-related emissions, indicating that care must be taken when assigning the emission peak at higher temperatures.

Three-dimensional (3D) Ta2O5/SiO2 photonic crystals in the visible-violet spectral region are fabricated by an auto-cloning technique on patterned substrates with triangular lattice configurations and their in-plane (the stack XY plane) optical properties are studied. Reflection measurements by normal incidence of light on to the cleaved facet of the photonic crystal reveal maximum reflections at certain photon energies. Comparison with calculated band structure demonstrates that the reflection peaks are either due to the photonic bandgap (PBG) within which the light propagation is forbidden, or due to heavy photons associated with flat bands. A two-step deposition method is adopted to insert luminescent rhodamine 590 into the photonic crystal and the emission property is strongly modified by the photonic crystal. Possible applications of such 3D photonic crystals in optical components are discussed.

High quality ZnO films on sapphire substrates were synthesized using metal organic chemical reactions, such as metal organic chemical vapour deposition (MOCVD) and metal organic decomposition (MOD) method. Stable solid source of Zn-acetylacetonate was used for MOCVD, and the sol-gel method from Zn-acetate, 2-methoxyethanol and 2-aminoethanol, and a commercial MOD source from Symetrix Co. were used for MOD. Dominant excitonic emission was obtained from these layers synthesized by these simple and economical methods, which are expected to develop powerful techniques for functional oxide fabrications.

We report on fabrication of SiGe single crystal film on insulator by a simple approach including a growth of a thin Ge film on a commercially available SOI substrate, formation of a SiO2 protective layer, and rapid thermal annealing (RTA) in an Ar atmosphere. Homogeneity of the local Si fraction in SiGe-on-insulator (SGOI) was found to be closely connected with the SiGe phase diagram, and RTA below the solidus line is required to obtain homogeneous SGOI. In spite of the high annealing temperature beyond the melting point of Ge, obtained SGOI was revealed to be single crystalline as evidenced by electron back scattering pattern analysis.

Growth characteristics and optical properties of ZnO films epitaxially grown on Al2O3 (0 0 0 1) substrates at temperatures of Tg=200–500 °C by metalorganic chemical vapor deposition were investigated. The in-plane orientation of ZnO unit cells was different for Tg=200 °C and Tg⩾300 °C. The surface morphology varied significantly: smooth surface with cracks at Tg⩽250 °C, facet and column growth at 300 °C⩽Tg

ZnO films were grown on Al2O3 (0001) substrates by metal organic chemical vapor deposition at temperatures of Tg=150∼300 °C. Epitaxial growth was obtained for Tg≥200 °C. The in-plane orientation of the ZnO unit cells was found to change from a no-twist one with respect to that of the substrate at Tg=200 °C to a 30°-twist one at Tg=300 °C. Absorption and photoluminescence were observed from the film grown at 150 °C, although there was no evidence of epitaxial growth. Films grown at Tg≤200 °C exhibited smoother surfaces. Moreover, all the films grown at Tg=150∼300 °C revealed acceptor-related emission peaks, indicating the incorporation of acceptors into the films.

We have grown nitrogen-doped ZnO (ZnO:N) films by laser molecular-beam epitaxy. The use of lattice-matched ScAlMgO 4 substrates prevented the degradation of crystallinity induced by the nitrogen incorporation to the films. Despite this improvement, we have not obtained ZnO:N films which showed p-type conductivity. We studied the optical properties of these ZnO:N films. Donor–acceptor pair (DAP) luminescence was observed. The results indicate the formation of an acceptor state. The energy position of the DAP luminescence is lower than that reported by Look et al. [Appl. Phys. Lett. 81 (2002) 1830]. The DAP luminescence band shifts to lower energy with increasing nitrogen concentration. A photoluminescence recombination possibly due to the free-electron-to-acceptor (FA) transition was observed at temperatures higher than 40 K. The acceptor ionization energy was estimated from the energy position of the FA luminescence to be 266 meV.

ZnO micro-whiskers were successfully prepared by oxidizing of sublimated zinc acetylacetonate (Zn(C5H7O2)2) products. Crystallinity of ZnO whiskers was considerably improved by increasing thermal oxidation temperature. Full width at half maximum (FWHM) of ZnO ( 1 0 1 1 ) plane peak observed in the X-ray diffraction was 0.186°. SEM images of the whiskers oxidized at 1000 °C were a bundle of very fine whiskers and almost uniform for surface morphology. Room temperature photoluminescence (PL) spectrum of the whiskers oxidized over 400 °C shows a blue emission at wavelength of 420 nm. In the low temperature (4.2 K) PL spectrum of the ZnO whiskers oxidized over 800 °C, the emission from exciton bound to natural donor and that from free-exciton recombination were observed at 3.361 and at 3.376 eV, respectively.

High-quality ZnO films were successfully prepared on Si wafers by low-pressure MO-CVD using zinc acetylacetonate (Zn(C5H7O2)2) and oxygen. The c-axis oriented ZnO films were grown on p-type Si wafers at temperature of 520 °C with ZnO buffers layers deposited by RF sputtering. Although, the ZnO layer deposited by sputtering has a poor c-axis orientation, the films prepared by MO-CVD on the ZnO buffer layer shows a sharp X-ray diffraction peak at 34.4° corresponding to the (0002) of hexagonal ZnO. Room temperature photoluminescence spectrum of the all film exhibits a strong peak consisted of near-band edges emission at 378 nm. Current–voltage characteristics of the ZnO(n)/Si(p) heterojunction exhibits non-linear and rectifying characteristics with a small current leakage in the reverse direction. A dark-blue light was clearly observed around the periphery of the top Al electrode by applying forward bias voltages.

Epitaxial ZnO films are grown on sapphire (α-Al2O3) (0001) substrates by metal-organic chemical vapor deposition under 6 and 0.05 Torr using diethyl zinc (DEZn, (C2H5)2Zn) and O2 as precursors and nitrogen as carrier gas. Measurements by X-ray diffraction and photoluminescence reveal that films grown under 6 Torr have better crystal quality. In ZnO films grown under both pressures, free excitonic transitions are observed by reflection. However, the emission behaviors are different. Low-temperature photoluminescence of the ZnO film grown under 6 Torr is dominated by donor-bound exciton emission, whereas that grown under 0.05 Torr exhibits strong acceptor-bound exciton emission, indicating pronounced acceptor incorporation in the latter. In-plane orientations of the ZnO films are well controlled by adjusting the growth process. Measurements by coaxial impact collision ion scattering spectroscopy (CAICISS) demonstrate that the ZnO films have +c polarity, regardless of their in-plane orientation. This finding differs from the results obtained by laser-molecular beam epitaxy where the polarity was found to depend on the in-plane orientation.

Recently, the absorption-edge singularity model accounting for the interaction between excess electrons and photocreated holes has been applied to room-temperature optical spectra in n -type ZnO epilayers [T. Makino et al. : Phys. Rev. B 65 (2002) 121201(R)]. This model predicts that the onset of the spectrum should exhibit a power-law singularity of the form [( E - E 1 ) -α ] with the threshold energy of E 1 located near the fundamental gap. The results of our fitting using this model are in fairly good agreement with available experimental data obtained for MgZnO thin films, which were reported by Kang et al. [Solid State Commun. 115 (2000) 127]. The power exponent α, which is related to the magnitude of screening between photocreated carriers relative to that provided by excess electrons, was enhanced with the incorporation of Mg and had a maximum at the Mg concentration of 8%. The possible reasons for this enhancement are discussed.

Polycrystalline ZnO (0 0 0 2) films with large grains were prepared by low-pressure MO-CVD of zinc acetylacetonate (Zn(C 5 H 7 O 2 ) 2 ) and oxygen. The films were deposited on Corning glass substrates at substrate temperatures between 475 and 540 °C. The size of the grains estimated from atomic force microscope patterns was as large as 200 nm. Room temperature photoluminescence (PL) spectrum of the films exhibits only a strong peak consisted of near-band edge emission at 378.8 nm. Low temperature (4.2 K) PL spectrum exhibits an emission from bound exciton of nature donors. The resistivity of the films critically depends on the amount of dopant, and changes in a range of 10 −2 –10 −4 Ω cm. The lowest resistivity of 6.9×10 −4 Ω cm was obtained in the Ga-doped films. The electron concentration and Hall mobility of the film with the lowest resistivity are 2.2×10 20 /cm 3 and 40.9 cm 2 /V s, respectively.

SiO2/air three-dimensional (3D) periodic structures were fabricated by removing Si layers partially from Si/SiO2 3D photonic crystals (PhCs) formed by using autocloning. CdS/SiO2 3D periodic structures were formed by introducing CdS into the SiO2/air structures by the TEA method and photoluminescence (PL) was observed from the introduced CdS. TiO2/air/CdS two-dimensional (2D) PhCs were also fabricated by introducing CdS into the voids of TiO2/air 2D periodic structures, in which SiO2 layers were partially etched out from TiO2/SiO2 2D PhCs fabricated by using autocloning. PL radiating normal to the surface was measured and large polarization dependence was observed.

High-quality ZnO (1120) epitaxial films have been grown on sapphire (0112) substrate by atmospheric pressure MOCVD method using zinc acetylacetonate (Zn(C 5 H 7 O 2 ) 2 ) and oxygen. The crystallinity of the ZnO films was considerably improved with increasing the film thickness. The full width at half maximum (FWHM) obtained from the ω rocking curve of X-ray diffraction indicated a minimum value of 0.35° at the film thickness of 0.30 μm. The lattice constant estimated from the diffraction angle 20 was almost equivalent to the value of single crystalline bulk ZnO. The room temperature photoluminescence spectrum of the ZnO films consists of band edge emission at 380.08 nm. The low-temperature (4.2 K) photoluminescence spectrum indicates two broad lines of 3.31 and 3.32 eV from donor-acceptor pairs and one sharp line of 3.363 eV from exciton bound nature donor.

A detailed study of molecular beam epitaxy of GaAs on homemade SiGe substrates has been performed. It was found that the initial migration-enhanced epitaxy process with As prelayer is crucial to obtain high-quality GaAs. By (004) x-ray diffraction, the lattice mismatch between GaAs and SiGe was demonstrated to be reduced compared with the conventional GaAs/Ge heterostructure. Furthermore, narrower halfwidth of the rocking curve and stronger photoluminescence intensity were found for GaAs on SiGe. These results show that SiGe is a promising material as an alternative substrate to Ge to realize exact lattice matching to GaAs for solar cell applications.

Nanometer scale islands were observed in air on CdSe/ZnSe surfaces grown by molecular beam epitaxy. Measurements by atomic force microscope revealed that the aspect ratio of the island increased first and then decreased with time. Surface analyses by Auger electron spectroscopy indicated clearly that the island was composed in large part of oxides and the outer shell of the island was Zn-enriched and Cd-depleted. These islands showed sharp emissions as quantum dots. This work demonstrates that the islands were formed mainly due to the oxidation of the surface and that it grew in a way similar to that generated from a strained film. In addition, intermixing of ZnSe and Zn segregation during the island formation occurred.

Microphotoluminescence is studied for fullerene-doped phosphate and fluorophosphate optical glasses, where microstructures are formed by connecting nearby -[PO4]- tetrahedra with chemical bonds between fullerenes and non-bridging oxygen anions. Fullerene-related tetrahedral chains result in significant changes of photoluminescence. Scanning photoluminescence measurements indicate that a large number of fullerene-related microdomains aggregate as self-organized islands. The temperature dependence of the photoluminescence demonstrates that the non-radiative decay and ionic environments of fullerene complexes are different at the various temperatures. The changes of the ionic environments and anionic potentials of the fullerene complexes are caused by laser excitation induced activation of cations followed by their percolation migration and retrapping in the vitreous matrix.

Microphotoluminescence and second-harmonic microscopy were used to study islands formed inside phosphate and fluorophosphate optical glasses with fullerene dopants. Scanning microphotoluminescence and second-harmonic microscopy indicated that fullerene dopants are subjected to strong influence from the glass matrix, which causes distortion of molecular symmetry, enhancement of fluorescence, and occurrence of noncentrosymmetry required by the macroscopic second-order optical nonlinearity.

We have fabricated ZnO thin films on sapphire substrates at temperatures ranging from 350 to 1000 degrees C by laser molecular-beam epitaxy. With increasing growth temperature, lateral grain size evaluated by X-ray reciprocal space mapping increased resulting in improved electron mobility. When the film was grown at 1000 degrees C, an electron mobility as large as 90 cm(2)/Vs was achieved. By annealing in 1 atm of oxygen at 1000 degrees C, thin films having much larger grain size (> 5 mu m(2)) and higher mobility(similar to 120 cm(2)/V s) comparable with those for bulk single crystals could be obtained.

Plasma-assisted molecular beam epitaxy (P-MBE) of ZnO films on Al 2 O 3 (0 0 0 1) substrates is reported. By introducing a thin buffer layer of MgO, surface morphology can be greatly improved at the initial growth stage, which leads to an atomically flat ZnO surface with (3×3) reconstruction. During the consequent ZnO film deposition, RHEED intensity oscillations longer than 50 periods can be observed, which evidences the two-dimensional epitaxial growth. Morphological, structural, and optical investigations indicate that by using the MgO buffer layer a great improvement of surface flatness and crystal quality is achieved for the ZnO films grown on Al 2 O 3 (0 0 0 1) substrates by P-MBE.

Acceptor doping into Mn incorporated II–VI diluted magnetic semiconductors of ZnMnTe and CdMnTe was carried out by molecular beam epitaxy (MBE). Activated nitrogen as an acceptor was introduced into these layers, using an RF plasma cell. The order of 10 18 cm −3 p-type ZnMnTe : N was successfully grown, where the Mn contents were less than 14%. Modulation doping was performed for the CdMnTe/ZnTe multi-quantum well structures. A sheet hole concentration of 2.0×10 14 cm −2 was achieved. Assuming that the hole accumulated in the CdMnTe well region, the actual hole concentration becomes 3×10 19 cm −3 .

The transmission and phase-shift spectra for millimeter electromagnetic waves are obtained for a two-dimensional (2D) square lattice array made of ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ spheres of diameter $\ensuremath{\simeq}3.2$ mm. The results are compared with the theoretical 2D photonic-band structures that take account of the lifetime effect due to the radiative energy decay. It is found that the incidence-angle dependence of the observed transmission spectra is in excellent agreement with the calculated in-plane dispersion curves of the photonic bands and that the frequency dependence of the phase shift agrees well with the calculated lifetime-broadened density of states. The radiative lifetimes of the photonic bands are estimated to be about ten times longer than those of whispering gallery modes of an isolated sphere, though the magnitudes depend rather strongly on the wave vector and band index.

Oriented thin (≈2 μm) films, CdS, prepared by laser ablation were characterized by the dependence of external and internal reflection on both the angle of incidence and the polarization of laser light. The samples exhibit perpendicular and parallel orientation of the crystallographic axis with respect to the surface of the glass substrate. The experiments were performed at 300 K using low intensity (

The low-temperature dynamic properties of photorefractive gratings in cobalt-doped potassium–strontium–sodium–barium–niobate crystals are reported. At low temperatures, the photorefractive space-charge field undergoes quasiperiodic oscillations if the crystal is preilluminated by one of the writing beams. The write–erase cycle of the index grating becomes shorter if the crystal is preilluminated by one of the writing beams, which provides a means for crystal sensitization. The magnitude of the index grating decreases significantly at low temperatures. The temperature dependence of the dark decay of the photorefractive grating is measured to complete our study and demonstrate the multiple shallow levels existing in the crystal. A model of double carriers with multiple shallow levels is assumed to explain the experimental results.

The effects of annealing oxygen partial pressure on the in-plane epitaxy and twin formation in (110)-oriented ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) thin films grown on (110) ${\mathrm{SrTiO}}_{3}$ substrates by pulsed laser deposition have been studied by high-resolution x-ray diffraction, using diffraction-space mapping with a four-circle diffractometer. These films are found to have a structure in which the crystalline a and b axes are tilted about $0.5\ifmmode^\circ\else\textdegree\fi{}$ away from those of the substrates, while keeping the (110) planes parallel to each other. A decrease of in situ annealing oxygen pressure induces a reduction in twinning, which is finally suppressed in the film annealed at an oxygen pressure of 600 mTorr. Our results suggest that twin formation during a tetragonal-to-orthorhombic transformation is controlled by competition between the uniaxial force exerted at the interface by the vicinal substrate surface and the thermodynamic force originating from the difference in the lattice parameters for the a and b axes of orthorhombic YBCO.

Nonlinear optical absorption and optical limiting behavior of a novel σ – π alternating polymer, poly(disilanylene-2,2′-bipyridine-5,5′-diyl) ruthenium complex were evaluated with nanosecond pulses at 532 nm. The limiting throughputs at three concentrations were investigated. The experimental results indicated that this sample is very efficient as an optical limiting material. Using the standard Z -scan technique, we obtained the effective two-photon absorption coefficient. The theoretical fits to the data give a value of β =3.5 cm/GW.

This article considers II-VI compound semiconductors, the realization of new optical devices based on the electrons and holes trapped in low-dimensional and nano-structures (such as quantum wells, quantum lines, and quantum dots) and excitons. Fabrication techniques and a new series of materials are discussed. As the first step, the formation of the three-dimensional trap structure (quantum dot) as well as its optical properties are described, focusing on the natural formation process. Then, aiming at the realization of a new light-emission device based on excitons, a series of materials with large exciton-binding energy (ZnS and ZnO) are described, and the present status of the optical properties is discussed. Especially, the characteristics of the optically pumped laser are examined, and the possibilities of new laser materials are considered. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(3): 51–60, 1999

Raman sideband excitations driven by counterpropagating Raman beams are analyzed for the trapped ion under the localization conditions in and beyond the Lamb-Dicke regime. Multiquantum vibrational couplings are demonstrated to produce significant effects on the Raman sideband transitions and the relevant Raman excitations of the trapped ion beyond the Lamb-Dicke regime. The quantum features of the vibrational states attained by exciting the motional ground state are closely associated with the nonlinear vibronic couplings, Raman excitation, and localization conditions. Quantum entanglement and quantum interference are discussed for the trapped ion under various Raman excitation and localization conditions. The results are compared with the recent experiments. Further experimental attempts are proposed to use the single trapped ${}^{25}{\mathrm{Mg}}^{+}$ ion in a linear ion trap.

The first sideband Raman excitations driven by counter-propagating Raman beams are analysed for the trapped ion under the localization condition in or beyond the Lamb-Dicke regime. It is demonstrated that multiquantum processes in the vibrational couplings produce significant effects on the the first sideband Raman transitions and the relevant Raman displacements for the trapped ion beyond the Lamb-Dicke regime. The quantum features of the vibrational states attained by displacing the motional ground state are demonstrated to be closely associated with the nonlinear vibronic couplings. Quantum entanglement, and quantum interference as well, are discussed for ion traps with various Raman excitation and localization conditions. The results are compared with the recent experiment reported by Monroe C et al in 1996 Science 272 1131-5.

A high quality ZnO thin film was grown by the laser molecular beam epitaxial technique. Under high-density excitation, the exciton-exciton collision process (P line) was observed at room temperature in ZnO thin films where the exciton binding energy is 60 meV. From the edge of the sample, a rapid increase in the P line was observed with increasing excitation power. A fine structure originating from the cavity mode was also observed. These facts suggest the lasing of the exciton at room temperature. Crystal growth of the ZnMgO mixed crystal and the stability of the ZnO/ZnMgO heterostructure were discussed. Optical properties of the ZnO/Zn0.8Mg0.2O multi-quantum-well show that the electrons and holes are well confined in this heterostructure.

Scanning second-harmonic microscopy was used to study the lateral distribution of the second-order optical nonlinearity of a - copolymer [poly(disilanylene-2,2'-bipyridine-5,5'-diyl) ruthenium complex (PDSBpy-Ru)] thin film on a glass substrate. The orientation of the dipolar chromophores and establishment of the noncentrosymmetry required by the macroscopic second-order optical nonlinearity were resulted from natural coordination of the PDSBpy-Ru molecules to the surface Si-O-H groups on the glass substrate. A homogeneous lateral distribution of the coordination-induced poling was observed.

The luminescent properties of a novel - polymer, poly(disilanylene-2,2´-bipyridine-5,5´-diyl) ruthenium complex (PDSBpy-Ru), have been investigated. A tetrahydrofuran solution of PDSBpy-Ru exhibits fluorescence with peaks dependent on the solution concentration. In a dilute solution, single PDSBpy-Ru molecules are excited, generating metal-to-ligand charge transfer excitons (or electron-hole pairs). The corresponding charge recombination produces fluorescence emission with a peak at about 650 nm. On excitation of a tetrahydrofuran solution of PDSBpy-Ru with a higher concentration, a linear PDSBpy-Ru molecule forms an excimer-like adduct with a neighbouring PDSBpy-Ru molecule. The excimer-like adduct emits fluorescence with redshifted peaks.