Reduction of dislocation density and improvement of optical quality in ZnO layers by MgO-buffer annealing

Optical properties of ZnO thin films with/without MgO-buffer annealing were investigated by low and room temperature photoluminescence measurements. The ZnO films were grown on c-sapphire substrates by plasma-assisted molecular-beam epitaxy employing a thin MgO-buffer layer. Dislocation density of ZnO layer was reduced from 5.3 × 10⁹ to 1.9 × 10⁹ cm⁻² by annealing MgO-buffer prior to the growth of ZnO. The intensity of free exciton emission from the sample with MgO-buffer annealing was almost twice of that from the sample without annealing, while the deep level emission from the sample with MgO-buffer annealing was about 1/3 of that without annealing. The MgO-buffer annealing improves optical quality of overgrown ZnO films.     

Optical characterization of CdTe/ZnSe fractional monolayer structures grown by atomic layer epitaxy

Luminescence properties of CdTe/ZnSe fractional monolayer grown by atomic layer epitaxy have been investigated. To investigate the origin of the highly efficient luminescence, various optical spectroscopic methods such as, photoluminescence (PL), temporal/spatial resolved PL, temperature dependence PL, and excitation power dependence PL have been used. It is found that structural inhomogeneities affect dominant influence on the line width and line shape of luminescence. The luminescence intensity greatly enhanced by the localization of exciton at the disorder induced localized states.     

The Fabrication and Characterization of Single‐Component Polymeric White‐Light‐Emitting Diodes

By using Ni⁰‐mediated polymerization, we have systematically synthesized a series of fluorene‐based copolymers composed of blue‐, green‐, and red‐light‐emitting comonomers with a view to producing polymers with white‐light emission. 2,7‐Dibromo‐9,9‐dihexylfluorene, {4‐(2‐[2,5‐dibromo‐4‐{2‐(4‐diphenylamino‐phenyl)‐vinyl}‐phenyl]‐vinyl)‐phenyl}‐diphenylamine (DTPA), and 2‐{2‐(2‐[4‐{bis(4‐bromo‐phenyl)amino}‐phenyl]‐vinyl)‐6‐tert‐butyl‐pyran‐4‐ylidene}‐malononitrile (TPDCM) were used as the blue‐, green‐, and red‐light‐emitting comonomers, respectively. It was found that the emission spectra of the resulting copolymers could easily be tuned by varying their DTPA and TPDCM content. Thus with the appropriate red/green/blue (RGB) unit ratio, we were able to obtain white‐light emission from these copolymers. A white‐light‐emitting diode using the polyfluorene copolymer containing 3 % green‐emitting DTPA and 2 % red‐emitting TPDCM (PG3R2) with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/PG3R2/Ca/Al was found to exhibit a maximum brightness of 820 cd m^–2 at 11 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33,0.35), which are close to the standard CIE coordinates for white‐light emission (0.33,0.33).     

Investigation of chemometric calibration performance based on different chemical matrix and signal-to-noise ratio.

The chemometric calibration performance was systematically investigated by two parameters (changing the chemical matrix as well as the signal-to-noise ratio) of the NIR (near-infrared) spectrum. Three different analytes (hexane, cyclohexane, toluene) were selected and heptane was used as a solvent. The degree of spectral difference significantly affected the calibration performance. The largest structural difference between the analyte and the solvent provided the best calibration result for a given signal-to-noise ratio. Additionally, the signal-to-noise ratio of the spectra also directly influenced the calibration performance. Overall, the spectral difference and signal-to-noise ratio were the major factors for governing the chemometric calibration performance, especially in the low-concentration range.     

Low-order modeling and dynamic characterization of rapid thermal processing

A low-order model of rapid thermal processing (RTP) of semiconductor wafers is derived. The first-principles nonlinear model describes the static and dynamic thermal behavior of a wafer with approximate spatial temperature uniformity undergoing rapid heating and cooling in a multilamp RTP chamber. The model is verified experimentally for a range of operating temperatures from 400° C to 900° C and pressures of 1 Torr and 1 atmosphere in an inert N₂ environment. Theoretical predictions suggest model validity over a still wider range of operating conditions. One advantage of the low-order model over previous high-order and statistical models is that the proposed model contains a small number of fundamental parameters and functions that, if necessary, are easily identifiable. Furthermore, because of reduced computational complexity, the low-order model can be used in real-time predictive applications including signal processing and process control design. In studying and verifying the model, the dynamic behavior of a semiconductor wafer undergoing rapid temperature changes is characterized. Close comparison between theory and experiment in terms of the wafer eigenvalue and dc gain is demonstrated; the strong nonlinear effects of temperature are shown. Convective heat transfer losses are also examined and are shown to increase with radial position on the wafer.     

Operation of a nonlinear optical loop mirror with orthogonally polarized waves in nonpolarization-preserving, single-mode fiber

We demonstrate stable operation of a NOLM using orthogonally polarized control and signal beams in nonpolarization-preserving, single-mode fiber. The NOLM can transcribe data from an optically incoherent input at one wavelength to a coherent output over a range of wavelengths. Operation of the NOLM without tuning for the input bit rate is possible over a range of bit rates from less than 1 Gb/s to more than 50 Gb/s.     

Structural Antecedents to Knowledge and Participation: Extending the Knowledge Gap Concept to Participation

This paper investigates relationships between community characteristics and levels of knowledge and participation examined at both the individual and the community levels. This research extends the knowledge gap concept to a parallel phenomenon, the participation gap. Results from the Social Capital Benchmark Survey 2000 showed that community density, education, and cohesion were significant positive predictors of knowledge but less consistent predictors of participation at the individual level. At the community level, relationships were even stronger, though cohesion was associated with higher mean levels of participation and reduced participation gaps, whereas population density was associated with lower levels of participation and increased gaps.     

Irradiation-induced reduction and luminescence properties of Sm doped in BaBPO5

Usually, Sm²⁺ ions could be reduced by heating the materials in reducing atmospheres. Exposure to ionizing radiations is also known to cause Sm³⁺→Sm²⁺ conversion. In this work, BaBPO₅ doped with the samarium ion was prepared by high temperature solid-state reaction. Sm²⁺ ions were obtained by two different reduction methods, i.e., heating in H₂ reduced atmosphere and X-ray irradiation. The measurements of X-ray diffraction (XRD), and scanning electron microscope (SEM) were investigated. It is found that the conversion of Sm³⁺→Sm²⁺ is very efficient in BaBPO₅ hosts after X-ray irradiation. Sm²⁺ ions under these two reduction methods exhibit different characteristics that were studied by measurements of luminescence and decay. The results showed that the luminescence properties of Sm²⁺ ions in BaBPO₅ were highly dependent on the sample preparation conditions.     

A 3.3-V single power supply 16-Mb nonvolatile virtual DRAM using aNAND flash memory technology

A 3.3-V 16-Mb nonvolatile memory having operation virtually identical to DRAM with package pin compatibility has been developed. Read and write operations are fully DRAM compatible except for a longer RAS precharge time after write. Fast random access time of 63 ns with the NAND flash memory cell is achieved by using a hierarchical row decoder scheme and a unique folded bit-line architecture which also allows bit-by-bit program verify and inhibit operation. Fast page mode with a column address access time of 21 ns is achieved by sensing and latching 4 k cells simultaneously. To allow byte alterability, nonvolatile restore operation with self-contained erase is developed. Self-contained erase is word-line based, and increased cell disturb due to the word-line based erase is relaxed by adding a boosted bit-line scheme to a conventional self-boosting technique. The device is fabricated in a 0.5-μm triple-well, p-substrate CMOS process using two-metal and three-poly interconnect layers. A resulting die size is 86.6 mm², and the effective cell size including the overhead of string select transistors is 2.0 μm²     

Palladium-catalyzed C-N bond formation: synthesis of 1-aryl-1H-pyrazoles from β-bromovinyl aldehydes and arylhydrazines

Cyclic and acyclic β-bromovinyl aldehydes are cyclized with an array of arylhydrazines in toluene at 125 °C in the presence of a palladium catalyst and a phosphorus chelating ligand together with NaO^tBu to give 1-aryl-1H-pyrazoles in moderate to good yields.