Key Engineering Materials Vols. 277-279

Abstract: Recently, the carbon-centered organic system with C-H hydrogen bonds is being examined and reported with particular focus on its chemical shifts. These properties are traditionally associated with the red shifted hydrogen bond due to the weak interaction of C-H hydrogen bonds. In a few cases, however, the strengthening of the C-H bond is characterized by the blue shift. In this study, organic-inorganic hybrid silica and fluorinated amorphous carbon films have been deposited on a p-type Si (100) substrate by inductively coupled plasma chemical vapor deposition. The reason for the chemical shift in the low dielectric constant materials with C-H hydrogen bonds was researched on, and the effect of the meso-structure of the films by the inverse electron demand Diels-Alder reaction of the C=C and C=O double bond was also studied.

Abstract: We improved the sensitivity of existing commercial Pirani-vacuum gauges employing the AC method in the vacuum range above 1 Torr. The signals obtained through the use of the AC method yield information related to the specific heat and heat conductivity of gas. The output signal is obtained by two components: the oscillating temperature amplitude, and its phase. The amplitude increases with the decrease of pressure in the vacuum range from the atmosphere to about 1 Torr, which arises from the decrease of the heat capacity with the decrease of gas density. In contrast, the phase decreases monotonically as pressure decreases and the slop of a dΘ/d(log P) is large at higher than 1 Torr. This provides a good advantage for developing a new Pirani gauge with high sensitivity.

Abstract: Silicon nanocrystals in a range from 2 nm to 5 nm were prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits that the reaction be completed in only a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanocrystals measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph confirmed the material identity of nanocrystals as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that are chlorine-or butyl-capped. The emission peak center moved to a longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation.

Abstract: Since a clean environment and finite mass flow control on the molecular level are continuously required in current R&D fields and actual process lines, technologies on vacuum generation and control have been playing a significant role in merging a variety of technologies like Bio, Information, Environment, Energy, Space and Nano. Currently, the drive towards dry vacuum pumping has broadly occurred across a spectrum of vacuum applications, from semiconductor manufacture to industrial processing, due to its most visible advantages: it is contamination free. The integrated characteristics evaluation system for dry vacuum pumps has been established in KRISS in collaboration with several branch dry pump suppliers in Korea. The evaluation system exploits a constant volume flow meter to measure mass flow rates real-timely in standard level, and facilitates the evaluation of spatially averaged sound power levels using a semi-anechoic chamber. New and overhauled roots, claw, classical screw, and scroll type pumps supplied from the manufacturers have been evaluated using the evaluation system in terms of ultimate pressure, pumping speed, vibration, and sound power. We selected the mass flow measuring method with a constant chamber volume of 875 L because of its direct monitoring capability which does not allow blind mass flow rate measurements, and proved that the method allows us to measure five decades of mass flow rates from 1×10-2 to 1×103 mbar-l/s with a measurement uncertainty of ±3%, which is within the internationally accepted standards limit. In this work, we demonstrate how the integrated pump characteristics evaluation and mass flow control method have been significant in the low vacuum range of 10-4 to 103 mbar.

Abstract: The synthesis and characterization of a series of square planar Pt(II) complexes, which are luminescent at room temperature, are reported. The complexes have the general structure of (C^N)Pt(O^O), where HC^N is 3-phenylpyridazine (ppdz), 3-(4’-biphenyl)pyridazine (4’phppdz), 3-(2’-naphthyl)pyridazine (2’napdz), or 3-(1’-naphthyl)pyridazine (1’napdz), and HO^O is acetylacetone (Hacac). The reaction of K2PtCl4 with HC^N forms the chloro-bridged dimer, (C^N)Pt( µ-Cl)2Pt(C^N), which are cleaved with an ancillary ligand to give the corresponding monomeric (C^N)Pt(O^O) complexes. The emission bands of these complexes are governed by the structure of the cyclometalating ligands, with emission band (lem) ranging from 516 to 645 nm. The two emission bands at (515 and 550 nm) of (ppdz)Pt(acac) complex have 7 and 6 ms of life time which imply those bands are due to phosphorescence decay. The conjugating ring on the pyridazine makes the emission more red shifted which is expected based on molecular orbital calculation. In addition to the alteration of cyclometalating ligands, ancillary ligands also change. These results can be compared with the corresponding Ir(III) complexes.

Abstract: By paying attention to the hole-doped two-dimensional systems of antiferromagnetically (strongly) correlated electrons, we discuss the cause of hole-rich phase formation in association with phase separation. We show that the phase diagram obtained from Maxwell's construction in the plane of temperature vs. hole density is consistent with one derived from the evaluation of hole-rich and electron-rich phases in real space. We observe that the formation of a hole-rich phase is attributed to the aggregation of hole pairs induced by spin singlet pairs present in the pseudogap phase, and that the direct involvement of correlations between hole pairs is not essential for phase separation.

Abstract: Phthalocyanine polymers substituted with polyethylene glycol (PEG), PPEGPc, were synthesized and characterized by photo electrochemistry. To examine the effects of the ethyleneoxy group on the photoconductivity of phthalocyanine polymers, different PEGs of Mw 164 ~ 750 were introduced by the esterification of the phthalocyanine polymer. A thin film of phthalocyanine polymer was coated onto a conductive ITO glass using a mixture of soluble PPEGPc in DMF. Phthalocyanine polymers substituted with polyethylene glycol showed a higher photocurrent generation compared to that of an unsubstituted polymer, suggesting that the PEG units facilitate transport of generated charge carriers. Maximum photocurrent was obtained from a PEG of Mw550. Photocurrent generation was highly dependent on the PEG chain length, indicating that ethyleneoxy groups in PEG participate in charge transport. The morphology of the polymer film was investigated on to correlate the domain structure of the PPEGPc with the charge transport property.

Abstract: We report effects of the size and the energy state distribution on the electrical and optical properties in self-assembled InAs quantum dots. The results of characteristics measured using atomic force microscopy, photoluminescence and dark current are analyzed by way of a simulation assuming a Gaussian distribution in size and related energies. The samples investigated in this study are InAs/GaAs quantum dot infrared photodetector structures with an AlGaAs blocking layer grown by molecular beam epitaxy at different growth modes.

Abstract: A new photobleacheable nanocomposite was developed as a reusable recording media. It is composed of polymer dye capsules containing TiO2 nanoparticles, leuco dyes, and a developer. The polymer dye capsules were prepared using the convenient one-step mini-emulsion polymerization. The morphology of the resultant polymer dye capsules were examined through a scanning electron microscopy (SEM), to show the capsule structure, which averaged 30~ 500 nm in size. The leuco dye was originally colorless, but it acquired color when it reacted with the developer. The blue colored dye capsule solution was stable under ambient conditions and could thus be utilized as a recording composition. The color of the recorded part, by coating the dye capsule solution on to a piece of white paper, was persistent. However, the recorded mark was bleached upon exposure to a UV light. Capsule morphology was not detected in the bleached region as examined by a SEM, indicating that titanium dioxide in the film acted as a photocatalyst to decompose the capsule structure. The bleaching was irreversible so that the recording media was reusable. The bleaching efficiency in photobleaching was shown to be higher than 75%.