Self-forming AlOx layer as Cu diffusion barrier on porous low-k film

The copper diffusion barrier properties of an ultrathin self-forming AlO_x layer on a porous low-k film have been investigated. Cu-3 at.% Al alloy films were directly deposited onto porous low-k films by co-sputtering, followed by annealing at various temperatures. Transmission electron microscopy micrographs showed that a ∼ 5 nm layer self-formed at the interface after annealing. X-ray photoelectron spectroscopy analysis showed that this self-formed layer was Al₂O₃. Sharp declines of the Cu and Si concentrations at the interface indicated a lack of interdiffusion between Cu and the porous low-k film for annealing up to 600 °C for 30 min. The leakage currents from Cu(Al)/porous low-k/Si structures were similar to as-deposited films even after a 700 °C, 5 min anneal while a Cu sample without Al doping failed at lower temperatures. Adding small amounts of Al to bulk Cu is an effective way to self-form copper diffusion layer for advanced copper interconnects.     

On the formation and photoluminescence of Si(1-x)Ge(x) nanoparticles

Si(1-x)Ge(x) nanoparticles were prepared from two annealed alloy ingots at the compositions of Si:Ge = 9.5:0.5 and 9:1 using a vapor condensation technique under Ar atmosphere. These nanoparticles are all spherical, and increasing the working pressure leads to an increased particle size and size dispersion. Comparing to the alloy ingots, the nanoparticles have a higher average content of Ge. In addition, increasing the working pressure also causes the Si(1-x)Ge(x) nanoparticles to become more Ge-rich. This can be ascribed to the lower melting point and higher kinetic energy of Ge than Si during the evaporation process. The photoluminescence of Si(1-x)Ge(x) nanoparticles ranges from visible light to infrared region, and the luminescence peak exhibits a red shift as the Ge content in the nanoparticles increases. This indicates that the incorporation of Ge into Si has a dominant effect in the radiative recombination process, in comparison with the constant luminescence peak position in the case of pure Si nanoparticles with similar size distribution.     

Thermal degradation mechanism of poly(ether imide) by stepwise Py–GC/MS

The thermal degradation of poly(ether imide) (PEI) was studied through a combination of thermogravimetric analysis and stepwise pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) techniques with consecutive heating of the samples at fixed temperature intervals to achieve narrow temperature pyrolysis conditions. The individual mass chromatograms of various pyrolysates were correlated with pyrolysis temperatures to determine the pyrolysis mechanism. The major mechanisms were two‐stage pyrolysis, involving main‐chain random scission, and carbonization. In the first stage, the scission of hydrolyzed imide groups, ether groups, and isopropylidene groups produced CO+CO₂ and phenol as the major products and was accompanied by chain transfer of carbonization to form partially carbonized solid residue. In the second pyrolysis stage, the decomposition of the partially carbonized solid residue and remaining imide groups formed CO+CO₂ as the major product along with benzene and a small amount of benzonitrile. The yield of CO+CO₂ was the largest fraction in the total ion chromatogram of the evolved gas mixtures. Hence, the thermal stability of the imide group was identical to the maximum thermogravimetry loss rates in the two‐stage pyrolysis regions. Afterward, carbonization dominated the decomposition of the solid residue at high temperatures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1151–1161, 2001     

Fabrication of TiN inverse opal structure and Pt nanoparticles by atomic layer deposition for proton exchange membrane fuel cell

A titanium nitride (TiN) inverse opal structure was fabricated on carbon paper as a support of Pt for application in proton exchange membrane fuel cell (PEMFC). Polystyrene spheres with different diameters were coated on carbon paper by spin coating in multilayers as a template. Titanium dioxide (TiO₂) thin film was then deposited on the template by atomic layer deposition (ALD). The TiN inverse opal structure was fabricated by direct nitridation of TiO₂ in flowing ammonia atmosphere at above 800 °C. Platinum nanoparticles were then deposited uniformly on TiN by ALD. The performances of PEMFC using Pt@TiN@carbon paper composite as electrodes were examined. The homemade electrodes showed at least 13 times higher platinum specific power density than commercial E-Tek electrodes.     

Effects of internal flow modification on the cell performance enhancement of a PEM fuel cell

This study presents a numerical investigation on the cell performance enhancement of a proton exchange membrane fuel cell (PEMFC) using the finite element method (FEM). The cell performance enhancement in this study has been accomplished by the transverse installation of a baffle plate and a rectangular block for the modification of flow pattern in the flow channel of the fuel cell. The baffle plates (various gap ratios, λ = 0.005–10) and the rectangular block (constant gap ratio, λ = 0.2) are installed along the same gas diffusion layer (GDL) in the channel at constant Reynolds number for the purpose of investigating the cell performance. The results show that the transverse installation of a baffle plate and a rectangular block in the fuel flow channel can effectively enhance the local cell performance of a PEMFC. Besides, the effect of a rectangular block on the overall cell performance is more obvious than a baffle plate.     

Effect of Boron Particle Surface Coating on combustion of solid propellants for ducted rockets

Combustion behavior of B/MA/AP/HTPB fuel rich propellants containing different coated boron particles was studied with several diagnostic facilities such as windowed strand burner, CO₂ laser ignition facility, rapid depressurization quenched device, thermal analyzer and micromotor static test. Materials selected for boron coating include LiF, Viton A and silane. Baseline propellant containing uncoated boron was also studied for comparison Results from windowed strand burner and static test show that LiF-propellant exhibits the most remarkable overall behavior. Ignition study indicates that LiF-propellant gives the shortest while Viton A-propellant gives the longest ignition time under the same heat flux. Moreover, mechanisms were proposed to elucidate the experimental results and the observed combustion phenomena.     

Mobilization of Hematopoietic Stem and Progenitor Cells during Dengue Virus Infection

Hematopoietic stem and progenitor cells (HSPCs) mobilization is the movement of HSPCs from the bone marrow to the peripheral blood or tissue induced by stress. HSPC mobilization is a well-known response to protect the host during infection through urgent differentiation of HSPCs to immune cells. Dengue virus (DENV) infection is known to cause stress in infected humans and the mobilizing capacity of HSPCs during DENV infection in affected patients has not been fully investigated. Here, we investigated whether DENV infection can induce HSPC mobilization and if the mobilized HSPCs are permissive to DENV infection. White blood cells (WBCs) were collected from dengue patients (DENV+) and healthy donors and analyzed by flow cytometry and plaque assay. Elevated HSPCs levels were found in the WBCs of the DENV+ group when compared to the healthy group. Mobilization of HSPCs and homing markers (skin and gut) expression decreased as the patients proceeded from dengue without symptoms (DWoWS) to severe dengue (SD). Mobilizing HSPCs were not only permissive to DENV infection, but infectious DENV could be recovered after coculture. Our results highlight the need for further investigation into HSPC mobilization or alterations of hematopoiesis during viral infections such as DENV in order to develop appropriate countermeasures.     

Task Scheduling for Context Minimization in Dynamically Reconfigurable Platforms

Dynamically reconfigurable hardware provides useful means to reduce the time-to-prototype and even the time-to-market in product designs. It also offers a good alternative in reconfiguring hardware logics to optimize the system performance. This paper targets an essential issue in reconfigurable computing, i.e., the minimization of configuration contexts. We explore different constraints on the CONTEXT MINIMIZATION problem. When the resulting subproblems are polynomial-time solvable, optimal algorithms are presented. We also present a greedy algorithm for the CONTEXT MINIMIZATION problem, that is proved NP\mathcal{NP}-complete. The capability of the proposed algorithm is evaluated by a series of experiments.     

Crystalline Gaq3 Nanostructures: Preparation, Thermal Property and Spectroscopy Characterization

Crystalline Gaq₃ 1-D nanostructures and nanospheres could be fabricated by thermal evaporation under cold trap. The influences of the key process parameters on formation of the nanostructures were also investigated. It has been demonstrated that the morphology and dimension of the nanostructures were mainly controlled by working temperature and working pressure. One-dimensional nanostructures were fabricated at a lower working temperature, whereas nanospheres were formed at a higher working temperature. Larger nanospheres could be obtained when a higher working pressure was applied. The XRD, FTIR, and NMR analyses evidenced that the nanostructures mainly consisted of δ-phase Gaq₃. Their DSC trace revealed two small exothermic peaks in addition to the melting endotherm. The one in lower temperature region was ascribed to a transition from δ to β phase, while another in higher temperature region could be identified as a transition from β to δ phase. All the crystalline nanostructures show similar PL spectra due to absence of quantum confinement effect. They also exhibited a spectral blue shift because of a looser interligand spacing and reduced orbital overlap in their δ-phase molecular structures.     

Automatic optical inspection system for IC molding surface

Success or failure of an IC product hinges on the quality of molding process which protects chips from the harm done by external force and moisture. Defects such as cracks, dilapidations or voids may be embedding on the molding surface while a chip was being molded. Human inspection often neglects a very tiny crack or a low-contrast void. Hence an automatic optical inspection system for the integrated circuit (IC) molding surface cannot be over emphasized. The proposed system is composed of a charged coupled device, a coaxial light, a back light and a motion control unit. Based on the characteristics of statistical textures of the molding surface, a series of digital image processing is carried out, including normalization, shrinking, segmenting and Fourier based image restoration and defect identification. Training of the parameter associated with defect inspection algorithm is also discussed. Results of the experiment suggest that the inspection system works effectively with high accuracy rate of 94.2 %, contributing to the inspection quality of IC molding surface.