Nanostructured CNx (0 < x < 0.2) films grown by supersonic cluster beam deposition

Nanostructured CN_x thin films were prepared by supersonic cluster beam deposition (SCBD) and systematically characterized by transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The incorporation of nitrogen in the films (0 < x < 0.2) and the nanostructure were controlled by using different synthesis routes. Films containing bundles of well-ordered graphene multilayers, onions and nanotubes embedded in an amorphous matrix were grown alongside purely amorphous films by changing the deposition parameters. Graphitic nanostructures were synthesized without using metallic catalysts. The structural and electronic properties of the films have been studied by EELS. The role played by N in the carbon nanostructures has been deduced from XPS line-shape analysis.     

Improvement in dynamic properties of laminated MWCNT-polystyrene composite beams via an integrated numerical–experimental approach

A new concept for the optimization of dynamic behavior of laminated nanocomposites is introduced where fiber orientation factor in continuous fiber-reinforced composites is replaced by different wt.% of carbon nanotubes (CNTs) in each layer. First, at a design concept level, an optimum distribution of multi-walled CNTs (MWCNTs) through the thickness of a typical cantilever beam is sought to achieve its highest fundamental natural frequency for a given weight percent of MWCNTs. This is done using a finite element (FE) model in ABAQUS along with a user-defined Python code. Next, based on the obtained optimum distribution, actual laminated MWCNT/polystyrene (PS) composite beams were fabricated and their effective stiffness, fundamental natural frequencies and damping ratios were measured through static deflection and free vibration tests. It was found that the optimum distribution of MWCNTs resulted in an increase of 21.9% and 10.4% in the effective Young’s modulus and the fundamental damped natural frequency values, respectively, which were almost two-fold higher than those of a beam with a uniform MWCNT distribution. In addition, compared to a pure polymer beam, 38.9% and 27.8% improvements in the damping ratio of the uniformly and optimally distributed MWCNT polymer composite beams were achieved.     

Room temperature wedge-wedge ultrasonic bonding using aluminum coated copper wire

The purpose of this work is to evaluate the feasibility of room temperature wedge-wedge bonding using commercially available copper wires, coated with aluminum. Bonding quality, reliability and aging resistance of the wire bonds have been investigated using standard wire pull tests immediately after bonding and after accelerated life tests, including temperature storage at 125 °C, 150 °C, and 200 °C for up to 2000 h. Using focused ion beam (FIB-) preparation and high resolution electron microscopy (SEM, TEM combined with EDX X-ray analysis), results of microstructure investigations of the Al-coating/Cu wire interface as well as of the bonding interconnect formed between the coated wire and the metallization on ceramic substrate will be presented. These investigations provide background information regarding the binding mechanisms and material interactions, and contribute to assess and to avoid potential reliability risks. Due to the found advantageous bond processing behavior and increased reliability properties, our results indicate that room temperature wedge-wedge bonding of coated copper wires has a remarkable application potential, for instance in medical and other high reliability as well as high power applications. It combines all known advantages of usual copper bonding like excellent contacting behavior, high reliability and favorable material price with the possibility of processing temperature damageable components and considerable improved storage capability. Therefore, room temperature bonding using coated copper wire can also reduce cycle time, manufacturing and material costs.     

求解区间图K-连接最短路径问题的在线算法

针对含有n个区间的区间图K-连接最短路径(K-SP)问题,提出一种求解区间图K-SP问题的在线算法。分析区间图及其最短路径问题的特有性质,利用改进的动态规划算法和贪心算法,优化在线算法的时间复杂度。理论分析结果表明,该算法的时间复杂度为O(nK+nlgn),与目前已知最优的离线算法复杂度相同。     

Surface pattern formation in UV-curable coatings

Some UV-curable coatings display matte surfaces after cure if they have undergone a certain period of leveling at a temperature above their glass transition temperature and the melting point of any crystalline co-reagents present in the formation. The matte finish of these coatings is due to the presence of coherent surface wrinkles after cure, which are similar in appearance to those induced by differential thermal contraction, when a metal layer is sputtered onto a rubbery or viscous substrate. However, the wrinkles in the UV-cured coatings appear under isothermal conditions, and it is, therefore, inferred that they are due to the dynamics of internal stresses induced by through-thickness variations in the extent of curing.     

A new generation of crystalline silicon solar cells: Simple processing and record efficiencies for industrial-size devices

In contrast to the general opinion that very high efficiencies can only be obtained using complex processing, with the novel technologically simple and environmentally sound obliquely evaporated contact (OECO) type solar cell efficiencies exceeding 21% could be obtained without applying masks or photolithography. Two different approaches of OECO cells using MIS contacts and exclusively Al as metallization are discussed: (i) with a diffused n⁺-emitter (MIS-n⁺p) and (ii) with an inversion layer emitter (MIS-IL). The most important results particularly for industrial production are efficiencies of 19% and 20% for simply to fabricate 10×10 cm² OECO cells on commercial CZ-Si and FZ-Si, respectively. These are the highest efficiencies ever reported for solar cells of industrial size.