"曼哈顿"现象的成因与防止措施

"曼哈顿"现象是由于再流焊过程中无源元件两端焊盘上锡膏的表面张力不平衡所致,其表现为元器件部分地或完全地竖起.本文对影响"曼哈顿"现象的各种因素的作用做了分析,并提出相应的防止措施.     

Engineering geological properties of Miocene hard clays along the middle line of the North–South Diversion Water Project in China

Miocene hard clays are widely distributed in eastern China and are associated with extensive damage to engineering structures. This paper presents the engineering geological properties of Miocene hard clays along the middle line of the North–South Diversion Water Project (NSDWP), including areas of the Nanyang Basin as well as the Fangcheng-Baofeng and Handan-Yongnian regions. Results of laboratory testing show that beneath the weathering zone the Miocene hard clays have similar engineering geological properties, including a high clay fraction with significant montmorillonite, high physico-chemical activity, high water content and high to very high shrink/swell. The effects of wetting and drying cycles on the swelling potential of the hard clays are summarized and attention drawn to the importance of these when considering excavation and construction.

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Surface modification of indium tin oxide anodes by self-assembly monolayers: Effects on interfacial morphology and charge injection in organic light-emitting diodes

Three silane derivatives including dodecyltrichlorosilane (DDTS), phenyltriethoxysilane (PTES) and 3-aminopropyl-methyl-diethoxysilane (APMDS) were used to modify the indium tin oxide (ITO) surfaces. The effects of various terminal groups of the self-assembled monolayers (SAMs) on the growth behavior and interfacial morphologies of N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) film deposited on the SAM-modified ITO were studied, as well as their effects on the performance of organic light-emitting diodes (OLED) devices. The results show that the growth behavior of NPB film over-deposited on the SAM-modified ITO is mainly determined by the wettability of the surface. The covering ability and thermal stability of NPB film on the SAM-modified ITO decrease in the order: bare ITO > ITO/PTES > ITO/APMDS > ITO/DDTS. However, the covering characteristic of NPB films on these substrates did not show direct relation to the transport of carriers across the anode/NPB interface as evaluated from the cyclic voltammogram and OLED performance. The turn-on voltages for these SMA-modified OLED devices increase in the order: ITO/PTES < ITO/DDTS ≤ bare ITO < ITO/APMDS. The enhancing effect of PTES on the hole injection is ascribed to the similar structure of PTES to NPB. On the contrary, the inhibition effect of APMDS is caused from the interaction of the lone-pair electrons of amine group to the transport carriers. Since these devices are known to be hole dominant, the luminance efficiency increase in a similar order as that for the turn-on voltage: ITO/PTES < ITO/DDTS ≤ bare ITO < ITO/APMDS.     

Capillary rise of a liquid on a solid grafted with long polymer chains

Very long grafted chains on a solid surface may turn out to be interesting adhesion promoters. Systems of this sort are now chemically accessible and must be characterized through their wetting properties. Here we discuss the climbing of a liquid along a vertical plane covered with long grafted polymer chains (N monomers per chain). Assuming that the liquid is a good solvent for the polymer, we calculate the thickness L of the swollen polymer brush as a function of the graft density o_s and reduced altitude h= k²-ah (where k^-1 is the capillary length and a is the monomer size). (1) At small altitudes (h<h_c1=o^4/3 _s), L(h) results mainly from a balance between excluded-volume and entropic effects, shift is not linear in h and is large. This remarkable effect reflects the existence of a parabolic concentration profile in the unperturbed brush, first derived by Milner, Witten and Cates (a simpler, Flory, model with a step function profile would give a much smaller effect). (2) At altitudes h > h_c1, the solvent condensation energy becomes the leading term and At even higher altitudes a third 'mushroom' regime may show up if the polymer does not wet the solid. Our results are consistent with some preliminary observations of Deruelle and Léger on very long brushes of p-dimethylsiloxane 4000). Their brushes show colour variations with altitude 1 cm). The corresponding values of are rather large; thus the colour effect may give a rather direct experimental proof of the parabolic profiles.     

Wetting Transitions on Post-Built and Porous Reliefs

Abstract

A comparative study of wetting transitions on porous and post-built polymer surfaces is reported. The transitions were observed under vibration of droplets of different volumes deposited on the surfaces possessing controlled roughness. Initial wetting states were identified as the Cassie air-trapping (‘Fakir’) state for porous and the Wenzel state for post-built relief, whereas the final wetting state was the Cassie impregnating one for both kinds of surfaces. For both porous and post-built surfaces, wetting transitions occurred under constant force acting on a unit length of the three-phase (triple) line. Wetting transitions for both porous and post-built surfaces start from the triple line.     

Investigation of physical and chemical property changes of ultra low-κ SiOCH in aspect of cleaning and chemical repair processes

The physical and chemical property changes of chemical vapor deposited ultra low-κ (ULK) SiOCH dielectric films due to different post ash treatments were studied by Auger electron spectroscopy, ellipsometric porosimetry and surface free energy evaluation. Structural changes in the ULK layer with respect to the carbon content were analyzed. Using a downstream and a reactive ion etch process for photo resist removal a reduction of carbon was observed. For different plasma gas chemistries the pore size reduction depends first on the process condition (downstream or reactive ion etch) and then on the gas. Differences in the pore size then also influence the amount of carbon depletion besides the influence of the gases used for photo resist processes. The damage at the surfaces was characterized by contact angle measurements providing both the polar and dispersive part of the surface free energy. The wettability of different solvents and repair chemicals was classified calculating their surface free energies and comparing those energies with the surface free energies of modified ULK surface. It is shown that especially reducing gases provide a surface free energy with a higher dispersive part compared to oxidative plasma treatments. Furthermore it was found that the wettability of repair chemicals and solvents strongly changes for reductive based strip processes with plasma exposure time, since a high variation of the surface free energy occur.     

An air-stable biomimetic Langmuir–Blodgett bilayer

The long-chain amphiphiles in biomembranes have their hydrophilic headgroups oriented outwards towards the aqueous environment, and their long aliphatic chains innermost. In Langmuir–Blodgett (LB) films the hydrophobic chains are normally outermost. LB films of long-chain derivatives can be prepared under water with the headgroups outermost and are stable while kept there, but the act of removing them from the aqueous environment removes the top monolayer. We demonstrate an adaptation of the LB technique which is appropriate for the preparation of biocompatible surfaces. It produces essentially bilayer films of long-chain derivatives on standard substrates with a hydrophilic outer surface. The films are stable in air. The films show large contact angle hysteresis with water, but the receding angle is in most cases less than 10°. The films can be immersed and withdrawn from water many times before wettability or average thickness change significantly. Compared to previously reported air-stable surfaces with a structure mimicking biological membranes, the substrate for the present surface is experimentally more convenient.     

The analysis of the withdrawal force curve of the wetting curve using 63Sn-37Pb and 96.5Sn-3.5Ag eutectic solders

To analyze the withdrawal force curve in the wetting balance curve, wetting balance tests using the 63Sn-37Pb and 96.5Sn-3.6Ag eutectic solders were conducted by varying the immersion speed, sample perimeter, and solder temperature. The mechanism of the withdrawal force curve was reviewed and a new method for calculating the surface tension of solders using the withdrawal force curve was introduced. The results showed that the maximum point of the withdrawal force curve is generated when the sliding solder meets the bottom corners of a sample and the contact angle is reduced to zero. The maximum withdrawal force subtracted by end force can be expressed using force balance equation as F=pγ. Therefore, the surface tension of the solder can be calculated by dividing the maximum withdrawal force by the sample parameter.     

Particle Adhesion to Drops

The adhesion of spheroidal particles to spherical drops is calculated and discussed in terms of an equilibrium-penetration index. The present study emphasizes the case of particles that are sufficiently large to affect the drop volume upon penetration. It is shown that the more elongated the particles, the steeper the dependence of the penetration index on the contact angle. The effect of line tension on nanoscale particles is considered. Positive line tensions increase the steepness of the dependence of penetration index on contact angle whereas negative line tensions decrease this dependence. In addition, the energy barrier caused by positive line tensions is presented and discussed.     

Search for a wetting layer in thin film growth of para-hexaphenyl on KCl(001)

The non-existence of a strongly bound wetting layer for the system para-hexaphenyl (6P)-KCl(001) was verified by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). The 6P films were grown by physical vapour deposition under ultrahigh vacuum conditions at 400 K. TDS showed just a single desorption peak even down to a coverage of 0.1 nm mean film thickness. The heat of evaporation for 6P was determined to 2.3 eV. From the change of the XPS K2p substrate signal as a function of the mean film thickness one can conclude that a strong de-wetting exists at the very beginning of the 6P layer growth at 400 K. Additional investigations with atomic force microscopy reveal that at this initial stage the film grows in a form of needle like islands with a high aspect ratio and subsequently terraced mounds of 6P are formed. No dissociation of 6P on KCl was observed.