A Study Of Surface Dynamics Of Polymers. II. Investigation By Plasma Surface Implantation Of Fluorine–containing Moieties

Macromolecules at the surface of a polymeric solid have considerable mobility, and the specific arrangement of functional groups of macromolecules at the surface is dictated by the environmental conditions in which the surface is placed. Consequently, the change of environmental conditions, such as immersion in water or placement in a biological surrounding, could cause a considerable degree of change in the surface characteristics of a polymer from those evaluated in the laboratory against ambient air. The mobile nature of a polymer surface can be investigated by surface‐implanting fluorine‐containing moieties, mainly—CF3, by the plasma implantation technique and following the disappearance and reappearance of fluorine atoms on the surface. The disappearance rates (based on the immersion time in water at room temperature) of ESCA F1s signals, the decay rates of (advancing) contact angle of water, and the recovery of these values on heat treatment of water‐immersed samples were measured as a function of crystallinity of polymer samples (at three levels of crystallinity) for poly (ethylene terephthalate) and nylon 6. Copyright © 1988 John Wiley & Sons, Inc

Plasma Polymerization Of Tetramethyldisiloxane By A Magnetron Glow Discharge

Plasma polymerization of tetramethyldisiloxane by a magnetron glow discharge was studied. The glow discharge was created between parallel electrodes with a 10 kHz electric power source with a superimposed magnetic field using permanent bar magnets. Polymers were deposited onto moving substrates placed on the surface of a rotating disc located in between the electrodes. The deposition rates were determined with a quartz crystal thickness monitor placed on the plane of the rotating disc and just outside the edge of the disc. The current-voltage relationship observed for plasma polymerization of the monomer depends on the monomer feed rate and the conditioning of the electrodes or the establishment of a steady state surface in the polymer-forming plasma, which also depends mainly on the monomer feed rate. Consequently, plasma polymerization cannot be correlated to single operational parameters such as the discharge current, the power or the monomer feed rate in a simple manner. However, when the deposition rate was expressed as Rp/FM, where Rp is the polymer deposition rate, F is the monomer feed rate and M is the molecular weight (FM is thus the monomer mass feed rate), it was found that Rp/FM is uniquely related to the parameter W/FM where W is the discharge power in Watts. It was shown that many polymer properties were also determined mainly by the same composite parameter. It was also found that the presence of O2 gas in the monomer feed reduced the carbon content in the polymer and made the surface more hydrophobic while O2 plasma treatment of the plasma polymer rendered the surface more hydrophilic. © 1983

In situ imaging of microstructure formation in electronic interconnections

The development of microstructure during melting, reactive wetting and solidification of solder pastes on Cu-plated printed circuit boards has been studied by synchrotron radiography. Using Sn-3.0Ag-0.5Cu/Cu and Sn-0.7Cu/Cu as examples, we show that the interfacial Cu6Sn5 layer is present within 0.05 s of wetting, and explore the kinetics of flux void formation at the interface between the liquid and the Cu6Sn5 layer. Quantification of the nucleation locations and anisotropic growth kinetics of primary Cu6Sn5 crystals reveals a competition between the nucleation of Cu6Sn5 in the liquid versus growth of Cu6Sn5 from the existing Cu6Sn5 layer. Direct imaging confirms that the β-Sn nucleates at/near the Cu6Sn5 layer in Sn-3.0Ag-0.5Cu/Cu joints

Polymerization Of Methane

Plasma polymerization of methane in a magnetically enhanced capacitively coupled bell jar reactor operating at a frequency of 10 kHz is reported. Dependence of polymer deposition rate on monomer feed rate (F), composite power parameter (W/FM), electrode temperature, and electrode cleanliness have been examined. Such functional properties as wettability, adhesion, and thermal stability of the polymer are found to depend on the composite power parameter (W/FM) of the plasma. The permeability studies indicate highly crosslinked nature of the polymer. ESCA studies reveal code position of electrode material with the polymer under high W/FM conditions, potential applications of plasma polymer of methane are suggested. Copyright © 1989 John Wiley & Sons, Inc

Field Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

The multiple reentrant quantum phase transitions in the $S=1/2$ antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with the interchain mean field approximation. It is assumed that the odd-th bond is antiferromagnetic with strength $J$ and even-th bond can take the values {\JS} and {\JW} ({\JS} > J > {\JW} > 0) randomly with probability $p$ and $1-p$, respectively. The pure version ($p=0$ and $p=1$) of this model has a spin gap but exhibits a field induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For $0 < p < 1$, the antiferromagnetism is induced by randomness at small field region where the ground state is disordered due to the spin gap in the pure case. At the same time, this model exhibits randomness induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between the transverse antiferromagnetic phases and disordered plateau phases with the increase of the magnetic field for moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and the jumps between them, It is also found that the antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.Comment: 5 pages, 8 figure

Electrodynamic trapping of spinless neutral atoms with an atom chip

Three dimensional electrodynamic trapping of neutral atoms has been demonstrated. By applying time-varying inhomogeneous electric fields with micron-sized electrodes, nearly $10^2$ strontium atoms in the $^1S_0$ state have been trapped with a lifetime of 80 ms. In order to design the electrodes, we numerically analyzed the electric field and simulated atomic trajectories in the trap, which showed reasonable agreement with the experiment.Comment: 4pages, 4figures, to appear in Phys. Rev. Let

Monte Carlo Simulation of Secondary Electron Emission From Thin Film/Substrate Targets

We have developed a Monte Carlo simulation model of secondary electron emission from thin film/substrate samples, taking into consideration their exact boundary condition. First, the validity of the model is checked in comparison with the experimental data reported such as the secondary electron emission and backscattering yields from thick Al, thick Au targets and Al thin films on a Au substrate, the energy distribution of secondary electrons, and the contribution of backscattering to the secondary electron emission yield. The agreement is relatively good. Next, we have applied the model to the secondary electron emission from Au films on an Al substrate. It has been found from the calculated results of the spatial distribution of secondary electrons that the Au film coating increases the background intensity and deteriorates resolution in the secondary electron image formation