Controlled/living radical polymerization of vinylcyclicsilazane by RAFT process and their block copolymers

High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 °C, using dithiocarbamate derivatives and 2,2′‐azobis‐isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinylcyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 °C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane‐block‐polystyrene as an inorganic–organic diblock copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4594–4601, 2008     

Structure-borne noise reduction for an infinite, elastic cylindrical shell

A theoretical model was developed to evaluate the reduction of structure-borne noise generated by an axially symmetric ring force which is applied on the interior of the cylindrical shell. The vibrating cylindrical shell is coated with a microvoided elastomer that is acoustically soft material designed for the reduction of the generated noise. The analytical model is a two-layer shell structure comprised of a cylindrical shell and an outer layer (coating) that is perfectly bonded to the cylindrical shell. The outer and inner surfaces of the coated shell are in contact with water and air, respectively. The analysis for this problem is based on the theory of elasticity, acoustic wave equations, and pertinent boundary conditions. Effects of various parameters such as coating thickness and material properties on the noise reductions are presented.     

Synthesis and properties of UV curable polyvinylsilazane as a precursor for micro‐structuring

Photosensitive acrylated polyvinylsilazanes were prepared by reacting a diacrylate containing compound, 1,1‐bis (acryloyloxyethyl) ethyl isocyanate (BAEI), with polyvinylsilazane (PVSZ) and utilized as an inorganic photoresist for generating SiCN‐based ceramic microstructures. The acrylate‐modified polymers (m‐PVSZ) were characterized by ¹H‐NMR, ¹³C‐NMR and FT‐IR methods to determine the chemical reaction mechanism. Differential photo‐calorimeter and FT‐IR analysis were employed to examine its photosensitive properties. Line patterns were fabricated by a UV nano‐imprinting method; multi‐layered octagon structures were fabricated by a two‐photon absorption stereolithography process. The results indicate that m‐PVSZ is quite a novel inorganic photoresist for the fabrication of micro ceramic structures. Copyright © 2015 John Wiley & Sons, Ltd.     

Metal bonding strength in low‐temperature processed titanium using atomic force microscopy with single‐wall carbon nanotube tip

We report the development of a Ti–Ti bonding process at a low bonding temperature below 200 °C using chemically surface‐activated Ti thin films and a reliable evaluation method for measuring the Ti–Ti bond strength by means of atomic force microscopy (AFM). Using Ti as an interlayer enables void‐free bonding because Ti exhibits fast diffusion and oxide solubility. On the other hand, wafer bonding is an important processing step for 3D circuit integration that requires a high reliability of the process. However, the reliability of bonding‐strength values obtained by employing conventional measurement devices is limited by comparably large measurement errors and restricted the availability of suitable sample material. In this study, the use of AFM to measure the bonding strength is proposed. The interfacial bonding properties depend on the Ti deposition parameters. A bonding temperature of 200 °C was found to be appropriate for the development of a low bonding temperature wafer‐bonding process. The pretreatment methods like plasma activation and chemical activation at 200 °C result in a Ti bonding strength of approximately 8.22 J/m², sufficient for applications in 3D circuit integration. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Landau levels of scalar QED in time-dependent magnetic fields

The Landau levels of scalar QED undergo continuous transitions under a homogeneous, time-dependent magnetic field. We analytically formulate the Klein–Gordon equation for a charged spinless scalar as a Cauchy initial value problem in the two-component first order formalism and then put forth a measure that classifies the quantum motions into the adiabatic change, the nonadiabatic change, and the sudden change. We find the exact quantum motion and calculate the pair-production rate when the magnetic field suddenly changes as a step function.