Yonglai Yang

Towards cost-efficient EMI shielding materials using carbon nanostructure-based nanocomposites

Using a combination of dispersing low-cost carbon nanofibers and a small quantity of carbon nanotubes within the polystyrene matrix, we have demonstrated the formation of a novel nanocomposite with superior microstructure and improved electromagnetic interference (EMI) shielding characteristic. This nanocomposite is very promising for use as an effective and practical EMI shielding material owing to its high shielding effectiveness, light weight, low cost, and easy processability.

The fabrication and electrical properties of carbon nanofibre?polystyrene composites

Carbon nanofibre?polystyrene (PS) composites were fabricated by ultrasonic dispersion in a solution followed by spraying to cast films. These films were then hot-pressed to form thicker structures. Direct current conductivity measurement results show that the conductivity of the composite reaches 2.6 ? 10?5?S?m?1 at 3?wt% carbon nanofibre loading, which is an increase of ten orders of magnitude over the pure PS matrix, indicating that the composite is electrically conductive at a very low nanofibre loading. The dielectric properties of carbon nanofibre?PS composites were investigated at room temperature within the Ku-band (frequency range: 12.4?18?GHz). The results reveal that the dielectric constants of the composites are slightly dependent on the frequency but increase rapidly with increasing carbon nanofibre loading in the composite. The experimental data show that the dielectric constant of carbon nanofibre?PS composite can reach more than 80 at a frequency of 15?GHz.

Electrical Conductivity and Electromagnetic Interference Shielding of Multi-walled Carbon Nanotube Filled Polymer Composites

Multi-walled carbon nanotube (MWNT) filled polystyrene (PS) composites were synthesized for electromagnetic interference (EMI) shielding applications. SEM images of composites showed the formation of the conducting networks through MWNTs within the PS matrix. The measured DC conductivity of composites increased with increasing MWNT loading, showing a typical percolation behavior. EMI shielding characteristics of MWNT-PS composites were investigated in the frequency range of 8.2–12.4 GHz (X-band). It was observed that the shielding effectiveness (SE) of such composite increased with the increase of MWNT loading. The SE of the composite containing 7 wt% MWNTs could reach more than 26 dB in the measured frequency region.

Kinetic Monte Carlo simulation of heterometal epitaxial deposition

Abstract Vapor deposited multilayers consisting of alternating ferromagnetic and nonferrous metals are being used for magnetic sensing and data storage devices. Their performance is dependent upon interface morphology which is a sensitive function of deposition condition such as the deposition rate, deposition temperature, and flux angle of incidence. A two-dimensional kinetic Monte Carlo method has been developed and used to explore these effects during the growth of model Ni/Cu/Ni multilayers under low adatom impact energy conditions where thermal diffusion is the only mechanism of atomic assembly. An embedded atom method potential with a two-body cross-potential was used for calculation of the activation energies. It takes into account both the atomic configuration of neighboring atoms and their species. Using an extended set of activation barriers the simulations demonstrate that the interface roughness increases almost linearly with increasing layer thickness during the growth, and is more pronounced when depositing a nickel layer than when depositing a copper layer. The deposition of copper is found to help smooth nickel layers. The simulations demonstrate the existence of an optimal growth window in deposition rate–temperature space where the interfacial roughness of a Ni/Cu/Ni multilayer could be minimized. By analyzing the details of individual atomic jumps, the cause of the surface instability is revealed to be the activation and rapid increase of reverse Schwoebel jumps above a temperature threshold.