Key Engineering Materials Vols. 326-328

Abstract: We propose to use electrostatic drop-on-demand devices, with precise metering and accurate delivery capabilities, to manipulate single-walled carbon nanotubes suspended in solution. The conductivity of the solution increases significantly by the addition of anionic surfactants and nanotubes, generating favorable conditions for electrostatic ejection. This technique could find applications, combined with chemical functionalization, in the fabrication of carbon nanotube field emission devices as well as electronic circuits. hanseoko@yurim.skku.ac.kr

Abstract: In this study, powder processing and severe plastic deformation (SPD) approaches were combined in order to achieve both full density and good particle-matrix bonding in CNT and Cu powder mixtures without grain growth, which was considered as a bottle neck of the bottom-up method in the conventional powder metallurgy of compaction and sintering. Equal channel angular pressing (ECAP), one of the most promising methods in SPD, was used for the powder consolidation. The powder ECAP processing with 1, 2, 4 and 8 passes was conducted at room temperature. It was found by microhardness tests and microstructure characterization that relatively high mechanical strength could be effectively achieved as a result of the well bonded powder contact surface during powder ECAP. The SPD processing of powders is a viable method to achieve both fully density and good particle bonding in CNT-metal matrix nanocomposites.

Abstract: We have attempted to observe straining responses of an individual multi-walled carbon nanotube (MWNT) by performing an in-situ tensile testing inside scanning electron microscope (SEM). The both ends of an individual MWNT was attached on the rigid support and the tip of the force sensor using electron beam and was elongated by a nano-manipulator. The nano-manipulator was automatically controlled by personal computer. Linear deformation and fracture behaviors of MWNT were successfully observed and its force-displacement curve was also measured from the bending stiffness and displacement of the force sensor and manipulator. The tensile properties of individual MWNT were evaluated from the tensile test results.

Abstract: Chemical vapor deposition (CVD) is one of the various synthesis methods that have been employed for CNT growth. In particular, Ren et al reported that large areas of vertically aligned multi-wall carbon nanotubes could be grown using plasma enhanced chemical vapor deposition (PECVD). In the present study, we synthesized aligned CNT arrays using a direct current (dc) PECVD system. The synthesis of CNTs requires a metal catalyst layer, etchant gas, and a carbon source. In this study, the substrate consisted of Si wafers with 10, 30, and 50 nm Ni-sputtered film. Ammonia (NH3) and acetylene (C2H2) were used as the etchant gases and carbon source, respectively. NH3 pretreatment was processed using a flow rate of 180 sccm for 10 min. CNTs were grown on pretreated substrates at 30% C2H2:NH3 flow ratios for 10 min. Carbon nanotubes with diameters ranging from 60 to 80 nanometers and lengths of about 2.7 μm were obtained. Vertical alignment of the carbon nanotubes was observed by FE-SEM.

Abstract: Fully flexible cell with Nose-Poincare method preserves Hamiltonian in structure, so the extended Hamiltonian is preserved in the real time domain. In the previous development of Nose- Poincare method for NVT, NPT, and N
T ensemble unit cell simulations, implicit algorithm such as generalized leapfrog integration scheme was used. The formulation and numerical implementatio n of the implicit formula is much more complicated because it includes nonlinear iteration procedur e. Furthermore, it is not easy to show time reversibility in implicit formula. Thus for these reasons, it is necessary to develop explicit formula in MD unit cell simulation. We develop fully flexible explicit Nσ T ensemble MD simulation algorithm. It guarantees the preservation of extended Hamil tonian in real time domain and time reversibility. The numerical implementation is easy and relative ly simple since it does not require iteration process. It is established by using the splitting time integ ration. It separates flexible cell Hamiltonian into several terms corresponding to each Hamiltonian part, so the simple and completely explicit recursion formula was obtained. Unit cell tension, shear test for bulk material tension and shear tests are performed to demonstrate the validity and performance of the present explicit molecular dynamics scheme formulated through the spitting method. We compare the results of the explicit splitting time integration scheme with those of the implicit generalized leapfrog time integration scheme. The proposed explicit N
T unit cell simulati on method should serve as a powerful tool in the prediction of the material behavior.

Abstract: A large-scale parallel computation is extremely important for MD (molecular dynamics) simulation, particularly in dealing with atomistic systems with realistic size comparable to macroscopic continuum scale. We present a new approach for parallel computation of MD simulation. The entire system domain under consideration is divided into many Eulerian subdomains, each of which is surrounded with its own buffer layer and to which its own processor is assigned. This leads to an efficient tracking of each molecule, even when the molecules move out of its subdomain. Several numerical examples are provided to demonstrate the effectiveness of this computation scheme.

Abstract: Nanoimprint lithography is a promising technology to produce sub-100 nm scale features on silicon chips. One of key issues in the nanoimprint lithography is how to make uniform contact between the stamp and the substrate on a large area. In this study a rubber membrane unit under substrate is introduced to resolve this problem. Two layers of membrane were designed to consider air flow in the middle of resist on a silicon wafer. The geometry design for accomplishing uniform contact was carried out using finite element analysis. The material modeling of hyperelastic properties of rubber is characterized by the Mooney-Rivlin strain energy functions. Material constants in the strain energy functions are able to be determined via the curve fitting of experimental stress-strain data. Simple tension and equi-biaxial tests were performed to determine the material constants. To evaluate the effects of a rubber membrane unit, nanoimprint lithography process with it was executed. We could confirm that a distinct improvement of uniform contact was shown and air flow problem was solved during the process.

Abstract: To study nanoparticles generated within the high-density plasma system, it is necessary to know the particle concentration (#/cm3), which is typically measured using laser light scattering of particles trapped inside the plasma. This technique has limitations because particles are localized due to the forces that act on the trapped particles inside the plasma and the localization point varies as the particles grow. Unless spatially averaged particle concentrations are obtained by scanning through the plasma, laser light scattering measurements of particle concentration might represent only the local variation of particle concentration. In this paper, novel method is presented to measure the particle concentration employing TEM measurement results and the simulation of particle transport for calculation of transport efficiency from the plasma region where the particles are generated to the TEM grid. As the particles were collected on the TEM grid after the plasma was extinguished, the simulation includes the effects of Brownian diffusion, aerodynamic drag and gravitational sedimentation but not electrostatic or ion drag force. Simulation results were obtained for particles ranging from 5 to 100 nm. For each particle size, transport efficiencies from 56 different starting positions were evaluated. It was found that transport efficiencies of particles in the 20 to 50 nm diameter range were highest, since these particles tend to follow the gas flow. Sampling efficiencies of particles smaller than this decreased due to Brownian diffusion. For larger particles, sampling efficiencies also decreased, due to gravitational sedimentation. The measured particle concentrations were found to be ~108 #/cm3 and roughly constant over time.

Abstract: The tribological performance of ordered mesoporous carbons (CMK-3) as lubricant additives is investigated at ambient temperature. The effects of CMK-3 on the frictional forces, wear amounts and cycles to scuffing are measured using a ball-on-disk tester. It was found that there was little difference in the frictional forces and wear amounts of the oils with and without CMK-3. However, the scuffing time of the oil with CMK-3 was much longer than that of the pure mineral oil in sliding tests. CMK-3 were very effective on maintaining the oil gap and protecting the surfaces in boundary lubricated sliding.

Abstract: This work uses nanoindentation and nanoscratch to measure the mechanical properties of evaporation copper thin films. The thin film is deposited on a silicon wafer substrate by using the physical vapor deposition method provided by a resistive heating evaporator. The mechanical properties are then determined by indentation test and lateral force test produced by nanoindenter and nanoscratch. The results show that, as the copper thin film is 500nm in thickness and the indentation depth increases from 100nm to 400nm, the Young’s modulus increases from 151GPa to 160GPa while the hardness increases from 2.8GPa to 3.5GPa. Moreover, both the Young’s modulus and the hardness decrease as the thickness of the thin film increases. Besides, the nanoscratch results show that the friction factor also increases as the scratch depth increases, and a thinner film thickness makes a larger friction factor. The results represent the substrate has a significant effect on the mechanical properties of the thin films.