Te-Hua Fang

Three-dimensional molecular dynamics analysis of processing using a pin tool on the atomic scale

A three-dimensional model of molecular dynamics (MD) is proposed to study the effects of tool geometry and processing resistance on the atomic-scale cutting mechanism. The model includes the utilization of the Morse potential function to simulate the interatomic force between the workpiece and a tool. The results show that the cutting resistance increases with the angle of the pin tool and the depth of cut, and the cutting force is essentially constant over the range of velocities simulated. In addition, the obtained cutting resistance of present MD simulation exhibits an evident relationship to the ratio of the vertical and the horizontal contact area between the tool and the workpiece within the range of a pin angle of 90-150°. Finally, work hardening and stick-slip phenomena during the process are also observed.

Effects of AFM-based nanomachining process on aluminum surface

Surface analysis of nanomachined material is studied by atomic force microscopy (AFM). To understand the influence of different machined conditions on surface characterization, several nanomachining experiments are performed. Multiple furrows are conducted on a silicon substrate coated with aluminum films under the four different applied loads, including 4, 8, 12, 16 μN. Results indicate that the average surface roughness and the root-mean-square roughness of nanometer-scale surface are improved after the nanomachining process. It can be seen that a smoother surface is obtained under an applied load of 12 μN, and it implies that the surface roughness of the case is minimum in all tests. The same result can also be seen in the fractal dimension analysis. In addition, the bulge edge effect on the nanomachining process is obvious after several scribing cycles.

Nanomechanical properties of copper thin films on different substrates using the nanoindentation technique

The nanoindentation technique is used to measure the hardness and Youngs modulus of copper thin films with substrates of Si, SiO2 and LiNbO3. The results show that in all instances with increasing applied load the penetration depth increases while the hardness at first decreases, and then slowly approaches different constant values depending on the effect of the substrate. The hardness of the film with a LiNbO3 substrate is the highest and that of a film with a Si substrate is the lowest under the same load. The obtained values of the hardness and the Youngs modulus of the copper films are compared with previous data, which show that the values obtained from this study are reasonable. The ratio of the critical depth to the film thickness for copper film is about 1:8 and this is also compared with that of different materials obtained by previous researchers. The relationship between the Youngs modulus and the hardness for a film is also derived. From this relationship, it can be found that the Youngs modulus increases with increasing hardness for different composite materials and shows different increasing ratios under different applied loads. For any given hardness, the modulus value of the Cu film on LiNbO3 is the highest and that of the film on Si is the lowest.

Molecular dynamics analysis of temperature effects on nanoindentation measurement

A three-dimensional molecular dynamics (MD) model is carried out to study the effects of temperature on the atomic-scale nanoindentation process. The model utilizes the Morse potential function to simulate interatomic forces between the sample and tool. The results show that both Youngs modulus and hardness become smaller as temperature increases. The results also indicate that elastic recovery is smaller at higher temperatures. The softening behavior is similar to the prior experiment and the estimated elastic moduli are much higher than the prior experiment. The discrepancy may be due to simulations performed on defect-free single crystals. In addition, some defects of vacancies, atomic steps and plastic indent are observed on the surface region.

Buckling characterization of vertical ZnO nanowires using nanoindentation

Nanomechanical characterization of vertical well-aligned single-crystal ZnO nanowires on ZnO:Ga/glass templates was performed by nanoindentation technique. The buckling loads were found to be 1465 and 215μN for the ZnO nanowires of 100 and 30nm diameters, respectively. Furthermore, the buckling energies for the ZnO nanowires of 100 and 30nm diameters were 3.62×10−10 and 3.69×10−11J, respectively. Based on the Euler buckling model, Young’s modulus of the individual ZnO nanowire has been derived from two possible modes in this work.

Molecular dynamics simulation of nano-lithography process using atomic force microscopy

A three-dimensional molecular dynamics (MD) model is utilized to study the effects of the scribing feed on the atomic-scale lithography process. The model utilizes the Morse potential function to simulate interatomic forces between the atoms of the workpiece and the tool, and also between the atoms of the workpiece themselves. MD simulation results are compared to atomic force microscopy (AFM) experimental results. Results show that both resultant force and surface roughness have a positive correlation with rate of feed when the feed is smaller than a critical value, after which they remain constant. Comparison of the feed effect behavior of the MD theoretical analysis and the AFM experiments shows good qualitative agreement.

Influence of temperature on tensile and fatigue behavior of nanoscale copper using molecular dynamics simulation

Abstract The tensile and fatigue behavior of nanoscale copper at various temperatures has been analyzed using molecular dynamics simulation. The stress–strain curve for nanoscale copper was obtained first and then the Youngs modulus of the material was determined. The modulus was larger than that obtained by previous studies and decreased with increasing temperature. From the fatigue test, the cyclic stress–number of cycles curve was obtained and the stress increased with increasing temperature. Furthermore, the ductile fracture configuration was observed in the fatigue testing process under the lower applied stress. It was also observed that nanoscale copper appears to have a fatigue limit of 10 5 cycles.

Growth of nanoscale InGaN self-assembled quantum dots

It has been demonstrated that we can use interrupted growth mode in metalorganic chemical vapor deposition (MOCVD) to fabricate nanoscale InGaN self-assembed quantum dots (QDs). With a 12-s growth interruption, we successfully formed InGaN QDs with a typical lateral size of 25 nm and an average height of 4.1 nm. The QDs density is about 2 x 10(10) cm(-2). In contrast, much larger InGaN QDs were obtained without growth interruption. Compared with samples prepared without growth interrupt, a much larger photoluminescence (PL) intensity and a large 67meV PL blue shift was observed from samples prepared with growth interrupt. These results suggest such a growth interrupt method is potentially useful in nitride-based optoelectronic devices grown by MOCVD

Nanoscale mechanical characteristics of vertical ZnO nanowires grown on ZnO:Ga/glass templates

The mechanical properties of vertical single-crystal ZnO nanowires on ZnO:Ga/glass templates were characterized by nanoindentation experiments in this work. The results from x-ray diffraction and Raman spectra show good crystal quality for the ZnO nanowires. The buckling loads were found to be 1465 and 215 μN for ZnO nanowires of 100 and 30 nm diameters, respectively. When the fixed‐fixed column mode was used, it was found that the Young’s modulus values of the ZnO nanowires of 100 and 30 nm diameters were 117 and 232 GPa, while the critical buckling strains were 0.62% and 0.35%, respectively. On the other hand, when we employed the fixed‐pinned column mode, it can be seen that the Young’s modulus values were 229 and 454 GPa, while the critical buckling strains were 0.32% and 0.18%, respectively. Buckling behaviour of the ZnO nanowires was significantly predicted by the Euler buckling model in this work.

A Large Area Flexible Array Sensors Using Screen Printing Technology

A flexible electronics sensor for large area sensing was developed using a screen printing technology with the thixotropy sol-gel materials to form the microstructure patterns on two polyimide (PI) sheets. A flexible sensor is 150times150 mm2, including posts, resistances, bumps, and electrode traces. The space between the top electrode and the resistance layer provided a buffer distance for large bending. Experimental results show that array microstructures have good morphological profiles at a screen speed of 10 mm/s, a squeegee pressure of 213 kPa, and a separation speed of 0.4 mm/s using the print-print mode. A membrane with a bump protrusion had a large displacement and a quick sensitive response because the bump provided a concentrated force of von Mises stress on the membrane center. For printing thick structures, diffusion effects and dimensional shrinkages can be reduced when a paste material with a higher viscosity is used. The results exhibit a potential for using in the flexible sensing and higher temperatures. In additional, the fabrication is the low cost and potential higher throughput in flexible electronics applications.