Ing-Chi Leu

Fabrication of ordered ZnO hierarchical structures controlled via surface charge in the electrophoretic deposition process

In this study, a fabrication of ordered ZnO hierarchical structures with nano- and microscale pores is presented. Tunable ordered hollow and solid nanostructures of dots and networks have been obtained utilizing the effect of surface-charge coupling between the latex particles and the oxide nanoparticles deposited in the electrophoretic deposition process. The force induced by an electrical field can move the charged particles towards an electrode, and the surface-charge coupling force can efficiently fine-tune the relative position of the neighbouring particles and thus result in the formation of various ordered assemblies.

Sheath-dependent orientation control of carbon nanofibres and carbon nanotubes during plasma-enhanced chemical vapour deposition

The aligned growth of carbon nanofibres (CNFs) and carbon nanotubes (CNTs) via a simple sheath-dependent technique for orientation control is demonstrated. Significant difference in the alignment behaviour of CNFs/CNTs, involving the transition of sheath-dependent electric fields, is found to depend on the relation between the sheath width and the sample dimension. The electric field within the plasma sheath contributes to the aligned growth of CNFs/CNTs with an absolute orientation, and can be used to direct the assembly of CNFs/CNTs in a predetermined manner relative to the substrate by tilting the sample in a sheath region. The consequent application for synthesis of kinked carbon nanostructures by altering the alignment angle to the substrate during growth is also achieved.

Structural and electrical characterizations of PbTiO3 thin films grown on LaNiO3-buffered Pt/Ti/SiO2/Si substrates by liquid phase deposition

Ferroelectric PbTiO 3 (PTO) thin films were successfully deposited on the LaNiO 3 (LNO) buffered Pt/Ti/SiO 2 /Si substrates by the liquid phase deposition method. The LNO layer served as both the bottom electrode and seeding layer for the PTO films. The structure, morphology, and electrical properties of the films were investigated by analytical techniques and electrical measurements. X-ray diffraction revealed that the as-deposited amorphous precursor films were decomposed and crystallized into perovskite structure after annealing at 650°C. Scanning electron microscopy showed that the thin films were smooth, dense, and crack-free with a grain size of ∼200 nm. The mechanism of liquid phase deposition for PTO is proposed. The room temperature dielectric constant and dielectric loss of the PTO films, measured at kHz are 96.8 and 0.09, respectively, for the film with 200 nm thickness as annealed at 650°C for 1 h. The capacitor exhibits a hysteresis loop with a remanent polarization of 2.1 μC/cm 2 and a coercive field of 33.4 kV/cm, respectively.

Fabrication of Various Nickel Nanostructures by Manipulating the One-Step Electrodeposition Process

By employing colloidal crystal templates with different colloid diameters, nickel well-ordered macroporous structures (inverse opal) with different void diameters can be fabricated via a template-mediated electrodeposition process. It was found that the different degrees of filling colloidal crystal template produces different nickel nanostructures during the electrodeposition process. Moreover, the filling behavior for electrodeposition of nickel into the template can be characterized in terms of the current transients recorded. Because of preferential nickel-filling into the interstitial spaces among the colloids, fabrication of well-ordered nickel nanorod and monolayer porous arrays are manipulated by controlling electrodeposition times accurately at 5 and 10 s, respectively. However, the macroporous structure covered with hollow sphere arrays on the surface can be formed in 120 s due to preferential nickel-coating around the colloidal surface. Therefore, various kinds of nickel-based structures derived from colloidal crystals can be constructed via a one-step, template-mediated electrodeposition process.

Nanostructures prepared on polyimide films by nanoimprinting with the assistance of residual solvent

An elastomeric stamp made from poly(dimethylsiloxane) (PDMS) was employed to prepare patterned polyimide (PI) films by a solvent-assisted nanoimprinting process. From FESEM observation and SPM scanning, it was found that patterns with 550 nm pitch size have been completely transformed from the PDMS mold into the PI films. By FTIR spectra analysis, it was observed that the poly-amic acid (PAA) precursor was converted completely to PI by thermal curing at 250 °C for 20 min. Throughout the whole work, it is suggested that the excellent performance of pattern transfer of PDMS to PI could be ascribed to the assistance of residual solvent. The present study provides a new approach to fabricate nanoimprinted PI films which was considered to be difficult by the conventional hot embossing technique.

Spatially oriented carbon nanofibres manipulated by a hollow cathode discharge process

The ability to manipulate the orientation of nanoscale materials is of great importance for applications in advanced devices. Here, we describe the controlled growth of aligned carbon nanofibres (CNFs) in a hollow cathode discharge (HCD) set-up. Instead of vertical alignment well demonstrated in other plasma-based chemical vapour deposition, CNFs with specific and symmetrically aligned configurations are grown on a flat surface during HCD. Experimental evidence shows that the alignment is not the result of the edge or flow effect, but results from a unique electric field distribution imposed on the substrate surface in the HCD environment. Due to the field reversal characteristic of the HCD, two alignment trends simultaneously occur. For the transverse direction of the channel, the grown CNFs on the substrate appear in a convergent manner, while those along the longitudinal direction exhibit a radiative arrangement. These results will open up the possibility of both tuning the electric fields on the basis of plasma design and tailoring the spatial orientations of CNFs using HCDs.

Morphology and growth behavior of P-type Si macropores in submicronmeter prepattern

This paper studies the pore morphology and growth behavior of p-type silicon macropores in submicronmeter prepattern by electrochemistry method. It was found that only random macropores with an average diameter of ~1 mum could be formed after electrochemical etching in 3M HF/DMSO solution, while ordered pore arrays are obtained with the assistance of pre-patterning on the Si substrate surface. For micrometer-scale patterns (e.g. 1.6 mum), the regular porous structure with high aspect ratio of about 60 is successfully formed after 120 mins of electrochemical etching. However, as the pattern scale reduces to submicronmeter, the capability of pre-pattems in guiding the growth of pores becomes weakened. Regular pore arrays with aspect ratios of 10 and 3 were obtained by etching samples with pre-pattem pitches of 870 nm and 550 nm, respectively.

Fabrication of ZnO micro-fluidic channels by ZnO sol-gel/PMMA bilayer structure

In this study, we describe simple fabrication methods to fabricate ZnO micro-fluidic channels by using a ZnO sol-gel/polymethymethacrylate (PMMA) bilayer structure. Two types of ZnO micro-fluidic channels were then created successfully after a hot-embossing step and the subsequent removal of PMMA by annealing.

Imprinting of polyimide without residual layers

In this study, imprinting condition of 180degC for 20 minutes is used to fabricate patterned polyimide (PI) films. Results provides a simple approach to fabricate patterns without residual layer due to the dewetting behavior between the poly-amic acid (PAA) solution and imprint stamp.

Fabrication and characterization of tunable photonic crystals by filling silica nanoparticles into the PS opals

The self-assembly of monodispersed colloids into an ordered three-dimensional structure, i. e., an opal (colloidal crystal) structure, is routinely employed to fabricate photonic crystals. In this study, high-quality polystyrene (PS) colloidal crystals in large area were fabricated during 24 hours via the capillary-enhanced process. Then, the tunable photonic crystals were formed by incorporating silica nanoparticles of different concentration into the void space via a dipping process. According to Ficks Law, the interstitial space of opal could be completely filled. Thereby, the monodisperse spheres of opal will form core-shell structure. Moreover, increase of silica nanoparticle concentration will result in an increased refractive index of the opal film. The absorptive peak of pure opal is 445nm as measured in UV-Vis spectrum, and the absorptive peak of core-shell opal is 453nm, 463nm and 469nm for suspensions with different concentration of silica nanoparticles of 0.017, 0.122, and 0.244wt%, respectively. Therefore, by using this dipping process to fill the opal film with colloidal nanoparticles, the characteristic absorption wavelength for opal film can be fine-tuned more easily, efficiently and cost effectively than by traditional methods of constructing opal from monodispersed colloids of different diameter.