Jun-Han Huang

Anisotropic Outputs of a Nanogenerator from Oblique-Aligned ZnO Nanowire Arrays

We studied the dependence of the output of the piezoelectric nanogenerator (NG) on the inclining orientation of the ZnO nanowire arrays (NWAs). The oblique-aligned NWAs were grown by combing a modified oblique-angle sputtering technique for preparing the seed layer and hydrothermal growth. The piezoelectric output of the NWAs was studied by scanning the tip of an atomic force microscope along four different directions in reference to the inclining direction of the NWs. The statistical outputs were analyzed in reference to the theoretically calculated piezopotential distribution in the NWs. Our study provides in-depth understanding about the performance of NGs.

Enhanced ferromagnetism in grain boundary of Co-doped ZnO films: A magnetic force microscopy study

Microscopic grain structures and magnetic properties of Co-doped ZnO-patterned films were studied by combinatorial atomic force microscopy and magnetic force microscopy (MFM) imaging. Whereas Co-doped ZnO was not uniformly magnetized, Co ions were homogeneously doped in the films and substitute from the Zn sites. Most Co:ZnO grains were weakly ferromagnetic (FM) and surrounded by strong FM foamlike grain boundaries networks. No MFM contrast was observed in pure ZnO films grown under similar conditions. The findings clearly demonstrate that defective grain boundaries and magnetic doping have key roles FM properties of diluted magnetic oxides.

Giant optical anisotropy of oblique-aligned ZnO nanowire arrays

A combined method of modified oblique-angle deposition and hydrothermal growth was adopted to grow an optically anisotropic nanomaterial based on single crystalline ZnO nanowire arrays (NWAs) with highly oblique angles (75°-85°), exhibiting giant in-plane birefringence and optical polarization degree in emission. The in-plane birefringence of oblique-aligned ZnO NWAs is almost one order of magnitude higher than that of natural quartz. The strong optical anisotropy in emission due to the optical confinement was observed. The oblique-aligned NWAs not only allow important technological applications in passive photonic components but also benefit the development of the optoelectronic devices in polarized light sensing and emission.

Rapid fabrication of a micro-ball lens array by extrusion for optical fiber applications

Batch-fabrication of a micro-ball lens array (MBA) could not only reduce micro assembly costs but also replace conventional ball lenses or costly GRINs (Gradient Refractive Index) without compromising performance. Compared with conventional half-spherical micro-lenses, the MBA is a spherical micro-lens that can focus light in all directions, thus providing the flexibility required for optical applications. Current MBAs are made of SU-8 photoresist by an extrusion process rather than the traditional thermal reflow process. The aim of this study was to develop a new process for MBA batch-fabrication, performed at ambient temperature, by spin-coating SU-8 onto a silicon-wafer surface, which serves as an extrusion plate, and extruding it through a nozzle to form an MBA. The nozzle consists of a nozzle orifice and nozzle cavity, the former being defined and made from SU-8 photoresist using ultra-violet (UV) lithography, which results in good mechanical properties. In this paper, the fabrication of 4 x 4 MBAs with diameters ranging from 60 to 550 um is described. Optical measurements indicated a diameter variance within 3% and a maximum coupling efficiency of approximately 62% when the single mode fiber (SMF) was placed at a distance of 10 um from the MBA. The results of this study proved that MBA fabrication by the extrusion process can enhance the coupling efficiency.

Microstructural effects on the magnetic and magneto-transport properties of electrodeposited Ni nanowire arrays

The magnetic and magneto-transport properties of Ni nanowire (NW) arrays, fabricated by electrodeposition in anodic-aluminum-oxide (AAO) templates, have been investigated. The AAO pores have diameters ranging from 35 to 75 nm, and the crystallinity of the Ni NW arrays could change from poly-crystalline to single-crystalline with the [111] and [110] orientations based on the electrodeposition potential. Notably, double switching magnetization loops and double-peaked magnetoresistance curves were observed in [110]-oriented NWs. The crystalline orientation of the Ni NW arrays is found to influence the corresponding magnetic and magneto-transport properties significantly. These magnetic behaviors are dominated by the competition between the magneto-crystalline and shape anisotropy.

Dependence of magnetism on the doping level of Zn1−xMnxTe nanoparticles synthesized by a hydrothermal method

Mn-doped ZnTe nanoparticles with various degrees of Mn-doping from 3 at.% to 18 at.% were synthesized by a hydrothermal method. A single-phase zinc-blende-structured sample was obtained only at the Mn-doping level of 3 at.%, while the impurity phase of MnO was present in the samples with higher degrees of Mn-doping. In all of the samples, the Mn valence states were lower than 2+. All samples exhibited both ferromagnetism and paramagnetism. The ferromagnetism is mainly attributable to the overlapping of the bound magnetic polarons and the paramagnetism is mainly caused by the isolated polarons and Mn ions. Samples that were doped with 3 at.% and 6 at.% Mn also exhibited superparamagnetism and antiferromagnetism. The superparamagnetism may have arisen from the presence of some tiny ferromagnetic nanoparticles. The antiferromagnetism is believed to have arisen mainly from the carrier-mediated interaction among Mn ions.

Tuning the transport and magnetism in a Cr–Bi2Se3 topological insulator by Sb doping

High-quality crystalline (Cr,Sb)-doped Bi2Se3 (Cr-BSS) films were synthesized using molecular beam epitaxy (MBE). The effect of Cr- and Sb-doping on the transport and magnetic properties of Cr-BSS films was systematically investigated. The sheet carrier density N2D was found to be reduced to ∼6 × 1012 cm−2 in this quaternary compound at room temperature. This has not previously been observed in a Cr–Bi2Se3-based magnetic topological insulator (TI). Moreover, owing to the Sb dopants, the weak localization (WL)-like positive magnetoconductance in magnetic Cr–Bi2Se3 (Cr-BS) was enhanced. The enhancement is attributed to the emergence of ferromagnetism, as evidenced from the field-dependent Hall resistance and magnetic moment. The obvious tunable electrical and magnetic properties by the Sb dopant in this system are well suited for applications based on magnetic TI devices.

Design and fabrication of a multi-degree-of-freedom microactuator using symmetric piezoelectric pusher element and its applications

A novel multi-degree-of-freedom (MDOF) microactuator was developed using a symmetric piezoelectric plate and a Ni-Co alloy micro-pusher element. A LIGA-like technique was employed to manufacture a Ni-Co alloy micro-pusher with a Vickers hardness value (HV) of 550, which was then attached at the midpoint of the long side of a piezoelectric plate with dual electrodes to construct a symmetric piezoelectric pusher element (SPPE). The research integrated the concept of LEGO® bricks, and three different vibration modes of the SPPE were designed to develop a high-power MDOF motion platform, which was able to rotate a spherical device along three perpendicular axes. This MDOF microactuator consisted of a stator and a rotor: the stator was created from two mutually orthogonal sets of parallel SPPEs to form a MDOF motion platform, and the rotor was a spherical device. The experiment demonstrated the high-power MDOF eyeball-like microactuator working frequencies along the X-, Y-, and Z-axes to be 223.4 kHz, 223.2 kHz, and 225 kHz and the rotation speeds to reach 50 rpm, 52 rpm, and 180 rpm, respectively, at a driving voltage of 30Vpp. In the future, this MODF eyeball-like microactuator may be used for a number of applications, such as sun-tracking systems for green energy harvesters and eyeball-like devices for use in the biomedical field.

A novel miniaturization actuator using a symmetric piezoelectric pusher element for pocket sun-tracking system

A novel pocket sun-tracking system was developed using a symmetric piezoelectric plate and a Ni-Co alloy micro-pusher element. A LIGA-like technique was employed to manufacture a Ni-Co alloy micro-pusher with a Vickers hardness value (HV) of 550, which was then attached at the midpoint of the long side of a piezoelectric plate with dual electrodes to construct a symmetric piezoelectric pusher element (SPPE). The research integrated the concept of LEGO® bricks, and three different vibration modes of the SPPE were designed to develop a miniaturization SPPE actuator, which was able to rotate a hemisphere concentrator lens along three perpendicular axes. The experiment demonstrated the pocket sun-tracking system moving precision to reach 1° and the rotation speeds to reach 50 rpm at a driving voltage of 30Vpp. In the future, this miniaturization SPPE actuator may be used for a number of applications, such as sun-tracking systems for green energy harvesters and bio-devices for use in the biomedical field.