Yuan Huei Chang

Distinguishing a multitude of optical labels is crucial to improving the spatial and temporal resolution of bioimaging. However, current multicolor imaging approaches are limited by the spectral overlap of employed fluorophores. We here discern different instances of a single optical label type through their emission intensity. Such multilevel optical labels are enabled by an optical writing process that permanently modifies their spectral response in a predictable manner and by a separate spectral feature that serves as normalization in the presence of sample variability. The proposed approach was realized by independently controlling the emission properties of highly functionalized fluorescent nanodiamond. Upon laser irradiation, the contribution of the spectral region associated with the N3 color center decreases in a predictable and permanent fashion, while the nitrogen vacancy (NV) emission remains stable. This selective photobleaching of N3 centers was found to originate from a two-photon-assisted dissociation process that results in a 10⁵ higher mobility of photoexcited carriers in N3 centers compared to NV. The resulting write once read many (WORM) memory exhibits multiple distinct memory levels that can be stored and read out with high robustness and reproducibility. The potential of our approach was demonstrated by characterizing markers in HeLa cells with high fidelity, despite the complex emission background. Finally, direct manipulation of label information inside of cells was demonstrated, opening up new routes in advanced bioimaging.

We report the growth of high quality Bi2Se3 thin films on Al2O3 substrates by using chemical vapor deposition. From the atomic force microscope, x-ray diffraction and transmission electron microscope measurements we found that the films are of good crystalline quality, have two distinct domains and can be grown epitaxially on the Al2O3 substrate. Carrier concentration in the sample is found to be 1.1 × 1019 cm−3 between T = 2 K to T = 300 K, and electron mobility can reach 954 cm2/V s at T = 2 K. Weak anti-localization effect is observed in the low temperature magneto-transport measurement for the sample which indicates that the thin film has topological surface state.

The fabrication and properties of n-ZnO nanowires/p-CuO coaxial heterojunction (CH) with a photoresist (PR) blocking layer are reported. In our study, c-plane wurtzite ZnO nanowires were grown by aqueous chemical method, and monoclinic CuO (111) was then coated on the ZnO nanowires by electrochemical deposition to form CH. To improve the device performance, a PR layer was inserted between the ZnO buffer layer and the CuO film to serve as a blocking layer to block the leakage current. Structural investigations of the CH indicate that the sample has good crystalline quality. It was found that our refined structure possesses a better rectifying ratio and smaller reverse leakage current. As there is a large on/off ratio between light on and off and the major light response is centered at around 424 nm, the experimental results suggest that the PR-inserted ZnO/CuO CH can be used as a good narrow-band blue light detector.

A Sb-doped ZnO microrod array was fabricated on an Al-doped ZnO thin film by electrodeposition. Strong violet luminescence, originated from free electron-to-acceptor level transitions, was identified by temperature-dependent photoluminescence measurements. This acceptor-related transition was attributed to substitution of Sb dopants for Zn sites, instead of O sites, to form a complex with two Zn vacancies (V_Zn), the Sb_Zn-2V_Zn complex. This Sb_Zn-2V_Zn complex has a lower formation energy and acts as a shallow acceptor which can induce the observed strong violet luminescence. The photoresponsivity of our ZnO p-n homojunction device under a negative bias demonstrated a nearly 40-fold current gain, illustrating that our device is potentially an excellent candidate for photodetector applications in the ultraviolet wavelength region.

The Working Group for Women in Physics in Taiwan was registered to the Physical Society of the Republic of China (PSROC) in December 1999 and was formally announced at the 2001 annual assembly of PSROC. In 2003 the group became a formal committee under PSROC. The current committee includes seven female and two male members. In the last 10 years, many milestones were achieved. In particular, the percentage of female physics faculties in universities and research institutes has increased to 12% from 8% within the last 10 years. In this paper we will present the results of our survey on the changes of the percentage of female physics faculties/students within the last 10 years and express our need to improve the working environment for female faculties in Taiwan in the future.

We study the temperature flow of conductivities in a gated GaAs two-dimensional electron gas (2DEG) containing self-assembled InAs dots and compare the results with recent theoretical predictions. By changing the gate voltage, we are able to tune the 2DEG density and thus vary disorder and spin-splitting. Data for both the spin-resolved and spin-degenerate phase transitions are presented, the former collapsing to the latter with decreasing gate voltage and/or decreasing spin-splitting. The experimental results support a recent theory, based on modular symmetry, which predicts how the critical Hall conductivity varies with spin-splitting.

We report the growth and characterization of ZnO/ZnTe core/shell nanowire arrays on indium tin oxide. Coating of the ZnTe layer on well-aligned vertical ZnO nanowires has been demonstrated by scanning electron microscope, tunneling electron microscope, X-ray diffraction pattern, photoluminescence, and transmission studies. The ZnO/ZnTe core/shell nanowire arrays were then used as the active layer and carrier transport medium to fabricate a photovoltaic device. The enhanced photocurrent and faster response observed in ZnO/ZnTe, together with the quenching of the UV emission in the PL spectra, indicate that carrier separation in this structure plays an important role in determining their optical response. The results also indicate that core/shell structures can be made into useful photovoltaic devices.