Browsing by Author "Chiang, Tun-Yuan"

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Cathodoluminescence study of defects in thermal treatment of zinc titanate thin films deposited by a cosputtering process
(2018-05-01)
Chiang, Tun-Yuan
;
Tsai, Chien-Huang
;
Huang, Ming-Chao
;
Wen, Hua-Chiang
;
Chou, Wu-Ching
The effects of thermal treatment of polycrystalline ZnO-TiO2 systems on their luminescence emission and phase properties were investigated using ex situ cathodoluminescence and back-scattering electron microscopy. The main features of the spectrum are a blue band at 2.75 eV for the phase of TiO and a complex visible band at 2.18 eV for the phase of ZnO, whose peak intensity depends on the annealing temperature. The spectrum intensity is dominated by the ZnO phase when annealing temperature was 720 degrees C, which is attributed to abnormal grain growth. Competition is observed between the broad band peaked at 2.18 eV and visible band peaked at 2.75 eV as the annealing temperature changed (820 degrees C-920 degrees C). The cathodoluminescence density is gradually governed by the TiO2 phase, and the emission in polychromatic and monochromatic imaging is stronger equally at 920 degrees C. The nucleation of the TiO2 and ZnO grains is present in the backscattering electron images as well.
Scratch Characteristics of ZnMgO Epilayers
(2015-05-01)
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Chiang, Tun-Yuan
;
Fan, Wen-Chung
;
Lee, Ling
Zn0.75Mg0.25O films were grown via metal organic vapor phase epitaxy on an M-plane sapphire substrate. We used nanoscratch tests to study the abrasive plow of the films; comparable cases of critical pileup were obtained on both sides of each scratch when the ramped load increased from 0 to 250 mu N. The film showed a crack in the bulge edge between the groove at ramped loads of 1000 mu N as well as full plastic deformation. The values of mu were 0.14, 0.33, 0.43, and 0.48 for the ramped loads of 250 mu N and 0.22, 0.26, 0.28, and 0.33 for the ramped load of 1000 mu N. We found that cracking dominated in the case of Zn0.75Mg0.25O films during plowing. Lower values of the coefficient of friction and shallower penetration depths were observed at RT, while higher values were observed in the annealed samples. It is suggested that higher growth temperatures induce lower bonding forces and reduce the shear resistances of Zn-0.75Mg0.25O films.
Solid solution strengthening and phase transformation in high-temperature annealed Si80Ge20 alloy
(2014-03-15)
Chiang, Tun-Yuan
;
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Tsai, Chien-Huang
;
電子物理學系
This investigation demonstrates the temperature-dependent mechanical properties of Si80Ge20 alloy films via a nanoindenter in the indentation depth of 100 nm. The roughly equal root mean square roughness (R-rms) values and repeatable load-displacement (P-delta) curves for the samples ensure the mechanical performances mainly contributed from the influences of annealing temperatures. The hardness (H) values of samples increase with the temperatures of an initial annealing in the range from RT to 900 degrees C, and, conversely, decrease for annealing temperatures over 900 degrees C. Accordingly, both E/H and h(r)/h(max) values, exhibiting an inverse tendency in the above temperature range, hints that the solid solution strengthening effect and the softening phenomenon occur for the initial-annealing and over-annealing stages, respectively. In addition, grazing incidence X-ray diffraction (GIXRD) analysis demonstrates the lattice expansion and the broadened peak that attribute to the solid solution strengthening of samples and the segregation of Ge, respectively. Through observing the value of the (200) lattice spacing of 5.624 A for a 900 degrees C-annealed sample by transmission electron microscopy (TEM) analysis, it is verified that the segregation of Ge is responsible for the decreased hardness for the 1000 degrees C-annealed sample. (C) 2013 Elsevier B.V. All rights reserved.
Thermal reliability of thin SiGe epilayers
(2012-04-01)
Wu, Ming-Jhang
;
Wen, Hua-Chiang
;
Chiang, Tun-Yuan
;
Tsai, Chien-Huang
;
Hsu, Wen-Kuang
The SiGe heterostructures can play a role that drastically enhances the carrier mobility of SiGe heterodevices, such as strained Si metal oxide semiconductor field effect transistors. However, it is difficult to access the both issues, that is, the propagation of the dislocation and thermal reliability of annealed SiGe films. In this study, we used ultrahigh-vacuum chemical vapor deposition to grow Si0.8Ge0.2 films (ca. 200 nm thick for heteroepitaxy) epitaxially on bulk Si. The samples were subsequently furnace-crystallized at temperatures of 800, 900, and 1000 degrees C. We used nanoscratch techniques to determine the frictional characteristics of the SiGe epilayers under various ramping loads and employed atomic force microscopy to examine their morphologies after scratching. From our investigation of the pile-up phenomena, we observed significant cracking dominating on both sides of the scratches on the films. The SiGe epilayers films that had undergone annealing treatment possessed lower coefficients of friction, suggesting higher shear resistances. (C) 2011 Elsevier B. V. All rights reserved.
Using nanoindentation and cathodoluminescence to identify the bundled effect of gallium nitride grown by PA-MBE
(2017-02-05)
Wen, Hua-Chiang
;
Chou, Wu-Ching
;
Chiang, Tun-Yuan
;
Jeng, Yeau-Ren
;
Fan, Wen-Chung
We performed cathodoluminescence (CL) investigations on GaN NCs grown using molecular beam epitaxy. Bundled GaN was used to form NCs that were deposited onto commercial sapphire templates. The structures of the bundled NCs were analyzed using nanoindentation. The samples were grown with a T-G of 700, 800, and 850 degrees C, and the H values were 7.4 +/- 0.2 and 6.4 +/- 0.2 GPa; the E values were 308.4 +/- 4.3, 296.4 +/- 3.8, and 75.5 +/- 1.4 GPa, respectively. It is suspected that the discrepancies of the mechanical parameters obtained by various indentation methods are partially a result of the stress distribution inherent in the different orientations on the sapphire substrate. A scanning electron microscopy (SEM) system equipped with CL allows the direct comparison of SEM images and CL maps, captured from exactly the same area of the samples. In addition to the SEM and CL images, photoluminescence spectroscopy (PL) profiling was obtained by collecting the 20 K PL spectra at the samples. The PL profiling enables the distinguishing of the emissions by the 5 meV of the blueshift from 3.440 to 3.445 eV due to localization effects. The bundled GaN NCs resulted from the (0002) reflection at 34.6 degrees for a wurtzite structure and a raised intensity difference when the TG was increased from 700 to 850 degrees C. The crystal texture of the GaN can influence the mechanical properties at different TG stages. (C) 2016 Elsevier B.V. All rights reserved.