Browsing by Author "Tsai, Wei-Chih"

Now showing 1 - 14 of 14

Effect of Oxygen Annealing on the Ultraviolet Photoresponse of p-NiO-Nanoflower/n-ZnO-Nanowire Heterostructures
(2011-07-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O(2)) ambient exhibited better rectification behavior (l(forward)/l(reverse) = 427), a lower forward threshold voltage (V(th) = 0.98 V), a lower leakage current (1.68 x 10(-5) A/cm(2)), and superior sensitivity (l(UV)/l(dark) = 57.8; l(visible)/l(dark) = 1.25) to UV light (lambda = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity. A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O(2) ambient indicate that they can be applied to nano-integrated optoelectronic devices.
Field-Emission Characteristics of Al-Doped ZnO Nanostructures Hydrothermally Synthesized at Low Temperature
(2011-07-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
The aluminum-doped ZnO (AZO) nanostructures with different Al concentrations were synthesized on AZO/glass substrate via a simple hydrothermal growth method at a temperature as low as 85 degrees C. The morphologies, crystallinity, optical emission properties, and chemical bonding states of AZO nanostructures show evident dependence on the aluminum dosage. The morphologies of AZO nanostructures were changed from vertically aligned nanowires (NWs), and NWs coexisted with nanosheets (NSs), to complete NSs in respect of the Al-dosages of 0 similar to 3 at.%, 5 at.%, and 7 at.%, correspondingly. The undoped ZnO and lightly Al-doped AZO (<= 3 at.%) NWs are single-crystalline wurtzite structure. In contrast, heavily Al-doped AZO sample is polycrystalline. The AZO nanostructure with 3 at.% Al-dosages reveals the optimal crystallinity and less structural defects, reflecting the longest carrier lifetime and highest conductivity. Consequently, the field-emission characteristics of such an AZO emitter can exhibit the higher current density, larger field-enhancement factor (beta) of 3131, lower turn-on field of 2.17 V/mu m, and lower threshold field of 3.43 V/mu m.
High Field-Emission Stability of Offset-Thin-Film Transistor-Controlled Al-Doped Zinc Oxide Nanowires
(2011-04-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
Aluminum-doped zinc oxide (AZO) nanowire (NW) arrays incorporating an offset thin-film transistor (offset-TFT) have been proposed to achieve high field-emission (FE) stability. The AZO NW field emission arrays (FEAs) were hydrothermally grown at a low temperature of 85 degrees C. The uncontrolled AZO NW FEAs demonstrated superior FE characteristics (i.e., turn-on field of similar to 2.17 V/mu m and threshold field of similar to 3.43 V/mu m) compared with those of the conventional CNT FEAs grown at a temperature below 600 degrees C. However, uncontrolled AZO NW FEAs show a larger current fluctuation of 15.6%. Therefore, the offset-TFTs were used to control the AZO NW FEAs. Consequently, the fluctuation of AZO NW FEAs could be significantly reduced to less than 2%. This novel field emission device exhibits good emission stability, low-voltage controllability, low-temperature processing, and structural simplicity, making it promising for applications in flat panel displays. (C) 2011 The Japan Society of Applied Physics
High-Performance ZnO Thin-Film Transistors with Location-Controlled Crystal Grains Fabricated by Low-Temperature Hydrothermal Method
(2012-07-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Chang, Yu-Cheng
;
Wang, Shui-Jinn
In this paper, high-performance bottom-gate (BG) thin-film transistors (TFTs) with zinc oxide (ZnO) artificially location-controlled lateral grain growth have been prepared via low-temperature hydrothermal method. For the proper design of source/drain structure of ZnO/Ti/Pt thin films, the grains can be laterally grown from the under-cut ZnO beneath the Ti/Pt layer. Consequently, the single one vertical grain boundary perpendicular to the current flow will be produced in the channel region as the grown grains from the source/drain both sides are impinged. As compared with the conventional sputtered ZnO BG-TFTs, the proposed location-controlled hydrothermal ZnO BG-TFTs (W/L = 250 mu m/10 mu m) demonstrated the higher field-effect mobility of 6.09 cm(2)/V.s, lower threshold voltage of 3.67 V, higher on/off current ratio above 10(6), and superior current drivability, reflecting the high-quality ZnO thin films with less grain boundary effect in the channel region.
Hsa-miR-122, a tumor suppressor microRNA that regulates intra-hepatic metastasis of hepatocellular carcinoma
(2009-05-01)
Tsou, Ann-Ping
;
Tsai, Wei-Chih
;
Hsu, Wei-Che
;
Huang, Hsien-Da
;
Chau, Gar-Yang
Identifying transcriptional start sites of human microRNAs based on high-throughput sequencing data
(2012-04-15)
Tsou, Ann-Ping
;
Chien, Chia-Hung
;
Chiang-Hsieh, Pei-Yun
;
Tsai, Wei-Chih
;
Huang, Hsien-Da
Identifying transcriptional start sites of human microRNAs based on high-throughput sequencing data
(2011-11-01)
Chien, Chia-Hung
;
Sun, Yi-Ming
;
Chang, Wen-Chi
;
Chiang-Hsieh, Pei-Yun
;
Lee, Tzong-Yi
MicroRNAs (miRNAs) are critical small non-coding RNAs that regulate gene expression by hybridizing to the 3'-untranslated regions (3'-UTR) of target mRNAs, subsequently controlling diverse biological processes at post-transcriptional level. How miRNA genes are regulated receives considerable attention because it directly affects miRNA-mediated gene regulatory networks. Although numerous prediction models were developed for identifying miRNA promoters or transcriptional start sites (TSSs), most of them lack experimental validation and are inadequate to elucidate relationships between miRNA genes and transcription factors (TFs). Here, we integrate three experimental datasets, including cap analysis of gene expression (CAGE) tags, TSS Seq libraries and H3K4me3 chromatin signature derived from high-throughput sequencing analysis of gene initiation, to provide direct evidence of miRNA TSSs, thus establishing an experimental-based resource of human miRNA TSSs, named miRStart. Moreover, a machine-learning-based Support Vector Machine (SVM) model is developed to systematically identify representative TSSs for each miRNA gene. Finally, to demonstrate the effectiveness of the proposed resource, an important human intergenic miRNA, hsa-miR-122, is selected to experimentally validate putative TSS owing to its high expression in a normal liver. In conclusion, this work successfully identified 847 human miRNA TSSs (292 of them are clustered to 70 TSSs of miRNA clusters) based on the utilization of high-throughput sequencing data from TSS-relevant experiments, and establish a valuable resource for biologists in advanced research in miRNA-mediated regulatory networks.
MicroRNA-122 plays a critical role in liver homeostasis and hepatocarcinogenesis
(2012-08-01)
Tsai, Wei-Chih
;
Hsu, Sheng-Da
;
Hsu, Chu-Sui
;
Lai, Tsung-Ching
;
Chen, Shu-Jen
"MicroRNA-122 (miR-122), which accounts for 70% of the liver's total miRNAs, plays a pivotal role in the liver. However, its intrinsic physiological roles remain largely undetermined. We demonstrated that mice lacking the gene encoding miR-122a (Mir122a) are viable but develop temporally controlled steatohepatitis, fibrosis, and hepatocellular carcinoma (HCC). These mice exhibited a striking disparity in HCC incidence based on sex, with a male-to-female ratio of 3.9:1, which recapitulates the disease incidence in humans. Impaired expression of microsomal triglyceride transfer protein (MTTP) contributed to steatosis, which was reversed by in vivo restoration of Mttp expression. We found that hepatic fibrosis onset can be partially attributed to the action of a miR-122a target, the Klf6 transcript. In addition, Mir122a(-/-) livers exhibited disruptions in a range of pathways, many of which closely resemble the disruptions found in human HCC. Importantly, the reexpression of miR-122a reduced disease manifestation and tumor incidence in Mir122a(-/-) mice. This study demonstrates that mice with a targeted deletion of the Mir122a gene possess several key phenotypes of human liver diseases, which provides a rationale for the development of a unique therapy for the treatment of chronic liver disease and HCC."
MicroRNA-122 regulates liver metabolism and hepatocyte differentiation
(2011-04-15)
Tsou, Ann-Ping
;
Tsai, Wei-Chih
;
Hsu, Sheng-Da
;
Hsu, Chu-Sui
;
Hsiao, Ming-Shi
MicroRNA-122, a Tumor Suppressor MicroRNA that Regulates Intrahepatic Metastasis of Hepatocellular Carcinoma
(2009-05-01)
Tsai, Wei-Chih
;
Hsu, Paul Wei-Che
;
Lai, Tsung-Ching
;
Chau, Gar-Yang
;
Lin, Ching-Wen
MicroRNAs (miRNAs), which are inhibitors of gene expression, participate in diverse biological functions and in carcinogenesis. In this study, we show that liver-specific microRNA-122 (miR-122) is significantly down-regulated in liver cancers with intrahepatic metastastasis and negatively regulates tumorigenesis. Restoration of miR-122 in metastatic Mahlavu and SK-HEP-1 cells significantly reduced in vitro migration, invasion, and anchorage-independent growth as well as in vivo tumorigenesis, angiogenesis, and intrahepatic metastasis in an orthotopic liver cancer model. Because an inverse expression pattern is often present between an miRNA and its target genes, we used a computational approach and identified multiple miR-122 candidate target genes from two independent expression microarray datasets. Thirty-two target genes were empirically verified, and this group of genes was enriched with genes regulating cell movement, cell morphology, cell-cell signaling, and transcription. We further showed that one of the miR-122 targets, ADAM17 (a disintegrin and metalloprotease 17) is involved in metastasis. Silencing of ADAM17 resulted in a dramatic reduction of in vitro migration, invasion, in vivo tumorigenesis, angiogenesis, and local invasion in the livers of nude mice, which is similar to that which occurs with the restoration of miR-122. Conclusion: Our study suggests that miR-122, a tumor suppressor microRNA affecting hepatocellular carcinoma intrahepatic metastasis by angiogenesis suppression, exerts some of its action via regulation of ADAM17. Restoration of miR-122 has a far-reaching effect on the cell. Using the concomitant down-regulation of its targets, including ADAM17, a rational therapeutic strategy based on miR-122 may prove to be beneficial for patients with hepatocellular carcinoma. (HEPATOLOGY 2009;49:1571-1582.)
Photoresponse of hydrothermally grown lateral ZnO nanowires
(2010-10-01)
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Tsai, Wei-Chih
;
Wang, Shui-Jinn
;
Lin, Jia-Chuan
In this paper, a simple self-assembled lateral growth of ZnO nanowires (NWs) photodetector has been synthesized by a hydrothermal method at a temperature as low as 85 degrees C. The ZnO NWs exhibit single-crystalline wurtzite with elongated c-axis and can be selectively lateral self-assembled around the edges of ZnO seeding layer. The current of ZnO NWs is sensitive to the variation of ambient pressures, i.e. 4.47 mu A was decreased to 1.48 mu A with 5 V-bias as 1.1 x 10(-6) Torr changed to 760 Torr. accordingly. Moreover, the current voltage characteristics of ZnO NWs photodetectors can be evidently distinguished by UV illumination (i.e. lambda = 325 nm). The photocurrent of ZnO NWs with UV illumination is twice larger than dark current while the voltage biased at 5 V. Consequently, this faster photoresponse convinces that the hydrothermally grown lateral ZnO NWs devices have a fairly good for the fabrication of UV photodetectors. (C) 2010 Elsevier B.V. All rights reserved.
Simulation and analysis of metamorphic high electron mobility transistors
(2007-02-01)
Lin, Jia-Chuan
;
Yang, Po-Yu
;
Tsai, Wei-Chih
;
光電工程學系
;
顯示科技研究所
In this paper, the metamorphic high electron mobility transistors (mHEMTs) are investigated numerically and compared with pseudomorphic high electron mobility transistors (pHEMTs). The two-dimensional device simulator, MEDICI, is used to solve the Poisson's equation and the electron/hole current continuity equations. The influences of delta-doping concentration and position, gate width, spacer thickness, etc. on the performances of HEMTs are explored. It shows clearly that mHEMTs have higher transconductances, drain currents and DC voltage swings than pHEMTs. (c) 2006 Elsevier Ltd. All rights reserved.
Structure design criteria of dual-channel high mobility electron transistors
(2007-01-01)
Lin, Jia-Chuan
;
Chen, Yu-Chieh
;
Tsai, Wei-Chih
;
Yang, Po-Yu
;
光電工程學系
The design criteria of dual-channel high electron mobility transistor (DHEMT) are proposed in this study. 8-Doped In(0.52)Al(0.48)As/ In(0.53)Ga(0.47)As/InP material systems are concentrated in this article. The DHEMT structures are explored numerically and compared with conventional single-channel high electron mobility transistor (SHEMT) structures. Some criteria of doping concentration and layer structure design are proposed. The simulation results reveal that DHEMT has a larger voltage swing, a lower gate leakage current, a better carrier confinement, a higher density of two-dimensional electron gas (2DEG) and an excellent transconductance than SHENIT. (c) 2006 Elsevier Ltd. All rights reserved.
Zinc Oxide Thin-Film Transistors with Location-Controlled Crystal Grains Fabricated by Low-Temperature Hydrothermal Method
(2011-04-01)
Cheng, Huang-Chung
;
Yang, Po-Yu
;
Wang, Jyh-Liang
;
Agarwal, Sanjay
;
Tsai, Wei-Chih
High-performance zinc oxide (ZnO) bottom-gate (BG) thin-film transistors (TFTs) with a single vertical grain boundary in the channel have been successfully fabricated by a novel low-temperature (i.e., 85 degrees C) hydrothermal method. The ZnO active channel was laterally grown with an aluminum-doped ZnO seed layer underneath the Ti/Pt film. Consequently, such BG-TFTs (W/L = 250 mu m/10 mu m) demonstrated the high field-effect mobility of 9.07 cm(2)/V . s, low threshold voltage of 2.25 V, high on/off-current ratio above 10(6), superior current drivability, indistinct hysteresis phenomenon, and small standard deviations among devices, attributed to the high-quality ZnO channel with the single grain boundary.