Effects of Hydrogen on the Optical and Electrical Characteristics of the Sputter-Deposited Al2O3-Doped ZnO Thin Films

In this study, AZO thin films were deposited on glass by using a 98 mol% ZnO + 1 mol% Al2O3 (AZO, Zn : Al = 98 : 2) ceramic target and a r.f. magnetron sputtering system. At first, the effects of different H2 flow rates (H2/(H2 + Ar) = 0%~9.09%, abbreviated as H2-deposited AZO thin films, deposition temperature was 200°C) added during the deposition process on the physical and electrical properties of AZO thin films were investigated. The optical transmittance at 400 nm~700 nm is more than 80% for all AZO thin films regardless of H2 flow rate and the transparency ratio decreased as the H2 flow rate increased. The Burstein-Moss shift effect was used to prove that the defects of AZO thin films decreased with increasing H2 flow rate. Also, the 2% H2-deposited AZO thin films were also treated by the H2 plasma at room temperature for 60 min (plasma-treated AZO thin films). The value variations in the optical band gap (Eg) values of the H2-deposited and plasma-treated AZO thin films were evaluated from the plots of αhν2=c(hν−Eg), and the Eg values increased with increasing H2 flow rate. The Eg values also increased as the H2-plasma process was used to treat on the H2-deposited Al2O3-doped ZnO (AZO) thin films

Role of the CCAAT-Binding Protein NFY in SCA17 Pathogenesis

Spinocerebellar ataxia 17 (SCA17) is caused by expansion of the polyglutamine (polyQ) tract in human TATA-box binding protein (TBP) that is ubiquitously expressed in both central nervous system and peripheral tissues. The spectrum of SCA17 clinical presentation is broad. The precise pathogenic mechanism in SCA17 remains unclear. Previously proteomics study using a cellular model of SCA17 has revealed reduced expression of heat shock 70 kDa protein 5 (HSPA5) and heat shock 70 kDa protein 8 (HSPA8), suggesting that impaired protein folding may contribute to the cell dysfunction of SCA17 (Lee et al., 2009). In lymphoblastoid cells, HSPA5 and HSPA8 expression levels in cells with mutant TBP were also significantly lower than that of the control cells (Chen et al., 2010). As nuclear transcription factor Y (NFY) has been reported to regulate HSPA5 transcription, we focused on if NFY activity and HSPA5 expression in SCA17 cells are altered. Here, we show that TBP interacts with NFY subunit A (NFYA) in HEK-293 cells and NFYA incorporated into mutant TBP aggregates. In both HEK-293 and SH-SY5Y cells expressing TBP/Q61∼79, the level of soluble NFYA was significantly reduced. In vitro binding assay revealed that the interaction between TBP and NFYA is direct. HSPA5 luciferase reporter assay and endogenous HSPA5 expression analysis in NFYA cDNA and siRNA transfection cells further clarified the important role of NFYA in regulating HSPA5 transcription. In SCA17 cells, HSPA5 promoter activity was activated as a compensatory response before aggregate formation. NFYA dysfunction was indicated in SCA17 cells as HSPA5 promoter activity reduced along with TBP aggregate formation. Because essential roles of HSPA5 in protection from neuronal apoptosis have been shown in a mouse model, NFYA could be a target of mutant TBP in SCA17

氮化鋁薄膜之製程、微結構與氧化行為研究

本研究以封閉式磁控濺射系統鍍著氮化鋁(AlN)薄膜於矽晶片上，利用X光繞射分析儀(XRD)、掃瞄式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)、原子力顯微鏡(AFM)、光電子能譜儀(XPS)和電子能量耗失能譜儀(EELS)，探討鍍膜在脈衝功率為900W、1000W與沈積時間為120min、360min條件下以及試片經過不同溫度氧化後，其微結構與化學成分變化情況。 在改變製程條件方面，由XRD結果得知，在較高的脈衝功率和較長的沈積時間下，鍍膜具有較佳的(002)優選方向，由SEM與TEM橫截面試片的觀察發現鍍膜呈現柱狀晶結構(columnar structure), 其晶粒尺寸隨著遠離基材的距離、鍍著功率與沈積時間增加而增加。AFM分析指出鍍膜的表面粗糙度隨沈積時間而增加, 其粗糙度平均值Ra介於1.0與6.0 nm之間，適合作為表面聲波元件(Surface acoustic device)材料之用。XPS與能量散佈光譜儀(EDS)分析提供鍍膜的化學組成與鍵結狀態。 另外在鍍膜氧化方面，由SEM的二次電子影像中發現, 氧化溫度低於900℃的試片, 其表面顏色與形貌與剛鍍著的試片相似, 鍍膜表面在1000℃氧化後，鍍膜表面出現大量角狀顆粒的形貌，粗糙度也隨氧化溫度昇高而增加。由氮化鋁膜橫截面TEM試片影像中得知，鍍膜試片經高溫氧化後於鍍膜表面生成一層等軸晶結構之氧化鋁層，隨氧化溫度昇高，等軸晶晶粒尺寸隨之成長。此外，由XRD與TEM繞射結果得知，氧化物開始出現於700℃氧化的試片中，經1000℃高溫氧化後，部分的AlN相轉換變成過渡相δ-Al2O3 與熱力學穩定相α-Al2O3的混合物，在氧化溫度為1100℃以上的試片中，AlN已完全相轉換成α-Al2O3。Aluminum nitride (AlN) coatings were produced by a closed field unbalanced magnetron (CFUBM) sputtering system on a type (001) Si wafer. Processing parameters of the deposition system were manipulated to study the evolution of the microstructure and properties of the AlN coatings. Characterization of the microstructure, chemistry, and thermal stability of the AlN-coated silicons and those oxidized at elevated temperatures in the range of 300~800℃ was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), plan-view and cross-section transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and EELS mapping. X-ray diffraction results show that the thin films exhibit enhanced (002) preferred orientation at higher pulse power and longer deposition time. It is also obtained that the AlN films have a columnar structure and that the size of the columns increases with the distance from the substrate pulse power, and the deposition time, as revealed by SEM and TEM. AFM analysis indicates that the surface roughness of the coatings increases with the deposition time. The surface of the thin films is smooth with an average roughness Ra = 1.0~6.0 nm, which is suitable for application in surface acoustic wave devices. XPS analysis gives the chemical composition of the coatings as well as the bonding states of the elements. Moreover, Energy dispersive spectroscopy (EDS) analysis gives the chemical composition of the coatings as well as the percentage content of the elements. For the oxidized AlN coatings, it was observed that the surface morphology and the color of the nitride specimens oxidized below 900℃ remains similar to the as-deposited specimen. A great amount of granular particles are present in the 1000℃ oxidized specimens and the roughness of the coating surfaces increases with the oxidation temperature. Cross-section TEM reveals that oxidation of the nitride-coated silicon at elevated temperatures produces an Al2O3 with an equiaxed grain structure on the coating surface, and the average grain size of the layer increases with the oxidation temperature. From XRD and TEM results, it is obtained that oxidation of the nitrides to form an Al2O3 oxide layer was initially observed in the specimen oxidized at 700℃. Phase transformation from partially AlN into the mixed oxides of δ-Al2O3 andα-Al2O3 in the coatings occurred at 1000℃ and the transformation into α-Al2O3 was completed at 1100℃.摘要…..…………………………….……………………….……………….. Ⅰ Abstract…………………………….……………………….……………….. Ⅱ Contents…………………………………...………………….……………... Ⅳ List of Tables………………………………..……………….………………. Ⅶ Figure Captions………………..……………………………..……………... Ⅷ Chapter 1. Introduction………………..…………………………………… 1 References…………………………………………………………………… 8 Chapter 2. Theoretical basis………………………………………….……. 10 2.1 Magnetron sputtering……...……………………………………….. 10 2.1.1 Conventional magnetron sputtering………...………………... 10 2.1.2 Unbalanced magnetron sputtering……………………………. 12 2.1.3 Closed-field unbalanced magnetron sputtering……..……….. 13 2.2 Structure zone model……………………………………………….. 17 2.3 Properties of Aluminum nitride…………………………………….. 22 2.4 Oxidation mechanism of AlN coatings…………………………..…. 27 2.4.1 Wagner''s parabolic oxidation theory………………………….. 28 2.4.2 Oxidation Behavior of AlN Coatings……………………….… 29 2.4.3 Phase evolution in the AlN coatings during tempering……….. 31 2.5 Electron energy loss spectroscopy in transmission electron microscope………………………………………………………….. 32 2.5.1 Interactions of electron with specimen……………………….. 32 2.5.2 Electron energy loss spectrum………………………………... 34 2.5.3 The energy loss near-edge structure (ELNES) and the extended energy loss fine structure (EXELFS)………………. 38 References…………………………………………………………................ 41 Chapter 3. Experimental procedure………..……………………………… 47 3.1 Deposition of AlN coatings…………………………………………. 48 3.1.1 Substrate preparation………………………………….……… 48 3.1.2 Deposition using a closed-field unbalanced magnetron sputtering system……………………………………...…….... 48 3.2 Oxidation of AlN coatings……….………………………………… 49 3.3 Characterization of AlN coatings……….………………………..… 49 3.3.1 X-ray diffraction (XRD) analysis………………………….…. 49 3.3.2 Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM)……………………………... 49 3.3.3 Microstructure and chemistry analysis by transmission electron microscope (TEM)………………………………….. 50 3.3.4 Chemical shift analysis of the coatings by X-ray photoelectron spectroscopy (XPS)………………….……….. 51 Chapter 4. Results and discussion…...…..……….………………………... 53 4.1 Microstructure and chemistry of the AlN coatings………………..... 53 4.1.1 Effect of pulse power…………………………………………... 53 4.1.1.1 X-ray diffraction analysis.………..………………….…. 53 4.1.1.2 SEM morphology………………………………….….... 55 4.1.1.3 Plan-view TEM………………………………………… 57 4.1.1.4 Cross-section TEM……………………………………... 60 4.1.1.5 AFM analysis….……………………………………...... 63 4.1.2 Effect of deposition time……..………………………….……... 65 4.1.2.1 X-ray diffraction analysis.……….…..……………....…. 65 4.1.2.2 SEM morphology…………………………………..…... 66 4.1.2.3 Plan-view TEM……………………………………....… 68 4.1.2.4 Cross-section TEM………………………….………..... 71 4.1.2.5 AFM analysis……………………………..…………...... 71 4.1.2.6 X-ray photoelectron spectroscopy…………...………..... 74 4.1.2.7 EDS analysis…………...……………………...…..…..... 77 4.1.2.8 EELS analysis…………...………………………...…..... 78 4.2 Oxidation behavior of the AlN coatings……………………………. 81 4.2.1 X-ray diffraction analysis.………..……………………..….…. 81 4.2.2 SEM morphology……………………….…………..…….….... 83 4.2.2.1 Surface morphology……………………………………. 83 4.2.2.2 Cross-sectional morphology…………………………… 96 4.2.3 Plan-view TEM……………………………………………….. 98 4.2.4 Cross-section TEM…………………………………………..... 110 4.2.5 AFM analysis….……………………………………................. 126 4.2.6 Elemental analysis by EELS…………………………………... 129 4.2.7 Composition depth profiling analysis by EELS mapping…….. 131 References……………………………………………………..…................. 134 Chapter 5. Conclusions………………………………………………...…... 138 Appendix……………………………………………………….….……….... 140 Publication list……………………………………………………………..... 14

Fabrication of Aluminum Oxide Thin-Film Devices Based on Atomic Layer Deposition and Pulsed Discrete Feed Method

This study demonstrates the low-temperature (<100 °C) process for growing a thin silica buffer layer and aluminum oxide by atomic layer deposition (ALD) in the same reaction chamber. Heterogeneous multilayer thin films are prepared by a dual-mode equipment based on atomic layer deposition and plasma-enhanced chemical vapor deposition (PECVD) techniques. The pulse discrete feeding method (DFM) was used to divide the precursor purging steps into smaller intervals and generate discrete feeds, which improved the saturated distribution of gas precursors, film density and deposition selectivity. The experimental results show that the process method produces a uniform microstructure and that the best film uniformity is ±2.3% and growth rate is 0.69 Å/cycle. The thickness of aluminum oxide film has a linear relationship with the cyclic growth number from 360 to 1800 cycles. Meanwhile, the structural and mechanical stress properties of aluminum oxide thin films were also verified to meet the requirements of advanced thin-film devices

Temperature-Dependent Residual Stresses and Thermal Expansion Coefficient of VO₂ Thin Films

This study aims to investigate the thermomechanical properties of vanadium dioxide (VO2) thin films. A VO2 thin film was simultaneously deposited on B270 and H-K9L glass substrates by electron-beam evaporation with ion-assisted deposition. Based on optical interferometric methods, the thermal–mechanical behavior of and thermal stresses in VO2 films can be determined. An improved Twyman–Green interferometer was used to measure the temperature-dependent residual stress variations of VO2 thin films at different temperatures. This study found that the substrate has a great impact on thermal stress, which is mainly caused by the mismatch in the coefficient of thermal expansion (CTE) of the film and the substrate. By using the dual-substrate method, thermal stresses in VO2 thin films from room temperature to 120 °C can be evaluated. The thermal expansion coefficient is 3.21 × 10−5 °C−1, and the biaxial modulus is 517 GPa

DNA-based nanowires and nanodevices

DNA (deoxyribonucleic acid) is a highly versatile biopolymer that has been a recent focus in the field of nanomachines and nanoelectronics. DNA exhibits many properties, such as high stability, adjustable conductance, vast information storage, self-organising capability and programmability, making it an ideal material in the applications of nanodevices, nanoelectronics and molecular computing. Even though native DNA has low conductance, it can easily be converted into a potential conductor by doping metal ions into the base pairs. Nickel ions have been employed to tune DNA into conducting polymers. Doping of nickel ions within DNA (Ni-DNA) increases the conductivity of DNA by at least 20 folds compared with that of native DNA. Further studies showed that Ni-DNA nanowires exhibit characteristics of memristors, making them a potential mass information storage system. In summary, DNA molecules have promising applications in a variety of fields, including nanodevices, nanomachines, nanoelectronics, organic solar cells, organic light emitting diodes and biosensors

Optical, Electrical, Structural, and Thermo-Mechanical Properties of Undoped and Tungsten-Doped Vanadium Dioxide Thin Films

The undoped and tungsten (W)-doped vanadium dioxide (VO2) thin films were prepared by electron beam evaporation associated with ion-beam-assisted deposition (IAD). The influence of different W-doped contents (3–5%) on the electrical, optical, structural, and thermo-mechanical properties of VO2 thin films was investigated experimentally. Spectral transmittance results showed that with the increase in W-doped contents, the transmittance in the visible light range (400–750 nm) decreases from 60.2% to 53.9%, and the transmittance in the infrared wavelength range (2.5 μm to 5.5 μm) drops from 55.8% to 15.4%. As the W-doped content increases, the residual stress in the VO2 thin film decreases from −0.276 GPa to −0.238 GPa, but the surface roughness increases. For temperature-dependent spectroscopic measurements, heating the VO2 thin films from 30 °C to 100 °C showed the most significant change in transmittance for the 5% W-doped VO2 thin film. When the heating temperature exceeds 55 °C, the optical transmittance drops significantly, and the visible light transmittance drops by about 11%. Finally, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to evaluate the microstructure characteristics of VO2 thin films

OLED Fabrication by Using a Novel Planar Evaporation Technique

Organic light-emitting diode fabrication is suffering from extremely high material wasting during deposition especially using a typical point or even line source. Moreover, the need of depositing a high number of emitters and host(s) with a precise composition control in a single layer makes traditional vapor codeposition systems nearly impossible, unless otherwise with a very low yield. To improve, we have developed a novel thin-film deposition system with a planar source loadable with any premetered solvent-mixed organic compounds, plausibly with no component number limitation. We hence demonstrate experimentally, along with a Monte Carlo simulation, in the report the feasibility of using the technique to deposit on a large area-size substrate various organic materials with a relatively high material utilization rate coupling with high film uniformity. Specifically, nonuniformity of less than ±5% and material utilization rate of greater than 70% have been obtained for the studied films

Band-Engineered Structural Design of High-Performance Deep-Ultraviolet Light-Emitting Diodes

In this study, systematic structural design was investigated numerically to probe into the cross-relating influences of n-AlGaN layer, quantum barrier (QB), and electron-blocking layer (EBL) on the output performance of AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) with various Al compositions in quantum wells. Simulation results show that high-Al-composition QB and high-Al-composition EBL utilized separately are beneficial for the enhancement of carrier confinement, while the wall-plug efficiency (WPE) degrades dramatically if both high-Al-composition QB and EBL are existing in a DUV LED structure simultaneously. DUV LEDs may be of great optical performance with appropriate structural design by fine-tuning the material parameters in n-AlGaN layer, QB, and EBL. The design curves provided in this paper can be very useful for the researchers in developing the DUV LEDs with a peak emission wavelength ranging from 255 nm to 285 nm