氨化Ga2O3 /Nb膜制备的GaN纳米线的光学和微观结构特性的研究

采用射频磁控溅射技术在硅衬底上制备Ga2O3/Nb薄膜,然后在900℃下于流动的氨气中进行氨化制备GaN纳米线.用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜详细分析了GaN纳米线的结构和形貌.结果表明:采用此方法得到的GaN纳米线有直的形态和光滑的表面,其纳米线的直径大约50nm,纳米线的长约几个微米.室温下以325nm波长的光激发样品表面,只显示出一个位于367 nm的很强的紫外发光峰.最后,简单讨论了GaN纳米线的生长机制.     

钽催化磁控溅射法制备GaN纳米线

利用磁控溅射技术通过氮化Ga2O3/Ta薄膜,合成大量的一维单晶纤锌矿型氮化镓纳米线.用X射线衍射、扫描电子显微镜、高分辨透射电子显微镜,选区电子衍射和光致发光谱对制备的氮化镓进行了表征.结果表明;制备的GaN纳米线是六方纤锌矿结构,其直径大约20～60 nm,其最大长度可达10 μm左右.室温下光致发光谱测试发现363 nm处的较强紫外发光峰.另外,简单讨论了氮化镓纳米线的生长机制.     

Effect of ammoniating temperature on microstructure and optical properties of one-dimensional GaN nanowires doped with magnesium

One-dimensional GaN nanowires doped with Mg element have been successfully prepared on Si (1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Mg thin films, and the effect of the ammoniating temperatures on the microstructure and optical properties of the GaN nanowires was investigated in detail. X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), FT-IR spectrophotometer, Scanning electron microscope (SEM), high-resolution transmission electron microscope (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN nanowires. The results demonstrate that ammoniating temperature has a significant effect on microstructure, morphology and optical properties of GaN nanowires. GaN nanowires after ammoniation at 900 °C for 15 min are straight, smooth and of uniform thickness along spindle direction with the highest crystalline quality. The growth direction of these nanowires is parallel to [1 0 0] orientation.     

Synthesis of one-dimensional GaN nanorods by Tb intermediate layer with different thicknesses

GaN nanorods were synthesized by magnetron sputtering and ammonification system, and the thickness of Tb intermediate layer was changed to study the effect on GaN nanorods. The resultant was tested by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra. The results show that the thickness of Tb layer has an evident effect on the modality, quality, and luminescence properties of GaN nanorods. PL spectra at room temperature show a very strong emission peak at 368 nm and a weak emission peak at 387 nm, and the intensities of the peak for the produced samples reach the maximum when Tb layer is 20 nm. Finally, the optimal thickness of 20 nm of Tb intermediate layer for synthesizing GaN nanostructures is achieved.     

Catalytic Growth of Large-Scale GaN Nanowires

A novel lanthanon seed was employed as the catalyst for the growth of GaN nanowires. Large-scale GaN nanowires have been synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(111) substrates. Scanning electron microscopy, x-ray diffraction, high-resolution transmission electron microscopy, and Fourier transform infrared spectroscopy were used to characterize the samples. The results demonstrate that the nanowires are single-crystal hexagonal wurtzite GaN. The growth mechanism of GaN nanowires is also discussed.     

自支撑GaN厚膜制备及其光学性能研究

采用镀Ti插入层在氢化物外延设备中制备了高质量自支撑GaN厚膜。X射线衍射测试发现(0002)峰摇摆曲线的半高宽为260 arcsec;5 K下样品带边发光峰的半高宽为3 meV,室温下样品的带边发光峰也只有20 meV,并且在室温的PL谱中观察不到黄光带;扫描电子显微镜观察显示,腐蚀后的自支撑GaN厚膜表面有位错延伸形成的六角坑,并估算出样品位错密度约为2.1×l07 cm-2。这些结果说明镀Ti插入层有助于提高GaN外延层的晶体质量。通过Raman和低温荧光分析,可以看出自支撑GaN厚膜表面应力已经完全释放。研究了不同温度下样品的荧光特性,证明得到的无应力自支撑GaN厚膜具有很好的晶体质量和光学质量     

Effect of Reaction Parameters on Morphology and Photoluminescence of Intrinsic and Mn-doped ZnS Microspheres Synthesized by Hydrothermal Method

Intrinsic and Manganese (Mn)-doped ZnS microspheres have been synthesized by hydrothermal method. Thiourea and amino acid, and l-histidine have been used as sulfur source and capping agent, respectively. The synthesized materials have been characterized using x-ray diffraction, field emission scanning electron microscopy, photoluminescence (PL) and UV–Vis spectroscopy. The above-said characterizations conveyed the information regarding the crystallinity, existence of microspheres, size and optical properties of synthesized ZnS and Mn-doped ZnS samples. Formation of microspheres of intrinsic and Mn-doped ZnS has been observed when the reaction parameters are kept at 150 °C for 4 h, and similarly, the micropores have been noticed when reaction parameters are kept at 150 °C for 8 h. The PL of ZnS microspheres shows multiple defect emissions. The nature of PL for pure ZnS has been regulated based on reaction parameters. Doping of Mn in the ZnS enhances the PL emission. This study reveals the role of reaction parameters and effect of Mn doping on tuning the morphology and emission behavior of ZnS microspheres.     

Oxidation-protective and mechanical properties of SiC nanowire-toughened Si–Mo–Cr composite coating for C/C composites

Oxidation-protective SiC nanowire-toughened Si–Mo–Cr composite coating prepared on the carbon/carbon (C/C) composites by chemical vapor deposition and pack cementation was investigated in this study. After incorporating SiC nanowires, the hardness, elastic modulus and fracture toughness of the composite coating were increased by 6.12%, 20.89% and 35.78%, respectively, due to the toughening and strengthening mechanisms including nanowire pullout, nanowire bridging, microcrack deflection and good interaction between nanowire/matrix interface. Thermogravimetric analysis revealed that the maximum weight loss of the coated C/C samples was decreased from 5.87% to 3.93% by incorporating SiC nanowires from room temperature to 1500 °C.     

Preparation and characterization of GaN films grown on Ga-diffused Si （111） substrates

Hexagonal GaN films were prepared by nitriding Ga2O3 films with flowing ammonia. Ga2O3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. This paper have investigated the change of structural properties of GaN films nitrided in NH3 atmosphere at the temperatures of 850, 900, and 950℃ for 15 min and nitrided at the temperature of 900℃ for 10, 15, and 20 rain, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure, surface morphology and composition of synthesized samples. The results reveal that the as-grown films are polycrystalline GaN with hexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained when nitrided at 900℃ for 15 min.     

Oxidation protection of SiC-coated C/C composites by SiC nanowire-toughened CrSi2–SiC–Si coating

Oxidation protective SiC nanowire-toughened CrSi₂–SiC–Si coating was prepared on SiC-coated carbon/carbon composites by chemical vapor deposition and pack cementation. SiC nanowires in the coating suppressed the cracking of the coating via various toughening mechanisms including nanowire pullout, microcrack bridging by nanowire and microcrack deflection, resulting in a good oxidation inhibition for the coated samples. The results showed that the maximal weight loss of the coated samples was only 2.55% in thermogravimetric analysis from room temperature to 1500 °C, and the weight loss of the coated samples was only 1.24% after isothermal oxidation at 1500 °C for 316 h.     

ZnO 3D flower-like nanostructure synthesized on GaN epitaxial layer by simple route hydrothermal process

The 3D type, flower-like ZnO nanostructures from particle to flower-like or chestnut bur are fabricated on the GaN epitaxial layer substrate through the simple-route hydrothermal process. Structural characterization was made for the ZnO 3D nanostructures synthesized in different pH ranging from 9.5 to 11.0. The growth model was proposed and discussed regarding the fabrication mechanism and morphology of ZnO 3D flower-like nanostructure. The flower-like ZnO is composed of many thin single crystals ZnO nanorods. Bigger and thicker ZnO structure is fabricated with the increase of pH in solution. The enhanced UV emission in the PL measurement and the spectra in the Raman spectroscopy for ZnO–GaN heterojunction material were discussed.     

Morphological,Structural and Optical Evolution of Ag Nanostructures on c-Plane GaN Through the Variation of Deposition Amount and Temperature

Owing to their tunable properties, Ag nanostructures have been widely adapted in various applications and the morphological control can determine their performance and effectiveness. In this work, we demonstrate the morphological and optical evolution of Ag nanostructures on GaN (0001) by the systematic control of deposition amount at two distinctive annealing temperatures. Based on the Volmer–Weber and coalescence growth models, the nanostructure growth commenced by the thermal solid-state-dewetting evolve in terms of size, density and configuration. At 450 °C, the round-dome shaped Ag nanoparticles (regime I), irregular Ag nano-mounds (regime II) and void-layer structures (regime III) are observed along with the gradually increased deposition amount. As a sharp distinction, the solid state dewetting process occur more radically at 700 °C and also, the Ag sublimation and the effect on the nanostructure formation are observed in a clear regime shift scaled by the deposition amount. Meanwhile, a strong dependency of reflectance spectra evolution on the Ag nanostructure morphology is witnessed for both sets. In particular, Ag dipolar resonance peaks are significantly red-shifted from VIS to NIR regions along with the nanostructure evolution. The reflectance, PL and Raman intensity variation are also observed and discussed based on the evolution of Ag nanostructures.     

热壁化学气相沉积Si基GaN晶体膜的研究

采用热壁化学气相沉积工艺在Si(111)衬底上生长GaN晶体膜，并对其生长条件进行研究。用X射线衍射(XRD)、扫描电镜(SEM)、荧光光谱(PL)对样品进行结构、形貌和发光特性的分析。测试结果表明：用此方法得到了六方纤锌矿结构的GaN晶体膜。实验结果显示：采用该工艺制备GaN晶体膜时，选择H2作反应气体兼载体，对GaN膜的形成起着非常有利的作用。     

The impact of high energy ion irradiation upon CO gas sensitivity of nanostructured GaN epilayers

Photoelectrochemically nanostructured GaN epilayers were found to exhibit good sensitivity towards CO in the temperature range from 180 to 280°C. We show that subjection of nanostructured GaN samples to 166 MeV Xe⁺²³ ion irradiation causes considerable reduction of the gas sensitivity, while post-irradiation rapid thermal annealing results in sensitivity restoration, the effect being dependent upon the dose of irradiation and annealing temperature. A 50% restoration of the relative sensitivity is demonstrated after rapid thermal annealing for 1 min at 800°C in samples irradiated by Xe⁺²³ ions at a dose of 10¹² cm⁻². The article is published in the original.     

Preparation and Properties of GaN Micro-Ribbons on Ga-Diffused Si （111） Substrates

用射频磁控溅射工艺在室温扩镓硅衬底上沉积Ga2O3膜,然后在氨气气氛下氮化Ga2O3膜得到GaN微米带,用X射线衍射(XRD)、扫描电镜(SEM)、选区电子衍射(SAED)、X射线光电子能谱(XPS)及光致发光谱(PL)对薄膜样品进行了结构、表面形貌、组分及发光特性分析.SEM图像显示直径约为100 nm～300 nm微米带随机分布在GaN薄膜表面.XRD、XPS及SAED分析表明GaN微米带呈六方闪锌矿多晶结构,择优沿[001]方向生长.P1显示了可能由量子限制效应引起的发光峰,其相对于报道的GaN晶体发光峰有显著蓝移.     

Synthesis of GaN nanorods on Si substrates with assistance of the volatilization of ZnO middle layers

GaN nanorods have successfully been synthesized on Si(111) substrates via ammoniating ZnO/Ga2O3 films at 950℃. Ga2O3 thin films and ZnO middle layers were deposited in turn on Si(111) substrates by r.f. magnetron sputtering system. ZnO volatilized at 950℃ in the ammonia ambience and Ga2O3 reacted to NH3 to fabricate GaN nanorods in the later ammoniating process. The volatilization of ZnO layers played an important role in the fabrication. The structure and composition of the GaN nanorods were studied by X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FTIR). The orphology ofGaN nanorods was investigated using scanning electron microscopy (SEM) and transmission electronic microscope (TEM). The analyses of measured results revealed that GaN nanorods with hexagonal wurtzite stxucture were prepared by this method.     

Broadband anti-reflection and enhanced field emission from catalyst-free grown small-sized ITO nanowires at a low temperature

Small-sized indium tin oxide (ITO) nanowires were fabricated using the electron beam evaporation (EBE) technique at low temperature (～150 °C) without adding any catalyst. The ITO nanowires have a typical diameter of around 10 nm and a length of more than 100 nm, with body-centered cubic crystal structures that grow along the 〈1 0 0〉 directions, as revealed by transmission electron microscopy. The growth mechanism of the branched ITO nanowires was found to be a vapor–solid process. The nanowire films show a broadband anti-reflection property due to the graded refraction index from the film surface to the substrate. Enhanced field emission properties with a low turn-on electric field and a high field enhancement factor were also observed in the ITO nanowires.     

一步阳极氧化法制备氧化铝纳米线及其形成机理

采用一步恒压阳极氧化法在草酸电解液中制备氧化铝纳米线,用扫描电子显微镜和X射线衍射仪等对阳极氧化后产物的形貌、晶相进行了分析,研究了氧化电压、反应温度和电解质浓度对氧化产物形貌的影响。结果表明,纳米线的最佳制备条件为40℃、40 V、0.1 mol/L的草酸电解液。新制备的纳米线为无定形结构,在800℃煅烧60 min后转变为立方相氧化铝。同时根据实验结果,从反应界面的温度分布角度,对氧化铝纳米线的形成机理进行了探讨。     

有机前驱体热解法合成单晶氮化硅纳米线

在高纯氮气气氛中采用有机前驱体热解法合成了氮化硅纳米线,对氮化硅纳米线所进行的详细的微观表征表明它们具有良好的单晶特性,其生长沿着α-Si_3N_4的[1010]方向并受VS机制所控制.在室温下用325 nm激光对样品激发,观察到样品有很宽的强光致发光带,在实验中用肉眼即能观察到从样品所发出的强光.考虑到通过稀土掺杂(如引入Nd、Eu、Er和Yb)等手段能够降低氮化硅纳米结构的能带从而进一步调控其光学性能,可以相信氮化硅纳米线在防伪发光材料领域将有着广阔的开发潜力.     

以CuSe纳米粒子为催化剂制备超长ZnSe纳米线

采用化学气相沉积的方法,以Zn粉末为原料,CuSe纳米粒子为催化剂,在Si衬底上成功制备了毫米级ZnSe纳米线。用X射线衍射、EDS和SEM对产物的结构、成分和形貌进行了测试与表征。结果表明：生长的ZnSe纳米线为立方闪锌矿结构,长度达0.35～0.7mm,Zn和Se的摩尔比为1？0.97,其室温光致发光谱显示在325nm波长激发下,ZnSe纳米线在439nm处呈现自由激子的强烈发射,表明生长的ZnSe纳米线具有高的结晶质量。纳米线生长符合氧化还原反应下的气液固生长机制,并证明Cu3Zn合金充当了实际的ZnSe纳米线生长催化剂。