Al2O3衬底无催化剂生长GaN纳米线及其光学性能

采用一种绿色的等离子增强化学气相沉积法,以Al2O3为衬底, Ga金属为镓源, N2为氮源,在不采用催化剂的情况下,成功制备获得了结晶质量良好的GaN纳米线.研究表明,生长温度可显著调控GaN纳米线的形貌,当反应温度为950℃时,生长出的GaN微米片为六边形;当反应温度为1000℃时,生长出了长度为10-20μm的超长GaN纳米线.随着反应时间增加, GaN纳米线的长度增加. GaN纳米线内部存在着压应力,应力大小为0.84 GPa.同时,也进一步讨论了GaN纳米线无催化剂生长机制. GaN纳米线光致发光结果显示, GaN纳米线缺陷较少,结晶质量良好,在360 nm处有一个较为尖锐的本征发光峰,可应用于紫外激光器等光电子器件.本研究结果将为新型光电器件低成本绿色制备提供一个可行的技术方案.     

GaAs纳米线及GaAs/In_xGa_(1-x)As/GaAs纳米线径向异质结构的无催化选区生长的实验研究

利用无催化选区金属有机化学气相沉积(SA-MOCVD)法在GaAs(111)B衬底上分别制备了GaAs纳米线和GaAs/InxGa1-xAs/GaAs纳米线径向异质结构.系统地研究了生长条件对GaAs纳米线生长的影响.实验结果显示,GaAs纳米线的形貌和长度依赖于生长温度、AsH3的分压以及SiO2掩膜表面的圆孔直径.因此可以通过调节以上因素来得到高质量的GaAs纳米线.并且发现扩散是影响无催化选区生长GaAs纳米线的主要机理.微区光致发光谱(μ-PL)表明,GaAs/InxGa1-xAs/GaAs纳米线径向异质结构被成功合成,室温(300 K)下它的发光波长为913 nm.这些结果对于GaAs纳米线及其异质结构制备的进一步研究及其在光电子器件中的应用具有很好的参考价值.     

金辅助催化方法制备GaAs和GaAs/InGaAs纳米线结构的形貌表征及生长机理研究

利用金（Au）辅助催化的方法,通过金属有机化学气相沉积技术制备了GaAs纳米线及GaAs/InGaAs纳米线异质结构.通过对扫描电子显微镜（SEM）测试结果分析,发现温度会改变纳米线的生长机理,进而影响形貌特征.在GaAs纳米线的基础上制备了高质量的纳米线轴、径向异质结构,并对生长机理进行分析.SEM测试显示,GaAs/InGaAs异质结构呈现明显的“柱状”形貌与衬底垂直,InGaAs与GaAs段之间的界面清晰可见.通过X射线能谱对异质结样品进行了线分析,结果表明在GaAs/InGaAs轴向纳米线异质结构样品中,未发现明显的径向生长.从生长机理出发分析了在GaAs/InGaAs径向纳米线结构制备过程中伴随有少许轴向生长的现象.     

真空热蒸发生长CdX(X=S,Te)纳米线研究性实验

将一维纳米结构的气—液—固生长机制与大学材料物理实验真空热蒸发镀膜结合,设计了生长半导体纳米线的研究性实验.利用金属铋或锡作为催化剂,真空热蒸发生长了CdS,CdTe等半导体纳米线.纳米线产物形貌均匀,并可实现选择性生长.     

MOVPE低温生长的n型GaN电学特性研究

系统研究了采用金属有机物化学气相外延方法在740℃和900℃条件下生长的n型GaN的电学特性. 电化学电容-电压测试表明,在低温条件下采用三乙基镓作为Ga源生长有利于降低非故意掺杂n型GaN的背景杂质浓度. 另外,对重掺Si的n型GaN的霍耳效应测试表明,随着Si掺杂浓度增大,电子浓度相应线性增大,表现出杂质带导电特性,而迁移率则相应减小. 同时,原子力显微镜测试和X射线衍射测试均表明生长温度和掺杂浓度对外延材料的表面形貌和晶体质量有影响,特别是在高掺杂浓度的情况下,样品的表面形貌恶化更严重. 在所研究的 关键词： n型GaN 电子浓度 迁移率     

ZnO纳米线薄膜的合成参数、表面形貌和接触角关系研究

水浴法合成ZnO纳米线薄膜的工艺参数直接影响其表面形貌, 并使其接触角及润湿性能发生变化. 本文仿真分析了轮廓算数平均偏差、偏斜度、峭度、相关长度等特征参数对随机粗糙表面特性的影响规律; 改变生长时间、种子层溶液和生长液的浓度, 批量制备了表面形貌不同的ZnO纳米线薄膜; 提出了取样长度的确定方法, 并基于扫描电镜图像和Matlab图像处理算子对ZnO纳米线薄膜表面形貌的特征参数进行了提取; 将表面形貌高度和水平方向的特征参数引入Wenzel模型, 分析了合成参数、表面形貌特征参数与接触角的影响关系. 结果表明, 合成参数变化时, 选择取样长度5.0 μm为宜; 生长液浓度大于0.125 mol/L时, ZnO纳米线之间发生重结晶, 并呈现疏水性; 改变种子层溶液浓度和生长时间, 均得到超亲水表面. 上述结论可用于不同氧化酶、细胞等在ZnO纳米线薄膜上的有效吸附及相应传感器测试性能的进一步提高. 关键词： ZnO纳米线 水浴合成 表面形貌 接触角     

衬底对化学气相沉积法制备氧化硅纳米线的影响

通过化学气相沉积法在不同衬底上制备了大量的氧化硅纳米线.选用衬底为Si片、带有约100nm厚SiO2氧化层Si片和石英片.利用场发射扫描电子显微镜(SEM)和透射电镜(TEM，配备有能谱仪)对样品的表面形貌、结构和成分进行研究.结果表明：这些纳米线都为非晶态，但在不同衬底上生长的纳米线形貌、尺寸和化学成分不同.讨论了各种衬底对不同特征氧化硅纳米线生长的影响. 关键词： 化学气相沉积 纳米线 纳米颗粒     

在GaN生长初期形貌发展的观察

报道了对GaN在生长初期形貌发展的观察和形貌的高度分布演化.形貌观察发现GaN外延层由分离的岛转化为连续的膜,形貌的发展显示GaN经历了横向生长的阶段.利用原子力显微镜有数字化记录的特点,从形貌的观察中也得到了外延层高度分布,发现高度分布可用单峰或多峰高斯分布拟合.通过与形貌特征的对比,发现宽而且不对称的分布对应着岛状的外延层形貌,可以用多峰高斯分布拟和;窄而且对称的分布则对应着比较连续的膜,可以用单峰高斯分布拟和.     

未钝化和H钝化GaN纳米线的电子结构

用密度泛函理论研究直径为9.5Å,15.9Å和22.5Å,未钝化和H钝化GaN纳米线的能带和态密度.结果表明:未钝化和H钝化GaN纳米线的能隙都是直接带隙,未钝化GaN纳米线的禁带宽度随着直径的增加减小,但是变化不明显,H钝化GaN纳米线的禁带宽度随着直径增大也是减小的,但是减小的幅度比未钝化的大.未钝化GaN纳米线表面N原子的2p电子主要聚集在价带顶,表面Ga原子的4p电子主要聚集在导带底,这两种电子都具有很强的局域性,而且决定着能隙值;加H钝化可以消除表面原子产生的表面效应.     

两步氧化法制备β-Ga2O3薄膜

为获得高质量的β-Ga_2O_3薄膜,对传统的GaN薄膜高温氧化方法进行了优化。我们通过对GaN薄膜分别进行一步或两步高温氧化的方法制备了β-Ga_2O_3薄膜,并通过X射线衍射、场发射扫描电子显微镜、拉曼光谱等对制备的样品进行了测试、对比与分析。结果表明,950℃下GaN薄膜无法完全氧化,而直接1 150℃氧化得到的样品并没有明显的晶向。相比之下,通过两步氧化法,GaN薄膜被完全氧化,且得到的β-Ga_2O_3薄膜具有明显的沿■方向的晶向,样品表面显示出明显的纳米线结构。最佳的氧化时间为在950℃下氧化3 h之后在1 150℃下氧化1 h,此时得到样品的纳米线结构最明显,其纳米线的直径约为30～40 nm。拉曼光谱测试证实了该条件下获得的样品具有较高的晶体质量。通过分析不同样品结构以及形貌特性,我们发现不同温度下的不同氧化模式是导致该结果的主要原因。     

Synthesis of GaN nanowires by Tb catalysis

Rare earth metal seed Tb was employed as catalyst for the growth of GaN wires. GaN nanowires were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. The samples characterization by X-ray diffraction and Fourier transform infrared indicated that the nanowires are constituted of hexagonal wurtzite GaN. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy showed that the samples are single-crystal GaN nanowire structures. The growth mechanism of the GaN nanowires is discussed.     

Metal catalyst-assisted growth of GaN nanowires on graphene films for flexible photocatalyst applications

We report the growth of high-areal-density GaN nanowires on large-size graphene films using a nickel (Ni) catalyst-assisted vapor-liquid-solid (VLS) method. Before the nanowire growth, the graphene films were prepared on copper foils using hot-wall chemical vapor deposition and transferred onto SiO₂/Si substrates. Then, for catalyst-assisted VLS growth, Ni catalyst layers with thickness of a few nanometers were deposited on the graphene-coated substrates using a thermal evaporator. We investigated the effect of the Ni catalyst thickness on the formation of GaN nanowires. Furthermore, the structural and optical characteristics of GaN nanowires were investigated using X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The GaN nanowires grown on graphene films were transferred onto polymer substrates using a simple lift-off method for applications as flexible photocatalysts. Photocatalysis activities of the GaN nanowires prepared on the flexible polymer substrates were investigated under bending conditions.     

Synthesis and characterization of GaN nanowires by ammoniating Ga2O3/Cr thin films deposited on Si(1 1 1) substrates

GaN nanowires have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Cr thin films at 950 °C. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), FT-IR spectrophotometer, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), and photoluminescence (PL) spectrum were carried out to characterize the microstructure, morphology, and optical properties of GaN samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure and high-quality crystalline, have the size of 30-80 nm in diameter and several tens of microns in length with good emission properties. The growth direction of GaN nanowires is perpendicular to the fringe of (1 0 1) plane. The growth mechanism of GaN nanowires is also discussed in detail.     

Growth and characterization of high-quality GaN nanowires by ammonification technique

GaN nanowires were successfully synthesized at high quality and large yield on Si (1 1 1) substrate through ammoniating Ga₂O₃/BN films deposited by radio frequency (RF) magnetron sputtering system. X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and selected-area electron diffraction (SAED) confirm that the as-synthesized nanowires are of a hexagonal GaN with wurtzite structure. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that the nanowires have a straight and smooth curved structure with extremely uniform diameter of about 60 nm, which is helpful to the application of GaN nanowires. The present results demonstrate that the BN is a very important intermedium in the growth of GaN nanowires by this method.     

The influence of growth temperatures on the characteristics of GaN nanowires

This paper presents the investigation of the properties of GaN nanowires synthesized from Ni-catalyzed chemical vapour deposition method under various growth temperatures. The influence of the growth temperatures on the morphological, structural and optical characteristics of the synthesized GaN nanowires was investigated in this work. Field-emission scanning electron microscopy images revealed that the 950 °C was the optimal growth temperature for synthesizing uniform, straight and smooth morphology of GaN nanowires. X-ray diffraction results demonstrated that the synthesized low dimensional GaN structures have the hexagonal wurtzite structure. Ultraviolet and blue emissions were detected from photoluminescence measurements. In addition, phonon replicas with the energy separation of 90 meV have been observed at the lower energy of the blue emission region in photoluminescence spectra.     

Large-scale crystalline GaN nanowires synthesized through a chemical vapor deposition method

Large-scale, high-density gallium nitride nanowires were successfully synthesized by the direct reaction of gallium and ammonia using gold as initiator. The as-synthesized product was characterized by XRD, SEM, TEM, SAED, and EDS. The results showed that the product is hexagonal wurtzite GaN with high purity. The nanowires have diameters in the range of 60–100 nm and are a few tens of micrometers in length. A remarkable feature is that catalyst particles were observed at the ends of the nanowires, indicating that the growth process can be controlled by the vapor–liquid–solid mechanism. The present results revealed that gold is an effective and advantageous catalyst for the growth of GaN nanowires. PACS 81.05.Ea; 81.10.Bk; 68.65.-k     

Synthesis of large-scale GaN nanowires by ammoniating Ga2O3 films on Co layer deposited on Si（111） substrates

A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.     

Synthesis of GaN nanowires on gold-coated SiC substrates by novel pulsed electron deposition technique

A two-step approach for macro-synthesis of GaN nanowires was developed in this study. GaN nanoparticles were firstly synthesized through a facile solid-state reaction using an organic reagent dicyandiamide (C₂N₄H₄) and Ga₂O₃ as precursors. Subsequently, single-crystalline wurtzite GaN nanowires were grown on gold-coated 6H-SiC substrates via novel pulsed electron deposition (PED) technique using the as-prepared GaN nanoparticles as target, which provides a new route employing nanoparticles as precursors to fabricate GaN nanowires. It is found that pulsed electron ablation induced Ga and N plasma directly towards the gold-coated substrate to initialize the vapor-liquid-solid (VLS) growth processes. The morphological and structural properties were investigated in detail and Raman scattering spectrum of these nanowires presented some new features.     

Synthesis and characterization of GaN nanowires

In this work, GaN nanowires were fabricated on Si substrates coated with NiCl₂ thin films using chemical vapor deposition (CVD) method by evaporating Ga₂O₃ powder at 1100 °C in ammonia gas flow. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM) and photoluminescence (PL) spectrum are used to characterize the samples. The results demonstrate that the nanowires are single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanowires is also discussed.