溅射辅助微波等离子体化学气相沉积SiCN晶体

在微波等离子体化学气相沉积系统中,利用脉冲氮离子束溅射二氰二氨靶产生的碳氮粒子作为合成前驱物,在石英玻璃基片上研究了SiCN晶体的合成。用扫描电子显微镜(SEM)、X射线能谱(EDX)、X射线衍射(XRD)和X射线光电子能谱(XPS)研究了基片温度对薄膜的形貌、成分和结构的影响。结果表明:随着基片温度的降低,沉积物由截面为六方形的结晶良好的SiCN晶体(800℃)变成发育不完全的聚片状晶体(700℃),直到变成颗粒细小的无定形碳氮薄膜(550℃)。衍射峰的强度以及晶胞参数a和c的值随温度的降低而减小。薄膜为C原子部分取代Si3N4中的Si原子位置而形成的SiCN晶体,其中N原子主要与Si原子结合,C原子以sp3C—N、sp2CN和sp2CC键的形式存在。降低基片温度有利于提高薄膜中的C含量和sp3C—N键的含量。     

溶胶-凝胶法制备纳米Si_3N_4(Y_2O_3)粉末的研究

本文以硅溶胶、尿素和炭黑为原料，采用溶胶-凝胶碳热氮化法在1500℃、2h条件下制得粒径为50～80nm的Si3N4纳米粉末．比较了由硅溶胶与尿素经氨解合成的前驱体和硅溶胶二种不同起始物料的反应活性，研究了氮化条件对合成反应的影响．结果表明：氨解前驱体使硅溶胶中的结构水排除，有助于加快反应速率，提高产物氮含量．本文同时以Y（NO3）3为添加剂，在溶液状态与硅源混合，合成了Si3N4－Y2O3纳米复合粉末.     

溶胶-凝胶法制备纳米Si3N4(Y2O3)粉末的研究

本文以硅溶胶、尿素和炭黑为原料，采用溶胶－凝胶碳热氮化法在１５００℃、２ｈ条件下制得粒径为５０－８０ｎｍ的Ｓｉ３Ｎ４纳米粉末。比较了由硅溶胶与尿素经氨解合成的前驱体和硅溶胶二种不同起始物料的反应活性，研究了氮化条件对合成反应的影响。结果表明：氨解前驱体使硅溶胶中的结构水排除，有助于加快反应速率，提高产物氮含量。本文同时以Ｙ（ＮＯ３）３为添加剂，在溶液状态与硅源混合，合成了Ｓｉ３Ｎ４－Ｙ２Ｏ３纳米复     

脉冲电弧放电电离甲醇/氨水溶液合成结晶氮化碳薄膜

利用脉冲电弧放电在大气压下产生的高密度等离子体研究了结晶氮化碳薄膜的低温合成。直流脉冲电弧等离子体由甲醇／氨水溶液液滴通过高压电极时诱导放电产生。利用扫描电子显微镜、X射线衍射、Raman光谱分析了薄膜样品的形貌和结构。在基片温度为450℃时所制样品的X射线衍射分析表明薄膜中含有α-C3N4和β-C3N4两种结构晶体，Raman光谱给出了明显的特征峰，这些特征峰与氮化碳晶体的理论预言值符合较好。当基片温度提高到550℃时．Raman光谱分析表明，样品为炭膜。     

β-C_3N_4的实验合成研究

作为人工预测材料,β-C_3N_4可能具有与金刚石相当的体弹性模量,并能够检验现代固体理论的预测性。 本研究首先采用离子注入、磁控溅射和微波等离子体化学气相沉积等方法,在不同基片材料和沉积温度下沉积碳氮薄膜,然后对薄膜进行成分、成键和晶体结构等方面的检测。 在成分方面,低温(<200℃)沉积薄膜的氮含量比较低,而高温(700～900℃)沉积时,氮合量有相当程度的提高;虽然在高温下硅基片上薄膜氮含量的提高不能排除氮化硅的影响,但铂基片上相当于C_4N_4成分晶态物质的获得,为β-C_3N_4的合成提供了成分上的可能。 在成键方面,低温沉积碳氮薄膜的红外吸收谱和拉曼谱中不出现与β-C_3N_4明显有关的信息;当在硅基片上高温沉积时,所得碳氮薄膜的拉曼谱中有251、302cm~(-1)峰,可能对应于β-C_3N_4,也可能对应于α-Si_3N_4。 在结构方面,硅基片上沉积碳氮薄膜与碳膜的X射线衍射谱没有明显的差别,而在石墨基体高能注氮并退火样品、铂基片上高温化学气相沉积的碳氮薄膜中,同时得到可以被解释为β-C_3N_4及其变体的X射线衍射谱,为β-C_3N_4的实际存在提供了较为可靠的证据。 总之,从室温到高温,从硅基片到石墨和铂基片,β-C_3N_4实验合成的结论逐渐明晰,为进一步的合成提供了必要的准备。     

等离子体增强原子层沉积技术制备铜薄膜

集成电路的高速发展为铜互连提出诸多要求, 其中, 如何低温条件 (≤ 150℃) 下在大深宽比的通孔或沟槽中沉积保形性好、纯度高、导电性好的铜籽晶层是亟需解决的问题。本文利用等离子体增强原子层沉积技术, 以脒基铜为铜前驱体, 以氢等离子体为还原物质, 在较低的沉积温度 (100℃) 下, 沉积了纯度高、导电性能优良的铜薄膜。在10:1的硅基沟槽中, 表面与沟槽底部厚度均匀 (~80 nm)。考察了放电输入功率对薄膜形貌的影响并利用时间分辨发射光谱技术对氢等离子体进行在线诊断。本论文研究表明铜脒基前驱体用于低温等离子体辅助原子层沉积工艺, 可有效地解决铜薄膜沉积过程中铜粒子的团聚问题, 并为其它类脒基前驱体进行金属薄膜的沉积提供借鉴。     

基于H—Si（100）表面上原子层沉积Al2O3的仿真研究

通过对原子层沉积过程的计算机仿真,分析不同沉积条件对沉积过程的影响.以H-Si(100)表面原子层沉积Al2O3的过程为基础,通过分析基片上不同表面功能团之间的相互作用,将整个沉积过程分为初始沉积和后续生长两个阶段.基于不同的阶段建立相应的前驱体到达事件模型、反应事件模型以及表面解吸事件模型.采用动力学晶格蒙特卡罗方法实现这一沉积过程的仿真.实现了不同温度、不同真空条件下Al2O3的原子层沉积仿真.结果表明:在一定的范围内,前驱体或基片的温度高,反应室真空度低,薄膜生长速率的增长快,表面粗糙度小;基片温度对于薄膜沉积过程的影响最大,其阈值约为200℃.而且薄膜的生长趋势由初始的三维岛状生长向二维层状生长逐渐转变.     

碳氮薄膜的结构分析

对不同沉积条件下沉积在硅基片上的纯碳薄膜、碳氮薄膜以及受不锈钢污染的碳氮薄膜的Ｘ射线衍射谱进行了比较分析，并结合晶态碳氮薄的Ｒａｍａｎ谱分析，认为在这几种工艺条件下是否已合成出β－Ｃ３Ｎ４尚特进一步研究。     

MPCVD合成β—C3N4晶态薄膜

采用微波等离子体化学气相沉积法（ＭＰＣＶＤ），以Ｎ２，ＣＨ４作为反应气体合成碳氢膜。通过控制反应温度，气体流量，微波功率，反应气压等工艺条件在Ｓｉ和Ｐｔ基片上，进行β－Ｃ３Ｎ４晶态薄膜的合成研究。扫描电镜下观察到生长在Ｓｉ基底上的薄膜晶有六角晶棒的密排结构。扫描隧道显微镜下观察到在Ｐｇ基底上生长的碳氮薄膜由针状晶粒组成。     

尿素对以硝酸铝和葡萄糖为原料合成氮化铝粉末反应过程中相变及反应速率的影响

以硝酸铝(Al(NO3)3·9H2O)和葡萄糖(C6H12O6·H2O)为原料,利用碳热还原法制备氮化铝粉末,研究了尿素对前驱物的制备及前驱物氮化反应的影响,研究发现添加尿素合成的前驱物和未添加尿素合成的前驱物在氮化反应过程中相变和反应速率存在较大差异。在没有添加尿素合成的前驱物的氮化反应过程中,出现了γ-Al2O3、α-Al2O3、AlON和AIN相,该前驱物的反应速率慢,完全氮化需要在1600℃下才能完成。对于添加尿素合成的前驱物而言,在其氮化反应过程中仅出现了γ-Al2O3和AIN相,没有α-Al2O3和AlON的生成,AIN直接由γ-Al2O3氮化生成,该前驱物的氮化反应速率快,氮化反应温度低,在1400℃下即可实现完全氮化。分析讨论了两种前驱物的氮化反应速率不同的主要原因,并利用XRD、SEM等分析方法对粉末进行了表征。     

Synthesis and single crystal growth of gallium phosphide by the liquid encapsulated vertical Bridgman technique

Gallium phosphide is a typical III–V compound semiconductor and is also an important electronic material. The synthesis and single crystal growth of this compound by melt methods is rendered very difficult because of the large phosphorus vapour pressure. A high pressure vessel with internal heating and a quartz reactor was first developed for the direct synthesis of gallium phosphide. The crystal growth was carried out in a second high pressure chamber rated for 100 bars gas pressure and equipped with the paraphernalia for crystal growth. Single crystals of gallium phosphide were grown from the polycrystalline starting material by the vertical Bridgman method and the vapour pressure problem was overcome by encapsulating the melt in a column of molten boric oxide. Both boron nitride and silica were employed as crucibles, and with the former, single crystal rods of 8–10 mm diameter and 10–15 mm length were obtained.     

Congruent melting of gallium nitride at 6 GPa and its application to single-crystal growth

The synthesis of large single crystals of GaN (gallium nitride) is a matter of great importance in optoelectronic devices for blue-light-emitting diodes and lasers. Although high-quality bulk single crystals of GaN suitable for substrates are desired, the standard method of cooling its stoichiometric melt has been unsuccessful for GaN because it decomposes into Ga and N(2) at high temperatures before its melting point. Here we report that applying high pressure completely prevents the decomposition and allows the stoichiometric melting of GaN. At pressures above 6.0 GPa, congruent melting of GaN occurred at about 2,220 degrees C, and decreasing the temperature allowed the GaN melt to crystallize to the original structure, which was confirmed by in situ X-ray diffraction. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions.     

Single crystal growth of organic photoconductors: phthalocyanine

An effective method of growing single crystals of organic photoconductors such as phthalocyanine in the presence of doping impurity such as iodine by vacuum sublimation is discussed in this paper. This method is very useful especially when an organic material does not have a melting point but decomposes above a particular temperature. So far, doping has been done by exposing the previously grown organic single crystals to the dopant vapour, but growing the crystal in the presence of dopant vapour makes the doped-crystal more efficient and stable. The photosensitivity as well as the photoconductivity of the doped crystals by this method increases significantly.     

Pressure effect on the solid–liquid equilibrium forms of even normal alkanes

This paper describes the changes in equilibrium forms of small even-numbered normal alkane crystals as functions of temperature, pressure and the carbon number of alkane chains. The crystals were grown by increasing pressure of the liquids using a diamond anvil cell (DAC). After single crystals were prepared in the DAC under high pressure, the crystals were maintained for a long period under constant pressure and temperature. During the changes in the shape of the single crystal, a thick plate of {001} plane with sharp edges was obtained within a narrow temperature range. The appearance of the thick plate is discussed with reference to the pressure and temperature dependencies of the anisotropy of the surface energy of the crystals.     

FTIR spectroscopy of multiwalled carbon nanotubes: a simple approach to study the nitrogen doping

The nitrogen doped multiwalled carbon nanotubes (MWNTs) were synthesized by microwave plasma chemical vapor deposition (MPCVD) technique. In this paper, we report the results of FTIR, Raman, and TGA studies to confirm the presence of N-doping inside carbon nanotubes. Fourier transform infrared (FTIR) studies were carried out in the range 400-4000 cm(-1) to study the attachment of nitrogen impurities on carbon nanotubes. FTIR spectra of the virgin sample of MWNTs show dominant peaks which are corresponding to Si-O, C-N, N-CH3, CNT, C-O, and C-Hx, respectively. The Si-O peak has its origin in silicon substrate whereas the other peaks are due to the precursor gases present in the gas mixture. The peaks are sharp and highly intense showing the chemisorption nature of the dipole bond. The intensity of the peaks due to N-CH3, C-N, and C-H reduces after annealing. It is interesting to note that these peaks vanish on annealing at high temperature (900 degrees C). The presence of C-N peak may imply the doping of the MWNTs with N in substitution mode. The position of this intense peak is in agreement with the reported peak in carbon nitride samples prepared by plasma CVD process, since the Raman modes are also expected to be delocalized over both carbon and nitrogen sites it was found that the intensity ratio of the D and G peaks, I(D)/I(G), varies as a function of ammonia concentration. The TGA measurements, carried out under argon flow, show that the dominant weight loss of the sample occurs in the temperature range 400-600 degrees C corresponding to the removal of the impurities and amorphous carbon.     

A new metal-organic crystal: Potassium thiourea chloride

The growth and characterization of a new nonlinear metal-organic crystal, potassium thiourea chloride (PTC), is reported. The growth of single crystals of PTC was accomplished by the slow evaporation solution growth method. Single crystal X-ray diffraction analysis confirms the crystal structure. The FT-IR analysis confirms the presence of sulfur to potassium bonds in the complex. From the optical spectrum PTC has a good optical transmission in the entire visible region, which is an essential requirement for a nonlinear crystal.     

液相法制备掺氮碳膜的实验研究

在低温和常压下,通过电解甲醇和氨水混合溶液,在硅基片上进行沉积掺氮碳膜的尝试,得到了含氮８％的类金刚石薄膜。通过拉曼光谱和Ｘ光电子能谱对样品的测试表明：碳和氮在薄膜中是以ｓｐ＾２和ｓｐ＾３进行化学成键,本文还提出了液相掺氮碳膜生长的化学机制。     

Crystal growth and characterization of Deuterated Glycine Phosphite single crystals

Deuterated Glycine Phosphite single crystals were grown by low temperature solution growth method using high purity deuterated water as solvent. Deuteration content of the as grown crystals was improved by repeated recrystallisation process. Structural perfection, transparency and the functional groups present in the grown crystals were identified using different characterization analyses. Dielectric behaviors of the as grown specimens were examined through thermal and impedance analysis. Partial deuteration of the grown crystal was confirmed from the DSC and dielectric results.     

Gallium nitride formed by vapour deposition and by conversion from gallium arsenide

Attempts to prepare single crystal gallium nitride in thin films and bulk form are reported. The thin films were prepared by reacting GaCl₃ and NH₃ and depositing on to single crystal silicon carbide substrates. The bulk gallium nitride was prepared by the conversion of single crystals of gallium arsenide using an intermediate oxide phase. The structural perfection of the gallium nitride material thus formed has been assessed using X-ray diffraction and electron diffraction techniques. Both methods of preparation produced single phase gallium nitride exhibiting a high degree of structural disorder.     

稀土氮化物ScN、YN微晶的制备与表征

利用直流电弧等离子体方法制备出稀土氮化物ScN、YN微晶, 这是一种快速、低成本、高产量的新方法, 可用来制备稀土金属氮化物。结构物性表征和能谱成分分析结果表明, 所制备的ScN晶体为满足化学计量比的单晶, 而YN晶体为非化学计量比的多晶, 其中Y的含量高于N。综合XRD、EDS、HRTEM和PL结果分析表明, YN晶体主要由大量随机取向的单晶颗粒组成, 单晶颗粒间分布着一些非晶的金属Y, 光谱结果分析表明YN中存在大量的N空位。此外, 对样品的微观结构形成机理进行了系统分析, 由于Y族金属氮化物中有限组分较高的解离压力以及产物在生长过程中经历较高的淬火速率(10³ K/s), 导致YN解离而形成的Y金属团簇的无序排列, 进而使其在冷却过程中形成了非晶结构。