大规模GaN纳米线阵列的制备及表征

氮化镓(GaN)纳米线阵列是制备下一代光电器件和电子器件最有前途的半导体材料。研究制备规则整齐排列的高质量GaN纳米线阵列,是其商业化应用的基础。本文主要研究气相化学沉积(CVD)法过程中NH_3流量、衬底类型以及生长温度实验条件对GaN纳米线阵列形貌结构的影响,并深入探索了不同长度GaN纳米线阵列的光学性质。对CVD生长GaN纳米结构进行SEM表征,表明Ga/N对生长取向影响较大;通过XRD图谱、Raman图谱分析,表明GaN纳米线的结晶度与衬底材料、生长温度等重要参数相关。使用PL对不同长度GaN纳米线表征,发现GaN纳米线阵列长度为5μm的结晶度最高光学性质最好,展现出了广阔的应用前景。     

低温等离子体气相沉积氮化镓薄膜的光谱特性研究

采用低温等离子体增强化学气相沉积工艺,以氮气N2和三甲基镓(TMG)为反应气源,在蓝宝石衬底-αAl2O3的(0001)面上低温生长了GaN薄膜。薄膜光致发光光谱(PL)出现两个发光带,一个是中心位置位于364nm的锐而强的带边峰。另一个是中心波长在550nm(2.2eV),范围在480~700nm的强而宽的黄光发光带。傅立叶红外光谱(FTIR)观察到GaN的A1(LO)的下沿峰和E1(TO)峰,说明这是六方结构的GaN薄膜。     

紫外可见分光光度法在食品检测中的应用研究进展

紫外可见分光光度法是利用物质对200～760 nm波长范围内的紫外可见光的吸收,以朗伯-比尔定律为理论基础,对物质进行定性和定量分析的仪器分析方法。常用的食品仪器分析方法有紫外可见分光光度法、红外吸收光谱法、原子吸收光谱法、电化学分析法、气相色谱法、高效液相色谱法等,紫外可见分光光度法因其灵敏度高、准确度较高、操作简便、适用范围广,在食品检测中应用较多。本文从食品营养成分、食品添加剂、其他有害物质等3个方面研究了近5年来紫外可见分光光度法在食品定量检测中的最新应用进展,以期为紫外可见分光光度法在食品定量检测中的进一步应用奠定基础。     

超临界二氧化碳/聚合物体系扩散度的测量方法

基于国外先进技术的发展,介绍了超临界二氧化碳/聚合物体系扩散度的各种测量方法.测量二元体系扩散度的方法包括测压法、测重法、光学观测法和光谱技术.测压法和测重法简单易用,是最重要的2种测量方法,但测压法难以测量高温高压体系,测重法需要防止因气体泄漏引起的误差,并需对结果进行浮力校正.光学观测法和光谱方法用于瞬态测量,不对溶解度量化测量.三元体系的测量方法只需对二元体系方法进行适当修正,目前使用的有经过修正的测重技术、利用紫外-可见吸收光谱法和傅里叶变换红外光谱技术等.另外,三元体系方法还包括测量超临界空气条件下的添加剂的传递性质的卷薄膜方法和强制Rayleigh散射法.     

青天葵中鼠李秦素在不同溶剂的紫外-可见吸收光谱测定

对青天葵中鼠李秦素不同溶剂的紫外-可见吸收光谱测定研究,考察其紫外-可见吸收光谱的特征。分别以甲醇溶液、甲醇钠甲醇溶液、三氯化铝甲醇溶液、三氯化铝盐酸甲醇溶液、醋酸钠甲醇溶液、醋酸钠硼酸甲醇溶液为溶剂,分别对其进行紫外-可见光谱测定。鼠李秦素在不同溶剂的紫外-可见吸收光谱图有所区别。本法可作为鼠李秦素紫外-可见吸收光谱特征鉴别的依据。     

5-（4-琥珀酰胺基）苯基-10,15,20-三苯基卟啉及其锌配合物的制备及光谱研究

合成了5-（4-琥珀酰胺基）苯基-10,15,20-三苯基卟啉配体（H2P）及其锌配合物（ZnP）,通过元素分析、质谱、紫外可见吸收光谱、核磁共振氢谱、红外光谱等测试方法对其结构进行确认,并对H2P和ZnP的拉曼光谱进行了研究。结果表明,H2P和ZnP的紫外可见吸收光谱、红外光谱及拉曼光谱都有很大区别。     

氢对非晶氮化硅薄膜键合结构和光学吸收特性的影响

采用对靶磁控反应溅射技术以H2和N2为反应气体在不同氢气流量(15~25 Sccm)条件下制备了氢化非晶氮化硅(a-SiN∶H)薄膜,并利用傅立叶红外透射光谱(FTIR)和紫外-可见透射光谱(UV-VIS)对薄膜的键合结构和光学吸收特性进行了分析。结果表明,氢气流量20Sccm时薄膜中氢的键密度最大,薄膜无序度最减小;薄膜的光学带隙Eg和E04逐渐增大。薄膜原子间键合结构和薄膜有序性的变化可归因于反应溅射过程中氢气的钝化和刻蚀作用。     

三(二乙胺基)氯化硅烷的合成

随着半导体集成电路技术的发展,器件表面钝化保护膜的重要性日益显著。氮化硅薄膜是半导体集成电路中最具应用前景的表面钝化材料之一,发展低温的热化学气相沉积(CVD)工艺来沉积氮化硅表面钝化膜是集成电路发展的趋势,而开发新的硅源、氮源前驱体是实现低温淀积氮化硅薄膜的有效途径。设计了一种新的低温CVD氮化硅薄膜的有机硅源前驱体——三(二乙胺基)氯化硅烷,以四氯化硅和乙二胺为原料,在氮气气氛下,研究了原料预处理、二乙胺用量、反应温度和反应时间等工艺因素对合成收率的影响。最佳工艺条件下,收率达77.4%,并利用核磁共振、元素分析及红外光谱表征了产物的组成及结构。     

窄能隙共轭聚合物:聚{[(3-辛基)噻吩-2,5-二基][(对二甲氨基)苯甲烯]}的合成与表征

聚噻吩甲烯是一类具有极低能隙的共轭聚合物,为了提高其溶解性和成膜性,采用3 辛基噻吩与对二甲氨基苯甲醛进行聚合反应得到了聚(3 辛基)噻吩对二甲氨基苯甲烷(POTDMAB),然后在氧化剂四氯苯醌的作用下进行脱氢反应得到聚(3 辛基)噻吩对二甲氨基苯甲烯(POTDMABQ)。用红外光谱、紫外-可见吸收光谱对POTDMAB和POTDMABQ的结构进行了表征。红外光谱上1653cm-1处的小吸收峰,紫外-可见吸收光谱上450～600nm的吸收说明POTDMAB含有部分醌化的成分。与POTDMAB相比,POTDMABQ的红外谱图在1653cm-1处的吸收强度增加,紫外-可见吸收光谱上450～600nm吸收强度的增加以及核磁共振氢谱都说明了醌化反应的发生和共轭结构的形成。热重分析表明POTDMABQ在200℃以上开始分解。采用了两种模型对POTDMABQ薄膜的光学禁带宽度进行了测量,发现具有很低的禁带宽度,分别为1 32eV(r=1)和1 69eV(r=2),具有用作三阶非线性聚合物光学材料的潜在能力。     

金属–半导体–金属结构非极性α-AlGaN深紫外探测器的制备

通过金属有机化学气相沉积(MOCVD)高温外延生长的未掺杂非极性α-AlGaN半导体薄膜,制备了金属–半导体–金属(MSM)结构的深紫外光电探测器,研究了在α-AlGaN半导体薄膜表面磁控溅射不同时间的SiO_2纳米颗粒对α-AlGaN MSM结构的深紫外探测器性能的影响。结果表明:5 V偏压下,探测器光谱响应峰值提高了大约3个数量级,深紫外近可见抑制比高达104,具有很好的深紫外特性,同时暗电流也下降了2~3个数量级,磁控溅射SiO_2纳米颗粒提升了α-AlGaNMSM结构深紫外探测器性能。     

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.     

Low roughness diamond films produced at temperatures less than 600°C

Recent progress has been made in the production of low-roughness Chemical Vapor Deposition (CVD) diamond films at temperatures less than 600°C. These films are particularly suitable for cutting tool applications. Such progress was achieved by simultaneously promoting the renucleation process and controlling the growth process at low temperatures. In this paper, we show that below 700°C (unlike what is usually observed at temperatures in the range of 750–900°C), secondary nucleation does not occur easily even on (111) faces. This makes the growth of low roughness films difficult. We also report on the role of a thin gold layer deposited on top of a diamond film in favoring smoother film formation. This observation was seen to be due to the ability of the thin gold layer in promoting renucleation. Furthermore, the effect of the percentage of methane introduced in the feed gas was studied.     

Fabrication and properties of ZnO/GaN heterostructure nanocolumnar thin film on Si (111) substrate

Zinc oxide thin films have been obtained on bare and GaN buffer layer decorated Si (111) substrates by pulsed laser deposition (PLD), respectively. GaN buffer layer was achieved by a two-step method. The structure, surface morphology, composition, and optical properties of these thin films were investigated by X-ray diffraction, field emission scanning electron microscopy, infrared absorption spectra, and photoluminiscence (PL) spectra, respectively. Scanning electron microscopy images indicate that the flower-like grains were presented on the surface of ZnO thin films grown on GaN/Si (111) substrate, while the ZnO thin films grown on Si (111) substrate show the morphology of inclination column. PL spectrum reveals that the ultraviolet emission efficiency of ZnO thin film on GaN buffer layer is high, and the defect emission of ZnO thin film derived from Zn_i and V_o is low. The results demonstrate that the existence of GaN buffer layer can greatly improve the ZnO thin film on the Si (111) substrate by PLD techniques.     

Chemical Kinetic Calculations of the Gas Phase in Filament-Assisted Chemical Vapor Deposition of Diamond

A chemical kinetic model was developed for the gas mixture in filament-assisted diamond chemical vapor deposition (CVD) systems. CH₄/H₂ mixture was studied as the starting gas mixture. The predictions of gas evolution calculated from this model were used to interpret certain published experimental observations. From the initial analysis, it was concluded that the thermodynamic state of the gas composition determined the effects of transport parameters on diamond growth. In many filament-assisted diamond CVD systems the gas composition was found to be kinetically controlled. The analysis also suggested that CH₃ is a major precursor of diamond films. When CH₄/H₂/O₂ was used as the starting gas mixture, the results indicated that the oxygen additive catalyzed the process to increase the concentrations of CH₃ and H, thereby increasing the growth rate and improving the quality of diamond films.     

Synthesis of boron-doped homoepitaxial single crystal diamond by microwave plasma chemical vapor deposition

The deposition of boron-doped homoepitaxial single crystal diamond is investigated using a microwave plasma-assisted chemical vapor deposition system. The objective is to deposit high-quality boron-doped single crystal diamond and establish the relationships between the deposition conditions and the diamond growth rate and quality. Experiments are performed using type Ib HPHT diamond seeds as substrates and growing diamond with varying amounts of diborane in a methane–hydrogen gas mixture. The deposition system utilized is a 2.45 GHz microwave plasma-assisted CVD system operating at 135–160 Torr. Experiments are performed with methane concentrations of 4–6% and diborane concentrations of 5–50 ppm in the feedgas. Diamond is deposited with growth rates of 2 to 11 µm/h in this study. The deposited diamond is measured to determine its electrical conductivity and optical absorption versus wavelength in the UV, visible and IR portions of the spectrum. Data is presented that relates the growth rate and diamond properties to the deposition conditions including substrate temperature and feedgas composition.     

Influence of purge gas on the characteristics of lead–zirconium–titanate thin films prepared by metalorganic chemical vapor deposition

In order to optimize the metalorganic chemical vapor deposition process for PbZr_xTi_1−xO₃ (PZT) thin films, the effect of purge gas species was investigated. Two steps of gas input process for stabilizing reaction chamber pressure, the gas flow prior to PbTiO₃ (PTO) seed layer deposition and PZT thin film deposition, were varied and their effect on structural and electrical properties were examined with regard to the memory device application. PZT film properties exhibited remarkable dependency on the gas species before PTO seed deposition, and insignificant dependency on the gas species before PZT film deposition. With the optimized pre-deposition gas flow, PZT thin film showed excellent properties such as high (1 1 1)-orientation (92.2%), high remnant polarization value of 71 μC/cm² at 3 V. Retention property also showed a heavy dependency on the pre-deposition gas flow that 91.1% of initial charge could be maintained after 100 h of baking at 150 °C.     

氧化钨（WO3）薄膜光电催化性能的改善及应用

半导体WO₃具有较小的禁带宽度和良好的稳定性,对可见光具有较强的吸收,在光催化和光电催化领域具有广泛的用途。然而,单一WO₃薄膜仍然存在着光生电子-空穴复合率高、光电催化活性与能量转换效率偏低等问题。本文从WO₃薄膜光电催化性能的改善及应用两个方面对近年来的研究进行了综述。在WO₃薄膜光电催化性能的改善方面,分别从有序纳米结构的构建、离子掺杂与表面修饰进行总结。同时,也归纳总结了WO₃薄膜作为光电极在分解水制氢、光电催化还原CO₂和降解有机污染物等方面的应用,并提出了WO₃薄膜在光电催化过程中存在的问题,指出WO₃有序纳米异质结的构建是提高WO₃薄膜光电催化活性的有效方法。WO₃薄膜光电极的规模制备、廉价助催化剂的使用、光电极的稳定性与耐蚀性是其实际应用过程中需要解决的问题。     

Morphology and growth mechanism of CVD alumina–silica

The purpose of the present paper is to examine the morphology and growth mechanism of the CVD alumina–silica film deposited at low temperatures and low pressure using the chemical reaction kinetics, the Gibbs–Thomson relation, solidification theory, and supersaturation condensation fusion mechanism. The dense CVD alumina–silica films were deposited on the surface of graphite paper using AlCl₃–SiCl₄–H₂–CO₂ as precursor in the temperature range of 300–550 °C. XRD and SEM were used to examine the phase composition and the microstructure of the CVD alumina–silica, respectively. The CVD alumina–silica films were composed of a large number of spherical particles accumulated by a number of fine-particles. The fusion took place among the solid particles. The spherical morphology and the fusion all resulted from the liquid droplets, which resulted from the supersaturation of the chemical reaction gaseous species in CVD alumina–silica. The liquid droplets were confirmed by comparing the morphology of the CVD alumina–silica with the typical and stable morphology of the solidified mass from liquid.     

二氧化碳加氢合成低碳烯烃的研究进展

大气中逐年升高的二氧化碳浓度对全球环境产生了严重的影响。通过可再生能源得到的H₂与CO₂反应生成低碳烯烃,不但可以使CO₂得到资源化利用,还能减少低碳烯烃的生产对于石油资源的依赖。该技术还有望实现从海水中得到燃油。本文主要对CO₂加氢合成低碳烯烃的热力学、反应机理和催化剂研究进行了综述。目前,该反应中使用的催化剂以Fe系为主。文中简要介绍了直接转化催化剂中的载体、助剂和双金属活性组分对反应性能的影响以及经甲醇路线制低碳烯烃的双功能催化剂在该反应中的应用。高性能催化剂的设计以及反应机理的探索是CO₂加氢合成低碳烯烃未来的发展方向。     

Substrate effects on the strain relaxation in GaN/AlN short-period superlattices

ABSTRACT: We present a comparative study of the strain relaxation of GaN/AlN short-period superlattices (SLs) grown on two different III-nitride substrates introducing different amounts of compensating strain into the films. We grow by plasma-assisted molecular beam epitaxy (0001)-oriented SLs on a GaN buffer deposited on GaN(thick)-on-sapphire template and on AlN(thin)-on-sapphire template. The ex-situ analysis of strain, crack formation, dislocation density, and microstructure of the SL layers has established that the mechanism of strain relaxation in these structures depends on the residual strain in substrate and is determined mainly by the lattice mismatch between layers. For growth on the AlN film, the compensating strain introduced by this film on the layer prevented cracking; however, the densities of surface pits and dislocations were increased as compared with growth on the GaN template. Three-dimensional growth of the GaN cap layer in samples with pseudomorphly grown SLs on the AlN template is observed. At the same time, two-dimensional step-flow growth of the cap layer was observed for structures with non-pseudomorphly grown SLs on the GaN template with a significant density of large cracks appearing on the surface. The growth mode of the GaN cap layer is predefined by relaxation degree of top SL layers.