分子束外延生长InGaN量子点及其结构和光学特性

采用射频等离子体辅助分子束外延 (RF-MBE)技术在蓝宝石衬底上,外延生长了发光波长位于407 nm的InGaN量子点结构,研究了InN成核层技术对其结构和光学特性的影响。材料生长过程中采用反射式高能电子衍射 (RHEED)进行了在位检测,通过原子力显微镜 (AFM),光致发光 (PL)等测试手段表征了InGaN量子点材料的结构和光学特性。结果表明,相对于直接在GaN层上自组织生长InGaN量子点,通过InN成核层技术可以获得高密度、高质量的InGaN量子点结构,量子点尺寸分布更加均匀,主要集中在35~45 nm之间;量子点的密度更高,可以达到3.2×1010/cm2;InN成核层上生长的InGaN量子点的PL发光峰强度为直接在GaN层上生长的InGaN量子点的2倍,发光峰的半高宽较窄,为10 nm     

掺Mn:MgAl2O4透明陶瓷的制备工艺和光学性能

采用熔盐焙烧法制得了不同掺杂浓度的Mn:MgAl2O4超细粉体,采用真空烧结法制得Mn:MgAl2O4透明陶瓷.通过紫外可见分光计、扫描电镜、荧光分光计等测试手段研究了可望用于可见波段的新型激光材料Mn:MgAl2O4透明陶瓷的光学透过率、微观形貌和光荧光特性.结果表明,通过简单的制备工艺可制得光学特性均一的Mn:MgAl2O4透明陶瓷,并且与单晶相比Mn:MgAl2O4透明陶瓷存在两条发光通道,一个中心在520 nm附近很强的荧光峰,其强度随着掺杂浓度的增加而加强;一个是中心在690 nm附近处微弱的荧光峰.这两条发光通道不是独立的,这与单晶是不相同的.     

MgAl2O4颗粒增强型AC4C基复合材料的微观组织及力学性能

采用搅拌铸造方法制造MgAl2O4颗粒增强型AC4C基复合材料。考察MgAl2O4颗粒的尺寸及尺寸的分布对颗粒分散度的影响,并且测试复合材料的微观组织、强度与疲劳性能。5～25gm范围内的MgAl2O4颗粒可以提高复合材料的抗拉强度。疲劳性能测试表明,在250℃、10^7循环周期内,MgAl2O4颗粒使复合材料的疲劳性能提高27％。在MgAl2O4颗粒周围,观察到了大量位错,产生这种情况的主要原因是MgAl2O4与Al两者之间的热膨胀系数不匹配。在MgAl2O4颗粒周围产生裂纹,但在扩展过程中大量的裂纹发生了转向和弯曲,这有助于材料疲劳性能的提高。     

单晶蓝宝石衬底晶片的化学机械抛光工艺研究

目的设计单晶蓝宝石衬底化学机械抛光的合理方案,探究主要抛光工艺参数对抛光衬底的表面质量和材料去除率的影响,并得到一组材料去除率高且表面质量满足要求的抛光工艺参数。方法借助原子力显微镜和精密天平分别对衬底表面形貌和材料去除率进行分析,采用单因素实验法探究了抛光粒子、抛光时间、抛光压力和抛光盘转速对蓝宝石衬底化学机械抛光的表面质量和材料去除率的影响,并设计合理的交互正交优化实验寻求一组较优的抛光工艺参数。结果在蓝宝石衬底化学机械精抛过程中,在抛光时间为0.5 h、抛光压力为45.09 k Pa、抛光盘转速为50 r/min、SiO_2抛光液粒子质量分数为15%、抛光液流量为60 m L/min的条件下,蓝宝石衬底材料的去除率达41.89 nm/min,表面粗糙度降低至0.342 nm,衬底表面台阶结构清晰,满足后续外延工序的要求。结论采用化学机械抛光技术和优化的工艺参数,可同时获得较高的材料去除率和高质量的蓝宝石衬底表面。     

掺Mn：MgAl2O4透明陶瓷的制备工艺和光学性能

采用熔盐焙烧法制得了不同掺杂浓度的Mn：MgAl2O4超细粉体，采用真空烧结法制得Mn：MgAl2O4透明陶瓷。通过紫外可见分光计、扫描电镜、荧光分光计等测试手段研究了可望用于可见波段的新型激光材料Mn：MgAl2O4透明陶瓷的光学透过率、微观形貌和光荧光特性。结果表明，通过简单的制备工艺可制得光学特性均一的Mn：MgAl2O4透明陶瓷，并且与单晶相比Mn：MgAl2O4透明陶瓷存在两条发光通道，一个中心在520nm附近很强的荧光峰，其强度随着掺杂浓度的增加而加强；一个是中心在690nm附近处微弱的荧光峰。这两条发光通道不是独立的，这与单晶是不相同的。     

掺杂MgAl2O4的Al2O3陶瓷材料研究

将MgO以MgAl2O4的形式掺杂到Al2O3中,研究MgAl2O4的掺杂量及其在不同烧结工艺条件下,对Al2O3陶瓷烧结性能和显微结构的影响.结果显示在氧化气氛1 640℃下烧结,掺杂MgAl2O4的Al2O3陶瓷烧结性能较掺杂MgO的Al2O3陶瓷差.而在氢气氛1 640℃下烧结,掺杂MgAl2O4的Al2O3陶瓷烧结性能优于掺杂MgO的Al2O3陶瓷,Al2O3陶瓷的相对密度可达99.1%,但晶粒尺寸分布不均匀,在3 μm～7 μm之间.当采用先在氧化气氛1 450℃下一次烧结后,再在氢气氛1 640℃下进行二次烧结时,发现不仅可以获得致密掺杂MgAl2O4的Al2O3陶瓷材料,而且还可以制备出存在大量长柱状晶粒的Al2O3陶瓷.     

氧化锌添加剂对固相合成镁铝尖晶石的影响

用含铝废渣和碱式碳酸镁为主要原料,通过固相反应合成镁铝尖晶石(MgAl2O4).探讨氧化锌(ZnO)添加剂对合成的MgAl2O4晶相、微观形貌及性能的影响.用X射线衍射(XRD),扫描电镜(SEM)及相关分析软件表征得到的MgAl2O4.结果表明:ZnO是一种有效矿化剂,添加ZnO可以提高样品中MgAl2O4的含量,最佳的ZnO添加量确定为2wt%,此时样品中MgAl2O4固溶体(Mg0.68Al0.32)(Al0.84Mg0.16)2O4的含量最高为93wt%,体积密度为3.36g/cm3,显气孔率为2.78%,常温抗弯强度达到136.2MPa.     

Electronic structures of new tunnel barrier spinel MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: first-principles calculations

The electronic structures of spinel MgAl2O4 and MgO tunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl2O4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5. 10 eV for MgAl2O4 and 4. 81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point (△ band), the coherent tunneling effect might be expected to appear in MgAl2O4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2. 9 J. m-2) and MgAl2O4 (2. 27 J·m-2) on the {100}orientation, and the smaller lattice mismatch between MgAl2O4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl2O4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.     

Mo-CVD法制备GaAs和CdTe的特种材料研究

用Mo-CVD技术已研制了几种特种半导体材料,(1)注氧GaAs衬底上生长GaAs:根据注氧剂量的不同,已获得各种结晶的GaAs外延层。这种材料将在选择外延中起重要作用;(2)Mo/Si衬底上生长GaAs:由于面积大,价格低和结晶性能较好,GaAs/Mo/Si材料可能成为有前途的太阳电池材料;(3)在GaAs衬底上生长CdTe:CdTe/GaAs是一种复合材料,它有望代替CdTe单晶成为HgCdTe外延的代用衬底。这三种材料的电性和结晶性能已用C-V,I-V,S.E.M和电子衍射以及用X射线能谱进行了研究和测量。     

热处理温度对MgO-ZnO-Al2O3-SiO2系玻璃晶化的影响

通过差热分析(DTA)、X射线衍射分析(XRD)、扫描电子显微镜(SEM)等手段,研究了热处理温度对MgO-ZnO-Al2O3-SiO2系玻璃晶化特性的影响.结果表明当采用单步热处理工艺,热处理温度为800℃时,玻璃发生分相;温度从820℃升到900℃时,不断有晶体析出,析出晶相分别为MgO·Al2O3·3SiO2和MgO·Al2O3·4SiO2.当采用两步热处理工艺时,样品在800℃形核,随晶化温度由950℃升高到1050℃,析出晶相由尖晶石相(包括ZnAl2O4,MgAl2O4)和MgO·Al2O3·4SiO2相转变为尖晶石相(包括ZnAl2O4,MgAl2O4)和β-石英.     

Deposition and properties of highly <Emphasis Type="Italic">c</Emphasis>-oriented of InN films on sapphire substrates with ECR-plasma-enhanced MOCVD

InN films with highly c-axis preferred orientation were deposited on sapphire substrate by low-temperature electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). Trimethyl indium (TMIn) and N2 were applied as precursors of In and N, respectively. The quality of as-grown InN films were systematically investigated as a function of TMIn fluxes by means of reflection high-energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), and atomic force microscopy (AFM). The results show that the dense and uniform InN films with highly c-axis preferred orientation are successfully achieved on sapphire substrates under optimized TMIn flux of 0. 8 ml·min-1. The InN films reported here will provide various opportunities for the development of high efficiency and high-performance semiconductor devices based on InN material.     

添加剂对镁合金微弧氧化的影响

为了解添加剂对镁合金微弧氧化陶瓷膜的成膜速度及微观组织结构的影响,用自制的微弧氧化实验装置对AZ91D压铸镁合金进行了微弧氧化,并用SEM、XRD分析其微观组织结构.结果表明,在槽液中添加Al复合化合物使起弧电压和稳态电压降低,氧化陶瓷膜的生成速度增加、硬度增大,膜层致密性提高,陶瓷膜中的晶胞以垂直于基底面的方式生长,陶瓷氧化膜中主要存在的相有Al2O3、MgAl2O4和MgO.但当含Al复合化合物的质量分数在30%以上时,其致密性和硬度反而下降.     

Effects of Nitridation Temperature on Characteristics of Gallium Nitride Thin Films Prepared Via Two-Step Method

In this research,the growth of GaN thin films on c-plane sapphire(0001) substrates via two-step method without the assist of buffer layer and catalysts was demonstrated.First,gallium oxide(Ga_2O_3) thin films were deposited on sapphire substrates by radio frequency magnetron sputtering method.The deposited Ga_2O_3 thin films were then nitridated at various temperatures.In this research,attention is focused on the influence of nitridation temperatures on the structural and optical properties of the synthesized GaN thin films.It is revealed that 950 ℃ is the optimal nitridation temperature for synthesizing hexagonal wurtzite GaN thin film with preferential(0002) growth direction.     

Aluminium-alumina interface morphology and thermodynamics from dewetting experiments

This work presents the morphology of micron-sized metallic drops (Al) equilibrated on ceramic substrates (sapphire), with emphasis on the interfacial region. The samples were made by controlled dewetting of a thin Al film on the basal surface of sapphire substrates, at temperatures above the melting point of Al. Morphological inspections showed that evaporation of the sapphire substrate atoms, which diffuse at the interface, has an important role in the evolution of the Al-sapphire interface morphology. The absolute value of the sapphire basal surface energy was extracted (1279 ± 78 mJ/m² at 900 °C). The values of the thermodynamic parameters determined from the interface morphology agree well with those from experiments made under identical conditions but using millimetre-sized drops. This confirms the validity of Young’s equation for large sessile drops in systems undergoing limited morphological changes (ridging) at the interface.     

不同厚度Tl-2212薄膜的表面形貌及超导特性研究

采用直流磁控溅射法和后退火技术在蓝宝石基片上制备了Tl-2212超导薄膜,考察了Tl-2212薄膜的厚度对其形貌和超导特性的影响。实验结果表明,随着超导薄膜厚度增加,其表面形貌由致密平整的结构演化为片状晶体结构,临界转变温度Tc和临界电流密度Jc先增大后减小,微波表面电阻Rs先减小后增大。在退火的CeO2缓冲层上所制备的无裂纹薄膜的最大厚度达到600nm,并仍然具有良好的超导性能。     

Laser-Welded Steel Foils with Sapphire Substrates

A nanosecond pulsed laser was used to weld stainless steel foils of 10 μm thickness to the sapphire substrates.The microstructure of the bonded interface was studied.Both materials were partially ablated under the influence of the laser beam.An inhomogeneous distribution of the steel and sapphire along the bonded interface is observed.The electrical resistance of the steel foil was measured before and after laser welding,showing that the weld slightly increases the electrical resistance but still keeps the values acceptable for electrical contacts.     

基片温度对Co掺杂ZnO薄膜室温铁磁性的影响

采用磁控共溅射法在Al2O3(0001)基片上沉积了Zn1-xCoxO(x=0.08～0.3%)薄膜,研究了基片温度对Co掺杂ZnO薄膜结构和磁性的影响.结果表明:Al2O3(001)基片很好地诱导了ZnCoO薄膜(002)取向生长,并且所有的薄膜均显示室温铁磁性.较低的基片温度不仅能有效抑制薄膜中Co2O3杂质相的产生,而且薄膜磁矩较大.紫外-可见光谱也表明,薄膜中Co2 取代了ZnO中Zn2 的位置.     

Substrate effect on mechanical characterizations of aluminum-doped zinc oxide transparent conducting films

The measurements of thin-film mechanical properties are generally influenced by the elastic and plastic responses of substrates and consequently may be inaccurate. Thus in this study, the effects of three different substrates, including sapphire, glass and polyimide, on the mechanical characterizations of aluminum-doped zinc oxide transparent conducting films are evaluated. From nanoindentation tests, it was found that a high film/substrate hardness ratio contributed an early-initiated substrate effect. For a hard film/soft substrate system (zinc oxide on polyimide), the measured hardness and elastic modulus markedly dropped at very small indentation depths due to the insufficient strength of the soft substrate to sustain the applied stress. A modification of the Bhattacharya model and the calibration of the King model were also made in this study; some important factors were established. Moreover, the interface adhesion energy between the film and soft substrate, measured by nanoscratch, was high because the compliant deformation of the soft substrate released accumulated stresses and then retarded interface delamination.     

MOCVD生长GaN力学性能研究

采用MOCVD技术在蓝宝石衬底（0001）面上生长了GaN外延膜，利用原子力显微镜AFM、扫描电镜SEM分析了薄膜表面形貌，利用纳米压痕仪和UMT试验机考察了GaN膜的硬度、临界载荷以及摩擦学性能等。结果表明，薄膜以二维模式均匀生长，表面平整，硬度达22．1MPa，弹性模量为299．5GPa，与衬底结合紧密，临界载荷达1．6N，与GCr15钢球对磨时摩擦系数仅为0．13，与Si3N4陶瓷球摩擦时膜很快就磨穿。