微重力ZnTe：Cu 晶体生长及阴极荧光光谱(CL)分析

利用Te熔剂方法,在天宫二号飞船上成功地生长了ZnTe:Cu晶体.微重力下生长的晶体质量优于地面生长的晶体,相同实验条件下,天宫二号上生长的晶体尺寸明显大于地面尺寸.通过阴极荧光光谱(CL)无损检测技术测试了5 kV、15 kV、25 kV高压下的ZnTe:Cu晶体的阴极荧光图谱及光谱.     

嘉陵江水体平水期水质的三维荧光光谱监测分析

嘉陵江是重庆的重要饮用水源,其水质与城市居 民的生活和生态环境息息相关。为研究其水质及其变化,在重庆主城区嘉陵江段平水期3~5月,采用三维荧光技术对7个取样点的水体样品进行 分析,得到了溶解性有机质(DOM)含量变化引起的三维荧光光谱变化数据,水体样品存在 两个荧光峰分 布,荧光峰Ⅰ激发波长λ_ex=330~350nm,发射波长λ_em=400~450nm;荧光峰Ⅱ激发波长 E_ex=270~300nm, 发射波长λ_em=320~350nm。结果 表明,取样江段水样三维荧光谱中的荧光峰主要由类腐殖 质和类蛋白质形成;同时,由于受到气温、降雨、地理环境等因素的影响,3-5月各河段水 样的荧光指数(f450/50)分别 在1.41~1.57、1.30~1.47和1.42~1.68之间,由此可以判断,采样时 间段内水质污染主要是陆源性输入形成。     

导数同步荧光光谱结合遗传优化算法测定鸭蛋蛋清中庆大霉素含量

为实现鸭蛋蛋清中庆大霉素(GM)残留含量的快速测定与检测模型精度的提高,应用遗传算法(GA)筛选导数同步荧光光谱特征波长,用遗传-支持向量回归(GA-SVR)建立鸭蛋蛋清中GM残留含量的预测模型。首先分析了样本的三维同步荧光光谱和确定了本实验研究的波长差Δλ为120nm;然后利用sym5小波的2层分解对一阶导数同步荧光光谱进行去噪处理,并利用GA筛选出了14个荧光特征波长;最后利用GA优化了SVR的径向基核函数(RBF)参数(c,g,p),进而比较了GA-SVR、PLS和MLR 3种预测模型的预测能力,研究表明,以GA-SVR模型的预测能力最强,其预测集的决定系数(R2)和均方根误差(RMSEP)分别为0.983 0和1.149 4mg/L。实验结果表明,GA能有效筛选出鸭蛋蛋清中GM的荧光特征波长和提高GA-SVR模型预测精度。     

基于独立成分分析的复杂光谱的定量分析

基于独立成分分析(ICA)算法,对超短脉冲激光与气体相互作用所产生的复杂的非线性荧光光谱数据进行了有效的特征提取,进而对空气中含有的3种杂质气体在不同浓度下的光谱进行了预测,得到的结果与实测值相比较误差很小.对这3种气体共计27组光谱数据进行浓度值的定量预测,达到了满意的实验结果.     

枸杞中维生素B2固体粉末的荧光光谱检测研究

利用日本岛津RF-5301PC荧光分光光度计,对枸杞子粉末中的维生素B2(VB2)直接进行荧光光谱检测,采集的光谱范围在530～650nm波段。采用MATLAB数值微分和高斯函数拟合方法,得到在激发波长为480nm、峰值波长为563nm时的荧光光谱信息;通过数值积分和线性拟合,得到荧光强度沿波长的积分与VB2含量呈良好的线性关系,其相关系数为0.998 43。实验测定枸杞粉末VB2含量为1.28±0.17μg/g,并阐释了枸杞子粉末荧光光谱红移的原因。研究表明:这种固体粉末荧光光谱检测方法具有快速、直接、简单和环保等优点,对药品成份检测、食品安全监测等领域的应用具有重要的参考价值。     

磷酸铁锂/小尺寸石墨烯复合锂离子电池阴极材料的制备及储能特性

磷酸铁锂(LiFePO4,LFP)是一种良好的阴极材料,然而导电率低和锂离子扩散系数小的缺点限制了其在高倍率下的电化学性能.寻找规模化工艺制备高倍率的锂离子电池阴极材料,对于高倍率锂离子电池的制备和应用意义重大.采用模板刻蚀法制备尺寸小于200 nm的小尺寸氧化石墨烯(SGO),用湿法球磨和高温固相法有效地制备碳包覆的...     

Er3+/Yb3+共掺氟氧微晶玻璃的光谱性质及Judd-Ofelt理论分析

制备了新的Er3+/Yb3+共掺氟氧硅酸盐微晶玻璃,测试了荧光光谱、吸收光谱。研究了氟氧化物微晶玻璃中Er3+离子的上转换发光特性,采用Judd-Ofelt理论对样品光谱进行了分析,拟合得到了强度参数,Ω2=4.4756,Ω4=1.0059,Ω6=1.2098。计算了样品的辐射寿命、跃迁几率、荧光分支比等光谱参数。结果表明,样品通过热处理形成了氟化物微晶,降低了声子能量,提高了上转换效率。绿光、红光上转换荧光强度比玻璃样品增强约2到3倍。Judd-Ofelt理论分析表明Er3+/Yb3+共掺氟氧微晶玻璃具有较高的上转换效率,是制作微型激光器和三维立体显示的优良材料之一。     

Characteristics of GaN stripes grown by selective-area metalorganic chemical vapor deposition

We report on the selective-area metalorganic chemical vapor deposition of GaN stripes in the size range of 50 to 125 urn and the characterization of the morphology, topography, and optical properties of these stripes. GaN films (∼1–3 μm) grown on (0001) sapphire are used as the substrates. Excellent surface morphology is achieved under optimized growth conditions which include a higher V/III ratio than broad area growth. It is found that, under certain growth conditions, (0001) terraces of ~5 μm in width develop at the edges of all stripes, independent of stripe size and orientation. The selectively grown GaN yields stronger band-edge emission than the “substrate” GaN which indicates an improvement in optical quality. However, the donor-acceptor pair recombination (or conduction band to acceptor transition) and yellow emission are also enhanced in certain areas of the stripes. The spatial correlation of these emission bands is established by cathodoluminescence wavelength imaging, and the origin of these emissions is speculated.     

Scanning electron microscopy and cathodoluminescence study of the epitaxial lateral overgrowth (ELO) process for gallium nitride

Traditional epitaxial growth of GaN by metalorganic vapor phase epitaxy (MOVPE) on mismatched substrates such as sapphire or SiC produces a columnar material consisting of many hexagonal grains ∼0.2–1.0 μm in diameter. The epitaxial-lateral-overgrowth (ELO) process for GaN creates a new material: single-crystal GaN. We have studied the ELO process for GaN grown by MOVPE in a vertical flow rotating substrate reactor. Characterization consisted of plan-view SEM and vertical-cross-section TEM studies, which revealed a large reduction in dislocation density in the overgrown regions of the GaN. Panchromatic and monochromatic cathodoluminescence images and spectra were used to study the spatial variation of the optical properties within the GaN ELO samples. The effects of growth temperature and stripe material on the overgrown layers were examined. Through the use of a higher substrate temperature during growth and the use of a SiN_x stripe material, the overgrown crystal shape has a smooth 2D top surface with vertical sidewalls. Applying a second ELO step, rotated by 60°, over a fully coalesced ELO layer yields a further reduction of defects in GaN overgrown surfaces.     

Control of ordering in GaInP and effect on bandgap energy

Ga_xIn_1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with 10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure (ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm deep) grooves, with maximum angles of <10°, are less effective. Within the large domains on each side of the groove, small domains of the other variant are observed. The boundary between the two domains is seen to wander laterally by a micron or more during growth, due to the change in shape of the groove during growth. For deep (1.5 μm) grooves, with maximum angles to the (001) plane of 35°, only a single variant is formed on each side of the groove. However, the domains are small, dispersed in a disordered matrix. For substrates with deep grooves on a GaAs substrate misoriented by 9° toward the [-110] direction, an interesting and useful pattern is produced. One half of the groove is a single domain which shrinks in size as the growth proceeds. The other half of the groove, where the misorientation is larger, is disordered. Thus, every groove contains large (>1 μm² cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence (CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition demonstrate that the shift in emission energy is not due to changes in solid composition. This is the firstdirect verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga_0.5In_0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several orders of magnitude.     

Deep level electronic structure of ZnSe/GaAs heterostructures

We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100) heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3 eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface defect densities.     

The effect of substrate misorientation on the optical, structural, and electrical properties of GaN grown on sapphire by MOCVD

We report the growth and characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on c-plane A1₂O₃ substrates either on-axis or intentionally misoriented 2° toward the a-plane (1120) or 5 or 9° toward the m-plane (10 10). The samples are characterized by 300K photoluminescence, cathodoluminescence, and Hall-effect measurements as well as by triple-axis x-ray diffractometry to determine the effect of the misorientation on the optical, electrical, and structural properties of heteroepitaxial undoped GaN. Ten different sample sets are studied. The data reveal enhanced photo-luminescence properties, increased electron mobility, a reduced n-type background carrier concentration, and a somewhat degraded surface morphology and crystalline quality for the misoriented samples compared to the on-axis samples.     

生长温度对Mn掺杂ZnO纳米棒铁磁性的影响

用化学气相沉积法(CVD),在生长温度为600、650和700 ℃条件下,未采用任何催化剂制备了Mn掺杂ZnO纳米棒.研究发现,随着生长温度的升高,样品中O空位的浓度逐渐增加.低浓度的O空位可以增强Mn掺杂ZnO纳米棒的铁磁性,但O空位浓度过高时,Mn掺杂ZnO纳米棒表现出超顺磁性或反铁磁性.在3个样品中,650 ℃的样品具有最好的室温铁磁性,其饱和磁化强度为0.85 μB/Mn,矫顽力为50 Oe.     

Photoluminescence of nitrogen-doped zinc selenide epilayers

Photoluminescence (PL) studies of nitrogen doped ZnSe epilayers grown by molecular beam epitaxy have been performed as a function of excitation wavelength, power density, and temperature. The broad emission from heavily doped ZnSe:N is composed of two distinct bands which we label as N_I and N_II. The dominant band N_I appears at 2.54 eV, while the N_II band position is sensitive to excitation power and occurs between 2.55 and 2.61 eV. The N_I emission energy is insensitive to incident power or temperature over the ranges studied. Further, a 69 meV localized phonon of the N_I band is observed. We propose that the N_I band is related to transitions within a (V_se+-Zn-N_se-)0 close-associate pair. The N_II band displays characteristics consistent with the conventional donor acceptor pair model. A third band N_III at 2.65 eV is observed under high-power pulsed excitation. Previous studies of heavily doped ZnSe:N had suggested that the broad emission band was described by a modified donor-acceptor pair model. Our PL study does not support this previous model. In addition, our data suggests that singly ionized selenium vacancy complexes form in heavily doped ZnSe:N and play a role in compensation.     

利用单载波模块实现多载波的配置及边界寻呼方式优化浅析

通过对网络升级后闲置的北电CDMA基站单载波模块SFRM的开发利用,降低了网络发展的成本,提高了设备资源的利用率。在优化过程中,必须对单、多载波边界区域进行良好的寻呼方式优化,保证单、多载波边界覆盖区域的通信质量。     

Crystallographic evaluation of ZnSe crystals by x-ray diffraction

Crystallographic quality and the lattice constant of ZnSe crystals grown from Te/ Se solutions by the temperature gradient solution growth method were evaluated by using a high resolution x-ray diffractometer. The full width at half maximum of the x-ray rocking curve was 5.7 sec, a value almost equivalent to that of GaAs. The distribution of crystallographic properties along the growth direction was nearly the same excepting just on the heat-sink. The accurate lattice constant of the ZnSe crystal measured by this system was 5.6700 ± 0.000025 A.