钴离子注入对二氧化钛晶体的结构和光学性能的影响

采用离子注入法制备了钴离子掺杂的金红石相TiO₂样品;离子注入能量、注量分别为40 keV(1×10¹⁶cm^-2),80 keV(5×10¹⁵,1×10¹⁶,5×10¹⁶,1×10¹⁷cm^-2),120 keV(1×10¹⁶cm^-2). 通过XRD,XPS和UV-Vis等手段对掺杂前后样品的结构和光学性能进行了表征,分析了掺杂元素在金红石TiO₂中的存在形式. XRD测试表明随着注入能量的增加晶体的损伤程度增加. UV-Vis测试表明掺杂后所有样品在可见光区的吸收增强; 并且随着注量的增加,注量为5×10¹⁵cm^-2到5×10¹⁶cm^-2范围内注入样品的光学带隙逐渐变小. 关键词： 钴 二氧化钛 离子注入 掺杂     

聚环氧乙烷硫氰化钠络合物(PEO-NaSCN)离子导体电学性能的研究

本文研究了分子量为6.0×10³,1.2×10⁴和2.0×10⁴的PEO-NaSCN络合物的电学性能。分子量为6.0×10³和2.0×10⁴的样品,络合反应不完全,因而在第一次升温过程中,继续进行络合反应,导致电导率随温度变化的复杂行为。分子量为1.2×10³的样品,络合反应相当充分,因而电学性能不受热历史的影响,过量的PEO对电导率的大小及其随温度的变化行为有显著影响。分子量为1.2×10⁴的样品含有较多的过量的PEO,电导率最高,而且在PEO熔点附近,电导率突然增加。分子量为6.O×10³的样品,含的过量PEO最少,电导率最低,而且随温度连续变化。 关键词：     

Ag离子注入非晶SiO2的光学吸收、拉曼谱和透射电镜研究

能量为200keV的Ag离子，以1×10¹⁶，5×10¹⁶，1×10¹⁷ cm^-2的剂量分别注入到非晶SiO₂玻璃，光学吸收谱显示：注入剂量为1×10¹⁶ cm^-2的样品的光吸收谱为洛伦兹曲线，与Mie理论模拟的曲线形状一致；注入剂量较大的5×10¹⁶，1×10¹⁷ cm^-2的谱线共振吸收增强，峰位红移并出现伴峰. 透射电镜观察分析表明，注入剂量不同的样品中形成的纳米颗粒的大小、形状、分布都不同，注入剂量较大的还会产生明显的表面溅射效应，这些因素都会影响共振吸收的峰形、峰位和峰强. 当注入剂量达到1×10¹⁷ cm^-2时，Ag纳米颗粒内部可能还形成了杂质团簇. 关键词： 离子注入 纳米颗粒 共振吸收 红移     

Ni熔体凝固过程中临界晶核和亚临界晶核的分子动力学模拟

本文用分子动力学模拟研究了Ni熔体以不同冷速凝固后微观结构的演变规律, 并通过理论计算确定出了Ni熔体凝固后获得理想非晶的临界条件. 模拟结果发现冷速小于10¹¹ K/s时, Ni 熔体凝固后形成晶态组织; 冷速在10¹¹ K/s到10^14.5 K/s之间时, Ni熔体凝固后形成由晶态结构与非晶态结构组成的混合组织. 冷速小于10¹⁰ K/s, Ni 熔体凝固后形成的晶态组织具有fcc结构; 冷速在10¹⁰ K/s到10^14.5 K/s之间时, Ni熔体凝固后组织中的晶态由fcc和hcp结构层状镶嵌排列构成. 通过分析模拟结果和计算结果, 确定出了Ni熔体凝固后形成理想非晶的临界冷速为10^14.5 K/s. 并发现Ni熔体中临界晶核(冷速等于10^14.5 K/s)和亚临界晶核(冷速大于10^14.5 K/s) 均由fcc和hcp组成层状偏聚结构, 这表明Ni熔体中生长的晶体、临界晶核和晶胚的结构是相同的. 关键词： 分子动力学模拟 晶体团簇 临界冷速 结构     

梯度掺杂与均匀掺杂GaN光电阴极的对比研究

为了提高负电子亲和势(NEA)GaN光电阴极的量子效率,利用金属有机化合物化学气相淀积(MOCVD)外延生长了梯度掺杂反射式GaN光电阴极,其掺杂浓度由体内到表面依次为1×10¹⁸ cm^-3,4×10¹⁷ cm^-3,2×10¹⁷ cm^-3和6×10¹⁶ cm^-3,每个掺杂浓度区域的厚度约为45 nm,总的厚度为180 nm.在超高真 关键词： NEA GaN光电阴极 梯度掺杂 量子效率 能带结构     

ZBLAN玻璃中Pr3+掺杂离子3P0和1D2能级的发光特性和寿命

对ZBLAN氟锆酸盐玻璃中Pr³⁺掺杂离子³P₀和¹D₂能级的寿命和发光特性进行了较详细的光谱学研究。首先测量了两种掺杂浓度(质量分数分别为1×10^-3,5×10^-3)的Pr³⁺:ZBLAN玻璃的吸收光谱,然后运用时间分辨激光光谱技术测量了³P₀和¹D₂能级在激光单光子共振激发下的荧光发射谱和能级寿命。将不同荧光发射谱带的强度和文献报道的Judd Ofelt理论计算辐射跃迁几率数值做了比较分析,证明了文献中理论计算结果的可靠性。由于浓度猝灭效应,在相同的激发条件下,掺杂浓度为1×10^-3样品的荧光发射强度明显大于5×10^-3样品的荧光发射强度。但是从我们的测量结果看,掺杂浓度对³P₀和¹D₂ 的能级寿命值无显著影响。掺杂浓度为1×10^-3时,Pr³⁺离子³P₀和¹D₂能级的寿命值分别为46,322μ_s。     

Mg5SnB2O10:Eu3+,Bi3+—一种用于发光二极管的红色荧光粉的制备及其发光性能的研究

采用高温固相法成功合成了单一相的Eu³⁺,Bi³⁺共掺的Mg₅SnB₂O₁₀红色荧光粉,并通过X射线衍射、漫反射光谱、光致发光光谱等手段对该体系的结构及其发光特性进行了测试和研究.激发光谱表明,该荧光粉在393 nm呈现Eu³⁺的⁷Fo—⁵L₆特征激发,可以与用于发光二极管的近紫外芯片很好地匹配.在393 nm激发下,其发射光谱在591,612,701 nm处呈现Eu³⁺的⁵Do—⁷F₁,⁵Do—⁷F₂,⁵D₀—⁷F₄的特征发射.并且当固定Eu³⁺的浓度时,随着Bi³⁺含量的增加,发现Bi³⁺,Eu³⁺在这一体系中存在能量传递现象,系列样品发光强度大幅度提高.通过研究系列样品在不同Bi³⁺,Eu³⁺掺杂浓度下的发光性能,得出最佳样品为Mg_4.89Eu_0.1Bi_0.01SnB₂O₁₀,其积分强度达到了商用Y₂O₂S:Eu³⁺的1.1倍.     

绿色荧光粉NaCaPO4：Tb3+的制备与发光特性

采用高温固相法合成了适用于UVLED芯片激发的NaCaPO₄:Tb³⁺绿色荧光粉并对其发光性质进行了研究。该荧光粉的发射峰位于418,440,492,545,586,622nm,分别对应Tb³⁺的⁵D₃→⁷F₅、⁵D₃→⁷F₄、⁵D₄→⁷F₆、⁵D₄→⁷F₅、⁵D₄→⁷F₄、⁵D₄→⁷F₃能级跃迁。其中位于492,545nm的发射峰最强,样品发射很好的绿光。主要激发峰位于380~400nm之间,属于4f→4f电子跃迁吸收,与UVLED芯片的发射相匹配。考察了Tb³⁺掺杂浓度和Li⁺,Na⁺和K⁺作为电荷补偿剂对样品发光性能的影响:Tb³⁺的最佳掺杂浓度为10%,以Li⁺的补偿效果最好。NaCaPO₄:Tb³⁺是一种适用于白光LED的绿色荧光材料。     

Tm3+,Yb3+共掺ZBLAN玻璃中的能量传递与上转换

ＺＢＬＡＮ∶Ｔｍ³⁺，Ｙｂ³⁺玻璃在９７０ｎｍ二极管激光照射下发射明亮丰富的蓝、红上转换荧光．¹Ｇ₄和³Ｆ₄能级的发光是由Ｙｂ³⁺向Ｔｍ³⁺的逐步能量传递而来．而¹Ｄ_２能级发光是进一步由Ｔｍ³⁺离子之间的交叉能量传递而来．分析了Ｔｍ³⁺离子间的交 关键词：     

μ-子催化核聚变中强脉冲激光对介原子μ3He的电离

数值求解了一维含时的Schr?dinger方程，研究了μ子催化核聚变反应中激光强度和波长对介原子μ³He电离的影响.发现当激光强度为10¹⁹—10²³W/cm²量级时，介原子μ³He有2.7%左右的电离率；当激光强度达到6.0×10²⁴W/cm²时，对介原子μ³He 有显著的电离，并且电离率随着激光的强度、波长而递增，进而会有效提高μ子的催化效率. 关键词： μ子 核聚变 激光 电离     

Atomic impact experiments with free helium-3 and helium-4 clusters

Free helium clusters with of the order of 10³ to 10⁷ atoms have been predicted to reach final temperatures of about 0.4 K in the case of⁴He, and of 0.15 K in the case of³He. In the first case, the clusters have to be expected to be superfluid, in the latter case to be normalfluid. Impact experiments with cesium atoms, which are calculated to be strongly repelled from inside liquid⁴He, and slightly from liquid³He, indicate cesium embedding into or onto⁴He clusters. Xenon atoms, calculated to be strongly bound to both quantum liquids, show incomplete momentum transfer to⁴He as well as to³He clusters at higher impact speeds.     

Quest for the 10He nucleus

The spectrum of ¹⁰He was studied by means of the ³H(⁸He, p)¹⁰He reaction at a laboratory energy of 25 MeV/A and small center-of-mass angles. Missing mass spectrum of ¹⁰He was derived from the obtained p-⁸He coincidence. A resolution of 0.7 MeV was achieved in this spectrum for the measured ¹⁰He energy. Most likely, a well isolated group of 10 events detected between 2 and 5 MeV and showing a maximum at about 3 MeV in the spectrum of the present work exhibits the ¹⁰He g.s. resonance.     

Laser photoionization detection of the rare isotope3He

Based on combination of the two-step collinear isotope-selective photoionization and time-of-flight separation of atoms in a fast modulated beam, a new technique has been developed for detecting the³He rare isotope with an isotopic selectivity of up to 10¹⁰. The technique helped to detect optically, for the first time,³He at a relative abundance of 4·10^–8.     

Correlation investigations of the low-energy 10He spectrum

The spectrum of low-lying states in the ¹⁰He nucleus is investigated for the two-neutron transfer reaction ³H(⁸He, p)¹⁰He. The secondary beam of ⁸He nuclei with the energy 21.5 MeV/nucleon and a cryogenic tritium target are used in the experiment. The ¹⁰He ground state is observed in the missing mass spectrum at the energy of 2.1 MeV (Γ ～ 2 MeV) above the decay threshold. Analysis of the angular correlations of the ¹⁰He decay products yields the spin and parity of two excited ¹⁰He states, J ^π = 1^? in the energy range from 4 to 6 MeV and J ^π = 2⁺ at energies above 6 MeV.     

Spectroscopy of excited states of 8He

The ¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of ⁸He. In addition to the known excited state of ⁸He at E_x = 3.6 MeV, with J^π = 2⁺, three additional states were found at excitation energies of 4.54(25) MeV, 6.03(10) MeV and 7.16(4) MeV.     

Defect-related light emission from processed He-implanted silicon

Photoluminescence (PL) from He⁺-implanted Si (Si:He, He⁺ dose—2×10¹⁶ cm⁻², at 150 keV) is related to its microstructure; it has been tuned by processing at 720-1400 K under hydrostatic Ar pressure (HP, up to 1.2 GPa). Processing of Si:He at 720 K for 10 h results in an appearance of the D2 and D3 dislocation-related PL lines, these last of the highest intensity. Only the D1 dislocation-related line of intensity increasing with HP has been detected after processing at 920-1070 K. The D1 (of the highest intensity), D2 and D3 PL lines are observed after the treatment at 1270 K. No dislocation-related PL has been detected for Si:He processed at 1400 K. The treatment of Si:He at 720-1270 K under HP makes it possible to produce Si:He of specific microstructure resulting in strong PL at 0.81, 0.87 or 0.94 eV.     

Properties of very n -rich He isotopes

Low-energy spectra of the ^{8, 10}He nuclei were investigated in the (t, p) -type reactions at small centre-of-mass angles using ～ 25 AMeV beams of ⁶He and ⁸He nuclei. The 0⁺ ground state (g.s.) of ⁸He and excited states, 2⁺ at 3.6-3.9MeV and (1⁺) at 5.3-5.5MeV, were populated with cross-sections of 200, 100-250, and 90-125μb/sr, respectively. To account for a near-threshold anomaly observed in the ⁸He spectrum the population of a 1^- continuum (soft dipole excitation) was considered. The lowest-energy group of events in the ¹⁰He spectrum was observed at ～ 3 MeV with a cross-section of ～ 140 μb/sr. This result is consistent with the previously reported observation of ¹⁰He providing a new g.s. position for ¹⁰He at about 3MeV.     

Field evaporation experiments with a magnetic sector atom-probe FIM

A magnetic sector atom-probe FIM has been successfully operated for dc field evaporation of tip materials such as Rh, W, Ir, Mo and Ti. A limited number of evaporated metal ions were clearly identified forming a line spectrum. Field evaporation of Rh in the presence of ³He and ⁴He gases showed that the formation of the helium compound (RhHe)²⁺ is quite sensitive to He gas pressure; no helium compound were observed below 5 × 10^?7 Torr and all ions detected as helium compound above 5 × 10^?5 Torr at 78 K.     

High-spin states in123Te

The¹⁰Be(¹²C,¹⁴O)⁸He-reaction has been used to study the levels of⁸He. In addition to the known excited state of⁸He at E _x =3.6MeV, withJ ^π=2⁺, three additional states were found at excitation energies of 4.54(25)MeV, 6.03(10)MeV and 7.16(4)MeV.     

Kinetics of the sorption of <Superscript>3</Superscript>He by C<Subscript>60</Subscript> fullerite. The quantum diffusion of <Superscript>3</Superscript>He and <Superscript>4</Superscript>He in fullerite

The kinetics of the sorption and subsequent desorption of gaseous ³He in a C₆₀ fullerite powder has been studied in the temperature range of 2–292 K. The temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite have been plotted using the measured characteristic times of filling of octahedral and tetrahedral interstices, as well as previous data. These temperature dependences of the diffusion coefficients of ³He and ⁴He impurities in fullerite are qualitatively similar. A decrease in the temperature from 292 to 79 K is accompanied by a decrease in the diffusion coefficients, which corresponds to the dominance of the thermally activated diffusion of helium isotopes in fullerite. A further decrease in the temperature to 8–10 K leads to an increase in the diffusion coefficients by more than an order of magnitude. The diffusion coefficients of ³He and ⁴He are independent of the temperature below 8 K, indicating the tunnel character of the diffusion of helium in C₆₀ fullerite. The isotope effect is manifested in the difference between the absolute values of the diffusion coefficients of ³He and ⁴He atoms at the same temperatures.