Ag-BaO薄膜内场助光电发射增强现象研究

通过在Ag-BaO薄膜表面真空沉积10nm厚的银电极,成功制备了内场助结构Ag-BaO光电阴极.测试结果显示,Ag-BaO薄膜光电发射电流随内场助偏压的增大而上升.理论分析表明,Ag-BaO薄膜内场助光电发射增强现象产生的机理在于内场助作用下Ag微粒和BaO介质间等效界面位垒的减小及薄膜表面真空能级的相对下降. 关键词： 内场助光电发射 能带弯曲 金属超微粒子 Ag-BaO薄膜     

不同能级加速过滤电弧沉积四面体非晶碳膜的结构和性能

采用过滤阴极真空电弧技术，通过施加0—2000 V衬底负偏压使沉积离子获得不同能级的入射能量，在单晶硅上制备了四面体非晶碳薄膜.拉曼光谱分析表明，薄膜的结构为非晶sp³骨架中镶嵌着平面关联长度小于1 nm的sp²团簇.原子力显微镜研究表明：在低能级、富sp³能量窗口和次高能级，薄膜中sp³的含量越多，其表面就越光滑，应用sp³浅注入生长机制能够圆满地解释薄膜表面形态与离子入射能量之间的关系；但在高 关键词： 四面体非晶碳 过滤阴极真空电弧 能级     

超薄类金刚石膜生长和结构特性的分子动力学模拟

利用分子动力学模拟方法研究了2—3nm厚的类金刚石(DLC)薄膜在金刚石基体(100)表面上的生长过程. 分析了用来表征沉积后无定型碳膜质量的重要结构特性，如sp³杂化比例、薄膜密度、径向分布函数等，计算结果和现有的实验结果基本一致. 不同入射原子能量对结构特性进而对薄膜性能有重要影响，入射原子能量在20—60eV时，薄膜可以获得最优性能. 载能原子入射是生长均匀、连续、致密固体薄膜的前提，稳定的中间区域对于保证薄膜优良的力学性质是必需的. 关键词： DLC膜 分子动力学模拟 3杂化比例')" href="#">sp³杂化比例     

大面积染料敏化太阳电池的串联阻抗特性研究

在电子扩散微分方程的基础上,研究了染料敏化太阳电池光生电流和光生电压随光照强度不同的变化关系.提出敏化太阳电池串联阻抗功率损耗模型,理论模拟了大面积电池（有效面积>1 cm²）光电转换效率随多孔薄膜有效面积宽度变化的曲线、透明导电基底膜与银栅极的比接触电阻以及在不同入射光强下银栅极体电阻对大面积染料敏化太阳电池光伏性能的影响.结果表明透明导电基底膜的方块电阻和银栅极体电阻对大面积染料敏化太阳电池的性能有很大影响,而这种影响随光强的减弱逐渐减小. 关键词： 染料敏化 太阳电池 串联阻抗 光电转换效率     

细菌视紫红质的自衍射效率与最佳入射角研究

研究了弱光强下细菌视紫红质膜(bR膜)的自衍射特性.给出了弱光强下相干光在bR膜中产生的振幅光栅光强分布模型，并用ysinαx近似表示透射光强分布，结果与实验吻合.给出了不同透射光强y与指数α的对应关系.结果表明，在bR膜及入射光波波长给定的情况下，入射光强越小，对应的α值越大，当入射光强为0.072/T(mW/cm2)时，α等于1.计算出不同入射光强和入射角下的自衍射效率.结果发现，对应于最大衍射效率的最佳入射角为2°.     

SrBi2Ta2O9铁电薄膜微结构及其抗疲劳等铁电特性的研究

在低温Pt/Ti/SiO₂/Si衬底上用脉冲准分子激光沉积技术结合氧气氛下700℃退火获得高质量的SBT薄膜，其择优取向为（008）和（115）．薄膜厚度约为200nm．铁电性能测试显示较饱和的、方形的电滞回线，其剩余极化和矫顽电场分别为10μC/cm²和57kV/cm，在10¹⁰次开关极化后没有显示任何疲劳，在5V直流电压下的漏电流密度约为4×10^-8A/cm²，直流击穿电场约为250kV/cm 关键词：     

Ag-BaO纳米薄膜红、蓝紫光波段光致荧光现象研究(Ⅰ)

金属纳米粒子/介质复合薄膜因其优良的光电特性和超快响应而成为应用背景很强的光电功能薄膜-采用真空沉积的方法制得了Ag-BaO纳米薄膜,测试到其在室温条件下的红光和蓝紫光波段的光致荧光光谱,认为Ag-BaO纳米薄膜的荧光发射主要来自于Ag纳米粒子的贡献-与该种材料的紫外-可见光吸收谱相比较,分析了Ag-BaO纳米薄膜材料不同可见光波段的荧光产生机理- 关键词：     

Yb3+：Pr3+：ZBLAN光纤中4f5d上转换激发的理论研究

利用粒子数速率方程和相关的辐射跃迁理论,计算了Yb³⁺:Pr³⁺:ZBLAN光纤中Pr³⁺离子4f5d能级两步上转换激发的动力学过程.得到不同Pr³⁺掺杂浓度下,激发光的光谱强度和粒子数密度的纵向分布和有效光纤长度随激发光的光谱强度的变化关系.另外,还得到了4f5d荧光强度与入射光强、光纤长度和Pr³⁺掺杂浓度的关系,给出了激发效率与激发光的光谱强度和Pr³⁺掺杂浓度的关系.     

斜入射离子束辅助沉积对类金刚石薄膜结构影响的分子动力学模拟

采用分子动力学（MD）模拟方法,从原子尺度上研究了离子束辅助沉积（IBAD）类金刚石（DLC）薄膜过程中离子束入射角对薄膜结构的影响.重点讨论了不同的离子束入射角所对应的薄膜表面模型,平均密度和sp³键含量.结果表明,离子束斜入射加强了入射原子的水平动能,从而加强了原子水平迁移;Ar离子斜入射时C原子迁移率均比垂直入射大,薄膜密度和sp³键含量都比垂直入射小.不同的离子束入射角随着到达比和入射能的变化,对薄膜结构的影响不同.离子束斜入射时可以得到不同结构的膜. 关键词： 类金刚石薄膜 入射角 离子束辅助沉积 分子动力学模拟     

多壁碳纳米管光限幅特性的研究

用化学气相沉积法制备了多壁碳纳米管,并将其溶解在甲苯溶液中.用波长为1064nm的皮秒脉冲激光测量该样品的透过率,发现了非常明显的光限幅特性.当入射光强较小时,透射光强度随入射光强度的增大而增大,输出与输入为线性关系;随着入射光强的增大,透射光强增长的速度明显变慢,并逐渐趋于饱和.当入射光强度较小时,样品的透过率接近100%;而当入射光强为8GW/cm²时,非线性透过率达到30%.根据三光子吸收理论计算,理论拟合与实验结果非常符合,说明多壁碳纳米管的三光子吸收产生了光限幅效应.实验测 关键词： 多壁碳纳米管 光限幅 三光子吸收     

Laser ablation loading of a radiofrequency ion trap

The production of ions via laser ablation for the loading of radiofrequency (RF) ion traps is investigated using a nitrogen laser with a maximum pulse energy of 0.17?mJ and a peak intensity of about 250?MW/cm². A?time-of-flight mass spectrometer is used to measure the ion yield and the distribution of the charge states. Singly charged ions of elements that are presently considered for the use in optical clocks or quantum logic applications could be produced from metallic samples at a rate of the order of magnitude 10⁵ ions per pulse. A linear Paul trap was loaded with Th⁺ ions produced by laser ablation. An overall ion production and trapping efficiency of 10^?7 to 10^?6 was attained. For ions injected individually, a dependence of the capture probability on the phase of the RF field has been predicted. In the experiment this was not observed, presumably because of collective effects within the ablation plume.     

Electron radiation effects on InAs/GaAs quantum dot lasers

The InAs/GaAs quantum dot laser diodes and corresponding quantum dot samples are irradiated by 1 MeV electron. The laser performance and quantum dot photoluminescence intensity at room temperature are enhanced over a fluence range of 4 × 10¹³ cm^?2. The radiation-induced defects increase the efficiency of carrier transfer to the quantum dots, which results in the improvement of photoluminescence performance under low level displacement damage. The contact resistant of quantum dot lasers decreases because the ohmic contact is also improved by electron irradiation.     

High quantum yield of photochemical reactions of protoporphyrin-IX induced by powerful ultrashort laser pulses

The action of powerful pulsed picosecond radiation from a Nd: YAG laser (λ=530 nm, pulse energy: 0.01 J, intensity: 2GW/cm²) and an argon laser (λ=515 nm, power: 50 mW) on protoporphyrin-IX dimethylether in three solvents (trichlormethane, carbon tetrachloride, dioxane) has been studied. Under continuous irradiation the quantum yield and resulting products do not differ materially from the ones produced under mercury lamp irradiation. When irradiation is performed by powerful laser pulses of picosecond duration the quantum yield of photodecomposition of protoporphyrin-IX dimethylether inereases substantially: by 10 in dioxane, by 4 in carbon tetrachloride and by 100 in trichlormethane. It is assumed that a quite different mechanism of multistep excitation is responsible for photodecomposition under powerful picosecond pulses.     

Effect of Host Medium on the Fluorescence Emission Intensity of Rhodamine B in Liquid and Solid Phase

In this work, we study the effect of concentration, host medium, PH and phase states on the fluorescence emission from the laser dye Rhodamine B pumped by UV laser as exited source. The polymethylmethacrylate PMMA is used as a host medium in case of solid phase samples while, ethanol and Tetrahydrofuran (THF) are used in case of a liquid one. Laser Induced Fluorescence (LIF) technique was used to study the fluorescence properties of both cases of liquid and thin film solid-state samples. In addition, the Dual Thermal Lens (DTL) technique was used to study the quantum yield of these samples. The concentrations of Rhodamine B in ethanol as solvent between 2 × 10⁻² M and 5 × 10⁻⁶ M were studied. The maximum fluorescence emission is observed at concentration of Rhodamine B C = 3 × 10⁻⁴ M. Comparison studies were investigated for different host medium such as ethanol, THF, PMMA in liquid phase state and PMMA in solid phase state. The measurements revealed that, the behavior of both phases state was analogous. Rhodamine B/PMMA thin film sample by ratio of 4:1 and thickness 0.12 mm was found to have the best photostability sample with a quantum yield about ≈0.82.     

生物大分子杂化处理的CdSe/ZnS核/壳量子点多层膜的超快三阶非线性研究

利用静电自组装技术，以生物大分子材料壳聚糖杂化处理具有稳定结构的CdSe/ZnS核/壳量子点，形成复合多层薄膜. 与薄膜的吸收谱线比较，在375nm飞秒激光激发下测量的量子点的光致发光谱存在Stokes位移. 采用Z扫描技术，利用790nm飞秒激光研究了其三阶非线性吸收和折射特性，发现饱和吸收信号来自CdSe/ZnS量子点，而自聚焦的折射信号则部分来自壳聚糖. 测出多层膜的三阶非线性系数分别是β＝6.5×10^-6cm/W，n₂＝1.5×10^-10cm²/W. 关键词： CdSe/ZnS量子点 非线性性能 光致发光谱     

Nonlinear laser UV photochemistry of maleic acid in aqueous solution

This work deals with photochemical transformations of maleic acid in an aqueous solution under powerful picosecond fourth-harmonic pulses of a YAG-Nd³⁺ laser with λ=266 nm and nanosecond pulses of an excimer KrF laser with λ-248 nm. It has been found that by changing the irradiation intensity only it is possible to produce selectively different products with a high quantum yield resulting from the following reactions of the ?C=C? bond of the maleic acid molecule: 1) cis-trans isomerization at radiation intensities up to 10⁸ W/cm² as a result of linear photochemistry; 2) radical dimerization of the maleic acid withJ=10⁸÷10⁹ W/cm² and water addition to the ?C=C? bond of the maleic acid withJ?10⁹ W/cm² as a result of nonlinear photochemistry.     

Effect of prepulses with various durations on the neutron yield in laser picosecond plasma

Experimental results on the effect of picosecond and nanosecond prepulses on the neutron yield in laser picosecond plasma on the surface of solid (CD₂)_n targets at a laser intensity of 10¹⁸ W/cm² are presented. It is demonstrated that the picosecond (nanosecond) prepulse decreases the neutron yield at a laser prepulse intensity of higher than 10¹³ (10¹²) W/cm². The estimates indicate three possible mechanisms for the realization of the observed effect: stimulated Mandelstam-Brillouin scattering of the main pulse by the preplasma, channels of the generation of fast ions, and their possible deceleration in the preplasma. The results of calculations are compared with the experimental data.     

Photoionization mass-spectrometry of benzene and benzaldehyde molecules with an excimer KrF laser

A laser photoionization time-of-flight mass-spectrometer has been developed and used to investigate the photoionization and photofragmentation of benzene and benzaldehyde molecules by an excimer KrF laser radiation at the wavelength of 249 nm in the intensity range from 5·10⁴ to 5·10⁹ W/cm². It has been found that at low laser intensity ions formed by two-step photoionization are most abundant in mass spectra. By increasing laser intensity an extensive fragmentation of molecules, up to C⁺ ions, was observed. The maximum ionization yield of benzaldehyde comes to 0.1% of the number of molecules in the photoionization volume and, according to calculations, to 10% for benzene molecules, when the radiation intensity is 5·10⁹ W/cm².     

Efficient two-photon absorption of CdSe-CdS/ZnS core-multishell quantum dots under the excitation of near-infrared femtosecond pulsed laser

We report that two-photon absorption (TPA) properties of semiconductor CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene under excitation of femtosecond laser at 800 nm. The results show efficient TPA process and large TPA cross section of three types of size QDs, which is 1900, 5710, and 16060 GM (1 GM = 10⁻⁵⁰ cm⁴ s photon⁻¹), respectively. TPA cross section dramatically increases with increased core size, showing a strong size-dependence effect. Furthermore, two-photon excitation (TPE) fluorescence intensity not only depends on TPA capacity, but also relies on improved quantum yield resulting from passivation of QD surface by different coated monolayers (MLs). These facts in combination with the narrow fluorescence bandwidth make these QDs as promising probes for multicolor two-photon microscopy.     

Linearly polarized photoluminescence from an ensemble of wurtzite GaN/AlN quantum dots

Microphotoluminescence from GaN/AlN quantum dots grown by molecular beam epitaxy on sapphire substrates along the (0001) axis has been studied. To produce quantum dots of different average sizes and densities, the nominal amount of deposited GaN has been varied from 1 to 4 ML. The density of the quantum dots was about 10¹¹ cm⁻², which corresponded to about 10³ quantum dots excited in the experiments. The photo-luminescence from the quantum dots was linearly polarized and the maximum polarization degree (15%) has been observed for the sample with the lowest amount of deposited GaN. The photoluminescence intensity from this sample under continuous laser excitation decreased by more than two orders of magnitude for about 30 min and then stabilized. The photoluminescence intensity from other samples under continuous excitation remained constant. We suggest that a rather high polarization degree is caused by anisotropy in the strain and shape of the quantum dots formed near the dislocations, which also act as the centers of nonradiative recombination.