Laser spectroscopy of CaF2:Eu:Sm thin films grown by pulsed laser deposition

Thin films of CaF₂ co-doped with low concentrations of Eu and Sm ions were grown by pulsed laser deposition (PLD) using a KrF (λ=248 nm) as the ablation source. To the best of our knowledge, the work presented here is the first report of rare-earth-doped CaF₂ films grown by PLD with this source. Combined laser excitation-emission spectroscopy was used to map out electronic transitions of Eu³⁺ with ⁷F₀→⁵D₁ excitation and the ⁵D₀→⁷F₁ emission. At the low concentrations used here the crystal field center of cubic symmetry is dominant in the films that are same for laser targets. However, charge compensated centers are present in the bulk crystal precursor. The removal of the charge compensated centers in the films and the target is likely caused by the target preparation where high pressure and temperature were applied.     

一种激光诱导灼蚀制备纳米硅的新方法

采用高强度激光灼蚀沉积(PLD)的方式,在流动N2做为保护气体的情况下,成功制备出Si纳米结构,并利用扫描电镜(SEM)、光致发光(PL)进行表征。结果表明,该方法制备的纳米Si尺寸在几nm到几10nm之间,同时它具有较强的发光,发光强度比同等测量条件下的多孔Si(PS)样品高10倍以上,而且方法比较简单。     

高分辨率时间数字转换电路的PLD实现

高分辨率时间数字转换系统(TDC)采用环形延时门单元(RGDS)高分辨率系统,在可编程器件(PLD)上实现,解决了延时门的综合、延时时间的离散性等问题.由于设计、实现和集成电路工艺无关,所以可以方便地移植到其他系统和PLD芯片中.本设计在Altera公司的CPLD芯片上的仿真测试表明,时间分辨率最高可达3.5ns.本实验通过了时序仿真和硬件测试.     

Studies on CdTe films deposited by pulsed laser deposition technique

Polycrystalline cadmium telluride films were successfully deposited on glass substrates by ablating a CdTe target by pulsed Nd–YAG laser. Microstructural studies indicated an increase in the average crystallite size from 15 nm to ∼50 nm with the increase in substrate temperature during deposition. The films deposited here were slightly tellurium rich. X-ray diffraction pattern indicated that the films deposited at 300 K had wurtzite structure while those deposited above 573 K were predominantly of zinc blende structure. Residual strain in the films deposited at 300 K was quite low as compared to those deposited at higher temperatures. PL spectra of all the CdTe films were dominated by a strong peak at ∼921 nm (∼1.347 eV) followed by a low intensity peak at ∼863 nm (∼1.438 eV). Characteristics Raman peaks for CdTe indicated a peak at ∼120 cm⁻¹ followed by peaks located at ∼140 cm⁻¹ and 160 cm⁻¹.     

High temperature x‐ray diffraction studies of zirconia thin films prepared by reactive pulsed laser deposition

Zirconium oxide thin films have been deposited on Si (100) substrates at room temperature at an optimized oxygen partial pressure of 3x10^‐2 mbar by reactive pulsed laser deposition. High temperature x‐ray diffraction (HTXRD) studies of the film in the temperature range room temperature‐1473 K revealed that the film contained only monoclinic phase at temperatures ≤ 673 K and both monoclinic and tetragonal phases were present at temperatures ≥ 773 K. The tetragonal phase content was significantly dominating over monoclinic phase with the increase of temperature. The phase evolution was accompanied with the increase in the crystallite size from 20 to 40 nm for the tetragonal phase. The mean thermal expansion coefficients for the tetragonal phase have been found to be 10.58x10^‐6 K^‐1 and 20.92x10^‐6K^‐1 along a and c‐axes, respectively. The mean volume thermal expansion coefficient is 42.34x10^‐6 K^‐1 in the temperature range 773‐1473 K. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

可编程逻辑器件的教学实践与思考

二年多来进行PLD教学的实践,提出了PLD教学的三个层次,以与大家探讨。     

PLD法生长Al2O3基ZnO薄膜的特性

在不同衬底温度下,用脉冲激光沉积法(PLD),在Al2O3(0001)平面上生长了ZnO薄膜。研究了衬底温度对其结晶质量、电学性质以及发光性质的影响。结果显示:XRD在2θ为34°处出现了唯一的ZnO(0002)衍射峰;ZnO薄膜的电阻率随衬底温度的升高而增大;在衬底温度为500℃时,出现了位于410nm附近的特殊的光致发光(PL)峰。     

NaF薄膜的脉冲激光沉积法制备与结构研究

 采用脉冲激光沉积(PLD)方法在Si(100)衬底上制备了NaF薄膜。在激光重复频率2 Hz,能量密度3 J/cm²,本底真空度5×10^-5 Pa的条件下,研究衬底温度对薄膜沉积速率及结构的影响。台阶仪分析表明：薄膜的沉积速率随衬底温度增加呈指数函数增加,算出NaF薄膜的反应激活能为48.67 kJ/mol。原子力显微镜分析表明：薄膜致密而光滑,均方根粗糙度为0.553 nm。扫描电镜截面微观形貌分析表明：薄膜呈现柱状结构。X射线衍射分析表明：NaF薄膜为面心立方晶体结构,并具有显著的择优取向;当衬底温度约为400 ℃时,平均晶粒尺寸最大(129.6 nm),晶格微应变最小(0.225%)。     

在钛酸锶衬底上外延生长ZnO薄膜及其性能研究

用脉冲激光淀积法(PLD)在(111)面SrTiO3衬底上外延生长ZnO单晶薄膜.样品分别在衬底温度为350℃、500℃、600℃下外延生长.X射线衍射(XRD)的结果表明,所得的ZnO单晶薄膜结晶性能好,只出现(002)和(004)两个衍射峰,(002)峰的半高宽度(FWHM)为0.23°.在荧光光谱中我们只观察到来源于带边激子跃迁的强UV发射,并且随着生长温度的升高,紫外峰的强度逐渐增强.样品的SEM图像表明所得ZnO薄膜表面平整,晶粒均匀.衬底温度为600℃时,所得到的ZnO薄膜结构完整,晶粒尺寸最大,均匀;而且紫外发射最强.     

ZnS薄膜生长温度对ZnS/PS体系结构和发光的影响

用电化学阳极氧化法制备了一定孔隙率的多孔硅(PS,Porous Silicon)样品,然后以PS为衬底用脉冲激光沉积(PLD)的方法在100℃、200℃和300℃下生长ZnS薄膜.X射线衍射(XRD)结果表明,样品都在28.5°附近有一个较强的衍射峰,对应于β-ZnS(111)晶向,说明薄膜沿该方向择优取向生长,但由于衬底PS粗糙的表面结构,衍射峰的半高全宽(FWHM)较大.随着ZnS薄膜生长温度的升高,薄膜的衍射峰强度逐渐增强.扫描电子显微镜(SEM)像显示,随着薄膜生长温度的升高,构成薄膜的纳米晶粒生长变大.室温下的光致发光(PL)谱表明,随着薄膜生长温度的升高,ZnS的发光强度增强而PS的发光强度减弱,把ZnS的蓝绿光与PS的红光叠加,在可见光区450～700 nm形成了一个较宽的光致发光谱带,呈现较强的白光发射.