CW CO_2激光退火在硅中产生的氧沾污

利用相衬显微术、电子吸收像、IR光谱、AES和ESCA谱研究了硅片经CW CO_2激光退火后的一些特征,其中着重分析氧的深度沾污问题。电子吸收像表明:我们的CW CO_2激光退火条件下,其效果并不很均匀。实验还证明:空气中的CW CO_2激光退火可以减少样品表面的碳沾污,但产生氧沾污。氧的沾污分两部分:表面是SiO_x,其下是自由氧原子,厚度不大于250。     

仿生异质结全太阳光谱催化CO2还原特性研究

为了突破光热催化CO₂还原中太阳能吸收、光热转化以及载流子传输受限的瓶颈，本文受蝴蝶翅膀的启发，将原子薄纳米片Bi₂MoO₆垂直生长在柚子皮衍生碳(CPP)表面形成具有波导效应的脊阵列，利用多重散射强化太阳光吸收，实现光催化与光捕获中心的有机集成；受植物对光选择性吸收的启发，利用分形结构诱导太阳光的多级吸收，实现全太阳光谱的梯级利用。通过UV-Vis DRS、XPS、瞬态光电流以及DFT研究表明，CPP@Bi₂MoO₆的脊阵列和分形结构导致禁带宽度降低至2.43 e V并且催化表面温度迅速升高至117.2?C,M-O-C电子桥实现电子跨界面传输并形成“电子–热能–CO₂”富集中心，光热效应导致富集在CPP表面的电子向CO₂吸附位点迁移，使得CO₂被大量电子活化并沿CO₂→CO₂*→CO₂-→COOH*→CO*→CO的反应机理转化。     

正弦交流电压驱动低气压CO2放电特性的对比:DBD结构与裸电极结构

火星大气富含CO₂(～95%),对其原位利用具有重要的科学和经济价值.高压放电转化CO₂具有绿色环保、可控程度高、使用寿命长等优势,在火星CO₂资源原位转化利用方面具有应用潜力.本文模拟火星低气压条件下CO₂氛围,针对kHz交流电压驱动两种典型电极结构(有/无阻挡介质)的放电特性开展对比实验研究,并辅以数值仿真分析两种电极结构下CO₂放电产物及其转化途径.结果表明,引入阻挡介质后,由于介质表面累积电荷和空间电荷畸变电场导致放电从半周期单次放电转变为多脉冲放电,不同放电脉冲对应的放电通道随机产生.主要放电产物中,CO依赖阴极位降区边界处电子与CO₂附着分解反应产生,O₂大部分产生于瞬时阳极表面或瞬时阳极侧介质表面电子与CO₂~+复合分解反应.进一步发现,介质引入不改变二者产生位置和主导反应路径,但会降低阴极位降区边界处电子密度和电子温度,使CO产量有所减少;并降低放电功率,使到达瞬时阳极表面和瞬时阳极侧介质表面的C...     

VO2薄膜表面氧缺陷的修复:F4TCNQ分子吸附反应

VO₂表面氧缺陷的存在对VO₂材料具有显著的电子掺杂效应, 极大地影响材料的本征电子结构和相变性质. 通过2, 3, 5, 6-四氟-7, 7', 8, 8'-四氰二甲基对苯醌(F₄TCNQ)分子表面吸附反应, 可以有效消除表面氧缺陷及其电子掺杂效应. 利用同步辐射光电子能谱和X射线吸收谱原位研究了修复过程中电子结构的变化以及界面的化学反应, 发现这种方式使得VO₂薄膜样品氩刻后得到的V³⁺失去电子成功地被氧化成原先的V⁴⁺, 同时F₄TCNQ分子吸附引起电子由衬底向分子层转移, 界面形成带负电荷的分子离子物种. 受电化学性质的制约, F₄TCNQ分子吸附反应修复氧缺陷较氧气氛退火更安全有效, 不会引起表面过度氧化形成V₂O₅.     

I掺杂金红石TiO$lt;sub$gt;2$lt;/sub$gt;(110)面的第一性原理研究

利用基于密度泛函理论的第一性原理研究了I掺杂金红石TiO₂（110）表面的形成能和电子结构,分析了不同掺杂位置的结构对TiO₂光催化性能的影响. 计算表明,氧化环境下I最容易替代掺杂表面五配位的Ti,而还原环境下最容易替代掺杂表面的桥位氧. I替位Ti或I替位O都能降低禁带宽度,可能使TiO₂吸收带出现红移现象或产生在可见光区的吸收,其中I替位桥位氧的禁带宽度最小. 吸收光谱表明,I掺杂不仅能提高TiO₂可见光响应,同时可增加紫外光的吸收能量,提高其可见光及紫外光下的光催化性能. 关键词： 第一性原理 I掺杂 2(110)')" href="#">金红石相TiO₂(110) 光催化     

紫外脉冲激光退火发次对KDP晶体抗损伤性能的影响

在R-on-1的辐照模式下, 利用355 nm的紫外脉冲激光以低于KH₂PO₄ (KDP)晶体零概率损伤阈值的通量对其进行不同发次的全域扫描, 目的是为了研究KDP晶体在接受不同发次的紫外激光辐照后其抗损伤能力的变化规律及机制. 辐照后的1-on-1损伤测试表明, 适当的紫外激光退火可以有效地提升KDP晶体的抗损伤能力, 提升的幅度与其接受激光扫描的次数有关. 通过荧光和紫外吸收检测深入探讨了晶体内缺陷对激光退火的影响, 结果表明: 紫外脉冲激光辐照后KDP 晶体内的氧空位电子缺陷的存在与否是导致其抗损伤能力变化的主要原因; 通过拉曼和红外光谱的测量表明, 辐照后KDP 晶体内的PO₄, P–OH和P＝O基团的极化变形也导致了其抗损伤能力的改变. 关键词： 激光退火 荧光 拉曼 红外     

黄绿色菱锌矿玉的谱学特征及颜色成因初探

菱锌矿颜色丰富,有黄色、蓝色、粉色、绿色等,矿物学特征及谱学特征的研究较少,对其不同颜色的成因认识亦不明确。选取黄绿色菱锌矿玉,利用X射线粉晶衍射仪、电子探针、激光剥蚀电感耦合等离子体质谱仪、傅里叶红外变换光谱仪、拉曼光谱仪、紫外-可见分光光度计、电子顺磁共振仪等分析显示,样品为纯净的菱锌矿,主要成分为ZnO,其平均含量为61.3%,次要成分有CaO,FeO,MnO,CdO及PbO。样品中含有微量过渡金属元素Fe和Mn,平均含量分别为7 363.5×10-6和3 558×10-6。样品在740,883和1 490 cm-1处出现菱锌矿的特征吸收带,740 cm-1归属于[CO₃]2-的面内弯曲振动单峰,883 cm-1属于[CO₃]2-的面外弯曲振动峰,1 490 cm-1处的强吸收谱带为[CO₃]2-反对称伸缩振动所致。拉曼谱有300,728和1 091 cm-1等方解石族特征峰,300 cm-1归属于ZnO对称伸缩振动,728 cm-1归属于[CO₃]2-面内弯曲振动,1 091 cm-1归属于[CO₃]2-对称伸缩振动。综合分析认为,Fe3+的6A₁→4E(D)跃迁、6A₁→4T₂(D)跃迁、Mn2+的d电子跃迁产生的紫外-可见光谱377,395和417 nm附近的吸收带是样品产生黄绿色的原因。EPR谱也显示出g=2.0左右的Mn2+的特征六重超精细共振谱线和g=1.98左右的Fe3+的特征谱线。结合样品成分和吸收光谱等特征,可以认为菱锌矿玉样品的黄绿色是由Fe3+和Mn2+的d—d轨道电子跃迁共同导致。     

管道中CaO颗粒吸收CO2的格子Boltzmann方法模拟

采用格子Boltzmann方法对多孔CaO颗粒与CO₂之间的气固反应过程进行模拟.主要研究在二维矩形截面管道中雷诺数(Re)和孔隙率对单个CaO颗粒吸收CO₂效率的影响.结果表明:增大Re会相应提高CaO颗粒吸收CO₂气体的效率.同时对于同一Re,CaO颗粒吸收CO₂气体的效率随其孔隙率呈非线性变化,这是由于不同孔隙率颗粒固体量和渗透率存在差别因而影响化学反应的速率.     

Pu(100)表面吸附CO2的密度泛函研究

采用广义梯度密度泛函理论的改进Perdew-Burke-Ernzerh方法结合周期性层晶模型,研究了CO₂分子在Pu（100）面上的吸附和解离.吸附能和几何构型的计算表明,CO₂以穴位C4O4构型吸附最为有利,吸附能为1.48 eV.布居分析和态密度分析表明,CO₂与Pu表面相互作用的本质主要是CO₂分子的杂化轨道2π_μ与Pu5f,Pu6d,Pu7s轨道通过强电子转移和弱重叠杂化的方式相互作用而生成了新的化学键.计算的CO₂→CO+O解离能垒为0.66 eV,解离吸附能为2.65 eV, 表明在一定热激活条件下CO₂分子倾向于发生解离性吸附.O₂,H₂,CO和CO₂在Pu （100）面吸附的比较分析表明,较低温度下的吸附强度顺序依次为O₂,CO,CO₂,H₂;较高温度下的吸附强度顺序依次为O₂,CO₂,CO,H₂. 关键词： 密度泛函理论 Pu （100） 2')" href="#">CO₂ 吸附和解离     

WO3表面的氧缺陷

用不同能量的Ar⁺和H⁺轰击WO₃表面,观察到W_4f峰的位移和加宽。通过谱分解处理得到相应于W_4f电子的W⁶⁺,W⁴⁺和W⁰3个不同的双峰。用表面产生氧缺陷的机理解释了还原过程。UPS谱显示出氧缺陷的存在增加了靠近费密能级处的态密度。H₂O的吸附结果说明WO₃表面的活性与W^{5+< 关键词：}     

Characterization of surface defects formation in strontium titanate(100)

The electronic properties of SrTiO₃(100) surfaces after various treatments have been studied by electron energy loss spectroscopy and Auger electron spectroscopy. A stoichiometric surface without contamination can be obtained by annealing at 910 K under oxygen atmosphere of 5 × 10⁻⁵ Pa. The surface heated under ultrahigh vacuum (UHV) at 910 K exhibits a new surface state in the band gap region, which comes from oxygen vacancies at the top Ti-O₂ layer. This state is also produced by electron irradiation or Ar-ion bombardment.     

CO2激光局域辐照对熔石英损伤特性的影响

研究了CO₂激光局域辐照对熔石英损伤特性的影响, 发现当辐照中心温度较低时(1139 K), 辐照对损伤阈值没有明显影响, 但辐照中心温度较高时(1638 K), 辐照对损伤阈值有明显的影响, 损伤阈值随距离辐照中心间距的增大而减小, 在残余应力产生光程差最大处附近, 损伤阈值降到最小, 随着与辐照中心间距的进一步增加, 损伤阈值略有上升. 对导致此现象的原因做了分析. 由于残余应力的存在, 在辐照中心发生再损伤产生的裂纹后, 裂纹先沿径向扩展, 在残余应力产生光程差最大处附近, 裂纹转而向切向扩展, 这可能与径向和环向张应力随半径的变化有关. 在采用热处理炉退火消除残余应力时, 必须注意元件的洁净处理, 否则退火会出现析晶现象, 对损伤阈值和透射率造成不良影响. 关键词： 2激光局域辐照')" href="#">CO₂激光局域辐照 熔石英 损伤特性     

Microstructure and transport properties of YBa2Cu3O7−δ films produced by laser ablation from a BaF2/Y2O3/CuO target

The effects of varying the temperature and duration of the post-deposition anneal in watersaturated oxygen were investigated for YBa₂Cu₃O_7−δ films of varying thickness. The films were produced by laser ablation from pressed powder targets consisting of BaF₂,Y₂O₃, and CuO mixtures. This technique produces superconducting films with a highly textured surface. The films were fabricated on SrTiO₃ substrates and were analyzed with X-ray diffraction, scanning electron microscopy, and temperature dependent resistivity. Critical current density (J_c) measurements were performed in magnetic fields up to 1 T. For film thickness on the order of 900 nm, completely c-axis oriented films were obtained with a 60 min anneal at 850°C. Thinner films required less annealing, either shorter times or lower temperatures, to achieve similar results, indicating that the optimal annealing conditions are dependent on film thickness.     

The interaction of oxygen and potassium on the Ru(001) surface

The interaction of oxygen and different coverages of potassium on Ru(001) has been investigated by thermal desorption spectroscopy (TDS), metastable quenching spectroscopy (MQS), electron stimulated desorption spectroscopy (ESD), and work-function change measurements. The results show that this is a complex surface system with several different oxides forming, depending on the surface stoichiometry and temperature. While we cannot uniquely identify all the surface species, our interpretation of the present data combined with previous information is as follows. For potassium coverages up to about three monolayers (θ_K ≈ 1), exposure to oxygen initially gives oxygen atoms on the surface. Further exposure produces some surface monoxide ions O²⁻, which are converted with additional exposure to Superoxide ions O⁻₂ and possibly peroxide ions O²⁻₂. Thermal annealing causes strong changes in the surface oxide composition, and with potassium multilayers (θ_K ≈ 10) all the oxides diffuse beneath the K surface layer with annealing to only 300 K. K₂O and K₂O₂ are found to desorb together in the 600–700 K region.     

退火对EBE,IBS和ALD沉积HfO2薄膜的抗激光损伤性能影响

结合自身实验条件采用电子束蒸发(EBE)、离子束溅射(IBS)和原子层沉积(ALD)三种工艺制备了HfO2薄膜,对其进行退火实验,采用1064 nm Nd:YAG激光测定了即时沉积和退火后各HfO2薄膜的抗激光损伤能力。研究发现,ALD HfO2薄膜的激光损伤阈值最高,EBE HfO2薄膜次之,IBS HfO2薄膜的损伤阈值最低;300℃退火对各工艺薄膜抗激光损伤能力的影响均为负面,500℃退火则会显著降低ALD HfO2薄膜的抗激光损伤能力。     

Formation of Ca-doped YBa2Cu4O8 phase in thin films

Ca-doped YBa₂Cu₄O₈ (124) thin films are prepared on (100) SrTiO₃ substrates by annealing the amorphous films deposited using a pulsed laser deposition technique. The X-ray diffraction measurements show that the Ca-doped YBa₂Cu₄O₈ phase is formed by annealing below 800°C at a oxygen pressure of 1 atm. The 124 films have c-axis orientation normal to the substrates. As the Ca content increases, the proportion of the 123 impurity phase in the samples increases. The onset temperature of superconductivity of the Y(Ca)Ba₂Cu₄O₈ films increases from 79 K to 88 K with an increase Ca-substitution for 5 to 10% of Y.     

Ultra short pulse laser annealing of FeB metallic glasses

We present the results of picosecond laser annealing of as-quenched Fe₈₅B₁₅ and Fe₈₂B₁₈ metallic glasses. The influence of the laser radiation on the surface and bulk properties are studied using CrK X-ray diffraction and transmission Mössbauer spectroscopy. The X-ray data show that the amorphous nature of the surface of the samples can be improved with laser treatment. The mat (cooling) surfaces of the ribbons appear to be more affected by the laser treatment, and show a higher stability. The Mössbauer data reveal that laser annealing of ribbon surfaces also affects the bulk properties of these materials due to induced stresses from the surface layer. The magnetic properties of these materials can be modified by laser annealing.     

Investigation of the role of oxygen in NO reduction by C2H4 on the surface of stepped Pt(3 3 2)

The influence of pre-dosed oxygen on NO–C₂H₄ interactions on the surface of stepped Pt(3 3 2) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(3 3 2), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350 K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx.

C₂H₄ molecules which are post-dosed at 250 K to adlayers consisting of ¹⁸O and NO do not have strong interactions with either the NO or the ¹⁸O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N₂ production appear to be absent. However, C₂H₄ is oxidized to C¹⁸O₂ by ¹⁸O atoms at higher annealing temperature. This reaction scavenges surface ¹⁸O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N₂ desorption which closely resembles that following only NO exposure on a clean Pt(3 3 2), both in peak intensity and desorption temperature. It is concluded that the presence of ¹⁸O₂ in the selective catalytic reduction (SCR) of NO with C₂H₄ on the surface of Pt(3 3 2) does not play a role of activating reactants.     

Aspects of annealing and free surface crystallization of YBCO thin films

We describe a method of high temperature annealing in which the control of oxygen partial pressure is the principal experimental determinant in obtaining highly c oriented thin films of YBa₂Cu₃O_{7 − δ} on YSZ. Film crystallization, morphology and substrate interactions are discussed with detailed reference to the equilibria existing in the YBCO system. A model based on the melt-assisted crystallization of the precursor tetragonal compound, beginning at the free film surface, is used to explain the observed c texturing. Excellent Josephson coupling between grains of YBa₂Cu₃O_{7 − δ} in our films is related to melt-assisted growth. We discuss the adverse effects of annealing in pure oxygen at high temperatures.