飞秒激光作用下高能离子的产生与加速

为了探索飞秒激光与固体靶相互作用中高能离子的 产生和加速机制,在超短超强激光装置 “SILEX-I”上进行了超强激光与平面薄膜Cu靶的相互作用中高能离子能谱分布的实验研究 。实验采用固 体核径迹探测器CR39和Thomson离子谱仪相结合的方式,在固体靶背表面法线方向测量了质 子和C离子能 量分布和产额。实验结果表明,实验观察到了质子和C4＋、C3＋、C2＋ 和C¹⁺离子信号;离子沿着靶背法线方 向发射,离子在一定能量处出现截断;质子和C4＋、C3＋、C2＋及C 1+离子的截止能分别是1221941keV、 1899、624、422keV;随着C离子电荷数增加, 产额也随着增加;质子的产额远远高于C离子。经分 析,高能离子的产生和加速是多种作用机制共同作用的结果,其中静电场中的靶后鞘层加速 (TNSA)机制则占主导地位。     

飞秒激光作用下高能离子产生的实验研究

为了探索飞秒脉冲激光与固体靶相互作用中高能 离子的能量分布特性,在超短超 强激光装置“SILEX-I”上进行了超强激光与平面薄膜Cu靶的相互作用中高能离子能谱分布 的实验研究。采用固体核径迹探测器CR39和Thomson离子谱仪相结合 的方式,在固体 靶背表面法线方向测量了质子和C离子能量分布和产额。结果显示,同时测量到了 H⁺质子和C1＋、C2＋、C3＋和C4＋信号,离子沿靶背法线 方向发射,离子出现能量截断, 离子的截止能量之比为1∶2∶3∶4。在CR39上 质子信号比C离子信号强,质子产额远高于C 离子产额;在同一发打靶中,C1＋、C2＋、C3＋和C⁴⁺随着 荷质比的减小,相应的离子的截 止能量也在减小。这一结果将为惯性约束聚变(ICF)“快点火”方案的可行性分析提供参 考依据。     

氟化非晶碳薄膜结构与热稳定性研究

在室温下以C4F8和CH4为前驱气体,用电子回旋共振化学气相沉积（ECR-CVD）的方法生长了氟化非晶碳（α-C：F）薄膜。通过傅立叶变化红外光谱分析（FTIR）和X射线光电子能谱分析（XPS）对薄膜的化学结构和成键情况进行了研究。CFx（x=2～3）以及位于DC交联结构末端用于构成CxFy大分子结构的C-C键的热稳定性较差,在N2气氛下退火后,会以气态形式进行分解,导致α-C：F薄膜膜厚的减小。随着源气体流量比R=[C4F8]／（[C4F8]＋[CH4]）的减小．α-C：F薄膜中C-CFx交联结构逐渐增多,CFx（x=2～3）基团及构成CxFy大分子结构的C-C键逐渐减少,薄膜的热稳定性得到著提高。α-C：F薄膜在退火后,由于取向极化的增大和电子极化的减小,以及薄膜密度的增加使得α-C：F薄膜的介电常数有所增加。     

248nm准分子激光加工玻璃微通道的实验研究

为了提高玻璃微通道的加工效率及质量,采用248nm准分子激光加工玻璃微通道的新型加工方法进行了理论分析和实验验证,取得了不同激光参量下玻璃微通道的加工工艺数据。结果表明,激光加工玻璃微通道的刻蚀阈值为4.54103mJ/mm2;随着激光能量的增加,刻蚀深度近似成对数增长,经线性拟合得到刻蚀深度随激光能量变化的公式;随着脉冲频率的增加,刻蚀深度近似成线性增长,经线性拟合得到刻蚀深度随频率变化的公式;且通道底面粗糙度随激光能量及脉冲频率的增加,呈增长趋势;激光的能量在400mJ～600mJ、脉冲频率在4 Hz～7 Hz范围的组合激光参量可实现刻蚀率高、粗糙度小的微通道加工。这些结果对于合理选择激光参量、提高玻璃微通道的加工效率及质量是有帮助的。     

离子径迹电光学性质的太赫兹时域光谱

为了深入研究离子径迹的电光学性质,室温下用太赫兹时域光谱（THz-TDS）测量高能重离子辐照的聚苯乙烯（PS）和聚乙烯（PE）,获得了辐照样品的光学常数。研究发现,在离子沉积能量或离子剂量较高时,辐照PS和PE的吸收系数相比未辐照样品都有显著增加,这是由于辐照产生的碳团聚体对太赫兹波有吸收作用;对折射率而言,辐照PS的折射率增加而辐照PE的折射率降低,这与2种聚合物的结构有关。用有效介质理论提取出辐照聚合物中离子径迹的光学常数,并用Drude-Lorentz模型对其进行拟合,由拟合参数计算出了离子径迹的直流电导率。与常规接触测量法获得的离子径迹的电学参数进行比较,发现2种测量结果的差异是由于沿径迹方向能量沉积的不均匀性造成,THz-TDS测量结果更能反映高能量沉积区域物质的电学性质。     

数字CR-(RC)n滤波器的脉冲成形技术研究

为保证放射性测量系统的能量分辨率,探测器输出脉冲通常被成形为高斯或类高斯波形。本文基于CR-(RC)ⁿ电路,将CR-(RC)ⁿ电路分解为CR电路和RC电路,然后采用数值微分方法分别建立CR电路、RC电路数学模型,实现数字CR-(RC)ⁿ脉冲成形。通过模拟串行噪声和并行噪声,对比了数字CR-(RC)ⁿ脉冲成形与梯形脉冲成形的滤波效果。实验结果表明,在相同达峰时间条件下,数字CR-(RC)ⁿ脉冲成形对串行噪声、并行噪声的滤波效果较梯形脉冲成形滤波效果好;CR-(RC)⁴脉冲成形对串行噪声、并行噪声的滤波效果较n=1,2,3时好;CR-RC脉冲成形对上升时间的免疫能力较CR-(RC)²,CR-(RC)³,CR-(RC)⁴脉冲成形强。     

准分子激光合成晶态C3N4薄膜机理研究

目前，科技工作者采用各种技术、方法试图合成晶态氮化碳（β-C3N4）材料，并在不同工艺条件下对氮化碳材料生长及表征进行了大量的研究．但由于对氮化碳薄膜生长过程缺乏系统的了解，对这种材料的生长规律的认识受到了限制．本工作对XeCI准分子激光溅射C靶并辅以氮气放电在不同工作气压和衬底温度下制备氮化碳薄膜过程进行了研究．采用拉曼光谱、X射线光电子能谱（XPS）、扫描电子显微镜、X射线衍射等手段分析了材料的性质，采用光学多道分析仪（OMA皿）对等离子体发射谱进行了分析，讨论了实验条件对材料键合特性的影响．实验中，Xe…     

紫外纳秒激光加工金刚石微槽工艺参数优化研究

金刚石微槽在微电子散热器件和光学器件等领域都有非常大的潜在应用价值。系统研究了激光脉冲能量、扫描速度、扫描次数、重复频率和离焦量对金刚石微槽形貌、微槽宽度、微槽深度及微槽深度与宽度的比值的影响规律。研究结果表明,金刚石微槽的深度与激光脉冲能量、扫描次数呈正相关,随着激光脉冲能量和扫描次数的增大,微槽深度逐渐增加,并且当激光脉冲能量达到200μJ,扫描次数增加到30时,微槽深度趋于稳定;金刚石微槽的深度与扫描速度呈负相关,当扫描速度为5 mm/s时,可获得深度较大的微槽;微槽的深度随着激光重复频率的增大而增加,当激光重复频率达到60 kHz时,微槽的深度趋于稳定。当离焦量从负值变化到正值时,微槽的深度先增加后减小,当离焦量为-1 mm时,微槽的深度达到最大。在激光脉冲能量为200μJ,扫描速度为5 mm/s,扫描次数为30,重复频率为60 kHz,离焦量为-1 mm的优化参数下,能够获得微槽深度与微槽宽度的比值大于12的金刚石微槽。     

基于电子束光刻的LIGA技术研究

提出了基于电子束的LIGA(Lithographie，Galvanoformung，Abformung)技术新概念。根据Grune公式就电子束能量对抗蚀剂刻蚀深度的影响进行了理论分析，并在SDS—2电子束曝光机上分别采用5keV、10keV、15keV、20keV、25keV、30keV等能量的电子束对国产胶苏州2号进行了曝光实验，得出了能量／刻蚀深度关系曲线。用5keV、30keV两种能量的电子束，通过改变曝光时间进行了曝光剂量对刻蚀深度的影响实验，得出了曝光剂量—刻蚀深度关系曲线。实验结果表明，增大电子束能量或增强曝光剂量，就可以增大刻蚀深度，证明了基于电子束光刻的LIGA技术不但是可行的，而且更易于加工各种带曲率的微器件。     

PASER 在混合气体激活介质中的理论计算

在受激辐射粒子加速中（PASER）, 受激介质中处于激发态的电子跃迁到基态时辐射的光子能量直接以量子形式转移给从它旁边经过的电子。本文首先对单个电子束团穿过受激介质时产生的电场进行了理论推导，并分别对受激的二氧化碳混合气体和受激氟化氩混合气体进行了计算。计算结果表明加速梯度可以达到1GV/m，比现有的普通的加速器加速梯度20~30MV/m高两个数量级。此外，通过二维模型进一步分析了电子微束团串穿过受激的混合气体介质获得的能量增益。结果表明电子束团串可以显著地吸收受激介质中的量子态能量，且吸收的能量与相互作用长度成正比。在相互作用长度等于0.5m时对束团参数和其它的量对能量交换的影响进行了分析。通过理论计算给出了电子获得最大能量增益时的优化参数。     

4H-SiC表面热氧化生长SiOx薄膜特性的研究

采用扫描电子显微镜（SEM）、原子力显微镜（AFM）和X射线光电子能谱（XPS）测试方法对4H-SiC上热氧化生长的氧化硅（SiOx）薄膜表面形貌进行观测，并分析研究SiOx薄膜和SiOx/4H-SiC界面的相关性质，包括拟合Si2p、O1s和C1s的XPS谱线和分析其相应的结合能，以及分析SiOx层中各主要元素随不同深度的组分变化情况，从而获得该热氧化SiOx薄膜的化学组成和化学态结构，并更好地了解其构成情况以及SiOx/4H-SiC的界面性质。     

基于改进盖尔-沙普利算法的自动识别系统与双频地波雷达断裂航迹关联

高频地波雷达(HFSWR)可以实现大范围海上船只目标的连续探测,但是海杂波等干扰因素的影响容易造成跟踪航迹的断裂。目前关于地波雷达航迹关联的研究中,通常忽略了航迹断裂的情况,将航迹关联视为二分图匹配问题,这会导致可能将单一目标的断裂航迹判断为多个目标,从而引起目标的误关联。针对上述情况,该文结合模糊综合评判和迭代搜索算法,首次将盖尔-沙普利(GS)算法引入航迹关联领域,并且对其进行改进以满足航迹断裂时的多对多航迹关联情况,提出了改进的盖尔-沙普利(IGS)算法。在该算法中,通过计算航迹之间的模糊综合评判值来得到航迹之间的倾向度序列,再由迭代搜索对航迹进行聚类以获得航迹集群,最后将航迹集群及倾向度序列输入盖尔-沙普利算法来进行数轮博弈以给出关联结果。利用双频率高频地波雷达和船只自动识别系统(AIS)的仿真数据与实测数据进行实验测试,实验结果表明：所提出的算法解决了在航迹断裂情况下的多传感器航迹关联问题,且在密集区域的航迹关联效果优于传统算法。     

A Morphological Model for the Solvent‐Enhanced Conductivity of PEDOT:PSS Thin Films

The well‐known enhanced conductivity of poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) thin films that is obtained by addition of high‐boiling solvents like sorbitol to the aqueous dispersion used for film deposition is shown to be associated with a rearrangement of PEDOT‐rich clusters into elongated domains, as evidenced from STM and AFM. Consistently, temperature dependent conductivity measurements for sorbitol‐treated films reveal that charge transport occurs via quasi 1D variable range hopping (VRH), in contrast to 3D VRH for untreated PEDOT:PSS films. The typical hopping distance of 60–90 nm, extracted from the conductivity measurements is consistent with hopping between the 30–40 nm sized grains observed with scanning probe microscopy.     

低能离子束制备(Ga,Gd,As)薄膜

室温条件下 ,用离子束外延设备制备 ( Ga,Gd,As)样品 ,X射线衍射 ( XRD)结果表明除了 Ga As衬底峰 ,没有发现其他新相的衍射峰。俄歇电子能谱 ( AES)分析了样品中元素随深度的变化 ,不同样品中元素的分布有着不同的特点。并运用原子力显微镜 ( AFM)研究了样品表面的形貌特点 ,表明样品表面的粗糙度与 Gd注入过程中在样品表面沉积的多少有关。运用交变梯度磁强计 ( AGM)对薄膜进行磁性分析 ,结果表明有的样品在室温条件下出现铁磁性 ,但金属钆本身具有室温铁磁性 ,因而需要进一步分析。     

In situ quantitative analysis of etching process of human teeth by atomic force microscopy

Etching is one of the most fundamental steps in the restoration of teeth by adhesion of composite resin in dental clinics. Atomic force microscope (AFM) was used for the in situ observation of the etching process of human enamel, dentin and synthetic hydroxyapatite in the three different acid agents, 2% phosphoric acid, 10% citric acid and 10% polyacrylic acid. To measure the absolute depth from the initial level before etching and to correlate the surface height between the changing AFM images obtained, the depth profiles were recorded with etching time by carrying out the line scan consecutively at the representative place of the observed area. These chronological series of depth profiles enabled us to perform quantitative analysis of etched amount in addition to the surface roughness obtained from relative depth profile within one image. The course of etching process from the dissolution of smear layer, appearance of enamel prizms or dentinal tubules to progress of demineralization could clearly be observed. The depth profile, surface roughness, etching amount, etching rate and smear layer thickness could then be evaluated. The different etching characteristics of three acid agents and the effect of surface roughness produced by different mechanical prepolish were compared and discussed.     

Joint impact of sensing time and IED parameter on the performance of an energy efficient cognitive radio system

Joint impact of sensing time and improved energy detector (IED) parameter is evaluated for an energy efficient cooperative cognitive radio (CR) system where the CR users use IED. The aim of this work is to design the CR system in such a way that it can achieve two objectives for a given level of protection on primary user: (i) optimization of sensing time to make balance between detection performance and throughput and (ii) appropriate allocation of energy between sensing time and transmission time so as to enhance the energy efficiency of the CR system. The key parameters such as sensing time and IED parameter are set appropriately to meet the objectives. The performance is assessed in terms of throughput and energy efficiency of the system. The effect of the sensing time and the IED parameter on the performance is evaluated under a collision constraint. Furthermore, the optimal sensing time and IED parameter are investigated jointly for which the higher throughput as well as maximum energy efficiency can be obtained, and at the same time, a desired detection probability can also be maintained by the CR system. Copyright © 2016 John Wiley & Sons, Ltd.     

PTCDA/ITO表面和界面的AFM和XPS分析

利用X射线光电子能谱(XPS)对苝四甲酸二酐[3,4,9,10-perylenetetracarboxylic dianhydride(PTCDA)]/铟锡氧化物(ITO)表面和界面进行了研究.用原子力显微镜(AFM)对PTCDA/ITO样品的表面形貌进行了分析.XPS表明,在原始表面的C1s精细谱存在两个主谱峰和一个伴峰,主谱峰分别由结合能为284.6eV的苝环中的C原子和结合能为288.7eV的酸酐基团中的C原子激发;而结合能为290.4eV的伴峰的存在,说明发生了来源于ITO膜中的氧对C原子的氧化现象.O原子在C=O键和C-O-C键的结合能分别为531.5和533.4eV.在界面处,C1s谱中较高结合能峰消失,且峰值向低结合能方向发生0.2eV的化学位移;O1s谱向低结合能方向发生1.5eV的化学位移.由此可以推断,在界面处PTCDA与ITO的结合是PTCDA中的苝环与ITO中的In空位的结合.AFM的结果显示,PTCDA薄膜为岛状结构,岛的直径约为100～300nm,表面起伏约为14nm.相邻两层PTC-DA分子由于存在离域大π键而交叠和PTCDA分子中的苝环与ITO的In空位的紧密结合是最终导致PTCDA岛状结构形成的原因.     

Throughput analysis in censoring-based cooperative cognitive radio network with energy harvesting

An energy harvesting (EH) and cooperative cognitive radio (CR) network (CRN) is studied in this paper where CR users transmit data through a primary user (PU) channel if the channel remains idle, else an optimal number CRs helps in transmission of PU. To achieve the optimum number of CRs (ONCR) involved in cooperation, a novel scheme based on a combination of channel censoring and total error is proposed. The performance of the proposed scheme is investigated under RF harvesting scenario. The EH is dependent on sensing decision and a CR source harvests energy from PU's RF signal. The harvested energy (HE) is split into two parts: One part is used by the CR network (CRN) for its own transmission, and the other part is used for supporting PU. The effect of the energy allocation factor on total throughput is also investigated. New expressions for optimal number of CRs and throughput are developed. The effect of network parameters such as sensing time, censoring threshold, and energy allocation parameter (EAP) on throughput is investigated. Impact of distance between nodes is also studied.     

Conductivity modification of silver salt-filled polyimide film by pulsed KrF laser

The ultraviolet (UV) laser treatment of polyimide films can lead to the formation of a conductive area. The formation of a conductive layer starts at a threshold dosage. This conductive layer consists of carbon-rich clusters. Silver salt added to the polyimide can modify the process and resulting parameters. Polyimide films filled with silver salt were investigated to study the effect of different salt concentrations. The influence of salt concentration and the influence and shot numbers of excimer laser on the electrical characteristics and on the structural parameters were obtained. Structural characterization was carried out by applying a scanning electron microscope (SEM) equipped with an energy dispersive x-ray analyzer (EDS) and atomic force microscope (AFM). The observations revealed “phonon-assisted hopping” could be accepted as a conduction model. The study showed that the silver salt promotes the carbonization of polyimide, and in this way, it has remarkable influence on the formation of an irradiated conductive layer.     

Cluster and thin layer of compound semiconductor growth on hexagonal and vicinal cubic surface and the simulation of atom behavior

The thin layer of the II–VI and IV–VI compound growths on crystalline substrates by laser deposition was analyzed. The influence of substrate properties on crystallite formation was determined. The initial stages of the growth of CdSe on ZnSe as well as ZnSe and PbS crystallite growth and layer formation on a Si substrate were investigated by ESCA or AFM and by the influence of clusters on the recombination of non-equilibrium carriers in substrates. The atom behavior on a terrace-step surface was analyzed and a few cases were simulated within the framework of the density-functional theory. The terrace step on Si (111) relaxation and preferred sites of Se adsorption were calculated from potential energy surfaces seen by adatoms.