六硼化镧薄膜场致发射的特性

阵列薄膜是在制备好的尖锥阵列上沉积其他材料的薄膜,以提高场发射阴极性能,它是一种有效的提高场发射阴极性能的方法。在n型硅片上先后采用氧化、光刻、干法刻蚀、氧化削尖等工艺,制备出曲率半径很小的硅尖锥场发射阵列,硅阵列中每个硅尖锥的底半径约2μm,锥高约1.04μm,每个硅尖之间间隔6μm,尖端的曲率半径约50nm,锥角约56°,尖锥阵列的密度约106/cm2。为了降低硅尖锥的功函数及提高抗离子轰击能力,通过电子束蒸发在硅尖阵列上沉积六硼化镧(LaB6)薄膜,薄膜的厚度大约50nm,锥尖曲率半径变为约111nm。X射线衍射(XRD)分析结果表明,电子束沉积在硅尖端的LaB6具有良好的结晶特性。硅尖锥及不同的真空度下阵列薄膜的场致发射I-V特性及电流发射稳定性的测试结果表明:沉积LaB6的薄膜阴极阵列的总发射电流达到125μA,是纯硅尖锥阵列125倍。并且硅阵列六硼化镧薄膜具有良好的场发射稳定性,是一种理想的薄膜场发射阵列。     

掺杂浓度对硅锥阴极特性的影响

基于漂移扩散模型和量子理论中的WKB方法,用数值模拟方法分析了材料掺杂浓度对硅锥阴极场致发射特性及工作状态的影响,结果表明,硅锥阴极单纯的场致发射IemitE特性受硅材料掺杂浓度的影响很小.但低掺杂硅锥阴极顶端的电位随发射电流增大而明显上升.锥体上电位变化可以等效为一个与锥体形状与掺杂相关的串联电阻的作用,这一电阻对单尖发射电流有负反馈作用.另外,在常规的工作状态下,硅锥阴级的温升并不严重.这些结果可以作为硅锥阴极设计的参考. 关键词： 硅 掺杂 场致发射     

碳纳米锥电子场发射的第一性原理研究

运用第一性原理研究了不同锥角和结构的碳纳米锥 （CNC） 电子场发射性能.结果表明：随外电场 （E_add） 增强,CNC电子结构变化显著,费米能级 （E_f） 处态密度 （DOS） 明显增大;赝能隙减小;体系电荷移向尖端.DOS,HOMO/LUMO及Mulliken电荷分析表明：CNC的电子场发射性能除依赖于尖端结构外,很大程度上还取决于锥角大小,特别顶层6个原子的CNC₃和CNC₄场发射性能 关键词： 碳纳米锥 电子场发射 第一性原理     

电场作用下锥翅表面强化池沸腾换热的介观数值方法

采用耦合电场模型的相变格子Boltzmann模型,数值研究了电场作用下锥翅结构表面的饱和池沸腾换热.为了定量分析电场对锥翅结构表面沸腾换热影响的机理,首先在无电场作用下对比调查了平滑表面和锥翅表面的沸腾换热现象.发现锥翅结构在核态沸腾阶段有更多的成核点,沸腾换热性能增强,临界热流密度(critical heat flux,CHF)提高.而在过渡沸腾阶段以及膜态沸腾阶段,由于锥翅结构增加了锥翅表面流体的流动阻力,阻碍了气液交换,换热性能低于平滑表面.基于以上发现,通过对锥翅表面池沸腾过程施加电场,进一步强化了锥翅表面沸腾换热.结果表明,在起始核态沸腾阶段,电场的存在稍微延后了气泡开始成核时间,气泡尺寸减小,沸腾轻微被抑制;充分核态沸腾阶段,由于电场力的作用以及电场与锥翅结构协同表现出的尖端效应,阻止了加热表面干斑的扩散和蔓延,促进沸腾换热;过渡沸腾以及膜态沸腾阶段,尖端效应更加明显,逐渐增大的电场强度使沸腾在更高过热度下处于核态沸腾状态,沸腾换热性能大幅度提高,且CHF逐渐提高.     

立方氮化硼薄膜生长过程中的界面控制

在立方氮化硼薄膜气相生长过程中生成的无定形初期层和乱层结构氮化硼中间层，一直是阻碍立方氮化硼薄膜外延生长的主要原因.系统地分析了硅衬底预处理对立方氮化硼薄膜中无定形初期层成分的影响，发现在等离子体化学气相生长法制备薄膜时，硅衬底上形成无定形初期层的可能原因有氧的存在、离子轰击以及高温下硅的氮化物的形成.在H₂气氛中1200K热处理硅衬底可以有效地减少真空室中残留氧浓度，除去硅表面的自然氧化层，保持硅衬底表面晶体结构.控制衬底温度不超过900 K，就能防止硅的氮化物的形成，成功地除去无 关键词： 立方氮化硼薄膜 等离子体化学气相生长 界面 电子显微镜     

氩离子轰击对四面体非晶碳膜内应力和摩擦系数影响的研究

利用磁过滤真空阴极电弧技术制备了sp³键大于80%的四面体非晶碳(ta-C)薄膜, 通过冷阴极离子源产生keV能量的氩离子轰击ta-C薄膜,研究了氩离子轰击能量对ta-C薄膜结构, 内应力以及耐磨性的影响.通过X射线光电子能谱和原子力显微镜研究了氩离子轰击对薄膜结构 与表面形貌的改性,研究表明,氩离子轰击诱导了ta-C薄膜中sp³键向sp²键的转化, 并且随着氩离子轰击能量的增大,薄膜中sp²键的含量逐渐增多, 薄膜内应力随着氩离子轰击能量的增大逐渐减小.氩离子轰击对薄膜的表面形貌有较大影响, 在薄膜表面形成刻蚀坑,并且改变了薄膜的表面粗糙度,随着氩离子轰击能量的增大, 薄膜的表面粗糙度也会逐渐增大.通过摩擦磨损仪的测试结果,氩离子轰击对薄膜的初始摩擦系数影响较大, 但是对薄膜的稳定摩擦系数影响较小,经过氩离子轰击前后的ta-C薄膜的摩擦系数为0.1左右, 并且具有优异的耐磨性.     

仿生纳米硅结构减反射及陷光性能模拟研究EI北大核心CSCD

仿造蝉翼凸起状结构,建立了硅纳米锥模型,在此基础上研究其减反射及陷光性能与其底部直径、高度的关系,确定直径150nm、高度500nm为其最优结构参数,该参数的纳米锥结构在300~1200nm波段平均反射率为1%.将优化的纳米锥结构与平板结构以及相同参数的纳米柱结构进行了比较,从反射曲线、电场强度分布、能量吸收密度分布、电子生成速度分布多个角度证实了纳米锥结构优异的减反射及陷光性能,为硅基光伏器件减反射陷光微结构设计提供了参考.     

仿生纳米硅结构减反射及陷光性能模拟研究

仿造蝉翼凸起状结构,建立了硅纳米锥模型,在此基础上研究其减反射及陷光性能与其底部直径、高度的关系,确定直径150nm、高度500nm为其最优结构参数,该参数的纳米锥结构在300~1200nm波段平均反射率为1%.将优化的纳米锥结构与平板结构以及相同参数的纳米柱结构进行了比较,从反射曲线、电场强度分布、能量吸收密度分布、电子生成速度分布多个角度证实了纳米锥结构优异的减反射及陷光性能,为硅基光伏器件减反射陷光微结构设计提供了参考.     

基于准连续介质方法模拟纳米多晶体Ni中裂纹的扩展

通过准连续介质方法模拟了纳米多晶体Ni中裂纹的扩展过程.模拟结果显示:裂纹尖端的应力场可以导致晶界分解、层错和变形孪晶的形成等塑性形变,在距离裂纹尖端越远的位置,变形孪晶越少,在裂纹尖端附近相同距离处,层错要远多于变形孪晶.这反映了局部应力的变化以及广义平面层错能对变形孪晶的影响.计算了裂纹尖端附近区域原子级局部静水应力的分布.计算结果表明:裂纹前端晶界处容易产生细微空洞,这些空洞附近为张应力集中区,并可能促使裂纹沿着晶界扩展.模拟结果定性地反映了纳米多晶体Ni中的裂纹扩展过程,并与相关实验结果符合得很好     

碳纳米锥与刚体平面作用的分子动力学模拟

采用Brenner势的分子动力学方法,模拟了47°、69°及93°锥度碳纳米锥与刚体平面压缩、分离的全过程;获得了三种碳纳米锥与刚体平面作用过程中的构形演变、能量-变形曲线以及力-变形曲线;根据模拟结果,分析了它们承载能力以及变形能力的差异.研究表明,47°纳米锥压缩后,锥尖倒向一边,而69°及93°纳米锥锥尖内陷;47°及69°碳纳米锥产生永久变形时的最小压缩量分别为15%和19%左右,而93°碳纳米锥大于38.9%;三种碳纳米锥的最大承受载荷均为29nN左右.     

Use of ion processing to improve the quality of fullerene-coated field emitters

The efficiency of tip field emitters covered by activated fullerene coatings is studied in a wide range of emission currents and residual gas pressures. Main mechanisms behind the influence of the gaseous medium and ion bombardment on the emitter efficiency are determined. The feasibility of improving the homogeneity of the fullerene coating by potassium ion bombardment is demonstrated. From data on the emitter performance in a technical vacuum, a previously unknown effect is discovered: the structure of activated fullerene coatings is reproduced under intense ion bombardment. It is found that intense bombardment by residual gas ions increases a limiting current extracted from fullerene-coated tip field emitters.     

LaB6场发射尖锥的场发射特性研究

 报道了六硼化镧（LaB₆）场发射尖锥的场发射性能。采用电化学腐蚀方法制作了LaB₆场发射尖锥，并在10^-2～10^-7 Pa 的宽真空度范围内对单尖LaB₆场发射二极管的发射特性进行了测试。发现残余气体电离产生的离子轰击对LaB₆场发射阴极尖锥表面起到了离子清洗作用，使LaB₆场发射尖锥在低真空工作后发射电流大幅度提高。离子轰击是一种适用于LaB₆场发射阴极的激活处理方法。     

Mechanism of negative ion emission from surfaces of ferroelectrics

Experimental studies of the mechanism of negative ion and cluster ion emission from surfaces of ferroelectrics are described. The emission was produced by negative voltage pulses with the amplitude of about 400 V, with a rapid rise-time (below 10 ns) and a slow decay‐time (several μs). The pulses were applied between the back side of the ferroelectric sample and the metal tip touching the front emitting side. The surface of the ferroelectrics could be cleaned in situ by 1 keV Ar⁺ bombardment. The morphologic changes around the tip were observed with an atomic force microscope (AFM). Mostly negative ions and cluster ions were emitted and studied in our experiments. Positive ions were detected with much lower probability and are produced by an entirely different microscopic process than negative ions. Masses as well as energies of emitted ions were measured with a time-of-flight (TOF) spectrometer and compared with available spontaneous desorption (SD) spectra and Cs‐SIMS spectra in order to clarify the mechanism of the emission. The trajectory of ions emitted from the sample was studied by computer simulation. The conclusion of these studies is that the negative ion emission is caused by the Coulomb explosion of a polarization cloud rapidly formed at the front edge of the pulse. The explosion takes place in the vicinity of the tip-sample contact at distances several tens of μm from the contact where the stabilizing effect of the positively charged tip is already small.     

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

The influence of argon ion bombardment on the electrical and optical properties of clean silicon surfaces

The effect of low energy noble gas ion bombardment on the electrical and optical properties of Si(211) surfaces has been investigated by surface conductivity and field effect measurements, ellipsometry and AES. With this combination of techniques, information is obtained concerning the electrical properties, the chemical composition and the damage of the surface layer. Upon ion bombardment in the energy range of 500–2000 eV, ellipsometry shows the formation of a damaged surface layer with optical properties close to those of an evaporated amorphous silicon film. In order to measure the conductivity changes as sensitive as possible, nearly intrinsic silicon crystals were used. For the clean, 5200 Ω cm Si(211) surface, bombarded only with a mass-analyzed argon ion beam, a small increase in conductivity is found to occur after a small ion dose (saturation after 5 × 10¹⁴ ions cm^?2 while after 5 × 10¹³ ions cm^?2 already half of the increase has occurred). The effect was found to be independent of ion energy between 500 and 2000 eV. As the field effect signal did not change after this treatment, it is concluded that the surface state density in the neighbourhood of the Fermi level shows a slight decrease.     

Generation of ions in a pulsed ion source with an interface based on a polymer track membrane

The time-of-flight spectra of ions generated during the extraction of negative ions from the KI solution in water–glycerin mixture by high-strength electric field pulses are studied using a source with an interface based on a polymer track membrane. It has been shown that the ions formed in secondary processes of bombardment of the membrane surface make a considerable contribution to the observed spectra. It has been found that the peaks of negative hydrogen ions have the highest intensity in the spectrum, indicating effective emission of these ions during the bombardment of polyethylene terephthalate by secondary ions with an energy of about 6 keV. The main trends in the modification of the membrane interface to reduce the fraction of secondary ions in the ion beam have been outlined.     

ESCA studies on changes in surface composition under ion bombardment

The influence of ion bombardment on the composition of surfaces was investigated by means of ESCA. The bombardment of metal oxides with inert gas ions results, not only in sputtering of the surface, but also in reduction of the oxides. The rate of reduction is particularly high when the oxide/metal interface is within the range of the bombarding ions. Ion induced reduction was found in oxide layers, thinner than the escape depth of the photoelectrons, on Mo, W, Nb, Ta, Ti, Zr, Si, and Bi. The relationship between reduction phenomena, on the one hand, and the ion energy, angle of incidence, mass of the gas used for bombardment, and ion current density, on the other hand, was investigated in the case of the Mo/Mo-oxide system. Ion bombardment of surfaces may also result in the formation of new compounds. Two examples of this are the formation of carbides through the bombardment of contaminated surfaces and the ion induced formation of C-F compounds from a mixture of K₂SiF₆ and carbon.     

Laser-stimulated field desorption of molecular ions from a tungsten emitter

We report here on a experimental observation of photon-stimulated field emission of molecular anthracene ions from the surface of a layer adsorbed on a tungsten field-emitter tip. When the tip is irradiated with laser pulses 249, 308, and 400 nm in wavelength falling within the absorption bands of anthracene, the stimulated ion signal is proportional to the pulse fluence. The efficiency of the process decreases with the increasing laser wavelength. Photon stimulation is believed to be due to the resonance excitation of the anthracene molecules, followed by the field ionization of the excited molecules.     

基于有限元方法的离子俘获装置模拟计算

利用有限元程序ANSYS,开展潘宁离子俘获装置的电场模拟计算。基于电场数据,结合Runge_Kutta_Fehlberg方法进行潘宁装置在多种模式下的离子俘获过程模拟工作,得到了准确的离子俘获结果。并对实际条件下具有偏离理想情况电极分布的俘获装置进行了优化计算及电场分析,同样实现了离子俘获过程的准确模拟。有限元方法用于离子俘获装置的电场计算以及后续离子俘获过程模拟流程的建立,为类似的电势阱离子俘获装置建造运行提供有效的技术支持。     

129Xeq+轰击N型和P型Si表面时的电子发射产额研究

在兰州重离子加速器国家实验室测量了1.8 MeV Xeq+离子分别轰击N型和P型Si两种靶材表面时的电子发射产额。实验中,通过改变入射离子的电荷态,研究了入射离子势能沉积对两种靶材表面电子发射产额的贡献。结果发现同一离子入射时,N型Si表面的电子发射产额高出P型Si表面的电子发射产额约12.5%;对于具有相同入射动能的Xeq+离子,两种靶材表面的电子发射产额均随着入射离子势能的增加而线性增加。此外,还测量了3.4 MeV Xeq+离子分别轰击以上两种靶材时的电子发射产额,得到了类似的结果。本文利用功函数分别从动能电子发射和势能电子发射两个角度对实验结果进行了分析讨论。The electron emissions from N-type Si and P-type Si induced by 1.8 MeV 129Xeq+are measured in the National Laboratory of Heavy Ion Research Facility in Lanzhou,The contribution to electron emission yield from potential energy of incident ions is studied through changing the charge state of incident ions.The results show that for the same incident ion,electron emission yield of N type Si surface is higher than that of P-type Si surface about 12.5%.For incident ions with the same kinetic energy,both electron emission yields of two targets increase linearly with incident ion energy.In addition,the electron emissions induced by 3.4 MeV 129Xeq+from N-type Si and P-type Si mentioned above are measured,which give similar results.The experimental results are analyzed and discussed using work function from two angles of the kinetic electron emission and the potential energy electron emission.