不同离子束参数诱导单晶硅纳米微结构与光学性能

使用微波回旋共振离子源,研究了低能Ar+离子束正入射时不同离子束能量和束流密度对单晶硅（100）表面的刻蚀效果及光学性能。结果表明,当离子束能量为1 000 eV,束流密度为88~310 A/cm2时,样品表面出现自组装纳米点状结构,且随着离子束流密度增加排列紧密而有序;粗糙度呈现先减小后迅速增大的趋势,在160 A/cm2附近达到极小值;刻蚀后,近红外波段内平均透过率由53%提高到57%以上,且随着纳米自组装结构有序性的提高而增大。当束流密度为270 A/cm2,能量为500~1 500 eV时,样品表面出现纳米点状结构,且随着离子束能量的增加趋于密集有序;粗糙度呈现先缓慢增加,在1 100 eV附近达到极大值,之后粗糙度迅速下降;刻蚀后样品透过率明显提高,且平均透过率随着点状结构有序性的提高而增大;刻蚀速率与离子束能量的平方成正比。自组织纳米结构的转变是溅射粗糙化和表面驰豫机制相互作用的结果。     

环形固体背散射探测器的最佳检测距离

当入射电子与物质相互作用后又能返回表面逸出，则这部份原入射电子称为背散射电子。通常以能量小于50eV的电子称为二次电子，大于50eV而小于E0的电子称为背散射电子，用背散射电子来扫描成像所获得的图像称为背散射电子像。     

蓝宝石表面纳米结构随杂质靶距离的演化

使用微波回旋共振离子源刻蚀蓝宝石（C向）表面，引入金属不锈钢杂质，研究了不同靶距处蓝宝石表面自组织纳米结构的演化规律及光学性能。采用原子力显微镜来观察样品表面的形貌变化，Taylor Surf CCI 2000白光干涉表面测量仪测量蓝宝石样片表面的粗糙度；选择X射线光电子能谱对样品表面的化学成分进行了表征。实验结果表明:当离子束能量为1000 eV，束流密度为487 μA/cm2，入射角度为65°，刻蚀时间为60 min，蓝宝石样片与杂质靶距离从1 cm增加到4 cm时，样片表面出现岛状结构并逐渐演变为连续的条纹结构。同时，自组织纳米结构随靶距增加，有序性增加，纵向高度逐渐减小，空间频率基本不变。刻蚀后样品表面的金属杂质残留很少，微结构的形成对蓝宝石具有增透作用。在离子束溅射过程中，岛状结构的出现促进了样品表面条纹纳米结构的生长，破坏了纳米结构的有序性。     

铌酸锂微纳米结构的制备与分析

为实现铌酸锂光学器件的高效集成，在其表面制备亚波长结构是实现其光学特性的最佳方式。然而，目前使用的聚焦离子束刻蚀、激光刻蚀、湿法刻蚀等方法很难简单、经济、较快地制备铌酸锂亚波长结构。鉴于此，本课题组基于有限元仿真及低能离子束刻蚀技术，研究了不同离子束参数下刻蚀的铌酸锂亚波长结构及其透射率。采用Lambda950分光光度计和原子力显微镜分别对刻蚀后的铌酸锂样品的透射率、均方根粗糙度、纳米结构的纵向高度和表面形貌进行了分析。结果表明：当离子束入射角度为70°、入射能量大于600 eV、束流大于40 mA、刻蚀时间大于60 min时，铌酸锂样品表面形成了大面积的锥形纳米结构，并且纳米结构的高度随着离子束刻蚀参数的增大而增大；在可见光波段，铌酸锂表面纳米结构越高，增透效果就越明显；当入射能量为1000 eV、离子束束流为40 mA、入射角度为70°、刻蚀时间为120 min时，铌酸锂表面刻蚀出了纵向高度为143.5 nm的锥形结构，此时在可见光范围内铌酸锂样片的峰值透射率为83.5%，相较于原片的透射率提高了约12.5个百分点。     

能谱重叠峰的线性剥离法

1.问题的提出:由于X射线能谱化的分辨率(Mn—Ka线)一般不低于140eV,造成谱中某些分析线发生重叠。2.重叠峰线性剥离法。2.1特征线的峰形及线性剥离法的定义。能谱图中每一特征X射线峰的轮廓可用一相应的高斯函数曲线来描述,其表达式为X_i=Aexp[-1/2((E-E_i)/σ)~2] (1)E_i为多道分析器第i道所对应的能量,X_i为该道内的计数,E为高斯峰值所对应的能量,可称为特征能量,σ为统计偏差,A为振幅。峰剥离实际上是峰叠加的逆过程。假设一合峰是N个子峰叠加而成,该合峰的轮廓可以由下面表达式     

数百eV低能电子束照射电介质样品带电效应

结合数值模拟和实验测量,以石英样品为例,研究了低于1keV的低能电子束照射下的动态带电特性。结果表明,使得电子总产额σ为1的第一临界能量约为200eV;随着电子束照射,表面电位逐渐趋于稳定;σ逐渐增大至一个略小于1的稳定值。随着电子束能量的增大,σ从不同初始值变化到相同稳定值的暂态时间基本不变;表面电位随电子束能量变化在约600eV时呈现一个极大值。随着束流的增大,暂态过程更容易趋于稳定。     

X射线条纹相机CsI光阴极的高能电子份额

为了得到X射线条纹相机中CsI光阴极的高能电子份额数据,通过蒙特卡罗方法建立模型来研究CsI光阴极在X射线照射下的光电发射特性.研究了CsI光阴极厚度为100～1 000 nm、入射X射线能量为1～30 keV时的二次电子(SE)能量分布.模拟结果显示,入射X射线的能量越高、CsI光阴极的厚度越大,从CsI光阴极出射的二次电子中高能电子(大于50 eV)的份额越高,在入射X射线能量为30 keV、CsI光阴极厚度为1 000 nm时,出射电子中的高能电子份额可以达到10.8％.但是当CsI光阴极厚度保持为100 nm、而入射X射线能量大于15 keV时,高能电子份额维持在3.4％左右而不再随入射X射线的能量增加而增加.     

电泳沉积纳米金刚石涂层场发射阴极工艺研究

采用电泳沉积(EPD)制备薄膜的方法,在金属钛片上均匀地涂覆纳米金刚石涂层,经真空热处理,制成场发射阴极.该文主要研究了不同的电泳液配方、电泳电压及电泳时间对涂层制备的影响.实验结果表明,粘度系数较大的电泳液及较低的电泳电压下适当延长电泳时间有利于改善涂层的均匀性和致密性;典型样品开启电场为5.5 V/μm,在20 V/μm场强下的电流密度达到169 μA/cm~2.发光测试表明,发光点密度较大且均匀分布,发光稳定,亮度较高.用X-射线衍射(XRD)和扫描电子显微镜(SEM)对样品的成份及形貌进行了分析,结合其场发射测试结果,解释了样品性能的差异和变化.     

InP(100)与(111)面的特征能量损失谱

用能量为300eV的入射电子测量了InP(100)与(111)面的电子能量损失谱,识别了能量损失为15.2eV的峰对应于InP的体等离子体损失,11.7eV和8.7eV 的两个峰分别由In的体和表面等离子体损失所引起.用费米能级以上1.8 eV和 4.0eV处存在两个空态.解释了19.3eV、20.2eV、22.7eV,3.8eV和 6.0eV 几个损失峰分别对应于从In 4d芯能级和价带到上述空态的跃迁.In的体和表面等离子体损失峰的存在说明表面形成了In岛.根据同纯In样品损失谱强度的比较,估计了表面In岛所占的面积.表面In岛是氩离子刻蚀所造成,经过退火,In岛所占面积缩小,但厚度增大.InP(100)表面形成的In岛比(111)表面更不易消除.     

微通道板最佳倾斜角的设计

本文根据铅硅玻璃次级电子产额公式，计算了对应于不同入射能量的原初电子进入微通道板的最佳入射倾斜角。指出不同材料制作的微通道板（不同的微通道板皮玻璃料方），工作在不同的条件下（入射电子能量不同），就必须设计不同的倾斜角，否则微通道板的电子倍增潜力得不到充分发挥。     

碳纳米管薄膜的电泳沉积与场发射性能

采用电泳法在Si基片上沉积碳纳米管(CNTs)薄膜。研究了电泳极间距、电泳时间及电泳电压等对沉积的薄膜形貌结构与场发射性能的影响。SEM、高倍光学显微镜和场发射性能测试结果表明,保持阴阳极间距为2cm,在100V的直流电压下电泳2min所获得的CNTs薄膜均匀、连续、致密且具有最好的场发射性能,其开启电场强度仅为1.19V/μm,当外加电场强度为2.83V/μm时,所获得的最大发射电流密度可达14.23×10–3A/cm2。     

Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.     

Basic studies of gallium nitride growth on sapphire by metalorganic chemical vapor deposition and optical properties of deposited layers

We have studied the growth of gallium nitride on c-plane sapphire substrates. The layers were grown in a horizontal metalorganic chemical vapor deposition reactor at atmospheric pressure using trimethylgallium (TMG) and ammonia (NH₃). Variation of the V/III ratio (150–2500) shows a distinct effect on the growth rate. With decreasing V/III ratio, we find an increasing growth rate. Variation of the growth temperature (700–1000°C) shows a weak increase in growth rate with temperature. Furthermore, we performed secondary ion mass spectroscopy measurements and find an increasing carbon incorporation in the GaN films with decreasing ammonia partial pressure and a growing accumulation of carbon at the substrate interface. Photoluminescence measurements show that samples with high carbon content show a strong yellow luminescence peaking at 2.2 eV and a near band gap emission at 3.31 eV. With increasing carbon content, the intensity of the 3.31 eV line increases suggesting that a carbon related center is involved.     

Investigation of carbon incorporation in znse: Effects on morphology,electrical, and photoluminescence properties

Observations of carbon incorporation in epitaxial ZnSe films grown by metalorganic chemical vapor deposition are presented. Carbon is detected by secondary ion mass spectroscopy (SIMS) measurements in all ZnSe films grown from methylallylselenide and dimethylzinc. The presence of carbon in the films is correlated with a new bound excitonic emission appearing at 2.7920 eV which dominates the near-band-edge low-temperature photoluminescence spectra of all carbon contaminated films. This peak is also observed when growth is commenced from diethylselenide, under certain growth conditions, but not from hydrogen selenide. The effect of the carbon contamination is discussed in terms of variations in surface morphology, electrical and luminescence properties of as-grown films. Control of the carbon concentration is demonstrated by alternating between hydrogen selenide and methylallylselenide during growth. Strategies to avoid carbon contamination in ZnSe are also proposed. Author to whom correspondence should be addressed     

Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths

The growth of nanocrystalline zinc sulfide thin films onto glass substrates by chemical bath deposition has been optimized at acidic pH. Powder X-ray diffraction (p-XRD) confirms the deposition of sphalerite, the cubic phase of ZnS. The crystallite size calculated by Scherrer equation was found to be 4.0 nm. Scanning Electron Microscopy (SEM) show clusters of spherical nanoparticles uniformly distributed over the surface of the glass substrates. Energy Dispersive X-ray (EDX) analysis of the deposited thin films show the zinc to sulfur ratio close to 1:1. The observed band gap (3.78 eV) of the deposited thin films is higher than that reported for cubic phase of bulk ZnS (3.54 eV) as expected due to nano-size crystallites. Binding energies calculated by X-ray Photoelectron Spectroscopy (XPS) confirm the material as ZnS and the photoluminescence measurements show the blue shift in emission maximum.     

Improvement of the field emission properties of carbon nanotubes by CNT/Fe_3O_4 composite electrophoretic deposition

A simple CNT/Fe_3O_4 composite electrophoretic deposition method to improve the field emission cathode properties of carbon nanotubes(CNTs) is proposed.It is found that CNT/Fe_3O_4 composite electrophoretic deposition leads to better field emission performance than that of single CNT electrophoretic deposition.The result is investigated using SEM,J-E and FE.After the process,the turn-on electric field decreases from 0.882 to 0.500 V/μm at an emission current density of 0.1 mA/cm~2,and the latter increase...     

Characterization of undoped and silicon-doped InGaN/GaN single quantum wells

We investigated the influence of doping and InGaN layer thickness on the emission wavelength and full width at half maximum (FWHM) of InGaN/GaN single quantum wells (SQW) of thicknesses between 1 nm and 5 nm by temperature and intensity resolved photoluminescence (PL). The crystalline quality of the GaN claddings was assessed by low temperature PL. The emission energy of 5 nm Si doped SQW could be tuned from 3.24 eV to 2.98 eV by reducing the deposition temperature. An increase of piezoelectric (PE) field screening with increasing deposition temperature is attributed to an increase of the SiH₄ decomposition efficiency. Piezoelectric (PE) fields between 0.5 MV/cm and 1.2 MV/cm in undoped structures of varying SQW thicknesses were calculated. Two activation energies of 15 meV and 46 meV of the SQW emission could be observed in temperature resolved measurements. The higher value was assigned to the confined exciton binding energy, whereas the activation energy of 15 meV is probably due to a decrease in carrier supply from the absorption zone in the GaN cladding into the SQW.     

电泳法制备场发射阴极的性能优化研究

电泳法是一种新型的大面积碳纳米管场发射阴极制备方法。文章在成功地用电泳法制备了适用于场发射显示器的碳纳米管阴极基础上,通过选用不同的碳纳米管原料、改变电泳条件等方法,进一步优化碳管阴极的性能。使用不同方法制备的碳纳米管配置电泳液,由于制备方法和碳管本身的特性,管子在电泳溶液中呈现不同的分散性。碳管管径较粗时由于表面自由能相对小,所以碳管在溶液中不易形成团聚物,电泳沉积的阴极会均匀平整;管径小的碳管则由于容易团聚,需要加入表面活性剂来改善其在电泳溶液中的分散性。场发射特性和发光显示图实验结果发现,即使得到相同均匀平整的阴极,但是由于碳管本身的发射能力的差异性最终导致电泳沉积得到的阴极的场发射特性的不同。另外,电泳的实验条件也会对沉积的阴极的场发射性能和形貌产生影响。在不同电泳直流电压条件下,碳管薄膜的密度分布和厚度不同,呈现出不同的场发射能力,结果表明当电压值在25V时可以得到性能最佳的场发射阴极。     

A two electron gun technique for the measurement of secondary emission characteristics of a variety of materials

A new technique and apparatus are described whereby the secondary emission ratio of a variety of materials can be measured. The experimental setup employs two electron guns in a demountable vacuum system and associated electronics. The system, which operates at a pressure of about 5 × 10^-7torr, has the advantage of taking data under steady-state conditions rather than employing pulsing techniques. Conductors, semiconductors, and dielectrics can be tested in the demountable. The principal features of this technique are 1) use of a flood electron gun to place the target surface at some fixed voltage, and 2) the use of an amplitude modulated probing electron beam and a narrow-band amplifier centered at the probing beam modulating frequency, to measure the collected probing current at the target. Secondary emission measurements on semiconductors are described for primary energies from zero through first crossover to approximately 50 eV above maximum. Modification of the system to enable measurements up to 10 kilovolts is also explained. Advantages of this apparatus as an important laboratory tool for the measurement of the secondary emission characteristic of materials for use in camera tubes, image converters, storage tubes, electron multipliers, and other devices, are emphasized.     

Influence of AlGaN deep level defects on AlGaN/GaN 2-DEG carrierconfinement

We have used low energy electron-excited nanoscale luminescence spectroscopy (LEEN) to detect the defects in each layer of AlGaN/GaN HEMT device structures and to correlate their effect on two-dimensional electron gas (2-DEG) confinement. We investigated AlGaN/GaN heterostructures with different electrical properties using incident electron beam energies of 0.5 to 15 keV to probe electronic state transitions within each of the heterostructure layers. AlGaN heterostructures of 25 nm thickness and nominal 30% Al concentration grown on GaN buffer layers on sapphire substrates by plasma-assisted molecular beam epitaxy exhibited a range of polarization-induced electron densities and room temperature mobilities. In general, the spectra exhibit AlGaN band edge emission at ~3.8 eV or ~4.0 eV, GaN band edge emission at ~3.4 eV, yellow luminescence (YL) features at 2.18 eV and 2.34 eV, and a large emission in the infrared (<1.6 eV) from the GaN cap layer used to passivate the AlGaN outer surface. These heterostructures also show high strain in the 2 nm-thick GaN layer with evidence for a Franz-Keldysh red shift due to piezoelectric charging. The LEEN depth profiles reveal differences between the structures with and without 2-DEG confinement and highlight the importance of AlGaN defects in the near 2-DEG region