单晶La_(0.2)Ce_(0.8)B_6的制备、表征及热发射性能研究

采用区域熔炼法制备了大尺寸、高质量多元稀土六硼化物La_(0.2)Ce_(0.8)B_6单晶体。结合X射线劳埃定向法对(110)和(310)晶面进行了定向,并系统研究了热发射性能。结果表明,当阴极温度为1 673,1 773和1 873K时(110)和(310)晶面最大电流密度分别为3.60,7.73,12.44A/cm~2和3.25,11.67,16.93A/cm~2。表明晶面间发射性能存在"各向异性"的特点。不同发射温度下的(110)和(310)晶面平均有效逸出功分别为2.85和2.80eV,表明单晶La_(0.2)Ce_(0.8)B_6具有良好的热发射性能。     

低逸出功Ce1-xGdxB6单晶体的制备及其热发射性能

以三元稀土硼化物Ce_1-xGd_xB₆为研究对象, 系统研究Gd掺杂对CeB₆阴极材料热发射性能的影响规律。采用放电等离子烧结结合光学区域熔炼法成功制备了高质量的Ce_1-xGd_xB₆(x=0~0.3)单晶体。借助360度Phi扫描单晶衍射仪对生长后的单晶进行了测试, 结果显示单晶质量良好。采用劳埃定向仪确定出(100)晶面, 并测试了该晶面在1673 K、1773 K、1873 K下的热电子发射电流密度。测试结果表明, Ce_0.9Gd_0.1B₆成分单晶体具有最优异的热发射性能, 在1873 K工作温度下, 4000 V电压条件下发射电流密度达到82.3 A/cm², 零场电流发射密度为24.70 A/cm², 平均有效逸出功为2.30 eV, 与相同条件下CeB₆单晶体热发射性能(热发射电流密度为78.2 A/cm², 零场电流发射密度为13.32 A/cm²)相比, 其具有更大的发射电流密度和更低的逸出功。因此, 采用该制备技术获得的Ce_1-xGd_xB₆单晶体具有良好的发射性能, 作为热阴极材料将会有更好的应用前景。     

[100]、[110]、[111]CeB_6单晶区熔生长与热电子发射性能研究

结合放电等离子烧结技术和光学区熔法成功制备了CeB_6单晶,采用X射线劳埃定向系统对单晶的晶向进行分析并精密切割,获得了[100]、[110]、[111]取向的CeB_6单晶,重点对[100]CeB_6单晶的结构和晶体质量进行系统表征和分析,结果表明获得的[100]CeB_6单晶晶体质量高,完整性好,半高宽仅为0.24o。热电子发射性能测试结果表明,随着阴极温度从1773 K增加到1973 K,[100]、[110]、[111]单晶的最大发射电流密度分别增加了2.6、3.2、1.5倍。[100]CeB_6单晶具有最好的热发射性能,在阴极加热温度T=1973 K、外加电压4 kV时,最大发射电流密度达到64.77 A·cm~(–2),有效逸出功为2.821 eV,其最大发射电流密度值高于目前文献已报道水平。实验结果显示,实验制备得到的[100]CeB_6单晶的热电子发射性能非常优异,具有良好的应用前景。     

悬浮区域熔炼法制备Ce1-xPrxB6单晶体及其热发射性能研究

以CeB₆和PrB₆粉末为原料, 采用放电等离子烧结结合悬浮区域熔炼法成功制备了晶体质量良好的多元稀土六硼化物Ce_1-xPr_xB₆(x=0.1、0.2、0.4)单晶体, 并系统研究了该系列单晶体(100)晶面热电子发射性能。结果表明: Ce_0.8Pr_0.2B₆单晶(100)晶面具有最好的热发射性能, 在1873 K, 最大电流发射密度达到66.07 A/cm², 比CeB₆单晶的电流发射密度提高约20%。此外, Ce_0.9Pr_0.1B₆、Ce_0.6Pr_0.4B₆单晶(100)晶面的热发射电流密度分别为65.81 A/cm²和65.31 A/cm²。Ce_0.8Pr_0.2B₆单晶(100)晶面的逸出功最低, 为2.61 eV, 其它单晶(100)晶面的逸出功在2.64~2.753 eV范围内。因此, Ce_1-xPr_xB₆多元稀土六硼化物单晶具有良好的发射性能和低的逸出功, 作为热阴极材料有很好的应用前景。     

多晶六硼化铈的制备及性能

采用放电等离子烧结技术(SPS)制备了高致密度CeB6多晶块体,考察了烧结工艺参数对多晶CeB6样品性能的影响。结果表明,随着烧结温度和烧结压力的升高,样品的致密度逐渐增大,力学性能显著提升。最佳烧结工艺参数为T=1 900℃,P=50 MPa,t=5 min,该工艺下多晶CeB6样品的致密度为95.88%,硬度为(19.37±0.65)GPa,抗弯强度为(124.82±6.24)MPa。分别在1 500,1 600,1 700℃条件下,测试了该样品的热发射电流密度,结果表明随着阴极温度的升高,多晶CeB6的最大热电子发射电流密度从3.14 A/cm2上升到18.45A/cm2,最小逸出功为3.05eV。     

一种浸渍式钨酸盐阴极的制备与发射性能

本文开展了活性物质为钨酸钡锶的浸渍式钨酸盐钡钨阴极的研究,主要包括钨酸钡锶盐的合成,浸渍式钨酸钡锶阴极的制备及其发射性能的测试。实验结果表明:在1400℃空气气氛中合成了主要相为Ba_3WO_6及Ba_2SrWO_6的钨酸钡锶盐。在1800℃浸渍该钨酸盐与氢化锆的混合物成功制备了浸渍式钨酸盐阴极,阴极发射性能测试结果表明在1050℃_(br)和1000℃_(br)时直流发射电流密度分别为7.54和4.30 A/cm~2。     

Ba掺杂对稀土硼化物GdB6结构,晶粒取向和热发射性能的影响（英文）

采用反应放电等离子烧结技术,以BaH2,GdH2纳米粉和B粉为原料,成功制备了多晶稀土硼化物(BaxGd1-x)B6(x=0,0.2,0.4,0.8).采用XRD、EBSD技术研究了掺杂元素Ba对GdB6晶体结构及晶粒取向的影响,并测量不同温度下的热发射性能.结果表明,所有烧结样品与传统烧结方法相比,具有高致密度(>97%)和很高的维氏硬度(2070 kg/mm2).GdB6在1873 K时,最大发射电流密度为11 A/cm2,该值远高于传统方法制备的电流密度值.随着Ba含量的增加,发射电流密度从11 A/cm2减小到2.25 A/cm2.     

MIM-MIS隧道结的发光光谱特性

对MIM(Au-SiO2-Al)和MIS(Au-SiO2-Si)隧道结的表面等离极化激元(surfaceplasmonpolariton,SPP)的激发与色散关系进行了讨论,对结的发光光谱进行了测试。结果表明其发射峰主峰位于610nm(2.00eV)～630mm(2.00eV)和700mm(1.77eV)～740nm(1.68eV)处,分别与Au/空气及Au/Al2O3(SiO2)界面SPP模式的激发相对应。结的发光过程应该是隧穿电子激发表面等离极化激元SPP,然后SPP与粗糙度耦合形成光发射。     

La1-xNdxB6阴极材料的制备及性能研究

以高纯金属La块、Nd块和B粉为原料, 通过蒸发-冷凝与放电等离子烧结(SPS)结合的技术成功制备了高纯高致密的多元稀土六硼化物La_1-xNd_xB₆块体材料。系统研究了La_1-xNd_xB₆材料的物相组成、力学性能、电阻率及热电子发射性能。结果表明, 采用上述工艺制备了高纯高致密的La_1-xNd_xB₆单相块体材料。烧结样品的维氏硬度和抗弯强度可达26.70 GPa和230.48 MPa。热电子发射性能测试结果表明, La_0.1Nd_0.9B₆成分块体具有最佳的热发射性能, 在1600℃, 4 kV外加电压条件下, 发射电流密度达到32.04 A/cm², 零场电流密度达到12.72 A/cm², 在同样条件下优于纯LaB₆和NdB₆块体材料的热发射性能。计算得到La_0.1Nd_0.9B₆在不同温度下的平均有效逸出功为2.72 eV, 表明适当比例的复合可以降低逸出功, 提高热电子发射性能。     

放电等离子体烧结(SPS)制备多晶La_(0.4)Pr_(0.6)B_6块体及其发射性能研究

采用氢直流电弧法制备了LaH2和PrH2粉末,然后利用放电等离子体烧结(SPS)技术制备了多晶的La0.4Pr0.6B6致密块体.系统分析了烧结温度对样品微观结构及性能的影响,研究结果表明:烧结温度高于1350℃时可形成La0.4Pr0.6B6纯相,且样品致密度随着烧结温度的升高而增加.所制备材料的密度、维氏硬度和抗弯强度的最大值分别达到4.82g/cm3、19.14GPa和225.13MPa;测试了40MPa、1400℃烧结样品的热电子发射性能,当阴极温度为1873K时最大发射电流密度为30.65A/cm2;利用Richardson直线法求出了所测试样品绝对零度时的逸出功φ0为2.165eV,并计算出了样品在不同加热温度时的有效逸出功φeff,其平均值为2.84eV。     

Use of thermionic emission for studying of point defects in NiO single crystals

The thermionic emission method has been used to study atomic point defects in NiO single crystals in the temperature range of 500 to 900 K and oxygen pressure range of 5×10^–2 to 5×10¹ Pa. The P _O2 ^1/n dependence of the thermionic emission has been observed and the n parameter increased from 4.25 to 4.80 with increasing temperature in the range of 500 to 900 K. The activation enthalpy of thermionic emission increased slightly from 1.0 to 1.2 eV with decreasing oxygen partial pressure in the range of 5×10¹ to 5×10^–2 Pa. This behaviour can be explained by the presence, in NiO single crystals under the above conditions, of the predominant singly ionized nickel vacancies and a small amount of the double ionized nickel vacancies with somewhat different energies of formation.     

Cathodoluminescence study of h– and c–GaN single crystals grown by a Na or K flux

Luminescence properties of hexagonal (h-) and cubic (c-) GaN freestanding single crystals were studied by means of cathodoluminescence spectroscopy. The h-GaN crystals of about 0.2–2 mm in dimension were synthesized at 750 °C by the reaction of Ga and N2 in a Na flux, while c-GaN crystals of about 0.3 mm or less in a K flux. The h-GaN showed rather strong band edge emission at room temperature compared with the crystal grown by using NaN3 as a nitrogen source. At 20 K, the band edge emission of h-GaN was split into four peaks. The main energy peak position was 3.478 eV, which was assigned as the A-free exciton emission. The energy position of the main peak of c-GaN was 3.268 eV. Assuming the binding energies of excitons in h- and c-GaN as 25 and 26 meV, respectively, the energy difference of bandgap between h-and c-GaN is estimated to be 209 meV. Since these crystals are free from strain from the substrates, the peak energies are reliable for the intrinsic GaN crystals. The full widths at half maximum of the emission of c-GaN were much broader than those of h-GaN, suggesting that the cubic phase is much defective compared with the hexagonal one.     

Sr掺杂对12CaO·7Al2O3电子化合物电输运及发射性能的影响

12CaO·7Al₂O₃电子化合物(C12A7:e ^-)是一种具有低工作温度和低逸出功等优点的新型电子化合物阴极材料。通过高温固相反应结合放电等离子烧结制备Sr掺杂(Ca_1-xSr_x)12A7 (0≤x≤0.05)块体, 并在1100 ℃采用Ti颗粒还原20 h成功制得电子化合物(Ca_1-xSr_x)12A7:e ^-。第一性原理计算结果表明, (Ca_1-xSr_x)12A7:e ^-与C12A7:e ^-相比, 框架导带下移, 费米能级附近态密度增加, 这将有利于电输运和发射性能的优化。室温电输运测试结果表明, Sr掺杂有利于C12A7:e ^-电输运性能的优化, 其中(Ca_0.96Sr_0.04)12A7:e ^-样品在室温下具有最高电导率(1136 S/cm)以及最高载流子浓度(2.13×10 ²¹ cm ^-3), 与相同条件下制备的C12A7:e ^-样品相比, 载流子浓度提高近2个数量级, 表明Sr掺杂可以有效缩短制备C12A7:e ^-的制备时间。热电子发射性能测试结果表明, 随着Sr掺杂量的增加, 热电子发射性能逐渐提高, 其中(Ca_0.96Sr_0.04)12A7:e ^-样品具有最佳的热发射性能, 在1100 ℃外加电压3500 V时, 发射电流密度达到1.45 A/cm ², 零场发射电流密度达到0.74 A/cm ², 理查生逸出功降低至1.86 eV。     

Conduction mechanism of metal-free phthalocyanine single crystals as a function of temperature

Metal-free phthalocyanine (H₂Pc) single crystals grown by vacuum sublimation were investigated for their conductivity (both in dark and light). The investigations consisted of dark- and photo-current variations with (i) applied electric field and (ii) temperature. The applied electric field ranged from 0·8 kV/cm to 6 kV/cm. The temperature range was from 300°K to around 570°K. The crystals were found to be photoconductive. Based on activation energies calculated from photoconductivity due to temperature dependence, an energy level scheme for H₂Pc single crystals is proposed. The model consists of two trapping levels within the forbidden gap — one at 0·4 eV below the conduction band edge from which electrons are thermally excited into the conduction band and the other acts as recombination centre at 0·3 eV above the valence band edge. The band gap is calculated to be 1·4 eV. Comparative study of the proposed model with that of earlier investigations on the same crystals of the H₂Pc is in good agreement, thereby indicating that H₂Pc is thermally stable even at relatively higher temperature as semiconductor.     

Quantitative Experimental Analysis of Schottky Barriers and Poole–Frenkel Emission in Carbon Nanotube Devices

In this paper, we investigated carbon nanotube FETs (CNT FETs) utilizing semiconducting single-walled CNTs (SWCNTs). Multiple devices, each of different metal source and drain contacts, were fabricated on a single SWCNT. Over specific temperature regimes, transport properties of the devices were found to be consistent with the Bethe theory of thermionic emission for Schottky contacts, and the Poole–Frenkel emission was dependent on the device position. As was expected, transport from thermionic emission over the barrier was found to be the dominant mechanism. Barriers of 25–41 meV were present, as found by activation energy analysis for temperatures ranging from 20 to 300 K for the devices. A Schottky diode was also fabricated on a separate nanotube using an ohmic contact at the Pd source and a Schottky contact for the Ag drain electrode. Assuming the same physical assumptions for an Si semiconductor device, the results indicate an ideality factor greater than 2, Schottky barrier of $sim$0.37 eV, and image charge lowering of $sim$0.1 eV.      

低成本溶液法制备厘米级Cs3Cu2I5单晶及其闪烁发光性能

近年来, 拥有高发光量子效率的低维钙钛矿/类钙钛矿结构金属卤化物在辐射探测领域展现出潜在的应用前景。本工作利用反溶剂扩散法生长了高光学质量的厘米级尺寸零维结构Cs₃Cu₂I₅单晶, 并系统研究了其光学吸收、透过、光致激发和发射、时间分辨光致发光、X射线辐照发光、余辉、热释光以及伽马射线探测性能。溶液法制备的Cs₃Cu₂I₅晶体的光学带隙为3.68 eV。在X射线激发下, Cs₃Cu₂I₅单晶的蓝光发射峰位于448 nm, 来源于自陷激子发光。闪烁衰减时间主分量为947 ns (96%)。Cs₃Cu₂I₅单晶的余辉水平与商用BGO晶体相当。此外, 该晶体作为伽马射线闪烁体也表现出29000 photons/MeV的高光产额, 与熔体法制备的Cs₃Cu₂I₅晶体闪烁性能相当。本研究证实了低成本制备高性能Cs₃Cu₂I₅闪烁晶体的可行性。     

钨酸铅晶体的生长及其闪烁性的研究

采用提拉法生长出直径 2 0 -2 5mm,长 2 5-3 0 mm优质 Pb WO4及 La3 +、Mg2 +、Mo6+和 Bi3 +掺杂 Pb WO4晶体。测试了晶体的 X射线衍射谱、透射光谱、激发发射光谱、光产额、抗辐照性能和发光衰减时间。总结并解释了掺杂对 Pb WO4晶体性能的影响以及氧退火对晶体抗辐照性能的影响 ,探讨了掺杂改善晶体闪烁性能的可能性。