钡钨阴极用大电流低蒸发发射物质的研究

采用不同工艺制备了浸渍钡钨阴极用的铝酸盐(612),并对其发射性能进行了测试,结果表明,采用二氧化碳烧结的发射物质发射性能最好.利用飞行时间质谱(ToFMS)测试了真空本底、浸渍阴极蒸发物的成分.研究了阴极蒸发速率与阴极温度的关系.比较了不同工艺制备的铝酸盐(612)蒸发速率的大小.     

M型扩散阴极用新型含锶低蒸散发射活性材料

聚焦真空器件用M型(Magic)阴极的蒸发性能,采用共沉淀法将Sr元素掺入阴极发射活性材料中,研究发射活性材料成分差异对阴极蒸发性能及发射性能的影响。研究结果显示,相同的制备及测试条件下,浸渍了新型含锶发射活性材料的M型阴极的蒸发速率显著下降,两种新型发射活性材料(AM1#和AM2#)浸渍的阴极样品的蒸发率在1060℃测试时,较常规阴极的蒸发率分别下降了49.95%和71.87%;在1100℃测试时,蒸发率与常规M型阴极相比,分别下降了40.27%和61.45%,与此同时,两种含锶的新型阴极发射电流密度仍能保持较高水平。Sr元素的掺入量对阴极的蒸发性能和发射性能均有明显影响,阴极样品的活性材料蒸发率和脉冲发射电流密度均随Sr含量的升高而降低。     

阴极蒸发动态测试研究

为了实现阴极蒸发定量测量,本文发展了一种基于石英晶体振荡原理的动态测试方法.研究表明,在选用高质量石英晶振片和对其进行强制冷却的情况下,既使晶振片近距离承受阴极的高温热辐射,晶振片频率降低趋势仍与阴极蒸发物增加的趋势保持良好的一致性,将单位时间的频率降低量代入公式计算,便可获得阴极蒸发的动态速率.与静态方法相比,这一方法可以提供阴极在蒸发之初的关键信息,因而可以更好地用于指导低蒸发覆膜钡钨阴极的制备.     

声场强化溶液蒸发的效果及机理

声场效应对溶液蒸发过程实验表明,声场促进溶液的蒸发,不同的声场作用参数和不同的温度,影响效果不同,溶液蒸发效率提高2％-6％,平均效率提高达4％以上。对水．乙醇以及苯．乙醇二组分溶液的超声蒸发动力学过程进行了分析,表明蒸发速率随时间的关系表现出线性的关系,两组分之间的体积百分比越接近,蒸发速率随时间越容易表现出线性的变化关系。通过液气两相平衡、成核和挥发等过程的分析．认为声场强化溶液蒸发的作用机理是声场具有“空化效应”。声场降低溶液的表面张力,从而降低了成核势垒．促进了液体内部的能量交换。增加了汽化成核几率,使溶液蒸发过程得以强化。     

真空条件下含银铅锑多元合金中锑的蒸发行为研究

根据真空冶金原理,以选择性分离银锑为目的,采用真空蒸馏法研究含银铅锑多元合金在真空(5～25 Pa)的条件下蒸馏过程中Sb的蒸发行为,考察蒸馏温度、蒸馏时间、多元合金中其它组元对锑蒸发的影响;并测定了不同温度下Sb元素的蒸发速率.实验结果表明:随着蒸馏温度的升高及恒温时间的延长,Sb的蒸发量和挥发率均增大.X射线衍射分析表明,蒸发物中锑为元素Sb,残留物中Cu与Sb形成化合物Cu2Sb及Cu10Sb3,Ag与Sb生成Ag3Sb,阻碍部分Sb的彻底蒸发.结合Sb元素的蒸发机制,根据实验结果计算得出Sb元素的蒸发速率为15.169～18.066g·cm-2·h-1.     

激光蒸发薄膜钪系阴极的研究

利用现代激光蒸发薄膜沉积技术，完成了Ｓｃ２Ｏ３＋Ｗ薄膜的沉积实验研究，并应用于薄膜型钪系阴极的研制。初步实验表明，这一方法具有稳定、易控、省时、省料和工艺重复性好的优点。所研制的阴极显示了优异的发射性能和良好的激活与耐高温特性。     

激光蒸发薄膜钪系阴极的研究

利用现代激光蒸发薄膜沉积技术，完成了Sc2O3＋W薄膜的沉积实验研究，并应用于薄膜型钪系阴极的研制。初步实验表明，这一方法具有稳定、易控、省时、省料和工艺重复性好的优点。所研制的阴极显示了优异的发射性能和良好的激活与耐高温特性。     

钛氧化物的蒸发特性

试验以Ti2O3、Ti3O5和TiO2作为初始膜料，在ZZS7OO—6／G型真空镀膜机上采用O^2-离子束辅助蒸发制备氧化钛薄膜。用XRD检测方法确定各种膜料和薄膜的相成分，并全面的分析了各种膜料的蒸发特性和薄膜；用分光光度计测量薄膜的透射率，并分析薄膜的光学性能。试验表明，在采用Ti2O3、Ti3O5和TiO2作为蒸发制备氧化钛薄膜时，在钛的氧化物中存在Ti3O5固态同一蒸发相；各种膜料在蒸发时，发生分解，熔池中的物质的成分逐渐转变并晟终完全成同一蒸发相成分。     

金属蒸发速率Langmuir公式的修正及金属镝、铽、铝蒸馏规律的实验研究

运用气体分子碰撞模型,研究了实际真空蒸馏金属的蒸发速率,对分子蒸馏状态下导出的金属蒸发速率Langmuir公式进行修正,并用金属镝、铽及铝做蒸馏蒸发速率实验研究,其蒸馏规律与修正后的Langmuir公式相符合,这一结果对蒸馏法制备高纯稀土金属具有实用价值,同时对探索其它金属蒸馏规律具有指导意义。     

电子束熔炼冶金级硅中杂质钙的蒸发行为

通过双枪电子束熔炼炉熔炼冶金级硅,主要研究了在一定熔炼功率不同熔炼时间下,杂质Ca含量的变化及其蒸发行为,讨论了杂质Ca含量与Si剩余率的关系。实验结果表明,熔炼初期杂质Ca含量显著降低,随着熔炼时间的延长,下降趋势逐渐减缓。在硅熔体表面2133K温度下,杂质Ca的自由蒸发反应遵循一级反应速率方程。杂质Ca的总传质系数为2.64×10-5m/s,并且杂质Ca从熔体内部迁移到硅熔体/气相界面层是其蒸发过程的速率控制步骤。     

Electrical properties of evaporated polycrystalline Ge thin-films

Electrical properties of Ge thin films evaporated on Si₃N₄ CVD-coated Si substrate were improved by introducing a heat treatment after the deposition of Ge films. Evaporation conditions were optimized by changing the substrate temperature and deposition rate, and then, heat treatment was performed. At substrate temperatures during the evaporation lower than 300 °C and higher than 400 °C, deposited films were amorphous and polycrystalline, respectively. At substrate temperatures lower than 400 °C, Ge films were evaporated without degrading the surface roughness. The Hall mobility of films evaporated at room temperature increased with increasing the substrate and heating temperature and showed about 400 cm² V⁻¹ s⁻¹ for the hole concentration of 4 × 10¹⁷ cm⁻³ at the heating temperature of 900 °C. This value was almost comparable to that of p-type Ge single crystal.     

Ion beam assisted texturing of polycrystalline Y2O3 films deposited via electron-beam evaporation

Ion-beam assisted deposition of polycrystalline Y₂O₃ films using e-beam evaporation was investigated. For growth on non-crystalline substrates, low temperature growth yields randomly oriented polycrystalline material. At elevated temperature, surface energy anisotropy yields a (111) uniaxial texture. For film deposition with irradiation from an Ar ion beam, the out-of-plane texture remained (111) in orientation. The incident Ar ion beam induces an in-plane alignment of the Y₂O₃ films that is relatively broad. A six-fold symmetry in the out-of-plane X-ray diffraction phi-scans was observed for the (111) textured Y₂O₃ films, indicating a multi-variant in-plane texture and suggesting anisotropic damage along both the (110) and (100) projections. The lack of a sharp, single variant in-plane texture with ion beam irradiation is consistent with the relatively weak bond strength in Y₂O₃.     

Epitaxial growth of gallium nitride by ion-beam-assisted evaporation

The epitaxial growth of gallium nitride thin film was obtained on the inclined Si(111) substrates by the process of ion-beam-assisted evaporation (IBAE) at the low temperature of 500 °C. The film composition determined by Rutherford backscattering spectrometry shows that the synthesized film is a stoichiometric nitride. The epitaxial quality of GaN film is enhanced by minimizing the bombardment-induced film damage by decreasing the ion flux. However, the crystallinity of the GaN film becomes very poor when the ion flux is not sufficient to densify the film. The optimum flux ratio of N⁺₂ to Ga and the energy of incident N⁺₂ ions for the epitaxial growth were found to be 3.4 and 50 eV, respectively. The GaN film deposited on the 4 °-inclined Si (111) with respect to substrate surface shows much better crystalline quality compared with that on the 0 ° inclined Si(111) due to many stable nucleation sites. A thin amorphous layer exists at the interface between GaN and Si(111) substrate and acts as a buffer zone enabling the subsequent epitaxial growth of GaN by relaxing the large misfit strain (23%) in the early stage of film growth. The epitaxial GaN film shows an orientational relation with the Si(111) substrate.     

Wetting of polycrystalline MgO by molten Mg under evaporation

The concomitant wetting and evaporation behaviors of molten Mg on polycrystalline MgO surfaces were studied at temperatures 973–1173 K in a controlled Ar atmosphere using an improved sessile drop method. Representative wetting modes were identified by correlating contact angle with contact diameter and drop height. The intrinsic wettability in this nonreactive system can be characterized by the initial contact angles obtained in better precision from solution to a diffusion model. In addition, the excess free energy stored in the system and the potential energy barrier opposing the movement of the triple line were evaluated to account for the distinct “stick-slip” behavior.     

Size effect on evaporation temperature of nanocrystals

Based on our model for size-dependent cohesive energy, the size-dependent evaporation temperature of nanocrystals has been modeled without any adjustable parameter. The model predicts a decrease of the evaporation temperature of nanocrystals with decreasing size. The model predictions are in good agreement with available experimental results for Ag, Au and PbS nanocrystals.     

Fast patterning of poly(methyl methacrylate) by a novel soft molding approach and its application to the fabrication of silver structures

A novel single-step approach for the fabrication of poly(methyl methacrylate) structures by soft molding of a 5 wt% solution in acetone is reported. The use of a low weight solution and of a solvent with high volatility ensures a very fast patterning, down to 10 s. In addition, the process is extremely simple and cost-effective, since just one elastomeric mold is needed, and areas as large as 1 cm² were patterned uniformly and defect-free. The process was applied to the fabrication of silver structures by silver deposition via electroless plating or evaporation followed by poly(methyl methacrylate) removal. Structures of various shapes and sizes, with dimensions in the micrometer and submicrometer range were successfully fabricated, showing the versatility of the process. This silver patterning process is particularly well suited for applications in microelectronics and optoelectronics, such as the fabrication of transparent electrodes for solar cells and displays, manufacturing of metal etching masks and wiring of printed circuits.     

冷却除湿机的最佳设计参数及实例的分析

本文介绍了除湿机的工作原理，分析了最佳参数的确定及实例分析。     

Capillary-driven assembly of ZnO nanowire arrays into micropatterns

The vertically aligned ZnO nanowire arrays prepared by vapor transport process can be assembled into complex micropatterns under capillary force. The deflection of the flexible ceramic nanowire is closely related to the liquid tension coefficient, mechanical and structural properties of the ZnO nanowires. The bended nanowires are adhesive together because the solid adhesion energy is sufficient to withstand the restoring elastic force of the deformed nanowires. The size of the bundling pattern can be controlled by varying the aspect ratio of the nanowire. The deflection of the ZnO nanostructure composed of a nanowire and a base is multifarious.     

气相合金化制备镁锌二元合金的研究

通过对粗镁、粗锌同时蒸发产生的高温金属蒸气流,经高温下的气态混合和300~350℃冷凝后得到较纯净的镁锌二元合金,并对不同时间段的冷凝产物进行显微组织和能谱分析,其结果表明:冷凝产物的组织不同于传统凝固态组织,冷凝初期形成了细长的柱状晶;且随着时间的延长,发生了元素间的扩散,柱状晶局部熔断,出现低熔点的固溶体,在随后的冷却过程中,形成了圆整度较好的α-Mg固溶体以及细小的Mg_7Zn_3化合物与α-Mg的共晶体组织。     

Wetting and evaporation behaviors of molten Mg–Al alloy drops on partially oxidized α-SiC substrates

The wetting and evaporation behaviors of Mg–Al alloys over a full composition range on partially oxidized polycrystalline α-SiC substrates were studied in a flowing Ar atmosphere using an improved sessile drop method. The time dependence of the changes in contact angle and drop geometry was monitored and representative wetting stages were identified. The initial contact angles at 1173 K were 100° for pure Al and 76° for pure Mg, with the maximum value of 106° for the 7.6 mol.% Mg–Al alloy. The interfacial reaction and the evaporation of Mg led to the decrease in the apparent contact angle in the spreading stage and their respective contribution was evaluated. After the pinning of the triple line, the decrease in the contact angle resulted from the diminishing drop volume as a consequence of the Mg evaporation. The effects of Mg concentration on the wetting and evaporation behaviors were discussed. A mechanism for the time-dependent diminishing drop volume was proposed in light of the competition between the Mg evaporation and its diffusion from the drop bulk to the surface. Finally, the interfacial reaction was analyzed based on thermodynamic considerations.