聚变堆第一壁连续W/Cu 梯度材料的热工性能优化

针对不同体积分布指数p的W/Cu连续功能梯度材料的偏滤器第一壁结构,采用有限元软件计算了 8MW•m⁻²稳态运行热加载以及等离子体破裂条件下1GW•m⁻²热流冲击下的力学响应。相同稳态加载条件下,W/Cu 连续功能梯度材料的最优分布指数与分层梯度材料存在较大差异,其最优等效应力比分层梯度材料要小26%,表现出更优异的性能。在热冲击响应过程中,连续梯度W/Cu材料塑性损伤随p值不同也存在较大变化,其最优p值与其稳态运行时热应力最优p值存在一定差异,从第一壁应用条件考虑,应综合选取,最佳p值在1.2附近。综合来看,连续梯度W/Cu材料具有更连续变化的热物理属性及力学性能,在聚变堆第一壁结构设计中具有更大的应用潜力。     

Cu_2O/C_(60)梯度薄膜的制备

功能梯度材料应用前景广阔 ,特别在 ICF研究中 ,梯度靶是一种重要的基础 -基准靶。以Cu2 O和 C60 为原料 ,用真空蒸镀法在石英基底上制备了 Cu2 O/C60 梯度薄膜 ,并用 XPS,AFM,紫外光谱仪对其成份分布、表面形貌、紫外吸收谱进行了测试。测量结果表明 ,薄膜的组成沿厚度方向呈连续梯度变化 ,符合梯度功能材料的变化规律     

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介绍了目前解决W/Cu连接界面缓解热应力的方法——添加适配层。在对不同适配层进行分析后,选出最佳W/Cu适配层,再对W/Cu适配层进行结构优化分析,得出选用W/Cu功能梯度材料作为适配层具有足够的结合强度,而且良好的导热性能能有效地缓解热应力。此外,重点阐述了目前成功的制备的W/Cu功能梯度材料用作W/Cu第一壁材料的适配层的常用方法。最后,对W/Cu功能梯度材料用作适配层解决W/Cu第一壁材料连接界面的问题做出了总结和展望。     

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针对不同体积分布指数p的W/Cu连续功能梯度材料的偏滤器第一壁结构,采用有限元软件计算了8MW.m?2稳态运行热加载以及等离子体破裂条件下1GW.m?2热流冲击下的力学响应。相同稳态加载条件下,W/Cu连续功能梯度材料的最优分布指数与分层梯度材料存在较大差异,其最优等效应力比分层梯度材料要小26%,表现出更优异的性能。在热冲击响应过程中,连续梯度W/Cu材料塑性损伤随p值不同也存在较大变化,其最优p值与其稳态运行时热应力最优p值存在一定差异,从第一壁应用条件考虑,应综合选取,最佳p值在1.2附近。综合来看,连续梯度W/Cu材料具有更连续变化的热物理属性及力学性能,在聚变堆第一壁结构设计中具有更大的应用潜力。     

金刚石材料对螺旋线慢波组件散热性能的影响

螺旋线慢波组件的散热性能是影响行波管输出功率、工作稳定性及可靠性的重要因素. 金刚石材料具有极高的导热性能,将金刚石材料应用于螺旋线慢波组件的制备,可以在一定程度上改善组件散热性能. 本文计算模拟分析了沉积金刚石薄膜的夹持杆、沉积金刚石薄膜的螺旋线以及金刚石夹持杆对慢波组件散热性能的影响. 结合实验和模拟对比研究,使计算机仿真与实验测试紧密关联,提高了计算机模拟研究准确性,为金刚石材料在慢波组件中的应用提供了重要的参考依据. 关键词： 螺旋线行波管 慢波组件 散热性能 金刚石     

Cu/La2NiO4电接触材料的制备及电弧烧蚀性能研究

解决铜基触点材料因易氧化而生成不导电物质导致触点失效的关键在于提高材料的导电性能,基于导电陶瓷La₂NiO₄因其具有导电性能,论文采用溶胶凝胶法制备获得了导电陶瓷La₂NiO₄粉体,用粉末冶金法制备出致密Cu/La₂NiO₄复合材料并进行微观形貌观察和物相分析。经过电弧烧蚀后,观察表面烧蚀形貌,探讨氧化层的微观组织,并进行温升测试。研究结果表明,电弧烧蚀后的Cu/La₂NiO₄复合材料表面有裂纹并且触点表面有多种侵蚀形貌特征并存,氧化层可能因接触力的作用而脱落以提高导电性能。本论文的研究工作表明,采用铜掺杂导电陶瓷La₂NiO₄的方法,可以有效提高电触点材料电弧烧蚀后的导电性。     

一种适合微条气体室探测器的理想衬底材料

微条气体室(Micro-strip Gas Chamber,MSGC)探测器最严重的问题是电荷积累效应,通过选择合适的衬底材料可以有效的避免.为此,D263玻璃上沉积类金刚石(Diamond-like Carbon,DLC)膜来进行表面改性,从而制备DLC膜D/263玻璃双层结构作为MSGC衬底.拉曼光谱说明DLC膜是由sp³(σ键)和sp²(π键)杂化碳原子组成,属于电子导电型材料,并且沉积出的是一种高质量的DLC膜;I V曲线表明DLC膜改性后的样品具有非常稳定和理想的电阻率,其值在10⁹—10¹²Ω·cm间;C-F曲线显示改性后样品具有小而稳定的电容.DLC膜D/263玻璃的优良性能正是MSGC衬底的最佳要求,这种新型材料用作衬底将有效克服电荷积累效应和衬底不稳定性.     

亚表面异质缺陷对功能梯度材料表面温度场的影响

基于双曲型热传导方程,采用镜像法和波函数展开法,求解了含亚表面异质圆柱缺陷的半无限功能梯度材料的表面温度场,给出了功能梯度材料中热波散射的一般解.分析了亚表面异质圆柱缺陷的几何参数(如埋藏深度)和热物理参数(如导热系数、热扩散长度、热扩散率及热弛豫时间等)对功能梯度材料表面温度场的影响.温度波由调制的超短脉冲激光在功能梯度材料表面激发,异质圆柱缺陷表面的边界条件为导热边界.研究结果可望为功能梯度材料的红外热波无损检测、导热反问题提供计算方法和参考数据.     

退火处理对ZnS: Cu,Mn电致发光材料亮度的影响

ZnS系列电致发光已经在低亮度照明、液晶显示、汽车和航空仪表等领域得到广泛的应用.Mn、Cu是ZnS电致发光材料常用的激活剂,Mn²⁺在晶体中形成橙色发光中心,发光中心波长580nm;Cu⁺在晶体中不但形成发光中心,还形成发光所必需的Cu_xS,因此二者对发光亮度有明显的影响.由于ZnS:Cu,Mn橙色发光材料中的Mn掺杂量较大,影响了发光材料的内在结构,在灼烧过程中Mn化合物的其他成分还可能对发光材料的亮度产生了不利的影响,导致发光材料的亮度远低于蓝绿色材料.采用在退火过程中添加适量的Mn、Cu化合物,通过低温扩散的方式,使Mn²⁺均匀进入到ZnS晶格,获得了亮度较高的ZnS:Cu,MnACEL粉末材料.并对制备工艺中Cu、Mn含量、掺杂Mn化合物的形式、退火温度等对发光亮度的影响进行了讨论.实验中发现,在三种Mn化合物中(碳酸锰、乙酸锰、硫酸锰),以乙酸锰掺杂的材料亮度最高.得到Mn(以乙酸锰为添加物)的添加量为2%、Cu的添加量为0.1%、退火温度为700℃时,所制备的材料亮度最高.低温退火时掺杂Mn的材料亮度比常规材料的亮度高出1倍.     

基于二维材料MXene的仿神经突触忆阻器的制备和长/短时程突触可塑性的实现

兼具长时程可塑性与短时程可塑性的电子突触被认为是类脑计算系统的重要基础.将一种新型二维材料MXene应用到忆阻器中,制备了基于Cu/MXene/SiO_2/W的仿神经突触忆阻器.结果表明, Cu/MXene/SiO_2/W忆阻器成功实现了稳定的双极性模拟阻态切换,同时成功模拟了生物突触短时程可塑性的双脉冲易化功能和长时程可塑性的长期增强/抑制行为,其中双脉冲易化的易化指数与脉冲间隔时间相关. Cu/MXene/SiO_2/W忆阻器的突触仿生特性,归功于MXene辅助的Cu离子电导丝形成与破灭的类突触响应机理.由于Cu/MXene/SiO_2/W忆阻器兼具长时程可塑性与短时程可塑性,其在突触仿生电子学和类脑智能领域将会具有巨大的应用前景.     

The preparation and evaluation of graded multilayer ta-C films deposited by FCVA method

In this study, a series of graded multilayer ta-C films were investigated by varying their sublayer thickness ratios, in which each film sublayer was prepared at different substrate bias by filtered cathode vacuum arc (FCVA) method. The experimental results show that the graded multilayer film structure can effectively decrease the internal stress level of deposited ta-C film, and meanwhile the graded multilayer ta-C films still have high sp³ fractions. The applied substrate bias voltage and sublayer thickness ratio can apparently influence the microstructure characteristics and internal stress of the graded multilayer ta-C films. The graded multilayer ta-C film has larger sp³ fraction when applying a larger negative substrate bias voltage and having a thicker outer sublayer during the film deposition process. However, the internal stress in the as-deposited film also increases with larger thickness of the outer sublayer, and the optimal ratio of sublayer thicknesses is 1:1:1:1 for graded ta-C film with four sublayers.     

Thermal conductive performance of deposited amorphous carbon materials by molecular dynamics simulation

A series of diamond-like carbon (DLC) films with different microstructure were prepared by depositing carbon atoms on diamond surface with incident energy ranging from 1 to 100 eV. The thermal conductivity of the deposited films and the Kapitza resistance between the film and the diamond substrate were investigated. Results show that the average density, the average fraction of sp³ bonding and the thermal conductivity of the DLC films increase first, reaching a maximum around 20–40 eV before decreasing, while the Kapitza resistance decreases gradually with increased deposition energy. The analysis suggests that the thermal resistance of the interface layer is in the order of 10^?10 m²K/W, which is not ignorable when measuring the thermal conductivity of the deposited film especially when the thickness of the DLC film is not large enough. The fraction of sp³ bonding in the DLC film decreases gradually normal to the diamond surface. However, the thermal conductivity of the film in normal direction is not affected obviously by this kind of structural variation but depends linearly on the average fraction of sp³ bonding in the entire film. The dependence of the thermal conductivity on the fraction of sp³ bonding was analysed by the phonon theory.     

极化诱导实现AlGaN薄膜材料中的超高电子浓度(1020cm-3)掺杂

材料的载流子浓度和迁移率是影响器件性能的关键因素, 变温Hall测试结果证明杂质掺杂AlGaN中的载流子浓度和迁移率随温度 降低而减小.然而极化诱导掺杂的载流子浓度和迁移率不受温度变化的影响.以准绝缘 的GaN体材料作为衬底, 在组分分层渐变的AlGaN中实现的极化诱导掺杂浓度 仅仅在10¹⁷ cm^-3数量级甚至更低. 本研究采用载流子浓度为10¹⁶ cm^-3量级的非有意n型掺杂GaN模板为衬底, 用极化诱导掺杂技术在分子束外延生长的AlGaN薄膜材料中实现了高 达10²⁰ cm^-3 量级的超高电子浓度. 准绝缘的体材GaN半导体作衬底时, 只有表面自由电子作为极化掺杂源, 而非有意掺杂的GaN模板衬底除了提供表面自由电子外,还能为极化电场 提供更多的自由电子"源", 从而实现超高载流子浓度的n型掺杂.     

The protective properties of ultra-thin diamond like carbon films for high density magnetic storage devices

With the increase of magnetic storage density, the thickness of the protective diamond like carbon (DLC) film on the surfaces of head and disk is required as thin as possible. In this paper, the structure, mechanical properties and corrosion and oxidation resistance of ultra-thin DLC films are investigated. The ultra-thin DLC films were deposited by using filtered cathodic vacuum arc (FCVA) technique. The exact thickness of the ultra-thin DLC film was determined by high resolution transmission electron microscope (HRTEM). Raman analysis indicates that the ultra-thin DLC film presents ta-C structure with high sp³ fraction. In the wear test, a diamond tip was used to simulate a single-asperity contact with the film surface and the wear marks were produced on the film surface. The wear depths decrease with film thickness increasing. If the film thickness was 1.4 nm or above, the wear depth was much lower than that of Si substrate. This indicates that the ultra-thin DLC film with thickness of 1.4 nm shows excellent wear resistance. Corrosion tests in water and oxidation tests in air were carried out to investigate the diffusion barrier effect of the ultra-thin DLC films. The results show that the DLC film with thickness of 1.4 nm provides adequate coverage on the substrate and has good corrosion and oxidation resistance.     

Fabrication and characterization of freestanding ultrathin diamond-like carbon targets for high-intensity laser applications

Here, we report the fabrication of diamond-like carbon (DLC) thin films using pulsed laser deposition (PLD). PLD is a well-established technique for deposition of high-quality DLC thin films. Carbon tape target was ablated using a KrF (248 nm, 25 ns, 20 Hz) excimer laser to deposit DLC films on soap-coated substrates. A laser fluence between 8.5 and 14 J/cm² and a target to substrate distance of 10 cm was used. These films were then released from substrates to obtain freestanding DLC thin foils. Foil thicknesses from 20 to 200 nm were deposited using this technique to obtain freestanding targets of up to 1-inch square area. Typically, 100-nm-thick freestanding DLC films were characterized using different techniques such as AFM, XPS, and nano-indentation. AFM was used to obtain the film surface roughness of 9 nm rms of the released film. XPS was utilized to obtain 74 % sp², 23 % sp³, and 3 % C–O bond components. Nano-indentation was used to characterize the film hardness of 10 GPa and Young’s modulus of 110 GPa. Damage threshold properties of the DLC foils were studied (1,064 nm, 6 ns) and found to be 7 × 10¹⁰ W/cm² peak intensity for our best ultrathin DLC foils.     

Nanoindentation measurements on modified diamond-like carbon thin films

In the present study, we explored the effect of metallic interlayers (Cu and Ti) and indentation loads (5-20 mN) on the mechanical properties of plasma produced diamond-like carbon (DLC) thin films. Also a comparison has been made for mechanical properties of these films with pure DLC and nitrogen incorporated DLC films. Introduction of N in DLC led to a drastic decrease in residual stress (S) from 1.8 to 0.7 GPa, but with expenses of hardness (H) and other mechanical properties. In contrast, addition of Cu and Ti interlayers between substrate Si and DLC, results in significant decrease in S with little enhancement of hardness and other mechanical properties. Among various DLC films, maximum hardness 30.8 GPa is observed in Ti-DLC film. Besides hardness and elastic modulus, various other mechanical parameters have also been estimated using load versus displacement curves.     

Study of well adherent DLC film deposited on piezoelectric LiTaO3 substrate

A well adherent diamond-like carbon (DLC) film was deposited on piezoelectric LiTaO₃ substrate using PECVD by inserting SiO₂ interlayer. DLC film was characterized using Raman spectroscopy and AFM. Physical and mechanical properties were measured using XRR, ellipsometry, scratch test and nano-indentation. The DLC film exhibits the characteristics of hydrogenated amorphous carbon and a very smooth surface with a 0.25 nm RMS. Scratch test shows that critical load (L_c) is 18 N, which is good enough for applying DLC film to SAW device. The measured mass density, refractive index, hardness and Young’s modulus of DLC film deposited on LiTaO₃ are comparable to the reported values for hydrogenated amorphous carbon film, irrespective of substrates on which the films were deposited.     

The effect of nitrogen and oxygen plasma on the wear properties and adhesion strength of the diamond-like carbon film coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the PTFE substrates were modified with O₂ and N₂ plasma to enhance the adhesion strength of the DLC film to the substrate. The effect of the plasma pre-treatment on the chemical composition and the surface energy of the plasma pre-treated PTFE surface was investigated by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated PTFE.In the N₂ plasma pre-treatment, the XPS result indicated that defluorination and the nitrogen grafting occurred on the plasma pre-treated PTFE surface, and the water contact angle decreased with increasing the plasma pre-treatment time. In the O₂ plasma pre-treatment, no grafting of the oxygen occurred, and the water contact angle slightly increased with the treatment time. In the pull-out test, the adhesion strength of the DLC film to the PTFE substrate was improved with the plasma pre-treatment to the PTFE substrate, and N₂ plasma pre-treatment was more effective than the O₂ plasma pre-treatment. In the ball-on-disc test, the DLC film with the N₂ plasma pre-treatment showed good wear resistance, compared with that with O₂ plasma pre-treatment.     

Effect of H2 and O2 plasma etching treatment on the surface of diamond-like carbon thin film

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O₂) and hydrogen (H₂) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H₂ and O₂ was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H₂ plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O₂ plasma. The surface roughness of plasma etching-treated DLC with H₂ or O₂ was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O₂ plasma was hydrophilic as well as smooth.     

Hydrogenated diamond-like carbon film deposited on UHMWPE by RF-PECVD

In this work, investigations were conducted to analyze the properties of diamond-like carbon (DLC) film deposited on ultra-high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at a low temperature of 50 °C. Composition and structure of the films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Hardness and wettability of the film were tested. Tribological characterizations were carried out on a universal micro-tribometer, and reciprocating friction against ZrO₂ ball was adopted with 25% bovine serum as lubrication. Results show that DLC film was successfully deposited on UHMWPE surface by RF-PECVD and the sp³ content was about 20% in the film. The film increased the macrohardness of the substrate by about 42% and the wettability was improved too. Tribology test showed a higher friction coefficient but a much smaller wear volume after the deposition due to the surface roughening and strengthening.