Influences of grain size and microstructure on optical properties of microcrystalline diamond films

Microcrystalline diamond(MCD)films with different grain sizes ranging from 160 nm to 2200 nm are prepared by using a hot filament chemical vapor deposition(HFCVD)system,and the influences of grain size and structural features on optical properties are investigated.The results show that the film with grain size in a range of 160 nm–310 nm exhibits a higher refractive index in a range of(2.77–2.92).With grain size increasing to 620±300 nm,the refractive index shows a value between 2.39 and 2.47,approaching to that of natural diamond(2.37–2.55),and a lower extinction coefficient value between 0.08 and 0.77.When the grain size increases to 2200 nm,the value of refractive index increases to a value between 2.66 and 2.81,and the extinction coefficient increases to a value in a range of 0.22–1.28.Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located in a range of 1331 cm-1–1333 cm-1,the content of diamond phase increases gradually as grain size increases,and the amount of trans-polyacetylene(TPA)content decreases.Meanwhile,the sp2 carbon clusters content and its full-width-at-half-maximum(FWHM)value are significantly reduced in MCD film with a grain size of 620 nm,which is beneficial to the improvement of the optical properties of the films.

Studies on Thermal Conductivity of Diamond Film

Diamond films were prepared by electron-assisted chemical vapor deposition (EACVD) system, and the thermal diffusivities of the films with or without substrate were studied by use of photothermal deflection (PTD) technique. The results show that less non-diamond component and larger crystalline size result in higher thermal conductivity of CVD diamond film. The influence of substrate on the measurement of thermal conductivity of the film was investigated, and a simple two-layer heat conduction model is given to account for the influence and used to draw the thermal conductivity of the film from the effective thermal diffusivity of film/substrate system.

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.

Thermal conductivity of diamond/copper composites with a bimodal distribution of diamond particle sizes prepared by pressure infiltration method

The thermal conductivity of diamond/copper composites with bimodal particle sizes was studied. The composites were prepared through pressure infiltration of liquid copper into diamond preforms with a mixture of 40 and 100 pm-size diamonds. The permeability of the preforms with different coarse-to-fine volume ratios of diamonds was investigated. The thermal conductivity of the diamond/copper composites with bimodal size distribution was compared to the theoretical value derived from an analytical model developed by Chu. It is predicted that the diamond/copper composites could reach a higher thermal conductivity and their surface roughness could be improved by applying bimodal diamond particle sizes.

Study on the Properties of Diamond Films on Aluminum Nitride Ceramics

Diamond films were successfully synthesized on aluminum nitride(AlN) ceramic substrates by hot filament chemical vapor deposition(HFCVD) method. It is notices that the thermal conductivity of the diamond film/aluminum nitride ceramic(DF/AlN) composite has reached 2.04 W/cm·K, 73%greater than that of AlN ceramic. Compared with the measurement of scanning electron microscopy(SEM) and Raman spectroscopy, the influence of diamond films on the thermal conductivity of the composites was pointed out. The adhesion and the stresses of diamond films were also studied. The unusual stability and very good adhesion of diamond films on AlN ceramic substrates obtained are attributed to the formation of aluminum carbide.

The Characteristics of Thermal Conductivity for Diamond Film

Diamond can be applied in high technology and future industry areas due to its high hardness, high thermal conductivity, ultrawide band optical transmission range and excellent semiconducting characteristics. Specially, the high thermal conductivity of diamond is its most attractive property, since it can be used as a heat sink in high-power semiconductor devices and medium-wave oscillators. However, the

Molecular dynamics study on thermal conductivity of nano-scale thin films

A simple and effective model of heat conduction across thin films is set up and molecular dynamics simulations are implemented to explore the thermal conductivity of nanoscale thin dielectric films in the direction perpendicular to the film plane. Solid argon is selected as the model system due to its reliable experimental data and potential function. Size effects of the thermal conductivity across thin films are found by computer simulations: in a film thickness range of 2-10 nm, the conductivity values are remarkably lower than the corresponding bulk experimental data and increase as the thickness increases. The consistency between the approximate solution of the phonon Boltzmann transport equation and the simulation results ascribes the thermal conductivity size effect to the phonon scattering at film boundaries.

陶瓷基复合材料编织结构参数对气膜冷却效果影响研究

针对陶瓷基复合材料(CMC材料)在航空发动机高温部件中应用时的冷却需求,考虑到CMC材料内部非均质非均匀结构和热物性特征与均质金属材料的巨大差异,探究了CMC材料编织结构几何参数对气膜综合冷却效果的影响,研究中以三维五向编织CMC材料为例,建立了反映材料内部细观编织结构的平板气膜全尺寸计算模型,从细观纱线尺度引入各组分热物性参数,计算分析了不同编织角度和纤维束截面尺寸等几何特征参数对气膜综合冷效的影响规律。研究结果表明,纤维束由于导热系数相对较高成为平板内部的主要热量传输通道,编织角发生变化时纤维束方向也随之改变,进而影响材料内部热量传输通道及整体各向异性等效导热系数。本文计算工况下,在气膜孔下游0~10D (D为气膜孔直径)区域,编织角度为40°时气膜综合冷效相对较高;在远离气膜孔区域,气膜板的冷却效果随着编织角度的增大而减弱。纤维束截面尺寸的改变对气膜综合冷效的影响较小,但是随着纤维束截面尺寸的增加,平板内部温度更加均匀。

大尺寸金刚石激光闪射法热导率测试研究

为解决大尺寸金刚石热导率的测试问题,本文在耐驰LFA467激光闪射仪的基础上,设计了垂直模式和In-Plane模式的φ100 mm测试样品架,从理论分析和实际测试两方面证明了φ100 mm样品架的可行性。从理论分析结果得出,新样品架带来的样品边界条件的变化对测试结果影响不大。从实际测试结果来看,垂直模式和In-Plane模式的φ100 mm样品架的热导率比标准样品架的热导率分别高3.6%和6.5%,仍在可接受范围内。本文设计的φ100 mm样品架最大能够测试φ100 mm的样品,有助于保护样品的完整性,实现激光闪射法大尺寸金刚石热导率的无损测试。

Solid-phase Crystallization of Hydrogenated Amorphous Silicon on Glass Substrates

Amorphous silicon films prepared by PECVD on glass substrate have been crystallized by conventional furnace annealing and rapid thermal annealing(RTA), respectively. From the Raman spectra, X-ray diffraction and scanning electron microscope, it is found that the grain size is crystallized at 850℃ in both techniques. The thin film made by RTA is smooth and of perfect structure, the thin film annealed by FA has a highly structural disorder. An average grain size of about 30nm is obtained by both techniques.

利用快速热退火法制备多晶硅薄膜

为了制备优质的多晶硅薄膜,该论文研究了非晶硅薄膜的快速热退火(RTA)技术。先利用PECVD设备沉积非晶硅薄膜,然后把其放入快速热退火炉中进行退火。退火前后的薄膜利用X射线衍射(XRD)仪、Raman光谱仪及扫描电子显微镜(SEM)测试其晶体结构及表面形貌,利用电导率测试设备测试其暗电导率。研究表明退火温度、退火时间以及沉积时的衬底温度对非晶硅薄膜的晶化都有很大的影响。

贫氢富氩气氛下超纳米金刚石薄膜的生长(英文)

利用微波等离子气相沉积法在5%～20%的氢气浓度下,制备出了超纳米金刚石薄膜(UNCD)。利用扫描电子显微镜、XRD、表面轮廓仪及拉曼光谱研究了氢气浓度对超纳米金刚石薄膜的微结构、形貌、以及相组成的影响。结果表明,随着氢气浓度的增加,晶粒粒径及粗糙度都明显增加变大;在不大于10%的氢气浓度气氛下,可以发现晶粒粒径下降到6nm,甚至更低;即便氢气浓度达到20%,晶粒粒径仍然小于10 nm。讨论了在富氩气氛下沉积的UNCD的实验结果以及沉积机制。这种极其光滑的UNCD薄膜有望在医疗,声表面波器件以及微机电系统,尤其是在重载和恶劣环境下作为超级密封材料的应用。

纳米氧化锆涂层晶粒度与隔热性能的关系

将纳米热障涂层隔热性能与微观组织联系起来并进行定量描述的工作还处于起步阶段,采用纳米ZrO2团聚体粉末在不同的喷涂参数下制备了3种不同的纳米热障涂层,利用扫描电子显微镜、IA32定量金相分析软件、X射线衍射仪对其进行了观察和分析,并结合非稳态激光脉冲法与差示扫描量热仪测量了涂层的热导率。研究表明:涂层中同时存在柱状组织和纳米级等轴组织,并以柱状组织为主;随着喷涂参数的改变,二者的相对比例发生变化;纳米级等轴组织含量对涂层的平均晶粒度和热导率都有重要影响;随着涂层晶粒度的减小,热导率随之降低。

快速光热退火法制备多晶硅薄膜的研究

为了制备应用于太阳电池的优质多晶硅薄膜,研究了非晶硅薄膜的快速光热退火技术。先利用 PECVD 设备沉积非晶硅薄膜,然后放入快速光热退火炉中进行退火。退火前后的薄膜利用 X 射线衍射仪(XRD)和扫描电子显微镜(SEM)测试其晶体结构及表面形貌,用电导率设备测试其暗电导率。研究表明退火温度、退火时间对非晶硅薄膜的晶化都有很大的影响,光热退火前先用常规高温炉预热有助于增大多晶硅薄膜的晶粒尺寸和暗电导率。

黑色组织对直流电弧等离子体喷射金刚石自支撑膜光学、热学性能的影响

利用直流电弧等离子体喷射化学气相沉积法进行不同质量的金刚石厚膜的制备。金刚石膜用倒置荧光显微镜(OM)、高分辨电镜(HRTEM)、电子能量损失谱(EELS)、拉曼谱(Raman)进行表征,同时测量了不同质量金刚石膜的红外透过率和热导率。研究结果表明,黑色组织主要是金刚石膜中的夹杂物,成分主要是非晶碳和杂质氮。对于光学级透明金刚石膜,具有很高的红外透过率和热导率,黑色组织的存在明显降低了金刚石膜的质量,对金刚石膜的红外透过率和热导率的影响非常显著。

纳米Pt膜的晶粒尺寸及其对热导率的影响

采用电子束-物理气相沉积法(EB-PVD)制备了6个厚度为15-62 nm的铂薄膜,研究了纳米薄膜的晶粒尺寸及其对热导率的影响规律．当薄膜厚度小于30 nm时,晶粒平均尺寸接近于薄膜的厚度;晶粒尺寸随着薄膜厚度的增加而增大并趋于定值;当薄膜厚度大于30 nm时,晶粒尺寸约为20 nm．受薄膜的表面和内部晶界的综合影响,铂纳米薄膜的热导率大大低于体材料的值,并且纳米薄膜的热导率随着薄膜厚度的增加而增大并趋于一个低于体材料热导率的值．

单晶硅薄膜法向热导率的分子动力学模拟

结合卫星“微型核”的特点,用分子动力学模拟的方法研究了硅晶体的热导率与其厚度的依变关系.采用Tersoff势能函数,用非平衡分子动力学方法（NEMD）研究了温度为400 K和500 K,厚度为2.715-10.86 nm的单晶硅薄膜的热导率.模拟结果表明：在温度为400 K和500 K时,薄膜热导率的计算值均随厚度的增加而增加,并显著小于体硅的实验值,在模拟范围内法向热导率与薄膜厚度呈近视线性关系.模拟结果表现出明显的尺寸效应.厚度为2.715 nm和8.145 nm的单晶硅薄膜的热导率随着温度的升高反而下降,且厚度越大,下降趋势越明显.

金刚石纳米薄膜法向热导率的分子动力学模拟

结合卫星“微型核”的特点,用分子动力学模拟的方法研究了金刚石晶体的热导率与其厚度和温度的依变关系。采用平衡分子动力学的方法(EMD)模拟了晶向(001)的金刚石纳米薄膜法向热导率;采用非平衡分子动力学(NEMD)方法模拟了晶向(111)的金刚石法向热导率。模拟的结果表明:金刚石纳米薄膜的法向热导率显著小于对应大体积晶体的实验值,并随着厚度的增加而增加;在模拟范围内法向热导率与薄膜厚度呈近似线性关系;薄膜热导率在模拟厚度为2.05334nm时随着温度的增加而增加;在模拟厚度为2.874676nm时,则随着温度的增加而下降。

南海东北部陆坡水合物钻探区海底表层热导率分布特征

依据获取的热导率测量数据和多波束数据所反映的海底地貌特征,分析了南海东北部陆坡天然气水合物钻探区表层沉积物矿物组成、粒级以及区域地貌特征对热导率分布的控制作用。研究结果表明,钻探区表层沉积物热导率平均值为(1.26±0.12)W/(m·k),相对于南海北部陆坡热导率背景偏高,沉积物组分中既含有陆源浊流沉积体中的高热导率矿物,也含有由甲烷等为主要气源的生物化学反应而形成的具有高热导率特性的碳酸盐。钻探区表层沉积物热导率区域细节分布具有非常明显的特征,2区和5区属于海台地貌,海底表层分布有大面积的碳酸盐结壳,由于底流的剥蚀作用导致沉积物粒级相对较粗,呈现高值热导率(1.32±0.06)W/(m·k)和(1.34±0.06)W/(m·k),并以此为中心向周缘逐级降低;位于海底海槽处的1区和8区则属于海槽地貌,海底表层易于接受来自海台的过滤沉积物,粒级相对较细但压实程度较低,呈现低值热导率,分别为(1.10±0.06)W/(m·k)和(1.01±0.06)W/(m·k)。钻探区表层沉积物热导率偏高主要受控于内生地质作用控制下高流体疏导所携带的化学组分,而热导率的非均匀分布则受控于外生地质作用诸如地貌地形变化导致的粒级分布状况。