硅油基底上受限金属薄膜自组装褶皱的原子力显微镜研究

利用喷雾装置在清洁载玻片上喷洒出各种尺寸(微米到毫米量级)的硅油滴,采用直流磁控溅射方法在硅油滴上沉积金属铬薄膜,研究了薄膜中由热应力引起的自组装褶皱.实验发现硅油滴上的铬薄膜受到油滴边缘的约束而具有受限的边界条件,其对褶皱的形貌具有很好的调控作用:褶皱呈垂直于边界的辐射状条纹;越靠近约束边界,褶皱的波长和振幅越小.褶皱的形貌特征还与薄膜厚度和硅油滴尺寸密切相关.随着膜厚的增加,褶皱在约束边界处首先形成,并逐渐扩展到油滴中心区域;相同尺寸油滴中心处的褶皱波长基本不变,而振幅随膜厚先增大随后减小.薄膜厚度相同时,随着油滴尺寸的增加,褶皱的波长和振幅都相应增加.进一步的研究表明:在沉积过程中,高能粒子的轰击和溅射源的热辐射导致硅油表面层的结构发生改变而形成聚合物层,在此基础上对褶皱的形貌特征和振幅演化给出合理的解释.     

基片下磁场磁控对溅射辉光及薄膜梯度的影响

溅射时在基片下方放置磁铁，让来自基片下方的磁场发挥磁控作用，以此来研究基片下磁场磁控溅射的方法.发现辉光形貌以及沉积的薄膜厚度分布均发生明显变化的同时，辉光的外形也随着外加磁铁直径的变化而变化.运用磁荷理论对空间磁场分布进行模拟，解释了辉光形貌变化的机理；运用沉积粒子在外加梯度磁场中运动理论解释了膜厚分布. 关键词： 磁控溅射 辉光 磁场模拟 膜厚梯度     

YBa_2Cu_3O_(7-δ)超导薄膜热解过程中表面形貌的形成规律及机理探讨

YBa_2Cu_3O_(7-δ)(YBCO)超导薄膜的表面形貌对于自身的超导性能起着至关重要的作用.低温热处理过程对于最终的YBCO超导薄膜的表面形貌有非常大的影响.我们研究了升温速率和气体流量对表面形貌的共同作用,发现以下规律:在高气体流量的作用下,当升温速率较低时,薄膜出现裂纹,提高升温速率,可得到光滑薄膜,进一步提高升温速率产生褶皱,直至出现裂纹与褶皱的共存态;在低气体流量下,升温速率较低时也能获得光滑的薄膜,而高升温速率则会导致薄膜褶皱.因此获得表面平整的薄膜,升温速率和气体流量必须匹配.结合在线实时观测的方式,观察了缺陷表面的形成温度及演化过程,给出了薄膜表面形貌与热处理条件关系的解释.原子力显微镜(AFM)粗糙度的测试结果与我们的解释吻合.     

低温制备微晶硅薄膜生长机制的研究

采用热丝化学气相沉积技术制备了一系列处于不同生长阶段的薄膜样品，用原子力显微镜系 统地研究生长在单晶硅衬底和玻璃衬底上薄膜表面形貌的演化.按照分形理论分析得到：在 玻璃衬底上的硅薄膜以零扩散随机生长模式生长；而在单晶硅衬底上，薄膜早期以有限扩散 生长模式生长，当膜厚超过某一临界厚度时转变为零扩散随机生长模式.岛面密度与膜厚的 依赖关系表明，在临界厚度时硅衬底和玻璃衬底上的岛面密度均出现了极大值.Raman谱的测 量证实，玻璃衬底上薄膜临界厚度与非晶/微晶相变之间存在密切的关系.不同的衬底材料直 接影响反应 关键词： 生长机制 微晶硅薄膜 表面形貌 热丝化学气相沉积     

基于液相AFM及干涉频谱法的多孔氧化铝薄膜在线测量系统研究

介绍了多孔氧化铝薄膜(PA)厚度在线测量系统的工作原理、系统结构及独特性能。在白光(宽光谱)照射下,薄膜的上表面和下表面反射的两路光线发生干涉,产生了携带薄膜光学厚度信息的反射光谱。同时,利用液相原子力显微镜(AFM)实时获得的PA膜的表面形貌信息,根据膜系统的Maxwell-Garnette有效介电常数理论,经相干势近似计算得到薄膜的有效折射率,进而得到此时PA膜的物理厚度。使用该系统对PA膜氧化制备过程进行了在线扫描和膜厚测量试验,成功的获得了PA样品的实时表面形貌图像,得到样品的孔隙率和有效折射率。并根据样品反射光谱,利用反射干涉频谱法计算得到氧化150和180 min时,PA膜厚分别为5.35和6.25 μm。本系统具有测量简便、实时性好、无损及测量精确的特点,在实时测量和监控膜厚的同时可获得样品的表面形貌、孔隙率、有效折射率等信息。     

非聚焦电子束照射SiO2薄膜带电效应

采用考虑电子散射、俘获、输运和自洽场的三维数值模型, 模拟了低能非聚焦电子束照射接地SiO₂薄膜的带电效应. 结果表明, 由于电子的迁移和扩散, 电子会渡越散射区域产生负空间电荷分布. 空间电荷呈现在散射区域内为正, 区域外为负的交替分布特性. 对于薄膜负带电, 电子会输运至导电衬底形成泄漏电流, 其暂态过程随泄漏电流的增加趋于平衡. 而正带电暂态过程随返回二次电子的增多而趋于平衡. 在平衡态时, 负带电表面电位随薄膜厚度、陷阱密度的增大而降低, 随电子迁移率、薄膜介电常数的增大而升高;而正带电表面电位受它们影响较小.     

低能电子束照射接地绝缘薄膜的负带电过程

为揭示低能电子束照射接地绝缘薄膜的负带电过程及其机理,建立了同时考虑电子散射与电子输运的计算模型,综合Monte Carlo方法和有限差分法进行了数值模拟,获得了内部空间电荷、泄漏电流和表面电位随电子束照射的演化规律.结果表明,入射电子因迁移、扩散效应会超越通常的散射区域产生负空间电荷分布,并经过一定的渡越时间后到达接地基板,形成泄漏电流,负带电暂态过程则随着泄漏电流的增加而趋于平衡.在平衡状态下,泄漏电流随电子束能量和电流而增大;薄膜净负电荷量和表面电位随膜厚而增加、随电子迁移率的增大而降低,随着电子束 关键词： 绝缘薄膜 电子束照射 带电效应 数值模拟     

体心立方金属W薄膜晶体取向的膜厚尺寸效应及其表面映射

体心立方W膜(110)织构系数T₁₁₀的变化存在非单调的厚度尺寸效应，这依赖于薄膜中晶粒形核和长大时表面能和应变能的相互作用，薄膜表面结构演变反映了两者的竞争过程.应用小波变换结合分形几何描述薄膜表面结构各向异性行为，用此法构建了薄膜织构系数T₁₁₀与表面结构各向异性的关系，表明薄膜晶体取向存在表面映射. 关键词： 金属薄膜 晶体取向 膜厚 表面形貌     

金属薄膜厚度小于电子自由程对其光反射率的影响

提出了金属薄膜厚度对薄膜中自由电子的平均自由程影响的物理模型,并给出了薄膜中自由电子的平均自由程的修正公式.理论研究表明:当膜厚小于自由电子的平均自由程时,薄膜中电子平均自由程随膜厚的减小而减小|当膜厚大于或等于自由电子的平均自由程时,薄膜中电子的平均自由程与块状材料一样.利用薄膜中电子平均自由程的计算公式,修正了薄膜导电率的基本理论表达式,再利用金属薄膜的反射率与薄膜导电率的关系,得出金属薄膜厚度对其光反射率的影响.计算机模拟表明:当薄膜厚度小于电子自由程时,金属薄膜反射率随薄膜厚度变化而呈非线性关系.     

低真空条件下制备的银薄膜的电阻率特性及结构

研究了在2.2 Pa低真空条件下用直流溅射法制备的银薄膜的电阻率特性和薄膜结构.实验表明,薄膜厚度对薄膜电阻率有显著影响,随膜厚的增加薄膜电阻率降低,在膜厚大于200 nm时趋于稳定,电阻率为2.54×10-8Ω.m.薄膜表面和晶粒间界对传导电子的散射导致了银薄膜电阻率的尺寸效应.研究结果表明,可以在2.2 Pa的低真空条件下制备金属银薄膜,将银靶用于目前大学物理实验课中金属薄膜制备及金属薄膜电阻率测量实验是可行的.     

Morphological evolutions of iron films on PDMS substrates under uniaxial compression/tension

We report on the morphological evolutions of iron films sputtering deposited on elastic polydimethylsiloxane (PDMS) substrates under uniaxial compression/tension. The experiment shows that the as-prepared film (no external strain) spontaneously forms cracks and wrinkles due to the residual thermal stresses stored up during/after the film deposition. The external uniaxial compression can generate delaminated buckles perpendicular to the loading direction (transverse direction) and new cracks in the loading direction (longitudinal direction). Subsequent reloading and further straining result in the formation of transverse cracks and longitudinal buckles. It is found that there exists a significant coupling effect between the cracking and buckling patterns during the compression/tension process. The morphological evolution behaviours and underlying physical mechanisms are discussed and analysed in depth in this paper.     

Transparent conductive reduced graphene oxide thin films produced by spray coating

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,N-Dimethylformamide.The dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray volume.AFM measurements revealed that the thin films have near-atomically flat surface.The chemical and structural parameters of the samples were analyzed by Raman and XPS studies.It was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared region.The sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 nm.The conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.     

含表面活性剂液膜去湿过程的数值模拟

对存在壁面滑移的含非溶性表面活性剂薄液膜在固体表面的去湿过程,采用PDECOL程序对描述其演化过程的液膜厚度和表面活性剂浓度方程组进行数值求解.基于液膜表面扰动波形的变化,分析各参数对去湿特性及液膜稳定性的影响规律.研究指出:Marangoni数M较小时其效应使液膜失稳区缩短,而M较大时液膜失稳区间无限延伸,稳定性降低;毛细力数减小使液膜失稳区间缩短,减至一定程度后可有效抑制去湿现象的发生;滑移效应对演化过程的影响与M有关,M较小时滑移使液膜失稳区间缩减,使扰动增长率增大,M较大时这一影响并不显著;随平衡液膜厚度增大,液膜表面的扰动程度减小,但扰动区间显著增大.相对于外源性表面活性剂而言,内源性情形的失稳区间更小,液膜稳定性更强.     

Combinatorial approach to the fabrication of organic thin films

We demonstrate combinatorial approach in investigation of organic thin film fabrication. “Combinatorial substrate screening”, which is the deposition onto several kinds of substrates simultaneously, is useful to choose suitable substrate for organic thin film growth. “Combinatorial thickness-gradient films” can be fabricated using a moving mask which travels from an edge to another edge of substrate continuously during the deposition. The combinatorial thickness-gradient film can be regarded as the library for time evolution of film growth during the deposition. This mapping can serve as a powerful method for the research of growth of thin film in an initial stage. Besides, combinatorial thickness-gradient film can be utilized for the examination of a buffer layer effect. These techniques enable us to quickly optimize for the fabrication of high-quality organic thin films.     

Effect of substrate elasticity on evaporation kinetics and evaporative deposition of aqueous polystyrene nanoparticles droplets

Evaporation of aqueous polystyrene(PS) nanoparticles droplets on silicon and polydimethylsiloxane(PDMS) surfaces was studied. Experimental results showed that softer PDMS surfaces yielded a longer constant contact radius(CCR) stage, which could be ascribed to surface deformation of PDMS induced by the vertical component of liquid-vapor interfacial tension. Ringlike depositions of nanoparticles with different crack patterns were found on both silicon and PDMS surfaces. In-situ observation of crack formation showed that nanoparticle movement on the silicon surface was impeded, resulting in radial cracks with periodic distribution. In contrast, nanoparticles were shown to move easily on the PDMS surface. This observation indicated the difference in crack patterns on surfaces could be attributed to the friction force between nanoparticles and the substrate. A large friction force between nanoparticles and the substrate prevented cracks from moving, resulting in a radial crack pattern with periodic distribution, while a small friction force produced multiple large cracks.     

Effect of substrate curvature on thickness distribution of polydimethylsiloxane thin film in spin coating process

The polymer spin coating is critical in flexible electronic manufaction and micro-electro-mechanical system(MEMS)devices due to its simple operation, and uniformly coated layers. Some researchers focus on the effects of spin coating parameters such as wafer rotating speed, the viscosity of the coating liquid and solvent evaporation on final film thickness.In this work, the influence of substrate curvature on film thickness distribution is considered. A new parameter which represents the edge bead effect ratio(re) is proposed to investigate the influence factor of edge bead effect. Several operation parameters including the curvature of the substrate and the wafer-spin speed are taken into account to study the effects on the film thickness uniformity and edge-bead ratio. The morphologies and film thickness values of the spin-coated PDMS films under various substrate curvatures and coating speeds are measured with laser confocal microscopy. According to the results, both the convex and concave substrate will help to reduce the edge-bead effect significantly and thin film with better surface morphology can be obtained at high spin speed. Additionally, the relationship between the edge-bead ratio and the thin film thickness is like parabolic curve instead of linear dependence. This work may contribute to the mass production of flexible electronic devices.     

Controlling the surface buckling wrinkles by patterning the material system of hard-nano-film/soft-matter-substrate

Wrinkling and buckling of nano-films on the compliant substrate are always induced due to thermal deformation mismatch.This paper proposes effective means to control the surface wrinkling of thin film on the compliant substrate,which exploits the curvatures of the curve cracks designed on the stiff film.The procedures of the method are summarized as:1)curve patterns are fabricated on the surface of PDMS(Polydimethylsiloxane)substrate and then the aluminum film with the thickness of several hundred nano-meters is deposited on the substrate;2)the curve patterns are transferred onto the aluminum film and lead to cracking of the film along the curves.The cracking redistributes the stress in the compressed film on the substrate;3)on the concave side of the curve,the wrinkling of the film surface is suppressed to be identified as shielding effect and on the convex side the wrinkling of the film surface is induced to be identified as inductive effect.The shielding and inductive effects make the dis-ordered wrinkling and buckling controllable.This phenomenon provides a potential application in the fabrication of flexible electronic devices.     

氧化钛薄膜调控金属铜的表面等离子体共振特性研究

提出了一种利用氧化钛薄膜对金属铜薄膜表面等离子体共振特性调制的想法。实验中首先使用电子束蒸发制备一批同等厚度的氧化钛薄膜,再利用磁控溅射方法在氧化钛薄膜上沉积厚度为5～80 nm不等的金属铜薄膜。测试结果表明,氧化钛膜层对不同厚度的金属铜薄膜表面等离子体共振增强具有不同调制效果,金属铜薄膜厚度小于20 nm时,底层的氧化钛薄膜对Cu薄膜表面等离子体共振增强效果显著,且随着金属Cu膜层厚度增加表面等离子体共振峰发生蓝移,而当金属铜膜层的厚度超过20 nm时,共振增强效果因金属Cu薄膜消光能力的上升而开始减弱。     

Topographic control on silicone surface using chemical oxidization method

The paper describes a wet process for modifying the surface of polydimethylsiloxane (PDMS) using H₂SO₄/HNO₃ solutions. The oxidation on the surface of PDMS was confirmed by the examinations of Fourier transform infrared spectrometry (FTIR), contact angle of water drop and X-ray photoelectron spectroscopy (XPS). The hydrophobic surface of pristine PDMS was not only changed to hydrophilic, but also formed wrinkles on it after chemical modification. Bilayer systems, stiff oxidized PDMS layers were capped on soft PDMS foundations, would generate easily compressive stresses due to the large difference in volumetric contraction rates and led to form wrinkles on the surface. Experimental results demonstrated the periodicity of wrinkles was controllable by controlling the duration of oxidation. Therefore, wrinkles could be arranged orderly by the guidance of external forces before oxidization. The potential technology for generating and ordering wrinkles on the PDMS surface is valuable in the applications of pressure sensors, biology, micro-optics and nano-/micro-fabrication in the future.     

A measurement of elastic moduli for tungsten films on polymer substrate using wrinkling analysis

The elastic moduli of ultra thin tungsten (W) films on polymers were assessed with wrinkling analysis. Thin W films with a range of thickness between 17 and 100 nm were deposited on compliant polymers and Si strips using DC magnetron sputtering method, causing the tensile stress in a few GPa scale with respect to the thickness of W films. By applying lateral compression on polymer, wrinkle patterns were developed in the W thin film with well-defined amplitude and wavelength. Using a simple equation on wrinkle analysis, the range of elastic moduli was estimated with increasing the thickness. It was found that the elastic modulus and the tensile stress decreased with increasing the film thickness.