Thin film and substrate cracking under the influence of externally applied loads

Cracking in thin film systems subject to residual tension is examined. The existing solution for the case of a crack tip in the substrate is modified to provide a solution of greater accuracy. The influence of external tensile loads on thin film and substrate cracking is examined. An approximate superposition scheme is presented for the determination of the energy release rate. Crack arrest is examined and parameters for determining the possibility of crack arrest are presented. For compliant films it was found that crack arrest does not occur when the substrate stress has the same magnitude as the residual stress. The influence of externally applied loads on crack channelling and conditions under which channelling will occur in the substrate are presented.     

铜／铝冷轧复合板剥离性能及界面摩擦分析

采用同步轧制方法制备铜／铝复合板,研究了轧制变形量对于铜／铝复合板结合强度和剥离表面形貌的影响,分析了轧制复合界面摩擦机理。研究结果表明,复合板结合强度、剥离表面粘铝、铜基体表面裂纹数都随着轧制变形量的增大而增大。变形量为50％时,结合强度为2N／mm,变形量为60％时,结合强度为7N／mm,变形量为70％时,结合强度为14N／mm。轧制过程中,新鲜金属从结合面裂纹中挤压出来,受界面摩擦力剪切作用,两新鲜金属搓合在一起形成良好结合。     

Experimental and finite element simulations of cold pressure welding of aluminium by divergent extrusion

In the present investigation, the aptness of the divergent extrusion process in simulating cold pressure welding (CPW) is further documented and explored. As a starting point, the situation existing both prior to and after cold bonding is adequately reproduced using finite element (FE) modelling. Combined extrusion and joining experiments are then carried out to unravel the conditions under which cold bonding takes place in commercial purity aluminium. Based on three-point bend testing and fracture surface investigations in the scanning electron microscope (SEM), it is observed that bond initiation occurs gradually during the course of the extrusion process. Full metallic bonding is achieved when the surface exposure, as determined by the x-component of the strain acting in the extrusion direction, reaches a value of 0.97. This surface exposure is comparable to that reported for bond formation using conventional CPW and cold roll bonding (CRB) in the presence of oxide and lubricant films at the mating interfaces under similar contact pressure conditions.     

Micropatterning: Ultrafast Large‐Area Micropattern Generation in Nonabsorbing Polymer Thin Films by Pulsed Laser Diffraction (Small 6/2011)

An ultrafast, parallel, and beyond‐the‐master micropatterning technique for ultrathin (30?400 nm) nonabsorbing polymer films by diffraction of laser light through a 2D periodic aperture is reported. The redistribution of laser energy absorbed by the substrate causes self‐organization of polymer thin films in the form of wrinklelike surface relief structures caused by localized melting and freezing of the thin film. Unlike conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre‐ablative process without loss of material, and without absorption/reaction with incident radiation. Self‐organization in the thin polymer film, aided by the diffraction pattern, produces microstructures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size, and geometry, and by changing the diffraction pattern.     

Ultrafast large-area micropattern generation in nonabsorbing polymer thin films by pulsed laser diffraction

An ultrafast, parallel, and beyond-the-master micropatterning technique for ultrathin (30-400 nm) nonabsorbing polymer films by diffraction of laser light through a 2D periodic aperture is reported. The redistribution of laser energy absorbed by the substrate causes self-organization of polymer thin films in the form of wrinklelike surface relief structures caused by localized melting and freezing of the thin film. Unlike conventional laser ablation and laser writing processes, low laser fluence is employed to only passively swell the polymer as a pre-ablative process without loss of material, and without absorption/reaction with incident radiation. Self-organization in the thin polymer film, aided by the diffraction pattern, produces microstructures made up of thin raised lines. These regular microstructures have far more complex morphologies than the mask geometry and very narrow line widths that can be an order of magnitude smaller than the openings in the mask. The microstructure morphology is easily modulated by changing the film thickness, aperture size, and geometry, and by changing the diffraction pattern.     

An elastic-plastic shear lag model for fracture of layered coatings

We present a phenomenological model describing cracking under uniaxial tensile strain of a brittle thin film on a deformable substrate with an elastic-plastic interface layer. The model yields an analytical solution predicting average crack density and average crack opening as a function of applied strain and material parameters. The model has been applied to experimental data for cracks in thin SiO_x films on PET substrates.     

Micro-patterned nanoscale Au films on PMMA: fabrication and effect of PMMA dewetting on Au patterning

Patterned metallic thin films have attracted a lot of attention, in recent years, due to their wide technological applications. On the basis of this fact, in the present work, we illustrate a simple, versatile, and low-cost methodology to prepare surface micro-patterns in nanoscale deposited Au films. The methodology is based on the following steps: (a) to perform nanoscale Au film depositions assisted by micrometric templates to obtain the deposited Au film micrometric patterned in specific and desired ways (micrometric squares, hexagons, …), and (b) by low-temperature thermal processes (<300 °C) to induce a dewetting process of the PMMA to guide specific patterning effects in the top nanoscale Au film. In this approach, the Au surface pattern order is established by the template confined deposition on a micrometric scale while the realization and control of the Au surface pattern is given by the control of the dewetting process of the underlaying substrate, without invoking high temperature thermal processes.     

Pure magnetooptic diffraction and Kerr microscopy of periodic domain structures

The fabrication of a periodic domain structure in a ferromagnetic thin film is reported. This periodic domain structure is formed in a thin continuous magnetic film by coupling it to a periodic array of magnetic elements grown on top. When the array and the continuous film are exchange decoupled, magnetostatic interactions produce in the continuous layer a domain structure replica of the topographic pattern at selected field values. The present work reports a direct confirmation of this periodic domain structure in the flat continuous film by Kerr microscopy, which is responsible for the pure magnetooptic diffraction. The effect on the magnetization processes of oneand two-dimensional structures with different periodicities and dimensions is studied in detail and compared with micromagnetic simulations, for Co and Fe films.     

Application of low-temperature substrate bonding in fabrication of reusable micro-fluidic devices

The plasma polymerised (PP) films were deposited on silicon substrates and used to bond the substrates at a low temperature (130 °C). Different types of monomers were used to deposit PP films on μ-electrode and μ-channel of micro-fluidic devices (MFD) to tailor the surface properties. To confirm the PP film deposition on the substrates the surface chemistry was characterized using X-ray photoelectron spectroscopy (XPS). The bond strength of about 100 nm PP acrylic acid, p-xylene, styrene, 1-vinyl-2-pyrrolininne and allylamine films were measured more than 2 Mpa. The bonding strength was also tested before and after passing the fluid in MDF and no significant change was observed. Generally, no change in the structure of μ-electrode was observed by the bonding, using a separating and cleaning process. Therefore, this bonding process is independent of the type of thin film deposited and the bonding can be easily carried out by me in the laboratory and the surface properties can be tailored for different applications. It also enables one to recycle and reuse the devices in production. This process allows the devices to be recycling and/or reusable for a better and cleaner global environment.     

Ductility of thin copper films on rough polymer substrates

Electronic components in modern flexible electronics are connected by interconnects, which typically have the form of metal films resting on polymer substrates. This paper firstly studies experimentally the ductility of Cu films deposited on polyimide substrate with roughened surface (due to sandblasting) and finds that, upon tensile loading along the direction of film surface, the density of surface cracks in the film decreases with increasing surface roughness. The method of finite elements is subsequently employed to study the distribution of tensile stresses in the film and their influence on film cracking (initiation and propagation). It is demonstrated that a rough (curved) interface can reduce the tensile stresses along the film surface so as to restrain channel cracking of the film. Finally, the cohesive zone model is used to study the initiation and spreading of damage in the film and interfacial debonding of the curved interface. Both the interfacial damage and interface crack length are reduced as a result of interface roughening.     

In-situ inspection of cracking in atomic-layer-deposited barrier films on surface and in buried structures

Thin inorganic barrier films deposited on plastics are essential to provide protection from moisture- and oxygen-aided degradation while maintaining a flexible substrate. Mechanical bending of the barrier films, causes stress-induced cracks that may lead to significant reduction or loss of barrier protection. In-situ characterization of film cracking on the nanoscale, transparent, and conformal atomic-layer-deposited (ALD) thin films is challenging especially when these films are in a buried layer structure. We developed a technique that can inspect in real-time the cracking of the stressed barrier films using laser scanning confocal microscopy. The in-situ inspection avoids the inaccurate measurement of the crack onset strain associated with the crack “close-up” phenomenon. SU8 cover-coat is applied to form a buried ALD layer structure and in-situ inspection demonstrates the cracking of the ALD film in real-time underneath the cover-coat. This technique is nondestructive, versatile, and allows rapid and large-area inspection of different types of barrier films.     

Wafer Scale Solventless Adhesive Bonding with iCVD Polyglycidylmethacrylate: Effects of Bonding Parameters on Adhesion Energies

Initiated chemical vapor deposition (iCVD) polyglycidylmethacrylate (PGMA) thin films are investigated as adhesives for wafer‐scale bonding of 300 mm silicon substrates and demonstrated to form highly uniform, void‐free bond interfaces. The effects of bonding temperature and pressure on critical adhesion energy (G_c) between iCVD PGMA and silicon are studied using the four‐point bend technique. G_c values can be varied over an order of magnitude (0.59–41.6 J m⁻²) by controlling the bonding temperature and the observed dependence is attributed to changes in the physical (diffusion) and chemical (crosslinking) properties of the film. Thermal degradation studies using spectroscopic ellipsometry reveal that the iCVD PGMA films can crosslink when annealed above 120 °C in air. Further, changes in polymer behavior associated with annealing temperature are demonstrated to influence the crack propagation interface between the bonded substrates. These findings demonstrate the feasibility of iCVD polymer films for both temporary “thermoplastic,” and permanent “thermoset” bonding with potential applications in 3D integrated circuit technologies.     

Characterization,Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr55Cu30Ni5Al10 Bulk Metallic Glass

The composition of oxide film of ZrssCu3oNi5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.     

SiO2薄膜制备的现行方法综述

在导电基体上制作薄膜传感器的过程中,需要在基体与薄膜电极之间沉积一层绝缘膜.二氧化硅薄膜具有良好的绝缘性能,并且稳定性好,膜层牢同,长期使用温度可达1000℃以上,应用十分广泛.通常制备SiO2薄膜的现行方法主要有磁控溅射、离子束溅射、化学气相沉积、热氧化法、凝胶-溶胶法等.本文系统阐述了各种方法的基本原理、特点及适用场合,并对这些方法做了比较.     

Cracking and deformation of surface scale during hot rolling of steel

Abstract

Hot rolling tests, using mild steel slabs with thin and thick oxide scales, have been conducted to investigate the cracking and deformation behaviour of the scale during hot rolling to various reductions. The effects of the variables other than temperature on scale cracking have been simulated by cold rolling tests, using lead slabs with brittle lacquer coatings. Using the point counting method, surface fractions of cracks in the scale and in the lacquer layers have been measured. The results indicate that thin scales can undergo a substantial amount of plastic elongation before cracking in the roll gap, while thick scales suffer from severe brittle cracking before entering the roll gap. Based on these comparative studies, the major parameters that control scale cracking and deformation behaviour during the hot rolling of steel are highlighted, and a quantitative relationship between scale crack fraction and rolling reduction is established.     

SEM in-situ investigation on failure of nanometallic film/substrate structures under three-point bending loading

Three-point bending tests on nanocrystalline Cu or Cu/Ni-film/Cu-substrate samples were conducted in-situ with scanning electron microscopy (SEM) observations. The SEM in-situ observations show undulation deformation of the surface of thin film, as the thin film fractures easily at the concave–convex points of deformation and multi-cracks appear on the surface of the thin film in a periodic fashion. The critical wavelength of undulation is calculated based on experimental observations, which are comparable with the theoretical predictions. For the Cu/Ni multi-layered films/substrate structures, the micro-cracking pattern depends on the interfacial strength between the film and the substrate, rather than the interfacial strength between the layers of films.     

周期性前驱体的预硫化处理对Cu2ZnSnS4薄膜的影响EI北大核心CSCD

Cu2ZnSnS4薄膜具有组成元素来源丰富、吸收系数高等优点,是理想的薄膜太阳能电池吸收层材料。采用磁控溅射法沉积周期性金属叠层前驱体,再进行两步硫化处理制备出Cu2ZnSnS4薄膜,分析第一步硫化(即预硫化)对Cu2ZnSnS4薄膜特性的影响。结果表明,预硫化处理可促进前驱体的硫化反应。经过预硫化处理的Cu2ZnSnS4薄膜的结晶度优于未进行预硫化处理的Cu2ZnSnS4薄膜。当预硫化温度为350℃时,增加预硫化时间有利于硫化反应的进行,并抑制Sn元素损失,但过长的预硫化时间导致Cu2ZnSnS4薄膜中易出现二次相,影响薄膜的特性。预硫化温度350℃、预硫化时间10 min的Cu2ZnSnS4薄膜结晶度最优,薄膜组分具有贫Cu、富Zn特性,且薄膜表面无孔隙。     

Fabrication and nano-imprintabilities of Zr-, Pd- and Cu-based glassy alloy thin films

With the aim of investigating nano-imprintability of glassy alloys in a film form, Zr(49)Al(11)Ni(8)Cu(32), Pd(39)Cu(29)Ni(13)P(19) and Cu(38)Zr(47)Al(9)Ag(6) glassy alloy thin films were fabricated on Si substrate by a magnetron sputtering method. These films exhibit a very smooth surface, a distinct glass transition phenomenon and a large supercooled liquid region of about 80 K, which are suitable for imprinting materials. Moreover, thermal nano-imprintability of these obtained films is demonstrated by using a dot array mold with a dot diameter of 90 nm. Surface observations revealed that periodic nano-hole arrays with a hole diameter of 90 nm were successfully imprinted on the surface of these films. Among them, Pd-based glassy alloy thin film indicated more precise pattern imprintability, namely, flatter residual surface plane and sharper hole edge. It is said that these glassy alloy thin films, especially Pd-based glassy alloy thin film, are one of the promising materials for fabricating micro-machines and nano-devices by thermal imprinting.     

硅烷偶联剂KH550对Parylene C膜与金属铝基体结合强度的影响

采用拉开法分析了KH550(γ-氨丙基三乙氧基硅烷)偶联剂浓度对Parylene C膜与金属铝基体间结合强度的影响,采用拉曼光谱(Raman)和红外光谱(FT-IR)分析了偶联剂在膜和基体间的作用机理。研究结果表明,使用10%的KH550偶联剂可提高Parylene C膜与铝基体的结合强度到7.5MPa。其增强作用机理为KH550偶联剂的烷氧基团水解后,-Si-OH与基体的Al-O键发生化学作用生成-Si-O-Al键,-NH2能与Parylene C膜分子间形成氢键,从而使Parylene C膜与金属铝之间产生化学键桥连。     

Wrinkling of thin films on a microstructured substrate

Surface wrinkling of thin films on substrates offers an effective strategy to create controllable surface patterns of wide application. In this article, both theoretical analysis and numerical simulations are performed to study the surface wrinkling of thin films bonded on a microstructured soft substrate under compression. We consider two typical kinds of substrates that have different mechanical properties. One possesses a periodic array of micropillars, and the other has a period of alternating unbonded—bonded regions at the film—substrate interface. The characteristics of surface wrinkling and postbuckling evolution of films are revealed. It is found that the interfacial microstructures modulate the normal mechanical properties of the substrate and, thus, tailor the buckling behavior of the thin film atop it. Under lateral compression, the film on the substrate shows periodic arrays of micropillars exhibiting sinusoidal wrinkling first, and then with further compression, the wrinkles give way to a deep fold accompanied by Euler buckling of the micropillars and the decay of neighboring wrinkles. For the system with periodic unbonded—bonded regions at the film—substrate interface, wrinkling of the film is characterized by a relative shift in the normal direction. This study offers potential applications in the fabrication of tunable surface morphologies.