Delamination Of Thin Films Research Articles

Laser interference induced nano-crystallized surface swellings of amorphous carbon for advanced micro tribology

We have investigated the direct laser interference patterning (DLIP) of tetrahedral amorphous carbon (ta-C) thin films in the nanometer region. In this paper we achieved texturing of ta-C from a surface swelling either by a phase change from sp3 to sp2 or thin film delamination. In contrast to surface ablation, the thin film is not removed from the silicon surface. With this technique a surface nano-swelling of ta-C with an area-speed of 1 m2 min−1 and nanometric resolution can be realized. The phase changes in the ta-C, due to DLIP material heating are undermined by thermal simulations of the patterning process. Additionally we investigated for the first time the influence of periodic nano-swelling on the coefficient of friction (COF). The COF of periodic graphitized surfaces was found to be lower (∼50%) compared to as grown ta-C. This reduction of the COF can be attributed to a reduced area of contact.

Ultra high-yield one-step synthesis of conductive and superhydrophobic three-dimensional mats of carbon nanofibers via full catalysis of unconstrained thin films

We directly synthesized large conductive and superhydrophobic 3D mats of entangled carbon nanofibers (CNFs). The mechanism is based on thin film delamination and bi-directional catalytic CNF growth.

Interface step-induced thin-film delamination and buckling

Atomistic simulations based on experimental observations provide the first evidence that the interface delamination of a thin film from its substrate may start from interface steps. Buckling of the film after interface gliding from both edges of its delaminated part is also observed. In the framework of the Föppl–von Kármán theory of thin plates, the expression of the critical strain beyond which the film buckles has been then analytically determined as a function of the step height and gliding displacements. Both numerical and analytical results confirm that the formation of blisters is favoured in the neighbourhood of interfacial imperfections.

Beta-induced reduction in Cu/Si-structure adhesion

The effect of low-flux (I ∼ 1.8 × 105 cm−2 s−1) β irradiation on the process of the delamination of thin copper films (with a thickness of ∼100 nm) from a silicon substrate under indentation by a Berkovich pyramid is studied. It is revealed that irradiation with a fluence of F = 3.24 × 1010 cm−2 leads to an increase in the perimeter and area of the copper-film delaminations formed upon penetration of the indenter. This indicates a β-induced reduction in adhesion in the Cu/Si structure.

The Behavior of Thin Film Delamination during Cutting by Using Micro Cutting Method

The Behavior of Thin Film Delamination during Cutting by Using Micro Cutting Method

Indentation stress in multi-layer delaminated thin films induced by a microwedge indenter

Indentation stresses in single- and multi-layer delaminated thin films made of elastic–perfectly plastic materials in microwedge indentation delamination tests are analyzed via finite element calculations with different wedge angles and other geometrical and mechanical parameters. Based on the formula for a single-layer thin film under indentation loading [Zhao et al. J Mater Res 2009;24:1943] and by introducing the equivalent material parameters, we developed simple analytical formulae for the loading indentation stress (as well as the energy release rate) in each layer of the multi-layer thin film, in terms of the residual stress, elastic modulus, Poisson’s ratio, yielding strength, and thickness of each layer. Our analytical solution is validated by the finite element calculations and should be useful to thin-film delamination tests.

Nanomechanical Testing of the Barrier Thin Film Adhesion to a Flexible Polymer Substrate

Polymers in the form of films are nowadays used in a wide range of applications, from the packaging of several products in food industry to the cutting edge organic optoelectronic devices. Despite their remarkable advantages, the polymer films suffer from poor mechanical and barrier properties. Overcoming of these drawbacks can be achieved by using inorganic, hybrid polymers and/or nanocomposite thin films to coat the flexible polymer substrate. In this way the permeation of the harmful atmospheric gases (H2O and O2) through the polymer can be significantly reduced and, as a result, the product service life is prolonged. In this work, the nanomechanical behavior of 50 μm thick flexible poly(ethylene terephthalate) (PET) substrate coated with AlOx barrier thin film (40 nm and 70 nm thick) is studied. A synergy of state-of- the-art experimental techniques, such as depth-sensing Nanoindentation, Scratch Test and Atomic Force Microscopy (AFM), was used to shed some light on the deformation mechanisms and the adhesion failures of the inorganic thin film on flexible PET substrate. Several nanoindents were made on each sample with a sharp Berkovich-type indenter, in various maximum normal applied load (P)/indentation depths. Analysis of the measured load-displacement (P–h) curves showed that for low loads (P ⩽ 35 μN) the contact between the indenter and the sample was almost elastic. The AFM images provided valuable information about deformation during higher normal applied load (P > 500 μN) nanoindentation, which induces elastic/plastic deformation to the samples. Delamination/cracking of the barrier thin film from the PET flexible substrate was not observed even though the indenter penetrated almost 7 times the thickness of the thin film. On the other hand, cracking, fragmentation and finally delamination of the barrier thin film occurred during the ramping load Scratch Test.

Effects of sliding on interface delamination during thin film buckling

A theoretical model for the simultaneous thin film buckling and interface delamination from its substrate has been derived from a Griffith’s criterion which includes plastic events localized at the film–substrate interface. The predictions of the model have been validated by atomistic simulations of the delamination and buckling of a Cu thin film deposited on a W substrate. This model accounts for the stable propagation of the buckle edges without requiring any estimate of the dependence of the adhesion energy on the mode mixity.

Method to deduce the critical size for interfacial delamination of patterned electrode structures and application to lithiation of thin-film silicon islands

Recent experiments have suggested that there is a critical size for patterned silicon (Si) thin film electrodes for delamination from a current collector during lithiation and delithiation cycling. However, no existing theories can explain this phenomenon, in spite of its potential importance in designing reliable electrodes for high-capacity lithium-ion batteries. In this study, we show that the observed delamination size effect can be rationalized by modeling thin film delamination in the presence of large scale interfacial sliding. A method is proposed to deduce the critical size for delamination based on the critical conditions for the nucleation and growth of edge or center cracks at the film-substrate interface under plane strain or axisymmetric conditions. Applications to lithiation of thin-film Si islands give results in excellent agreement with experimental observations.

Delamination of Cu and Ti Thin Films Deposited by Magnetron Sputtering on Cu Substrate: Analysis of Reasons

Multilayer thin-film structures are widely used in microelectronic, optoelectronic and micro-/nanoelectromechanical devices. Mechanical properties and mechanical stresses are very critical for such devices. Structural stresses are composed of an intrinsic part resulting from growth defects and a thermal part caused by the mismatch of the thermal expansion coefficients of the different materials in the multilayer system and between coating and substrate. Excessive tensile stresses result in cracking of the film and/or substrate, and compressive stress can cause buckling. Determination and control of stress is an important scientific issue for both functional thin films and engineering coatings from the viewpoint of performance and integrity. In the present study the in situ stress measurements for thin films of Ti (300nm thick) and Cu (1000nm thick) sputtered on Cu substrates were performed using a method proposed in [6]. The stresses that occurred in the Ti film were tensile, stresses that occurred in the Cu film were compressive. The continuous measurements were performed both during the process of the deposition and after the magnetron cut off. The film delamination from a substrate occurred in both cases. The analysis of obtained curves (the specific force versus time) was performed. Analysis revealed that the arising stresses are not caused by any nonstationary heating process of the material surface. Local buckling due to interatomic binding weakening can lead to Cu film delamination. The major cause of Ti film delamination can be a microcracking due to substrate’s thin surface layer yielding.

Automated micro-transfer printing with cantilevered stamps

This paper demonstrates the use of a flexible instrumented stamp to enable automated micro transfer printing as a route to large-area, deterministic assembly of microstructured device components or ‘inks’. The ability to instrument the stamp, a critical component for retrieval and placement of a micro device, to detect contact and monitor localized forces during critical events in the printing process not only allows for the development of a robust manufacturing process, but also for a unique vantage point from which to study fundamental issues and phenomena associated with adhesion and delamination of thin films from a variety of substrate materials. This paper presents basic design analysis on the requirements of the cantilevers for compatibility with a typical transfer printing environment. Off-the-shelf thin film strain gages are integrated with a thin elastomeric post as a preliminary prototype and the feasibility of transfer printing with it is demonstrated. Further, the set-up is calibrated to produce force signals for event detection and in situ diagnosis of the process.

Calculations of Buckle-Driven Delamination Using Cohesive Elements

Plane strain, elastic calculations of buckle-driven thin film delamination from compliant substrates using finite element models are considered. The interfacial properties between the film and the substrate are modeled using cohesive elements with a tractionseparation law formulated in terms of a potential. The model yielded the geometry of the buckles given the properties of the film and the substrate, the interfacial toughness and the value of the compressive equi-biaxial stress. Results for the relation between the buckle width and the interfacial toughness were very close to similar results by Yu and Hutchinson (2002), thus giving confidence that the cohesive element approach presented can be used in applications where buckle-driven delamination of thin films is an issue.

The surface effect on the strain energy release rate of buckling delamination in thin film–substrate systems

Gurtin–Murdoch continuum surface elasticity model is employed to study the buckling delamination of ultra thin film–substrate system. The effects of surface deformation and residual stress on the large deflection of ultra thin film are considered in analysis. A concept of effective bending rigidity (EBR) for ultra thin plate is proposed on the basis of Gurtin–Murdoch continuum theory and the principle of minimum potential energy. The governing equations with EBR are formally consistent with the classical plate theory, including both small deflection and large deflection. A surface effect factor is introduced to decide whether there is need to consider the surface effect or not. Combining the buckling theory and interface fracture mechanics, we obtain analytical solutions of the critical buckling load and the energy release rate of the interface crack in the film–substrate system. It is seen that the surface deformation and residual stress have significant effects on the buckling delamination of ultra thin film–substrate system.

Size scaling of strength in thin film delamination

We investigate by means of numerical simulation the system-size dependence of the sheardelamination strength of thin elastic films. The films are connected to a rigid substrateby a disordered interface containing a pre-existing crack. The size dependenceof the strength of this system is found to depend crucially on the crack shape.For circular cracks, we observe a crossover between a size-independent regime atlarge crack radii which is controlled by propagation of the pre-existing crack,and a size-dependent regime at small radii which is dominated by nucleation ofnew cracks in other locations. For cracks of finite width that span the systemtransversely, we observe for all values of the crack length a logarithmic system-sizedependence of the failure stress. The results are interpreted in terms of extreme valuestatistics.

Nanosecond UV laser graphitization and delamination of thin tetrahedral amorphous carbon films with different sp3/sp2 content

We have produced hydrogen-free tetrahedral amorphous carbon films with different densities and Young's modulus by coating silicon with a filtered vacuum arc under different angles. The films were modified with a pulsed laser (wavelength 355nm) into sp2 rich amorphous carbon and nano crystalline carbon films. The graphitization threshold of the films depends on the film thickness as well as on the carbon density. Simulations of the optical absorption of the different carbon films permitted to confirm the experimental results. On the other side, the delamination threshold of carbon films increases with the film thickness and was found to be controlled by thermal properties of the film. The thin film graphitization and delamination is investigated by optical microscopy, atomic force microscopy, scanning electron microscopy and Raman spectroscopy.

A Dugdale model based geometrical amplifier enables the measurement of separation-to-failure for a cohesive interface

Regardless of all kinds of different formulae used for the traction-separation relationship in cohesive zone modeling, the peak traction σm and the separation-to-failure δ0 (or equivalently the work-to-separation Γ) are the primary parameters which control the interfacial fracture behaviors. Experimentally, it is hard to determine those quantities, especially for δ0, which occurs in a very localized region with possibly complicated geometries by material failure. Based on the Dugdale model, we show that the separation-to-failure of an interface could be amplified by a factor of L/rp in a typical peeling test, where L is the beam length and rp is the cohesive zone size. Such an amplifier makes δ0 feasible to be probed quantitatively from a simple peeling test. The method proposed here may be of importance to understanding interfacial fractures of layered structures, or in some nanoscale mechanical phenomena such as delamination of thin films and coatings.

MOF thin films: existing and future applications

The applications and potentials of thin film coatings of metal-organic frameworks (MOFs) supported on various substrates are discussed in this critical review. Because the demand for fabricating such porous coatings is rather obvious, in the past years several synthesis schemes have been developed for the preparation of thin porous MOF films. Interestingly, although this is an emerging field seeing a rapid development a number of different applications on MOF films were either already demonstrated or have been proposed. This review focuses on the fabrication of continuous, thin porous films, either supported on solid substrates or as free-standing membranes. The availability of such two-dimensional types of porous coatings opened the door for a number of new perspectives for functionalizing surfaces. Also for the porous materials themselves, the availability of a solid support to which the MOF-films are rigidly (in a mechanical sense) anchored provides access to applications not available for the typical MOF powders with particle sizes of a few μm. We will also address some of the potential and applications of thin films in different fields like luminescence, QCM-based sensors, optoelectronics, gas separation and catalysis. A separate chapter has been devoted to the delamination of MOF thin films and discusses the potential to use them as free-standing membranes or as nano-containers. The review also demonstrates the possibility of using MOF thin films as model systems for detailed studies on MOF-related phenomena, e.g. adsorption and diffusion of small molecules into MOFs as well as the formation mechanism of MOFs (101 references).

A Theoretical Study of Thin Film Delamination Using Clamped Punch-Loaded Blister Test: Energy Release Rate and Closed-Form Solution

Using an exact analytical solution of axisymmetric deformation of a circular membrane centrally connected to a rigid plate under the action of concentrated load at its center, we present an exact formula for the energy release rate applicable to ultrathin film–substrate systems without residual stresses or with small residual stresses. Also, a closed-form solution of axisymmetric deformation of circular membrane under the action of concentrated load at its center is presented.

Buckling of Thin Films in Nano-Scale

Investigation of thin film buckling is important for life prediction of MEMS device which are damaged mainly by the delamination and buckling of thin films. In this paper�» the mechanical and thermal properties of compressed thin film titanium films with 150 nm thickness deposited on an organic glass substrate under mechanical and thermal loads were measured and characterized. In order to simulate the thin films which subjected to compound loads and the buckle modes�» the external uniaxial compression and thermal loading were subjected to the specimen by the symmetric loading device and the electrical film in this experiment. The temperature of the thin film deposited on substrate was measured using thermoelectric couple. The range of temperature accords with the temperature range of the MEMS. It is found that the size and number of the delamination and buckling of the film are depended upon the pre-fixed mechanical loading and thermal temperature. The thermal transient conduction and thermal stability of the film and substrate was studied with finite element method.

Buckle Driven Delamination in Thin Hard Film Compliant Substrate Systems

Deformation and fracture of thin films on compliant substrates are key factors constraining the performance of emerging flexible substrate devices. [1-3] These systems often contain layers of thin polymer, ceramic and metallic films and stretchable interconnects where differing properties induce high normal and shear stresses. [4] As long as the films remain bonded to the substrates, they may deform far beyond their freestanding form. Once debonded, substrate constraint disappears leading to film failure. [3] Experimentally it is very difficult to measure properties in these systems at sub-micron and nanoscales. Theoretically it is very difficult to determine the contributions from the films, interfaces, and substrates. As a result our understanding of deformation and fracture behavior in compliant substrate systems is limited. This motivated a study of buckle driven delamination of thin hard tungsten films on pure PMMA substrates. The films were sputter deposited to thicknesses of 100 nm, 200 nm, and 400 nm with a residual compressive stress of 1.7 GPa. An aluminum oxide interlayer was added on several samples to alter interfacial composition. Buckles formed spontaneously on the PMMA substrates following film deposition. On films without the aluminum oxide interlayer, an extensive network of small telephone cord buckles formed following deposition, interspersed with regions of larger telephone cord buckles. (Figure 1) On films with an aluminum oxide interlayer, telephone cord buckles formed creating a uniform widely spaced pattern. Through-substrate optical observations revealed matching buckle patterns along the film-substrate interface indicating that delamination occurred for large and small buckles with and without an interlayer. The coexistence of large and small buckles on the same substrate led to two distinct behaviors as shown in Figure 2 where normalized buckle heights are plotted against normalized film stress. The behaviors deviate significantly from behavior predicted by rigid elastic solutions. To address this issue we developed a finite element analysis technique that employed a cohesive zone model to simulate interfacial crack growth. Specifying the traction-separation relationship, cohesive strength, and work of separation along with film thickness, film stress, and film and substrate properties, buckle width and height were determined as a function of interfacial toughness. The simulations indicate that an analysis based on rigid substrate solutions significantly underestimate toughness for prescribed buckle widths: a result consistent with an analysis by Yu and Hutchinson [5] that pieced together a solution based on non-linear plate theory with a solution for the linear film on substrate problem. More importantly, the results defined a lower limiting bound to seemingly disparate buckle deflection data (Figure 2). The variance from linear elastic behavior, especially for the small buckles, indicates more than substrate compliance is controlling behavior. Comparison of the experimental results with cohesive zone simulations suggests that the two buckle behaviors are associated with different levels of substrate yielding. In this presentation we will use the results to show how substrate compliance and deformation affect delamination and buckling of films on compliant substrates and provide a means to predict device performance.