Film Cracking Research Articles

Graphene mitigated fracture and interfacial delamination of silicon film anodes through modulating the stress generation and development

Silicon film is an attractive anode candidate in lithium ion batteries due to its two-dimensional (2D) morphology that is beneficial to buffer the large volume expansion of traditional silicon anodes. Even so, the generation of stress during the lithiation/delithiation process can still lead to the cracking and delamination of the silicon film from the current collector, ultimately resulting in the fast failure of the electrode. Laying a graphene layer between the silicon film and the current collector has been demonstrated to alleviate the stress generated during the battery cycling, but its universal application in commercial silicon structures with other dimensionalities remains technically challenging. Putting graphene on top of a 2D silicon film is more feasible and has also been shown with enhanced cycling stability, but the underneath mechanical mechanisms remain unclear. Herein, using the combination of 2D graphene and 2D silicon films as a model material, we investigate the stress generation and diffusion mode during the battery cycling to disclose the mechanical and electrochemical optimization of a silicon anode experimentally and theoretically. As a result, the optimum thickness of the silicon film and the coated graphene layers are obtained, and it is found the in-plane cracking and out-of-plane delamination of the silicon film could be mitigated by coating graphene due to the slow transfer of the normal and shear stresses. This work provides some understanding of the electrochemically derived mechanical behaviors of the graphene-coated battery materials and guidelines for developing stable high-energy-density batteries.

Electrodeposition of Rhenium-Iron Alloy from Water-in-Salt Electrolytes

Rhenium is a refractory metal and has distinguished properties, including excellent wear resistance, superior tensile strength, high creep-rupture, and resistivity in elevated temperatures [1]. More interestingly, it is also a superconductor at cryogenic temperatures. Electrodeposited superconducting materials can be used to fabricate superconducting circuits for cryogenic quantum devices [2,3]. As rhenium oxide is often inevitably formed during rhenium deposition, which prevents further reduction of itself into rhenium metal, highly acidic electrolytes are typically required for rhenium electrodeposition [4]. A significant amount of proton in the electrolyte, however, exacerbates hydrogen evolution reaction, resulting in not only a low current efficiency but also hydrogen incorporation into the metal deposit. The latter often, causes cracks and pin holes in the deposited films. Water-in-salt electrolyte is an aqueous solution with super high concentration of salt, e.g. LiCl, where the hydration of salt depletes or significantly decreases free water molecules, thus disrupting the hydrogen bond network, and suppressing proton reduction. In our previous work, a water-in-salt electrolyte of super high concentration of LiCl was applied to electrodeposit rhenium and rhenium-cobalt alloy to mitigate hydrogen evolution reaction and film cracks [5,6].In this presentation, the study has been extended to rhenium-iron alloy. While the rate decrease of hydrogen evolution reaction upon the use of water-in-salt electrolyte was expected, a surprisingly strong enhancement of Re deposition rate in the presence of Fe was also observed. Figure 1 shows the partial current densities of rhenium during alloy deposition, where it not only showed more than 10x deposition rate compared with an elemental Re water-in-salt electrolyte.The morphology and crystallographic structure of ReFe films and the effect of annealing will be characterized with microscopic and diffraction techniques and will be discussed in conjunction with pure metal films. Superconductivity and the effect of alloying on the critical temperature will also be discussed in detail in the talk. Figure 1 . The rhenium partial current in the deposited films from different applied potential from four electrolytes with 0, 10, 20, and 35 mM iron.

A Novel Mg-Al-Co LDH/ MAO Composite Films on LA103Z Magnesium-Lithium Alloy and Its Active Anti-corrosion Performance

In order to further improve the corrosion resistance of the micro-arc oxidization (MAO) film on LA103Z magnesium-lithium alloy, a Mg-Al-Co layered double hydroxide (LDH) film was fabricated on MAO film by an in-situ hydrothermal method. The results showed that with the extension of hydrothermal treatment time, the dense LDH film sealed the micro-pores and cracks in the MAO film successfully. In addition, LDH film treated with a hydrothermal treatment at 90°C for 24 h has the best electrical insulation. The hydrogen evolution rates (mL.cm–2.h−1) of the LDH/MAO composite films rank as LDH/MAO-24 h ≈ LDH/MAO-30 h (0.12) < LDH/MAO-18 h (0.15) < LDH/MAO-12 h (0.16) < MAO (0.25). Meanwhile, the results of potentiodynamic polarization curves showed that the corrosion potential of LDH/MAO-24 h film increased from –1.5349 to −1.388 V, and the corrosion current density decreased by three orders of magnitude. Therefore, the LDH/MAO film has better corrosion resistance than a single MAO film and adds long-term corrosion resistance to the magnesium alloy, which owes to the sealing effect of LDH on inherent defects and trapping effect on corrosion ions.

The formation of atomic and sub-nano scale pores under tensile strain in oxide films on Zr alloys: A first-principles study

The corrosion resistance of Zr alloys tightly connects to the oxide films on Zr alloys. We use first-principles computational tensile test to perform a systematical investigation on the tensile strain–stress behaviors of monoclinic zirconia, and reveal the formation mechanism of initial pores and cracks in the oxide films. Based on calculated results, we propose a new mechanism of initiation of pores in the oxide films, which has solved the puzzle of pore formation at oxide/metal (O/M) interface of pure Zr. Moreover, our results are also well consistent with many previous microstructure characterization results of Zr alloys.

Extended Barrier Lifetime of Partially Cracked Organic/Inorganic Multilayers for Compliant Implantable Electronics

Flexible and soft bioelectronics display conflicting demands on miniaturization, compliance, and reliability. Here, the authors investigate the design and performance of thin encapsulation multilayers against hermeticity and mechanical integrity. Partially cracked organic/inorganic multilayer coatings are demonstrated to display surprisingly year-long hermetic lifetime under demanding mechanical and environmental loading. The thin hermetic encapsulation is grown in a single process chamber as a continuous multilayer with dyads of atomic layer deposited (ALD) Al2 O3 -TiO2 and chemical vapor deposited Parylene C films with strong interlayer adhesion. Upon tensile loading, tortuous diffusion pathways defined along channel cracks in the ALD oxide films and through tough Parylene films efficiently postpone the hermeticity failure of the partially cracked coating. The authors assessed the coating performance against prolonged exposure to biomimetic physiological conditions using coated magnesium films, platinum interdigitated electrodes, and optoelectronic devices prepared on stretchable substrates. Designed extension of the lifetime preventing direct failures reduces from over 5 years yet tolerates the lifetime of 3 years even with the presence of critical damage, while others will directly fail less than two months at 37 °C. This strategy should accelerate progress on thin hermetic packaging for miniaturized and compliant implantable electronics.

Dual-pulse photoactivated atomic force microscopy

Photoactivated atomic force microscopy (pAFM), which integrates light excitation and mechanical detection of the deflections of a cantilever tip, has become a widely used tool for probing nanoscale structures. Raising the illuminating laser power is an obvious way to boost the signal-to-noise ratio of pAFM, but strong laser power can damage both the sample and cantilever tip. Here, we demonstrate a dual-pulse pAFM (DP-pAFM) that avoids this problem by using two laser pulses with a time delay. The first laser heats the light absorber and alters the local Grüneisen parameter value, and the second laser boosts the mechanical vibration within the thermal relaxation time. Using this technique, we successfully mapped the optical structures of small-molecule semiconductor films. Of particular interest, DP-pAFM clearly visualized nanoscale cracks in organic semiconductor films, which create crucial problems for small-molecule semiconductors. DP-pAFM opens a promising new optical avenue for studying complex nanoscale phenomena in various research fields.

Effect of Al and Cr alloying by arc cladding on the high-temperature oxidation resistance of MoSi2 materials

Different proportions of Al and Cr alloying MoSi2 were prepared by arc cladding with different mass fractions of MoSi2, Al, and Cr as raw materials. The work studied the effects about of Al and Cr on the phase, high-temperature oxidation morphology, products, and high-temperature oxidation property of MoSi2. The results confirmed that the volume expansion coefficient of Al2O3 generated by material oxidation was low which could reduce the degree of mismatch and the cracks in the oxide film. Cr element had a poor effect on enhancing the continuity and compactness of the oxide film, however, it could improve the stability of t-MoSi2 formation after arc cladding. MoO3 was not formed in the MoSi2 material added with Al and Cr show the surface oxidation. A dense and continuous Al2O3–SiO2 oxide film was formed, and no cracks holes were found in the oxide film. After oxidation at 800 °C–1200 °C for 120 h, the sample still maintained good oxidation protection. According to the calculation of oxidation kinetics, the MoSi2 material added with Al and Cr had good oxidation resistance. 3% Al + 9% Cr + 88% MoSi2 had the optimal high-temperature oxidation resistance about four times than pure MoSi2.

Contact cracking and delamination of thin solid lubricating films on deformable substrates

Effects of substrate plastic deformation on the cracking and delamination damage of thin solid lubricating films at sliding contacts were investigated. Diamond-like carbon films were evaluated by using micro-scratch tests. A three-dimensional finite element method was applied to analyze the stress-strain evolution of the film−substrate systems with consideration to the interfacial adhesion. Intense plastic deformations were generated in the softer SUS304 substrate due to the low shear strength, leading to parallel cracks along the track borders. A pile-up effect resulted in the film buckling and fragmentation ahead of the sliding stylus. However, on the harder M50 substrate, angular cracks in DLC films were generated at the trailing edge of the contact area, which led to wing-shaped spallation of the films.

Damage Behavior in Simulated Service Environment of Thermal Control Oxidation Film of 2A12 Alloy

In order to obtain the service performance of the black anodic oxidation film of 2A12 aluminum alloy, the influence of humidity and temperature in storage environment and heat on the performance of black oxidation film were studied. And the morphologies were analyzed by using optical microscopy (OM) and scanning electron microscopy (SEM). The results showed that after the black anodic oxidation film is produced, "aging" will occur in the natural environment, which can lead to the structure change of the sealing pore and affect the service performance of the film. The film exfoliates off slightly under the humidity of 90%, and the film exfoliates off more seriously when the humidity over 95%. The temperature has a greater influence on the film cracking, especially when the temperature is above 120°C, it is easy to exfoliate off. The exfoliation model was established and the affection mechanism was discussed.

Asphalt mixtures for bituminous coatings with BF slag filler

Asphalt mixtures, as a construction material intended to produce bituminous coatings, consists of a homogenous mixture made from natural aggregates and bitumen. Replacing one of the natural rocks, the filler with artificial filler, a metallurgical industry waste material, will determine a saving of material and financial resources. This can be used as an actual method of environmental protection by conserving the relief, protecting localities from noise produced in stone quarries and reusing a waste material. The processing of granular blast furnace slag from the Liberty Galati plant by grinding it exceptionally fine, into filler and their subsequent use in the preparation of asphalt mixtures, leads to obtaining favourable results on two of the most used currently in the country, AC16 surf50/70 and AC 22.4 bin50/70.These values will provide an image on the behaviour resistance and their deformability under traffic. A high-water absorption can indicate a porous mixture and favours the penetration of water into the layer, water that can change its volume during freezing-thawing and can lead to cracks in the bitumen film, stripping, dislocation of pieces in the layer. A high creep can indicate a mixture which will deform under traffic, will form slopes, or will favour the phenomenon of exudation.High stability may indicate a rigid mixture and under traffic does not have an elastic conduct, which can lead to cracks in the road surface.Framing of the results and the appreciation of this conduct of asphalt mixture made with bf slag filler compared to a standard, leads us to the finding that the mixture is accurate and will withstand environmental factors.

Stamp-Perforation-Inspired Micronotch for Selectively Tearing Fiber-Bridged Carbon Nanotube Thin Films and Its Applications for Strain Classification.

Cracks typically deteriorate the structural and electrical properties of materials when not properly controlled. A few papers recently reported the controlling methods of crack formation in the brittle materials utilizing the lateral V-notch structure. For ductile materials, however, there have been few papers reporting cracking phenomenon, but full cracking control including predesigned initiation, propagation, and termination has not been reported yet. Therefore, we report a predesigned full cracking control in ductile conductive carbon nanotube (CNT) films by introducing inkjet-printed L-shape micronotch (LMN) structures inspired by directional stamp perforation marks. In spite of the high fracture toughness of CNT films, the LMNs determine locations of initial crack formation and guide crack propagation in a predesigned way. Selective connection of isolated cracks in the CNT film increases its resistance monotonically under tensile strain and thus tremendously well maintains high linearity (adj. R2 value > 0.99) in resistance change over record large strain ranges of 0.01-100%, which enables us to quantitatively classify strain values accurately for previously reported practical body signals for the first time. We believe that our facile printing-based crack control strategy not only provides a comprehensive solution to various stretchable sensor applications but also builds a new milestone for cracking mechanism studies in fracture mechanics.

Interplay between cracking and delamination in incrementally deposited plasma sprayed coatings

Cracking and delamination in constrained films and coatings during fabrication and service has been an important subject of scientific inquiry for several decades. Considerable past efforts have focused on developing analytical models based predicting steady state energy release rates to determine the occurrence of either cracking and/or delamination in thin films. Such models have been reconciled into a ‘Design Map’. However, the extent of available experimental validation of such Design Maps is limited. In addition, these analytical Design Maps lack the description of nuances in the processing of layered films such as progressive incremental deposition.In this study, the interplay between cracking and delamination in progressively deposited plasma sprayed coatings is defined based on the aforementioned models. Following the adaptation of the models and presiding assumptions, a carefully designed set of experiments to probe responses from different ceramics and process conditions have been conducted, which allowed the controlled observation of cracking and/or delamination events. These experiments elucidated the underlying conditions that determine the onset of such stress relaxation events. The experimental data is reconciled with an adapted analytical Design Map for single, isolated, rapidly solidified droplets (splats) and for incrementally deposited thick plasma sprayed coatings, thus providing a framework for the robust design and processing of advanced coatings.

Structural and optoelectronic properties of combining Nb-doped SrTiO3/ITO films on (0 0 1)-YSZ substrate

Functional oxides combined with conventional conductive films are competitive alternative candidates as electrode and electron transport layer. This work explored the film and interface structures and the optoelectronic properties of the combined films of Nb-doped SrTiO3 (Nb-STO) as a classical functional oxide and ITO. The combined films were deposited on a (001)-YSZ substrate via laser molecular beam epitaxy method. In-situ high-energy electron diffraction, X-ray diffraction, and transmission electron microscopy shew [011]Nb-STO azimuth orientation and a two-fold symmetry rotation of the Nb-STO layer. Interestingly, the Nb-STO film growth at 650 °C or higher was able to induce cracks in ITO film. Besides, the growth temperature of Nb-STO from 400 °C to 700 °C changed its structures from amorphousness to polycrystal, the Nb-STO/ITO interface relationships, sheet resistance (from 25 to 83 Ω/sq) and electron mobility (40 to 2 cm·V−1·s−1); however, this had little influence on the transmittance. This work provided an insight into the combination of functional oxides and ITO for the fabrication of the electron transport layer.

Fabrication and function examination of PZT-based MEMS accelerometers

In this study, a hybrid sol-gel method was used to fabricate Pb(Zr0.52Ti0.48)0.98Nb0.02O3 (PNZT) piezoelectric thick films. By preparing Pb(Zr0.52Ti0.48)0.98Nb0·02O3 sol-gel solutions and mixing them with PZT-5A piezoelectric powders, therefore, the thickness of single layer coating can be increased and reduce the risk of film cracks. The proposed PNZT films have the dielectric constant of 1750, dielectric loss of 0.063, remnant polarization of 58 μC/cm2, and d33 of 133 p.m./V. Piezoelectric cantilever beam MEMS accelerometers were then designed, simulated and fabricated via photolithography methods on Si substrates. The sensitivity and natural frequency of the cantilever beam accelerometer are 16.8 mV/g and 200Hz, respectively. Finally, a cantilever beam accelerometer is successfully applied for the server hard-drive fault detection.

Controllable preparations and anti-corrosion properties of reduced graphene oxide films by binder-free electrophoretic deposition

This work assesses anti-corrosion properties of reduced graphene oxide (rGO) film deposited on copper by a binder-free electrophoretic deposition (EPD) method. Morphology of the samples is characterized by optical microscope and scanning electron microscopy (SEM) analysis. X-ray photoelectron spectroscopy (XPS), Raman and FT-IR analyzes confirm the reduction of GO with L(+)-Ascorbic acid (LAA). The results of water contact angle (WCA) measurements demonstrate that the hydrophilic copper surface is changed to hydrophobic after graphene oxide (GO) is reduced by LAA. Electrochemical tests indicate that rGO film have greater corrosion resistance than GO film, but different reduction ratio influences the corrosion resistance of rGO film. A plausible explanation for this finding is that the increase in the reduction ratio leads to an increase in the rGO interaction forces, resulting in cracks in the rGO film, which leads to a decrease in its anticorrosion efficiency. This approach provides a viable and scalable route for the use of rGO to protect metal surfaces from corrosion.

Effect of zinc injection on the electrochemical behavior and crack growth rate of a 316 L stainless steel in simulated primary coolant of pressurized water reactors

Zinc was added to high-temperature borated and lithiated water and its effect on the oxide film formation, electrochemical behavior and crack growth rate of 316 L stainless steel was investigated. The actual concentrations of zinc in the coolant solution at 300 °C and 350 °C were determined by ICP-Mass spectrometry. Zinc improved the electrochemical corrosion parameters of steel and reduced the crack growth rate of the sample by more than 13 times. Zinc also reduced the thickness of the formed oxide layers on steel and modified the chemical composition of the oxides to a mainly zinc and iron rich spinel.

Calcination-Free Fabrication of Highly b-Oriented Silicalite-1 Zeolite Films by Secondary Growth in the Absence of Organic Structure-Directing Agents

Calcination-free fabrication of highly b-oriented silicalite-1 (S-1) zeolite films in the absence of organic structure-directing agents (OSDAs) is attractive but still challenging. Herein, for the first time, we show a novel route for calcination-free synthesis of a b-oriented S-1 zeolite film in the absence of OSDAs. The key to this success is a rational secondary growth of zeolite crystals on the surface of supports by avoidance of the formation of zeolite nuclei in the system due to the absence of OSDAs. Because of OSDA-free synthesis of S-1, it not only reduces the cost of zeolite films but also avoids the calcination of OSDAs in the synthesis, thus avoiding the formation of cracks in the zeolite films. In addition, the calcination-free fabrication is favorable for reduction of zeolite film defects such as a terminal OH group. As a result, the zeolite films obtained from this work exhibit higher hydrophobicity than the conventional one. Furthermore, the current polarization curve of this S-1 zeolite film shows excellent corrosion resistance. The aforementioned features would be potentially important for industrial application of zeolite films in the near future.

Wrinkled p-phenylenediamine grafted graphene oxide as reinforcement for polyvinyl butyral anti-corrosive coating

Wrinkled p-phenylenediamine (PPD)-functionalized graphene oxide (PGO) is synthesized, characterized, and subsequently incorporated in a ethanol-based polyvinyl butyral (PVB) film (ca. 10 μm thick). The anti-corrosive properties of the pure PVB and nanocomposite (PVB-PGO and PVB-GO) films are tested on steel and compared. Electrochemical impedance spectra reveal that the PGO-reinforced PVB nanocomposite film exhibits the slowest corrosion rate (4 × 10−4 mm a−1 after a 20-day immersion) among the samples, and the results of 7-day saline spray bombardment tests show it is the most robust and durable. The PVB-PGO coating protects the steel substrate from visible corrosion. Incorporation of GO in the PVB matrix results in a reduction of the PVB film anti-corrosion properties. However, by functionalizing GO with PPD, highly dispersible wrinkled PGO flakes are obtained, thus leading to a uniform film that presents a highly tortuous path for impeding liquid and gas molecules. The PVB-PGO nanocomposite film exhibits high, stable capacitance without film delamination, cracking, or other visible damage. Readily accessible as a simple and environmentally friendly, this approach may present an advantageous strategy for creating protective coatings in marine and other applications. PGO with wrinkle structure, as nanometer reinforcing materials in PVB coatings, improved the corrosion resistance of the coatings by extending the permeation path of the corrosive medium.

On-chip environmentally assisted cracking in thin freestanding SiO2 films

An on-chip fracture mechanics method is extended to characterize subcritical crack growth in submicron freestanding films. The method relies on a self-actuated concept based on MEMS fabrication principles. The configuration consists of a notched specimen attached to actuator beams involving high internal stress. Upon release, a crack initiates at the notch, propagates, and arrests. Several improvements are worked out to limit the mode III component and to avoid crack kinking. The method is applied to subcritical crack growth in 140-nm-thick SiO2 films under different humidity conditions. The data reduction scheme relates crack growth rate to stress intensity factor. The static fracture toughness value is ~ 0.73 MPa sqrt{mathrm{m}}, with standard error of 0.01 MPa sqrt{mathrm{m}} and standard deviation of 0.17 MPa sqrt{mathrm{m}}. Subcritical crack growth rates are much smaller than in bulk specimens. A major advantage is that many test samples can be simultaneously monitored while avoiding any external equipment.Graphic

Analysis of spatial orientation distribution of highly oriented polyimide film using micro ATR-FTIR spectroscopic imaging method

Molecular orientation of aromatic polyimides (PIs) and their precursor of poly(amic ester)s (PAE) in the biaxially oriented films were analyzed by polarized microscopic attenuated-total-reflection Fourier-transform infrared absorption spectroscopy (micro pATR-FTIR) imaging. The films were prepared by shearing a lyotropic liquid crystal (LC) solution of the PAE on a glass substrate and subsequent drying under a N2 flow, and the long axis of polymer chains were distributed around the shear direction. In the film, streak-shaped defects were observed along the shear direction with optical microscopy. Such structural heterogeneities on the micrometer (μm) scale are expected to be visualized in spatial distribution map of molecular orientation order acquired with micro pATR-FTIR imaging. In this study, uniaxial orientation order parameter, S, and a mean square cosine value, ⟨cos2ψ⟩, were used to quantify the degree of orientation of the PI main chain and that of aromatic imide plane, respectively. It was revealed that the films are apparently homogeneous in the spatial distribution map of the S, while the films exhibited obvious heterogeneity in that of ⟨cos2ψ⟩, in which “face-on” and “edge-on” orientation domains coexist. The results indicate that orientation direction of the rigid PI chains is fixed in the averaged orientation direction of the oriented PAE matrix during thermal imidization, while the aromatic imide ring can be rotated around the main chain. Furthermore, cracks in the PI film were successfully visualized by ATR-FTIR imaging, and the orientation distribution inside the cracks was investigated. Through this structural study, we validated the quantitative capability of the micro pATR-FTIR imaging method thorough the analyses of highly oriented PI films and demonstrated its ability to investigate μm-scale heterogeneity on the basis of molecular orientation analyses.