Optimum Interlayer Thickness Research Articles

Evaluation of stress and energy relief efficiency of ZrN/Ti and ZrN/Zr

The purpose of this study was to investigate the extent of stress relief (Δσ%) and energy relief efficiency (ξtot) of metal interlayers in bilayer ZrN/Zr and ZrN/Ti thin films using an energy balance model based on the concept that the stored elastic energy in the ZrN coating could be partly relieved by the plastic deformation of metal interlayer. ZrN/Zr and ZrN/Ti specimens with different thicknesses of metal interlayers ranging from 100 to 300 nm were deposited on Si substrate using unbalanced magnetron sputtering. ZrN/Ti specimens were also deposited at different substrate bias voltages for investigating the energy relief efficiency by Ti interlayer under different stress levels in ZrN. The metal interlayers, Zr and Ti, were selected due to their different strain hardening behavior. Laser curvature method (LCM) and average X-ray strain combined with nanoindentation technique were employed to accurately measure the residual stresses in the entire specimen and the ZrN coating, respectively. Experimental results showed that Δσ% was more significant by Ti interlayer than by Zr interlayer. Δσ% of the entire specimen increased with interlayer thickness, while decreased with increasing stress of the top ZrN layer. The energy balance model was employed to evaluate ξtot by the interlayers. The contributions of energy relief from the ZrN coatings (ηZrN) and bending curvature relaxation of Si substrate (ηSi) could be separately assessed by the model. The results revealed that ξtot decreased by increasing Zr or Ti interlayer thickness, where the energy relief was mainly contributed from ηSi for ZrN/Zr specimens, while ηZrN was substantial for ZrN/Ti specimens, and there was an optimum interlayer thickness close to 100 nm, by which ξtot could reach up to 79.0 and 83.1% for Zr and Ti interlayers, respectively. For the ZrN coatings with different stress level ranging from −2.87 to −3.94 GPa, the variation of ξtot was less distinct, ranging from 39.1 to 48.8%, and the energy relief was mostly from ηZrN, except for σZrN close to −4 GPa, where the energy relief was mostly from ηSi. Although ξtot could serve as a better measure than Δσ% in evaluating the effectiveness of a metal interlayer, ηZrN and ηSi are the critical indexes that could reveal the actual energy relief in the hard coating. It is found that ηZrN and ηSi are related to the strength coefficient (k) of the interlayer. Therefore, in selecting a metal interlayer, it should be considered not only the capacity of energy absorption (Wp,max) but also the malleability (k) of the metal.

Effect of various interlayers on the performance of cesium formamidinium lead mixed halide (CsFAPbX3) – Formamidinium tin iodide (FASnI3) two-terminal tandem solar cell

In this work, 2D-Sentaurus TCAD has been used to investigate two terminal all-perovskite tandem solar cells (TSCs) having the structure Glass | ITO | PEDOT:PSS | CsFAPbX3| PCBM | Interlayer | PEDOT:PSS | FASnI3| PCBM | Ag. The thicknesses of active perovskite layers for both the bottom (FASnI3) and top (CsFAPbX3) sub-cells have been optimized for maximizing the device efficiency. Various metals (Ag, Au, Ti, Al, etc.), transparent conducting oxides (TCOs) such as ITO, FTO, and ZnO, and a polymer (PFN-Br) have been investigated for the interlayer. The dependence of solar cell performance on the thicknesses and optical constants of these interlayers, and on the angle of light incidence (θ) have been analyzed using the integrated optical generation rates. The metal-interlayer TSCs show a monotonic decrease in efficiency with increasing interlayer thickness. A 1 nm Ti-interlayer, for example, gave an efficiency of 12.9% at normal incidence. On the other hand, ITO-interlayer TSC gave its highest efficiency at an optimum interlayer thickness of 5 nm. While some of the metal-interlayer TSCs have been found to generate power for θ values up to 80°, those with more commonly used interlayers such as Ag and Au showed poor angle dependence. TSCs with all the TCO- as well as the PFN-Br- interlayers gave their highest efficiencies at oblique angles of incidence rather than at normal incidence. A peak efficiency of 12.55% was obtained at an angle of 50° for the TSC with this interlayer. To estimate the maximum amount of energy that these TSCs can generate in an year, the energy densities generated per day (Eday) were integrated and compared using the solar irradiation and temperature data from Photovoltaic Geographical Information System (PVGIS-SARAH, European Commission) database. Among all the interlayers studied here, Ti and ITO have been found to be the best metal and TCO respectively. For example, despite generating the highest short circuit current density at normal incidence, the Ag-interlayer TSC generates 79% and 82% lower energy density than these TSCs on the longest day of the year.

Strengthening Cu/Ni nanolayered composites by introducing thin Ag interlayers: A molecular dynamics simulation study

Experiments have shown that the ultrahigh strength of nanolayered metallic composites originates from their high-density interfaces of special characteristics. Hence, the modulation of interface structures becomes an effective route to enhance the mechanical performance of the nanolayered composites. One of the general ways to tune the interfacial feature is to introduce interlayers of several nanometers among constituent layers, such as amorphous (disordered) and crystalline (ordered) interlayers. Here, the deformation of a Cu/Ni layered composite with Ag interlayers of different thicknesses was simulated by molecular dynamics simulations. Our simulations show that the yield stress of 25 nm Cu/25 nm Ni nanolayered composites with Ag interlayers can be significantly enhanced, i.e., it can be 56.4% higher than that of their counterparts without interlayers. We also found that the yield strength of the new composites can be maximized by selecting an appropriate thickness for the Ag interlayer. The optimum interlayer thickness is 2.1 nm in tension and 4.2 nm for compression. It is revealed that the extra strength results from the alleviation of stress concentration by stimulating abundant interfacial dislocations at the Cu–Ag and Ag–Ni interfaces. These findings show that the introduction of additional interlayers is a new route to design stronger nanolayered metallic composites.

ENHANCEMENT OF ADHESION STRENGTH AND TRIBOLOGICAL PERFORMANCE OF CVD DIAMOND FILMS ON TUNGSTEN CARBIDE SUBSTRATES WITH HIGH COBALT CONTENT VIA AMORPHOUS SiC INTERLAYERS

In this study, the diamond films are deposited on tungsten carbide substrates with 10[Formula: see text]wt.% Co via hot filament chemical vapor deposition (HFCVD). Amorphous SiC (a-SiC) interlayers with various thicknesses are fabricated between the diamond films and tungsten carbide substrates via precursor pyrolysis to promote the adhesion and friction performance of diamond films. Indentation tests are performed to evaluate the adhesion of the as-fabricated diamond films, which show that the a-SiC interlayers can greatly improve the adhesive strength between diamond films and tungsten carbide substrates with 10[Formula: see text]wt.% Co. Moreover, the thickness of a-SiC interlayer is of great importance for the effectiveness on the film–substrate adhesion enhancement. The optimum thickness of a-SiC interlayer is 1[Formula: see text][Formula: see text]m. Afterwards, ball-on-disc experiments are chosen to check the tribological properties of the as-fabricated a-SiC interlayered diamond film specimen with the optimum interlayer thickness, which exhibits lower friction coefficient than the conventional diamond film with no interlayer.

Comparison of performances of three active layers cascade OPVCs with those obtained from corresponding bi-layers

In this study, organic photovoltaic cells based on planar heterojunctions using small-molecules were fabricated. Two cell configurations were used, planar heterojunctions based on a classical electron donor/electron acceptor couple and planar heterojunctions using three active layers, one donor, one acceptor and a central ambipolar layer. The donor is a thiophene derivative called BSTV, the acceptor is the fullerene while the ambipolar material is a phthalocyanine dye, the SubPc. After studying the performances of cells based on the couples SubPc/C60, BSTV/C60 and BSTV/SubPc, we explore the dependence of the short circuit current and the external quantum efficiency on the SubPc interlayer thickness in cells with three active layers. By comparison with the optimum couple SubPc/C60 the ternary structure BSTV/SubPc/C60 exhibits higher short circuit current but smaller fill factor. Nevertheless, for an optimum interlayer thickness of 12.5 nm, the ternary structure allows an improvement of the cell efficiency of 11% by comparison with the highest result obtained with the best couple. As shown by optical measurements, long range Föster energy transfer from the larger band gap donor, BSTV, to the smaller band gap, SubPc, is possible. Therefore, the increase of Jsc is attributed to two-step exciton dissociation process. Excitons produced in the outer BSTV layer are transferred to the SubPc central layer and then dissociated at the interface.

Probabilistic Strength Estimation for Ceramic-Metal Joints with Various Interlayer Thicknesses

Residual stress generated by thermal expansion coefficient mismatch between ceramic and metal is an important problem affecting the strength of ceramic-metal joints. An interlayer, which is a ductile metal, is often inserted between ceramic and metal in order to relax this residual stress. In this study, the residual stress produced in the joint-cooling process is analyzed and 4-point bending tests are carried out. From the viewpoint of experimental observations and fracture mechanics, the effects of interlayer thickness on joint strength in ceramic/metal joints are discussed considering the superimposed stress distribution of the residual stress and the bending stress. Joint strength is then estimated based on fracture mechanics and fracture probability considering the superimposed stress, crack size and position of pre-existing defects in the ceramics. The optimum interlayer thickness for the present specimen is identified, and the estimation method is extended to the analysis of generic joint strength using normalized strength of ceramic by expressing joint strength in terms of normalized strength considering the scatter of joint strength and the effective volume.

Enhanced nucleation density of chemical vapor deposition diamonds by using interlayer

Effects of interlayers on diamond nucleation were investigated for the Si substrates. Interlayers were deposited on the diamond-abraded Si substrates by rf sputtering prior to diamond growth using microwave plasma chemical vapor deposition (CVD). Compared with 1 × 108/cm2 for the just abraded substrate, the nucleation density was greatly enhanced to 1 ∼ 2 × 109/cm2 by 50 nm thick interlayer, irrespective of the kind of interlayer material used in this study (Si, Mo, Ti, Pt, Ag, TiN, or SiO2). As the thickness of the Si interlayer increased from 20 to 500 nm, the nucleation density reached a maximum value, 3 × 109/cm2 at 100 nm. However, the growth rate was monotonically reduced from ∼300 nm/h to ∼100 nm/h. For the 700 nm thick Si interlayer, no diamond growth was observed. These results indicate that there is an optimum interlayer thickness around 100 nm for the higher nucleation density. The role of the interlayer in enhancing the nucleation density is believed to protect the nucleation sites generated by the diamond abrasion, otherwise they could be considerably etched away by atomic hydrogen during the initial diamond deposition.

Permeability of microstrip thin films of various materials

Soft magnetic bilayered microstrip films have been studied for various materials such as Ni–Fe–Mo–Cu, Co–Zr–Mo–Ni, Fe–Si–N, and Ni–Fe in terms of their magnetization dynamics. Effects of the strip width and the interlayer thickness on permeability were investigated. An optimum interlayer thickness was found for obtaining the maximum permeability for those films except Fe–Si–N, but the optimum value differs in magnetic film material. A scanning Kerr effect microscope observation reveals that permeability variations with strip width related to changes of the dynamic domain configurations of the strips. All magnetic film materials except Fe–Si–N show a high permeability of more than 1000 at 2 μm strip width at each optimum interlayer thickness. When the film width is reduced to 1 μm, however, the permeability decreases significantly regardless of the interlayer thickness and kinds of the film materials. For such narrow strip film, a higher permeability is obtained for higher anisotropy field. It is concluded that the shape anisotropy of the micropatterned films must be controlled for achieving a higher permeability.

Laminated media for high-density recording

The magnetic recording properties of laminated media structures on hard disks are discussed, including an overview of work on this topic. The primary performance advantage of laminated media is a significant reduction in media noise. The various mechanisms proposed for this noise reduction are considered. Other issues discussed include the optimal properties for the nonmagnetic interlayers, the influence of lamination on bulk magnetic properties, soft error rate measurements, and process challenges. The most important mechanism for the improved performance that has been obtained is decoupling of the noise sources in the various layers. The optimum interlayer thickness is in the range of 20-50 AA and seems to depend on the sputtering system and process conditions used. >

Techniques for improving thin film adhesion

In most engineering applications the minimum criterion for adequate performance of a coated component is that the coating survive in the operating environment for the component lifetime. In practice this means that good adhesion of the coating to the substrate is of prime importance in dictating the lifetime of the component and a number of techniques have been developed to improve coating/substrate adhesion based on this requirement. Cleaning of the components prior to coating in order to remove protective layers, organic contaminants, adsorbed layers, dust and fingerprints is essential and several multi-stage cleaning processes have been developed to achieve this. Once loaded in the coating system some pre-heating of the components in vacuum or in a reducing plasma can be used to remove friable adsorbates and weak surface oxides. At this stage, sputter cleaning is also an important technique; this is used to break up more tenacious oxides and sputter contaminants from the component surface. However, this process can change the surface chemistry and properties of the components and does tend to lead to redistribution of sputtered material elsewhere in the system which can be a disadvantage. For deposition technologies which operate at high temperature a certain amount of diffusional intermixing at the interface can be achieved once coating starts which can be beneficial for adhesion and similar mixing is possible by the use of ion bombardment during the early stages of film deposition. Finally, for ceramic coatings, the use of metallic interlayers or bond coats can be used to improve adhesion and there is an optimum interlayer thickness to maximise coating/substrate adhesion. In this paper the effects of cleaning pre-treatments, sputter cleaning and interlayers on adhesion (assessed using the scratch adhesion test) will be illustrated with results for titanium nitride coatings on a stainless steel substrate.

The interphasial regions in interlayer fiber composites

AbstractThe interaction between the fiber and matrix in a fiber‐reinforced material plays an important role in determining the mechanical behavior of the composite. An efficient technique to simultaneously improve fiber‐matrix interfacial shear strength and impact behavior of the composite is to deposit a flexible interlayer onto the fiber. This results in the creation of three bulk phases, the fiber, matrix, and the interlayer and two interphasial regions. A phenomenological model that defines the variation of the fiber‐interlayer interphase and that of the interlayer‐matrix interphase has been developed. In the model, the elastic moduli of these regions vary continuously, so as to bridge the two bulk phases on either side of the interphase. The interaction between the bulk phases is also taken into consideration. The model has the potential for the use of dynamic mechanical analysis to obtain, relatively, adhesion/interaction parameters of different fiber‐interlayer‐matrix systems. These parameters can be used to determine the optimum interlayer thickness for improved toughness and good stress transfer efficiency.

Effects of reactive and non‐reactive fiber coatings upon performance of graphite/epoxy composites

AbstractInterlayers of controlled composition and thickness were applied to commercial graphite fiber bundles by electrochemical copolymerization, and the impact and interlaminar shear strength of composites from these coated fibers were examined. Glycidyl acrylate/methyl acrylate copolymers represented coatings that were reactive to the epoxy matrix during curing; acrylonitrile/methyl acrylate copolymers represented non‐reactive systems. The reactive systems showed 10 to 30 percent simultaneous improvement in impact and interlaminar shear strengths, while the non‐reactive system failed at the interlayer‐epoxy interface and showed no improvement. There is an optimum interlayer thickness of 0.1 to 0.15 micron; the possible reasons are discussed. A detailed scanning electron microscope study illustrates how the structure of the composite fracture surface varies with the systematic changes in interlayer reactivity, composition, and thickness. Determination of the locus of failure is discussed. The observations are consistent with the mechanical property measurements.

Impact strength of thick‐interlayer composites

AbstractThe impact strength of a thicker interlayer fiber filled composite material is evaluated as a function of both interlayer thickness and glass transition temperatures (Tg). The results confirm that for maximum strength, an optimum interlayer thickness is required. It is shown that this result is a function of the interlayer's Tg. Comparison with studies on other rubber reinforced systems are noted.