Nanoscratch Tests Research Articles

Evaluation of the Adhesion Strength of Ultrathin Gold Coatings on Substrates of Soda-Lime Glass and Cyclo-Olefin-Polymer by Cross-Cut and Scratch Tests under the Influence of a Thermal Shock Test for Use in Biosensors.

The current demand for highly sensitive, optical sensors in biodiagnostics has prompted the development of ultrathin metal coatings on a range of substrates. Given the potential attenuation of the signal from a plasmonic sensor for the detection of fluorescent molecules when an adhesion layer between the substrate and coating is employed, this study examines the impact of various factors on the adhesion strength between gold coatings and substrates comprising glass and cyclo-olefin-polymer (COP). The objective is to identify potential configurations for high adhesion strength, thereby eliminating the need for an adhesion layer in the fabrication of optical sensors with gold coatings for diagnostic applications or to utilize a minimal adhesion layer thickness. The influence of pretreatments prior to coating deposition with oxygen plasma, ultrathin adhesion layers of titanium as well as the impact of thermal shock tests with various cycles on the coating's integrity are investigated. Two methods of adhesion strength testing were applied to ultrathin coatings on glass and polymer substrates. Cross-cut and nano scratch tests were used to assess the adhesion of the ultrathin metal layers, which provided qualitative and quantitative results. The results of the two test methods on glass substrates are in good accordance, demonstrating the highest adhesion strength for gold coatings on glass with an adhesion layer, in combination with or without plasma treatment. The cross-cut testing on COP demonstrates a constant high adhesion strength when using an adhesion layer alone or without any pretreatment, while a low adhesion strength is observed in combination with plasma treatment. Following the thermal shock test, alterations in adhesion strength were observed for the remaining configurations. The rise in the coefficient of thermal expansion of COP between +30 and 85 °C in comparison to lower temperatures, as evidenced by thermomechanical analysis, may account for the disparate adhesion strengths of COP following thermal shock tests.

Strategy To Enhance Interfacial Properties: Preparation of Porous Polytetrafluoroethylene Fibers and the Adsorption of Initiators/Curing Agents.

Polytetrafluoroethylene (PTFE) fibers exhibit high inertness and demonstrate limited interfacial bonding capabilities with other materials. To overcome this limitation, PTFE@ZnO fibers were developed by depositing the porous ZnO layer onto PTFE fibers via a hydrothermal reaction, and porous fibers were adsorbed curing agents or initiators. The interfacial shear strength (ILSS) of the composites demonstrated a significant improvement, particularly in the case of composites containing PTFE/initiator fibers, where the ILSS increased by 104.8% compared to PTFE alone (from 8.3 to 17.0 MPa). The digital image correlation (DIC) method revealed a more uniform stress distribution in the modified fiber composites at the point of fracture. Additionally, nanoscratch tests indicated a significant enhancement in the interfacial bonding between the modified fibers and the resin. The porous structures facilitated mechanical interlocking between the modified fibers and the resin. Furthermore, the presence of an adsorbed initiator/curing agent within the porous structure served as the initiation site for the free radical polymerization of vinyl ester resin 901, thereby enhancing the interfacial bonding between the modified fibers and the resin. The novel strategy presents a general and viable approach for the extensive modification of PTFE fibers, focusing on achieving exceptional interfacial bonding properties.

Surface Damage by Physical Cleans during Semiconductors Manufacturing

Keywords: physical damage, surface, cracks, defect revelation Introduction More than one third of process operations in integrated circuits manufacturing rely on Wet cleans. They’re used to remove contaminants such as particles which are a dies’ yield killer. This is achieved either by a chemical action lifting the particles at the cost of a significant materials loss and device performances. This can be also done with some physical cleans (acoustic wave [1], cryogeny [2], high velocity spray [3]) or a combination of both. Whereas features damage by physical cleans has been widely studied [4], surface damage is poorly documented [5] due to lack of evidence. Experimental and characterizations In this work, FDSOI wafers (12 nm Si on 20nm buried oxide) are used. Physical cleans consist in either bi fluidic (aqueous liquid and nitrogen) high velocity sprays, or nitrogen cryogeny methods. Defects inspection on bare wafers is performed on a SP3 Surfscan tool from KLA-Tencor at detection such as 53 nm. Results and discussion Several physical cleans are considered in this paper.First and foremost, high velocity sprays are considered. Their activation and deactivation are the most critical steps due to high risk of erratic behavior (figure 1). Therefore, only well stabilized sprays are hereby discussed. Surface damage on FDSOI surfaces has already been reported [6]. Nano cracks on hard surface can’t be directly detected. A revelation method is used to enlarge the defects, by etching the box (buried oxide) underneath the 12 nm Si layer, thanks to concentrated HF. The wet chemistry can’t penetrate the nano cracks (trapped air [7] and steric hindering [8]) until the path is slightly enlarged. Hence an oxidation step is performed either by ozonated water or plasma to oxidize the silicon along the nano crack and generate after HF step, a 5 nm hole for HF to etch µm wide cavities underneath the damaged silicon (figure 2). Other solid films have been characterized the same way, by changing the enlarging and revealing chemistry. Secondly, a direct characterization method has been developed to quicker compare physical cleaning methods. Indeed, the first method has one drawback, only cracks deep enough are revealed. Soft films are hence used to directly reveal surface damage. A relevant choice of the polymer has enabled to evidence various kind of defects [9] with the high velocity spray (figure 3) and also some alumina particles damaging the resist surface during a nitrogen cryogenic clean (figure 4). These latter weren’t detected on hard films. The various defects maps and tests are summarized in table 1. Eventually, nano indentation and nano scratch tests have been performed on the photo resist films to reproduce the behavior of high energy droplets. And consequences from surface damage will be discussed. Conclusions Physical cleans are widely used in semiconductors manufacturing and are mandatory to achieve a high yield. Whereas damage to features is well documented and easily detected, surface damage is not. Two methods are given to evidence these phenomena: either directly on soft matter or by indirect revelation on hard surfaces.Some new particles cleaning solutions like polymer coat and peel methods are emerging [10] [11]. They combine both an excellent cleaning performance without any damage.

Cleavage and anisotropy dependence of material removal behavior of monocrystalline β-Ga2O3 in abrasive machining

Beta-phase gallium oxide (β-Ga2O3) is recognized as a promising next-generation semiconductor material with an ultra-wide bandgap and broad application prospects. However, its pronounced cleavage and anisotropy presents great challenges in precision abrasive machining, hindering the advancements in related device manufacturing. In this work, systematic nanoscratching and nanogrinding tests, combined with characterization methods such as SEM, TEM, and Raman spectroscopy, as well as stress field theory were performed to explore the effects of easy-cleavable and anisotropy properties on material removal behaviors, specifically the machining directions parallel and perpendicular to the cleavage planes. The results indicate that when the direction is parallel to the cleavage plane, the scratch morphology is dominated by oriented cracks and bulk fractures, and cleavage cracks and stacking faults extending into the matrix cause more severe subsurface damage; when the direction is perpendicular to the cleavage plane, the scratch morphology is mainly induced by free damaged groove, with the subsurface comprising a mixed phase of nanocrystals and amorphous, and a few stacking faults, resulting in a much shallower damage layer. These results were further validated through nanogrinding tests, which showed that when the direction is parallel to the cleavage plane, the ground surface is dominated by cleavage facets, and both surface roughness and subsurface damage are much worse compared to the direction perpendicular to the cleavage plane. A mechanistic model was established, depicting that cracking on the cleavage plane and slip plane, coupled with crack deflection under stress fields, primarily leads to anisotropy in of material removal during abrasive machining. These results enhanced the understanding of the cleavage and anisotropy dependence in the machining process and provided insights for controlling the surface/subsurface damage in precision abrasive machining of β-Ga2O3.

Anisotropy and symmetry in the elastoplastic deformation of single crystals under scratching: Unravelling the microscopic deformation mechanisms

The nanoscratch test, as an established technique for assessing material tribological properties has received significant attention. However, the symmetry and anisotropy in scratching performances as well as the quantitative correlation between the orientation-dependent deformation and inherent microscopic deformation mechanism remain unexplored. Herein, crystal plasticity simulations can quantitatively capture scratching forces, elastic recovery, and surface pile-ups, as well as accurately describe inner deformation fields and lattice rotation patterns, as confirmed by experimental results. The simulation results reveal that surface pile-up and elastic recovery mappings on (001)-, (011)-, and (111)-oriented samples exhibit eight-fold, four-fold, and six-fold symmetries, respectively. The orientation-dependent location and intension of both slip activities and lattice rotation, determine the features of macroscopic elastoplastic deformation under scratching.

Tribomechanical characterization of ceramic reinforced composite coatings for modification of cylinder liner of heavy-duty diesel engines

Heavy-duty diesel engines are essential mechanic power generation tools for industry and transporting freight and passengers. Therefore, increasing engine efficiency and minimizing maintenance and repair costs is crucial. This study examines and characterizes three thermal spray coatings (Cr3C2/NiCr, NiCr, and Al2O3/TiO2) utilized on cylindrical gray cast iron substrate specimens. The coatings were tested for their microstructural (optical microstructure, SEM, EDS, XRD, and AFM topography), mechanical (nanoindentation and nano scratch), and tribological (short and long-distance wear test) properties. Microstructural tests showed that an average coating thickness of 120 to 170 µm was successfully achieved on the cast iron base substrate using different thermal coating methods. The Cr3C2/NiCr coating, observed through the AFM mapping method, achieved the most uniform roughness distribution on the surface. The elasticity of the coatings was measured with a nanoindentation test, and Al2O3/TiO2 coating exhibited high rigidness (177 GPa). The nano scratch test showed that the highest load-carrying capacity was achieved with the Cr3C2/NiCr coated sample. NiCr-coated sample exhibited approximately similar rigidness (61 GPa) to cast iron (67 GPa). Short- and long-distance wear tests showed that the coatings provided significantly better wear resistance than the cast iron base. The coatings’ efficacy was evident. At the long-distance tests, while the cast iron base sample had a wear rate of 19.874 (10−7mm3/Nm), the wear rates of Al2O3/TiO2, Cr3C2/NiCr, and NiCr coatings were 3.835, 4.020, and 6.466 (10−7mm3/Nm), respectively. The Al2O3/TiO2 and Cr3C2/NiCr coatings had superior tribological performance than the NiCr coating, yet the NiCr coating showed much higher wear performance than the uncoated base. The Cr3C2/NiCr coating exhibited superior tribomechanical performance in all the coatings.

Effect of crystallographic texture and grain orientation on tribological properties of WAAM deposited IN625 alloy in weaving deposition strategy

Understanding the variation in the local microstructure and texture of the as-built fabricated by wire arc additive manufacturing (WAAM) is highly challenging. They affect the mechanical and tribological properties of the builds. The deposition patterns and the process parameters are key factors that determine the microstructures and hence other properties. In the present study, builds of Inconel 625 alloy have been manufactured through WAAM by using a weaving pattern. The microstructure and their texture at the different locations of the deposited build have been investigated through electron backscattered diffraction (EBSD) and optical microscopy. The detailed evolution mechanisms of the micro-structure of the build have been studied followed by the quantitative analysis of the grain size, misorientation angles, fraction of recrystallized and deformed grains, and textures. Later the effect of texture components on the hardness, elastic modulus, and coefficient of friction (COF) of the build has been studied by using nano-indetation and nano-scratch tests. The grain size was found to be 33 μm, 110 μm, and 66 μm at the bottom, middle, and top, respectively. The top region was dominated by Cube {001}<uvw>, Goss {011}<100>, and E {111}<110> orientations, which changed to deformed texture Brass {110}<112> and Goss {011}<100> orientations in the middle region and cube texture at the bottom. Hardness was highest at the top region 5.33 GPa, followed by 4.02 GPa in the middle region and 4.74 GPa at the bottom. The COF was highest in the middle region at 0.456, which reduced to 0.323 in the bottom region. Sheared textured grains {111}<uvw> have shown greater value of COF and hardness than the {101}< uvw> and {100}<uvw> texture grains. The study has been carried out to investigate the variation in local mechanical properties due to microstructural variations. It will help industries to design components with homogeneous mechanical properties.

Microstructure, mechanical and tribological characterization of magnetron sputtering ZrN and ZrAlN coatings

In this research paper, mechanical and tribological characterization of novel high wear-resistant ZrN-ZrAlN coatings are presented. The varying concentrations of AlN is chosen to evaluate the influence of AlN the surface morphological, nanomechanical, and tribological properties of the composite coating. The coatings were developed on D9 steel substrates using nitrogen reactive gas radio frequency (RF) magnetron sputtering of zirconium and aluminium targets in an argon plasma. Variable power density for the aluminium target and constant power density for zirconium, was used to obtain in a systematic way, the variable concentration of AlN in the coating. Surface morphological studies were carried out to evaluate composition and crystal structure using X-ray diffraction (GIXRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). Coatings display a polycrystalline structure, but the level of crystallinity decreases with higher AlN concentration. Nanomechanical and nano scratch testing, along with tribological experimental studies were performed to comprehensively analyse performance of the developed coatings. Higher hardness of composite coating is achieved with optimal concentration of AlN in ZrN-ZrAlN coating. Adhesion strength of the coatings increased with the increase in the concentration of AlN. ZrN-ZrAlN coatings depicted low wear, however coatings containing AlN exhibits superior wear resistance.

Nano-tribological behavior and structural evolution of 304 stainless-steel by molecular dynamics simulation and experiment

304 stainless-steel has excellent mechanical properties and is commonly used in ultra-precision instrumentation. Nevertheless, the research on the intricate nano tribological behavior of 304 stainless-steel during ultra-precision machining remains limited. In this work, the tribological behavior of 304 stainless-steel is investigated at different indentation depths and scratching velocities by molecular dynamics (MD) simulations and nano-scratch tests. The results show that higher indentation depths lead to more serious damage on the surface and subsurface of 304 stainless-steel. The friction force and friction coefficient also increase significantly with higher indentation depths. It is worth noting that the dislocation density is much smaller at the low-indentation depth, which is due to the large-scale dislocation annihilation at this depth. As the scratch velocity increases, the subsurface shear stress decreases, the dislocation length rises, and it is accompanied by the generation of V-shaped dislocations, which are caused by dislocation entanglement within the substrate. In addition, nano-scratch tests were performed and similar trends were obtained by comparing the results with simulations. This work provides theoretical guidance for a deeper understanding of the deformation behavior of 304 stainless-steel during nano-scratching and its engineering applications at the micron and nano-meter scales.

Investigating the mechanism of enhancing interfacial adhesion of SiOx films on GaAs substrates through process optimization

In the manufacturing of GaAs-based quantum well (QW) lasers, the adhesion between the Silicon dioxide (SiOx) film layer and the Gallium arsenide (GaAs) substrate is crucial for the performance and durability of semiconductor devices. This study focused on depositing SiOx films on GaAs substrates using plasma-enhanced chemical vapor deposition (PECVD). The research aimed to investigate the impact of different coating processes on the deposition rate, properties, and composition of the coatings. The interfacial adhesion of various samples was assessed using nano-scratch tests. The results revealed that samples with lower SiH4 gas flow and RF power, or higher process pressure exhibited stronger adhesion strength. It's further observed that optimizing the process parameters reduced residual stresses in the film, thereby enhancing the GaAs-SiOx interfacial bonding. This work has the potential to significantly reduce the possibility of QW lasers malfunctions, improve the reliability of semiconductor devices and provide valuable insights for future studies on enhancing film-substrate adhesion.

Understanding the Influence of Carbon Interlayers on Material Removal and Tribochemical Evolution in Multilayer Coatings Through In-Situ Analysis

The carbon interlayers in the multilayer coatings can improve the load-bearing capacity and oxidation resistance, promote the layer-by-layer wear mechanism, and extend the lifespan of the multilayer coating, which is crucial to improving their tribological properties. To investigate the role of C interlayers in the competitive relationship between tribochemistry and material removal in multilayer coatings, this study comprehensively examines the tribological behavior of single layer MoS2 and multilayer MoS2/C coatings through in-situ tribotests and nanoscratch tests. Key findings reveal that the C interlayers enhance the tribological behavior by reducing the oxidation rate of MoS2, improving the load distribution, and delaying the onset of coating failure. Specifically, the single layer MoS2 coating demonstrated a lifespan of 55,000 cycles, whereas the multilayer MoS2/C coating achieved 80,000 cycles, reflecting a 45% enhancement. The critical load increased from 8 mN to 18 mN, indicating a 125% improvement in removal resistance. The presence of C layers results in a more stable and enduring tribofilm, which leads to reduced friction and wear. This study underscores the importance of in-situ analysis by combining nanoscratch with Raman mapping to elucidate the complex tribological behavior of coatings. These insights are crucial for designing efficient, wear-resistant, low-friction multilayer coatings for diverse industrial applications.

Enhanced bioactivity and mechanical properties of silicon-infused titanium oxide coatings formed by micro-arc oxidation on selective laser melted Ti13Nb13Zr alloy

The titanium scaffolds and surface-porous implants are manufactured by fast and cheap additive methods such as selective laser melting (SLM). The obtained irregularity and relative biological inertness of the titanium need proper surface modification. This research is aimed at forming bioactive multicomponent oxide coatings by micro-arc oxidation (MAO) at different process parameters on the selective laser-melted Ti13Zr13Nb alloy. The MAO process was carried out in a base solution containing 0.15 mol/L Ca and 0.1 mol/L GP, with different amounts of metasilicate added under two different applied voltages. Scanning electron microscopy, atomic force microscopy, X-ray electron diffraction spectroscopy, nanomechanical and nano scratch tests, water contact angle measurements, phosphate deposition observed in long-term immersion tests, and biological LDH and MTT assays were performed. The results showed that the coating microstructure, morphology, and properties were significantly dependent on process parameters. In particular, the metasilicate addition and its rising content in the electrolyte resulted in the higher development of the surface followed by better viability of osteoblasts at no necrosis, with no negative change in the other parameters, usually close to those obtained on silicon-free coatings. The obtained results prove that the addition of silicon to the electrolyte at the partial expense of calcium can be favorable for long-term titanium implants made by selective laser melting.

Differences in tissue-level properties as assessed by nano-scratching in patients with and without atypical femur fractures on long-term bisphosphonate therapy: a proof-of-concept pilot study.

Atypical femur fractures (AFFs) are a well-established complication of long-term bisphosphonate (BP) therapy, but their pathogenesis is not fully understood. Although many patients on long-term BP therapy have severe suppression of bone turnover (SSBT), not all such patients experience AFF, even though SSBT is a major contributor to AFF. Accordingly, we evaluated tissue level properties using nano-scratch testing of trans-iliac bone biopsy specimens in 12 women (6 with and 6 without AFF matched for age and race). Nano-scratch data were analyzed using a mixed-model ANOVA with volume-normalized scratch energy as a function of AFF (Yes or No), region (periosteal or endosteal), and a first-order interaction between region and AFF. Tukey post hoc analyses of the differences of least squared means of scratch energy were performed and reported as significant if p<.05. The volume-normalized scratch energy was 10.6% higher in AFF than in non-AFF patients (p=.003) and 17.9 % higher in the periosteal than in the endosteal region (p=.004). The differences in normalized scratch energy are suggestive of a higher hardness of the bone tissue after long-term BP therapy. The results of this study are consistent with other studies in the literature and demonstrate the efficacy of using Nano-Scratch technique to evaluate bone tissue that exhibits SSBT and AFF. Further studies using nano-scratch may help quantify and elucidate underlying mechanisms for the pathogenesis of AFF.

The impact of titanium alloying on altering nanomechanical properties and grain structures of sputter-deposited cobalt for electromigration reliability enhancement

Cobalt (Co) has recently become a highlighted on-chip interconnection material for advanced metallization scheme of microelectronic circuits. Here, electromigration behaviors of sputter-deposited Co and Co(Ti; 0.9 at%) interconnection lines embedded in Si are comparatively studied. These lines were annealed (500 °C/30 min) prior to further accelerated electromigration testing under high current densities in the range of 3 × 107–9 × 108 A cm−2. A collection of the obtained electromigration failure lifetimes, current scaling factors and activation energies confirms a noticeable enhancement in the electromigration reliability of the Co lines by the added Ti. Results by scanning transmission electron microscopy (STEM) and nanoscratch testing reveal that 3–5 nm-sized Ti crystallites are uniformly dispersed in the Co-interconnect matrix, effectively inhibiting Co grain growth, promoting the formation of nanotwinned Co and elevating film’s mechanical properties for ensuring the electromigration reliability. With deteriorated hardness and adhesion energy, reduced planar defects and many big grains all spanning transversely the entire interconnect line, Co is vulnerable to electromigration failures, also giving accelerated thermally-induced interfacial diffusion and chemical reactions with the surrounding Si, as proven by depth-profiling secondary spectrometry and STEM analysis.

Frictional resistance and delamination mechanisms in 2D tungsten diselenide revealed by multi-scale scratch and in-situ observations

Friction phenomena in two-dimensional (2D) materials are conventionally studied at atomic length scales in a few layers using low-load techniques. However, the advancement of 2D materials for semiconductor and electronic applications requires an understanding of friction and delamination at a few micrometers length scale and hundreds of layers. To bridge this gap, the present study investigates frictional resistance and delamination mechanisms in 2D tungsten diselenide (WSe2) at 10 µm length and 100–500 nm depths using an integrated atomic force microscopy (AFM), high-load nanoscratch, and in-situ scanning electron microscopic (SEM) observations. AFM revealed a heterogenous distribution of frictional resistance in a single WSe2 layer originating from surface ripples, with the mean increasing from 8.7 to 79.1 nN as the imposed force increased from 20 to 80 nN. High-load in-situ nano-scratch tests delineated the role of the individual layers in the mechanism of multi-layer delamination under an SEM. Delamination during scratch consists of stick-slip motion with friction force increasing in each successive slip, manifested as increasing slope of lateral force curves with scratch depth from 10.9 to 13.0 (× 103) Nm−1. Delamination is followed by cyclic fracture of WSe2 layers where the puckering effect results in adherence of layers to the nanoscratch probe, increasing the local maximum of lateral force from 89.3 to 205.6 µN. This establishment of the interconnectedness between friction in single-layer and delamination at hundreds of layers harbors the potential for utilizing these materials in semiconductor devices with reduced energy losses and enhanced performance.

Interlayer design for strong adhesion in the double-layer flexible copper clad laminate via HiPIMS deposition

By designing different interlayers (Al, Si/SixNy and Cr interlayer) and oxygen plasma pretreatment of the substrate, strong adhesion was realized for the double-layer flexible copper clad laminate on polyimide (PI) substrate via high power impulse magnetron sputtering (HiPIMS) technology. The microstructures and properties of Cu films on PI substrate were characterized by an X-ray powder diffractometer (XRD), X-ray photoelectron spectroscope (XPS), atom force microscopy (AFM), scanning electron microscope (SEM), nano-scratch test, scotch tape test and four-probe detector. With the introduction of interlayer and oxygen plasma pretreatment, the critical load of Cu film (300 nm thick) peaked at 43.5 mN and the sheet resistance ranged from 124 to 227 mΩ/sq. The oxygen plasma pretreatment resulted in the drastic oxidation to generate functional groups on the PI substrate surface, which contributed to the improvement of adhesion strength by chemical interaction in terms of the film with Si/SixNy or Cr interlayer. Besides, for the Cu film with Si/SixNy interlayer, the resistance against copper diffusion by the SixNy layer can also promote the enhancement of adhesion strength.

The evolution of microstructure and mechanical properties of Inconel 625 alloy fabricated by laser powder bed fusion via novel hybrid scanning strategy

Four innovative hybrid scanning strategies (0° + 67°, 45° + 67°, 67° + 67° and 90° + 67°) of laser powder bed fusion (LPBF) have been proposed to tailor the microstructure and mechanical properties of Inconel 625 alloy for the first time. The experiment results revealed in sample I (0° + 67°) and sample IV (90° + 67°) a gradient structure is formed, progressing from randomly textured slender columnar crystals (001) to randomly textured equiaxial fine crystals, and finally to equiaxial and fine columnar crystals. In samples II (45° + 67°) and III (67° + 67°), isometric and columnar crystals are uniformly distributed throughout the sample. The tensile strengths of samples treated via hybrid scanning strategy in LPBF (sample I: 1270 ± 8 MPa, sample II: 1400 ± 6 MPa, sample III: 1390 ± 5 MPa and sample IV: 1360 ± 5 MPa) surpassed those of conventionally manufactured samples, including Inconel 625 alloy fabricated by LPBF using a single scanning strategy. This superiority can be attributed to the presence of fine grains, elevated residual stress levels, and the formation of stacking faults. The results of the nanoscratch test reveal that the bottom surface of samples I and IV demonstrates superior abrasion resistance in comparison to the top surface, which can be attributed to the higher relative density, finer grain size, lower elastic modulus and lower Schmidt factors in the bottom surface. These findings hold significant implications for tailoring the microstructure and properties of Inconel 625 alloy, especially in the realm of additively manufactured materials featuring heterogeneous structures.

Anisotropy Dependence of Material Deformation Mechanisms in Nanoscratching Monocrystalline BaF2: Experiments and Atomic Simulations.

Monocrystalline barium fluoride (BaF2), known for its exceptional optical properties in the infrared spectrum, exhibits anisotropy that influences surface quality and material removal efficiency during ultraprecision machining. This research explores the impact of anisotropy on the deformation and removal mechanisms of monocrystalline BaF2 by integrating nanoscratch tests with molecular dynamics (MD) simulations. Nanoscratch tests conducted on variously oriented monocrystalline BaF2 surfaces using a ramp loading mode facilitated the identification of surface cracks and a systematic description of material removal behaviors. This study elucidates the effect of crystal orientation on the ductile-brittle transition (DBT) of monocrystalline BaF2, further developing a critical depth prediction model for DBT on the (111) crystal plane to reveal the underlying anisotropy mechanisms. Moreover, nanofriction and wear behaviors in monocrystalline BaF2 are found to be predominantly influenced by scratch direction, crystal surface, and applied load, with the (110) and (100) planes showing pronounced frictional and wear anisotropy. A coefficient of friction model, accounting for the material's elastic recovery, establishes the intrinsic relationship between anisotropic friction and wear behaviors, the size effect, and scratch direction. Lastly, MD modeling of nanoscratched monocrystalline BaF2 reveals the diversity of dislocations and strain distributions along the (111) [-110] and [-1-12] crystal directions, offering atomic scale insights into the origins of BaF2 anisotropy. Thus, this study provides a theoretical foundation for the efficient processing of fluorine-based infrared optic materials exhibiting anisotropy.

Research on the improvement of the adhesion strength of the Cu films deposited on the Al2O3 films

Due to the significant discrepancy in the coefficient of linear thermal expansion between Cu and ceramic in T-type thin film thermocouples, the Cu thin films often exhibit a low adhesion strength with the ceramic layers (Al2O3). In order to improve the adhesion strength of the Cu with the Al2O3 films, several methods during preparation were studied. First, different thicknesses of the Cu thin films deposited at different deposition temperatures on the Al2O3 thin films prepared by the magnetron sputtering were studied. Second, the Ti/Ni buffer layer between the Cu and the Al2O3 thin films was prepared. Finally, the average roughness of Al2O3 was studied. The adhesion strength of the Cu with the Al2O3 thin films, the microstructure of the surface and the cross section of the Cu and the Al2O3 thin films, and the grain size and the roughness of the films are characterized by nanoscratch testing, scanning electron microscopy, and atomic force microscopy. The adhesion strength of the Cu films with the Al2O3 films increases with an increase in the thickness of the Cu thin films and the roughness of the Al2O3 thin films and the addition of the Ti/Ni buffer layers.

The feasibility of an ultrathin dual-barrier scheme to inhibit interfacial diffusion and reactions in contact stacks of Co/NiSi/Si

Self-assembled monolayers (SAMs) and self-forming barriers (SFBs) are highly effective barriers of copper (Cu) interconnect systems. However, the barrier capability of SAMs and SFBs to contact metallization of cobalt (Co), a new important interconnect material, is yet to be explored. Here, contact layers of NiSi are grown by a two-step silicidation process on Si. Then, an all-wet SAM-seeding and electroless-plating process is used to coat (in sequence) an amine SAM and a MnO-added (only 0.1%) Co film onto NiSi/Si, using a specifically formulated N2H4-CoSO4-MnSO4 bath. The thermal stability of the Co(MnO)/SAM/NiSi/Si is evaluated, using (unalloyed) Co/SAM/NiSi/Si as a control. The 1.3 nm-thin SAM cannot protect the Co/SAM/NiSi/Si from catastrophic failure upon annealing, associated with serious Co/Si interfacial diffusion and the formation of faceted CoSi crystallites and a layered Co2Si/CoSi2 nanostructures at specific locations. By contrast, the Co(MnO)/SAM/NiSi/Si maintains an intact stack after annealing. Collaborative research results generated from (scanning) transmission electron microscopy, nanoscratch testing and surface-energy measurements suggest that the thermal stability enhancement of the whole Co(MnO)/SAM/NiSi/Si contact stack is related to the interfacial segregation of the added MnO as sub-5-nm dispersive crystalline particles, giving multiple functionalities as a SFB, Co-grain strengthening agent, and wetting/adhesion promoter.