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We investigate the time evolution of ZnO thin film growth in oxygen plasma-enhanced atomic layer deposition using in situ spectroscopic ellipsometry. The recently proposed dynamic-dual-box-model approach [Kilic et al., Sci. Rep. 10, 10392 (2020)] is used to analyze the spectroscopic data post-growth. With the help of this model, we explore the in-cycle surface modifications and reveal the repetitive layer-by-layer growth and surface roughness modification mechanisms during the ZnO ultrathin film deposition. The in situ complex-valued dielectric function of the amorphous ZnO thin film is also determined from the model analysis for photon energies of 1.7–4 eV. The dielectric function is analyzed using a critical point model approach providing parameters for bandgap energy, amplitude, and broadening in addition to the index of refraction and extinction coefficient. The dynamic-dual-box-model analysis reveals the initial nucleation phase where the surface roughness changes due to nucleation and island growth prior to film coalescence, which then lead to the surface conformal layer-by-layer growth with constant surface roughness. The thickness evolution is resolved with Angstrom-scale resolution vs time. We propose this method for fast development of growth recipes from real-time in situ data analysis. We also present and discuss results from x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy to examine crystallographic, chemical, and morphological characteristics of the ZnO film. 

Adhesively bonded joints contain stress concentrations at geometric and material discontinuities within the joint, causing the joint to be inefficient. This study investigates a method to grade the material properties of an adhesive across the bondline to have a soft, flexible adhesive near the stress concentration and a stiff, strong adhesive elsewhere. Theoretical studies and a few experiemental studies have shown an that the load is distributed more evenly along the joint and strength is increased. Adhesive gradation is achieved through a secondary crosslinking system in the adhesive which is activated via radiation. After an adhesive is initially cured, the joint can be exposed to varying levels of radiation to grade the properties. Initial results demonstrate the ability to grade stiffness using radiation shielding, and final results will demonstrate the application in an adhesively bonded joint. 

Functionally graded adhesive bondlines are currently being researched to relax stress concentrations at the re-entrant corner of bonded joints and improve the strength of joints. Bi-adhesive joints have been under development for some time, but lately adhesives with continuous gradation have been shown to theoretically enable more stress reductions and greater strength benefits. Several researchers have shown the potential to create a working adhesive gradation system with very promising results, but adhesive stability over long periods of time has proven difficult to realize. Nearly as important as adhesive development are analysis methods for functionally graded adhesive joints, since the gradation must be designed to yield beneficial results. Therefore, this work addresses the potential gains provided by design of functionally graded adhesive joints driven by finite element analysis. A parametric study on a strap joint with homogenous adhesive is conducted to highlight parameters which influence the global strength of an adhesively bonded joint. A statistical approach is used to identify significant correlations between strength and adhesive material parameters. Results from the statistical study are applied to drive strategies to create joints with optimized gradation and validated by failure analysis within the finite element model. A strap joint is analyzed as example of the potential gain of functionally graded joints. 

Abstract Variability in the position and strength of the subtropical jet (STJ) and polar front jet (PFJ) streams has important implications for global and regional climate. Previous studies have related the position and strength of the STJ to tropical thermodynamic processes, whereas the position and strength of the PFJ are more associated with midlatitude eddies. These conclusions have largely resulted from studies using idealized models. In this study, ERA‐Interim reanalysis and CMIP6 global climate models are used to examine month‐to‐month and interannual variability of the wintertime Northern Hemisphere (NH) STJ and PFJ. This study particularly focuses on the regional characteristics of the jet variability, extending previous studies on zonal‐mean jet streams. Consistent with idealized modeling studies, a close relationship is found between tropical outgoing longwave radiation (OLR) and the STJ and between midlatitude lower tropospheric temperature gradients and the PFJ. Variations of both jets are also linked to well‐known teleconnection patterns. Variations in tropical convection over the Pacific Ocean are associated with variations of the NH STJ at most longitudes, with different phases of the El Niño–Southern Oscillation (ENSO) associated with the shift and strengthening of the STJ in different regions. CMIP6 models generally capture these relationships, but the models’ tropical convection is often displaced westward when compared to observations, reflecting a climatological bias in OLR in the western tropical Pacific Ocean in many models. The displaced tropical convection in models excites different paths of Rossby wave propagation, resulting in different ENSO teleconnections on the STJ over North America and Europe.