Papers by Keyword: Interface Roughness

Abstract: Modern surface processing of semiconductors or oxide materials requires highly precise temporal control of each processing step. In addition, large wafers must be processed quickly for high throughput. We have developed a numerically controlled sacrificial oxidation method with atmospheric-pressure plasma using electrode arrays. In this method, we oxidized the surface of a wafer with atmospheric-pressure plasma applied precisely by an electrode array, and then dipped the wafer in HF solution to remove the surface oxide layer. The plasma process time can be controlled independently at each electrode area. The oxidation rate and surface profile of the treated wafer are crucial for precision processing. We investigated the oxidation rate of atmospheric-pressure plasma oxidation by spectroscopic ellipsometry and examined the surface morphologies of untreated and treated wafers by atomic force microscopy. The surface profile smoothness correlated with the plasma oxidation time and electrode voltage during oxidation. The surface roughness tended to increase when the sample was oxidized for longer times with higher electrode voltage. This correlation between surface roughness and oxidation time resembled the results of Si/SiO₂ interfacial roughness in the case of thermal oxidation. In the plasma sacrificial oxidation process, the increase of surface roughness at the Si/SiO₂ interface by plasma oxidation must be considered.

Abstract: The depth profiles of Ni-coated copper substrates polished by different mesh size sandpapers were measured by the glow discharge optical emission spectroscopy (GDOES) depth profiling technique. The measured depth profiles were well fitted by the MRI-CRAS model developed recently on the basis of the Mixing-Roughness-Information depth (MRI) model and the CRAter-Simulation (CRAS) model, taking into account the pronounced crater effect upon GDOES depth profiling. The crater effect upon depth profiling was characterized quantitatively and the interface roughness values between the coated Ni layer and the Cu substrates were determined and compared with the ones measured by AFM.

Abstract: Thick film systems with coating thicknesses between 50 and 1000 µm are often fabricated by thermal spray processes. During the deposition and due to the substrate pre-treatment residual stresses, which influence the coating properties, develop. Due to the substrate preconditioning thermal spray coatings exhibit a large interfacial roughness. This study investigates the application of the incremental hole-drilling method on thermal spray coatings. The focus is on the influence of the interfacial roughness on the residual stress evaluation. A systematic FE-study was carried out in order to minimize the final error for the residual stress evaluation. The simulation results are transferred to experimental hole-drilling results of a thermally sprayed model thick film system. Finally, the hole-drilling results are compared to the residual stress depth profile that was determined by X-ray diffraction in combination with successive electrochemical layer removal. The results clearly show that the effect of the interfacial roughness can be neglected for residual stress calculation if the mean coating thickness is properly considered for calculation of the calibration function / parameters.

Abstract: Based on the analysis of the early shrinkage mechanism of concrete, shrinkage experiment of new concrete restrained by old concrete were conducted to analyze the impact of the different interface roughness on shrinkage stress of new concrete and bonding surface. It is shown that the inner tensile stress of new concrete decreases with increasing of interface roughness, and increase restrained thickness of the new concrete, but it is not significant effect of interface roughness on the shrinkage at bonding surface; the shrinkage strain of section reduces with reduction of the distance of section to bonding surface and reaches minimum on bonding surface, which reflecte significant nonuniformity and increases gradually with age.

Abstract: The effects of strain and interface roughness at the Co/Pd interface are investigated from the viewpoint of perpendicular magnetic anisotropy (PMA) using the DV-Xα cluster model calculation method. It is found that spin projected occupation number ratio of magnetic quantum number |m| = 2 for the Co 3d electrons enhances by expanding the lattice within a close-packed plane of fcc stacking and, hence, enhances the PMA. Rough interface decreases the spin projected occupation number ratio of |m| = 2 and, hence, decreases the PMA. These results explain the PMA properties of Co/Pd multilayers fabricated using molecular beam epitaxy (MBE) technique and RF sputtering techniques.

Abstract: We present a study of the improvement in interface roughness of platinum/carbon multilayers for X-ray mirrors. The X-ray reflectivity of multilayers strongly depends on interface quality. In an effort to reduce the interface roughness caused by crystallization during deposition, carbon doping of platinum was proposed, and its effectiveness was evaluated. We compared 45-nm-thick single-layer platinum to carbon-doped platinum films. The films were deposited on a silicon (100) substrate by dc magnetron sputtering deposition. The surface roughness and X-ray diffraction spectrum of each film were measured by atomic force microscopy and X-ray diffraction, respectively. We concluded that the increase in carbon concentration suppresses the crystallization of platinum and causes the surface roughness to decrease.

Abstract: We have used ferromagnet/antiferromagnet/ferromagnet sandwich structure to probe the antiferromagnetic layer thickness dependence of exchange bias in sputter-deposited Co/CoO/Co trilayer. The exchange coupling occurring at the upper ferromagnetic/antiferromagnetic interface is always found to be stronger than the one at the lower antiferromagnetic/ferromagnetic interface. The grain growth with increasing antiferromagnetic layer thickness can lead to a gradient of grain size distribution through the whole antiferromagnetic layer. Consequently, the relatively large grains at the upper interface would results in a rougher interface which we treat as structural defects and can significantly enhance exchange bias through domain state model. The slightly decrease of exchange coupling with increasing antiferromgnetic layer thickness indicates that the exchange bias is only governed by the grains that are thermally stable but whose anisotropy energy is low enough to be set.

Abstract: The phase transition of Nb/Cu0.41Ni0.59/Nb triple layers from the normal to the superconducting state has been studied experimentally by measuring the temperature dependence of the electrical resistance, R(T). It is shown that the shape of the R(T) curves is different depending on the Cu0.41Ni0.59 thickness. To explain the experimental data we developed a qualitative model which makes more evident the interconnection between the superconducting phase transition and the 0 to  crossover in SFS structures.

Abstract: The in-plane optical anisotropy of three groups of GaAs/AlGaAs quantum well structures has been studied by reflectance-difference spectroscopy (RDS). For GaAs/Al0.36Ga0.64As single QW structures, it is found that the optical anisotropy increases quickly as the well width is decreased. For an Al0.02Ga0.98As/AlAs multiple QW with a well width of 20nm, the optical anisotropy is observed not only for the transitions between ground states but also for those between the excited states with transition index n up to 5. An increase of the anisotropy with the transition energy, or equivalently the transition index n, is clearly observed. The detailed analysis shows that the observed anisotropy arises from the interface asymmetry of QWs, which is introduced by atomic segregation or anisotropic interface roughness formed during the growth of the structures. More, when the 1 ML InAs is inserted at one interface of GaAs/AlGaAs QW, the optical anisotropy of the QW can be increased by a factor of 8 due to the enhanced asymmetry of the QW. These results demonstrate clearly that the RDS is a sensitive and powerful tool for the characterization of semiconductor interfaces.