Papers by Author: Yoshitada Morikawa

Abstract: We have developed a novel abrasive-free planarization method, which we term catalyst-referred etching (CARE). In silicon carbide (SiC) CARE, Pt is used as a catalyst and HF solution is used as an etchant. CARE produces a crystallographically undamaged and smooth SiC surface. To understand the removal mechanism at the topmost surface of SiC in the CARE process, we performed first-principles reaction path simulations using the simulation tool for atom technology (STATE) program package. These calculations are based on the density functional theory within the generalized gradient approximation of Perdew et al. The barrier height of the dissociative adsorption of HF on a SiC surface was evaluated by the climbing image nudged elastic band method. We present simulation results for the initial stages of the etching process. The reaction barrier height for adsorption of the first HF is 1.2 eV.

Abstract: In this study, we developed aA novel abrasive-free polishing method called the catalyst-referred etching (CARE) has been developed. CARE can chemically remove SiC chemically with using an etching agent activated by a catalyst. Platinum and hydrofluoric (HF) acid are used for the planarization of SiC substrates as a catalyst and etchant, respectively. CARE can produce an atomically flat surface of 4H–SiC (0001) with a root-mean-square roughness of less than <0.1 nm, regardless of the cut-off angle. However, the mechanism of CARE has hasis not yet been clarified to date. In this study, to clarify the mechanism, KF and NH4F are added to the etchant to clarify the mechanism. The An investigation of removal rate revealeds that the removal rate is proportional to [HF]×([F^- ]+[〖HF_2〗^- ]), and it is shown that both the HF molecule and fluorine ions (F− and HF2−) arethe reactive species of the CARE process are both HF molecule and fluorine ions (F- and HF2-).

Abstract: We have developed a novel abrasive-free planarization method, which we term catalyst-referred etching (CARE). In SiC CARE, Pt is used as a catalyst and HF solution is used as an etchant. CARE produces a crystallographically undamaged and smooth SiC surface. To understand the removal mechanism at the topmost surface of SiC in the CARE process, we performed first-principles reaction path simulations using the Simulation Tool for Atom Technology (STATE) program package. These calculations are based on the density functional theory within the generalized gradient approximation of Perdew et al. The barrier height is evaluated by the climbing image nudged elastic band method. We present simulation results for the initial stages of the etching process. The reaction barrier heights for the adsorption of HF molecules on the first, second, and third Si–C bonds at the edge of the topmost Si-face are 1.8, 1.9, and 1.2 eV, respectively. These barrier heights are reasonably small for a consideration of effect of the Pt catalyst.

Abstract: It has been reported that SiC surface can be etched off in a concentrated aqueous solution of hydrogen fluoride with making contacts with Pt plate catalyst, named Catalyst-referred Etching (CARE) [1]. In this report, we present first-principles molecular-dynamic simulations on the initial stage of the etching process. Reaction barrier heights of dissociative absorption reactions of hydrogen fluoride molecule breaking into back-bonds at step edge of 3C-SiC(111) are analyzed.

Abstract: Ab initio pseudopotential calculations of Cu/Al2O3 and Au/TiO2 interfaces have revealed strong effects of interface stoichiometry. About the Cu/Al2O3 system used for coatings and electronic devices, the interfacial bond of the O-terminated (O-rich) Cu/Al2O3(0001) interface is very strong with ionic and covalent Cu-O interactions, although that of the Al-terminated (stoichiometric) one is rather weak with electrostatic and Cu-Al hybridization interactions. About the Au/TiO2 system with unique catalytic activity, the adhesive energy between non-stoichiometric (Ti-rich or O-rich) TiO2(110) surface and a Au layer is very large, and there occur substantial charge transfer and orbital hybridization, which should have close relations to the catalytic activity.