Self-Smoothening of an Ion-Beam-Sputtered Ag (100) Surface: Evolution of Surface Morphology Using RHEED
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UCTION
DETAILED knowledge of surface and interface properties is important to understand a wide variety of phenomena such as catalysis,[1] surface reactivity[2] and thin film growth.[3] In case of single crystals, the surface and morphologic evolution of the growing material as well as diffusion of metal atoms on surfaces is known to be one of the most important factors responsible for recrystallization,[4] surface reconstruction[5] and the roughening and smoothening process.[6] Interest in this area is thriving because of the substantial effect of surface morphology on the optical, electrical and mechanical properties.[7] Therefore, the influence of the surface and interface morphology has been widely investigated on various two-dimensional structures such as Au,[8] Ag,[9] Co[10] and Fe.[11] The interest is also motivated by the fact that such systems are very important for magnetic and optical devices, where surface smoothness is often desirable and enhances the performance of most devices.[12] For example, in case of high electron mobility transistors, the smoothness of the surface is essentially required to improve transistor
ANUP KUMAR BERA and DILEEP KUMAR are with the UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore 452001, India. Contact e-mail: [email protected] Manuscript submitted October 13, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
performance.[13] Similarly, in case of magnetic thin film systems, coercive fields, magnetization reversal processes and giant magnetoresistance (GMR) effects are significantly affected by the surface and interface roughness that develops during thermal annealing because of the diffusion process.[14,15] Therefore, surface morphologies and the roughness of the two-dimensional nanostructures are important parameters for achieving the desired functionality of the material. The development of the surface morphology is often related to the ion beam cleaning process, preparation conditions and substrate properties during the thin film and crystal growth. The direction of thin film deposition also has a definite relationship with the anisotropic morphology in the film developed during deposition.[16] Recently, low-energy ion-beam-induced surface morphology change was demonstrated to be a powerful method to induce self-organized nanoscale morphologic structures on the surfaces of semiconductors, single crystals and metal films,[10,11,17] where the energy transfer from energetic ions to the surface or near-surface atoms can cause atomic motions on the surface and even ejection (sputtering) of atoms; this causes various kinds of surface modifications and may lead to a roughening-smoothing process on the surface.[18] A variety of techniques[19,20] such as scanning tunneling microscopy (STM) measurements during progressive stages of deposition, X-ray reflectivity (XRR), atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to obtain direct and indirect
information about the surface morphology. However, most of the techniques either do not have suffi
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