Initial Growth Characterization of Au Thin Films on SnO[sub x] Substrate by In Situ Conductivity Measurement

Abstract

The initial growth behaviors of Au thin films on tin oxide substrates were investigated by in situ conductance measurement. The crystallinity of tin oxide films fabricated by ion-beam-assisted deposition was changed from amorphous to preferred oriented structure with ion beam energy. As the surface energy of tin oxide substrates increases with the irradiation of ion beams, an onset thickness of Au films is decreased. That means high surface energy of the substrate enhances surface mobility of Au adatoms so that it changes the growth mode of Au films from 3D to 2D growth. So the distance between islands where electron tunneling can occur is decreased with the surface energy of the substrate. Therefore, we conclude that different surface properties of tin oxide substrates play an important role in the early growth aspects of Au thin films.The nucleation and initial growth of thin films are important because these are major factors in determining the microstructure and physical/chemical properties of thin films. In general, the initial growth of thin films depends on the relationships between depositing species and substrate atoms such as surface energy, lattice mismatch, and interfacial bonds. To get uniform and smooth thin films with layered microstructure, high substrate energy and low interfacial energy are necessary to minimize total free energy. It has been reported that the initial growth behaviors play an important role in texture, surface morphology, epitaxial growth, and residual stress of thin films, 1-4 especially in the case of a deposition of metal on oxide substrate. 5-8 Therefore, the precise and exact analysis for initial growth is important to control thin-film properties. As usual, to characterize initial growth of thin films at nanoscale, in situ measurement including ellipsometry 9 and laser-reflectance interferometry, 10 and microscopy such as transmission electron microscopy ͑TEM͒ and high-resolution scanning electron microscopy ͑HRSEM͒ 11 are indispensable. But sample preparation is difficult in these techniques and costs a great deal due to expensive apparatus. Conversely, in situ conductance measurement is simple and economical and obtains more accurate information. Therefore, recently much research has focused on electrical conductance due to its simplicity and accuracy. 12-16 In our previous papers, we suggested a new conduction model during the early state of film growth and showed that this model is useful for the in situ study of the growth of ultrathin films prior to the onset of tunneling conductance. 12,13 The surface properties can be modified by immersing in wet solution, plasma, and ion beam treatment. [17][18][19] Particularly, ion beam irradiation is useful in the control of surface energy by formation of functional species and morphological change. In addition, ion beam irradiation during film deposition can improve adatom mobility on the substrate surface by means of momentum transfer. So in the present work, through in situ conductance measurement, we investigated the effect...