JOURNAL OF MATERIALS SCIENCE LETTERS 9 (1990) 1055-1057 Scanning tunneling microscopy of a magnetic shielding material in amorphous and in crystalline forms K. HABIB, A. ABDULLAH Materials Application Department, Kuwait Institute for Scientific Research, P.O. Box 24885 SAFA T, 13109 Kuwait Since the invention of metallic glasses in 1960 [1], it took 13 years of industrial effort to produce the first commercial metallic glass [2]. It was originally the efforts of Allied Chemical Inc. which succeeded in the production of a continuous ribbon of a Fe-Ni glass (Fe40Ni40P~4B6, known as 2826 Metglas) at a time when many laboratories around the world had found no visible method of producing commercial metallic glasses. Consequently, the alloy became a widely studied material because it has many practical values owing to its extreme homogeneous and disordered atomic structure. Recently, Allied Chemical has succeeded in develop- ing a new Co-based metallic glass (Co66Fe4Nit B~4 Si~5, known as 2714A Metglas). The alloy is found to possess very high magnetic permeability and extremely low core loss. Also, it is ideally suited for switch-mode power applications such as magnetic amplifiers, semi- conductor noise suppression cores and high-frequency transformers. Furthermore, the alloy has been found to exhibit high corrosion resistance and insensitivity to mechanical strain. These properties suggest that this sort of material can be used in electromagnetic shielding and sensor applications [3]. In the present work, a fundamental study of the C066Fe4NiLB~4Sit5 glass was carried out. The study was focused on characterizing the nature of the sur- face atomic structures of the glass in the amorphous and the crystalline forms. As a result, a correlation between data obtained from surface structures of the glass in amorphous and crystalline forms was estab- lished based on the applications of scanning tunneling microscopy (STM). A set of prepared samples was annealed above the crystallization temperature of the glass [3J, at nearly 560 ° C, for 1 h, then slowly cooled. These steps were I= Bragg angle, 20 Figure 1 X-ray diffraction pattern of a specimen in the amorphous condition. conducted in order to ensure the production of a stable crystalline microstructure. A second set of prepared samples was used without heat treatment, and will be referred to as theamorphous structure. The difference between the amorphous and the crys- talline structures was non-destructively determined by showing the contrast between the X-ray diffraction patterns of both structures. The surface structure of the glass in both conditions was examined by Nano- scope I & II STM made by Digital Instruments Inc. Surface images were obtained based on a tunneling current equivalent to ~ 1.0 to 2.0 hA. In order to verify whether the glass had crystallized during the annealing process, the X-ray diffraction technique was applied to both set of samples. Figs 1 and 2 show the X-ray diffraction patterns (intensity against Bragg angle) for the amorphous and the annealed samples. The difference between the diffrac- tion patterns is quite obvious for the amorphous and the annealed structures, at which intensity peaks are detected at certain Bragg angles in the annealed sample but not in the amorphous samples. Moreover, different surface structures of a specimen in the amorphous form are shown in Figs 3, 4 and 5. Fig. 3 is basically a three-dimensional line plot of the surface topography in which a completely disordered structure is observed along a 200rim scanning dis- tance. This is in agreement with work done by Habib and Husain [4] where a similar disordered structure has been noted in Fe40Ni38Mo4Bj8 Metallic glass. Fig. 4 is a perspective view of the surface topography obtained from a 175 nm scanning distance. The view indicates some surface bumps whose sizes are about 15 to 40 nm. One can readily describe the profile of the Bragg angle, 20 Figure 2 X-ray diffraction pattern of a specimen in the annealed condition. Intensity peaks are detected at certain Bragg angles due to the polycrystalline nature of the specimen. 0261-8028/90 $03.00 + .12 © 1990 Chapman and Hall Ltd. 1 055