Evaluation of Surface Characteristics of ZnS and Zn 2 SiO 4 Powders by SFM
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ABSTRACT The surface characteristics of ZnS and Zn 2 SiO 4 powders were evaluated by scanning force microscopy (SFM) to optimize the coating process. The different characteristics of uncoated and coated powder are presented.
INTRODUCTION SFM was originally introduced by G. Binnig and C. F. Quate in 1986.1,2 SFM measures the force exerted on a sharp tip by the sample surface. The force reflects the surface characteristics and structure. This method is capable of analyzing surface structure of materials, both conductors and insulators. Its applications have spread to a variety of areas of scientific research and industry. Scanning force microscopy (SFM) is a useful tool for surface characterization and to optimize the coating process and thin film depositing process. 3-7 ZnS and Zn 2 SiO 4 powders are lighting materials and have been applied for improvement of life time of fluorescence lamps. A sample preparation method using a thermoplastic adhesive and heating to the appropriate temperature was found to be significant for atomic force
microscopy (AFM) imaging of ZnS and Zn2 SiO 4 powders. AFM not only can be used for distinguishing the difference between uncoated and coated powders but is also useful for studying the surface characteristics of powder samples with different coating time.
SAMPLE PREPARATION The thermoplastic adhesive was used for the preparation of ZnS and Zn 2 SiO 4 powder samples. Some thermoplastic adhesive was applied to AFM sample stage and then heated to above 1201C. Once thermoplastic adhesives were melted and cooled for several minutes sample powders were sprinkled on them. Then, the sample stage was reheated to 40-600 C for several minutes and cooled to room temperature in air. This sample preparation method was found to be significant for surface evaluation of ZnS and Zn2 SiO 4 powders using AFM. If the sample stage was reheated to 400 C for 1 or 2 minutes and cooled to room temperature in air, most of powder particles seemed to be shallowly immersed into the resin and easier swept away by a AFM tip after scanning the surface of a sample. As a result, some holes or dips were left on the surface of the thermoplastic adhesive since powder particles were not very well stuck on the surface of thermoplastic
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Mat. Res. Soc. Symp. Proc. Vol. 355 0 1995 Materials Research Society
adhesives. If the sample stage was reheated to 50-60'C for several minutes and cooled to room temperature in air, the particles were mid or deeply immersed into the resin, very well adhered to the surface of thermoplastic adhesives and were employed for the AFM investigation. For powder grains with very rough surface, for example uncoated powder grains, because they were exerted by larger friction it is preferable that the sample stage be reheated to near 600 C.
SURFACE CHARACTERISTICS Because of the random shape and very rough surface of ZnS and Zn 2 SiO 4 particles, we have imaged hundreds of particles to find out surface characteristics of these particles. The major difference in morphology of uncoated and co
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