Field Ion Images of Some Non-Metallic Materials
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FIELD ION IMAGES OF SOME NON-METALLIC MATERIALS
Chong-lin Chen and Tien T.
Tsong
Physics Deaprtment, The Pennsylvania State Universtiy University Park, Pennsylvania 16802
Abstract A progress report is given on our attempt to image non-metallic materials using the field ion mciroscope. Field ion images have been obtained for different forms of graphite and a Y-123 compound, and preliminary interpretations of these images are presented. While the quality of field ion images of these materials is not too bad, it is not yet good enough to observe the atomic arrangements.
INTRODUCTION It is well known that most metals and many alloys can be imaged in the field ion microscope with atomic resolution. Less known is the fact that many intermetallic compounds and an oxide of metals, such as PtCo and 2 3 Ni4Moi LaB6 and IRO2 , have also been imaged in the field ion microscope with atomic resolution. Recently, the material applicability of the field ion microscope has been further widened with the successful imaging of thermally annealed silicon surfaces by Liu et. al.,' and field evaporated 5 surfaces of high temperature superconductors by Kellogg and Brenner, and 6 7 Melmed et. al. Tagawa et. al. reported an attempt to image a carbon fiber reinforced carbon (CFRC) using a high voltage field ion microscope, but the image contains only some random spots and no structures of any sort could be seen despite the high voltage. In this paper, we present a progress report on an attempt to image non-metallic materials, such as graphite rods and whiskers, pencil leads, and a high temperature Yttrium-123 compound using a regular field ion microscope.
EXPERIMENTAL PROCEDURES Field ion tips of graphite are prepared by electrochemical-polishing of piece of graphite rod of -0.1 mm diameter, or a graphite whisker, or of 0.3 mm pencil lead using an electrolyte solution of 25% KOH + 25% NaOH + 5% NH4OH + H20 mixture, similar to that used for polishing a tungsten tip. The tip is squeezed into a Ni tube which is spot welded on a Mo wire 8 loop, as usually done in field ion microscopy. The electrochemical polishing is done in dc of a few volts. After a sharp tip is installed into the FIM chamber, the system is baked to 100 *C for about 10 hours. This 0 overnight baking usually give us a vaccum better than ixI°0l Torr. For imaging all these different forms of graphite tips, helium gas of -3x10-5 Torr is used. The tip is cooled down with a Displex He Refrigerator, and the tip temperature can be adjusted all the way from about 20 K to 300 K. Good images for graphite tips are obtained at about 30 K. A Y-123 compound, Y BaCu307is prepared by firing a uniform mixture of Y2 0 3, BaCO 3 and CuO3 powder in'• atm pressure of oxygen for 12 hours. The mixture is granuated and pressed into disks of I inch in diameter and 1/16 inch in thickness in air at 15 atm pressure. This material is made
"asmall "apiece
Mat. Res. Soc. Symp. Proc. Vol. 139. -1989 Materials Research Society
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The critical superconducting by further annealing to 975 °C in oxygen
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