Graphite surface contamination

Figure 9.12 Contamination on graphite surface measured by LA-iCP-MS. The measurement started 2 cm fmm the enrt nf electrode tat this Doint the relative ion intensity is defined as 1) (a) lateral distribution of Si on graphite surface, (b) distribution of27Al+, 48Ti+, 53Cr+, 56Fe+ and58Ni+ (J. S. Becker, Spectrochim. Acta 57B, 1805 (2002). Reproduced by permission of Elsevier.)...

The chemical treatment of samples containing U or Pu depended on the matrix. Filter paper smears were digested in nitric acid soils, ores, and rocks were dissolved in nitric/hydrofluoric acid and graphite or metal pieces with suspected surface contamination were leached with nitric or hydrochloric acid. Certain analytical techniques such as isotope dilution MS required that the samples undergo further chemical processing steps. Thus the analysis of one sample could involve a significant amount of effort and measurements with several analytical techniques. 

Oxygen Chemisorption.—Most studies on Pt have used polycrystalline wires, foils, or specially cut single-crystal faces. In all cases, samples are initially heavily contaminated with graphitic surface layers. Pignet, Schmidt, and Jarvis, for example, showed by AES that heating at 400 °C in 1 atm of oxygen effectively removed surface C and S and that the resulting surface was not... 

Germanium [7440-56-4] M 72.6, m 937 , 925-975 , b 2700 , d 5.3. Copper contamination on the surface and in the bulk of single crystals of Ge can be removed by immersion in molten alkali cyanide under N2. The Ge was placed in dry cyanide powder in a graphite holder in a quartz or porcelain boat. The boat was then inserted into a heated furnace which, after a suitable time, was left to cool to room temperature. At 750°, a 1mm thickness requires about Imin, whereas 0.5cm needs about half hour. The boat was removed and the samples were taken out with plastic-coated tweezers, carefully rinsed in hot water and dried in air [Wang J Phys Chem 60 45 7956]. 

Because STM measures a quantum-mechanical tunneling current, the tip must be within a few A of a conducting surface. Therefore any surface oxide or other contaminant will complicate operation under ambient conditions. Nevertheless, a great deal of work has been done in air, liquid, or at low temperatures on inert surfaces. Studies of adsorbed molecules on these surfaces (for example, liquid crystals on highly oriented, pyrolytic graphite ) have shown that STM is capable of even atomic resolution on organic materials. 

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