Sugio Ohtani

Heating effects on modifying carbon surface by reactive plasma

Abstract In the surface modification by plasma, surface properties changes with time after the plasma treatment. Such changes should be avoided for practical application. Glassy carbon (GC) was subjected to simultaneous plasma and heat treatments in order to investigate the respective effects. Source gases were tetrafluoromethane (CF4) and oxygen (O2). Treatment time and heating temperature of the GC plate were 30 min and 200–500°C, respectively. The surface properties before and after plasma treatment were studied with contact angle measurements and ESCA. When the GC was heated at 400°C during CF4 plasma treatment, the contact angle after plasma treatment was 133° and constant even after 24 h. At 500°C during O2 plasma treatment, the contact angle after plasma treatment was 0° and constant even after 24 h. It is found that heating carbon surface during CF4 or O2 plasma treatment is effective to stop the change with time after plasma treatment.

Investigation of characteristics of carbon materials with various structures modified by plasmas using plasma diagnostics and materials-surface analysis

Abstract This investigation was conducted on the surface modification of the carbon materials by the reactive plasma (O 2 and SF 6 plasma) and the inert gas plasma (Ar plasma) with objective of investigating the effects of plasma on various carbon materials with different structure. The carbon materials used were artificial graphite and glassy carbon. The contact angle and its elapsed change to their surfaces before and after plasma treatment was measured. Moreover, their surfaces were analyzed by ESCA, and we observed them by SEM. O 2 plasma or Ar plasma treatment makes the surface of the carbon materials hydrophilic, and the level of Ar plasma treatment was approximately one-half that with O 2 plasma. SF 6 plasma treatment makes its surface hydrophobic. The modification source was Ar + with the Ar plasma. The modification sources were radicals and ions with O 2 plasma, SF 5 + and SF 3 + and radicals. The role of Ar ion was mainly in the formation of highly reactive radicals with long lifetimes on the surface of samples by the bombardment of Ar ion. The differences in the results of plasma treatment using different types of plasma between AG and GC are considered to be due to the differences in the structure of materials. AG surface is less resistant to shock against plasmas than a GC one and due to the presence of many edge-type carbon sections, the surface becomes highly reactive.

Effects of the modified materials on plasma in surface modification by plasma

Abstract We have developed an in situ system in which material can be inserted into and removed from the plasma apparatus in order to measure the transient variations of plasma with minimum changes in discharge chamber and measurement vessel. By using this system, the transient variations of O 2 + ion, O + ion, O radical, electron temperature and electron density were measured when the materials were put into and taken out from the oxygen plasma. Also, the difference between the steady state value without material in the plasma and that with material, in relation to each parameter, was measured. The following facts were found in this study. O 2 + and O + mass spectra decreased when the material was inserted into plasma. Then it returned to the original value when the material was taken out. The condition of the transient change of O 2 + differed remarkably according to the material. By optical emission analysis intensity of O radical was observed more remarkably than that of O 2 ion. Whatever the material was, the transient change did not vary much. The electron density greatly decreased by the material being included into the plasma. However, the electron temperature was constant even if the material was inserted into the plasma. The reflection power was constant by putting material in and out of plasma whatever the material was. The weight decrease in case of Teflon was larger than the other materials after the treatment in the same plasma condition.