TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: The interelectrode gap comprises a vacuum, and encapsulated and low-pressure vapor system. The vapor coats the electrode surfaces resulting in a reduced work function. The thermionic emissive material is used in the composition of an electrode from emitter electrode or collector electrode. The microthermionic converter further includes metal capping layer disposed on the thermionic emissive material, thermal heat barrier, electrically insulating material disposed between non-interacting portions of the emitter and collector electrodes, and fuel cap. The collector and emitter electrodes comprise a diode. The fuel cap comprises an outer surface. The outer surface is coated with a thermionic emissive material having emitter electrode. Preferred Process: The conversion of heat to electrically energy further includes utilizing a heat barrier on the non-diode regions of the thermal source. The manufacture of self-powered microthermionic converter further includes enclosing the fuel source in the emitter electrode, disposing a thermal heat barrier internally on the base of the fuel cup, providing a vacuum in the micron-spaced interelectrode gap, and incorporating the converter in a micromachine or microcircuit. The providing of a micron-spaced interelectrode gap between collector and emitter electrodes comprises providing a low-pressure vapor in the micron-space interelectrode gap. The vapor coats the electrode surfaces to result in a reduced work function. The formation of fuel cup includes forming a fuel grid, inserting the thermal power source in the fuel cup, capping the fuel cup, and dissolving the fuel grid. The capping of fuel cup includes capping the fuel cup with a non-reactive metal, gold, or highly reflective non-reactive material. The formation of fuel grid includes fabricating a precision grid having dissolvable source buckets. Preferred Condition: The temperature for operation is between approximately 850-1200 K. Preferred Property: The interelectrode gap is between approximately 1-10, preferably 1-3mum. The length of the emitter electrode is less than approximately 200, preferably between 50-100mum.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The vapor is cesium or barium vapors. The thermal power source comprises a radioactive isotope. The radioactive isotope comprises an alpha-emitting isotope from curium-242, curium-244, or polonium-210. The thermionic emissive material comprises alkaline earth oxide; adjunct oxide from aluminum oxide or scandium oxide; and metal from tungsten, rhenium, osmium, iridium, and/or ruthenium. The alkaline earth oxide comprises material from barium oxide, strontium oxide, or calcium oxide. The metal capping layer comprises material from scandium and/or scandium oxide. The thermionic emissive material comprises material from tungsten, molybdenum, tantalum, tungsten oxide, molybdenum oxide, and/or tantalum oxide. The environment in the interelectrode gap comprises a vacuum, and vapor from cesium or barium vapors.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Component: The vapor is cesium or barium vapors. The thermal power source comprises a radioactive isotope. The radioactive isotope comprises an alpha-emitting isotope from curium-242, curium-244, or polonium-210. The thermionic emissive material comprises alkaline earth oxide; adjunct oxide from aluminum oxide or scandium oxide; and metal from tungsten, rhenium, osmium, iridium, and/or ruthenium. The alkaline earth oxide comprises material from barium oxide, strontium oxide, or calcium oxide. The metal capping layer comprises material from scandium and/or scandium oxide. The thermionic emissive material comprises material from tungsten, molybdenum, tantalum, tungsten oxide, molybdenum oxide, and/or tantalum oxide. The environment in the interelectrode gap comprises a vacuum, and vapor from cesium or barium vapors.