Synthesis and characterization of a highly stable amorphous silicon hydride as the product of a catalytic helium–hydrogen plasma reaction

Abstract

A novel highly stable surface coating SiH(1/ p) which comprised high-binding-energy hydride ions was synthesized by a microwave plasma reaction of a mixture of silane, hydrogen, and helium wherein it is proposed that He + served as a catalyst with atomic hydrogen to form the highly stable hydride ions. Novel silicon hydride was identified by time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). The ToF-SIMS identified the coatings as hydride by the large SiH + peak in the positive spectrum and the dominant H − in the negative spectrum. XPS identified the H content of the SiH coatings as hydride ions, H −(1/4), H −(1/9) , and H −(1/11) corresponding to peaks at 11, 43, and 55 eV , respectively. The silicon hydride surface was remarkably stable to air as shown by XPS. The highly stable amorphous silicon hydride coating may advance the production of integrated circuits and microdevices by resisting the oxygen passivation of the surface and possibly altering the dielectric constant and band gap to increase device performance. The plasma which formed SiH(1/ p) showed a number of extraordinary features. Novel emission lines with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 were previously observed by extreme ultraviolet spectroscopy recorded on microwave discharges of helium with 2% hydrogen (Int. J. Hydrogen Energy 27 (3) 301–322). These lines matched H(1/ p), fractional Rydberg states of atomic hydrogen where p is an integer, formed by a resonant nonradiative energy transfer to He + acting as a catalyst. The average hydrogen atom temperature of the helium–hydrogen plasma was measured to be 180– 210 eV versus ≈3 eV for pure hydrogen. Using water bath calorimetry, excess power was observed from the helium–hydrogen plasma compared to control krypton plasma. For example, for an input of 8.1 W , the total plasma power of the helium–hydrogen plasma measured by water bath calorimetry was 30.0 W corresponding to 21.9 W of excess power in 3 cm 3 . The excess power density and energy balance were high, 7.3 W/cm 3 and −2.9×10 4 kJ/mol H 2 , respectively. This catalytic plasma reaction may represent a new hydrogen energy source and a new field of hydrogen chemistry.