Effects of sputtering pressure on the field emission properties of N-doped SrTiO3 thin films coated on Si tip arrays

The influence of sputtering pressure on the electron emission properties of Si tips coated with N-doped SrTiO3 ultrathin films was investigated. X-ray diffraction studies revealed that the N-doped SrTiO3 films deposited at different pressures remain the perovskite structure. However, the threshold electric field of electron emission decreased markedly when the sputtering pressure is increased, and reached a minimum value of 17.37 V/mum while deposited at 1.6 Pa. The decrease in the threshold field is attributed to the narrowed band gap and the lowered surface energy of SrTiO3 thin films with nitrogen doped, as confirmed using spectroscopic ellipsometry and water contact angle measurement. Furthermore, it is revealed using XPS that such sputtering pressure dependence is accompanied with the change of nitrogen bonding state in the films, which changes from poorly screened gamma-N2 state to atomic beta-N state when the sputtering pressure is increased. A mechanism of bonding and band-forming was proposed for the enhanced electron emission with nitrogen incorporation in the sputtered SrTiO3 films.