Tianyin Sun

Combined visible light photo-emission and low temperature thermionic emission from nitrogen doped diamond films

This study reports a photoemission threshold of ∼1.5 eV from nitrogen-doped nanocrystalline diamond, which ranks among the lowest photo-threshold of any non-cesiated material. Diamond films on molybdenum substrates have been illuminated with light from 340 to 550 nm, and the electron emission spectrum has been recorded from ambient to ∼320 °C. The results display combined thermionic and photo-electron emission limited by the same low work function and indicate that the two emission processes are spatially separated. These results indicate the potential for a solar energy conversion structure that takes advantage of both photoemission and thermionic emission.

Cu film thermal stability on plasma cleaned polycrystalline Ru

The first part of this study examined oxide stability and cleaning of Ru surfaces. The surface reactions during H2 plasma exposure of Ru polycrystalline films were studied using x-ray photoelectron spectroscopy (XPS). The ∼2 monolayer native Ru oxide was reduced after H-plasma processing. However, absorbed oxygen, presumably in the grain boundaries, remains after processing. A vacuum thermal anneal at 150 °C substantially removes both surface oxide and absorbed oxygen which is attributed to a reduction by carbon contamination. The second part of the study examined the thermal stability of Cu on a Ru layer. The thermal stability or islanding of the Cu film on the Ru substrate was characterized by in situ XPS. After plasma cleaning of the Ru adhesion layer, the deposited Cu exhibited full coverage. In contrast, for Cu deposition on the Ru native oxide substrate, Cu islanding was detected and was described in terms of grain boundary grooving and surface and interface energies. The oxygen in the grain boundar...

Electron affinity of cubic boron nitride terminated with vanadium oxide

A thermally stable negative electron affinity (NEA) for a cubic boron nitride (c-BN) surface with vanadium-oxide-termination is achieved, and its electronic structure was analyzed with in-situ photoelectron spectroscopy. The c-BN films were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition employing BF3 and N2 as precursors. Vanadium layers of ∼0.1 and 0.5 nm thickness were deposited on the c-BN surface in an electron beam deposition system. Oxidation of the metal layer was achieved by an oxygen plasma treatment. After 650 °C thermal annealing, the vanadium oxide on the c-BN surface was determined to be VO2, and the surfaces were found to be thermally stable, exhibiting an NEA. In comparison, the oxygen-terminated c-BN surface, where B2O3 was detected, showed a positive electron affinity of ∼1.2 eV. The B2O3 evidently acts as a negatively charged layer introducing a surface dipole directed into the c-BN. Through the interaction of VO2 with the B2O3 layer, a B-O-V layer str...

Photo induced electron emission from nitrogen doped diamond films on silicon

Results are presented on the photo-induced electron emission from nitrogen doped diamond films prepared on doped silicon substrates. In contrast to results for films on metal substrates, a significant increase of emission intensity was observed at elevated temperatures. The results suggest a contribution from photon enhanced thermionic emission.

9.1: Negative electron affinity ultra-nano crystalline diamond based thermionic electron emitters for low to moderate temperature operation

Diamond based electron sources utilize two key materials properties presenting a method of efficient electron emission. Negative electron affinity (NEA) characteristics of diamond surfaces, where the vacuum level is positioned below the conduction band minimum eliminates the surface emission barrier. With suitable dopants, an electronic band configuration can be achieved resulting in a low effective work function. We have prepared nitrogen-doped diamond emitter structures by plasma assisted chemical vapor deposition. These materials exhibit a low effective work function of about 1.3 eV with detectable thermionic electron emission at temperatures lower than 250 ºC.