טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBaibich Eitan
SubjectThe Energy Distribution of Thermionic Electron Emission
from Polycrystalline Diamond Films Grown on
B-Doped Si Substrates Using HF-CVD
Method
DepartmentDepartment of Chemistry
Supervisor Professor Alon Hoffman
Full Thesis textFull thesis text - English Version


Abstract

In this work the effect of moderate temperatures (in the range of 500-700°C) on the energy distribution of the thermionic electron emission from diamond films was studied. An exponential dependence was found between the diamond film temperature and the total electron emission (expressed by the integral intensity of the peak), where each increase of 50°C resulted in a tenfold amplification of the integral intensity. The highlight of this work is attributed to the novel method developed here which is based on the solid state physics of semiconductors. In this method, by correlating the measured integral intensity of the temperature-dependent energy distributions to a temperature-dependent function derived from the model, the electron affinity at the surface is obtained - in the case of positive electron affinity; while the band gap can be derived - in the case of negative electron affinity. In addition, the thermal stability of the diamond surface was investigated. When held at 700°C, the thermionic electron emission from the diamond film decreased monotonically with time (in a time scale of ~100 minutes), while the shape and location of the distribution remained unchanged. This led to the conclusion that slow desorption of hydrogen from the diamond surface occur at 700°C, while a minor desorption was also observed at 650°C. The effect of negative electric bias applied at the diamond surface was also studied within the frame of this work. The shape, width and relative position (with respect to the applied bias) of the thermionic energy distributions were found to be very consistent when biases higher (in absolute values) than -35V were applied; the integral intensity however, increased linearly with the applied bias. Moreover, the interrelation between different physicochemical pretreatments and the obtained thermionic electron energy distribution was investigated. Heating to 1000°C was found to completely eliminate the thermionic electron emission, as oppose to in-situ atomic hydrogenation that restored it; both effects were related to the desorption and adsorption (respectively) of the hydrogen terminal layer covering the diamond surface. Lastly, preliminary measurements of photo-enhanced thermionic electron emission distribution were conducted where an impressive gain in the electron emission intensity was found due to the contribution of wavelengths in the region of 230-350 nm.