Study of optical and electronic properties of Ultrananocrystalline diamond

Recently Ultrananocrystalline diamond (UNCD) emerged as an engineered material with excellent mechanical, electrical and optical properties. The unique properties were attributed to densely packed sp3 bonded carbon grain of 3-15 nm and the presence of pi-bonded carbon (sp 2) in ≤ 1 nm grain boundaries. It is believed that in nanocomposite carbon films sp2 bonded carbon sites controls the electronic and optical properties due to their pi-states close to Fermi level, while sp3 matrix control the mechanical properties. We propose that other than the size of sp2 bonded carbon grain boundaries, the ratio of sp3/sp2 bonded carbon volume fraction has significant effect on the optical and electronic (electron field emission) properties.; UNCD films were synthesized in Ar-rich (H-poor) high energy density gas plasmas resulting new growth and nucleation mechanism, which involve insertion of C2 into C-C and C-H bonds rather generally accepted atomic hydrogen abstraction and carbon radical (CH3,CH2) insertion in hydrogen rich gas ambient. The high energy density plasma systems used in UNCD synthesis poses serious up-scaling engineering problems for bigger wafer processing and it would be of both fundamental understanding on growth and up-scalability point of view if UNCD can be grown by low energy density hot filament chemical vapor deposition (HFCVD) system over wide parameter window of Ar gas concentration.; Continuous UNCD films were grown in Ar-rich gas atmosphere with relatively high growth rates by providing low power (5-10 W) DC plasma in HFCVD system. A detailed study on the parameter window of UNCD films growth in the new system by varying the volume fraction of CH4/(CH4+H2) ∼ 2.5- 17% and Ar/(Ar+H2) ∼ 80-95% were done. The parameter window for the synthesis of UNCD films was studied as a function of argon, methane and hydrogen concentrations, as well as substrate temperature and DC bias. The Energy Filtered Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, Raman Spectroscopy and X-ray Photoelectron Spectroscopy were employed to study the nanocrystalline and diamond-like nature of the UNCD films.; Spectroscopic ellipsometry was employed to study the optical and structural properties of UNCD films deposited by DC plasma-assisted Ar-rich HFCVD. The intrinsic optical properties of UNDC were measured in the 1.45-2.88 eV photon range. The compositional analysis were done by modeling (&psgr;, Delta) spectra using Bruggeman effective medium approximation with layer structure (surface roughness/bulk) and each layer composed of different volume fractions of sp3, sp2 bonded carbon. The Mueller Matrix Spectroscopic Ellipsometry as complementary method to identify the phase purity of UNCD films by measured 16 elements of Mueller matrix was explained.; The temporal current stability and the current fluctuations of the field emission current obtained from UNCD films were investigated. The field emission properties were correlated to the films composition (sp2 and sp3 bonded carbon volume fractions) and nanostructure. The results of the compositional analysis obtained from modeling analysis Spectroscopic Ellipsometry [&psgr; (E), Delta (E)] data applied to understand the Electron Field Emission behavior.