Contribution of Drude and Brendel Model Terms to the Dielectric Function; A case of TiO2:Nb Thin Films

Parametric modeling provides a mean of deeper understanding to the properties of materials. Dielectric function is one of the key parameters which can provide information on the dielectric nature of a thin film or bulk materials. It can be obtained by modeling the material using appropriate existing, new or modified models. In our work, we utilized existing Brendel and Drude models to extract the optical constants from spectrophotometric data of fabricated undoped and niobium doped titanium oxide thin films. The individual contributions by the two models were studied to establish influence on the dielectric function. The effect of dopants on their influences was also analyzed. Results indicate a minimal contribution from the Drude term due to the dielectric nature of the undoped films. However as doping levels increase, the rise in the concentration of free electrons favors the use of Drude model.

Atomic Layer Deposition of Ruthenium Films on Hydrogen terminated Silicon

Atomic Layer deposition of thin Ruthenium films has been studied using a newly synthesized precursor (Cyclopentadienyl ethylruthenium dicarbonyl) and O2 as reactant gases. Under our experimental conditions, the film comprises both Ru and RuO2. The initial growth is dominated by Ru metal. As the number of cycles is increased, RuO2 appears. From infrared broadband absorption measurements, the transition from isolated, nucleated film to a continuous, conducting film (characterized by Drude absorption) can be determined. Optical simulations based on an effective-medium approach are implemented to simulate the in-situ broadband infrared absorption. A Lorentz oscillator model is developed, together with a Drude term for the metallic component, to describe optical properties of Ru/RuO2 growth.

INFRARED EVIDENCE FOR THE COEXISTENCE OF FREE AND BOUND CHARGES IN Nd2-xCexCuO4 AND Bi2Sr2CuO6

Electron-doped Nd 2-x Ce x CuO 4 and hole-doped Bi 2 Sr 2 CuO 6 have been studied in the infrared to discriminate between the existing models of the optical conductivity σ(ω) in metallic cuprates. In Nd 2-x Ce x CuO 4 an absorption peak clearly visible in the insulating phase softens for increasing x and for decreasing temperature, until it reaches the far infrared (FIR peak) at the insulator-to-metal transition. In the superconducting phase it persists beside the free-carrier Drude absorption, as shown by fitting procedures, and disappears only in the overdoped normal metal. Direct evidence for the presence of the FIR peak in a metallic cuprate comes from the reflectivity of a Bi 2 Sr 2 CuO 6 film, measured down to 10 cm -1, where we could resolve the FIR peak from a normal Drude term as narrow as 35 cm -1 at low T. This observation provides direct evidence for the coexistence of free and "bound" charges in a superconducting cuprate.

In-Situ Optical Characterization of Titanium Nitride Thin Films for Applications in Microelectronics

ABSTRACTTitanium Nitride (TiNx) thin films were deposited on Si(100) by reactive magnetron sputtering. The varied deposition conditions were the substrate temperature (Td) (27 - 650 °C) and the negative bias voltage (Vb) applied to the substrate (0 - 200 V) in order to produce TiNx films with various compositions and structural characteristics. The deposition process was monitored in-situ by Spectroscopic Ellipsometry in the spectral range 1.5–5.5 eV. Determination of the film composition was made through the measured screened plasma energy ωps while the electrical resistivity of TiNx was studied in terms of the unscreened plasma energy ωpu. ωpu was calculated by an optical model including a Drude term and Lorentz oscillator terms and their dependence on Td and Vb was studied. The ωpu was found to increase with Vb until a saturation value was obtained. The saturation value of ωpu depends on the Td.ωpu describes better the TiNx films, since it is directly correlated with their metallic character in terms of the electrical resistivity.