Papers by Keyword: Ellipsometry

Abstract: In this study, AZO films were deposited by RF sputtering technique. Then, the state of residual stress in the AZO films was investigated by using spectroscopic ellipsometry (SE) and XRD methods. Our experiments show that a suitable SE model could provide useful indication about the variation of stress in the as-deposited films. However, there is a disparity in the results of the SE fitting and XRD stress analysis for annealed AZO films. Further investigation is required in order to understand the cause of this contradiction. Despite this disparity, the SE technique enables us to monitor strain relaxation in TCO films with a faster and simpler way compared with other methods.

Abstract: Mg_xZn_1-xO films with hexagonal structure are prepared by radio frequency (rf) magnetron sputtering on Si substrate. The refractive indices and absorption coefficients of these films in the wavelength range from 300 to 800nm are determined by using ellipsometry at room temperature. The results show that the refractive index increases as the wavelength decreases in the transparent region (400-800nm). It reaches its maximum value around 340nm and 331nm, which is close to the fundamental absorption edge. Then the refractive index decreases as the wavelength gets shorter. The value of the refractive index is also a function of the Mg content. The higher the Mg content is in the film, the smaller the refractive index of the film is in the wavelength range from 330nm to 850nm. The band gap energy of the Mg_xZn_1-xO film is obtained by analyzing its absorption spectrum. An increase in the Mg content causes the fundamental absorption edge to shift toward shorter wavelength. In addition, UV and strong blue emission have been observed when the Mg_xZn_1-xO film is excited with light wave of 260nm at room temperature, and the emission mechanism is discussed.

Abstract: Recent studies have shown that even inherently hydrophilic surfaces (θ < 90 ̊) can become hydrophobic as a consequence of nanopatterning (1-4). This creates an issue in semiconductor manufacturing as aqueous chemistries (e.g. dilute HF solutions) are preferred to organic chemistries for their lower cost of ownership and greener environmental profile.

Abstract: The characteristics of cadmium sulphide (CdS) and lead sulphide (PbS) nanoparticles, grown inside Langmuir-Blodgett (LB) multilayer films of 5,11,17,23-tetra-tert-butyl-25,27-dicarboxymethoxy-26,28-dihydroxycalix [arene (I), have been studied using ellipsometry, UV-visible spectroscopy, and transmission electron microscopy (TEM). Multilayer films were formed by transferring a floating Langmuir monolayer of I onto substrates using LB deposition and water subphase containing Pb²⁺ or Cd²⁺ ions. The nanoparticles were fabricated by exposing cadmium-or lead-containing multilayer films of I (20-80 monolayers thick) to hydrogen sulphide (H₂S) gas for 12 hours. By Gaussian fitting of the absorbance - energy spectra, the size of the clusters and their dispersion were found to be 1.43±0.18 nm and 1.21±0.05 nm for CdS and PbS respectively. This is the first time that such thick LB films of an amphiphilic compound possessing such high thermal stability (m.pt. ~270°C) have been used as the vehicle for the formation of CdS and PbS semiconductor particles.

Abstract: This paper investigates the adsorption behavior of triblock copolymer Poly (propylene oxide)-poly (ethylene oxide)-poly (propylene oxide), PPO-PEO-PPO on silicon and iron surfaces by using the contact angle goniometer, spectroscopic ellipsometer and atomic force microscopy (AFM). After adsorption, the decrease of water contact angle was observed on each surface; and a larger reduction of water contact angle occurred on the surface covered by the copolymer film with longer and higher weight percent of hydrophilic PEO block. This means that the PEO block may be on the top of the adsorbed copolymer film. The film thickness measurement shows that the copolymer with longer and higher weight percent of PPO block forms a thicker film on the hydrophobic surface, which suggests that the hydrophobic PPO block of the copolymer in the aqueous solution plays the main role during the adsorption of PPO-PEO-PPO onto the hydrophobic surface. It has been found from the AFM results that the roughness of the surface decreased after adsorption and the smoother topography was observed on the surface adsorbed by a thicker adsorbed film.

Abstract: An ultra- thin Ti film with a thickness of less than 30 nm was deposited on the surface of a silicon wafer by the filtered arc deposition system. A novel technique was adopted to create a height step between the coated area and non-coated area (silicon wafer) during deposition. The surface morphology and thickness of the film was detected by atomic force microscopy (AFM). The AFM results showed that the deposited film formed a smooth structure on the silicon wafer and the height step between the coating and silicon wafer was clear enough to give the thickness of the deposited film. The composition of the deposited film was detected by a combined use of Ellipsometry and AFM. Natural oxidisation of Ti (TiO2) was found on the top of the Ti film after deposition, and the thickness of TiO2 was determined by ellipsometry to be about 0.6 nm.

Abstract: Composite SiN_x/DLC films were deposited on silicon substrate by co-deposition system. The carbon plasma was generated by filtered cathodic arc source, simultaneously incorporated with silicon nitride from RF magnetron sputtering. The silicon nitride sputtering rate was maintained by fixed RF power at 100W while the arc current of FCA was varied from 20 to 80A.The SiN_x/DLC film composition and optical properties were investigated by X-ray photoelectron spectroscopy and spectroscopic ellipsometry respectively. The results revealed that the atomic concentration of carbon increased while those of silicon and nitrogen decreased with increasing arc current. The oxidation was found on the film surface and related to the atomic concentration of silicon. The optical properties can be changed as a function of carbon concentration by setting different arc current. In this work, the volume percentage of carbon obtained from spectroscopic ellipsometry using Bruggeman EMA model showed good numerical correlation with the atomic percentage of carbon from XPS analysis with the range spanning across 75-95 at. %.

Abstract: The growth of AlGaN solid solutions on 3C-SiC(111)/Si(111) is demonstrated. The residual stress of the grown layer was investigated by high resolution X-ray diffraction (HRXRD) and infrared ellipsometry. Analysis of the HRXRD data showed that the observed lattice distortion was caused partially by hydrostatic pressure and partially by biaxial tension. The residual stress depends on the layer composition and weakly on the growth temperature.

Abstract: Optical properties of thin films of vanadium thermally oxidized at air were studied by ellipsometric method using wavelength of He-Ne laser. Multipart composition of these films was revealed and method of optimization of technological conditions based on dynamic of changing optical constants near 68°C was developed.

Abstract: In depositing nitrogen doped tungsten oxide thin films by using reactive dc pulsed magnetron sputtering process, nitrous oxide gas (N2O) was employed instead of nitrogen (N2) as the nitrogen dopant source. The nitrogen doping effect on the structural and optical properties of WO3 thin films was investigated by X-ray diffraction, transmission electron microscopy and UV-Vis spectroscopy. The thickness, refractive index and optical band gap energy of these films have been determined by analyzing the SE spectra using parameterized dispersion model. Morphological images reveal that the films are characterized by a hybrid structure comprising nanoparticles embeded in amorphous matrix and open channels between the agglomerated nanoparticles. Increasing nitrogen doping concentration is found to decrease the optical band gap energy and the refractive index. The reduced band gaps are associated with the N 2p orbital in the N-doped tungsten oxide films.