Film Properties/Structure/Deposition Process Relationships

Tuesday, May 1, 2001 2:30 PM in Room Sunset

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2:30 PM C2-1-4 Evaluation of Optical Degradation of Aluminized Sapphire Flown on Russian Mir Space Station
C.L. Bungay (University of Nebraska-Lincoln); D.A. Jaworske, K.K. de Groh (NASA Glenn Research Center); J.A. Woollam (University of Nebraska-Lincoln)
Materials degradation in Low Earth Orbit (LEO) is of continued concern, particularly for long duration space applications such as the International Space Station (ISS). The Passive Optical Sample Assembly (POSA) experiment flown on the exterior of the Mir as a risk mitigation experiment for the ISS was designed to better understand the potential contamination threats that may be present in the vicinity of the spacecraft. Deterioration in the optical performance of candidate space power materials due to the LEO environment and contamination must be evaluated in order to propose measures to mitigate such deterioration. The optical properties of optically thick aluminum (>800 angstroms)on sapphire substrates were evaluated prior to and after the POSA flight. Total, diffuse, and specular reflectance measurements were acquired to quantify the degradation in reflectivity due to contamination. Variable angle spectroscopic ellipsometry (VASE) covering a spectral range from 0.25 microns to 14 microns was used to identify the type and thickness of the contamination. This paper summarizes the results of pre- and post-flight optical measurements, identifies the mechanisms responsible for optical properties deterioration, and suggests improvements for the durability of materials in future missions. @FootnoteText@ @footnote 1@ Research funded by NASA Glenn Grant NAG3-1802.
2:50 PM C2-1-5 Impedance Spectroscopic Measurements of Nanostructured Thin Solid Films Based on Tantalum Oxide
E. Bertran, C. Person, I. Porqueras (Universitat de Barcelona, Spain)
Nanostructured thin films of dense stoichiometric Ta@sub 2@O@sub 5@ have been deposited at low substrate temperature (T@sub S@ < 100@super o@C) by PVD in a thermal evaporation system using electron beam assisted by argon bombardment. The films consist of a stack of alternated nanometric layers deposited with and without argon bombardment, which affects the structure and properties of the films. Optical and electrical transport properties have been studied in order to determine the characteristics of the nanostructured tantalum pentoxide to be employed as solid electrolyte layer in an electrochromic thin film structure. Impedance spectroscopy measurements have been done in nanostructured samples having different layer period and number of bilayers. The main parameters concerning the ionic and electronic transport through the nanostructure have been correlated to the structural characteristics determined by TEM and selective area electron diffraction (SAED). A complete optical characterization in the ultra violet, visible and infrared range was carried out using ultra violet-visible transmittance and FTIR spectroscopy. The results have been discussed in terms of the effects of the nanostructure on the ion diffusion, on the dielectric behavior and on the optical properties.
3:10 PM C2-1-6 Characteristics of Ag-Zn Alloy Thin Films as Optical Memory Materials
S.H. Bae (The Pennsylvania State University)
Characteristics of Ag-Zn alloy thin films have been studied for phase-change type optical memory materials. Ag-Zn alloy thin films have been co-evaporated on glass substrates and investigated in the atomic composition range of 75 - 40 Ag %. In the composition range we have explored, we have examined the reflectance of pink-colored beta' phase and silver-colored seta phase with a 633 nm incident laser. The difference of reflectance between two phases is a function of atomic composition in Ag-Zn alloy thin films. Ag-51 % Zn alloy shows the largest difference in the reflectance between beta' and seta phases; i.e., 15 % is the largest reflectance difference in these alloy thin films. According to X-ray diffraction analysis, low deposition rate (~8 Å /sec) results in dominant volume fraction of beta' phase (pink-colored) in as-deposited Ag-50 % Zn thin films while fast deposition rate (~58 Å/sec) leads to more formation of seta phase (silver-colored) at the same composition of Ag-Zn alloy thin films. In these two cases (slow and fast depositions), the volume fraction of beta' phase in these thin films is increased as they are aged at room temperature; i.e., effect of residual stress evolves in the Ag-Zn thin films and the films show more pink phase as time progresses. In as-deposited Ag-Zn thin films, preferred orientation of seta phase depends upon deposition rate while preferred orientation of beta' phase does not vary with deposition rates. (111) preferred orientation results from slow deposition of seta phase whereas (300) orientation is found from fast-deposited seta phase. It is also noted that gamma phase, which is an equilibrium phase in 51 – 68 % Ag-Zn bulk alloys, is not found in any Ag-Zn alloy thin films we have examined.
3:30 PM C2-1-7 Pulsed Dual Bipolar Unbalanced Magnetron Sputtering for Alumina: Variation With Pulse Frequency.
J. O'Brien (University of Salford, England); P.J. Kelly (University of Salford, United Kingdom)
The pulsed magnetron sputtering (PMS) process has transformed the deposition of dielectric materials. However, the industrial exploitation of the pulsing process is impeded by the fact that, during long-term deposition runs, eventually all surfaces will be covered by the insulator. This causes a gradual shift of the electric field shape and can generate serious changes in the deposition pattern of the magnetrons and possibly wreck the deposition uniformity. A more viable approach is to use two magnetrons in a dual bipolar (dual cathode) arrangement. If both magnetrons are connected to the same bipolar power supply then each magnetron can act alternately as an anode and a cathode. In this arrangement, the periodic pole changing prevents arcing and also effectively maintains a clean anode surface. In this study, alumina films have been deposited by dual bipolar pulsed sputtering, using unbalanced magnetrons arranged in the vertically opposed configuration. The variations in specific process parameters with pulse frequency (100-350 kHz) and phase relationship have been investigated. In addition, structural, optical and tribological film properties have been determined. Preliminary findings indicate that the suppression of arcs is critical to obtaining defect-free films. Once this is achieved, little variation is then observed in many coating properties, despite the wide variation in plasma properties.
3:50 PM C2-1-8 Characterization of Aluminum Nitride Thin Films Deposited by Filtered Cathodic Arc Process
S.J. Dikshit, A.K. Rai, R.S. Bhattacharya (UES, Inc.); S. Guha (AFRL/MLP Wright Patterson Research Laboratory)
Thin films of Aluminum Nitride ( AlN) have been grown on Silicon, glass and sapphire substrates, using a Filtered Cathodic Arc Deposition process. The process parameter's viz. gas pressure, substrate temperature and bias voltage were varied in order to investigate their influence on the structural and optical properties. The as grown films have been characterized by Transmission Electron Microscopy, Auger Electron Spectroscopy, optical microscopy, ellipsometry and Visible/ infrared transmission spectroscopy. An Atomic Force Microscope was used to reveal the three dimensional topographs of the surface of the films. Smooth, stoichiometric films of nanocrystalline AlN grains having hexagonal structure were grown. In this paper, the microstructural and optical properties have been correlated with the deposition conditions.
4:10 PM C2-1-9 Effects of Nitrogen Content and Deposition Temperature on the Characteristics of AlN Thin Films
I.C. Oliveira (LPP-ITA-CTA, Brazil); M.A. Djouadi (ENSAM, France); M. Massi (LPP-ITA-CTA, Brazil); S.G. Santos (LSI PEE EPUSP, Brzail); H.S. Maciel, C. Otani (LPP-ITA-CTA, Brazil)
Aluminium nitride( AlN) thin films have been investigated in recent years for their technological applications, especially in opto-electronics devices. We have studied the growth of AlN films on unheated and heated Si polished wafers and quartz substrates by reactive DC-magnetron sputtering from Al pure target using argon and nitrogen gas mixtures. By changing the nitrogen gas content at fixed total pressure, we have observed a high nitridation of the AlN films when the nitrogen gas reaches the percentage of about 20% irrespective of the substrate temperature. EDS, FTIR and XPS measurements have confirmed this nitridation process. Increasing the substrates temperature leads to a change of the dielectric properties of the AlN films, as inferred from C-V curves. Self-annealing of the material during deposition is probably the cause for this dielectric properties behaviour with temperature. FTIR analysis of the films appears to corroborate this observation.
4:30 PM C2-1-10 Rf Sputter Deposition of Zno Thin Films on Si with Copper Metallization
J. Ting, Y. Chang (National Cheng Kung University, Taiwan)
ZnO thin films were deposited on copper metallized Si substrates using a RF sputter deposition technique. The substrate temperature and the oxygen/Ar ratio were varied during the deposition of ZnO. The microstructure and properties of the resulting ZnO films were examined using a-step, scanning electron microscopy, transmission electron microscopy, x-ray diffractometry, secondary ion mass spectrometry, and energy dispersive spectrometry. The characteristics of ZnO film were found to depend on not only the deposition conditions but also the substrate preparation methods. The intensity and degree of the c-axis preferred orientation of ZnO were addressed. Other characteristics of ZnO, including surface morphology, grain size, interface diffusion, and crystallinity were also investigated.
4:50 PM C2-1-11 Growth and Properties of Alumina Films Obtained by Low-Pressure Metal-Organic Chemical Vapor Deposition
D. Kuo, B Cheung (National Dong Hwa University, Taiwan); R Wu (Industrial Technology Research Institute, Taiwan)
Amorphous alumina films with film thickness of 0.35-2.0 µmm were prepared on glass and silicon substrates by low-pressure metal-organic chemical vapor deposition using aluminum tri-sec-butoxide (ATSB) and argon. These films were studied by choosing different substrate temperature, amount of argon carrier gas through ATSB vaporizer (Ar(ATSB) flow rate), and oxygen amounts. Films deposited at low temperatures with high Ar(ATSB) flow rate had shown cracked surfaces. The study of growth kinetics was focused on the growth rate, apparent activation energy, and ATSB reaction order. Oxygen did not have a strong effect on growth rate, but produced a small amount of carbon of less than 0.3% in films. No carbon was detected for films deposited at argon atmosphere. The film had higher compositional Al/O ratio at higher deposition temperatures. Microstructure of the deposited alumina was observed by using scanning electron microscopy and atomic force microscopy. Mechanical properties, e.g. hardness, internal stress, and adhesion, of the alumina films were evaluated. Optical properties, e.g. refractive index and optical transmittance, were also measured.
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