Now showing 1 - 10 of 10
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    Modeling of thermodynamic and transport phenomena in CVD processes for nano-scale applications
    (01-01-2008) ;
    Gorai, P.
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    Chawla, N.
    To illustrate the concept of the inter-dependence between multicomponent chemical reactions and transport phenomena, a theoretical investigation of a halogen-cycle tungsten filament incandescent lamp was undertaken based on local thermochemical equilibrium (LTCE) coupled with Fickian and thermal (Soret) transport of species. Deposition of tungsten on the bulb wall leads to 'bulb blackening', resulting in reduction in the luminous efficiency of the lamp, a problem typically combated by addition of small amounts of halogen and oxygen. Utilizing temperature-dependent Soret diffusion factors, elemental fluxes were analyzed. Zero element flux (ZEF) maps were generated based on temperature-dependent Soret diffusion factors. The element solubilities and the filament-to-wall element segregation were found to be strongly dependent on the bulb wall temperature, oxygen fill pressure and Soret diffusion factors. Transport-affected shifts in element solubilities from pure LTCE condition were studied. Implications of this study for the modelling of nano-scale CVD processes are highlighted. © The Electrochemical Society.
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    Particle science and technology education and research at IIT madras: A synergistic approach
    Historically, the particulate research and education effort in the Particle Science & Polymers (PSP) Laboratory in the Department of Chemical Engineering at IIT Madras may be described as being focused on "Mechanical Operations", which encompasses traditional technologies such as size reduction and size classification, and addresses applications such as: biomass fuel preparation, material recycling from electronic scrap, fly-ash classification and computer simulation of size reduction and classification processes of industrial importance. More recently, nano-particle research has emerged as a critical research initiative of the Laboratory. The educational curriculum is now being modified to provide necessary expertise to student researchers working in this field. Fine-particulate research and education are being intertwined in such a way as to maximize benefit to academia and industry. Course delivery methods are also being upgraded in step with web-based learning and distance-learning scenarios.
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    Use of ultrasonic cavitation in surface cleaning: A mathematical model to relate cleaning efficiency and surface erosion rate
    (01-12-2005)
    Ultrasonic cleaning, employing frequencies in the range between 40 kHz to 200 kHz, is widely used in many industries requiring precision cleanliness in the micrometer to submicron particle size range-e.g., semiconductor wafer fabrication, hard disk drive manufacturing, integrated circuit assembly, etc. One overriding concern with the use of ultrasonic cleaning for delicate components and assemblies has been the specter of cavitation erosion-surface material loss and other functional degradation due to impact of shock waves generated by collapsing bubbles and bubble-clusters in an oscillating acoustic field. The simultaneous processes of surface cleaning and of surface erosion in the presence of a highfrequency ultrasonic field (>/= 58 kHz) are described here mathematically, and the equations are coupled in such a way as to allow conceptual optimization of parametric settings to maximize the cleaning efficiency, even while minimizing the level of erosion damage. This theoretical analysis is presented for various ultrasonic field conditions (frequency, intensity, etc.), fluid medium properties (viscosity, density) and various surface conditions (hardness, smoothness, etc.). The contribution of "acoustic streaming" to surface cleaning is incorporated in the model, and is shown to have minimal influence on the optimum cluster collapse pressure, but to have a significant effect on the net cleaning efficiency for the surface.
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    Application of high-intensity ultrasonics in nanotechnology: Sono-fragmentation
    (01-12-2010) ;
    Doggolu, P.
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    Khinchi, K.
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    Gopi, K. R.
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    Optimization of post-CMP ultrasonic cleaning parameters by Taguchi DOE
    (01-01-2009) ;
    Rahul, V.
    Post-CMP cleaning effectiveness is best assessed by studying the cleanliness of polished wafers obtained directly from the CMP process. In this study, a Taguchi DOE was designed as an L27 orthogonal array, and 3 levels of ten CMP and ultrasonic parameters were incorporated in the experimental matrix. The CMP parameters studied were: CMP velocity, pressure, slurry concentration, pH and temperature. The sonication parameters investigated were: frequency, amplitude, pH of the cleaning solution, surfactant type and concentration. The output properties measured were erodability and cleanability. High Level Analysis (HLA) of the DOE data indicate that under conditions of CMP that can embed particles with greater force, lower-frequency (more cavitational) conditions are more effective in particle removal. In general, ultrasonic frequencies in excess of 132 kHz are ineffective in removing strongly-adhered or embedded particles. Ionic surfactants are, in general, more conducive to CMP residue removal compared to non-ionic surfactants (natural, or man-made). ©The Electrochemical Society.
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    Optimization of ultrasonic cleaning for erosion-sensitive microelectronic components
    (01-01-2006) ;
    Diwan, M.
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    Awasthi, P.
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    Shukla, A.
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    Sharma, P.
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    Goodson, M.
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    Awad, S.
    In this paper, we describe an experimental study undertaken to investigate ultrasonic fields in the frequency range 58-192 kHz with respect to their surface cleaning and erosion potential. Measurements are performed using three different methods - gravimetric weight-loss, surface profilometry, and precision turbidimetry - to assess these mechanisms for a variety of materials, including semiconductors. Conclusions are drawn regarding the nature of interaction between high-frequency, high-intensity ultrasonic fields and immersed surfaces. Recommendations are provided for optimal settings to maximize surface cleanability and minimize erodibility of sensitive substrates. © 2006 IEEE.
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    Effect of cavitation on removal of alkali elements from coal
    (03-12-2015)
    Srivalli, H.
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    Nirmal, L.
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    The main impurities in coal are sulphur, ash and alkali. On combustion, the volatile forms of these impurities are either condensed on the boilers, or emitted in the form of potentially hazardous gases. The alkali elements present in coal help the fly ash particles adhere to boiler surfaces by providing a wet surface on which collection of these particles can take place. Use of ultrasonic techniques in cleaning of coal has stirred interest among researchers in recent times. Extraction of alkali elements by cavitation effect using low-frequency ultrasound, in the presence of reagents (HNO3 and H2O2) is reported in this paper. Powdered coal was dissolved with the reagent and exposed to ultrasonic fields of various frequencies at different time intervals. The treated solution is filtered and tested for alkali levels.
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    Experimental and theoretical investigation of thermodynamic and transport phenomena in polysilicon and silicon nitride CVD
    (01-01-2009)
    Chawla, N.
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    The performance of chemical vapor deposition (CVD) reactors is strongly dependent on fluid flow, heat transport and mass transport. In this work, the deposition of polysilicon in a LPCVD batch reactor is modeled by using the local thermochemical equilibrium approach coupled with transport effects. The focus is on understanding how the interplay of flow and kinetic factors influences deposition in a CVD reactor. Experiments were conducted to study the effect of temperature on deposition rate. Comparisons between the modeling and experimental results were used to obtain an insight into the parameters affecting deposition. PECVD reactors are being increasingly used in the industry for carrying out deposition at low temperatures. A review is presented of the challenges faced in PECVD modeling and the approaches that could be followed. An empirical model for PECVD deposition of silicon nitride deposition is also presented. ©The Electrochemical Society.