On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\pm$ 14 GPa, s0 = 420 $\pm$ 8 and u = 0.29.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Multilayer TiB2/X hard coatings by sputtering deposition

Titanium diboride has been investigated as a potential candidate for aerospace structures, cutting tools, surface coatings of first-wall components and diffusion barriers in integrated circuit metallization. Titanium diboride is a very stable hard refractory compound but its brittleness is the main drawback. It was possible to lessen the TiB2 brittleness by producing TiB2/X coating designs by the multi-target RF magnetron sputtering process. X is the metal layer (Al, Ti, NiCr, Mo) in the composite system. The influence of the composition wavelength and volume fraction of ceramic has been studied over a range of sputtering conditions. The most suitable multilayer coating design (TiB2/NiCr) on steel substrate, for maximum hardness (18.81GPa) and elastic modulus (304.6GPa) was found to be with a composition wavelength of 50nm and volume fraction of ceramic of 75%. The greatest improvement of the elastic modulus measured by nanoindentation was found to be for a TiB2/Al two-layer coating design either on steel or on aluminium substrate, giving 36.2% and 40% improvement above the rule of mixtures respectively, when compared with TiB2 coatings deposited under the same sputtering conditions. Several pieces of three-point bent apparatus were designed for measuring the inplane elastic modulus of the coatings. The three-point bent test by nanoindenter shows promise as a method for measuring the in-plane elastic modulus on uncoated beams. A comparison between traditional and non-traditional methods of measuring mechanical properties of the coatings was performed in this study. The nanoindentation technique was found to be an appropriate method to measure the mechanical properties of multilayer coating designs.Ph

Diffusion of diluents in glassy polymers

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1994.Includes bibliographical references.by Paul Franklin NEaley.Ph.D

Stress analysis, dielectric, piezoelectric, and ferroelectric properties of PZT thick films. Fabrication of a 50MHz Tm-pMUT annular array

PZT films up to 35 μm thick were fabricated, using a composite sol gel route combining a PZT powder and a PZT sol. The maximum temperature for the process was 710°C. A demonstration of single layer and multilayer structures was given to show the flexibility of this technology. With Stoney’s Equation, studies of the in-situ film stress development as a function of the film thickness and density was effectuated. It helped to understand that the internal forces increase considerably with the film thickness and density. This study yields to set up experimental conditions in which a crack free surface finish of a 28μm thick film revealed the adaptability of the spin coating technique to fabricate thick films. The wet etching technology revealed the possibility of a great adaptability to pattern and shape innovative devices such as bars 10 μm wide of 21μm PZT thick film. The results open the way to a wide range of new industrial application requiring small features and/or multilayer PZT thick film with embedded electrodes. The single element and annular array devices have been shown to resonate at approximately 60MHz in air and 50 MHz in water. Three types of the composite thick film – 2C+4S, 2C+5S and 2C+6S – were used to fabricate the Tm-pMUT devices. In each case the most effective poling was obtained by maintaining the poling field of 8.4V/μm during cooling from the poling temperature (200ºC) to ‘freeze’ poled domains in place. This ‘freezing’ was required to prevent the tensile stresses within the film from reorienting the domains at high temperatures when the poling field is removed. Increasing values of thickness mode coupling coefficient (kt) were observed with increasing levels of sol infiltration (decreasing density). Such behaviour is thought to be due to non linear effects on the piezoelectric coefficient (e33) at high levels of porosity. For very dense thick film material a kt of 0.47 was observed which is comparable to that observed for the bulk material

Stress analysis, dielectric, piezoelectric, and ferroelectric properties of PZT thick films. Fabrication of a 50MHz Tm-pMUT annular array

PZT films up to 35 μm thick were fabricated, using a composite sol gel route combining a PZT powder and a PZT sol. The maximum temperature for the process was 710°C. A demonstration of single layer and multilayer structures was given to show the flexibility of this technology. With Stoney’s Equation, studies of the in-situ film stress development as a function of the film thickness and density was effectuated. It helped to understand that the internal forces increase considerably with the film thickness and density. This study yields to set up experimental conditions in which a crack free surface finish of a 28μm thick film revealed the adaptability of the spin coating technique to fabricate thick films. The wet etching technology revealed the possibility of a great adaptability to pattern and shape innovative devices such as bars 10 μm wide of 21μm PZT thick film. The results open the way to a wide range of new industrial application requiring small features and/or multilayer PZT thick film with embedded electrodes. The single element and annular array devices have been shown to resonate at approximately 60MHz in air and 50 MHz in water. Three types of the composite thick film – 2C+4S, 2C+5S and 2C+6S – were used to fabricate the Tm-pMUT devices. In each case the most effective poling was obtained by maintaining the poling field of 8.4V/μm during cooling from the poling temperature (200ºC) to ‘freeze’ poled domains in place. This ‘freezing’ was required to prevent the tensile stresses within the film from reorienting the domains at high temperatures when the poling field is removed. Increasing values of thickness mode coupling coefficient (kt) were observed with increasing levels of sol infiltration (decreasing density). Such behaviour is thought to be due to non linear effects on the piezoelectric coefficient (e33) at high levels of porosity. For very dense thick film material a kt of 0.47 was observed which is comparable to that observed for the bulk material.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The design of a microfabricated air electrode for liquid electrolyte fuel cells

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references.In this dissertation, the microfabricated electrode (MFE) concept was applied to the design of an air electrode for liquid electrolyte fuel cells. The catalyst layer of the electrode is envisioned to be fabricated by using a microfabricated die to apply a three-dimensionally patterned macro-texture upon a microporous carbon matrix. The resulting dual porosity structure consists of an array of cylindrical holes that are formed from the die and micropores present in the carbon matrix. The holes are used for gas transport while the micropores are saturated with a liquid electrolyte for ion transport. The catalyst is loaded into the microfabricated structure by electrodepositing thin catalyst films within the cylindrical holes. In this dissertation, three issues concerning the design of the MFE were investigated: 1) identification of the best material to use for the microporous carbon matrix, 2) the study of electrokinetic parameters of electrodeposited Pt films, and 3) the study of oxygen transport behavior within a Pt film supported on the surface of a microporous carbon matrix. Two types of polymer-bonded carbon materials have been identified as suitable materials for the carbon matrix. They are carbon black particles bonded into a microporous matrix either by polytetrafluoroethylene (PTFE) fibrils or by polyethersulfone (PES), which is a soluble polymer in common solvents. Experiments and modeling have indicated that these materials will allow the microfabricated catalyst layer to have an effective ionic conductivity that is 4 to 5 times greater than the conventional catalyst layer. Rotating disk electrode experiments on electrodeposited Pt films in 0.5 M sulfuric acid show that these films have an oxygen reduction reaction mass activity that is 2.5 times greater than that of Pt particles supported on carbon black.(cont.) Furthermore, oxygen gain experiments on electrodeposited Pt films supported on a microporous membrane indicate that these films experienced no oxygen transport losses in air, up to a current density of 130 mA/cm2. These results strongly support the use of thin catalyst film technology in catalyst layers of fuel cells. The experimental results presented this dissertation were used to develop a half-cell model of the MFE in concentrated phosphoric acid. The results of the model suggest that the MFE is capable of producing a current density 3.5 times greater than that of the conventional electrode. It is believed that such potential improvements in the performance of the air electrode support continued efforts to fabricate and test the MFE design concept presented in this dissertation.by Pierre Fritz, Jr.Ph.D

Microgravity Science and Applications: Program Tasks and Bibliography for Fiscal Year 1996

NASA's Microgravity Science and Applications Division (MSAD) sponsors a program that expands the use of space as a laboratory for the study of important physical, chemical, and biochemical processes. The primary objective of the program is to broaden the value and capabilities of human presence in space by exploiting the unique characteristics of the space environment for research. However, since flight opportunities are rare and flight research development is expensive, a vigorous ground-based research program, from which only the best experiments evolve, is critical to the continuing strength of the program. The microgravity environment affords unique characteristics that allow the investigation of phenomena and processes that are difficult or impossible to study an Earth. The ability to control gravitational effects such as buoyancy driven convection, sedimentation, and hydrostatic pressures make it possible to isolate phenomena and make measurements that have significantly greater accuracy than can be achieved in normal gravity. Space flight gives scientists the opportunity to study the fundamental states of physical matter-solids, liquids and gasses-and the forces that affect those states. Because the orbital environment allows the treatment of gravity as a variable, research in microgravity leads to a greater fundamental understanding of the influence of gravity on the world around us. With appropriate emphasis, the results of space experiments lead to both knowledge and technological advances that have direct applications on Earth. Microgravity research also provides the practical knowledge essential to the development of future space systems. The Office of Life and Microgravity Sciences and Applications (OLMSA) is responsible for planning and executing research stimulated by the Agency's broad scientific goals. OLMSA's Microgravity Science and Applications Division (MSAD) is responsible for guiding and focusing a comprehensive program, and currently manages its research and development tasks through five major scientific areas: biotechnology, combustion science, fluid physics, fundamental physics, and materials science. FY 1996 was an important year for MSAD. NASA continued to build a solid research community for the coming space station era. During FY 1996, the NASA Microgravity Research Program continued investigations selected from the 1994 combustion science, fluid physics, and materials science NRAS. MSAD also released a NASA Research Announcement in microgravity biotechnology, with more than 130 proposals received in response. Selection of research for funding is expected in early 1997. The principal investigators chosen from these NRAs will form the core of the MSAD research program at the beginning of the space station era. The third United States Microgravity Payload (USMP-3) and the Life and Microgravity Spacelab (LMS) missions yielded a wealth of microgravity data in FY 1996. The USMP-3 mission included a fluids facility and three solidification furnaces, each designed to examine a different type of crystal growth

Международная конференция "Физическая мезомеханика. Материалы с многоуровневой иерархически организованной структурой и интеллектуальные производственные технологии", посвященная 90-летию со дня рождения основателя и первого директора ИФПМ СО РАН академика Виктора Евгеньевича Панина в рамках Международного междисциплинарного симпозиума "Иерархические материалы: разработка и приложения для новых технологий и надежных конструкций", 5-9 октября 2020 года, Томск, Россия : тезисы докладов

Издание содержит тезисы Международной конференции "Физическая мезомеханика. Материалы с многоуровневой иерархически организованной структурой и интеллектуальные производственные технологии", проводимой в рамках Международного дисциплинарного симпозиума "Иерархические материалы: разработка и приложения для новых технологий и надежных конструкций". Физическая мезомеханика является научным направлением, в рамках которого материал представляется как иерархическая система взаимосвязанных структурных (масштабных) уровней. В книге отражены последние достижения в области развития принципов и методологии физической мезомеханики и результаты их применения к созданию перспективных материалов в интересах развития новых производственных технологий, освоения космического пространства, в том числе дальнего космоса, электроники, атомной энергетики, нефтегазового комплекса, медицины, транспорта и др. Книга адресована научным сотрудникам, инженерам, аспирантам и специалистам, занимающимся вопросами физической мезомеханики, разработки наноструктурных объемных и наноразмерных материалов, наноструктурированием поверхностных слоев, тонкими пленками и покрытиями, нанотехнологиями, компьютерным конструированием новых материалов и технологий их получения, технологиями локальной нестационарной металлургии и обработки материалов, неразрушающими методами контроля