Engineering Commons^™

Magnetic Properties Of Gamnas Nanodot Arrays Fabricated Using Porous Alumina Templates, S. Bennett, L. Menon, D. Heiman

Donald Heiman

Ordered arrays of GaMnAs magnetic semiconductor nanodots have been fabricated using anodic porous alumina templates as etch masks. The magnetic behavior is studied for prepared arrays with 40 nm dot diameter, 15 nm dot thickness, and 80 nm periodicity. The disklike nanodots exhibit an easy axis for fields applied in the radial direction and a hard axis in the smaller direction. In the radial direction superparamagnetism is observed with a blocking temperature of 30 K. The fabrication technique is convenient for preparing nanodot arrays of compound semiconductors that cannot be formed by self-assembly techniques.

Thermoelectric Module-Variable Conductance Heat Pipe Assemblies For Reduced Power Temperature Control, Corey Melnick, Marc Hodes, Gennady Ziskind, Martin Cleary, Vincent Manno

Vincent P. Manno

Thermoelectric modules (TEMs) are used to precisely maintain the setpoint temperature of photonic components generating variable heat loads under varying ambient conditions. The non-component side of TEMs is mounted onto conventional heat sinks (CHSs). At any combination of setpoint temperature, heat load and ambient temperature, there is a unique thermal resistance between the non-component side of a TEM and the ambient corresponding to minimal TEM power consumption. Indeed, a zero thermal resistance heat sink minimizes power consumption when a TEM operates in refrigeration mode, but when it operates in heating mode a relatively high thermal resistance one is optimal. This …

Optimized Thermoelectric Module-Heat Sink Assemblies For Precision Temperature Control, Rui Zhang, David Brooks, Marc Hodes, Vincent Manno

Vincent P. Manno

Robustprecision temperature control of photonics components is achieved by mountingthem on thermoelectric modules (TEMs) which are in turn mountedon heat sinks. However, the power consumption of TEMs ishigh because high currents are driven through Bi2Te3-based semiconducting materialswith high electrical resistivity and finite thermal conductivity. This problemis exacerbated when the ambient temperature surrounding a TEM variesin the usual configuration where the air-cooled heat sink aTEM is mounted to is of specified thermal resistance. Indeed,heat sinks of negligible and relatively high thermal resistances minimizeTEM power consumption for sufficiently high and low ambient temperatures,respectively. Optimized TEM-heat sink assemblies reduce the severity of thisproblem. …

Measurement Of Microscale Shear Forces During Chemical Mechanical Planarization, Robert White, Andrew Mueller, Minchul Shin, Douglas Gauthier, Vincent Manno, Chris Rogers

Vincent P. Manno

Polydimethylsiloxane (PDMS) posts with a diameter of 80 mu m were used to measure the shearing forces at the wafer-pad interface during chemical mechanical planarization (CMP). Measurements are made at 10 kHz with measurable forces between 40 and 400 mu N. The structures were polished using a stiff, ungrooved pad and 3 wt % fumed silica slurry at velocities of 0.3 and 0.6 m/s and average wafer-pad normal load of 5.0 and 9.1 kPa. Due to the small fraction of the pad that contacts the wafer, the local microscale forces can be much larger than the global average force might …

Non-Traditional Assessments For New Learning Approaches: Competency Evaluation In Project-Based Introductory Materials Science, Jonathan Stolk, Mark Somerville, Steven Krumholz

Mark Somerville

Over the last twenty years, NSF and the engineering community have called for systemic changes in engineering education, including an emphasis on contextual understanding; increased teaming skills, including collaborative, active learning; and an improved capacity for life-long, self-directed learning. In addition, ABET has called for engineering graduates that demonstrate an ability to apply science and engineering, and ABET requires assessment processes designed to measure student achievement of learning outcomes. Olin College has responded to these calls for change by embracing new learning approaches and assessment techniques, and by developing project-based courses that encourage experiential understanding of content and aid the …

Rapidly Prototyped Orthotweezers For Automated Microassembly, Aaron Hoover, Ronald Fearing

Aaron M. Hoover

We describe the design, fabrication, and testing of an ultra-low cost orthotweezers system for microassembly. By utilizing rapid prototyping technology, compliant mechanisms, and commodity-grade actuators and sensors, we significantly reduce the complexity and cost of the previous Orthotweezers system without sacrificing functionality. With a force resolution of 0.7mN and a worst case mean positioning repeatability of 23 mum, the system is capable of dexterously manipulating rectangular parts with dimensions 200 mum times 200 mum times 100 mum. Such blocks can then be temporarily attached to thin, delicate, or oddly shaped parts to enable handling and ultimately assembly of micromechanical structures. …

Lumbar Vertebral Density And Mechanical Properties In Aged Ovariectomized Rats Treated With Estrogen And Norethindrone Or Norgestimate, Carla Vanin, Neil Maclusky, Debbie Chachra, Mehran Kasra, Marc Grynpas, Robert Casper

Debbie Chachra

OBJECTIVE: This study was designed to investigate the effects of estrogen alone or combined with two different progestins, norethindrone or norgestimate, on bone density and compressive mechanical properties in an aged rat model.

STUDY DESIGN: Twenty 11-month-old female Sprague-Dawley rats were sham operated (intact control) and 80 wee overiectomized. Three groups of 20 ovariectomized rats were implanted with Silastic silicon rubber (Dow Corning, Midland, Mich.) capsules containing 5% estradiol (wt/wt) in cholesterol. All rats in the intact control (group 1) and the ovariectomized (group 2) and the first of the overiectomized plus estrogen (group 3) groups were injected subcutaneously daily …

The Effect Of Fluoride Treatment On Bone Mineral In Rabbits, Debbie Chachra, C. Turner, A. Dunipace, Marc Grynpas

Debbie Chachra

Fluoride therapy has been used clinically for many years, but its use remains controversial and many basic questions remain unanswered. Accordingly, this study returns to an animal model to study the effects of high doses of fluoride on bone mineral in rabbits. Twelve rabbits, aged 3½ months at the start of the study, received drinking water fluoridated at 100 ppm while their 12 control counterparts drank distilled water. All rabbits were sacrificed after 6 months. Fluoride was readily incorporated into femoral cortical bone (7473 ± 966 ppm F versus 1228 ± 57 ppm in controls; P < 0.00005). Fluoride therapy led …

Creating A Project-Based Curriculum In Materials Engineering, Jonathan Stolk, Katherine Chen, Linda Vanasupa, Blair London, Trevor Harding, Richard Savage, William Hughes

Jonathan Stolk

For the past two years, the Cal Poly Materials Engineering department has been on an endeavor to create a modern, innovative curriculum to train a more diverse set of materials engineers for the global and complex world of the 21^st century. The traditional lecture and laboratory activities have evolved into more open-ended, project-based experiences that help students develop additional skills and contextualize the learning of theories. Different types of projects are embedded throughout the curriculum to achieve particular learning objectives while emphasizing different content. During class time, students are extremely active and the faculty act as coaches and mentors …

Chemical Synthesis And Characterization Of Low Thermal Expansion- High Conductivity Cu-Mo And Ag-Mo Composites, Jonathan Stolk, Arumugam Manthiram

Jonathan Stolk

Heat dissipation and thermal expansion mismatch are extremely important issues in many electrical and electronics applications, and the materials used for thermal managementin such applications have attracted a great deal of attention in recent years. The move in the microelectronics industry toward higher circuit board chip densities and packageless chip designs such as flip chips has prompted the need for improved thermal management materials. If heat extraction and thermal expansion are not properly addressed, thermal mismatch among the materials in electronic assemblies may lead to high interfacial shear strains and premature component failure.

Chemical Synthesis And Properties Of Nanocrystalline Cu-Fe-Ni Alloys, Jonathan Stolk, Arumugam Manthiram

Jonathan Stolk

The chemical reduction of Cu²⁺, Fe³⁺, and Ni²⁺ ions with sodium borohydride in aqueous solution followed by heat treatments at 300–900°C in a H₂ atmosphere was investigated to obtain nanocrystalline Cu–Fe–Ni, which may have low thermal expansion and enhanced thermal and electrical conductivities. The samples were characterized by X-ray diffraction, optical microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermomechanical analysis, and electrical conductivity measurements. Thermal conductivity was estimated using the Wiedemann–Franz law. Sintering lead to the formation of a Cu-rich phase and a γ–(Fe, Ni) Invar phase. The growth and stability of the …

Implementation Of Paul Revere: Tough As Nails, An Integrated Project-Based Course On Materials Science And History Of Technology, Jonathan Stolk, Robert Martello

Robert Martello

Olin College sophomores participate in integrated course blocks that merge technical content with business, arts, humanities, and social science topics, allowing students to work on engineering projects that have broader implications than the purely technical. In this paper, we present Paul Revere: Tough as Nails, a multidisciplinary course block that combines an introductory materials science course with a history of technology course and a large scale project. In Paul Revere, students explore connections between historical and technological materials science developments through examinations of Paul Revere's metallurgical work and analyses of the relevant social, environmental, political, and economic aspects that contribute …

A Cost-Effective Fabrication Method For Ionic Polymer-Metal Composites, Jonathan Stolk, Michael Siripong, Susan Fredholm, Que Anh Nguyen, Brian Shih, Johannah Itescu

Jonathan Stolk

To date, many processes have been used for the preparation of ionic polymer-metal composite (IPMC) artificial muscle membranes from conductive metals and perfluorosulfonic polymers such as Nafion. The most widely used of these methods is the platinum plating process, which involves chemical reduction of ionic salt solutions. Although these chemical electroding techniques produce IPMCs with outstanding surface electrodes and excellent performance characteristics, they are relatively costly and time-consuming. In this paper, we describe a novel fabrication process for fast preparation of low-cost Ni-Au-Nafion IPMCs. The process involves the formation of an adherent surface layer on prepared Nafion through DC sputter …

Non-Traditional Assessments For New Learning Approaches: Competency Evaluation In Project-Based Introductory Materials Science, Jonathan Stolk, Mark Somerville, Steven Krumholz

Jonathan Stolk

Over the last twenty years, NSF and the engineering community have called for systemic changes in engineering education, including an emphasis on contextual understanding; increased teaming skills, including collaborative, active learning; and an improved capacity for life-long, self-directed learning. In addition, ABET has called for engineering graduates that demonstrate an ability to apply science and engineering, and ABET requires assessment processes designed to measure student achievement of learning outcomes. Olin College has responded to these calls for change by embracing new learning approaches and assessment techniques, and by developing project-based courses that encourage experiential understanding of content and aid the …

Synthesis And Processing Of Nanocrystalline Ag-Fe-Ni For Low Thermal Expansion- High Conductivity Thermal Management Applications, Jonathan Stolk, Michael Gross, Daniel Stolk, Arumugam Manthiram

Jonathan Stolk

Nanocrystalline Ag–Fe–Ni powders were produced by a reduction of the aqueous metal ion solutions with sodium borohydride and then converted to fine-grained silver–Invar alloys that offer attractive thermal, electrical, and mechanical properties. The samples were characterized by x-ray diffraction, scanning electron microscopy, wavelength dispersive x-ray spectrometry, thermomechanical analysis, microhardness measurements, and electrical conductivity measurements; thermal conductivity was estimated using the Wiedemann–Franz law. Sintering of a specimen with a nominal composition of 60 wt% Ag–25.6 wt% Fe–14.4 wt.% Ni led to the formation of a two-phase silver–Invar alloy with a grain size of approximately 2 μm, a hardness of 133 HK200g, …

Implementation Of Paul Revere: Tough As Nails, An Integrated Project-Based Course On Materials Science And History Of Technology, Jonathan Stolk, Robert Martello

Jonathan Stolk

Olin College sophomores participate in integrated course blocks that merge technical content with business, arts, humanities, and social science topics, allowing students to work on engineering projects that have broader implications than the purely technical. In this paper, we present Paul Revere: Tough as Nails, a multidisciplinary course block that combines an introductory materials science course with a history of technology course and a large scale project. In Paul Revere, students explore connections between historical and technological materials science developments through examinations of Paul Revere's metallurgical work and analyses of the relevant social, environmental, political, and economic aspects that contribute …

Sodium Borohydride Reduction Of Aqueous Silver-Iron-Nickel Solutions: A Chemical Route To Synthesis Of Low Thermal Expansion-High Conductivity Ag-Invar Alloys, Jonathan Stolk, Elizabeth Sterling, Lauren Hafford, Michael Gross

Jonathan Stolk

Thermal management is a critical concern in the design and performance of electronics systems. If heat extraction and thermal expansion are not properly addressed, the thermal mismatch among dissimilar materials may give rise to high thermal stresses or interfacial shear strains, and ultimately to premature system failure. In this article, we present a chemical synthesis process that yields Ag-Invar (64Fe-36Ni) alloys with a range of attractive properties for thermal management applications. Sodium borohydridereduction of an aqueous Ag-Fe-Ni metal salt solution produces nanocrystalline powders, and conventional powder processing converts this powder to fine-grained alloys. The samples are characterized by X-ray diffraction …

Converting Traditional Materials Labs To Project-Based Learning Experiences: Aiding Students' Development Of Higher-Order Cognitive Skills, Jonathan Stolk, Linda Vanasupa, Katherine Chen, Richard Savage, Trevor Harding, Blair London, William Hughes

Jonathan Stolk

Against a backdrop of compelling societal needs, graduates in science and engineering now must master their disciplines and demonstrate a sophisticated level of cognitive, affective and social development. This has lead a number of national and international commissions on science and engineering to urge educators to re-think the way in which STEM disciplines are taught. We have chosen to “repackage” a traditional undergraduate materials engineering curriculum in a form designed to promote the development of higher-order cognitive skills like self-directed learning and design. Classic metallurgy experiments have been converted to project-based learning experiences where students are put in the role …

The Stiffness Of Three-Dimensional Ionic Self-Assembling Peptide Gels Affects The Extent Of Capillary-Like Network Formation, Alisha Sarang-Sieminski, A Was, G Kim, Haiyan Gong, Roger Kamm

Alisha L. Sarang-Sieminski

Improving our ability to control capillary morphogenesis has implications for not only better understanding of basic biology, but also for applications in tissue engineering and in vitro testing. Numerous biomaterials have been investigated as cellular supports for these applications and the biophysical environment biomaterials provide to cells has been increasingly recognized as an important factor in directing cell function. Here, the ability of ionic self-assembling peptide gels to support capillary morphogenesis and the effect of their mechanical properties is investigated. When placed in a physiological salt solution, these oligopeptides spontaneously self-assemble into gels with an extracellular matrix (ECM)-like microarchitecture. To …

Forisome Performance In Artificial Sieve Tubes, Michael Knoblauch, Mike Stubenrauch, Aart J.E. Van Bel, Winfried S. Peters

Winfried S. Peters

A Parallel Circuit Model For Multi-State Resistive-Switching Random Access Memory, Albert Chen

Albert B Chen

Large, rapidly growing literature is available on bipolar resistive-switching random access memories (RRAM) made of myriad of simple and advanced materials. Many of them exhibit similar resistance switching behavior but, until now, no unifying model can allow quantification of their voltage and time responses. Using a simple parallel circuit model, these responses of a newly discovered RRAM made of a thin-film random material are successfully analyzed. The analysis clearly reveals a large population of intermediate states with remarkably similar switching characteristics. Such modeling framework based on simple circuit constructs also appears applicable to several RRAM made of other materials. This …