Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

Fabrication and characterization of self-sensing and self-actuating piezoresistive microscale silicon cantilevers for an integrated scanning probe microscopy and scanning electron microscopy system

Zum ersten Mal ist eine Kombination aus SPM und REM in einem System mit einem selbstaktuierenden und selbstdektierenden piezoresistiven mikrometerkleinen Siliziumcantilever erfolgreich demonstriert worden. Es ermöglicht hochauflösende AFM- und REM-Aufnahmen. Der Vorteil besteht darin, dass AFM die Topographie der Probenoberfläche liefert, während REM-Aufnahmen nur zweidimensional sind und nicht zwingend deutlich ist, wo sich Berg oder Tal befinden. Die Integration von Aktuation und Detektion in den Cantilever reduziert nicht nur die Größe des AFMs und macht das Lasersystem für die Erfassung der Cantileververbiegung überflüsissig, sondern bietet ein einfach zu bedienendes System, weil der Laserstrahl nicht mehr justiert werden muss. Die Doktorarbeit präsentiert die erste umfassende Charakerisierung der Verhaltens eines selbstaktuierenden und selbstdektierenden piezoresistiven mikrometerkleinen Siliziumcantilevers. Der Verhalten ist von parasitärer Wärme beeinflusst, die von der thermischen Anregung und der Verbiegungserfassung herrührt, von der Luftdämpfung, dem Rauschen und dem Übersprechen. Die lineare Abhängigkeit von der Temperatur und der Anregungsleistung zeigen die Resonanzfrequenz, die Güte, die statische Verbiegung und die Schwingungsampltitude in den Messungen. Auch die Wheatstone-Brücke bringt Temperaturänderung in den Cantilever, die die Resonanzfrequenz stärker beeinflusst als die Anregungsleistung, denn die Brücke ist an einer kritischen Stelle plaziert, wo die mechanische Spannung am größten ist. Die Änderung der Güte und der Schwingungsamplitude mit dem Luftdruck lässt sich in den intrischen, den molekularen und den viskosen Bereich einteilen, während die Resonanzfrequenz linear mit dem Luftdruck abfällt. Ein komplett neues SPM-REM-System mit einem selbstaktuierenden und selbstdektierenden piezoresistiven mikrometerkleinen Siliziumcantilever, das hochauflösende Bilder, Charakterisierung und Manipulation der Probenoberfläche in verschiedenen SPM-Moden ermöglicht, ist präsentiert worden.For the first time, the combination of SPM and SEM within one system using a self-actuating and self-sensing piezoresistive microscale silicon cantilever has been successfully demonstrated. It is capable of high resolution AFM and SEM images. The advantage is that AFM gives the topography of the specimen surface, wheeas the SEM image is only two-dimensional and it is not necessarily clear where there is a hill or a valley. The integration of the actuation and sensing into the cantilever does not only reduce the size of the AFM and make a laser system for beam deflection detection redundant, it also offers an easy-to-use system by obviating the need for laser beam alignment. The PhD thesis presents the first extensive characterization of the performance of the self-sensing and self-actuating piezoresistive microscale silicon cantilever. The performance is influenced by parasitic heating resulting from the thermal beam actuation and deflection detection, by air damping, noise, and cross-talk. The linear temperature and drive power dependency of fundamental frequency, quality factor, deflection at pure beam bending, and maximum amplitude of beam oscillation is demonstrated by measurements. The Wheatstone bridge also introduces a temperature change to the beam, which affects the fundamental frequency more than the drive power does, because the bridge is placed at a crucial position where there is maximum stress. The variation of quality factor and maximum amplitude of beam oscillation in relation to air pressure clearly falls into three regions, intrinsic, molecular and viscous, whereas the fundamental frequency decays linearly with air pressure. A completely new SPM-SEM system with a self-actuating and self-sensing piezoresistive microscale silicon cantilever is presented that is capable of high resolution imaging, characterization, and manipulation in different SPM modes

A study on thermal and dielectric characteristics of solid glass microsphere filled epoxy composites

This thesis reports on the research dealing with the processing and characterization of solid glass micro-sphere filled epoxy composites. The first part of the work includes the development of two theoretical correlations based on one dimensional heat conduction models for estimation of effective thermal conductivity of polymer composites with single and multiple fillers.The second part depicts the details of the test procedures and test results in regard tothe physical, mechanical and micro-structural characteristics of the epoxy composites filled with solid glass microspheres (SGM) and/or micro-sized boron nitride (BN). The last part throws light on the thermal and dielectric characteristics of the composites with different filler type and concentrations. The estimation of effective thermal conductivity of the composites using finite element method (FEM) and using the proposed theoretical models is done and the results are validated by corresponding experimental results. The effects of inclusion of SGM and/or BN on the effective thermal conductivity (keff), glass transition temperature (Tg), coefficient of thermal expansion (CTE), electrical resistivity (ρ) and dielectric constant (Dk) of epoxy composites are studied. With the addition of SGM, the thermal conductivity, dielectric constant as well as volume resistivity value decreases. Again, the embedment of both SGM and BN fillers results in lowering the CTE of the composites whereas the Tg of the composites is improvedsubstantially. This work shows that the FEM serves as a very good predictive tool for assessment of thermal conductivity of composites.The proposed theoretical correlations too can serve as very good empirical models for spherical inclusions to estimate keff for composites within the percolation limit. With light weight and improved insulation capability, the solid glass micro-spheres filled epoxy composites can be used for applications such as insulation boards, food containers, thermo flasks, building materials, space flight and aviation industry etc.Similarly, with enhanced thermal conductivity, improved glass transition temperature, reduced coefficient of thermal expansion and modified dielectric characteristics, the epoxy composites with appropriate proportions of solid glass micro-spheres and boron nitride can be used in micro-electronics applications like electronic packaging, encapsulations, printed circuit board substrates etc

Assessment of Effective Thermal Conductivity of Epoxy-TiO2 Composites

The development of microelectronic devices like PCB, electronic packaging etc. requires high thermal conductivity materials for fabrication. This provoke the needs of development of particulate filled polymer matrix composites (PMCs) that possess high thermal conductivity. This research provides a potential material system to address this problem. An analytical model is proposed to estimate the effective thermal conductivity of polymer composites filled with cubical particulate fillers. By using the mathematical correlation developed by this model, effective thermal conductivity is calculated and compared with values obtained from models by previous authors in this regard for different volume fractions (13.4 and 26.8 vol.%) of cubical shaped TiO2 particulates. UnithermTM2022 tester is used to measure the effective thermal conductivity (keff) of epoxy-TiO2 composite for these volume fraction as per ASTM E-1530. These values of effective thermal conductivity (keff) obtained from the experiment are compared with these model developed in previous literature and the proposed model. It is found that the the values of effective thermal conductivity calculated by proposed model are very near to the experimental values of effective thermal conductivity

GTE laboratories microelectronics research program

Issued as Quarterly progress reports [nos.1-8], and Final report, Project no. E-25-669 (subproject under B-10-628

Using Porous Media to Enhancement of Heat Transfer in Heat Exchangers

According to increasing human needs for energy and to avoid energy waste, researchers are struggling to increase the efficiency of energy production and energy conversion. One of these methods is increasing heat transfer and reducing heat dissipation in heat exchangers. Using porous materials in the fluid flow is one of the passive methods to increase heat transfer in heat exchangers. The existence of porous media in the flow path, improve the matrix of thermal conductivity and effective flow thermal capacity and also matrix of porous-solid increase radiation heat transfer, especially in two phase flow (gas-water) systems. In this paper, recent studies on the effect of using porous media on enhancement the amount of heat transfer in heat exchangers has been investigated via using porous media with difference porosity percentage, material and geometric structure in the flow path in numerical simulations and laboratory studies

Thermal and Dielectric Behaviour of Polymer Composites with Hybrid Fillers

This thesis reports on the analytical and experimental study on thermal and dielectric behaviour of hybrid filler polymer composites. The objective is to explore the possibility of using multiple ceramic fillers in polymers to make composites suitable for microelectronic applications. The first part of the report is on the development of theoretical heat conduction models based on which mathematical correlations have been proposed for estimation of effective thermal conductivity of polymer composites with single as well as hybrid fillers. The second part has provided the description of the materials used, routes adopted to fabricate the various epoxy and polypropylene composites and the details of the experiments that are conducted during this research. It also presents the test results in regard to the physical, micro-structural and mechanical characteristics of all the epoxy and polypropylene based composites filled with single filler i.e. micro-sized Aluminium nitride (AlN)/ Aluminium oxide (Al2O3). A comparative evaluation of the effects of premixing of solid glass microspheres with micro-sized AlN/Al2O3 on the different physical and mechanical properties of composite systems is also reported. The last part has emphasized on the thermal and dielectric characteristics of the composites under this investigation. It includes an assessment of the effective thermal conductivity of these composites using the proposed theoretical models. Effects of inclusion of various combinations of single/hybrid fillers on the effective thermal conductivity (keff), glass transition temperature (Tg), coefficient of thermal expansion (CTE) and dielectric constant (ɛc) of the composites are presented. Analytical models developed in this work for evaluating effective thermal conductivity of single/hybrid filler reinforced polymer composites are based on the principle of law of minimal thermal resistance and equal law of specific equivalent thermal conductivity. The values obtained from the theoretical model for single filler polymer composites are in close approximation with the corresponding measured values up to percolation threshold. For hybrid filler model, the calculated values are in good approximation for the entire range of filler content as no percolation is seen for hybrid composites. Percolation is the phenomenon which occurs when the content of conductive filler in matrix becomes substantially high so as to form thermal bridges across the planes throughout the system resulting in a sudden improvement of conductivity. The volume fraction of filler at which sudden jump in the composite effective thermal conductivity occurs is called the percolation threshold of that filler-matrix combination. This phenomenon however has not occurred for hybrid filler composites. The present research also shows that the selected aluminum based ceramic powders have the potential to be successfully used as functional filler materials in both thermoset and thermoplastic polymers. It is also noticed that the epoxy based composites have higher void fraction compared to that in the polypropylene based composites. Inclusion of spherical particles in these polymeric resins has not resulted in any improvement in the load bearing capacity (tensile strength). On the other hand, hardness and compressive strength values have been found to have improved invariably for all the composites. Inclusion of single filler i.e. micro-sized AlN/Al2O3 appreciably enhances the effective thermal conductivity of polymers. Other thermal properties like CTE and Tg also get modified accordingly. But, with addition of these fillers, little increase in the value dielectric constant is noted. The polymer composite fabricated in present work must possess low dielectric constant which does not get completely fulfilled with single fillers. So SGM is introduced as a secondary filler to overcome this problem. With the addition of SGM in combination with AlN/Al2O3 modifies various physical, mechanical and thermal properties. But most importantly, a noticeable change is observed in case of dielectric constant value. With SGM as the secondary filler, much lower value of dielectric constant is obtained which is almost around that of the neat polymer. It is seen that apart from the effective thermal conductivity, all the other properties shows positive modification for hybrid filler composites as compared to single filler composites as far as their applications in microelectronics are concerned. The particulate filled polymer composites developed for this investigation are expected to have adequate potential for a wide variety of applications particularly in microelectronic industries. With enhanced thermal conductivity, improved glass transition temperature, reduced thermal expansion coefficient and modified dielectric characteristics, the epoxy and polypropylene composites with appropriate proportions of fillers can be used in microelectronic applications like electronic packaging, encapsulations, printed circuit board substrates etc

Publications of the Jet Propulsion Laboratory, 1988

This bibliography describes and indexes by primary author the externally distributed technical reporting, released during calendar year 1988, that resulted from scientific and engineering work performed, or managed, by the Jet Propulsion Laboratory. Three classes of publications are included: JPL publications in which the information is complete for a specific accomplishment; articles from the quarterly Telecommunications and Data Acquisition (TDA) Progress Report; and articles published in the open literature