NASA/CR—2004-213311 Study of Vacuum Energy Physics for Breakthrough Propulsion G. Jordan Maclay Quantum Fields LLC, Richland Center, Wisconsin Jay Hammer and Rod Clark MEMS Optical, Inc., Huntsville, Alabama Michael George, Yeong Kim, and Asit Kir University of Alabama, Huntsville, Alabama October 2004 The NASA STI Program Office . . . in Profile Since its founding, NASA has been dedicated to • CONFERENCE PUBLICATION. Collected the advancement of aeronautics and space papers from scientific and technical science. The NASA Scientific and Technical conferences, symposia, seminars, or other Information (STI) Program Office plays a key part meetings sponsored or cosponsored by in helping NASA maintain this important role. NASA. The NASA STI Program Office is operated by • SPECIAL PUBLICATION. Scientific, Langley Research Center, the Lead Center for technical, or historical information from NASA’s scientific and technical information. 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Jordan Maclay Quantum Fields LLC, Richland Center, Wisconsin Jay Hammer and Rod Clark MEMS Optical, Inc., Huntsville, Alabama Michael George, Yeong Kim, and Asit Kir University of Alabama, Huntsville, Alabama Prepared under Contract NAS3–00093 National Aeronautics and Space Administration Glenn Research Center October 2004 This report contains preliminary findings, subject to revision as analysis proceeds. Trade names or manufacturers’ names are used in this report for identification only. This usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration. Available from NASA Center for Aerospace Information National Technical Information Service 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076 Springfield, VA 22100 Available electronically at http://gltrs.grc.nasa.gov Contents 1 Summary 2 2 Development of AFM Instrumentation 6 2.1 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.1 Assembly of Cantilevers . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.2 Cavity Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.3 Electrostatic Calibration . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.1.4 Results for AFM Attractive Force Measurements . . . . . . . . . . . 14 2.1.5 Results for AFM Repulsive Force Measurements on Cavities . . . . . 20 3 Theoretical Calculations of Vacuum Forces 21 3.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 Repulsive Forces for a Rectangular Cavity with Finite Conductivity . . . . . 22 3.3 Casimir Forces in Slab Geometries using Real and Inhomogeneous Materials 23 4 Gedanken Vacuum Powered Spacecraft 24 5 Newly Fabricated Materials with Negative Index of Refraction 25 6 Conclusions and direction for future work 26 7 Publications 27 7.1 Journal Papers Submitted and Published . . . . . . . . . . . . . . . . . . . . 27 7.2 Conference Articles Published . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.3 Presentations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7.4 Articles in Popular Press/Video . . . . . . . . . . . . . . . . . . . . . . . . . 29 7.5 Important Recent Citations in MEMS Research to our work: . . . . . . . . . 30 8 Appendix 31 NASA/CR—2004-213311 iii Final Report: Study of Vacuum Energy Physics for Breakthrough Propulsion G. Jordan Maclay Quantum Fields LLC Richland Center, Wisconsin 53581 Jay Hammer and Rod Clark MEMS Optical, Inc. Huntsville, Alabama 35806 Michael George, Yeong Kim, and Asit Kir University of Alabama Huntsville, Alabama 35805 Abstract This report summarizes the accomplishments during a three year research project to investi- gate the use of surfaces, particularly in microelectromechanical systems (MEMS), to exploit quantum vacuumforces. During this project we developed AFMinstrumentation to repeat- ably measure Casimir forces in the nanoNewton range at 10 6torr, designed an experiment − to measure attractive and repulsive quantum vacuum forces, developed a QED based theory of Casimir forces that includes non-ideal material properties for rectangular cavities and for multilayer slabs, developed theoretical models for a variety of microdevices utilizing vacuum forces, applied vacuum physics to a gedanken spacecraft, and investigated a new material with a negative index of refraction. NASA/CR—2004-213311 1 1. Summary During this contract we focused our efforts in several areas related to vacuum forces and surfaces, with the following accomplishments: 1. development of methods and instrumentation to measure vacuum forces in the 10s of nanoNewtons with good repeatability and signal to noise ratio using an AFM (Atomic Force Microscope), operating in an excellent vacuum (10 6torr). − 2. obtaining cavity structures formed using X-ray photolithography and interferometry that have dimensions in the 10s and 100s of nanometers, 3. calculating repulsive forces in rectangular cavities of all aspect ratios for both perfect conductors and imperfect conductors for the first time, and determining the optimum geometries for the measurement of repulsive vacuum forces. 4. calculatingvacuumforcesarisingfromparallelslabsmadefromlayersofmaterialswith different dielectric functions for the first time, 5. calculating temperaturedependent Casimir forces arisingfromthetemperature depen- dence of the permittivity for the first time, 6. applying vacuum forces to a "gedanken spacecraft,"and 7. exploring a new material with a negative index of refraction. The experiment to measure repulsive Casimir forces is part of our three-year effort to begin to build, step by step, the knowledge base necessary for the development of engineered devices of use to the NASA mission based on quantum vacuum effects. Our objective was to develop theoretical models of elementary systems that utilize vacuum forces and energy, to understand how these models behave, and then to explore some of these models experi- mentally. Some of the theoretical models are discussed in [J. Maclay, ”A Design Manual for MicromachinesusingCasimirForces: PreliminaryConsiderations,”ProceedingsofSTAIF-00 (Space Technology and Applications International Forum-2000, Albuquerque, NM, January, 2000)„ edited by M.S. El-Genk, AIP Conference Proceedings 504, American Institute of Physics, New York 2000. Published in hardcopy and CD-ROM by AIP], and [J. Maclay, J. Hammer, ”Vacuum forces in Microcavities,” Proceedings of the Seventh International Con- ference on Squeezed States and Uncertainty Relations (ICSSUR), Boston, MA, June 4-6, 2001. Proceedings are now available on line at http://www.physics.umd.edu/robot, click on Proceedings]. Since the critical dimensions for these devices are typically micron to submicron, the experimental research utilizes microfabrication technology and the methods developed for MicroElectromechanicalSystems (MEMS). NASA/CR—2004-213311 2 ThegreatdifficultyofexperimentsinvolvingCasimirforceswashighlightedindiscussions withthethreemostactiveexperimentalgroupsintheworldmeasuringCasimirforces. These discussions took place at a conference November 14-18, 2002 in Cambridge, MA at the Harvard-Smithsonian Center for Astrophysics, where Jordan Maclay and Carlos Villarreal each presented a paper. The Italian group worked for seven (7!!) years before obtaining publishableCasimirforcesforflatparallelplates. Theyworkedfortwoyearsjusttoeliminate dust! The Riverside group of Mohideen says they use hundreds of cantilevers and flat surfaces until they get a good one. Mohideen’s group has achieved high precision in their experiments, and developed very creative solutions to difficult experimental problems. The group at Lucent headed by Frederico Capasso (Bell Labs) says a minimum of two years is required for an experiment. The beautiful work at Lucent is particularly interesting and relevant to our efforts since they have utilized MEMS structures in their experiments. We have come a long way in our efforts at UAH, and have developed an instrument that has an excellent signal to noise ratio, can measure surface forces with excellent repeatability in the 10s of piconewtons at a vacuum of 10 6torr, which is the highest vacuum of any of − the systems currently making Casimir force measurements. This instrument can serve as a platform for the measurement of Casimir forces in a variety of geometries and experiments. At this time, we are disappointed to report that the most recent data, although encouraging, is still not as good as is required. Some of the difficulties that have plagued the experiment and our efforts at their solution are the following: 1. Dust and contamination of the experimental surfaces; dust adhering to spheres on cantilever. We have tried to eliminate this problem by building a clean room around the instrument and doing all assembly in clean room environment. 2. Oxides on the surfaces of the sample fixturing trapping electrostatic charges. We hope we have eliminated oxides by coating all surfaces with a thick coating of gold. More effort may be required if large residual potentials persist. 3. Interference of laser diode light in the photodiode detector. We completely redesigned the optical system several times, but still it appears we may not have eliminated this very challenging and very persistent problem. 4. Difficultyofgettingaccurategoldcavitieswithverysmalldimensions. Weobtainedthe best cavities we could from those expert in their fabrication, however the manufacture of such cavities is an art, and a major research project in itself. 5. Problems with contact resistance in applying voltages to the substrate and grounding the AFM cantilever. We tried to use very good connections to the substrate (the best seemed to be silver epoxy rather than pressure fittings) and to insure good electrical contact to the sphere by coating the sphere with gold first and then using silver epoxy to attach it to the gold coated cantilever. 6. Difficulties in getting smooth surfaces on the sphere and the substrates. We tried using the smoothest surfaces for sputtering deposition for flat substrates. We need to develop some method to get smoother spheres. NASA/CR—2004-213311 3 During the last three years we have made major accomplishments in the theoretical understanding and calculation of vacuum forces. Three years ago, we did numerical compu- tations to evaluate the vacuum forces in all geometric configurations of a rectangular cavity [J. Maclay, ”An analysis of vacuum fluctuation energy and Casimir forces in conductive rec- tangular cavities,” Phys. Rev. A., 61, 052110 (2000)]. We assumed, as is done in most calculations of Casimir forces for metals, an infinite conductivity at all frequencies. Only for the case of two infinite parallel plates have calculations been done using the actual material properties. Today, three years later, one of the key issues in the development of practical devices based on quantum vacuum effects, such as Casimir forces, is the effect of the real material properties, such as the dielectric function. In the last year we developed a powerful theory that gives the Casimir force for planar structures with arbitrary dielectric function, or composed of layers of different media. This theory can serve as the basis for design tool, allowing one to design a material with the desired Casimir force, within limits. IN addition we developed a theory to compute the vacuum force in a rectangular cavity as a function of the plasma frequency of the metal. The finite conductivity reduces the repulsive Casimir force, but does not dramatically alter the physics. Our proposal to measure repulsive forces has stimulated continued discussion among researchers, and some theoretical disagreement as to how one includes the binding energy of the material, and whether it is possible to have repulsive forces between two separate surfaces. Some theorists maintain that if one imagines splitting a closed cavity, then the attractive forces where the surfaces are in close proximity will generate an attractive force that will overpower any repulsive forces. In part this argument is based on one of the usual interpretations of Casimir forces, that is that they can be viewed as originating as fluctuations within matter, as in the Lifshitz model, not in the the quantum vacuum as in the original Casimir calculation. If Casimir forces do in fact arise from fluctuations within the vacuum, then is may be that repulsive forces are observed. At this point the theory is not precise on these predictions, but interesting developments are to be expected. At the Harvard-Smithsonian conference, Capasso said he is considering doing an experi- ment to measure repulsive forces, and he and his associate asked me many questions. Our theoretical presentations linking Casimir forces and MEMS in the past years have, in part, stimulated important work at Lucent Technology by Capasso’s group, where MEMS devices were made and tested that verified the model of an anharmonic Casimir oscillator the PI had done in 1995. The Lucent group then used the Casimir force for the oscillating system to make a very sensitive position sensor. Two of the stated goals of the BPP program are to sponsor credible research, subject to peer review, and to disseminate the results of the research to the broader scientific com- munity. With BPP support, during this contract, collectively we published six journal articles, with three addition articles under review, published seven conference proceedings (three on line), and made 13 technical presentations. In addition, our work was featured in an hour long TV segment done by NHK (Japanese Public Television) on Science in the New Millennium, and featured in an article in the popular press [ ”Energy Unlimited,” by Henry Bortman appeared in New Scientist Magazine, pp32-34, 1/22/2000]. Our work was mentioned in Science News [”Force from empty space drives a machine”, Science News, Feb. 10, 2001, Vol. 159, No. 6, p. 86]. NASA/CR—2004-213311 4 At the workshop we just participated in, Casimir Forces: Recent Results in Experiment and Theory, most of the key researchers in Casimir forces were present, and it was therefore a most excellent workshop. We were pleased that numerous researchers were aware of and interested in the work we have been doing. NASA/CR—2004-213311 5 2. Development of AFM Instrumentation The instrument for measuring Casimir forces is based on an Atomic Force Microscope and has been developed at the University of Alabama by Prof. Michael George, Dr. Young Kim, and Dr. Asit Kir. We proposed to measure repulsive vacuum forces, which have never been measured. This experiment may have implications about the nature and origin of quantum forces as well as provide the basis for the development of new MEMS devices using Casimir forces. The experiment is done using an AFM (atomic force microscope) operating in a vacuum chamber, which is required for a precision measurement. We measure the force between a gold coated substrate and a cantilever on which we have mounted a 210 µm diameter sphere metallized with gold. When the sphere gets to within several hundred nm of the substrate, it experiences a vacuum force (called a Casimir force), which is what we are interested in observing very carefully (schematic of experiment is shown in Figure 2.1). This force is due to the change in the quantum vacuum caused by the surfaces. In order to calibrate the actual cantilever deflection and determine absolute magnitudes of the forces, we also applya potential difference betweenthe substrate and cantilever andmeasure the electrostatic deflection of the cantilever. Since we have calculated the electrostatic force exactly for this geometry using a finite element model, we can obtain an electrostatic calibrationof thecantilever. Details of this experiment are givenin [Maclay, J. Hammer, M. George, R. Ilic, Q. Leonard, R. Clark, ”Measurement of repulsive quantum vacuum forces,” AIAA-2001-3359, AIAA/ASME/SAE/ASEE 37th Joint Propulsion Conference, Salt Lake City, 2001] The AFM instrument built at UAH for measuring Casimir forces is shown in Fig.2.2. A view of the instrument and the associated electronics is shown in Fig. 2.3. The entire systemisenclosedina cleanroomstructurecontainingtwolaminar flowHEPAworkstations as shown in Fig. 2.4. A 50 µm sphere mounted on a triangular cantilever is shown in Fig. 2.5. Forallexperimentsweusedpolystyrenespheresabout200 µmindiameterontriangular cantilevers approximately 300 µm long. Fig. 2.6 shows the CCD image of a cantilever above a University of Wisconsin cavity array. There are two parts to this experiment. The first part is to make measurements of the force between the sphere and a very flat, gold surface that are in agreement with theory. This force, which is attractive, was measured for the first time since Casimir made his original prediction half a century ago in two classic experiments in the last three years. The most accurate measurement, done by Mohideen using an AFM approach similar to ours, verified the correctness of the theory to within about 1%. During this last year we made experimental progress, eliminating most of the drift in the data and most of the slope at large separations, but we still do not have publication quality data. After Prof. George has obtained credible results for the attractive Casimir force using the flat, gold plates, he will make measurements on the cavity arrays we have obtained and characterized by SEM. One NASA/CR—2004-213311 6 RED LED PHOTODIODE CALIBRATED MICROMACHINED CANTILEVER METALLIZED 200 mm SPHERE (F=-KX) METALLIZED CAVITY (gold >60 nm thick) Figure2.1: SchematicofthemeasurementofCasimirforcesbetweenagoldmetallizedsphere and a gold cavity using an Atomic Force Microscope (AFM). Figure 2.2: Shows one of the configurations for the AFM Casimir force microscope (CFM). Several configurations were tested during the contract. The cylinder in the upper right is the z-scanner, to its left is the CCD video camera, and below is the scanner is the stage with the sample. The red laser can be seen coming from back of the image, toward the sample rather than perpendicular through the scanner as before. On the left side of the picture and on the bottom center one can see the white cabling leading to the three piezo motors that enable x-y actuation of the sample and also of the detector while the system is in vacuum. The vacuum flange is visible at bottom of the AFM. NASA/CR—2004-213311 7 Figure 2.3: The vacuum chamber for the AFM is on the far left. The black shock cords supporting the chamber from the top of the white metal frame are visible. To the right are the electonics, including the monitor showing an image of a cantilever sphere from the CCD camera inside the vacuum chamber. Figure 2.4: Clean room structure surrounding the AFM force measuring instrument. The structure contains two laminar flow HEPA hoods which maintain a positive pressure. The plastic walls stop about 1 inch above the ground to allow flow lines to remove dust from the cleanroom. NASA/CR—2004-213311 8 Figure 2.5: CCD image of a metallized gold sphere on the AFM cantilever in vacuum above a cavity array defined using X-ray photolithography. Figure 2.6: Image from a CCD camera mounted in the AFM that shows the cantilever and sphere above a test array of cavities. NASA/CR—2004-213311 9 Figure 2.7: AFM image of a polystyrene sphere, showing striations, possibly due to tweezers or interference effects. set of arrays was made using x-ray lithography at the University of Wisconsin Center for NanoTechnology and have characteristic dimensions in the hundreds of nanometers. This lastyearweobtainedasecondsetofarraysfromaresearcheratMIT. TheMITcavitywidth is 40 nm, which is very narrow, and a wall thickness of 60 nm. Based on the theoretical calculations we have done, it is possible that we may observe a repulsive force for these very narrow cavities. 2.1. Experimental Methods We briefly mention some of the experimental issues of some importance to one entering this field. 2.1.1. Assembly of Cantilevers Fig. 2.7 shows what may be additional roughness on a polystyrene sphere, possibly induced by the use of tweezers or other fixtures to hold the sphere. The rms roughness of a gold metallized sphere is shown to be about 12.8 nm in the AFM image Fig. 2.8.Cleanliness of the process is also an issue, as can be seen in the SEM image Fig. 2.9 in which inhomogenieties can be seen as the white specs on the surface of the sphere mounted on an AFM cantilever with silver epoxy.Another surprising problem occurred during Casimir force measurements of which we remained unaware until Dr. Kim did an AFM of the sphere after the measurements were complete, as shown in Fig. 2.10. It is important to fully characterize the spheres after mounting, and sometimes after the measurements are complete. 2.1.2. Cavity Substrates Makingcavitystructuresisverydifficultsincethefeaturesaresmall, inthe50-100nmrange, and the aspect ratios are comparatively large, about 4 or more. We obtained cavities from NASA/CR—2004-213311 10 Figure 2.8: AFM image and analysis of the surface of a polystyrene sphere. The rms roughness is about 12 nm. Figure 2.9: SEM image of a gold coated polystyrene sphere mounted on an AFM cantilever. Figure 2.10: SEM image of a gold coated polystyrene sphere with a fractrure mounted on an AFM cantilever. NASA/CR—2004-213311 11 Figure 2.11: SEM of the gold array made at the University of Wisconsin Center of Nan- otechnology. The dark regions are cavities about 125 nm across and 500 nm deep. The white regions are the walls about 225 nm thick Each cavity is 100 µm long. Prof. France Cerrina, Director of the University of Wisconsin Center for Nanotechnology, that were fabricated using X-ray photolithography. The structures are essentially long narrow gratings. The wall or lines are about 225 nm thick, and the cavities or lines are about 125 nm across. The depth is 500 nm. The geometry is well formed, as shown in Fig. 2.11. Althoughaprecisemeasurementofthesurfaceforceswithsuchagratingwouldprovide new and very interesting information,.our theoretical model predicts that the features sizes needtobereducedtomeasureanetrepulsiveforcesasopposedtoareducedattractiveforce. We were able to obtain cavity substrates from Prof. H. Smith at MIT, who uses an interferometric method to fabricate narrow line gratings. We obtained a 10 X. 20 mm. substrate with a gold grating structures, with a cavity width of 40 nm, a wall thickness of 60 nm, and a depth of about 160 nm. This is a very narrow cavity formed using optical interferencemethods. SeveralAFMimagesofthecavitiesareshownbelow. Fig. 2.12shows a view over a 500 nm square region. The image on the left is the usual AFM height mode image that gives a good indication of the surface topography. On the right is the equivalent of the DI (Digital Image Inc.) tapping mode image, which gives a good indication of the immediate region of the surface but with little sensitivity to the large scale variations in overall surface height. The image from this mode is obtained from the shift in the resonant frequency of the vibrating cantilever as it nears the surface. The data in the last image may be presented quantitatively as a scanacross the cavity, as shown in Fig. 2.13.This scan shows that in addition to the surface roughness corresponding to the presence of the cavities, there is a roughness of several nm. A SEMof the cavity Fig. 2.14 shows that the walls may not be of uniform thickness, and may be thicker at the top. From the SEM scale, the openings are close to the nominal 40 nm.BasedontheAFMimagesandSEMimages, itappearsthat thecavityopenings maynot be as well defined as we would prefer, although it is difficult to interpret the SEM and AFM data very accurately. It is difficult to make such small structures with such high aspect ratios. In order to measure the parallel plate Casimir force we have made flat gold surfaces using NASA/CR—2004-213311 12 Figure 2.12: AFM image of a gold grating structrure, formed with a spacing or cavity width of 40 nm, a line or wall thickness of 60 nm, and a depth of about 160 nm. Figure 2.13: Surface roughness analysis for the cavity from MIT shown in Fig. 2.12. Figure 2.14: SEM image of cavity array from MIT. The walls are nominally 60 nm thick, the cavities are nominally 40 nm wide. NASA/CR—2004-213311 13 Figure 2.15: AFM roughness analysis for a flat gold surface used in the measurement of the Casimir force between flat surfaces. silicon wafers or sapphire optical flats, or cleaved mica. The roughness is typically about 5 nm as shown in Fig. 2.15. 2.1.3. Electrostatic Calibration The electrical wiring and grounding was checked, and a new voltage source installed. The voltage is applied to the substrate, measured with a separate voltmeter, while the AFM cantilever is at ground potential. Calculations were done by Jay Hammer of MEMS Optical ofthetheoreticalelectrostaticforceusingafiniteelementmodel. Inthemodelheconsidered an array of 18 cavities, which gave a result that was insensitive to adding more cavities. 2.1.4. Results for AFM Attractive Force Measurements As an indicator of the proper functioning of the UAH AFM instrument, we first are en- deavoring to reproduce the know results for the Casimir force between a gold sphere and a flat gold plate. Curves showing the variation of the photodiode signal versus the relative separation between the plate and sphere are shown in Fig. 2.16. These curves are the result of averaging 30 runs and show a excellent signal/noise ratio.However, note that there is a periodic component to the signal present in all curves. The noise level is much less than the amplitude of the interference component. This periodic signal is very visible if we plot the signal for low photodiode signals. This periodic component may be due to interference effects in the LED beam. It is greatly reduced from what it was last year, but is still a problem at the level of precision this measurement is approaching as can be seen in Fig. 2.17. The photodiode signal is due to the combined Casimir and electrostatic force. By equating the difference, for example, between the curve for 61 mV and the curve for 0 mV, to a theoretical electrostatic force, we can obtain a set of equations that best fit the data and provide the calibration information. The fit of a theoretical electrostatic force to the difference curve for the data at 61 mV and 0 mV applied voltage is shown in Figl.2.18. NASA/CR—2004-213311 14 500 1000 1500 2000 2500 3000 -0.5 -1 -1.5 -2 -2.5 Figure 2.16: AFM curves of the photodiode signal versus the nominal relative separation between the gold sphere and the flat gold plate. The top curve is for zero applied bias, the next three from top to bottom with applied biases of 61 mv, 121 mv, 161 mv, respectively. 0.1 500 1000 1500 2000 2500 3000 -0.1 -0.2 Figure 2.17: AFM photodiode signal versus separation for the data shown in the previous figure, plotted for low values of the photodiode signal. NASA/CR—2004-213311 15 500 1000 1500 2000 2500 3000 -0.1 -0.2 -0.3 -0.4 -0.5 Figure 2.18: Theoretical fit (solid line) to the electrostatic force between a gold sphere and a flat gold surface. This is the electrostatic force obtained as the difference between the measured curves at 60 mV and 0 mV, respectively. 0.15 0.14 0.13 0.12 0.11 80 100 120 140 160 180 Figure 2.19: Electrostatic fit coefficient/voltage vs applied voltage for the three voltages. By doing a similar fit for the data at all applied voltages, we find the best values of the residual potential, the cantilever calibration, and the absolute separation. The three fits indicate that we need to shift the relative separation by a distance of 49.6nm, 53.9nm, 52.9 nm, respectively to obtain the absolute separation. The average shift is 52.1 nm, which correspondstoadistanceofclosestapproachof33nm. Itisveryencouragingthatthescatter in the shifts is very small, about 4 nm In order to obtain the built in potential and the force constant, we do a least squares fit to a plot of the overall fit coefficients divided by the appliedvoltagevstheappliedvoltageasshowninFig. 2.19. Thex- intercept/2 isthebuilt inpotential 80.6mV. Theslopecorrespondstoaforceconstantofmconf1016*kpdf1016= − 0.0400 µN/µm. With these parameters we can determine the absolute force corresponding to a photodiode signal, correct for the residual potential, and obtain the final expression for the Casimir force. NASA/CR—2004-213311 16 250 500 750 1000 1250 1500 1750 0.9 0.8 0.7 0.6 0.5 0.4 Figure 2.20: Multiplicative force correction for gold in parallel plate-sphere geometry. 2.2 2 1.8 1.6 1.4 1.2 50 100 150 200 Figure 2.21: Multiplicative correction to the Casimir force for a RMS roughness of 15 nm. WeneedtobeabletocomparethedatatoatheoreticalexpressionfortheCasimirforcefor agoldsurface. Amultiplicative correctionforfiniteconductivitywas computedbyAstridet alandisplottedinFig. 2.20. Correctionsmustalsobemadeforthesurfaceroughness. The roughness correction really depends on the detailed distribution of the various height regions on the surface. If we assume a normal distribution, we can approximate the multiplicative correction as a polynomial. The correction is plotted for a roughness of 15 nm as a function of the (maximum) separation in nm in Fig. 2.21. For a roughness this large, the correction is quite large. Ideally the roughness should be below 5nm, and the correction is then just several percent. We need to process the spheres so that the roughness is reduced. Using the conductivity correction for gold, the roughness correction, and the expression for the ideal Casimir force for a sphere and a flat plate, we can make a theoretical prediction to plot with the measured Casimir force. The theoretical result (solid line) and experimental result (points) for a measurement of the Casimir force between a gold metallized sphere 220 µm in diameter and a flat gold surface are shown in Fig.2.22. Plotting just the region for separation less than 500 nm shows the disagreement between theory and experiment more clearly in Fig. 2.23. The agreement is not too bad when we consider that there are no arbitrary fitting parameters, and that the curve for the Casimir force follows precisely from the data shown in the previous figure. In the computations, we have made a correction for the surface roughness. By AMFmeasurement, the rms roughness for the sphere is 6 nmand 12 nm for the gold plate. The corresponding corrections are significant, about a factor of 2 at the distance of closest separation. The experimental and theoretical curves agree more NASA/CR—2004-213311 17 Figure 2.22: Plot of the force in nN versus the separation in nN for a gold metallized sphere near a flat gold surface. The data curve is to the left, the theoretical calculation to the right. The surface roughness is assumed to be 12 nM, and corrections for the conductivity of gold have been included. 100 200 300 400 500 -0.0005 -0.001 -0.0015 -0.002 Figure 2.23: Plot of the force in nN versus the separation in nN for a gold metallized sphere near a flat gold surface. The data curve is to the left, the theoretical calculation to the right. The surface roughness is assumed to be 12 nM, and corrections for the conductivity of gold have been included. NASA/CR—2004-213311 18 100 200 300 400 500 -0.0005 -0.001 -0.0015 -0.002 Figure 2.24: The data in the previous figure has been shifted 13 nM to the right to make the calculation and measured values agree more closely. 30 20 10 75 100 125 150 175 200 -10 Figure 2.25: The percent deviation between the measured and calculated values for the data plotted in the previous figure, shown as a function of the separation. closely if we arbitrarily assume that the data points should be shifted about 13 nm to the right, as shown in Fig. 2.24. After this shift, the fit is much better, however, a residual error remains that varies approximately periodically between about +15% and - 15%. as shown in Figure 2.25. This error is much larger than the precision in the data, and is probably due in part to a systematic error, for example the periodic interference in the photodiode signal. Comments on Current Results These experiments are very difficult. The other groups engaged in such measurements have spent a minimum of two years (Bell Labs and Riverside groups), and a maximum of 7 years (Italian group).before obtaining data for a given experiment. The data we have obtained after about two years is therefore very encouraging. The current thrust of the work at UAH is to improve the smoothness of the samples, getting it in the nm range instead of the 10 nm range where it currently is, and to improve the cleanliness of the samples. The periodic noise appears to be due to an interference of the laser diode beam reflected NASA/CR—2004-213311 19 0.75 0.7 0.65 -1000 -500 500 1000 1500 2000 0.55 Figure 2.26: off the cantilever with another component of the beam reflected off a stationary source, probably the lens in the optical system. Such an interference would be expected to give maxima that are separated by a distance of 1/2 the wavelength of the laser diode or about 325 nm. However, the maxima are separated by about 150 nm, or half the expected distance. Perhaps this arises from multiple reflections. Much effort has gone into trying to eliminate this interference. As soon as this is accomplished, we will be able to make credible measurements of the cavity arrays to determine the nature of corresponding vacuum forces. 2.1.5. Results for AFM Repulsive Force Measurements on Cavities Measurements were made of the force between the gold metallized sphere on the AFM and cavities made by University of Wisconsin and the cavities made at MIT. In both cases, we did not observe a net repulsive force. The raw data for the most recent measurements 11/08/02 on the MIT cavities are shown in Fig. 2.26 for applied voltages ranging from 0 to 160 mv. The periodic interference appears to have a significant effect on the shape of the highest curve, 0 mv, which will cause errors in the derived Casimir force.Until we can obtain good results with the parallel plate experiment, we are not confident of our results with other geometries. NASA/CR—2004-213311 20 3. Theoretical Calculations of Vacuum Forces 3.1. Summary In the first year of this effort, we computed and analyzed the vacuum forces in a perfectly conducting rectangular cavity, giving us a good knowledge base to move forward [J. Maclay, ”An analysis of vacuum fluctuation energy and Casimir forces in conductive rectangular cavities,” Phys. Rev. A., 61, 052110 (2000)]. We determined the optimum geometries for the measurement of repulsive forces, and developed a corresponding experiment and an approximate theory [Maclay, J. Hammer, M. George, R. Ilic, Q. Leonard, R. Clark, ”Mea- surementofrepulsivequantumvacuumforces,”AIAA-2001-3359,AIAA/ASME/SAE/ASEE 37thJointPropulsionConference, SaltLakeCity, 2001]. Wethenusedourknowledgeabout the theoretical forces in rectangular cavities to explore some gedanken machines [J. Maclay, ”A Design Manual for Micromachines using Casimir Forces: Preliminary Considerations,” ProceedingsofSTAIF-00(SpaceTechnologyandApplicationsInternationalForum-2000, Al- buquerque, NM, January, 2000); J. Maclay, J. Hammer, ”Vacuum forces in Microcavities,” Proceedings of the Seventh International Conference on Squeezed States and Uncertainty Relations (ICSSUR), Boston, MA, June 4-6, 2001]. Our work stimulated other scientists to consider the question of repulsive forces in real systems, and the meaning of the theoretically calculated stress-energy tensor in QED. We explored some approximate calculations of Casimir forces, and the meaning of the repulsive forces computed for a sphere, in collaboration with Gabriel Barton, who has suggested that the discarded divergent energy terms representing intermolecular forces may overpower any repulsive forces in certain experiments [J. Maclay, P. Milloni, H. Fearn, ”Of some theoretical significance: implicationsofCasimireffects,”EuropeanJournalofPhysics22,463-469,2001]. In our proposed experiment, the cavity structure is open, and some physicists maintain that this causes therepulsive force todisappear, orattractive forces at the edgeto dominate. On the other hand, no one has yet calculated the Casimir force for this geometry. In the approximate calculation we did, we included the attractive Casimir force from the edges of the cavity, as well as the repulsive force from the cavity. With improvements in theory and experiment, we may find the force may depend on the separation and the details of the experiment. As mentioned previously, the results of experiments to measure repulsive forces might have implications regarding the source of vacuum fluctuations. At this time it is too early to make any definite conclusion because exact theoretical calculations using the different models of vacuum energy for the proposed experiment have not been done. Our work then focused on developing more realistic model for the materials, including the finite conductivity and the methods of measuring the forces [Jordan Maclay, and Car- NASA/CR—2004-213311 21 los Villarreal, " A Model for Casimir Forces in Closed Cavities with Finite Conductivity," presented at the symposium Casimir Forces: Recent Results in Experiment and Theory, Harvard-Cambridge Center for Astrophysics, Harvard University, Cambridge, MA, Nov. 14, 2002]. We determined that finite conductivity reduces the forces, but does not dramatically alter the physics. To allow for materials with arbitrary dielectric function, Carlos Villarreal and his collaborators developed new methods for computing forces for planar and spherical geometries[R.Esquivel-Sirvent, C.Villarreal, G.Cocoletzi, ”Superlattice-mediatedtuningof Casimir forces,” Phys. Rev A 64, 052108 (2001), R. Esquivel-Sirvent, C. Villarreal, and W. L. Mochan., "Casimir Forces in nanostructures," Physica Status Solidi(b) 230, 409 (2002)]. .Stimulated by the possibility of experiments with non-planar geometries, other theoretical groups began exploring the divergences that arise from the assumption of perfect corners, and attempting to develop more realistic representations of surfaces and corners and thereby eliminate some of the divergences that appear in the calculations. Several new approaches are being developed that avoid the idealization of infinitely sharp boundaries that implicitly require very large amounts of energy to sustain. We now briefly discuss some of our results that have not yet appeared in the literature. 3.2. Repulsive Forces for a Rectangular Cavity with Finite Conduc- tivity Carlos Villarreal and the PI presented a paper describing a QED based theory to compute vacuumenergyandforceforrectangularmetalcavitiesoflengtha,widthb,heightcthathave finite conductivity at the symposium Casimir Forces"Recent Developments in Experiment and Theory held at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Nov. 14-16, 2002. In our approach, we compute the energy density and the pressure on the walls of the rectangular cavity as a function of a cut-off frequency. Above the cut off frequency, we assume there is an exponentially decreasing effect of the vacuum fluctuations. Physically the cut offfrequencyacts like the plasma frequencyof a real metal. The electrons in a metal are not able to respond faithfully to electric fields that have frequencies above the plasma frequency, consequentlyforfrequenciesabovetheplasmafrequency, themetalistransparent. The most important result from our calculations, the prediction of a repulsive force for our geometry, seems to be a robust conclusion since it does not depend on the magnitude of the plasma frequency cut off. For the MIT cavities the predicted effect of the conductivity of gold is to lower the repulsive force by about 30% as shown in Fig. 3.1. One of the important topics that we brought up in our presentation at the Symposium in Cambridge was the specific way in which one might measure the repulsive force. Indeed, there is no method that was acceptable to all scientists present at the conference. The approach we have proposed this last year, using an AFM sphere near an open array of cavities has the drawback that the cavities are not really closed. In this approximation, we notsureof preciselywhatoneshouldmeasuresincenoonehasyetmadeanexactcalculation for such an open structure. On the other hand, one could measure the deformation of a wall in a closed cavity, the stress being due to the vacuum stress or alternatively to an experimentally applied force. Such a measurement has the advantage of involving closed cavities,buttheaddedcomplicationthatonemustconsiderthedetailedmaterialproperties. NASA/CR—2004-213311 22 750 500 250 0 -250 MIT gold cavity λ p = 0 nm MIT gold cavity λ = 136 nm -500 p -750 -1000 0 200 400 600 800 1000 )Np( ecroF Cavity height (nm) Figure 3.1: Total force on the top of a cavity 40 nm wide and 100 µm long, as a function of the depth of the cavity, for a cavity made of gold (bottom curve) and made of a perfect conductor (top curve). Our discussions regarding repulsive Casimir forces over the last few years have focused attention and stimulated discussion in the scientific community. Recently we have high- lighted the uncomfortably large gap between most theoretical Casimir force calculations and the conceptual methods by which one might measure Casimir forces in various geometries. 3.3. Casimir Forces in Slab Geometries using Real and Inhomoge- neous Materials Carlos Villarreal and his collaborators have developed powerful methods to predict the Casimir force for slabs that are formed from multiple layers of various materials, for example dielectrics and metals. The force is given in terms of a frequency dependent reflectivity of the slabs. The metals were characterized by a dielectric function in the Drude approxima- tion, and the dielectrics by the Lorentz approximation, although other behavior is possible since they do a numerical integration. They also have considered spherical geometries using the proximity force approximation. This approach is very helpful for the design of future MEMS devices that are based on Casimir forces. With the machinery they have developed, one could, within limits, tailor a desired force distance function. This work is described in several papers that credit the BPP program with partial sup- port: C. Villarreal, R. Esquivel-Sirvent, andG. H. Cocoletzi, "Modificationof Casimir forces duetobandgapsinperiodicstructures,".International Journal of ModernPhysicsA17, 798 (2002), R. Esquivel-Sirvent, C. Villarreal, andW. L. Mochan., "CasimirForces innanostruc- tures," Physica Status Solidi(b) 230, 409 (2002),.and .W. L. Mochán, R. Esquivel-Sirvent, and C. Villarreal, "On Casimir forces in media with arbitrary dielectric properties," Re- vista Mexicana de Física 48, 339 (2002). It was also discussed at the Harvard-Cambridge symposium: Carlos Villarreal, "Casimir Forces in Non-Homogeneous Planar and Spherical Systems," presented at the symposium Casimir Forces: Recent Results in Experiment and Theory, Harvard-Cambridge Center for Astrophysics, Harvard University, Cambridge, MA, Nov. 14, 2002. NASA/CR—2004-213311 23 4. Gedanken Vacuum Powered Spacecraft An attempt to address some of the key issues of the BPP program using the properties of the quantum vacuum was made in a collaboration between the PI and Robert L. Forward. A paper has been submitted for publication. A Gedanken spacecraft is described that is propelled by means of the dynamic Casimir effect, which describes the emission of real photons when a conducting surface is moved in the vacuum with a high acceleration. The maintenanceoftherequiredboundaryconditionsatthemovingsurfacerequirestheemission ofreal photons, sometimesdescribedastheexcitationofthevacuum. Therecoilmomentum from the photon exerts a force on the surface, causing an acceleration. If one imagines the moving surface is attached to a spacecraft, then the spacecraft will experience a net acceleration. Thus we have a propellantless spacecraft. However, we do have to provide the energy to operate the vibrating mirror. In principle, it is possible to obtain this power from the quantum vacuum, and this possibility is explored. Unfortunately with the current understanding and materials, the acceleration due to the dynamic Casimir effect is very small, on the edge of measurability. One of the objectives in this paper is to demonstrate that some of the unique properties of the quantum vacuum may be utilized in a gedanken spacecraft. We have demonstrated that it is possible, inprincipal, to cause a spacecraft to accelerate due to the dissipative force an accelerated mirror experiences when photons are generated from the quantum vacuum. Furtherwehaveshownthatonecouldinprincipalutilizeenergyfromthevacuumfluctuations to operate such a vibrating mirror assembly. The application of the dynamic Casimir effect and the static Casimir effect may be regarded as a proof of principal, with the hope that the proven feasibility will stimulate more practical approaches exploiting known or as yet unknown features of the quantum vacuum. A model gedanken spacecraft with a single vibrating mirror was proposed which showed a very unimpressive acceleration due to the dynamic Casimir effect of about 3x10 20m/s2 with a very inefficient conversion of total − energy expended into spacecraft kinetic energy. Employing a set of vibrating mirrors to form a parallel plate cavity increases the output by a factor of the finesse of the cavity, 1010, yielding an acceleration per meter squared of plate area of about 3x10 10m/s2 and a − conversion efficiency of about 10 16. After 10 years at this acceleration, a one square meter − spacecraft would be traveling at 0.1m/s. Although these results are rather unimpressive, it is important to remember this is a proof of the principal, and to not take our conclusions regarding the final velocity in our simplified models too seriously. The choice of numerical parameters is a best guess based on current knowledge and can easily affect the final result by 5 orders of magnitude. In about 1900 an article was published in Scientific American provingthatitwasimpossibletosendarocket, usingaconventionalpropellant, tothemoon. The result was based on the seemingly innocuous assumption of a single stage rocket. NASA/CR—2004-213311 24 5. Newly Fabricated Materials with Negative Index of Refraction In the last several years materials that have a negative index of refraction in a narrow fre- quency band in the microwave have been developed using microfabrication methods. These materials have very unusual properties that might be of interest in the BPP mission and therefore we conducted a preliminary investigation. A classical electromagnetic wave analy- sisofnegativeindexmaterialsindicatesthat: 1)themomentumofaphotonisintheopposite direction of the Poynting vector, which is the direction the light is propagating; 2) if light reflects off a surface, the force on the surface is toward the source of the light rather than away from it; 3) the Doppler effect is reversed, the frequency shift is negative (to lower frequencies) if the source is moving toward the detector; 4) Snell’s Law applies, but the light wave bends in the opposite direction as for a normal medium. An open question is what happens to the Casimir force if a negative index material is between two plates. If the material had a negative index for wavelengths near twice the separation between the plates, then it is conceivable that the force would be attractive. One of the complications for Casimir forces is that one needs to integrate over a wide frequency region to obtain the force, and over most of this spectral range, the index will be positive. Wedidthefirsttheoreticalinvestigationintonegativeindexphenomenausingaquantized field representation. We examined several of the predicted properties, such as the Doppler shift, and the use of negative index materials as near perfect lenses. A paper , "Quantized Field Description of Light in Negative-Index Media," by Peter Milonni and Jordan Maclay has been submitted for publication. NASA/CR—2004-213311 25 6. Conclusions and direction for future work Ten years ago many researchers in quantum physics and Casimir forces were working on rather unphysical issues, such as Casimir forces due to different topologies, or Casimir forces in various dimensional spaces, or for various fields, not the usual electromagnetic field in three dimensions. It seemed that there was not a great interest in the more mundane world of precision measurements of Casimir forces. Then several breakthrough measurements were done, by Lamoroux and Mohideen, that verified the basic theory, and gave the hope of providing a testing ground for more precise and realistic calculations. During the course of this three year effort, there has been an increasing interest among physicists regarding the possible behavior of real systems designed to measure and exploit forces arising from the quantum vacuum. There is an increased interest in the behavior of real materials, with real boundary conditions. Two important experiments, done by the Lucent group, used MEMS structures to measure and exploit vacuum forces. The behavior of these structures was modeled in our earlier work. Several groups experienced in Casimir measurements are interested in measuring repulsive forces. We think this trend will continue, and even accelerate as more measurements are done of Casimirforces. Moredeviceswillbebuilt, withnewmodesofoperation. Asanindicationof this trend, I was just asked to serve as a referee for a reviewof newphenomena at nanometer scales, including quantized heat flow, charge discreteness and the Casimir effect, and how these phenomena impact nanoscale electromechanical devices. As knowledge of Casimir phenomena increases and disseminates into engineering areas, commercially valuable devices will probably emerge. Researchers will continue their efforts at exploring the boundaries of predictions based on current theories. It may be that new experiments, perhaps involving repulsive forces, will shed new light on our understanding of vacuum forces and open new possibilities. WestronglyrecommendthatNASAstayabreast of thesedevelopments, andconsiderthe implications with respect to the mission of NASA, especially the BPP program. It is very possible, that new developments may provide the basis for significant progress in reaching the BPP objectives. NASA/CR—2004-213311 26 7. Publications 7.1. Journal Papers Submitted and Published 1. Jordan Maclay and Robert L. Forward, "A Gedanken Spacecraft that accelerates by pushingonthevacuum(DynamicCasimirEffect), submittedforpublicationtoPhysics Letters A. In Appendix 1. 2. .Jordan Maclay, andCarlos Villarreal, "AModel for Casimir Forces inClosedCavities withFiniteConductivity,"submittedforpublicationtoPhysicsLettersA.InAppendix 1. 3. P. Milonni, and J. Maclay, "Quantized-Field Description of Light in Negative-Index Media," Submitted to Physical Review A. In Appendix 1. 4. J. Maclay, ”An analysis of vacuum fluctuation energy and Casimir forces in conductive rectangular cavities,” Phys. Rev. A., 61, 052110 (2000). 5. R.Esquivel-Sirvent,C.Villarreal,G.Cocoletzi,”Superlattice-mediatedtuningofCasimir forces,” Phys. Rev A 64, 052108 (2001) 6. J. Maclay, P. Milloni, H. Fearn, ”Of some theoretical significance: implications of Casimir effects,” European Journal of Physics 22, 463-469, 2001 7. R. Esquivel-Sirvent, C. Villarreal, and W. L. Mochan., "Casimir Forces in nanostruc- tures," Physica Status Solidi(b) 230, 409 (2002). 8. C. Villarreal, R. Esquivel-Sirvent, and G. H. Cocoletzi, "Modification of Casimir forces due to band gaps in periodic structures," .International Journal of Modern Physics A 17, 798 (2002). 9. W. L. Mochán, R. Esquivel-Sirvent, and C. Villarreal, "On Casimir forces in media with arbitrary dielectric properties," Revista Mexicana de Física 48, 339 (2002). 7.2. Conference Articles Published 1. J. Maclay, “Unusual Properties of Conductive Rectangular Cavities in the Zero Point Electromagnetic Field: Resolving Forward’s Casimir Energy Extraction Cycle Para- dox,”,”SpaceTechnologyandApplicationsInternationalForum1999,”,Albuquerque, NM, Feb., 1999, El-Genk, M. S., ed, American Institute of Physics Conference Pro- ceedings 458. NASA/CR—2004-213311 27 2. J. Maclay, ”A Design Manual for Micromachines using Casimir Forces: Preliminary Considerations,” Proceedings of STAIF-00 (Space Technology and Applications Inter- nationalForum-2000, Albuquerque, NM,January, 2000)„ editedbyM.S.El-Genk, AIP ConferenceProceedings504, AmericanInstituteof Physics, NewYork2000. Published in hardcopy and CD-ROM by AIP. 3. Maclay, J. Hammer, M. George, R. Ilic, Q. Leonard, R. Clark, ”Measurement of repul- sive quantum vacuum forces,” AIAA-2001-3359, AIAA/ASME/SAE/ASEE 37th Joint Propulsion Conference, Salt Lake City, 2001 4. J. Maclay, J. Hammer, ”Vacuum forces in Microcavities,” Proceedings of the Sev- enth International Conference on Squeezed States and Uncertainty Relations (IC- SSUR), Boston, MA, June 4-6, 2001. Proceedings are now available on line at http://www.physics.umd.edu/robot, click on Proceedings. In Appendix. 5. Jordan Maclay, and Carlos Villarreal, " A Model for Casimir Forces in Closed Cavities withFiniteConductivity,"presentedatthesymposiumCasimirForces: RecentResults in Experiment and Theory, Harvard-Cambridge Center for Astrophysics, Harvard Uni- versity, Cambridge, MA, Nov. 14, 2002. This presentation will be available shortly on line at ITAMP (Institute of Theoretical Atomic and Molecular Physics) website http://itamp.harvard.edu/ . 6. Carlos Villarreal, "Casimir Forces in Non-Homogeneous Planar and Spherical Sys- tems," presented at the symposiumCasimir Forces: Recent Results in Experiment and Theory, Harvard-Cambridge Center for Astrophysics, Harvard University, Cambridge, MA, Nov. 14, 2002. This presentation will be available shortly on line at ITAMP (In- stituteofTheoreticalAtomicandMolecularPhysics)websitehttp://itamp.harvard.edu/ . 7. Raúl Esquivel-Sirvent, Carlos Villarreal, and Cecilia Noguez, "Casimir forces between thermallyactivatednanocomposites,"MaterialsResearchSocietySymposiumProceed- ings 703, 99 (2002). 7.3. Presentations 1. ”Much Ado about Nothing: The Role of Empty Space in Modern Science,”J. Maclay, Illinois Institute of Technology, Dept. of Chemistry, Physics, and Biology, 1999 2. ”Much Ado about Nothing: The Role of Empty Space in Modern Science,” J. Maclay, University of Wisconsin at Richland Center, Feb. 2000. 3. ”Quantum Vacuum Forces in Rectangular Cavities: What are they and how can we use them?”, J. Maclay, UNAM, Physics Institute, Mexico City, Feb. 2000. 4. ”Quantum Vacuum Forces in Rectangular Cavities: What are they? How can we measure them? Can we make use of them to power rockets??,” J. Maclay, Dept. of Chemistry/Physics” University of Alabama, MSC, June 22, 2000. NASA/CR—2004-213311 28 5. ”Measurement of Quantum Vacuum Forces using an Atomic Force Microscope”, M. George, L. Sanderson, J. Maclay, J. Hammer, R. Clark, Eleventh International Confer- ence on Scanning Tunneling, Microscopy/Spectroscopy and Related Techniques, Van- couver, Canada July 15, 2001 (National Research Council of Canada). 6. Superlattice-mediated tuning of the Casimir forces, R. Esquivel-Sirvent, C. Villarreal and G.H. Cocoletzi, Pan-American Advanced Studies Institute: Physics and Technol- ogy at the Nanometer Scale, San Jose, Costa Rica, June 24th - July 3rd (2001). 7. Casimir forces in Electromagnetically Induced Transparent,Materials.,C. Villarreal, F.J.Lopez,andR.Esquivel-Sirvent,Pan-AmericanAdvancedStudiesInstitute: Physics and Technology at the Nanometer Scale, San Jose, Costa Rica, June 24th - July 3rd (2001). 8. Controlling Casimir forces using heterostructures, R. Esquivel-Sirvent, C. Villarreal and G.H. Cocoletzi, V Workshop on Quantum Field Theory Under the Influence of External Conditions, Leipzig, Germany, September 11th-14th (2001) 9. A three dimensional formula for Casimir forces in finite dielectric slabs,.C. Villarreal, W.L. Mochan, and R. Esquivel-Sirvent, V Workshop on Quantum Field Theory Under the Influence of External Conditions, Leipzig, Germany, September 11th-14th (2001). 10. Casimir forces between thermally activated nanocomposites., R. Esquivel-Sirvent, C. Villarreal, andC.Noguez, 2001MaterialsResearchSocietyFallMeeting, Boston, USA, November 26th-30th (2001). 11. J. Maclay, J. Hammer, ”Vacuum forces in Microcavities,” Proceedings of the Seventh International Conference on Squeezed States and Uncertainty Relations (ICSSUR), Boston, MA, June 4-6, 2001. 12. Jordan Maclay, and Carlos Villarreal, " A Model for Casimir Forces in Closed Cavities with Finite Conductivity," presented at the symposium Casimir Forces: Recent Re- sults in Experiment and Theory, Harvard-CambridgeCenter for Astrophysics, Harvard University, Cambridge, MA, Nov. 14, 2002. 13. Carlos Villarreal, "Casimir Forces in Non-Homogeneous Planar and Spherical Sys- tems," presented at the symposiumCasimir Forces: Recent Results in Experiment and Theory, Harvard-Cambridge Center for Astrophysics, Harvard University, Cambridge, MA, Nov. 14, 2002. 7.4. Articles in Popular Press/Video 1. On Sept. 27, 2001, the Japanese broadcasting company NHK visited our experiment at the University of Alabama. They filmed the fabrication of the cantilevers, the operation of the AFM, and some of the data as shown on the monitor. Theyfilmed an interview with J. Maclay for about 45 minutes. The experiment and discussion will be in the last segment of a 8 part series discussing science in the new millennium, and will NASA/CR—2004-213311 29 be broadcast in Japan. HNK is also negotiating with European and US companies to show the series, appropriately reedited, in these countries. The vacuum energy segment has been described by the senior staff at NHK as ”one of the most interesting segments.” NASA will be credited fully with sponsoring the research. 2. Feature Article on our Quantum Vacuum Project; ”Energy Unlimited,” by Henry Bortman appeared in New Scientist Magazine, pp32-34, 1/22/2000. 3. The article in Science News about the Casimir experiments at Bell Labs: ”Force from empty space drives a machine”, Feb. 10, 2001, Vol. 159, No. 6, p. 86, describes our effort to measure repulsive Casimir forces, and listed us and NASA Breakthrough Propulsion Physics as a source of additional information, online as http://www.sciencenews.org/20010210/fob5ref.asp 4. ”Space at Warp Speed” by Mariette DiChristina, Popular Science, pp 46-51, 5/2001 7.5. Important Recent Citations in MEMS Research to our work: 1. H. B. Chan, V. A. Aksyuk, R. N. Kleiman, D. J. Bishop, F. Capasso (at Bell Labs) ”Quantum mechanical actuation of microelectromechanical systems by the Casimir force”, Science 291:1941 (2001) cited our work in MEMS systems. 2. H. B. Chan, V. A. Aksyuk, R. N. Kleiman, D. J. Bishop, F. Capasso (at Bell Labs), ”Nonlinear micromechanical Casimir oscillator,” Phys. Rev. Lett., 87, 211801 (2001), measured Casimir force effects in a MEMS oscillatory system originally proposed by M. Serry, D. Walliser, J. Maclay, ”The role of the casimir effect in the static deflection and stiction of membrane strips in microelectromechanical systems (MEMS),” Journal of Applied Physics. 84, 5, pp2501-2506(1998) 3. E.BuksandM.Roukes(atCal Tech), ”Stiction, adhesionenergy, andtheCasimireffect in micromechanical systems,”Phy. Rev. B 63, 033402 (2001), presented measurements of adhesion energy based on M. Serry, D. Walliser, J. Maclay, ”The role of the Casimir effectinthestaticdeflectionandstictionofmembranestripsinmicroelectromechanical systems (MEMS),” Journal of Applied Physics. 84, 5, pp2501-2506(1998). NASA/CR—2004-213311 30 8. Appendix For lack of space, we have only included articles not yet available in the literature or on the web. 1. Jordan Maclay and Robert L. Forward, "A Gedanken Spacecraft that accelerates by pushingonthevacuum(DynamicCasimirEffect), submittedforpublicationtoPhysics Letters A. 2. .Jordan Maclay, andCarlos Villarreal, "AModel for Casimir Forces inClosedCavities with Finite Conductivity," submitted for publication to Physics Letters A. 3. P. Milonni, and J. Maclay, "Quantized-Field Description of Light in Negative-Index Media," Submitted to Physical Review A. Addendum to Final Report Of the three articles cited in the appendix as unpublished, two of them have now been published and are available in the open literature: 1. Milonni, P.W., and Maclay, "Quantized-Field Description of Light in Negative- Index Media," Optics Communications, 228 (2003), pp. 161-165. 2. Maclay, J. and Forward, R., "A Gedanken spacecraft that operates using the quantum vacuum (adiabatic Casimir effect)", Foundations of Physics, 34 (March, 2004) pp. 477-500. The third paper is still under review. For completeness, the submitted text for this paper is included in this Appendix. – Maclay, J. and Villarreal, C., "A Model for Casimir Forces in Closed Cavities with Finite Conductivity", submitted to Physics Letters A. NASA/CR—2004-213311 31 NASA/CR—2004-213311 33 NASA/CR—2004-213311 34 NASA/CR—2004-213311 35 NASA/CR—2004-213311 36 NASA/CR—2004-213311 37 NASA/CR—2004-213311 38 NASA/CR—2004-213311 39 NASA/CR—2004-213311 40 NASA/CR—2004-213311 41 NASA/CR—2004-213311 42 NASA/CR—2004-213311 43 NASA/CR—2004-213311 44 NASA/CR—2004-213311 45 NASA/CR—2004-213311 46 NASA/CR—2004-213311 47 NASA/CR—2004-213311 48 Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED October 2004 Final Contractor Report 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Study of Vacuum Energy Physics for Breakthrough Propulsion WBS–22–62–949–10–01 6. AUTHOR(S) NAS3–00093 G. Jordan Maclay, Jay Hammer, Rod Clark, Michael George, Yeong Kim, and Asit Kir 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Quantum Fields LLC 20876 Wildflower Lane E–14771 Richland Center, Wisconsin 53581 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER National Aeronautics and Space Administration Washington, DC 20546–0001 NASA CR—2004-213311 11. SUPPLEMENTARY NOTES G. Jordan Maclay, Quantum Fields LLC, 20876 Wildflower Lane, Richland Center, Wisconsin 53581; Jay Hammer and Rod Clark, MEMS Optical, Inc., 205 Import Circle, Huntsville, Alabama 35806; and Michael George, Yeong Kim, and Asit Kir, University of Alabama, 301 Sparkman Drive, Huntsville, Alabama 35805. Project Manager, Marc G. Millis, Turbomachinery and Propulsion Systems Division, NASA Glenn Research Center, organization code 5870, 216–977–9535. 12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Unclassified-Unlimited Subject Categories: 20 and 70 Distribution: Nonstandard Available electronically at http://gltrs.grc.nasa.gov This publication is available from the NASA Center for AeroSpace Information, 301–621–0390. 13. ABSTRACT (Maximum 200 words) This report summarizes the accomplishments during a three year research project to investigate the use of surfaces, particularly in microelectromechanical systems (MEMS), to exploit quantum vacuum forces. During this project, we developed AFM instrumentation to repeatably measure Casimir forces in the nanoNewton range at 10–6 torr, designed an experiment to measure attractive and repulsive quantum vacuum forces, developed a QED based theory of Casimir forces that includes non-ideal material properties for rectangular cavities and for multilayer slabs, developed theoreti- cal models for a variety of microdevices utilizing vacuum forces, applied vacuum physics to a gedanken spacecraft, and investigated a new material with a negative index of refraction. 14. SUBJECT TERMS 15. NUMBER OF PAGES 54 Interstellar travel; Spacecraft propulsion; Physics; Gravitation; Antigravity 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. Z39-18 298-102