News

  • June 14, 2003
    Linear motion carriage with aerostatic bearings preloaded by inclined iron core linear electric motor
    A.H. Slocum, M. Basaran, R. Cortesi, A.J. Hart. J. Int’l. Soc. Precision Engineering and Nanotechnology 27:382-394, 2003.   A fundamentally precise and simple linear motion axis design is discussed where the attractive force from the linear motor is used to preload a carriage supported by six rigidly attached porous carbon air bearings. The air bearings are assembled by vacuuming the pads to two orthogonal planes, positioning the carriage above the pads, and then injecting epoxy between the bearings and the carriage. Control of flatness tolerances of the bearings and planes permits over-constraint of the carriage by the bearings, which leads to a high degree of...
  • September 24, 2003
    Kinematic coupling interchangeability
    A.J. Hart, A.H. Slocum, P.J. Willoughby. J. Int’l.Soc. Precision Engineering and Nanotechnology, 28:1-15, 2004.   The deterministic nature of kinematic couplings enables closed-form characterization of interchangeability error, parametrized in terms of the magnitudes of manufacturing tolerances in the interface manufacturing and assembly processes. A process is suggested for calibrating kinematic couplings to reduce the interchangeability error, based on measurement of the contact points and calculation of a transformation matrix between the interface halves. A Monte Carlo analysis is developed and validated for predicting interchangeability of canoe...
  • April 15, 2004
    Segmented and shielded structures for reduction of thermal expansion-induced tilt errors
    A.J. Hart, A.H. Slocum, J. Sutin. J. Int’l. Soc. Precision Engineering and Nanotechnology, 28:443-458, 2004.   The design and prototype tests of a segmented and shielded instrumentation structure, based on tube modules connected by canoe ball type kinematic couplings, are presented with application to a high-precision microscope for biological science experiments. The segmented tube design is shown to be significantly less sensitive to deformation from uneven thermal disturbances than a single tube structure. The gaps between the tube segments relieve thermal strains and restrict axial heat conduction, and the large-radius kinematic couplings provide high thermal resistance interconnects without significantly degrading structural stiffness. Simulation results,...
  • August 26, 2005
    Growth of conformal single-walled carbon nanotube films from Mo/Fe/Al2O3 deposited by electron beam evaporation
    A.J. Hart, A.H. Slocum, L. Royer. Carbon, 44(2):348-359, 2006.   We discuss growth of high-quality carbon nanotube (CNT) films on bare and microstructured silicon substrates by atmospheric pressure thermal chemical vapor deposition (CVD), from a Mo/Fe/Al2O3 catalyst film deposited by entirely electron beam evaporation. High-density films having a tangled morphology and a Raman G/D ratio of at least 20 are grown over a temperature range of 750–900 °C. H2 is necessary for CNT growth from this catalyst in a CH4 environment, and at 875 °C the highest yield is obtained from a mixture of 10%/90% H2/CH4. We demonstrate for the first time that physical...
  • February 10, 2006
    Uniform and selective CVD growth of carbon nanotubes and nanofibers on arbitrarily microstructured silicon surfaces
    A.J. Hart, B.O. Boskovic, A.T.H. Chuang, V.B. Golovko, J. Robertson, B.F.G. Johnson, A.H. Slocum. Nanotechnology 17:1397-1403, 2006.   Carbon nanotubes (CNTs) and nanofibres (CNFs) are grown on bulk-micromachined silicon surfaces by thermal and plasma-enhanced chemical vapour deposition (PECVD), with catalyst deposition by electron beam evaporation or from a colloidal solution of cobalt nanoparticles. Growth on the peaked topography of plasma-etched silicon 'micrograss' supports, as well as on sidewalls of vertical structures fabricated by deep-reactive ion etching demonstrates the performance of thermal CVD and PECVD in limiting cases of surface topography. In thermal CVD, uniform films of tangled single-walled CNTs (SWNTs) coat the structures despite oblique-angle...
  • March 11, 2006
    Rapid growth and flow-mediated nucleation of millimeter-scale aligned carbon nanotube structures from a thin-film catalyst
    A.J. Hart, A.H. Slocum.  J. Physical Chemistry B 110(16):8250-8257, 2006.   We discuss the rapid growth of films and lithographically templated microstructures of vertically aligned small-diameter multiwalled carbon nanotubes (VA-MWNTs), by atmospheric-pressure thermal chemical vapor deposition (CVD) of C2H4/H2/Ar on a Fe/Al2O3 catalyst film deposited by electron beam evaporation. The structures grow to 1 mm height in 15 min and reach close to 2 mm in 60 min. The growth rate and final height of CNT microstructures grown from catalyst patterns depend strongly on the local areal density of catalyst, representing a reverse analogue of loading effects which occur in plasma etching processes. Abrupt...
  • May 5, 2006
    Force output, control of film structure, and micro-scale shape replication by carbon nanotube growth under mechanical pressure
    A.J. Hart, A.H. Slocum.  Nano Letters 6:1254-1260, 2006.   We demonstrate that a film of vertically aligned multiwall carbon nanotubes (CNTs) can exert mechanical energy as it grows, and in our experiments the average force output is approximately 0.16 nN per CNT, for CNTs having an outer diameter of 9 nm and five walls. The film thickness after a fixed growth time and the alignment of CNTs within the film decrease concomitantly with increasing pressure which is applied by placing a weight on the catalyst substrate prior to growth, and CNTs grown under applied pressure exhibit significant structural faults. The measured mechanical energy density of CNT...
  • July 7, 2006
    Experimental determination of kinematic coupling repeatability in industrial and laboratory conditions
    P.J. Willoughby, A.J. Hart, A.H. Slocum. SME J. Manufacturing Systems 24:108-121, 2005.   While kinematic couplings are frequently used as components of repeatable interfaces in ideal environments, their use in heavily loaded industrial interfaces is less frequent, as previous studies have validated couplings mostly under modest loads and controlled environmental conditions. On the other hand, the performance of heavily loaded industrial equipment, such as robots used in automotive production, could benefit from highly repeatable interfaces for assembly and replacement of modules. A series of tests was conducted to assess the industrial repeatability performance of large kinematic couplings on an ABB 6400R industrial robot....
  • August 23, 2006
    Creating Patterned Carbon Nanotube Catalysts through the Microcontact Printing of Block Copolymer Micellar Thin Films
    R.D. Bennett, A.J. Hart, A.C. Miller, P.T. Hammond, D.J. Irvine, R.E. Cohen.  Langmuir 22:8273-8276, 2006.   We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al2O3) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the...