Vertically aligned multiwall carbon nanotubes were grown by water-assisted chemical vapor deposition on a large-area lithium tantalate pyroelectric detector. The processing parameters are nominally identical to those by which others have achieved the "world's darkest substance" on a silicon substrate. The pyroelectric detector material, though a good candidate for such a coating, presents additional challenges and outcomes. After coating, a cycle of heating, electric field poling, and cooling was employed to restore the spontaneous polarization perpendicular to the detector electrodes. The detector responsivity is reported along with imaging as well as visible and infrared reflectance measurements of the detector and a silicon witness sample. We find that the detector responsivity is slightly compromised by the heat of processing and the coating properties are substrate dependent. However, it is possible to achieve nearly ideal values of detector reflectance uniformly less than 0.1% from 400 nm to 4 microm and less than 1% from 4 to 14 microm.

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Materials with similar chemical compositions often exhibit different optical properties due to their structural composition. PTFE is widely used in many applications for both its mechanical and optical properties. Low density sintered PTFE has optical properties that make it desirable for use as a white diffuser in applications such as remote sensing. The contrast between the commonly available high density material and the low density material may be useful for those interested in optical modeling of scattered light. Additionally, some applications may find high density PTFE suitable for some optical applications. This paper describes measurements of BRDF, 8º/hemispherical reflectance, and directional hemispherical transmittance for both high density (HD) and low density (LD) sintered PTFE. *Benjamin.tsai@nist.gov; phone 1 301 975-2347; fax 1 301 869-5700; nist.gov 1. BACKGROUND Description of high density PTFE and low density PTFEPolytetrafluoroethylene (PTFE) is a synthetic fluoropolymer, which is made either by the emulsion polymerization of tetrafluoroethylene or by the direct substitution of hydrogen atoms on polyethylene with fluorine. It is most well known by its trademark, Teflon. PTFE has many desirable properties, because it is hydrophobic, non-reactive, chemically inert, is a good lubricant, and has a high melting point, low coefficient of friction, and excellent dielectric properties.Sintering is a method for making PTFE from powder by heating it below its melting point until its particles adhere to each other. The result is a porous plastic fused together as a cohesive mass of resin particles. Particle size and shape of resin powders can be manipulated to optimize pore size, void volume, surface texture, and strength. Some advantages of sintering include: the possibility of very high purity, great uniformity, the preservation of purity from the strict fabrication process, and the stabilization of the details of repetitive operations by control of grain size in the input stages. ApplicationsSince water-containing substances do not wet PTFE, PTFE is often used as a non-stick coating for pans and cooking utensils. Also, because it is very non-reactive, it is used in containers and pipework for reactive and corrosive chemicals. Due to its excellent dielectric properties, PTFE is used as an insulator in cables and printed circuit boards. Its extremely high bulk resistivity makes it an ideal material for fabricating long life electrets, useful devices that are the electrostatic analogues of magnets. Due to its low friction, PTFE is used to make computer mice feet and in applications involving bearings, bushings, and gears. PTFE has also been used in body piercings, machinery lubricant, armor-piercing bullets, thread seal tape, grafts to bypass stenotic arteries in peripheral vascular disease, and painted surfaces to prevent insects from climbing. PTFE's high corrosion resistance makes it ideal for laboratory environments as containers, magnetic stirrers and tubing for highly corrosive chemicals such as hy...

Deviations from ideal blackbody (BB) behavior can be characterized by a BB's effective emissivity. The cavity emissivity is most often obtained through a model, given a particular set of input parameters associated with the BB cavity geometry and surface optical properties. It can also be measured directly (radiance) or indirectly (reflectance). A study of BB cavity emissivity using the reflectance method is presented. Several types and designs of blackbody cavities, including those from fixedpoint and water bath BBs, using our infrared total integrated scatter (ITIS) instrument for emissivity evaluation are examined. The emissivity is characterized as a function of position on the output aperture, as well as a function of output angle. The measurements have revealed emissivity values, both significantly greater than, and in confirmation of, modeling predictions. For instance, the emissivities of three fixed point BB cavity designs were found to vary significantly despite modeling predictions in the design process of similar behavior. Also, other BB cavities that exhibited poor emissivity performance were re-painted and re-machined, in one case more than once, before the predicted performance was achieved.

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We have measured the polarization-resolved bidirectional reflectance distribution function (BRDF) for two types of graphite used in the fabrication of high-temperature fixed point blackbody cavities in and out of the plane of incidence. Measurements were made at room temperature using 405 nm and 658 nm laser sources, and the samples were illuminated at angles of incidence varying from normal incidence to 70 •. All of the samples exhibited non-Lambertian behaviour, including enhanced forward scatter at high incident angles, especially for s-polarized incident light. The directional-hemispherical reflectance for unpolarized incident light, obtained by integrating the BRDF measured at individual points in a hemisphere over the sample, ranged from 0.083 to 0.101, depending upon sample and incident angle. The potential impact of these measurements on emissivity models for graphite blackbody radiators and radiance temperature scale dissemination is discussed.

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Routine NIST spectral responsivity calibrations are needed for the infrared range. Low-NEP pyroelectric radiometers have been developed for traditional monochromator applications to extend the responsivity scale to the infrared. After NEP tests, the best pyroelectric detectors were converted to transfer-standard radiometers. The relative spectral responsivities were determined from spectral reflectance measurements of the organic black detector coatings. The absolute tie points were measured against a domed pyroelectric radiometer standard and a sphere-input extended-InGaAs transfer-standard radiometer. The infrared spectral power responsivity scale has been extended for the 2 µm to 14 µm wavelength range. A single-grating monochromator has been adapted to the calibration facility and used to characterize and calibrate infrared detectors.