Spectral responsivity of pyroelectric detectors coated with carbon nanotubes
John H. Lehman
We have begun to demonstrate the next generation of coatings for laser power and energy measurement standards, which are based on carbon nanotubes on a variety of detector platforms. These coatings must be resistant to damage and aging while maintaining desirable optical and thermal properties over a range of laser wavelengths served by our calibration services (0.157 m to 10.6 m). To investigate the optical properties of these coatings we have employed a variety of techniques that are useful to understanding fundamental detector properties. In particular, the spectral responsivity of a thermal detector coated with carbon nanotubes may be used to gain a greater understanding of purity, species, and geometry of the carbon nanotubes. In this talk, we will describe a process of experiment and analysis that is potentially useful for distinguishing between metallic and semiconducting carbon single-wall carbon nanotubes (SWNTs) that is cheap and accurate (uncertainty ~ 10 % or less). This process is based on an effective medium approximation (EMA) and the idea that different species of SWNTs have different optical properties. Similarly we will discuss an EMA that is potentially useful for verifying tube geometry and spacing on various thermal-detector platforms, which may corroborate our experimental results and EMA analysis in the literature. We have recently demonstrated the process of growing carbon multiwall nanotubes (MWNTs) directly on lithium niobate and lithium tantalate by the process of hot wire chemical vapor deposition (HWCVD) and chemical vapor deposition (CVD). Carbon nanotubes may also be prepared and purified in bulk form and easily applied to a thermal detector using an airbrush technique. We are the first to demonstrate this and to publish the results. Our spectral responsivity measurement results for the wavelength range from 1 'm to 14 'm indicate that the absorptance of a MWNT coating is uniform with variations of approximately 1 %. We have also observed spectral responsivity variations of several percent with SWNT-based coatings. Variation in the responsivity, though less desirable for practical applications, is useful scientifically within the validity of the EMA. By varying growth conditions such as the catalyst metal, growth temperature and duration, we can vary the topology and therefore optimize the optical properties of the MWNT coating. We believe that it is necessary to grow the MWNTs directly on the detector surface if we are to achieve the highest thermal diffusivity and damage resistance. Theoretical and experimental investigations reported in the literature indicate that desirable properties may be achieved while maintaining properties that have a significant advantage over present alternatives such as carbon based paints or metal blacks.
January 26-28, 2005
2nd Joint Workshop on Measurement Issues in Single Wall Carbon Nanotubes: Purity and Dispersion Part II
Spectral responsivity of pyroelectric detectors coated with carbon nanotubes, 2nd Joint Workshop on Measurement Issues in Single Wall Carbon Nanotubes: Purity and Dispersion Part II, Gaithersburg, MD
(Accessed June 10, 2023)