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2 Experiments

The production method of QCC described in detail by Sakata et al. ([1984]) is summarized here. The QCC condensate is prepared by the technique of hydrocarbon plasma deposition. The source gas of methane is ionized by microwave discharge, and is spouted out into a vacuum chamber through a small nozzle. The plasma gas adiabatically expands and is immediately quenched to solid material. The condensate is deposited onto NaCl or CaF2 substrates placed in the vacuum chamber. The NaCl/CaF2 substrates are used because of high transmittance and no spectral features in the 3 $\mu $m region.

Then the QCC films are moved into an evacuated quartz tube, and set in an electronic furnace. The temperature of the furnace is raised at a rate of 5 K per minute to a predetermined temperature. The sample is heated in the furnace at the temperature for 20 minutes. A portion of deposited QCC film evaporates by heating, and re-sticks to the cooler part of the quartz tube. The amount of evaporation grows with the annealing temperature, for instance, more than 90% in mass is lost from the fresh deposition after the annealing at 800 K. We adjust the duration of deposition process five to ten times longer than the sample for no annealing in order to prepare the thicker deposition for annealing at higher temperature. As a result we obtain eight samples at the temperatures of 600, 700, 723, 740, 760, 823, 873 K as well as as-deposited film whose absorptions are fairly constant ($\sim$15%).

In order to obtain the thermal emission spectra of QCC we use a near-infrared spectrograph originally developed for astronomical observations Imanishi et al. ([1996]). The spectrograph is equipped with an InSb detector array and covers $2.8-4.2~\mu$m in a single exposure with a wavelength resolution of about 1300. The annealed and as-deposited samples are fixed in a holder in front of the spectrograph window, and heated by a ceramic resistance that contacts to the substrate. So as to reduce the background emission from the environment, a liquid nitrogen surface is viewed through a mirror put behind the sample holder. We measure the temperature of the emitting material with Pt resistance attached to the substrate.

A net spectrogram of QCC sample is obtained by subtracting a spectrum of a blank substrate. The sensitivity of the spectrograph is calibrated by measuring thermal emission spectrum of the room temperature assuming a blackbody emission. The baseline of the spectrum is fitted with spline function and subtracted to compare the extracted spectral features with the observational data.

The absorbance of QCC films is taken by a Shimazu FTIR - 8600 PC spectrophotometer at room temperature with a wavelength resolution of about 1500. The baseline of the absorption spectra attributable to the the net continuum absorption of QCC and substrates are fitted with spline function and subtracted.


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