Two types of microwave filters, metallic powder filters and a filter using a resistive coaxial cable, were tested. Attenuation of the metallic powder filters using copper or stainless steel (SUS304L) was measured at 300 K, 77 K, and 4.2 K, and it was found that SUS304L powder of nominal 30 m grain size gives best result as the microwave filter for single electron tunneling (SET) experiments. Attenuation of a coaxial filter, or Thermocoax with SMA connectors attached at both ends is larger at low temperatures than that at room temperatures, and the temperature dependence of the attenuation does not agree with Zorin's model. The filter arrangement in our cryostat designed for SET experiments, is also reported.

The photoluminescence of diamondoids in the solid state is examined. All of the diamondoids are found to photoluminesce readily with initial excitation wavelengths ranging from 233 nm to 240 nm ( 5.3 eV). These excitation energies are more than 1 eV lower than any previously studied saturated hydrocarbon material. The emission is found to be heavily shifted from the absorption, with emission wavelengths of roughly 295 nm (4.2 eV) in all cases. In the dissolved state, however, no fluorescence is observed for excitation wavelengths as short as 200 nm. We also discuss predictions and measurements of the quantum yield. Our predictions indicate that the maximum yield may be as high as 25%. Our measurement of one species, diamantane, gives a yield of 11%, the highest ever reported for a saturated hydrocarbon, even though it was likely not at the optimal excitation wavelength.

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Using a home-made transparent two-zone furnace, single crystals of diamond molecules (or diamondoids) up to ∼1 cm3 were grown under real time observation using the vapor transport technique. This process proved to be an environmentally friendly means of refining diamond molecules. Optical measurements were performed to evaluate the purity of diamond molecules before and after the process, which demonstrated that even a trace amount of impurities in commercial samples was successfully removed by our method. The thus-obtained high-purity single crystals will accelerate fundamental and applied research on diamond molecules in the solid state, especially in the field of optoelectronics.

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