Carbon nanotubes (CNTs), with their exceptional electrical properties, chemical stability, and mechanical strength, have attracted a great deal of attention. This makes the material attractive for a wide range of applications, including composite materials, 1 battery electrode materials, 2 nanoelectronics, 3,4 and nanoscale sensors. 5 However, the properties of CNTs are highly dependent on their structure and size. Such sensitivity to size and structure imposes a potential barrier to the realization of the novel properties of CNTs in many applications. In the growth of CNTs by chemical vapor deposition (CVD), the diameters of CNTs are determined by the sizes of catalysts. 6 One way to obtain CNTs with fewer chiral arrangements is to use smaller catalyst particles. Thus, CNTs with smaller diameters, for example less than 2 nm, are most likely to be single-walled with fewer geometrical arrangements. This should limit the band gap range and allow the possibility of having all metallic or all semiconducting CNTs from a given growth. Moreover, such small-diameter nanotubes have larger band gaps, which minimize off-state leakage, thereby increasing the transistor on/off current ratio in transistor applications. 7 Significant progress has been made in driving catalyst size, and thus nanotube diameters, down

We present the development of a high power, tunable far-infrared p-germanium laser spectrometer for the study of dissolved biomolecules in the THz range. As a first application we report on the measurement of the absorption coefficient α for liquid water in the frequency range from 81to96cm−1. Using the p-Ge laser spectrometer we were able to penetrate through layers of up to 100μm thickness. We discuss the advantages and the limitations of this THz spectrometer. We present an analysis of the experimental data based on a χ2 test to provide an objective procedure to minimize the influence of systematic effects, for example of interference due to multiple reflections within the sample chamber. The measured absorption coefficient α lies between (410±6) and (490±6)cm−1 at 81 and 96cm−1, respectively.

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