Optoelectronics with Carbon Nanotubes

Polarized measurements were taken with a linear polarizer, i.e. a Glan-Taylor prism in
the infrared, in the parallel section of the beam bath as indicated in figure 3. The polarizer was
rotated normal to the beam path to specific angles with respect to the tube orientation. The CNT
orientation was determined by an optical microscope (not shown in figure) using the metal
contacts as reference and comparing them to an SEM image of the device.
In low-temperature experiments, the sample stage was first cooled down as much as
possible (~20 K). For physical stability, the liquid helium transfer line was subsequently
disconnected from the stage in order to mechanically decouple the measurement system from the
environment. The probe needles were then lowered onto the contact pads, allowing the
temperature to rise and then stabilize around 90 K for the first set of measurements. Since in this
set-up, the temperature returns slowly to room temperature over several hours, it was possible to
contact probe needles to the contact pads periodically to take a measurement at a given
temperature. A resistor heater attached to the cold pad of the sample stage was used to raise the
temperature when necessary. Only the sample stage was cooled, while the rest of the optical
path remained at room temperature.
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