Biomedical Engineering Reference
In-Depth Information
Fig. 4. AFM topographic scans showing surface structure of the cuticle; (a) is a map from the
scan on a larger area of about 3×10
5
square pixels (b) is a scan on a single pixel of about
2.5×10
6
nm
2
. Doted lines on (a) represents the region shown by (b). Scale bars ∼ 0.5nm.Taken
from (Kipnusu et al., 2009).
5. Electrical characterization and charge transport mechanism
This section discusses electrical characteristics of the cuticle samples. Current-voltage (I-V)
data measured as a function of annealing temperature, irradiation and pooling temperature
was used in analyzing the electrical characteristics .Samples were separately annealed and
irradiated before electrode coating was done. When annealing, cuticles were placed inside a
temperature-controlled furnace, which was fitted inside an electrical shielded cage of a
Lindberg/Blue Tube Furnace of model TF55035C. Samples were annealed at various
temperatures of 320K, 350K and 400K for a constant period of 12hrs each. Irradiation of the
sample was done with He-Ne laser beam of wavelength 632.8nm in a dark room each for a
different period of 10minutes, 30minutes, and 60minutes. Electrode coating on the film of
pristine, pre-annealed and pre-irradiated samples was done by using quick drying and
highly conducting Flash-Dry silver paint obtained from SPI Supplies (USA). A mask of a
circular aperture of 0.56 cm diameter was used while coating to ensure uniformity in size of
coated surface. Circular aluminum foil of the same diameter was placed on freshly coated
surface such that the sample was sandwiched between two aluminum electrodes. These
metal-sample-metal sandwiches were left to dry at room temperature for a period of 24hrs
to ensure that there was good ohmic contacts between aluminum electrode and the sample.
The same Flash-Dry Silver paint was used to connect thin wires onto the aluminum
electrodes. When measuring I-V at different temperatures, a sample sandwiched between
aluminium electrodes was placed inside the Lindbarg/Blue Tube Furnace and temperature
varied in steps of 5K between 350K and 500K at constant electric fields of 0.75V/cm,
1.50V/cm 2.25V/cm, 3.00V/cm, and 3.75V/cm.
Fig. 5(a) shows the I-V characteristics of pristine and annealed samples. These indicate
clearly that there was electrical switching and memory effect in the cuticle samples. At