5
electronic noise. In this case, do not block the beam so that the 0%TBaseline
accounts for the light reflecting on the edges of the aperture.
Performing a Zero/Baseline Correction
:
Select this option to apply a 100%T
baseline correction (100%TBaseline) and a zero-line correction (0%TBaseline) to
the sample scan (S). This correction is performed with the raw transmission data
and is thus:
𝑆
−
0%
𝑇𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒
100%
𝑇𝐵𝑎𝑠𝑒
𝑙𝑖𝑛
−
0%
𝑇𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒
With this option, the Cary will prompt you to perform a 100%TBaseline first,
followed by a 0%TBaseline when you perform a baseline collection.
Basics of measurement acquisition
The wavelength range is 1800 nm to 250 nm. Scans normally go from long to short
wavelengths. There are two detectors, a PMT and an InGaAs. The wavelength at which
the system changes from one to the other (accompanied by a grating change) can be
adjusted. Usually 750 to 800 nm is a good value for this change over. You can see the
change in the spectrum when you take a baseline (% Transmission or Reflection). If
you see a step in the spectrum, it may mean your baseline is bad or that your sample
has a polarization dependency.
Setup
– The setup button located in the upper left-hand corner defines the scan
parameters. The following useful tabs can be found under Setup.
Cary tab
Here you can set the units of the x-and y axes (nm, cm
-1
, etc. and A, %T, %R, etc.),
as well as the range for the axes. Under scan controls, the average time per data
point and the data interval can be set can be controlled. Note that you only have
independent control over two of these values.
Options tab under Setup
Here you control the Beam Mode, Slit Band Width, and Slit Height (
see Appendix
A of this guide for more info
). The Double beam mode needs to be used for the
integrating sphere measurements and the SBW is typically set to 2nm.
As mentioned earlier, the Slit Height can be used to decrease the beam spot size
Typically, the UV-Vis button will be selected. If you do not need to go to shorter
wavelengths than 400 nm, you can select the Vis button, which will save on the
lifetime of the UV lamp.
You can also set the wavelength at which the Detector and grating change. Both
of these are typically set at 800 nm, if you have an important spectroscopic
feature at 800 nm, you can move the change over +/- 50 nm
Baseline tab
This tab enables you to choose the type of baseline(s) that you want to use in the
Scan run. The different types of baseline corrections are particularly useful with
