Installation and User Guide
80SpecTM 80 Degree Specular Reflectance
Accessory
The information in this publication is provided for reference only. All
information contained in this publication is believed to be correct and
complete. PIKE Technologies, Inc. shall not be liable for errors contained herein
nor for incidental or consequential damages in connection with the furnishing,
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Copyright 1991-2011 by PIKE Technologies, Inc., Madison, WI 53719. Printed in
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Address Comments to:
PIKE Technologies, Inc.
6125 Cottonwood Drive
Madison, WI 53719
Phone
Fax
E-mail
Website
Jan. 1, 2012
PN 350-001200-02
(608) 274-2721
(608) 274-0103
[email protected]
www.piketech.com
Contents
Introduction
Unpacking Your Accessory
Packing List
Installation
Performance Verification
Using Your 80Spec Accessory
Example Application: Hard Disk Analysis
Effect of Dispersion
Kramers-Kronig Transform
Precautions
Maintenance Parts
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Introduction
A common method for the non-destructive measurement of thin infrared transmitting layers on metallic
substrates is by performing an infrared specular reflectance analysis.
R. G. Greenler in his paper (Chem. Phys. 44, 310 (1966)) showed that the sensitivity of a measurement of
a thin film on a reflecting metallic substrate can be significantly enhanced by performing the analysis at
a grazing angle. This analysis may also be enhanced by using light that has its E vector perpendicular to
the plane of incidence (parallel polarization).
The PIKE Technologies 80Spec is an 80° specular reflectance accessory designed for use in FTIR
spectrometers. The infrared beam from the spectrometer is reflected at the input mirror to strike the
sample at an incident angle of 80°. The reflected beam from the sample strikes the output mirror and is
directed to the instrument detector.
Figure 1: 80Spec cutaway view showing optics
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Unpacking Your Accessory
In order for you to quickly verify receipt of your accessory, we have included a packing list. Please
inspect the package carefully.
Packing List
80Spec Manual
80Spec Accessory
Gold Alignment Mirror
PN 350-001200
PN 012-10XX
PN 300-0002
Quantity 1
Quantity 1
Quantity 1
Mask Set
PN 010-3010
(For 012-11XX model only)
Quantity 1
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Installation
The 80Spec accessory has been aligned and tested in the PIKE Technologies facility to ensure that it
performs to specifications. There is no additional alignment required. The following is the procedure for
accessory installation.
1.
The 80Spec accessory fits into the sample compartment of the FTIR spectrometer. Your 80Spec is
set to an appropriate configuration to fit the sample compartment of the FTIR instrument you
specified. Before inserting the accessory in the sample compartment, ensure that your
spectrometer is aligned. If the instrument is not aligned, follow the manufacturer’s instructions for
maximizing the interferogram signal (the IR energy throughput) of your FTIR spectrometer.
2.
In order to locate the accessory in the correct position, simply place the entire accessory into the
FTIR sample compartment with the PIKE 80Spec label facing the front and line up the base plate
provided with the holes/pins in your FTIR Spectrometer.
3.
Fasten the accessory onto the FTIR sample compartment base plate using the captive screw(s)
located on the 80Spec base plate (some accessories may have two mounting screws or a mounting
screw/pin combination, depending on spectrometer configuration).
4.
Tighten the captive mounting screw (with flat head screwdriver or by hand) to firmly position the
accessory base onto the FTIR sample compartment base plate. The 80Spec accessory is now ready
for use.
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Performance Verification
1. With the accessory removed from the sample compartment, collect a background spectrum.
2. Place the 80Spec accessory in the sample compartment. Place the gold alignment mirror face down
on the top surface of the accessory.
3. Collect a transmission spectrum using the same collection parameters as used to collect the
background spectrum.
The minimum transmission of the accessory should be 15% at 1000 cm-1.
Using Your 80Spec Accessory
In order to collect a spectrum with your 80Spec accessory, perform the following steps:
1.
Place the gold coated alignment mirror face down on the top surface of the accessory.
2.
Collect a background spectrum.
3.
Remove the gold alignment mirror and place your sample face down on the top of the accessory.
4.
Collect a sample spectrum.
Note that the enhancement in signal by performing a measurement at a grazing angle is only true when
the sample is placed on a metallic substrate. If the sample layer is very thin, such as a monolayer film,
an improvement in the signal may be achieved by using a polarizer. The polarizer may be placed at
either the input or output of the accessory. The polarizer should be set to 0° for P-Polarization (90° for
S-Polarization). If a large sample is to be analyzed, then one or both of the polarizer mounts may be
removed from the accessory.
When using the smaller sample masks the beam may reflect off the underneath side of the mask. This
creates a fringing pattern in the spectrum. It is recommended that you soot the underneath side of the
mask with a burning candle to create an absorbing surface.
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Example Application: Hard Disk Analysis
In the manufacture of magnetic disks, fluorocarbon lubricants are applied to the disk surface. This
lubricant layer is used to reduce head wear during operation and to reduce friction during start up and
landing of the head. Knowledge of the thickness of the lubricant layer is critical in predicting disk
performance.
A common method for the non-destructive measurement of this lubrication layer is by performing an
infrared specular reflectance analysis at a grazing angle. The analysis in complicated somewhat in that
the lubrication layer is not placed on the metallic disk surface but over the magnetic medium. The
lubrication layer is also very thin, its thickness being much less than the wavelength of the light used for
analysis.
The spectrum shown on the following page is of a lubricated disk, ratioed to an unlubricated disk. The
lubricant thickness of this sample was 18 angstroms. Sixteen scans were co-added at a resolution of
eight wavenumbers using an MCT detector.
Figure 2: IR spectrum of lubricant layer
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Effect of Dispersion
The spectra of many samples are distorted by anomalous dispersion in the sample. The reflectivity of
a sample is dependent upon the refractive index of the sample and is governed by the Fresnel
equations. For light hitting a sample at normal incidence, the reflection at the sample is given by the
following equation:
Refractive Index n1
R=
(n1 – n2)2
(n1 + n2)2
Sample,
Refractive Index n2
2
For example, the amount of reflection at the first glass surface is equal to R= (0.5/2.5) = 4% for light
passing through a pane of glass, which has a refractive index of about 1.5.
Refractive Index
In the vicinity of an absorption band the refractive index varies considerably, an effect known as
anomalous dispersion. So a reflection spectrum is formed because the refractive index changes around
an absorption band.
Absorption
Band
Absorption
Band
Wavelength
Figure 3: Spectrum exhibiting anomalous dispersion
Kramers-Kronig Transform
In order to produce a spectrum that is corrected for this anomalous dispersion, a correction known as a
Kramers-Kronig transformation may be performed on the spectrum. This transformation attempts to
produce a spectrum that does not contain any derivative peak shapes. The raw data and the result of a
Kramers-Kronig transform are shown on the following page.
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Figure 4: Reflectance spectrum of Poly (Methyl Methacrylate)
Figure 5: KKT absorption spectrum of Poly (Methyl Methacrylate)
The above curve is generated using the double FFT algorithm. Note that Kramers-Kronig transforms are
approximations and the resulting spectra should be used with caution when attempting quantitation.
The transform should only be performed on spectra that show derivative peaks. If a Kramers-Kronig
transform is performed on a spectrum with non-derivative peaks, the results may be erroneous.
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Precautions
In order to provide the maximum transmission in infrared, with the minimum spectral interferences, the
mirrors used in this device are uncoated (bare) gold on a glass substrate. Since the coatings are soft,
care must be taken to avoid damage. Normally, these mirrors will not need cleaning, since they are
contained within the housing of the accessory. If they do need cleaning, they may be gently wiped with
a lint-free, abrasive-free cloth, such as lens tissue, or with a camel hair brush. Under no circumstances
must the mirrors be rubbed with paper products such as “Kleenex” since this will produce scratching of
the mirror coating.
Maintenance Parts
The following parts may be ordered separately:
Part Number
300-0002
010-3010
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Description
80Spec Gold Alignment Mirror
80Spec Sample Mask Set (3/8, 5/8 and 2”)
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6125 Cottonwood Drive · Madison, WI 53719-5120 · (608) 274-2721 (TEL) · (608) 274-0103 (FAX)
[email protected] · www.piketech.com