Diffuse Reflectance Accessory (Internal) Note: This document is also available in PDF format for improved print quality. PDF files are stored in the "\Manuals" folder on the Help & Videos CD-ROM.
NIR reflectance measurements (Cary 5000 only) Specular-only reflectance measurements Measurement calibration and corrections Maintenance Standards Troubleshooting Spare parts Alignment targets Sample mounting kits References o o • • • • • • • • Introduction The three different internal DRAs are compatible with each of the Cary 4000, 5000 and 6000i instruments. While all of the following variations are available the configurations indicated by ticks in the table below offer optimal operation.
Figure 1: The two components of reflection: specular and diffuse reflection. n represents the surface normal, an imaginary line at 90° to the sample surface. Traditionally, the accessory used to measure diffuse reflectance is the integrating sphere. Applications include characterizing solar materials, color measurement and characterization, and obtaining reflectance spectra of a painted surface.
Integrating spheres measure reflectance and transmittance factors, commonly called reflectance and transmittance. The relative spectral reflectance (transmittance) is defined as the ratio of the flux reflected (transmitted) by the specimen to that of a standard surface under identical geometrical and spectral conditions. For transmittance the standard surface is air, and for reflectance the standard surface is a secondary white standard calibrated relative to the perfectly reflecting diffuser.
Figure 2: Collection of scattered light by an integrating sphere. Io = incident light, Is = scattered light. In order to perform useful measurements on scattering samples, it is necessary to collect a high proportion of the scattered radiation. The integrating sphere is a highly efficient collector of scattered radiation.
Some of the reflected light escapes through the ports. This has the effect of reducing the signal to noise ratio, and thus the precision of the measurement. The Commission Internationale de l' Eclairage (CIE) recommendation is a ratio of <10%. This figure is only 3% for the Cary internal DRA. Coating non-uniformity, ageing, or contamination This accessory has been coated with PTFE via a unique process that ensures both a uniform coating on the inside of the sphere and the correct powder density.
Figure 4: Some of the wide-angle reflection is intercepted by the sphere wall The edges of the reflectance port are feathered to reduce this error. A protruding PTFE reference plate is provided with the accessory to more accurately represent the perfect diffuser. Reference beam attenuation Reference beam attenuation is most useful when the accessory or sample in the sample beam attenuates the light beam considerably.
Surface type Reflectivity Reference Matt High PTFE reference plate Matt Low Labsphere diffuse reflectance standards Glossy High Protruding PTFE reference plate Glossy Low NIST SRM 2021 The Troubleshooting section contains information on the available reference surfaces.
Optical design Figure 7: The optical design of the DRA 1. The sample beam hits mirror M1 and is then reflected to M2. 2. The beam travels through the lens and is focused into the transmission port, and onto the reflectance port. 3. The reflected beam is diffused throughout the sphere before being measured by the detector. 4. The reference beam enters the sphere directly through the reference port and is dispersed. 5.
Figure 8: Position 'D' measures diffuse reflectance only. Position 'S' measures total reflectance by including the specular component. The sphere has five ports: 1. 2. 3. 4. 5. Sample beam transmission port (19 x 17 mm) Sample measurement port (16 mm diameter) Reference beam port (11 x 13 mm) NIR detector port (11 mm diameter) PMT port (oval, 30 mm long x 14 mm wide) The PMT, PbS and InGaAs detectors are mounted on top of the sphere, which is alternately illuminated by sample and reference beams.
Detectors UV/VIS NIR Sphere diameter Internal coating Coating density Coating thickness Sample plane normal deviation Port area/total surface area ratio reflectance port size Minimum sample size Maximum sample size Power input Size packed Size unpacked Weight packed Weight unpacked R928 PMT R928 PMT TE# cooled InGaAs R928 PMT TE# cooled PbS 110 mm Polytetrafluoroethylene (PTFE) 1 g/cm3 4 mm 0° (diffuse reflectance only) 3° 20 min (total reflection) (CIE recommendation: <10°) 3% (CIE recommendation: <1
Figure 10. The internal DRA. Note the clips on the left hand side of the accessory. These are for attaching metal screens during reference beam attenuation. Caution This accessory includes mirrors, lenses and other fragile parts. Treat the packaging and accessory with care. Do not jar the accessory. Avoid finger contact with mirrors and lenses. Do not attempt to clean or repair damaged surfaces.
1 Sample mount ledge Permits mounting of 1” and 2” samples in %T and %R modes 08 101697 00 The Standard Sample Holder Kit will accommodate mounting of reflectance standards, specifically: Item Description Protruding PTFE reference plate Large PTFE reference plate 2” Reflectance standards 1” color standards 1 ¾” diameter Reflectance standards (Spectralon) 2”, for use with Diffuse reflectance accessories Calibrated diffuse color standards set for DRA. Set includes four 1” D diffuse color standards.
Figure 11: The Cary 4000, 5000 and 6000i Internal Diffuse Reflectance accessory with the optics cover removed. The large reference plate is clamped over the reflectance port at the centre of the sphere cap. Warning This accessory contains electrical circuits, devices, and components operating at dangerous voltages. Contact with these circuits, devices and components can cause death, serious injury or painful electrical shock.
1. Click the Windows Start button, then Programs, then Cary WinUV, and then Align. 2. Click the Cary tab. 3. Set the following parameters: Double beam: Normal Y mode: %R Ave time: 0.1 SBW: 2 Slit height: reduced 4. Select the Zero order check box and click OK. Caution The DRA should not be plugged in and operated with the instrument set to 0 nm. If it is, the detectors will be flooded with white light, which will decrease the sensitivity of the accessory and increase noise.
10. Adjust the vertical alignment of the beam on mirror M2 by adjusting the hexagonal screw at the front of mirror M1. 11. Check that the light is not clipping the lens, the transmission port to the sphere (at the back of the sphere), or the reflectance port on the sphere (at the front of the sphere). 12. If necessary, adjust M2 in the same way as M1.
Figure 12: Simplified beam diagram of the accessory with the sphere cap in the 'D' position. The specular component is reflected back out of the sphere onto the lens. The reflection from the lens should be about 10 mm from the transmission port. 5. Re-tighten the screws and re-check the alignment, to see if any lens adjustment is necessary. 6. Position the sphere cap so that the 'S' mark is facing up.
Figure 13: Simplified beam diagram of the accessory with the sphere cap in the 'S' position 7. Carefully remove the m ask from the diffuser (see step 7). Turn off the instrument and remove the DRA from the sample compartment. 8. Replace the optics cover on the DRA. 9. With the spectrophotometer turned off, place the DRA in the sample compartment and plug it into the corresponding socket at the top of the sample compartment.
Figure 14: DRA socket 10. Place the PTFE reference disc over the reflectance port. 11. Install the Extended Sample Compartment according to its instruction manual. 12. Close the sample compartment, turn on the instrument and wait for correct initialization to be completed. Note Improper alignment of the DRA may prevent the Cary from finding the 656.1 nm wavelength calibration line.
Correction None Autostore tab File Storage: Storage OFF 4. Click the 'Goto' button to open the 'Goto wavelength' dialog box. Enter '500' in the wavelength field and click OK. The instrument will then drive to 500 nm. Zero %R error check 1. With the transmission ports uncovered, place the large reference plate over the reflectance port. 2. From the main 'Scan' dialog box, click the Zero button and wait for the instrument to zero. 3.
Installing attachments Attachments can be installed into the DRA to increase its flexibility and versatility. The following are optional attachments: • • • • • • Liquid sample holder Small sample holder; Powder cell Small sample mount Polarizer/Depolarizer Double Aperture Installing the liquid sample holder Figure 17. The liquid cell holder. "A" the flat side that must sit against the DRA, "B" the raiser screw and "C" the screw for securing the attachment to the posts on the DRA. 1.
You must first install the liquid sample holder. 1. Place the protruding reference plate in position in the reflectance port, and position the cuvette at the transmission port. 2. Set the instrument as detailed in the transmission measurements section. Note Parameters activated by a radio button that are not specifically mentioned in the following procedure should be set to 'Off' (e.g., the Signal-to-noise mode radio button). These parameters will not affect the procedure. 3. Fill the cuvette with solvent.
The small sample holder is used to measure reflectance of small samples. The powder cell can be mounted in the small sample holder to enable the reflectance of powder samples to be measured. The small sample holder is also used to hold the small sample mount when measuring the reflectance of very small samples. 1. Install the DRA into the instrument. 2. Screw the posts into position at either the reflectance or transmission port. 3. Slide the small sample holder onto the posts. 4.
Figure 20. Insert the powder cell into the small sample holder. 8. Tighten the screw on the small sample holder to secure the powder cell. Figure 21. The powder cell fitted into the small sample holder, note that the textured edge of the powder cell sits flush with the edge of the small sample holder. The screw to the right of the powder cell is used to secure the powder cell. 8. You must now check the alignment of the attachment. 9. You can use the powder cell to perform reflectance measurements.
Installing the small sample mount The small sample mount enables you to take reflectance readings of very small solid samples, for example gemstones. The kit features five different mounts and three different apertures. The sizes of the apertures are 1mm, 3mm and 5mm. A PTFE reflectance standard is also included. Figure 21. The Small Sample mount. "A" sample mounts, "B" apertures, "C" sample cup and "D" PTFE standard. 1. Install the DRA into the instrument. 2. Install the Small Sample Holder onto the DRA.
Figrue 23. The mask and sample are placed on the sample cup. Note The sample mounts have V-shaped cutouts that enable small samples to assist in the mounting of samples. 5. Fit the aperture (the aperture size used is determined by the size of your sample) onto the sample cup, lining up the marking on the lid and the sample cup. Figure 24. Align the markings on the sample cup and the lid before fitting them together. 6.
Figure 24. The small sample mount fits into the small sample holder. Note that in this picture the small sample holder and small sample mount are in the correct position for performing transmission measurements. 7. Tighten the screw on the small sample holder to secure the small sample mount. Note Ensure that the small sample mount is sitting forward in the small sample holder, so that the thumb screw does not prevent the lid of the small sample mount from sitting up against the DRA.
Figure 25. The PTFE standard fits into the sample cup. b) Fit the aperture onto the sample cup. c) Place the sample cup over the reflectance or transmission port. Note It is recommended that you use the same aperture size to run the baseline as the one you are going to use for the sample. d) Click the Zero/Baseline button in the Scan application to collect the 100% T baseline.
Figure 26. The polarizer installed on the polarizer mount. You can install the Polarizer/Depolarizer into the DRA to control the plane polarization of the light beam in a spectrophotometer. For example: if the sample being measured is sensitive to plane polarized light e.g. liquid crystals, the transmission of the sample will change as the plane of polarization changes. It is thus important to control the plane of polarization of the incident beam. To install the polarizer/depolarizer: 1.
Figure 27. The Double Aperture attachment. A indicates the locating pin at the bottom of the attachment. 1. Turn on the instrument and allow it to warm up for at least two hours. 2. Remove the optics cover. 3. Mount the double aperture base onto the polarizer mount. Figure 28. Install the double aperture base onto the polarizer mount. 4. Install the DRA into the instrument. 5. You must now align the attachment as follows. 6. Place the mask onto the double aperture base so that both apertures are open.
Figure 29. The mask fits onto the double aperture base. This figure shows only one aperture is open. 7. Click the Windows Start button, then Programs, then Cary WinUV, and then Align. 8. Set the SBW to 2.00. 9. Close the sample compartment lid. 10. Tick the Zero Order check box, click the Apply button to drive the instrument to zero. 11. Open the sample compartment lid and adjust the height adjustment screw on the side of the polarizer mount until the image is centred over the apertures.
14. Adjust the height adjustment screw on the side of the polarizer mount until the transmission reading is half (+/- 1%) of the reading noted in step 12. 15. Open the sample compartment lid and rotate the aperture mask so that only the upper aperture is open. Repeat the measurement until the reading for the upper aperture is half (+/- 1%) of the reading when both apertures are open. 16. Use the Validate application to check the photometric accuracy of the DRA with the double aperture attachment.
that the instrument to be turned on and off at various times. It is important to take care that you follow these steps as failure to do so can cause damage to your DRA. Reflectance measurements (%R) The sample should be homogeneous, substantially flat, and large enough to completely cover the image. Finely powdered samples may be studied using a powder cell. There is also a mounting option available for small samples. When measuring diffuse only reflectance, position the sphere cap with the 'D' mark up.
8. Click the Setup button. 9. From the Setup menu, set the following parameters: Cary tab X mode: Mode Nanometers X mode: Start 700 X mode: Stop 400 Y mode: Mode %R Y mode: Y min -5.00 Y mode: Y max 110.00 Scan controls: Ave time (s) 0.100 Scan controls: Data interval (nm) 1.000 Scan controls: Scan rate (nm/min) 600.00 Options tab SBW/Energy: Fixed SBW SBW/Energy: SBW (nm) SBW/Energy: Beam mode SBW/Energy: Slit height Source: Lamps Source: Source changeover (nm) ON 2.00 Double Reduced UV-Vis 350.
Figure 16. The sample mount ledge. 13. Click the Start button. The Save As dialog box will appear, allowing the method to be saved as either a data file or a batch file. If the file is saved as a batch file, all of the method parameters will be stored with the scan. This procedure will measure the % reflectance relative to the PTFE reference disk. Note To determine the absolute diffuse reflectance of a sample, you need to purchase an NBS standard and calibrate your PTFE disks.
1. Click the Windows Start button, then Programs then Cary WinUV and then Scan. 2. Click the Setup button. 3. Set the following parameters: Cary tab X mode: Mode X mode: Start X mode: Stop Y mode: Mode Y mode: Y min Y mode: Y max Show status display Nanometers 1800 300 %R -5.00 110.00 ON Options tab SBW/Energy: Beam mode Double SBW/Energy: Slit height Reduced Source/Detector: Lamps UV-Vis Source: Source changeover (nm) 350.0 Source: Detector changeover (nm)800.
4. Click the Goto button to open the 'Goto wavelength' dialog box. Enter '801' in the wavelength field and click OK. The instrument will then drive to 801 nm. Note Note the SBW reading in the Status Display dialog box. 5. The SBW reading needs to be at approximately 18. This can be adjusted by changing the NIR Energy level in the Setup page, under the Independent tab. If the reading is greater than 18, raise the value of the Energy level field. If the SBW is under 18, lower the energy level.
X mode: Stop 300 Y mode: Mode %R Y mode: Y min -5.00 Y mode: Y max 110.00 Scan controls: Ave time (s) 0.100 Scan controls: Data interval (nm) 1.000 Scan controls: Scan rate (nm/min) 600.00 Options tab SBW/Energy: Fixed SBW SBW/Energy: SBW (nm) SBW/Energy: Beam mode SBW/Energy: Slit height Source: Lamps Source: Source changeover (nm) ON 2.00 Double Reduced UV-Vis 350.0 Baseline tab Correction Zero baseline/correction Autostore tab File Storage: Storage Storage on (prompt at start) 2.
12. From the Maths dialog box choose Selected Trace and then the '=' (equals) sign. 13. The results of this specular data equation will be displayed in a new graph. Transmission measurements (%T) Note Parameters activated by a radio button that are not specifically mentioned in the following procedure should be set to 'Off' (e.g., the Signal-to-noise mode radio button). These parameters will not affect the procedure. 1.
3. Click the Baseline button in the Scan dialog box. Follow the on-screen prompts to perform a 100%T baseline scan and a 0%T baseline scan. Hot Tip When performing the 0%T baseline collect, block the sample beam in the transmission position with a blanking plate (a large solid object). 4. Once the baseline correction is complete, the Ordinate status display in the top left corner of the dialog box will show 'Zero baseline' in red text. 5.
Caution Both instrument and DRA are calibrated at the factory and should be recalibrated only when tests indicate the need for it. When should I perform a calibration? Below are some common reasons that may indicate the necessity for calibration. Calibrate PGA (Programmable Gain Amplifier) PGA calibration should be executed each time a DRA is installed in a Cary instrument for the first time, and after each time it is removed.
This option causes the Cary system to use the deuterium lamp to calibrate the instrument at 2624.4, 1312.2 and 0.00 nm. Note When performing a wavelength calibration you must firstly remove the DRA, perform the calibration, then return the DRA to the instrument. Refer to the Wavelength Accuracy help in the Validate application. Calibration using Cary Win UV Software The recommended method for performing calibration is by using the Auto Calibrate function in the Validate application.
This allows the user to view the Wavelength offsets stored in the EEPROM. Performing a correction to ASTM E903-C-OS/2 If you are using a NIST Standard Reference material (SRM) (e.g. White ceramic tile) as the reference disk then you should enter the calibrated reflectance values as a continuum in the Cary system. To do this, create an ASCII file and enter the list of X and Y data pairs (separated by commas). Save this ASCII file in the '.CSV' format.
Baseline tab Correction Zero x std ref correction Autostore tab File Storage: Storage Storage on (prompt at start) Place the reference disk or SRM in the DRA. Run a baseline as follows: 1. Select the Baseline button in the Scan dialog box. Follow the on-screen prompts to perform a 100%T baseline scan and a 0%T baseline scan.
You may gently flush the accessory with pure nitrogen to remove water by using the N2 connector lines at the back of the instrument. Keep the reference plates clean; if they become dirty, new plates are available from Varian. The part number for the flat PTFE reference plate is 04 1014439 00, and for the protruding PTFE reference plate 04 101988 00.
• • • • Black ceramic tile Colored tiles Aluminium mirrors Absorbing glass NPL also have transmittance standards of neutral glass filters with transmittance values of 0.92 to 0.001. Contact: Division of Electrical Science National Physical Laboratory Teddington, Middlesex TW11 OLW UK Troubleshooting Warning This accessory contains electrical circuits, devices and components operating at dangerous voltages.
Cannot select the required wavelength Check that the wavelength ranges of instrument and DRA are compatible. Refer to the Specifications table. Spare parts The following spare parts are available from Varian for the Diffuse Reflectance accessory. Only Varian-supplied parts should be used, unless specified otherwise: Item Description Part number 1 x Mirror Alignment target 2010062590 M4 3mm hexagonal ball driver 1 x Ball driver 7210020800 for horizontal mirror alignment 1 x 5.
375 380 390 400 450 500 550 600 650 0.991 0.991 0.992 0.993 0.993 0.994 0.994 0.994 0.994 1450 1500 1550 1600 1650 1700 1750 1800 1850 0.992 0.992 0.992 0.992 0.991 0.990 0.990 0.990 0.986 2130 2140 2150 2160 2170 2180 2190 2200 2210 Sample Mounting Kits Liquid Cell %T Holder Only standard 10 mm path length cells can be used. Item Description 1 x Cuvette Holder Holds standard 10 mm quartz cuvettes in %T port of DRA. Mounts on standard poles.
2. Zwinkels J., Dodd C.X.: Workshop on Optical Property Measurement Techniques, Commission of the European Communities. (1988). 3. Weidner V.R., Hsia J.J., Adams B.
