iLab Name: XRD
iLab Kiosk: BRK Metrology Core
FIC: Mike Capano
Owner: Dmitry Zemlyanov
Location: BRK 1045
Maximum Wafer Size: 4"/100 mm Diameter, 11 mm maximum Z travel (sample thickness axis)

Overview

Panalytical X'Pert Pro MRD System is perfectly safe if operated as described in the user guide.

General Description

The X'Pert PRO MRD (Materials Research Diffractometer) systems offer advanced and innovative X-ray diffraction solutions from research to process development and process control.  Standard and in-plane geometries on one system offers a wide range of diffraction experiments for polycrystalline and highly perfect thin films.  With the PreFIX concept, reconfiguring is easy and optics positioning is accurate.

Accessories:

• Two sample stages:
  • Standard 4” wafer mount
  • Anton Paar DHS 900 domed hot stage for data collection from RT up to 900 °C
• Incident beam optics:
  • 5 arc sec Ge(440) point focus module (Bartels monochromator)
  • 19 arc sec hybrid (combination x-ray mirror + channel cut Ge(220) monochromator) line focus module
  • X-ray mirror
• Diffracted beam optics
  • Triple axis module with triple axis detector and rocking curve detector
  • X'Celerator detector
  • Parallel plate collimator

Technology Overview

X-ray diffraction is a method of analyzing the internal structure of materials based on the scattering pattern produced when a beam of x-rays interact with its crystal structure.  A typical experiment consists of an x-ray source, various x-ray optics, a sample, and a detector.  See the Wikipedia article X-ray crystallography for further information.

Equipment Overview

XRD Cabinet/Enclosure

1. X-rays ON lamp is lit whenever high tension is applied to the X-ray tube.
2. Experimental Space.  Anything in this space can be exposed to high intensity X-rays.
   1. Parts of the enclosure exposed to direct X-ray beam are 12 mm thick steel.
3. Interlocked lead glass sliding doors provide access and allow visibility of the sample and stages.
   1. X-ray absorption equivalent to 1 mm of lead.
4. Instrument front control panel with the following buttons and displays:
   1. Power On - Turns the power on to the instrument, not necessarily the X-ray tube.
   2. Stand by - Turns off the high tension generator.
   3. Light - Switches interior cabinet lighting ON/OFF
   4. HT (Key) - Keyed lockout for the high tension generator.
   5. Shutter close - Closes the shutter on the tube shield irrespective of the system's current operating state.
   6. θ, 2θ, c/s - Displays the angle or intensity of the X-ray beam measured by the detector.  The choice of information displayed is made in the data collector software.
   7. kV, mA - Displays the high tension generator's voltage and current settings.
   8. Shutter open - Displays a 1 if the shutter is open.  Displays three dots if the safety interlocks are not met (i.e. - doors closed)  
5. Anton Parr heated stage controller

6. Vacuum pump controller

   Cabinet construction conforms to the most stringent X-ray safety standards. The absorbed dose equivalent rate is less than 1 µSv/h at 10 cm distance from teh outside surface of the enclosure.

   
   

   IF EITHER OF THE WINDOWS IS BROKEN, SWITCH THE SYSTEM OFF IMMEDIATELY!

   
   

XRD Lab Instrument control PC and data anlaysis PC

1. PC 1 is a non domain PC that does not require a log on.  This PC is intended for you to use when accessing the iLab kiosk and to analyse your data, its use is free.  Software available here includes Epitaxy, High Score, Reflectivity, and Data Viewer.
2. PC 2 is a Purdue domain PC that requires you to log on using your Purdue credentials (Career Account).  This PC is interlocked in iLab and you must enable the tool to power on the monitor.  This PC is used to control the XRD instrument during data collection.

XRD Components

Incident Beam Optics

Sample Platform or Stage

Diffracted Beam Optics

*PreFIX - Pre-aligned Fast Interchangeable X-ray modules.  These are factory aligned and can be dismounted from the system and mounted again without the need for system alignment by the user.

Applications and Equipment Used

Phase Analysis

Phase identification is the most important application of X-ray diffraction. XRD is applied on polycrystalline solids and thin films. A phase is a crystalline solid with a regular 3-dimensional arrangement of the atoms. The measured diffraction peak positions and intensities are like a fingerprint of a particular crystalline phase. Identification is accomplished by comparison of the measured pattern with the entries in reference databases using a search-match algorithm. This is also known as qualitative phase analysis.  An example where phase is criticle in application of nanomaterials is the devolpment and testing of sunscreen.  The rutile phase of nano-titania is required for UV blocking applications whereas photocatalytic activity requires the anatase phase.

Residual stress

In measuring residual stress using X-ray diffraction (XRD), the strain in the crystal lattice is measured and the associated residual stress is determined from the elastic constants assuming a linear elastic distortion of the appropriate crystal lattice plane. Since X-rays impinge over an area on the sample, many grains and crystals will contribute to the measurement. The exact number is dependent on the grain size and beam geometry.  Although the measurement is considered to be near surface, X-rays do penetrate some distance into the material: the penetration depth is dependent on the anode, material and angle of incidence. Hence the measured strain is essentially the average over a few microns depth under the surface of the specimen.

Crystallography

A technique used for determining the atomic and molecular structure of a crystal, in which the crystalline structure cause a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their crystallographic disorder, and various other information.

Reflectometery

X-Ray reflectometry, whish is essentially analysis of the specular reflection of the sample, can be used to non-destructively investigate film thickness (nm, +/- 0.5-1%), roughness of the layer interfaces (nm, model dependent, reproducible 3%), and density of the sample materials (g/cm3, +/- 1-2%).  Futhermore, the scale of roughness parallel to the interface (lateral correlation) and perpendicular to the interface (lateral correlation) can be investigated using off-specular reflection of the sample.  Since XRR relies on specular and off-specular reflection of the beam rather than Bragg's law diffraction, it works with most thin films including epitaxial, non-epitaxial, and even non-crystalline films.

In reflectivity experiments, the X-ray reflection of a sample is measured around the critical angle. This occurs around grazing incidence angles. Below the critical angle of total external reflection, X-rays penetrate only a few nanometers into the sample. Above this angle the penetration depth increases rapidly. At every interface where the electron density changes, a part of the X-ray beam is reflected. The interference of these partially reflected X-ray beams creates the oscillation pattern observed in reflectivity experiments. From these reflectivity curves, layer parameters such as thickness and density, interface and surface roughness can be determined, regardless of the crystallinity of each layer (single crystal, polycrystalline or amorphous).

This section describes the steps necessary to manually align a sample and collect X-Ray Reflectometry (XRR) measurements using the Panalytical X'Pert Pro MRD.  This document is designed as a general guide to sample aligment and reflectometry measurement, adjustments may need to be made based on your sample.

Instrument Hardware Configuration

1. 76887839

2. For films < 100 nm thick, data must be collected at very high angles which requires high incident beam intensity, therefore the 76887839 PreFIX will be needed.

   1. 76887839:  76887839
      1. Install 1/32° 76887839 into the PreFIX module
      2. Set the adjustable anti scatter slit to 0.08 mm 
      3. If your sample is smaller in height than 20 mm, then set the adjustable beam mask to about 50% of the samples total height.
         1. An X-Ray beam falling off the sample decreases the beam intensity per unit area of the sample surface and increases the likelihood of background scatter from the sample holder.
   2. Update Data Collector configuration by selecting the Incident Beam Optics tab and double clicking one of the blue item lines to open the dialog window
      
      1. Select the PreFIX module tab and set the selection to Cu Mirror Module
      2. Select the Divergence Slit tab and set the selection to 1/32° divergence slit
      3. Select the Beam Attenuator tab and set the selection to Ni 0.15 mm automatic
         1. Usage selection set to Do Not Switch
         2. Activated box is checked.
            1. It is recommended to cycle the automatic attenuator from activated to deactivated to activated to check its functionality.  What is feedback?

3. For films > 100 nm thick, data must be collected at very high angular resolution requiring the use of a monochromator, therefore the 76887839 PreFIX will be needed.

   1. 76887839:  76887839

      1. Install 1/32° 76887839 into the PreFIX module

   2. Update Data Collector configuration by selecting the Incident Beam Optics tab and double clicking one of the blue item lines to open the dialog window
      
      1. Select the PreFIX module tab and set the selection to Hybrid Monochromator Module
      2. Select the Divergence Slit tab and set the selection to 1/32° divergence slit
      3. Select the Beam Attenuator tab and set the selection to Ni 0.15 mm automatic
         1. Usage selection set to Do Not Switch
         2. Activated box is checked.
            1. It is recommended to cycle the automatic attenuator from activated to deactivated to activated to check its functionality.  What is feedback?
4. 76887839: 76887839
   
   1. If not already in place, install the 76887839
   2. Install the 76887839
   3. Update Data Collector configuration by selecting the Diffracted Beam Optics tab and double clicking one of the blue item lines to open the dialog window
      
      1. Select the PreFIX module tab and set the selection to Parallel Plate Collimator
         1. Set the  Recieving slit to 0.027°
      2. Select the Detector tab and set to Mini prop large window 1 or 2
         1. Wavelength is Kα₁
5. 76887839
6. Set the 76887839

Alignment Proceedure

1. 76887839
2. 76887839

3. Set the automatic attenuator for automatic control

   1. Select the Incident Beam Optics tab and double clicking one of the blue item lines to open the dialog window
   2. Select the Beam Attenuator tab and set the Usage field to Switch at preset intensity.  
      1. Set the Activate Level to 500,000
      2. Set the Deactivate Level to 400,000

4. Collect preliminary reflectivity curve

   1. Using the Instrument Configuration tab, move to position 2Theta = 1.6° and Omega = 0.8°
   2. Open the manual scan window and perform the following scan
      
      1. Set Scan axis to 2Theta-Omega
         
      2. Set Scan mode to Continuous
      3. Set range to 3°
      4. Set step size to 0.005°
      5. Set Time per Step to 0.3 sec/step
   3. Right mouse click on the graph and select Axes, set Y axis scale type to Logarithmic.
   4. Right click and select Move mode, then click and drag the green line to the maximum intensity of the first (lowest angle) clearly visible fringe.  
      1. If no fringes are visible pick a point just to the right of the critical angle (typically 2θ > 1.0°)
      2. This animation could be better
      3. 
         
      4. 
         
   5. Open the manual scan window and perform the following scan
      1. Set Scan axis to Omega axis
         
      2. Set Scan mode to Continuous
      3. Set range to 1°
      4. Set step size to 0.005°
      5. Set Time per Step to 0.3 sec/step
      6. The scan usually produces three peaks, with the center peak being the most intense.  The two side peaks are a result of surface scattering effects.  If there is no middle peak, or the scan has two broad low intensity peaks, the film is too rough for reflectivity measurements.
         
   6. Right mouse click on the graph and select Axes, set Y axis scale type to linear.
   7. Align the green vertical line with the most intense peak using Peak mode, FWHM mode, or Manual mode.  Select mode by right-clicking on the data chart, then select "move to" in Peak and FWHM modes or click and drag the line in manual mode.  
   8. Open the manual scan window and perform the following scan
      
      1. Set Scan axis to Chi Axis
         
      2. Set Scan mode to Continuous
      3. Set range to 4°
      4. Set step size to 0.01°
      5. Set Time per Step to 0.3 sec/step
   9. Align the green vertical line with the peak using Peak mode, FWHM mode, or Manual mode.  Select mode by right-clicking on the data chart, then select "move to" in Peak and FWHM modes or click and drag the line in manual mode.
   10. Repeat steps e through i until alignment has been achieved.  When alignment is achieved, repeated scans will not require adjustment to center on peaks in omega scan or Chi scan.
   11. Make a note of current Omega Offset value.  Move 2Theta to zero. Apply Omega offset that you made note of leaving 2Theta at 0.  Select User Settings > User Offsets > Set new 0.
   12. Verify correctly shifted offsets by moving 2Theta just beyond the critical angle again and performing an Omega scan of 2 degrees.  There should be no adjustment needed to be centered on the peak.

Sample Measurement Procedure

1. Set the automatic attenuator for automatic control if not already set

   1. Select the Incident Beam Optics tab and double clicking one of the blue item lines to open the dialog window
   2. Select the Beam Attenuator tab and set the Usage field to Switch at preset intensity.  
      1. Set the Activate Level to 500,000
      2. Set the Deactivate Level to 400,000
2. Collect specular reflectivity measurement
   
   1. Thinner films require a longer scan range.  Films < 10 nm thick should have data collected out to 8-10 degrees 2Theta angle.  Intensity greatly decreases at higher angles.
   2. Thicker films can be well characterized with data collected only to 6 degrees 2Theta angle.  There is no harm, outside of lost time, in collecting data to 10 degrees 2Theta on thick samples.
   3. Move 2Theta to 2.75 degrees and Omega to 1.375 degrees
   4. Open the manual scan window and perform the following scan
      
      1. Set Scan axis to 2Theta-Omega Axis
         
      2. Set Scan mode to Continuous
      3. Set range to 4.5°
      4. Set step size to 0.005°
      5. Set Time per Step to 0.5 sec/step
         1. The time per step may need to be longer, typical values are between 0.5 to 5 seconds
         2. You can improve the high angle singnal by using Pre-Set Counts instead of Continous mode.  This will take a long time and would be appropriate for an overnight scan.  Typical values for Pre-Set Counts would range from 10,000 to 100,000.

      6. 76887839

      7. 

3. Collect Off-Specular reflectivity measurement
   1. Move 2Theta to 2.75 degree and Omega 1.375 degrees
   2. Open the manual scan window and perform the following scan
      
      1. Set Scan axis to Omega Axis
         
      2. Set Scan mode to Continuous
      3. Set range to 1.375°
      4. Set step size to 0.005°
      5. Set Time per Step to 1.5 sec/step
      6. 76887839
      7. 76887839
      1. 
4. Collecting data from another sample
   1. To collect data from another sample you will need to remove the current sample and mount an new sample.  This will change the sample position and require new alignment procedures to be executed.  Start from Step #2 in 76887839above.

When you are done

1. Remove your sample and clean any tape, grease, etc. from the sample chuck in preparation for the next user.
2. 76887839
3. Close Data Collector software
4. Log off of the instrument control PC
5. Finish your iLab session

High resolution diffraction

High-resolution X-ray diffraction (HRXRD) is a collection of application techniques for the non-destructive analysis of mostly layered, nearly-perfect crystalline structured materials.  Film properties are largely determined by their compositional and structural parameters. Information such as layer thickness, composition, strain, relaxation and structural quality is obtained by measuring rocking curves and reciprocal space maps using high-resolution X-ray optics. The spatial distribution of defects can be visualized by X-ray diffraction imaging methods such as X-ray topography.

In-plane diffraction

In-plane diffraction refers to the diffraction technique where the incident and diffracted beams are both nearly parallel to the sample surface.  The penetration depth of the beam is limited to within about 100 nm of the surface and is used to examine surface layers.  This method measures diffracted beams which are scattered nearly parallel to the surface, thus measuring planes that are perpendicular to the sample surface and are inaccessible with other techniques.

Standard Operating Procedures

The following instructions are meant to be a guide, but many of the scan parameters may change based on your samples and experience. Please note that the optics are delicate; do not bump or drop the optic housing units. If the x-rays are off, NEVER attempt to turn them back on unless specifically instructed by a lab staff member.

Control PC Sign-in and Connect to Instrument

1. Log into iLab, navigate to the BRK Metrology Kiosk, and activate your XRD Session to power on the control PC monitor.  There is a separate PC located in the lab where you can interface with iLab, that PC does not require a log in.
2. The control PC is a Purdue domain PC, which means you will need to use your Purdue Career account credentials to log in.  
3. Go the the Start Menu > Data Collector Folder > Data Collector link to launch the XRD control software.  This software requires a log in, please use the credentials below for this sign in.
   1. Username: xrduser1
   2. Password: xrd1045
4. Select the Instrument menu > click Connect.
5. Select the Beam Path 1 (MRD Cradle) configuration.
6. A message box will open displaying yellow triangles stating the instrument assumptions, if no red stop signs are shown, press the OK button.  If a red stop sign appears, you cannot continue, please contact the lab staff.
7. If the previous user had sample offsets stored in memory, you will receive a message asking if you want to apply these offsets.  Select No to clear these offsets.  XRD techniques require very high precision, it is not a good idea to use others alignments.
8. The PC is now connected to the XRD instrument.

Open / Close the X-ray Tube Shutter

1. There are several ways to open or close the X-ray tube shutter
   1. Press the Shutter Close button on the instrument front panel to close the shutter.
      1. 
   2. Start a manual scan and the shutter will open if not already open.  Closing the Manual Scan window will close the shutter.
   3. Click the Open / Close shutter button in the Data Collector toolbar
      1. 
   4. Select the Instrument Settings tab and double click on one of the item lines, then click the Generator tab
      1. Check or Uncheck the Open Shutter box and press apply

Incident Beam PreFIX removal / installation

Data Collector Configuration Options

Select the Incident Beam Optics tab and double click on one of the item lines:
a. PreFIX Module: Cu Mirror Module.
b. Divergence Slit: 1/32o divergence slit.
c. Beam Attenuator: Ni 0.15 mm automatic, Usage should be Do Not Switch and the Activated box should be checked. It is highly recommended to cycle from Activated → Deactivated → Activated to check if the attenuator is working properly.

Diffracted Beam PreFIX removal / installation

Data Collector Configuration Options

Select the Diffracted Beam Optics tab and double click on one of the item lines:
a. PreFix Module: Parallel Plate Collimator.
b. Receiving Slit: Parallel Plate Collimator Slit.
c. Detector: Mini prop large window 1 and the Wavelength is K alpha 1.

Set X-ray Tube to Operational / Idle Settings

Select the Instrument Settings tab, double click an item, select the X-ray tab, and set the Generator to 45 kV and 40 mA.

Common Sample Mounting Techniques

Align 2θ Axis to Beam Center and Set 2θ Offset to 0.0°

In this section, you will position the system so that the X-ray beam is aimed directly into the detector and you will determine the intensity of the direct X-ray beam.

1. Clear all stored offsets: User Settings > User Offsets > Clear all Offsets
   
2. Open instrument configuration and set all axis to 0
3. Open the manual scan window and perform the following scan
   1. Set Scan axis to 2Theta Axis
      
   2. Set Scan mode to Continuous
   3. Set range to 2°
   4. Set step size to 0.005°
   5. Set Time per Step to 0.1 sec/step
      
4. Align the green vertical line with the peak using Peak mode, FWHM mode, or Manual mode.  Select mode by right-clicking on the data chart, then select "move to" in Peak and FWHM modes or click and drag the line in manual mode.
5. Record the direct beam intensity, or count rate, shown in the status bar on the bottom of the data collector screen, you will use this to align the sample next.  The count rate should be less than 700,000, if it was larger then attenuation is necessary.
6. Select User Settings > User Offsets > Set new 0
   

Align Sample to the X-ray Beam

The sample height must be adjusted within a couple of micrometers of the true zero, and the sample surface must be perfectly level with the X-ray tube and detector. In this section, you will position the system so that the X-ray beam is aimed directly into the detector in order to allow you to adjust the sample height and tilt (offset). 

1. Open instrument configuration and set z axis to 6mm.
2. Open the manual scan window and perform the following scan
   1. Set Scan axis to Z Axis
      
   2. Set Scan mode to Continuous
   3. Set range to 11 mm
   4. Set step size to 0.05 mm
   5. Set Time per Step to 0.1 sec/step
   6. Set slope crossing 1/2 Direct Beam Intensity found in 76887839 instructions above (target is +/- 10% of 1/2 Direct Beam Intensity)
   7. 
      
3. Open the manual scan window and perform the following scan
   1. Set Scan axis to Omega Axis
      
   2. Set Scan mode to Continuous
   3. Set range to 2°
   4. Set step size to 0.01°
   5. Set Time per Step to 0.1 sec/step
   6. Center on Peak
   7. 
      
4. Open the manual scan window and perform the following scan
   
   1. Set Scan axis to Z Axis
      
   2. Set Scan mode to Continuous
   3. Set range to 2 mm
   4. Set step size to 0.01 mm
   5. Set Time per Step to 0.1 sec/step
   6. Set slope crossing 1/2 Direct Beam Intensity found in 76887839 instructions above (target is +/- 1% of 1/2 Direct Beam Intensity)
   7. 
      
5. Repeats steps 3 and 4 until alignment has been achieved.  When alignment is achieved, repeated scans will not require adjustment to center on peaks in omega scan or to center on 1/2 max intensity in Z scan.
6. Select User Settings > User Offsets > Set new 0 (make sure instrument axis are positioned at 0, with exception of Z and Omega before shifting offsets)

Setting the Automatic Attenuator for Automatic / Manual Control

Save Manual Measurement Data

Sample Requirements and Preparation

Large flat samples (> 1 cm2) are easiest to work with, other samples may be possible.  Maximum penetration depth is about 1,000 nm.

Notes:

1. Curved, undulating, irregular surfaces cause rocking curve broadening and deformation, preventing accurate alignments.
   1. 
      
   2. 
   3. 
      
   4. 
      

Hardware Procedures

Initialize the XRD Instrument

1. In order to initialize the XRD instrument, it first needs to be placed in Stand by.
   1. To do this, press the stand by button on the instrument front panel. All lights will turn off indicating the instrument is powered down. 
      
   2. 
2. Next remove the incident beam prefix and remove the diffracted beam prefix  (create these instructions and link here)
   1. 
   2. 
3. Make sure the cable attached to the stage is pulled up from the back to allow free movement of the axis.
   1. 
      
4. Close the instrument doors, and press the Power on button on the front panel of the instrument.
   1. 
      
5. On the control PC go to the start menu and launch Data Collector Software.
   1. 
6. After Data Collector window opens, click the Instrument menu, followed by Connect to establish communication with the instrument.
   1. 
7. Select the appropriate configuration and beam path for your usage, typically "Configuration 1", unless using the heated stage.  Beam path is dependent on hardware configuration.
   1. 
8. Next Data Collector will report a series of warnings concerning the instrument, assuming all are yellow exclamations, press the OK button.
   1. 
9. Data Collector will launch the In-Plane Initialization Wizard.

   1. 
      

      
      

      It is possible for the instrument to crash into the mounted hardware during initialization causing mechanical damage! From this point forward please carefully read and follow all instructions given in the wizard. All incident beam PreFIX modules must be removed before proceeding All diffracted beam PreFIX modules must be removed before proceeding Anton Parr heated stage if mounted, must be removed before proceeding

      
      

      
      

   2. Please watch the video below.  This video shows the range of motions the instrument will go through during initialization, demonstrating why you must remove all prefixes and the heated stage if present.
   3. 
   4. Press the Next button once these items are removed.
   5. 
10. Data Collector will ask you to identify the approximate location of the Chi axis before proceeding.  Look closely at the images, and select the one that best describes the current location of the Chi axis, and press the Next button and the wizard will Chi to a safe position.  Chi at 0 degree is typical measurement position, while Chi at 90 degree is typical sample loading position.  
    1. 
11. The instrument will move all axis to their home positions for absolute referencing, then return to the neutral position for operation.
    
    1. 
12. After the initialization wizard completes you will receive a message stating the diffractometer has been initialized.
    1. 

Anton Paar heated Stage SOP

1. in horizontal position.  Remove aluminum stage screws (3), T10 torx.  Tool kit located in drawer, accessory kit, Heated stage graphite dome.
2. bolt on new stage 4 screws, T15.  
3. align tube support to post, push on and screw down.
4. move to vertical.
5. turn on anton paar controller.
6. select anton paar configuration.

Questions & Troubleshooting

Data collector will not connect to the instrument.

See Initializing the XRD

Process Library

Create process template for tool, allows a user to fill in the details of their process. 

References

Rocking Curve - A scan where the detector (2Theta) is left stationary, while the omega axis is scanned.  The data is plotted as intensity vs Omega.

Detector Scan (2Theta Scan) - A scan where the 2Theta axis is scanned, while other axis are stationary.  The data is plotted as intensity vs 2Theta

Coupled Scan - A scan where both omega and 2Theta are scanned so that 2Theta = 2*Omega.  The data is plotted as intensity vs 2Theta

Critical angle (Θ_c) - Below the critical angle the X-Ray beam is completely reflected (total external reflection).  The critical angle for a layer is a function of its electron density and composition.  For a given composition, as the density of the film increases the critical angle often increases.  If either the composition or the density of a layer is known, the other can be determined using XRR.

Scott A Speakman, Ph.D - Center for Materials Science and Engineering at MIT

Joachim F. Woitok - Panalytical

XRD Quick Start Guide - September 2012.pdf

E7555 - Purdue University - Chiller to Replace HB16445.pdf

XRD screens.pptx

PersonalPresentation1.pptx