Microstructure analysis

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MTRL 451 Final Report Materials Analysis Report

Instructor: Dr. Rizhi Wang

Writer:

Hans Saputra

43941087

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Table of Contents

I. Introduction ..................................................................................................................................... 3

A. Objective ...................................................................................................................................... 3

B. Background .................................................................................................................................. 3

II. Acronyms ........................................................................................................................................ 3

III. X-Ray Diffraction (XRD) ............................................................................................................... 4

A. Sample Preparation ...................................................................................................................... 4

B. Observation/Discussion and Results ............................................................................................ 4

IV. Scanning Electron Microscopy / Energy Dispersive X-Ray Spectrometer (SEM/EDS).............. 6

A. Sample Preparation ...................................................................................................................... 6

B. Observation/Discussion and Results ............................................................................................ 6

V. EDS ............................................................................................................................................... 11

A. Observation/Discussion and Results .......................................................................................... 11

B. Analysis ...................................................................................................................................... 15

VI. Optical Microscopy (OM)............................................................................................................. 16


VII. Transmission Electron Microscopy (TEM) .................................................................................. 18


VIII. Experimental redesign................................................................................................................... 22

IX. Conclusion .................................................................................................................................... 22

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I. Introduction

A. Objective

The Objective of this final report is to produce a material analysis report in which the basic operations and capability of each instruments, chemical composition and microstructure and crystal phase analysis,

and skills of obtaining high quality results are addressed.

B. Background

As shown in figure 1, a Pentium 4 CPU was given as a sample to be analyzed. In order to visualize the

microstructure of this sample, four different techniques including OM (Optical Microscopy), SEM (Scanning Electron Microscopy), EDS (Electron Diffraction Spectroscopy), and XRD (X-day Diffraction) were performed. The microstructure of the material is related to composition, properties,

and the performance.

II. Acronyms

EDS Electron Diffraction Spectroscopy OM Optical Microscopy

SEM Scanning Electron Microscopy TEM Transmission Electron Microscopy

XRD X-Ray Diffractometer WD Working Distance DOF Depth of Field

SE Secondary Electron BSE Back Scattered Electron

NA Numerical Aperture Note: all italicized fonts throughout this report represent the operating conditions of the machines.

Figure 1. Pentium 4 CPU

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III. X-Ray Diffraction (XRD)

XRD technique is used to determine the crystal structure of a material. The purpose of this lab is to learn

how to obtain the XRD data and to analyze the results. This involves the basic principal of Bragg’s law.

A. Sample Preparation

A clamp and a pair of needle-nose pliers are used to cut the specimen into several pieces. Also, we used

a tiny tweezers to obtain the scrapped silicon powder from sample. This powder is to be examined using XRD method to determine or confirm its chemical composition.

B. Observation/Discussion and Results

The model, running parameters, monochromator, and operating voltage are summarized in the table below.

Table 1. Summary of the model, running parameters, monochromator, and operating voltage.

Using Braggs Law and lambda = 1.5405, the inter-planar spacing can be calculated. Tables

1 and 2 show the angle, intensity of each peak and the calculated inter planar spacing at two different scanning speeds.

Si PDF FILE

2ѳ ѳ counts d spacing (A) d spacing (nm) 2ѳ d (Å)

27.5 13.75 632 3.24 0.324 28.127 3.17

30.72 15.36 167 2.9 0.29

46.5 23.25 758 1.95 0.195 47.306 1.92

55.26 27.63 847 1.66 0.166 56.403 1.63

68.38 34.19 238 1.37 0.137 69.583 1.35 Table 2. calculated d-spacing for peaks at 2o/min

Model Rigaku X-ray diffractometer, Multiflex 2kW

2Theta 10° – 70°

Scanning speeds 10°/min and 2°/min

O perating voltage 40 kV

Intensity of current 20 mA

Monochromater Graphite single crystal (allows more specific detection of Kα by deflecting away

any continuous X-ray and Kβ by Cu source )

Radiation Cu/Kα1

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Si PDF FILE

2ѳ ѳ counts d spacing (A) d spacing (nm) 2ѳ d (Å)

27.5 13.75 708 3.24 0.324 28.401 3.14

30.6 15.3 217 2.91 0.291

46.6 23.3 542 1.94 0.194 47.306 1.92

55.3 27.65 517 1.65 0.165 56.029 1.64

68.3 34.15 200 1.37 0.137 68.998 1.36 Table 3. calculated d-spacing for peaks at 10o/min

To find what element our CPU consists of, the d-spacing of 5 strongest peaks need to be calculated.

Comparing those calculated d-spacing with the d-spacing from the PDF file help us confirm the chemical composition of the sample. As shown in the graph below, it is observed that the peaks for silicon (the vertical lines) are almost perfectly aligned with the peaks. This means the peaks almost

perfectly match with the peaks of the expected element; i.e. Silicon. Therefore, it is acceptable to say that the powder we analyzed is mainly made of silicon.

Graph 1. XRD pattern at 10o/min scan rate Graph 2. XRD pattern at 2o/min scan rate

Both graphs were taken at different scanning speeds and seem to produce similar results in terms of the

location of peaks. However, it is observed that at faster scanning rate, the graph produces quite significant noise as shown in the graph taken at 10o /min.

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IV. Scanning Electron Microscopy / Energy Dispersive X-Ray Spectrometer (SEM/EDS)

SEM technique is used to analyze surface topography of the sample. By directing electron beam into the

sample and capturing the secondary electron or back scattered electron, a high resolution and magnification image can be obtained. Two types of detector such as SE and BSE detector were used. SE detector captures secondary electron and provides topographical information of the surface. BSE

detector captures mostly BSE and provides compositional information.

A. Sample Preparation

Using the hot and pressurized mounting device the sample was mounted. To prevent the sample from a

mechanical damage, we maintained the pressure at certain level. The purpose of mounting is to make the specimen easier to handle. After mounting, the sample was polished. The sample was first grinded onto

a rotating disk of coarse abrasive paper and then moved on to the disks with finer paper. Before the sample is placed in the SEM vacuum chamber to be analyzed, it has to be coated with gold using the sputter coater to conduct electricity. This step is very important because electron beam is directed to the

conductive sample and deflected to the detectors (SE/BSE); so that the topographical and compositional information of the sample can be obtained.

B. Observation/Discussion and Results

The images (A,B,C and D) were taken at constant 20kV voltage and working distance of 30 mm and

different magnifications of x500, x1000, x5000 and x10000, respectively.

Figure 2. SEM images from cross sectional area of the CPU

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From the images above, at 500 and 1000 magnification is very clear. Also, we observed that at 1000

magnification we can see more details without sacrificing the sharpness of the image.

Effects on working distance

Figure 3. SEM images taken at different working distance. A and B (10 mm and 30mm)

During the lab, our sample was moved and therefore a direct comparison between the two different working distances cannot be made. However, variation of WD is expected to change resolution and

depth of field. Images A and B were taken at 10mm and 30mm WD. Working distance is a distance between the sample and the objective lens. In this case the objective lens refers to the condenser lens which is located closest to the sample.

With magnification and operating voltage remain the constant; the working distance affects the depth of

field and the resolution of the images. When the working distance is increased, the depth of field increases. However, excessively increasing the working distance may cause spherical aberration which leads to produce low resolution image. When the working distance decreased, the effect of aberration

will become less as the spot striking the sample become smaller and therefore produce a high resolution image. Other way to minimize spherical aberration is to adjust the aperture size (Goodhew, 2001).

It is very important to note that increasing WD does not give us the optimal resolution. Therefore, choosing the right working distance is very important. For example, if the sample has a large

topographical variation, it is better to increase the working distance to cover as much area into focus as possible. Therefore, a balance between resolution and depth of field is necessary to obtain the best

quality image.

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Operating voltage effect

Figure 4. SEM images taken at different operating voltage

We expect lower operating voltage will produce better quality image. However, from those images we cannot make a direct comparison because accidentally the sample was moved.

Stigmator adjustment effect on the quality of the images

Unadjusted stigmator results in a blurry image. This is due to asymmetric magnetic lens that produces different focal point. In contrast, adjusted stigmator produces sharp and focused image.

Figure 5. SEM images taken with stigmator unadjusted (A) and adjusted (B)

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Figure 6. SEM images with 20kV operating voltage with tilting effect.

The images above were taken at 20 mm working distance with tilting effect. The effect of brightness and

contrast cannot be seen very clearly. Also the sample was moved during the lab and therefore a direct

comparison cannot be made.

The tables with the images below were taken using two different detectors; i.e. SE and BSE.

SE

Relatively high resolution

Sensitive to topography

Low escape depth

BSE

Relatively low resolution

Sensitive to surface orientation

High escape depth

A B

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BSE is used to detect different chemical composition. Different density of the components will have different amount of electron scatter; i.e. heavier components appear brighter in the image. In conclusion,

BSE resulted in better contrast and brightness as seen above.

The table below summarizes the advantage and disadvantage of Optical Microscopy and SEM (Scanning Electron Microscopy)

OM SEM

Works best on flat surface.

Some out of focus area will be seen.

Resolves up to ~100 nm

Produces 3D like image / obtains both topographical and compositional

information.

Great DOF, cover all area in focus.

Produces high resolution ~1 nm

Table 4. Comparison between OM and SEM

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V. EDS

The same sample from previous lab (SEM) was used. During EDS analysis, the sample is bombarded primary electrons and emits unique X-ray from the chemical elements which will be detected as peaks.

EDS is used to analyze the chemical compositions of the selected areas on the sample. The cross sectional area of the CPU consists of many layers and areas of interest as labeled in the image below. To quantitatively analyze this specimen, a careful observation and decision in selecting the areas are

necessary.

A. Observation/Discussion and Results

Figure 7. Secondary electron image from the CPU cross-section

The following are the steps of operating the machine to analyze the chemical compositions of the

interested area: 1. Scan a general map of the sample 2. Select the areas of interest

3. Perform EDS analysis of each area to detect the elements in each particular area. 4. Obtain the chemical compositions of each area in table form.

5. Remove elements with concentration less than 0.01%. 6. Copy each table to word document

The quantitative analysis of the selected areas will be discussed later in detail in the analysis subsection in this EDS section

The EDS system is operated at 20 kV, WD of 15.2 mm and x200 magnification. Quantitatively, the amount of element present in the selected square region can be determined. This machine is very

sensitive that even a very little amount of an element can be detected. Also, it can perform very quick quantitative analysis; i.e. within a minute.

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SPOT ANALYSIS CPU layer1, area 1

Element Line Method Intensity KRatio ZAF Concentration 2 Sigma Z A F

C KA PRZ 970.97 0.190 3.995 75.91 wt% 0.457 wt% 0.971 4.116 1.000

O KA PRZ 69.06 0.007 9.148 6.68 wt% 0.160 wt% 1.024 8.938 1.000

Si KA PRZ 3936.10 0.143 1.217 17.41 wt% 0.055 wt% 1.119 1.088 1.000

CPU Layer 2, Area 1

Area 1 on layer 1 was analyzed and consists of mainly carbon and silicon. Area 1 on layer 2 was also

analyzed and consists of mainly carbon and copper and silicon. A little amount of fluorine is observed. Area 1 layer two is the cross sectional area of the microcircuit of the CPU. It is worth noting that oxygen is pervasive and is present in the selected areas on the sample.


C KA PRZ 670.83 0.193 3.584 69.04 wt% 0.489 wt% 0.944 3.796 1.000

O KA PRZ 70.89 0.011 8.053 8.86 wt% 0.209 wt% 0.996 8.088 1.000

F KA PRZ 5.93 0.001 5.476 0.33 wt% 0.054 wt% 1.073 5.109 0.999

Si KA PRZ 1247.59 0.067 1.432 9.53 wt% 0.055 wt% 1.088 1.316 1.000

Cu KA1 PRZ 183.15 0.093 1.311 12.25 wt% 0.152 wt% 1.331 0.985 1.000

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CPU Layer3, Area 1

An ‘x’ mark which represents a very small area of the glob (area 1, layer 3) was analyzed. This spot mainly consists of lead and partly tin. It is interesting that oxygen was not detected when ‘x’ mark

technique was used. The ZAF value for this area is close to one. This means we may confirm the accuracy of this machine since the Z and A correction factor are very small; i.e. 0.5% for Pb.

CPU Layer 3, Area 2

Area 2 on layer 3 has very similar chemical compositions as area 1 on layer 1 which contains mainly carbon and silicon. However, the correction factors (ZAF) are very large for each element in this area.


Sn LA PRZ 69.87 0.049 1.493 7.27 wt% 0.266 wt% 0.917 1.629 1.000

Pb MA PRZ 1467.17 0.918 1.010 92.73 wt% 0.402 wt% 1.005 1.005 1.000


C KA PRZ 860.29 0.258 2.997 77.44 wt% 0.514 wt% 0.977 3.068 1.000

O KA PRZ 76.69 0.012 8.971 11.17 wt% 0.260 wt% 1.030 8.708 1.000

Si KA PRZ 1635.89 0.091 1.249 11.39 wt% 0.060 wt% 1.126 1.109 1.000

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LINE SCANNING AND X-RAY ‘DOT’ MAPPING

Compositional fluctuation across the specimen using X-ray mapping was performed. The result is presented below.

The images above represent the dot distribution map of the cross-sectional area of the CPU. The green dots represent silicon. Using XRD, the upper part of the CPU was analyzed and it’s found that

the powder is mainly silicon. From two different techniques, the same result is obtained and therefore is confirmed that the upper part (layer 1) of the cross sectional area of the CPU is made out of silicon.

Figure 8. Dot Distribution map of the cross-sectional area of the CPU

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B. Analysis

In quantitative analysis in EDS, the assumption (the concentration of an element depends on its relative X-ray intensity compared to pure element) has been made.

(

) , where

Cspec = Concentration of Element in the selected area Nspec = X-Ray Intensity of the Specimen

Nstd = X-Ray Intensity of the Pure Element Cstd = Concentration of Pure Element

However, in reality X-ray intensity is a function of atomic number effect (Z), absorption (A), and Fluorescence effect (F). It is difficult to estimate the concentration of a specimen because in some cases,

a specimen may contain many elements. When it is compared with a series of standards, each of which is a pure element, and the sample may differ from each standard in its density and in the average of

atomic number of its constituent atoms. Consequently, ZAF technique is used to correct that difference. , where

Cspec = Concentration of Element in the selected area k = X-Ray Intensity Ratio

Z = Atomic Number Correction A = Absorption

F = Fluorescence Effect The atomic number correction, Z depends on how far the electrons penetrate the specimen before they

lose energy to excite further X-ray.

The absorption correction may be quite large. It is observed that in almost every area being analyzed in this lab, the correction factor A is very large. This may happen due to the fact that the selected areas contain several elements with significant different of atomic weight.

For the sample containing many elements, fluorescence effect needs to be considered. This is due to the

fact small portion of high energy X-ray may excite lower energy fluorescence radiation. For example, the presence of chromium in steel, a correction of 15% (F=0.85) is necessary (Goodhew, 2001).

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VI. Optical Microscopy (OM)

Optical microscope uses visible light as a source of light. OM can provide two dimensional magnified

image of a surface. Also, OM produces a high resolution image.


Figure 9. OM images: A ,B, C and D with variation of magnification(x5,x10,x20,x50) and NA ( 0.15, 0.30, 0.45, 0.80) respectively

NA = 0.15 NA = 0.30 NA = 0.45 NA = 0.80

Table 5 The images of the same area taken at different NA and using image software to adjust to identical magnification.

The wave length of 600 nm is used as assumption. The denominator in the equation represents the numerical aperture. The calculated resolution for each numerical aperture is shown in the table below

using this equation,

.

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NA λ (nm) Resolution (µm)

0.15 600 4.00 0.30 600 2.00 0.45 600 1.33

0.80 600 0.75 Table 6. Calculated resolution with variation of NA

It is found that the larger the numerical aperture the more light the lens can collect, therefore the more

likely it is to see finer details. From the equation above, numerical aperture is directly proportional to the resolution. It is important to note that better resolution means smaller value of r as resolution is defined

as the minimum distance between two points that the microscope can detect as two separate entities.

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VII. Transmission Electron Microscopy (TEM)

In this lab, contrast mechanisms were studied. The tutorial session discussed about the gold ring pattern

to determine the camera constant and analyzed the FCC pattern of the brass. Detail observation is described in the next section.


Figure 10. Images from STEM, Microstructure of thin films of annealed α-brass

The images were taken at 20 kV operating voltage.

Dislocations appear as dark lines in the TEM bright field image. The dislocation structures of the

annealed α brass are shown in figure 10. It is observed that the dislocation density is quite low for the

annealed materials. Near the core of a dislocation, lattice planes are usually bent severely and a dark line in the TEM images represent the edge of dislocations. This diffraction technique is very useful to

characterize defects in detail. Dislocation network can be seen clearly in image C.

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Figure 11 SAD diffraction pattern of evaporated gold with 50kV operating voltage

Diffraction occurs as electron beam enters the specimen and some electrons get diffracted. The un-diffracted electrons produce a bright field image while the diffracted electrons produce a dark field image. Grain morphology can be observed in the figure above.

Figure 12. gold ring pattern taken at 80kV voltgae

Before indexing single crystal pattern, the camera constant must be determined. The figure above was

used to calculate the camera constant. L.λ represents the camera constant. Summary of the calculated

camera constant is presented below in the table.

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Figure 13 Brass under TEM, with zone axis.

h k l d, Å Intensity r (mm) L.λ = r.d

(mm.Å)

111 2.35458 100 9 21.191

200 2.03921 51.3 10 20.392

220 1.44188 38.5 14 20.186

311 1.22964 47.2 16 19.674

222 1.17729 13.7 22 25.900

400 1.01956 6.4 24 24.469

Average 21.969

Table 7. Camera constant calculation

vector Ratio

G1 G2 G3 θ (G1,G2) G3/G1 G2/G1

r (mm) 10.5 10.5 12.5 110 1.190 1.000

hkl (-1,1,-1) (-1,-1,1) (-2,0,0)

cal d (Å) 2.092 2.092 1.758

database d(Å) 2.087 2.087 1.808

Table 8. G’s ratio, theta, calculated d

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To index single crystal pattern, the steps are as follow: vector G1, G2, and G3 need to be measured. G1 is the smallest distance from the zone axis and G2 must be located counter

clockwise to G1 and G3 is the addition of vector G1 and G2 and must be the largest in value, and the ratio of G2:G1 and G3:G1 need to be calculated. As calculated above the inter -planar

spacing for copper with lattice parameter that matched the FCC index card, have similar values as calculated d-spacing.

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VIII. Experimental redesign

The order of the experiment should be changed as follow: OM, SEM, EDS, TEM, and XRD. This order will help students visualize the surface with OM and also choose the relevant surface area to be further analyzed using electron microscopy techniques.

Chart 1. Summary of the order of experiment from right to left

For sample preparation, it is very crucial that any specimen for quantitative analysis must be flat

on the scale of electron beam diameter. It is common to polish the sample before analysis with an abrasive of 1 µm particle size so that only very fine defects are present.

During SEM lab, problems related to locating the sample occurred. Also the machine is very sensitive to vibration. The students should have been informed about this prior to the lab.

IX. Conclusion

The sample given for this project is the Intel Pentium 4 CPU. The fracture surface (cross sectional area) was analyzed using OM, SEM, and EDS. The upper part of the CPU was scrapped into powder and was analyzed using XRD.

In OM analysis, a high magnification and resolution of the images can be obtained. SEM provides

higher magnification and resolution than that of OM. Also, SEM technique enables us to visualize 3-D like image from the fracture surface of the sample. EDS gives us compositional information on the selected areas. Using the line mapping technique, the elemental distribution across the specimen can be

obtained. XRD technique was performed to confirm the existence of the elements on the selected area. It is confirmed that the powder scrapped from the upper part of the cross section contains mostly silicon.

Both XRD and EDS analysis show the same results.

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Reference

Peter J. Goodhew, Electron microscopy and analysis, 3rd ed. London ; New York : Taylor & Francis,

2001.

Microstructure analysis

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